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How to solve the problem"Attempt to evaluate non-integral power of negative number. Function: ^"

Posted 6 févr. 2013, 18:56 UTC−5 Heat Transfer & Phase Change, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.4 2 Replies

Rajib MD
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Hello,

I am solving a Drift diffusion model for plasma using general form PDE. However, I am facing the following error,

Failed to find consistent initial values.
Attempt to evaluate non-integral power of negative number.
Function: ^
Failed to evaluate variable.
Variable: mod1.uth, Defined as: (((mod1.Te*(k B const*8))/(pi*mod1.me))^0.5)
Failed to evaluate expression.
Expression: d((0.5*mod1.uth*mod1.u*test(mod1.u))*(dvol),{test0})
Last time step is not converged.


Here, Te= (2/3)*(n/ne)
n, ne is the dependent variables for the problem and their initial ratio is 3. So it is positive. And also k_B_const is Boltzman constant is a constant, me is the mass of electron also a positive quantity.

Can you tell me why it happens?

Thanks is advance.

Rajib
2 Replies Last Post 15 juin 2017, 18:09 UTC−4
COMSOL Moderator

Hello Rajib MD

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Niklas Huber
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Posted: 9 years ago 28 déc. 2015, 14:26 UTC−5
Hi,

I'm also wondering about that same behavoiur by using:
T^2*8.227e-07-0.0004936*T+0.153 for defining heat source

Thanks in advance
Niklas

Hi, I'm also wondering about that same behavoiur by using: T^2*8.227e-07-0.0004936*T+0.153 for defining heat source Thanks in advance Niklas
João Santos
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Posted: 7 years ago 15 juin 2017, 18:09 UTC−4
Hello Guys,

I'm having a problem to model an adsorption column using Freundlich isotherm in coefficient form PDE module. My initial value of u1 is zero. Could you give me some help?

Attempt to evaluate negative power of zero.
- Function: ^
Failed to evaluate expression.
Expression: d((-(comp1.u2t+S*comp1.u2-9.468679245283018E-5 (0.158*comp1.u1)^0.09)*test(comp1.u2))*(dvol),{test2})
Failed to evaluate Jacobian of expression.
Expression: (-(comp1.u2t+S*comp1.u2-9.468679245283018E-5*(0.158*comp1.u1)^0.09)*test(comp1.u2))*(dvol)
Last time step is not converged.
- Feature: Time-Dependent Solver 1
Regards,

João
Hello Guys, I'm having a problem to model an adsorption column using Freundlich isotherm in coefficient form PDE module. My initial value of u1 is zero. Could you give me some help? Attempt to evaluate negative power of zero. - Function: ^ Failed to evaluate expression. Expression: d((-(comp1.u2t+S*comp1.u2-9.468679245283018E-5 (0.158*comp1.u1)^0.09)*test(comp1.u2))*(dvol),{test2}) Failed to evaluate Jacobian of expression. Expression: (-(comp1.u2t+S*comp1.u2-9.468679245283018E-5*(0.158*comp1.u1)^0.09)*test(comp1.u2))*(dvol) Last time step is not converged. - Feature: Time-Dependent Solver 1 Regards, João

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