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서유덕(Yu-Deok Seo),김현중(Hyun-Jung Kim),박상훈(Sang-Hoon Park),김지연(Ji-Yeon Kim),엄태경(Tae-Kyoung Uhm),윤성기(Sung-Kie Youn),이상률(Sang-Ryool Lee),이승훈(Seung-Hoon Lee),이덕규(Deog-Gyu Lee),이응식(Eung-Shik Lee),장홍술(Hong-Su 한국항공우주학회 2006 韓國航空宇宙學會誌 Vol.34 No.10
반사경 지지부의 접착 특성은 인공위성카메라 반사경의 광학적 성능에 지대한 영향을 미치므로 이에 대한 연구가 필수적이다. 이를 위해 본 연구에서는 세 종류의 우주용 접착제의 접착 특성에 관한 연구를 수행하였다. 반사경의 재료인 제로더(Zerodur)와 금속이 접착된 시편을 사용하여 중첩 전단(lap shear) 시험을 수행하였고 금속과 금속이 접착된 시편에 대해서도 시험을 수행하였다. 또한 다양한 온도 환경을 겪더라도 안정적인 접착력이 보장되는지의 여부를 확인하였으며 세 접착제의 접착력을 비교하였다. Optical performance of the mirror for satellite camera is highly dependent on the adhesive properties of its support. Therefore, in this paper, the adhesive properties of three kinds of space adhesives are investigated. For this purpose, the lap shear test is performed with Zerodur-to-metal lap shear specimen as well as metal-to-metal one. And it is also investigated whether reliable adhesive strength can be secured after the specific thermal cycle. Finally, the properties of three adhesives are compared with each other.
서유덕(Yu-Deok Seo),윤성기(Sung-Kie Youn) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Recently, spline finite element analysis was proposed for the purpose of direct interaction between modeling and numerical analysis. In this method, spline basis functions and control points which determine geometries play the same roles with shape functions and nodes in FEM, respectively. Since the CAD data of geometries such as NURBS(Non-Uniform Rational B-Splines) are employed for numerical analysis, finite element analysis can be performed in natural way with efficiency and geometrically exact analysis results can be obtained. In this work, for the integration of analysis and optimization, structural optimization approach incorporating with spline finite element analysis is presented. Control points are used as design variables and spline basis functions are used to represent geometry, field variables and optimal design. The validity and efficiency of the proposed approach is verified by applying benchmarking problems.
T-스플라인 국부세분화를 고려한 스플라인 기반 유한요소해석
서유덕(Yu-Deok Seo),김기승(Ki-Seung Kim),윤성기(Sung-Kie Youn) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
In many CAD systems, NURBS has been employed to construct exact geometries. Recently, NURBS finite element analysis methods were proposed by some authors for convenient connection between CAD and finite element analysis. Additional advantages of NURBS FEA, such as exact geometry and no mesh generation, are obtained. However, NURBS is inefficient in local refinement and merging patches. For refinement of local region in interest, additional control points should be inserted into the entire row or column which contains the local region. There is another inefficiency of NURBS during merging patches into a large structure due to propagation of control points. In order to overcome these inefficiencies of NURBS, Tspline was proposed by Sederberg. In this work, T-spline based finite element method is proposed for efficient local refinement and merging patches. At first, accuracy and efficiency of NURBS FEA is verified and efficiency of T-spline FEA is verified by comparing with NURBS FEA.
서유덕(Yu-Deok Seo),김현중(Hyun-Jung Kim),박상훈(Sang-Hoon Park),김지연(Ji-Yeon Kim),엄태경(Tae-Kyoung Uhm),윤성기(Sung-Kie Youn),이상률(Sang-Ryool Lee),이승훈(Seung-Hoon Lee),이덕규(Deog-Gyu Lee),이응식(Eung-Shik Lee),장홍술(Hong-Su 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Optical performance of mirror for satellite camera is highly dependent on the adhesive properties of its support. Therefore, in order to design the mirror with high optical performance, the mechanical properties of adhesives should be well defined. In this paper, the mechanical properties of three kinds of space adhesives are studied. First, the elastic moduli of the adhesives are investigated. Tension tests of the adhesives are performed at some chosen temperatures within the prescribed temperature range. From the tension test results, the elastic moduli of the adhesives are expressed as a function of temperature and the sensitivity with respect to temperature are discussed. Secondly, the adhesive strengths of the adhesives are investigated by the lap shear test. The lap shear tests are performed with Zerodur-to-metal lap shear specimen as well as metal-to-metal one. And it is also investigated whether reliable adhesive strength can be secured after the specific thermal cycle.
김현중(Hyun-Jung Kim),서유덕(Yu-Deok Seo),윤성기(Sung-Kie Youn) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.2
In this present work, spline FEA for the trimmed NURBS surface of the 2D linear elasticity problem is presented. The main benefit of the proposed method is that no additional efforts for modeling of trimmed NURBS surfaces are needed and the information of the trimming curves and trimmed surfaces exported from the CAD system can be directly used for analysis. For this, trimmed elements are searched by using NURBS projection scheme. The integration of the trimmed elements is performed by using the NURBS-enhanced integration scheme. The formulation of constructing stiffness matrix of trimmed elements is presented. In this formulation, the information of the trimming curve is used for calculating the Jacobian as well as for obtaining integration points. The robustness and effectiveness of the proposed method are investigated through various numerical examples.
김현중(Hyun-Jung Kim),서유덕(Yu-Deok Seo),윤성기(Sung-Kie Youn) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11
In this present work, trimmed surface analysis for the 2D elasticity problem is presented. The main benefit of the proposed method is that no additional modeling for analysis of a trimmed surface is necessary. As the first attempt to deal with a trimmed surface in spline FEM, the information of the trimming curve and trimmed surface exported from CAD system is directly utilized for analysis. For this, trimmed elements are searched through employing projection scheme. For the integration of the trimmed elements, NURBSenhanced integration scheme which is used in NEFEM is adopted. The quadtree refinement of integration cell is performed for the complicated trimmed cases. The information of trimming curve is used for obtaining integration points as well as constructing stiffness matrix. The robustness and effectiveness of the proposed method are investigated by presenting various numerical examples.
실험계획법을 이용한 인공위성 주반사경 플렉셔 마운트의 최적 설계
김현중(Hyun-Jung Kim),서유덕(Yu-Deok Seo),윤성기(Sung-Kie Youn),이승훈(Seung-Hoon Lee),이덕규(Deog-Gyu Lee),이응식(Eung-Shik Lee) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.8
The primary mirror system in a satellite camera is an opto-mechanically coupled system for a reason that optical and mechanical behaviors are intricately interactive. In order to enhance the opto-mechanical performance of the primary mirror system, opto-mechanical behaviors should be thoroughly investigated by using various analysis procedures such as elastic, thermo-elastic, optical and eigenvalue analysis. In this paper, optimal design of the bipod flexure mounts for high opto-mechanical performance is performed. Optomechanical performances considered in this paper are RMS wavefront error under the gravity and thermal loading conditions and 1st natural frequency of the mirror system. The procedures of the flexure mounts design based on design of experiments and statistics is as follows. The experiments for opto-mechanical analysis are constructed based on the tables of orthogonal arrays and analysis of each experiment is carried out. In order to deal with the multiple opto-mechanical properties, MADM (Multiple-attribute decision making) is employed. From the analysis results, the critical design variables of the flexure mounts which have dominant influences on opto-mechanical performance are determined through analysis of variance and F-test. The regression model in terms of the critical design variables is constructed based on the response surface analysis. Then the critical design variables are optimized from the regression model by using SQP algorithm. Opto-mechanical performance of the optimal bipod flexure mounts is verified through analysis.
트리밍 기법을 이용한 임의의 형상을 갖는 NURBS 곡면의 스플라인 유한요소해석
김현중(Hyun-Jung Kim),서유덕(Yu-Deok Seo),윤성기(Sung-Kie Youn) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Trimming technique is a powerful way of endowing an arbitrary complex topology to CAD files created by using NURBS. In the present work, it is shown that any complex multiply-connected NURBS domain can be described by using trimming curves only. Spline FEM for linear elasticity problems of arbitrary topology described in this way is presented. For fully communicative interaction between CAD and CAE, a specific searching algorithm and an integration scheme of trimmed elements are introduced. Special treatments for imposing essential and traction boundary conditions on trimming curves are also required. It has been demonstrated that with the presented schemes any boundary conditions on trimming curves can be successfully treated. With the examples of complex topology that could be described by employing trimming curves only, effectiveness and robustness of present method are demonstrated.
실험계획법을 이용한 복합재 경통 적층각의 최적 설계에 관한 연구
박병욱(Byong-Ug Park),서유덕(Yu-Deok Seo),김현중(Hyun-Jung Kim),윤성기(Sung-Kie Youn),이승훈(Seung-Hoon Lee),이덕규(Deog-Gyu Lee),이응식(Eung-Shik Lee),장수영(Su-Young Chang) 한국항공우주학회 2009 韓國航空宇宙學會誌 Vol.37 No.7
복합재는 인공위성 카메라 경통의 재료로 많이 사용되는 재료이다. 하지만 적층된 복합재는 층간응력에 의한 층간분리 현상으로 약화된다 이러한 파괴모드는 경통의 구조적 불안정을 유발하며, 카메라의 광학적 성능도 저하시킨다. 따라서 경통은 층간분리에 대해서 강건해야하며, 또한 고강성, 충분히 높은 고유진동수 및 작은 열 팽창 계수 등을 가져야한다. 본 연구에서는 실험계획법을 바탕으로 설계를 진행하였다. 각 실험과정은 직교배열표를 기준으로 설계되었으며, 여러 속성을 고려하기 위해서 MADM 방법을 사용하였다. 그리고 분산분석과 F-검정을 통해서 영향력 인자를 결정하여 경통의 최종 적층각을 결정하였다. Composite has become one of the most frequently used material for a tube of satellite camera due to its attractive characteristics. However, laminated composites can be weakened by delamination which comes from interlaminar stress. Such failure mode cause structural instability of the camera as well as degradation of optical quality. Therefore composite tube should be robust in delamination. Also, composite tube should have high stiffness, sufficient high natural frequency and small coefficient of thermal expansion. The design procedures presented in this paper are based on design of experiments. The experiments for mechanical analysis are designed by the tables of orthogonal arrays. In order to manipulate the various mechanical properties systematically, multiple-attribute decision making(MADM) is employed. Through analysis of variance and F-test, the critical design variables which have dominant influences on mechanical performance are determined. Finally improved ply angles for composite tube are determined.
김현중(Hyun-Jung Kim),서유덕(Yu-Deok Seo),박상훈(Sang-Hoon Park),윤성기(Sung-Kie Youn),이승훈(Seung-Hoon Lee),이덕규(Deog-Gyu Lee),이응식(Eung-Shik Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
The optical performance of the mirror for satellite camera is highly dependent on the adhesive properties between the mirror and its support. In order to design a mirror with high optical performance, the mechanical properties of adhesives should be well defined. In this research, the mechanical properties of three kinds of space adhesives are studied. In case of the materials which show nearly incompressible behavior such as space adhesives, it is important to measure shear modulus which governs deviatoric stress components. Shear moduli of the adhesives are determined by using single lap adhesively bonded joint. For the shear tests, several points have been selected from - 20℃ to 55℃ which is operating temperature range of the adhesive. The shear modulus of each adhesive is expressed as a function of temperature. Characteristics of the adhesives are discussed regarding their temperature sensitivity. The analysis results of RMS wavefront error w.r.t shear modulus are presented.