著者

下田 昌利 近藤 晃 劉 陽

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集C編 (ISSN:18848354)

巻号頁・発行日

vol.79, no.807, pp.4014-4027, 2013 (Released:2013-11-25)

参考文献数

21

被引用文献数

2

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This paper presents an optimum design method considering structural performances and Kansei, which has been becoming an important issue for product designs with maturation of consumer demands. The response surface methodology combined with the design of experiment technique is applied to a bicycle frame design problem. The strength and the rigidity calculated by FEM are used as the evaluation functions for the structural performances. Three dimensional rendering models are constructed with computer graphics software, and used for the Kansei evaluation. The Kansei performances such as “individual” and “elegant” are evaluated by the Semantic Differentials technique and quantified. A road-bicycle frame is focused on as an application example of this method. Sizes of the cross section at both ends, position and angle of rotation at the midpoint of each frame are defined as the design variables to be optimized. By using the response surfaces between the design variables and the performances, the form of road-bicycle frame is optimized under various objectives and constraints. The form with the optimized design variables is visualized with the CG software.

著者

下田 昌利 山根 滉一

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集C編 (ISSN:18848354)

巻号頁・発行日

vol.79, no.807, pp.4353-4367, 2013 (Released:2013-11-25)

参考文献数

21

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This paper proposes a convenient numerical form-finding method for designing the minimal surface, or the equally tensioned surface, of membrane structures with specified arbitrary boundaries. Area minimization problems are formulated as a distributed-parameter shape optimization problem. The internal volume or the perimeter is added as a constraint according to the structure type such as a pneumatic or a suspension membrane. It is assumed that the membrane is varied in the normal and/or the tangential direction to the surface. The shape sensitivity function for each problem is derived using the material derivative method. The minimal surface is determined without shape parameterization by the free-form optimization method, a gradient method in a Hilbert space, where the shape is varied by the traction force in proportion to the sensitivity function under the Robin boundary condition. The calculated results show the effectiveness and practical utility of the proposed method for optimal form-finding of membrane structures.

著者

中山 展空 下田 昌利

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.84, no.858, pp.17-00484-17-00484, 2018 (Released:2018-02-25)

参考文献数

29

被引用文献数

3

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In this paper, we present a simultaneous optimization method of shape and topology for designing a light-weight plate and shell structure. The free-form optimization method for shells and SIMP method are respectively employed for shape and topology optimization, and combined effectively. Shape and fictitious homogenized-density variations are used as the design variables, and simultaneously determined in one iteration of the convergence process. With this method, the optimal topology is determined in the variable design surface optimized by shape optimization. Compliance is used as the objective functional, and minimized under the volume constraint. The optimal design problem is formulated as a distributed-parameter optimization problem, and the sensitivity functions with respect to shape and density variations are theoretically derived. Both the optimal shape and density variations are determined by the H1 gradient method, where the sensitivity functions are applied as the Robin condition to the design surface. With the proposed method, the optimal lighter and stiffer shell structure with smooth surface can be obtained without any design parameterization and numerical instabilities such as checkerboard and zigzag-shape problems.

著者

史 金星 大村 渓一朗 下田 昌利

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.853, pp.17-00077-17-00077, 2017 (Released:2017-09-25)

参考文献数

28

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Because of their superior mechanical, structural, and electronic properties, carbon nanomaterials (CNs) (e.g. graphene sheets and carbon nanotubes) are supposed to be base materials for nanoelectromechanical systems (NEMS). In the present work, we propose a structural optimization method of carbon nanomaterials by introducing topological defects, which consists of the molecular mechanics method, the free-form optimization method, the Phase-Field-Crystal (PFC) method, Voronoi tessellation, and molecular dynamics (MD) simulation. The C-C bonds of CNs are simulated as equivalent continuum beams by a combination of molecular and continuum mechanics, so the atomic structures of CNs can be treated as frame structures. We adopt the free-form optimization method for frames to determine the optimal shapes of CNs in stiffness maximization problem. For obtaining the stable atomic structures of the optimal shapes of CNs, topological defects are introduced in the optimal shapes of CNs using a combination of PFC method, Voronoi tessellation, and MD simulation. The numerical results show that the compliance of CNs can be significantly reduced according to the structural optimization method, which is helpful for designing CNs components in NEMS.

著者

村松 吉晃 下田 昌利

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.851, pp.17-00158-17-00158, 2017 (Released:2017-07-25)

参考文献数

18

被引用文献数

3

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In this study, we propose a parameter-free optimization method of material orientation for a shell structure consisting of orthotropic materials. We consider the compliance as an objective function and minimize it under the state equation constraint. The material orientation distribution is the design variables to be determined. This optimum design problem is formulated as a distributed-parameter optimization problem, and the sensitivity function with respect to the orientation variation is theoretically derived based on the variational method. The optimum orientation variations are determined by the H1 gradient method with the Poisson's equation, where the sensitivity function is applied as the internal heat generation on the shell surface, a driving force to vary the orientation in order to reduce the objective function while maintaining the smooth material orientation distribution. The optimum and continuously distributed orientation variations are determined as the temperature distribution of this fictitious heat transfer analysis without design parameterization. The optimum design examples show that the optimum the material orientation for the minimum compliance can be effectively obtained with the proposed optimization method.

著者

下田 昌利

出版者

湘南工科大学

雑誌

湘南工科大学紀要 = Memoirs of Shonan Institute of Technology (ISSN:09192549)

巻号頁・発行日

vol.37, no.1, pp.17-29, 2003-03-18

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In this paper, a numerical shape optimization method of continua is presented for typical strength, rigidity and vibration problems in structural designs. As the strength problems, the minimization problem of maximum stress and the shape determination problems that achieve a given desired stress distribution are formulated. The rigidity problems involve the minimization problem of external work and the shape determination problems that achieve a given desired displacement distribution. Also, the vibration problems involve maximization of eigen frequency with mode tracking. Each problem is formulated and sensitivity functions are derived using the Lagrangian multiplier method and the material derivative method. The traction method, which is a shape optimization method, is employed to find the optimal domain variation that reduces the objective functional. The proposed numerical analysis method makes it possible to design optimal structures efficiently. Examples of computed results are presented to show the validity and practical utility of the proposed method.

著者

下田 昌利 塚田 聡

出版者

一般社団法人日本機械学会

雑誌

計算力学講演会講演論文集 (ISSN:1348026X)

巻号頁・発行日

vol.2010, no.23, pp.368-370, 2010-09-23

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In this paper, we present a free-form optimization method for designing shell's form in order to control the vibration mode at a prescribed frequency to a target mode. With the free-form optimization method, an optimum shell with smooth free-form surface can be obtained without any shape parameterization. We introduce a squared displacements error norm at the prescribed surface as the objective functional to control the vibration mode to a desired one in a frequency response problem. It is assumed that the shell was varied in the normal direction to the surface and the thickness is constant. A non-parametric shape optimization problem is formulated, and the shape gradient function is theoretically derived using the material derivative method. The shape gradient function is applied to the shell surface as the pseudo traction force to vary the form. The calculated results show the effectiveness of the proposed method for the optimal free-form design of shell structures aiming at mode control.