Automatic Mesh Generation

All finite element products developed by SoilVision Systems Ltd. have always made use of automatic mesh generation as a time-saving feature to end users. SoilVision System Ltd. was a pioneer in the application of automatic mesh generation methods to geotechnical models.

Some of the benefits of AMG are as follows:

1. Meshing off AutoCAD drawings
2. Modeling thin layers
3. Modeling complex geometry
4. Why not just simplify model geometry?

1. Meshing off AutoCAD drawings
Many engineering consultants make use of AutoCAD drawings routinely when dealing with site plans. Traditional approaches to numerical model design have involved "tracing" over drawings or developing highly simplistic versions of real-world conditions. Often so many simplifications are made that the final numerical model is highly different than real-world conditions.

We have implemented DXF import and the ability to create a mesh directly off AutoCAD plans since 2001. The advantages of this approach are as follows:

a) The inherent subtleties of a real world situation are not lost in the transition to a numerical model.
b) Model creation is significantly faster as models can be imported and mesh extremely fast. (link to movie clip).
Case study

The following cross-section had been developed by a consultant through a combination of survey data and borehole readings. Exact replication of this data in a numerical model would have been complex and time consuming. The AutoCAD DXF import feature of our software was employed in order to import the geometry in several polygons. The automatic mesh generation then allowed quick generation of a mesh which then led to the quick solution of the numerical model.

2. Modeling thin layers
Modeling of extremely time layers such as geomembranes, thin clay or gravel layers, anchors, or other such fine functions is made possible with advanced automatic mesh generation. Specific examples of solving these types of models may be seen through the following links.
a) Geomembranes
b) Thin clay layers
c) Soil anchors

3. Modeling complex geometry
Sometimes the real world is complex and a simplification of the geometry can inherently change the outcome of the model. These are the cases where our software shines. As highlighted in the following complex dam cross-section soil layers may be complex. Such models can be imported from DXF files or drawn using our CAD user interface and meshed in a matter of minutes. The following complex dam geometry provides a fitting example of the abilities of the software:

4. Why not just simplify model geometry?
When creating a numerical model there is natural process that is performed by the modeler. This process involves converting the real world site to a theoretical abstraction of the site which is illustrated is the following figure.

Through this process the geometry of the real world is often significantly simplified. Why is this? It is often not because of anything more than the numerical modeler being worried of the abilities of their current software to create a proper mesh based on the complex geometry.

The following example illustrates this issue with clarity. In this case we have an earth dam created over many years which is about 300 ft high. This earth dam is designed to contain mine tailings.

Due to the formidable complexity in geometry it may be tempting to follow the below logic:

a) The clay core controls the flow
b) Let's remove all other layers except the clay core and analyze

However, if this logic is followed in this case it leads to numerical difficulty in solving. The reason for the instability is that the tailing water table is placed high on a very dense clay core with a low permeability. This creates the situation of infiltration into a dense dry soil of whose problems with numerical instability are well documented.

The physics in this case dictates that the model actually becomes easier to solve with more complex geometry! Why is this? It is because the high gradients from the tailings to the till to the clay core are buffered or transitioned through the other materials such that they become less sharp by the time they reach the clay core.