NAFEMS LE11 test case

General Questions
1

Hi

Inspired by this post, i wanted to make my own test .. it supposes to be simple (“piece of cake”) however i’m far from the result and i do not figure out what i’m doing wrong.

Note: the thermal field seems correct

Data from this website

Input file
Nafems_L11.pmx (930.4 KB)

Paul

2

You just missed one further BC: the upper surface must also be fixed in the Z direction, just like the lower one.

You can also run this as a simple static step, where the temperature must be applied using “Define Field.”

3

Thanks for your remarks; however none of the 2 models work and i don’t understand what i’m missing here …

Nafems_L11.pmx (929.0 KB)
Nafems_L11_static_step.pmx (1.5 MB)

4

I forgot, you need also to define the initial condition for the part = 0°C

Edit
For the static step you applied it, but the value needs to be changed to 0.

5

Close enough for a coarse mesh:

image
image631×669 90.2 KB

1 Like
6

Ok that’s the root cause but I’m a bit confuse:

  • implicitly the intial temperature is supposed to be 0°C if nothing is specified, isn’t it?
  • the reference temperature for the thermal expansion is 0°C, so whatever is the initial temp, at the final stage it should have computed the expansion (i.e. from °C)?

Both previous model work if T=0°c is specified as Initial_condition

Thanks for the support

Paul

7

For the static step, the crucial point is that delta T between the initial and applied temperatures must be 1. Thus, for example, “initial T = 100°C” and a temperature under “define field = 101°C” would produce the same result. This is due to the formula entered under “Distribution.” Thus, it would also work if the formula were adjusted, e.g., with delta T = 2°C, the forms would have to be =Sqrt(Pow((x/2000),2)+Pow((y/2000),2))+(z/2000).

8

Theoretically yes (at least that’s how it works in Abaqus) but in CalculiX it’s crucial to always define initial temperature for analyses involving temperatures (even for steady-state heat transfer). I’ve seen some cases where incorrect results were obtained only because of this omission.

The equation here shows it well taking into account all temperatures - final (T), reference (T_ref) and initial (T_0):

exp
exp948×334 47.1 KB

9

Then a question comes from to me: if no initial temperature is specified, what Calcilix uses?

Is it relevant (in prepromax i mean), to automatically initiate T=0 at t=0 if no “Initial_Conditions” is implemented while a thermal “card” is specified ?

Thanks all for you feedbacks

10

It will be 0, you can check it by disabling all the applied temperature fields and checking NT11 in results. But, as I said above, I wouldn’t rely on it in CalculiX. It’s better to explicitly specify it, especially since it’s usually not 0*C but e.g. room temperature.

In transient thermal or thermo-mechanical analyses, CalculiX forces you to provide initial temperature.

11

At least it’s reported as 0 but stresses and strains will be non-zero if you don’t explicitly define the initial temperature - hence the need to always do it.