Papers by Keyword: Level Set Method (LSM)

Abstract: The problem of free surface deformation is involved in variable fields ranging from material processing to metallurgy. In order to investigate the transient evolution of fluid field and free surface deformation numerically, three numerical simulation methods are proposed among which one is based on level set method, the other two are based on moving mesh method. Afterwards, a benchmark problem of sessile droplet is chosen to test and verify each numerical method. A comparison of each numerical result and experimental result shows a good agreement between each other. Comparison and discussion of three numerical methods are made in the end.

Abstract: The level set method (LSM) is one of the methods used frequently to get the precise contours of the targets when the background is dynamic. In order to use the motion information and improve the processing efficiency, an adaptive level set method (ALSM) is proposed. In this approach, the particle filter algorithm is used to track the targets, so we get the rough external contours and their centroids. Then the level set curve evolution is performed to get the precise external contours of the targets. Lastly, the detection results are fed back to the tracking frame to revise the updating regions. The experiment results show that the proposed algorithm can adapt to the motion variations of the targets, and distinguish the targets.

Abstract: Based on the detonation shock dynamics (DSD) theory, Level Set method for propagation of detonation wave was researched. In order to compute the propagation of small curvature bending detonation wave accurately, and according to characteristic of the Hamilton-Jacobi equation, the unstructured quadrilateral and Galerkin finite element difference scheme for solving Level Set function equation was studied.The finite-element code LS-DYNA was used to compute the experimental models about the propagation of detonation wave and the motion of flyers driven by explosive. The computation results are in good agreement with the experimental data. The results indicate that the difference scheme is of high accuracy and universal application.

Abstract: Outward directed surface extraction from imaging modalities is the first task in the design of implants. In this paper a method based on level set method is proposed to extract the directed surface from CT images. The process is composed of two steps. In the first step, Level Set method with a new speed function is employed to evolve zero level set to its destination and used to cut the desired bone part from the input CT images. In the second step, a simple method is used to extract the directed surface, usually the outward surface, from the separated bone part by removing the interior surface. The experimental results show the proposed method works well.

Abstract: Modeling of fatigue crack growth (FCG) under variable amplitude (VA) loading has been a topic of intensive research for decades. This paper proposed an efficient numerical simulation procedure of the FCG process under VA loading via extended finite element method (XFEM). The procedure can describe the integrative effect of several factors (specimen thickness, stress ratio, Poisson’s ratio and so on) simultaneously with a general model. In order to improve the computation efficiency, the whole continua domain is divided into two parts by the level set functions and the global stiffness matrix is divided into four parts accordingly. Then, the inverse operation of global stiffness matrix can be calculated rapidly with the LDU decomposition and the equilibrium equation can be solved effectively. Several sets of fatigue test data in 2024-T351 and 7075-T6 aluminum alloys are used to verify the procedure, the predictions are in good agreement with the test data.

Abstract: This paper presents a general algorithm for topological optimization of the incompressible Navier-Stokes fluid flow based on a level set method. This is a direct extension of our previous work on Stokes flow of such problems. First we obtain the shape sensitivity analysis using the material derivative concept and adjoint variable technique, and then we couple the shape sensitivity analysis result into the level set function as the advection velocity. Since the level set method is implemented in an Euleran framework, the computational cost of the proposed algorithm is moderate. A Benchmark example is provided to illustrate the efficiency and validity of this method.

Abstract: The principle of the structure of displacement function, the establishment of governing equations, level set method were briefly outlined in this paper. Numerical simulations on three dimensional single edge notched specimens with different crack length in tension were performed using Abaqus software based on extended finite element method (XFEM), the stress intensity factor at static crack front was analyzed and the simulated results were in good agreement with analytical solutions. Numerical simulations in the present paper indicated that the extended finite element method is very suitable to deal with nonlinear fracture problems.

Abstract: A model based on level set function is proposed to predict gas shielded arc welding. The model describes not only the free surface tracking of molten drop and metal transfer in gas metal arc welding, but it simulates the phase change on substrate during heat transfer，which is based on porous media theory. The result of simulation shows that this model can describe the drop diameters, transfer frequency and the shape of solidification precisely.

Abstract: Abstract.are preferentially eliminated, thus leading to interface texture development and a higher pop-ulation of low energy grain boundaries. However, when stress is introduced as an additionaldriving force, the dynamics of grain growth change. To model these effects, a three dimensionalanisotropic multi-level set model was modified in order to account for the effect of stress field ongrain growth. For this mesoscale study, grain boundaries were treated as dislocation structuresand their associated net Burgers vectors were calculated using the misorientation informationand boundary inclinations. Using these net Burgers vectors and their associated densities, ad-ditional forces due to stress field were calculated via the Peach-Koehler equation. Qualitativecomparisons of 5 parameter grain boundary character distribution will be carried out in orderto analyze the differences in texture evolution during grain growth.

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.