Does anyone know of a technique to simulate a damper with different compression and rebound coefficients?
I think this may be a limitation but I might have seen someone do dampers with springs in parallel or series to do something similar. You may have to get fancy with some equations though. I'd check the swx kb if you haven't already.
I've done a fair bit of looking around- and so far as I can see it is in fact a limitation that dampers have a single coefficient for both directions of motion (there are at least two enhancement requests for additional functionality, one of which is mine).
Poking around I did come across a few answers in the knowledge base which looked helpful, but dead-ended because they applied to motors and forces, and not dampers. As you say, it's possible to get fancy using equations- but only for motors and forces. Dampers can't be specified in the same way.
Which is an unexpected weakness in SolidWorks. Sophisticated shock/damper units are sold by the thousands by Fox and other performance suppliers, which in addition to the primary spring rate also have preload settings, distinct compression and damping adjustments, and a spring to soak up the shock from fast piston returns to the top of stroke. Maybe other tweaks as well which I haven't looked at yet. At the moment, any serious suspension designer will be disappointed using SW Motion.
Unless I've still missed something!
At the moment I'm using Excel to solve my problem. It's not a bad way to go- for visualization I'll bring the Excel output into SW to drive a motor. Results will still be good .
Thanks for the reply.
might be worth describing what you're trying to do to see if anyone can come up with a workaround.
regarding the limitation, i'm wondering if the solver behind the scenes (Adams) even has what you're looking for. it is basically the premiere motion analysis tool that we get access to as part of solidworks motion. are you aware of any other programs that have that funcionality?
I'm working on a damped, forced oscillation problem using a Fox air shock having progressive spring rates, separate compression and rebound settings, and other tweaks to suit offroad applications.
The physics is straightforward- mass, spring, periodic force and damping. At issue is the lack of the same sort of "import data" for Dampers as is provided for Forces and Springs. I want to generate a curve in Excel which specifies the damping rate vs. velocity, and "import data" that curve to a Damper in SW.
We can do this for Springs or Motors already, each a function of "x" rather than "dx/dt". Maybe you're right that this particular limitation is with ADAMS, but my guess is it's rather a question of designing and implementing the interface. SW will get around to it at some point, probably.
I'm a longtime subscription customer and all-around strong SW user and supporter. Any criticism in these posts is constructive only, reflecting a desire to see the software continue to grow. SW is a great program.
If you have access to the tech people at hq, perhaps you could do a bit of digging, and let us know what you find ! Cheers-
have you spoken with your reseller about this yet? they can connect with tech support to see if there is a workaround and as part of your subs, help you escalate the issue to get the software limitation reviewed for a change.
HawkRidge! I'll be in touch, thanks.
I am experiencing a similar problem. For my thesis I am performing a study on a formula student shock absorber, for which I have under carried a Solidworks motion analysis.
My design is a simple twin tube shock absorber, I have assigned two dampers, the first (between compression faces) for the compression stage with a damping constant of 0.2 and the second (between rebound faces) with a damping constant of 0.7.
I believe shock absorbers have a higher damping constant during rebound, because it damps the unsprung masses, which are of a larger mass than the sprung masses (damped by compression).
Having said this, I obtain the graph below for the reaction forces of the damper and linear spring, when a step force of 1000N is applied. As you can see both dampers (rebound and compression) are actuated during compression and rebound stages and their forces counter-act each other? If I was able to set the action time of each damper (by editing the key point time), this problem would be solved. However, this is just possible with forces.
At this point I'm not sure how correct this results are and if there is some other way to improve them. I would appreciate the help. The simulation seems to work (visually) the spring is compressed and extends back, however the piston should take longer time to displace during rebound than compression.
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