ABAQUS Analysis User's Manual  

25.2.18 UCORR
User subroutine to define cross-correlation properties for random response loading.

Product: ABAQUS/Standard  

References

Overview

User subroutine UCORR:

  • can be used to define the coefficients for the cross-correlation matrix in a random response analysis;

  • will be called once for the combination of any two degrees of freedom with nonzero prescribed loads for each load case specified as a concentrated or distributed load or once for the combination of any two excitation directions specified as a base motion;

  • allows correlation coefficients to be defined as a function of nodal coordinates; and

  • ignores any data specified outside the user subroutine for the associated cross-correlation matrix.

Cross-correlation for base motion excitation

The spatial correlation matrix for base motion excitation is defined by the coefficients in user subroutine UCORR, where are excitation directions and corresponds to the th frequency function referenced under load case .

Cross-correlation for point loads and distributed loads

The spatial correlation matrix of the load is defined as follows. Let be the load applied to degree of freedom at node in load case , through the use of a concentrated or distributed load. Let correspond to the th frequency function referenced under load case . The spatial correlation matrix used in the random response analysis for this load case is then

where are the coefficients defined in user subroutine UCORR. Typically the load magnitude is given as 1.0; therefore, the load definition is simply selecting the nonzero terms that will appear in .

User subroutine interface

      SUBROUTINE UCORR(PSD,CORRR,CORRI,KSTEP,LCASE,JNODE1,JDOF1,
     1 JNODE2,JDOF2,COOR1,COOR2)
C
      INCLUDE 'ABA_PARAM.INC'
C
      DIMENSION COOR1(3),COOR2(3)
      CHARACTER*80 PSD

      user coding to define CORRR and CORRI

      RETURN
      END

Variables to be defined

CORRR

Real part of the cross-correlation scaling factor.

CORRI

Imaginary part of the cross-correlation scaling factor.

Variables passed in for information

PSD

User-specified name for the frequency function that references this correlation, left justified.

KSTEP

Step number.

LCASE

Load case number, .

JNODE1

First node involved, (not used for base motion excitation).

JDOF1

Degree of freedom at the first node (for concentrated or distributed load excitation) or global excitation direction (for base motion excitation).

JNODE2

Second node involved, (not used for base motion excitation).

JDOF2

Degree of freedom at the second node (for concentrated or distributed load excitation) or global excitation direction (for base motion excitation).

COOR1

An array containing the coordinates of the first node (not used for base motion excitation).

COOR2

An array containing the coordinates of the second node (not used for base motion excitation).

Example