2D Advanced Geometry with SVOffice™ 2009
Presented by: Dr. Murray Fredlund, President of SoilVision Systems Ltd.
Hi, my name is Murray Fredlund. Welcome to the session 2D Geometry - Advanced CAD Drawing Tools within the SVOffice 2009 Next Generation Geotechnical software suite.
This presentation is entitled "2-D Geometry – Advanced CAD Drawing Tools" and is designed to cover the advanced tools available for creating and editing numerical models in the SVOffice geotechnical software suite. Once this presentation is completed the user should have a clear idea of how to manipulate 2D model geometry in an advanced fashion. The concepts presented in this presentation are applicable to all of our finite element software products.
In this presentation we are looking at covering entering of layered geometry, overlapping regions, cutouts, and the use of sticky points in the software. These tools represent slightly more advanced CAD drawing tools in the software and once they are covered, it provides the user with more advanced functionality.
Entering Layered Geometry
It is important to note that historical software packages for two-dimensional slope stability analysis have traditionally made use of entry of a series of node points and then joining the node points to form surfaces or layers. There was no restriction that the regions had to be closed. While this methodology gained a certain amount of commonality it also opens the user up to a number of potential problems. This type of methodology is also not conducive for finite element numerical modeling were every shape must be closed by definition.
Therefore SVOffice has adopted a closed region approach for entry of all shapes within the software.
The primary advantage of this older methodology is that points on the layer beneath the top layer did not have to be redrawn as each successive layer is created. SVOffice has added tools to our geometry input such that we can replicate this behavior and successive layers in a 2-D model can be added easily in a manner similar to the historical method.
In this example we have a model which has been created to simulate a historical situation where model geometry is entered first as node points and then as line segments which define the surfaces. All geometry has been created as drawn art objects on the canvas therefore no actual points which affect model outcome have been created. The purpose of this example is to draw over top of the art objects and input model geometry in a layered fashion. More specifically the point is to avoid having to trace over layer interfaces when drawing new layers on the CAD interface.
It should also be noted that SVOffice supports overlapping regions in all of the software packages. It is found that this greatly simplifies the entry of certain models as the requirements for geometry input are relaxed.
An example of this can be seen in the model below which is one of the distribution models contained within the SVOffice software. It is ideal if when the blue earth dam region is entered it does not have to wrap around the Earth core. It is easier if the core is entered as a region which overlaps onto the blue earth dam. SVOffice supports the entry of the earth dam as an overlapping interior region.
If we look at a specific example where one region might be interior to another region, the SVOffice software determines which region overlaps through the region list dialog. Regions which are defined lower on the list override anything previously defined.
So in the example shown the Earth's core material properties override the properties of the surrounding earth dam. Alternatively if the order of these regions is reversed then the core region essentially disappears as the earth dam material properties override and the model becomes homogeneous.
It may also be necessary when defining a region in SVOffice to define an area of the model which contains no material. Such a region is also referred to as a void region. Such regions are primarily used with tunnels or in situations where drainage is installed to control slope stability.
When defining a region, normally only one shape is required. In order to add a drain, the user must create an additional shape and mark one shape as dominant. Once the dominant shape is specified then the remaining shapes on the region either become cut-outs if they are within the region which is dominant, or they become additional separately gridded shapes if they are outside the dominant region. The following example illustrates this concept in more detail.
In this example a drain is added as a circular shape within a parent shape. Therefore both shapes are entered in the same region. The parent shape which encloses the drain is marked as the dominant shape in the region properties dialog. The second shape, which represents the drain, then becomes a void shape.
It's worth noting that it is possible to define a boundary condition on the interior drainage circle. In this case a review boundary condition may be appropriate such that any water which encounters the drain is removed from the model.
Sticky Points is this feature which is useful when moving nodal points on the geometry. As previously mentioned, duplicate nodal points on adjacent regions must align perfectly. If a user decides to move one particular point, they must also move the other one to maintain consistency between regions. Sticky points is a user defined option which recognizes duplicate points and causes them to stick together when moving.
This is illustrated in the following example.