The feature constraints include constraint lines/curves, constraint points, and local refinement/coarseness. For some engineering analysis, the loads and boundary conditions need to be applied along the internal lines, or directly on some fixed points in the interior. These situations require that the nodes must be generated along the lines or on the fixed points. These internal lines are called constraint lines and the fixed points are called constraint points. For example, in the city flood analysis model, the roads and rivers in the city are regarded as constraint lines; in the floor analysis system, the loads are usually applied along the lines/curves or on the fixed points on the planar region. If the analysis model is composed of different regions, the boundaries of neighbor regions also belong to constraint lines. For the analysis such as stress analysis or crack analysis, the mesh needs to be refined over specific areas in order to improve calculation accuracy. Under this situation, the mesh density needs to be specified along some lines or on some points in the interior and the mesh generator then produce fine elements around the lines and points according to the density. These lines are called density lines and the points are called density points.

Figure 9. The mesh generation with internal feature constraints

Figure 9 shows the result of the mesh generation for a domain with internal feature constraints. The domain is composed of two sub-domains as shown in Figure 9(a). There are one line constraint, four constraint points, one density line and one density point in first sub-domain. The second sub-domain is a circle region. The quadrilateral mesh generated based on the element size information is shown in Figure 9(b). Figure 10 shows the mesh generation of the floor analysis model, in which the load is applied to the constraint lines and points.

Figure 10. The mesh generation for floor analysis model