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Apr 13, 2020
11:47 PM

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Apr 13, 2020
11:47 PM

Define Unit in ODEs

Dear all

Could you find the error of unit in equation why i can not find solution? attachment Pic&file below

Thank you

Solved! Go to Solution.

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1 ACCEPTED SOLUTION

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Apr 14, 2020
08:25 AM

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Apr 14, 2020
08:25 AM

The dimension of stiffness is force per length or mass per time^2.

So you would have to change the unit for "k" to something like "N/m" or "kg/s^2" for the solve block to work.

But using the initial conditions you provide, the solution x(t) trivially would be constant zero.

I guess that you would have to change one of x.0 or x'.0 from zero to a non-zero value.

Here's an example:

BTW, you may already have noticed - the diagram components you are trying to use are not unit aware

5 REPLIES 5

Apr 14, 2020
04:18 AM

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Apr 14, 2020
04:18 AM

The units of

M * z''

C * z'

k * z

Must be the same. If the units of C and M are OK, then that of k is wrong. Or the equation is wrong.

The unit of z is m, that of z' is m/s and that of z'' is m/s^2.

Success!

Luc.

Apr 14, 2020
07:01 AM

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Apr 14, 2020
08:25 AM

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Apr 14, 2020
08:25 AM

The dimension of stiffness is force per length or mass per time^2.

So you would have to change the unit for "k" to something like "N/m" or "kg/s^2" for the solve block to work.

But using the initial conditions you provide, the solution x(t) trivially would be constant zero.

I guess that you would have to change one of x.0 or x'.0 from zero to a non-zero value.

Here's an example:

BTW, you may already have noticed - the diagram components you are trying to use are not unit aware

Apr 14, 2020
09:12 AM

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Apr 14, 2020
02:02 PM

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Apr 14, 2020
02:02 PM

Just for information. The exact solution to your, or any resembling problem is:

Success!

Luc