30.1.4 Contact blockage

**Product: **ABAQUS/Explicit

The blockage of flow out of a cavity due to an obstruction caused by contacting surfaces:

can be defined selectively for particular surfaces that may fully or partially cause the blockage; and

can be accounted for only when the surfaces are used with the general contact algorithm.

Surfaces used to account for contact blockage

To consider an obstruction by contacting surfaces as discussed in “Accounting for blockage due to contacting boundary surfaces” in “Defining fluid exchange,” Section 11.6.3, you must define a surface to represent the leakage area on the boundary of the fluid cavity. In addition, you must specify that the contacting surfaces can potentially cause blockage. All the surfaces (the surface on the boundary of the fluid cavity and the contacting surfaces) must be included in a general contact domain. To account for contact blockage, the nodes on the surfaces must be in node-to-face contact. When the nodes on the surface on the boundary of the fluid cavity come into contact with the contacting surfaces, the slave nodes are marked as active nodes for contact blockage. The contact blockage is also considered in the edge-to-edge contact (see “Contact formulation for general contact,” Section 29.3.4).

Input File Usage: | Use the following options to specify that two contacting surfaces can cause blockage: |

*CONTACT PROPERTY ASSIGNMENT |

Determining the obstruction area

ABAQUS/Explicit determines the obstruction area by calculating the area fraction of the surface on the boundary of the fluid cavity that is not blocked by contacting surfaces. For each element face of this surface representing the leakage area, the blocked area is calculated based on the active nodes for contact blockage. The element blocked area is determined by

where is the element blocked area, is the element area, is the total number of element nodes, and is the total number of active nodes for contact blockage in the element. The element is fully blocked by the contacting surfaces when all element nodes are active for contact blockage. The total obstruction area is the sum of all the element blocked areas. The leakage area used in the fluid exchange calculation is obtained by subtracting the total obstruction area from the total area of the surface if the effective area is not specified for the fluid exchange. If both the effective area and a surface are specified (see “Defining fluid exchange,” Section 11.6.3), the leakage area used in the fluid exchange calculation is obtained by using the ratio of the total obstruction area to the total area of the surface multiplied by the effective area. In this case a node-based surface can be used, and the leakage area is obtained by using the ratio of the total active contact blockage nodes to the total number of nodes defined in the surface.