Diagnostics for implicit constraint systems in Abaqus/Explicit models

Newly added diagnostics inform you about large implicit constraint systems in your model. Large implicit constraint systems are typically associated with overlaps among constraints or overlaps among constraints and connector element. Solving these large systems of equations in each increment of Abaqus/Explicit can degrade performance significantly. The sizes of such systems and estimates of the number of operations required to solve each system are tabulated in the status file. Abaqus/Explicit issues an error message if severe performance degradation is expected. Optionally, you can change the error message to a warning.

Figure 1 shows an example of a model with an implicit system of constraint equations associated with the highlighted nodes. This region has redundant surface-based tie specifications with opposite main and secondary surface roles.

Figure 1. Highlighted diagnostic node set.

After running this job, the status file shows the following output:

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CONSTRAINT SYSTEM DIAGNOSTIC OUTPUT
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***WARNING: Abaqus/Explicit has formed at least one moderately-sized implicit
            system of equations associated with enforcing constraints. Solving
            this system of equations would  moderately degrade performance.
            Please refer to Abaqus/Explicit constraints documentation about
            implicit systems of equations for suggestions on how to reduce the
            size of, or avoid, these systems of equations.  Additional details
            on individual systems of equations follows:

System               Solve           Number of       Node set             TriggerNodeSet
 Rank              Operations        Variables
--------------------------------------------------------------------------------------------------
    1              140499               201          InfoNsetSystNodes1   InfoNsetSystNodes1_Trigger

This output informs you about a moderately sized implicit system that has 201 degrees of freedom and would require 140,499 operations to solve during each iteration of the solution. The diagnostic message for this implicit system of equations is informational (rather than a warning or error message) because the number of computational operations to solve the system of equations is moderate. The nodes highlighted in Figure 1 are associated with an automatically generated node set referred to by the diagnostic message. The TriggerNodeSet is a set of nodes that most likely have constraints that require implicit solution. In general, studying constraints and connections associated with such node sets might help you understand the source of overlap associated with the implicit system of equations. Avoiding redundant tie specifications enable this simulation to run about 30% faster. Larger speedups can occur for larger implicit systems of constraint equations.