• Structural Engineering and Mechanics
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• 제6권2호
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• pp.173-183
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• 1998

In the shape design of flexible structures, it is useful to predict the initial shape from the desirable large deformed shapes under some loading conditions. In this paper, we present a numerical procedure of an initial shape determination problem for hyperelastic materials which enables us to calculate an initial shape corresponding to the prescribed deformed shape and boundary condition. The present procedure is based on an Arbitrary Lagrangian-Eulerian (ALE) finite element method for hyperelasticity, in which arbitrary change of shapes in both the initial and deformed states can be treated by considering the variation of geometric mappings in the equilibrium equation. Then the determination problem of the initial shape can be formulated as a nonlinear problem to solve the unknown initial shape for the specified deformed shape that satisfies the equilibrium equation. The present approach can be implemented easily to the finite element method by employing the isoparametric hypothesis. Some basic numerical results are also given to characterize the present procedure.

• 대한기계학회논문집A
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• 제26권8호
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• pp.1512-1519
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• 2002

Most of mechanical failures are caused by repeated loadings and therefore they are strongly related to fatigue. To avoid the failures caused by fatigue, determination of an optimal shape of a structure is one of the very important factors in the initial design stage. Shape optimization fer two types of specimens, which are very typical ones in opening mode in fracture mechanics, was accomplished by the linear elastic fracture mechanics and the growth-strain method in this study. Also shape optimization for a cantilever beam in mixed mode was carried out by the same techniques. The linear elastic fracture mechanics was used to estimate stress intensity factors and fatigue lives. And the growth-strain method was used to optimize the shape of the initial shape of the specimens. From the results of the shape optimization, it was found that shapes of two types of specimens and a cantilever beam optimized by the growth-strain method prolong their fatigue lives significantly. Therefore, it was verified that the growth-strain method is an appropriate technique for shape optimization of a structure having a crack.

• 소성∙가공
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• 제24권4호
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• pp.234-240
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• 2015

Multi-pass shape drawing is very important to produce steel profiles in round samples. In the current study, a process design system is developed for a multi-pass shape drawing. In general, the number of passes for a multi-pass shape drawing is 2 to 3 when the reduction ratio, drawing stress, and productivity are considered. Therefore, calculating the drawing stress and designing the intermediated die shapes are very important. In order to calculate the drawing stress, a shape drawing load prediction method is proposed using a general axisymmetric drawing load prediction model. An intermediate die shape design method is proposed using the initial and the final product shapes. Based on this analysis, a process design system is developed for multi-pass shape drawing for steel profiles. The system works with AutoCAD. The system was applied to design a shape drawing of a spline.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.1876-1881
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• 2003

When a projectile travels at high speed underwater, supercavitating flow arises, in which a huge cavity is generated behind the projectile so that only the nose, i.e., the cavitator, of the projectile is wetted, while the rest of it should be surrounded by the cavity. In that case, the projectile can achieve very high speed due to the reduced drag. Furthermore if the nose of the body is shaped properly, the attendant pressure drag can be maintained at a very low value, so that the overall drag is also reduced dramatically. In this study, shape optimization technique is employed to determine the optimum cavitator shape for minimum drag, given certain operating conditions. Shape optimization technique is also used to solve the potential flow problem for any given cavitator, which is a free boundary value problem having the cavity shape as unknown a priori. Analytical sensitivities are derived for various shape parameters in order to implement a gradient-based optimization algorithm. Simultaneous optimization technique is proposed for efficient cavitator shape optimization, in which the cavity and cavitator shape are determined in a single optimization routine.

• 한국의류산업학회지
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• 제24권6호
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• pp.812-824
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• 2022

This study proposes to develop a 3D printed re-entrant(RE) strip by shape memory thermoplastic polyurethane that can be deformed and recovered by thermal stimulation. The most suitable 3D printing infill density condition and temperature condition during shape recovery for mechanical behavior were confirmed. As the poisson's ratio indicated, the higher the recovery temperature, the closer the poisson's ratio to zero and the better the auxetic properties. After recovery testing for five minutes, it appeared that the shape recovery ratio was the highest at 70℃. The temperature range when the shape recovery ratio appeared to be more than 90% was a recovery temperature of more than 50℃ and 60℃ when deformed under a constant load of 100 gf and 300 gf, respectively. This indicated that further deformation occurred after maximum recovery when recovered at a temperature of 80℃, which is above the glass transition temperature range. As for REstrip by infill density, a shape recovery properties of 100% was superior than 50%. Additionally, as the re-entrant structure exhibited a shape recovery ratio of more than 90%, and exhibited auxetic properties. It was confirmed that the infill density condition of 100% and the temperature condition of 70℃ are suitable for REstrips for applying the actuator.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1361-1370
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• 2012

본 논문은 응력 등가정하중을 이용하여 금속제조공정에서 원하는 성형품과 단조품의 최종형상을 얻기 위한 형상최적화 방법을 제안한다. 성형품의 최종형상은 블랭크의 형상에 따라 달라지고 단조품의 최종형상은 빌렛의 형상에 따라 달라진다. 따라서 원하는 형상의 제품을 얻기 위해 구조최적화방법 중 형상최적화방법을 적용하였다. 금속성형 공정은 비선형 동적해석을 수행하므로 등가정하중법을 이용한다. 등가정하중법 중 가상모델을 이용한 응력 등가정하중은 등가정하중을 산출하는 새로운 방법으로 재료 특성의 가치를 재정의하여 응력 등가정하중을 계산한다. 본 논문에 포함된 예제를 통해 원하는 제품의 최종형상을 얻기 위한 최적의 블랭크 및 빌렛 형상을 도출하여 제안한 방법의 유용성을 검증한다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.180-180
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• 2000

The shape of cold strip for the stainless process has been become issue in quality recently, and hence POSCO (Pohang Iron & Steel Co., Ltd) developed an automatic control system for strip shape in the sendzimir mill. The strip shape is measured by an outward measuring roll and is controlled by As_U roll and first intermediate roll. As_U roll consists of 8 saddles, which are controlled vertically. The fist intermediate rolls, which are controlled horizontally, consist of two pairs of rolls up and down. A developed shape control system is applied to real plant by using fuzzy logic and neural network method to control actuators; As_U roll and first intermediate roll. This system composes mainly of three parts as a real-time system, input to output conditioner board, and man-machine interface. The actual shape is recognized by neural network and converted into symmetric shape. The fuzzy controller, based on the shape from neural network and sensor, controls positions of the As_U roll and first intermediate roll. This paper verifies the shape controller performance. The experiments are made on line for the sendzimir mill. The shape control performance shows very efficient for the target tracking, shape symmetry, and fluctuation of shape.

• 한국생산제조학회지
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• 제18권5호
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• pp.462-468
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• 2009

In this study, a workpiece-chucking device that generates a chucking force from a shape memory alloy is introduced. This paper first presents train procedure to transform a commercial one-way shape memory alloy into a two-way shape memory alloy, which makes unclamping mechanism of the chucking device simpler than that using the one-way shape memory alloy Second, it describes a conceptual design of the workpiece-chucking device using the two-way type shape memory alloy. Third, it presents a prototype and its chucking characteristics, such as time-response of clamping/unclamping operations and a relationship between temperatures and chucking forces. Finally, it describes a mill-machining test conducted with the prototype. The results confirm that the proposed workpiece-chucking device is feasible for micro machine-tools.

• 지능정보연구
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• 제8권1호
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• pp.75-85
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• 2002

이 논문은 입술의 형태와 입술 외곽선 부근의 화소값을 이용하여 입술을 효과적으로 인식하는 방법을 제안하였다. 입술의 형태는 학습 영상을 통계적으로 분석하는 능동적 형태 모델을 기반으로 구성하였다. 이 방법은 탐색시 초기 위치의 영향을 받기 때문에 이 논문에서는 입술의 형태에 기반한 가중치 벡터를 이용하여 두 입술 사이의 경계선을 찾고 탐색의 초기 위치로 사용하였다. 다양한 입술 영상들을 대상으로 실험하여 좋은 결과를 얻었다.

• 대한기계학회논문집A
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• 제26권12호
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• pp.2503-2510
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• 2002

Since the first shape-form-shading technique was developed by Horn in the early 1970s, many different approaches have been continuously emerging in the past three decades. Some of them improve existing techniques, while others are completely new approaches. Using the image reflectance equation, they estimate the 3-D shape of an object utilizing adequate constraints. Each algorithm applies different constraints such as brightness, smoothness, and integrability to solve the shape-from-shading problem. Especially for symmetric objects, a symmetry constraint is proposed to improve the performance of existing shape-from-shading algorithm in this paper. The symmetry constraint is imposed to a conventional algorithm and then the improvement in the performance of 3-D shape reconstruction is proved by quantitatively comparing the depth and gradient errors.