Young Kong Ahn

Adaptive Vibration Control by a Variable-Damping Dynamic Absorber Using ER Fluid

This paper describes a variable-damping dynamic absorber applying Electrorheological (ER) fluid to the damping element of a conventional-type dynamic absorber. A prototype of variable-damping dynamic absorber was constructed and its performance was verified with a three-story structural model. The special ability of the present dynamic absorber is to reduce the vibration amplitude at several frequencies by a single dynamic absorber. ER fluid is functional fluid whose yield shear stress can be changed by the applied electric field strength. Because of its peculiar property, ER fluid has been applied to various mechanical components such as shock absorbers and engine mounts for vehicles, clutches, valves, etc. One of the practical ways in applying ER fluid to mechanical components may be to expand the performance of conventional mechanical components by combining ER fluid effectively with them. In this sense, this paper shows a successful application of ER fluid to a conventional-type dynamic absorber. An adaptive neural network control system composed of a forward model network for system identification and a controller network was introduced to control the variable-damping element of the dynamic absorber. The numerical simulations show good agreements with the experimental results.

Optimal design of engine mount using an artificial life algorithm

Abstract When designing fluid mounts, design parameters can be varied in order to obtain a desired notch frequency and notch depth. The notch frequency is a function of the mount parameters and is typically selected by the designer to occur at the vibration disturbance frequency. Since the process of choosing these parameters can involve some trial and error, it seems to be a great application for obtaining optimal performance of the mount. Many combinations of parameters are possible to give us the desired notch frequency, but the question is which combination provides the lowest depth? Therefore, an automatic optimal technique is needed to optimize the fluid mount. In this study, the enhanced artificial life algorithm (EALA) is applied to minimizing transmissibility of a fluid mount at the desired notch frequency, and at the notch and resonant frequencies. The present hybrid algorithm is the synthesis of a conventional artificial life algorithm with the random tabu search (R-tabu) method and then, the time for searching optimal solution could be reduced from the conventional artificial life algorithm and its solution accuracy became better. The results show that the performance of the optimized mount by using the hybrid algorithm has been better than that of the conventional fluid mount.

A Small-sized Variable-damping Mount using Magnetorheological Fluid

This paper deals with an application study of a magnetorheological (MR) fluid to a small-sized variable-damping mount for precision equipment of automobiles. MR fluids are a class of functional fluids with a controllable yield stress due to the applied magnetic field strength. A typical MR fluid is a suspension where pure iron particles of 1-20 mm diameter are dispersed in a liquid such as mineral or silicone oil, at a concentration of 20-40 vol%. A variable-damping mount filled with an MR fluid is combined with a magnetic coil at the bottom, and its performance is investigated experimentally and its damping mechanism is estimated analytically.

Optimal design of an engine mount using an enhanced genetic algorithm with simplex method

This study provides an analysis of the applications of optimization routines for designing fluid mounts. After summarizing the concept of fluid mounts and their dynamic characteristics, we review the importance of the notch and resonance peak that occur in dynamic stiffness of fluid mounts. Fluid mounts are tuned for specific application so that their notch frequency coincides with the disturbance frequency, by selecting the proper parameters for the mount. Additionally, the mount parameters are selected such that the notch remains as deep (close to zero) as possible and the resonance peak is kept as short as possible. The notch depth and resonance peak present opposing requirements for the selection of mount parameters in the sense that lowering one will result in increasing the other. Using a bond graph model, this study will evaluate the effect of various parameters on the mount notch depth and resonance peak height characteristics. The results show that different parameters can have a varying effect on the notch frequency and depth, as well as the resonance frequency and peak height. The results of the study are extended by examining the effectiveness of two different optimization methods—namely, the Enhanced Genetic Algorithm (EGA) and Sequential Quadratic Programming (SQP)—for selecting the combination of parameters that can yield the deepest notch and shortest resonance peak. Using two different design cases, the study shows that SQP exhibits much more sensitivity to the initial conditions that are selected for the mount parameters than EGA. Both methods, however, are able to converge to an optimal solution within the constraints that are selected for the parameters. For both cases, EGA is able to converge to the set of parameters that provide a deep notch and a short resonance peak.

Performance Analysis of Magneto-Rheological Mounts

The effect of various parameters for a magneto-rheological (MR) mount on the vibration isolation performance of the mount is studied. The mount that is used for this study incorporates MR fluid in a conventional fluid mount to open and close an inertia track between the fluid chambers of the mount. It has been shown in previous studies that such switching of the inertia track improves the mounts isolation effect by eliminating the large transmissibility peak that commonly exists at frequencies larger than the notch frequency for conventional fluid mounts. A sensitivity analysis is conducted to evaluate the effect of different parameters, such as the rubber stiffness, inertia track, fluid resistance, piston area, and volumetric stiffness on the transmissibility of the mount. The results show that varying the rubber stiffness, piston area, and volumetric stiffness of the mount have the greatest effect on the vibration performance of the mount, as measured by its transmissibility.

A New Type Controllable Squeeze Film Damper Using an Electromagnet

The paper presents stability of a rotor system with a squeeze film damper (SFD) using an electromagnet. The electromagnet is installed in the inner damper of the SFD. The proposed SFD has basically the property of a conventional SFD and variable damping according to the strength of the applied electric current. Therefore, when the applied current is controlled, the whirling amplitude of the rotor system can be effectively reduced in a wide operational speed range. In the present work, the performance of the SFD was experimentally investigated according to the magnetic field strength. When the applied current increased, the whirling amplitude greatly reduced at the critical speeds and damping ratio increased.

Optimal Design of a Squeeze Film Damper Using an Enhanced Genetic Algorithm

This paper represents that an enhanced genetic algorithm (EGA) is applied to optimal design of a squeeze film damper (SFD) to minimize the maximum transmitted load between the bearing and foundation in the operational speed range. A general genetic algorithm (GA) is well known as a useful global optimization technique for complex and nonlinear optimization problems. The EGA consists of the GA to optimize multi-modal functions and the simplex method to search intensively the candidate solutions by the GA for optimal solutions. The performance of the EGA with a benchmark function is compared to them by the IGA (Immune-Genetic Algorithm) and SQP (Sequential Quadratic Programming). The radius, length and radial clearance of the SFD are defined as the design parameters. The objective function is the minimization of a maximum transmitted load of a flexible rotor system with the nonlinear SFDs in the operating speed range. The effectiveness of the EGA for the optimal design of the SFD is discussed from a numerical example.

Optimal Design of Nonlinear Hydraulic Engine Mount

This paper shows that the performance of a nonlinear fluid engine mount can be improved by an optimal design process The property of a hydraulic mount with inertia track and decouplen differs according to the disturbance frequency range. Since the excitation amplitude is large at low excitation frequency range and is small at high excitation frequency range, mathematical model of the mount can be divided into two linear models One is a low frequency model and the other is a high frequency model The combination of the two models is very useful in the analysis of the mount and is used for the first time in the optimization of an engine mount in this paper Normally, the design of a fluid mount is based on a trial and error approach in industry because there are many design parameters In this study, a nonlinear mount was optimized to minimize the transmissibilities of the mount at the notch and the resonance frequencies for low and high-frequency models by a popular optimization technique of sequential quadratic programming (SQP) supported by MATLAB(r) subroutine. The results show that the performance of the mount can be greatly improved for the low and high frequencies ranges by the optimization method

Directionally controllable squeeze film damper using electro-rheological fluid

Electro-Rheological (ER) fluid is a class of functional fluid whose yield stress can be changed by an electric field applied to the fluid, which is observed as a variation of apparent viscosity. This functional fluid is applied to a controllable squeeze film damper (SFD) for stabilizing a flexible rotor system. In applying ER fluid to a conventional passive SFD, a pair of rings in the damper can be used as electrodes. When the electrodes are divided into a horizontal pair and a vertical one, the SFD can provide external damping in each direction independently. A prototype of the directionally controllable SFD was constructed and its performance was experimentally and numerically investigated in the present work.

Dynamic characteristics of squeeze-type mount using magnetorheological fluid

Abstract This paper presents an analytical and experimental analysis of the characteristics of a squeeze-type magnetorheological (MR) mount which can be used for various vibration isolation areas. The concept of the squeeze-type mount and details of the design of a squeeze-type MR mount are discussed. These are followed by a detailed description of the test set-up for evaluating the dynamic behaviour of the mount. A series of tests was conducted on the prototype mount built for this study, in order to characterize the changes occurring as a result of changing electrical current to the mount. The results of this study show that increasing electrical current to the mount, which increases the yield stress of the MR fluid, will result in an increase in both stiffness and damping of the mount. The results also show that the mount hysteresis increases with increase in current to the MR fluid, causing changes in stiffness and damping at different input frequencies.