Discussion Forum

Hi, guys

I am a COMSOL newbie and need some help on defining time dependent interpolation function.

I have a pretty simple model, a sphere. I need to define an volumetric force input F( t, r, z )as below, which varies both with time and space:

F( t, r, z ) = I * sin(t) * f( r , z ) %%% I is const, t is time, r & z are space coordinates with unit meter

Basically, F consists of two parts, one is time dependent : sin ( t ) and the other space dependent part is grid point values for defining interpolation function : f(r, z).

Since I was successful before with the static model (only f(r, z)). So, I just defined firstly a interpolation function f (r,z) and then the new time-variant force input as a analytic function with the following expression:

I * sin(t) * f (r[m^-1],z[m^-1]) %%%% arguments: t, r, z

COMSOL complains:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Undefined variable.
- Variable: r
- Function name: F
Error in multiphysics compilation.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Aren't r & z implicitly defined already when I defined the interpolation function and checked "Use space coordinates as arguments"? Do I need to explicitly define them again somewhere else?

So I changed the expression:

I * sin(t) * f %%%%% argument: t

COMSOL complains again:
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Undefined variable.
- Variable: f
- Function name: F
Error in multiphysics compilation.
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Now, this time COMSOL can not recognize the interpolation function f...

Thank you in advance!

Best,
Xiao