09-28-2021, 04:38 AM
I came across and issue with the RBE3 element. I have already emailed Bill about the issue, but I thought I would post here for the benefit of the rest pf the community.
I am using a RBE3 to distribute load at a bolted joint. The joint is in thin sheet metal structure so I do not want the fasteners to take out of plane load. I used the following RBE3 to accomplish this.
RBE3 17 17 123456 0.189 13 9901 0.189+
+ 13 9902 0.189 13 9903 0.189 13 9904+
+ 0.189 12 9905 0.189 12 9906 0.189 12+
+ 9907 0.189 12 9908 0.189 12 9909 0.189+
+ 12 9910 0.189 12 9911 0.189 12 9912+
+ 0.189 13 9913 0.189 13 9914 0.189 13+
+ 9915 0.189 13 9916
When I run this through MYSTRAN the SPC forces are not equal and opposite the applied loads. The SPC forces in the Y and Z directions are half of what they should be. It appears that the RBE3 is incorrectly calculating the weighted average when one or more independent nodes are not effective in all three translational DOF. To check this I changed the RBE3 to have Ci = 123 for every independent node. I also ran my original model through NXNASTRAN. In both cases the SPC forces were equal and opposite to the applied loads.
I have attached copies of the BDF and F06 files for the original run and the run with Ci = 123.
Cheers.
Jon
I am using a RBE3 to distribute load at a bolted joint. The joint is in thin sheet metal structure so I do not want the fasteners to take out of plane load. I used the following RBE3 to accomplish this.
RBE3 17 17 123456 0.189 13 9901 0.189+
+ 13 9902 0.189 13 9903 0.189 13 9904+
+ 0.189 12 9905 0.189 12 9906 0.189 12+
+ 9907 0.189 12 9908 0.189 12 9909 0.189+
+ 12 9910 0.189 12 9911 0.189 12 9912+
+ 0.189 13 9913 0.189 13 9914 0.189 13+
+ 9915 0.189 13 9916
When I run this through MYSTRAN the SPC forces are not equal and opposite the applied loads. The SPC forces in the Y and Z directions are half of what they should be. It appears that the RBE3 is incorrectly calculating the weighted average when one or more independent nodes are not effective in all three translational DOF. To check this I changed the RBE3 to have Ci = 123 for every independent node. I also ran my original model through NXNASTRAN. In both cases the SPC forces were equal and opposite to the applied loads.
I have attached copies of the BDF and F06 files for the original run and the run with Ci = 123.
Cheers.
Jon