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3.12.3.5 Surface Attraction
A surface attraction body force can be used to attract a mesh toward a boundary surface, for the purpose of creating a mesh bias. This can be useful for fluid analyses where a finer mesh is needed in the vicinity of a no-slip boundary. The benefit of this tool over other existing tools for creating a biased mesh is its ability to work with structured and unstructured meshes, as well as linear and higher-order elements.
For each element in the mesh, its shortest distance to the selected boundary surface is evaluated using a surface projection algorithm. Then, an attractive body force per mass, is evaluated along the unit vector directed along the shortest projection distance. Here, is a characteristic boundary layer thickness (blt) and is a scale factor for the body force (bsf), whose value may be adjusted relative to account for the stiffness of the elastic solid material assigned to the mesh.
<body_load type="surface attraction" elem_set="EB1" surface="PressureLoad1">
<blt>0.5</blt>
<bsf lc="1">20</bsf>
<search_radius>0.1</search_radius>
<search_tol>0.01</search_tol>
</body_load>
Note that this body force requires the specification of an attractive surface; optionally, it also accepts the specification of the element set subjected to this attractive body force. The search_radius and search_tol parameters are used for the projection algorithm. They have the same meaning as in Section 3.13.1↓.