Dropped Test Simulation of a falling object including gravity

[StathPol12]

Dear all,

I would like to ask if anyone can help me with an issue that I came in contact with.

I am trying to model an impact event of a dropped test and I would like to model the gravity as well. The simulation consists of an analytical rigid surface for the projectile including a reference point to apply the weight, velocity and gravity. The second part is a concrete beam (100x100x600) meshed using C3D8R elements .

The weight is 10.6 kg dropped in a free fall with an impact velocity of 4.43 m/s. I also have restrained the degrees of freedom on the bullet, except from the translation movement in the vertical direction.

I have defined three steps for the impact.
1st step: application of boundary conditions
2nd step: application of velocity
3rd step: application of weight x gravity using a load (also an amplitude was used).

The results do not seem to be realistic as I think something goes wrong with the definition of the steps. I am wondering if anyone can provide me with any help on this issue.

Many thanks to all,
StathiPol12

 

[Mustaine3]

Why do you do that?
Why not using a initial velocity and starting the simulation right before the impact?

 

[StathPol12]

Hello Mustaine3,

I have attached an image for your convenience. I would like to simulate the gravity on the projectile so I guess this needs to be in a different step. The steps I followed are as follows:

I have applied an isotropic point mass thought the interaction step on the reference point on the projectile of 0.0106 tonne.
I have applied an initial velocity on the reference point, and then I would like to deactivate the initial velocity and leave the projectile to interact with the concrete surface. Is there any other way to model gravitational force?

Regards,
StathPol

 

[Mustaine3]

Do you really think that the gravity is doing anything? Calculate the impact velocity by hand (E_kin = E_pot) and start the simulation with that.

The initial velocity is a initial condition - not a BC. So it does no constraint anything during the simulation and just defines the starting situation.

 

[StathPol12]

Hi Mustraine3,

Thank you for your quick reply. As aforementioned, the calculated velocity is 4.43 m/s and was defined on the reference point as load x gravity during the second step. I also have defined a point mass to account for the inertial. In the step module, I defined the following:

Incrementation tab - Stable increment estimation - element by element
Time scaling factor - 0.9

It does not converge now as it aborts the analysis. The analysis is elastic analysis before I apply the plasticity values in the model.

Regards,

 

[Mustaine3]

Explicit analysis have no convergence or nonconvergence, since there are no iterations.

Why does the analysis abort? What is written in the .msg or .sta?

Is your unit system consistent?

 

[StathPol12]

Thanks for your reply Mustaine3.

Well, I had a small issue which I sorted out with the steps..Is there any way that we can create a separate short step to give the velocity and then the next step to suppress it? I will finish what I am doing and then attach the file.

http://www.eng-tips.com/viewthread.cfm?qid=269563

 

[Mustaine3]

You can create as many steps as you want and you can create loads and BC and deactivate them later. But I say again that it makes no sense for such cases. Especially in Explicit it can create heavy problems.