Thermal expansion

General Questions
1

Good morning,

I want to make a uniform thermal expansion of a simple beam fixed on the edges. After having selected the material “2014_Alloy”:
1- I want to set an initial condition of 15 °C of the entire body. Despite I have set it, When I run the simulation, the initial temperature is 0 °C.
2- Considering the simulation starting from 0 °C, 2014_Alloy has a zero temperature of 20 °C. When the animation starts, I see that the expansion starts when the first step after the time “zero” is 15 °C. And so, I have stresses when the animation is at 14 °C. As you can see from the pics. It is set in automatic type, but there shouldn’t be any expansion at 14 °C.
3- In order to heat the beam by air/steam, I have considered a load with convective film : sink temperature = 200 °C. Is there a list of proper film coefficient? I set that at 0.45 mW/(mm^2 °C) only because I found it on a video “PrePoMax & CalculiX - Coupled thermo-mechanical analysis”.

Thanks in advance.

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2

Is the analysis transient or steady-state ? Can you share the file ?

You can find some tables in the literature, depending on the type of convection (forced, natural) and fluid medium.

3

I would like to share the file, but I am not allowed because bigger than 8 MB. It is a steady-state analysis.

4

You can use some hosting website, like WeTransfer, Google Drive, Dropbox and so on and share the link here.

Initial conditions are meant for transient analyses, maybe try with this type of simulation.

5

Here it is the file.

6

I’ve tried to disable “steady state”, but the starting temperature remains 0 °C, and the final temperature doesn’t reach 200 °C

7

Apparently, CalculiX doesn’t display initial conditions in 0 increment. But if you adjust the incrementation settings and check the first frame, you can see the expected temperatures:

inc
inc1441×681 90.5 KB

8

Where can I adjust the incrementation? from the step or the animation settings?

9

You can do it in step settings, when you change the Incrementation to Automatic.

10

Thank you, what about the point 2?

11

You could try using two steps. In the first step you will assign onyl the initial conditions and in the second step the rest of the loads.

The initial results that are not saved by CalculiX are a big problem in some cases. Maybe we could ask Guido to add such capability.

1 Like
12

That could be a point. It’s strange that the expansion starts before the zero temperature.

13

Be careful. PrePoMax, in most cases, adds an all zero artificial result at step 0, increment 0.