Learning Forum

[Diona Çejku]

Hello everyone,

So, I used the *DMAT command in ANSYS APDL to export mass and stiffness matrices. But now, when ANSYS writes the solution in MMF Format,  I'm a bit lost on how it arranges the matrices. Does ANSYS write the solution node-wise or degree-of-freedom-wise?

Thank you for your help. 

[Aurojyoti Prusty]

Hi,

The MAPDL solver calculates two types of results data, 1. Primary results such as displacements, temperature etc. and 2. Derived results data like strains, stresses, thermal gradients etc.

In ANSYS, primary results data consists of degrees of freedom solutions available at each node which is stored in List of solutions.

You can use command \PLNSOL to display nodal solutions as continuous contour in post processing for both primary and derived quanities.

[dlooman]

There are files that give you the dof order of the matrices created with *DMAT, but what is your purpose in exporting it?  There is the alternative HBMAT command to export files in the Harwell-Boeing format.  For small, academic exercizes it is more user-friendly to create a superelement with master dof for some or all of the dof.  SELIST,superelement name,3 will output the superelement mass and stiffness matrices in a readable format.

[Diona Çejku]

Hello,
Thank you for your reply. I am using *DMAT command to get the stiffness and mass matrix of a wind turbine blade. However, firstly for comparison purposes I just created a simple block with 8 nodes (36degrees of freedom but 24 of them are fixed, so I get a matrix of 12x12). I have also tried the HBMAT command, but the same question is applied in that case too. My question is whether the first three numbers in the matrix respresent the values of for example Node 2 in the x, y, and z directions or, alternatively, the values of Nodes 2, 3, and 4 in the x direction? So, Does ansys writes the mass and stiffness matrices node-wise or degrees-of-freedom-wise? 

Here is the code that I used for exporting the matrices 

*dmat, k0, D, import, full, Benchmark_Study_Block.full, stiff
*dmat, m0, D, import, full, Benchmark_Study_Block.full, mass

 

*export, k0, mmf, matkMMF.txt ! Exports Stiffness as MMF

*export, m0, mmf, matmMMF.txt ! Exports Mass as MMF

 

Example of the exported Stiffness matrix: 

 

%%MatrixMarket matrix array real general 
%============================================================
% Creator: ANSYS Inc
% 
% This is a 12 x 12 Matrix
%============================================================
12 12
1.88648504E+05
0.00000000E+00
0.00000000E+00
-3.81036325E+04
0.00000000E+00
0.00000000E+00
-3.81036325E+04
0.00000000E+00
0.00000000E+00
-8.41720085E+04
0.00000000E+00
0.00000000E+00
0.00000000E+00
3.22366453E+05
-1.31810897E+05
0.00000000E+00
8.12553419E+04
-2.80448718E+03
0.00000000E+00
-1.82366453E+05
2.80448718E+03
0.00000000E+00
-2.13178419E+05
1.31810897E+05
0.00000000E+00
-1.31810897E+05
3.22366453E+05
0.00000000E+00

.

.

Thank you for your help. 

[Chandra Sekaran]

These terms are DOF wise. However there are different ordering schemes for degrees of freedom. The .full file uses an internal Degree of freedom number order as explained in section 4.4 of the APDL guide ( https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v232/en/ans_apdl/apdldofordering.html ). A snippet is shown below. This ordering is different from the external node ID order that a user sees. 

4.4. Degree of Freedom Ordering

Degrees of freedom (DOFs) are numbered 1-n, where n is the total number of DOFs in the system. Mechanical APDL maintains three orderings of the DOF set:

1. The user ordering is based on the user's node numbers. As an example, this ordering corresponds to what would be printed in the POST1 postprocessor by the PRNSOL,U command.

2. The internal ordering is obtained by compressing the unused node numbers from the user's set and renumbering them based on the reordered element set. This reordering is performed to obtain better cache performance as these items are referenced in the solution phase. The map between the user ordering and this internal ordering is referred to as the "nodal equivalence table" in the descriptions of binary data files (see Format of Binary Data Files in the Programmer's Reference).

3. The solver ordering is obtained by reordering the equations (DOFs) in order to minimize the solver time and disk requirements. Also, the effects of any constraints (D command), couplings (CP command), and constraint equations (CE command or MPC contact) are accounted for, thereby reducing the DOF set. This ordering represents the "independent" DOFs of the system.

The matrices and load vector imported from the .FULL file (*SMAT,,,FULL) are in terms of the solver ordering; mapping from the internal ordering to this ordering is required when working with these matrices.