Prime 7 and odesolve

[KevinFinity]

I recently encountered an issue with Prime 7. The function odesolve doesn't work the way it used to in Prime 5 and I can't figure out why. 

I'm updating my MathCAD sheets to Prime 7 and my current header and coding standards, and finding that there's an issue with odesolve. 

Here is my solve block showing the differential equation for deflection of a beam. It's a simply supported beam, so deflection delta at 0 and at the beam's end L are both zero. 

E is in units of GPa, Iy in units of mm^4, length l in units of m, and M(x) in units of kN*m. I have verified that all units are correct. 

When I open this MathCAD sheet in Prime 7, I get an error "These units are not compatible", but when I open it in Prime 5, I get no error and the thing works. 

What is different about Prime 7 that causes the functionality not to work anymore? MathCAD sheet attached. 

Please help!

Thanks!

[KevinFinity · Accepted solution]

OK... I don't know why this is, but I solved my problem. You're not gonna believe the solution.

In the boundary condition at d(l) = 0 in, I had to delete the units from the right hand side of the equation.

I don't know why, and it definitely shouldn't work this way, but it works. 

[terryhendicott]

Hi,

Glad you found the problem.

You could directly calculate the maximum deflections.

Cheers

Terry

[KevinFinity]

Thanks, Terry.  The reason I do it using odesolve and not the direct formula is because I sometimes need to change the M(x) equation. It's easier and I make fewer mistakes to only change one thing. 

[LucMeekes]

Some calculus. if I made no mistake, gives:

You should be able to compare that with the Odesolve result.

(I'll leave the other ODE to you...)

Success!

Luc

[KevinFinity]

Hi Luc,

Your answer is really close to the formula published at

Digital Edition - 14th Edition Steel Construction Manual (usc.edu)

Well done with your calculus!