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Substructure Generation

This procedure can be used to create the stiffness matrix of a substructure
(sometimes also called a superelement) and store it in a file. A substructure
consists of selected degrees of freedom of a model. It can be used in a
subsequent linear analysis (this option is not available in CalculiX). In such an analysis,
only the selected degrees of freedom are addressable, e.g. to apply loads or
boundary conditions. The other degrees of freedom have been removed, thereby
substantially reducing the size of the stiffness matrix. The retained degrees
of freedom kind of constitute a new element (which explains the term
superelement).

The substructure generation is triggered by the procedure card
*SUBSTRUCTURE GENERATE. The degrees of freedom
which should be retained can be defined by using the *RETAINED NODAL
DOFS card. No transformation is allowed, consequently,
the degrees of freedom apply to the global Carthesian system. Finally, the
storage of the stiffness matrix is governed by the *SUBSTRUCTURE
MATRIX OUTPUT card, specifying the name of the
file without extension. The extension .mtx is default.

The output in the .mtx file constitutes the input one needs to use the
superelement in ABAQUS. It consists of:

- a *USER ELEMENT card specifying the number of degrees of freedom involved in the
substructure (misleadingly defined as ``nodes'').
- a list of the nodes. Each node is listed as many times as the number of
its degrees of freedom in the substructure.
- for each retained degree of freedom its global direction. The format for
the first degree of freedom of the substructure is just the global
direction. For the subsequent degrees of freedom it consists of the number
of the degree of freedom followed by the global direction
- a *MATRIX,TYPE=STIFFNESS card followed by the upper triangle (including
the diagonal) of the stiffness matrix, column by column, and comma
separated.

Since substructures cannot be used in CalculiX, the generation of the
substructure stiffness matrix is meant to be used by other programs.

** Next:** Electromagnetism
** Up:** Types of analysis
** Previous:** Three-dimensional Navier-Stokes Calculations
** Contents**
guido dhondt
2018-12-15