Apparent wind that measures wind speed in knots and wind direction in degrees relative to the heading of the boat. Modern instrumentation can calculate the true wind velocity when the apparent wind and boat speed and direction are input. In sailboat racing, and especially in speed sailing, apparent wind is a vital factor, when determining the points of sail a sailboat can effectively travel in. A vessel traveling at increasing speed relative to the "prevailing wind" will encounter the wind driving the sail at a decreasing angle and increasing velocity. Eventually, the increased drag and diminished degree of efficiency of a sail
Rotational sampling in wind turbines tower. In fluid dynamics, there exists the no slip boundary condition. This states that the velocity of a fluid at the surface of a solid body, such as the Earth, is zero. A consequence of that is that the wind speed varies with height above ground. This effect is known as wind shear. As a result, a blade at the highest part of its cycle will experience a greater wind speed than that of one at the lowest part of its cycle. The drive train of a wind turbine comprises the hub, the low speed shaft, the gearbox, the high