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rwhirley
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Comments
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My recommendation would be to include as much of the actual support design as you can into your model. Computing power is plentiful these days, and there are many opportunities to miss important aspects of the structural response by introducing BC …
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Looks like the small bar is not merged to the round connecting bar? Should it be?
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I had a few more minutes to play with this model over lunch today. This was a bit tricky, but at least the contact is sorted out. 1. Tank density increased 10X to account for contents weight 2. Deleted forward & aft tanks; something about their…
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I have played with your model a bit and I think there are some problems beyond the contact. I deleted all the contact and fully fixed the ends of the tank cylinders. I changed the gravity load to ramp from 0 to 9.8 m/s2 over 1 s. Still, the model…
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The attached file clearly shows the problem after just one step. For simplicity I deleted all the ring stiffeners, but the problem is still present. My suspicions (in addition to a contact surface normal vector issue, as discussed above): 1. It is…
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Hello Aftab, I had a quick look and I believe some of the normal vectors in your contact surface definitions may be inconsistent. I got a partial solution by deleting contact surface #2, changing to nonlinear dynamic analysis (so inertia will smoot…
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Great. Let us know how it works.
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I was thinking you would define a contact surface between the sling shell surface facing the tank and the outer surface of the tank (shell or solid elements) facing the sling. That would allow the tank to buckle and pull away from the sling should …
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Try using thin shell elements with a high elastic modulus in a nonlinear (static or transient dynamic) analysis. Those elements will deform out-of-plane due to low bending stiffness but will be very stiff in membrane tension, thereby representing y…
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While I can't speak to those specific standards, typically "shall" is used to indicate a requirement and "may" is used to indicate a recommendation.
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Mark - what you want to do is set the shear modulus an order of magnitude below the bulk modulus K, not below the Young's modulus E. Here's a link to a table that can then give you the E and nu to input to achieve a target K and G for your fluid. …
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Agree - these problems can be challenging (but fun!). A few thoughts: 1. Set the pipe elastic modulus and yield stress to the desired values. Set the tool to be elastic with elastic modulus ~2X that of the pipe. This usually makes the contact wor…
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Often it's helpful to run some simple static analyses first, just to be sure the model constraints are doing what you want, before running the modal analysis. It's usually very quick as a model debugging tool.
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If you set up the entire nonlinear dynamic problem in Mecway (for CCX) and output the .inp file for CCX, I think it isn't hard to edit in a block of data to specify an initial velocity for all "car" nodes. This will be much easier than accelerating…
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Agree on starting with a coarse model so you can quickly scope out the right timescale and debug any model definition errors early. Make the target surface 10x stiffer than the structure so it's effectively rigid to get things working. I like to b…
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Thanks Victor. Good suggestions. I'll try these ideas and report back. -Robert
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Great summary - thanks Victor! This is a strong support community.
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Thanks for the suggestions. I'll try doing it with CGX and with Paraview.
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For tied interfaces the contact search should be done only once at initialization (since the parts do not move relative to each other), and thus should not influence CPU time very much for a nonlinear problem with many iterations or steps. The cont…
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Salome seems to have some powerful hex mesh tools, although I haven't personally had much experience with them on complex parts. If I can find a good way to get those meshes into Mecway it might be possible to leverage it also. Since I use the FEA…
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Thanks. I'll give the above ideas a try. -Robert
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I agree with Victor's comment above. Also, in my (limited) experience with CCX, I often find it's useful to start with NODE_TO_SURFACE contact and no friction to get things working, as NODE_TO_SURFACE seems 3x-5x faster and more efficient at multit…
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Oops - apologies to you both. VMH - thank YOU for the helpful suggestion. -Robert
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That worked perfectly. Thanks Victor.
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As an update, using Mecway4 on a Dell XPS 8300 with Intel Core i5 and 16GB I've been comfortably working today with a model containing about 250k nodes and a relatively high connectivity. Model rotation in the graphic window is nearly real-time; so…
