- #1
J_R
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Homework Statement
In my homework I have to determine how do the speed (constant speed) (V) of damped mass and geometric characterictis of ground (b, h) influence on oscillation values of a model represented on a picture below. Model represents a vehicle driving on a sine wave ground. I should determine values of accelerations, velocities and displacements and explain why the results are as they are at different speeds and at different geometric characteristics.
k ... spring constant
d ... damping coefficient
h ... amplitude of a sine function (ground)
2*b ... period of a sine function (ground)
m ... mass ( of a vehicle)
y ... absolute displacement of a mass
z ... relative displacement of a mass
Homework Equations
[tex]y_0(x)=h*sin(\frac{pi*x}{b})[/tex]
[tex]y_0(t)=h*sin(\frac{pi*V}{b}*t)[/tex]
[tex]z(t)=y(t)-y_0(t)[/tex]
[tex]m*\frac{d^2y}{dt^2}=-d*(\frac{dy}{dt}-\frac{dy_0}{dt})-k*(y-y_0)[/tex]
[tex]m*\frac{d^2z}{dt^2}+d*\frac{dz}{dt}+k*z=-m*\frac{d^2y_0}{dt^2}[/tex]
+ other equations that i don't think are relevant for what i am about to ask
The Attempt at a Solution
So, I have solved differential equations and got relative displacements, velocities and displacements of a mass. But for high speeds V and short periods of sine function of the ground b, i got enormous values for accelerations, and displacements equal the amlpitudes of sine function of the ground.
My guess is this happens because the mass cannot follow the ground at such high speeds and therefore lifts-off of the ground.
My questions are:
Is my thinking correct?
How can i determine the contact force, so that i would see when its value changes from + to - ; that is why the mass lifts-off, right?
Thank you for your help.