Learning Forum

[Rocco Bombardieri]

I am attempting to evaluate the modal response of a pressurized membrane-like structure.

I have created a simple example consisting of a square membrane, simply supported along the edges, and subjected to uniform pressure. Here are some additional details:

1. I am utilizing a fully integrated Belytschko-Tsay membrane (ELFORM=9) that is designed to be hourglass-free.

2. I am using a linear elastic material (*MAT_ELASTIC).

3. The pressure load is applied using the *LOAD_SHELL_SET_ID keyword.

4. Currently, I have opted for the explicit solver, applying the pressure linearly.

5. I am constraining the translational degrees of freedom (DOF) of the edges only.

6. I am using version R13.1.1-13-g5480eca294 mpp_dp for Windows.

Upon running the simulation, I immediately observe what I thin kto be significant hourglassing in the membrane deformation and am unsure about the cause (please see the attached picture).

How can I suppress this behavior? What is causing it?

 

Best regards,

Rocco

 

 

 

[Rocco Bombardieri]

Interestingly enough, reducing the time step using keyword *CONTROL_TIMESTEP delivered a very good result. Also the implicit solver was able to deliver the same robust results using the following settings:

*CONTROL_ACCURACY
$#     osu       inn    pidosu      iacc    
         1         4         0         0
*CONTROL_IMPLICIT_AUTO
$#   iauto    iteopt    itewin     dtmin     dtmax     dtexp     kfail    kcycle
         1        30        10       0.0    1.0E-4       0.0         0         0
*CONTROL_IMPLICIT_DYNAMICS
$#   imass     gamma      beta    tdybir    tdydth    tdybur     irate     alpha
         1       0.6      0.38       0.01.00000E281.00000E28         0       0.0
*CONTROL_IMPLICIT_GENERAL
$#  imflag       dt0    imform      nsbs       igs     cnstn      form    zero_v
         1    1.0E-4         2         1         1         0         0         0
*CONTROL_IMPLICIT_SOLUTION
$#  nsolvr    ilimit    maxref     dctol     ectol     rctol     lstol    abstol
        12        15        15     0.001      0.011.00000E10       0.91.0000E-20
$#   dnorm    diverg     istif   nlprint    nlnorm   d3itctl     cpchk     
         1         1         1         1         0         1         0
$#  arcctl    arcdir    arclen    arcmth    arcdmp    arcpsi    arcalf    arctim
         0         0       0.0         1         2         0         0         0
$#   lsmtd     lsdir      irad      srad      awgt      sred    
         5         2       0.0       0.0       0.0       0.0

[Rocco Bombardieri]

Interestingly enough, reducing the time step by keyword *CONTROL_TIMESTEP  help achieve a good solution. Same soluction could be obtained using the implicit solver with the following settings. 

*CONTROL_ACCURACY
$#     osu       inn    pidosu      iacc    
         1         4         0         0
*CONTROL_IMPLICIT_AUTO
$#   iauto    iteopt    itewin     dtmin     dtmax     dtexp     kfail    kcycle
         1        30        10       0.0    1.0E-4       0.0         0         0
*CONTROL_IMPLICIT_DYNAMICS
$#   imass     gamma      beta    tdybir    tdydth    tdybur     irate     alpha
         1       0.6      0.38       0.01.00000E281.00000E28         0       0.0
*CONTROL_IMPLICIT_GENERAL
$#  imflag       dt0    imform      nsbs       igs     cnstn      form    zero_v
         1    1.0E-4         2         1         1         0         0         0
*CONTROL_IMPLICIT_SOLUTION
$#  nsolvr    ilimit    maxref     dctol     ectol     rctol     lstol    abstol
        12        15        15     0.001      0.011.00000E10       0.91.0000E-20
$#   dnorm    diverg     istif   nlprint    nlnorm   d3itctl     cpchk     
         1         1         1         1         0         1         0
$#  arcctl    arcdir    arclen    arcmth    arcdmp    arcpsi    arcalf    arctim
         0         0       0.0         1         2         0         0         0
$#   lsmtd     lsdir      irad      srad      awgt      sred    
         5         2       0.0       0.0       0.0       0.0