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Chapter 15: State-Space Matrices Export

The goal of reduced-order modeling based on state-space matrices is to generate a model using fewer equations while still showing the same dynamics characteristics. The state-space matrices formulation is an easy way to define this reduced model as a function of the inputs and the outputs. It is used in multi-domain simulation software like Simplorer.

15.1. State-Space Matrices Based on Modal Analysis

The SPMWRITE command can be used to export state-space matrices based on a modal analysis when:

The damping is proportional (e.g., no element damping).

The mass and stiffness matrices are symmetric.

Prior to calculating the state-space matrices, you need to perform a modal analysis using the LANB, LANPCG, SNODE, or SUBSP eigensolver (MODOPT command). When obtaining the modal solution, consider the following:

Modes do not need to be expanded.

If you are applying nodal loads (forces or torques), you may specify them directly through table parameter input (inputs on the SPMWRITE command). For other types of loads (e.g. pressure) you must define the loads in the modal analysis and use the MODCONT command to generate the corresponding load vectors.

If you need an initial condition for your reduced model, you must define the load in the modal analysis to generate the corresponding load vector (NIC on the SPMWRITE command).

Damping must be specified (see DMPRAT, MDAMP, BETAD, or ALPHAD command).

State-space matrices are calculated in postprocessing using the file Jobname.MODE. They are written to the file Jobname.SPM using the requested format (FileFormat on the SPMWRITE command).

15.1.1. Examples of SPMWRITE Command Usage

This section describes how to use SPMWRITE to export state-space matrices based on two sets of model criteria.

1.The first set of model criteria for export to Simplorer are as follows:

10 modes are taken into account.

There are 2 inputs specified in the array parameter ‘inputTab’.

The inputs labels are defined in the character array parameter ‘inputLab’.

There is 1 output specified in the array parameter ‘outputTab’.

The output label is defined in the character array parameter ‘outputLab’.

Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential information

 

of ANSYS, Inc. and its subsidiaries and affiliates.

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