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[DEVICHANDAN.PADALA]

Hi all,

Kindly let me know the reson for below issue

iam doing an impact analysis projectile hitting inside an enclosed wall with initial velocity of 189m/s. i have included gravity to acompeny with initial veloity due to self weight of the other structure on top of enclosed structure could aid the impact deformations,

the initial conditions is given through displacement and time integration effects (Initial Displacement ≠ 0, Initial Velocity ≠ 0)

Step1:

1) displacement - 13mm with time 6.5991e-005sec

2) time integration -off 

3) gravity includes

Step2:

1) displacement - 13mm with time 9.e-004 sec - Displacement -deactivated

2) Time integration -ON

3) gravity diactivated

the problem is when iam trying to increase the 2nd step end time the gravity effect still adding up and creating huge stress and deformations due to self weight of the top structure hanging on the top of enclosed structure

although iam able to see the after effects of impact but the stress due to gravity effects keeps on increasing with step end time.

what should i do to stop the gravity effect and keep at constant? please suggest if iam missing any other analysis settings options.

[Erik Kostson]

 

 

Hi

Gravity will always be there so do not deact.

I would say use 3 steps

First Gravity on and no dynamic effects (so time int . off)

Second is a dummy step. Gravity on time int on. This (results) should be similar to the first step.

Third apply the dynamic impact load (gravity on of course here and time int. also on).

 

On another note, for impact do one need gravity when we have such a huge impact – consider for this to use LS-Dyna which is more suitable.

All the best

Erik

 

 

[DEVICHANDAN.PADALA]

 

Hi Erik,

Thanks for the method suggested, i tried this method and did not work to solve the issue.

To identify the problem i have prepared a simple case of a block hanging from a wall, just want to check the stresses due to self weight of the object in transient analysis

in this model i have not given any dynamic loading except for the gravity acting downwards, i have identified that at 0.000032996 sec with time integration OFF the result is same that of a static structural results regardless of time we specify.

but when i introduce the 2nd step without any dynamic load and increased time 0.001sec with time integration ON, so the results should be same as first step results right? but unfortunately the stresses and deformation gets increased drastically, this behaviour is not true in actual

what could be the solution to get the same stresses and deformation under gravity loading in both steps, because gravity wont increase with time in real life, so how to make the results (due to gravity) constant in all load steps?

FYI - i tried supressing gravity in 2nd load step but did not work.

 

[Erik Kostson]

 

 

Hi

It is because of the Number of Substeps = 1. So use 5 say for step 1 and 10 for step 2 (dynamics / time int. is On).

All the best

Erik

 

 

[DEVICHANDAN.PADALA]

Hi Erik,

Yes this is working, thank you for the help.