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Simulation Toppling Analysis (tip - over) in Inventor Nastran

phi.dodat
Participant

Simulation Toppling Analysis (tip - over) in Inventor Nastran

phi.dodat
Participant
Participant

I have a furniture product model in Inventor, and I am checking the tipping-over capability of the component to meet the ASTM F2057-23 standard before proceeding with production. (ASTM F2057-23 is a standard that tests simulating the weight of children up to 60 pounds interacting with the unit)

 

Previously, I used Dynamic Simulation, but the actual results differed significantly from the standard results. Additionally, the two rear legs of the component are elevated by 1 inch.

 

I attach my model when used Dynamic Simulation.

phidodat_0-1717644865715.png

 

Can you please advise if there is a solution in Inventor Nastran to simulate the tipping-over capability of the component?

Thank you very much.

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Accepted solutions (3)
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Replies (12)

John_Holtz
Autodesk Support
Autodesk Support

Hi @phi.dodat . Welcome to the Inventor Nastran forum.

 

Tipping occurs when the center of gravity (CG) is outside of the feet. Here are some questions that come to mind:

  1. Do you need to do a simulation, or can you calculate the CG with Inventor? You would need to do a simulation if the structure deforms significantly which changes the location of the CG.
  2. If you do need (or want) to do a simulation, can it be a static analysis, or does it need to be a dynamic analysis? A dynamic analysis would be better if there is some time-related aspect to the test. For example, if the child climbing up the structure can jump off before it tips over, then the design is okay. ๐Ÿ™‚

For item 2, if a static analysis is sufficient, you would use a nonlinear static analysis so that the deformation updates the CG. The feet would have fixed constraints. If the reaction force indicates the feet need to be held down, you know the structure will tip.

 

A dynamic analysis would be a longer runtime:

  • Most likely use contact between the feet and ground so that you can actually watch it tip.
  • Apply gravity and wait for the structure to stabilize.
  • Add the load that causes it to tip. I am not sure how you will do that since the load should be a mass, not a force.

Let us know what you want to do and what questions you have.

 

John



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius ๐Ÿ˜‰

phi.dodat
Participant
Participant

Hi @John_Holtz. Thank you for your information.

  1. I tried to simulate this product by Dynamic Simulation but the result not show correctly. Could you introduce me to simulate it by your way?

  2. I simulated it Nastran by Static Analysis. I can define displacement, stress of this product (with force = 270 N, application point the same my picture in post). But I can't conclude with 270 N, have the product will be tip over.
How do you it with Nastran for tips over?

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John_Holtz
Autodesk Support
Autodesk Support

Hi @phi.dodat 

 

You need to look at the reaction force at the bottom of each leg. If the reaction force indicates the leg needs to be held down, you know the structure will tip.

 

See Tip #48 in the PDF document attached to my forum post Suggested Reading - Tips and Tricks on the Inventor Nastran forum.

 

Let us know if you have any other questions. If it would be helpful to send your model, see What files to provide when the model is needed - Autodesk Community - Inventor Nastran.

 
John


John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius ๐Ÿ˜‰

phi.dodat
Participant
Participant

Hi @John_Holtz

I can define Reaction Force for every legs. How can I conclude with 270 N, the product won't be tip over?

screenshot_1718086369.png

โ€ƒ

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John_Holtz
Autodesk Support
Autodesk Support
Accepted solution

Hi,

 

The sum of all reactions will always be 270 N. You cannot look at all the reactions together.

 

You need to look at the reactions in each leg one-by-one. (Delete three of the selected faces in the "Selected" box and leave only one face in the list.) When you look at the individual legs, you will see when the reaction force in the rear leg goes from positive to 0 to negative. The floor cannot provide a negative force to the leg, so you know it will tip.

John_Holtz_1-1718109106989.png

 

  1. The reaction force in all legs is positive. The floor can do this! It will not tip.
  2. The reaction force in the rear legs is 0. The model is ready to tip.
  3. The reaction force in the rear leg is negative. Since the leg is not nailed or glued to the floor, the floor cannot create a negative reaction force. The model will tip.

Let us know if you have any questions.

 

John



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius ๐Ÿ˜‰

phi.dodat
Participant
Participant

Hi @John_Holtz,

How can I create an angle for rear legs the same in Dynamic Simulation in Nastran? 

I defined leg one-by-one but It's always show value = 0 for 2 rear legs with every force.

screenshot_1718161937.png

 

I constrained 2 legs (fixed) and free for 2 rear legs. Have I set up correctly? 

 

screenshot_1718160451.png

โ€ƒ

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John_Holtz
Autodesk Support
Autodesk Support

Hi @phi.dodat 

 

All 4 legs need to be constrained. If there is no constraint (and I see there is no constraint) then there is no reaction force.

 

You asked "How can I create an angle for rear legs". I do not understand what you mean by an angle. However, you have the following options:

  • You have complete control over your CAD model. If the orientation is not what you want it to be, you can change it.
  • You have complete control over the analysis. "Down" can be in any direction you want it to be if the cabinet is tipped at some angle relative to XYZ. Apply gravity in the correct direction to represent "down". Apply the force in the correct direction to represent "down".

By the way, I see that gravity is no longer included in the analysis. Is that a mistake? The weight of the cabinet helps to hold it down.

 

John

 



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius ๐Ÿ˜‰
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phi.dodat
Participant
Participant

Hi @John_Holtz ,

Thank you for your suggestion.

4 legs have been constrained.
I have defined the force (270 N) and the gravity follow Y axis but the result show it's rotate around Y axis. If I'm right, I think the model will be rotate around X axis to tip-over.

 

phidodat_1-1718337149795.png

phidodat_2-1718337189210.png

Could you explain it to me?

 

 
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John_Holtz
Autodesk Support
Autodesk Support
Accepted solution

Hi,

 

I see you have two mistakes, one in the setup and one in the design of the CAD model.

 

1) Constraints:

You are doing a static analysis. The model must be statically stable.  The constraints need to prevent the model from moving in all six (6) directions: X, Y, and Z translation, and rotation about X, Y, Z. It is clear that you have not prevented rotation about the Y. My guess is other directions are also wrong.

 

For reasons that are too complex to explain now, the only constraints that have an effect on solid elements are Tx, Ty, and Tz. The Rx, Ry, Rz on the constraint dialog do nothing when applied to a solid. The fastest and easiest thing for you to do is fully fix all 4 legs so that you get results.

 

A more accurate setup is as follows (see the image below for the location of the 4 legs):

  1. Fully fix.
  2. Fix Tx and Ty. The X constraint prevents the model from rotating around the Y axis.
  3. Fix Ty.
  4. Fix Ty.

 

2) Model:

I see the doors are swinging in your results as shown by the yellow arrows in the figure. Swinging is not allowed in a static analysis because it means the doors are statically unstable. A static analysis requires everything to be stable. There are two methods to fix this second issue:

  • Add a Tx constraint to one vertex on each door. (Do not apply the Tx constraint to a face or edge. Apply it to a corner of the door; that is, the vertex or point.) This will prevent the doors from swinging.
  • Change the CAD model so that the door is imbedded into the cabinet. Change the model from "A" to "B".

John_Holtz_0-1718366404445.png

 

One final note. You are not going to see the model tip over. Your second image that says "Not tip-over" is what you are going to see. The model cannot be allowed to tip over because you are doing a static analysis, the model must be statically stable, and tipping is not a static condition. You know it will tip or not tip by viewing the reactions forces.

 

Good luck!

 

John



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius ๐Ÿ˜‰

phi.dodat
Participant
Participant

Hi @John_Holtz,

 

Thank you for your information. It's very useful for me.

I would like to confirm with you about defining result.

As you mentioned above,  "the reaction force in the rear leg is negative. Since the leg is not nailed or glued to the floor, the floor cannot create a negative reaction force. The model will tip." My model have reaction force on Y axis so when Ty vaule is negative, the model will be tip?

phidodat_0-1718676251525.png

 

Thank you so much!

 
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John_Holtz
Autodesk Support
Autodesk Support
Accepted solution

Hi @phi.dodat 

 

That is correct. Your model will tip because the the reaction force on the rear leg is negative which says the reaction would need to hold the leg down. Since that cannot happen in reality, you know it will tip.

 

John



John Holtz, P.E.

Global Product Support
Autodesk, Inc.


If not provided already, be sure to indicate the version of Inventor Nastran you are using!

"The knowledge you seek is at knowledge.autodesk.com" - Confucius ๐Ÿ˜‰

phi.dodat
Participant
Participant

Hi @John_Holtz,

Thank you for your help. You're very kind.
Have a great day!

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