Moving constraint and or moving load: Can it be done? How? 1

[TennisGuy543]

I have bar that extends in and out of a socket. At the contact points between this socket and rod, a moment and forces are induced. We do not know exactly how the moment/forces are imposed onto the structure, we just know the area of contact, its magnitude, sign, and time-variation. I want to impose this data of a time varying load (forces and moments) onto a moving region of contact in ABAQUS, representing the area of contact between the bar and socket. This area of contact changes as the rod moves in and out of the socket. The two main regions move up and down the rod at the same rate that this rod is moving in and out of the socket.

Basically, the load changes for every time step, but I also want its location to change for every time step, as defined by a plot of data providing information of the position of this load. Is there a way to do this? Would I somehow use a constraint equation?

One method I was pondering was to define an analytically rigid structure representing the contact region (a simple ring or something). Then, prescribe a displacement boundary constraint, enforcing the location of the region at each time step. But I do not know how to use this to transfer loads to the rod, if it's even possible. Is there a step-by-step way to do this? Also, is it feasible, or is this something that cannot be done on ABAQUS.

 

[TennisGuy543]

And thanks in advance!

 

[TennisGuy543]

Any ideas? Surely someone has had to model a moving pressure before.

I was wondering if there is a common method on how to do it.

Could I prescribe a pressure over the entire object being analyzed, then implement a "user-defined" pressure distribution such that the distribution is 1 at the area where I want to have pressure and 0 at the area where I do not want any pressure. The values of 1 and zero would change throughout the field as a function of time, such that I could have the pressure move by changing the regions that are equal to 1. Then obviously multiple the field by a the magnitude. Is this feasible?

Again, I have an array of data in which both the load magnitude and location change with time on an object and I am wondering how to accurately model this. I have been trying multiple methods but I am worried that there is a better/easier way to do this since moving loads/pressures are relatively common.

thanks!

 

[IceBreakerSours]

If I understand the problem correctly, all you need to do is apply a time-varying force to a surface that is in contact with another surface. Variation with time can be accomplished by using the amplitude definition. Search the archives/documentation/google for more.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[TennisGuy543]

That is indeed part of what I want but I want the pressure moving with respect to time also. So, I have the pressure's amplitude and location change with time.

A physical example would be modeling a road with tires moving on top of it, which causes a moving pressure. Except now the amplitude of this moving pressure is also changing with time.

 

[IceBreakerSours]

Option 1:

Spatial variation could be provided by the surface of the bar/rod (in the example mentioned by you) which is in contact with the socket. The bar may be moved by applying a displacement b.c. while using an amplitude definition to allow time variation.

Option 2:

User defined spatial variation of a load may be applied using the DLOAD subroutine. If you have used subroutines before, then using this subroutine will be straightforward. If your machine isn't set up for subroutines, then it may take a while before you get up and running. You will also need a working knowledge of FORTRAN.

User defined time variation can be applied using UAMP subroutine.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[TennisGuy543]

IceBreakerSours, Thank you.

You're post makes sense and is consistent with other research I've been doing on this. I prefer option 1. I understand that option 2 is a good brute force was of applying the moving pressure to the rod, but I have limited experience with FORTRAN.

However, I now have a question on actually applying the load to the rod. I'm obviously familiar with applying all sorts of loads on ABAQUS - my question is more directed on the best method to do so. Imposing the correct time-varying displacement (using amplitude like you said) on the rod will get me the correct locations (the contact surfaces at a given time) in which the load is applied. But what mechanism do I use to construct a load/pressure at this time-varying contact region that we've now created.

Obviously I want to use these contact regions now to apply a pressure with a time-varying amplitude. So, how to I use these regions of contact to apply a load? Do I somehow isolate this region of contact and apply a pressure to it? Or do I use a surface contact?

thanks for you help so far

 

[IceBreakerSours]

Try the default element surface-based contact formulation first.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[SwimBikeRun4342]

Thanks again IceBreakerSours. Surface based contact seems to work well, as you suggested. So I currently have a moving object with loads applied, functioning as a moving pressure on the rod. Now, I was wondering if I could somehow use this moving object to transfer not just pressures but also moments. Would it be possible to transfer moments through the contact surface using the moving object?

I wanted to apply a time dependent array of moment data to the rod, at the same region of the moving pressure. I was originally thinking of applying the moments through the moving contact surface, but this may not be physically accurate. Does anyone have any suggestions? Thanks!

 

[IceBreakerSours]

Try your ideas out on a simple model and let us know if you are encountering any issues.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083