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2019-08-15 | This paper deals with the characterization of dry sand-rubber tire shred mixtures to find shear strength and dynamic properties. A series of ordinary triaxial shear tests, direct shear tests and dynamic triaxial tests were performed on dense dry sand-rubber tire shred mixtures for various rubber replacement levels such as 0, 10, 30, 50 and 100% by weight. The effects of rubber content, confining pressures and rates of shearing on the angle of internal friction of the mixtures were investigated. Also, the influence of rubber content and the rate of horizontal displacement on the volumetric strain is presented. In addition, this paper proposes an appropriate method to find the angle of repose of dry sand-rubber tire shred mixtures. The angle of repose of the mixtures is compared with the angles of internal friction obtained from triaxial shear and direct shear tests. Finally, the effects of saturation, rubber content, axial strain, frequency and number of cycles of loading on the strain-dependent stiffness and damping properties of these mixtures were studied. | Factors Affecting Strength and Stiffness of Dry Sand-Rubber Tire Shred Mixtures | 10.1007/s10706-018-00792-y |
2019-08-15 | This paper presents a detailed analysis of squeeze film air damping effects on dynamic responses of RF-MEMS switches under varying environmental conditions, etch holes’ configuration and air gap thickness values. The effect operating conditions like air pressure, temperature and humidity on the closing time of RF-MEMS switches is analyzed. The air pressure distribution beneath the top suspended plate of switches and corresponding damping parameters extraction, under varying conditions, is obtained using finite element method based modal projection technique. The extracted damping parameters are used in the subsequent coupled field electrostatic-structural dynamic analysis to analyze the effect of variation in environmental variations and geometric parameters on the closing time of RF-MEMS switches. The effect of change in etch holes’ configuration on the damping parameters is obtained to be minimum while change in switch operating conditions and air gap thickness values have significant effect on the air damping value and closing time of switches. | Effect of environmental conditions and geometric parameters on the squeeze film damping in RF-MEMS switches | 10.1007/s10470-018-1283-5 |
2019-08-06 | As the rheology of a magneto-rheological (MR) fluid can be controlled by an externally applied magnetic field, the damping force generated by a MR damper can be controlled by varying the current supplied to an electromagnet inside the damper. This paper presents the experimental evaluation of such a MR damper RD-8040-1 by Lord Corporation, USA, and its application in a semi-active suspension. The experiments were carried out in damping force testing machine. Sinusoidal displacement input was given to the test damper. The set of experiments were repeated for different levels of current (0–1.5 A in steps of 0.25 A) supplied to the MR damper. Plots of force versus displacement for each frequency of excitation and plots of maximum force versus frequency of excitation show that higher values of current lead to elevated values of MR damper forces. This increase in MR damper load with current supplied is studied and analyzed to develop a mathematical model of the MR damper under investigation. The nonlinear softening hysteretic behavior of the MR damper is simulated by using genetic algorithm provided in the optimization toolbox of MATLAB. Calculations on energy dissipation and equivalent damping coefficient of the MR damper show that the same damper can make the suspension system behave as an underdamped system, critically damped system or overdamped system depending on the value of current supplied to it. The application of this MR damper for heavy vehicle driver’s seat suspension is explored with the help of MATLAB simulations. | Evaluation of a commercial MR damper for application in semi-active suspension | 10.1007/s42452-019-1026-y |
2019-08-06 | After the Northridge and Kobe earthquakes, several destruction of the structural beams were occurred. The difficulty and cost-effectiveness of beam replacement after earthquakes is a major problem on steel structures. For this purpose, the idea of using replaceable connection is suggested. A slit steel damper (SSD) is introduced that leads to the further energy damping and the ability to move the plastic joint outside of structural elements. The stiffness and damping characteristics of SSD is related to the thickness, height and number of sheets of the damper. The usage of SSD is more progressive and at the same time, the optimal design of SSDs should be proposed to meet the economical criterion and the reduction of the stress and deflection. In this study, an optimal SSD connection is proposed to enhance the performance of the classical SSD connection to meet the criterion of AISC to utilize in special moment frames. The results demonstrated that increasing the thickness and reduction of the steel sheets in the damper had a greater effect on the performance of the SSD connection, in comparison with the increase in the number of sheets. Therefore, the Cuckoo Search (CS) was utilized to optimize the several SSD parameters. Furthermore, a comparison between the CS-SSD and Reduced Beam Section (RBS) which is known as a common moment steel fixed-connection was accomplished. Results indicate that CS-SSD connection can reach the same function as the RBS connections under cycling loadings, in addition to the easy replacement capability after seismic excitations. The performance of the proposed CS optimization algorithm in designing of the optimal SSD was compared with the traditional Genetic Algorithm and the particle swarm optimization (PSO) with considering several designing constraints. High capabilities of the proposed CS optimization algorithm in terms of weight, energy absorption, stiffness and bearing capacity of SSD connections are simultaneously clarified by the results. | Design of Optimal Slit Steel Damper Under Cyclic Loading for Special Moment Frame by Cuckoo Search | 10.1007/s13296-019-00206-6 |
2019-08-05 | Abstract The objective of this research work is to investigate the effect of multiwall carbon nanotube (MWCNT) content (0.3–1.2 wt%) on a potassium sodium niobate (KNN)-based piezoelectric unimorph harvester for enhancing the energy generation capacity. KNN–MWCNT composites were fabricated by using a microwave solid state technique. The energy-harvesting performance of the KNN–MWCNT composite was determined by the base excitation method and sized to resonate between 20 and 100 Hz at 1 $$\hbox {M}\Omega $$ M Ω load resistance. The energy performance of the KNN composite at percolation threshold (0.6 wt% MWCNT) showed a maximum power generation of $$2.94\, \upmu \hbox {W}$$ 2.94 μ W , the power density of 7.15 $$\upmu \hbox {W}$$ μ W $$\hbox {m}^{-3}$$ m - 3 and overall efficiency of 83.75% at an input acceleration of 0.5 g and a load resistance of 1 $$\hbox {M}\Omega $$ M Ω . Improvements observed in the power generation by percolation phenomena and ionic flow over the nanotube surface of KNN composites prove to be a boon for low-power sensing devices. Graphic abstract | Energy-harvesting enhancement in composites of microwave-exfoliated KNN and multiwall carbon nanotubes | 10.1007/s12034-019-1938-6 |
2019-08-05 | In this paper, we aim to obtain the existence of at least three classical solutions for nonlinear impulsive problems neither adding superlinear or local sublinear conditions to nonlinear term at zero nor adding superlinear assumptions to nonlinear term at infinity. Our approach relies on variational methods, more specifically, on a three critical points theorem. | Triple solutions for a damped impulsive differential equation | 10.1186/s13662-019-2269-z |
2019-08-01 | Experiments show a strong increase in damping with the vibration amplitude during nonlinear vibrations of beams, plates and shells. This is observed for large size structures but also for micro- and nanodevices. The present study derives nonlinear damping from viscoelasticity by using a single-degree-of-freedom model obtained from standard linear solid material where geometric nonlinearity is inserted in. The solution of the problem is initially reached by a third-order harmonic balance method. Then, the equation of motion is obtained in differential form, which is extremely useful in applications. The damping model developed is nonlinear and the parameters are identified from experiments. Experimental and numerical results are compared for forced vibration responses measured for two different continuous structural elements: a free-edge plate and a shallow shell. The free-edge plate is interesting since it represents a case with no energy escape through the boundary. | Derivation of nonlinear damping from viscoelasticity in case of nonlinear vibrations | 10.1007/s11071-018-4312-0 |
2019-08-01 | We study uniform stabilization and the continuous dependence of solutions to an initial and boundary value problem for a nonlinear hyperbolic equation with (possibly strong) linear damping. | Energy Decay and Continuous Dependence for Damped Semilinear Wave Equation | 10.1007/s40995-017-0471-y |
2019-08-01 | A variable air volume (VAV) air handling system can significantly reduce fan power under partial load conditions. The focus of this study is developing a modeling program to predict the potential energy saving by the secondary HVAC system strategies. Comprehensive steady-state models are established to describe the energy performance of different control strategies for secondary HVAC systems. With building loads, minimum fresh air flow rate, pressure losses, supply air temperature control, dampers control and coil characteristic as inputs, the objectives were to develop a simulation model to evaluate performance of an air handling system. The potential energy savings of constant air volume (CAV) and VAV strategies are investigated in a representative residential building. The simulation results show that about 13% of electrical power can be saved by the proposed VAV strategy in respect of the CAV. Also, life cycle cost analysis is applied on the considered system. It is found that VAV system is not economically good for the considered building because of low electricity price in Iran. Finally, a sensitivity analysis was conducted to demonstrate how the electricity price affects the economic performance of the VAV system. | Energy and economic analysis of model-based air dampers strategies on a VAV system | 10.1007/s13762-018-1863-z |
2019-08-01 | In this paper, for the high frequency part of the solution u ( x , t ) to the linear fractional damped wave equation, we derive asymptotic-in-time linear estimates in Triebel-Lizorkin spaces. Thus we obtain long time decay estimates in real Hardy spaces H ^p for u ( x , t ). The obtained results are natural extension of the known L ^p estimates. Our proof is based on some basic properties of the Triebel-Lizorkin space, as well as an atomic decomposition introduced by Han, Paluszynski and Weiss. | Estimates of Damped Fractional Wave Equations | 10.1515/fca-2019-0053 |
2019-08-01 | Semi-active suspension control with magnetorheological (MR) damper is one of the fascinating systems being studied in improving the vehicle dynamics. By using the MR damper system, a controllable system can be produced dynamically and the majority of the performance of a fully active system can potentially be achieved. Since the conventional optimization method always has a problem in identifying the optimum values and it is time consuming, the evolutionary algorithm is the best approach in replacing the conventional method as it is very efficient and consistent in exploring the values for every single space. In this study, the semi-active control schemes, namely fuzzy logic based controllers tuned using a novel optimization algorithm called advanced firefly algorithm (AFA) is proposed to regulate the body of the vehicle’s suspension from any disturbances acted to the system. The AFA is to be introduced based on the improvement of the original firefly algorithm (FA) to enhance the solution quality of the FA. The comparative assessment study of the proposed optimizer with other evolutionary algorithm, called the particle swarm optimization (PSO) is also presented. A simulation of semi-active suspension system with two degree of freedom is developed within MATLAB Simulink environment. The simulation result indicates that the FL-AFA exhibits an improvement in terms of sprung acceleration and sprung displacement response, with 51.4% and 52.3% as compared with the FL-FA controller, FL-PSO controller, FL controller and passive systems. | Fuzzy logic with a novel advanced firefly algorithm and sensitivity analysis for semi-active suspension system using magneto-rheological damper | 10.1007/s12652-018-1044-4 |
2019-08-01 | The authors provide an estimation of the “wall viscosity” and its increment (“magneto-viscous” effect) in a thin near-wall layer of a column of magnetic fluid oscillating in the tube when a strong transverse magnetic field is applied. The calculation is performed according to the formula obtained on the basis of two different theoretical approaches and applied to the previously published experimental results of the complex measurement of oscillation frequency and saturation magnetization of the magnetic fluid. These results are commented upon, stemming from the assumed absence of the field dependence of viscosity. The estimates of “wall viscosity” “from above” and “from below” are used to calculate their contribution to the damping coefficient of oscillations. | “Wall Viscosity” of Magnetic Fluid Oscillations in a Strong Magnetic Field | 10.1007/s11182-019-01751-7 |
2019-08-01 | The mathematical model based on the Volume-Averaged/Reynolds-Averaged Navier—Stokes (VARANS) equations has been adopted in recent years to generally simulate the interaction between waves and porous structures. However, it is still hard to determine the two experimental coefficients ( α and β ) included in VARANS equations. In the present study, VARANS equation is adopted to describe the flow inside and outside the porous structures uniformly, with applying the volume averaged k − ε model to simulate the turbulence effect. A new calibration method is used to evaluate the accuracy of numerical simulation of wave motion on porous seabed with different coefficients, by taking the wave damping rate as an index. The calibration is achieved by completing a simulation matrix on two calibration cases. A region can be found in the parameter space to produce a lower error, which means that the simulation results are better consistent with the experimental results. | Investigation on A Resistance-Type Porosity Model and the Experimental Coefficients | 10.1007/s13344-019-0044-2 |
2019-08-01 | This study proposes a frequency domain vehicle-track coupling model for the CRTS (China railways track system)-III type damping track system based on the two-dimensional vehicle-track-viaduct coupling model, and utilizes dynamic compliance method to determine the dynamic compliance for the vehicle and track systems. The accelerations for the viaduct are hereinafter obtained and are compared between CRTS-III damping track system and conventional CRTS-III track system, and the structure-borne noises for near field and far field of the viaduct are assessed with finite element method (FEM). The acoustic contribution rates for the substructures of the viaduct to the near-field and far-field noises are analyzed. The results reveal that in comparison with the conventional CRTS-III system, the CRTS-III damping track system can mitigate the viaduct acceleration peak with 69.9%, and mitigate the average acceleration with 60.4%. The near field and far field noise measurement points are captured for the CRTS-III damping track system, the sound pressure levels decline by 8.15 dB and 8.36 dB, respectively. The acoustic contribution rates for the viaduct top plate reach 65.28% and 68.30%, respectively. The viaduct top plate thus becomes the major noise source and the damping track system can effectively mitigate the structure-borne noise of the viaduct. | Noise and Vibration Mitigation Performance of Damping Pad under CRTS-III Ballastless Track in High Speed Rail Viaduct | 10.1007/s12205-019-1947-4 |
2019-08-01 | This paper investigates a hybrid structural control system using tuned liquid dampers (TLDs) and lead-rubber bearing (LRB) systems for mitigating earthquake-induced vibrations. Furthermore, a new approach for taking into account the uncertainties associated with the steel shear buildings is proposed. In the proposed approach, the probabilistic distributions of the stiffness and yield properties of stories of a set of reference steel moment frame structures are derived through Monte-Carlo sampling. The approach is applied to steel shear buildings isolated with LRB systems. The base isolation systems are designed for different target base displacements by minimizing a relative performance index using Genetic Algorithm. Thereafter, the base-isolated structures are equipped with TLDs and a combination of the base and TLD properties is sought by which the maximum reduction occurs in the base displacement without compromising the performance of the system. In addition, the effects of TLD properties on the performance of the system are studied through a parametric study. Based on the analyses results, the base displacement can be reduced 23% by average, however, the maximum reduction can go beyond 30%. | A combined control strategy using tuned liquid dampers to reduce displacement demands of base-isolated structures: a probabilistic approach | 10.1007/s11709-019-0524-8 |
2019-07-24 | The smart behavior of magneto-rheological (MR) fluid is used in the present work in designing, experimentally characterizing and analyzing a MR damper for automotive application using the twin-tube damper concept. A commercially available passive damper of a passenger van was tested to find the characteristic damping requirement of the vehicle. With this as reference, a twin-tube MR damper working in valve mode was designed and fabricated. The magnetic flux density induced in the fluid flow gap is maximized using Taguchi analysis and finite element method magnetics (FEMM) software. The FEMM results are validated by verifying with results obtained analytically using electromagnetic circuit theory. The MR damper filled with commercially available MR fluid was experimentally tested in damper testing machine. The results demonstrate that the force developed by the MR damper is indeed increasing with the value of the current supplied. At various frequencies of input oscillation, the energy dissipated by the MR damper in a single cycle increases significantly with current supplied. The novelty of this work is that a twin-tube MR damper working in valve mode was designed as a replacement for the passive damper used in a passenger van. The MR damper thus developed is capable of producing practical levels of damping force at actual operating frequencies and amplitudes of the passive damper in the passenger van. For further analysis, the behavior of the MR damper is modeled by using the Bouc–Wen model for hysteretic systems. A proportional–integral–derivative controller is used to track the desired damping force in time domain to demonstrate the application of the MR damper in a semi-active suspension system. | Design and experimental characterization of a twin-tube MR damper for a passenger van | 10.1007/s40430-019-1833-5 |
2019-07-17 | In this article, we investigate a system of two viscoelastic equations with Dirichlet boundary conditions. Under some suitable assumptions on the function g i ( ⋅ ) $g_{i}(\cdot )$ , f i ( ⋅ , ⋅ ) $f_{i}(\cdot ,\cdot )$ ( i = 1 , 2 $i=1,2$ ) and the initial data, we obtain general and optimal decay results. Moreover, for certain initial data, we establish a finite time blow-up result. This work generalizes and improves earlier results in the literature. The conditions of the relaxation functions g 1 ( t ) $g_{1}(t)$ and g 2 ( t ) $g_{2}(t)$ in our work are weak and seldom appear in previous literature, which is an important breakthrough. | On decay and blow-up of solutions for a system of viscoelastic equations with weak damping and source terms | 10.1186/s13660-019-2155-y |
2019-07-16 | Mechanical damping caused by frequency, confining stress, and deformation is measured that is strongly dependent on fluid flow in partially saturated sandstone. This effect is observed as a function of frequency, stress amplitude, confining pressure, strain amplitude, and moisture content. The damping peak in response to low peak frequency can be obtained at high strain amplitude. Results suggest the evidence of damping caused by frequency, confining pressure, and amplitude in partially saturated sandstone. We conclude that the contribution of fluid flow to damping effect in partially saturated sandstone is not negligible at low frequency, especially at high strain level and high confining pressure. | Laboratory measurements of the mechanical damping capacities in partially saturated sandstone | 10.1007/s12517-019-4625-4 |
2019-07-15 | Intermediate isolation system (IIS) is currently spreading and gaining significant popularity, mainly in Japan. However, its potentials are not so well-known in European countries, and in USA only one application to building retrofit is registered. The dynamic behaviour of intermediate isolation systems, more complex than the two-degree-of-freedom behaviour of base isolation systems, gives rise to a twofold control mode, which combines isolation and mass damping strategies. However, the research contributions provided in the scientific literature usually concentrate on one single control mode, either isolation or mass damping, and the relevant design methods and criteria. This paper addresses the IIS design problem from a wider perspective and presents an explorative study on the vibration characteristics and dynamic behaviour of IIS, in order to identify the range of different behavioural modes and to propose relevant design guidelines. For these aims, a parametric analysis is carried out, varying the main design parameters, namely: isolation period and ratio, location of isolation layer and mass ratio, distributions of stiffness and mass in the upper and lower structures. A classical modal approach is initially assumed for assessing the contributions of each vibration mode on the global dynamic behaviour of IIS, with a particular focus on the effect of coupling of higher modes. However, since IIS is a non-proportionally damped system, a state space formulation is subsequently adopted for establishing the cases for which the simplified classical approach, only considering two damping values for the isolation and structural parts, can be adopted in a preliminary design stage. Finally, frequency response analysis is carried out for identifying the ranges of predominant isolation and mass damping behaviour and the effect of mode coupling both in terms of local and global response of the isolated models. Design implications are finally derived from the analysis results. | Vibration characteristics and higher mode coupling in intermediate isolation systems (IIS): a parametric analysis | 10.1007/s10518-019-00637-w |
2019-07-15 | In this paper, we consider a one-dimensional porous system damped with a single weakly nonlinear feedback. Without imposing any restrictive growth assumption near the origin on the damping term, we establish an explicit and general decay rate, using a multiplier method and some properties of convex functions in case of the same speed of propagation in the two equations of the system. The result is new and opens more research areas into porous-elastic system. | A General Decay for a Weakly Nonlinearly Damped Porous System | 10.1007/s10883-018-9407-x |
2019-07-15 | Leakage of agricultural pipes has been increasingly frequent problems due to corrosion, loosening of joints, and cracks, which result in the subsidence of peripheral roads and dwelling land in the worst case. Generally, leakage has been detected by listening for noisy leak signals or measuring water loss during 24 h in a section closed by a valve. But these methods have weak points: They are costly, inaccurate, and time-consuming. This study investigated a new method of leakage detection that is accurate and easily accomplished by monitoring pressure for the purpose of preventing the destruction of pipes. During a transient event, where a large pressure wave is generated suddenly by sharp valve closure, the pressure wave damps out and the reduction wave is reflected when passing through a leakage point. Applying the propagation characteristics to leak detection, two methods were proposed: In the first method, a location and leakage volume was estimated by reading the signal of reflected wave from the leakage point and the validity of the method was confirmed by experiment in case that the ratio of leakage volume to flow rate in the pipe was more than approximately 5%. In the second method, which focuses on damping of pressure due to leakage, the leakage location could be estimated with an accuracy of < 5% of the total pipe length by fitting the calculated “damping rate” to the measured “damping rate” using method of characteristics in the cases where the leakage could not be detected by the first method. | Leak detection by monitoring pressure to preserve integrity of agricultural pipe | 10.1007/s10333-019-00730-5 |
2019-07-15 | Yaw damper, widely employed in high-speed railway vehicles, has played an important role in improving the hunting stability. This paper mainly makes a comprehensive analysis on the effect of yaw damper with its series stiffness value on the stability and bifurcation type of the railway bogie. With the prerequisite of the linear critical speed calculated by mathematical method, Center Manifold Theorem is adopted to reduce the dimension of the model to a planar dynamical system. And the symbolic expression associated with yaw damper and its series stiffness to determine bifurcation type at the critical speed is obtained by the method of Normal Form. As a result, the influence of the variation tendency of the yaw damper and series stiffness on the bifurcation type of the bogie is given qualitatively in contrast to different couples. Finally, numerical analysis of corresponding bifurcation diagrams is given to verify the accuracy of the conclusion. | Bifurcation analysis of railway bogie with yaw damper | 10.1007/s00419-018-1475-6 |
2019-07-08 | In his classic work Hydrodynamics, Horace Lamb devoted a significant amount of effort to the mathematical analysis of atmospheric waves, i.e. waves in a compressible medium under the influence of a local gravitational field and a variable temperature (and hence sound speed) profile. In so doing, he derived equations for both the divergence and the curl of the velocity field, yielding expressions of considerable mathematical beauty and complexity. Eight decades later, Derek Moore and Edward Spiegel extended Lamb’s analysis to include an arbitrary external applied force in the equations of motion. By a suitable choice of such force, the governing wave equations for a wide variety of Lorenz force/Coriolis force-induced wave motions can be derived. However, they chose to investigate the radiation field resulting from the application of a concentrated vertical force. In so doing, they were able to utilize an important theorem by James Lighthill concerning the asymptotic radiation field from a source with compact support, using the concept of a wavenumber surface. This paper has two main components: the first is to extend the work of Moore and Spiegel to ion-damped acoustic-gravity waves in the ionospheric F -region, based on the seminal work of C. H. Liu and K. C. Yeh. The second part is a consequence of the first: the corresponding wavenumber surface becomes complex, and so Lighthill’s method has to be modified to account for the effects of this. Furthermore, a significant inconsistency in the formulation of the physical problem by Liu and Yeh has been corrected and the corresponding derivations have been reformulated. Some graphical information has also been provided in special cases to illustrate the comparative effects of damping on the asymptotic behaviour of the acoustic-gravity radiation field. A final feature of the paper is that the equations derived are very general and can provide the basis for investigation of more realistic atmospheric temperature profiles in future work. | The asymptotic solution of the ion-damped acoustic-gravity wave equation | 10.1007/s00033-019-1163-6 |
2019-07-01 | Motor drivers employ film capacitors instead of the conventional electrolytic capacitors to achieve better reliability and smaller volume. However, these drivers have an instability problem because of a resonance between the small dc-link capacitance and grid side line inductance. In order to solve the problem, this paper proposes an active damping method using d-axis current injection. Since the injected current acts as damping impedance, the proposed method suppress dc-link voltage fluctuations. The relationship between the injected current and the virtual damping impedance is mathematically analyzed. Moreover, the proposed method is able to reduce the torque ripple caused by the injected current in spite of system loss increase. The increased loss also can be minimized by characteristics of the motor. The feasibility of the proposed method is proved by several experimental results. | DC-Link Voltage Stabilization Using d-Axis Current Injection for SPMSM Driver with Small DC-Link Capacitance | 10.1007/s42835-019-00176-z |
2019-07-01 | The study is presented of the aircraft landing gear deformations in the axial direction of the aircraft (gear-walk) under the load from a runway. Some beam-based model is proposed to describe the elastic properties of landing gear and the oleo strut behavior. The primary verification of the model is carried out: The characteristic frequencies of oscillations are found, and the behavior of the system under harmonic load is investigated. | Numerical Simulation of Planar Oscillations of a Landing Gear Leg along the Longitudinal Axis of an Aircraft During the Landing Impact | 10.1134/S1990478919030013 |
2019-07-01 | Recent studies show an interest on the static and dynamic mechanical properties in applications where both influence the overall performance of mechanical systems. This study explores the impact of the T6 heat treatment in the elastic and damping properties of Al–Si–Mg alloys. Consequently, the role of such properties is characterized by the stresses that are developed in resonant structures. Experimental testing shows that, due to pinning length modifications, the heat treatments generate a progressive increase in Young’s modulus and a reduction in loss factor. Recurring to finite element analysis, it is concluded that such modifications in material properties generate a reduction in resonant stress after solution treatment. This stress tends to increase as the artificial ageing progresses. A model, based on an exponential decay function, is proposed to describe the variation of resonant stress as the elastic and damping properties are changed during the T6 treatment. | T6 Heat Treatment Impact on the Random Frequency Vibration Stress of Al–Si–Mg Alloys | 10.1007/s12540-019-00244-z |
2019-07-01 | In this present study, static and dynamic properties of hybrid fiber-reinforced concrete (HFRC) were experimentally investigated. The mechanical properties accompanied by compressive strength, splitting tensile strength and flexural strength were evaluated for several combinations of mixtures containing hybrid fibers. In addition, dynamic properties such as damping ratio, mode shape and fundamental natural frequency have also been experimentally determined for the prismatic beams in free–free condition in order to evaluate the damage characteristics of HFRCs. Total fiber volume fractions of 0.25, 0.5 and 0.75% with different combinations of steel and polypropylene (PP) fibers have been considered in this investigation. Among various percentage additions of hybrid fibers, a mixture that contains 0.25% of total fiber volume fraction with the combination of 75% of steel and 25% of PP fibers has acquired the best performance. Furthermore, the natural frequencies of HFRC specimens decrease with the increase in fiber content as well as decrease with the increase in structural damage, whereas the damping ratio increases with the increase in fiber content and structural damage. Numerical modeling was also developed for control and HFRC specimens using ANSYS software to compare the experimental results with the analytical model prediction. It was also found that the HFRC with the combination of 75% of steel and 25% of PP fibers with total fiber volume fraction of 0.75% has the highest damping properties. | Experimental and numerical study on damage evaluation of hybrid fiber-reinforced concrete | 10.1007/s42107-019-00141-1 |
2019-07-01 | Tuned liquid damper (TLD) and tuned liquid column damper (TLCD) are two types of passive control devices that are widely used in structural control. In this study, a real-time hybrid simulation (RTHS) technique is employed to investigate the difference in control performance between TLD and TLCD. A series of RTHSs is presented with the premise of the same liquid length, mass ratio, and structural parameters. Herein, TLD and TLCD are physically experimented, and controlled structures are numerically simulated. Then, parametric studies are performed to further evaluate the different performance between TLD and TLCD. Experimental results demonstrate that TLD is more effective than TLCD under different amplitude excitations. | Control performance comparison between tuned liquid damper and tuned liquid column damper using real-time hybrid simulation | 10.1007/s11803-019-0530-9 |
2019-07-01 | This paper gives several sets of sufficient conditions which guarantee that all radially symmetric solutions of $$\begin{aligned} \text {div}(D(u)\nabla u) + \frac{k(||\mathbf {x}||)}{||\mathbf {x}||}\,\mathbf {x}\cdot (D(u)\nabla u) + \omega ^p|u|^{p-2}u = 0 \end{aligned}$$ div ( D ( u ) ∇ u ) + k ( | | x | | ) | | x | | x · ( D ( u ) ∇ u ) + ω p | u | p - 2 u = 0 converge to zero as $$||\mathbf {x}||\rightarrow \infty $$ | | x | | → ∞ . Here, $$\mathbf {x}$$ x is an N -dimensional vector in an exterior domain and $$N \in \mathbb {N}\setminus \{1\}$$ N ∈ N \ { 1 } ; $$D(u) = ||\nabla u||^{p-2}$$ D ( u ) = | | ∇ u | | p - 2 with $$p > 1$$ p > 1 ; k is a nonnegative and locally integrable function on $$[a,\infty )$$ [ a , ∞ ) ; $$\omega $$ ω is a positive constant. All of the obtained sufficient conditions have the advantage that it is possible to check relatively easily. In that sense, our results are practical enough. The relationships between those sufficient conditions are also clarified. To achieve our purpose, we discuss the asymptotic stability of the equilibrium of the equation $$\begin{aligned} \left( |x'|^{p-2}x'\right) ' + h(t)|x'|^{p-2}x' + \omega ^p|x|^{p-2}x = 0, \end{aligned}$$ | x ′ | p - 2 x ′ ′ + h ( t ) | x ′ | p - 2 x ′ + ω p | x | p - 2 x = 0 , where $$h: [0,\infty ) \rightarrow [0,\infty )$$ h : [ 0 , ∞ ) → [ 0 , ∞ ) is locally integrable. | Sufficient conditions for convergence of solutions of damped elliptic equations | 10.1007/s00605-018-1192-9 |
2019-07-01 | The dynamics of beams equipped with tuned mass dampers is of considerable interest in engineering applications. Here, the purpose is to introduce a comprehensive framework to address the stochastic response of the system under stationary and non-stationary loads, considering inertia effects along the spring of every tuned mass damper applied to the beam. For this, the key step is to show that a tuned mass damper with spring inertia effects can be reverted to an equivalent external support, whose reaction force on the beam depends only on the deflection of the attachment point. On this basis, a generalized function approach provides closed analytical expressions for frequency and impulse response functions of the system. The expressions can be used for a straightforward calculation of the stochastic response, for any number of tuned mass dampers. Numerical results show that spring inertia effects may play an important role in applications, affecting considerably the system response. | Random vibration mitigation of beams via tuned mass dampers with spring inertia effects | 10.1007/s11012-019-00983-8 |
2019-06-27 | In this paper, we prove the existence of forward discretely self-similar solutions to the MHD equations and the viscoelastic Navier–Stokes equations with damping with large weak $$L^3$$ L 3 initial data. The same proving techniques are also applied to construct self-similar solutions to the MHD equations and the viscoelastic Navier–Stokes equations with damping with large weak $$L^3$$ L 3 initial data. This approach is based on Bradshaw and Tsai (Ann Henri Poincaré 18(3):1095–1119, 2017 ). | Forward Discretely Self-similar Solutions of the MHD Equations and the Viscoelastic Navier–Stokes Equations with Damping | 10.1007/s00021-019-0443-4 |
2019-06-15 | We consider a fluid–structure interaction system composed by a three-dimensional viscous incompressible fluid and an elastic plate located on the upper part of the fluid boundary. The fluid motion is governed by the Navier–Stokes system whereas we add a damping in the plate equation. We use here Navier-slip boundary conditions instead of the standard no-slip boundary conditions. The main results are the local in time existence and uniqueness of strong solutions of the corresponding system and the global in time existence and uniqueness of strong solutions for small data and if we assume the presence of frictions in the boundary conditions. | On the Existence of Strong Solutions to a Fluid Structure Interaction Problem with Navier Boundary Conditions | 10.1007/s00021-019-0440-7 |
2019-06-15 | In multibody dynamics, the Euler parameters are often used for the numerical simulation of rigid body rotations because they lead to a relatively simple form of the rotation matrix which avoids the evaluation of trigonometric functions and can thus save computational time. The Newmark method and the closely related Hilber–Hughes–Taylor (HHT) method are widely employed for solving the equations of motion of mechanical systems. They can also be applied to constrained systems described by differential algebraic equations. However, in the classical versions, the use of these integration schemes have a very unfavorable impact on the Euler parameter description of rotational motions. In this paper, we show analytically that the angular velocity for a rotation about a single axis under a constant moment will not increase linearly but grows slower. This effect, which does not appear for Euler angles, can be even observed if the numerical damping parameter α $\alpha $ in the HHT method is set to zero. To circumvent this problem without losing the advantage of Euler parameters, we present a modified HHT method which reduces the damping effect on the angular velocity significantly and eliminates it completely for α = 0 $\alpha =0$ . | A modified HHT method for the numerical simulation of rigid body rotations with Euler parameters | 10.1007/s11044-019-09672-6 |
2019-06-15 | Despite the effectiveness of carbon fibre reinforced polymers (CFRPs) and steel braces equipped with hysteretic dissipative devices (HYDBs) to improve the seismic performance of r.c. framed structures, the only use of CFRPs may be unsatisfactory for the retrofitting of buildings designed for gravity loads only while HDYBs may be unsuitable without a preliminary upgrading. The use of CFRP and HYDB as a combined technique for the seismic retrofitting of reinforced concrete (r.c.) buildings is investigated herein. To this end, two-, four- and eight-storey r.c. framed structures are designed with reference to the structural codes for r.c. buildings in force in Italy before and after 1971. A computer code for the nonlinear static and dynamic analysis of r.c. framed structures is modified to include CFRPs and HYDBs. Firstly, the nonlinear static analysis of the original test structures is carried with the aim of improving preliminarily strength and displacement capacities by applying CFRPs laminates, at the top and bottom sides of r.c. frame members, and CFRPs wraps, at the critical end zones of columns, respectively. Then, a displacement-based design procedure of HYDBs is adopted to complete the seismic retrofitting, starting from capacity curves of the upgraded test structures. To check the reliability of the combined CFRP–HYDB technique, nonlinear dynamic analysis of the original and retrofitted structures is performed considering two sets of seven near- and far-fault ground motions scaled to the seismic design level. Results highlight that the insertion of the HYDBs is effective in reducing the seismic demand of previously upgraded CFRP structures, with Post71 types generally performing better than Ante71 ones. | Seismic retrofitting of gravity-loads designed r.c. framed buildings combining CFRP and hysteretic damped braces | 10.1007/s10518-019-00593-5 |
2019-06-15 | The design, principle of operation, and budget of errors of a laser interference oil manometer developed at the Mendeleev All-Russia Research Institute of Metrology (VNIIM) and subsequently incorporated into the State Primary Standard of the unit of pressure GET 101–2011 are described. The results of studies of precision instruments for measurements of pressure with the use of the laser interference oil manometer are presented. Summaries of key comparisons and international cooperation in the field of liquid manometry are presented. | Laser Interference Oil Manometer of State Primary Standard of the Unit of Pressure Get 101–2011 | 10.1007/s11018-019-01604-2 |
2019-06-15 | Soil–structure interaction (SSI) plays an important role in overall structural seismic behavior. However, there is a scarcity of experimental studies evaluating the SSI effects on a full bridge including superstructure, pile foundations and site soil. This paper focused on shaking table investigations on the effects of SSI on a super long-span cable-stayed bridge model with pile groups and mixture soil modelled by using uniaxial laminar shear boxes. The cable-stayed bridge model was subjected to a series of earthquake excitations in the longitudinal direction, including white noise and various earthquake waves. The dynamic interactive behavior of the cable-stayed bridge model was explored for various shaking amplitudes and frequency components. Furthermore, the influences of the soil on the system dynamic characteristics were clarified statistically. The test results show that the SSI obviously affects the seismic response of the cable-stayed bridge model in the longitudinal direction, and corresponding accelerations of structural members are amplified. The bridge seismic response may be underestimated and misinterpreted to some extent while the SSI effects are ignored. It is, therefore, suggested that more attentions should be poured into the SSI effects when performing the seismic design of super long-span cable-stayed bridges. Moreover, the SSI effects on the bridge seismic responses decrease with the increase of shaking amplitude, and significantly change as the frequency components of the input motions vary. When evaluating the system damping ratio with the SSI, the system seismic responses may be varied to a certain degree if the soil viscous damping contribution is neglected. | Experimental assessment of soil–structure interaction effects on a super long-span cable-stayed-bridge with pile group foundations | 10.1007/s10518-019-00574-8 |
2019-06-14 | Because of high hinge moment of planar fin in supersonic flow, designers have become more attentive to the grid fin configuration in recent years. One of the disadvantages of the grid fin is its high drag force. Fortunately, this problem could be handled by implementing sweep-back angle. Few studies have been carried out to investigate the effects of the sweep-back angle on dynamic coefficients. In this paper, computational fluid dynamics is used to investigate the effect of grid fin’s sweep-back angle on the rolling and pitching dynamic coefficients in supersonic flow regime. The first step is dedicated to simulating two experimental geometries and detecting optimal mesh number and appropriate turbulence model. Unsteady dynamic coefficients along with moving mesh have been extracted by simulations. These coefficients are reported for different Mach numbers. In order to scrutinize the results, the static stability derivatives have been discussed, too. According to the simulations, each sweep-back angle has a unique trend of changing dynamic and static coefficients in terms of the Mach number. This trend is justified by studying Mach number contours for few states. Afterward, dynamic coefficients of the planar fin are presented and compared with the grid fin. | Numerical analysis of the effect of sweep-back angle on the stability derivatives of the grid fin | 10.1007/s40430-019-1788-6 |
2019-06-12 | This research work deals with tip vibration control of a Two-Link Flexible manipulator using hybrid control technique. This technique involves the implementation of unconstrained viscoelastic damping layer on the links in conjunction with active damping using piezoelectric sensors and actuators. Mathematical modelling of the complete system is done using the finite element approach in the inertial frame. Viscoelastic damping is modelled using Kelvin–Voigt elements for which a damping matrix is derived. Active damping is modelled as time-dependent uniformly distributed load applied by the piezoelectric actuator on the flexible link working under feedback control. The angular and linear velocities of the tips of flexible links are used for direct feedback. The unconstrained viscoelastic damping layer effectively reduces the vibrations of the system. The effectiveness of the active control depends upon the relative position of sensors and actuators on the links . The novelty of the work lies in control of torsional and flexural vibrations through the application of passive and active damping methods to the non-inertial frames represented by the manipulator links . | Hybrid vibration control of a Two-Link Flexible manipulator | 10.1007/s42452-019-0691-1 |
2019-06-01 | We improve the preceding results obtained by Ammari and Choulli (J Differ Equ 259(7):3344–3365, 2015 ). They concern the stability issue of the inverse problem that consists in determining the potential and the damping coefficient in a wave equation from an initial-to-boundary operator. We partially modify the arguments in Ammari and Choulli ( 2015 ) to show that actually we have a local Hölder stability instead of logarithmic stability. | Hölder stability in determining the potential and the damping coefficient in a wave equation | 10.1007/s00028-018-0476-9 |
2019-06-01 | This paper investigates cylindrical samples made of vacuum packed particles. Such structures are composed of granular media placed in a hermetic encapsulation where, in the final stage, a partial vacuum is generated. The main advantage of such a structure is that the underpressure value makes it possible to control the global physical properties of granular systems. Materials with various grains are analyzed in the paper. A modified Bouc-Wen hysteresis model is adopted to describe the nonlinear properties of the tested specimens. To identify the model parameters, a genetic algorithm is applied. The proposed model is found to be in good agreement with the experimental data. | Parameter identification of Bouc-Wen model for vacuum packed particles based on genetic algorithm | 10.1016/j.acme.2018.11.002 |
2019-06-01 | Particle damping is a passive control technology with strong nonlinearity whose damping effect is relative to the vibration intensity where a particle damper is installed. Then, seeking the optimal installing location of the particle damper to improve the damping effect and vibration control performance is an important research project. To this problem, bound optimization by quadratic approximation (BOBYQA) was employed to discuss the optimal location of a particle damper at the both fixed end plate. For theoretically evaluating the damping effect and invoking it into BOBYQA, the principle of gas-solid flow was used to study the damping effect and establish the theoretical model of particle damping. Further, the estimation precision of the mathematical model was verified by experiment; the results indicate that the proposed mathematical model can more accurately predict the dynamic response of a particle damper installed at both fixed end plate. Therefore, a mathematical model was employed to discuss the optimal position of the particle damper for minimizing maximum amplitude (MMA). The results indicate that particle damper should be installed at the model top close to the monitoring point; if there are two resonances whose amplitudes are equivalent or approximate, the particle damper should be installed at the junction of these model tops. | Optimizing location of particle damper using principles of gas-solid flow | 10.1007/s12206-019-0506-8 |
2019-06-01 | Micro-cantilevers are very effective and reliable devices for bio-sensing applications. In this work, a novel biosensor based on micro-cantilever array was designed, simulated and optimized for different bio-sensing applications with high sensitivity, high accuracy, high throughput, and high Q factor. A truss structure designed in the anchored end of the micro-cantilever which was effective in improving the sensitivity to increase detection accuracy. Also, the effects of the surrounding medium are minimized by this structure to achieve high Q factor and longer vibration for bio-sensor. All the results are compared by the conventional micro-cantilever. As a result, the Q factor is increased from 52.1 to 126.1 within water medium and from 51.8 to 120 within ethanol medium. The actuation of novel MCL is simulated by different piezoelectric materials, the results proof that the amplitude of displacement for the PZT-5H is more efficient than AlN. | Numerical simulation for sensitivity and accuracy enhancement of micro cantilever-based biosensor employing truss structure | 10.1007/s00542-018-4092-y |
2019-06-01 | Thin flexible parts are widely used in the aerospace industry and require a more precise surface finish. The main problem in achieving high-quality product is the vibration induced during machining of thin-walled parts. Clamping these thin parts or using rigid supports for parts, such as for propeller blades, lead to distortion. This issue may be solved using a non-contact auxiliary fixture. The new fixture developed in this research is an eddy current damper for passive control of vibrations in electrically conducting workpieces, using neodymium permanent magnets without any external power source. Two thin aluminum beams with different cross-section and same length were used to test the developed fixture. To increase the overall damping, conducting sheets were attached at the free end of beams. Impact and machining tests were conducted to validate the new fixture. The results showed higher damping and better machining stability leading to enhanced surface quality of the workpiece. | Non-contact auxiliary fixture for machining stability improvement of thin flexible workpieces using eddy currents | 10.1007/s12008-018-0495-3 |
2019-06-01 | The behaviour of granular soil is mainly dependent upon the nature and arrangement of particles, which in turn affect fabric anisotropy. It has been known for many years that depositional method plays an important role in the results of laboratory testing of granular soils. Despite extensive studies on the dynamic properties of granular soil, previous research has lacked a quantitative study of the effects of depositional methods on the dynamic properties of the granular soil. The primary objective of the current study was to evaluate the effect of fabric anisotropy on the dynamic properties of granular soil for practical applications. The influence of depositional method, mean effective consolidation stress, shear strain amplitude and relative density on the maximum shear modulus ( G _max), shear modulus curve ( G - γ ), normalized modulus curve ( G / G _max- γ ) and damping curve ( D - γ ) of pure sand, pure gravel and sand-gravel mixtures is investigated. The results of the tests indicate that depositional method has a significant effect on G _max that this effect was more pronounced for the pure sand specimens than for the pure gravel or sand-gravel mixture specimens. However, the depositional method had no significant effect on the shear modulus at large shear strain amplitudes. The effects of depositional method on the G / G _max- γ and D - γ curves are dependent on effective confining pressure and relative density. | Influence of Depositional Method on Dynamic Properties of Granular Soil | 10.1007/s40999-019-00412-7 |
2019-06-01 | A sound knowledge of the dynamic properties of soils is needed to solve several geotechnical engineering problems associated with earthquakes. Here we describe a laboratory investigation performed to measure the dynamic properties of the Plaisancian deposit of marls in the Algiers region using cyclic triaxial tests, cyclic double specimen direct simple shear tests, cyclic torsional shear tests and dynamic resonant column tests. The key parameters governing the nonlinear soil behavior under cyclic/dynamic loading and their relative importance in terms of affecting the dynamic properties of soils, wich are communaly represented by the normalized equivalent shear modulus reduction and damping ratio curves, are illustrated and discussed. We also address the differences in the deduced parameters obtained with different tests, procedures and interpretation criteria. The comparison between test results and empirical or semi-empirical relations for normalized equivalent shear modulus and damping ratio curves highlights a number of limitations and shortcomings of predictive models currently widely used. | Investigation on shear modulus and damping ratio of Algiers marls under cyclic and dynamic loading conditions | 10.1007/s10064-018-1310-x |
2019-06-01 | A two-dimensional numerical Computational Fluid Dynamics (CFD) model is established on the basis of viscous CFD theory to investigate the motion response and power absorption performance of a bottom-hinged flap-type wave energy converter (WEC) under regular wave conditions. The convergence study of mesh size and time step is performed to ensure that wave height and motion response are sufficiently accurate. Wave height results reveal that the attenuation of wave height along the wave tank is less than 5% only if the suitable mesh size and time step are selected. The model proposed in this work is verified against published experimental and numerical models. The effects of mechanical damping, wave height, wave frequency, and water depth on the motion response, power generation, and energy conversion efficiency of the flap-type WEC are investigated. The selection of the appropriate mechanical damping of the WEC is crucial for the optimal extraction of wave power. The optimal mechanical damping can be readily predicted by using potential flow theory. It can then be verified by applying CFD numerical results. In addition, the motion response and the energy conversion efficiency of the WEC decrease as the incident wave height increases because the strengthened nonlinear effect of waves intensifies energy loss. Moreover, the energy conversion efficiency of the WEC decreases with increasing water depth and remains constant as the water depth reaches a critical value. Therefore, the selection of the optimal parameters during the design process is necessary to ensure that the WEC exhibits the maximum energy conversion efficiency. | Analysis of the Hydrodynamic Performance of an Oyster Wave Energy Converter Using Star-CCM+ | 10.1007/s11804-019-00076-8 |
2019-06-01 | Low-resilience polyurethane foams including several additive constituents were synthesized to improve their vibro-acoustic performances, as well as the thermal insulation. viscoelastic polymer additive can attenuate vibrations and absorb sound energy. the vibro-acoustic properties of two innovative viscoelastic treatments fabricated with polyurethane foams are discussed in this paper using a typical aeronautical panel test setup. Since an aircraft insulation arrangement must provide both noise and thermal insulation for the specified operating conditions and expected thermal comfort of passengers, the thermal conductivity of the samples has been examined assuming a testing range between 20 °C (room temperature) and − 40 °C (cruise altitude). the results highlighted an optimal behavior of the novel viscoelastic foams in terms of both acoustic and thermal performance, offering a very interesting self-embedded solution with a good weight to performance ratio, compared to standard blanket composed by extra viscoelastic treatments. | Sound proofing and thermal properties of an innovative viscoelastic treatment for the turboprop aircraft fuselage | 10.1007/s13272-018-0326-z |
2019-06-01 | Damping vibration analysis of multi-phase viscoelastic nanocrystalline nanobeams on viscoelastic medium is carried out accounting for nano-grains and nano-voids sizes. For the first time, a contribution of nonlocal, couple stress and surface energy effects is applied for vibration analysis of nanocrystalline nanobeams. In fact, couple stress theory considers grains microrotations, while nonlocal elasticity theory considers long-range interactions between the particles. Viscoelastic medium is described as infinite parallel springs as well as shear and viscous layers. Hamilton’s principle is employed to derive the governing equations and the related boundary conditions which are solved applying differential transform method. The frequencies are compared with those of nonlocal and couple stress-based beams. It is observed that damping frequencies of a nanocrystalline nanobeam are significantly influenced by the grain size, grain rotations, porosities, interface, damping coefficient, surface energy, nonlocality and structural damping. | Damping Vibration Behavior of Viscoelastic Porous Nanocrystalline Nanobeams Incorporating Nonlocal–Couple Stress and Surface Energy Effects | 10.1007/s40997-017-0127-8 |
2019-06-01 | We show that solutions of the periodic KdV equations $$\begin{aligned} u_t+\gamma u +u_{xxx}+uu_x=f, \end{aligned}$$ u t + γ u + u xxx + u u x = f , are asymptotically determined by their values at three points. That is if there exists $$x_1,x_2,x_3$$ x 1 , x 2 , x 3 such that $$0< x_3-x_2<<x_3-x_1<<1$$ 0 < x 3 - x 2 < < x 3 - x 1 < < 1 and $$\begin{aligned} \lim _{t\rightarrow +\infty } |u_1(t,x_j)-u_2(t,x_j)|=0, \; \mathrm{for} \; j=1,2,3, \end{aligned}$$ lim t → + ∞ | u 1 ( t , x j ) - u 2 ( t , x j ) | = 0 , for j = 1 , 2 , 3 , for two solutions $$u_1,u_2$$ u 1 , u 2 of the KdV equation above, then $$\begin{aligned} \lim _{t\rightarrow +\infty }||u_1(t)-u_2(t)||_{H^1}=0. \end{aligned}$$ lim t → + ∞ | | u 1 ( t ) - u 2 ( t ) | | H 1 = 0 . | Determining Nodes for the Damped Forced Periodic Korteweg-de Vries Equation | 10.1007/s10884-019-09737-2 |
2019-06-01 | Alloying is a good approach to increasing its strength but leads to a reduction of damping to pure magnesium. Classifying the alloying characteristics of various alloying elements in magnesium alloys and their combined effects on the damping and mechanical properties of magnesium alloys is important. In this paper, the properties of the Mg-0.6wt%X binary alloys were analyzed through strength measurements and dynamic mechanical analysis. The effects of foreign atoms on solid-solution strengthening and dislocation damping were studied comprehensively. The effect of solid solubility on damping capacity can be considered from two perspectives: the effect of single solid-solution atoms on the damping capacities of the alloy, and the effect of solubility on the damping capacities of the alloy. The results provide significant information that is useful in developing high-strength, high-damping magnesium alloys. This study will provide scientific guidance regarding the development of new types of damping magnesium alloys. | Effect of alloying elements on magnesium alloy damping capacities at room temperature | 10.1007/s12613-019-1789-6 |
2019-06-01 | The use of base isolation to protect a structure and its contents from earthquake damage has proven to be an effective anti-seismic strategy during past earthquakes. Modelling of the isolation system is one of the key steps in understanding the response of the structure and more importantly to evaluate the effectiveness of the isolation system. This paper presents a study on the effect of damping in an isolation system using a linear spring and linear viscous damper to model the response of the isolated superstructure. Although this model may not be representative of the mechanical behaviour of a real isolation system, most nonlinear systems can be linearised in some form to provide an estimate to the response and thus the use of this model in this study. From the floor response spectra of the roof mass, the increase in damping in the isolation system leads to the excitation of response in higher modes. The floor response spectra also show that the effectiveness of isolation reduces with increasing damping in the isolation system and could be detrimental to the contents of the building. The bilinear model, also the basis of design codes such as the ASCE 7-16, is used in this study to model isolators. The analysis using the bilinear model with various design scenarios shows that the model delivers a significant amount of damping into the system when the system is experiencing regular intensity earthquake events. The presence of a high damping ratio in the isolation system, as in the linear model, excites the higher modes thus counteracts the objective of base isolating a structure. The paper concludes with a comparison of the isolator displacement estimated using the design code and the average response obtained through dynamic analyses. The difference between the displacement values is not large. | The effect of damping in isolation system on the performance of base-isolated system | 10.1007/s42464-019-00012-z |
2019-06-01 | Purpose The structure should be retained in elastic range under cyclic loading due to earthquake and this can be achieved by addition of energy dissipators. This work represents the effectiveness of two types of metallic dissipaters (X-plate and accordion damper). Methods In the first part of the study, the behaviour of the structure considering the devices for four earthquake records is investigated. For this study, the damper has been modeled in each storey at the outer frame of the building. Time history analysis is done. Results Due to use of the damper, all damage measures such as displacement and drift are reduced significantly. But it is not possible to provide a damper in each storey. Thus, in the next part, location-based optimization is done using the genetic algorithm. This optimization is done for four and eight numbers of dampers and for that some best location has been indicated depending on the minimum value of function. The entire study is done for both types of dampers. Conclusions For reducing the seismic effect on the building, metallic damper is more effective. Genetic algorithm gives the optimal location format for a fixed number of dampers having maximum reduction in responses compared to other possible locations. | Optimization of Metallic Damper Location for Seismic Response Control | 10.1007/s42417-019-00110-7 |
2019-06-01 | In this study, a new hybrid damper (HD) is introduced that consists of elastomeric layers, which act as a viscoelastic damper (VED), and metallic dampers (MDs). Metallic part is composed of flexural yielding strips. This HD not only removes the limitations of each of these two types of dampers, but also facilitates its application for multi-level vibration control. Based on operational mechanism and design objectives of the proposed HD, three specimens have been manufactured and tested under quasi-static cyclic loading to evaluate the functional objectives. Two types of elastomers and two types of metallic dampers are used in these specimens. Experimental results show stable hysteretic behavior and high energy dissipation capacity. Also, the multi-phase behavior of the proposed HD confirms the proper function that is intended. However, the HD that is made of natural rubber (NR) and comb-teeth damper (CTD) can tolerate more cycles and possesses more ductility in comparison with the HD made of butyl rubber (IIR) and steel slit damper (SSD). A finite element model (FEM) is also used to simulate the behavior of the proposed HD. A good correlation between numerical outputs, analytical equations and experimental results indicates the accuracy of the proposed FEM. | A new hybrid energy dissipation system with viscoelastic and flexural yielding strips dampers for multi-level vibration control | 10.1016/j.acme.2018.12.005 |
2019-05-24 | In this work, we study the asymptotic behavior of a system of two-coupled plate equations where one of these equations is conservative and the other one has dissipative properties. The dissipative mechanism is given by the fractional damping $$(-\Delta )^{\theta }v_t$$ ( - Δ ) θ v t where $$\theta $$ θ lies in the interval [0, 1]. We show that the semigroup decays polynomially with a rate that depends on $$\theta $$ θ and some relations between the structural coefficients of the system. Explicit decay rates are obtained. | Exact decay rates for coupled plates with partial fractional damping | 10.1007/s00033-019-1135-x |
2019-05-19 | Due to the increasing esthetic requirements and complex functional specifications of machined components, peripheral milling of curved geometries is becoming increasingly important in the aerospace, automotive, and the injection molds industries. However, one of the major difficulties encountered by manufacturers is that peripheral milling of the curved surfaces which is characterized by significant amount of engagement variation along the tool path causing a sudden change in cutting forces and consequently a deterioration of the surface roughness of the machined parts and lowers productivity. The present paper presents a two-dimensional machining model allowing the simulation of cutting forces including the cutting process damping in curvilinear peripheral milling. In the study, we attempt to analyze the effect of various milling parameters such as cutting speed, feed rate, axial and radial depth of cut, tool diameter, and tool helix angle on cutting forces generated by the peripheral milling of a curved surface profile. The cutting forces obtained through simulation model are compared with experimental results. | Modeling of cutting forces in curvilinear peripheral milling process | 10.1007/s00170-018-03249-x |
2019-05-16 | In this article, we study the existence of mild solutions for damped elastic systems in Banach spaces. The discussion is based on the operator semigroup theory and fixed point theorem. In addition, two examples are given to illustrate our results. | Existence of solutions for damped elastic systems in Banach spaces | 10.1186/s13662-019-2130-4 |
2019-05-15 | In this paper, we investigate the effect of the filter for the hyperbolic moment equations (HME) (Cai et al. in Commun Pure Appl Math 67(3):464–518, 2014 ; Cai et al. in SIAM J Sci Comput 35(6):A2807–A2831, 2013 ) of the Vlasov–Poisson equations and propose a novel quasi time-consistent filter to suppress the numerical recurrence effect. By taking properties of HME into consideration, the filter preserves a lot of physical properties of HME, including Galilean invariance and conservation of mass, momentum and energy. We present two viewpoints—collisional viewpoint and dissipative viewpoint—to dissect the filter, and show that the filtered hyperbolic moment method can be treated as a solver of the Vlasov equation. Numerical simulations of the linear Landau damping and two stream instability demonstrate the effectiveness of the filter in restraining recurrence arising from particle streaming. Both the analysis and the numerical results indicate that the filtered method can capture the evolution of the Vlasov equation, even when phase mixing and filamentation dominate. | Filtered Hyperbolic Moment Method for the Vlasov Equation | 10.1007/s10915-018-0882-8 |
2019-05-15 | In the framework of seismic design of structures, response spectrum analysis (RSA) is the most commonly used approach in practice. The most popular combination rule is the complete quadratic combination (CQC) which is also prescribed by the most of seismic design codes and is based on the assumptions that the seismic acceleration is a white noise process and the peak factor ratios associated to the total and modal responses are unitary. Recently, the damping adjusted combination (DAC) rule has been developed for base-isolated structures to overcome the aforementioned simplified assumptions. Although it has been proved that the simplifications about peak factors lead to noticeable errors in the case of base-isolated structures, the accuracy gain of DAC with respect to CQC in the case of fixed-base structures is still unknown. Therefore, the paper presents an in-depth study on the RSA of three-dimensional frame structures, aimed to evaluate the accuracy of the above methods. Two reference classes of frame structures having different degree of complexity are considered. Average interstorey drift and floor torsion responses, obtained from a set of Time History Analyses are compared with those of the modal combination rules. Lognormal joint probability density functions of the predictive errors from CQC and DAC are finally evaluated for a reliability assessment of the two combination rules under bidirectional seismic excitations. | Response spectrum analysis of frame structures: reliability-based comparison between complete quadratic combination and damping-adjusted combination | 10.1007/s10518-019-00559-7 |
2019-05-06 | In this manuscript, we study the coherent single-excitation energy transfer for a dimer system consisting of a donor and an acceptor modeled by two-level systems (TLSs), which are immersed in common thermal environment. We illustrate the effects of the distance between TLSs and temperature of the thermal reservoir on the energy transfer process considering collective damping and dipole–dipole interaction. Concretely, the control and enhancement of the probability during the time evolution is performed by a suitable choice of the distance between TLSs with respect to the temperature of the reservoir. On the other hand, we study the time evolution of the quantum and classical correlations of the TLSs-state through calculating concurrence and quantum discord. We find that the dynamical behavior of quantum and classical correlations dynamics in thermal reservoir is similar to vacuum reservoir with slight decrease in the amount of correlations. These correlations are also very sensitive to the TLSs-distance and when the distance becomes significantly large, the amount of correlations exponentially decrease with the time. Finally, we explore the relationship between the probability and correlations during the evolution and shows that quantum and classical correlations can be created during the process of excitation energy transfer. | Energy transfer, correlations and decoherence in a dimer in terms of the two-level atomic distances | 10.1007/s11128-019-2276-8 |
2019-05-01 | This paper is a small review devoted to the dynamics of a point on a paraboloid. Specifically, it is concerned with the motion both under the action of a gravitational field and without it. It is assumed that the paraboloid can rotate about a vertical axis with constant angular velocity. The paper includes both well-known results and a number of new results. We consider the two most widespread friction (resistance) models: dry (Coulomb) friction and viscous friction. It is shown that the addition of external damping (air drag) can lead to stability of equilibrium at the saddle point and hence to preservation of the region of bounded motion in a neighborhood of the saddle point. Analysis of three-dimensional Poincaré sections shows that limit cycles can arise in this case in the neighborhood of the saddle point. | A Parabolic Chaplygin Pendulum and a Paul Trap: Nonintegrability, Stability, and Boundedness | 10.1134/S1560354719030067 |
2019-05-01 | A particular hydro-elastic model is considered to examine a radiation problem involving an immersed sphere in an infinitely extended ice-covered sea, where the lower surface is enveloped by a flexible base surface. Both the flexible base surface and floating ice-plate are modelled as thin elastic plates with different configurations and are based on the Euler–Bernoulli beam equation. The appearance of surface tension at the surface below the floating ice-plate is ignored. Under such circumstance, two different modes of propagating waves appear in the fluid for any particular frequency. One of the modes with lower wavenumber propagates along the surface beneath the ice-plate and the other with higher wavenumber propagates along the elastic base surface. The method of multipole expansions is used to calculate the solutions of the heave and sway radiation problems involving a submerged sphere in an ice-covered fluid. Furthermore, this procedure gives rise to an infinite system of linear equations, which can be solved computationally by any regular method. The added-mass as well as damping coefficients in case of heave as well as sway motions are calculated, and displayed graphically in various submergence depths of the oscillating sphere and elastic specifications of both the flexible base surface as well as the floating ice-plate. | Effects of flexible bottom on radiation of water waves by a sphere submerged beneath an ice-cover | 10.1007/s11012-019-00998-1 |
2019-05-01 | The single-degree-of-freedom linear oscillator (LO) under the action of harmonic forcing is coupled to a light attachment that acts, in essence, as a nonlinear energy sink (NES). The complex dynamics of this two-degree-of-freedom system is investigated. Strong stiffness and damping nonlinearity in this system is introduced by coupling the LO and NES by two inclined linear spring-damper elements. The inclination of the coupling elements during the motion introduces strongly nonlinear geometric effects in the forced dynamics. A slow/fast partition of the dynamics is introduced by applying a complexification-averaging method, based on which a bifurcation analysis is performed. The effects of the initial angle, i.e., the initial inclination angle of the spring-damper elements, are thoroughly studied. The topology of the trajectories on the slow manifold of the dynamics is studied, and the different steady-state response regimes are predicted analytically. The conditions for existence of strongly modulated responses and of “folding singularities” are studied, and their effects on the nonlinear dynamical responses are revealed. Comparisons between analytical and numerical results indicate a good agreement between the two and provide a means of verification of the analytical findings. The analytical results show that, by increasing the initial angle of inclination, one can shrink, and even completely eliminate, unwanted high-amplitude steady-state responses of the LO that co-exist with desirable low-amplitude forced responses over definitive frequency ranges. This finding has significant practical implications for the vibration mitigation efficiency and robustness of the proposed NES, enhancing drastically the vibration suppression of the forced response of the LO. The presented results and the associated analytical modeling can be used to design and enhance the performance of nonlinear vibration absorbers as vibration mitigating devices. | A new way to introduce geometrically nonlinear stiffness and damping with an application to vibration suppression | 10.1007/s11071-019-04886-x |
2019-05-01 | High-damping rubber (HDR) has been commonly used to dissipate cyclic energy and reduce the bumping effect of a building structure. Studies on the application of HDR in precast reinforced concrete structures have mainly focused on the effects caused by lateral cyclic loads, but joints in precast structures are also highly susceptible to damage when frames are subjected to vertical cyclic loads. Therefore, this research aimed to develop a new hook-end U-shaped joint by using HDR so that the formation of cracks on precast frames could be minimized and the accumulated energy dissipation capacities could be enhanced under the actions of a vertical cyclic load. The developed joint was experimentally tested and compared with a single dowel beam-column-connected precast frame. Results revealed that the performance of the joint was similar to that of hysteresis loops and yield force. But, its maximum force and strength ratio were slightly lower than that of the control precast frame. A nonlinear 3D numerical model was also created and subjected to a vertical cyclic load to predict the behavior of the precast frame with the proposed and single dowel beam-column connections. Differences between numerical and experimental results were identified by comparing numerical data with experimental data. | Vertical Cyclic Performance of Precast Frame with Hook-end U-shaped High-damping Rubber Joint | 10.1007/s12205-019-1115-x |
2019-05-01 | The potential of antagonistic bacteria isolated from tomato rhizosphere soils of Oman in the control of damping-off disease of tomato was investigated. A total of 27 bacterial isolates were isolated from 18 soil samples collected from the rhizosphere of tomato from Al-Batinah South, Al-Sharqia North and Muscat Governorate. These bacterial isolates were tested in vitro for their antagonistic activity against Pythium aphanidermatum using a dual culture technique. Of the 27 bacterial isolates tested, four isolates designated D1/3, D1/8, D1/17 and D1/18 were effective in inhibiting the mycelial growth of P. aphanidermatum, by inducing an inhibition zone of 32.3, 10.3, 6.3 and 9.9 mm, respectively. Compatibility tests using a cross-streak assay on nutrient agar medium indicated that these four bacterial isolates were compatible with one another. The bacterial isolates were identified as Klebsiella oxytoca (D1/3), Exiguobacterium indicum (D1/8) and Bacillus cereus (D1/17 and D1/18), on the basis of the rRNA gene sequences. Among the isolates tested for in vitro plant growth promoting activity, D1/8 induced the maximum shoot length and seedling vigor. The potential of bacterial antagonists either individually or in combination in the control of damping-off disease of tomato was tested under greenhouse conditions. Among the biocontrol treatments, the combined application of D1/8 and D1/17 was the most effective, where damping-off incidence was reduced by 27% relative to the infected control. These bacterial antagonists appear to be potential candidates to be developed as bio-inoculants for the ecofriendly management of damping-off of tomato under desert farming ecosystem. | Biological control of damping-off of tomato caused by Pythium aphanidermatum by using native antagonistic rhizobacteria isolated from Omani soil | 10.1007/s42161-018-0184-x |
2019-05-01 | We analyze the dynamic characteristics of layered plates formed by rigid outer layers and inner layers with magneto-rheological properties. We estimate the influence of magnetic field on the frequency and loss factor for different magneto-rheological and rigid outer layers of materials. The applied improved theoretical model takes into account the deformations of each layer, including the transverse-shear and transverse normal deformations, as well as the nonlinear variations of displacements across the thickness of the plate. | Evaluation of the Dynamic Characteristics of Beams with Magneto-Rheological Interlayers | 10.1007/s11003-019-00275-2 |
2019-05-01 | To obtain more precise and rational calculation details of the loss and heat of a damper winding in a tubular hydro-generator, this study develops a three-dimensional, finite-element, electromagnetic-temperature field close-coupling model of the damper winding. On the basis of multi-physical field coupled theory, the model fully considers the temperature effects of the damper winding resistivities and heat conductivities, and the eddy current loss in the end region of the damper winding. The model was verified by direct tests of the damper winding temperature. Unlike the conventional weak-coupling model, the proposed close-coupling model fully captures the interaction between the electromagnetic and temperature fields. Therefore, of the model more accurately and reasonably calculates the loss and heat of the damper winding than the conventional model. The proposed calculation model can properly assess the loss and heat of damper windings in large hydro-generators, which is helpful for improving the design standards of hydro-generators. | 3D Electromagnetic-Temperature Field Close-Coupling Calculation of Losses and Heat in the Damper Winding of a Large Tubular Hydro-Generator | 10.1007/s42835-019-00143-8 |
2019-05-01 | Predicting Arctic sea ice extent is a notoriously difficult forecasting problem, even for lead times as short as one month. Motivated by Arctic intraannual variability phenomena such as reemergence of sea surface temperature and sea ice anomalies, we use a prediction approach for sea ice anomalies based on analog forecasting. Traditional analog forecasting relies on identifying a single analog in a historical record, usually by minimizing Euclidean distance, and forming a forecast from the analog’s historical trajectory. Here an ensemble of analogs is used to make forecasts, where the ensemble weights are determined by a dynamics-adapted similarity kernel, which takes into account the nonlinear geometry on the underlying data manifold. We apply this method for forecasting pan-Arctic and regional sea ice area and volume anomalies from multi-century climate model data, and in many cases find improvement over the benchmark damped persistence forecast. Examples of success include the 3–6 month lead time prediction of Arctic sea ice area, the winter sea ice area prediction of some marginal ice zone seas, and the 3–12 month lead time prediction of sea ice volume anomalies in many central Arctic basins. We discuss possible connections between KAF success and sea ice reemergence, and find KAF to be successful in regions and seasons exhibiting high interannual variability. | Predicting regional and pan-Arctic sea ice anomalies with kernel analog forecasting | 10.1007/s00382-018-4459-x |
2019-04-30 | The static and dynamic mechanical properties of polymeric materials can greatly be enhanced by using carbon nanotubes as reinforcement material. However, studies still need to be carried out to characterize the dynamic mechanical properties of the Carbon-Nanotube-Reinforced-Polymer (CNRP) material. Experimental investigations for this purpose have severe limitations and, in most cases, appropriate and reliable experimental work could not be carried out. Computational modelling and simulation encompassing multiscale material behavior provides an alternate approach to study the material behavior. The objective of the present work is to study the enhancement of stiffness and dynamic mechanical properties of Carbon-Nanotube-Reinforced-Polymer (CNRP) material by using a 3D multiscale finite-element model of the representative volume element of the CNRP material. A composite material model consisting of a polymer matrix, an interface region, and a Single-Walled Carbon Nanotube (SWCNT) is constructed for this purpose. The polymer matrix is modeled with the Mooney-Rivlin strain energy function to calculate its non-linear response and the interface region is modeled via van der Waals links. The SWCNT is modeled as a space frame structure by using the Morse potential and as a thin shell model based on Donnell’s Shell Theory. The stiffness response of the CNRP is calculated and the natural frequencies of the CNRP are also determined. The viscoplastic behavior of the polymer matrix material is considered and the rate-dependent characteristics of the CNRP are studied. The damping properties of the CNRP are investigated based on its viscous and structural damping mechanisms. The effectiveness of the SWCNT reinforcement is quantified and characterized. | Enhancement of stiffness and dynamic mechanical properties of polymers using single-walled-carbon-nanotube – a multiscale finite element formulation study | 10.1007/s10965-019-1774-9 |
2019-04-16 | This paper is concerned with the initial value problem for semilinear wave equation with structural damping $$u_{tt}+(-\Delta )^{\sigma }u_t -\Delta u =f(u)$$ u tt + ( - Δ ) σ u t - Δ u = f ( u ) , where $$\sigma \in (0,\frac{1}{2})$$ σ ∈ ( 0 , 1 2 ) and $$f(u) \sim |u|^p$$ f ( u ) ∼ | u | p or $$u |u|^{p-1}$$ u | u | p - 1 with $$p> 1 + {2}/(n - 2 \sigma )$$ p > 1 + 2 / ( n - 2 σ ) . We first show the global existence for initial data small in some weighted Sobolev spaces on $${{\mathbb {R}}}^n$$ R n ( $$n \ge 2$$ n ≥ 2 ). Next, we show that the asymptotic profile of the solution above is given by a constant multiple of the fundamental solution of the corresponding parabolic equation, provided the initial data belong to weighted $$L^1$$ L 1 spaces. | Asymptotic profile of solutions for semilinear wave equations with structural damping | 10.1007/s00030-019-0562-x |
2019-04-16 | We consider the stability of a system of two strongly coupled wave equations by means of only one boundary feedback. We show that the stability of the system depends in a very complex way on all of the involved factors such as the type of coupling, the hidden regularity and the accordance of boundary conditions. We first show that the system is uniformly exponentially stable if the undamped equation has Dirichlet boundary condition, while it is only polynomially stable if the undamped equation is subject to Neumann boundary condition. Next, by a spectral approach, we show that this sensitivity of stability with respect to the boundary conditions on the undamped equation is intrinsically linked with the transmission of the vibration as well as the dissipation between the equations. | On the sensitivity of the transmission of boundary dissipation for strongly coupled and indirectly damped systems of wave equations | 10.1007/s00033-019-1110-6 |
2019-04-15 | We investigate the dynamics of the Vlasov-Poisson system in the presence of radiation damping. A propagation result for velocity moments of order k > 3 $k>3$ is established in (Kunze and Rendall in Ann. Henri Poincaré 2:857–886, 2001 ). In this paper, we prove existence of global solutions propagating velocity and velocity-spatial moments of order k > 2 $k>2$ and establish an explicit polynomially growing in time bound on the moments. | Moment Propagation of the Vlasov-Poisson System with a Radiation Term | 10.1007/s10440-018-0200-3 |
2019-04-15 | In this paper, we consider an abstract viscoelastic equation. We use memory-type damping with a general assumption on the relaxation function and establish explicit energy decay result from which we can recover the optimal exponential and polynomial rates. Our result generalizes the earlier related results in the literature. | Asymptotic Stability for the Second Order Evolution Equation with Memory | 10.1007/s10883-018-9410-2 |
2019-04-15 | The integrated optimization of component layout and structural topology is studied in this paper to improve the dynamic performance of the multi-component structure systems under harmonic base acceleration excitations. Considering linear systems, including multi-point constraints interconnecting the components and structures as an integrity, the dynamic responses and the corresponding design sensitivities are analytically derived based on the mode acceleration method. To obtain precise dynamic response, structural real damping characteristics are measured using vibration experiments, which are relevant to the structural dynamic response, especially when the excitation frequencies fall into the resonant frequency band. Further verifications are done by the comparison of Rayleigh damping, constant damping ratio, and hysteretic damping model with experimental results of structures achieved by resin-based additive manufacturing. In this way, structural real damping characteristics are taken into account in the integrated optimization. Numerical examples and vibration testing results are presented to show the validity of the optimization procedure and its potential application in engineering. | Integrated layout and topology optimization design of multi-component systems under harmonic base acceleration excitations | 10.1007/s00158-019-02200-2 |
2019-04-15 | Background This study explored the role of outdoor air pollution [nitrogen dioxide (NO_2) and sulphur dioxide (SO_2)] and indoor air quality (measured with damp or condensation and secondhand smoke exposures) at age 9 months in emotional, conduct and hyperactivity problems at age 3 years. Method Data from 11,625 Millennium Cohort Study children living in England and Wales were modelled using multilevel regression. Results After adjusting for a host of confounders, having a damp or condensation problem at home was related to both emotional and conduct problems. Secondhand smoke exposure was associated with all three problem types. Associations with outdoor air pollution were less consistent. Conclusions Exposures to damp or condensation and secondhand smoke in the home are likely to be risk factors for child emotional and behavioural problems. Parents should continue to be educated about the dangers of exposing their children to poor air quality at home. | The quality of air outside and inside the home: associations with emotional and behavioural problem scores in early childhood | 10.1186/s12889-019-6733-1 |
2019-04-13 | Circulating tumor cell (CTC) isolation has made positive impacts on metastatic detection and therapy analysis for cancer patients. Microfluidic-elasto-filtration (MEF) device based on the critical elasto-capillary number ( Ca _ e ^* ) has been proposed to utilize the optimal multi-parameter conditions, including cell diameter ( d _c), the diameter of cylindrical filter pores ( d _p), nonlinear cell elasticity and hydrodynamic drag force, for selectively capturing CTCs and depleting white blood cells (WBCs). In this paper, we propose a novel two-degree-of-freedom nonlinear mass–damper–spring ( m–c–k ) model to predict the dynamic behaviors of CTCs and WBCs in a generic MEF device. This model enables the optimization of the device design to achieve extremely high CTC capture efficiency and WBC depletion efficiency. In particular, the function of nonlinear cell stiffness specific to different cell types and MEF’s pore diameters is first determined by finite element method with neo-Hookean hyperelastic model, based on which the mechanical behaviors of CTCs and WBCs in MEF devices are systematically studied. Herein, the predicted normalized deformations of a CTC and WBC as a function of Ca _ e are used to determine the optimized Ca _ e of 0.043, consistent with the experimental results from the fabricated MEF devices using MCF-7 cells (0.04 ± 0.006). In addition, the normalized cell diameter versus Ca _ e phase diagram is proposed for the first time as a useful tool for design optimization of MEF devices and other microfiltration devices. | A nonlinear two-degree-of-freedom mass–damper–spring model to predict the isolation of circulating tumor cells in microfluidic-elasto-filtration devices | 10.1007/s10404-019-2240-z |
2019-04-08 | The most commonly used base isolator is the lead rubber bearing which is used in the experiments carried out in the present study. The performance of this isolator is then studied in an attempt to develop one with a better performance. In the model, thus, developed, hereafter called the ‘Ring Rubber Bearing’, the lead core is replaced with a rubber cylinder around which steel rings are placed. The results show the enhanced absorbed energy in each cycle, lower effective stiffness, and higher damping percentage of the new base isolation system compared with lead rubber bearing. | An innovative base isolator with steel rings and a rubber core | 10.1007/s42107-018-00107-9 |
2019-04-06 | Recent years have witnessed the development of so-called relaxation tribometers, the free oscillation of which is altered by the presence of frictional stresses within the contact. So far, analysis of such oscillations has been restricted to the shape of their decaying envelope, to identify in particular solid or viscous friction components. Here, we present a more general expression of the forces possibly acting within the contact, and retain six possible, physically relevant terms. Two of them, which had never been proposed in the context of relaxation tribometry, only affect the oscillation frequency, not the amplitude of the signal. We demonstrate that each of those six terms has a unique signature in the time-evolution of the oscillation, which allows efficient identification of their respective weights in any experimental signal. We illustrate our methodology on a PDMS sphere/glass plate torsional contact. | Relaxation Tribometry: A Generic Method to Identify the Nature of Contact Forces | 10.1007/s11249-019-1168-5 |
2019-04-06 | In internal turning operation of long holes, the tool is not rigid, since it must be out from the lathe turret in a length longer than the machined hole length. This problem is even more serious in the internal turning of hardened steels, where the requirements for surface quality are more restrict, due to the fact that this is a finishing operation, which aims to replace grinding. Therefore, some procedures have to be taken in order to minimize vibration and, consequently, to make the attainment of a good workpiece surface quality possible. One of these procedures is the use of a damped tool. In this work, we tried a simple and different kind of impact damped tool bar, using spheres placed in a cavity manufactured in the tool bar. The performance of this impact damper with three different sizes of spheres was compared to the performance of a solid steel bar, in terms of workpiece surface roughness, tool vibration, and tool life. The main conclusion of this work is that the use of the kind of impact damper tested in this work makes possible the increase of the tool overhang (tool length outside the machine turret) without damaging surface roughness and tool life and, consequently, it also makes possible the turning of longer holes than when a solid bar is used. | Evaluating the use of a new type of impact damper for internal turning tool bar in deep holes | 10.1007/s00170-018-3039-x |
2019-04-05 | In this study, the behaviour of conventional concrete tapered piles subjected to lateral harmonic excitation is assessed. For a constant volume of pile material, the tapered pile is modelled in two different series. The first series is modelled with a constant pile tip diameter and the second series comprises of constant length of the pile. The response curves of the soil–pile system under horizontal vibration are obtained from three-dimensional finite element numerical simulation. The dynamic properties of the soil–pile system, i.e., the stiffness and the damping ratio are calculated from the response curves. It is observed that the tapered piles in the first series exhibit 4.14–8.87% lower resonant frequency than cylindrical piles of the same volume of pile material, whereas the tapered piles in the second series display a resonant frequency 2.95–7.69% higher than that of the cylindrical piles. Further, the resonant amplitude and frequency obtained from the finite element simulation are compared with a modified analytical solution. The resonant frequencies obtained from the finite element simulation are within an error limit of ± 0.57–10% as compared to that obtained from the analytical approach. | Behaviour of tapered piles subjected to lateral harmonic loading | 10.1007/s41062-019-0211-6 |
2019-04-05 | A lower pad adjustable journal bearing is proposed in this paper. This bearing can adjust the working status of the rotor system by changing the position of the bearing pad and improve the stability of the rotor system. The adjustable bearing structure achieves the function of changing the characteristic parameters of the bearing under continuous operation and makes up for the shortcomings of the traditional fixed-pad bearing. In this paper, the evaluation method of the dynamic characteristics of the adjustable bearing is introduced. The stiffness and damping characteristics of the bearing are calculated by the analytical method. Then, the rotor bearing system model is established using the finite element method. Finally, the dynamic response of the rotor system is solved by Runge–Kutta variable step length integration. The numerical results show that the stability of the system can be improved by reducing the ellipticity of the adjustable bearing when the rotor system crosses the critical speed. The experimental study shows that when the oil film is unstable in the rotor system, the oil film whip is effectively eliminated by reducing the ellipticity, which proves that the adjustable bearing can improve the stability of the rotating machine. | Enhancing the stability of rotating machinery using a lower pad adjustable journal bearing | 10.1007/s42452-019-0419-2 |
2019-04-03 | Concrete dams are one of the most important infrastructures in every country and the seismic safety assessment of them is a major task in dam engineering field. Dam–foundation–reservoir system analysis is a complex interaction problem because this system consists of three domains with different behaviors. For accurate analysis of this system, some important factors should be considered such as foundation mass and earthquake input mechanism. In this paper, the effect of foundation mass and earthquake input mechanism on seismic response of concrete gravity dam is investigated. For this purpose, two different methods are introduced for modeling of massed semi-infinite foundation in finite element method, namely free-field boundary condition and domain reduction method (DRM). To verify the feasibility of proposed methods for seismic analysis of dam–foundation–reservoir system, the displacement and stress outputs using proposed methods are compared with EAGD-84 results. The obtained results indicate that both methods are accurate enough for finite element modeling of massed foundation. Finally, Koyna concrete gravity dam is analyzed for rigid, massless and massed foundation cases using DRM and it is concluded that the foundation has significant effect on dam response and the common massless foundation approach overestimates the dam response. | Assessment of Foundation Mass and Earthquake Input Mechanism Effect on Dam–Reservoir–Foundation System Response | 10.1007/s40999-018-0325-9 |
2019-04-01 | Abstract The elastic hysteretic properties of various polymer damping composite materials, namely, a composite material based on a rubber mixture, a rubber fiber composite material, and thermoplastic elastomers, are studied during static and dynamic loading at a load of 20–90 kN and a temperature of 23 and –40°C. The conditions of effective application of each composite material for a damping element for the upper structure of a railway track and rolling stock are determined. | Comparison of the Composite Materials Intended for Damping Elements for the Infrastructure of Rail Transport and Rolling Stock | 10.1134/S0036029519040232 |
2019-04-01 | There have been few experimental and numerical studies on damping effects in fluid-structure interaction (FSI) problems. Therefore, a comprehensive experimental study was conducted to investigate such effects. In experiments, a water column in a container was released and hit a rubber plate. It continued its motion until hitting a downstream wall where pressure transducers had been placed. The experiments were repeated using rubber plates with different thickness and material properties. Free-surface profiles, displacements of the rubber plates, and pressures were recorded. In addition, a numerical model was developed to simulate the violent interaction between the fluid and the elastic structure. Smoothed particle hydrodynamics (SPH) and finite element method (FEM) were used to model the fluid and the structure. Contact mechanics was used to model the coupling mechanism. The obtained numerical results were in agreement with the experimental data. We found that damping is a less important parameter in the FSI problem considered. 目的 1. 通过全面的实验研究考察阻尼在流固耦合(FSI)问题中的影响作用;2. 提出一套光滑粒子流体动力学(SPH)和有限元方法(FEM)相结合的耦合算法,并对流固耦合系统进行数值模拟。 创新点 1. 通过一系列实验研究惯性驱动问题中阻尼的影响并使用本文提出的数值方法进行验证;2. 该数值方法能够在不解耦的情况下对完整系统进行求解。 方法 1. 构建数值模型模拟流体和弹性结构之间的强烈相互作用;2. 利用SPH 和FEM对流体和结构分别进行模型化;3. 采用接触力学对系统中的流固耦合机理进行建模。 结论 1. 基于SPH-FEM 耦合的FSI 模型可成功模拟自由液面形状、橡胶板的位移以及容器壁上的压强;2. 模拟结果显示,在连续相互作用的惯性驱动问题中阻尼并不是必要的考虑因素。 | Numerical and experimental investigation of damping in a dam-break problem with fluid-structure interaction | 10.1631/jzus.A1800520 |
2019-04-01 | An application of electromagnetic devices of the motional type (i.e. eddy-current dampers) to improve the dynamic stability of a cantilever pipe discharging fluid is proposed. When the flow velocity reaches a critical value, this system loses stability through the flutter. A contactless damping device is used. This actuator is made of a conducting plate attached to the pipe that moves together with it within the perpendicular magnetic field that is generated by the controlled electromagnets. During the motion the eddy currents in the plate and a resultant drag force of a viscous character are generated. First, an optimal control problem that aims to stabilise the system with the optimal rate of decrease of the system’s energy is posed and solved. Then a state-feedback parametrization of the obtained optimal control, which can be used in a closed-loop scheme is proposed. The effectiveness of the designed optimal controller is validated by making a comparison with the corresponding passive solutions on the specially designed and constructed experimental test stand of a pipe conveying air. | Semi-active stabilisation of a pipe conveying fluid using eddy-current dampers: state-feedback control design, experimental validation | 10.1007/s11012-019-00988-3 |
2019-04-01 | Gradient methods are popular due to the fact that only gradient of the objective function is required. On the other hand, the methods can be very slow if the objective function is very ill-conditioned. One possible reason for the inefficiency of the gradient methods is that a constant criterion, which aims only at reducing the function value, has been used in choosing the steplength, and this leads to a stable dynamic system giving slow convergence. To overcome this, we propose a new gradient method with multiple damping, which works on the objective function and the norm of the gradient vector simultaneously. That is, the proposed method is constructed by combining damping with line search strategies, in which an individual adaptive parameter is proposed to damp the gradient vector while line searches are used to reduce the function value. Global convergence of the proposed method is established under both backtracking and nonmonotone line search. Finally, numerical results show that the proposed algorithm performs better than some well-known CG-based methods. | Gradient method with multiple damping for large-scale unconstrained optimization | 10.1007/s11590-018-1247-9 |
2019-04-01 | Background Despite the increased awareness of vibration control, vibration still causes many problems, such as performance degradation of the equipment and stability violation of flexible structures. In general, the vibration in machines can be caused due to the misalignment, malfunction of mounting parts, changes in temperature, and unbalanced rotating parts. Moreover, the fluctuation in magnetic force due alternating current in transformers and magnetically actuated device can cause unwanted vibrations. Purpose The development of sandwich-like structural system with combination of control capabilities plays a very important role to control the unwanted vibrations and to avoid resonance phenomenon due to external disturbances in the system. This problem can be resolved by applying a new sandwich structure incorporating smart fluids such as magnetorheological fluid. Methods Here in this research work, design and fabrication of a sandwich beam consisting of three layers are undertaken; two outer layers of aluminium and one core layer of MR fluid. The fabricated sandwich beam is tested to effectively achieve vibration control under various magnetic field conditions. Results The research work results show that as the magnetic field intensity increases, the natural frequency of the beam increases, while the peak amplitude, loss factor, and quality factor are decreased. Conclusion The principal criterion on the vibration control undertaken in this research work is the increment of the natural frequency as the field intensity increases. Therefore, the resonance behaviour of flexible structure, which can be occurred by external disturbances possessing several frequency spectrum, can be avoided by applying an appropriate magnetic field intensity. This directly means that the natural frequency of the smart sandwich beam can be adaptively controlled by using MR fluid which provides high damping and stiffening effect by means of the semi-active control which does not require any external input power. | Experimental Investigation of Damping Effect in Semi-active Magnetorheological Fluid Sandwich Beam Under Non-Homogeneous Magnetic Field | 10.1007/s42417-019-00093-5 |
2019-04-01 | Thermoelastic damping (TED) is considered to be the main internal energy dissipation mechanism in microresonators, the study of which has become increasingly significant in the design of microresonators with high quality factor. In this paper, the bilayered cantilever, fixed-fixed and fully clamped rectangular microplate resonators are taken as the research object, and then three theoretical models of thermoelastic damping with three-dimensional heat conduction are built. The analysis on convergence items of the present three-dimensional models with different combinations of materials are carried out, and the influence of material plating on TED in Si microplate resonators is also analyzed. The analysis on the effects of the geometry size and boundary conditions on thermoelastic damping of microresonators at the first-order natural frequency are both carried out. Moreover, in order to verify the validation and accuracy of the present three-dimensional (3-D) models, the previous one-dimensional (1-D) models and the FEM models built in this paper are used to compare with the present models. Finally, the validation and accuracy of the present three-dimensional models are confirmed. | Analysis of thermoelastic damping in bilayered rectangular microplate resonators with three-dimensional heat conduction | 10.1007/s12206-019-0329-7 |
2019-04-01 | Conveyor surging, a phenomenon in which the conveyor repeatedly moves and stops, causes inconvenience to workers and reduces the quality of manufacturing. It is difficult to anticipate the surging motion because it occurs owing to the combination of several causes such as inertia, friction, and motor power. This paper reports on a dynamic simulation of a conveyor system to predict and eliminate the surging motion. The dynamic model of a conveyor system is based on a multimass, spring-damper system to reflect the characteristics of the real conveyor system. The surging motion is considered a stick–slip motion, in which the stick–slip is primarily caused by friction. Stribeck friction is applied to model the stick–slip motion. In the model, lubrication, motor capacity, and polygonal effects are included to simulate the actual surging motion precisely. Based on the model, we analyzed three industrial cases involving surging and nonsurging motions. For the surging cases, we investigate the primary causes of the surging motion and suggest a method to achieve the motion without surging. We expect the model to be useful in designing an improved conveyor belt without surging motion. | Methods to Eliminate Surging Motion in a Conveyor System Considering Industrial Case Studies | 10.1007/s12541-019-00042-y |
2019-04-01 | The initial value problem for a damped coupled non-linear Schrödinger system is investigated. Global existence and scattering are proved depending on the size of the damping coefficient. | Damped Non-linear Coupled Schrödinger Equations | 10.1007/s11785-018-0841-2 |
2019-04-01 | Purpose In this paper, Bouc–Wen type magnetorheological fluid damper has been used to monitor the ride quality of a prevailing rail vehicle in lateral vibrations. Methods Modelling of the rail vehicle is done in such a manner that it has an entire 9 degrees of freedom by significant considerations of lateral, roll and yaw motions of the car body, rear, and the front chassis. 200 km/h is considered as train speed for tracks with two varying disturbances. A system consisting of multibody in VI-rail software is provided by a track input and ergo, wheel response it obtained. SIMULINK (software) is responsible for the representation of the motions of the wheel as mathematical models. Two different types of analysis are done firstly with conventional passive lateral damper and secondly with semi-active MR lateral damper in subordinate suspension. To diminish lateral vibrations, the disturbance refusal and non-stop state controller algorithms were executed to manage the damper force. Results Results acquired are in the form of acceleration and displacement of the center of mass of the body under consideration is done by comparing in terms of reduction indices of their vibrations. A significant improvement in the index is seen in which a semi-active lateral damper is mounted. Conclusions The results show that the proposed system significantly improves both, the vibration attenuation ability and the ride quality of the vehicle. | Semi-active Control to Reduce Lateral Vibration of Passenger Rail Vehicle Using Disturbance Rejection and Continuous State Damper Controllers | 10.1007/s42417-019-00088-2 |
2019-03-15 | In this work, the damping mechanisms of C5 petroleum resin/chlorinated butyl rubber composites were studied by experimentation, molecular dynamics (MD) simulation, and statistical analysis. At the macro level, damping parameters, including glass transition temperature and effective damping temperature region, loss modulus, contact angle, relaxation time, and activation energy were obtained through dynamic mechanical thermal analysis, drop shape analysis, broadband dielectric relaxation spectroscopy, and differential scanning calorimetry. At the micro level, four intermolecular interaction parameters, including binding energy, fractional free volume, mean square radius of gyration, and mean square displacement, were calculated by MD simulation. The quantitative relationships between the damping and intermolecular interaction parameters were obtained by linear regression analysis. The results are expected to provide useful information for understanding damping mechanisms and a quantitative tool for predicting the damping properties of rubber composites. | Experimental and molecular dynamics simulation study on the damping mechanism of C5 petroleum resin/chlorinated butyl rubber composites | 10.1007/s10853-018-3134-2 |
2019-03-15 | In this paper, we obtain several asymptotic profiles of solutions to the Cauchy problem for structurally damped wave equations $$\partial _{t}^{2} u - \varDelta u + \nu (-\varDelta )^{\sigma } \partial _{t} u=0$$ ∂ t 2 u - Δ u + ν ( - Δ ) σ ∂ t u = 0 , where $$\nu >0$$ ν > 0 and $$0< \sigma \le 1$$ 0 < σ ≤ 1 . Our result is the approximation formula of the solution by a constant multiple of a special function as $$t \rightarrow \infty $$ t → ∞ , which states that the asymptotic profiles of the solutions are classified into 5 patterns depending on the values $$\nu $$ ν and $$\sigma $$ σ . Here we emphasize that our main interest of the paper is in the case $$\sigma \in (\frac{1}{2},1)$$ σ ∈ ( 1 2 , 1 ) . | Asymptotic Profiles of Solutions for Structural Damped Wave Equations | 10.1007/s10884-019-09731-8 |
2019-03-15 | Purpose Peristaltic pumps (PP) are favored in flow bioreactors for their non-contact sterile design. But they produce pulsatile flow, which is consequential for the cultured cells. A novel pulse damper (PD) is reported for pulsatility elimination. Methods The PD design was implemented to target static pressure pulsatility and flow rate (velocity) pulsatility from a PP. Damping effectiveness was tested in a macro-scale, closed-loop recirculating bioreactor mimicking the aortic arch at flow rates up to (4 L/min). Time-resolved particle image velocimetry was used to characterize the velocity field. Endothelial cells (EC) were grown in the bioreactor, and subjected to continuous flow for 15 min with or without PD. Results The PD was found to be nearly 90% effective at reducing pulsatility. The EC exposed to low PP flow without PD exhibited distress signaling in the form of increased ERK1/2 phosphorylation (2.5 folds) when compared to those exposed to the same flow with PD . At high pump flow without PD , the cells detached and did not survive, while they were perfectly healthy with PD. Conclusions Flow pulsatility from PP causes EC distress at low flow and cell detachment at high flow. Elevated temporal shear stress gradient combined with elevated shear stress magnitude at high flow are believed to be the cause of cell detachment and death. The proposed PD design was effective at minimizing the hemodynamic stressors in the pump’s output, demonstrably reducing cell distress. Adoption of the proposed PD design in flow bioreactors should improve experimental protocols. | A Novel Pulse Damper for Endothelial Cell Flow Bioreactors | 10.1007/s13239-018-00394-y |
2019-03-15 | In this paper Ikeda’s method for roll damping prediction is revisited and the applicability of the method to modern volume carriers is considered. For volume carriers the hull lift and bilge keel components are the dominating components and the estimation of these components in the original method are benchmarked and scrutinized. It is concluded that the speed dependence of the bilge keels damping is underestimated by the original method. This is partially explained by that Ikeda seems to have underestimated the lift force of the bilge keels in his analytical expressions. Correcting for this and taking account of the lift force-generated pressure on the hull surface gives overall better agreement with model tests. It is also concluded that the hull lift damping component is significantly overestimated with the original method. Non-viscid CFD is used to propose a new generic expression for estimating the lift coefficients for volume carriers which greatly improve the accuracy in comparison to model test results. With these improvements Ikeda’s method is revitalized and the applicability is extended to unconventional volume carriers. | Ikeda revisited | 10.1007/s00773-017-0497-z |
2019-03-13 | Modern, low-emission aero-engine concepts, such as, for instance, Ultrahigh-Bypass Ratio (UHBR) designs, claim higher demands on the damping performance of acoustic wall treatment, called liner, installed in the engine. New liner concepts are needed providing a more broadband damping efficiency ranging explicitly to the low-frequency range. However, space and weight constrains are still also one of the crucial criteria which need to be fulfilled by the liner structure. To overcome this challenge, two novel liner concepts are presented here. One concept, the hybrid ZML, combines the classical Single-Degree-of-Freedom (SDOF) liner with a Zero-Massflow-Liner (ZML) principle. The other one, the FlexiS concept, takes advantage of the intrinsic material damping of flexible walls within the liner structure. A proof of concepts study of both novel concepts is provided highlighting the enhanced damping performance with respect to broadband capacity and low-frequency damping. | Novel liner concepts | 10.1007/s13272-019-00380-7 |
2019-03-13 | The design of an electric active mass dampers (AMD) system requires the knowledge of the structure properties behavior and the soil where it is installed. These properties must be accurate to ensure the effectiveness of the AMD. In the previous works, the researchers consider that the structure is constructed on fixed-base. If the structure is constructed on soft soil, the properties of the structure can change due to the soil–structure interaction (SSI) effect. This, can lead to a considerable effect on the performance of the AMD system. This paper evaluates the LQG vibration control effectiveness of an electric active mass damper considering SSI effects for buildings subjected to seismic excitation. Dynamic model of a multi-story building including the AMD system and considering SSI effect is developed. The SSI analysis is performed using the substructure method. To control the electric AMD, a Linear Quadratic Gaussian algorithm is adopted. A five-story concrete building subjected to the El Centro earthquake excitation is used as a model structure. Different types of soils are considered. Simulation results show that the SSI leads to a considerable effect on the vibration control effectiveness of the electric AMD. Consequently, in the design of electric types AMD, the consideration of SSI become very important when the structure is constructed on soft soil. | LQG vibration control effectiveness of an electric active mass damper considering soil–structure interaction | 10.1007/s40435-018-0428-9 |
2019-03-12 | Damper seals might have a great impact on rotordynamics, but the values of their coefficients are difficult to be determined and have a significant uncertainty. In the present paper, a probabilistic model is proposed to model damper seal coefficients, which are frequency dependent. A stochastic process (frequency indexed) is constructed such that modeling errors are taken into account. The impact of these uncertainties on the rotordynamic behavior of a compressor is analyzed. The deterministic seal coefficients are determined considering a bulk-flow model, and values are calculated by a compressor manufacturer based on experimental data. The results obtained show that uncertainties in these coefficients have a considerable impact on the compressor Campbell diagram, stability, and unbalance response. | Impact of damper seal coefficients uncertainties in rotor dynamics | 10.1007/s40430-019-1652-8 |
2019-03-11 | Control moment gyroscope (CMG) is an ideal device for satellite attitude transformation, which inevitably has micro-vibration in that process, and it will seriously affect the high precision imaging of the satellite. To restrain the interference with micro-vibration caused by CMG, a magnetorheological (MR) damper and its control method are designed in this study. Besides, the structure, the dynamic model, and the fuzzy PID algorithm of the MR damper are proposed. The magnetic circuit structure is designed according to the requirements of MR dampers for magnetic field, the finite element analysis of magnetic force line and magnetic induction intensity is completed in Maxwell, and the simulation shows that the designed magnetic circuit meets the requirements. The simulation test is carried out by Simulink under the stimulation of vibration source. The vibration suppression effect of the MR damper is tested on the vibration test platform, from which we know the designed MR damper can effectively control the micro-vibration suppression. | Development of a Magnetorheological Damper of the Micro-vibration Using Fuzzy PID Algorithm | 10.1007/s13369-018-3464-z |
2019-03-08 | In this work, we adopt a semi-analytical model to study a capacitive MEMS accelerometer based in silicon (Si). Such model takes into account the thermoelastic stiffness and linear expansion coefficients of anisotropic bulk Si. In addition, an analytical damping model, derived from the Reynolds equation, is incorporated in the model, in order to study dynamical characteristics of a MEMS capacitive accelerometer. Such approach takes into account the inertial effects on squeeze film damping in air, argon and helium gases, assumed as being ideal gases. The simulation model was compared with experimental measurements. The main figure of merit adopted is the electromechanical sensitivity ( S _EM), assuming frequency response and considering the effect of gas pressure, as well as temperature, on the damping loss mechanisms in such devices. The resulted model implementation shows a good agreement with the experimental data. For all gases, the sensitivity at 20 Pa presents less variation than at 200 Pa. At 20 Pa, the linear response of the device reaches up to 300 Hz, approximately, for air and helium, assuming variation of ≈ 0.5 dB, no matter which temperature. For 200 Pa, the linear response drops down to about 150 Hz. Also, for the three gases, the variation of S _EM as a function of temperature is below 0.17 dB in the entire operational range, for both evaluated pressures, depending only on the silicon mechanical properties at low frequencies. | MEMS capacitive accelerometer: dynamic sensitivity analysis based on analytical squeeze film damping and mechanical thermoelasticity approaches | 10.1007/s42452-019-0327-5 |
2019-03-04 | Based on the properties of nonlocal fractional calculus generated by conformable derivatives, we establish some sufficient conditions for oscillation of all solutions for fractional differential equations with damping term. Forced oscillation of conformable differential equations in the frame of Riemann, as well as of Caputo type, is established. Examples are provided to demonstrate the effectiveness of the main results. | Forced oscillation of fractional differential equations via conformable derivatives with damping term | 10.1186/s13661-019-1162-8 |
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