Search

Legged robots have the advantage of strong terrain adaptability in lunar exploration. A new robust controller is designed for axial flux permanent magnet motors applied on the legged lunar robots to diminish the disturbance from uncertainty and external circumstance. The theoretical verification is carried out through Lyapunov stability theory. The numerical simulation and real-time experiment are carried out to access the stability and dynamic property of the systems adopting the proposed controller. The results are compared with the traditional control strategies to demonstrate the advantages of the proposed controller. The new robust controller contributes to the dynamic stability of legged lunar robots and is also appropriate for the similar mechanical systems. [ABSTRACT FROM AUTHOR]

To improve the efficiency of conventional isolation trench and lighten the impact of the excavation on neighbor buildings, a novel high damping isolation trench is proposed. The viscoelastic braces equipped in the high damping isolation trench can dissipate the energy of ground-borne vibration while providing supporting force to ensure the stability of the soil on both sides. According to two actual ancient buildings, two types of high damping isolation trenchs with the plane shape of U and L are designed to solve the potential damages caused by long-term train-induced vibration. First, three-dimensional finite/infinite models based on these two buildings are established, respectively. Then, the energy dissipation characteristics are obtained by experiments. Through calculation, the control effects of the high damping isolation trenchs for these two buildings are investigated. The results indicate that the viscoelastic braces possess high energy dissipation capacity. After setting the high damping isolation trenchs around the structures, even at a small excavation depth, the acceleration and velocity responses of the two buildings are reduced significantly. Furthermore, the selected U-shaped and L-shaped trenches also show superiority compared with the conventional linear-shaped trench in this project. [ABSTRACT FROM AUTHOR]

Experimental results show that mechanical behaviors of viscoelastic dampers are greatly affected by ambient temperature. Neglecting the ambient temperature effect will lead to an inaccurate seismic evaluation on viscoelastically damped structures. This study investigates the ambient temperature effect on the seismic performance of viscoelastically damped structures. An efficient algorithm is proposed to solve the seismic response of viscoelastically damped structures at different ambient temperatures based on the time–temperature correspondence. Numerical simulations of a ten-story viscoelastically damped steel frame under historical earthquakes are presented to illustrate the ambient temperature effect on the seismic performance. The results show that the natural frequency decreases with the increase in ambient temperature, whereas the damping ratio change with ambient temperature greatly depends on the viscoelastic damper properties. The seismic displacement reduction, in general, decreases with the increase in ambient temperature. The seismic acceleration reduction with ambient temperature is affected by the viscoelastic damper properties, structural parameters, and earthquakes together. [ABSTRACT FROM AUTHOR]

Asymmetric structures experience torsional effects when subjected to seismic excitation. The resulting rotation will further aggravate the damage of the structure. A mathematical model is developed to study the translation and rotation response of the structure during seismic excitation. The motion equations of the structures which cover the translation and rotation are obtained by the theoretical derivations and calculations. Through the simulated computation, the translation and rotation response of the structure with the uncontrolled system, the tuned mass damper control system, and active tuned mass damper control system using linear quadratic regulator algorithm are compared to verify the effectiveness of the proposed active control system. In addition, the linear quadratic regulator and fuzzy neural network algorithm are used to the active tuned mass damper control system as a contrast group to study the response of the structure with different active control method. It can be concluded that the structure response has a significant reduction by using active tuned mass damper control system. Furthermore, it can be also found that fuzzy neural network algorithm can replace the linear quadratic regulator algorithm in an active control system. Because fuzzy neural network algorithm can control the process on an uncertain mathematical model, it has more potential in practical applications than the linear quadratic regulator control method. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to investigate the contribution of viscoelastic material (VEM) to the control performance of the viscoelastic tuned mass damper (VTMD). Firstly, the equivalent fractional derivation Kelvin model is used to describe the frequency dependence of viscoelasticity in VTMD, and an index is proposed to characterize the level of frequency dependence. Then the effects of the high loss factor of VEM and frequency dependence of viscoelasticity on the effectiveness and robustness of VTMD control are analyzed by numerical examples. At last, a design strategy for VTMD is proposed to select the type of VEM and optimize its stiffness contribution. The results show that the frequency dependence of shear storage modulus of VEM is beneficial to further reduce the dynamic response of the primary structure equipped with VTMD, and the loss factor of VEM determines the optimum frequency ratio and control effect of VTMD. Compared to the conventional tuned mass damper, VTMD has a better robustness for the positive error of the natural frequency of VTMD but has a worse robustness for the negative error. The frequency dependence of shear storage modulus of VEM is beneficial to the robustness of VTMD for both the positive and negative errors of the natural frequency of the primary structure. The VEM with a strong frequency dependence of shear storage modulus is the ideal VEM for VTMD, and the proposed design strategy can deal with the trade-off between the control effectiveness and control robustness of VTMD. [ABSTRACT FROM AUTHOR]

A new viscoelastic micro-vibration isolation and mitigation platform is proposed to reduce disturbances generated by flywheels on board spacecraft. Firstly, property tests on the high-damping viscoelastic material used in the micro-vibration isolation and mitigation element are conducted. Experimental results show that the developed viscoelastic material has better energy dissipation capability under micro-vibration conditions. A mathematic model is employed to describe the dynamic properties of the high-damping viscoelastic material and is used to model the isolation and mitigation element. Secondly, a viscoelastic micro-vibration isolation and mitigation platform, which consists of four elements, is proposed and the analytical model of the coupled system that consists of the platform with flywheel is established. Finally, the isolation and mitigation performances of this micro-vibration isolation and mitigation platform are analyzed and discussed. The results show that the isolation and mitigation platform can effectively reduce the micro-vibration disturbances induced by the flywheel. [ABSTRACT FROM AUTHOR]

In this paper, tests on viscoelastic (VE) dampers are carried out, and the results indicate that VE dampers have high energy dissipation capacity and excellent anti-fatigue properties. To clarify the mechanical properties of VE dampers, a new mathematical model, named the equivalent fractional Kelvin model, which considers temperature and frequency effects simultaneously, is proposed. The numerical results using this model are in good agreement with experimental results. Then, through analysis on a five-story reinforced concrete frame structure with and without VE dampers, it is found that the seismic responses of the structure with VE dampers are significantly reduced and VE dampers have high energy dissipation capacity. [ABSTRACT FROM AUTHOR]

A multi-dimensional earthquake isolation and mitigation device for long-span reticulated structures is a type of newly invented passive control device. In order to acquire the earthquake isolation and mitigation effect of the new devices on long-span reticulated structures under horizontal excitations, the pseudo-dynamic tests for a 1:3 modeled long-span reticulated structure with a size of 3 m × 3 m with and without the devices are carried out. Horizontal dynamic responses of the structure with and without the devices are compared, and the earthquake isolation and mitigation effect of the devices is evaluated under the horizontal excitations. It can be shown from the experimental and finite element numerical results that the proposed new devices have a good effect on earthquake isolation and mitigation on long-span reticulated structures under horizontal earthquake excitations. [ABSTRACT FROM PUBLISHER]

The multi-dimensional earthquake isolation and mitigation device (MEIMD) for long-span reticulated structures is a newly invented passive vibration control device. In order to explore the vertical earthquake isolation and mitigation ability of the device, vertical pseudo-dynamic tests on a 1:3 scaled long-span reticulated structure with and without devices are carried out. In the tests, dynamic responses of the structure with the devices are compared with those without the devices under different earthquake waves. It can be seen from experimental results that the devices can obviously reduce the displacement, acceleration, and members’ strain responses of a long-span reticulated structure. Moreover, the finite element analyses are also performed to verify the seismic reduction effect of MEIMD. The numerical results fit well with the experimental results and this indicates that the finite element analysis has high simulation precision. [ABSTRACT FROM AUTHOR]

The earthquake excitation is a complicated multidimensional motion, which will cause the damage or even collapse of structures. Consequently, some measures to prevent structure failure must be taken under multidimensional excitations, especially for long-span reticulated structures and high-rise buildings. Many earthquake isolation or mitigation devices have been manufactured to reduce the horizontal dynamic responses of structures, but there are few reports concerning the device isolating and mitigating earthquake actions both in horizontal and vertical directions simultaneously. In this paper, a new multidimensional earthquake isolation and mitigation device for long-span reticulated structures is developed and tested under different cases. Effects of excitation frequency and amplitude on vertical properties of this device are studied. Then, the modified equivalent standard solid model is proposed to describe the vertical properties of the device. Experimental and numerical studies show that this device has good capability of energy dissipation in vertical direction. [ABSTRACT FROM PUBLISHER]

Earthquake excitation is a kind of complicated multi-dimensional ground motion. Therefore, anti-earthquake measuresfor complex and important engineering structures, such as long-span structures and high rise buildings under multi-dimensional earthquake excitations, have become an extremely important research topic. In this paper, a new multi-dimensional earthquake isolation and mitigation device (MEIMD) is proposed for protecting long-span reticulated structures due to strong earthquake motions. It consists of a viscoelastic bearing and several viscoelastic dampers. Property tests on the MEIMD under different excitation frequencies, excitation amplitudes and vertical pressure forces are carried out. Then, a mathematical simulation is carried out for the equivalent stiffness and the equivalent damping of the device, and the numerical results agree reasonably well with the experimental data. Experimental and numerical results show that the MEIMD has a fine energy dissipation capacity, and can be used for anti-earthquake purposes for long-span reticulated structures. [ABSTRACT FROM PUBLISHER]

Many kinds of dampers are invented to reduce the dynamic responses due to earthquake or strong wind. Viscoelastic damper is a kind of commonly used passive control device for vibration mitigation of structures. Its energy dissipation characteristics are affected by environmental temperature and excitation frequency. In order to describe the complex characteristics of viscoelastic dampers changing with temperature and frequency, a new model — the equivalent standard solid model, which is based on the standard linear solid model and temperature-frequency equivalent theory, is proposed. The comparison results between experimental and numerical data of viscoelastic dampers show that the equivalent standard solid model can precisely describe energy dissipation behavior of viscoelastic dampers under different temperatures and frequencies. At the same time, 52 viscoelastic dampers are applied for seismic retrofit design on Xi’an Petrol Hotel, and the finite analysis for structures with and without dampers are carried out under frequent-earthquake and infrequent-earthquake excitations. The dynamic responses of structures with and without dampers are compared. Analytical results show that viscoelastic dampers can reduce the earthquake responses effectively, and they are high-performance energy dissipation devices. [ABSTRACT FROM PUBLISHER]