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Micro structures of viscoelastic materials (VEM) play an important role in their mechanical properties and energy dissipation capacities. This work shows a mathematical modeling of VEMs considering...

Viscoelastic (VE) dampers are one of the most promising techniques for reducing vibration in engineering structures caused by earthquakes and wind. This work aims to develop a kind of high-...

In this work parameters are optimized for a proposed precision platform with a well-designed vibration isolation and mitigation (VIM) system, in which VIM devices, magnetorheological (MR) dampers and viscoelastic (VE) dampers are adopted to mitigate vibration responses. The optimization method is on the basis of the Non-dominated sorting genetic algorithm (NSGA-II), in which the dynamic responses as well as the maximum damping forces of MR dampers of the platform are chosen as objective functions. The optimization parameters, the constrain conditions and the objective functions are determined in accordance with the characteristics of the VIM system. Finally, a series of Pareto solutions are obtained and one Pareto solution is selected to compare with a preliminarily well designed VIM system. Numerical results show that the optimization method can effectively mitigate the vibration of the precision platform and reduce the maximum control forces of MR dampers simultaneously, which will lead to the miniaturization of MR dampers.

This paper aims to develop viscoelastic dampers, which can effectively suppress vibration in a wide frequency range. First, several viscoelastic materials for damping performance were selected, and different batches of cylindrical viscoelastic dampers were fabricated by overall vulcanization. Second, the dynamic mechanical properties of the cylindrical viscoelastic dampers under different amplitudes and frequencies are tested, and the hysteretic curves under different loading conditions are obtained. Finally, by calculating the dynamic mechanical properties of the cylindrical viscoelastic dampers, the energy dissipation performance of these different batches of viscoelastic dampers is compared and analyzed. The experimental results show that the cylindrical viscoelastic damper presents a full hysteretic curve in a wide frequency range, in which the maximum loss factor can reach 0.57. Besides, the equivalent stiffness, storage modulus, loss factor, and energy consumption per cycle of the viscoelastic damper raise with the frequency increasing, while the equivalent damping decreases with the increase of frequency. When the displacement increases, the energy consumption per cycle of the viscoelastic damper rises rapidly, and the equivalent stiffness, equivalent damping, storage modulus, and loss factor change slightly.

Aiming at the difficult problem of on-site real-time vibration responses monitoring and remote data transmission of the civil engineering structures, based on LabVIEW a remote data acquisition and ...

Viscoelastic dampers are a kind of classical passive energy dissipation and vibration control devices which are widely utilized in engineering fields. The mechanical properties and energy dissipation capacity of the viscoelastic damper are significantly affected by ambient temperature. In this work, dynamic properties tests of the sandwich type viscoelastic damper at different environmental temperatures are carried out. The equivalent fractional Kelvin model which can characterize the mechanical behavior of the viscoelastic damper with varying frequencies and temperatures is introduced to describe the dynamic properties and energy dissipation capability of the sandwich viscoelastic damper. The self-heating phenomenon of the sandwich viscoelastic damper is studied with a numerical simulation, and the dynamic properties and energy dissipation variation of the viscoelastic damper with self-heating processes are also analyzed. The results show that the dynamic properties of the viscoelastic damper are significantly affected by temperature, excitation frequency and the internal self-generated heating.

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.

Multi-dimensional earthquake isolation and mitigation device (MEIMD) is a newly developed structural vibration control device. First, the horizontal and vertical property tests are performed to study the influences of excitation frequency and displacement amplitude on the dynamic properties of the MEIMD. In order to accurately describe the nonlinear characteristics of the device caused by the complex viscoelasticity, an integrated mathematical model based on fractional-derivative equivalent standard solid model is then proposed. Next, the horizontal and vertical shaking table tests on a 1/5-scale three-story steel frame structure equipped with and without the MEIMDs are presented, respectively. Finally, a dynamic response analysis method considering the nonlinearity of the MEIMD is proposed to analyze the dynamic responses of the controlled structure. The analysis results show that the MEIMD can provide excellent horizontal isolation ability, and good vertical isolation performance can be achieved through selecting reasonable pre-pressure value of the springs. The proposed mathematical model and dynamic response analysis method can effectively describe the nonlinearity of the MEIMDs and the structure with MEIMDs.

In the present paper, several dynamic properties tests of the viscoelastic damper at -5oC are conducted under different frequencies and displacements to investigate the dynamic behavior of the viscoelastic damper at low temperature. The seven-parameter fractional derivative model is modified with the temperature-frequency equivalent principle and utilized to describe the dynamic properties of the viscoelastic damper. The 9050A and ZN22 viscoelastic materials are used to verify the modified seven-parameter fractional derivative model. The experimental and numerical results reveal that the viscoelastic damper has perfect energy dissipation capacity at low temperature, and the modified seven-parameter fractional derivative model can well capture the dynamic behavior of viscoelastic materials and dampers.

Harmful vibrations can cause many engineering problems, such as disasters of civil engineering structures, failure of precision equipment, and the disruption of some spacecraft components. In most situations, the vibrations are usually three-dimensional excitations. Therefore, research on multi-dimensional vibration control has become a world-wide hotspot in engineering. This article presents a comprehensive assessment of recent developments of multi-dimensional vibration mitigation devices and the material applied in such devices. The vibration mitigation materials mainly include the passive vibration mitigation materials and smart vibration mitigation materials. Subsequently, the vibration mitigation devices in civil engineering, mechanical engineering, and aerospace engineering are reviewed and commented, respectively. Above all, the multi-dimensional vibration mitigation devices and materials are found to be effective for reducing multi-dimensional vibrations. However, enhancing the mitigation performance of the devices in each direction, including improving the mitigation capability of materials, is still a challenging issue.

Viscoelastic materials are a kind of representative passive vibration control materials with many applications in civil engineering for earthquake mitigation in building structures, and these materials often serve in a thermo-elastic coupling environment. In this work, a one-dimensional magneto-thermoviscoelastic problem of a single-layer viscoelastic plate is investigated with memory-dependent derivative and nonlocal effect in the context of generalized thermo-elasticity. The plate is placed in a magnetic field, and the upper surface is subjected to a thermal shock. The governing equations for the single-layer plate are formulated considering the time delay and the kernel function of the memory-dependent derivative, nonlocal effect, temperature-dependent properties, and magnetic field. The Laplace transform and its numerical inversion are employed to solve this problem. The nondimensional temperature, displacement, and stress are calculated and presented graphically. Based on the numerical results, the influence of time delay and kernel function of the memory-dependent derivative, nonlocal effect parameters, temperature-dependent properties, and magnetic field parameters on the distributions of the nondimensional temperature, displacement, and stress are discussed.

Viscoelastic dampers are one of the most popular earthquake mitigation devices for building structures with a large number of applications in civil engineering. The seismic performance of viscoelastic dampers is greatly affected by viscoelastic materials. The present paper addresses the theoretical and experimental studies of the viscoelastic damper. The regular polyhedron chain network models for viscoelastic materials are proposed based on the molecular chain network microstructures and the temperature–frequency equivalent principle. Several dynamic property tests for the viscoelastic damper at different temperatures, frequencies, and displacements are carried out, and the proposed models are verified by comparing the numerical and experimental results. The comparisons show that the viscoelastic damper has perfect energy dissipation capacity, and the regular polyhedron chain network models can well describe the mechanical properties of the viscoelastic damper at different environmental temperatures and excitation frequencies.

The bridge stay cable, one of the most critical components in cable-stayed bridges, is vulnerable to vibrations owing to its low inherent damping capacity. Thus effective vibration control technology for bridge stay cables is extremely critical to safe operations of cable-stayed bridges. Several countermeasures have been presented and/or implemented to mitigate this vibration; however the passive method can only add a small amount of damping to the cables, excessive energy demand of active control devices severely limits its practicality, the semi-active control methods still have the drawbacks of complex state estimation module and a large amount of control algorithm calculation. This paper proposes a practical magnetorheological pseudo negative stiffness (MR-PNS) control system coupled with control strategy for bridge stay cables. The current reference point is introduced in the dynamic modeling of the MR-PNS control system to characterize the current control strategy. This paper investigates the adjustable of MR-PNS control system performance and energy consumption caused by different current strategies. Taking the vibration control of the Nanjing Second Yangtze River Bridge J20 cable as an example, the simulation results highlight the advantages of the MR-PNS control system that the failure area is small, the quasi-optimal area is wide, and it can still keep sort of vibration damping performance in the degenerate area. The model cable vibration control test proves the feasibility and efficiency of the single input MR-PNS bridge stay cables control method.

In research on damage identification, conventional methods usually face difficulties in converging globally and rapidly. Therefore, a fast in-time damage identification approach based on the Kalman filter and energy equilibrium theory is proposed to obtain the structural stiffness, find the locations of damage, and quantify its intensity. The proposed approach establishes a relationship between the structural stiffness and acceleration response by means of energy equilibrium theory. After importing the structural energy into the Kalman filter algorithm, unknown parameters of the structure can be obtained by comparing the predicted energy and the measured energy in each time step. Numerical verification on a highway sign support truss with and without damage indicates that the updated Young’s modulus can converge to the true value rapidly, even under the effects of external noise excitation. In addition, the calculation time taken for each step of the approach is considerably shorter than the sampling period (1/256 s), which means that, this approach can be implemented in-time and on-line.

The earthquake excitation is a kind of complicated multi-dimensional motion. It is not safe and accurate enough if only considering the horizontal earthquake excitation, especially for complex and important engineering structures. Therefore, anti-earthquake measures for engineering structures considering multi-dimensional excitations have become an extremely important research topic. In this paper, a new multi-dimensional earthquake isolation and mitigation device (MEIMD) is developed and tested under different cases at both horizontal and vertical directions. Effects of excitation frequency and displacement amplitude on both horizontal and vertical properties of this device are considered. At the same time, a modified equivalent standard solid model is proposed, which can effectively describe the effects of frequency and displacement on the horizontal and vertical properties of the device. Research indicates that the MEIMD possesses high-energy dissipation capacity at both horizontal and vertical directions and the proposed model can accurately simulate the value of the storage modulus and the loss factor.

In order to investigate the collapse mode of double-layer space trusses, the whole collapse process is simulated by the explicit finite element methods. The calculation results indicate that horizontal earthquake and vertical earthquake waves will lead to two typical collapse modes of the structure. The collapse mode of the structure under horizontal earthquake are mainly strength failure, which is characterized by the failure of members connected to the columns; the collapse mode of the structure under vertical earthquake are mainly dynamic instability, which is characterized by the V shape deformation. The analytical results agree with the experimental results.

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.

Earthquake is a complex multi-dimensional excitation. Counter-measures of such multi-dimensional excitation on many critical structures, such as long-span structures and high-rise buildings, must be taken into account to avert the structural failure. Many types of earthquake mitigation or isolation devices for mitigating earthquake-induced effects in the horizontal direction have been proposed and applied to real applications. However, study on multi-dimensional earthquake isolation and mitigation devices for structures has been received much less attention. In this paper, a new multi-dimensional earthquake isolation and mitigation device was developed and tested. Effects of excitation frequency and environmental temperature on horizontal properties of this device were considered. At the same time, fatigue properties of the device under different amplitude horizontal excitations were also studied experimentally. The equivalent standard solid model which can effectively describe the effect of frequency and temperature on the horizontal properties of the device was proposed and verified. From the experimental results, it may be concluded that the multi-dimensional earthquake isolation and mitigation device owns fine energy dissipation and fatigue resistance capabilities.

The collapse processes of three typical long-span reticulated shell structures were simulated using nonlinear dynamic finite element analysis under strong seismic excitations. The plastic kinematic hardening model, which considers failure stain, was adopted for simulating steel. Both geometric and contact nonlinearities were considered in this study. The three failure states—i.e., dynamic local bucking, dynamic overall buckling, and whole collapse—were identified in accordance with the analysis results. Taking the Schwedler reticulated shell structure as an example, seismic waves were applied to the structure in three directions. The critical loads were obtained by the incremental dynamic analysis method (IDAM), and some critical state indices were obtained according to the dynamic responses. The results showed that all the critical indices need to be considered simultaneously in order to judge the dynamic collapse states.

The semi-active control technology has been paid more attention in the field of structural vibration control due to its high controllability, excellent control effect and low power requirement. When semi-active control device are used for vibration control, some challenges must be taken into account, such as the reliability and the control strategy of the device. This study presents a new large tonnage compound lead extrusion magnetorheological (CLEMR) damper, whose mathematical model is introduced to describe the variation of damping force with current and velocity. Then a current controller based on the fuzzy logic control strategy is designed to determine control currents of the CLEMR dampers rapidly. A ten-floor frame structure with CLEMR dampers using the fuzzy logic control strategy is built and calculated by using MATLAB. Calculation results show that CLEMR dampers can reduce the seismic responses of structures effectively. Calculation results of the fuzzy logic control strategy are compared with those of the semi-active limit Hrovat control structure, the passive-off control structure, and the uncontrolled structure. Comparison results show that the fuzzy logic control strategy can determine control currents of CLEMR dampers quickly and can reduce seismic responses of the structures more effectively than the passive-off control strategy and the uncontrolled structure.