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Posted 15 oct. 2009, 16:24 UTC−4 7 Replies
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Maybe you can import your data with an interpolation function:
Options=>Functions...
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i never solved time dependent, but you may try this:
-Options=>Functions...
-New...
-put in a function name, e.g. testfunction
-Interpolation, Use data from Table
-Put your values in the table,e.g.
x | f(x)
0 | 15
0.5| 42
1 | 51
... | ....
-instead of your constant parameter use "testfunction(t)",
if t is the time.
(Instead of the table you should also be able to read the data from a file.)
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I have some problems to follow you here, if the body weight applies on the top of the tibia, I would expect to see the reaction force of the weight from below, in addition to the measured force (because the values you give are so small that they do not fit to half of a human body weight) then your measured force is gives the vertical acceleration of the tibia (related to the tibia weight and the body weight).
If your measured force represents the total verticl upward force on the tiba then just ignore my remark above, and correct below.
To set up a mass representing the body, you can either just model a geometrical block with a given density, or add a lumped mass by equations to the top surface of the tibia.
The gravity field in COMSOL is simulated by an external volumic force given typically by Fz=-G0*rho_smsld (assuming gravity along -Z, and application mode "smsld" and G0 defined as a constant
G0 = 1[lbf/lb] )
And to the lower surface you add the surface pressure (F/Area) repesenting your force function + a vertical upwards static force (nominal ground reaction force) to keep the tibia in rest for no surface force, hence to cancel the static weight.
Then you need to restrain the motion to 1D by blocking the x,y motion and allowing only "z" to be free. That should do most I believe.
Try it out with some simple values that you can easily check by hand, and then use the discrete force function as described earlier.
Good luck
Ivar