The Coupled Structural/Thermal/Electromagnetic (CSTEM) computer program implements an integrated multidisciplinary approach to analysis and optimization of the designs of graded composite-material structures. The name of the program reflects recognition of the coupling among thermal, electromagnetic, mechanical, and other phenomena in such structures. The integrated multidisciplinary approach is necessary because the coupling among the phenomena gives rise to complexity and contributes to nonlinearity in the characteristics and responses of the structures, such that separate analyses of a structure according to traditionally separate disciplines (e.g., acoustics, structural vibrations, structural loads, thermal effects, and electromagnetic properties taken by themselves) could lead to erroneous conclusions.

CSTEM is written in FORTRAN and is an extended and updated version of the program described in "Multidisciplinary Design of Hot Composite Structures" (LEW-15977), NASA Tech Briefs, Vol. 20, No. 3 (March 1996), page 24. As in that program, an essential feature of the multidisciplinary approach is finite-element numerical simulation of the relevant physical phenomena according to the applicable disciplines. The code includes (1) analysis modules that perform calculations pertaining to the separate disciplines and (2) an executive subprogram that controls an iterative solution procedure in which coupling and nonlinearity are taken into account by means of communication of input results among, and coordination of the functions of, the analysis modules. Each analysis module receives the relevant input geometric and control data and transmits any results that may be needed as input for another analysis module.

A notable advanced feature of CSTEM is a capability for analysis of a heterogeneous composite-material structure that contains multiple material layers or other regions, without the necessity of using one element for each layer or region. Such properties as the stiffness, thermal conductivity, and electromagnetic absorptivity of an element that comprises multiple layers or other regions are calculated by use of integration points located at the centroids of the layers or other regions within the element. The composite gradients control the finite-element definition of a structure, with two parameters that can be varied: the number of elements along the gradient and the number of numerical quadrature points within an element.

The structural-analysis module performs a large-deformation analysis, using a unique incrementally updated Lagrangian with iterative refinement. Associated with the large-deformation structural-analysis module is a deformed-position vibration-mode-analysis module. The thermal- and electromagnetic-analysis modules use the same finite elements as does the structural-analysis module; this feature facilitates coupling among the modules.

Some other notable features of CSTEM include the following:

  • Capabilities for nonlinear-buckling, transient-heat-transfer, internal-damage (creep, plasticity, fatigue), and acoustical analyses;
  • Computation of macroscopic properties of a composite material from the properties of the constituent materials at the microscopic level;
  • Computation of electromagnetic absorption of a composite material by use of an easily modifiable database of absorption properties of constituent materials; and
  • A capability for generation of internal computational meshes.

This program was written by Christos C. Chamis, Charles A. Farrell, and Bruce N. Canright of Glenn Research Center and Richard L. McKnight, Michael S. Hartle, and Hsin-Tien Huang of General Electric Co. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Software category.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4 —8
21000 Brookpark Road
Cleveland
Ohio 44135.

Refer to LEW-17052.