Transient axisymmetric heat transfer

[aa579]

Dear Abaqus experts/users,

I have a question regarding my Abaqus axisymmetric heat transfer model (please see attached). Initially, I wanted to run the heat transfer case first then get the temperature to find thermal stresses. The model is a very simple one, a cylinder (rectangle in 2D), with inner surface heat flux load and outer convection boundary condition. What I'm trying to do is to vary the surface heat flux with time. The code works perfectly when there's no time dependence but when I change the amplitude from instantaneous to tabular or decay and insert the time variables. I get the following error message: "Time increment required is less than the minimum specified".

Well..., I tried to lower the minimum increment as the message suggests but still no hope. It works when the time increment is ridiculously small (e-9!!!!). This is obviously not a solution as the run will take literally for ever to finish.

I would highly appreciate your help, I need this to be sorted out ASAP and would be grateful for your quick responses.

Kate

http://files.engineering.com/getfil...4ad6406f00&file=Cladding-thermal-analysis.inp

 

[Ingeniosus]

Hi!
In the STEP module ABAQUS uses a defoult value for the max number of increments; so you have to change it because the analysis will be aborted due to a not enough increments.

Try this:

In the STEP module EDIT your step and modify this (in the second page):

Maximum number of increment: 1000

 

[aa579]

Thanks for your swift reply, though I don't understand how your suggestion is related to my problem. I did what you suggested anyway and nothing has changed. I suspect that the problem I'm facing is related to applying time varying load such as the heat flux in my model.

Kate

 

[DanStro]

When I try to run it the message file shows that the "Time Integration" was exceeded. So I think it is your setting of 0.1 for th "Max Allowable emissivity change per increment". I changed it to 0.5 and it ran for the 300 increments you have set as the max. So as Ingeniosus suggested you should increase that. The initial increment size should probably be closer to 1e-5. I set it to 0.01 and that increment failed but 1e-5 worked.

HTH,
Dan

 

[aa579]

Thanks Dan. I managed to get to work. The problem was in the time distribution of the load. My load starts at a very hight value at t=0 and therefore the temperature increment is higher than the maximum. And that's why the msg file gives the "time integration" thing. The problem solved by increasing the load gradually to the maximum and/or increasing the max temperature increment.