Implementation of a vibrating system

[Alessio]

Hello everyone, 

I'm trying to simulate the behaviour of different non-spherical particles under varying gravity and some physical parameters like friction and restitution coefficients. I've modelled an open cubic container for the particles which rests on a reference floor which is fixed. I should now implement horizontal oscillations, in particular I was thinking about sinusoidal inputs. What could be the best way to do it? I was thinking of implementing an engine or a prismatic link to which the sinusoidal forcing is added, but I'm not sure if these are the best choices, as I am new to using Chrono. Also, I am undecided whether to make the reference floor move and then vibrate the box or to implement it directly on it, depending on which is the easiest way.

Thanks to anyone who can give me some advice.

[Radu Serban]

You can use a linear motor with whatever activation function you want (at position, velocity, or force level).  See demo_MBS_motors for examples.  Alternatively, you can use a weld joint (ChLinkLockLock) which allows specifying a motion function along one of the constrained DOFs.  See demo_MBS_earthquake.

In either case, you would connect one of the “links” above between the box and the fixed ground body.

 

--Radu

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[Alessio]

Hello,

thank you so much for the help, in the end I opted for the implementation via the earthquake demo and it seems to work. 

I have a few more questions:

• I need to not start the sinusoidal pulse immediately at the beginning of the simulation but instead I would like the particles to have a certain settling time before they start oscillating, how could I do this? I've found something about ChFunction commands but I'm not sure how to go about it.
• Then I'd like to analyze the ascent of a specific particle that I define as an intruder, I'd need an array of data about its height relative to the reference plane over time so that I can then plot it as various physical parameters change. For this purpose I thought of defining a .csv file to collect the data but I am not sure how to include it in the simulation loop. Is there a better method for doing this? Is there a need for the postprocessing module?

I enclose a copy of my script if it can be useful.

Thank you in advance.

~Alessio 

[Radu Serban]

You can address both issues with ChFunction objects.

• For your first question, use a ChFunctionSequence which allows you to stitch together several functions.  You can start with a constant zero function and then the sinusoidal. Alternatively, simply implement a custom function (by deriving from ChFunction and implementing the GetVal() method).  You can see examples of both in demo_CH_functions.
• The second one is not really a Chrono question.  You collect and manage simulation data however you want. You can use a CSV file (there’s simple support in Chrono for that through the utils::ChWriterCSV class). Or else you can use a ChFunctionInterp to collect data points during the simulation loop. Search through Chrono demos for uses of either of these. Or anything else you want – you have full control to extract whatever data you want during the simulation loop and log it however you want.  You do not need the Chrono::Postprocess module for any of this.

To view this discussion on the web visit https://groups.google.com/d/msgid/projectchrono/a6733f1f-645c-4047-8d2c-0a09e46db5c0n%40googlegroups.com.