Game Development Reference
In-Depth Information
Figure 16-5. Planing craft resistance versus speed
Notice the hump region. This is where the vessel trims aft in the transition mode and
there is a rise in the resistance. There have been embarrassing cases where a vessel,
although having enough power to make the design speed once over the humps, lacked
the power to make the transition.
Virtual mass
The concept of virtual mass is important for calculating the acceleration of a ship in a
real-time simulator. Virtual mass is equal to the mass of the ship plus the mass of the
water that is accelerated with the ship.
Back in Chapter 3 we told you about the viscous boundary layer, and we said that the
relative velocity (relative to the moving body) of the fluid particles near the moving
body's surface is 0 at the body surface and increases to the free stream velocity as distance
from the body surface increases. Essentially, some of the fluid sticks to the body as it
moves and is accelerated with the body. Since the velocity of the fluid varies within the
boundary layer, so does the acceleration. The added mass , the mass of water that gets
accelerated, is a weighted integration of the entire mass of fluid that is affected by the
body's acceleration.