modal_analysis

Mapdl.modal_analysis(method='lanb', nmode='', freqb='', freqe='', cpxmod='', nrmkey='', modtype='', memory_option='', mxpand='', elcalc=False)

Run a modal with basic settings analysis

Parameters:

methodstr

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

nmodeint, optional

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.

freqbfloat, optional

The beginning, or lower end, of the frequency range of interest.

freqefloat, optional

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.

cpxmodstr, optional

Complex eigenmode key. Valid only when method='QRDAMP' or method='unsym'

• 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.

nrmkeybool, optional

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.

modtypestr, optional

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_optionstr, optional

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 INCORE memory mode, the solver will then attempt to run in the OUTOFCORE memory mode.

• 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.

mxpandbool, optional

Number of modes or array name (enclosed in percent signs) to expand and write. If -1, do not expand and do not write modes to the results file during the analysis. Default "".

elcalcbool, optional

Calculate element results, reaction forces, energies, and the nodal degree of freedom solution. Default False.

Returns:

str

Output from MAPDL SOLVE command.

Return type:

str

Notes

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.

Examples

Modal analysis using default parameters for the first 6 modes

>>> mapdl.modal_analysis(nmode=6)