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Assing a sinusoidal body force F(x,y,z,t) in comsol 4.3
Posted 18 ott 2012, 10:31 GMT-4 Geometry, Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.2, Version 4.2a, Version 4.3, Version 4.3a 3 Replies
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I am trying to simulate shear wave propagation in tissue using a PDE wave equation (I manually defined the equations).
In my geometry, I have a 3D box (imaging it is tissue) and in the center of the box (point(0,0,0)) there should be a sinusoidal force of the form:
F(x,y,z,t) = force(x,y,z)cos(2pi*df*time)
which means that at every point (xi,yi,zi) in the neighborhood of point(0,0,0) a force is applied that depends on time.
My question is how to define that in Comsol ?
what I did so far, was to define an Interpolation function force(x,y,z), where I load the values of the force at time t=0 from a txt file.
I also define a pfunction = pforce(t) = cos(2pi*df*t)
and then in the physics, I select point (0,0,0) and I assign it a Point Source, where I give it the value:
pforce(t)*force(x,y,z).
I am thinking that by this way, in every point around the center, I will be having a sinusoidal force excitation.
Does this seem correct? or if not, can you suggest another way of doing so?
Many thanks
Alexia
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you are right, I understand that's wrong to define a point source like this.
Would a correct way be to define as the "source" of the PDE equations (for the domain that corresponds to the 3D box) the same function, pforce(t)*force(x,y,z)? If I did that, I assume it would mean that all points xi,yi,zi within the extents of the force distribution would act as a source?
another way that I thought, was to leave the "source" term for this domain = 0, and then go to PDE -> right click -> add Source and there to define the equation above?
which way do you think is correct? or are they both equivalent?
finally, another question, is there any way that I can define that this force has a direction along the z-axis? how can I do that by using PDE general form?
thanks in advance for your help
Alexia
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try to avoid applying loads or constraints on anything lower than "Boundaries" (<1 dimension below your "Domain" entity check the doc or see
www.comsol.eu/products/multiphysics/glossary/
for the definitions)
This would avoid "singularities". Then when you do transient analysis do not forget to first set our initial conditions correctly (i.e. solve a stationary case first) and then apply temporal BC loads such that you know how many "modes" you excit:e use smooth step functions with corresponding "fine" time stepping
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Good luck
Ivar