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Jan 29, 2020
08:09 AM

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Jan 29, 2020
08:09 AM

Differential equation

Hi,

I'm trying to solve the Differential equation of motion using the comand rkfixed, however I'm not getting.

The correct form to write the equation is in the captura in the attachment, but the Mathcad not solves it, just solve if the mass divide all terms (stiffiness and damper)

Can anyone help me please?

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6 REPLIES 6

Jan 29, 2020
08:58 AM

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Jan 29, 2020
08:58 AM

I believe your mathcad sheet is correct and your png is wrong, from the equation for forced harmonic motion:

**But** that does not explain why the png form doesn't work. Since I have only Express I can't do more, sorry!

Jan 29, 2020
09:06 AM

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Jan 29, 2020
09:06 AM

Hi FredKohlhepp, thanks for your answer

In fact you're right. thanks very much for your help

Jan 29, 2020
10:37 AM

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Jan 29, 2020
10:37 AM

Note that Prime can use units in differential equations (I don't think that Rkfixed can, but a solve block using Odesolve can.) Units, and the proper conversion of them, was/is one of the primary benefits of this software. So you can use:

Jan 29, 2020
01:01 PM

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Jan 29, 2020
01:01 PM

Fredkohlhepp, I used to solve using odesolve comand, however I stoped to use it when a try to input a second fredom degree (TMD). The Odesolve comand didn't work well, the response was different from analytical solution.

Jan 29, 2020
12:38 PM

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Jan 29, 2020
12:38 PM

You may consider using a solve block with odesolve

Jan 29, 2020
01:02 PM

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Jan 29, 2020
01:02 PM

Werner_E, Thanks for your answer