Multibody dynamics: reverse bungee

[sneakster]

1. I need to simulate a reverse bungee ejection seat (carnaval ride). This is a vehicle attached to two masts with bungee cords. I know the mass, air drag and acceleration (4.8 g). The first step is to calcutate the spring constants of the bungee cords and the damping constant (relative damping of 10%)



2. In order to calculate the spring and damping constants I have used: F=m*a. Thus F=400*4.8*9.81. I have used the original length of the ropes to calculate k and used the critical damping (critical damping=2*sqrt(k*m)) to determine c. (c=0.1* critical damping)




3.The trouble I am encountering is with the movement of the vehicle. The displacement depends on the accelerations, but the acceleration changes over time. For the movement in upward direction I have used the following: F=m*a+Fs+Fd-m*g-D. But there are also rotational forces, becuase the vehicle spins around its y-axis, which causes forces in the z and x-direction.

Can anyone help me with determining the proper forces?

 

[NateD]

4. The rotational forces can be determined by considering the angular momentum. The angular momentum is defined as L=I*ω, where I is the moment of inertia and ω is the angular velocity. So, the force in the z-direction is Fz=I*α, where α is the angular acceleration. The force in the x-direction is Fx=-L*ω. You can use these equations to determine the forces acting on the vehicle in the different directions.