Impact Analyses

[equitus.engineering]

Hello all,

I am trying to set up two different impact analyses as follows:

1. Nonlinear transient response

I am dropping a wooden ball on to a steel floor with wooden reinforcement. I know the impact velocity, drop height etc and it works when the mesh is quite coarse. However, as soon as I go to a fine mesh, my analysis starts bisecting, and fails. Why is this happening?

2. Simple Impact analysis

I have a block of brick falling on an aluminium floor, travelling along a trajectory (sketch that connects the 'brick' to the 'floor') from a pre-defined height and 0 initial velocity and 9810mm/s^2 acceleration, but it's not behaving like the Autodesk video shows. As far as I remember it should in the first instance drop the brick to the floor and then do the computation for post impact. But that's not what's happening. What am I doing differently compared to the videos?

Happy to share my files if need be.

Any help anyone can offer me to solve these problems will be appreciated.

Regards,

Raam

[John_Holtz]

Hi Raam,

1. My guess is that the finer mesh is able to capture the vibration and/or sound waves propagating through the body more accurately, so it needs a smaller time step to converge. Another possibility is that a finer mesh allows less penetration (I think the penetration allowance is based on the mesh size in the contact area), so it may require more iterations to transition from "no contact" to contact.
2. You did not mention what your analysis is doing (other than it is not doing what some video shows). For example, is there stress created due to impact? Keep in mind that while the analysis is running, the deformed shape is based on an arbitrary scale factor. This makes it impossible to look at the displaced shape during the analysis and decide if the body is moving. After the analysis completes, you can change the deformed shape to actual, and then you should see the bodies moving properly.

[equitus.engineering]

Hi John,

Thank you for getting back to me.

For analysis 1, I am rerunning it as we speak with reduced contact stiffness. I'll update you once it's done.

For analysis 2, I can share a link with you to the drive folder where I have the files that you could perhaps look at and get back to me.

Regards,

Raam

[equitus.engineering]

Hi John,

Sorry for the delay in responding to you. I'd like to attach the zip file of the model I am trying to solve. I want the projectile to hit the floor after travelling along the trajectory, defined by the line. That should give you a better idea.

Regards,

Raam

[John_Holtz · Accepted solution]

Hi Raam,

I ran your model with out making any changes. I do not see anything obviously wrong.

• The solid is moved from the starting point of the projectile path to the ending point of the projectile path. (Be sure to set the deform scale to an actual value of 1 when viewing the deformed shape.)
• The analysis includes 105 steps during the impact over a span of 0.013 seconds.

One thing that may be unexpected is the constraints around the perimeter of the plate may be missing on one of the edges. There are 6 edges around the perimeter; the constraint is applied to 5 of the edges. See the attached animation of the results.

(edit) Another thing to keep in mind is that the gravity/acceleration is along the projectile path. So even though the model looks like the block is dropping "down" and with a "side-to-side velocity" (in the Z direction), the analysis is really for a model that has the floor rotated (15 degrees? 20 degrees). The block is also rotated the same amount, and it is dropped straight down. In other words, if you rotate the screen so that the projectile path is vertical, that is a better representation of the actual analysis.

Let me know if I am overlooking something.

[equitus.engineering]

Thank you John, much appreciated!

Regards,

Raam