Keyword type: step
This procedure is used to perform a pure heat transfer analysis. A heat transfer analysis is always nonlinear since the material properties depend on the solution, i.e. the temperature.
There are six optional parameters: SOLVER, DIRECT, STEADY STATE, FREQUENCY, MODAL DYNAMIC and STORAGE.
SOLVER determines the package used to solve the ensuing system of equations. The following solvers can be selected:
Default is the SGI solver. If this solver is not installed, default is SPOOLES. If neither the SGI solver nor SPOOLES are installed, default is TAUCS. Finally, if neither the SGI solver, nor SPOOLES nor TAUCS are installed, the default is the iterative solver, which comes with the CalculiX package.
The SGI solver is the fastest, but is is proprietary: if you own SGI
hardware you might have gotten the scientific software package as well, which
contains the SGI sparse system solver. SPOOLES is also very fast, but has no
out-of-core capability: the size of systems you can solve is limited by your
RAM memory. With 2GB of RAM you can solve up to 250,000 equations. TAUCS is
also good, but my experience is limited to the decomposition, which
only applies to positive definite systems. It has an out-of-core capability
and also offers a
decomposition, however, I was not able to run either of
them so far. Next comes the iterative solver. If SOLVER=ITERATIVE SCALING is
selected, the preconditioning is limited to a scaling of the diagonal terms,
SOLVER=ITERATIVE CHOLESKY triggers Incomplete Cholesky
preconditioning. Cholesky preconditioning leads to a better convergence and
maybe to shorter execution times, however, it requires additional storage
roughly corresponding to the nonzeros in the matrix. If you are short of
memory, diagonal scaling might be your last resort. The iterative methods
perform well for truely three-dimensional structures. For instance,
calculations for a hemisphere were about nine times faster with the ITERATIVE
SCALING solver, and three times faster with the ITERATIVE CHOLESKY solver than
with SPOOLES. For two-dimensional structures such as plates or shells, the
performance might break down drastically and convergence often requires the
use of Cholesky preconditioning. SPOOLES (and any of the other direct solvers)
performs well in most situations with emphasis on slender structures but
requires much more storage than the iterative solver.
The parameter DIRECT indicates that automatic incrementation should be switched off. The increments will have the fixed length specified by the user on the second line.
The parameter STEADY STATE indicates that only the steady state should be calculated. For such an analysis the loads are by default applied in a linear way. Other loading patterns can be defined by an *AMPLITUDE card. If the STEADY STATE parameter is absent, the calculation is assumed to be time dependent and a transient analysis is performed. For a transient analysis the specific heat of the materials involved must be provided and the loads are by default applied by their full strength at the start of the step.
In a static step, loads are by default applied in a linear way. Other loading patterns can be defined by an *AMPLITUDE card.
The parameter FREQUENCY indicates that a frequency calculation should be performed. In a frequency step the homogeneous governing equation is solved, i.e. no loading applies, and the corresponding eigenfrequencies and eigenmodes are determined. This option is especially useful if the heat transfer option is used as an alias for true Helmholtz-type problems, e.g. in acoustics. The option FREQUENCY cannot (yet) be applied to cyclic symmetry calculations.
The parameter MODAL DYNAMIC is used for dynamic calculations in which the response is built as a linear combination of the eigenmodes of the system. It must be preceded by a *HEAT TRANSFER, FREQUENCY,STORAGE=YES procedure, either in the same deck, or in a previous run, either of which leads to the creation of a file with name jobname.eig containing the eigenvalues and eigenmodes of the system. A MODAL DYNAMIC procedure is necessarily linear and ideally suited of problems satisfying the classical wave equation (Helmholtz problem characterized by a second derivative in time, thus exhibiting a hyperbolic behavior), e.g linear acoustics.
Finally, the parameter STORAGE indicates whether the eigenvalues, eigenmodes, mass and stiffness matrix should be stored in binary form in file jobname.eig for further use in a *MODAL DYNAMICS or *STEADY STATE DYNAMICS procedure. Default is STORAGE=NO. Specify STORAGE=YES if storage is requested.
First line:
Second line if FREQUENCY nor MODAL DYNAMIC is not selected:
Example:
*HEAT TRANSFER,DIRECT .1,1.
defines a static step and selects the SPOOLES solver as linear equation solver in the step (default). The second line indicates that the initial time increment is .1 and the total step time is 1. Furthermore, the parameter DIRECT leads to a fixed time increment. Thus, if successful, the calculation consists of 10 increments of length 0.1.
Example files: beamhtcr, oneel20fi.
Second line if FREQUENCY is selected:
Example: *HEAT TRANSFER,FREQUENCY 8
defines a frequency step for the heat transfer equation. The eight lowest
eigenvalues and corresponding eigenmodes are calculated. Notice that for the
heat equation the following relation applies between the eigenvalue
and eigenfrequency
:
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If, on the other hand, the heat transfer option is used as an alias for the Helmholtz equation, e.g. for acoustic problems, the same relationship as in elastodynamics
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applies.
Second line if MODAL DYNAMIC is selected:
Example files: aircolumn.