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

• Shaheen Uqab
You have your work cut out for you.In summary, the person is looking for the method to manually calculate the mass moment of inertia for an assembly consisting of an angle L bent in the form of a parabola and attached to a H section bent in the form of a circle. They have a diagram of the assembly and are currently using Solid Edge as a CAD program. The expert suggests using a CAD program to do the calculations, but the person wants to do it mathematically. The expert advises that the calculation would require a long process using calculus and recommends using Autodesk Inventor, a free student edition of a CAD program. The person is doing a project and wants to do the calculations themselves.

#### Shaheen Uqab

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 Uqab said:
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!

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

Shaheen Uqab said:
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.

Shaheen Uqab said:
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

#### Attachments

• joint assembly.jpg
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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?

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

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.

Good Luck!

## 1. What is the moment of inertia of a "L" angle bent in a parabola?

The moment of inertia of a "L" angle bent in a parabola is a measure of its resistance to changes in rotational motion. It is a mathematical property that depends on the shape, size, and distribution of mass in an object.

## 2. How do you calculate the moment of inertia of a "L" angle bent in a parabola?

The moment of inertia of a "L" angle bent in a parabola can be calculated by using the equation: I = (1/12) * m * (h^2 + 3b^2), where m is the mass of the object, h is the height of the parabola, and b is the base length of the angle.

## 3. What is the significance of calculating the moment of inertia of a "L" angle bent in a parabola?

The moment of inertia of a "L" angle bent in a parabola is important in engineering and physics as it helps in understanding and predicting the behavior of objects under rotational motion. It also plays a crucial role in designing structures and machines that require stable and efficient movement.

## 4. Are there any other methods for calculating the moment of inertia of a "L" angle bent in a parabola?

Yes, there are other methods for calculating the moment of inertia of a "L" angle bent in a parabola, such as the parallel axis theorem and the perpendicular axis theorem. These methods can be used to calculate the moment of inertia for more complex shapes and distributions of mass.

## 5. How does the moment of inertia of a "L" angle bent in a parabola affect its rotational motion?

The moment of inertia of a "L" angle bent in a parabola directly affects its rotational motion. Objects with a higher moment of inertia require more torque to rotate and have a slower rate of rotational motion. Objects with a lower moment of inertia require less torque and have a faster rate of rotational motion.