Discussion Forum

Hi

yu can only get pressure information if "p" is in the dependent variable list, or can be derived of the dependent variables, so it depends on your model set-up. Is it part of your "physics" solved for ? is the question you should ask yourself

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Good luck
Ivar

Thanks Ivar,

When I am simulating the model to get the temperature distribution, I am not defining the temperature as a variable in the simulation but still I am able to get the temperature distribution.

In addition, if I define the properties of my material changing as a function of pressure, will I be able to get the pressure distribution?If no, how can I define pressure as a variable?


Thanks.

Hi

it would be easier if you state the identifier of your physics used. i.e. HT fort heat transfer, which indeed solves for the dependent variable "T"

but HT does not act solve for the pressure (check the equation tab) so if you add a pressure dependent material property, you need to define yourself the actual pressure, or add another physics that would solve the pressure based on the other parameters. (all depends on your model, start to write out the main variables, and the physics needed, then check the doc w.r.t. the physics and you will see what is solved for and if you get all variables.

By the way, there are a few weaknesses in the early 4.0, I would advice you to upgrade to a newer version

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Good luck
Ivar

Thanks Ivar for your response!

I tried to define pressure as a variable in properties of my material "oil" and COMSOL is giving an error indicating "wrong number of function arguments".I think I am getting this error because I have defined the basic properties of oil as a function of temperature and pressure, in addition I have defined temperature and pressure as input variables as well. But I need to define the properties as function of pressure as well in addition to temperature.

I want to define the density (rho) as a function of pressure as well while until now it is only a function of temperature.But I have no idea how I can do it in interpolation function. I tried to define the second variable of density as a function of pressure defined as interpolation function but then I got the duplication error.

Can you please look into the attached model and suggest some solution?

Thanks in advance!

Hi
first of all you need to define materials in ALL your domain, your domain 4 is without any material definitions, COMSOl is flagging that with a red X on the main material node icon

try to avoid the name "eps" in the Oil material as that name is already used by COMSOL as a global definition.

I agree one are missing a list of names to avoid conflicts, my way is to try them out in the Parameter list with a dummy parameter name to see if they are flagged red or if they reply with a value. Do note that often you need to load tzhe initial values to get all active variables of all physics defined

You also have a unit typo in the Convective cooling tab and W/m/K is not equal W/m*K and "." is not a valid multiplier sign

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Good luck
Ivar

Thanks Ivar,

Domain 4 was left without any material in error, actually it is oil.I have also renamed the variables such eps is renamed as eps1 etc.
I have also removed the units error from the convective cooling section.

I have redefined the density in two parts, initially it is defined as changing with the change of temperature under the function "rho1".While it is also changing with the change of pressure under the function "rho2".I have selected the same values of rho for each step of temperature and pressure.

Now I am getting the temperature distribution which is the same which I was getting earlier. But when I tried to put the pressure plot (which is now available


Is my formulation correct ? For me, it is not logical.Because I am unable to define a second density for the same material.I am also unable to define given density "rho1" changing as a function of temperature and pressure both.

One way which I can think about is just keep "rho1" and disable"rho2" and get the temperature distribution.Then disable "rho1" and enable "rho2" and get the pressure distribution.Since I would be defining the same densities for step change in temperature and pressure, so considering"rho1" which is a function of temperature will automatically incorporate "rho2" and vice versa. Am I thinking right?

I just want to define a change in density with the change of temperature and pressure.

Can you please comment on it by looking into the modified model attached?I am not sending the file after running because it becomes of huge size.Please open the file run it and see the temperature plot and then redraw the pressure plot by changing expression. The pressure plot just shows a green screen.

Thanks in advance!