• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.72-77
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• 2001

The computational efficiency of an shape optimization procedure is highly dependent upon the proper selection of shape representation methods and design variables. In this study, shape functions, Bezier and NURBS(non-uniform rational B-splines) curves are selected as configuration generation methods and their efficiencies on the nose shape design of high-speed air vehicles, are compared. The effects of the number of control points, weighting factors and the optimization methods when utilizing the NURBS curves, are investigated. By implementing Bezier and NURBS curves, shapes having lower drag than the optimization case utilizing the shape functions, were obtained, hence it was demonstrated that these curves have better capability in representing the configuration. Efforts will be given to improve the convergence behavior when utilizing the NURBS, hence to reduce the number of Navier-Stokes analysis calculations.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.3
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• pp.239-245
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• 2008

A level set based topological shape optimization using extended B-spline basis functions is developed for steady-state heat conduction problems. The only inside of complicated domain identified by the level set functions is taken into account in computation, so we can remove the effects of domain outside parts in heat conduction problem. The solution of Hamilton-Jacobi equation leads to an optimal shape according to the normal velocity field determined from the sensitivity analysis, minimizing a thermal compliance while satisfying a volume constraint. To obtain exact shape sensitivity, the precise normal and curvature of geometry need to be determined using the level set and B-spline basis functions. Using topological derivative concept, the nucleation of holes for topological changes can be made whenever and wherever necessary during the optimization.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.11
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• pp.2705-2712
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• 2000

In meshless methods some techniques to impose essential boundary conditions have been developed since the approximations do not satisfy Kronecker delta properties at nodal points. In this study, new scheme for imposing essential boundary conditions is developed. Weight functions are modified by multiplying with auxiliary weight functions and the resulting shape functions satisfy Kronecker delta property on the bound ary nodes. In addition, the resulting shape functions possess and interpolation features on the boundary segments where essential boundary conditions are prescribed. Therefore the essential boundary conditions can be exactly satisfied with the new method. More importantly, the impositions of essential boundary conditions using the present method is relatively easy as in finite element method. Numerical examples show that the method also retains high convergence rate comparable to Lagrange multiplier method.

• Journal of the Korean Society of Industry Convergence
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• v.22 no.6
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• pp.627-635
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• 2019

In this study, we developed for processing complex features using CAM software that satisfies precision for example practice and related qualification tests suiTable for CNC training purposes. In addition, functions such as location control, speed control, and processing path generation, which are the main functions of CNC machining machines, were constructed using small equipment parts, servo motors, inverters, general purpose PCs, and commercial NC software and researched with the goal of developing low-cost education equipment. In the static accuracy inspection, the degree of machine when measuring the parallelism of the X, Y and Z axes and the vibration of the main shaft did not reach the allowable value. However, we have obtained a finished product that satisfies the CNC machine book sample shape machining, detailed functions of the position control function of the CNC machine tool, linear interpolation function, circular interpolation function, and tool offset function. In the qualification test shape processing, a shape with a degree of 1/100 mm was processed to obtain position accuracy that satisfied the tolerance.

• Structural Engineering and Mechanics
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• v.10 no.2
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• pp.93-110
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• 2000

An alternative interpretation of the completeness requirements for the higher order elements is presented. Apart from the familiar condition, $\sum_iN_i=1$, some additional conditions to be satisfied by the shape functions of higher order elements are identified. Elements with their geometry in the natural form, i.e., without any geometrical distortion, satisfy most of these additional conditions inherently. However, the geometrically distorted elements satisfy only fewer conditions. The practical implications of the satisfaction or non-satisfaction of these additional conditions are investigated with respect to a 3-node bar element, and 8- and 9-node quadrilateral elements. The results suggest that non-satisfaction of these additional conditions results in poorer performance of the element when the element is geometrically distorted. Based on the new interpretation of completeness requirements, a 3-node element and an 8-node rectangular element that are insensitive to mid-node distortion under a quadratic displacement field have been developed.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1496-1506
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• 2003

The SIMP (solid isotropic material with penalization) approach is perhaps the most popular density variable relaxation method in topology optimization. This method has been very successful in many applications, but the optimization solution convergence can be improved when new variables, not the direct density variables, are used as the design variables. In this work, we newly propose S-shape functions mapping the original density variables nonlinearly to new design variables. The main role of S-shape function is to push intermediate densities to either lower or upper bounds. In particular, this method works well with nonlinear mathematical programming methods. A method of feasible directions is chosen as a nonlinear mathematical programming method in order to show the effects of the S-shape scaling function on the solution convergence.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.12
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• pp.2626-2631
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• 2011

CST(C-shape sharp turn) represented the motion whereby fish bend their tail quickly in a C-shape to achieve an emergent changing of its swimming direction on fish swimming. But there is not yet the general motion trajectory functions related to CST. In this paper, we proposed the very simple motion functions related to CST sequence recorded from a real fish by biologists. Through the computer simulations, we confirmed the usefulness of the proposed function.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1057-1062
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• 2008

Representing a complex, three-dimensional shape, such as an automobile, requires a large amount of CAD data consisting of millions of approximated discontinuous points, which makes it difficult or even impossible to efficiently optimize the entire shape. For this reason, in this paper, function based design method is proposed to optimize the external shape of an automobile. A vehicle modeling function was defined in the form of a Bernstein polynomial to smoothly express the complex 2D and 3D automobile configurations. The sub-sectional parts of the vehicle modeling function are defined as section functions through classifying each subsection of a box model. It is shown that the use of the vehicle modeling functions has the useful advantages in an aerodynamic shape optimization.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.183-189
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• 2014

In this paper, a polyhedral element is presented to solve three-dimensional problems by developing shape functions based on Wachspress coordinates and moving least square approximation. A subdivision of polyhedrons into tetrahedral domains is performed for the construction of shape functions of polyhedral elements, and numerical integration of the weak form is carried out consistently over the tetrahedral domains. The weight functions for moving least square approximation are defined by solving Laplace equation with boundary values based on Wachspress coordinates on polyhedral element faces. Polyhedral elements presented in this paper have similar properties to conventional finite element regarding the continuity, the completeness, the node-element connectivity and the inter-element compatibility. Numerical examples show the effectiveness of the present method for solving three-dimensional problems using polyhedral elements.

• The Research Journal of the Costume Culture
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• v.6 no.4
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• pp.1-12
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• 1998

The research was done against female workers in public officers to find out the actual conditions and usage of uniforms worn in government and other public offices, to find out the degree of their satisfaction for it's appearance, costs, functions and representation. The research was done by questioning 402 female workers about their uniforms in various government and other public offices and the results analysed from the research are as it follows below. 1. The shape of uniforms in public offices were mostly in three piece(jacket+vest+skirt) shape, many of them in gray color and the material were made of blended fabrics. 2. The satisfactory garde of the uniform couldn't even reach the level of '3 point', in which it is easy to tell that the workers had low satisfaction with their uniforms. The level of satisfaction in it's appearance, functions, costs and representation were below average, the rankings starting with functions, representation, appearance, costs and it was shown that the most satisfied category was in it's functions and the lest in costs.