No abstract

A three-dimensional extended finite element algorithm coupled with the level set method is developed for curvilinear crack front problems. This method does not need to force the discontinuities to be in conformity with the mesh. In order to compute the pointwise stress intensity factors along the curvilinear crack front, an orthogonal curvilinear coordinate system is constructed at the intersection point between the crack front and a surface of the crack front element. As the crack surface is expressed by the level set method, no explicit meshing of the crack geometry emerges on the crack front. This makes the domain integral more difficult. An independent grid of hexahedral cells around the crack front needs to be built as the virtual extension domain for accomplishing the domain integral. To assess the accuracy of the approach, an example with semi-elliptic crack surface is considered. The results show excellent agreement with the results calculated by the standard finite element method and those obtained from the literature.

Taking a pumping station project with large scale centrifugal pumps as working example, an extreme transient flow in the pumping system caused by tripping pump due to electric supply failure was analyzed, and hydraulic disturbance or impulsion to the rest working running pumps were investigated by using the software of the Deltares WANDA 3.73. The results show that the rest running pumps in the system due to a sudden tripping pump disturbance are heavy disturbed when the tripping pump is suddenly failed from the pumping system. The flow rate and input power for the working pumps are greatly jumped shortly. The strongly transient impulsion to the pumping system is quite significant.

This paper is concerned with an analytical solution of transient flow on the four-equation model in fluid-structure interaction (FSI) for a reservoir-pipe-vane system subjected to a sudden closure of hydro turbine vane. The analytical solution is derived corresponding to the junction coupling based on a vane motion. The result obtained from the analytical solution is used to analyze the coupling features between pipe transient flow and hydro turbine vane motion.

A new energy approach is proposed by coupling the virtual crack extension with the extended finite element method (X-FEM) to extract the Strain Energy Release Rates and then convert it to stress intensity factors. By means of meshes independence of the location and geometry of the crack, the proposed approach avoids the mesh perturbation around the crack tip to compute the stiffness derivatives with respect to a virtual extension of the crack. In comparison to the interaction integral, this combined method is implemented more easily without the post-processing of the numerical results. The effect of different enriched region around the crack tip on the accuracy of results is discussed. Numerical results presented are in excellent agreement with the available analytical and those obtained using the interaction integral.