Skip to main content
V
vlehner1-Visitor
1-Visitor
May 25, 2017
Solved

Problem with the solver Odesolve

  • May 25, 2017
  • 3 replies
  • 4811 views

Hi!

I'm trying to solve the deflection of a beam with a constant load along it's length.

I have a differential equation of 4th degree with four initial conditions.

The moments in the bearings are zero and the deflections too.

Now my question is: Why don't i get a solution with "Odesolve" in MP4 although i initialized all four conditions completely?

Without Units, it works!

The Error Message is:

Any help will be appreciated

Thank you.

Best Regards, Volker

Best answer by Fred_Kohlhepp

" I need a quick solution like creating a short solve block working with units."

Attached is your quick solution with units.  Note that you can make both I and q functions of position along the beam.

Enjoy.

3 replies

-
-MFra-21-Topaz II
21-Topaz II
May 25, 2017

Hi Volker,

In my opinion, being the differential equation of the fourth order, the initial conditions for the first and third derivatives of y are missing.

missing initial condition.jpg

In fact, by solving analytically with Laplace, the given equation, I need all the initial conditions, as can be seen from the following calculation:

invlaplace.jpg

Greetings

FM

W
Werner_E25-Diamond I
25-Diamond I
May 25, 2017

> In my opinion, being the differential equation of the fourth order, the initial conditions for the first and third derivatives of y are missing.

They aren't missing - you simply solve a different problem.


In Volkers problem we know the values of y and y'' at the end of the interval instead (something Mathcads odesolve ever so often has its problems with).

Volker already told  us and Fred had shown that the information is sufficient and odesolve is able to solve if no units are used.

So it looks like Prime cannot deal with units that perfect as we may have thought and wished.

At least I could not spot any error in the way Volker had set up the problem and the "unknown exception error" thrown may indicate a bug in Prime.

Maybe someone finds it worth the trouble to report the bug.

    -
    -MFra-21-Topaz II
    21-Topaz II
    May 25, 2017

    It could be said that mathcad automatically considers null the initial conditions missing in the solution block, which are, instead, present in the analytical solution. So there is a certain probability of error in the mathcad solution.

      F
      Fred_Kohlhepp23-Emerald I
      23-Emerald I
      May 25, 2017

      If it works without units, then do it without units.  (Like we did in version 15!)

      M
      mvenich14-Alexandrite
      14-Alexandrite
      May 25, 2017

      Symbolic solution from Maple. If you want more complicated loading conditions (like partially distributed load plus several point loads) then Maple will give the symbolic deflection/moment/shear equations (it won't handle units in the ODE, though).

      beam.png

      V
      vlehner1-VisitorAuthor
      1-Visitor
      May 25, 2017

      Thanks to all, but i need a quick solution like creating a short solve block working with units.

      I want a quick numerical solution- a short solution like engineers want to have for work.

      When having a beam for example with 4 forces and a moment, the symbolical solution kills time and is not practical.

      Best regards, Volker

      F
      Fred_Kohlhepp23-Emerald IAnswer
      23-Emerald I
      May 25, 2017

      " I need a quick solution like creating a short solve block working with units."

      Attached is your quick solution with units.  Note that you can make both I and q functions of position along the beam.

      Enjoy.

        Terms & ConditionsCookie settingsAccessibility statement