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이종남,장강원,이신영 한국공작기계학회 2006 한국공작기계학회 추계학술대회논문집 Vol.2006 No.-
In this work, the vibration of an automobile exhaust system is measured by using a recently-developed magnetic sensor. The magnetic sensor is composed of a solenoid and two pairs of permanent magnets generating an antisymmetric magnetic field in the lateral direction inside the solenoid. Lateral movement of a ferromagnetic pipe inside the magnetic field of the suggested sensor induces an electromotive force in the solenoid corresponding to the lateral velocity of the pipe. Due to the simplicity and non-contact characteristics of the magnetic sensor, dynamic behaviors of the structures operating under high temperature such as an exhaust pipe can be efficiently observed. It is shown that the lateral vibration of the exhaust system can be successfully measured by the suggested sensors. The Campbell diagram of the exhaust system is plotted to examine the vibration characteristics of the exhaust system.
안서욱,이신영,윤민수,장강원 한국공작기계학회 2009 한국공작기계학회 춘계학술대회논문집 Vol.2009 No.-
A new design for a lightweight flatbed trailer with high bending and torsional stiffness is presented by using an integrated CAE-based optimization procedure. The integrated design procedure consists of two main steps: topology optimization and thickness optimization. During topology optimization, a creative frame layout different from existing ladder-type frames can be obtained by searching the best layout out of all possible layouts of a simplified design domain model. After approximating the result of topology optimization as a thin-walled structure, the approximated thicknesses of the plates are optimized to minimize the mass of a trailer.
Topology optimization using non-conforming finite elements: three-dimensional case
Jang, Gang-Won,Lee, Sangkeun,Kim, Yoon Young,Sheen, Dongwoo John Wiley Sons, Ltd. 2005 International journal for numerical methods in eng Vol.63 No.6
<P>As in the case of two-dimensional topology design optimization, numerical instability problems similar to the formation of two-dimensional checkerboard patterns occur if the standard eight-node conforming brick element is used. Motivated by the recent success of the two-dimensional non-conforming elements in completely eliminating checkerboard patterns, we aim at investigating the performance of three-dimensional non-conforming elements in controlling the patterns that are estimated overly stiff by the brick elements. To this end, we will investigate how accurately the non-conforming elements estimate the stiffness of the patterns. The stiffness estimation is based on the homogenization method by assuming the periodicity of the patterns. To verify the superior performance of the elements, we consider three-dimensional compliance minimization and compliant mechanism design problems and compare the results by the non-conforming element and the standard 8-node conforming brick element. Copyright © 2005 John Wiley & Sons, Ltd.</P>
Gang-Won Jang(장강원),Yoon Young Kim(김윤영) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
In this investigation, thin-walled closed beams are modeled by a higher-order beam theory that incorporates warping and distortional degrees of freedom in addition to the standard Timoshenko degrees of freedom. In the proposed approach, no artificial spring is inserted between beams connected at an angled joint, but a systematic technique to match all degrees of freedom of the connected beams is employed. Although specific numerical examples consist of relatively simple thin-walled box beams, the present analysis suggests a possibility to handle arbitrarily-cross-sectioned closed beams meeting at multiple joints by a higher-order beam theory without using joint springs. Two cases were investigated: two box beams connected at an angled joint and a box beam forming a closed loop. The predicted vibration results by the developed approach were compared with shell analysis results.
Topology Optimization of MEMS Structures Considering Etching Uncertainty
Gang-Won Jang(장강원),Nico P. van Dijk,Fred van Keulen 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Topology optimization for reliable micro mechanical structures with respect to geometric uncertainties during etching process is presented by using the level-set method. The etching uncertainty is treated as the bounded-but-unknown parameter and the performance drops by the worst etched micro structures are limited as the constraint form of optimization. To this end, models of the over-or under-etched structures should be consistently built from the nominal models during the whole optimization process, which is very hard by using conventional SIMP-based topology optimization methods. By using the level-set method, due to the implicit boundary representation and the signed distance property of the level-set function, models according to the uncertain etching parameter can be easily constructed. The effectiveness of the proposed approach is verified through design examples for mean compliance minimization problems and compliant mechanism problems.
Discrete thickness optimization of an automobile body by using the continuous-variable-based method
Gang-Won Jang,Young-Min Choi,Gyoo-Jae Choi 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.1
Design optimization of an automobile body for dynamic stiffness improvement is presented. The thicknesses of plates consisting of a monocoque body of an automobile are employed as design variables for optimization whose objective is to increase the first torsional and bending natural frequencies. By allotting one design variable to each plate of the body, compared to previous works based on element-wise design variables, the design space of optimization can be reduced to a large extent. Because the present optimization is based on continuous-variable-based algorithms, considering manufacturability of the optimized result, the converged values of plate thicknesses should be approximated to commercially available discrete values. A new straightforward thickness discretization scheme considering design sensitivities and employing a subsequent reduced optimization problem is proposed. The validity of the proposed thickness discretization scheme is verified through numerical experiments.
Sensitivity analysis for fixed-grid shape optimization by using oblique boundary curve approximation
Jang, Gang-Won,Kim, Yoon Young Elsevier 2005 International journal of solids and structures Vol.42 No.11
<P><B>Abstract</B></P><P>The remesh-free property is the most attractive feature of the various versions of fixed-grid-based shape optimization methods. When the design boundary curves do not pass through the predetermined analysis grids, however, the element stiffness as well as the stress along the curves may be computed inaccurately. Even with the popular area-fraction-based stiffness evaluation approach, the whole optimization process may become quite inefficient in such a case. As an efficient alternative approach, we considered a stiffness matrix evaluation method based on the boundary curve approximation by piecewise oblique curves which can cross several elements. The main contribution of this work is the analytic derivation of the shape sensitivity for the discretized system by the fixed-grid method. Since the force term in the sensitivity equation is associated only with the elements crossed by the design boundary curve, we only need the design velocities of the intersecting points between the curve and the fixed mesh. The present results obtained for two-dimensional elasticity and Poisson’s problems are valid for both the single-scale standard fixed-grid method and the multiscale fictitious domain-based interpolation wavelet-Galerkin method.</P>