Beam-Based Submodeling

Beam-based submodeling enables a strategy to use beam elements in a global model to obtain an approximate solution efficiently followed by a submodel with solid or shell elements to study a region in more detail. Results from the global model impose conditions on cut surfaces of the submodel.

Creating and executing a submodel in the context of beam-based submodeling involves the following:

• Named surfaces that will be associated with submodel cuts must be specified as model data.
• Conditions at driven submodel cuts are specified with submodel cut definitions within the context of an overall submodel conditions definition.
• Data that is common to all submodel cuts, such as the associated step and increment of the global model, is specified as part of the submodel conditions definition for a step.
• The name of the associated global model is specified with the globalmodel parameter on the Abaqus command line.

SUBMODEL CONDITIONS
SUBMODEL CUT, LOCAL SURFACE=element_based_surface

Beam-based submodeling in Abaqus/Standard imposes boundary conditions on primary degrees of freedom of a submodel based on results from the global model with beam elements. Figure 1 shows superimposed global and local models for beam-to-solid and beam-to-shell submodeling examples. Abaqus/Standard internally generates a distributing coupling with the nodes on cut surfaces acting as cloud nodes. These distributing couplings are represented with lines from the reference node to each of the cloud nodes at the four submodel cuts in Figure 1. Reference nodes for these distributing couplings are located at the intersection of the plane of the cut surface and the beam element reference line in the global model. Abaqus/Standard obtains the values of the imposed degrees of freedom at the reference node in the submodel by interpolation from the global model solution for the beam element at the location of the intersection. The distributing coupling causes the average displacement and rotation of the cut surface to match that of the reference node, without imposing rigidity. For example, the distributing coupling does not prevent warping of the cut surface during the submodel simulation.

Figure 1. Superimposed global and local models for beam-to-solid (left) and beam-to-shell (right) submodeling.

Accurate beam-based submodel behavior for beam-based submodeling requires consistency of the beam cross-section configuration in the global and local models. Initial nodal positions of the local submodel must account for:

• Beam section offset in the global model
• The orientation of principal beam axes in the global model
• Beam section dimensions and thicknesses

You must provide the step number from the global model whose solution you would like to use to impose the submodel conditions. If the submodel analysis step is a perturbation step that refers to a general step in the global analysis, you must also provide the increment number within the general step.

SUBMODEL CONDITIONS, GLOBAL STEP=step_number, INC=increment_number

The time period for the global model step and the submodel might differ, especially when one of the models is dynamic and the other is quasi-static. You can scale the time in the global model such that it will match the time period in the submodel. You can also scale the amplitude of the global model solution.

SUBMODEL CONDITIONS, AMPLITUDE SCALE=value, TIME SCALE

A search algorithm identifies the global beam element associated with each local cut surface. The default search algorithm usually does not require user control. Optionally, you can specify a global element set as input to this algorithm to limit which global elements are considered as candidates. If a cut surface of the local model corresponds to the location of a node shared by multiple beam elements in the global model, specifying one of these elements in a global element set will remove uncertainty in which global element is chosen to drive the submodel conditions at that cut. Similarly, you can define tolerances to include or exclude entities that lie outside the boundaries of the submodel. You can specify the tolerances either as a percentage of the average element size or as absolute values.

SUBMODEL CUT, ABSOLUTE EXTERIOR TOLERANCE=value, EXTERIOR TOLERANCE=value,GLOBAL ELSET=element_set_name

By default, Abaqus/Standard assumes that all available primary degrees of freedom are being imposed based on results of the global model at a submodel cut. However, you can selectively choose which degrees of freedom to impose, or you can exempt a specific degree of freedom. You can modify the imposed conditions across the steps.

SUBMODEL CUT, MAIN IMPOSED CONDITIONS=PRIMARY, OP=MOD or NEW
degree of freedom, PRIMARY, degree of freedom, PRIMARY

SUBMODEL CUT, MAIN IMPOSED CONDITIONS=NONE, OP=MOD or NEW
degree of freedom, PRIMARY, degree of freedom, PRIM
degree of freedom, NONE, degree of freedom, NONE