Damping Coefficient Changes Research Articles

Influence of an Engineered Notch on the Electromagnetic Radiation Performance of NiTi Shape Memory Alloy.

This work explores the influence of a pre-engineered notch on the electromagnetic radiation (EMR) parameters in NiTi shape memory alloy (SMA) during tensile tests. The test data showed that the EMR signal fluctuated between oscillatory and exponential, signifying that the specimen's viscosity damping coefficient changes during strain hardening. The EMR parameters, maximum EMR amplitude, and average EMR energy release rate remained constant initially but rose sharply with the plastic zone radius with progressive loading. It was postulated that new Frank-Read sources permit dislocation multiplication and increase the number of edge dislocations participating in EMR emissions, leading to a rise in the value of EMR parameters. The study of the correlation between EMR emission parameters and the plastic zone radius before the crack tip is a vital crack growth monitoring tool. An analysis of the interrelationship of the EMR energy release rate at fracture with the elastic strain energy release rate would help develop an innovative approach to assess fracture toughness, a critical parameter for the design and safety of metals. The microstructural analysis of tensile fractures and the interrelation between deformation behaviours concerning the EMR parameters offers a novel and real-time approach to improve the extant understanding of the behaviour of metallic materials.

Effect of damping coefficients on a free-piston Stirling engine under a constant power condition based on a thermodynamic-dynamic coupled model

The Free Piston Stirling Engine (FPSE) is a complex system, in which the transient behaviors of its thermal and dynamic characteristics are coupled. To examine the strong coupling system under constant heating power and evaluate the effect of damping coefficients on engine performance, prediction of the aforementioned characteristics is essential. To this end, this study develops an FPSE system model based on quasi-static thermodynamics and piston dynamics to determine the thermal performance of the working fluid and the dynamic behavior of the displacer and piston, and the model is validated on the Re-1000. Then, the model is applied to examine the influence of the damping coefficients of two pistons on reactor core heater temperature, power, efficiency, amplitude, frequency, and phase angle under constant power condition. The results indicate that the model can well capture the transient behaviors of thermal and dynamic characteristics at Re-1000. After 0.7 s, the engine reaches a steady-state operation. Under the constant heating power of 3000 W, the displacer and piston damping significantly affect the engine's performance. Four displacement damping coefficient points are specified, and the piston damping coefficient changes in the range of Cp = 500 ∼ 1600Ns/m. As a result, the heater's stable working-point temperature changes from 590 K to 1060 K leading to an increase in indicated power from 1000 W to approximately 1500 W. The displacer and piston amplitudes show an increasing and decreasing trend respectively, with a decreasing trend in frequency and phase angle, but enhanced heat transfer performance. The dynamic-thermodynamic coupling model provides an opportunity to instantly calculate the open-loop response of the FPSE, which is a reference for future FPSE power-load matching designs.

Nonlinear Dynamics Study of Giant Magnetostrictive Actuators with Fractional Damping

Since the structural mechanics of the super magnetostrictive actuator (GMA) system involves problems related to viscoelastic damping materials, the fractional order is more accurate than the integer order calculus to characterize the viscoelastic features in the structure. In order to further investigate the intrinsic mechanism and dynamical characteristics of the GMA dynamical system, the dynamical equations of the nonlinear GMA system containing fractional damping terms are established and the main resonance of the system is analyzed using the averaging method. The mechanism of the influence of some parameters on the GMA system is analyzed by MATLAB numerical simulation to study the bifurcation and chaotic motion phenomena of the system from the qualitative and quantitative perspectives. The results show that the fractional damping coefficient, external excitation amplitude and fractional order have significant effects on the amplitude-frequency characteristics of the system; the fractional order has a greater influence on the bifurcation and chaotic behavior of the system; the dynamic behavior of the system caused by the change of external excitation amplitude and fractional damping coefficient at different damping orders is similar but the chaotic region is different.

Eventual differentiability of coupled wave equations with local Kelvin-Voigt damping

<p style='text-indent:20px;'>In this work, we consider a coupled wave equations with partially and locally distributed Kelvin-Voigt damping, where only one equation is dissipative.</p><p style='text-indent:20px;'>Under the assumption that the damping coefficient changes smoothly near the interface of the damped and undamped regions, we investigate the effectiveness of the indirect control, and we prove that the associated semigroup is eventually differential.</p>

Mathematical Model of Root Crop Digging with Longitudinal Vibrations

The problem how to reduce damage to tubers when they are dug up is urgent. For the new design of a vibrating digging working body for root crops the mathematical model of longitudinal vibrations of a root crop in the soil is developed as an elastic body in an elastically damped medium. The Ostrogradsky-Hamilton variational principle is applied for the analytical description of the process. The Ritz method was applied to find the frequencies of natural vibrations, the amplitudes of forced vibrations of a root crop as a solid elastic body when it is captured by a vibrating digging body. The frequency equation for the discussed vibrational process was obtained. The values of the first proper frequency of longitudinal vibrations of the considered elastic body of the root crop with specific geometric physical parameters are found. Graphs of the dependence of the first natural frequency upon the elastic deformation coefficient, the damping coefficient of the soil as an elastic damping medium are obtained. When the soil damping coefficient changes within 0 to 10 N∙s²∙m^–3, the first proper frequency changes within 500 to 750 s^-1 (80 to 119 Hz) at soil elastic deformation coefficient 2∙10⁵ N∙m^–3. Dependence of the elastic body forced vibration amplitude upon the change in the amplitude of the disturbing force have been obtained. When the amplitude of the disturbing force changes within 100 to 600 N, the amplitude of forced vibrations of the root crop body changes within 0.30 to 0.68 mm.

Influence of Variable Damping Coefficient on Efficiency of TMD with Inerter

In this paper, we study the dynamics of a two-degree freedom system consisting of the main body and tuned mass damper with inerter (TMDI). We add the dash-pot with variable damping coefficient to TMDI to study the overall efficiency of the device. We investigate different types of the non-linear characteristic of the dash-pot. We investigate devices in which damping coefficient change according to the relative displacement or the relative velocity between the damped mass and tuned mass damper. We also include in the investigation of different types of control functions. We show the two-parameter diagrams presenting the main body’s maximum amplitude versus the frequency of excitation of the damped body and different control parameter. We show how the application of a non-linear damper lets us control the main system’s oscillation amplitude.

Comparative analysis of strategies for a semi-active suspension of a ¼ vehicle

The vehicle suspension isolates the chassis from road irregularities, reacting to forces produced by the tires and the braking torques, always keeping the road tire contact, providing stability and safety. Stability and safety are two antagonistic characteristics in suspension design, when improving one the other is impaired and vice versa. The semi-active suspension is a type of vehicle suspension that can change its stiffness and/or damping in real time depending on the vehicle response to the actual road profile. The On-Off semi-active suspension changes its damping coefficient between two fixed limit values. This work proposes an On-Off semi-active suspension model, in which the damping coefficient changes its values considering the road profile function frequency. A control strategy is proposed in a way to improve performance keeping the same simplicity, without any structural change of the semi-active suspension. On the proposed control strategy one of the damping coefficients is obtained through the linear quadratic regulator (LQR) algorithm, with the aim to set the coefficient from the gain matrix associated to the velocity of the suspended mass. This model is compared to anothers found in literature.

Influence of dash-pot with controllable damping coefficient on damping efficiency of TMDI

In this paper we study the dynamics of two degree freedom system, which is consist of main body and tuned mass damper with inerter (TMDI). We add the dash-pot with variable damping coefficient to TMDI to study the overall efficiency of the device. The shape of non-linear characteristic of the dash-pot is dependent on one control parameter which governs the steepness of the function and the value of damping coefficient changes according to the relative displacement or velocity between main mass and tuned mass damper. We show the two parameters diagrams showing the maximum amplitude of the main body versus frequency of excitation of main body and controlling parameter.

Partial Stator Overlap in a Linear Generator for Wave Power: An Experimental Study

This paper presents a study on how the power absorption and damping in a linear generator for wave energy conversion are affected by partial overlap between stator and translator. The theoretical study shows that the electrical power as well as the damping coefficient change quadratically with partial stator overlap, if inductance, friction and iron losses are assumed independent of partial stator overlap or can be neglected. Results from onshore experiments on a linear generator for wave energy conversion cannot reject the quadratic relationship. Measurements were done on the inductance of the linear generator and no dependence on partial stator overlap could be found. Simulations of the wave energy converter’s operation in high waves show that entirely neglecting partial stator overlap will overestimate the energy yield and underestimate the peak forces in the line between the buoy and the generator. The difference between assuming a linear relationship instead of a quadratic relationship is visible but small in the energy yield in the simulation. Since the theoretical deduction suggests a quadratic relationship, this is advisable to use during modeling. However, a linear assumption could be seen as an acceptable simplification when modeling since other relationships can be computationally costly.

Analysis of Dynamic Stability of Nonlinear Suspension concerning Slowly Varying Sprung Mass

In this paper, the stability of vehicle concerning the slow-varying sprung mass is analyzed based on two degrees of freedom quarter-car model. A mathematical model of vehicle is established, the nonlinear vibration caused by sprung mass vibration is solved, and frequency curve is obtained. The characteristics of a stable solution and the parameters affecting the stability are analyzed. The numeric solution shows that a slow-varying sprung mass is equivalent to adding a negative damping coefficient to the suspension system, making the effective damping coefficient change from negative to positive. Such changing parameters lead to Hopf bifurcation and a shrinking limit cycle. The simulation results indicate the existence of static as well as dynamic bifurcation and the result is a change in the final stable vibration of the suspension. Even the tiny vibration of the sprung mass will lead to amplitude mutation, leading to the sprung mass instability.

Hard-Spring Bistability and Effect of System Parameters in a Two-Degree-of-Freedom Vibration System with Damping Modeled by a Fractional Derivative

The harmonic balance coupled with the continuation algorithm is a well-known technique to follow the periodic response of dynamical system when a control parameter is varied. However, deriving the algebraic system containing the Fourier coefficients can be a highly cumbersome procedure, therefore this paper introduces polynomial homotopy continuation technique to investigate the steady state bifurcation of a two-degree-of-freedom system including quadratic and cubic nonlinearities subjected to external and parametric excitation forces under a nonlinear absorber. The fractional derivative damping is considered to examine the effects of different fractional order, linear and nonlinear damping coefficients on the steady response. By means of polynomial homotopy continuation, all the possible steady state solutions are derived analytically, i.e. without numerical integration. Coexisting periodic solutions, saddle-node bifurcation and various effects of fractional damping on the steady state response are found and investigated. It is shown that the fractional derivative order and damping coefficient change the bifurcating curves qualitatively and eliminate the saddle-node bifurcation during resonance. Moreover, the system response depicts bigger and bigger region of hard-spring bistability with increasing fractional derivative order, but the region of hard-spring bistability of steady response becomes gradually small and then disappears when we increase the linear and nonlinear damping coefficients. In addition, the analytical results are verified by comparison with the numerical integration ones, it can be found that the present approximate resonance responses are in good agreement with numerical ones.

Оценка эксплуатационных характеристик объемного гидропривода на этапе его проектирования с использованием эволюционного моделирования

In a number of engineering problems in the development of automated systems arises a necessity in the computation and design of a fluid power drive (FPD) in conformity with particular technological schemes for which there are no finished industrial products or it is necessary to carry out a sufficiently exact correspondence of operating characteristics with specified engineering data. In this case one does not carry out the selection of standard elements for a fluid power drive, but performs their designing, where there were used modern approaches and methods of the computeraided design.
 As operation results show, a designed fluid power drive in most cases cannot possess required for system functioning dynamic properties: performance, capacity for a decrement, sensitivity and so on. According to the investigations, they depend in many respects upon such characteristics of a hydrosystem as static fluid of a hydrocylinder and piping, time constant of transient and damping coefficient.
 If we consider the process of FPD designing as a procedure of a parametric synthesis, then the research of its variants with different combinations of parameter values gives a possibility not only to choose geometrical dimensions for a unit, but to estimate its potential operational functionalities. 
 At present time as one of the effective approaches in the realization of such a solution may be the application of methods for the evolutionary simulation, where each object analyzed is considered as an individual.
 As an example of the evolutionary simulation there are considered the results of FPD servicing characteristics estimate computed on bases of design data for a forklift truck. The graphic dependences obtained establish the extreme correlations of hydraulic actuator operational characteristics which stipulate for a stable work of the fluid power drive in the transient behavior without special damping devices. Results of the evolutionary simulation allow analyzing the influence of parameters mentioned upon the damping coefficient changes and drawing a conclusion for decision making for the choice of such a design variant of a fluid power drive at which there would be ensured the best servicing characteristics of the plant.

Reflected and Transmitted Powers of Electromagnetic Waves through a Ferrite-Dielectric Photonic Crystal

In this work, reflection and transmission of electromagnetic wave by a periodic ferrite-dielectric photonic crystal are investigated theoretically and numerically. The ferrite material is described and its main parameters are given in detail. After the construction of the problem, the reflection and transmission coefficients are derived in a closed form by a transfer matrix method. The reflected, transmitted, and loss powers of the crystal are calculated using these coefficients. In the numerical results the mentioned powers are computed and illustrated as a function of frequency, angle of incidence, dielectric thickness, and applied magnetic field intensity when the damping coefficient changes.

Reflected and Transmitted Powers of Electromagnetic Waves through a Ferrite-Dielectric Photonic Crystal

In this work, reflection and transmission of electromagnetic wave by a periodic ferrite-dielectric photonic crystal are investigated theoretically and numerically. The ferrite material is described and its main parameters are given in detail. After the construction of the problem, the reflection and transmission coefficients are derived in a closed form by a transfer matrix method. The reflected, transmitted, and loss powers of the crystal are calculated using these coefficients. In the numerical results the mentioned powers are computed and illustrated as a function of frequency, angle of incidence, dielectric thickness, and applied magnetic field intensity when the damping coefficient changes.

차세대 분산형 고속열차의 후미진동 저감에 관한 연구

본 연구는 차세대 분산형 고속전철 시제차량(HEMU-430X)의 후미진동저감에 관한것이다. VAMPIRE 해석을 통한 주행거동 관찰에서 HEMU-430X는 전두부 유선형 형상유지를 위하여 설치된 한방향 요댐퍼 때문에 후미차량에서 횡방향 진동이 예상되었으며, 430km/h에서 기준치를 초과하는 경우가 있었다. 이 후미진동을 감소시키기 위하여 차륜답면 형상변경, 횡댐퍼 댐핑계수조정, 요댐퍼 계수조정 등 다양한 방법을 시도하였으나 후미진동이 없어지지 않았다. 최종적으로 요댐퍼를 양방향으로 바꾸었을 때 횡방향 진동이 사라졌다. 실제 시운전에서는 150km/h로 주행하였을 때 횡방향 후미진동이 나타났으며, 요댐퍼를 양방향으로 바꾸어 300km/h 주행 시에도 후미진동이 나타나지 않았다. 추후 430km/h까지 최고속도시험을 수행할 예정인데 높은 속도에서 후미진동이 다시 발생한다면 본 연구에서 제시한 차륜답면 형상변화, 횡댐퍼 계수 조정 등의 방법을 이용해서 진동을 저감시킬 수 있을 것이다. This study describes the tail vibration reduction for the next generation high speed EMU(HEMU-430X). The model of 6 cars was generated and the calculation was performed using VAMPIRE(railway vehicle dynamic software). In view of ride characteristics, HEMU-430X was expected to sway at the tail because of the yaw damper direction. The lateral acceleration of vehicle body exceeded the criteria because of hunting. To reduce this hunting motion, some methods such as wheel profile change, the change of damping coefficient for the 2nd lateral damper, the damping coefficient change of yaw damper were tested, but had little effect. Finally, the yaw damper direction was changed and the tail vibration disappeared. In real running test, the tail vibration appeared at the speed of 150km/h and the yaw damper direction change made the vehicle stable at the speed of 300km/h. The maximum test speed of HEMU-430X is 430km/h. If the tail vibration appears at higher speed, some other methods in this study may be considered to reduce it.

Quarter Car Suspension System With One Degree Of Freedom Simulated Using Simulink

Abstract Simulate the behavior of a quarter car suspension system with Simulink®. Consider only vertical movement of the car, neglecting roll and pitch. All movements of the car axes are modeled as having equal amplitude. The characteristic equations that describe the behavior of dynamical systems based on FBD (Free Body Diagram) of automotive suspension. We make the simulation model in six steps. In simulation we consider the damping coefficient, c, variable. The rest of parameters are constant (mass, speed and stiffness). The simulation parametrs are defined in Mathlab®. We follow the final signal created on the oscilloscope. At the end of the study, we concluded the effect of damping coefficient changes over the comfort.

Measurement of Leak Rate for MEMS Vacuum Packaging

Many Micro-Electro-Mechanical Systems (MEMS) devices such as accelerators, gyroscopes, uncooled infrared sensors, etc., require vacuum packaging. The vacuum maintaining lifetime directly determines the vacuum packaging reliability. This research presented a quantitative analysis of the relationship between the leak rate and the vacuum maintaining lifetime, and demonstrated that the leak rate measurement plays an important role. This paper also explored the application limitations in vacuum packaging using a helium spectrometer leak tester to measure the leak rate because the measured leak rate was nonlinear with respect to the actual leak size. According to the fact that the damping coefficient changes with the pressure, a tuning fork crystal chip as a pressure sensor was used to monitor the pressure changes in the package cavity. The leak conductance was also calculated from the pressure tracking data to analyze the leak modes; the molecular flow model and gas desorption model were found to fit the measurement results of leak conductance.

Study of the damping characteristics of sectional flight vehicles of different length

The dependence of the damping characteristics of axisymmetric tri-sectional flight vehicles executing plane oscillations about the zero angle of attack on their geometric parameters is investigated on the supersonic range of uniform oncoming air flow Mach numbers. Systematic data are obtained using the least laborious approach, namely, by calculating the steady-state inviscid flow past equivalent bodies determined from the principle of the local similarity of force interaction. Ranges of the vehicle design parameters on which the dependence of the damping moment coefficient in pitch on the length of the conical or cylindrical-conical stabilizer of the vehicle is nonmonotonic are found. Typical viscosity effects on the characteristics under study are estimated using a method based on the assumptions of the linear theory for finite-thickness bodies. It is established that the damping coefficient increases monotonically with decreasing Reynolds number; moreover, even transition to oscillation antidumping regimes is possible when the sign of the damping coefficient changes.

Control Effect for 20-Story Benchmark Building Using Passive or Semiactive Device

In this paper, we study the control effect for a 20-story benchmark building and apply passive and semiactive control devices to the building. First, we take viscous damping walls as a passive control device which consists of two outer plates and one inner plate, facing each other with a small gap filled with viscous fluid. The damping force is related to the interstory velocity, temperature, and the shearing area. Next, we take a variable oil damper as a semiactive control device which can produce the control forces by little electrical power. We propose a damper model in which the damping coefficient changes according to the response of the damper and control forces calculated by the controller based on a linear quadratic Gaussian control theory. It is demonstrated from the results of some simulations that both passive device and semiactive device can effectively reduce the response of the structure in various earthquake motions.

An Experimental Study on Improvement of a Passive Type Superconducting Magnetic Bearing System.

This paper describes the improvement of dynamics for a passive type superconducting magnetic bearing (SMB) system. The SMB system is composed of a pair of SMB's with high Tc (critical temperature) superconductors, and a rotor with some permanent magnets. The rotor is passively supported by the SMB's without any control mechanism. The superconductors of the SMB's were field-cooled in the experiments. After the superconductors were cooled, the bearing housings of the SMB's were forced to change in the axial direction. Then, the stiffness change and damping coefficient change resulting from the housing displacements were investigated. From the experimental results, it is found that the static stiffness is related to the dynamic stiffness, and that the stiffness and the coefficient change according to the housing displacements. The rotor displacement and the rotation angle near the resonance rotation speeds also change according to the housing displacements. These results show that the stifiness and the damping coefficient of the SMB system can be adjusted using the housing displacements.