Discussion Forum

Hi all,

I have been trying to simulate implosion of a closed aluminum pipe underwater. Inside the pipe is just ambient air. The pipe rests at the center of a water box with a slightly smaller air box above the water. I created the geometry in SolidWorks and imported this to COMSOL with the intention of using the Fluid-Solid Interaction Multiphysics interface. I used the built-in properties of Air, 3004 aluminum alloy, and Water. The Moving Mesh has been defined as the water box and air box. I have Laminar Flow Water that is just the water that surrounds the pipe and Laminar Flow Air that is the air box and water box together. I have an inlet on the top of the water that I tried to define total pressure as a function of time (basically applying 1 psi/second to the air). I also have a fluid-fluid interface between the air and the water. The solid mechanics is defined as the pipe with closed endcaps. I fixed the ends of the endcap so it was similar to the experiment we did. Under study time dependent is selected and I have output times as range(0,1,60).

However, when I run this simulations I get a lot of convergence issues. First I get a warning that states: There is no feature constraining the pressure. A pressure constraint is required to specify the pressure level. Ignore this warning if the pressure is constrained using pointwise or weak constraints. - Node: Laminar Flow Water (spf).

So then I tried to put an inlet to the water with 0 pressure defined and lowered the total pressure function in air. Then I started to get this error: This is my new warning: - Feature: Time-Dependent Solver 1 (sol1/t1) Nonlinear solver did not converge. Maximum number of segregated iterations reached. In Velocity u_fluid, Pressure p: There was an error message from the linear solver. Maximum number of intermediate iterations reached. In Velocity u, Pressure p2: There was an error message from the linear solver. Maximum number of intermediate iterations reached. Time: 1.171096941623891 s. Last time step is not converged.

I have even tried to simplify the geometry by just making a solid aluminum cylinder with no gap inside using COMSOLs geometry tab. If anyone has any ideas, I would appreciate the input! This is my first time with COMSOL and I am pretty confused. Thank you.