mathcad: help with Numerical Soln to Differential Eqn

[hrishibhor]

Please help to implement following differential equation numerical solution in mathcad

Numerical solution for single degree of freedom elastic system.
Spring stiffness = k = 2000 lbf/ft
Weight = W = 64 lbf

Force function:
F(t) = 500t+50 if t <=0.1
=-1250t+225 if 0.1 <=t<= 0.14
= 50 if t>=0.14
Acceleration function:
A(t) = ½ F(t) – 1000 *Y

Say time step = dt = 0.02
Initial Condition:
Displacement:
Y0 = 0 that is displacement is zero when t = 0
Y1 = ½ * A0 *dt^2 that is first time step which t = 0.02 this gives displacement but in terms of Acceleration at t =
Acceleration:
A0 = 0 when t = 0

Solution:
Y (t+dt) = 2 * Y (t) – Y(t-dt) + A(t) * dt^2
For t – 0 to 0.4 with dt = 0.02

Return:
Y, A

[MikeArmstrong]

Please provide a worksheet.

Mike

[hrishibhor]

attached is the mathcad sheet. This is all i could do

[RichardJ]

Please post the worksheet in the other thread you started, where everyone has been commenting.

This is why we don't like cross posts.

[hrishibhor]

this all i coul do. This is the first time i am posting question on mathcad so by mistake i have opened up another discussion in "programming...." pleas bear with me.

[AlanStevens]

Here's how you might do it using Mathcad's inbuilt ode solver block (which might or might not be what you are looking for!).

Alan

[hrishibhor]

Thanks for your help.

Although how would one solve it using the the numerical procedure i explained in my original post ?

The step by step solution is kind of easier to understand as to whats going. What i am not able to get right is that

---------

dt = time step.

Y(t+dt) is in terms of a(t) (Please see the original post) so should there be loop inside a loop ?

---------------------------

Please bear with me i am not good at programming at all.

[AlanStevens]

hrishi bhor wrote:

Thanks for your help.

Although how would one solve it using the the numerical procedure i explained in my original post ?

The step by step solution is kind of easier to understand as to whats going. What i am not able to get right is that

---------

dt = time step.

Y(t+dt) is in terms of a(t) (Please see the original post) so should there be loop inside a loop ?

---------------------------

Please bear with me i am not good at programming at all.

I'll see if I can find time to look at this next week. Meantime, note that there was an error in the way I removed the units of k in my earlier file. Corrected version attached (well, corrected as far as k is concerned - who knows what other errors may still be there!!).

Alan

[hrishibhor]

Appreciate that Alan.

[AlanStevens]

Ok, found some time. See Example_13ptc2.

Also, corrected (yet again!) my original approach using Odesolve (see Example13_ptc1c). It's those pesky Imperial units - they get me every time!

Alan

[hrishibhor]

Really appreciate your help.

Thanks

[f.kohlhepp]

Took a bit of work, but:

[hrishibhor]

Thanks for your help.