• 대한토목학회논문집
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• 제34권3호
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• pp.895-906
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• 2014

대수심 부유 구조물의 하부기초 기술 중 하나인 dynamically penetration anchor (DPA 또는 흔히 torpedo anchor로 칭함)의 거동특성을 시험결과 및 수치 해석적 접근을 통해 분석하였다. 기존의 유한요소 해석기법으로는 이러한 대수심 anchor 구조물의 거동 특성을 적절히 모사하기 어렵기 때문에 본 연구에서는 이러한 부분을 해결하기 위해 Coupled Eulerian-Lagrangian (CEL) 법을 통해 지반-구조물 사이에서 발생하는 메쉬(mesh)의 distortion 현상 및 경계조건 등의 문제점을 대변형의 관점에서 해결하고자 하였다. 실측치와의 비교를 통해, CEL 기법의 타당성을 검증하였고, 그 결과 본 연구에서 적용한 CEL 기법이 기존 유한요소 기술로는 구현이 불가능한 대수심 anchoring system의 자유낙하에 의한 전반적인 거동 및 지반의 변형특성을 적절히 예측함을 알 수 있었다. 또한 검증된 기법을 바탕으로 dynamic anchor의 거동에 영향을 주는 여러 요소들에 대한 매개변수 연구를 추가로 수행하였다.

• Steel and Composite Structures
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• 제9권5호
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• pp.473-497
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• 2009

For the spatially coupled free vibration analysis of composite box beams resting on elastic foundation under the axial force, the exact solutions are presented by using the power series method based on the homogeneous form of simultaneous ordinary differential equations. The general vibrational theory for the composite box beam with arbitrary lamination is developed by introducing Vlasov°Øs assumption. Next, the equations of motion and force-displacement relationships are derived from the energy principle and explicit expressions for displacement parameters are presented based on power series expansions of displacement components. Finally, the dynamic stiffness matrix is calculated using force-displacement relationships. In addition, the finite element model based on the classical Hermitian interpolation polynomial is presented. To show the performances of the proposed dynamic stiffness matrix of composite box beam, the numerical solutions are presented and compared with the finite element solutions using the Hermitian beam elements and the results from other researchers. Particularly, the effects of the fiber orientation, the axial force, the elastic foundation, and the boundary condition on the vibrational behavior of composite box beam are investigated parametrically. Also the emphasis is given in showing the phenomenon of vibration mode change.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.314-319
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• 1995

The effect of liquid level on the natural frequencies and mode shapes of a partially liquid-filled circular cylindrical shell with various boundary conditions is investigated by means of a theoretical analysis based upon Fourier series expansion method and a finite element analysis using ANSYS computer program. Two dimensional mode shapes of the liquid-coupled shell structure are obtained by the ANSYS finite element analysis and show that the liquid level affect the nodal point movement. It is found that the variation of normalized naturalfrequencies (natural frequencies of liquid-filled shell/antural frequencies ofempty shell) to the liquid level is depend on the axial mode numbers and circumferential wave numbers. Additionally, it is found that the number of variational steps of normalized natural frequencies is identicial to that of axial nodal points of the mode shape.

• 대한조선학회지
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• 제24권3호
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• pp.25-34
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• 1987

Whereas the finite element method is well established today, the boundary element method is a fairly recent development. Both are general-purpose methods for the solution of various structural analysis problem. The B.E.M has several potential advantages relative to the F.E.M. One of them is that the number of unknowns in algebraic system obtained by discretization is proportional to the number of boundary nodes. Anothor advantage is the ease of discretization and input data preparation. However, the B.E.M. always leads to a fully populated and unsymmetric system of equations. Even though the number of degree-of-freedom is reduced as compared with F.E.M, since nodes exist on the boundary only in the B.E.M, to follow that the effort to solve the equations can be greater. It has been shown also that the time spent in setting up the coefficient matrix is a significant and can, in some cases, be greater than the time required to solve the equation. Thus, one can naturally consider the idea that two methods should be coupled, then the advantages of both methods can be taken. And further, by using this coupling method the HATCH CORNER was analyzed to give initial design data.

• 한국정밀공학회지
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• 제22권5호
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• pp.205-213
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• 2005

This paper addresses a method for numerical simulation in the pressing process of hot glass. Updated Lagrangian finite element formulations are employed for the flow and energy equations to accommodate moving meshes. The model is assumed axi-symmetric and creep flow is assumed due to the high viscosity. Commercial software ANSYS is used to solve the coupled flow and energy equations. Moving contact points as well as free surface during the pressing are effectively calculated and updated by utilizing API functions of CAD software Unigraphics. The mesh distortion problem near the wall is overcome by automatic remeshing, and the temperatures of the new mesh are conveniently interpolated by using a unique function of ANSYS. The developed model is applied to the pressing process of TV glasses. In conclusion, the presented method shows that the pressing process accompanying moving boundary can be simulated by effectively combining general purpose software without resorting to special dedicated codes.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.347-352
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• 1998

An analytical method for evaluating the free vibration of two circular plates coupled with water was developed by assuming the clamped boundary condition of the plates and an ideal fluid. The method was applied to analyze the transverse vibration modes, in-phase and out-of-phase, and the results were compared to those obtained by the finite element method (FEM) using a commercial ANSYS 5.2 software. It was found that the theoretical results can predict well the coupled natural frequencies for all in-phase modes with good accuracy. However, the analytical method shows some discrepancies compared with FEM analysis in predicting the coupled natural frequency of the out-of-phase modes, except when m = 0, the zero nodal circle. The analytical method also applied to evaluate the characteristics of the natural frequency with respect to the major parametric variation in mode numbers and distance between the circular plates.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.180-187
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• 1998

One of the major difficulties in the seismic analysis of a dam-reservoir system is the treatment of the energy radiation in the upstream direction of the reservoir. In this paper a new transmitting boundary is presented that can model properly the radiation of energy in the far field direction of a semi-infinite reservoir with constant depth. In the newly developed method, effects of surface wave motion are taken into account and the reservoir-foundation interaction is approximately accounted for with an absorbing boundary condition. If a dam has vertical upstream face and the infinitely long reservoir maintains constant depth, then the proposed transmitting boundary can be directly coupled with the model of dam body. In present study, the dam body is assumed to behave elastically and modeled by finite element method. Seismic responses of a dam model are investigated using the newly developed transmitting boundary.

• Coupled systems mechanics
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• 제12권2호
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• pp.127-149
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• 2023

A theoretical method is developed to analyze the free vibration of an elastic annular plate in contact with an ideal liquid. The displacement potential functions of the contained liquid are expressed as a combination of the Bessel functions that satisfy the Laplace equation and the liquid boundary conditions. The compatibility condition along the interface between the annular plate and the contained liquid is taken into account to consider the fluid-structure coupling. The dynamic displacement of the wet annular plate is assumed to be a combination of dry eigenfunctions, allowing for prediction of the natural frequencies using the Rayleigh-Ritz method. The study investigates the effect of radial liquid boundary conditions on the natural frequencies of the wet annular plate, considering four types of liquid bounding: outer container bounded, outer and inner bounded, inner bounded, and radially unbounded. The proposed theoretical method is validated by comparing the predicted wet natural frequencies with those obtained from finite element analysis, showing excellent accuracy. The results indicate that the radial liquid bounding effect on the natural frequencies is negligible for the axisymmetric vibrational mode, but relatively significant for the mode with one nodal diameter (n =1) and no nodal circle (m' = 0). Furthermore, the study reveals that the wet natural frequencies are the largest for the plate with an inner bounded cylinder among the radial liquid boundary cases, regardless of the vibration mode.

• Journal of Mechanical Science and Technology
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• 제20권11호
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• pp.1790-1800
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• 2006

Dynamic behavior of flexural-torsional coupled vibration of rotating beams using the Rayleigh-Ritz method with orthogonal polynomials as basis functions is studied. Performance of various orthogonal polynomials is compared to each other in terms of their efficiency and accuracy in determining the required natural frequencies. Orthogonal polynomials and functions studied in the present work are: Legendre, Chebyshev, integrated Legendre, modified Duncan polynomials, the special trigonometric functions used in conjunction with Hermite cubics, and beam characteristic orthogonal polynomials. A total of 5 cases of beam boundary conditions and rotation are studied for their natural frequencies. The obtained natural frequencies and mode shapes are compared to those available in various references and the results for coupled flexural-torsional vibrations are especially compared to both previously available references and with those obtained using NASTRAN finite element package. Among all the examined orthogonal functions, Legendre orthogonal polynomials are the most efficient in overall CPU time, mainly because of ease in performing the integration required for determining the stiffness and mass matrices.

• 대한조선학회논문집
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• 제56권1호
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• pp.94-101
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• 2019

Underwater acoustic power should be measured in a free field, but it is not easy to implement. In practice, the measurement could be performed in a reverberant field such as a water-filled steel tank and concrete tank. In this case, the structure and the acoustic field are strongly or weakly coupled according to material properties of the steel and water. So, characteristics of the water tank must be investigated in order to get the accurate underwater acoustic power. In detail, modal frequencies, mode shapes of the structure and frequency response functions of the acoustic field could represent the characteristics of the reverberant water tank. In this paper, the structure-acoustic coupling has been investigated on a reverberant water tank numerically and experimentally. The finite element analysis has been carried out to estimate the structural and acoustical modal parameters under the dry and water-filled conditions, respectively. In order to investigate the structure-acoustic coupling effect, the numerical analysis has been performed according to the structure stiffness change of the water tank. The acoustic frequency response functions were compared with the numerical analysis and acoustic exciting test. From the results, the structural modal frequencies of the water-filled condition have been decreased compared to those of the dry condition in the low frequency range. The acoustic frequency response functions under the coupled boundary conditions showed different patterns from those under the ideal boundary conditions such as the pressure release and rigid boundary condition, respectively.