model foot as mass-spring-damper system

[Dawn6]

I am trying to model a foot as a mass-spring-damper system in free vibration. I have done impact tests and am trying to get the model to match the experimental data. I have tested the foot using several different deflection rates quasi-statically to get an equivalent spring constant function. From this spring function, I can use the normal underdamped equation for x(t) and then calculate the velocity and acceleration to get the Force. I am having trouble getting my results to compare to the impact tests (data includes force-time). Does anyone have any ideas on what variables I can change besides the quasi-static test rate or time step (found that didn't work)?

 

[zekeman]

You mean a human foot?
I would hardly think that a foot could be accurately modeled as a one degree of freedom system, when in fact it is a nonlinear distributed system.
Try making it a linear 2 or 3 degree of freedom and see if you can get a better correlation with your data.
And why use impact data for this. I would think a sinusoidal data sweep would be easier to implement, but maybe yours is just as good.

 

[Dawn6]

I am trying to model a prosthetic foot. Sorry for not clarifying better. I am only using a 1 dof system because I cannot take apart the foot to measure the k and m of each part separately. I am trying to test it and model it as "equivalent" springs and masses meshed together.