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Elastic ball impact with rigid flat target vs Hertz equation analytical solution

Dear Readers

 

I was trying to perform a drop test of a
flexible (elastic) solid sphere on a rigid flat target with ANSYS LS
dyna. Do you know what is the best element and the corresponding
options of that elemet, how to mesh the ball to get best results,
which is better ANSYS or ANSYS LS Dyna for this problem? iam a student and have been
trying to solve this problem, but my results sometimes are very far from
the anlytical solution of HERTZ dynamic equation. Please guide me. Also when I refine the meshes
more, my computer ask for more memory using -m command which i do not
understand. Please help meCry!!!!!

 

my email  a.abeed@tu-bs.de

Comments

flong208's picture

I'm anlysis the ball-track contact of a bearing like part using ANSYS but not LS-DYNA, I also meet similar problem like you,-the FEM result is far away from HERTZ solution. now,I'm try to improve it.I think, first, the mess near the contact area must be fine enough, you can get contact area imformation via  HERTZ solution, and, you mess size near the contact area must be much less than the size of the contact area, or, you cann't get the right result; secondly, the parameter the contact pair is also important! you can try to change them.

thank you, in fact today i got good results with ansys LS Dyna (DTM: Drop Test Module) with 3% error but i still have the problem when i refine the mesh gradually (for whole ball) the finte elemet curve and hertz curve get closer until i reach certain refinement (which is not too fine) ansy ls dyna curve start geting further from  hertz curve until it coincide approximately with the 1st mesh (the coarser mesh), what is the problem? is it the time step?or what?

 

this causes headache for me since one does not know which curve he/she must trust, or what is the criteria, assume we do not know hertz law then we are in trouble becase we will select the results of the finest mesh which appeared to be not true.

 

second question how can one refine the elements surrounding the south pole and how can one force the ball to move i the y-direction during the impact

 

i am trying to refine the elements at the contact but i still do not know, here is the ball entire meshing with only pure hexahedraon (better results if full integration and lagragian than tetrahedron with reduced integration + single point ALE):

 

/PREP7 
ET,1,SOLID45
SPH4,0,0,1                  ! Create a solid sphere of radius 1 centered at origin
VSBW, ALL                     ! Divide the sphere, cuting knife is the current WP
WPLANE,-1,0,0,0,1,0,0,0,0,1        ! change the work plane (New cuting knife)
VSBW, ALL 
WPLANE,-1, 0,0,0,0,0,1,0,1,0
VSBW, ALL
!WPCSYS,-1   
LESIZE, ALL,,,12                !
TYPE,1                        ! set element type attribute pointer to 1 (SOLID45)
MSHKEY,1                      ! Mapped mesh option  
MSHAPE,0,3D                   ! Hexahedron Elements option
VMESH, ALL                    ! Mesh All The Volumes
 
FINISH 

 

just put it in the ansys current directory as dat or txt file, then open ansys go to 'file' then 'read input from', select that file and modify it please by refining the south pole of the ball and then go to 'File' then 'write as DB lgw file'  and send the file please to me:   a.abeed@tu-bs.de     i will be very thankful

 

 

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