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15-Moonstone

## 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

1 ACCEPTED SOLUTION

Accepted Solutions
24-Ruby V
(To:SPRstructur)

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
23-Emerald III
(To:SPRstructur)

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.

15-Moonstone
(To:LucMeekes)

could you correct for me in attachment above?

Thank u

24-Ruby V
(To:SPRstructur)

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

15-Moonstone
(To:Werner_E)

23-Emerald III
(To:SPRstructur)

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

Success!

Luc

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