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Dropped Test Simulation of a falling object including gravity

Dropped Test Simulation of a falling object including gravity

Dropped Test Simulation of a falling object including gravity

(OP)
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

RE: Dropped Test Simulation of a falling object including gravity

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

RE: Dropped Test Simulation of a falling object including gravity

(OP)
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

RE: Dropped Test Simulation of a falling object including gravity

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.

RE: Dropped Test Simulation of a falling object including gravity

(OP)
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,

RE: Dropped Test Simulation of a falling object including gravity

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?

RE: Dropped Test Simulation of a falling object including gravity

(OP)
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

RE: Dropped Test Simulation of a falling object including gravity

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.

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