*EIGENVIV

Data format:

One line with 3parameters followed by one line with NBMODES parameters, as follows:

NBMODES XLOCMIN XLOCMAX
MODEID(1) MODEID(2) ... MODEID(NBMODES)

Status :

Optional.

Purpose:

To select the modes identification numbers to be taken into account in a VIV analysis based on the modal approach (DEEPVIV). This supersedes the automated selection of bending modes that are out-of-plane with respect to the current flow direction. Selection of modes through this keyword is useful when coupled modes are found from the modal analysis.

Restrictions:

Used with VIV analyses based on the modal superposition approach only.

Details :

Parameter	Description
NBMODES	Number of modes to be selected.
XLOCMIN	XLOCMIN is the minimum curved abscissa cutoff. This parameter is useful only in conjunction with the VIVIL keyword and can be omitted when VIVIL is not included. The location of the maximum modal amplitude is determined for each modes I1 to INMO. If the location is not comprised between XLOCMIN and XLOCMAX based on the arc length of the group of elements studied, the mode is not taken into account in the freespan VIV analysis.
XLOCMAX	XLOCMAX is the maximum curved abscissa cutoff. This parameter is useful only in conjunction with the VIVIL keyword and can be omitted when VIVIL is not included. The location of the maximum modal amplitude is determined for each modes I1 to INMO. If the location is not comprised between XLOCMIN and XLOCMAX based on the arc length of the group of elements studied, the mode is not taken into account in the freespan VIV analysis.
MODEID(I)	Identification number of the ith mode to be accounted for.

Note

This keyword can be used under certain circumstances when complex mode shapes are obtained from the VIV analysis and the algorithm used to select the potentially excited modes may fail to consider all the relevant modes.

Example:

*EIGENVIV
3
2 4 6

The VIV response will be computed based on modes 2, 4 and 6 only.