Modal Analysis of Baseball Bat

[Anonymous]

Hi, this is my first question posted so I'm not sure if this is the right place but here goes!

I am trying to do a modal analysis of a baseball bat in Inventor 2014 to estimate the first two natural frequencies and plot the first two mode shapes.  I've assigned the material and set fixed-free boundary conditions--but I'm not sure what to do from here.  This is my first modal analysis--so how do I disrupt the model in order to observe the vibrational response?  The only option I can see is to apply a load (i.e. a ball striking the bat), but there is nowhere to set it so that the load only acts for a certain amount of time.  Help=much appreciated.  Thanks!

[AstroJohnPE]

Hi gruenhir,

Modal analysis does not require any loads, so it sounds like your setup is complete. (Recall from your vibration classes that the frequency is proportional to sqrt(k/m). Note that there is no load in this equation!)

Click the run button and let us know what the frequencies are. Someone can probably estimate the answer from their personal experience. (It has been a long time since I batted a ball and felt the vibration of the bat.)

[Anonymous]

Hi, thanks!  I did do this--the only difference is that I had to get rid of the fixed boundary condition (apparently we are supposed to do free-free).  Here is a screencap of my results--it has F1 and F2 at zero hertz.  Not sure what I'm missing here! It appears as though nothing really happened.

[AstroJohnPE]

Assuming that Inventor's simulation behaves the same as Simulation Mechanical, there will be 6 "frequencies" of 0 Hz when the model has no boundary conditions. The model can translate in X, Y, or Z without any bending, and rotate about X, Y, or Z. So to get the "first" two modes in your model, you will need to solve for a minimum of 8 frequencies. Some solvers need to solve for more frequencies than desired, so I suggest that you ask for 10 frequencies.

[Anonymous]

Ah perfect!  I get 180.80 Hz and 138.96 Hz.  Compared to the others being all zeros, those two values seem to be pretty close to me...is that to be expected?

Thanks for the help!  That explains so much that I have been unable to figure out, even after scouring the internet...