Novel exact solutions of one-dimensional transient dynamic piezoelectric problems for thickness polarized layers and disks, or length polarized rods, are obtained. The solutions are derived using a time-domain Green’...Novel exact solutions of one-dimensional transient dynamic piezoelectric problems for thickness polarized layers and disks, or length polarized rods, are obtained. The solutions are derived using a time-domain Green’s function method that leads to an exact analytical recursive procedure which is applicable for a wide variety of boundary conditions including nonlinear cases. A nonlinear damper boundary condition is considered in more detail. The corresponding nonlinear relationship between stresses and velocities at a current time moment is used in the recursive procedure. In addition to the exact recursive procedure that is effective for calculations, some new practically important explicit exact solutions are presented. Several examples of the time behavior of the output electric potential difference are given to illustrate the effectiveness of the proposed exact approach.展开更多
Optimal design theory for linear tuned mass dampers （TMD） has been thoroughly investigated, but is still under development for nonlinear TMDs. In this paper, optimization procedures in the time domain are proposed f...Optimal design theory for linear tuned mass dampers （TMD） has been thoroughly investigated, but is still under development for nonlinear TMDs. In this paper, optimization procedures in the time domain are proposed for design of a TMD with nonlinear viscous damping. A dynamic analysis of a structure implemented with a nonlinear TMD is conducted first. Optimum design parameters for the nonlinear TMD are searched using an optimization method to minimize the performance index. The feasibility of the proposed optimization method is illustrated numerically by using the Taipei 101 structure implemented with TMD. The sensitivity analysis shows that the performance index is less sensitive to the damping coefficient than to the frequency ratio. Time history analysis is conducted using the Taipei 101 structure implemented with different TMDs under wind excitation. For both linear and nonlinear TMDs, the comfort requirements for building occupants are satisfied as long as the TMD is properly designed. It was found that as the damping exponent increases, the relative displacement of the TMD decreases but the damping force increases.展开更多
Tension cables are easily prone to generating varied vibrations under the action of external loads, which adversely affects the safety of bridges. Therefore, it is necessary to take effective measures to suppress the ...Tension cables are easily prone to generating varied vibrations under the action of external loads, which adversely affects the safety of bridges. Therefore, it is necessary to take effective measures to suppress the vibrations of tension cables. Cable end dampers are widely used in vibration reduction for cable-stayed bridges due to their convenient installation and low costs. However, the previous studies on the tension cable-viscous damper systems mostly adopt the linear method, and the weakening effect of the flexibility of mounting brackets on the damper vibration reduction is not sufficiently taken into account. Therefore, this paper adopts the improved Kelvin model to conduct the derivation, solution, and parametric analysis of vibration equations for the stay cable-nonlinear viscous damper systems. The results of parametric analysis show that the maximum modal damping ratio that can be obtained by cables and the corresponding optimal damping coefficient of dampers are correlated with the damping nonlinear coefficient α, stiffness nonlinear coefficient β, vibration order n, installation position a/L, and stiffness coefficient μ, etc.;among them, n damping nonlinear coefficient α and stiffness nonlinear coefficient β are the key parameters that affect the parameter design of dampers, where damping nonlinear coefficient α mainly controls the optimal damping coefficient and stiffness nonlinear coefficient β mainly controls the maximum damping ratio. Based on the parametric analysis, the design principles of dampers and value requirements of key parameters under different vibration suppression objectives are presented.展开更多
Due to their intrinsically nonlinear characteristics,development of control strategies that are implementable and can fully utilize the capabilities of semiactive control devices is an important and challenging task.I...Due to their intrinsically nonlinear characteristics,development of control strategies that are implementable and can fully utilize the capabilities of semiactive control devices is an important and challenging task.In this study,two control strategies are proposed for protecting buildings against dynamic hazards,such as severe earthquakes and strong winds,using one of the most promising semiactive control devices,the magnetorheological (MR) damper.The first control strategy is implemented by introducing an inverse neural network (NN) model of the MR damper.These NN models provide direct estimation of the voltage that is required to produce a target control force calculated from some optimal control algorithms.The major objective of this research is to provide an effective means for implementation of the MR damper with existing control algorithms.The second control strategy involves the design of a fuzzy controller and an adaptation law.The control objective is to minimize the difference between some desirable responses and the response of the combined system by adaptively adjusting the MR damper.The use of the adaptation law eliminates the need to acquire characteristics of the combined system in advance. Because the control strategy based on the combination of the fuzzy controller and the adaptation law doesn't require a prior knowledge of the combined building-damper system,this approach provides a robust control strategy that can be used to protect nonlinear or uncertain structures subjected to random loads.展开更多
According to the structural characteristics of embedded fluid elastomeric damper and dynamic modeling method of bearingless rotor(BR)system,a time-domain dynamic model based on multilayer elastomeric theory and fluid ...According to the structural characteristics of embedded fluid elastomeric damper and dynamic modeling method of bearingless rotor(BR)system,a time-domain dynamic model based on multilayer elastomeric theory and fluid dynamic equations is developed.The parameters contained in the analysis model are identified by dynamic experiment data of embedded fluid elastomeric damper.The dynamic characteristics curves calculated through dynamic model are compared with those derived from experimental data.The consistent results illustrate that the model can describe the nonlinear relationship between stress and strain of embedded fluid elastomeric damper under different displacement amplitude and frequency.Due to the validity and reliability of the dynamic analysis model,it can be used in aeroelastic characteristics calculation of BR with embedded fluid elastomeric damper for helicopters.展开更多
A new stochastic optimal control strategy for randomly excited quasi-integrable Hamiltonian systems using magneto-rheological (MR) dampers is proposed. The dynamic be- havior of an MR damper is characterized by the ...A new stochastic optimal control strategy for randomly excited quasi-integrable Hamiltonian systems using magneto-rheological (MR) dampers is proposed. The dynamic be- havior of an MR damper is characterized by the Bouc-Wen hysteretic model. The control force produced by the MR damper is separated into a passive part incorporated in the uncontrolled system and a semi-active part to be determined. The system combining the Bouc-Wen hysteretic force is converted into an equivalent non-hysteretic nonlinear stochastic control system. Then It?o stochastic di?erential equations are derived from the equivalent system by using the stochastic averaging method. A dynamical programming equation for the controlled di?usion processes is established based on the stochastic dynamical programming principle. The non-clipping nonlin- ear optimal control law is obtained for a certain performance index by minimizing the dynamical programming equation. Finally, an example is given to illustrate the application and e?ectiveness of the proposed control strategy.展开更多
To enhance the system damping,a permanent magnet set which served as an eddy current damper was added to the magnetic levitation positioning stage which consists of a moving table,four Halbach permanent magnetic array...To enhance the system damping,a permanent magnet set which served as an eddy current damper was added to the magnetic levitation positioning stage which consists of a moving table,four Halbach permanent magnetic arrays,four stators and displacement sensors.The dynamics model of this stage was a complex nonlinear,strong coupling system which made the control strategy to be a focus research.The nonlinear controller of the system was proposed based on the theory of differential geometry.Both simulation and experimental results show that either the decoupling control of the movement can be realized in horizontal and vertical directions,and the control performance was improved by the damper,verifying the validity and efficiency of this method.展开更多
An analytical model of hydraulic damper was presented in forward flight accounting for pitch/flap/lag kinematic coupling and its nonlinear force-velocity curve. The fourth order Runge-Kutta was applied to calculate th...An analytical model of hydraulic damper was presented in forward flight accounting for pitch/flap/lag kinematic coupling and its nonlinear force-velocity curve. The fourth order Runge-Kutta was applied to calculate the damper axial velocity in time domain. Fourier series based moving block analysis was applied to calculate equivalent linear damping in terms of transient responses of damper axial velocity. Results indicate that equivalent linear damping will be significantly reduced if pitch/flap/lag kinematic coupling introduced for notional model and flight conditions.展开更多
The optimal distribution of fluid viscous dampers（FVD）in controlling the seismic response of eccentric,single-storey,moment resisting concrete structures is investigated using the previously defined center of dampin...The optimal distribution of fluid viscous dampers（FVD）in controlling the seismic response of eccentric,single-storey,moment resisting concrete structures is investigated using the previously defined center of damping constant（CDC）.For this purpose,a number of structural models with different one-way stiffness and strength eccentricities are considered.Extensive nonlinear time history analyses are carried out for various arrangements of FVDs.It is shown that the arrangement of FVDs for controlling the torsional behavior due to asymmetry in the concrete structures is very dependent on the intensity of the peak ground acceleration（PGA）and the extent of the structural stiffness and strength eccentricities.The results indicate that,in the linear range of structural behavior the stiffness eccentricity es which is the main parameter in determining the location of optimal CDC,is found to be less or smaller than the optimal damping constant eccentricity e＊d,i.e.,｜e＊d｜ 〉 ｜es｜.But,in the nonlinear range of structural behavior where the strength eccentricity er is the dominant factor in determining the location of optimal CDC,｜e＊d｜ 〉 ｜er｜.It is also concluded that for the majority of the plan-asymmetric,concrete structures considered in this study with er ≠ 0,the optimal CDC approaches the center of mass as er decreases.展开更多
Professor T. T. Soong is one of the early pioneers in field of earthquake responsc control of structures. A new type of smart damper, which is based on an Energy Dissipating Restraint （EDR）, is presented in this pap...Professor T. T. Soong is one of the early pioneers in field of earthquake responsc control of structures. A new type of smart damper, which is based on an Energy Dissipating Restraint （EDR）, is presented in this paper. The EDR by Nims and Kelly, which has a triangle hysteretic loop, behaves like an active variable stiffness system （AVS） and possesses the basic characteristics of a linear viscous damper but has difficulty in capturing the output and large stroke simultaneously needed for practical applicataions in engineering structures. In order to overcome this limitation, the friction surface in the original Sumitomo EDR is divided into two parts with low and high friction coefficients in this paper. The results of finite element analysis studies show that the new type of smart friction damper enables large friction force in proportion to relative displacement between two ends of the damper and has a large allowable displacement to fit the demands of engineering applications. However, unlike the EDR by Nims and Kelly, this type of friction variable damper cannot self re-center. However, the lateral stiffness can be used to restore the structure. The nonlinear time history analysis of earthquake response for a structure equipped with the proposed friction variable dampers was carried out using the IDARC computer program. The results indicate that the proposed damper can successfully reduce the earthquake response of a structure.展开更多
文摘Novel exact solutions of one-dimensional transient dynamic piezoelectric problems for thickness polarized layers and disks, or length polarized rods, are obtained. The solutions are derived using a time-domain Green’s function method that leads to an exact analytical recursive procedure which is applicable for a wide variety of boundary conditions including nonlinear cases. A nonlinear damper boundary condition is considered in more detail. The corresponding nonlinear relationship between stresses and velocities at a current time moment is used in the recursive procedure. In addition to the exact recursive procedure that is effective for calculations, some new practically important explicit exact solutions are presented. Several examples of the time behavior of the output electric potential difference are given to illustrate the effectiveness of the proposed exact approach.
文摘Optimal design theory for linear tuned mass dampers （TMD） has been thoroughly investigated, but is still under development for nonlinear TMDs. In this paper, optimization procedures in the time domain are proposed for design of a TMD with nonlinear viscous damping. A dynamic analysis of a structure implemented with a nonlinear TMD is conducted first. Optimum design parameters for the nonlinear TMD are searched using an optimization method to minimize the performance index. The feasibility of the proposed optimization method is illustrated numerically by using the Taipei 101 structure implemented with TMD. The sensitivity analysis shows that the performance index is less sensitive to the damping coefficient than to the frequency ratio. Time history analysis is conducted using the Taipei 101 structure implemented with different TMDs under wind excitation. For both linear and nonlinear TMDs, the comfort requirements for building occupants are satisfied as long as the TMD is properly designed. It was found that as the damping exponent increases, the relative displacement of the TMD decreases but the damping force increases.
文摘Tension cables are easily prone to generating varied vibrations under the action of external loads, which adversely affects the safety of bridges. Therefore, it is necessary to take effective measures to suppress the vibrations of tension cables. Cable end dampers are widely used in vibration reduction for cable-stayed bridges due to their convenient installation and low costs. However, the previous studies on the tension cable-viscous damper systems mostly adopt the linear method, and the weakening effect of the flexibility of mounting brackets on the damper vibration reduction is not sufficiently taken into account. Therefore, this paper adopts the improved Kelvin model to conduct the derivation, solution, and parametric analysis of vibration equations for the stay cable-nonlinear viscous damper systems. The results of parametric analysis show that the maximum modal damping ratio that can be obtained by cables and the corresponding optimal damping coefficient of dampers are correlated with the damping nonlinear coefficient α, stiffness nonlinear coefficient β, vibration order n, installation position a/L, and stiffness coefficient μ, etc.;among them, n damping nonlinear coefficient α and stiffness nonlinear coefficient β are the key parameters that affect the parameter design of dampers, where damping nonlinear coefficient α mainly controls the optimal damping coefficient and stiffness nonlinear coefficient β mainly controls the maximum damping ratio. Based on the parametric analysis, the design principles of dampers and value requirements of key parameters under different vibration suppression objectives are presented.
基金Hong Kong Research Grant Council Competitive Earmarked Research Grant HKUST 6218/99Ethe National Science Foundation under grant CMS 99-00234.
文摘Due to their intrinsically nonlinear characteristics,development of control strategies that are implementable and can fully utilize the capabilities of semiactive control devices is an important and challenging task.In this study,two control strategies are proposed for protecting buildings against dynamic hazards,such as severe earthquakes and strong winds,using one of the most promising semiactive control devices,the magnetorheological (MR) damper.The first control strategy is implemented by introducing an inverse neural network (NN) model of the MR damper.These NN models provide direct estimation of the voltage that is required to produce a target control force calculated from some optimal control algorithms.The major objective of this research is to provide an effective means for implementation of the MR damper with existing control algorithms.The second control strategy involves the design of a fuzzy controller and an adaptation law.The control objective is to minimize the difference between some desirable responses and the response of the combined system by adaptively adjusting the MR damper.The use of the adaptation law eliminates the need to acquire characteristics of the combined system in advance. Because the control strategy based on the combination of the fuzzy controller and the adaptation law doesn't require a prior knowledge of the combined building-damper system,this approach provides a robust control strategy that can be used to protect nonlinear or uncertain structures subjected to random loads.
文摘According to the structural characteristics of embedded fluid elastomeric damper and dynamic modeling method of bearingless rotor(BR)system,a time-domain dynamic model based on multilayer elastomeric theory and fluid dynamic equations is developed.The parameters contained in the analysis model are identified by dynamic experiment data of embedded fluid elastomeric damper.The dynamic characteristics curves calculated through dynamic model are compared with those derived from experimental data.The consistent results illustrate that the model can describe the nonlinear relationship between stress and strain of embedded fluid elastomeric damper under different displacement amplitude and frequency.Due to the validity and reliability of the dynamic analysis model,it can be used in aeroelastic characteristics calculation of BR with embedded fluid elastomeric damper for helicopters.
基金Project supported by the Zhejiang Provincial Natural Sciences Foundation (No. 101046) and the foundation fromHong Kong RGC (No. PolyU 5051/02E).
文摘A new stochastic optimal control strategy for randomly excited quasi-integrable Hamiltonian systems using magneto-rheological (MR) dampers is proposed. The dynamic be- havior of an MR damper is characterized by the Bouc-Wen hysteretic model. The control force produced by the MR damper is separated into a passive part incorporated in the uncontrolled system and a semi-active part to be determined. The system combining the Bouc-Wen hysteretic force is converted into an equivalent non-hysteretic nonlinear stochastic control system. Then It?o stochastic di?erential equations are derived from the equivalent system by using the stochastic averaging method. A dynamical programming equation for the controlled di?usion processes is established based on the stochastic dynamical programming principle. The non-clipping nonlin- ear optimal control law is obtained for a certain performance index by minimizing the dynamical programming equation. Finally, an example is given to illustrate the application and e?ectiveness of the proposed control strategy.
基金Supported by the National Natural Science Foundation of China (60674052)
文摘To enhance the system damping,a permanent magnet set which served as an eddy current damper was added to the magnetic levitation positioning stage which consists of a moving table,four Halbach permanent magnetic arrays,four stators and displacement sensors.The dynamics model of this stage was a complex nonlinear,strong coupling system which made the control strategy to be a focus research.The nonlinear controller of the system was proposed based on the theory of differential geometry.Both simulation and experimental results show that either the decoupling control of the movement can be realized in horizontal and vertical directions,and the control performance was improved by the damper,verifying the validity and efficiency of this method.
文摘An analytical model of hydraulic damper was presented in forward flight accounting for pitch/flap/lag kinematic coupling and its nonlinear force-velocity curve. The fourth order Runge-Kutta was applied to calculate the damper axial velocity in time domain. Fourier series based moving block analysis was applied to calculate equivalent linear damping in terms of transient responses of damper axial velocity. Results indicate that equivalent linear damping will be significantly reduced if pitch/flap/lag kinematic coupling introduced for notional model and flight conditions.
文摘The optimal distribution of fluid viscous dampers（FVD）in controlling the seismic response of eccentric,single-storey,moment resisting concrete structures is investigated using the previously defined center of damping constant（CDC）.For this purpose,a number of structural models with different one-way stiffness and strength eccentricities are considered.Extensive nonlinear time history analyses are carried out for various arrangements of FVDs.It is shown that the arrangement of FVDs for controlling the torsional behavior due to asymmetry in the concrete structures is very dependent on the intensity of the peak ground acceleration（PGA）and the extent of the structural stiffness and strength eccentricities.The results indicate that,in the linear range of structural behavior the stiffness eccentricity es which is the main parameter in determining the location of optimal CDC,is found to be less or smaller than the optimal damping constant eccentricity e＊d,i.e.,｜e＊d｜ 〉 ｜es｜.But,in the nonlinear range of structural behavior where the strength eccentricity er is the dominant factor in determining the location of optimal CDC,｜e＊d｜ 〉 ｜er｜.It is also concluded that for the majority of the plan-asymmetric,concrete structures considered in this study with er ≠ 0,the optimal CDC approaches the center of mass as er decreases.
基金National Basic Research Program of China (973 Program) Under Grant No. 2007CB714200
文摘Professor T. T. Soong is one of the early pioneers in field of earthquake responsc control of structures. A new type of smart damper, which is based on an Energy Dissipating Restraint （EDR）, is presented in this paper. The EDR by Nims and Kelly, which has a triangle hysteretic loop, behaves like an active variable stiffness system （AVS） and possesses the basic characteristics of a linear viscous damper but has difficulty in capturing the output and large stroke simultaneously needed for practical applicataions in engineering structures. In order to overcome this limitation, the friction surface in the original Sumitomo EDR is divided into two parts with low and high friction coefficients in this paper. The results of finite element analysis studies show that the new type of smart friction damper enables large friction force in proportion to relative displacement between two ends of the damper and has a large allowable displacement to fit the demands of engineering applications. However, unlike the EDR by Nims and Kelly, this type of friction variable damper cannot self re-center. However, the lateral stiffness can be used to restore the structure. The nonlinear time history analysis of earthquake response for a structure equipped with the proposed friction variable dampers was carried out using the IDARC computer program. The results indicate that the proposed damper can successfully reduce the earthquake response of a structure.
