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Reference Guide
This manual provides a detailed list and usage information regarding input entries, output entries, and parameters available in OptiStruct.
Input Data
Element Quality Check
In order to prevent analyses from being carried out on badly discretized models, an element quality check is incorporated into the pre-processing phase.
CPENTA Element Checks and Default Bound Values
Reference Plane for Quadrilateral Element or Face
In order to measure the distortion of the quadrilateral face of a solid element, a unique reference plane is defined by two auxiliary plane vectors.

Welcome
What's New
View new features for OptiStruct 2025.
Overview
OptiStruct is a proven, modern structural solver with comprehensive, accurate and scalable solutions for linear and nonlinear analyses across statics and dynamics, vibrations, acoustics, fatigue, heat transfer, and multiphysics disciplines.
Tutorials
Discover OptiStruct functionality with interactive tutorials.
User Guide
This manual provides detailed information regarding the features, functionality, and simulation methods available in OptiStruct.
Reference Guide
This manual provides a detailed list and usage information regarding input entries, output entries, and parameters available in OptiStruct.
- Input Data
  - Bulk Data Input File
    The input file in OptiStruct is composed of three distinct sections.
  - I/O Options and Subcase Information Entries Guidelines
    The following guidelines apply to all entries in the I/O Options and Subcase Information sections.
  - Bulk Data Guidelines
    The following guidelines apply to all entries in the Bulk Data Entry section.
  - Solution Sequences - Data Selectors
    The Data Selectors table is available in an Excel spreadsheet.
  - Supported Optimization Type Chart
    Supported types of optimization for various analysis sequences are outlined.
  - I/O Options Defaults Summary
  - I/O Options by Function
    Descriptions for individual I/O Option Entries can be accessed by selecting from the links for each entry, listed below in groups according to their purpose and alphabetically on the I/O Options section page.
  - Subcase Information Entries by Function
    Descriptions for individual Subcase Information Entries can be accessed by selecting from the links for each entry, listed below in groups according to their purpose and alphabetically on the Subcase Information Section page.
  - Bulk Data Entries by Function
    Guidelines for using Bulk Data Entries are listed in Bulk Data Guidelines.
  - I/O Options Section
    Alphabetical listing of the I/O Options Entries.
  - Subcase Information Section
    Alphabetical listing of the Subcase Information Entries.
  - Bulk Data Section
    Alphabetical listing of the Bulk Data Entries.
  - Element Quality Check
    In order to prevent analyses from being carried out on badly discretized models, an element quality check is incorporated into the pre-processing phase.
    - CGASK6 Element Checks and Default Bound Values
      The element check and default bounds of the CGASK6 element are identical as those of the first-order (6-noded) CPENTA element.
    - CGASK8 Element Checks and Default Bound Values
      The element check and default bounds of the CGASK8 element are identical as those of the first-order (8-noded) CHEXA element.
    - CGASK12 Element Checks and Default Bound Values
      The element check and default bounds of the CGASK12 element are identical as those of the second-order (15-noded) CPENTA element. Notice that CGASK12 has six 3-node edges of which Hoe Normal Offset and Hoe Tangent Offset are checked.
    - CGASK16 Element Checks and Default Bound Values
      The element check and default bounds of the CGASK16 element are identical as those of the second-order (20-noded) CHEXA element. Notice that CGASK16 has 8 3-node edges of which Hoe Normal Offset and Hoe Tangent Offset are checked.
    - CTRIA3 Element Checks and Default Bound Values
    - CQUAD4 Element Checks and Default Bound Values
    - CQUAD8 Element Checks and Default Bound Values
    - CTAXI / CTRIAX6 Element Checks and Default Bound Values
    - CTRIA6 Element Checks and Default Bound Values
    - CTETRA Element Checks and Default Bound Values
    - CPENTA Element Checks and Default Bound Values
      - Reference Plane for Quadrilateral Element or Face
        In order to measure the distortion of the quadrilateral face of a solid element, a unique reference plane is defined by two auxiliary plane vectors.
    - CHEXA Element Checks and Default Bound Values
    - CPYRA Element Checks and Default Bound Values
  - Material Property Check
    In order to prevent analyses from being carried out on models with poor material definitions, a material property check is incorporated into the pre-processing phase. The material property check is controlled by the CHECKMAT parameter (see the PARAM input format).
- Output Data
- Legacy Data
Example Guide
The OptiStruct Example Guide is a collection of solved examples for various solution sequences and optimization types and provides you with examples of the real-world applications and capabilities of OptiStruct.
Verification Problems
This manual presents solved verification models including NAFEMS problems.
Frequently Asked Questions
This section provides quick responses to typical and frequently asked questions regarding OptiStruct.

Reference Plane for Quadrilateral Element or Face

In order to measure the distortion of the quadrilateral face of a solid element, a unique reference plane is defined by two auxiliary plane vectors.

The plane vectors are calculated as:

{PL}_{1} = (V_{3} + V_{2}) - (V_{1} + V_{4})

{PL}_{2} = (V_{3} + V_{4}) - (V_{1} + V_{2})

where,

V_{1}

V_{2}

V_{3}

, and

V_{4}

are the vectors that connect the four corner nodes with the centroid of the quadrilateral. These two plane vectors and the centroid are then used to construct the reference plane.

Figure 1. Vectors of a Non-warping Quadrilateral Face