This paper investigates the influence of a single tensile overload (OL) on fatigue life by means of finite element method. For a realistic evaluation of fatigue life, a combination of elastic-plastic material and fracture mechanics approach was applied. The interaction integral method available in WARP3D code, a multifunctional open source code, was employed to calculate stress intensity factor (SIF) based on elastic-plastic analyses. Numerical analyses performed in this study are based on experimental data taken from literature. A Single Edge Notch Tension model was applied in the numerical analyses. Two loading conditions, namely, pure constant amplitude loading (CAL) and CAL with a single tensile OL were employed. On the other hand, the geometry of the crack due to fatigue-cyclic loading was investigated. The distributions of stress/strain ahead of the crack tip, as well as the size of the induced plastic zone, were also examined. The behavior of SIF along the crack tip was discussed for loading and unloading cycles. Further, fatigue crack propagation material properties (C and m) were proposed based on elastic-plastic analyses to be used in crack propagation calculations in which their effectiveness was verified with experiments. The evaluated fatigue lives under pure CAL and CAL with a single tensile OL were validated with experiments.
This paper presents an improvement of a mathematical interpretation of moving particle semi-implicit (MPS) method. The mathematical interpretation leads to a mathematical reformulation of MPS (MRMPS) based on Taylor expansions. The improvement of MRMPS in this paper is featured by solving a system of 9 × 9 (or 5 × 5 for two dimensional settings) equations for the gradient vector and for all the components of the Hessian matrix. Numerical experiments with various types of target functions showed that the improved MRMPS possesses a second-order convergence rate for the relative error of the gradient and a first-order convergence rate for the relative error of the Laplacian, in three-dimensional settings with randomly distributed neighboring particles. Moreover, there is no deterioration of accuracy for realistic particle configurations near free surfaces, where the neighboring particles are distributed not only randomly but also one-sided. Further, the aforementioned accuracy of the improved MRMPS can be obtained by using about 40 to 50 neighboring particles considerably less than conventional particle methods. A simplification for the improved MRMPS is also presented with less computational complexity, solving two 3 × 3 systems instead of one 9 × 9 system, at the cost of losing one order of convergence rate of error.
本研究では，数値計算手法を検証する方法としてRoy等によって提案された近傍問題法(Method of Nearby Solutions)をゴム材料等を表すために用いられる微圧縮超弾性体の大変形問題に適用する．この方法は，対象とする問題の近似解から滑らかな関数で構成された近傍解を構成し，この近傍解を厳密解とする問題を導出することで近似解の検証を行うものである．特に本研究では，近傍解を構成する際に体積変形に対する制約をペナルティ法により課したH1投影を行うことで微圧縮性が考慮された近傍解を得る手法を提案する．この手法により，微圧縮材料に対して物理的設定に近い近傍問題を得ることが可能となる．
The local minimum pressure in embankment initiated by the base deflection is revisited by an elastic model; whereby, the effect of elastic input parameters such as Young's modulus, Poisson's ratio, and basal roughness conditions on the pronounced local minimum pressure is also disclosed by mean of the elastic model. On the other hand, the characteristic of stress dip from the elastic solution was evaluated by comparing with that of an elasto-plastic solution. Finally, the effect of the geometric features such as the height of the embankment as well as the inclination angle of the slope on the pronounced local minimum pressure was also considered. The method of IsoGemetric Analysis (IGA) was implemented for discretizing the spatial domain instead of Finite Element Method; therefore, the superiority of IGA over FEM in terms of computational cost was also demonstrated.
We have performed a systematic simulation study of dry, granular, gravity-driven, free-surface steady flow in two-dimension, investigating the rheology of cohesionless granular particles in rough inclined plane geometries by discrete element method (DEM). DEM simulation results are compared to a widely accepted μ(I)-rheology model. Microscopic parameters such as coefficient of inter-granular friction and particle size distribution are changed to investigate the influence on macroscopic behaviors like velocity field, volume fraction and effective bulk friction qualitatively. It turned out that more polydisperse system and more frictional particles leads to a low volume fraction and high effective friction. Influence of the inter-granular friction becomes stronger when it is smaller than 1 and becomes weak rapidly when it increases continuously.
Flow structure around permeable pile-group dikes was investigated experimentally by PIV method. The purpose was to reduce the flow velocity to protect the bank while the influence on the mainstream is small and reduced local scour is expected. The effects of number of piles and arrangement type on the flow structure were studied. The flow structure generated by two pile-group types, namely in-line and staggered arrays was compared. Different number of piles per group which was defined as pile-group density was considered. The results indicate that by changing the arrangement of the piles from in-line to staggered arrays, desirable changes on the flow structure occurred. The following features are particularly noteworthy for staggered array cases. It generated suitable velocity pattern in the downstream of the pile-group. In a lateral section at downstream of the structure it minimized the velocity near the bank and then it was increasing gradually to the mainstream, however, for the in-line arrays it was the opposite. Furthermore, to obtain a certain velocity near the bank, staggered arrays had the advantages of using less number of piles and hence less effect on the mainstream flow. In addition, staggered arrangement significantly reduced the generation of strong turbulence in the channel.
In open channel flow, a secondary flow can be generated using a strip roughness that is at an angle to the direction of flow. In this study, we investigated the influence of the oblique angle of installation of the roughness elements on the secondary flow generation experimentally by the PIV method. A clear secondary current was formed due to oblique sharpness, which flows upwards at the near wall region and downward at the middle of the channel in the lateral direction, but the strength and structure of each of the components of the secondary currents varied depending on the installation angle. In the vicinity of the bottom surface, the flow velocity in the lateral direction (V) is remarkably weak in the case of the installation angle of 30°, and in the case of 45° and 60°, the flow velocity becomes almost equally large. On the other hand, the vertical flow (W) at the near wall region is noticeably strong in the case of installation angle of 60° and becomes weak and weaker in magnitude in the case of installation angle 45° and 30° respectively. Furthermore, the downflow at the middle of the channel is weak in the case of installation angle of 60° and increase in magnitude in the case of 45° and attains peak in the case of 30°.