Learning Forum

[mohammedlaminemekhalfia]

Dear all,

I would like to study the effect of fixation torque on the blade modal analysis.

I constructed the attached assmebly where the blade is inside a clamp where I can adjust the force that the clamp impose on the blade root.

I created a harmonic response environment 

I removed the connections and Insert Two translational joints and one fixed.

I would like to know please if my approach is correct or wrong and how to make the simulation of this problem ?

[Erik Kostson]

 

Hi

If you share some more inline images of the set up (loads, boundary conditions, joints, etc) in your next post, then members of this forum might be able to provide some feedback.

The best way to check if your model represents reality is by running the same but as a physical test and verifying the FEA results against testing.

Also can you clarify : 

You said: “I would like to study the effect of fixation torque on the blade modal analysis.”

Where is the torque coming from and how it is applied and what do you want to study (say frequencies). So much more information so members can provide feedback.

 

 

All the best

Erik

 

[mohammedlaminemekhalfia]

Dear

I meant about a clamping force like the one we obtain using a bench vises. and I would like to see how the values of the natural fequencies would change in the function of changing the clamping force. I am focusing on just the 3 first modes. below the screen shots for my simulation.

Since I am a biginner I would like to know if I am proceeding with the right way and what needed to do to make this experiment in the correct shape.

for the frequency range in the analysis settings I chose 0 to 600 as the Blade natural frequencies for the 1st mode is 57 and 289 for the 2nd mode and 535 for the 3rd one while I wanted to have a resolution of 0.1 thus I picked 6000 points.

 

[peteroznewman]

There are at least two flaws in the approach.

A vise has a stationary jaw and a sliding jaw.

The model has two sliding jaws. This is wrong because any tiny difference between the applied forces will allow the blade and slides to move toward infinity. Also, there is no stiffness that acts to return the blade to the center of the fixed base of the vise, introducing a zero frequency mode. One of the joints should be fixed and the force on the translation joint will cause a clamping force to be experienced on both sides of the blade. This change will correct both those flaws.

You don’t say how the blade root and the jaws are connected. Perhaps you used nonlinear Frictional Contact, intending to allow the blade root to rock in the jaws. This is possible in a nonlinear (large deflection) structural analysis, but Harmonic Response is a linear analysis. ANSYS automatically converts any closed nonlinear Frictional Contacts to linear Bonded Contacts so the entire face of the blade root will be glued to the jaw faces and prevent any rocking of the blade root. Once glued with bonded contact, the force applied to the translating slide is almost irrelevant.

[mohammedlaminemekhalfia]

Dear.

 

in the previous design, I was thinking that applying same force on both side would not create any trouble resolving the model. Yet I agree to your advise and I have to thank you a lot for teh explanation as I updated the model based on that.

I am trying to make a modal study on the effect of clamoing force on the natural frequencies, using a direct modal analysis was not possible as I can not apply a joint load in a force forme, this is why I thought that the harmonic would be the best solution. so I assigned a frictional contact with 0.2 coefficient between the base of the part and the base of the vise.

is performing a static structural analysis followed by an FFT for the deformation results to have the power spectrum is the only solution?

and I wonder if my model is correctly set this time.

again thank you a lot for all the kind help

[peteroznewman]

There are many mistakes in this Statics model. The Part_Force1 body has a Translational Joint to Ground on one end, but no contact was defined at the other end to press against the blade. That means the Part_Force1 body will pass right through the blade and cause the Statics analysis to fail. Similarly, the other Translational Joint to Ground holds the blade, but there is no contact for the blade to push against.

You have not understood that Harmonic Response analysis will automatically convert any closed Frictional Contacts to Bonded Contacts.

You need to study how to build models for Statics, for Modal and for Harmonic Response analysis. You need to study how Joints and Contacts work. There are many free courses available on this website.

You need to study how to break an assembly of parts down into components and draw a free-body diagram for each component to track the transfer of forces through the assembly. Search for that using Google or YouTube.

[mohammedlaminemekhalfia]

Dear, Thanks a lot for the feedback.

I trully went through all the material provide in the learning platform and saw a lot of videos and exmaple on the internet and youtube but I could not link to my case, I tried several examples but none had the results I am looking for in terms of boundaries, thus I posted this in the learning forum.

I would highly apreciate if you can advise more on how to resolve this

[mohammedlaminemekhalfia]

Any suggestions, please?