Moselling of arrow vibration

barrtibarrti
Hi,
Slightly different problem I guess. I'm trying to verify the lateral deflection of an archery arrow. If you look up "Archer's Paradox" you will see that all arrows have this to some degree. It's quite significant.

Attached is the Dynamic Response 3D file using 2d beam elements.

Initially I only applied a 312N time varying load in the direction of flight (X-Axis). The arrow accelerated as you would expect. No lateral deformation as you would expect (in Y or Z directions).

I then applied 3N in the Z direction hoping to start the arrow buckling. It does show a few mm deflection laterally which is about what one would expect from this size lateral load but I do not see any buckling effect from the 312N load in the X direction.

Can anyone suggest a better model? Should I be using diffent elements?

Cheers

Comments

  • VictorVictor
    The linear Dynamic Response 3D analysis type can't model buckling. Use Nonlinear Dynamic Response 3D with the CCX solver instead. You'll have to change the elements to line3 for that too.

    I didn't get much different a result until I doubled the force to 600 N and that dramatically increased the lateral deflection, so I hope this is the effect you're looking for.

    I also increased the Time step size from 0.00001 s to 0.0001 s for speed.


  • barrtibarrti
    Victor,thanks for your input.

    I found a few papers on this phenomenon and it seems that when the arrow is released using 3 fingers on the bowstring, this imparts a lateral displacement to the arrow at the string.

    Also, this phenomenon is most pronounced when using the traditional bow which results in a difference between the line of action of the string force and the axis of the arrow.

    These two factors would enhance any buckling.

    For a compound bow (which I am modelling), which has a mechanical release (not fingers) and a centre-shot design, the lateral deflection may only be a few mm anyway, so we are not far off.

    The centre-shot design means that the line of action of the string force is in line with the arrow axis.

    The mechanical release means that the arrow is not given a lateral displacement apon release.

    cheers
  • barrtibarrti
    Here is one paper that discusses the complexities https://www.ocf.berkeley.edu/~archery/wp-content/uploads/docs/knsu.pdf

    It is discussing an olympic recurve bow which has the same issues I discussed with the traditional bow.
  • JohnMJohnM
    Just looked at that paper, fascinating stuff. I think it's useful to run the modal analysis first, as this will give you some idea about your required time stepping. For example: 1/(frequency * 10) might be a good start.
  • barrtibarrti
    John M
    Thanks for the tip.
    I'll give it a shot when I get back to my pc
Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Sign In Register