Meifal Rusli

Performance of Micro-Hole Drilling by Ultrasonic-Assisted Electro-Chemical Discharge Machining

Electro-chemical discharge machining (ECDM) is one of nontraditional processes for micro-fabrication of non-conductive materials. A high applied voltage is preferable to form a gas film and to generate discharge in the film. However, accumulation of discharge heat often causes cracks of the surface because non-conductive materials have low heat conductivity. In this study, the effect of ultrasonic vibration and the electrolyte level on the performance of gravity-feed drilling by ECDM was investigated. Ultrasonic vibration was applied to a glass plate. A tungsten rod as a tool electrode was fed by gravity. Ultrasonic vibration changed the discharge behavior and improved electrolyte circulation. Although high amplitude ultrasonic vibration caused very dense and wide current pulses consistently during machining process, it decreased removal rate significantly. In addition, electrolyte levels affect single bubble size and the resistance in the electrolyte. Low electrolyte level will cause higher resistance, and higher temperature of the tool electrode and workpiece. A high bias current flew at a low electrolyte level without ultrasonic vibration. In this case, removal rate decreased and surface integrity was improved.

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.

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.

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.