Discussion Forum

March 12, 2010 7:17am UTC in response to Sabine Kling

Re: parameter problem

Hi

If you define a parameter in the solver window of name "param" it should not have units, I agree.

When you define a force in the BC window such as Fx=MyFx*param you should define MyFx as the amplitude with units in i.e. the constants, and then "param" without units is OK

But you can also write Fx = (1000[N])*param or even Fx=param[N]
(pls check the last one I d not have access to COMSOL just now from here)

But Fx=param would give an unit error if param has no units, but this is normally just a warning, the results should still be OK if your param values are truely expressing the value you want in oyur units

I use "param" mostly from "0 to 1" and have amplitude values defined as constants, as that is the cleanest for later understanding of the model

Hope this helps
Good luck
Ivar

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March 12, 2010 8:43pm UTC in response to Sabine Kling

Re: parameter problem

Hi Sabine

Well for me there is something else wrong, you might have picked a variable already defined in COMSOL ? which then might have "units" associated.

My way to check this, as it happens often, is to define a simple model (square) in the given application mode, run a "get initial value" to populate the matrices and go into the postpro session and plot/evaluate the value of the variable name, if COSMOL recognises it, it will even show you the associated units.

Or you dump the model as a "m" file and you do a txt search for your variable name.

It's true that I seldom use two parameters, but I have never had difficulties with the first one, it's unitless for me ;)
at least when I call it "param or param_1" and that I have not defined it as such anywhere else.

Short note/trick: when i switch between stationary an parameric solving, I often define a Constant as param = 0 or what ever else I need. As the Constants are evaluated once at programme start the, value will be overwritten later if I use it, and take a "default" value handy for me if not used later. This avoids the need to re-write all equations when you switch between the different applications modes.

If I remeber right (my COMSOL licence is fully booked by a colleague, connot try just now ;) the order of the parameters when you use several is 1.1 1.2 2.1 2.2 3.1 3.2 alternatively. Try a simple check by using it as an x & y forced displacement of a simple canteliever, or something else simple enough to rapidly test it out.

Good luck
Ivar

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