Velocity problem of drop test in radioss

anqi

Hi all,

I am working on 3 m landing gear drop test in radioss. The material is aluminum. I set it as M2. Partial model is listed blow. I cannot put the whole model due to confidential problem. I chose type 7 in self contact interface. I chose infinite plane as rigid wall, with a distance 10 mm from the bottom of landing gear. Then, I set initial velocity as -7500 mm/s along Z direction, calculate by v=(2gh)^(1/2).

 

Now results confused me. In velocity, when the bottom of landing gear impact on ground, the velocity became slower, however, the top part did not stop, retaining 7500 mm/s velocity, even if the bottom part deformed. Results are listed blow.

 

Is that right? Can anyone help me. Thanks in advance.

 

Regards,

ANQI

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anqi

can any one help, please?

Simon Križnik

Hi,

 

it is expected segments away from the impact zone will experience delayed deceleration. 

can you share slow motion animation (gif format) with many frames per second?

anqi

hello, hyperman,

I can only upload the screenshot per second, since the gif format is also confidential. 

 

     

 

  

 

 

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anqi

 

 

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anqi

it really confused me. 

Altair Forum User

Hi anqi,

 

I hope you have applied the INVEL to all the nodes.

Kindly check once the node connectivity between the solid and shell elements and try running the simulation to a longer duration (As I can see only 3e-3 sec of run time at last frame, which is small time to bring whole model to rest. [assuming unit system: mm, s, ton, N]).

Kindly verify the initial velocity value also.

 

Thanking You. 

anqi

HI Pritam,

 

Thanks to your reply. 

 

Yes, the INVEL have already been applied to all the nodes, the value was 7500 mm/s. The ground was near the bottom of landing gear. 

After changing Tstop to 0.02 sec, the velocity also show the same trend.  At time 1.5e-2 sec, the bottom panel show a significant deformation, but the whole structure still have a big velocity. The parameters of type 7 I used are shown below. both types I have used, but show the same trend.

 

Could you help explaining that?

Many thanks in advance.

 

ANQI

 

 

 

 

Simon Križnik

@anqi

 

as can be seen from the animation below, the top of the column (away from impact) decelerates only after the stress wave propagates through the whole length.

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