gmmonkey
Mechanical
- Jan 10, 2006
- 4
Hey everyone,
I posted this in the ABAQUS forum also but I thought some non-ABAQUS users might have some thougts and advice on my problem too. Ok, I don’t even know where to start, so I’ll tell you what I’m designing first of all, and then my problems leading up to where I am now.
What I’m doing
I’m designing a picture frame. A picture frame is a rig that shear tests viscous textile composites. Heres a picture of it without the composite clamped in,
A tensile force is applied across diagonally opposing corners of the picture frame rig causing the picture frame to move from an initially square configuration into a rhomboid. Consequently the sample clamped within the frame experiences pure shear.
What I’m using a FEA picture frame model for
I’m using it mainly for two things (there was other things that I was going to use it for but it was too ambitious, and I’ll leave that for another thread some other time…).
1) to analyze my design and see if I can make any improvements on it
2) to test constitutive composite models
I’m using an explicit method to model the picture frame. The arms are pinned together with rigid body pins. I had problems with my meshing initially on the arms of the picture frame. I couldn’t partition it properly and I was getting squashed and distorted tet elements along boundarys. I was getting a warning of ‘more than 300,000 increments….use the double point precision method’ and convergance problems. I tried mass scaling, to the point of giving the arms a near density of a collapsed star, which helped, but that obviously gave me a funny simulation. I managed to mesh it with quads eventually,and get a very accurate mesh with zero warnings or errors.I'm just trying to get it working without any composite in it just now. Here's a picture of it without the composite or the clamping plates to secure the composite.
I thought this would reduce my time increments, which it did, when I ran the simulation without moving the arms. But, when I created a velocity boundary condition on the rigid body pin at the top, to simulate the tensile testing machine, I get these messages.
***WARNING: THE OPTION *BOUNDARY,TYPE=DISPLACEMENT HAS BEEN USED; CHECK STATUS FILE BETWEEN STEPS FOR WARNINGS ON ANY JUMPS PRESCRIBED ACROSS THE STEPS IN DISPLACEMENT VALUES OF TRANSLATIONAL DOF. FOR ROTATIONAL DOF MAKE SURE THAT THERE ARE NO SUCH JUMPS. ALL JUMPS IN DISPLACEMENTS ACROSS STEPS ARE IGNORED
***WARNING: In contact pair 5, node 138 of instance ARM3 on the slave surface ASSEMBLY_ARM3-UPPER-INNER has 3244.0 times more mass than the mass associated with the rigid master surface ASSEMBLY_PIN3. Significant contact noise may result with the kinematic contact algorithm when the slave nodes have significantly greater mass than the mass associated with the rigid master surface. Suggested workaround includes using mass-scaling to adjust the ratio of masses or using the penalty contact algorithm.
I get the second warning 3 times, for every pin that moves. The bottom pin stays fixed, so I don’t get an error for that. The top pin moves in the y-direction and restriced on the x and z axis, pulling the arms fixed to it. The other 2 pins are free to move in the x and y direction but restricted in the z direction.
Ok, I thought the first warning meant the 3 pins couldn’t accelerate instantly to the defined boundary velocity. So I Inserted a step and defined an acceleration up to the next steps required velocity. But I got this instead of the previous warnings and it stopped the analysis,
***ERROR: THIS DEGREE OF FREEDOM HAS BOTH VELOCITY AND ACCELERATION SPECIFIED. THIS IS NOT ALLOWED. NODE 154 INSTANCE RIGIDPIN-3 DOF 2
***NOTE: DUE TO AN INPUT ERROR THE ANALYSIS PRE-PROCESSOR HAS BEEN UNABLE TO INTERPRET SOME DATA. SUBSEQUENT ERRORS MAY BE CAUSED BY THIS OMISSION
***ERROR: 1 nodes have dof on which velocity/displacement/acceleration/base
motion etc. constraints are specified simultaneously. The nodes have
been identified in node set ErrNodeBCRedundantDof.
I had these messages before when I couldn’t mesh the model properly. I ignored it because I felt the large number of increments were mainly to do with my meshing. It feels like I’m a snake eating its tale and I’m back to square one. Sometimes this program makes me cry. Now I don’t know what to do. Any help or ideas would be more than welcome (complete understatement).
I posted this in the ABAQUS forum also but I thought some non-ABAQUS users might have some thougts and advice on my problem too. Ok, I don’t even know where to start, so I’ll tell you what I’m designing first of all, and then my problems leading up to where I am now.
What I’m doing
I’m designing a picture frame. A picture frame is a rig that shear tests viscous textile composites. Heres a picture of it without the composite clamped in,
A tensile force is applied across diagonally opposing corners of the picture frame rig causing the picture frame to move from an initially square configuration into a rhomboid. Consequently the sample clamped within the frame experiences pure shear.
What I’m using a FEA picture frame model for
I’m using it mainly for two things (there was other things that I was going to use it for but it was too ambitious, and I’ll leave that for another thread some other time…).
1) to analyze my design and see if I can make any improvements on it
2) to test constitutive composite models
I’m using an explicit method to model the picture frame. The arms are pinned together with rigid body pins. I had problems with my meshing initially on the arms of the picture frame. I couldn’t partition it properly and I was getting squashed and distorted tet elements along boundarys. I was getting a warning of ‘more than 300,000 increments….use the double point precision method’ and convergance problems. I tried mass scaling, to the point of giving the arms a near density of a collapsed star, which helped, but that obviously gave me a funny simulation. I managed to mesh it with quads eventually,and get a very accurate mesh with zero warnings or errors.I'm just trying to get it working without any composite in it just now. Here's a picture of it without the composite or the clamping plates to secure the composite.
I thought this would reduce my time increments, which it did, when I ran the simulation without moving the arms. But, when I created a velocity boundary condition on the rigid body pin at the top, to simulate the tensile testing machine, I get these messages.
***WARNING: THE OPTION *BOUNDARY,TYPE=DISPLACEMENT HAS BEEN USED; CHECK STATUS FILE BETWEEN STEPS FOR WARNINGS ON ANY JUMPS PRESCRIBED ACROSS THE STEPS IN DISPLACEMENT VALUES OF TRANSLATIONAL DOF. FOR ROTATIONAL DOF MAKE SURE THAT THERE ARE NO SUCH JUMPS. ALL JUMPS IN DISPLACEMENTS ACROSS STEPS ARE IGNORED
***WARNING: In contact pair 5, node 138 of instance ARM3 on the slave surface ASSEMBLY_ARM3-UPPER-INNER has 3244.0 times more mass than the mass associated with the rigid master surface ASSEMBLY_PIN3. Significant contact noise may result with the kinematic contact algorithm when the slave nodes have significantly greater mass than the mass associated with the rigid master surface. Suggested workaround includes using mass-scaling to adjust the ratio of masses or using the penalty contact algorithm.
I get the second warning 3 times, for every pin that moves. The bottom pin stays fixed, so I don’t get an error for that. The top pin moves in the y-direction and restriced on the x and z axis, pulling the arms fixed to it. The other 2 pins are free to move in the x and y direction but restricted in the z direction.
Ok, I thought the first warning meant the 3 pins couldn’t accelerate instantly to the defined boundary velocity. So I Inserted a step and defined an acceleration up to the next steps required velocity. But I got this instead of the previous warnings and it stopped the analysis,
***ERROR: THIS DEGREE OF FREEDOM HAS BOTH VELOCITY AND ACCELERATION SPECIFIED. THIS IS NOT ALLOWED. NODE 154 INSTANCE RIGIDPIN-3 DOF 2
***NOTE: DUE TO AN INPUT ERROR THE ANALYSIS PRE-PROCESSOR HAS BEEN UNABLE TO INTERPRET SOME DATA. SUBSEQUENT ERRORS MAY BE CAUSED BY THIS OMISSION
***ERROR: 1 nodes have dof on which velocity/displacement/acceleration/base
motion etc. constraints are specified simultaneously. The nodes have
been identified in node set ErrNodeBCRedundantDof.
I had these messages before when I couldn’t mesh the model properly. I ignored it because I felt the large number of increments were mainly to do with my meshing. It feels like I’m a snake eating its tale and I’m back to square one. Sometimes this program makes me cry. Now I don’t know what to do. Any help or ideas would be more than welcome (complete understatement).
