# Calculate moment of inertia of a "L" angle bent in a parabola

## Main Question or Discussion Point

I want to calculate moment of inertia of an angle L bent in form of a parabola. The parabola is attatcehd to a H section bent in form of a circle such that the center of circle and focus of parabola lie at the same point. I want to know how to calculate the moment of inertia for the whole assembly

SteamKing
Staff Emeritus
Homework Helper
I want to calculate moment of inertia of an angle L bent in form of a parabola. The parabola is attatcehd to a H section bent in form of a circle such that the center of circle and focus of parabola lie at the same point. I want to know how to calculate the moment of inertia for the whole assembly
Shaheen, welcome to PF! :)

This forum is provided by new members to introduce themselves. You should not post anything here but "Hi, I'm Shaheen, and I'm new to PF" and other such introductions. I'm sure you don't introduce yourself to your friends by saying, "I have this beam bent in the shape of a parabola ..."

If you wish to start a thread with a technical question, PF has several different forums in which to post. Good Luck!

jtbell
Mentor
Note: this thread was moved here from the "New Member Introductions" forum, where SteamKing saw it.

SteamKing
Staff Emeritus
Homework Helper
I want to calculate moment of inertia of an angle L bent in form of a parabola. The parabola is attatcehd to a H section bent in form of a circle such that the center of circle and focus of parabola lie at the same point. I want to know how to calculate the moment of inertia for the whole assembly
To be clear, are you talking about calculating the mass moment of inertia of this construction?

Yes i am talking about mass moment of inertia.

SteamKing
Staff Emeritus
Homework Helper
Yes i am talking about mass moment of inertia.
Do you have any drawings or sketches of this construction?

Yes this is the diagram. The parabola and half circle are connected trough trusses

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SteamKing
Staff Emeritus
Homework Helper
Since this assembly appears to have been created in some sort of CAD program, there may be a utility in the program which will calculate the MMOI for you. If the particular program you used to create this assembly does not have this functionality, perhaps your design can be exported to a program which can calculate the MMOI.

In any event, calculating the MMOI could conceivably be done manually by means of a mass take-off, but it would be a pretty tedious process.

Can you tell me the basic method to calculate manually MMOI?

SteamKing
Staff Emeritus
Homework Helper
Not in a few words.

Let me ask you this. Have you ever taken a university course in dynamics? Studied integral calculus?

Yes, currently i am doing Mechanical Engineering

SteamKing
Staff Emeritus
Homework Helper
Well, this structure is no simple shape like you find in typical course work problems, so forget about using a few simple formulas. It will require a long slog thru the basic definition of the MMOI using calculus, along with a helping of the parallel axis theorem, rotated coordinate systems, etc.

This was why I mentioned using a CAD program to do the calculations. It's a lot quicker and much less prone to error. IDK if you are using any particular CAD programs in your ME studies, but a package like Autodesk Inventor should have the tools necessary to do MMOI calculations for this structure.

http://www.imaginit.com/software/autodesk-products/inventor

Thanks for your help, I am using solid edge as a cad program. Basically i am doing a project which requires every calculation to be done. CAD will help but i want to do it mathematically. Using a cad i would just be an operator but i want to do it my self.

SteamKing
Staff Emeritus