- #1

jeeloong

- 12

- 0

I really need help with the calculation of virtual mass and drag of an object.

Firstly, I am doing final year project called Drag reduction in swim cap. Before I go into using swim cap. I am try to measure the drag using accelerometer that inside a bottle but I am damn confuse... the requirement is just equations of motion according to my supervisor.

F_Buoyancy = buoyancy force = density, displaced volume x gravity

F_Drag = Drag force = Cd. 1/2 x density . Velocity^2 . Area

F_w = weight = mass x gravity

ok when an object rises F_B > F_W which means the object accelerate up. If we include drag after some point terminal velocity will reach and the object no longer accelerate.

when F_B < F_W the object sinks

I was told to calculate virtual mass which is the mass added when the object pushes a finite amount of water away when it accelerates

The equation of motion can be given as

F_B - F_W - F_D = (m + mh)a

Where mh is added mass.

I really wondering how do I measured the drag by using accerelometer?

I already launch the object from water and the accelerometer show the g-force either increasing or decrease depends on how I point it.

I am very grateful if some dynamic people could point it out.

Regards,

JL