Shared Topology occurs when bodies are grouped into multi-body parts. It allows for a continuous mesh across common regions where bodies touch, instead of having to define Contact Regions in Simulation. Consider the example below. The models shown in both pictures are identical. The bodies on the left are two separate bodies, meshed independently. The connection between them must be defined by a contact region in Simulation. The bodies on the right have been grouped into a part in DesignModeler. These bodies share topology in the region where they are in contact, so the mesh is continuous across the part. It is often more desirable for the analysis to have a continuous mesh across the parts than to use contact.
It is important to understand how shared topology works in DesignModeler so you can have better success with multi-body parts. There are several key elements to shared topology.
First, the bodies you see in DesignModeler do not immediately share topology. Each body in the part is treated as its own separate entity with respect to modeling operations. Common regions among the bodies in the part are not combined until the model is transferred out of DesignModeler. Therefore, you will not actually see the shared topology until the model is in Simulation.
Second, the method in which shared topology is created varies depending on the types of bodies that make up your part. There are two methods in which DesignModeler can share topology: Edge Joints and Automatic.
Edge Joints are essentially coincident edge pairs that are tracked in DesignModeler. They are created automatically by several features, such as the Surfaces From Edges and Lines From Edges features. Edge joints can also be created by the Joint feature, where the user chooses a set of bodies to join together. Edges that are paired in an edge joint must belong to bodies that reside in the same part in order to share topology. During transfer of the model out of DesignModeler, each edge joint will combine its coincident source edges into a single edge. The edge joint method cannot be applied to solid bodies.
Advantages: User can specifically choose which bodies join together in case they do not want topology shared among all regions of contact. Also, edge joints can be seen when the Show Edge Joints display option is enabled.
Disadvantages: More time consuming than the automatic method. Also edge joints can sometimes expire due to tolerance failures. Additionally, edge joint creation may depend on how your model is built.
This method shares topology automatically for all bodies in the part using a generalized Boolean operation. All common regions among the bodies in the part will be shared during transfer of the model out of DesignModeler. When using the automatic method, any edge joints that reference edges in the part are ignored. The automatic method cannot be applied to line bodies.
Advantages: Easy to use and faster than using edge joints. Also, it is not affected by the tolerance issues that can invalidate edge joints.
Disadvantages: There is no display of where the shared topology will be. Sometimes the user does not want topology shared throughout the entire part.
The types of bodies in the multi-body part often dictate how the part will share topology. See the chart below to see how DesignModeler chooses which method to employ.
Table 1 Part Type versus Shared Topology Method
|PART TYPE||SHARED TOPOLOGY METHOD|
|Line Bodies only||Edge Joints|
|Line Bodies and Surface Bodies||Edge Joints|
|Surface bodies only||Edge Joints or Automatic|
|Solid Bodies only||Automatic|
In most cases, you cannot choose how the bodies within the part are shared. Also, solid bodies can only be grouped with other solid bodies. A part which contains solid bodies along with bodies of another type is invalid. A part containing only surface bodies is the only type of part in which you may choose the shared topology method. The method being used by the part is displayed in the Shared Topology Method property in the Details View.