並列2平板の相互干渉が著しい配列であるすきま・幅比S/B=2.06,1.1,0.5を対象に,離散うず法を用いた流れモデルにより数値実験を行い,風胴および水槽による実測結果と比較して干渉流れ特性を解析した.その結果,S/B=2.06では対称なうず放出位相関係が支配的だが外乱によりも存在し得ること,S/B=1.1では平板間通り抜け流れが方向の逆転を伴う偏り流れとなるが.S/B=0.5では偏りが安定することなどが明らかとなった

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π電子数が4個であるシクロブタジエンはπ電子4n+2のヒュッケル則による代表的な反芳香族化合物である。この分子が6員環,8員環,10員環…(C_2nH₄)へと伸びた四員環連続体(ブタレン、ジシクロブタジエニレン等)の芳香族性や構造など興味ある問題である。そこで、本研究ではこれらの化合物の安定性と芳香族性について、簡単なケクレ構造の重ね合わせによる予測法とその結果について報告する。

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The strip method is in common use for predicting the hydrodynamic forces on ships oscillating in sway and yaw motions. However, as well known, it breaks down in the high-speed regime. On the other hand, Chapman's numerical method is known as a powerful method, but it is not applicable to bodies of arbitrary shape. Therefore it is essential to establish the new procedure which can be applied to ships of general shape and can also account for the forward-speed effect correctly in the high-speed range. In this paper a theoretical method using Fourier transform technique is presented. This method is considered to be an extension of Chapman's method, and the relationship of this method to the strip method can be shown analytically. Computational results are presented for uniform slender bodies with the cross section of general shape. The influences of the cross-sectional forms on the hydrodynamic sway force and yaw moment are investigated. Furthermore, the relations between the forward-speed effect and the cross-sectional forms are also discussed.

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The central burst defect, also called chevron crack, in axi-symmetric extrusion is analyzed. For the prediction of central bursting the criterion based on plastic instability is used. It satisfies the sufficient condition s_uε_u=0 for multiplicity of solution, which is derived from the discussion based on its necessary condition Δs_uΔε_u=0, where s_u denotes the nominal stress rate, and Δ shows the difference of any two multiple solutions. Stress and strain in the specimen are evaluated using FEM. As the parameter representing the risk for the occurrence of central bursting the measure y_M is introduced and it is calculated using the stress and strain on the central line of the product. When y_M<0, the bursting occurs. The value of y_M is shown in the range of combination between the cone angle of die and the reduction in working. From these values the working condition predicting y_M=0 is interpolated for several work hardening exponents, which shows the boundary between workings with and without cracking. The boundary curve predicted is compared with experimental values obtained by Zimerman and Avitzur. The prediction is found to be, on the whole, similar to the experimental results.

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The extended finite element method (X-FEM), which can model the domain without explicitly meshing the crack surface, can be used to perform stress analyses for efficiently solving fracture mechanics problems. In this study, the constraint condition enforcement for X-FEM analysis considering symmetry is presented. Since the interpolation functions utilized in X-FEM analysis include the enrichment basis functions, the freedoms of the node on the symmetric plane should be constrained properly in X-FEM model with symmetric conditions. Moreover evaluation of the energy release rate by the domain integral method should be performed considering symmetry conditions. In this paper the constraint conditions for three-dimensional X-FEM analysis considering symmetric conditions are summarized and the numerical examples using symmetric X-FEM models are shown. The proposed procedure can be used to perform efficient X-FEM analyses of practical fracture problems.

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The necessary condition for the multiplicity in deformation rate was given by Hill. The condition is Δε_uΔs_u=0, where s_u denotes the nominal stress rate, and Δ shows the difference between any two multiple solutions. However, many proposed criteria of plastic instability in published literature did not take into consideration this necessary condition. They were based on phenomenological aspects. The sufficient condition for the multiplicity is deduced from the requirement which makes the equivalent strain rate ε_s indefinite. This is given by ε_uε_u=0, which is called Z-plane in s_u space. Plastic instability or unloading from a stable state always occurs on Z-plane. With respect to the formability in metal forming, especially, the possibility of plastic instability, processes are examined in plane stress, plane strain and three dimensional conditions. In sheet forming alternative cniterion, s₁=0 is also proposed for positive γ which is defined by the ratio ε₂/ε₁. In bulk forming, the dependency of ductility upon mean normal stress is discussed, and the decrease of ductility is shown with increasing the mean stress. Furthermore, the occurrence of shear banding and its mode are studied. Since the shape of loading path is normally monotonic in s_u space, a loading path intersects Z-plane only once and then plastic instability also can occur only once. Therefore, localized necking, in general, is merely the plastic deformation confined into a very thin layer with a rigid region on its both sides.

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