• Journal of the Korean Society for Precision Engineering
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• 제9권1호
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• pp.126-136
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• 1992

In this paper, a simple structured feedback compensation scheme for a electro-hydraulic servo system to keep the response characteristics unchanged regardless of the load variation is proposed. In electro-hydraulic servo system, servovalve is most important control element. But the relation between input corrent and output flowrate of the servovalve has properties as follows; firstly, in spite of constant input current, output flowrate decreases as load pressure increases, secondly, according to frequency response of typical servovalve, the characteristics of gain and phase shift is something like 2'nd order system. Load pressure feedback compensation method has been applied to eliminate the first influence, the second influence has been improved by phase lead compensation method. As a result of above compensation methods, regardless of variation load condition, spring and inertia load, the compensation scheme has been verified to be effective within the range of frequency less than 25Hz by static response and dynamic response in time domain and frequency domain through experiments.

• Transactions of the Korean Society of Automotive Engineers
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• 제8권6호
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• pp.238-246
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• 2000

In this paper, an optimization method of thin walled beam structures is proposed, Stiffnesses of a thin walled beam are characterized by the thickness of thin plates and the shape of the typical section of the beam. Explicit formula for section properties such as area, area moment of inertia, and torsional constants are derived using the response surface method. The explicit formula can be used for the optimal design of a structural system which consists of complicated thin walled beams. A vehicle structural system is optimized to demonstrate the proposed method.

• International Journal of Aeronautical and Space Sciences
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• 제18권1호
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• pp.99-107
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• 2017

In this work, the nutation control of rigid spacecraft with only two momentum wheels is addressed by applying the feedback linearization technique. In this strategy, the primary performance index is to regulate the nutational angle by the momentum control of wheels. The spacecraft attitude equations of motion are transformed to a general linearized form by feedback linearization technique, including a guaranteed control law promising the internal dynamics stability to accomplish the nutation angle small. It is proven that the configuration of inertia properties plays a key role in analyzing spacecraft energy level. The behavior of the momentum wheels is also studied analytically and numerically. Finally, the effectiveness of the proposed nonlinear control law for the momentum transfer is verified by conducting numerical simulations.

• Steel and Composite Structures
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• 제35권6호
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• pp.729-737
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• 2020

The goal of this study is to investigate dynamic responses of laminated composite beams under a moving load with thermal effects. The governing equations of problem are derived by using the Lagrange procedure. The transverse-shear strain and rotary inertia are considered within the Timoshenko beam theory. The material properties of laminas are considered as the temperature dependent physical property. The differential equations of the problem are solved by the Ritz method. The solution step of dynamic problem, the Newmark average acceleration method is used in the time history. A compassion study is performed for accuracy of used formulations and method. In the numerical results, the effects of velocity of moving load, temperature values, the fiber orientation angles and the stacking sequence of laminas on the dynamic responses of the composite laminated beam are investigated.

• The Journal of the Acoustical Society of Korea
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• 제21권2E호
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• pp.63-70
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• 2002

In this paper, an optimization technique for thin walled beams of vehicle body structure is proposed. Stiffness of thin walled beam structure is characterized by the thickness and typical section shape of the beam structure. Approximate functions for the section properties such as area, area moment of inertia, and torsional constant are derived by using the response surface method. The approximate functions can be used for the optimal design of the vehicle body that consists of complicated thin walled beams. A passenger car body structure is optimized to demonstrate the proposed technique.

• Journal of Korean Society of Steel Construction
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• 제9권1호통권30호
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• pp.3-11
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• 1997

Laminated composite shells exhibit properties comsiderably different from those of the single-layer shell. Thus, to obtain the more accurate solutions to laminated composite shells ptoblems, effects of shear strain should be condidered in analysis of them. A higher-order shear deformation theory requires no shear correction coefficients. This theory is used to determine the buckling loads of elastic shells. The theory accounts for parabolic distribution of the transverse shear through the thickness of the shell and rotary inertia. Exact solutions of simply-supported shells are obtained and the results are compared with the exact solutions of the first-order shear deformation theory, and the classical theory. The present theory predicts the buckling loads more accurately when compared to the first -order and classical theory.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 1997년도 제25회 춘계학술대회
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• pp.47-52
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• 1997

Friction properties of two different types of automotive friction materials were studied. They were nonasbestos organic and semi-metallic friction materials. The two friction materials were tested using an inertia brake dynamometer to investigate friction stability, rooster tailing phenomena, temperature change of riction couples during drags and stops. Results showed that the level of the friction force is strong function of time, temperature, and speed regardless of the type of friction materials. The change of triction coefficient during braking (rooster tailing) was pronounced when the applied pressure was increased in the case of semi-metallic friction materials. This phenomena appears strongly dependent on the applied pressure, initial brake temperature and ingredients in the friction material.

• Journal of the Korea Institute of Military Science and Technology
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• 제12권2호
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• pp.152-158
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• 2009

In this paper, the right arm was modelled by muscle-skeleton elements to obtain the behavior of right arm of human under impact condition, where physical and geometrical properties of human body such as Young's modulus, shear modulus, cross sectional area, length, density, moment of inertia and position were defined. Based on the numerical model of the right arm, the impact response of the right arm was obtained. By the comparison with the experimental results, the model of the right arm was verified.

• Journal of the Earthquake Engineering Society of Korea
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• 제21권4호
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• pp.197-204
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• 2017

This paper aims to analyze the economic feasibility and investigate the possibility of elastic seismic design of wind-designed highrise concentrically braced frames considering change of mechanical properties of Korean steel under the strong wind and the low seismicity in Korea. To this end, first, highrise concentrically braced frames were designed considering strong wind load. And then, analyses of the economics of them were performed. The seismic performance evaluation of wind-designed highrise buildings was conducted using the response spectrum analysis procedure. Analysis results show that it is possible to save up to approximately 90% of the amount of steel on the 10% increase in steel strength without serviceability. However, with serviceability, the design sectional area of the steel with relatively high strength tends to increment considerably because of the lateral stiffness due to reduction of the inertia moment and so on. This point might apply to limitation of the steel with high tensile yield strength.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.399-406
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• 2001

Thermally induced vibration response of composite thin walled beams is investigated. The thin-walled beam model incorporates a number of nonclassical effects of transverse shear, primary and secondary warping, rotary inertia and anisotropy of constituent materials. Thermally induced vibration response characteristics of a composite thin walled beam exhibiting the circumferentially uniform system(CUS) configuration are exploited in connection with the structural bending-torsion coupling resulting from directional properties of fiber reinforced composite materials and from ply stacking sequence. A coupled thermal structure analysis that includes the effects of structural deformations on heating and temperature gradient is investigated.