This geometric description of the die is usually in

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Unformatted text preview: ator. This geometric description of the die is usually in the form of a computer-aided design (CAD) file. This file is parsed by the mesh generator (such as FEMAP) to produce the surface mesh of the die and volume meshes for the die volume and for the liquid metal. The nodes of the mesh become the positions of the SPH boundary particles. For the surface meshes, the boundary normals are calculated. For all particles, masses are calculated, material properties and other state variables are set to give the complete initial set-up for SPH simulation. The boundary normals are required for computing the boundary force described above. If it is required, the mesh generator will also produce a volume mesh in the selected region of the 3D object. The nodes of the volume mesh are positions of the initial fluid particles. Boundary Conditions To simulate confined fluid flow, such as die filling in high pressure die casting, it is necessary to prevent the fluid penetrating the physical boundary. One approach that has proved to be flexible and applicable to many problems is to replace the boundaries by boundary particles, which interact with the fluid by forces that are dependent on the orthogonal distance of the particle from the boundary. Arbitrary boundary surfaces can be readily represented by boundary particles. They have a further advantage that it is easy to simulate the motion of boundary particles. To work with boundary particles, it is necessary to find a way to ensure the fluid particles feel a continuous boundary when two straight/curved boundaries are joined at edges or corners. If the boundary force is not continuous then nearby particle motions are unphysical and generally catastrophic for the simulation. The present implementation of the normal boundary force is described in Monaghan (1995) and involves the use of a repulsive Leonard-Jones potential force field that connects the adjacent boundary particles and repels the fluid particles. As fluid particles approach the boundary, the repulsive force rises rapidly and prevents them from penetrating. This approach is very flexible allowing arbitrary, smoothly varying boundary shapes. In the tangential direction, the particles are included in the summation for the shear force to give non-slip boundary conditions for the walls. Details are contained in Cleary and Monaghan (1993). NUMERICAL RESULTS In this section, SPH simulations of two dies are presented. The two dies are the C-shaped mould (see Figure 1) and a die cast object (see Figure 3) chosen to exhibit typical features of cast objects. The C-shaped mould is geometrically simple, enabling its initial set-up to be built by hand. The simple geometry also allows any programming problem that is associated with the geometry to be identified relatively more readily. Furthermore, it allows easier capture of “clean” experimental images from water analogue modelling. The second die shown in Figure 3 is more representative of industrial and engineering casting...
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This note was uploaded on 10/30/2013 for the course ENG 101 taught by Professor Cheng,m. during the Fall '13 term at Nevada State College.

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