• 대한조선학회지
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• 제24권4호
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• pp.9-18
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• 1987

The hydrodynamic radiation forces acting on a ship travelling in waves have been conventionally treated by strip theories or by direct three dimensional approaches, most of which have been formulated in frequency domain. If the forward speed of a ship varies with time, or if its path is not a straight line, conventional frequency domain analysis can no more be used, and for these cases time domain analysis may be used. In this paper, formulations are made in time domain with applications to some problems the results of which are known in frequency domain. And the results of both domains are compared to show the characteristics and validity of time domain solutions. The radiation forces acting on a three dimensional body within the framework of a linear theory. If the linearity of entire system is assumed, radiation forces due to arbitrary ship motions can be expressed by the convolution integral of the arbitrary motion velocity and the so called impulse response function. Numerical calculations are done for some bodies of simple shapes and Series-60[$C_B=0.7$] ship model. For all cases, integral equation techniques with transient Green's function are used, and velocity or acceleration potentials are obtained as the solution of the integral equations. In liner systems, time domain solutions are related with frequency domain solutions by Fourier transform. Therefore time domain solutions are Fourier transformed by suitable relations and the results are compared with various frequency domain solutions, which show good agreements.

• Tribology and Lubricants
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• 제23권5호
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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.

• KSTLE International Journal
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• 제1권1호
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• pp.43-47
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• 2000

Oil seals will experience a small amplitude dynamic excitation due to the shaft eccentricity as well as out-of-roundness of the shaft. The direct integration method is selected to analyze the time domain response of the seal lip-shaft contact. The physical properties of rubber seal materials are experimentally analyzed. Effects of both frequency and temperature on the material stiffness behavior are investigated for the linear viscoelastic materials of the seal. Using the nonlinear transient model, a finite element analysis of the lip-shaft contact behaviors under dynamic conditions is presented as a function of the shaft eccentricity, the shaft interference and the garter spring stiffness. The FEM results based on the experimental data indicate that the increased rotating speed may produce the separation conditions. These results will be very useful in predicting the leakage of oil seals under dynamic conditions.

• Structural Engineering and Mechanics
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• 제26권4호
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• pp.363-376
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• 2007

A FE-BE procedure is presented for dynamic analysis of concrete arch dams. In this technique, dam body is discretized by finite elements, while foundation rock is handled by three dimensional boundary element formulation. This would allow a rigorous inclusion of dam-foundation rock interaction, with no limitations imposed on geometry of canyon shape. Based on this method, a previously developed program is modified, and the response of Morrow Point arch dam is studied for various ratios of foundation rock to dam concrete elastic moduli under an empty reservoir condition. Furthermore, the effects of canyon shape on response of dam, is also discussed.

• 대한전자공학회논문지
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• 제23권6호
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• pp.950-956
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• 1986

In this paper, a direct addressing mode of a microprocessor is introduced to save memory capacity, and also a dedicated digital filter is constructed to speed up the filter processing and to enable an easy selection of the impulse response types. A theoretical analysis has been conducted on the errors caused by the finite word klength, rounding-off and multiplication procedures. The digital filter designed by the proposed method is made into a module which can function as a 7th-order recursive or a 14-order nonrecursive type with a simples witch operation. The proposed filter is implemented on a printed-circuit board. The frequency characteristics of this filter can be controlled by the multiplication values stored in ROMs. A low-pass, a high-pass and a band-pass filter have been designed and their frequency characteristics are verified by actual measurements. For a order higher filer, two filter modules have been cascaded into an integrated filter of 23rd-order non-recursive low-pass type and a 12th-order recursive multiband type. Their frequency characteirstics have been found to agree with the theory.

• Structural Engineering and Mechanics
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• 제53권5호
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• pp.897-919
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• 2015

In this study, the effects of ground shocks due to explosive loads on the dynamic response of historical masonry bridges are investigated by using the multi-point shock response spectrum method. With this purpose, different charge weights and distances from the charge center are considered for the analyses of a masonry bridge and depending on these parameters frequency-varying shock spectra are determined and applied to each support of the two-span masonry bridge. The net blast induced ground motion consists of air-induced and direct-induced ground motions. Acceleration time histories of blast induced ground motions are obtained depending on a deterministic shape function and a stationary process. Shock response spectrums determined from the ground shock time histories are simulated using BlastGM software. The results obtained from uniform and multi-point response spectrum analyses cases show that significant differences take place between the uniform and multi-point blast-induced ground motions.

• 한국의류산업학회지
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• 제10권3호
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• pp.298-306
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• 2008

The purpose of this study was to consumer's evaluation toward salesperson attributes, satisfaction of salesperson and apparel store on relationship continuity. To this end, a total of 500 questionnaires were distributed to men and women university students and 443 samples were used for the final analysis. Data were analyzed by using frequency, percentage, factor analysis, cluster analysis, One-way ANOVA, crosstabs, Pearson's correlation analysis, regression analysis. The results of this study were as follows; Looking at the effects of evaluation toward salesperson attributes, satisfaction of salesperson on relationship continuity, they showed satisfaction of salesperson had direct influence on relationship continuity extremely when men and women university students are purchasing their clothing. Uniformity, customer orientation, expertise, kindness were as follows. Looking at the effects of evaluation toward salesperson attributes, satisfaction of apparel store on relationship continuity, it showed uniformity has direct influence on maintaining relations extremely when men and women university students are purchasing their clothing. Customer orientation, satisfaction of apparel store, expertise, kindness were as follows. Through this study, it will be applied into program development data for consumer management and education, and salesperson's efficient consumer response as well.

• 대한토목학회논문집
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• 제13권5호
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• pp.53-65
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• 1993

본 연구에서는 강성기초의 동적응답을 얻기 위해서 비완화 경계조건(non-relaxed boundary condition)을 적용한 3차원 경계요소를 사용하였다. 경계요소는 장래의 비선형문제의 확장을 위해서 시간영역에서 형식화되었으며 기본해는 무한영역의 Stokes 해를 사용하였다. 본 연구는 검증되었으며 지반기초 및 임의 형상의 지하구조물외 동적응답을 얻는데 이용할 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.449-454
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• 2000

A three-parameter model of viscoelastic damper, which has a non-linear spring as an element is incorporated into an oscillator. The behavior of the damper model shows non-linear hysteresis curves which is qualitatively similar to those of real viscoelastic materials. The motion is governed by three-dimensional non-linear dynamical system of equations. The harmonic balance method is applied to get analytic solutions of the system. The frequency-response curves show that multiple solutions co-exist and that the jump phenomena can occur. In addition, it is shown that separate solution branch exists and that it can merge with the primary response curve. Saddle-node bifurcation sets explain the occurences of such non-linear phenomena. A direct time integration of the original equation of motion validifies the use of the harmonic balance method to this sort of problem.

• 한국소음진동공학회논문집
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• 제13권2호
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• pp.99-107
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• 2003

The finite element method(FEM) is the most widely used and powerful method for structural analysis. In general, in order to analyze complex and large structures, we have used the FEM. However, it is necessary to use a large amount of computer memory and computation time for solving accurately by the FEM the dynamic problem of a system with many degree-of-freedom, because the FEM has to deal with very large matrices in this case. Therefore, it was very difficult to analyze the vibration for plate structures with a large number of degrees of freedom by the FEM on a personal computer. For overcoming this disadvantage of the FEM without the loss of the accuracy, the finite element-transfer stiffness coefficient method(FE-TSCM) was developed. The concept of the FE-TSCM is based on the combination of modeling technique in the FEM and the transfer technique in the transfer stiffness coefficient method(TSCM). The merit of the FE-TSCM is to take the advantages of both methods, that is, the convenience of the modeling in the FEM and the computation efficiency of the TSCM. In this paper, the forced vibration analysis algorithm of plate structures is formulated by the FE-TSCM. In order to illustrate the accuracy and the efficiency of the FE-TSCM, results of frequency response analysis for a rectangular plate, which was adopted as a computational model, were compared with those by the modal analysis method and the direct analysis method which are based on the FEM.