Lovely Son

Experiment of Shock Vibration Control Using Active Momentum Exchange Impact Damper

In the authors’ previous study, we proposed a novel shock vibration control method using the active momentum exchange impact damper (AMEID). By using this method, the shock vibration of the vibratory system is greatly reduced by transferring part of its momentum to the damper mass. This feature is effective for suppressing the first large peak value of the acceleration response due to a shock load. However, the validity of AMEID for actual implementations has not yet been investigated. In this paper, the active control of shock vibration using AMEID under real conditions is evaluated by simulation and experiment. A one-degree-of-freedom vibratory system is used as the controlled object. The controller is designed using the linear quadratic regulator optimal control theory. Reductions in the acceleration response and transmitted force to the base are investigated using simulations. Experiments are carried out to verify the simulation results.

Dynamic Vibration Absorber for Squeal Noise Suppression in Simple Model Structures

In recent research it was found that squeal noise caused by friction-induced vibration can result in mode coupling instability. Presently, there is no method that can be reliably used to eliminate this kind of noise. This paper is focused on the use of dynamic vibration absorbers (DVAs) to suppress the generation of squeal noise. The performance of the DVA is investigated numerically for two simple cases, i.e. a simple two-degree of freedom model, and an L-shape space frame. It is found that the DVA can be applied to shifting or reducing the unstable region of mode coupling, by which the unstable region is removed from the operating condition. Particularly, the addition of the DVA in horizontal direction on the near-point-of-friction can possibly avoid unstable mode coupling. However, the addition in vertical direction will increase the possibility of squeal noise incident. Moreover, a high frequency DVA in horizontal direction at the near-point-of-friction shifts the unstable region into higher normal contact stiffness and higher friction coefficient. Consequently, addition of a mass with very stiff spring or a rigid mass in the horizontal direction can prevent the occurrence of unstable mode coupling, as long as it is not coupled with the vertical direction. If the added mass affects the dynamic behaviors in both vertical and horizontal directions, squeal noise in the original normal contact stiffness can still occur.

Proposal of active momentum exchange impact damper and its application to floor shock vibration control

The momentum exchange impact damper (MEID) has already proposed for reducing the shock vibration of the floor. In the MEID, the shock energy of the floor is suppressed by transferring a part of its kinetic energy to the damper mass during collision time. In this study, an active shock control using the momentum exchange impact damper (AMEID) and its application to reducing shock vibration of the floor is proposed. The floor is modeled as a one-degree-of-freedom system. The actuator is installed between the contact spring and the damper mass. A linear motor is assumed as the actuator. The LQR optimal control is applied to design the controller of AMEID. It is verified that the performance of AMEID is not affected by the mass ratio between the impact damper mass and the floor mass. In addition, the performance of AMEID is compared with the conventional passive momentum exchange impact damper (PMEID) and the conventional active control method in reducing the floor shock vibration. It is shown that the shock reduction performance obtained by AMEID is larger than that obtained by PMEID. Furthermore, the transmitted force obtained by AMEID is smaller than that of the conventional active control.

Response Reduction of Two DOF Shear Structure Using TMD and TLCD by Considering Absorber Space Limit and Fluid Motion

A Combination of dynamic vibration absorbers (DVAs) consist of Tuned Mass Damper (TMD) and Tuned Liquid Column Damper (TLCD) for reducing vibration response of a two-DOF shear structure model is proposed. The absorber parameters are optimized using Genetic Algorithm (GA). The cost function is derived from the ratio between structure response and the excitation signal. The limitation in absorber space and fluid motion are considered during optimization process. The simulation results show that GA optimization procedure is effective to get the optimal absorber parameters in the case of limited absorber size and motion.

The influence of TLCD junction angle on the structure response with TLCD

A Tuned Liquid column Damper (TLCD) performance depends on the TLCD natural frequency and damping ratio. Theoretically, the TLCD natural frequency is determined by its dimension and the length of fluid inside TLCD column. The damping ratio of TLCD is influenced by several factors such as friction between the fluid and TLCD column, TLCD junction angle and a built-in orifice plate with a small opening. In this research, the effect of TLCD junction angle to its performance in reducing the structural response is evaluated by varying the TLCD angle from 30° to 90°. An experimental model of two DOF shear structure with TLCD is governed to evaluate the TLCD performance. The experimental results show that a TLCD with junction angle 60° filled with 325 ml water is better than others in reducing the vibration response of a two DOF shear structure.A Tuned Liquid column Damper (TLCD) performance depends on the TLCD natural frequency and damping ratio. Theoretically, the TLCD natural frequency is determined by its dimension and the length of fluid inside TLCD column. The damping ratio of TLCD is influenced by several factors such as friction between the fluid and TLCD column, TLCD junction angle and a built-in orifice plate with a small opening. In this research, the effect of TLCD junction angle to its performance in reducing the structural response is evaluated by varying the TLCD angle from 30° to 90°. An experimental model of two DOF shear structure with TLCD is governed to evaluate the TLCD performance. The experimental results show that a TLCD with junction angle 60° filled with 325 ml water is better than others in reducing the vibration response of a two DOF shear structure.

A new concept for UAV landing gear shock vibration control using pre-straining spring momentum exchange impact damper

This study proposes a new method for reducing the shock vibration response of an Unmanned Aerial Vehicle (UAV) during the landing process by means of the momentum exchange principle (MEID). The performance of the impact damper is improved by adding a pre-straining spring to the damper system. This research discusses the theoretical application of the damper to the UAV landing gear system. The UAV dynamics is first modeled as a simple lumped mass translational vibration system. Then we analyze a more complex two-dimensional model of UAV dynamics. This model consists of the main wheel, nose wheel and main body. Three cases of UAV landing gear mechanisms: without damper, with passive MEID (PMEID) and with pre-straining spring MEID (PSMEID) are simulated. The damper performance is evaluated from the maximum acceleration and force transmission to the main body. The energy balance calculation is conducted to investigate the performance of PSMEID. The simulation results show that the proposed PSMEID method is the most effective method for reducing the maximum acceleration and force transmission of UAV during impact landing.