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2021-03-11 | In this paper, we consider the nonlinear abstract equation $$\begin{aligned} u_{tt}+Au-\int _{0}^{t}g(t-s)Au(s)\mathrm{d}s+h(u_{t})=j(u) \end{aligned}$$ u tt + A u - ∫ 0 t g ( t - s ) A u ( s ) d s + h ( u t ) = j ( u ) subject to a competing effect of viscoelastic and frictional dampings. With very general assumptions on the behavior of g at infinity and the behavior of h near 0, we establish explicit and optimal energy decay result. To the best of our knowledge, this is the first time we have such combination of generality and optimality in one explicit formula for the energy decay rates of this system. | Optimal energy decay result for nonlinear abstract viscoelastic dissipative systems | 10.1007/s00033-021-01498-7 |
2021-03-09 | We prove by using an iteration argument some blow-up results for a semilinear damped wave equation in generalized Einstein–de Sitter spacetime with a time-dependent coefficient for the damping term and power nonlinearity. Then, we conjecture an expression for the critical exponent due to the main blow-up results, which is consistent with many special cases of the considered model and provides a natural generalization of Strauss exponent. In the critical case, we consider a non-autonomous and parameter dependent Cauchy problem for a linear ODE of second order, whose explicit solutions are determined by means of special functions’ theory. | Blow-up results for semilinear damped wave equations in Einstein–de Sitter spacetime | 10.1007/s00033-021-01494-x |
2021-03-01 | This study is aimed at analysing damping and gyroscopic effects on the stability of parametrically excited continuous rotor systems, taking into account both external (non-rotating) and internal (rotating) damping distributions. As case-study giving rise to a set of coupled differential Mathieu–Hill equations with both damping and gyroscopic terms, a balanced shaft is considered, modelled as a spinning Timoshenko beam loaded by oscillating axial end thrust and twisting moment, with the possibility of carrying additional inertial elements like discs or flywheels. After discretization of the equations of motion into a set of coupled ordinary differential Mathieu–Hill equations, stability is studied via eigenproblem formulation, obtained by applying the harmonic balance method. The occurrence of simple and combination parametric resonances is analysed introducing the notion of characteristic circle on the complex plane and deriving analytical expressions for critical solutions, including combination parametric resonances, valid for a large class of rotors. A numerical algorithm is then developed for computing global stability thresholds in the presence of both damping and gyroscopic terms, also valid when closed-form expressions of critical solutions do not exist. The influence on stability of damping distributions and gyroscopic actions is then analysed with respect to frequency and amplitude of the external loads on stability charts in the form of Ince–Strutt diagrams. | Damping and gyroscopic effects on the stability of parametrically excited continuous rotor systems | 10.1007/s11071-020-06106-3 |
2021-03-01 | Subsynchronous oscillations (SSOs) induced during the generation of wind power constitute an important problem that affects the safety and the stability of power systems. It is useful to study the impact of wind turbines on the damping of the SSOs of a synchronous generator (SG). On the one hand, the relevant studies have been based mainly on eigenvalue analysis, which is insufficient, and on the other, an examination of the general mechanism of the SSO is still lacking. Based on the net electrical damping analysis method, this paper examines the dynamic interaction between the SG and doubly fed induction generator-based wind turbines (DFIGs). The self-stabilizing damping coefficient and the mutually stabilizing damping coefficient are proposed from the perspective of the SG, and the effects of different numbers and current loop control parameters of the DFIGs on torsional modes of the SG are analyzed using different grid structures. A time-domain simulation model of DFIGs connected to a power grid is built in EMTDC/PSCAD to verify the correctness of the theoretical analysis. | Impact of DFIG-Based WTs on Subsynchronous Oscillation Damping of SG Based on the Net Electrical Damping Method | 10.1007/s42835-020-00620-5 |
2021-03-01 | Heave plates are structural components used for reducing the vibrations caused by environmental forces on marine and offshore structures by changing the hydrodynamic properties. The fact that the added mass increase via heave plates does not always lead to the structural response reduction underscores the role of damping in maintaining the vibration amplitude within allowable limits. In the present experimental study, a novel combined rigid-elastic design is used to improve the damping through the velocity increase in the elastic part and added mass creation in the central rigid part. The desired percentage of total added mass and damping can be adjusted by changing the rigid-to-elastic parts diameter ratio, which is the main scope of this experimental research. Frequency of vibration, which affects the elastic edge excited mode shapes, also affects the forming of the vortex shedding. Experimental tests show that the frequency increase generally causes high damping performance provided that the excited mode shapes are axisymmetric, which strongly depends on equivalent stiffness and mass. | Hydrodynamic damping enhancement by implementing a novel combined rigid-elastic heave plate | 10.1007/s00773-020-00732-7 |
2021-03-01 | A model for calculating the thickness and heat transfer of a turbulent film moving under the action of gravity and the shear stress of friction of a gas flow is constructed. The aim of this work is to supplement the previously proposed simple model of turbulent viscosity using a cubic law of damping in a viscous sublayer and a logarithmic asymptotic velocity far from the wall with additional linear damping near the free surface and to take into account the damping of turbulent transfer caused by intermittency of turbulence in flowing wave films of liquid. | Effect of intermittency on thickness and heat transfer of turbulent falling liquid film | 10.1134/S0869864321020049 |
2021-03-01 | Damping is largely increasing with the vibration amplitude during nonlinear vibrations of rectangular plates. At the same time, soft materials present an increase in their stiffness with the vibration frequency. These two phenomena appear together and are both explained in the framework of the viscoelasticity. While the literature on nonlinear vibrations of plates is very large, these aspects are rarely touched. The present study applies the fractional linear solid model to describe the viscoelastic material behavior. This allows to capture at the same time (i) the increase in the storage modulus with the vibration frequency and (ii) the frequency-dependent nonlinear damping in nonlinear vibrations of rectangular plates. The solution to the nonlinear vibration problems is obtained through Lagrange equations by deriving the potential energy of the plate and the dissipated energy, both geometrically nonlinear and frequency dependent. The model is then applied to a silicone rubber rectangular plate tested experimentally. The plate was glued to a metal frame and harmonically excited by stepped sine testing at different force levels, and the vibration response was measured by a laser Doppler vibrometer. The comparison of numerical and experimental results was very satisfactorily carried out for: (i) nonlinear vibration responses in the frequency and time domain at different excitation levels, (ii) dissipated energy versus excitation frequency and excitation force, (iii) storage energy and (iv) loss factor, which is particularly interesting to evaluate the plate dissipation versus frequency at different excitation levels. Finally, the linear and nonlinear damping terms are compared. | Nonlinear vibrations and damping of fractional viscoelastic rectangular plates | 10.1007/s11071-020-05892-0 |
2021-03-01 | This study investigated the perceptual characteristics of pulsive brakes presented by passive haptic interfaces. A passive-type haptic interface based on the damping brake of a DC motor was used to generate impact; this has merits of inherent safety and energy efficiency. This haptic interface expresses impacts by resisting the operator’s hand via the resistive force generated by a damping brake. In terms of impulse or momentum, maximum impact was achieved by continuously operating the damping brake after colliding with a virtual object. We found that instantaneous release of the brake immediately after collision increases the perceived impact. We computed several physical indices associated with the force against the hand as well as the hand velocity and investigated their relationships with the perceived magnitudes of the impacts. A high correlation was found between the absolute change ratio of the hand velocity and the perceived impact, which suggests that instantaneously releasing the brake is effective in terms of impact perception. Our findings indicate that the performance of passive haptic interfaces can extend physical limits, and the range of applications can be expanded by incorporating human perceptual characteristics. | Passive haptics: greater impact presented by pulsive damping brake of DC motor and physical indices for perceived impact | 10.1007/s10055-020-00452-8 |
2021-03-01 | This paper proposes an approach for the determination of the analytical boundaries of continuous, stick-slip and no motion regimes for the steady-state response of a multi-degree-of-freedom (MDOF) system with a single Coulomb contact to harmonic excitation. While these boundaries have been previously investigated for single-degree-of-freedom (SDOF) systems, they are mostly unexplored for MDOF systems. Closed-form expressions of the boundaries of motion regimes are derived and validated numerically for two-degree-of-freedom (2DOF) systems. Different configurations are observed by changing the mass in contact and by connecting the rubbing wall to: (i) the ground, (ii) the base or (iii) the other mass. A procedure for extending these results to systems with more than 2DOFs is also proposed for (i)–(ii) and validated numerically in the case of a 5DOF system with a ground-fixed contact. The boundary between continuous and stick-slip regimes is obtained as an extension of Den Hartog’s formulation for SDOF systems with Coulomb damping (Trans Am Soc Mech Eng 53: 107–115, 1931). The boundary between motion and no motion regimes is derived with an ad hoc procedure, based on the comparison between the overall dynamic load and the friction force acting on the mass in contact. The boundaries are finally represented in a two-dimensional parameter space, showing that the shape and the extension of the regions associated with the three motion regimes can change significantly when different physical parameters and contact configurations are considered. | Multi-degree-of-freedom systems with a Coulomb friction contact: analytical boundaries of motion regimes | 10.1007/s11071-021-06278-6 |
2021-03-01 | This paper presents a comparison of results between inserted and non-inserted series compensation technology in the network during healthy and faulty conditions. The numerous types of fault have been examined in compensated and uncompensated conditions. It was found in the literature that the transfer of power without series compensation led to increase the transient current and voltage. Therefore, a fixed series compensation scheme is adopted in normal and faulty conditions of the transmission line to solve the problem mentioned above using MATLAB/SIMULINK. Also, this paper introduces the addition of two compensated units associated with a suitable protection system in a transmission line. This technique can improve the performance of 500 kV extra high voltage transmission line and mitigate the fault current magnitude during various type of faults such as phase to ground (Ph-G), double phase to ground (2Ph-G), three phase to ground (3Ph-G). In addition, concerning the overvoltage problems across a series capacitor bank during the disturbance, the system is boosted by a protection technique associated with a suitable control system. The design is inserted into the system to protect the series capacitor bank, which in turn overcomes the severity of overvoltage on several types of faulty conditions. It also simulated and evaluated with the help of MATLAB/SIMULINK. | Transient and Protection Performance of a Fixed Series Compensated 500 kV Transmission Line During Various Types of Faulty Conditions | 10.1007/s42835-020-00646-9 |
2021-03-01 | In this paper, damages as well as damping effects present in a structure have been identified through the use of a two-stage damped updating method. The structure was damaged with the help of hacksaw by imparting six cuts (damages) of varying depths in the lateral direction of the structure at six different locations. These cuts resulted in significant changes in structural parameters as well as experimental structural dynamic responses (eigenvalues, eigenvectors and receptance-functions). A damped updating method was used to minimize error norms related to dynamic responses in two distinct stages. During the first stage, frequency- and eigenvector-based dimensionless desirability functions were maximized, thereby leading to the development of correct mass and stiffness matrices. As a result, structural damages were evaluated accurately. Damages (reductions in flexural rigidity) at six locations of the structure were found to be 21.05, 51.87, 50.93, 37.16, 48.00 and 7.84%. During the second stage, desirability functions related to resonant points of receptance-functions were maximized to identify damping matrix of the structure. Accurate evaluation of damages, as well as damping, was supported by the fact that the updated model of the structure was able to predict frequencies, eigenvectors and receptance-functions within an average error of only 0.00%, 0.42% and 0.27% compared to an initial average error of 15.84%, 1.83% and 22.24%, respectively. Major novelty of this work lies in actual experimental validation of desirability function-based multi-objective optimization approach in solving complex identification problems of a real structure by identifying the damage as well as damping parameters accurately. The proposed technique was earlier used in solving numerical problem only, while in this work, identification of a real-life structure’s parameters has been performed for the first time by using the proposed technique. | Damage and Damping Identification in a Structure Through Novel Damped Updating Method | 10.1007/s40996-020-00388-8 |
2021-03-01 | In semi-urban setting where availability of land can afford construction of low-rise buildings, confined masonry may compete with other alternatives of seismic resilient system provided well-articulated design standards and construction guidelines are available. Most seismic standards do not make explicit recommendations on the natural period and vertical distribution of base shear for the design of confined masonry buildings. In such a case, one of the two alternatives, such as (1) reinforced concrete (RC) frame building with masonry infill walls and (2) RC frame building with structural walls, is tacitly extrapolated. This paper is first aimed to explore the possible recommendations from the ambient vibration testing of a class of confined masonry building stock. Nine (G + 3) confined masonry hostel buildings are considered for Ambient Vibration Testing (AVT). Recorded signatures are processed and modal characteristics (primarily restricted to the first triplet of fundamental modes) are extracted. Each building is modelled numerically and fine-tuned followed by a comparison of natural frequencies and mode shapes in numerical model and experimental results. The fine-tuned numerical models are analysed against a set of recorded ground motions. Possible design recommendations for natural period and distribution of base shear along the height are the key contributions. Empirical equation for natural periods is derived from the seismic code recommendation on that of reinforced concrete (RC) buildings but removing the bias contributed from the height shorter than one storey while using the experimental results. Distribution of the base shear along the height follows a parabolic profile with an exponent close to 0.4. Results of AVT indicate the inherent damping ratio on an average of about 5% which, however, may not be directly used for seismic excitation. The building stock used for AVT in this paper does not include considerable variations in height and different varieties of confined masonry constructions. Therefore, recommendations of this paper should be verified against a larger size of dispersed building stock. | Natural period and vertical distribution of base shear in confined masonry buildings using ambient vibration test | 10.1007/s10518-021-01046-8 |
2021-03-01 | 由于镁或镁合金的化学活性比较高, 利用常规方法制备镁基复合材料时具有一定的困难。本研 究提出一种新的制备金属基复合材料的方法―原位反应浸渗技术, 该方法综合了原位合成法和无压浸 渗法的优势, 可以低成本、简洁高效地制备出界面清洁, 且增强体与基体结合良好的金属基复合材料。 针对原位反应浸渗法制备的(B_4C+Ti)/Mg 复合材料, 研究了B_4C 颗粒尺寸对其微观组织、生成物相及 阻尼行为的影响规律。结果表明, B_4C 颗粒尺寸越小越利于原位反应的进行, 而当B_4C 和Ti 颗粒尺 寸相近时, 复合材料的组织最为均匀; 该复合材料的室温阻尼性能随着振幅的增加而提高, 其主要机 制为位错阻尼和塑性区阻尼, 高温阻尼性能随着测试温度的升高而提高, 其主要机制为界面阻尼或晶 界阻尼。 To study the influence of B_4C particle size on the microstructure and damping capacities of (B_4C+Ti)/Mg composites, in situ reactive infiltration technique was utilized to prepare Mg-matrix composites. The microstructure, produced phases and damping capacities of the composites prepared with different particle size of B_4C were characterized and analyzed. The results show that the reaction between B_4C and Ti tends to be more complete when finer B_4C particle was used to prepare the composites. But the microstructure of the as-prepared composites is more homogenous when B_4C and Ti have similar particle size. The strain-dependent damping capacities of (B_4C+Ti)/Mg composites improve gradually with the increase of strain amplitude, and composites prepared with coarser B_4C particles tend to have higher damping capacities. The temperature-dependent damping capacities improve with increasing the measuring temperatures, and the kind of damping capacities of the composites prepared with 5 B_4C are inferior to those of coarser particles. The dominant damping mechanism for the strain-damping capacity is dislocation damping and plastic zone damping, while that for the temperature-damping capacity is interface damping or grain boundary damping. | Influence of B_4C particle size on microstructure and damping capacities of (B_4C+Ti)/Mg composites | 10.1007/s11771-021-4634-9 |
2021-03-01 | A steady-state roll motion of ships with nonlinear damping and restoring moments for all times is modeled by a second-order nonlinear differential equation. Analytical expressions for the roll angle, velocity, acceleration, and damping and restoring moments are derived using a modified approach of homotopy perturbation method (HPM). Also, the operational matrix of derivatives of ultraspherical wavelets is used to obtain a numerical solution of the governing equation. Illustrative examples are provided to examine the applicability and accuracy of the proposed methods when compared with a highly accurate numerical scheme. | Estimation of Rolling Motion of Ship in Random Beam Seas by Efficient Analytical and Numerical Approaches | 10.1007/s11804-020-00183-x |
2021-03-01 | The dynamic analysis of systems with nonlinearities has become an important topic in many engineering fields. Apart from the forced response analyses, nonlinear modal analysis has been successfully extended to such non-conservative systems thanks to the definition of damped nonlinear normal modes. The energy balance method is a tool that permits to directly predict resonances for a conservative system with nonlinearities from its nonlinear modes. In this work, the energy balance method is extended to systems with non-conservative nonlinearities using the concept of the damped nonlinear normal mode and its application in a full-scale engineering structure. This extended method consists of a balance between the energy loss from the internal damping, the energy transferred from the external excitation and the energy exchanged with the non-conservative nonlinear force. The method assumes that the solution of the forced response at resonance bears resemblance to that of the damped nonlinear normal mode. A simplistic model and full-scale structure with dissipative nonlinearities and a simplistic model showing self-excited vibration are tested using the method. In each test case, resonances are predicted efficiently and the computed force–amplitude curves show a great agreement with the forced responses. In addition, the self-excited solutions and isolas in forced responses can be effectively detected and identified. The accuracy and limitations of the method have been critically discussed in this work. | An extended energy balance method for resonance prediction in forced response of systems with non-conservative nonlinearities using damped nonlinear normal mode | 10.1007/s11071-020-05793-2 |
2021-03-01 | In this study, the use of the displacement-based fibre element (DBFE) method for modelling the nonlinear seismic response of reinforced concrete shear wall structures with a variation of damping ratios and types of structural damping is evaluated. The experimental seismic responses of the CAMUS I and NEES-UCSD shear wall structures are compared with nonlinear time-history analysis results obtained using the DBFE method. Comparisons are made in terms of the absolute maximum values of the top displacement, the base shear force, the base bending moment values and minimum differences between overlaps of top displacement time-history graphs. The Hilber-Hughes-Taylor-α integration method is selected for the dynamic solution algorithm. Recommendations are made for appropriate damping ratios for stiffness-proportional, mass-proportional, and Rayleigh damping to be used for the structural damping of nonlinear seismic analyses of the shear walls. The minimum difference between experimental and numerical analysis results is obtained less than 11% using Rayleigh damping. Additionally, the optimal number of fibre elements is researched with regard to the ratio of the mean length of the fibre elements to the longitudinal length of the shear wall. When the ratio is smaller than 3%, the differences between experimental and numerical analysis results for both shear walls are less than 2% at the optimal damping ratios. | Investigation of Uncertainties in Nonlinear Seismic Analysis of the Reinforced Concrete Shear Walls | 10.1007/s40999-020-00567-8 |
2021-03-01 | Polyurethane foam adhesive (PFA) has been introduced as an alternative stabilizer in geotechnical applications because PFA can improve the engineering characteristics of soil by filling the pore space and generating adhesive bonding among the particles. However, the dynamic properties of PFA-reinforced soils are not well understood. To analyze the dynamic characteristics of PFA-reinforced gravels, a series of cyclic triaxial tests were carried out to investigate the shear modulus and damping ratio of PFA-reinforced gravels, and to determine the corresponding effects of the PFA content, confining pressure, consolidation stress ratio and loading frequency. The results showed that the shear modulus increased, and the damping ratio decreased as the PFA content, confining pressure and consolidation stress ratio increased. In contrast, the effect of the loading frequency, which ranged from 0.05 to 1 Hz, was negligible. A modified hyperbolic empirical model can consider the effect of the PFA content on the maximum shear modulus and predict the relationship between the normalized shear modulus and the normalized shear strain was proposed. Moreover, the upper and lower bounds of the damping ratio were also proposed. | Dynamic properties of polyurethane foam adhesive-reinforced gravels | 10.1007/s11431-020-1707-5 |
2021-03-01 | In this paper, the effects of linear damping on the post-critical behavior of the Ziegler’s column are discussed. To this end, the well-known double-pendulum, loaded at the free-end by a follower force, firstly introduced by Ziegler, is considered in regime of finite displacements. The multiple scale method is applied to the equations of motion expanded up to the cubic terms, to analyze the nonlinear behavior of a generically damped column, close to the simple-Hopf bifurcation triggered by the follower force. The obtained bifurcation equations are shown to be useful in providing qualitative information about the nonlinear mechanical response of the column in the whole damping plane. Validation of the asymptotic solution, carried out via numerical analyses of the exact equations of motion, points out the effectiveness of the proposed analysis also on the quantitative side. | On the effects of linear damping on the nonlinear Ziegler’s column | 10.1007/s11071-020-05797-y |
2021-03-01 | The paper is focused on analyzing the conservation issues of stochastic 𝜃 -methods when applied to nonlinear damped stochastic oscillators. In particular, we are interested in reproducing the long-term properties of the continuous problem over its discretization through stochastic 𝜃 -methods, by preserving the correlation matrix. This evidence is equivalent to accurately maintaining the stationary density of the position and the velocity of a particle driven by a nonlinear deterministic forcing term and an additive noise as a stochastic forcing term. The provided analysis relies on a linearization of the nonlinear problem, whose effectiveness is proved theoretically and numerically confirmed. | On the numerical structure preservation of nonlinear damped stochastic oscillators | 10.1007/s11075-020-00918-5 |
2021-03-01 | Abstract We study the damping efficiency of torsional vibrations of a body using a dynamic vibration damper containing a system of successive impactor pairs with magnets as colliding elements. Dimensionless essentially nonlinear differential equations of motion of the protected body and magnetic elements are obtained. The influence of the designed parameter selection of the vibration damper on the vibrations of the carrying body is considered. The features of damper tuning in a wide vibration damping band mode are described. The optimal variant of damper tuning with the most effective damping of body vibrations is established. | Dynamic Properties of a Damper of Torsional Vibrations with Magnetic Impact Pairs | 10.3103/S1052618821020072 |
2021-02-27 | Power system oscillations are the primary threat to the stability of a modern power system which is interconnected and operates near to their transient and steady-state stability limits. Power system stabilizer (PSS) is the traditional controller to damp such oscillations, and flexible AC transmission system (FACTS) devices are advised for the improved damping performance. This paper suggests a technique for controller parameters tuning of PSS and a shunt connected FACTS device to be operated in coordination. A static synchronous compensator (STATCOM) connected in a two-machine system is considered as a test power system for the system studies. A recent meta-heuristic algorithm, Multi-Verse optimizer (MVO) has been suggested and compared with the other state-of-the-art algorithms. Improvement in system damping has been achieved by minimizing the oscillating nature of the system states by framing the objective function as a function of damping ratio and location of poles of the system. The Phillips-Heffron model of the test system has been designed by considering the system dynamics. The coordinated system behavior under the perturbation in system parameters has been observed satisfactory with the tuned controller parameters obtained from the suggested algorithm. | Power and energy system oscillation damping using multi-verse optimization | 10.1007/s42452-021-04349-2 |
2021-02-27 | An asymptotic perturbation solution for a linear oscillator of free damped vibrations in fractal medium described by local fractional derivatives was obtained in Yang and Srivastava (Commun Nonlinear Sci Numer Simul 29(1–3):499–504, 2015). In this paper, we obtain the numerical solution of damped forced oscillator problems by employing the operational matrix of integration of Bernoulli orthonormal polynomials. The operational matrix of integration is determined with the help of the integral operator on Bernoulli orthonormal polynomials. Numerical examples of two different problems of spring are given to delineate the performance and perfection of this approach and compared the results with the exact solution. | An efficient algorithm to solve damped forced oscillator problems by Bernoulli operational matrix of integration | 10.1186/s42787-021-00115-w |
2021-02-22 | As wind turbine blades are getting softer and thinner, the demand for their capability of vibration suppression is improving day by day. Drawing from bamboo’s quick recovery to its former position and mimicking the microstructure of bamboo wall, this paper puts forward a porous damping structure on the blade and sets up its mathematical model. The formula for its structural loss factor is deduced on the vibration theory. Then numerical simulation method is adopted to investigate its damping performance on one wind turbine blade by ABAQUS. The results indicate that the vibration damping property of the wind turbine blade with the porous damping structure is significantly increased. The porous damping structure dissipates more heat very quickly and its single material also displays advantages over composite material. This paper provides a reference for the design of highly efficient damping structures. | Research on vibration suppression of wind turbine blade with a multi-layer porous damping structure based on bamboo wall microstructure | 10.1007/s40430-021-02888-8 |
2021-02-18 | Consider a double degenerate parabolic equation arising from the electrorheological fluids theory and many other diffusion problems. Let v ε $v_{\varepsilon }$ be the viscous solution of the equation. By showing that | ∇ v ε | ∈ L ∞ ( 0 , T ; L loc p ( x ) ( Ω ) ) $|\nabla v_{\varepsilon }|\in L^{\infty }(0,T; L_{\mathrm{loc}}^{p(x)}(\Omega ))$ and ∇ v ε → ∇ v $\nabla v_{\varepsilon }\rightarrow \nabla v$ almost everywhere, the existence of weak solutions is proved by the viscous solution method. By imposing some restriction on the nonlinear damping terms, the stability of weak solutions is established. The innovation lies in that the homogeneous boundary value condition is substituted by the condition a ( x ) | x ∈ ∂ Ω = 0 $a(x)| _{x\in \partial \Omega }=0$ , where a ( x ) $a(x)$ is the diffusion coefficient. The difficulties come from the nonlinearity of | ∇ v | p ( x ) − 2 $\vert {\nabla v} \vert ^{p(x)-2}$ as well as the nonlinearity of | v | α ( x ) $|v|^{\alpha (x)}$ . | On a doubly degenerate parabolic equation with a nonlinear damping term | 10.1186/s13661-021-01493-x |
2021-02-18 | The seismic performance of conventional tuned mass damper (TMD) has been often improved when more TMD mass ratio is utilized. One limitation in using higher TMD mass ratios for tall buildings is the challenges of designers from the practical point of view. So far, conventional TMD has been more uneconomical. The research on the seismic performance of friction tuned mass dampers (FTMD) is still going on. This paper aimed at evaluating the advantages of the optimal design of friction TMD over conventional TMD for tall structures. For this aim, an optimal design was developed based on a multi-objective cuckoo search optimization algorithm to find the optimal TMD and FTMD parameters, including mass, damping, frequency ratios, and the friction coefficient. Here, the seismic performances of a 40-storey tall building were evaluated and compared from structural responses and energy. Results showed that both dampers could significantly reduce the maximum floor displacement, drift, and acceleration. Furthermore, the FTMD system exhibited a better performance in reducing the roof displacement against the TMD system when the mass ratio was less than 0.03. These advantages are considered to be very important from a practical point of view. | An evaluation of the advantages of friction TMD over conventional TMD | 10.1007/s41062-021-00473-5 |
2021-02-17 | The present work envisaged the development of a novel method for computing the damping coefficients of thermal elastohydrodynamic lubricated point contacts based on energy conservation. The effects of load, entrainment velocity, and slide–roll ratio were studied, and the results were compared with the ISO thermal results. Multi-level method and discrete convolution fast Fourier transform method were employed to improve the solution convergence efficiency, and a sequential column sweeping technique was employed to solve the energy equations. The results indicated an increase in the damping coefficients with an increase in the load, and a corresponding decrease with an increase in the speed. When the entrainment velocity was relatively low, or the slide–roll ratio was relatively small, the influence of the slide–roll ratio was negligible. Subsequently, the relation between the damping coefficients and the load, speed, and slide–roll ratio was established using the least-square method. | Damping characteristics of thermal elastohydrodynamic lubricated point contacts | 10.1007/s40430-021-02842-8 |
2021-02-05 | We investigate the stabilization of a locally coupled wave equations with only one internal viscoelastic damping of Kelvin-Voigt type (see System ( 1.2 )-( 1.4 )). The main novelty in this paper is that both the damping and the coupling coefficients are non smooth (see ( 1.5 )). First, using a general criteria of Arendt-Batty, combined with an uniqueness result, we prove that our system is strongly stable. Next, using a spectrum approach, we prove the non-exponential (uniform) stability of the system. Finally, using a frequency domain approach, combined with a piecewise multiplier technique and the construction of a new multiplier satisfying some ordinary differential equations, we show that the energy of smooth solutions of the system decays polynomially of type t − 1 $t^{-1}$ . | Stability Results of an Elastic/Viscoelastic Transmission Problem of Locally Coupled Waves with Non Smooth Coefficients | 10.1007/s10440-021-00384-8 |
2021-02-04 | Mechanisms usually transmit power by welded links into a shaft. Should this weld be partial, like fillet welds, there will be an area of stress concentration that could behave like a crack due to sharp corners. These can lead to structural failures due to fatigue. Consequently, to properly design, inspect and maintain these mechanisms it is necessary to use fracture mechanics stress intensity factors. The crack mesh simplicity required by the boundary element method allows easy modeling even for complex geometry. This technique will be used to obtain such parameters for a double fillet weld found in a diverter damper mechanism responsible for controlling hot gas flow to heat recovery steam generator in power plants. But the solutions presented can be used for similar geometrical configurations, specially to shaft link mechanisms. Empirical equations were also obtained to further ease fracture mechanics and fatigue analysis for this kind of geometry. | Diverter damper force analysis and stress intensity factors for its double fillet welds by boundary element method | 10.1007/s40430-021-02812-0 |
2021-02-02 | A two-step third order method on a variable mesh for the approximation of nonlinear IVP: $$u^{\prime\prime}=f(t,u,u{^{\prime}}), u({t}_{0})={\gamma }_{0}$$ u ″ = f ( t , u , u ′ ) , u ( t 0 ) = γ 0 , $$u{^{\prime}}({t}_{0})={\gamma }_{1}$$ u ′ ( t 0 ) = γ 1 is proposed. For computation, only a monotonically decreasing mesh will be employed. The method when applied to a test equation $$u^{\prime\prime}+2\alpha u{^{\prime}}+{\beta }^{2}u=g(t), \alpha >\beta \ge 0,$$ u ″ + 2 α u ′ + β 2 u = g ( t ) , α > β ≥ 0 , is shown to be unconditionally stable. The proposed method is applicable to solve singular problems. A special technique is required to compute the method near the singular point. Several problems of physical significance including three problems on boundary layer are examined to illustrate the convergent character and usefulness of the approximation. Approximate solutions are provided to validate the functionality of the suggested approximation. | On the absolute stability of a two-step third order method on a graded mesh for an initial-value problem | 10.1007/s40314-021-01416-7 |
2021-02-01 | Acoustic characteristics of a thrust chamber with quarter-wave resonators are numerically studied based on the unsteady Reynolds-averaged Navier-Stokes (URANS) method. Organized pressure disturbance model and constant-volume bomb model are applied as artificial disturbances to excite pressure oscillations in the chamber. Eigenfrequencies and amplitudes of acoustic modes of the chamber are obtained by fast fourier transform (FFT) analysis, while damping characteristics are evaluated by the half-power bandwidth method. Predicted damping capacities of the chamber with and without quarter-wave resonators agree well with experimental results. Pressure oscillations can be controlled by a quarter-wave resonator mainly through reducing the amplitude of target acoustic mode, rather than increasing damping capacity of the chamber. Major damping mechanism of the resonator is cutting down pressure peak of target acoustic mode and raising up its pressure trough (CPRT); therefore the amplitude of target acoustic mode is reduced significantly. Moreover, acoustic energy can be dissipated by vortex at the orifice and by viscosity on the surface of a resonator, which increase damping capacity of the chamber slightly. Under the condition with multi-modes pressure oscillations, a resonator can still suppress pressure oscillations of target acoustic mode through CPRT. However, it may enhance pressure oscillations of other modes due to redistribution of oscillation energy among all acoustic modes. | Numerical evaluation of acoustic characteristics of a thrust chamber with quarter-wave resonators | 10.1007/s11431-019-1575-6 |
2021-02-01 | The current paper reports the results of a series of small-scale physical model tests conducted to study the marine fouling effects on the wave attenuation/build-up around/inside a 3D floating gravity net cage. The artificial fouling modelled was representative of hydroids, an important fouling organism in the marine aquaculture industry. Regular wave groups with different heights, periods, and steepness were examined. The cage hydraulic response inside and around the cage models was analysed. Changes made by the cage presence to the height, energy flux, geometry and nonlinearity of the waves traversing the cage models were studied. Attenuation of the wave height and energy was observed downstream of the cage models, which grew smaller in the fouling presence and further by the fouling length. Build-ups of the wave height and energy occurred inside the cage models, which grew weaker in the fouling presence and with longer fouling. The fouling effects on the hydraulic response were more pronounced downstream as compared to those inside and upstream of the cage. The experimental data were used to derive nonlinear regression equations, indicative of the primary trends for the wave attenuation/build-up, around/inside the cage. | Wave attenuation/build-up around and inside marine fouled floating aquaculture cages under regular wave regimes | 10.1007/s40722-021-00186-y |
2021-02-01 | In a few of the isolated DC power-transmission systems with hydropower units (and the associated water hammer effect), inappropriate governor control parameters may weaken the system damping and stability. It has the potential to result in ultra-low-frequency oscillations (ULFO) which is below 0.1 Hz. To carry out this issue, a linearized state-space model of a multi-machine system that includes hydropower and steam turbine governor control systems is presented in this paper. The oscillation mode of ULFO about the damping characteristics of the governor control system is analyzed by the damping torque analysis method. A governor power system stabilizer (GPSS) design model predicated on phase compensation principle to heighten the damping of the governor control system to subdue ULFO is planned. To verify its effectiveness, the designed GPSS is applied to a single-machine system, a 4-machine 2-area system as well as the Yunnan power grid system of China. The simulation results demonstrate that GPSS effectively suppresses ULFO with heightened ULFO damping by the optimized settings of governor control parameters. | Parameter design of governor power system stabilizer to suppress ultra-low-frequency oscillations based on phase compensation | 10.1007/s00202-020-01101-8 |
2021-02-01 | Magnetorheological (MR) fluids are a talk of the day due to their potential applications in various fields. In the present work, six different MR fluids were prepared based on the variation in the percentage of carbonyl iron (CI) particles and carrier liquid. The smart material CI particle was well characterized by XRD, SEM-EDAX and VSM measurements. The effect of carrier fluid on sedimentation was tested using CI 50% and compared with the other carrier oil used. The Magnatec oil acts as a better candidate due to its sedimentation stability and thermal resistance. Therefore, the rheological measurement was examined for the three magnetorheological fluids (MRF) prepared, namely MRF 32, MRF 50 and MRF 80 with Magnatec oil as carrier liquid. The three various size annular gaps between the piston and the inner cylinder casing was also studied. Among the three variations, 1, 1.5 and 2 mm, the maximum damping force was obtained for 1-mm annular gap. A number of experimentations were carried out to investigate the performance of the MR fluid as well as the annular gap. Cyclic load test was performed with various annular gaps, and 0.536 kN was the maximum damping force for 1-mm annular gap. | Study on Magnatec oil-based MR fluid and its damping efficiency using MR damper with various annular gap configurations | 10.1007/s40974-020-00170-6 |
2021-02-01 | Sabkha (salt-encrusted flat) soils are problematic because they lose strength due to wetting, and they have liquefaction potential. These soils are spread in North Africa, Australia, and most of the Eastern Province of Saudi Arabia. Owing to a lack of experimental studies, the cyclic behavior of sabkha soils is relatively unknown. The monotonic and cyclic behaviors of sabkha soil were studied based on effective stress (50, 100, and 150 kPa) and cyclic stress ratio (CSR) (0.15, 0.35, and 0.65) using cyclic triaxial and bender element tests. Results indicate that the sabkha exhibits ductile behavior with the cohesion value of 9.33 kPa and a friction angle of 33°. The maximum shear moduli are 18,900, 49,500, and 63,500 kPa for effective confining pressures of 50, 100, and 150 kPa, respectively. Furthermore, the shear modulus tended to decrease with shear strain for different cyclic stress ratios. On the other hand, the damping ratio depends on the level of the cyclic stress ratio. At a cyclic stress ratio of 0.15, the damping ratios remained constant with shear strain. For a cyclic stress ratio of 0.65, the damping ratios decreased with shear strain. However, at a cyclic stress ratio of 0.35, the damping ratio varied with shear strain depending on effective stress. | Monotonic and Cyclic Behavior of Salt-Encrusted Flat (Sabkha) Soil | 10.1007/s40999-020-00561-0 |
2021-02-01 | A Korteweg–de Vries (KdV) equation including the effect of linear Landau damping of electrons is derived to study the propagation of weakly nonlinear and weakly dispersive ion acoustic waves in a collisionless unmagnetized plasma consisting of warm adiabatic ions and two species of electrons at different temperatures. It is found that the coefficient of the nonlinear term of this KdV-like evolution equation vanishes along different family of curves in different parameter planes. In this context, a modified KdV (MKdV) equation including the effect of linear Landau damping of electrons describes the nonlinear behaviour of ion acoustic waves. Again, the coefficients of the nonlinear terms of the KdV and MKdV-like evolution equations are simultaneously equal to zero along a family of curves in the parameter plane. In this situation, we have derived a further modified KdV (FMKdV) equation including the effect of linear Landau damping of electrons. The multiple time scale method has been applied to obtain the solitary wave solution of the evolution equations having the nonlinear term $$ \left( \phi ^{(1)}\right) ^{r}\frac{\partial \phi ^{(1)}}{\partial \xi }$$ ϕ ( 1 ) r ∂ ϕ ( 1 ) ∂ ξ , where $$\phi ^{(1)}$$ ϕ ( 1 ) is the first-order perturbed electrostatic potential and $$r =1,2,3$$ r = 1 , 2 , 3 . The amplitude of the ion acoustic solitary wave decreases with time for all $$r =1,2,3$$ r = 1 , 2 , 3 . | Effect of Landau damping on ion acoustic solitary waves in a collisionless unmagnetized plasma consisting of nonthermal and isothermal electrons | 10.1007/s12648-020-01731-5 |
2021-02-01 | We consider a coupled wave system with partial Kelvin–Voigt damping in the interval $$(-1,1)$$ ( - 1 , 1 ) , where one wave is dissipative and the other is not. When the damping is effective in the whole domain $$(-1,1)$$ ( - 1 , 1 ) , it was proven in Portillo Oquendo and Sànez Pacheco (Appl Math Lett 67:16–20, 2017) that the energy is a non-increasing function of the time variable, with a rate equals to $$t^{-\frac{1}{2}}$$ t - 1 2 . In this paper, using the frequency domain method, we show the effect of the coupling and the non smoothness of the damping coefficient on the energy decay. Actually, as expected we show the lack of the exponential stability, that the semigroup loses speed and it decays polynomially with a slower rate than the one given in Portillo Oquendo and Sànez Pacheco (loc. cit.) [ 20 ]. | Stability for coupled waves with locally disturbed Kelvin–Voigt damping | 10.1007/s00233-020-10142-1 |
2021-02-01 | Background Vibration present on various levels in many engineering fields and hence vibration mitigation has become a subject of intense study. The nonlinear vibration isolation devices are effective for broad frequency bandwidth and can provide better vibration isolation than linear devices. The need for nonlinearity in stiffness and damping characteristics has motivated researchers to apply the nonlinearity found in mechanisms or materials in the passive vibration control devices. Review Factor This review discusses the applications of nonlinearity in the passive vibration control devices to provide an understanding of how the nonlinearity is applied and useful in the implemented system. Further, applications for nonlinearity can also be extended in the energy harvesting devices, Nonlinear energy sink, metamaterials for the purpose of vibration isolation and energy harvesting. The need for nonlinearity also encouraged research work through inspiration from the nature called bio-inspired devices. The bio-inspired devices mimic the nonlinearity of the biological system to suppress the vibrations. Conclusions The nonlinear passive isolation is effective for wide frequency bandwidth than the linear isolation system. Further, the nonlinear systems also reduce transmissibility much efficiently than the linear system. The nonlinear energy harvesting system shows a great scope to harvest energy from wide ranges of excitations. The bio-inspired devices also are proven to be effective in vibration isolation. Additionally the design of the metamaterial with nonlinearity in the microstructure, proves to be promising in the vibration suppression applications. Based on the review, the nonlinearity introduced into the systems has greater benefits than the linear systems. | Applications of Nonlinearity in Passive Vibration Control: A Review | 10.1007/s42417-020-00216-3 |
2021-02-01 | In the design of a high-performance diaphragm-based static/dynamic pressure sensor (DB-S/DPS), researchers have mostly carried out studies on static deflection and frequency analysis without including diaphragm vibration damping and the effect of the operating medium (OM). However, diaphragms and OM usually contain dynamic processes where vibration damping occurs with constantly changing frequency parameters. Therefore, to design a sensor that will work in such an OM, the effect of the dynamic pressure performance of the diaphragm materials on the sensor parameters (sensitivity, bandwidth, linearity) becomes even more important. In this study, for the first time in the literature, the effect of many different parameters on sensor parameters at the same time was analyzed by theoretically examining the dynamic deflection and static deflection expressions that the researchers did not consider in the pressure sensor design. Also, for the first time in the literature, the analysis of the dynamic parameters of many diaphragm materials and sensor operating media was carried out with this study. In order to determine the effect of the dynamic pressure performance of the diaphragms on sensor parameters in high-performance DB-S/DPS design, multiple parameter implementation (MPI) was carried out with MATLAB software. MPI has been realized considering various diaphragm materials, alternative operating media, and all the dynamic parameters (the damping ratio of the medium, added virtual mass incremental factor). In the work, metallic (Al, Au), polymer (cellulose triacetate), semiconductor (Si), glass derivative (SiO_2), and two-dimensional (graphene) materials which are frequently reported in the literature were chosen as the diaphragm. The effects of these selected materials and OMs (air, water, mineral oil) on sensor parameters were examined in detail. To the best of our knowledge, there is no comprehensive study in the literature involving such dynamic pressure parameters. With this valuable research, considering the forced oscillations and damping, valuable and interesting results are presented that can guide DB-S/DPS designers. | Analyzing the effect of dynamic properties of materials and operating medium on sensor parameters to increase the performance of diaphragm-based static/dynamic pressure sensors | 10.1007/s10825-020-01633-z |
2021-02-01 | Nonlinear damping with respect to vibration amplitude is particularly important in mechanical dynamics. The addition of short fibers to damping materials is considered to result in strong nonlinear damping due to interfacial peeling at the edges of the fibers. However, little has been reported on the occurrence of nonlinear damping in short-fiber reinforced rubber due to compounding difficulties. In this study, we investigated the relationship between the damping characteristics and deformation behavior of microdeformed short-fiber reinforced rubber by X-ray computed tomography (CT). We prepared a damping material with a natural rubber (NR) matrix and micrometer-sized polyethylene terephthalate (PET) fiber filler. The loss factor was identified by dynamic mechanical analysis, and three-dimensional strain maps were obtained using marker tracking in the CT data. The addition of 5 wt% PET fibers to NR resulted in an increase in the loss factor. Experimentally, we found that the nonlinear damping of the composite rubber is affected by the peeling of the filler/matrix interface and the strain inside the material. | Effect of Fiber Orientation on Nonlinear Damping and Internal Microdeformation in Short-Fiber-Reinforced Natural Rubber | 10.1007/s40799-020-00404-6 |
2021-02-01 | This article proposes a real-time power system stabilizers (PSS) parameter optimization technique employing extreme learning machine (ELM) to enhance overall system stability by damping out the low-frequency oscillations. It models two electric networks, i.e., single machine infinite bus systems where the first network's synchronous machine is equipped with a PSS only, and the second network's synchronous machine is equipped with a unified power flow controller coordinated PSS. It uses diverse loading conditions to investigate the performance of the proposed ELM model-tuned PSS technique and compares it with conventional PSS and the referenced works in terms of the eigenvalues and minimum damping ratios. Additionally, the satisfactory values of the well-known statistical performance indices including the root mean squared error (RMSE), mean absolute percentage error, RMSE-observations-to-standard deviation ratio, coefficient of determination ( R ^2), Willmott’s index of agreement, and Nash–Sutcliffe model efficiency coefficient provide confidence in the developed technique in predicting PSS parameters. Besides, comparisons of results from time-domain simulation demonstrate the ELM model tuned system's superiority over the conventional approach for both test cases. Furthermore, the ELM models require less than a cycle to predict PSS parameters for any loading condition that endorses the developed technique's real-time application. | Extreme learning machine for real-time damping of LFO in power system networks | 10.1007/s00202-020-01075-7 |
2021-02-01 | In this paper, we study the well-posedness and regularity of mild solutions for a class of time fractional damped wave equations, which the fractional derivatives in time are taken in the sense of Caputo type. A concept of mild solutions is introduced to prove the existence for the linear problem, as well as the regularity of the solution. We also establish a well-posed result for nonlinear problem. By applying finite dimensional approximation method, a compact result of solution operators is presented, following this, an existence criterion shows that the Lipschitz condition or smoothness of nonlinear force functions in some literatures can be removed. As an application, we discuss a case of time fractional telegraph equations. | Well-posedness and regularity for fractional damped wave equations | 10.1007/s00605-020-01476-7 |
2021-02-01 | Purpose The aim of the present work was to suppress the free space acoustic radiation of a truss-cored sandwich panel through the use of the decentralized resonant shunt method. Methods and Results First, the finite element model of the structure was established and its sound radiation characteristics were studied using the elemental radiators decomposition method. Then the decentralized modal piezoelectric shunt vibration control strategy of the Kagome sandwich panel was described in detail. In this approach, a small number of rods in the bottom truss of the sandwich panel were replaced by a piezoelectric stack transducer; each transducer was connected to a single resonant shunt which was tuned to suppress the vibration of a specific mode. The biggest advantage of the independent modal resonant shunt method is that the circuits of each mode are independent of each other; thus the large-scale parameter optimization can be decomposed into small-scale optimization problems. The results of the numerical simulation have shown that the approach that has been proposed in this paper is very effective in controlling the sound radiation of the examined structure at its resonant frequency. Conclusions The results of this study can be useful in the study of the sound radiation suppression of a sandwich panel. | Acoustic Radiation Suppression of a Truss Core Sandwich Panel Using Decentralized Resonant Shunt Damping | 10.1007/s42417-020-00224-3 |
2021-02-01 | Curve-shaped laser-cut steel plate dampers named curved damper have been recently introduced, and their performance has been experimentally investigated through cyclic loading tests. Using the same concept, this study aims to propose a novel cost-effective toggle brace–curved damper (TBCD) system, which combines the toggle braces and curved dampers to provide a practical passive control device. The seismic performance of three-, six-, and nine-story steel moment–resisting structures utilized with TBCD is analyzed using nonlinear time history analysis (NTHA). For better comparison, the TBCD system is optimized using the multi-objective nondominated sorting genetic algorithm (NSGA-II). The seismic performance of the proposed system is then compared against the optimized viscous dampers (VDs), viscoelastic dampers (VEDs), and buckling-restrained braces (BRBs). The results of the optimization process show that the TBCD has comparable performance to the other passive control devices presented, while it leads to more cost-effective design solutions by reducing the constructional, installation, life cycle maintenance and repair cost, and downtime. Hence, the proposed TBCD system can be considered as an efficient alternative to conventional seismic force–resisting systems for both newly built structures and the seismic retrofitting of existing structures. | Development of a novel cost-effective toggle-brace-curveddamper (TBCD) for mid-rise steel structures using multi-objective NSGA II optimization technique | 10.1007/s00158-020-02718-w |
2021-02-01 | The dynamic contact characteristics of mechanical interface significantly impact the performance of machine tools. The static contact behaviors of mechanical interface have been studied. However, most mechanical interfaces are exposed to dynamic load. It is necessary to study the dynamic contact characteristics of mechanical interface. A normal dynamic microcosmic contact model is built using the statistical method, and the interactional effects of adjacent asperities are considered. The influences of the normal preload, vibrational frequency and displacement amplitude on normal contact stiffness and damping of mechanical interface are revealed. The predicted contact stiffness and damping of mechanical interface are verified by a series of simulations and experiments. | Investigation on Normal Dynamic Contact Characteristics of Mechanical Interface of Machine Tools | 10.1007/s10338-020-00183-y |
2021-02-01 | In this study, the mechanical properties and damping capacities of cast Mg-5.5Zn-0.6Zr (weight percent, ZK60) alloys have been simultaneously improved by a facile multi-directional forging (MDF) processing, and the mechanisms of microstructure evolution and texture modification are systematically investigated. The activation of tension twinning occurs during the initial MDF stage, due to the coarse-grained structure of the as-cast alloy. With increasing MDF passes, the continuous dynamic recrystallization (CDRX) results in a fine equiaxed-grain structure. The typical non-basal texture is formed in the as-MDFed alloy for 6 passes, with the (0001) planes inclined 60°–70° to forged direction and 10°–20° to transverse direction, respectively. A good balance between the strength (~ 194.9 MPa) and ductility (~ 24.9%) has been achieved, which can be ascribed to the grain refinement, non-basal texture and fine precipitate particles. The damping capacity is remarkably improved after MDF processing, because the severe deformation increases the dislocation density, which effectively enlarges the sweep areas of mobile dislocations. | Simultaneously Enhanced Mechanical Properties and Damping Capacities of ZK60 Mg Alloys Processed by Multi-Directional Forging | 10.1007/s40195-020-01137-6 |
2021-02-01 | The current study chiefly endeavours about adjudicating the heat treatment characteristics on the energy dissipation behaviour of nickel surface-deposited Al/RHA metal matrix composites (MMC). The base A356.2 matrix system is reinforced with rice husk (RHA) at three dissimilar wt.%, viz. (2, 4, and 6%), by engaging customary stir casting practise. Then, the fabricated Al/RHA composites are nickel surface deposited through conventionally stirred electrolytic aqueous watts solution. The energy dissipation behaviour of the relatively surface-deposited MMCs preceding and succeeding T6 heat treatment is examined by engaging a dynamic mechanical analyser at three distinct frequencies, viz. (0.1, 1, and 10 Hz). The surface deposition morphology is reviewed thoroughly using XRD, SEM, and FESEM techniques. It is evident the T6 heat-treated nickel-deposited test specimen’s yielded enhanced energy dissipation tendencies in comparison with the test samplings specimens before heat treatment. | Effect of Heat Treatment on the Damping Characteristics of Ni Surface-Deposited Agro Reinforced Metal Matrix Composites | 10.1007/s12666-020-02166-6 |
2021-02-01 | With the application of the particle damping technology to cable vibration attenuation, the rootless cable damper overcomes the limit in installation height of existing dampers. Damping is achieved through energy dissipation by collisions and friction. In this paper, a coupled multi-body dynamics—discrete element method is proposed to simulate the damping of the damper—cable system under a harmonic excitation. The analyses are done by combining the discrete element method in EDEM and multi-body dynamics in ADAMS. The simulation results demonstrate the damping efficiency of rootless particle damper under different excitations and reveal the influence of the design parameters on its performance, including the filling ratio, particle size, coefficient of restitution, and coefficient of friction. | Application of coupled multi-body dynamics—discrete element method for optimization of particle damper for cable vibration attenuation | 10.1007/s11709-021-0696-x |
2021-02-01 | Active control schemes are quite promising because of their capability of achieving high level of control of structural response under seismic excitations. Level of control is a function of many parameters associated with structure, excitation and the scheme of control considered. Optimal level of control may be achieved by optimization of control parameters. Basically, elements of weighing matrix primarily govern the relationship of control force and the level of response reduction. But which parameters are predominant in governing this relationship is the matter of investigation. Weighing element associated with velocity of actuated tuned mass damper has been chosen by some researchers as an important parameter in case where force actuation was done through an active mass driver system. But other elements of weighing matrix need to be investigated with a possibility of being predominant in controlling the response. An extensive parametric study is needed to arrive at the best combination of parameters that may lead to the optimal structural control. Keeping in view the same, an effort is made here by trying various combinations of the different elements corresponding to displacement and velocity terms of the state vector to obtain the optimum level of control of structural response with a least possible level of control force. | Identification of critical parameters in active control schemes for optimal structural control | 10.1007/s42107-020-00309-0 |
2021-02-01 | Purpose A close form solution was developed in this paper to find the nonlinear tuning parameters of symmetric/asymmetric rotor—Squeeze film damper system. Methods Initially, close form solution was developed to find the optimum tuning criteria using linear models. Later, it has been extended to nonlinear unbalanced rotor damper system using circular centre orbit condition. Analytical modeling of Squeeze film damper forces is carried out considering viscous, inertial and temporal contributions under laminar and turbulent conditions. Modified Reynolds equation with short damper approximation is used to derive the SFD forces for 2π-film. The solution of the system of equations helped to predict optimum tuning parameters, such as cross-over frequency and maximum possible amplitudes. Contributions of various governing parameters are discussed. Conclusion Mass ratio of damper-to-rotor mass and nonlinear radial/tangential damper forces play an important role in finding the tuning parameters of symmetric system. Additional shaft parameter, f_p, plays an important role in getting the optimum tuning parameters of asymmetric system as compared to symmetric system. | Tuning Criteria of Nonlinear Flexible Rotor Mounted on Squeeze Film Damper Using Analytical Approach | 10.1007/s42417-020-00229-y |
2021-02-01 | Choosing the installation location of a tuned mass damper (TMD) is the most important factor to consider when controlling dynamic response of a structure. It is also necessary to study whether the mass of the TMD installed on the structure effectively reduces the seismic response to the dynamic load. This study investigates the control performance of a seismic load was using a TMD installed on the spatial structure of a retractable roof. The optimum mass ratio and installation location of the TMD were analyzed. The mass of one TMD was set as 1% of the total mass of the analytical model. One TMD mass was fixed, and the optimal position was examined by changing the number of TMDs installed. The displacement response ratio of the model with the TMD was compared to that of a base model without the TMD. The numerical analysis results showed that the displacement responses of the example structure with 8 TMDs were reduced by about 90% compared to the uncontrolled case. The TMDs were most effective when they were installed at the edge rather than concentrated at the center of the spatial structure. After selecting three analytical models that were most effective, we tried to reduce the mass ratio of one TMD to find the optimal one. Using the optimum mass ratio, the TMD mass ratios differed according to the truss position. The analysis results could be used as a reference in TMD design for large space structures. | Seismic Response Control Performance Evaluation of Tuned Mass Dampers for a Retractable-Roof Spatial Structure | 10.1007/s13296-020-00431-4 |
2021-02-01 | The structural response modification factor ( R ) is a parameter, which determines the performance of a structure in a nonlinear range during strong earthquakes. Hence, in the previous research, the effect of viscose dampers on the coefficient of structural modification has been measured. In this research, the effect of friction dampers on the R factor in steel structures with regard to traditional and advanced methods of nonlinear static analysis has been investigated. With the development of the application of pushover analysis, in recent years, several advanced pushover methods have been proposed to consider the realistic behaviors of structures, including the effect of higher modes or the effect of changes in the structural modal characteristics during the analysis owing to the yielding of members. Therefore, the adaptive pushover analysis was used to consider the impact of near- and far-field records. In general, the factors affecting the R factor are distinguishable from the following two perspectives: strength and ductility. Structural analysis has been carried out by the finite element method and by taking into account the nonlinear method of the members in an extended fiber section method, with and without frictional damper in different places and positions. The results show that in particular the R factor has increased 52.45% on average, under different conditions. Therefore, using the results of numerous cases and the application of dampers with different slip loads and the variable number of dampers in each story, a new equation ( R _ d ) is proposed for the R factor of structures along with a friction damper (slip force, number of story, and bay of equipped with damper). | Numerical analysis method for evaluating response modification factor for steel structures equipped with friction dampers | 10.1007/s42107-020-00315-2 |
2021-01-21 | In this paper we consider a Timoshenko system subject to a complementary effect of frictional damping and viscoelastic damping. Under very general assumptions on the relaxation function and the frictional damping term, we establish, for the first time as per our knowledge, explicit and optimal energy decay rates for this system. Our result generalizes and improves earlier related results in the literature. | On the Control of Dissipative Viscoelastic Timoshenko Beams | 10.1007/s00009-020-01680-7 |
2021-01-21 | We prove the global existence of small data solution in all spaces of all dimensions n ≥ 1 $n\geq 1$ for weakly coupled systems of semilinear effectively damped wave, with different time-dependent coefficients in the dissipation terms. Moreover, we assume that the nonlinearity terms f ( t , u ) $f(t,u) $ and g ( t , v ) $g(t,v) $ satisfy some properties of parabolic equations. We study the problem in several classes of regularity. | Modified different nonlinearities for weakly coupled systems of semilinear effectively damped waves with different time-dependent coefficients in the dissipation terms | 10.1186/s13662-021-03215-0 |
2021-01-11 | In this paper, the parameters optimization of a tuned mass damper (TMD) is presented to enhance the seismic performance of a six-story steel structure based on the ductility damage index. Herein, the six-story frame is modeled nonlinearly in the OpenSees software by a concentrated plasticity model. Finally, the most suitable algorithm is selected among several optimization algorithms based on the convergence rate and the objective function's values. In this process, the water cycle algorithm has shown the best results. Therefore, the optimal parameters of the TMD are calculated by this algorithm in such a way that the ductility damage index is minimized in the six-story structure under earthquake loads. For this purpose, the nonlinear dynamic analysis of the structure is performed under earthquakes loads using the OpenSees software. Also, the optimum parameters of the TMD are computed to minimize the ductility damage index under the earthquake loads by linking the OpenSees and Matlab software. The results show that the optimum parameters of the TMD system obtained by the water cycle algorithm could appropriately decrease the ductility damage index. It can simultaneously increase the structure's seismic performance to reduce the displacement, stories damage, and drift ratio. | Improving the nonlinear seismic performance of steel moment-resisting frames with minimizing the ductility damage index | 10.1007/s42452-021-04141-2 |
2021-01-09 | In this paper, we derive an incompressible Oldroyd-B model with hybrid dissipation and partial damping on stress tensor $$\tau $$ τ via the velocity equations and the generalized constitutive law so that global well-posedness of the model is established in the Sobolev space framework. Precisely speaking, the proof is based on the curl-div free property of $$\tau - {\nabla }\frac{1}{\Delta } \mathbb {P}\mathrm{div}\tau - ( {\nabla } \frac{1}{\Delta } \mathbb {P}\mathrm{div}\tau )^T $$ τ - ∇ 1 Δ P div τ - ( ∇ 1 Δ P div τ ) T , the low frequency dissipation and high frequency damping of $$\tau $$ τ and the dissipation of u . | Global Solutions to the 2-Dimensional Incompressible Oldroyd-B Model with Hybrid Dissipation and Partial Damping on Stress Tensor | 10.1007/s00025-020-01331-z |
2021-01-08 | In order to solve the contradiction between high load-carrying capacity and low natural frequency in designing ship water-lubricated stern bearing, an idea of independent design of load carrying and vibration reduction functions was proposed, and the squeeze film damper technology was innovatively introduced into a conventional water-lubricated stern bearing (CWSB) to form a water-lubricated damping stern bearing (WDSB). Harmonic responses of two bearings were calculated, and a dynamic characteristic experiment was carried out. The results show that the maximum displacement response (MDR) decreases with the increase in oil film clearance. With the increase in inner flange height, MDR increases first and then decreases. MDR decreases first and then increases with the increase in distribution angle. As rotation rate speeds, the difference between two bearings’ Root Mean Square (RMS) vibration amplitude remains unchanged. As load increases, relative reductions of two bearings’ maximum amplitude and RMS decrease. Amid a load of 0.2 MPa and a rotational speed of 200r/min, compared with CWSB, the maximum amplitude of WDSB in the vertical direction is reduced by about 71.8%, and the relative reduction in RMS is about 47.8%, which verifies the damping effect of WDSB is remarkable. | Simulation and experimental investigations on water-lubricated squeeze film damping stern bearing | 10.1007/s40430-020-02785-6 |
2021-01-06 | In this note, some well-posedness issues for a class of fourth-order Schrödinger equations with a time-dependent damping and a pure power non-linearity are investigated. Indeed, global and non-global existence of solutions is obtained under suitable conditions on the damping and the source term. | Global and Non-global Solutions for a Class of Damped Fourth-Order Schrödinger Equations | 10.1007/s00009-020-01692-3 |
2021-01-05 | We show that the linearized Vlasov-Poisson equations around traveling wave-like non-homogeneous states near zero contain the full plasma echo mechanism, yielding Gevrey 3 as a critical stability class. Moreover, here Landau damping may persist despite blow-up: We construct a critical Gevrey regularity class in which the force field converges in $$L^2$$ L 2 . Thus, on the one hand, the physical phenomenon of Landau damping holds. On the other hand, the density diverges to infinity in Sobolev regularity. Hence, “strong damping” cannot hold. | On Echo Chains in Landau damping: Traveling Wave-like Solutions and Gevrey 3 as a Linear Stability Threshold | 10.1007/s40818-020-00090-y |
2021-01-04 | We consider the linear wave equation with the time-dependent scale-invariant damping and mass. We also treat the corresponding equation with the energy critical nonlinearity. Our aim is to show that the solution scatters to a modified linear wave solution and to obtain its asymptotic order. | Scattering and asymptotic order for the wave equations with the scale-invariant damping and mass | 10.1007/s00030-020-00671-7 |
2021-01-02 | The main aim of this paper is to develop a nonconforming mixed finite element method for the time-dependent Navier–Stokes problem with nonlinear damping term. The superconvergent analysis of a backward Euler fully-discrete scheme is presented, where the constrained nonconforming rotated (CNR) $$Q_1$$ Q 1 element and the $$Q_0$$ Q 0 element are used to approximate the velocity $${\varvec{u}}$$ u and the pressure p , respectively. By use of the characters of the element pair together with some striking skills, i.e., mean-value skill and a new transforming skill with respect to $$\tau $$ τ , the superclose estimates of $$O(h^2+\tau )$$ O ( h 2 + τ ) for $${\varvec{u}}$$ u in broken $$H^1$$ H 1 -norm and p in $$L^2$$ L 2 -norm are deduced rigorously. Furthermore, the global superconvergent results are obtained through the interpolated postprocessing technique. Finally, some numerical results are provided to confirm the theoretical analysis. Here, h is the subdivision parameter and $$\tau $$ τ , the time step. | Superconvergent analysis of a nonconforming mixed finite element method for time-dependent damped Navier–Stokes equations | 10.1007/s40314-020-01381-7 |
2021-01-01 | For the discussions in this chapter, we’ll use what is referred to as a lumped parameter model , to describe free vibration. The “lumped” designation means that the mass is concentrated at a single coordinate (degree of freedom) and it is supported by a massless spring and damper. Recall from Sect. 1.2.1 that free vibration means that the mass is disturbed from its equilibrium position and vibration occurs at the natural frequency, but a long-term external force is not present. The lumped parameter model is typically depicted as shown in Fig. 2.1. Here, the linear spring, k , exerts a force, f , proportional to displacement, x . See Fig. 2.2, where the slope of the line represents the spring constant, k . This linear relationship is referred to as Hooke’s law . Typical SI units for k are N/m. | Single Degree of Freedom Free Vibration | 10.1007/978-3-030-52344-2_2 |
2021-01-01 | We consider systems with finite numbers n > 1 of degrees of freedom. Systems with infinite numbers of degrees of freedom, referred to as continuous systems, are discussed in the subsequent chapter. It will be seen that the methods for solving MDOF and continuous systems are conceptually similar and involve three steps. | Multi-Degree of Freedom (MDOF) Systems | 10.1007/978-3-030-64552-6_4 |
2021-01-01 | This paper presents an interesting mechanical system which can be used to experimentally demonstrate both viscous (Rayleigh) and friction (Coulomb) damping. The system consists of a cantilever beam, hanger and some weights. Although such a simple mechanical system is used in this experiment, two distinctly different damping mechanisms can be observed through minor changes in the structural configuration. The two structural configurations are the different orientations of hanger on the cantilever, since these orientations affect the primary mechanism of damping. During this investigation, the free response of the beam was measured in both the configurations, and damping mechanism and ratio were estimated from the time series data. For ensuring repeatability of results, the experiment was conducted on multiple combinations of three beams and hangers. The same type of phenomenon (two different damping mechanisms) was consistently observed on all three beams. | Investigation of Viscous and Friction Damping Mechanisms in a Cantilever Beam and Hanger System | 10.1007/978-3-030-47717-2_42 |
2021-01-01 | Honeycomb sandwich laminates with aluminum and carbon fiber reinforce polymer (CFRP) face—sheets are widely used in spacecraft structures and aerospace industries. The damping behavior of such structures is reported to improve when the granular particles, called damping particles, are inserted in the honeycomb cells. The discrete element method (DEM) has been successfully used and found to give a reasonably accurate estimate of the impact damping. In DEM formulation, Newton’s laws of motion are used to obtain the equations of motions of each damping particle considering the contact forces from immediate neighboring particles and other sources, if any. The use of DEM for the real structure where the number of particles is of order 10^8 or more is inefficient and impractical to perform optimization. In this paper, a damping model dissipating equivalent energy is presented for a system consisting of a small honeycomb sandwich coupon filled with damping particles and has resonance frequencies beyond the bandwidth of the model. The coupon is subjected to a range of harmonic excitations (varying frequency and amplitude). The energy dissipated by the damping particles is estimated by DEM. The normal and tangential components of contact forces are modeled using Hertz’s nonlinear dissipative and Coulomb’s laws of friction, respectively. Then the parameters of the equivalent damper are obtained which dissipates the same energy. The damping model presented incorporates the effect of fill fraction, particle size, and material, as well as the amplitude and frequency of excitation. The comparisons of the DEM model for some of the load cases are done with the experimental data showing reasonably good agreement. The model presented could be readily incorporated in the FEM model like zero-stiffness proof-mass actuator, and the effect of impact damping can be studied without actually solving the DEM governing the motions of the particles. | A Simplified Impact Damping Model for Honeycomb Sandwich Using Discrete Element Method and Experimental Data | 10.1007/978-981-15-5862-7_28 |
2021-01-01 | A classically damped linear system possesses classical normal modes, which constitute a linear coordinate transformation that decouples the undamped system. This process of decoupling the equation of motion of a dynamical system is the time-honored procedure termed modal analysis. In general, damping is not classical and thus passive linear systems cannot be decoupled by modal analysis. This chapter shows how classical modal analysis can be extended to decouple damped linear systems in configuration space through a procedure called phase synchronization. Similar to modal analysis, decoupling by phase synchronization possesses ample physical insight based upon a consideration of the physics of damping. In this regard, phase angles are shifted in each non-classically damped mode of vibration so as to transform it into a classical mode. Eleven illustrative examples are provided. | Phase Synchronization and the Physics of Damping | 10.1007/978-3-030-60846-0_2 |
2021-01-01 | The equation of motion of linear systems is one of the most commonly used equations in science and engineering. It has long been recognized that coordinate coupling in linear systems is a considerable barrier to analysis and design. In this context, it is common for engineers to seek coordinate decoupling techniques. Coordinate decoupling is the process of simultaneously diagonalizing the coefficient matrices of a dynamical system. The main objective of this chapter is to provide an overview of configuration-space decoupling techniques. Three decoupling algorithms are provided and eleven examples are supplemented. | Linear Systems and Configuration-Space Decoupling Techniques | 10.1007/978-3-030-60846-0_1 |
2021-01-01 | In this chapter, we focus on the motion of the structure and study how it responds to an external force. In particular, we study the classical vibrations problem in which a mass is supported by a spring and a damper (known as a mass-spring-damper system) and is free to oscillate. We discuss the cases of a one-degree-of-freedom (1 DOF) and a 2 DOF vibratory systems. There is no fluid involved in a classical vibrations problem. In the very last section of this chapter, we will study the response of a mass-spring-damper system when it is placed in otherwise still fluid to study how the presence of fluid around a vibrating system affects its motion. We call this “otherwise still fluid” to emphasize that before the structure starts to oscillate, the fluid is at rest, and it starts moving only because the structure is moving. This will be the first fluid-structure interaction system that we will study in this book. | Vibrations of One and Two Degree-of-Freedom Systems | 10.1007/978-3-030-85884-1_3 |
2021-01-01 | We review briefly the second law of Newton and its impulse-momentum and work-energy versions and use them to write equations of motion for single degree of freedom systems. These equations are solved by analysis in the time and frequency domains. Analytical and numerical methods are used for solution. Multi-degree of freedom and continuous systems are considered in Chaps. 4 and 5 . | Single Degree of Freedom (SDOF) Systems | 10.1007/978-3-030-64552-6_2 |
2021-01-01 | Laminate composite plates have several significant applications in aerospace and automobile industries due to their high strength-to-weight ratio, thermal stability, etc. However, thin laminated composite plate has a tendency of buckling when subjected to some adverse loading conditions. The addition of stiffener can avoid the buckling tendency of the thin laminated composite plate. The effect of stiffener on natural frequency and random modal damping are studied herein. The effect of uncertainty in modal damping is accounted while analyzing the composite plate to evaluate the uncertainty in damped dynamic response of the stiffened composite plate. The modal damping of the composite is determined using visco-elastic damping (VED) model. The randomness in the modal damping is propagated from uncertainty in loss factor of the lamina, and stochastic finite element method (SFEM) based on generalized polynomial chaos (gPC) is applied to evaluate the uncertainty in the modal damping of the stiffened laminated composite plate. First-order shear deformation theory (FSDT), including rotary inertia, is adapted to develop collocation-based stochastic finite element formulation of the composite plate with stiffener. Addition of the stiffener increases the frequency of the composite structure. Uncertainty in the modal damping due to the varying layers of the plates and stiffener directions have been investigated. | Stochastic Modal Damping Analysis of Stiffened Laminated Composite Plate | 10.1007/978-981-15-8138-0_49 |
2021-01-01 | In this chapter, we consider one of the fundamental problems in Fluid-Structure Interactions (FSI): that of a mass-spring-damper placed in flow. Although this is a rather simple system, it results in rather complicated interactions between the flow and the structure, and it helps us understand some fundamental concepts in FSI. The vibrations that we will observe in this system are due to the shedding of vortices in the wake of the structure, and that is why we call this problem Vortex-Induced Vibrations (VIV). In this chapter, we consider a body with a circular cross-section. To begin with, we consider a cylinder which is allowed to move in one direction only. First, we consider the case where the degree of freedom is perpendicular to the direction of the flow, i.e., the crossflow (CF) direction, and we will study crossflow VIV. Then, we will consider the case where the degree of freedom is in the direction of the flow, i.e., the inline (IL) direction. At the end of the chapter, we will consider a cylinder which is allowed to oscillate in both the CF and IL directions, i.e., a 2 DOF system. | Vortex-Induced Vibrations | 10.1007/978-3-030-85884-1_4 |
2021-01-01 | When the dynamic design of a structure is carried out by using finite element method, the dynamic characteristics of the member of the structure have to be identified in advance. Especially, the damping property of the actual complex shaped member is sometimes assumed to be the same as the one of a simple shaped member with the same material. The damping properties often become a function of the frequency, so it is not certain whether we can apply the dynamic characteristics of the simple shaped member to the complex shaped one or not. In this study, a beam specimen made of steel is adopted, and the modal properties of both uniform shaped specimen and L-shaped one are identified; then the influence of the shape processing is investigated on the damping property. As a result, it is recognized that the damping property is high in the low-frequency band and low constant in the high-frequency band. Furthermore, the damping property of the L-shaped specimen is higher in the low-frequency band than the case of uniform specimen, while it is almost the same in the higher-frequency band. | Study of the Effect of Shape Processing of a Specimen on the Modal Properties | 10.1007/978-3-030-46466-0_12 |
2021-01-01 | A brief description of measuring means, a free-oscillation setup with a transverse sting of the model, and test conditions is reported. A procedure for processing experimental data is described. Quasi-steady and damping aerodynamic characteristics of the pitching moment of the model in the range of Mach numbers M = 1.75–6 are obtained. A comparison of research results with calculated data, as well as with the previous experimental data obtained using the base sting is given. It was found that at M = 3–6, regular undamped oscillations of the model are excited. | Methodical research of unsteady aerodynamic characteristics of the main-stage separation unit of emergency rescue system at supersonic speeds | 10.1134/S0869864321010017 |
2021-01-01 | We would like to prove a blow-up result for Sobolev solutions to the Cauchy problem for semi-linear structurally damped σ -evolution equations, where σ ≥ 1 and δ ∈ [0, σ ) are assumed to be any fractional numbers. To deal with the fractional Laplacian (− Δ)^ σ and (− Δ)^ δ as well-known non-local operators, a modified test function method is applied to prove a blow-up result in the subcritical case and in the critical case as well. | Blow-Up Results for Semi-Linear Structurally Damped σ-Evolution Equations | 10.1007/978-3-030-61346-4_10 |
2021-01-01 | A Magneto rheological damper is one of the most advanced devices used in a semi-active control system to mitigate unwanted vibrations because the damping force can be controlled by changing the viscosity of the internal Magneto Rheological (MR) fluids. The most widely used configuration of MR Damper incorporates an annular gap through which the magnetically active MR Fluid is forced to flow. The numerical analysis was carried on a double slot piston rod of varying slot lengths. The analysis was done using COMSOL. The analysis showed that a double slot piston rod with equal slot dimensions was most feasible to be used for experimentation. The experimentation was carried on a typical double slot MR Damper with two coils in parallel connection. It has been experimentally seen that response of Magnetic Rheological fluid damper is better to 10 V (2 Hz) as compared to 5 V (1 Hz) frequency. | Numerical and Experimental Analysis of Magnetic Rheological Damper of Light Duty Load Carrying Vehicle | 10.1007/978-3-030-69925-3_18 |
2021-01-01 | Abstract In the current paper, a modified algebraic method (MAGM) is proposed as an effective semi-analytical technique for solving nonlinear damped oscillatory systems. A polynomial is supposed as the trial solution, and its unknown coefficients are easily determined through the algebraic method (AGM). In order to improve the solution, the Laplace transformation is applied to the series solution, and then the Padé approximants of the resultant equation are constructed. Finally, the inverse Laplace transformation is adopted to obtain a periodic solution for the nonlinear problem under consideration. The proposed method is then applied for obtaining approximate analytical solutions of a damped rotatory oscillator as well as nonlinear vibrations of a flexible beam excited by an axial force. The results are compared with those obtained by the fourth-order Runge–Kutta method, and good agreement is observed. | APPROXIMATE ANALYTICAL SOLUTIONS TO NONLINEAR DAMPED OSCILLATORY SYSTEMS USING A MODIFIED ALGEBRAIC METHOD | 10.1134/S0021894421010090 |
2021-01-01 | Abstract The most critical element of Hemispherical Resonator Gyroscope (HRG) is the high quality factor ( Q -factor) mechanical resonator. This paper discusses the role of thermoelastic damping (TED) on effective Q -factor. Finite element method (FEM) is used to solve this highly coupled field problem involving vibration, solid mechanics, heat transfer and thermodynamics. The major contribution of this paper is the sensitivity analysis of the effect of material property, operating temperature and dimensions to arrive at macro scale resonator configuration. Hybrid hemispherical-cylindrical configuration is proposed by studying the performance parameters such as effective mass and angular gain.The uniqueness of the present work is the sensitivity study of ultra thin film coating (volume fraction of 0.01%), coating variations and different coating configurations. The coating can reduce the Q -factor by a few orders compared to uncoated shell. It hs been found that coating material selection and coating configuration are very important factors. Another significance of the present work is the realization and detailed characterization of the hybrid fused silica resonator. Thin film gold coating is done on the 3D surfaces of the realized precision resonator. Detailed coating characterization is carried out using sophisticated instruments. Very fine balancing to the order of a few mHz is achieved after coating. Q -factor measurement of the coated resonator is carried out using LDV and achieved a few millions in the final functional hybrid resonator. | Thermoelastic Damping Based Design, Sensitivity Study and Demonstration of a Functional Hybrid Gyroscope Resonator for High Quality Factor | 10.1134/S2075108721010107 |
2021-01-01 | The results of computer quantum-chemical modeling of the operator structure of the process of occurrence of acoustic emission signals under load are presented. The regularities of changes in the oscillatory properties of acoustic emission signals with force field parameters are established. The existence of a correspondence between changes in spectral characteristics and the moments of occurrence of acoustic emission signals is proved. Using the GaussView program with the Hartree-Fock method in the 3-21G basis and graph theory, the parameters of the loaded anharmonic oscillator were calculated. Based on the studies, an algorithm for a multifactor model of information diagnostics of the mechanical properties of materials is proposed. A meaningful interpretation of the operator structure of dynamic processes and numerical methods for recovering information about the strength properties of materials from the characteristics of sources of initiation of acoustic emission signals is given. | Technique of System Operator Determination Based on Acoustic Emission Method | 10.1007/978-3-030-54215-3_1 |
2021-01-01 | We prove the existence and uniqueness of periodic solutions to linear and semilinear evolution equations. Our method is based on the analysis of the conditional stability of the semigroups generated by the corresponding linear equations and connection with the choice of the initial data from which emanates the periodic solution. We also give applications to damped wave equations and damped Timoshenko beam systems. | Conditional Stability of Semigroups and Periodic Solutions to Evolution Equations | 10.1007/978-3-030-61346-4_15 |
2021-01-01 | Floating Production Storage and Off-loading (FPSO) systems are being utilized world widely by offshore industries. The surge response of FPSO subjected to severe sea states needs to be suppressed in order to keep a particular station for operational purposes. The oil cargo tanks of FPSO can be used as passive dampers for minimizing the surge displacement response of FPSO. These cargo tanks can act as Tuned Liquid Dampers (TLDs) if the natural frequency of the liquid oscillation in containers is tuned to the surge natural frequency of FPSO or tuned to the excitation frequency. The containers can be partitioned into several tanks (as Multiple Tuned Liquid Dampers, MTLDs) with different lengths and liquid depths. The natural frequencies of MTLDs can also be distributed over a range around the natural frequency of FPSO. The present study attempts to comprehend the response control of FPSO under surge motion and so the FPSO is modeled as a single degree of freedom under random sea state. The containers can be modeled as either linear TLDs or nonlinear TLDs. Each linear TLD can be modeled by an equivalent Tuned Mass Damper (TMD) analogy based on linear wave theory. In order to account the nonlinear liquid motion in TLD, an impact damper analogy is used along with the TMD analogy. The study includes the efficiency and robustness of MTLD and it compares the response control obtained by using linear MTLDs and nonlinear MTLDs. | Surge Response Control of FPSO Using Nonlinear MTLDs | 10.1007/978-981-15-8506-7_11 |
2021-01-01 | In Japan, including the Great East Japan Earthquake, the fall of ceiling caused by earthquake has repeatedly occurred every time. In the year of 2013, “ceiling notice” was enforced. As a countermeasure, the technology of setting up diagonal members and improving the stiffness and bearing strength of seismic ceiling has become the mainstream. However, the ceiling notice is supposed to be a medium earthquake level, and even larger inputs can be considered at the large earthquake encountered in the future. As a result, it is necessary to increase the proof stress of the components in order to respond to earthquakes and resonance with buildings with earthquake-resistant ceilings. Therefore, in this research, we aim to add damping to suspended ceilings and to prevent damage and fall of suspended ceilings from large earthquakes. The damping control ceiling system we proposed allows a certain amount of deformation not only during the mid-earthquake targeted by the current ceiling notification but also during severe input during a large earthquake, and can suppress the acceleration response of the ceiling surface. In addition, considering the application to an actual building, we will conduct vibration experiments using the placement method, damper installation angle, and vibrating direction as parameters to confirm the usefulness of the damping ceiling system. In this experiment, it was confirmed that the acceleration response was reduced in the entire region including the resonance region by installing the damping control ceiling system. It was confirmed that the difference in additional damping was confirmed by the damper installation angle, and that the difference in the arrangement method and vibrating direction had a small effect on the damping control ceiling system. As a result, it was confirmed that the response of the ceiling surface can be reduced by the damping control ceiling system even under various conditions. | Study on Practical Application of Damping Control Ceiling | 10.1007/978-981-15-8079-6_49 |
2021-01-01 | A performance-based seismic design method for plane steel moment resisting and braced framed structures is presented. It is a force-based design method employing equivalent viscous modal damping ratios ξ _ k instead of the behavior (or strength reduction) factor q (or R ) to account for inelastic energy of dissipation. These modal damping ratios ξ _ k are defined for an equivalent linear multi-degree-of-freedom structure to the original non-linear multi-degree-of-freedom structure, which has the same mass and elastic stiffness as the non-linear one. In addition, they are functions of the structural period, the target inter-storey drift ratio and member plastic rotation and the soil type. Empirical expressions of these ξ _ k for the first few significant modes are obtained through extensive parametric studies involving non-linear time-history analyses of many frames under many far-fault earthquakes and different deformation targets. These ξ _ k are used for seismic design through an elastic acceleration design spectrum with high amounts of damping. The presented method, which is illustrated by numerical examples, is more rational and provides results of higher accuracy in one step (strength checking) than code-based design methods requiring two steps (strength and deformation checkings). | Design Using Modal Damping Ratios | 10.1007/978-3-030-80687-3_8 |
2021-01-01 | Mignolet (J Sound Vib 349:289–298, 2015) demonstrated mathematically that his proposed five-parameter Iwan-type model weakens the coupling between the change in effective stiffness and change in effective damping of the model as vibration amplitude changes. Several experimental studies on bolted-joint structures have experienced difficulty in fitting a traditional Iwan model to match measurements, so this advantage is sorely needed. However, Mignolet’s work only considered steady-state harmonic motion, and the stiction behavior of the internal sliders was not studied in great detail. In this work, the force-constitutive formulation of the five-parameter Iwan-type model is implemented computationally and then examined to understand its behavior in more general transient scenarios. The five-parameter model is found to have a complicated dependence on its displacement history. If the model reaches a maximum steady-state displacement after a ring-up response (such as occurs when the system is excited at resonance by a shaker), the stiffness and damping it exhibits is consistent with those formulated by Mignolet. When the vibration decays below the maximum-achieved displacement, however, the effective stiffness and damping revert to power-law behavior with amplitude. The power-law behavior is functionally similar to that of the four-parameter Iwan model (on which the five-parameter model is based), so the advantage of the weakened coupling between the stiffness and damping is lost in a ring-down response. | Towards an Understanding of the Transient Behavior of the Five-Parameter Iwan-Type Model | 10.1007/978-3-030-47626-7_19 |
2021-01-01 | The existence of global BV solutions for the Aw-Rascle system with linear damping is considered. In order to get approximate solutions we consider the system in Lagrangian coordinates, then by using the wave front tracking method coupling with and suitable splitting algorithm and the ideas of [1] we get a sequence of approximate solutions. Finally we show the convergence of this approximate sequence to the weak entropic solution. | On the Cauchy problem for Aw-Rascle system with linear damping | 10.1007/s10473-021-0118-0 |
2021-01-01 | Mathematical modeling of magneto-rheological damper has been an intriguing field of research ever since the invention of the device itself. An accurate magneto-rheological damper model results in development of an efficient current controller in a semi-active seat suspension system featuring magneto-rheological damper. Hence, a number of models have been put forward to accurately predict the magneto-rheological damper behavior. This paper presents another mathematical model for magneto-rheological dampers based on their equivalent damping. A commercially available magneto-rheological damper has been used for characterization in this study. The magneto-rheological damper behavior is characterized using two models, Bingham model and equivalent damping model. These models are then used to simulate the magneto-rheological damper in a quarter car model with four degree of freedom featuring semi-active seat suspension that is subjected to bump road input and random road input. The magneto-rheological damper model is supplied with current using two control logics, on–off Skyhook logic and Proportional Integral and Differential logic. The performance of the two models are compared based on driver mass response in each case of seat suspension model and computation time. The results show that equivalent damping model can represent the magneto-rheological damper behavior with sufficient accuracy while reducing computational time by 30% irrespective of type of road input or type of control logic implemented. The reduced computational time is an added advantage when magneto-rheological damper is used in real-time. | Dynamic Analysis of a Quarter Car Model with Semi-Active Seat Suspension Using a Novel Model for Magneto-Rheological (MR) Damper | 10.1007/s42417-020-00218-1 |
2021-01-01 | Micro-vibrations in satellites mainly originate from the control moment gyroscope because of its mass imbalance, which seriously affect the image accuracy of high-resolution optical payload, so it must be isolated. Bellows-type fluid viscous damper (FVD) can be used to isolate micro-vibrations. In this paper, a simplified model of the damping element in bellows-type FVD under medium- and high-frequency excitation is proposed according to the concept of bellows effective area. Based on this theoretical model, nonlinear stiffness and damping at different design parameters are extracted by nonlinear fitting method. Then, the main cause of nonlinear stiffness and damping is analyzed by the velocity distribution in the cross section of damping orifice. The factors that affect the intensity of nonlinear stiffness and damping are discussed by using the flow resistance. The results show that the velocity term in the corrected hydraulic resistance is the cause of nonlinear damping and stiffness. Damping orifice diameter, length and silicone oil viscosity will affect the intensity of nonlinear characteristics of this damper. At low viscosity, the nonlinear damping is more obvious. The larger the diameter, the more obvious the nonlinear damping. In the frequency domain between 1 and 200 Hz, the velocity index is not a constant, but changes with frequency. Hydraulic stiffness can be divided by linear stiffness and nonlinear stiffness; both of them can affect the elastic force. | Research on nonlinear stiffness and damping of bellows-type fluid viscous damper | 10.1007/s11071-020-06146-9 |
2021-01-01 | In this paper we consider a Klein–Gordon model with time-dependent periodic coefficients. The aim is to investigate how the presence of the mass term influences energy estimates with respect to the case of vanishing mass, already treated by J. Wirth (Hiroshima Math J 38:397–410, 2008). The approach is based on a diagonalisation argument for high frequencies and a contradiction argument for bounded frequencies. | Decay Estimates for a Klein–Gordon Model with Time-Periodic Coefficients | 10.1007/978-3-030-61346-4_14 |
2021-01-01 | Magnetorheological (MR) fluids with exceptional rheological properties are skilled in exhibiting quick performance to control vibrations during earthquakes. The significant damping properties of MR fluids were effectively controlled with the help of externally applied magnetic field and current. Currently, MR fluids with nano Fe_3O_4 iron particles are used in the preparation of MR fluid to reduce sedimentation. Fabrication of MR damper consists of nylon material to reduce the weight and resist high-temperature distortion. The weight of the proposed MR damper was about 445 g with the magnetic core. The MR fluid of proportions 30% (MRF30), 45% (MRF 45) and 60% (MRF 60) of iron particle is prepared, and the cyclic load test frequency is 0.5 Hz and amplitude, ± 5 mm. The maximum damping force was found to be 1.032 kN obtained from the MR fluid containing 60% Fe_3O_4 particles in magnatec oil. For variable frequency, the time history loading test was done with El Centro ground acceleration data where the maximum damping force for MRF 60 is 1.3 kN. | Smart Lightweight MR Damper for the Enhancement of Seismic Mitigation | 10.1007/978-981-15-5235-9_7 |
2021-01-01 | The ground response to seismic waves is governed by the geometry and the mechanical properties of the site. A proper characterization of the soil behavior is thus a fundamental aspect, and it should account for the uncertainties associated with the model parameters. In particular, the quantification of the small-strain damping is a critical task, especially in low-to-moderate seismicity areas. In the present paper, the main issues related to the definition of the damping at small strains are firstly treated in the light of the biases affecting both laboratory and in situ tests. Higher values of damping are expected in field, where wave scattering phenomena take place. The influence of the parameter on the overall site response is subsequently assessed through a stochastic database of ground response analyses. The results highlight a reduction of the expected ground motion at the surface, especially for deep and soft sites when site-based small-strain damping is selected. Finally, the differences between site and laboratory values are analyzed regarding a specific case study. The influence of the damping at small strains resulted to be comparable or even higher with respect to the uncertainties related to the shear wave velocity profile and the modulus reduction and damping curves. Therefore, a proper evaluation of the uncertainties in the small-strain damping evaluation should not be neglected. | Uncertainties in Small-Strain Damping Ratio Evaluation and Their Influence on Seismic Ground Response Analyses | 10.1007/978-981-16-1468-2_9 |
2021-01-01 | This paper deals with the optimization of BONASILENCE damping ring inserted into a groove on a monoblock railway wheel to suppress radial and axial mode shapes of vibrations that cause rolling and curve squeal noise. A free open-ended damping ring has a slightly larger diameter than the groove and, when inserted, pre-stress of the ring is assured. However, when the circular ring of larger diameter is inserted into a smaller circular groove, the deformation of the ring is such that the ring and groove are not in contact along the entire circumference. Therefore, a noncircular shape of the free damping ring modeled by beam theory for providing even pressure distribution between the ring and groove along the entire circumference is under development. For evaluation of the damping ring effect on different circumferential pre-stresses, a new approach of measurement of slip between the ring and the groove based on the optical correlation method was used. Patches of speckle images with stochastic structure were generated and glued on the ring and the rim on their boundary at the places of presumed maximal wheel vibration. Vibration of the wheel was then excited, and the area of speckle images was recorded by a high-speed camera. Then the local relative motion between the ring and the wheel which is in the range of micrometers and up to 2 kHz of vibration frequency was evaluated. This method can be used for the finding of an optimal setting of the pre-stresses in the damping ring to achieve the maximal damping. | New Approaches for Design and Experimental Analysis of Damping Ring and Its Influence on Railway Wheel Dynamics | 10.1007/978-981-15-8049-9_80 |
2021-01-01 | The objective of our work is to develop a fast and efficient code to compute the damped parameters (the complex eigenvalues, the damped eigenfrequencies, and the corresponding loss factors) of viscoelastic twisted multilayer beams rotating at a constant angular speed. The beam is twisted, and its cross section is uniform. The governing equations are developed using the Hamilton principle and discretized using the finite element method. The related nonlinear eigenvalue problem is resolved by combining the homotopy method and the asymptotic numerical method. The obtained complex eigenparameters are coherent with those found in the literature. In addition, our calculation code makes it possible to directly compute the loss factors without using the bandwidth method used in some commercial codes. | Eigenfrequencies Calculation of Rotating Multilayer Beams Using the Asymptotic Numerical Method | 10.1007/978-981-16-0945-9_47 |
2021-01-01 | A dynamic analysis of the behavior of sandwich beams with a viscoelastic core under the action of a moving load is performed considering their geometrical asymmetry. The use of viscoelastic materials integrated into structures in front of the moving load is considered as a new suggestion to enhance their stability. A high-order theory, taking into consideration longitudinal and rotational inertias was used to examine the viscoelastic damping properties composite sandwich beams with account of their geometrical asymmetry and the frequency-dependent behavior of their viscoelastic core. | Dynamic Analysis of Composite Sandwich Beams with a Frequency-Dependent Viscoelastic Core under the Action of a Moving Load | 10.1007/s11029-021-09921-w |
2021-01-01 | Purpose Free vibrations of non-homogenous (functionally graded material (FGM)) axisymmetric nonlocal thermoelastic hollow sphere has been taken into consideration for investigation. The material of nonlocal thermoelastic sphere is supposed to be graded using power law in radial direction. Methods The solution of continued power series is employed to resolve the differential equations and to investigate the analytical solutions for field functions i.e. temperature, stress and displacement. Results and Conclusions The analytical results have been authenticated using numerical computations with computer based software like MATLAB. The numerical results have been shown graphically for the comparison of frequency shift and thermoelastic damping for local and nonlocal elastic materials. Deduction of results has been validated with the already published literature. | On the Analysis of Free Vibrations of Nonlocal Elastic Sphere of FGM Type in Generalized Thermoelasticity | 10.1007/s42417-020-00217-2 |
2021-01-01 | In many instances, saturated cohesive soils are subjected to various types of cyclic/dynamic loading conditions such as earthquake loading, blast loading, oceanic wave storms, machine vibrations and traffic loading, etc. All of these loadings are different based on the rate and magnitude of loading cycles. Hence, the aim of the current study is to evaluate the undrained cyclic shear behaviour of saturated Nagpur soil subjected to various loading conditions. A series of strain-controlled cyclic simple shear tests were carried out on the compacted specimens of Nagpur soil at varying shear strain amplitudes (γ_s = 0.25, 0.5, 1.5, 2.5, 3.75, and 5%) and loading frequencies (f = 0.1, 0.5, 1, and 2 Hz). The hysteresis response was analysed in terms of shear modulus and damping ratio variation along with cyclic stiffness degradation and cumulative strain energy dissipation. Shear modulus and damping ratio were found highest for specimens loaded at the highest frequency with the lowest excess pore pressure generation. Rate and magnitude of stiffness degradation were reduced with a decrease in shear strain amplitude. Dissipated cumulative strain energy was observed to be maximum for higher shear strain amplitude and rate of loading. The results indicated that the frequency and amplitude variation greatly influenced the hysteresis response of saturated Nagpur soil. | Cyclic Shear Behaviour of High Plasticity Cohesive Soil Subjected to Variation of Frequency and Amplitude | 10.1007/978-3-030-64514-4_18 |
2021-01-01 | During earthquakes, the ground shakes in all three directions. The inertia of freestanding structures, such as buildings, bridges, and dams, prevents them from moving in unison with the ground. As a result, structures deform and develop stresses. This chapter discusses the ground motion characteristics which affect the response of structures. This chapter also explains how seismic loads are different from gravity and wind loads. | Ground Motions from Past Earthquakes | 10.1007/978-3-030-57858-9_1 |
2021-01-01 | We present an approach for solving optimization problems with or without constrains which we call Dynamical Functional Particle Method (DFMP). The method consists of formulating the optimization problem as a second order damped dynamical system and then applying symplectic method to solve it numerically. In the first part of the chapter, we give an overview of the method and provide necessary mathematical background. We show that DFPM is a stable, efficient, and given the optimal choice of parameters, competitive method. Optimal parameters are derived for linear systems of equations, linear least squares, and linear eigenvalue problems. A framework for solving nonlinear problems is developed and numerically tested. In the second part, we adopt the method to several important applications such as image analysis, inverse problems for partial differential equations, and quantum physics. At the end, we present open problems and share some ideas of future work on generalized (nonlinear) eigenvalue problems, handling constraints with reflection, global optimization, and nonlinear ill-posed problems. | Damped Dynamical Systems for Solving Equations and Optimization Problems | 10.1007/978-3-319-57072-3_32 |
2021-01-01 | A lateral spin sliding was applied orthogonally in the direction of the sliding velocity at a rotary sliding contact in a rotary sliding system. When the velocity of the lateral spin sliding was sufficiently high, the friction-induced vibration was completely suppressed. The experimental results show that the lateral spin sliding provides a positive damping effect in the rotary sliding system. | Suppression of Friction-Induced Vibration in Rotary Sliding System Using Lateral Spin Sliding | 10.1007/978-3-030-46466-0_22 |
2021-01-01 | In this study, two dynamic systems are experimentally investigated using control-based-continuation (CBC) near their resonant frequencies. One system is a single mass oscillator with a stiffness nonlinearity, the other system is a pair of slim beams with a friction element in between and thus significant nonlinear damping. The focus of this study is on the implementation of the CBC-method and the interpretation of the experimental results. The dynamic load-displacement characteristics of both systems (s-curves) at different frequencies and the backbone-curves are presented. | Experimental Application of Control-Based-Continuation for Characterization of Isolated Modes on Single- and Multiple-Degree-of-Freedom Systems | 10.1007/978-3-030-47626-7_22 |
2021-01-01 | Friction in assembled structures is of great interest due to its ability to reduce the vibration amplitude of critical components. The nonlinear behaviour of a structure depends on a variety of physical parameters. Among these parameters, the contact pressure distribution and the contact area have shown to be critical for the behaviour of the joint and the responses of assembled structures. In most application cases the impact of the interface geometry is not considered as a design parameter, although some attempts have been reported to shape the interface geometry for a specific dynamic response. Taking this idea of designing an interface geometry for a better dynamic performance a step further, the concept presented here propose an actively controlled interface geometry and contact pressure distribution, to change the joint behaviour during a vibration cycle. The concept consists of a device capable of manipulating the shape and pressure of a flexible membrane in contact with a rigid punch, subjected to a normal load and a tangential excitation, via a row of piezoelectric actuators. | Analysis of an Actuated Frictional Interface for Improved Dynamic Performance | 10.1007/978-3-030-47626-7_33 |
2021-01-01 | In this paper, the dynamic characteristics of the in-arm type hydropneumatic suspension unit (ISU) of armed tracked vehicle are theoretically analyzed and numerically investigated. Accurate spring and damping models are introduced and combined to secure the analysis reliability. One is the Benedict-Webb-Rubin equation of state which is adopted to model the spring behavior of real nitrogen gas in ISU system. The other describes the behavior of a damper during four distinct ISU motions; jounce-loading, jounce-unloading, reboundloading and rebound-unloading. For the comparison purpose, the numerical results of the dynamic behavior of ISU system using a real gas model and two ideal gas models are presented and compared. | Numerical analysis of dynamic characteristics of in-arm type hydropneumatic suspension unit | 10.1007/s12206-020-1223-z |
2021-01-01 | Relying solely on strength to resist ground motions can be expensive. A good seismic design utilizes deformability and damping to reduce the strength demand on a structure. A nonlinear analysis is needed to consider all sources of deformability and damping in a structure. Ground-supported, upright, cylindrical, liquid-storage tanks are massive structures. Strength demands on tanks can be quite high. Fortunately, there are some inherent sources of deformability and damping which can be utilized to significantly reduce the strength demand on tanks. This chapter discusses progressively refined analyses to capture various sources of deformability and damping in ground-supported liquid-storage tanks. | Seismic Response of Liquid-Storage Tanks | 10.1007/978-3-030-57858-9_8 |
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