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dramosblanco1-Visitor
1-Visitor
December 7, 2018
Solved

Issues solving a second order ODE

  • December 7, 2018
  • 2 replies
  • 3546 views

Hi folks,

 

I am trying to solve a second order differential equation in Mathcad 15 to model the diffusion of a substrate in a spherical pellet. Regrettably, Odesolve gives me the following message: 'This function cannot be used here' (see attached file). I have tried to rearrange the equation in different forms to see if that helped, but I still have the same problem. Do you know how can I solve the issue? 

 

Best,

Daniela

Best answer by dramosblanco

This indeed solves the issue. Thanks Alvaro!

 

Best,

Daniela

2 replies

L
LucMeekes23-Emerald IV
23-Emerald IV
December 7, 2018

Did you set up the Odesolve block correctly? For example:

- Wrote the derivatives using the proper symbols and operators?

- Is the highest derivative linear (not multiplied with t or the solution function y(t))?

- Did you provide sufficient/enough initial conditions?

 

Success!
Luc

D
dramosblanco1-VisitorAuthor
1-Visitor
December 7, 2018

Thanks for your answer. Regarding your points:

 

- I used prime notation for the ODE and boundary conditions in addition to using the boolean equal. I think there should be no problems with this point. 

- Yes, the highest derivative is linear

- Yes, it's a second order ODE and I specified 2 boundary conditions. 

 

I attached the file in case you want to have a look at it 🙂

 

Best,

Dan

 

 

 

 

F
Fred_Kohlhepp23-Emerald I
23-Emerald I
December 7, 2018

No file attached!

A
AlvaroDíaz12-Amethyst
12-Amethyst
December 7, 2018

Hi. You have 2/r*cs'(r) as part of the differential equation, and set c(0)=0. (The other condiont isn't initial, it's boundary, and have not problems) Mathcad can't handle r=0 here. Or change to c(0.000001)=0 or change the numerator where r appears as r+0.0000001.

 

Best regards.

Alvaro.

    D
    dramosblanco1-VisitorAuthorAnswer
    1-Visitor
    December 8, 2018

    This indeed solves the issue. Thanks Alvaro!

     

    Best,

    Daniela

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