Issue with Units

[sshastry]

Hi

Attached is pdf file. If the value of h/1000 (See last page) is OK when used in isolation why is there a problem when it is used along with an equation. Program says there is an issue with units. Please advice.Sriprakash

[ValeryOchkov]

You have h as length but 1.6 is dimensionless!

[sshastry]

So what is the work around. 1.6 is a constant according to the equation. How do I obtain the solution for this.

Shastry

[Werner_E]

Thats the problem with those empiric and pseudo-empiric equations which are not unit consistent and depend on values of a specific unit dor the input.

You have to find out what the reason for the 1000 in your formula may be and have to find out which unit h should be provided when using the formula with numbers only.

My guess is that h usually is provided in mm and the denominator 1000 should convert it to meter.

If that guess is correct, you simply have to replace the "1000" by "1 m" to make it work.

For future questions please attach you Prime worksheet as well. For more complicated problems its simply hard to impossible to debug just a static picture or pdf.

If you are using Prime its a good idea to additionally attach a pic or pdf because many of us can't read files created by newer versions of Prime.

[sshastry]

Ive managed to resolve that and got into some new trouble. THe term lambda is a constant without units (page 2 of 3). When this is multiplied by the term c with a unit of m, I expect the program to return a unit of m for lambda x c. However it throws up 1/s * m. Dont know why?

The second issue is on page 3 of 3. I need the program to report a new variable fctmfl to be the maximum of both fctmfl1 and fctmfl2. How do I do this. Im stuck.

Kindly assist.

Shastry

[RichardJ]

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@sshastry wrote:

Ive managed to resolve that and got into some new trouble. THe term lambda is a constant without units (page 2 of 3). When this is multiplied by the term c with a unit of m, I expect the program to return a unit of m for lambda x c. However it throws up 1/s * m. Dont know why?

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Your evaluation of lambda x c is above your definition of c. By default,c is defined as the speed of light, hence your units. Move the evaluation down.

The equation for positive moment fails because you can't have units in an exponent.

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@sshastry wrote:
The second issue is on page 3 of 3. I need the program to report a new variable fctmfl to be the maximum of both fctmfl1 and fctmfl2. How do I do this. Im stuck.

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fctmfl:=max(fctmfl1, fctmfl2)

[sshastry]

Hi

I corrected that error. However, I notice that it wont accept lambda * c as an exponent. Dont know why.

Sshastry

[RichardJ]

You corrected which error? If lambda x c still has units, that is the main error. An exponent can't have units.

[Werner_E]

Guess you should delete the mm when you define lambda, so lambda hast dimension 1/length.

Possubly you should multiply by 1000 instead, not sure, thought.

That way c*lambda is dimensionless as it should be and your moment will also get the correct unit Nm.

[sshastry · Accepted solution]

Werner

Thank you for helping out. I managed to correct it. However, the last step where I calculate wcap, Im expecting the answer to be in KN/sq.m. Kindly take a look.

Sriprakash

[RichardJ]

Since the units for Mn are correct, the units for lambda obviously aren't.

[LucMeekes]

With the remainder of the expression parts accounted for, that depends on the unit of your constant 0.168.....

Where does it come from? What is it supposed to mean?

Like wise: What is the unit of the constant 0.161 in the formula for M.pmax (top of that page), or is it supposed to be "0.161 m" and is that the reason that you multiplied the expression with a unit of "m"?

Success!
Luc

[RichardJ]

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LucMeekes wrote:

or is it supposed to be "0.161 m"

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Or some other unit of length?

[LucMeekes]

You're right, what about feet, or furlongs...?