- Mapdl.modal_analysis(method='lanb', nmode='', freqb='', freqe='', cpxmod='', nrmkey='', modtype='', memory_option='', elcalc=False)¶
Run a modal with basic settings analysis
Mode-extraction method to be used for the modal analysis. Defaults to lanb (block lanczos). Must be one of the following:
LANB : Block Lanczos
LANPCG : PCG Lanczos
SNODE : Supernode modal solver
SUBSP : Subspace algorithm
UNSYM : Unsymmetric matrix
DAMP : Damped system
QRDAMP : Damped system using QR algorithm
VT : Variational Technology
The number of modes to extract. The value can depend on the value supplied for Method. NMODE has no default and must be specified. If Method = LANB, LANPCG, or SNODE, the number of modes that can be extracted can equal the DOFs in the model after the application of all boundary conditions.
The beginning, or lower end, of the frequency range of interest.
The ending, or upper end, of the frequency range of interest (in Hz). The default for Method = SNODE is described below. The default for all other methods is to calculate all modes, regardless of their maximum frequency.
Complex eigenmode key. Valid only when
AUTO : Determine automatically if the eigensolutions are real or complex and output them accordingly. This is the default for
method='UNSYM'. Not supported for Method = QRDAMP.
ON or CPLX : Calculate and output complex eigenmode shapes.
OFF or REAL : Do not calculate complex eigenmode shapes. This is required if a mode- superposition analysis is intended after the modal analysis for Method = QRDAMP. This is the default for this method.
Mode shape normalization key. When
True(default), normalize the mode shapes to the mass matrix. When False, Normalize the mode shapes to unity instead of to the mass matrix. If a subsequent spectrum or mode-superposition analysis is planned, the mode shapes should be normalized to the mass matrix.
Type of modes calculated by the eigensolver. Only applicable to the unsymmetric eigensolver.
Blank : Right eigenmodes. This value is the default.
BOTH : Right and left eigenmodes. The left eigenmodes are written to Jobname.LMODE. This option must be activated if a mode-superposition analysis is intended.
Memory allocation option:
DEFAULT- Default Memory mode
Use the default memory allocation strategy for the sparse solver. The default strategy attempts to run in the INCORE memory mode. If there is not enough available physical memory when the solver starts to run in the
INCOREmemory mode, the solver will then attempt to run in the
INCORE- In-core memory mode
Use a memory allocation strategy in the sparse solver that will attempt to obtain enough memory to run with the entire factorized matrix in memory. This option uses the most amount of memory and should avoid doing any I/O. By avoiding I/O, this option achieves optimal solver performance. However, a significant amount of memory is required to run in this mode, and it is only recommended on machines with a large amount of memory. If the allocation for in-core memory fails, the solver will automatically revert to out-of-core memory mode.
OUTOFCORE- Out of core memory mode.
Use a memory allocation strategy in the sparse solver that will attempt to allocate only enough work space to factor each individual frontal matrix in memory, but will store the entire factorized matrix on disk. Typically, this memory mode results in poor performance due to the potential bottleneck caused by the I/O to the various files written by the solver.
Calculate element results, reaction forces, energies, and the nodal degree of freedom solution. Default
Output from MAPDL SOLVE command.
For models that involve a non-symmetric element stiffness matrix, as in the case of a contact element with frictional contact, the QRDAMP eigensolver (MODOPT, QRDAMP) extracts modes in the modal subspace formed by the eigenmodes from the symmetrized eigenproblem. The QRDAMP eigensolver symmetrizes the element stiffness matrix on the first pass of the eigensolution, and in the second pass, eigenmodes are extracted in the modal subspace of the first eigensolution pass. For such non- symmetric eigenproblems, you should verify the eigenvalue and eigenmode results using the non-symmetric matrix eigensolver (MODOPT,UNSYM).
The DAMP and QRDAMP options cannot be followed by a subsequent spectrum analysis. The UNSYM method supports spectrum analysis when eigensolutions are real.
Modal analysis using default parameters for the first 6 modes