Hello Joel Dugdale
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Posted:
1 decade ago
8 juin 2010, 14:10 UTC−4
I'm trying to solve for a variable that depends on the time derivative of an internal variable. When I try and solve it, it gives me the error "system matrix is zero"
The equation is entered in the global equations box as follows, what am I missing? I am using a parametric segregated solver to solve.
Global Equations:
u:
a11
f(u,ut,utt):
2/3*d(epx_smps,t)-a11t
I am trying to do a similar problem. In 2D domain I want to add a surface impedance (area counductance S/m^2 and pecific capacitance F/m^2) so that voltages in the domain can drive currents normal to the domain. Thus I want to specify an external current density JN=V*S+C*dV/dt applied in the external current density routine of elelctric currents. How do I put JN in the ODE? I can use the DC term as V*S in the external desnity expression window but I cannot seem to figure out how to introduce dV/dt where V(t), the voltage, is the state variable that COMSOL is solving. I can't write C*dV(t)/dt. It is marked in red in teh expression window although V*S is OK.
So I added ODEs physics and tried to define JN that way but I can't see how to refer to V(t) and the derivative of V(t) in the eqaution specification. I just want JN to be: JN=V*S+C*dV/dt . How do I do that? Is there a simpler routine?
[QUOTE]
I'm trying to solve for a variable that depends on the time derivative of an internal variable. When I try and solve it, it gives me the error "system matrix is zero"
The equation is entered in the global equations box as follows, what am I missing? I am using a parametric segregated solver to solve.
Global Equations:
u:
a11
f(u,ut,utt):
2/3*d(epx_smps,t)-a11t
[/QUOTE]
I am trying to do a similar problem. In 2D domain I want to add a surface impedance (area counductance S/m^2 and pecific capacitance F/m^2) so that voltages in the domain can drive currents normal to the domain. Thus I want to specify an external current density JN=V*S+C*dV/dt applied in the external current density routine of elelctric currents. How do I put JN in the ODE? I can use the DC term as V*S in the external desnity expression window but I cannot seem to figure out how to introduce dV/dt where V(t), the voltage, is the state variable that COMSOL is solving. I can't write C*dV(t)/dt. It is marked in red in teh expression window although V*S is OK.
So I added ODEs physics and tried to define JN that way but I can't see how to refer to V(t) and the derivative of V(t) in the eqaution specification. I just want JN to be: JN=V*S+C*dV/dt . How do I do that? Is there a simpler routine?