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2019-03-01 | A new simplified parametric model, which is more suitable for pantograph–catenary dynamics simulation, is proposed to describe the nonlinear displacement-dependent damping characteristics of a pantograph hydraulic damper and validated by the experimental results in this study. Then, a full mathematical model of the pantograph–catenary system, which incorporates the new damper model, is established to simulate the effect of the damping characteristics on the pantograph dynamics. The simulation results show that large $$F_{\mathrm{const}}$$ F const (saturation damping force of the damper during compression) and $$C_{\mathrm{0}}$$ C 0 (initial damping coefficient of the damper during extension) in the pantograph damper model can improve both the raising performance and contact quality of the pantograph, whereas a large $$C_{\mathrm{0}}$$ C 0 has no obvious effect on the lowering time of the pantograph; the nonlinear displacement-dependent damping characteristics described by the second item in the new damper model have dominating effects on the total lowering time, maximum acceleration and maximum impact acceleration of the pantograph. Thus, within the constraint of total lowering time, increasing the nonlinear displacement-dependent damping coefficient of the damper will improve the lowering performance of the pantograph and reduce excessive impact between the pantograph and its base frame. In addition, damping performance of the new damper model would vary with the vehicle speeds, when operating beyond the nominal-speed range of the vehicle, the damping performance would deteriorate obviously. The proposed concise pantograph hydraulic damper model appears to be more adaptive to working conditions of the pantograph, and more complete and accurate than the previous single-parameter linear model, so it is more useful in the context of pantograph–catenary dynamics simulation and further parameter optimizations. The obtained simulation results are also valuable and instructive for further optimal specification of railway pantograph hydraulic dampers. | Effect of the nonlinear displacement-dependent characteristics of a hydraulic damper on high-speed rail pantograph dynamics | 10.1007/s11071-019-04766-4 |
2019-03-01 | The vortex-induced vibrations of a circular cylinder attached as a tip mass at the end of a cantilever beam are investigated for hybrid energy harvesting using two different transduction mechanisms, namely piezoelectric and electromagnetic. The high aeroelastic oscillations generated for a range of wind speeds are translated into electrical energy by both transducers. The aerodynamic force is modeled by a modified van der Pol wake oscillator model. The Euler–Lagrange principle and Galerkin procedure are utilized to develop a nonlinear distributed-parameter model to evaluate performance of the hybrid energy harvester. The effects of the external load resistances, placement and mass of the magnet on coupled damping, frequency, and performance of the hybrid energy harvester are deeply studied. It is shown that performance of the hybrid energy harvester is highly dependent on both the external load resistances. It is demonstrated that, in the synchronous region, placement of the magnet has a huge effect on tip displacement of the harvester, generated current in the electromagnetic circuit, and generated voltage in the piezoelectric circuit. On the contrary, mass of the magnet has a negligible effect on behavior of the considered hybrid system. A comparative study between the hybrid energy harvester with the classical piezoelectric and electromagnetic counterparts is also carried out. It is indicated that, by carefully choosing the external load resistances and harvesters’ properties, energy harvesting in a hybrid configuration is an effective replacement for two different classical harvesters working separately. It is concluded that hybrid energy harvesters come out to be an effective choice for powering multiple electronic devices. | Characteristics and comparative analysis of piezoelectric-electromagnetic energy harvesters from vortex-induced oscillations | 10.1007/s11071-018-04757-x |
2019-03-01 | This paper systematically investigates the ground current crosstalk (GCC) of high-power cascaded chopper braking circuit (CCBC). Turning on and off the IGBTs of the CCBC will generate GCC problem between the upper and lower chopper braking circuits. The GCC may cause the freewheeling diode to be hard-off, resulting in strong electromagnetic interference and serious losses, and even causing the freewheeling diode to fail due to reverse recovery. This paper establishes the ground current model of CCBC and the GCC is predicted base on the model. To minimize the influence of GCC, the solutions of inserting damping resistors to the ground current path and optimizing IGBT timing are proposed. The correctness of the analysis is verified by simulations and experiments. The proposed methods are of great significance for improving the reliability of high-power cascaded chopper braking devices and reducing electromagnetic interference and losses. | Ground Current Crosstalk Analysis and Suppression in High Power Cascaded Chopper Braking Circuit | 10.1007/s42835-019-00116-x |
2019-03-01 | Abstract The effectiveness of vibration-damping coatings is assessed by simulation. The experimental characteristics of the coatings are presented. An algorithm is proposed for assessment of the expected dynamic parameters of structures as a function of their shape and the characteristics of the vibration-damping materials. | Effectiveness of Vibration-Damping Coatings | 10.3103/S1068798X19030158 |
2019-03-01 | We study the behavior of the trajectories of a second-order differential equation with vanishing damping, governed by the Yosida regularization of a maximally monotone operator with time-varying index, along with a new Regularized Inertial Proximal Algorithm obtained by means of a convenient finite-difference discretization. These systems are the counterpart to accelerated forward–backward algorithms in the context of maximally monotone operators. A proper tuning of the parameters allows us to prove the weak convergence of the trajectories to zeroes of the operator. Moreover, it is possible to estimate the rate at which the speed and acceleration vanish. We also study the effect of perturbations or computational errors that leave the convergence properties unchanged. We also analyze a growth condition under which strong convergence can be guaranteed. A simple example shows the criticality of the assumptions on the Yosida approximation parameter, and allows us to illustrate the behavior of these systems compared with some of their close relatives. | Convergence of inertial dynamics and proximal algorithms governed by maximally monotone operators | 10.1007/s10107-018-1252-x |
2019-03-01 | In this study, we investigated the hydrodynamic and energy conversion performance of a double-float wave energy converter (WEC) based on the linear theory of water waves. The generator power take-off (PTO) system is modeled as a combination of a linear viscous damping and a linear spring. Using the frequency domain method, the optimal damping coefficient of the generator PTO system is derived to achieve the optimal conversion efficiency (capture width ratio). Based on the potential flow theory and the higher-order boundary element method (HOBEM), we constructed a three-dimensional model of double-float WEC to study its hydrodynamic performance and response in the time domain. Only the heave motion of the two-body system is considered and a virtual function is introduced to decouple the motions of the floats. The energy conversion character of the double-float WEC is also evaluated. The investigation is carried out over a wide range of incident wave frequency. By analyzing the effects of the incident wave frequency, we derive the PTO’s damping coefficient for the double-float WEC’s capture width ratio and the relationships between the capture width ratio and the natural frequencies of the lower and upper floats. In addition, it is capable to modify the natural frequencies of the two floats by changing the stiffness coefficients of the PTO and mooring systems. We found that the natural frequencies of the device can directly influence the peak frequency of the capture width, which may provide an important reference for the design of WECs. | Oscillation and Conversion Performance of Double-Float Wave Energy Converter | 10.1007/s11804-019-00083-9 |
2019-03-01 | In Richardson’s cascade description of turbulence, large vortices break up to form smaller ones, transferring the kinetic energy of the flow from large to small scales. This energy is dissipated at the smallest scales due to viscosity. We study energy cascade in a phenomenological model of vortex breakdown. The model is a binary tree of spring-connected masses, with dampers acting on the lowest level. The masses and stiffnesses between levels change according to a power law. The different levels represent different scales, enabling the definition of “mass wavenumbers.” The eigenvalue distribution of the model exhibits a devil’s staircase self-similarity. The energy spectrum of the model (defined as the energy distribution among the different mass wavenumbers) is derived in the asymptotic limit. A decimation procedure is applied to replace the model with an equivalent chain oscillator. For a significant range of the stiffness decay parameter, the energy spectrum is qualitatively similar to the Kolmogorov spectrum of 3D homogeneous, isotropic turbulence and we find the stiffness parameter for which the energy spectrum has the well-known $$-\,5/3$$ - 5 / 3 scaling exponent. | An intriguing analogy of Kolmogorov’s scaling law in a hierarchical mass–spring–damper model | 10.1007/s11071-018-04749-x |
2019-03-01 | This article shows the significant decrease in the dynamic elasticity modulus of the OT-4 titanium alloy within the frequency range of 0–25 Hz as compared with the static elasticity modulus with further stabilization of the mentioned dynamic modulus at 25–80 Hz based on study of the damping flexural vibrations of the cantilevered test specimens. The procedure of identification of the damping properties of the mentioned alloy during expansion-compression, with account of the internal and external aerodynamic damping based on the finite element method and minimization of the target function containing the experimental and calculated logarithmic vibration decrements of the test specimen, was developed. The matrix of aerodynamic damping of the finite element, on the basis of the Morison approximation aimed at conceptualization of the force per unit length of the aerodynamic resistance during vibration of the test specimen, was made. The averaged amplitude dependence of the logarithmic vibration decrement presenting the damping properties of the investigated OT-4 alloy was obtained by several test specimens. | Identification of the Dynamic Elasticity Characteristics and Damping Properties of the OT-4 Titanium Alloy Based on Study of Damping Flexural Vibrations of the Test Specimens | 10.3103/S1052618819020110 |
2019-03-01 | This paper presents a new optimization methodology called movable damped wave algorithm for solving global optimization problems. The proposed methodology mimics mathematically the behavior of waveform induced by oscillating phenomena. It starts by creating multiple initial random solutions which are updated through introducing a mathematical model based on a damped wave function. In the proposed methodology, the updating mechanisms of solutions are based on designing a mathematical relation for the movable wave with the aim to effectively achieve robust solutions. Therefore, this methodology can be more robust, statistically sound, and convergent quickly to the optimal global solution. The performance of the proposed is validated by carrying out on 23 benchmark problems and three engineering design problems. The results show vividly that the proposed is a reliable algorithm and outperforms the comparative algorithms in most cases. | A movable damped wave algorithm for solving global optimization problems | 10.1007/s12065-018-0187-8 |
2019-02-15 | A probabilistic seismic demand modeling approach with the optimal intensity measure ( IM ) parameters determined a posteriori (POS-PSDM) is employed to examine and compare the full potential of the explanatory power of different IM formulations. A total of six IM formulations adopting the optimal IM parameters determined a posteriori (i.e. POS - IM s) are studied, including two spectral IM s with the optimal period T* , two fractional order IM s with the optimal fractional order α *, as well as two spectral IM s with the optimal period T* and the optimal damping ratio ζ* . A comprehensive IM comparative study is conducted based on hysteretic single-degree-of-freedom systems, considering a wide range of structural parameters. The POS - IM s manifest substantially improved performance (i.e. efficiency and sufficiency) compared with their conventional counterparts, revealing the value of adopting this POS-PSDM approach to ensure the PSDM predictive performance. In particular, the spectral acceleration at the optimal period and damping ratio, S _ a ( T*,ζ* ), which is introduced as an IM candidate for the first time, not only consistently demonstrates superior explanatory power but also exhibits fairly good hazard computability. The POS-PSDM approach in conjunction with S _ a ( T*,ζ* ) exhibits good potential in further improving the accuracy and reliability of probabilistic seismic risk assessment with negligible increase in computation cost. | A posteriori optimal intensity measures for probabilistic seismic demand modeling | 10.1007/s10518-018-0484-8 |
2019-02-15 | Friction stir processing (FSP) was conducted on an Al-Si casting alloy. The Si phase and Al grains of an Al-Si casting alloy were refined through FSP. Furthermore, FSP with high rotation rate led to the precipitation of Mg and Si atoms and the formation of Mg_2Si phase in the Al-Si alloy. Precipitation improved the low-strain damping capacity but deteriorates high-strain damping capacity of the FSP sample at room temperature. At low rotation rate, the FSP sample exhibited excellent high-temperature damping capacity mainly because of its fine grain structure and the low density of its pinning points. The plastic instability of the Al-Si alloy was eliminated by FSP because of the refinement of the Si phase. The increase in the strength of each FSP sample was attributed to the increase in second-phase and boundary strengthening effects. Thus, the mechanical properties and damping capacity of Al-Si were enhanced after FSP. | Effect of Friction Stir Processing on the Microstructure, Damping Capacity, and Mechanical Properties of Al-Si Alloy | 10.1007/s11665-018-3844-2 |
2019-02-12 | Coherent vortices are often observed to persist for long times in turbulent 2D flows even at very high Reynolds numbers and are observed in experiments and computer simulations to potentially be asymptotically stable in a weak sense for the 2D Euler equations. We consider the incompressible 2D Euler equations linearized around a radially symmetric, strictly monotone decreasing vorticity distribution. For sufficiently regular data, we prove the inviscid damping of the $$\theta $$ θ -dependent radial and angular velocity fields with the optimal rates $$\left\| u^r(t)\right\| \lesssim \langle t \rangle ^{-1}$$ u r ( t ) ≲ ⟨ t ⟩ - 1 and $$\left\| u^\theta (t)\right\| \lesssim \langle t \rangle ^{-2}$$ u θ ( t ) ≲ ⟨ t ⟩ - 2 in the appropriate radially weighted $$L^2$$ L 2 spaces. We moreover prove that the vorticity weakly converges back to radial symmetry as $$t \rightarrow \infty $$ t → ∞ , a phenomenon known as vortex axisymmetrization in the physics literature, and characterize the dynamics in higher Sobolev spaces. Furthermore, we prove that the $$\theta $$ θ -dependent angular Fourier modes in the vorticity are ejected from the origin as $$t \rightarrow \infty $$ t → ∞ , resulting in faster inviscid damping rates than those possible with passive scalar evolution. This non-local effect is called vorticity depletion . Our work appears to be the first to find vorticity depletion relevant for the dynamics of vortices. | Vortex Axisymmetrization, Inviscid Damping, and Vorticity Depletion in the Linearized 2D Euler Equations | 10.1007/s40818-019-0061-8 |
2019-02-07 | This study aims to evaluate hysteresis response behavior of circular hollow steel damper (CHSD). Steel dampers are a type of passive dampers and commonly used for seismic dissipation in civil engineering structures. Steel dampers are widely used for seismic energy dissipation because they are easy to install, maintain and they are also inexpensive. CHSD is among steel dampers which dissipates seismic energy through metallic deformation and geometrical elasticity of circular shape and fatigue resistance around welded connection to the end plates. Finite element analysis was conducted in order to evaluate the hysteresis characteristics and low cycle fatigue behavior of CHSD using failure index. To verify the analysis simulation quasi static loading was conducted and the result was compared and satisfactory result was obtained. | Low-Cycled Hysteresis Characteristics of Circular Hollow Steel Damper Subjected to Inelastic Behavior | 10.1007/s13296-018-0097-8 |
2019-02-01 | Abstract The article presents results of investigating the influence of elastic damping devices that secure the rotor and the stator under high-amplitude oscillations under unfavorable development of an accident, e.g., upon rubbing of the rotor against the stator. Motion equations for the oscillations of the rotor in the clearance between the rotor and the stator and the oscillations of the rotor rubbing against the stator are written at adopted parameters of the stator considering not only the rigidity of the stator but also the energy losses under deformation of the stator components during the oscillations. Sudden unbalance of the rotor is taken as the initial excitation. A case of severe unbalance of the rotor is examined when, under oscillations accompanied by rubbing, the damping devices experience fairly severe strains in different rolling modes. The investigations were conducted using a rotor that had been affected by accidents accompanied by destruction of the bearings under rubbing in the absence of damping devices. A dynamic model of a symmetrical two-bearing rotor is considered. ADP-2400 shock absorbers served as dampers; the dynamic impact properties of the former had been determined using shock-testing machines. A possibility of the development of self-excited oscillations in the form of asynchronous rolling is considered depending on the absorption factor of the elastic damping devices. It is shown that no asynchronous rolling develops at definite absorption factor values. The oscillations of the rotor are restricted to the synchronous rolling at rotor–stator contact interaction forces that do not endanger the integrity of the turbine plant structure. The elastic damping devices with absorption factors above certain values eliminate the possibility of the development of self-excited oscillations in the form of asynchronous rolling and a practically unlimited increase in the rotor–stator interaction forces and, consequently, eliminate the danger of destruction (self-destruction) of the power-generating plant. In a sense, we can speak about the damping capacity of elastic damping devices during the evolution of an accident accompanied by rubbing of the rotor against the stator. The rigid mount of the stator on the foundation in the absence of damping devices increases the risk of the catastrophic development of the emergency considerably reducing the evolution time of the rolling and the possibility of using safety devices. A conceptual scheme that systemizes the general regulations for preventing TP accidents is provided. | The Damping Capacity of Damping Devices during Rotor-over-Stator Rolling | 10.1134/S004060151902006X |
2019-02-01 | Constrained layer damping treatments are widely used in mechanical structures to damp acoustic noise and mechanical vibrations. A viscoelastic layer is thereby applied to a structure and covered by a stiff constraining layer. When the structure vibrates in a bending mode, the viscoelastic layer is forced to deform in shear mode. Thus, the vibration energy is dissipated as low grade frictional heat. This paper documents the efficiency of passive constrained layer damping treatments for low frequency vibrations of cylindrical composite specimens made of glass fibre-reinforced plastics. Different cross section geometries with shear webs have been investigated in order to study a beneficial effect on the damping characteristics of the cylinder. The viscoelastic damping layers are placed at different locations within the composite cylinder e.g. circumferential and along the neutral plane to evaluate the location-dependent efficiency of constrained layer damping treatments. The results of the study provide a thorough understanding of constrained layer damping treatments and an improved damping design of the cylindrical composite structure. The highest damping is achieved when placing the damping layer in the neutral plane perpendicular to the bending load. The results are based on free decay tests of the composite structure. | Damping Analysis of Cylindrical Composite Structures with Enhanced Viscoelastic Properties | 10.1007/s10443-018-9684-2 |
2019-02-01 | In the present paper, the effective damping properties of a symmetric foam-core sandwich beam with composite face plates reinforced with coated fibers is studied. A glass fiber-epoxy composite with additional rubber-toughened epoxy coatings on the fibers is considered as the material of the face plates. A micromechanical analysis of the effective properties of the unidirectional lamina is conducted based on the generalized self-consistent method and the viscoelastic correspondence principle. The effective complex moduli of composite face plates with a symmetric angle-ply structure are evaluated based on classical lamination theory. A modified Mead-Markus model is utilized to evaluate the fundamental modal loss factor of a simply supported sandwich beam with a polyurethane core. The viscoelastic frequency-dependent behaviors of the core and face plate materials are both considered. The properties of the face plates are evaluated based on a micromechanical analysis and found to implicitly depend on frequency; thus, an iterative procedure is applied to find the natural frequencies of the lateral vibrations of the beam. The optimal values of the coating thickness, lamination angle and core thickness for the best multi-scale damping behavior of the beam are found. | Optimal Damping Behavior of a Composite Sandwich Beam Reinforced with Coated Fibers | 10.1007/s10443-018-9698-9 |
2019-02-01 | New analytical solutions to water wave radiation by vertical truncated circular cylinders are developed based on linear potential flow theory. Two typical cylinder configurations of a surface-piercing cylinder and a submerged floating cylinder are considered. The multi-term Galerkin method is employed in the solution procedure, in which the fluid velocity on the interface between different regions is expanded into a set of basis function involving the Gegenbauer polynomials, and the cube-root singularity of fluid velocity at the side edges of the truncated cylinders is correctly modeled. The present solutions have the merits of very rapid convergence. The results with six-figure accuracy for added mass and radiation damping can be obtained using a few truncated numbers in the basis function for three motions (surge, heave and roll). The calculated results of the present solutions agree well with that by a higher-order boundary element method solution. Calculation examples are presented to investigate the influence of the motion frequency on the added mass and the radiation damping of the truncated cylinders with different geometric parameters. The present solutions can be used as a reliable benchmark for numerical solutions to water wave radiation by complicated structures. | New analytical solutions to water wave radiation by vertical truncated cylinders through multi-term Galerkin method | 10.1007/s11012-019-00964-x |
2019-02-01 | The dynamic rotor behavior is significantly affected by the stiffness and damping characteristics of the bearings. Therefore, it is important to identify these bearing parameters. For active magnetic bearings (AMBs), these bearing parameters not only could be identified from rotor dynamic response, but also from electrical control system transfer function. Some identification works from rotor dynamic response have been reported, but identification from electrical control system transfer function is relatively few. In this paper, we deduced the equivalent stiffness and damping expressions with electrical control system transfer function for rotor AMBs and identified these values from electrical control system model. To evaluate the identified results, previous reported results from rotor dynamic response is employed for comparison. We found that for the stiffness, a complete and precise electrical control model will obtain relatively consistent values; however, for the damping, the accurate electrical control model is still not enough and the eddy current loss should be included. | Identification of dynamic stiffness and damping in active magnetic bearings using transfer functions of electrical control system | 10.1007/s12206-019-0110-y |
2019-02-01 | Abstract The composition of surface layers formed during high-temperature interaction between Fe_70Si_15B_15 alloy and air impurities in an inert atmosphere is determined using equilibrium thermodynamic means. It is shown that at T = 1473 K, Fe_3O_4, FeSiO_3, and B_2O_3 are at the interface between the alloy and the gas. Intermediate layers of internal oxidation contain FeSiO_3, B_2O_3, SiO_2, and BN. The iron-based region adjacent to the alloy contains silicides Fe_3Si and FeSi; borides Fe_2B and FeB; and nitride BN. At a relatively low concentration of air impurities in the inert gas, the destruction of a surface film consisting mainly of SiO_2 is detected in the temperature range of 1600–1800 K as an anomaly on the damping decrement polytherm of free torsional vibrations of the crucible with the melt. | Formation of Surface Layers on Fe_70Si_15B_15 Alloy upon Heating in an Inert Atmosphere with Air Impurities | 10.1134/S0036024419020122 |
2019-02-01 | Footbridges usually suffer from vibrations induced by the actions of pedestrians, which calls for various control measures to improve the serviceability. This study described the dynamic analysis and Tuned Mass Damper (TMD) implementation for a single-pylon cable-stayed footbridge scaled model, aimed at providing an experimental case study regarding of vibration control design of slender structures. A scaled model for the real footbridge was designed based on similarity principles. Then, the dynamic behavior of the footbridge was assessed by ambient vibration tests. The natural frequencies and mode shapes were identified from operational vibration measurements by covariance-driven stochastic subspace identification algorithm. The frequency of first vertical bending modes is 2.10 Hz, falling into the human walking frequency range [1.6, 2.4] Hz. Therefore, the footbridge needs vibration control to improve its serviceability. Finally, a self-made TMD using lead, spring and oil buffer was implemented on the scaled model of the footbridge. The laboratory forced vibration test was employed to illustrate the effectiveness of the TMD. By installing TMD, the acceleration response at mid-span of the footbridge was remarkably reduced. The study could provide meaningful reference for vibration control design of the full-scale footbridge. | Footbridge Serviceability Analysis: From System Identification to Tuned Mass Damper Implementation | 10.1007/s12205-018-0985-7 |
2019-01-30 | The ideal gas molecular movement (IGMM) algorithm has been introduced by the authors recently. Detailed studies on its behaviors uncover the fact that the gas molecules also experience a local self-vibration as they move. A comprehensive study was carried out here to introduce the molecular vibration thoroughly as a damping phenomenon supporting convergence rationally with a hindering behavior as molecules travel toward the global best. Thus, a new algorithm containing a molecular operand on vibrational effect (MOVE) was introduced and three different functions were employed to simulate molecular vibrations and pursue investigation. They include simple harmonic, driven harmonic and damped harmonic motions. A number of optimization problems were attempted including a set of unconstrained problems, 23 benchmark functions consisting of unimodal, multimodal and multimodal functions with fix dimensions, and also three well-known constrained engineering problems. Moreover, in a statistically significant way, Wilcoxon’s rank-sum nonparametric statistical test was carried out at the 5% significance level. Overall, the damped harmonic motion function as a molecular vibration simulator supported the optimization procedure best among the other two vibrational functions and other algorithms involved in the research. It showed a relatively better act, causing a faster escalation in the convergence throughout the optimization process. The results intensely show that the MOVE operand significantly boosts the performance of the IGMM and one could certify the significance of VIGMM, proposed in the present study, over some other metaheuristic optimization algorithms. | Damping vibration-based IGMM optimization algorithm: fast and significant | 10.1007/s00500-017-2804-3 |
2019-01-25 | In this paper, we prove the linear damping for the 2-D Euler equations around a class of shear flows under the assumption that the linearized operator has no embedding eigenvalues. For the symmetric flows, we obtain the same decay estimate of the velocity as the monotone shear flows. Moreover, we confirm a new dynamical phenomena found by Bouchet and Morita: the depletion of the vorticity at the stationary streamlines, which along with the vorticity mixing leads to the damping for the base flows with stationary streamlines. | Linear Inviscid Damping and Vorticity Depletion for Shear Flows | 10.1007/s40818-019-0060-9 |
2019-01-24 | Combined with the finite element analysis (FEA) technology of fluid–structure interaction and nonlinear large deformation material, the integral FE models of a type of hydraulically damped rubber mount (HDM) with resonant column channel are set up. Based on the visualized simulation results, the working process of the HDMs is analysed, and the dynamic stiffness and the loss angles are compared. The calculation results show that the variation of the dynamic stiffness and the loss angle in the low-frequency domain is related to the flux and its hysteresis in the column channel. The effects of the decoupling membranes and the disturbing plate on the low-frequency dynamic characteristics are investigated by calculations. Results show that the setting of the decoupling membranes and their stiffness greatly change the dynamic stiffness and the loss angle of the HDM in the frequency domain below 50 Hz. And the disturbing plate and the variation of its diameter also affect the dynamic characteristics in the same frequency range. The accuracy of the FEA calculation is verified by the experiment. | Visualization analysis of the working process and dynamic characteristics comparison of a hydraulically damped rubber mount with resonant column channel | 10.1007/s40430-019-1598-x |
2019-01-23 | Many buildings require reinforcement for various reasons including earthquake damage, change in design regulations and occupancy, adding stories, and lack of proper construction. One of the retrofitting systems that, in addition to increasing the lateral strength, provide the structure with significant ductility is the ADAS yielding damper and is of great interest today. The main objective of this research is to numerically investigate the effects of ADAS plates and columns’ axial loads on the seismic parameters of reinforced concrete (RC) moment resisting frames. Therefore, based on 48 calibrated numerical models, the Pushover analysis was performed and the effects of axial force and number of ADAS plates on the seismic parameters of the frame such as effective stiffness, ultimate strength, energy dissipation, and ductility were investigated. In addition, analytical relationships were presented to determine the ultimate strength and stiffness of the reinforced frame. The results show that the number of ADAS plates should be determined in such a way so that the shear strength of the RC frame is at most about 3 times greater than that of the original concrete frame. | Investigation of retrofitting RC moment resisting frames with ADAS yielding dampers | 10.1007/s42107-018-0092-6 |
2019-01-22 | In this paper, we study the initial boundary value problem for a Petrovsky type equation with a memory term, nonlinear weak damping, and a superlinear source: u t t + Δ 2 u − ∫ 0 t g ( t − τ ) Δ 2 u ( τ ) d τ + | u t | m − 2 u t = | u | p − 2 u , in Ω × ( 0 , T ) . $$ u_{tt}+\Delta ^{2} u- \int _{0}^{t} g(t-\tau )\Delta ^{2} u(\tau )\,\mathrm{d} \tau + \vert u_{t} \vert ^{m-2}u_{t}= \vert u \vert ^{p-2}u,\quad \text{in }\varOmega \times (0,T). $$ When the source is stronger than dissipations, we obtain the existence of certain weak solutions which blow up in finite time with initial energy E ( 0 ) = R $E(0)=R$ for any given R ≥ 0 $R\geq 0$ . | Blow-up of solutions for a nonlinear Petrovsky type equation with initial data at arbitrary high energy level | 10.1186/s13661-019-1136-x |
2019-01-18 | Fe-17Mn alloy has been attracted as a high damping alloy due to its excellent damping capacity and tensile properties. For its industrial application, it is necessary to improve both wear resistance and anti-oxidation. To solve this problem, gas nitriding was performed at 520 °C for 10 h using cold-rolled specimens. The nitrided specimen revealed a thick nitride layer of ~ 68 μm with ~ 20%Mn and a hardness value of ~ 650 Hv on the matrix of ε martensite and γ austenite without the diffusion layer. The damping capacity of the nitrided specimen was decreased with increasing the thickness ratio of nitride layer to matrix. However, when the thickness ratio was ≤ 1.5%, the damping capacity of the nitrided specimen was similar to that of the nitride-free specimen. This indicates that the wear resistance and anti-oxidation of Fe-17Mn alloy can be improved by a thin nitride layer without the loss of its damping capacity. | Influence of Gas Nitriding on the Damping Capacity of Fe-17Mn Alloy | 10.1007/s12540-018-0157-9 |
2019-01-17 | Intrinsic self-healing coatings have been drawing more and more attention over recent years. A self-healing coating that is able to maintain its original appearance and performance after damage is attractive for a huge scope of applications. This article reports the synthesis of a polyurethane-urea coating with 1-(2-aminoethyl)-imidazolidin-2-one (UDETA) units showing temperature- and moisture-triggered self-healing. Calorimetric and spectroscopic analyses give insight into the self-healing mechanism showing that the absorbed water is able to disturb inter- and intramolecular hydrogen bonds of the polymer chains and decrease the glass transition temperature of the polymer. Temperature-mediated self-healing can be performed from 80 up to 200°C. Aside from self-healing, the molecular dynamics in the polyurethane-urea polymer prove to be beneficial for damping applications as confirmed by dynamic mechanical analysis. Thus, the polymer system features properties that are useful for two different applications, namely in coatings with self-healing and corrosion protective properties and in dampening materials. | Stimuli-responsive polyurethane-urea polymer for protective coatings and dampening material | 10.1007/s11998-018-0114-z |
2019-01-17 | Background ALRs (AIM2-like Receptors) are germline encoded PRRs that belong to PYHIN gene family of cytokines, which are having signature N-terminal PYD (Pyrin, PAAD or DAPIN) domain and C-terminal HIN-200 (hematopoietic, interferon-inducible nuclear protein with 200 amino acid repeat) domain joined by a linker region. The positively charged HIN-200 domain senses and binds with negatively charged phosphate groups of single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) purely through electrostatic attractions. On the other hand, PYD domain interacts homotypically with a PYD domain of other mediators to pass the signals to effector molecules downwards the pathways for inflammatory responses. There is remarkable inter-specific diversity in the numbers of functional PYHIN genes e.g. one in cow, five in human, thirteen in mice etc., while there is a unique loss of PYHIN genes in the bat genomes which was revealed by Ahn et al. (2016) by studying genomes of ten different bat species belonging to sub-orders yinpterochiroptera and yangochiroptera . The conflicts between host and pathogen interfaces are compared with “Red queen’s arms race” which is also described as binding seeking dynamics and binding avoidance dynamics. As a result of this never-ending rivalry, eukaryotes developed PRRs as antiviral mechanism while viruses developed counter mechanisms to evade host immune defense. The PYHIN receptors are directly engaged with pathogenic molecules, so these should have evolved under the influence of selection pressures. In the current study, we investigated the nature of selection pressure on different domain types of IFI16-like ( IFI16-L ) PYHIN genes in ruminants. Results Three transcript variants of the IFI16-like gene were found in PBMCs of ruminant animals-water buffalo, zebu cattle, goat, and sheep. The IFI16-like gene has one N-terminal PYD domain and one C-terminal HIN-200 domain, separated by an inter-domain linker region. HIN domain and inter-domain region are positively selected while the PYD domain is under the influence of purifying selection. Conclusion Herein, we conclude that the nature of selection pressure varies on different parts (PYD domain, HIN domain, and inter-domain linker region) of IFI16-like PYHIN genes in the ruminants. This data can be useful to predict the molecular determinants of pathogen interactions. | Nature of selection varies on different domains of IFI16-like PYHIN genes in ruminants | 10.1186/s12862-018-1334-7 |
2019-01-15 | Thin-wall water piping systems are key to the functionality of important facilities, such as hospitals and schools. Recent earthquakes have demonstrated the vulnerability of these systems. Conventional bracing of thin-wall water piping systems does not guarantee adequate seismic performance. Due to their flexibility, dynamic amplification of long piping runs between bracing elements can occur. This paper evaluates, through a case study, the feasibility of introducing viscous dampers within bracing elements of suspended thin-wall water piping systems to improve seismic performance. Three-dimensional dynamic response analyses were conducted on a suspended thin-wall water piping system under seismic floor motions of various intensities. The dynamic response of the piping system with viscously damped bracing is compared to that of the unbraced and conventionally braced piping system. The numerical results indicate an improvement in seismic response for viscously damped braced configurations. The properties of the viscous dampers that causes the largest reductions in the seismic response of the piping system are noted and practical implementation aspects are discussed. | Seismic response of viscously damped braced thin-wall piping system: a proof-of-concept case study | 10.1007/s10518-018-0447-0 |
2019-01-15 | To overcome the scale discontinuity of the Delayed Detached-eddy simulation (DDES) based on the v 2 ¯ − f $\overline {v^{2}}-f$ Reynolds-averaged Navier-Stokes (RANS) model developed by Jee and Shariff (International Journal of Heat and Fluid Flow 46(2014) 84), an improvement is proposed in the present work. For the new DDES formulation, the scale discontinuity is avoided in the transition region and the RANS mode is correctly recovered for the shielded region. However, the numerical stability of the new DDES formulation is poor, and the relaxation factor in some locations is extremely large. To improve the numerical stability, the underlying v 2 ¯ − f $\overline {v^{2}}-f$ RANS model is modified. Besides, a damping function is introduced to damp the RANS region when the grid resolution is fine enough and the flow is filled with an abundance of turbulence. Numerical simulations are carried out for some typical wall-bounded flows and special attention is paid to distinguish the effect of the damping function to the resolution capability of the flowfields. | An Enhanced Version of Delayed Detached-Eddy Simulation Based on the
v
2
¯
−
f
$\overline {v^{2}}-f$
Model | 10.1007/s10494-018-9957-8 |
2019-01-15 | We introduce Hermite-polynomial-field excited coherent state (HPFECS) and then investigate analytically its evolution in an amplitude damping channel. We find that it evolves into a Laguerre-polynomial-weighted-chaotic photon field in this process, which turns out to be a new nonclassical state. The Q-function of this novel state is also given. | Amplitude Damping of Hermite-Polynomial-Field Excited Coherent State | 10.1007/s10773-018-3928-7 |
2019-01-15 | A sharp and prolonged change in developing population processes requires mathematical methods to be improved. Unusual phase changes in the development of mass reproduction of insect species stipulated the idea to develop a new model in which not the final form of an asymptotically stable state after bifurcations but transient modes are of importance. In concrete situations, it is proposed to consider the phenomena, which are identified with population outbreaks (non-stationary heterogeneous processes) in environmental studies, within the context of a long oscillatory mode only as peaks of the phases of sharp nonharmonic oscillations. The proposed new dynamic model in the form of a differential equation describes a decreasing pseudoperiodic damping trajectory of sudden sharp oscillations that implement a non-bifurcation scenario of spontaneous completion for a particular variant of mass forest pest reproduction. Situations in two provinces of eastern Canada are considered as examples. | Continuous Model for the Devastating Oscillation Dynamics of Local Forest Pest Populations in Canada^* | 10.1007/s10559-019-00119-6 |
2019-01-15 | We estimate the quantum state of a two-level atom and the coherent field in a Kerr medium subject to the cavity damping. The density matrix of the field is considered within the framework of the dispersive approximation. We study dynamical properties of the linear entropy, Wehrl entropy, and the Wehrl phase density during the time of interaction. The effects of the Kerr medium and cavity damping on the time evolution of different quantities are examined. The results refer to the sensitivity of these aspects to changes either in the decay parameter or in the Kerr-like medium and Stark-shift parameters. Linear entropy and nonclassical properties of the field quantified by the Wehrl entropy are also very sensitive to the Kerr medium and Stark-shift parameter. | Effects of Kerr Medium and Stark Shift Parameter on Wehrl Entropy and the Field Purity for Two-Photon Jaynes–Cummings Model Under Dispersive Approximation | 10.1007/s10946-019-09764-w |
2019-01-15 | A performance-based seismic design method for plane reinforced concrete (R/C) moment-resisting frames (MRF) is proposed. The method is a force-based seismic design one, utilizing not a single strength reduction factor as all modern codes do, but different such factors for each of the first significant modes of the frame. These modal strength reduction factors incorporate dynamic characteristics of the structure, different performance targets, and different soil types. Thus, the proposed method can automatically satisfy deformation demands at all performance levels without requiring deformation checks at the end of the design process, as it is the case with code-based design methods. Empirical expressions for those modal strength reduction factors as functions of the period, deformation/damage and soil types, which can be used directly in conjunction with the conventional elastic pseudo-acceleration design spectra with 5% damping for seismic design of R/C MRFs, are provided. These expressions have been obtained through extensive parametric studies involving non-linear dynamic analyses of 38 frames under 100 seismic motions. The method is illustrated by numerical examples which demonstrate its advantages over code-based seismic design methods. | A seismic design method for reinforced concrete moment resisting frames using modal strength reduction factors | 10.1007/s10518-018-0436-3 |
2019-01-14 | The paper studies the behavior of horizontally polarized shear wave (SH-wave) in an initially stressed fiber-reinforced viscoelastic composite structure, where the elastic parameters vary linearly along the depth of the crustal layer. The displacements in each media have been calculated analytically and closed form dispersion equation has been derived with the help of intrinsic boundary conditions. The dispersion equation thus obtained is a complex valued function, whose real part contains the phase velocity and the imaginary part contains the damped velocity. To demonstrate the effect of various parameters, numerical simulations have been conducted and graphs have been plotted for the phase velocity and the damped velocity against the wave number. Furthermore, a comparative study has been undertaken by means of graphical illustrations to explain its remarkable effects. | SH-wave propagation in linearly varying fiber-reinforced viscoelastic composite structure uninitial stress | 10.1007/s12517-018-4211-1 |
2019-01-12 | In this paper, we study the linearly damped stochastic differential equations, which have the invariants satisfying a linear differential equation whose coefficients are linear constant or time-dependent. A stochastic exponential integrator is proposed for linearly damped stochastic differential equations to preserve their intrinsic properties. Then, the conformal symplecticity of stochastic Hamiltonian systems with linearly damped term is studied. For linearly damped stochastic Hamiltonian systems, it is shown that the stochastic exponential integrator can exactly preserve conformal quadratic invariant and conformal symplecticity. The mean-square convergence order of the method is analyzed. Numerical tests present the good performance of the proposed stochastic exponential integrator in structure-preserving. | Structure-preserving stochastic conformal exponential integrator for linearly damped stochastic differential equations | 10.1007/s10092-019-0302-y |
2019-01-01 | Knowledge of first-order ordinary differential equations (calculus) | Transient Circuit Fundamentals | 10.1007/978-3-319-96692-2_7 |
2019-01-01 | We have seen in the preceding chapter that the simple oscillator under idealized conditions of no damping, once excited, will oscillate indefinitely with a constant amplitude at its natural frequency. However, experience shows that it is not possible to have a device that vibrates under these ideal conditions. Forces designated as frictional or damping forces are always present in any physical system undergoing motion. These forces dissipate energy; more precisely, the unavoidable presence of these frictional forces constitute a mechanism through which the mechanical energy of the system, kinetic or potential energy, is transformed to other forms of energy such as heat. The mechanism of this energy transformation or dissipation is quite complex and is not completely understood at this time. In order to account for these dissipative forces in the analysis of dynamic systems, it is necessary to make some assumptions about these forces, on the basis of experience. | Damped Single Degree-of-Freedom System | 10.1007/978-3-319-94743-3_2 |
2019-01-01 | In this chapter, we will study the motion of structures idealized as single-degree-of-freedom systems excited harmonically, that is, structures subjected to forces or displacements whose magnitudes may be represented by a sine or cosine function of time. This type of excitation results in one of the most important motions in the study of mechanical vibrations as well as in applications to structural dynamics. Structures are very often subjected to the dynamic action of rotating machinery which produces harmonic excitations due to the unavoidable presence of mass eccentricities in the rotating parts of such machinery. Furthermore, even in those cases when the excitation is not a harmonic function, the response of the structure may be obtained using the Fourier Method , as the superposition of individual responses to the harmonic components of external excitation. This approach will be dealt with in Chap. 20 as a special topic. | Response of One-Degree-of-Freedom System to Harmonic Loading | 10.1007/978-3-319-94743-3_3 |
2019-01-01 | A vertical rigid gyroscopic rotor with linear and cubic nonlinear damping of the support where the disk has a mass imbalance is considered herein. The motion equations in the form of Lagrange equations of the second kind have been composed to describe the motion of the rotor. The expressions have been found to determine the amplitude of the fundamental oscillations harmonic and the amplitude of the dynamic influence moment with the help of the harmonic balance method. Analysis of the results of amplitude-frequency characteristic studies and of the dependence of the dynamic influence moment amplitude on the oscillations frequency for different values of the linear and nonlinear damping coefficients show that both linear damping and cubic nonlinear damping have almost no effect on the amplitude-frequency characteristic in the lower resonant frequencies range, linear and cubic nonlinear damping can significantly suppress the resonance peak of the main harmonic in the resonance region, nonlinear damping, in contrast to linear damping, can slightly suppress the vibration amplitude of the rotor in the region where the velocity is above the critical velocity. The results of the studies can be successfully used to create passive vibration isolators used for damping of rotary machines vibrations. | Resonant Oscillations of a Vertical Hard Gyroscopic Rotor with Linear and Nonlinear Damping | 10.1007/978-3-030-20131-9_331 |
2019-01-01 | Auxiliary Mass Dampers (AMD) are often used to reduce excessive vibration amplitude in mechanical systems. It is also known that their performances are susceptible to changes in the frequency or in the nature of the excitation force. Therefore, to improve the robustness of the AMD it is necessary to design new systems which are adaptable to the excitation, i.e., tunable devices that could be used over large frequency range. In this work a friction damper, which is the association of an elastic element and a scratcher, is used to tune the AMD by changing the normal force in the scratcher at the same time that it dissipates the mechanical energy of the principal mass. This AMD is named Tunable Auxiliary Mass Damper (TAMD). Three normal force control strategies, and two combinations of them, are studied: (i) The normal force is assumed constant; (ii) The normal force is obtained from the solution of the equation of motion assuming null displacement for the principal mass; (iii) The normal force is obtained based on the vibratory system’s movement, warranting that the direction of the friction force promotes the movement of the principal mass toward its static equilibrium position. The effectiveness of the proposed TAMD is numerically evaluated based on mass and frequency ratios variations for each strategy. Therefore, a multi-degree-of-freedom (MDOF) system analysis is made in order to verify the TAMD’s robustness and efficiency. | Tunable Auxiliary Mass Damper with Friction Joint: Numerical Assessment | 10.1007/978-3-319-91217-2_4 |
2019-01-01 | This chapter presents a summary of dynamic analytical methods for high-rise buildings in Japan. The following indispensable items for the dynamic analysis of skyscrapers are briefly introduced: Structural design criteria, analytical model, earthquake motion used for dynamic analysis, acquisition of earthquake ground motions, various dynamic analysis methods and its application range, and modal analysis. | Earthquake Response Analysis of High-Rise Buildings | 10.1007/978-981-13-7185-1_2 |
2019-01-01 | This chapter describes regenerative chatter in milling. Similar to Chap. 3 , both analytical and numerical analyses are presented to predict the process behavior. The analytical, frequency domain stability lobe diagram is adapted to milling. Two algorithms are described: average tooth angle and Fourier series. Time domain simulations for square (straight teeth and helical teeth) and ball endmills (helical teeth) are detailed. The cutting force model is then extended and an experimental procedure for identifying the cutting force coefficients is derived for two different fitting approaches. Finally, the effect of process damping on milling stability at low speeds is presented. | Milling Dynamics | 10.1007/978-3-319-93707-6_4 |
2019-01-01 | Chapter 3 describes regenerative chatter in turning. To predict turning behavior, both analytical and numerical analyses are presented. The analytical, frequency domain stability lobe diagram is derived that describes the limiting stable chip width as a function of spindle speed. A time domain simulation is detailed that determines the dynamic cutting force and tool displacement in turning by numerical integration. The simulation is then used to identify stable and unstable cutting conditions. Finally, the specific application of modulated tool path turning and the effect of process damping on turning stability at low speeds are presented. | Turning Dynamics | 10.1007/978-3-319-93707-6_3 |
2019-01-01 | In the previous chapters, we determined the natural frequencies and modal shapes for undamped structures when modeled as shear buildings. We also determined the response of these structures using the modal superposition method. In this method, as we have seen, the differential equations of motion are uncoupled by means of a transformation of coordinates that incorporates the orthogonality property of the modal shapes. | Evaluation of Absolute Damping from Modal Damping Ratios | 10.1007/978-3-319-94743-3_20 |
2019-01-01 | During the last 2 decades, new code generations have been introduced which incorporate the achieved scientific and technological state of the art that has been proven its usefulness in practical application. The Eurocodes and the CICIND model codes are examples of this development. The Eurocode applies a modified gust response factor to model in-line wind loading and resonance due to turbulence through increasing the peak velocity pressure by a factor which depends on the individual size and dynamic features of the structure considered. The CICIND model codes for steel and concrete chimneys take account of the particular mechanical behaviour and the specific design requirements of these structures and utilizes the mean and the gust wind force, where the gust load defines an equivalent static load scaled to reproduce the real base bending moment of the chimney induced by wind gustiness. The cross-wind excitation of chimneys by vortex shedding is calculated in the CICIND model applying a negative aerodynamic damping to incorporate the motion induced forces, and a bandwidth factor to account for the reduction of the lift force spectrum caused by wind turbulence. Contrarily, the Eurocode relies on an empirical concept. In addition, it contains a further method, where the aerodynamic damping parameter is given for zero turbulence only. The principal issues of the chapter are to identify the merits and the drawbacks of the different concepts and to identify their dominant fields of application. | Structural Oscillations of High Chimneys Due to Wind Gusts and Vortex Shedding | 10.1007/978-3-662-57550-5_6 |
2019-01-01 | This paper is concerned with the asymptotic behavior of the solution to the Euler equations with time-depending damping on quadrant ( x , t ) ∈ ℝ^+ × ℝ^+, $${\partial _t}v - {\partial _x}u = 0,{\partial _t}u + {\partial _x}p\left( v \right) = - \frac{\alpha }{{{{\left( {1 + t} \right)}^\lambda }}}u,$$ ∂ t v − ∂ x u = 0 , ∂ t u + ∂ x p ( v ) = − α ( 1 + t ) λ u , , with the null-Dirichlet boundary condition or the null-Neumann boundary condition on u. We show that the corresponding initial-boundary value problem admits a unique global smooth solution which tends time- asymptotically to the nonlinear diffusion wave. Compared with the previous work about Euler equations with constant coefficient damping, studied by Nishihara and Yang (1999), and Jiang and Zhu (2009, Discrete Contin Dyn Syst), we obtain a general result when the initial perturbation belongs to the same space. In addition, our main novelty lies in the fact that the cut-off points of the convergence rates are different from our previous result about the Cauchy problem. Our proof is based on the classical energy method and the analyses of the nonlinear diffusion wave. | Convergence to diffusion waves for solutions of Euler equations with time-depending damping on quadrant | 10.1007/s11425-017-9271-x |
2019-01-01 | This chapter offers an overview of the theoretical foundations and the standard numerical methods for solving structural dynamics problems, with emphasis placed firmly on the latter. Starting with the analysis of single degree of freedom (SDOF) systems both in the time and in the frequency domain, it includes sections on the computation of elastic and inelastic response spectra, filtering in the frequency domain, the analysis of nonlinear SDOF systems and the generation of spectrum compatible ground motion time histories. Discrete multi-degree of freedom (MDOF) systems, condensation techniques and damping models are considered next. Both modal analysis (“response modal analysis”) and direct integration methods are employed, focussing especially on the behaviour of MDOF systems subject to seismic excitations described by response spectra or sets of specific ground motion time histories. Detailed descriptions of the software used for solving the numerous examples presented complete with full input-output parameter lists conclude the chapter. | Basic Theory and Numerical Tools | 10.1007/978-3-662-57550-5_1 |
2019-01-01 | The primary purpose of this paper is to identify performance indices and evaluate a design of a mono-tube MR damper valve, as a result of which relations among performance indices and possible design approaches are explored. To achieve this, initial design of a mono-tube MR damper valve is considered. Common MR damper valve configuration is adopted to which initial design parameters are specified. Performance indices that need to be considered while evaluating the design of a mono-tube magnetorheological (MR) damper valve are identified, and mathematical models are developed. The performance indices of the damper valve depend upon the magnetic circuit design of the valve; hence, for the adopted MR damper valve configuration, finite element model is built to analyze and investigate the performance indices of a 2-D axisymmetric MR damper valve. All performance indices of the damper valve are simulated within given range of input current and number of turns of coil. The simulation results show that the design of the MR dampers is highly dependent on the performance indices, and hence, the MR damper design should be application oriented. The results obtained in this work provide an insight for designers to create more efficient and reliable MR dampers. | Design Evaluation of a Mono-tube Magnetorheological (MR) Damper Valve | 10.1007/978-981-13-2718-6_15 |
2019-01-01 | Frequencies associated with self-excited vibrations are, in most cases, the natural frequencies of the system. The natural frequencies are not proportional to the rotational speed. Therefore, self-excited vibration is a form of non-synchronous vibration. In rotor systems, the lowest natural frequency is often below the rated rotational speed and it may become unstable, hence self-excited vibration is also known as sub-synchronous vibration. This chapter describes various case studies of self-excited vibrations, which are inherent in rotating machinery, as for a journal bearing, seal, centrifugal impeller, and blade for an axial flow machine. Also, the phenomena of internal friction, fluid trapped in a rotor, and rotor contacting with a stator, may produce strong self-excited vibration. While illustrating these unstable phenomena, the cause or mechanism of the instabilities and appropriate solutions are discussed by citing the v_BASE data. In addition, squeeze film dampers, which are used to stabilize the system by adding a damping effect, are explained. | Case Studies of Self-excited Vibration of Rotor Stability Problems | 10.1007/978-4-431-55453-0_8 |
2019-01-01 | The energy losses generated in rolling element bearings rise with increasing magnitude of the force transmitted between the rotor and the stationary part. A frequently used technological solution, which makes it possible to minimize the transmitted force, consists in adding damping devices to the rotor supports. To achieve their optimum performance in a wide range of operating speeds, their damping effect must be adaptable to the current angular velocity. This is offered by magnetorheological squeeze film dampers. Their main parts are two concentric rings separated by a layer of magnetorheological oil. Its squeezing produces the damping force. As magnetorheological fluids are sensitive to magnetic induction, the change of magnetic flux passing through the lubricating film changes the damping force. The goal of the carried out investigations was to study the influence of controllable damping in rotor supports on energy losses and driving moment of the motor in different velocity ranges. The investigations were performed by computational simulations. The rotor was rigid, supported by magnetorheological squeeze film dampers, and excited by its unbalance. The results show that appropriate adaptation of the magnitude of the damping force to the current operating speed arrives at minimizing the energy losses generated in the rotor supports. The performed analysis shows a new possibility of magnetorheological squeeze film dampers, which leads to improvement of performance of rotating machines and points out at a new field of their prospective application. | Application of the Controllable Magnetorheological Squeeze Film Dampers for Minimizing Energy Losses and Driving Moment of Rotating Machines | 10.1007/978-3-319-99262-4_10 |
2019-01-01 | Research has shown that the damping of a vibrating structure is highly dependent on its stress function. In this study, the bending stress and damping of wide cantilever beams under free vibration were analyzed using the classical plate and beam theory. The damping stress equation for cantilever beams under free vibration was derived based on the empirical function of unit dissipating energy, whereas the plate bending equation was derived using the double finite integral transform method. The bending stress and damping ratio results from the beam and the plate theory were compared with simulation results from finite element analysis (FEA) for different length-to-width ratios. Results show that the plate theory displayed a good agreement with FEA results in terms of estimated value and trending curve shape when a significantly large number of terms were used. Using a small number of terms resulted in large errors at high length-to-width ratios, but provided sufficient estimates when the length-to-width ratio dropped below four. It was found that the beam theory was only valid for beams with very high length-to-width ratios or square plates. Beyond this ratio, the beam theory recorded a higher error estimate than the plate theory. Overall, the most accurate stress and damping estimations come from the use of plate theory with a very high number of terms. | Stress and damping of wide cantilever beams under free vibration | 10.1007/s12206-018-1203-8 |
2019-01-01 | In this paper, we are concerned with the existence of mild solution and controllability for a class of nonlinear fractional control systems with damping in Hilbert spaces. Our first step is to give the representation of mild solution for this control system by utilizing the general method of Laplace transform and the theory of ( α , γ)-regularized families of operators. Next, we study the solvability and controllability of nonlinear fractional control systems with damping under some suitable sufficient conditions. Finally, two examples are given to illustrate the theory. | Existence And Controllability For Nonlinear Fractional Control Systems With Damping in Hilbert Spaces | 10.1007/s10473-019-0118-5 |
2019-01-01 | The increasing of operation speed and demand for precision in machinery make lubrication conditions a crucial aspect in order to maximize lifetime of rotor dynamic components. The elastohydrodynamic (EHD) regime more frequently occurs in nonconforming lubricated contacts with local elastic deformation due to high pressure in small contact area. The objective of this work is to analyze the EHD force reduced model applied to line contact based on restitutive and dissipative terms. In restitutive force term, an EHD stiffness approach is evaluated considering an explicit force-displacement relation with two independent parameters - stiffness and a constant surface separation force. Steady-state EHD contact numerical results allow estimating the restitutive parameters. The dissipative force term is composed by linear viscous damping. The damping is characterized by numerical simulation using the principle of energy conservation in transient elastohydrodynamic lubricated system. The influence of load and speed variations in damping fluctuations are investigated. The EHD reduced force model characterizes the lubricated contact in just three parameters (oil film stiffness, EHD constant surface separation force and viscous damping), simplifying the lubrication problem in comparison of solving EHD system of equations at each work condition and time step. This model can be applied to any nonconforming EHD line contact as cams, gears, needle element rolling bearings and cylindrical roller bearings in dynamic analysis and project stage development. Furthermore, an accurate contact model increases machine reliability, being promising to be used in model-based fault identification. | Stiffness and Damping Reduced Model in EHD Line Contacts | 10.1007/978-3-319-99262-4_4 |
2019-01-01 | Timbre is a complex auditory attribute that is extracted from a fused auditory event. Its perceptual representation has been explored as a multidimensional attribute whose different dimensions can be related to abstract spectral, temporal, and spectrotemporal properties of the audio signal, although previous knowledge of the sound source itself also plays a role. Perceptual dimensions can also be related to acoustic properties that directly carry information about the mechanical processes of a sound source, including its geometry (size, shape), its material composition, and the way it is set into vibration. Another conception of timbre is as a spectromorphology encompassing time-varying frequency and amplitude behaviors, as well as spectral and temporal modulations. In all musical sound sources, timbre covaries with fundamental frequency (pitch) and playing effort (loudness, dynamic level) and displays strong interactions with these parameters. | The Perceptual Representation of Timbre | 10.1007/978-3-030-14832-4_2 |
2019-01-01 | This chapter presents the expanded rod theory developed to simplify dynamic analysis of skyscrapers. This method replaces skyscrapers with a rod having equivalent rigidity and can be used to calculate the analysis considering axial deformation, bending deformation, shear deformation, shear-lag, and torsional deformation of the skyscraper subject to static and dynamic external loads. In addition, as a measure against seismic reinforcement, the dynamic analysis of a skyscraper with oil-damper can be easily calculated. | Extended Rod Theory | 10.1007/978-981-13-7185-1_4 |
2019-01-01 | The Floating Production Storage and Off-loading (FPSO) vessels are being used widely in offshore industries. The motion of FPSO subjected extreme sea condition needs to be controlled in order to maintain the station keeping of the vessel. The crude oil containers of an FPSO can be utilized as passive dampers for controlling the response of FPSO. These containers can act as Tuned Liquid Damper (TLD) if the natural frequency of the liquid oscillation in containers is tuned to the natural frequency of FPSO. FPSO container (tank) can be divided into several tanks (Multiple Tuned Liquid Damper, MTLD) with different tank length and liquid depths. The natural frequencies of MTLD can be intelligently distributed over a range around the natural frequency of FPSO or over a band of excitation wave frequencies. Each TLD can be modelled by using an equivalent Tuned Mass Damper (TMD) analogy. The present study attempts to comprehend the response control of FPSO under surge motion only, and the vessel is modelled as a single degree of freedom system subjected to random waves. Both time domain and frequency domain analyses have been carried out to verify the response control. From the present study, it has been found that MTLD for FPSO will be effective if they are tuned to a range of wave excitation frequencies. | Response Control of FPSO Using Multiple Tuned Liquid Dampers | 10.1007/978-981-13-3119-0_4 |
2019-01-01 | Interest on numerical models able to estimate the damping capacity of gas bearings has been recently grown up. These models are based on the discretization of Reynolds equation with distributed parameters (DP) or can also be simplified models taking into account a few lumped parameters (LP), which are able to describe the dynamic characteristics of the bearing as well. In this paper a simple LP model is compared with the analytical solution for the case of the infinite parallel plates. It is shown that the model is able to predict correctly the damping capacity. | Identification of a Lumped Parameters Numerical Model of Gas Bearings: Analysis of 1D Parallel Plates | 10.1007/978-3-030-03320-0_51 |
2019-01-01 | The effects of axial compressive load and internal viscous damping on the free vibration characteristics of Timoshenko beams are carried out using the dynamic stiffness formulation and the differential transformation method. The governing equations of motion are derived using the Hamilton’s principle. After the analytical solution of the equation of motion has been obtained, the dynamic stiffness method (DSM) is used and the dynamic stiffness matrix of the axially loaded Timoshenko beam with internal viscous damping is constructed to calculate natural frequencies. Moreover, an efficient mathematical technique called the differential transform method (DTM) is used to solve the governing differential equations of motion. The calculated natural frequencies of Timoshenko beams with various combinations of boundary conditions using the DSM and DTM are presented and compared with the analytical results where a very good agreement is observed. | Free Flexural Vibrations of Axially Loaded Timoshenko Beams with Internal Viscous Damping Using Dynamic Stiffness Formulation and Differential Transformation | 10.1007/978-3-319-93157-9_15 |
2019-01-01 | Chapter 2 describes how to use modal analysis, or the study of a system’s dynamic properties in the frequency domain, to describe the tool point dynamics for tool-holder combinations. It first reviews the fundamentals of single and two degree of freedom free and forced vibrations to establish notation conventions for a description of modal analysis. The text then discusses frequency response functions, details a modal fitting technique for extracting modal parameters, and describes the experimental procedures and equipment used to measure tool point frequency response functions. | Modal Analysis | 10.1007/978-3-319-93707-6_2 |
2019-01-01 | In the preceding chapter, the free undamped and damped vibration of single degree of freedom systems was discussed, and it was shown that the motion of such systems is governed by homogeneous second-order ordinary differential equations. The roots of the characteristic equations, as well as the solutions of the differential equations, strongly depend on the magnitude of the damping, and oscillatory motions are observed only in underdamped systems. In this chapter, we study the undamped and damped motion of single degree of freedom systems subjected to forcing functions which are time-dependent. Our discussion in this chapter will be limited only to the case of harmonic forcing functions. The response of the single degree of freedom system to periodic forcing functions, as well as to general forcing functions, will be discussed in the following chapter. | Forced Vibration | 10.1007/978-3-319-94271-1_4 |
2019-01-01 | For the past 50 years or so, Kolmogorov’s (1962) correction (K62) to his 1941 hypotheses (K41) has been embraced by an overwhelming majority of turbulence researchers. Our recent work suggests that there are no valid reasons for abandoning K41. In particular, analytical considerations, based on the NS equations, which take into account the finite Reynolds number (FRN) effect, together with the available experimental laboratory data, seem to confirm a tendency towards the simple and elegant predictions of K41 as the Reynolds number increases. This is especially true when the focus is on the length scales which lie in the dissipative range. Incorrectly accounting for the FRN effect and the inclusion of the atmospheric surface layer (ASL) data, likely to have been affected by the proximity to the surface, appear to be the major factors which have contributed to a nearly unchallenged acceptance of K62. | K41 Versus K62: Recent Developments | 10.1007/978-981-10-7542-1_1 |
2019-01-01 | This paper presents the characterization of a Carbon Fibre Reinforced Plastic (CFRP) and a couple of damping materials, particularly suited to the manufacturing process of composites. Young’s modulus and loss factor of each material are defined by means of the Oberst beam test method, where a specific curve fitting technique replaces the half-power bandwidth procedure to ameliorate the estimates of the parameters. Effects of both temperature and aging are reported, since operational conditions are various and time duration very important for most components, for sure in the automotive sector. Two sandwich beams, formed by the sequence CFRP/damping material/CFRP, are also tested to experimentally verify the effectiveness of this configuration to provide damping. Finally, two complete car doors have been produced with a CFRP composite, with and without an intermediate damping layer. Their modal parameters have been extracted by an experimental modal analysis and show that the damping material can effectively ameliorate the noise and vibration response of the structure. | Composite and Damping Materials Characterization with an Application to a Car Door | 10.1007/978-3-030-03320-0_19 |
2019-01-01 | In this paper, plane strain surface waves, also named generalized Rayleigh surface waves, in a transversely isotropic piezoelectric semiconductor half space are investigated. The governing equations of generalized Rayleigh surface waves include the equations of motion, Gauss’ law of electrostatics and the conservation of charge. Based on the basic theory of elastic-dynamic equations, the governing equations are deduced as equations related to the displacement, the electric potential and the perturbation of the carrier density and are solved analytically. We discuss dispersion curves and the attenuation tendency of generalized Rayleigh waves for real wave number cases. The results reveal that the semiconductor should lead to phase velocity decreasing, and the anomalous dispersion and damping of generalized Rayleigh waves. However, enough in-plane biasing electric field along the wave propagation should lead to the amplification of the waves. The influence of the out-plane biasing electric field is so slight that it can be omitted. These properties should be reproduced in the case of real frequencies. The results obtained may provide theoretical guidance for the design of high-performance surface acoustic wave devices made of piezoelectric semiconductors. | Generalized Rayleigh surface waves in a piezoelectric semiconductor half space | 10.1007/s11012-019-00944-1 |
2019-01-01 | Organizations follow a certain path or track which they have created in accordance with their strategic planning. Like any other organizational process, the continuous innovation of design is required in order to ensure that it is effectively adapted to changes in the environment, organizational behavior, as well as collaborator attitudes and needs. It has become trendy to follow organizational design trends, as they are typically in tune with environmental changes; however, design challenges lie within the organization rather than outside it; that is, while trends are informative, following them is complex. Shifts in competition paradigms are telling of organizational designing efforts, environmental receptiveness, as well as the effectiveness of their test of time; however, it is the organization’s innovativeness that will lead to a design that drives responsiveness and the co-creation of value. | Organizational Designing | 10.1007/978-3-030-03347-7_5 |
2019-01-01 | Among the problems encountered in rotordynamics, the phenomena of instability generally due to the hydrodynamic bearings and interns damping, the gyroscopic effect due to the discs and shafts, the excitations due to the unbalance as well as the nonlinear phenomena related on the bearings which support the rotor and the elements carried by the rotor. The objective of this paper is to investigate the effects of damping and rigidity of hydrodynamic bearing on the stability of a Lalanne-Ferraris rotor. This study was conducted with respect to the stability criterion seen in a natural frequencies’ equation. The process begins with the establishment of the characteristics of rotor elements. This is to assess the expressions of the kinetic and deformation energies, as well as the corresponding virtual work for rotor components: disk, shaft, unbalance and hydrodynamic bearing. The Rayleigh-Ritz method and Lagrange’s equations were used to determine the equations of motion. A computational program in FORTRAN is elaborated to solve the characteristic equation in free vibration. The roots are pairs of complex conjugate quantities. In forced vibration, the resolution of the linear algebraic system is conducted by the Gauss-Jordan direct method. Also a computational program in FORTRAN is elaborated. A numerical example of Lalanne and Ferraris rotor is computed. According to the results presented herein, the presence of damping for certain values of rigidities was found to be a possible source for instability of the rotor at defined speeds. | Dynamic Behavior and Stability of a Flexible Rotor | 10.1007/978-3-319-94616-0_4 |
2019-01-01 | Eccentric shaft-disk system with internal damping driven by a non-ideal power source exhibits Sommerfeld effect characterized by nonlinear jump phenomena of amplitude and rotor speed upon exceeding a critical power input around the critical speed. This effect causes instability in high speed rotors. So the diminution of such effect is extremely important in order to smooth running of the rotors at high speeds. The aim of this paper is to attenuate the Sommerfeld effect of an internally damped unbalanced flexible shaft-disk system via linearized active magnetic bearings. The shaft-disk system is excited through a brushed DC motor which acts as a non-ideal energy source. The characteristic equation of fifth order polynomial in rotor speed is obtained through energy balance of supplied power and the mechanical power dissipated at steady-state condition. Using MATLAB simulations, amplitude frequency responses are obtained close to system resonance for several values of bias current of active magnetic bearings. Thus the Sommerfeld effect is found to be attenuated as bias current increases gradually. The complete disappearance of Sommerfeld effect is also reported when the bias current reaches a specific value under certain conditions. A few numerical results are validated with established results when bias current is made to zero. | Attenuation of Sommerfeld effect in an internally damped eccentric shaft-disk system via active magnetic bearings | 10.1007/s11012-018-00936-7 |
2019-01-01 | This paper is based on a Search Engine ranking algorithm. It proposes the technique for improving the page rank algorithm. The work focuses on the change in page rank algorithm, which helps in reducing the time complexity. We have calculated the normalized page rank by using the median value as it reduces the calculation work and time complexity. The comparison has been done between both the algorithms, i.e., old PR algorithm and the new proposed PR algorithm. This work also focuses on the research to increase the rank of the website. Various hybrid approaches are used to increase the rank of the website. | Improved Google Page Rank Algorithm | 10.1007/978-981-13-2285-3_63 |
2019-01-01 | The laser powder bed fusion AM process has been used to manufacture beams with unique internal geometries that are capable of increasing inherent damping in a part. The concept of the internal design is to have densely packed, unfused powder pockets that dissipate energy via particle interaction. Four Inconel (IN) 718 beams have been tested and all demonstrated the capability to suppress vibration 10X more effectively than a fully fused beam. The mechanism presumed to dissipate energy and thus suppress vibration is the sliding of unfused particles. This mechanism has been associated with a crack opening under Mode II fracture. Based on this assumption, a proportional expression has been developed as a criterion for optimizing unfused powder locations for vibration suppression effectiveness and was validated with 3.175 mm thick beams. This study investigates five uniquely designed IN-718 beams created via the optimizing criterion to assess accuracy of the expression. The intent of this study is to investigate the predictability of the unfused pocket optimization criterion. The results of this study will lead to a more robust design criterion for more complex 3D structures with improved damping capability. | Forced-Response Verification of the Inherent Damping in Additive Manufactured Specimens | 10.1007/978-3-319-95083-9_15 |
2019-01-01 | Since the first appearance of synchrophasor Synchrophasor measurement technology, it has been playing a fundamental role for many advanced power system monitoring, analysis, and control applications Applications around the world. Phasor measurement unit (PMU) Phasor Measurement Unit (PMU) and wide-area measurement system (WAMS) Wide Area Measurement System (WAMS) are becoming the critical measurement infrastructures for transmission and generation systems. In this chapter, firstly the recent development of PMU Phasor Measurement Unit (PMU) / WAMS Wide Area Measurement System (WAMS) , communication, and synchronization network in China is summarized briefly. Then, some basic applications Applications , such as power system model parameter identification and validation Power system model parameter identification and validation , disturbance recognition and location Disturbance recognition and location , are introduced. Next, some major advanced applications Applications utilizing synchrophasor Synchrophasor measurement are emphasized and presented, including oscillation mode identification Oscillation mode identification based on ambient PMU Phasor Measurement Unit (PMU) data, wide-area backup protection Wide area backup protection , wide-area damping control Wide area damping control using HVDC modulation HVDC modulation . Considering the operational problems caused by integration of large-scale renewable energy resources, such as cascading tripping and subsynchronous resonance phenomena, synchrophasor technology Synchrophasor technology is expanded to meet the monitoring needs. Some pilot projects are utilized to illustrate the effectiveness of wide-area monitoring Wide area monitoring and control system. | Use of Synchrophasor Measurement Technology in China | 10.1007/978-3-319-89378-5_5 |
2019-01-01 | Hysteresis and vibration are main factors in reducing the accuracy and the speed of a nanopositioner. In order to improve the positioning accuracy and the speed, a robust adaptive resonant damping control is proposed for trajectory tracking of a nanopositioner system driven by a piezoelectric actuator. Radial basis function neural network is employed to approximate unknown nonlinearities in the controller so as to reduce the dependence on model information. Linear and hysteresis model are establish based on nanopositioning stage measured data. The proposed control strategy is verified by simulation using an identified model. | Robust Adaptive Resonant Damping Control of Nanopositioning | 10.1007/978-3-030-22808-8_14 |
2019-01-01 | The beam oscillations are modeled by the fourth-order hyperbolic partial differential equation. The minimized functional is the energy integral of an oscillating beam. Control is implemented via certain function appearing in the right side of the equation. It was shown that the solution of the problem exists for any given damping time, but with decreasing this time, finding the optimal control becomes more complicated. In this work, numerical damping of beam oscillations is implemented via several fixed point actuators. Computational algorithms have been developed on the basis of the matrix sweep method and the second order Marquardt minimization method. To find a good initial approximation empirical functions with a smaller number of variables are used. Examples of damping the oscillations via a different number of actuators are given. It is shown that the amplitude of the oscillations of any control functions increases with the reduction of the given damping time. Examples of damping the oscillations in the presence of constraints on control functions are given; in this case, the minimum damping time exists. The damping of oscillations is considered also in the case when different combinations of actuators are switched on at different time intervals of oscillation damping. | Numerical Damping of Forced Oscillations of an Elastic Beams | 10.1007/978-3-030-10934-9_20 |
2019-01-01 | Two methods are developed for determining the equivalent aerodynamic damping of reentry vehicle models. In the first method, the equivalent aerodynamic damping is determined on the basis of the experimental envelopes of the transitional process for the angle of attack changing with time; in the second method, all experimental points of the transitional process are involved. Both methods are found to produce similar results. The adequacy of the methods is verified by an example of a reentry vehicle model, which demonstrates that the predicted transitional processes for the angle of attack changing with time are in good agreement with the experimental data. | Methods for determining the equivalent aerodynamic damping of reentry vehicle models tested in a setup with free oscillations | 10.1134/S0869864319010013 |
2019-01-01 | A specific class of rotary machines is the high rotation turbochargers, to automotive application, wherein the shaft is continually subjected to axial forces of different magnitudes due to gas flows in the turbine and the compressor. These forces are supported by axial lubricated thrust bearings. The thrust bearings are modeled through equivalent stiffness and damping coefficients and the objective of the work is to get good estimates of these coefficients, comparing simulated results with experimental results. The stiffness coefficient is first obtained by small perturbation around the equilibrium position and used in a finite element model of the system at specific rotational speeds, and this value is compared to experimental results. Then, the damping coefficient is estimated, by running an optimization problem on this parameter, to approximate the simulated dynamic response of the system to experimental results of the turbocharger excited by an impact hammer, where both the displacement and force were measured. | Experimental Estimation of Equivalent Damping Coefficient of Thrust Bearings | 10.1007/978-3-319-91217-2_2 |
2019-01-01 | The paper presents free-vibration wind tunnel tests performed at WIST Boundary Layer Wind Tunnel at Ruhr-Universität Bochum (Germany) on a 3D aeroelastic cylindrical model with circular cross-section. The aim of the tests is to validate a model extension to the original spectral method developed by Vickery & Basu, able to calculate the maximum oscillation of a structure subjected to vortex-induced vibration in the lock-in region. The peculiarity of the extension is the implementation of an experimental curve for the negative aerodynamic damping. It was previously developed by the authors through forced vibration wind tunnel tests. The model extension is based on a linear differential equation. In fact, linear – in case iterative – approaches are usually preferred for the design of structures. However, limitations due to linearization of an intrinsically non-linear phenomenon are unavoidable. Strengths and weaknesses of the linear approach are discussed in the paper. | A Model Extension for Vortex-Induced Vibrations | 10.1007/978-3-030-12815-9_33 |
2019-01-01 | Oil-lubricated plain bearings are used widely to support the main rotors of rotating machinery, because the hydrodynamic oil films formed in the bearing clearances can guarantee smooth rotation of shafts and effectively prevent or suppress rotor vibrations. This chapter explains the principles of oil film formation in typical plain bearings, based on conventional hydrodynamic lubrication theory. The circumferential oil film shape at the steady-state equilibrium is determined, so that the hydrodynamic pressure generated in the oil film can balance the oil film reaction force vectorially with the applied bearing load. In other words, the oil film separates the journal from the bearing surface and the journal can float and rotate on the oil film. The oil film shape determines the journal center position represented by the journal eccentricity ratio and the attitude angle in polar coordinates. The steady-state journal center position and in turn the corresponding oil film shape vary with the operating condition of the journal bearing, that is, Sommerfeld number. When the journal center is slightly perturbed at the equilibrium, the oil film is slightly deformed, resulting in the slightly modified pressure distribution. Then, the corresponding oil film force is found to consist of the static reaction force at the equilibrium and also the two mutually perpendicular components of the small dynamic reaction force. Each of the two components is expressed by the linear sum of the two stiffness components and also the two damping components. In total, four stiffness components and four damping coefficients are determined at the equilibrium. These coefficients are the key factors that dominate the vibrational behavior of the rotor supported in the plain bearings. The coefficients obtained for various types of journal bearing are found to vary with the Sommerfeld number. Consequently, journal bearings need to be selected and designed so that the dynamic coefficients of the hydrodynamic oil films can enable satisfactory control of rotor vibration. | Basics of Plain Bearings | 10.1007/978-4-431-55453-0_2 |
2019-01-01 | The major problem in forced vibration response is resonance, where the frequencies of exciting forces coincide with the natural frequencies. Rotating machinery has different characteristics in resonance problems from general non-rotating structures. Therefore, the problems need be solved with this knowledge in mind, not only at the design stage, but also on-site. In the case of forced vibration, centrifugal forcing due to unbalance is a very typical example; however, various other external forces produced by different mechanisms may also become problematic and be experienced routinely. Examples include mechanically induced forces in gears, cross joints, and pulley belt systems; an electromagnetic force in a motor/generator; and rotating stall and impeller/blade interaction forces, which are induced by the fluid flow. Furthermore, torsional vibration is inevitable for rotating machinery and may become a large problem. In this chapter, these phenomena and appropriate countermeasures to implement are elucidated while referring to previously mentioned examples. | Case Studies of Forced Vibration Problems of a Rotor | 10.1007/978-4-431-55453-0_7 |
2019-01-01 | Increase in demand for environmental friendly engineered structures make the natural fiber reinforced composites as the best option to synthetic fiber in polymer composite structures. In this study, the influence of stacking sequence of natural hybrid laminates on mechanical and vibration characteristics that are beneficial for structural applications have been focused. To study the effect of stacking sequence efficiently, a high modulus natural fiber, i.e., Flax and a low modulus natural fiber, i.e., Sisal are preferred. The preferred natural hybrid composite laminates were made by hand layup technique. The hybrid laminates were tested for mechanical properties and free vibration characteristics by means of ASTM procedure. The experimental modal frequency values were used for finding the effective elastic constants of natural hybrid composite laminates adopting by simple regression analysis. These effective elastic constants were used for performing theoretical modal analysis of natural composite beams at high frequency level using finite element method. Based on the results of experimental and theoretical modal analysis of Flax/Sisal composite beams, the effective stacking sequence for structural application was suggested. | Influence of Stacking Sequence on Free Vibration Characteristics of Epoxy-Based Flax/Sisal Composite Beams | 10.1007/978-981-13-1780-4_18 |
2019-01-01 | This work examines the distribution of vibration absorber mass for a lumped mass metastructure model designed to suppress vibrations in the axial direction. Metastructures, a metamaterial inspired concept, are structures with distributed vibration absorbers. In automotive and aerospace industries, it is critical to have low levels of vibrations while also using lightweight materials. Previous work has shown that this design can effectively reduce vibrations by comparing the response of the metastructure to a structure with no vibration absorbers but with equal mass. Previous work constrained the vibration absorber masses to be the same throughout the structure. This work looks at the added performance that can be realized by allowing these masses to varying throughout the length of the metastructure. Additionally, the performance of the metastructure is also compared a host structure with a single tuned mass damper to show how this new technology differs from traditional vibration suppression methods. | Lumped Mass Model of a 1D Metastructure with Vibration Absorbers with Varying Mass | 10.1007/978-3-319-74642-5_6 |
2019-01-01 | The vibration-absorbing properties of the plate under the action of a spherical harmonic wave in the soil are studied. In the soil model, an elastic isotropic medium is used. The main goal is to determine the total vector field of accelerations. The mathematical formulation of the problem includes the assignment of the incident wave, the equations of motion of the soil and the plates, the boundary conditions for the slab and the soil, the conditions at infinity, and the conditions of contact of the earth with the obstacle, where we neglect the connection of the plate to the ground. The motion of the plate is described by the system of equations of Paimushin V.N. The kinematic parameters of the plate and the parameters of the disturbed stress-strain state of the soil are represented in the form of double trigonometric series satisfying the boundary conditions. After that, the constants of integration, displacement and vibration acceleration are determined. | Determination of Vibrations at Different Points in the Ground After the Passage of a Spherical Wave Through a Vibration-Absorbing Obstacle | 10.1007/978-3-319-91989-8_86 |
2019-01-01 | The aim of this paper is to derive higher order energy estimates for solutions to the Cauchy problem for damped wave models with time-dependent propagation speed and dissipation. The model of interest is $$\begin{aligned} {\left\{ \begin{array}{ll} u_{tt}-\lambda ^2(t)\omega ^2(t)\varDelta u +\rho (t)\omega (t)u_t=0, &{} (t,x)\in [0,\infty )\times \mathbb {R}^n, \\ u(0,x)=u_0(x), \,\,\,\, u_t(0,x)=u_1(x), &{} x\in \mathbb {R}^n, \end{array}\right. } \end{aligned}$$ The coefficients $$\lambda =\lambda (t)$$ and $$\rho =\rho (t)$$ are shape functions and $$\omega =\omega (t)$$ is a bounded oscillating function. If $$\omega (t)\equiv 1$$ and $$\rho (t)u_t$$ is an effective dissipation term, then $$L^2-L^2$$ energy estimates are proved in Bui and Reissig (Fourier analysis, trends in mathematics. Birkhäuser, Basel, [ 2 ]). In contrast, the main goal of the present paper is to generalize the previous results to coefficients including an oscillating function in the time-dependent coefficients. We will explain how the interplay between the shape functions and oscillating behavior of the coefficient $$\omega =\omega (t)$$ will influence energy estimates. | The Influence of Oscillations on Energy Estimates for Damped Wave Models with Time-dependent Propagation Speed and Dissipation | 10.1007/978-3-030-26748-3_17 |
2019-01-01 | Large amplitude vibration of mast arm structures due to wind loads are the primary contributing factor to the reduced fatigue life of signal support structures. To alleviate this problem of wind-induced in-plane vibration of mast arm signal structures, a particle-thrust damping based turned mass damper (PTD-TMD) device is adopted and its damping effect is characterized experimentally. The particle-thrust damping is a passive damping device that does not require electric power and is temperature independent. Based on the calibration test, an equivalent dynamic model of the PTD-TMD device is developed and used for numerical simulation study. The damping effects of this PTD-TMD device on signal support structures was investigated through both numerical analysis and laboratory testing of a 50-ft (15.24 m) mast arm structure including both free vibration and forced vibration tests. The experimental test and numerical study results show that vibration response behavior of mast arm signal support structures can be significantly reduced by installing the PTD-TMD that can increase the critical damping ratio of the mast arm signal structures to 4%. The stress range at the welded connection between the mast arm and traffic pole is also reduced. | Experimental study of vibration mitigation of mast arm signal structures with particle-thrust damping based tuned mass damper | 10.1007/s11803-019-0500-2 |
2019-01-01 | The damping of steel welded machine tool bodies is usually insufficient in a perspective of functional properties of the machine. Therefore, methods are sought to increase their ability to dissipate energy. One of the solutions is to fill steel welded body with a composite material based on an epoxy resin. Such a structure should maintain its good damping abilities during machine tool lifetime regardless of time-varying loads accompanying cutting process. In the paper an analysis of the time-varying load influence on damping abilities of steel beams filled with composite material is presented. Three beams differing in terms of composition of composite material were subjected to time-varying load and for each four hundred thousand cycles, damping was determined using the half power method. Based on the obtained results, it was found that increase of the number of cycles of time-varying load does not affect the damping properties. | Assessment of the time-varying load influence on damping abilities of steel beams filled with composite material | 10.1007/978-3-030-20131-9_327 |
2019-01-01 | Ships are prone to large roll motions in beam and oblique seas at encounter frequencies near the design frequency of the vessel. The nonlinearity of roll damping and roll motion has been investigated in the past by various researchers. The prediction of roll damping and roll motion of ships becomes difficult by simplified approaches. Ship roll motion is highly influenced by viscous flow around the hull. Vortex formation and its shedding from the hull and appendages have larger contribution to roll damping. Therefore, the popular approach for prediction of roll damping and roll motion of ships is with the help of model experiments and more recently URANS (Unsteady Reynolds-averaged Navier–Stokes)-based simulations. Free roll decay experiments in calm water conditions give a good estimate of roll damping of ships at natural frequency. The flow characteristics around the hull may not be the same when the ship is moving at a forward speed. Hence, it is important to take into consideration the effect of forward speed on roll damping obtained from free roll decay of the ships. This paper addresses the effect of forward speed on roll damping of a 1:100 (Froude) scaled container ship model. The model is 2.88 m in length, 0.345 m in beam and was loaded to a draft of 0.12 m; free roll decay experiments at zero forward speed were carried out in a wave flume at Department of Ocean Engineering, IIT Madras. The wave flume is 4 m wide, 90 m long and has water depth of 2.5 m. The held-over free roll decay tests were carried out by subjecting the model to known initial heel and releasing it. The roll angle was measured using inclinometer via data acquisition CPU. The URANS-based simulations of the free roll decay experiments at zero forward speed were carried out in a commercial computational fluid dynamics (CFD) software and validated. The CFD model was then used to carry out the free roll decay simulations at two forward speeds of the ship model. The effect of forward speed on roll damping of the ship model was assessed from the results of CFD simulations. | Effect of Forward Speed on Roll Damping of a Container Ship Using URANS Simulations | 10.1007/978-981-13-3119-0_12 |
2019-01-01 | Seismic analysis of structures will not be complete without a proper investigation of underlying soil behavior to dynamic loading. Such dynamic behavior is complex in nature due to many influencing parameters. The complex dynamic soil behavior can be represented using the strength and stiffness properties such as low-strain shear modulus ( G _ max ), modulus ratio ( G / G _ max ), and damping ratio ( D ) variation with shear strain along with the liquefaction potential of soils. Several field and laboratory element testing techniques are available for assessing the behavior of soils to dynamic loads. This article describes some of the widely used field and laboratory testing techniques for the dynamic investigations of soils. Typical results using each test are also provided for easy and comprehensive understanding to the reader. Analytical formulations based on the experimental results were provided and the present experimental data is compared with the data of Indian sandy soils from the literature. Furthermore, a seismic ground response study has been performed to demonstrate the applicability of the proposed formulations. | Dynamic Characterization of Soils Using Various Methods for Seismic Site Response Studies | 10.1007/978-981-13-5871-5_13 |
2019-01-01 | In this paper, a damping estimation method based on distribution of zero-crossing times and its applications are presented. The method is empirically derived and it is based on Rice distribution operating on probability distribution of zero-crossings. The method’s assertion is that a relationship exists between said probability distribution and the bandwidth of a mechanical system and this can be used as a means of increasing confidence in more traditional damping estimation methods. The method is applicable to responses that are due to broadband random excitation featuring a mono-harmonic response. Given that a multitude of modes will be active in aero-engines; its application has to be preceded with a suitable band-pass filter to isolate modes of interest. Such filtering is shown to affect the damping estimates. Some controlled laboratory tests are performed to verify the accuracy of the method and to study the effects of preceding filtering amongst other factors such as modal density, data length etc. The performance of the method is compared with Fourier transform based damping estimation methods. The results of application of the method to real engine measurements and carefully controlled laboratory tests are also presented. | A Distribution-Based Damping Estimation Method for Random Vibration Response and Its Applications | 10.1007/978-3-319-74793-4_24 |
2019-01-01 | In mechanical systems, the mechanical power is often provided by an electric motor. This power is supplied to a load by means of a shaft or a mechanical transmission that is made of steel. Despite the mechanical strength of steel, flexibility becomes a significant phenomenon when large loads are present. This situation is common in large radio telescopes, for instance. | Control of a Servomechanism with Flexibility | 10.1007/978-3-319-75804-6_12 |
2019-01-01 | Magnetorheological fluid is a smart material which can change its viscosity in milliseconds depending on the magnetic field applied. This brings a great advantage to create variable damping ability if it is used in an absorber. The stiffness of the absorber can be manipulated by an external magnetic field which effects the apparent viscosity of the magnetorheological fluid inside the absorber. Various control algorithms can be used to provide an effective absorption for any kind of structural vibration. Because of these features, magnetorheological absorbers have received great attention of researchers in the last decade. In this study, it is aimed to simulate a magnetorheological absorber under a sinusoidal vibration with Computational Fluid Dynamics and Magnetic Field Finite Elements Analysis. The magnetorheological fluid is modelled as a Non-Newtonian fluid and Herschel-Bulkley viscosity model is used to determine the apparent viscosity. Magnetic field is modelled for a constant current which generates different magnetic flux densities inside the absorber body. The Computational Fluid Dynamics and Finite Elements Analysis solutions are coupled in a two-dimensional axisymmetric domain and the results are revealed. The coupled solution of both are realized for the first time in the literature by means of an apparent viscosity approach. The numerical solution is compared with the experiments. A good agreement is observed between both results. | Coupled Magnetic and CFD Modelling of a Structural Magnetorheological Vibration Absorber with Experimental Validation | 10.1007/978-3-319-89911-4_9 |
2019-01-01 | Higher demands on the dynamic behavior of feed drives of machine tools require better system identification methods to identify the controlled system to optimize better controllers. Most modern CNC systems have still simple PI-controllers for speed and current loop and a P-controller with further filters for the position loop. Current research has shown that the bandwidth of the position control loop can be increased by optimal control methods like LQG- or H _∞-control. To achieve higher bandwidths or to create uncertainty models it is required also to identify the position dependent effects in the transfer function of the controlled system. Moreover, the identification process of the controlled system requires often manual help. This publication presents a method on how to measure more exactly the transfer behavior of a feed drive and identify automatically the poles and zeros of the transfer function. | Automatic System Identification of Forward Feed Drives in Machine Tools | 10.1007/978-3-030-03451-1_15 |
2019-01-01 | The aim of this study is to obtain information about the influence of cross section changes to dynamic behavior of vibrating beam. It was found that location of the changed cross sections influences energy dissipation in the structure and could be used for damping structural vibrations. The contacting interaction of structure with support is characterized by a rich spectral content of excitation impulses capable to excite a wide range of natural modes. The finite element method is used for the defected beam free vibration analysis. The adequacy of mathematical model to physical one is shown employing developed experimental setup. By providing the first three natural frequencies through vibration simulation, amplitude-frequency characteristics are plotted. The most favorable conditions for energy dissipation in the structure material appear when the frequencies of divided by structural defects parts differ twice because its vibrations are pre-phasic, which excites the higher vibration modes. | Vibration peculiarity of impacting variable cross section cantilever structure | 10.1007/978-3-030-20131-9_416 |
2019-01-01 | Due to increase in the rate of occurrence of earthquakes and associated damages, site-specific dynamic models are attracted to research in the recent past. The shear modulus degradation curve, damping characteristics and shear wave velocity profile are indispensable input properties required for carrying out the site response analysis. However, most of the site response studies are being carried out using existing dynamic model developed for generic soil. In the present study, results of resonant column and cyclic triaxial tests on reconstituted dry silty-sands specimens obtained from the recently liquefied site of Tripura, India is presented. The shear modulus degradation curve and damping ratio for a low (<10^−3) to high strain range (up to 5%) are presented and compared with the available well-known curves and discussed. Also, the effects of confining pressure and relative density on dynamic properties are presented. Further, comparison has been made between the shear wave velocity measured in the liquefied field using Multichannel Analysis of Surface Waves (MASW) and laboratory results of low strain shear wave velocity. These results can be used for amplification estimation or micro-zonation studies in Tripura. | Dynamic Properties of Surface Liquefied Site Silty-Sand of Tripura, India | 10.1007/978-3-030-01920-4_12 |
2019-01-01 | In this work, we explore the possibilities of passive damping the resonance vibrations of a cantilevered duralumin plate located on the free surface of a quiescent fluid. The harmonic excitation with a specified frequency is provided by the electromagnetic field, which is generated under a combined action of a light neodymium magnet attached to the structure and a superposed coil. Passage of the alternating current produced by the generator through the coil generates an electromagnetic force, which oscillates the plate. The oscillations are damped by a piezoelectric element connected to an external passive electric RL-circuit. Measurements of the plate vibrations are taken using a Polytec PDV-100 digital laser vibrometer with a sampling frequency of 48 kHz. The amplitude-frequency characteristics of the plate were obtained from the experimental studies. The values of inductance and resistance parameters of the external RL-circuit were selected in such a way as to ensure the most effective damping of the harmonic vibrations of the plate. It was shown that the peak value of the vibration velocity can be reduced by 20 times in air environment and by 2.5 times in the case of interaction with fluid. | Damping of Hydroelastic Vibrations of the Plate Using Shunted Piezoelectric Element. Part II: Experiment | 10.1007/978-3-030-21894-2_64 |
2019-01-01 | Gas foil Bearing (GFB) are oil-free, high-speed and light bearings, which work according to the principle of fluid film lubrication. Thanks to their elastic structure, GFBs are able to compensate for minor pressure changes in the lubrication films. This paper presents the experimental structural analysis of first-generation gas foil bearings. The aim of the experimental investigation is to determine the behaviour of GFBs at static and dynamic loads. The tests are carried out with rotor speeds close to 0 rpm. In the course of the static investigation, the GFB was mounted on shafts with different diameters and loaded with a force of −150 N to 150 N. Results from the static measurement show that not only the shaft diameter plays a role in determining the bearing clearance but also the number of activated bumps. It also shows that with a small bearing clearance ( $$ {\le }10\,{\upmu }\mathrm{m} $$ ), the GFB has an almost linear static stiffness. In the dynamic study, the GFB was mounted on a non rotating shaft and was excited by the shaker with a mono-frequency load. The goal of the dynamic investigation was to determine the dynamic stiffness behaviour and damping behaviour of GFBs at different amplitudes (2 $$\upmu $$ m, 6 $$\upmu $$ m and 10 $$\upmu $$ m) and over the frequency range of 30 Hz to 1000 Hz. In addition, this study aimed to find out whether the formation of subharmonic vibrations observed in the rotordynamic investigation can be attributed to the GFB structure. These subharmonic vibrations, as previous studies show, occur at speeds starting at about 20 000 rpm (333 Hz). For this reason, the dynamic measurement was performed up to 1000 Hz. The results show that the damping decreases with increasing frequency up to 490 Hz before rising again. This behaviour is amplitude independent. The stiffness of the bearings increases with increasing frequency. To verify the formation of subharmonic vibrations through the structure of GFBs, a Fourier transformation of the measurement signal was performed. However, no subharmonic vibration can be detected. | Experimental Structural Analysis of Gas Foil Bearings | 10.1007/978-3-319-99262-4_19 |
2019-01-01 | This [aut] Huss, M. paper [aut] Kuttenkeuler, J. presents [aut] Werner, S. unique [aut] Soder, C, -J. experimental set-ups in model scale and full scale for evaluating roll damping Roll damping properties of a Panamax Pure Car and Truck Carrier at speed. The purpose of this study is to develop a method for the assessment of roll damping based on full scale trials and to validate the use of roll damping derived from model tests for full scale vessels. Experimental data are also used to assess a semi-empirical method that today provides input for the prediction of critical rolling events such as parametric rolling Parametric roll and severe rolling motions in general. | Assessment of Ship Roll Damping Through Full Scale and Model Scale Experiments and Semi-empirical Methods | 10.1007/978-3-030-00516-0_10 |
2019-01-01 | Owing to the growth in human population, the land-scarce island countries and countries with long coastline are expanding their horizon to ocean environment through very large floating structures (VLFS) for different purposes as these are cost-effective, environment-friendly and can be manufactured easily. VLFS applications include floating airports, artificial islands, mobile offshore base and Mega-Float and are built using Pontoon-type or semi-submersible-type structures. In these types of structures, because of its large size, elastic deformations are more important than their rigid body motions. In this paper, hydroelastic behaviour of a barge Pontoon-type VLFS under various water depths is investigated. Analysis is based on three-dimensional linear hydroelastic theory to obtain the wave-induced hydroelastic response of the structures in the frequency domain. For solving this coupled fluid-structure interaction problem, the modal expansion method and the dry normal modes of vibration is commonly used for the floating structure. The structure is modelled using PATRAN [ 1 ], and the hydroelastic analysis is carried using HYDRAN-XR software. Responses in regular wave in the vertical mode at salient point along the length of the VLFS are presented for various wave headings and frequency. Vertical displacements at both edges of the structures and at the centre portion are found. Response for the six water depth conditions has been examined, and the observed results emphasize that vertical displacements are dominant in deep water conditions in relative to the shallow water conditions. Results also suggest that horizontal displacement is significantly higher in shallow water conditions. | Hydroelastic Responses of a Pontoon-Type VLFS in Different Water Depths | 10.1007/978-981-13-3119-0_18 |
2019-01-01 | One of the main concerns in using commercial software for finite element analyses of dam-foundation-reservoir systems is that the simplifying assumptions of the massless foundation are unreliable. In this study, an appropriate direct finite element method is introduced for simulating the mass, radiation damping and wave propagation effect in foundations of dam-foundation-reservoir systems using commercial software ABAQUS. The free-field boundary condition is used for modeling the semi-infinite foundation and radiation damping, which is not a built-in boundary condition in most of the available commercial software for finite element analysis of structures such as ANSYS or ABAQUS and thus needs to be implemented differently. The different mechanism for modeling of the foundation, earthquake input and far-field boundary condition is described. Implementation of the free-field boundary condition in finite element software is verified by comparing it with analytical results. To investigation the feasibility of the proposed method in dam-foundation-reservoir system analysis, a series of analyses is accomplished in a variety of cases and the obtained results are compared with the substructure method by using the EAGD-84 program. Finally, the massed and massless foundation results are compared and it is concluded that the massless foundation approach leads to the overestimation of the displacements and stresses within the dam body. | Seismic analysis of dam-foundation-reservoir system including the effects of foundation mass and radiation damping | 10.1007/s11803-019-0499-4 |
2019-01-01 | Dry-friction damping effect to reduction of self-excited vibrations due to aero-elastic instability is studied on numerical reduced model of rotating turbine wheel with 30 blades. The aerodynamic excitation arises from the spatially periodical flow of steam through the stator blades cascade. Dry friction contact damping is considered as one of the very effective methods for self-excited “flutter” vibrations. The study is oriented on the narrow frequency range and therefore the blades are modelled as systems with one degree of freedom (DOF). The selfexcited aero-elastic forces of blades are described by two different types of Van der Pol model. It is shown for both self-excitation models that the dry friction forces needed for suppression of dangerous flutter vibrations strongly depends on the complexity of modes and also on the mutual positions of excitation forces to damping elements. | Study of dry-friction damping effect on two simplified models of flutter oscillations | 10.1007/978-3-030-20131-9_337 |
2019-01-01 | With the increase of wind power installed capacity, research on the dynamic behavior and stabilization mechanism of the power system has had a certain impact. Frequent small disturbances will affect system stability and cause huge economic losses. In this context, based on the concept and analysis method of small signal stability, three different types of wind turbines are adopted, the eigenvalue analysis method in PSAT is used, the wind turbines have been studied in different types, different wind farm access distances and under different conditions of wind power penetration rate on the influence of the small signal stability when accessing WSCC 3-machine, 9-bus system. The result showed that the wind turbine type, the access distance, and the wind power penetration rate had different degrees of impact on the system. | Influence of Wind Farm Access on System Small Signal Stability | 10.1007/978-981-13-5841-8_12 |
2019-01-01 | The reliable guided wave inspection techniques depend on the accurate understanding of dispersive properties. The classic finite element method has been proven to be very practical for modeling wave propagation in arbitrary waveguides. However, when it comes to modeling on complex geometries, it still has a major drawback: the geometric discrete errors and the high consumption of resources to improve accuracy. Recently, Isogeometric analysis has been found advantageous over the classic finite element method on geometry representation and mesh generation. Here, a wave isogeometric analysis (WIGA) method is proposed for the computation of guided wave characteristics in rotating damped cylinders, based on the Floquet’s principle. According to the linear incremental theory and the principle of virtual power, elastodynamic wave equation is established, with regard to the WIGA. To ensure its effectiveness, the convergence and accuracy of the proposed method are considered compared with that of the wave finite element method. The size of unit cell and the solvable frequency range are discussed in detail. Furthermore, dispersive behaviors are computed considering the effects of damping and rotation. The results demonstrate that flexural wave modes are very sensitive to the rotation effect. Particularly, in phase velocity spectra the characteristic frequency at the amplitude peak equals to the rotational angular speed, where wave propagating and attenuating both vanish. | Wave isogeometric analysis method for calculating dispersive properties of guided waves in rotating damped cylinders | 10.1007/s11012-018-0921-4 |
2019-01-01 | The adoption of wind turbines to produce electric energy nowadays represents one of the most promising alternatives to the use of the exhausting fossil fuel stocks. The actual tendency is toward the design of taller towers that can produce more power because excited by stronger winds. There is the need of designing these structures in a cost effective way, aiming to reduce the wind induced growing structural demand. Three different control systems are investigated and compared herein to this aim, on the basis of the experimental results gathered at the Structural Dynamics Laboratory of the Denmark Technical University. Two of these are passive (tuned rolling-ball damper, spherical tuned liquid damper), while the third one is semi-active and aims at realizing a time-variant base restraint. The experimental comparison of the three strategies, tested against two types of wind loads, allow to draw interesting conclusions and to provide useful hints to give rise to further developments of the technologies investigated. | Mitigation of Structural Demand to Wind Turbines: Experimental Investigation of Three Control Strategies | 10.1007/978-3-030-12815-9_14 |
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