I’ve been trying to solve a transient heat transfer problem where a plate emits heat by radiation to a sphere. I solved the problem considering the sphere’s initial temperature equal to 25 ºC and a plate temperature magnitude equal to 1000 ºC (constant) over time. It is expected that the sphere will heat over time, and it happens.
However, I intend to solve a case where the plate temperature magnitude changes over time, i.e., the plate temperature magnitude will start at 600 ºC in the first time increment until 1400 ºC in the last time increment. I didn’t see an option in the user interface to set the temperature BC as an equation or as a table to set a temperature in each time step. I’m calculating for a time period of 200000 seconds.
I also looked at the *TEMPERATURE input deck format in the CalculiX user guide ccs_2.19. I didn’t see an option to set the temperature variation along a time step. Is there any way to do this?
Time variation of boundary conditions and loads can be defined using the amplitude feature, already implemented in PrePoMax.
Thank you for answering me. I tried to set it using the amplitude feature but was unsuccessful. I didn’t understand how to configure the shift time and amplitude properly. Also, I configured the tabular to vary the temperature from 25 to 100 °C, and the plate temperature variated from 0 to 2500 °C. I’m doing something very wrong here. Is there any tutorial or guide you could send me to help me understand how to configure the BC with tabular data?
You don’t have to use those shift parameters at all, just fill in the Data points tab - specify the time and corresponding amplitude pairs. Keep in mind that you also have to select the previously defined amplitude in the BC/load definition to make it work. What’s also crucial here is that the amplitude values are multiplied by the magnitude specified in the BC/load definition so you should use a magnitude of 1 and input the actual temperatures in the amplitude definition. Another way would be to specify some magnitude other than 1 and treat amplitude values as scaling coefficients but it’s usually utilized in other cases.
Thank you so much for the explanation. You helped me a lot. I’m sending the figure to illustrate to the other users the configurations:
I have a case where steam passes over a turbine rotor. The sink temperature and heat transfer coefficients will vary with time. I have solved this problem with Elmer but I would like to use Calculix.
Is there a way to implement this in PrePoMax or even Calculix?
Time variation can be defined using amplitudes. In PrePoMax, they are supported for sink temperatures but not for film coefficients. However, you can define this using Keyword Editor:
*FILM, FILM AMPLITUDE
In defining sink temperatures, I did not see an opportunity to input a amplitude. I will keep experimenting.
Again, thank you.
I was able to perform the thermal analysis and have temperatures for the nodes.
Now I want to calculate stresses from temperatures. As I said earlier, I have solved this problem with Elmer and now want to do it with PrePoMax.
Then you should use the Coupled temperature-displacement step. It’s available in PrePoMax. You define thermal and mechanical boundary conditions and loads within it.
I was actually not aware of this difference. So, I should add the option to select two amplitudes. One for the sink temperature and one for the film coefficient?
Yes, I created a feature request for this some time ago: Amplitude support for film coefficient and emmissivity
As stated in that thread, the same applies to radiation.
Yes, adding amplitude for film coefficient would be great. As practical example attached a study where increaseing the film amplitude between 11 and 12s is used to cool down a workpiece to initial temperature. The goal was to study the increase of temperature in the tooling after hours of production (the assumption of a constant temperature of the workpiece was not accurate enough).