Immersed boundary Finite Element Method (IBFEM) uses geometry, created as a solid model in CAD software, and immersed in a background mesh for finite element analysis (FEA). The background mesh is independent of the geometry and is used for piecewise interpolation or approximation of the solution. Therefore, the background mesh need not conform to the geometry and it can be a uniform mesh with regular-shaped or undistorted elements. Such a mesh is easy to generate automatically. Traditional finite element analysis uses conforming mesh that has proven to be very difficult to generate automatically without user input and intervention. This is  especially true for mesh consisting of hexahedral (or brick) elements when the geometry is complex. As a result, mesh generation is the most time-consuming aspect of creating a finite element model.. The real advantage of the immersed boundary approach is apparent when one applies it to really complex 3D geometry where mesh generation is nontrivial and time consuming. Figure 1(a) shows the geometry of a tire rack wheel created as a solid model in CAD software. The background mesh for this geometry shown in Fig. 1(b) consists of regular hexahedral elements. This mesh is generated first as a uniform Cartesian mesh within the bounding box of the geometry, and then, all the external elements that do not intersect with the geometry are removed. The result as shown in Fig. 1(c) is the magnitude of the displacement, and it is plotted directly on the solid model.

Figure 1.  Tire rack wheel model: (a), geometry, (b) background mesh, and (c) deformed shape

A survey of immersed boundary methods for finite element analysis can be found in the following paper:

A.V. Kumar, Survey of immersed boundary approaches for finite element analysis, J. Comput. Inf. Sci. Eng. 20 (2020) 1–13, https://doi.org/10.1115/1.4045054.