• International Journal of Aeronautical and Space Sciences
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• 제8권2호
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• pp.89-97
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• 2007

COMS(Communication, Oceanography, and Meteorology Satellite) is the first Korean multi-purpose satellite which is planned to be deployed at the altitude of geosynchronous orbit above the Korean peninsular. Noting that COMS is composed of the main BUS structure, two deployable solar panels, one yoke, five reactions wheels, COMS is treated as a collection of 9 bodies and its nonlinear equations of motion are obtained using the multi-body dynamics approach. Also, a computer program is developed to analyze the COMS motion during the various mission phase. Quite often, the equations of motion have to be derived repeatedly to reflect the fact that the spacecraft dynamics change as its configuration, and therefore its degree of freedom varies. However, the equations of motion and simulation software presented in this paper are general enough to represent the COMS dynamics of various configurations with a minimum change in input files. There is no need to derive the equations of motion repeatedly. To show the capability of the simulation program, the spacecraft motion during the solar array partial and full deployment has been simulated and the results are summarized in this paper.

• 대한산업공학회지
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• 제17권2호
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• pp.131-142
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• 1991

The concept of criterion function is proposed as a framework for comparing the geometric and computational characteristics of various nonlinear programming approaches to linear programming such as the method of centers, Karmakar's algorithm and the gravitational method. Also, we discuss various computational issues involved in obtaining an efficient parallel implementation of these methods. Clearly, the most time consuming part in solving a linear programming problem is the direction finding procedure, where we obtain an improving direction. In most cases, finding an improving direction is equivalent to solving a simple optimization problem defined at the current feasible solution. Again, this simple optimization problem can be seen as a least squares problem, and the computational effort in solving the least squares problem is, in fact, same as the effort as in solving a system of linear equations. Hence, getting a solution to a system of linear equations fast is very important in solving a linear programming problem efficiently. For solving system of linear equations on parallel computing machines, an iterative method seems more adequate than direct methods. Therefore, we propose one possible strategy for getting an efficient parallel implementation of an iterative method for solving a system of equations and present the summary of computational experiment performed on transputer based parallel computing board installed on IBM PC.

• 한국수자원학회논문집
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• 제38권6호
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• pp.461-469
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• 2005

본 연구에서는 지진해일에 의하여 동해안에 발생하는 처오름을 모의하기 위하여 2차 정확도의 풍상차분기법을 사용하였으며, 그 결과는 현장관측값과 1차 정확도의 풍상차분기법의 산정 결과와 비교하였다. 수치해석 모형에서는 지배방정식으로 원해에서는 선형 천수 방정식, 근해에서는 비선형 천수방정식을 사용하였다. 대상 지진해일은 1983년 지진해일과 1993년 지진해일이다. 수치해석 결과 동해안의 처오름높이를 잘 재현하는 것으로 확인되었다. 또한, 지진해일 처오름 모의 결과를 범람도 작성에 이용할 수 있을 것으로 판단된다.

• 한국군사과학기술학회지
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• 제10권4호
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• pp.12-19
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• 2007

In this study, nonlinear flow-induced vibration(flutter) analyses of a 2-DOF launch vehicle airfoil have been conducted in supersonic and hypersonic flow regimes. Advanced aeroelastic analysis system based on computational fluid dynamics and computational structural dynamics is successfully developed and applied to the present analyses. Nonlinear unsteady aerodynamic analyses considering strong shock wave motions are conducted using inviscid Euler equations. Aeroelastic governing equations for the 2-DOF airfoil system is solved by the coupled integration method with interactive CFD and CSD computation procedures. Typical wedge type airfoil shapes with initial angle-of-attacks are considered to investigate the nonlinear flutter characteristics in supersonic(15). Also, the comparison of detailed aeroelastic responses are practically presented as numerical results.

• Structural Engineering and Mechanics
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• 제75권1호
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• pp.59-69
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• 2020

The purpose of this study is to develop practical tools for the mechanical design of cylindrical porous media subjected to a broad gap in a hygrothermal environment. The planar axisymmetrical and transient hygrothermoelastic field in a porous hollow cylinder that is exposed to a broad gap of temperature and dissolved moisture content and is free from mechanical constraint on all surfaces is investigated considering the nonlinear coupling between heat and binary moisture and the diffusive properties of both phases of moisture. The system of hygrothermal governing equations is derived for the cylindrical case and solved to illustrate the distributions of hygrothermal-field quantities and the effect of diffusive properties on the distributions. The distribution of the resulting stress is theoretically analyzed based on the fundamental equations for hygrothermoelasticity. The safety hazard because of the analysis disregarding the nonlinear coupling underestimating the stress is illustrated. By comparing the cylinder with an infinitesimal curvature with the straight strip, the significance to consider the existence of curvature, even if it is infinitesimally small, is demonstrated qualitatively and quantitatively. Moreover, by investigating the bending moment, the necessities to consider an actual finite curvature and to perform the transient analysis are illustrated.

• 대한토목학회논문집
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• 제8권3호
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• pp.1-10
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• 1988

본 연구에서는 고차 판 유한요소의 판의 기하학적 비선형 해석에의 적용성을 고찰한다. 고차판요소는 3 차원 연속체로부터 Total Lagrangian 형태로 나타낸 운동방정식을 이산화하고 고차 판이론을 도입하여 유도한다. 유한변형을 고려한 기하학적 비션형 방정식은 Newton-Raphson반복법으로 내력벡터를 선형화하여 강도매트릭스를 반복계산하여 푼다. 요소매트릭스는 shear locking 현상을 피하기 위하여 Gauss 적분법을 이용한 선택적 감차적분으로 계산한다. 여러가지 예제해석을 통하여 고차 판요소의 효율성과 정확도를 고찰하였다.

• Smart Structures and Systems
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• 제18권1호
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• pp.155-181
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• 2016

In the present paper we discuss the stability and the post-buckling behaviour of thin piezoelastic plates. The first part of the paper is concerned with the modelling of such plates. We discuss the constitutive modelling, starting with the three-dimensional constitutive relations within Voigt's linearized theory of piezoelasticity. Assuming a plane state of stress and a linear distribution of the strains with respect to the thickness of the thin plate, two-dimensional constitutive relations are obtained. The specific form of the linear thickness distribution of the strain is first derived within a fully geometrically nonlinear formulation, for which a Finite Element implementation is introduced. Then, a simplified theory based on the von Karman and Tsien kinematic assumption and the Berger approximation is introduced for simply supported plates with polygonal planform. The governing equations of this theory are solved using a Galerkin procedure and cast into a non-dimensional formulation. In the second part of the paper we discuss the stability and the post-buckling behaviour for single term and multi term solutions of the non-dimensional equations. Finally, numerical results are presented using the Finite Element implementation for the fully geometrically nonlinear theory. The results from the simplified von Karman and Tsien theory are then verified by a comparison with the numerical solutions.

• 대한조선학회지
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• 제27권1호
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• pp.11-16
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• 1990

거친 해상에서 케이블이 형성된 수 있는 큰 동장력(large dynamic tensile forces)과 기하학적 비선형성(geometric nonlinearity)의 고려는 비선형 케이블 운동방정식(nonlinear cable dynamics)의 해에 상당한 영향을 끼치며 이 결과의 응용은 케이블의 극단장력(extreme tensions)과 slack-and-snapping 케이블의 연구에서 필수적인 부분이 될 것이다. 비선형 유체항력만을 포함한 경우와 기하학적 비선형성과 큰 동장력항을 함께 포함하는 경우의 케이블 운동방정식의 해를 비교하여, 케이블의 동적 거동에 대한 기하학적 비선형과 큰 동장력항의 복합적인 영향을 연구한다. 큰 동장력항과 기하학적 비선형성의 고려는, 최대 동장력의 증가를 가져오나 반면에 최소 동장력의 크기에서의 감소를 가져옴으로, 결국 동장력의 평균값의 상승과 그로인한 케이블의 피로수명 단축을 유발할 수 있다.

• 대한기계학회논문집A
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• 제20권4호
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• pp.1251-1262
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• 1996

In this paper, a mathematical model for a belt driven system is proposed to analyse the vibration characteristics of the driving units with belts and the free and forced vibraiton anlyses are carried out. The mathematical model for a belt-driven system includes belts, pulleys, spindle and bearings. By using Hamilton's principle, four nonlinear governing equations and twelve nonlinear boundary conditions are derived. To linearize and discretize the nonlinear governing equations and boundary conditions, the perturbation method and Galerkin method are used. Also, the free vibration analyses for various parameters of a belt driven system, which are the tension of a belt, the length of a belt, the material properties of belts, the velocity of a velt and the mass of pulley are made. The forced vibration analyses of the system are performed and the dynamic responses for main parameters are anlysed with a belt driven system.

• Steel and Composite Structures
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• 제34권2호
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• pp.227-239
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• 2020

The aim of this study is to obtain the nonlinear and post-buckling responses of relatively thick functionally graded plates with oblique elliptical cutouts using a new semi-analytical approach. To model the oblique elliptical hole in a FGM plate, six plate-elements are used and the connection between these elements is provided by the well-known Penalty method. Therefore, the semi-analytical technique used in this paper is known as the plate assembly technique. In order to take into account for functionality of the material in a perforated plate, the volume fraction of the material constituents follows a simple power law distribution. Since the FGM perforated plates are relatively thick in this research, the structural model is assumed to be the first order shear deformation theory and Von-Karman's assumptions are used to incorporate geometric nonlinearity. The equilibrium equations for FGM plates containing elliptical holes are obtained by the principle of minimum of total potential energy. The obtained nonlinear equilibrium equations are solved numerically using the quadratic extrapolation technique. Various sets of boundary conditions for FGM plates and different cutout sizes and orientations are assumed here and their effects on nonlinear response of plates under compressive loads are examined.