# A Computational Platform for Automatic Signal Processing for Bender Element Sensors +
## 3 Description of the GeoHyTE Platform
### Computational Architecture
#### 3.2.4 Algorithmic and Material Parameters
However, the convergence to a strong solution using such solvers can be extremely slow. If the solving system is ill-conditioned, decreasing the order of domain and boundary refinements and increasing the mesh refinement is typically the safest option. GeoHyTE offers regular and non-regular mesh generators. The regular mesh generator divides rectangular domains into rectangular finite elements of similar sizes. It can only be used for rectangular, simply connected geometries. The definition of the geometry is produced in the GUI 2 (_Geometry and meshing_ zone) by specifying the structural dimensions and the number of finite elements in each Cartesian direction. The origin of the global referential is taken by default in the lower left corner of the domain and cannot be changed. The non-regular mesh generator is based on the Matlab-native pdetool interface. It features a simple click-and-drag interface for the geometry creation. Basic shapes such as rectangles, ellipses, and polygons are used as building blocks and all geometries are combinations of such shapes. The non-regular mesh generator can be used for any type of geometry, simply or multiply connected, which is meshed into triangular elements (see Figure 5). The boundary types are defined in GUI 3 (see Figure 6). All exterior boundaries are listed in the _External boundaries_ table. Four types of boundaries may be assigned. Displacements in the solid phase and the fluid seepage are enforced on the Dirichlet (kinematic) boundaries. On Neumann (static) boundaries, the applied forces and pore pressures are specified. Robin boundaries are elastic boundaries, where flexibility coefficients must be defined to enforce a linear relationship between displacements and stresses. It is noted that Robin boundaries are considered impervious, meaning that the fluid seepage in their normal direction is assumed null. Robin boundary conditions can be used to control the impedance difference between the geomaterial and the testing apparatus to control the wave energy reflected back into the material from the sample apparatus interface. Finally, absorbing boundaries are designed to absorb incoming waves. They are useful to set the impedance difference between the sample and the testing apparatus to nearly zero, thus preventing wave reflections. Figure 5: Sample geometry and non-regular mesh (dimensions in meters) [19]. Figure 6: Layout of GUI 3. On the left of GUI 3, a small scale image of the mesh created in the previous step is shown, along with three buttons that control the visualisation. If, as is the case of the mesh displayed in Figure 6, the image is too small for a clear visualisation of the structural data, a separate visualisation interface with zoom, pan, and data cursor capabilities can be accessed using the Enlarge image button. The values of the enforced boundary conditions are defined in GUI 4 (Figure 7) according to the boundary types defined in GUI 3. Information on the boundary conditions are required for Dirichlet, Neumann and Robin boundaries. The stiffness of the absorbing boundaries is computed automatically, based on the mechanical parameters of the material. Dirichlet boundary conditions are defined by specifying the normal and tangential displacements in the solid phase and the normal fluid seepage. Neumann boundary conditions are defined by specifying the normal and tangential components of the applied forces in the solid phase and the pore fluid pressure. Boundary fields may vary in time and in space.