Mechanical Event Simulation

[timputtock]

Just wondering if anybody ca help me with a problem I am having with a MES model I am trying.

I have created a simple MES setup with a plate that is constrained and a brick that is falling with gravity toward the plate. Instead of the brick hitting the plate it goes straight through it. I have set up the surface contact with the top surface of the plate and the bottom surface of the brick, but it doesn't seem to make any difference.

Any help would be greatly appreciated.

 

[GBor]

I'm assuming you are using surface to surface contact between the two surfaces that you mentioned. Make sure that the contact pair is active in the surface to surface contact screen (this is not always the case). Also make sure (using hand calculations) that the time step isn't so large that the block would be well on the other side of the plate before the next time step...try to come close to the impact time.

By the way, what version of Algor are you using?

Garland

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.

http://www.borowskiengineering.com

Lower Alabama SolidWorks Users Group

http://laswug.borowskiengineering.com

 

[timputtock]

Garland,

Thanks for your reply. Firstly, yes I am using surface to surface contact and the contact pair is active. Secondly, I have tried a number of different time steps, with the same result. Thirdly, I am using Algor v.16 which i know has a tolerance issue in the contact pair options, which i have changed from 2.54e-1 to 0.01 mm as i am working in mm not inches.

Thanks again for your help.

Tim

 

[GBor]

Hmmm...v.16 was pretty early in the process. I seem to recall something about the element normals of the plate elements needing to point in a specific direction. I'm sorry I don't recall whether it is toward or away from the object that is coming toward it. Do you know how to flip element normals for plate elements?

Garland

 

[Stringmaker]

I'm a bit rusty when it comes to Algor but what Garland has said thus far holds true. You need to make sure that the element normals are facing each other (I think it's facing...that's how most FE programs are). You may try creating a symmetric contact pair if possible or try flipping the contact and target surfaces. Also, in the advanced contact options does Algor give you any means or way of changing what the pinball radius for that contact is? This is the radius through which contact detection takes place from each element on the contact surface for each time step. If your brick is moving a greater distance in that time step than the pinball radius is set to contact will not be detected.

Another way to approach this would be to instead of having the brick fall towards the plate have them almost initially touching with just a very small gap. Give the brick an initial velocity of what speed it should be going according kinematics and specify a small starting time step. If no matter how small you make the time step contact still is not detected you will probably need to play around with your mesh. I would start with the element size of the plate elements being larger than that of the brick. If this doesn't work try vice versa...then same size on each.

Once you do get the model to recognize contact one more things which pops to mind is the sharp corners of the brick. If you have convergence issues shortly after cotact occurs it will likely be due to these.

Good luck!
-Brian

 

[GBor]

Tim,

Just for fun, I ran a block falling onto a plate. I was using v.19, but here are some of the specifics:

Time Step: 0.01s

Distance block above plate: 0.5 inches (sorry, didn't think about you working in metric, so 12.7mm)

I reduced the convergence criteria to 0.01 inches (this may not be entirely accurate, but I was just trying to get some settings that would work, not get really accurate results)

I applied gravity (negative z-direction, 386.4in/sec -- perpendicular to the plate)

I have the block hitting the plate with a contact distance of 0.25 inches and a maximum penetration (I don't think you have this in v.16) of 0.1 inches. These numbers are huge, but I have a large mesh on my block and plate of about 0.5 inch.

The block is made of steel and the thin plate (0.1 inches) is made of Nylon 6/6, so I get some permenant deformation and good "bounce" from the block.

 

[timputtock]

Thanks Garland, I have followed a similar mathod to the one outlined in your last post and the block still falls through the plate. When i inspected the the two parts more closely i realised that the two are both surface meshed only, will this make a difference? I am struggling to get the two parts solid meshed, but I am not sure whether this is the problem with the solution.

Tim

 

[GBor]

I don't recall whether v.16 would impact with bricks to shells. In v.19 there is a switch for "solid mesh before analysis" or some such switch that tells the mesh engine not to perform the full brick mesh until the analysis button is pressed. This speeds up the user interface since it doesn't have to generate the internal elements when you manipulate your model.

In my mind, for something as simple as a brick and flat plate, it is easier to "Copy: Join" to build the internal mesh. If you aren't familiar with this, let me know. I also "Copy", but not join, to make sure that the nodes of the brick line up with the nodes of the plate. Then, I make sure that my contact distance is 1/2 the length of an element edge. This should make certain that, as long as my time steps are small enough, the nodes have to make contact.

If I'm just trying to learn how to make this contact happen, place the block about 1/2" above the plate, make the contact distance 0.49 and the penetration 0.5". Put a really small time step and a really small duration, so you don't fill your hard drive with useless data. Run "Monitor" so you can see what is happening and output results from every time step.

If you keep having trouble, e-mail me and archive of your model...my address can be found on my website. I'm not sure if v.19 can even read back to v.16, but I can take a look.

Garland

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group