Tag Archives: SystemModeler

Research Tutorial

Dynamic Arches...

Tinkering about with SystemModeler a little further, I've managed to finally build a sprung arch, complete with dampers on the revolute joints.  I'm intending on using this principle in my research to create folded structures, so it's interesting to see what effect the spring stiffness will have on the behaviour of the arch during the unpacking process - specifically looking at the accelerations on the masses at key points.

The thing that I was struggling with was creating a structure that had a set of equations that could be solved, the key concept I was initially missing was the closing of the structure with the special type of revolute joint to complete the chain.  Without this special revolute chain the equations are essentially unsolvable, so it's important that one of these joints sits in the system somewhere.

Sprung Arch

Another concept is that the structure in the video has 3 straight segments, each 1m long; but the supports are only 2m apart.... forcing the arch to pop into a stable shape that balances the weights at each of the joints.  This is essentially what makes the arch wobble when solving the initial set of equations.  Next step is applying external forces and measurement points along the structure for displacement etc...



I've had SystemModeler for a while, but struggled to get on with it.  I guess the issue that I've had with it is that there are very few learning resources and tutorials around to help cut your teeth.  Mathematica has been around for years, so there are endless resources that are suited to the individuals preferred method of learning, from PDF's, Stack Exchange, and even Lynda.com now has a video based learning method for the basics.  Given that even simple models have dozens of flags that can be plotted and graphed and that certain flanges aren't enabled by standard, I've waited until I've had a few minutes spare to start tinkering.

Today I've been fiddling about with a mass and two springs with dampers, what I've been trying to do (and failed) is to make both supports displace over a given time period to push a displacement through the system to see what effect spring stiffness and damping have on the system, eventually this will be scaled up to a chain of springs of about 40-50 elements and used to model a structural system but this is my validation model.

Screenshot 2014-09-10 17.55.26

I've not worked out how to give the supports a nudge (something that we do when modelling in ANSYS) so I've cheated a bit by essentially shortening the left hand spring to give a similar effect and then watched to see how the system has damped down. Parameter settings below for the spring/damper system.

Screenshot 2014-09-10 18.33.22

By specifying the spring length as 1m, then setting the nominal value for it as 0.5m to start with it gives the system a nudge to start it bouncing.  I'm sure there's another more elegant way of achieving this but I'll have to figure it out over the next few days.

Screenshot 2014-09-10 18.19.11

I'll keep tinkering over the coming days, to try and refine the process.   Hopefully I can find some more learning materials or a decent community... something comparable to the Mathematica StackExchange community would be ideal.

If anyone's come across a decent text or resource I'd love to hear about it.