Weui-Bong Jeong

Comparison of vibration sources between symmetric and asymmetric HDD spindle motors with rotor eccentricity

The permanent magnet motor is often the most important element in hard disk drive (HDD) spindles and also a frequent source of vibration and acoustic noise. The eccentricity between stator and rotor is inevitably introduced during manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper analytically discusses effects of rotor eccentricity on motor performances for symmetric and asymmetric motors, such as local traction, unbalanced force, cogging torque, back EMF, phase current and torque ripple. An asymmetric motor, mostly chosen to reduce the cogging torque, shows a worse effect on cogging torque and unbalanced force when the eccentricity exists. It also adversely affects the flux linkage and introduces variation of the phase back EMF depending on winding and rotating eccentricity, thus yielding increased mutual torque ripple.

Frequency response analysis of cylindrical shells conveying fluid using finite element method

A finite element vibration analysis of thin-watled cylindrical shells conveying fluid with uniform velocity is presented The dynamic behavior of thin-walled shell is based on the Sanders’ theory and the fluid in cyhndrical shell is considered as inviscid and incompressible so that it satisfies the Laplace’s equation A beam-like shell element is used to reduce the number of degrees-of-freedom by restricting to the circumferential modes of cylindrical shell An estimation of frequency response function of the pipe considering of the coupled effects of the internal fluid is presented A dynamic coupling condition of the interface between the fluid and the structure is used The effective thickness of fluid according to circumferential modes is also discussed The influence of fluid velocity on the frequency response function is illustrated and discussed The results by this method are compared with published lesults and those by commercial tools

Vibration and noise control of structural systems using squeeze mode ER mounts

This paper presents vibration and noise control of flexible structures using squeeze mode electro-rheological mounts. After verifying that the damping force of the ER mount can be controlled by the intensity of the electric fild, two different types of ER squeeze mounts have been devised. Firstly, a small size ER mount to support 3 kg is manufactured and applied to the frame structure to control the vibration. An optimal controller which consists of the velocity and the transmitted force feedback signals is designed and implemented to attenuate both the vibration and the transmitted forces. Secondly, a large size of ER mount to support 200 kg is devised and applied to the shell structure to reduce the radiated noise. Dynamic modeling and controller design are undertaken in order to evaluate noise control performance as well as isolation performance of the transmitted force. The radiated noise from the cylindrical shell is calculated by SYSNOISE using forces which are transmitted to the cylindrical shell through two-stage mounting system.

Optimization of Crank Angles to Reduce Excitation Forces and Moments in Engines

The forces from the engine firings and the rotational motion of a crankshaft cause excitations in vehicle engines. In conventional in-line engines, crank angles might be evenly assigned by dividing 360 degrees by the number of cylinders. In this paper, allocation of crank angles was carried out in two different ways, (1) to minimize the moments excited in an engine and (2) to minimize the forces transmitted to the engine mounts. The forces and moments due to gas pressure and reciprocating parts in the engine were formulated, and a computer program to predict the excitation forces and moments was developed. The developed program was applied to a four-stroke seven-cylinder engine to reduce the first- and the second- order moments produced by the engine. Then, it was also applied to minimize the forces transmitted to the engine mounts. The optimized crank angles, in contrast to those of conventional engines, were not evenly distributed. The moments and forces were reduced with the optimized crank angles.

Minimization of cogging torque in permanent magnet motors by teeth pairing and magnet arc design using genetic algorithm

Cogging torque is often a principal source of vibration and acoustic noise in high precision spindle motor applications. In this paper, cogging torque is analytically calculated using energy method with Fourier series expansion. It shows that cogging torque is effectively minimized by controlling airgap permeance function with teeth pairing design, and by controlling flux density function with magnet arc design. For an optimization technique, genetic algorithm is applied to handle trade-off effects of design parameters. Results show that the proposed method can reduce the cogging torque effectively.

Human Response to Idle Vibration of Passenger Vehicle Related to Seating Posture

Human characteristic responding to idle vibration on passenger vehicle was studied to find if affected by seating posture of passenger. When twelve male subjects are exposed to moderate vertical vibration of 0.224 r.m.s. at frequency range from 3 Hz to 40 Hz, it was found that seating posture significantly affects to biodynamical characteristics, apparent mass and apparent eccentric mass, at most range of idle vibration frequency(20~40 Hz). The supported thigh contact on rigid seat showed bigger values in the two biodynamical characteristics than the average thigh contact. The bigger apparent mass and apparent eccentric mass in the seating posture of the supported thigh contact can be assumed more strengthened muscle at the frequency range.

Development and application of new evaluation system for ride comfort and vibration on railway vehicles

Vibrations related to ride comfort should be considered at the beginning of design stage. In general, ride comfort of human is mainly affected by vibration transmitted from the floor and seat. Also, vibration level is very important regarding with running safety on freight wagon. To ensure ride comfort for passenger coach and vibration level for freight wagon, tests had been repeated by different test procedures with several equipments. With different measuring and evaluations for these results, it took much time to evaluate test results. In this paper, a new evaluation procedure was developed combining several software for ride comfort and vibration level test on railway vehicles. In addition, this developed system is capable of ride comfort test and vibration test by a single integrated system that is capable of immediate reporting the test result. With this developed system, the comfort in a passenger coach and the vibration in a freight car were evaluated. And the simulation results from the proposed system are verified by a field test.

Effect of rotor eccentricity on spindle vibration in magnetically symmetric and asymmetric BLDC motors

The permanent magnet motor is often the most important element in hard disk drive (HDD) spindles and also a frequent source of vibration and acoustic noise. Ecentricity between stator and rotor is inevitably introduced during the manufacturing process, such as mass unbalance, shaft bow and bearing tolerances. This paper analytically discusses the effects of rotor eccentricity on motor performance for symmetric and asymmetric motors, such as local traction, unbalanced force, cogging torque, back EMF, phase current and torque ripple. Based on the results of the unbalanced radial forces, the radial runout of the spindle motor is analyzed using finite element transfer matrices. An asymmetric motor, mostly chosen to reduce the cogging torque, shows a worse effect on cogging torque, unbalanced force and radial runout when the eccentricity exists. It also adversely affects the flux linkage and introduces variation of the phase back EMF depending on winding and rotating eccentricity, thus yielding increased mutual torque ripple.

Analysis of Effects of Mooring Connection Position on the Dynamic Response of Spar type Floating Offshore Wind Turbine

This paper deals with the analysis of dynamic characteristics of mooring system of floating-type offshore wind turbine. A spar-type floating structure which consists of a nacelle, a tower and the platform excepting blades, is used to model the floating wind turbine and connect three catenary cables to substructure. The motion of floating structure is simulated when the mooring system is attached using irregular wave Pierson-Moskowitz model. The mooring system is analyzed by changing cable position of floating structure. The dynamic behavior characteristics of mooring system are investigated comparing with cable tension and 6-dof motion of floating structure. These characteristics are much useful to initial design of floating-type structure. From the simulation results, the optimized design parameter that is cable position of connect point of mooring cable can be obtained.

Experiment on Sloshing of Annular Cylindrical Tank for Development of Attitude Control Devices of Floating Offshore Wind Turbines

The floating offshore wind turbines are usually exposed to the wave and wind excitations which are irregular and undirected. In this paper, the sloshing characteristics of annular cylindrical tank were experimentally investigated to reduce the structural dynamic motion of floating offshore wind turbine which is robust to the irregular change of excitation direction of wind and wave. The formula for the natural sloshing frequencies of this annular cylindrical tank was derived theoretically. In order to validate this formula, the shaking equipment was established and frequency response functions were measured. Two types of tank were considered. The first and second natural sloshing frequencies were investigated according to the depth of the water. It has been observed that between theoretical and experimental results shows a good agreement.