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August 30, 2010 6:52pm UTC

Defining a probe relative to a moving mesh boundary

I am working with a model which is using the moving mesh interface to oscillate a domain(plate) in my model. I know how to define probes based on static coordinates but I need to define a probe relative to the position of my oscillating plate. For example in the attached model I would like to define a point probe which is always 0.05m away from boundary 5. Since boundary 5 is oscillating I need to be able to define this probes position relative to boundary 5.

Under Model1 - Definitions - Domain Point Probe 1 - Point Selection is it possible do to something like this;

x: 0 y: boundary5 - 0.05?

If I knew the correct reference notation for "boundary5" would this work?

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August 30, 2010 9:41pm UTC in response to Danial Tz

Re: Defining a probe relative to a moving mesh boundary

Ok, that didn't take long :)

- Define an integral probe:
http://cl.ly/b730da4b4d8dfab72a15

- Define a variable
http://cl.ly/f9c5f7ab754e7786feee

- Use a global probe:
http://cl.ly/b69d397f2db2b6ba8707

- You get this:
http://cl.ly/ff4a99042fbbb5c05293

Right? ;)

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August 31, 2010 9:41am UTC in response to Ivar Kjelberg

Re: Defining a probe relative to a moving mesh boundary

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August 31, 2010 6:51pm UTC in response to Danial Tz

Re: Defining a probe relative to a moving mesh boundary

Thanks for the information. I think I am still missing the link between the model coupling and being able to make a probe that plots more than just the "y" position.

For example in the attached model above, I had a domain point probe which was offset 0.05m from the bottom of boundary 5(on my oscillating plate). When the plate starts to oscillate the probe remains exactly in it's original position(x:0 y:-0.05). What I need to do instead is have the probe move with the oscillating plate but always be at a constant offset position. The formula for the oscillating plate is 0.1*sin(2*pi*2*t). So at t=0.125s, the plate has moved postive 0.1m in the y direction therefore I need my probe to be at x:0, y:0.05 at this time.

I added an offset to my posy variable, see posy_offset.png. Now when doing a Global Variable Probe I get a plot of the offset position from the oscillating plate, i.e. a sinusoid from -0.05 to 0.05. This is great but what I really need is to be able to plot the other model parameters like Voltage and Electric field at this offset oscillating position. I then went back to my Domain Point Probe and put in "posy" for my y position, see domain_no_posy.png. However as can be seen in the screenshot I get a unknown model parameter error when entering it. COMSOL seems to ignore this change and use the previously defined static postion. Do you have any tips?

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September 7, 2010 6:12pm UTC in response to Ivar Kjelberg

Re: Defining a probe relative to a moving mesh boundary

Thank you for your reply. I'm not clear on how splitting my object could help though. Could you provide some more information regarding that?

One issue I can't seem to work around is the fact that a Domain Point Probe seems to require a number entered into it's coordinates. I can not enter an expression or a variable. Therefore it doesn't seem like I can create a Domain Point Probe which moves with time.

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September 8, 2010 7:48pm UTC in response to Brian Gow

Re: Defining a probe relative to a moving mesh boundary

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September 9, 2010 8:42pm UTC in response to Danial Tz

Re: Defining a probe relative to a moving mesh boundary

Thank you again for thinking about this issue. I'm still not sure exactly how to get to the Voltage or Electric Field. Creating the posy variable as outlined allows one to track the oscillation of the moving mesh(or an offset from it) with time. I now need to figure out how to determine the Voltage or Electric Field at the positions given by posy Vs time. For Example I'd like to know the following;

posy - is given by intop1(y)-0.05 based on the above method. using intop1(y-Y) returned the same result. see the attachment for a plot of posy Vs time. This represents the point(in spatial y domain) that is offset -0.05 from the bottom of the moving mesh(point 3), controlled by 0.1*sin(2*pi*2*t).

t, posy, es.Ey(posy), V(posy)
0, -0.05, ?, ?
0.125, 0.05, ?,?
0.375, -0.15, ?, ?

where es.Ey(posy) means the Electric Field in the Y direction at location x = 0, y = posy. Similarly for V(posy). I don't see how I can use a Global Variable Probe to get the Electric Field or Voltage though. Is this possible? When I try to use a Domain Point Probe with coordinates x = 0, y = posy, I get the uknown model parameter error mentioned about. I am somewhat new to COMSOL so if there is a way to get the Electric Field and Voltage at this varying(w/r/t time) y position let me know. I will probably contact support tomorrow regarding this. Thanks again!

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