MYSTRAN Forum

I'm trying to implement my own RBE3 according to the Mystran manual and I've noticed something that looks like a familiar type of wrong behavior. I'm not really sure if it is wrong or not or if Mystran also behaves this way. I haven't used Mystran before but I'd like see what other people think of it before setting up Mystran and learning how to define a model.

In my implementation, when I apply a moment load about the x axis, it causes the correct moment about x but also another moment about the y axis as shown in the attached picture. Note that the independent nodes are on an inclined face, not in a plane normal to the applied moment.

If you've used RBE3 before, would you expect this beam to bend as well as twist?

I'm suspicious of this because CalculiX has a similar issue with its moment loads on beams which are internally converted to MPCs similar to an RBE3.

I've made a simpler example and solved with Mystran. It's a single CHEXA element supported on one face (grids 1,2,3,4) by SPCs and with a moment about Z applied to the opposite face (grids 5,6,7,8) via RBE3 from a separate grid 9.

Input file:

Code:
SOL STATICS

CEND

SPC = 1

LOAD = 1

SPCFORCES = ALL

BEGIN BULK

GRID    1       0       0.      -1.     0.0

GRID    2       0       1.      0.      0.0

GRID    3       0       0.      1.      0.0

GRID    4       0       -1.     0.      0.0

GRID    5       0       0.      -1.     1.2

GRID    6       0       1.      0.      1.0

GRID    7       0       0.      1.      0.8

GRID    8       0       -1.     0.      1.0

GRID    9       0       0.      0.      1.0

C Element Connectivity: CHEXA

CHEXA   1       1       1       2       3       4       5       6       +CH1

+CH1    7       8

PSOLID  1       1       0       2       FULL

MAT1    1       200.E9          0.

SPC     1       1       1       0.

SPC     1       1       2       0.

SPC     1       1       3       0.

SPC     1       2       1       0.

SPC     1       2       2       0.

SPC     1       2       3       0.

SPC     1       3       1       0.

SPC     1       3       2       0.

SPC     1       3       3       0.

SPC     1       4       1       0.

SPC     1       4       2       0.

SPC     1       4       3       0.

MOMENT  1       9       0       100000. 0.      0.      1.

RBE3    2               9       123456  1.0     123     5       6       +1

+1      7       8

ENDDATA

Here's the solution for reaction forces on the SPC nodes (T1-T3) and my hand calculated moments about the 3 axes due to those forces (Moment X, Moment Y, Moment Z):

Code:
           GRID     COORD      T1            T2            T3       Moment X      Moment Y      Moment Z

                     SYS

              1        0 -2.431020E+04  9.081890E+02  5.563799E+02 -5.563799E+02               -2.431020E+04

              2        0  5.401138E+02 -2.440502E+04  4.443620E+03  0.0          -4.443620E+03 -2.440502E+04

              3        0  2.581279E+04 -1.975163E+03  5.563799E+02  5.563799E+02               -2.581279E+04

              4        0 -2.042702E+03  2.547199E+04 -5.556380E+03  0.0          -5.556380E+03 -2.547199E+04

            Sum                                                     0.0          -1.000000E+04 -1.000000E+05

The total reaction moment about Z (-1.000000E+05) is the opposite of the applied moment which looks correct. However, there's also a reaction moment about Y (-1.000000E+04) which I think should be zero. It doesn't balance with the applied moment.

Any thoughts?

Gotcha...we use this forum sometimes for general info and some static links and such. But all of the action is on Discord.

Victor

Victor

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