• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2004년도 가을 학술발표회 논문집
• /
• pp.355-362
• /
• 2004

An efficient boundary-based technique is developed for addressing shape design sensitivity analysis in various problems. An analytical sensitivity formula in the form of a boundary integral is derived based on the continuum formulation for a general functional defined in problems. The formula, which is expressed in terms of the boundary solutions and shape variation vectors, can be conveniently used for gradient computation in a variety of shape design problems. While the sensitivity can be calculated independent of the analysis means, such as the finite element method (FEM) or the boundary element method (BEM), the FEM is used for the analysis in this study because of its popularity and easy-to-use features. The advantage of using a boundary-based method is that the shape variation vectors are needed only on the boundary, not over the whole domain. The boundary shape variation vectors are conveniently computed by using finite perturbations of the shape geometry instead of complex analytical differentiation of the geometry functions. The supercavitating flow problem and fillet problem are chosen to illustrate the efficiency of the proposed methodology. Implementation issues for the sensitivity analysis and optimization procedure are also addressed in these problems.

• Journal of Information Processing Systems
• /
• 제16권2호
• /
• pp.343-359
• /
• 2020

In this paper, a new algorithm is proposed for three-dimensional (3D) shape recognition using local features of model views and its sparse representation. The algorithm starts with the normalization of 3D models and the extraction of 2D views from uniformly distributed viewpoints. Consequently, the 2D views are stacked over each other to from view cubes. The algorithm employs the descriptors of 3D local features in the view cubes after applying Gabor filters in various directions as the initial features for 3D shape recognition. In the training stage, we store some 3D local features to build the prototype dictionary of local features. To extract an intermediate feature vector, we measure the similarity between the local descriptors of a shape model and the local features of the prototype dictionary. We represent the intermediate feature vectors of 3D models in the sparse domain to obtain the final descriptors of the models. Finally, support vector machine classifiers are used to recognize the 3D models. Experimental results using the Princeton Shape Benchmark database showed the average recognition rate of 89.7% using 20 views. We compared the proposed approach with state-of-the-art approaches and the results showed the effectiveness of the proposed algorithm.

• 한국전산구조공학회논문집
• /
• 제18권3호
• /
• pp.255-263
• /
• 2005

본 논문에서는 다양한 문제들의 형상 설계 민감도 해석에 대한 효율적인 경계기반 기법을 제시하였다 우선 문제에서 정의된 일반적인 함수들에 대한 연속체 형태의 식에 근거하여, 경계 적분 형태의 해석적 민감도 식을 유도하였다. 이 식은 다양한 형상 설계 문제들의 경사를 계산하는데 편리하게 사용할 수 있다. 그리고 경계법은 형상 변분 벡터가 전체 도메인이 아닌 경계에서만 요구된다는 장점이 있는데, 여기서 경계 형상 변분은 형상 함수의 복잡한 해석적 미분 대신 형상을 미소 증분시킴으로써 편리하게 계산할 수 있다. 제시한 방법의 효율성을 보이기 위해 포텐셜 유동 문제와 필렛(fillet)에서의 응력 집중 문제에 이를 적용하였다.

• 동력기계공학회지
• /
• 제22권6호
• /
• pp.58-66
• /
• 2018

The use of external gear pumps is an effective way to achieve adequate performance at low cost when composing hydraulic systems. The biggest drawback, on the other hand, is the accompanying noise. Gears of continuous contact shape are actively used for the pump recently. The continuous contact shape must be the helical type due to the nature of the gear pump that is driven only by the drive gear. In this paper the theoretical shape of continuous contact gear is analyzed using simple rack shape of straight lines and two circular arcs. Using such geometry, the theoretical equation will be developed by envelope curves according to the conjugate gear shape rules. After checking the validity of the theory by the shape of gear rules, the grinding shape was also developed. The 3D shapes using equation can be also drawn. It was also shown that contact ratio and radius of curvature are easily developed by the theoretical equations.

• 한국복합재료학회:학술대회논문집
• /
• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
• /
• pp.51-54
• /
• 2005

Shape memory alloys (SMAs) find many applications in smart composite structural systems as the active components. Their ability to provide a high force and large displacement makes them an excellent candidate for an actuator for controlling the shape of smart structures. In this paper, using a macroscopic model that captures the thermo-mechanical behaviors and the two-way shape memory effect (TWSME) of SMAs smart morphing polymeric composite shell structures like shape-changeable UAV wings is demonstrated and analyzed numerically and experimentally when subjected to various kinds of pressure loads. The controllable shapes of the morphing shells to that thin SMA strip actuator are attached are investigated depending on various phase transformation temperatures. SMA strips start to transform from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recover the prestrain, and thus cause the shell structures to deform three dimensionally. The behaviors of composite shells attached with SMA strip actuators are analyzed using the finite element methods and 3-D constitutive equations of SMAs. Several morphing composite shell structures are fabricated and their experimental shape changes depending on temperatures are compared to the numerical results. That two results show good correlations indicates the finite element analysis and 3-D constitutive equations are accurate enough to utilize them for the design of smart composite shell structures for various applications.

• Geomechanics and Engineering
• /
• 제23권5호
• /
• pp.455-466
• /
• 2020

This paper presents analysis of the interaction between tunnel and Qanat with a particular interest for the optimization of Qanat shape using the discrete element code, PFC2D, and the results will be compared with the FEM results of PLAXIS2D. For these concerns, using software PFC2D based on Discrete Element Method (DEM), a model with dimension of 100m ^⁎ 100 m was prepared. A circular tunnel with dimension of 9 m was situated 20 m below the ground surface. Also one Qanat was situated perpendicularly above the tunnel roof. Distance between Qanat center and ground surface was 8 m. Five different shapes for Qanat were selected i.e., square, semi-circular, vertical ellipse, circular and horizontal ellipse. Confining pressure of 5 MPa was applied to the model. The vertical displacement of balls situated in ground surface was picked up to measure the ground subsidence. Also two measuring circles were situated at the tunnel roof and at the Qanat roof to check the vertical displacements. The properties of the alluvial soil of Tehran city are: γ_dry=19 (KN/㎥), E= 750 (kg/㎠), ν=0.35, c=0.3(kg/㎠), φ=34°. In order to validate the DEM results, a comparison between the numerical results (obtained in this study) and analytical and field monitoring have been done. The PFC2D results are compared with the FEM results. The results shows that when Qanat has rectangular shape, the tensile stress concentration at the Qanat corners has maximum value while it has minimum value for vertical ellipse shape. The ground subsidence for Qanat rectangular shape has maximum value while it has minimum value for ellipse shape of Qanat. The vertical displacements at the tunnel roof for Qanat rectangular shape has maximum value while it has minimum value for ellipse shape of Qanat. Historical shape of Qante approved the finding of this research.

• 한국자기학회지
• /
• 제20권2호
• /
• pp.45-51
• /
• 2010

비파괴검사는 탐지물체에 물리적 손상을 가하지 않고 내부 정보를 파악할 수 있어 다양한 분야에서 이용되고 있다. 그 중 전자기를 이용한 물체의 형상추정방법의 경우 역 유한요소법을 이용하여야 하지만 이는 비선형성이 강하고 수치계산이 복잡하고 측정 센서의 개수가 미지수의 개수보다 훨씬 적어 정확한 결과를 얻는데 어려움이 있다. 본 논문에서는 탐지물체에 의한 자기장 변화 신호만을 이용하여, 물체의 시스템 내 각 센서별 위치에서 물체와 등가면적의 원의 비교를 통해 비교적 간편하게 자성물체의 부피를 판정하고 형상추정을 위한 다양한 보정과정을 거쳐 탐지물체의 형상판정이 가능한 알고리즘을 제안하고 검증하였다.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2012년도 춘계학술대회 논문집
• /
• pp.1053-1054
• /
• 2012

• 한국정밀공학회지
• /
• 제22권4호
• /
• pp.13-18
• /
• 2005

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2007년도 춘계학술대회 논문집
• /
• pp.231-232
• /
• 2007