• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.1
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• pp.82-87
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• 1987

In this study a method of shape optimization is applied to two dimensional heat transfer system. For this the optimization problem is defined in a functional form including cost, constraints and the system governing equation. Then the material derivative concept in continuum mechanics and the adjoint variable method are employed for the shape design sensitivity analysis. With the sensitivity analysis results, an optimum is sought with the gradient projection optimization algorithm. The two dimensional isoparametric finite elements are used for accurate analysis and sensitivity calculations. The above method is employed to find the boundary shape to achieve a desired temperature distribution along a segment of the boundary subject to the maximum area constraint.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.21-30
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• 1990

Theoretical and experimental techniques to analyze the two-dimensional liquid motion in a tank are discussed. A Lagrangian FEM with a velocity correction procedure is introduced to describe incompressible free surface fluid flow. A mesh rezoning technique is used to prevent strong distortion of finite elements in the Lagrangian description. Model test technique for sloshing tank is developed using a hydraulic type bench tester. The influence of the variation in the exciting frequency and amplitude are observed for various fill depths. The results of theoretical calculations are compared with those of experiments.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.1
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• pp.152-159
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• 2005

The dynamic properties between catenary and pantograph of high-speed train are very important factors to affect the stable electric power supply. So as to design the reliable current collection system, a multibody simulation model is needed. In this paper, the dynamic analysis method for a pantograph-catenary cable system of high-speed train is presented. The very deformable motion of a catenary cable is demonstrated using nonlinear continuous beam theory, which is based on an absolute nodal coordinate formulation, and the pantograph is modeled as a rigid multibody. The proposed method might be very efficient, because this method can present the nonlinear properties of a flexible catenary cable and set a various boundary conditions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.2
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• pp.150-156
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• 2004

In this paper, the dynamic behavior of a very flexible cable due to moving multibody system along its length is presented. The very deformable motion of a cable is presented using absolute nodal coordinate formulation, which is based on the finite element procedures and the general continuum mechanics theory to represent the elastic forces. Formulation for the sliding joint between a very flexible beam and a rigid body is derived. In order to formulate the constraint equations of this joint, a non-generalized coordinate, which has no inertia or forces associated with this coordinate, is used. The modeling of this sliding joint is very important to many mechanical applications such as the ski lifts. cable cars, and pulley systems. A multibody system moves along an elastic cable using this sliding joint. A numerical example is shownusing the developed analysis program for flexible multibody systems that include a large deformable cable.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.8 s.239
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• pp.1123-1131
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• 2005

In this paper, a formulation for a spatial sliding joint, which a general multibody can move along a very flexible cable, is derived using absolute nodal coordinates and non-generalized coordinate. The large deformable motion of a spatial cable is presented using absolute nodal coordinate formulation, which is based on the finite element procedures and the general continuum mechanics theory to represent the elastic forces. And the non-generalized coordinate, which is neither related to the inertia forces nor external forces, is used to describe an arbitrary position along the centerline of a very flexible cable. In the constraint equation for the sliding joint, since three constraint equations are imposed and one non-generalized coordinate is introduced, one constraint equation is systematically eliminated. Therefore, there are two independent Lagrange multipliers in the final system equations of motion associated with the sliding joint. The development of this sliding joint is important to analyze many mechanical systems such as pulley systems and pantograph/catenary systems for high speed-trains.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1069-1078
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• 1990

It is shown that the performance of finite element based on energy orthogonal functions may be superior to conventional formulation for plane stress problem. Using this finite element, it is then attempted to show the distribution of stress concentration effect for subsurface under loading point. It turned out that the stress concentration effect for subsurface is not dependent on the width of the member but the loading area. And then it is shown that the solution attained by taking the stress function as a Fourier series is not satisfactory in y<0.1B.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.3
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• pp.49-59
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• 1985

Formulation of the geometric optimization for truss structures based on the elasticity theory turn out to be the nonlinear programming problem which has to deal with the Cross sectional area of the member and the coordinates of its nodes simultaneously. A few techniques have been proposed and adopted for the analysis of this nonlinear programming problem for the time being. These techniques, however, bear some limitations on truss shapes loading conditions and design criteria for the practical application to real structures. A generalized algorithm for the geometric optimization of the truss structures which can eliminate the above mentioned limitations, is developed in this study. The algorithm developed utilizes the two-phases technique. In the first phase, the cross sectional area of the truss member is optimized by transforming the nonlinear problem into SUMT, and solving SUMT utilizing the modified Newton-Raphson method. In the second phase, the geometric shape is optimized utilizing the unidirctional search technique of the Rosenbrock method which make it possible to minimize only the objective function. The algorithm developed in this study is numerically tested for several truss structures with various shapes, loading conditions and design criteria, and compared with the results of the other algorithms to examme its applicability and stability. The numerical comparisons show that the two-phases algorithm developed in this study is safely applicable to any design criteria, and the convergency rate is very fast and stable compared with other iteration methods for the geometric optimization of truss structures.

• Journal of the Korean Institute of Gas
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• v.7 no.4 s.21
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• pp.44-52
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• 2003

In this work dynamic heat transfer in a CPFS (cable penetration fire stop) system built in the firewall of nuclear power plants is three-dimensionally investigated to develop a test-simulator that can be used to verify effectiveness of the sealant. Dynamic heat transfer in the fire stop system is formulated in a parabolic PDE (partial differential equation) subjected to a set of initial and boundary conditions. First, the PDE model is divided into two parts; one corresponding to heat transfer in the axial direction and the other corresponding to heat transfer on the vertical planes. The first PDE is converted to a series of ODEs (ordinary differential equations) at finite discrete axial points for applying the numerical method of SOR (successive over-relaxation) to the problem. The ODEs are solved by using an ODE solver In such manner, the axial heat flux can be calculated at least at the finite discrete points. After that, all the planes are separated into finite elements, where the time and spatial functions are assumed to be of orthogonal collocation state at each element. The initial condition of each finite element can be obtained from the above solution. The heat fluxes on the vertical planes are calculated by the Galerkin FEM (finite element method). The CPFS system was modeled, simulated, and analyzed here. The simulation results were illustrated in three-dimensional graphics. Through simulation, it was shown clearly that the temperature distribution was influenced very much by the number, position, and temperature of the cable stream, and that dynamic heat transfer through the cable stream was one of the most dominant factors, and that the feature of heat conduction could be understood as an unsteady-state process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.11
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• pp.205-212
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• 2018

In order to overcome shortcomings of commercial analysis program for solving certain geotechnical problems, finite element method adopting isoparametric quadrilateral element was selected as a tool for analyzing soil behavior and calculating process was programmed. Two examples were considered in order to verify reliability of the developed program. One of the two examples is the case of acting isotropic confining pressure on finite element and the other is the case of acting shear stress on the sides of the finite element. Isoparametric quadrilateral element was considered as the finite element and displacements in the element can be expressed by node displacements and shape functions in the considered element. Calculating process for determining strain which is defined by derivatives using global coordinates was coded using the Jacobian and the natural coordinates. Four point Gauss rule was adopted to convert double integral which defines stiffness of the element into numerical integration. As a result of executing analysis of the finite element under isotropic confining pressure, calculated stress corresponding to four Gauss points and center of the element were equal to the confining pressure. In addition, according to the analyzed results for the element under shear stress, horizontal stresses and vertical stresses were varied with positions in the element and the magnitudes and distribution pattern of the stresses were thought to be rational.

• Journal of Korean Society of Steel Construction
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• v.15 no.2
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• pp.219-229
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• 2003

The extended tangent stiffness matrices and force-deformation relations of the elastic catenary element were initially derived through the addition of the unstrained length of cables to unknown nodal 'displacements. A beam-column element was then introduced to model the deck and pylon of cable-stayed bridges. The conventional geometric nonlinear analysis, initial force method, and TCUD method were summarized, with an effective method combining two methods presented to determine the initial shapes of cable-stayed bridges with dead loads. In this combined method, TCUD method was applied to eliminate vertical and horizontal displacements at cable-supported points of decks and on top of pylons, respectively. The initial force method was also adopted to eliminate horizontal and vertical displacements of decks and pylons. Finally, the accuracy and validity of the proposed combined method were demonstrated through numerical examples.