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01-02-2014
02:03 AM

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01-02-2014
02:03 AM

Help required for calculations in Mathcad

Hi All,

could you please help me with the calculations i want to do in mathcad as per the attached pdf?

I have to plot 3 2D graphs ( as mentioned in the pdf, where A (area) = pi * r(square), r = 31.2mm

& n = l/r (where l = 60mm)

Please help

Thanks,

Shashank

8 REPLIES 8

01-02-2014
03:16 AM

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01-02-2014
03:16 AM

1. Check your equations. The first term on the right-hand side of TL seems to have different dimensions from the second term. Also Tm (2nd eqn) doesn't look like it has the same dimensions as J.d^2theta/dt^2 (3rd equation).

2. Replace dtheta/dt by omega and d^2theta/dt^2 by domega/dt.

3. Insert the first 2 equations into the third to get an equation for domega/dt.

4. Use a Given ... Odesolve block to solve the two ODEs (dtheta/dt = omega and domega/dt = ...).

5. Check the initial conditions. A quick look suggests that the denominator of the second term of TL will give a divide by zero error if the initial value of theta is zero.

Alan

01-02-2014
04:01 AM

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01-02-2014
04:01 AM

Hi Alan,

First of all thank you for your revert and helping me out of the way.

If we talk about the denominator of the second term of TL, for initial condition of theta equal to Zero, its coming out to be one and not zero.

as term mu Sin 0 will become zero, Sin inverse 0 will become zero & Cos 0 is 1.

Alan, i am not that much proficient on Mathcad will it be possible for you to create a mathcad 15 sheet for the same, i'll do small amendments for the errors.

I forgot to mention the value of V1 = 245.8831431 CC

Thanks,

Shashank

01-02-2014
04:08 AM

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01-02-2014
04:08 AM

Shashank Sharma wrote:

Alan, i am not that much proficient on Mathcad will it be possible for you to create a mathcad 15 sheet for the same, i'll do small amendments for the errors.

Yes, but *first *you need to start a Mathcad worksheet by entering all the data, and writing the correct equations.

Alan

01-02-2014
05:35 AM

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01-02-2014
05:35 AM

Hi Alan,

I have created the Mathcad Sheet, please find it attached.

Thanks,

Shashank

01-02-2014
06:58 AM

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01-02-2014
06:58 AM

The attached file doesn't run yet because your equations don't yet make sense - there are inconsistencies in the units of various terms. However, the file shows how to obtain theta and omega as a function of time once you have sorted these inconsistencies.

Alan

Attached file changed (the way I removed units in the solve block was incorrect in the previous version).

01-06-2014
01:55 AM

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01-06-2014
01:55 AM

Hi Alan,

I've removed all the dimenssions to make this sheet work,

Can you please help with how to plot the desired graphs?

Thanks,

Shashank

01-06-2014
03:52 AM

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01-06-2014
03:52 AM

Shashank Sharma wrote:

Hi Alan,

I've removed all the dimenssions to make this sheet work,

Can you please help with how to plot the desired graphs?

Thanks,

Shashank

See attached for the graphs. **However, the equations (and hence the results) are still wrong! **Just removing all the units doesn't alter that.

Alan

01-02-2014
01:57 PM

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01-02-2014
01:57 PM

I do not see angle theta defined as a function of time before it is used in the first equation.