**MODOPT**,
* Method*,

`NMODE`

`FREQB`

`FREQE`

`Cpxmod`

`Nrmkey`

`ModType`

`BlockSize`

`--`

`--`

`--`

`FREQMOD`

Compatible Products: DesSpc | Pro | Premium | Enterprise | Ent PP | Ent Solver | –

`Method`

Mode-extraction method to be used for the modal analysis.

**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

`NMODE`

The number of modes to extract. The value can depend on the value supplied for

.`Method`

has no default and must be specified. If`NMODE`

= 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.`Method`

*Recommendation:*When = LANPCG,`Method`

should be less than 100 to be computationally efficient.`NMODE`

When = SNODE,`Method`

should be greater than 100 for 2-D plane or 3-D shell/beam models and greater than 250 for 3-D solid elements to be computationally efficient.`NMODE`

`FREQB`

The beginning, or lower end, of the frequency range (or eigenvalue range if

is specified) of interest.`FREQMOD`

For

= LANB, SUBSP, UNSYM, DAMP, and QRDAMP,`Method`

also represents the first shift point for the eigenvalue iterations. If values for UNSYM or DAMP are zero or blank, the default value is -1.0. For the other methods, the default is internally computed. Eigenvalue extraction is most accurate near the shift point; multiple shift points are used internally in the LANB, SUBSP, UNSYM, and QRDAMP methods. For LANB, LANPCG, SUBSP, UNSYM, DAMP, and QRDAMP methods with a positive`FREQB`

, eigenvalues are output beginning at the shift point and increase in magnitude. For UNSYM and DAMP methods with a negative`FREQB`

value, eigenvalues are output beginning at zero magnitude and increase.`FREQB`

Choosing higher

values with the LANPCG and SNODE methods may lead to inefficient solution times because these methods will find all eigenvalues between zero and`FREQB`

before finding the requested modes between`FREQB`

and`FREQB`

.`FREQE`

`FREQE`

The ending, or upper end, of the frequency range (or eigenvalue range if

is specified) of interest (in Hz). The default for`FREQMOD`

= SNODE is described below. The default for all other methods is to calculate all modes, regardless of their maximum frequency.`Method`

The default is 100 Hz for

= SNODE. To maintain solution efficiency, you should not set the`Method`

value too high; for example, not higher than 5000 Hz for an industrial problem. The higher the`FREQE`

value used for the SNODE method, the more accurate the solution will be and the more eigenvalues it could produce; but the solution time will also be longer. For example, if`FREQE`

is set to 1e8, it will cause the underlying supernodal structures to find all the possible eigenvalues of each group of supernodes; hence, it will take an excessive amount of solution time. The accuracy of the SNODE solution is controlled by both`FREQE`

and the`FREQE`

value on the`RangeFact`

**SNOPTION**command. Refer to**SNOPTION**for more information on using the SNODE eigensolver options to control solution efficiency and accuracy.`Cpxmod`

Complex eigenmode key. (Valid only when

= QRDAMP or`Method`

= UNSYM).`Method`

**AUTO**—

Determine automatically if the eigensolutions are real or complex and output them accordingly. This is the default for

= UNSYM. Not supported for`Method`

= QRDAMP.`Method`

**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

= QRDAMP. This is the default for this method.`Method`

`Nrmkey`

Mode shape normalization key:

**OFF**—

Normalize the mode shapes to the mass matrix (default).

**ON**—

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 (

= OFF).`Nrmkey`

`ModType`

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.`BlockSize`

The block vector size to be used with the Block Lanczos or Subspace eigensolver (used only when

= LANB or SUBSP).`Method`

must be an integer value between 0 and 16. When BlockSize = zero or blank, the code decides the block size internally (normally, a value of 8 is used for LANB and a value of 6 is used for SUBSP). Typically, higher`BlockSize`

values are more efficient under each of the following conditions:`BlockSize`

When running in out-of-core mode and there is not enough physical memory to buffer all of the files written by the Block Lanczos or Subspace eigensolver (and thus, the time spent doing I/O is considerable).

Many modes are requested (>100).

Higher-order solid elements dominate the model.

The memory usage only slightly increases as

is increased. It is recommended that you use a value divisible by 4 (4, 8, 12, or 16).`BlockSize`

`--`

Unused field.

`--`

Unused field.

`--`

Unused field.

`FREQMOD`

The specified frequency when the solved eigenvalues are no longer frequencies (for example, the model has the Floquet periodic boundary condition). In a modal analysis, the Floquet periodic boundary condition (body load FPBC) is only valid for the acoustic elements FLUID30, FLUID220, and FLUID221.

Specifies modal analysis (**ANTYPE**,MODAL) options. Additional options used
only for the Supernode (SNODE) eigensolver are specified by the **SNOPTION**
command. Additional options used only for the Subspace (SUBSP) eigensolver are specified by the
**SUBOPT** command. Additional options used only for
the Block Lanczos (LANB) eigensolver are specified by the **LANBOPTION** command.
Additional options used only for the QRDAMP eigensolver are specified by the
**QRDOPT** command.

If * Method* = LANPCG, ANSYS automatically switches to the PCG
solver internally for this modal analysis. You can further control the efficiency of the PCG
solver with the

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.

In a modal analysis, the Floquet periodic boundary condition (body load FPBC) is only valid for the acoustic elements FLUID30, FLUID220, and FLUID221.

This command is also valid in PREP7.

**Distributed ANSYS Restriction **The VT extraction method is not supported in Distributed ANSYS. All other
extraction methods are supported. Block Lanczos, PCG Lanczos, SUBSP, UNSYM, DAMP, and QRDAMP are
distributed eigensolvers that will run a fully distributed solution. However, the Supernode
eigensolver is not a distributed eigensolver; therefore, you will not see the full performance
improvements with this method that you would with a fully distributed solution.

Command Option Method | Available Products |

LANB | DesSpc | Pro | Premium | Enterprise | Ent PP | Ent Solver | – |

LANPCG | DesSpc | Pro | Premium | Enterprise | Ent PP | Ent Solver | – |

SNODE | – | Pro | Premium | Enterprise | Ent PP | Ent Solver | – |

SUBSP | DesSpc | Pro | Premium | Enterprise | Ent PP | Ent Solver | – |

UNSYM | – | – | Premium | Enterprise | Ent PP | Ent Solver | – |

DAMP | – | – | Premium | Enterprise | Ent PP | Ent Solver | – |

QRDAMP | – | – | Premium | Enterprise | Ent PP | Ent Solver | – |