Hydrostatic pressure in a simple cube - need help getting off the ground

[Anonymous]

Hi, I did a search and nothing came up that addresses these problems in simple enough terms for me.

My ultimate aim is to design parameters for concrete formwork (moulds for casting concrete). The formwork I have chosen to be birch plywood, and I am assuming that the wet concrete exhibits hydrostatic pressure. So I want to see the effect concrete has on my formwork as I build it up, so I can iteratively improve the design.

I've started as simply as possible, making a cube fixed together with finger joints (Screencast 1). On the Simulation screen I have chosen the right direction for gravity, hydrostatic pressure to the top of the cube, then tried to run a Solve. Unfortunately there are errors all over the shop (Screencast 2).

In solving these errors, I have started from the beginning and tried changing the material's "invalid properties". Under Material > Study Material, all of my "Plywood, Sheathing" is springing up with error icons. When I inspect the properties, it describes them as "Non linear material" (despite plywood sheathing being under the material selections for linear material...). The only solution I could think of to that, was changing the plywood's shear modulus so it was the same in all directions, but in doing so and assigning all the bodies I'm using with this new material, I cannot "unassign and delete" the original material, which doesn't seem to be applied to any objects anyway... In other words, I am stuck on stage 1 trying to troubleshoot my hydrostatic analysis, and there are probably more stumbling blocks to come down the road.

Does anyone have any initial suggestions? Is there anyone comfortable enough with hydrostatic simulation who is willing to fiddle around with my model a bit? It's destroyed my temper for the night and it's just me learning this software from scratch, so I don't have anyone to approach in person for help.

Thanks a tonne in advance.

[tyler_henderson]

Hi Pliny,

I'm happy to help you with this.  Unfortunately, it's not an easy fix, but we can get you where you want to go.

First, the Plywood material you are using is Anisotropic (actually, in the Material Browser it is defined as Orthotropic).  The Linear and Nonlinear Static Stress studies in Fusion do not allow Anisotropic or Orthotropic materials.  Even though all of the directions in the material definition have the same values, the solver still recognizes it as Orthotropic.  Also, unfortunately right now you there is no way to change an Orthotropic material to Isotropic.  Your best bet is to create a new Isotropic material and copy the properties (just the X direction for example) from your Plywood and into your new material.

Next, you'll want to use the "Study Materials" command to apply your new material in your Study.

Next, it looks like you have a conflict between the Hydrostatic Pressure Load and a Fix Constraint.  Make sure that you don't have a Fix Constraint applied to any of the same faces where the Hydrostatic Load is applied. It's ok if the Constraint is on the same Body as the Load, just not on the same face or edge, etc.

Lastly, the error you're getting about "unconstrained groups" is likely because you haven't ran Automatic Contacts yet.  That's ok.  If you don't manually run Automatic Contacts we will run them for you during the solve.  That will make sure all of your boards are connected together.

I hope this helps.  Let me know how it goes and if you have any more problems we can work through them.

Regards,