A performance optimization based on Computational Fluid Dynamics (CFD) for exhaust hoods of low pressure steam turbine wasconducted A low pressure exhaust hood must be designed promptly m a design process of a steam turbine plant In order to design a low pressure exhaust hood for longer rotor blades rapidly, a database based on conventional CFD analysis results was applied By using this database, the number of CFD analysis for performance designs of low pressure exhaust hoods was reduced Further, validations of these designs were conducted using air test apparatus From these results, the effectiveness of this performance optimization process was confirmed

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A semi-intrusive approach to the surrogate modeling in aerodynamic shape optimization problems is presented and its approximating accuracy is analyzed quantitatively The method is semi-intrusive as it uses flow field information m the training of the surrogate models A set of CFD flow field samples obtained with design of experiment are processed through a proper orthogonal decomposition, a decomposition into orthonormal basis of the flow field covariance matrix, which recovers the sample data as the subspace spanned by the orthonomal basis The surrogate model is constructed by establishing a functional relationship between the set of design parameters which generated the sample set and the coefficients of the POD The radial basis function network was used for this purpose The resulting POD-RBFN surrogate model was tested for its approximating accuracy by two validation methods, leave-one-out cross-validation and validation with a fixed set of validating samples The results shows the POD-RBFN approach performs much better than a simple RBFN approach which dmodels the relationship between the design parameters and the scalar objective functions directly

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This paper presents a non-parametric shape design methodology of energy absorbing panels under cyclic load with the elastic-plastic behavior The Green-Lagrange strain, the 2nd Piola-Kirchhoff stress and the stiffness tensor are employed to express the elastic-plastic problem involving material and geometric nonlinearity in finite element method The optimal shape of the panel is determined by applying the sensitivity as the fictitious external forces to the design boundaries to change the shape, while maximizing the energy absorption A calculated result is demonstrated to show the effectiveness of the convenient methodology

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In this paper, we present a parameter-free free-form optimization method for weight reduction in the strength design of shell structures A volume is minimized under inequality constraints of von Mises stress The optimum design problem is formulated as a distributed-parameter shape optimization problem under the assumptions a shell is varied in the out-of-plane direction to the surface and the thickness is constant The local inequality stress constraints are transformed to an integral equality constraint The shape gradient function and the optimality conditions are derived using the material derivative method, and applied to the free-form optimization method With this method, the smooth optimal free-form of a shell structure is obtained without any shape design parameterization while minimizing the volume and satisfying the stress constraints The validity of this method is verified though a design example

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In deep drawing, tearing and wrinkling are major defects In order to avoid these defects, variable blank holder force (VBHF) trajectory should be optimized for successful sheet forming Numerical simulation is so expensive that sequential approximate optimization (SAO) is valid for optimization In particular, the relationship between tearing and wrinkling is conflicting, and multi-objective design optimization is considered in this paper To find VBHF trajectory under conflicting relation, sequential approximate multi-objective optimization (SAMOO) is applied The forming limit diagram (FLD) is used to evaluate tearing and wrinkling Also, the total stroke is divided, and the blank holder force of each sub-stroke step variable is taken as the design variables Numerical result shows that the VBHF trajectory can successfully form the product without tearing and wrinkling

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本稿では発見的多点探索手法の群知能(PSO, ABC, FA)を自由曲面シェル構造の形状最適化に適用する。群知能は自然界の自己組織化現象を模倣した計算手順であり、多くの解法が提案されている。ここでは構造最適化の適用性から3解法を取り上げ、各解法の基本特性を調べた後に、最適化により得られる形態を比較検討する。

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In our study, a design system is developed for generating gear trains under design constraints in a specified area The design specifications are input position, output position, input torque, output torque, rotation direction, and so on Spur gear trains are generated by using random method combined with local optimization method The objective function evaluates weight, efficiency and operating life of generated gear train Multi-objective design optimizations in spur gear train generation problems are examined by the gear tram generation system The advantage of the optimization approach to generating effective gear trains is reported through several examples

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不均質材の弾性解析を行う場合,従来の境界要素法では内部セルを用いて行う.内部セルを使用しない方法がいろいろ提案されているが,完全な手法がない.二重相反境界要素法では,多くの種類のあるRBFの選択に工夫が必要である.内部セルを使用しない方法が提案されているが,ポアソン比は一定である必要がある.一方,著者は,三重相反境界要素法により,セルを用いないで任意の物体力を伴う二次元弾性問題を解析する方法を提案している.本論文では多重相反境界要素法により,傾斜機能材や複合材などの不均質材をメッシュレスで解析する方法を示す本手法では,ポアソン比も任意の分布でよく,さらに複合材の計算のための行列式が非常に小さくできることを示す境界積分方程式を用いて疑似物体力を補間し,この補闇値を用いて精度よく解析する方法を示す.本手法では境界上および,領域内の幾つかの任意点での物性値を使用する.また,計算例により本手法の有効性を示した.

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近年,圧電材料における表面弾性波(SAW)からのテラヘルツ波発生が報告されており,新たな計測原理につながると期待されている 本研究はGaAsにおけるナノスケールでのSAW伝搬の特性理解と制御,またSAWを集束する構造の設計を目的として,並列分子動力学法によるSAWの伝搬過程のシミュレーション解析を行う制御方法として空孔欠陥を周期的に配置したフオノニック構造を用いる これより,空孔周期による周波数選択性と[110]方向における指向性の強さが確認でき, SAW集束化への指針を得ることができた.

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本研究では,硬さや密度が異なる複数の材料を周期的に並べた人工結晶「フォノニツク結晶」の負の屈折現象に着目し,凸型やパラボラ型の構造なしで全方向の到来波を焦点化する高効率音響レンズの設計を,時間領域差分(FDTD)法に基づく計算機シミュレーションによって行っている 今回,非一様な構造によって与えられる屈折率勾配(GRIN)を利用した音響レンズの設計を計算機シミュレーションで行った その結果,エネルギー輸送効率が自由空間に比べ約2倍となる音響レンズを設計したので,超音波実験によって実証実験を行う.

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Crack growth under the elastic-plastic fracture is an important issue of the structural integrity, because seismic wave causes low cycle fatigue in the engineering structure We developed automated FEM analysis framework for elastic-plastic crack growth simulation The framework consists of 4 major modules In this work, we employ crack tip opening angle (CTOA) and displacement (CTOD) which are the angle between crack surfaces and the displacement vector to be defined near the crack tip The present work is applied to the cyclic loading analysis of a pipe with a single notch The work shows automated mesh generation capability and fracture mechanics parameters to evaluate crack growth criterion

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