• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1281-1293
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• 2013

A sophisticated finite element model is illustrated to analyze the behavior of Prefabricated Parallel Wire Strand(PPWS) sockets for main cables of suspension bridges. An orthotropic model is proposed for the casting material by considering both effects of individual wires and a casting alloy, and the contact between surfaces of a socket and a casting alloy is idealized by using the Coulomb friction and the surface-based contact model. The proposed FE model is verified by comparing the strain distributions obtained from the tensile test and FE analysis. The mechanical behavior of a socket is investigated with respect to the variation of the frictional coefficient. The result shows that the friction between surfaces significantly diminishes the stress concentration of a socket and a casting alloy, and the normal stress from the design equation represents the averaged value of the upper and lower quartiles in the distribution of contact stresses between a socket and a casting alloy.

• Tribology and Lubricants
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• v.23 no.5
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• pp.219-227
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• 2007

The dynamic performance of air foil bearings relies on a coupling between a thin air film and an elastic foil structure. A number of successful analytical techniques to predict dynamic performance have been developed. However, the evaluation of its dynamic characteristic is still not enough because of the mechanical complexity of the foil structure and strong nonlinear behavior of friction force. This work presents a nonlinear transient analysis method to predict dynamic performance of foil bearings. In this method, time dependent Reynolds equation is used to calculate pressure distribution and a finite element method is used to model the bump foil structure. The analysis is treated with a direct implicit integration technique that can handle nonlinear problems and the stick-slip algorithm is used to consider friction force. Using this method the response to the mass unbalance excitation is investigated for various design parameters and operating conditions. The results of analysis show that foil bearing is very effective on the restriction of vibration at the resonance frequency compared to the rigid surface bearings and the effectiveness depends on the operating conditions, static load and a amount of mass unbalance. In addition, there exist optimum values of friction coefficient, bump foil stiffness and number of circumferential slit with regards to minimizing dynamic response at the resonance frequency. These optimum values are system dependent.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.43-47
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• 2006

Since the sheet metal forming of Mg alloy is performing at elevated temperature, the effect of process conditions related with the forming temperature is very important factor. Therefore, the investigation for process variables is necessary to design the tools and process conditions. In this study, the effects of process variables were studied by the experimental and FE analysis using the square cup deep drawing. The temperature, forming speed, and lubricant condition were investigated. When forming temperature was $250^{\circ}C$, speed forming was low, and teflon sheet was used as lubricant, the formed parts were good without defects.

• Journal of Drive and Control
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• v.12 no.4
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• pp.54-59
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• 2015

Due to the tendency to use high speed pneumatic cylinders to improve productivity, cushioning devices are adopted to decelerate the piston motion of pneumatic cylinders to reduce noise, vibration, and impact. This paper presents a comparison of the cushion characteristics of a high speed pneumatic cylinder with a relief valve type cushioning device. The system parameters selected are the damping coefficient, Coulomb friction, heat transfer coefficient, and cracking pressure of the relief valve in the air cushioning device. The integral of the time multiplied square error (ITSE) is used to quantitative measure the cushioning performance to assess the effect of varying these. The cushioning performance achieved good results when the ITSE is a minimum value. In a comparison of the piston displacement and velocity with the variations in system parameters, the heat transfer coefficients are not as significantly affected as the other. Also, the cracking pressure of the relief valve is mainly affected by the pressure and temperature in the cushion chamber.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.12
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• pp.1080-1085
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• 2012

In this paper a sharp-edged type damping orifice for an aircraft door damper were designed, where the dynamic viscosity of working fluid were assumed to change up to 400cSt. The discharge coefficient of the damping orifice were investigated by CFD analyses and experiments. In particular, the influences of orifice diameter, edge angle, flow direction and the Reynolds number were taken into consideration. Based on this, it has been deduced how high Coulomb friction forces of damper seals is to be allowed to meet the performance criterion with respect to the orifice size.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.2
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• pp.458-466
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• 1998

In this work, a frequency domain method is tested numerically and experimentally to improve nonlinear model parameters using the frequency response function at the nonlinear element connected point of structure. This method extends the force-state mapping technique, which fits the nonlinear element forces with time domain response data, into frequency domain manipulations. The force-state mapping method in the time domain has limitations when applying to complex real structures because it needd a time domain lumped parameter model. On the other hand, the frequency domain method is relatively easily applicable to a complex real structure having nonlinear elements since it uses the frequency response function of each substurcture. Since this mehtod is performed in frequency domain, the number of equations required to identify the unknown parameters can be easily increased as many as it needed, just by not only varying excitation amplitude bot also selecting excitation frequency domain method has some advantages over the classical force-state mapping technique in the number of data points needed in curve fit and the sensitivity to response noise.

• Computational Structural Engineering
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• v.10 no.2
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• pp.161-169
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• 1997

It is known that tire plays an important role to the dynamic performances of a vehicle such as noise, vibration, ride and handling. Therefore, force and moment measurements have been a part of the traditional tire engineering process. In this paper, a computational analysis technique has been explored. A FE model is made to simulate inflation, vertical load due to the vehicle weight, and the slow rolling of a radial tire. A rigid surface with Coulomb friction is included in the model to simulate the slow rolling contact. The tire slip during the in-plane motion of the rigid surface is calculated. Results are presented for both lateral and vertical loads, as well as straight ahead free rolling. The calculated and measured tire slips are in good correlation. A Study on slow Rolling Tire for perdiction of tire Forces and Moments.