Rotating wind

The wind systems on Jupiter and Saturn are strongly westward at the equator, with eastward jets at latitudes above and below the equator. Equatorial wind speeds on Jupiter approach 150 ms in the direction of rotation, and are 3-4 times higher still on Saturn. Measurements by the Galileo probe indicate that the winds persist down to the deepest level, 20 bar, measured by the probe. Uranus shows prograde (in the direction of rotation) winds of 150 m s at midlatitudes, which decline in speed toward the equator. Because of the low contrast of the Uranian clouds at the time of the Voyager flyby, optical tracking... 

While the overall circulation of the mesocyclone extends outward 5-10 km from its axis of rotation, peak rotational wind speeds of 20-25 m sec typically are found at a radius of 2.5-3 km. During a mesocyclone s organizing stage, such rotational wind speeds, or alternatively vertical vorticity (>1 x 10 sec ), are found primarily at middle altitudes. Some mesocyclones do not develop beyond this stage. Those that do reach maturity ... 

A hurricane by definition is a cyclone storm having rotational wind velocities in excess of 70 mph (119 km/h). The dynamic strength of a hurricane builds up over water, but as it comes inland boundary layer drag forces cause a tremendous dissipation of the kinetic energy of the storm and the wind. 

Ship-shaped FPSOs must be designed to weather vane i.e. must have the ability to rotate in the direction of wind or current. This requires complex mooring systems and the connections with the well heads must be able to accommodate the movement. The mooring systems can be via a single buoy or, in newer vessels designed for the harsh environments of the North Sea, via an internal or external turret. Figure 10.33 shows a schematic of the Shell-BP Foinaven FPSO. 

The coin-tap test is a widely used teclinique on thin filament winded beams for detection of disbonded and delaminated areas. However, since the sensitivity of this teclinique depends not only on the operator but also on the thickness of the inspected component, the coin-tap testing technique is most sensitive to defects positioned near the surface of the laminate. Therefore, it was decided to constructed a new scaimer for automated ultrasonic inspection of filament winded beams. A complete test rig illustrated in figure 6 was constructed in order to reduce the scanning time. While the beam rotates the probe is moved from one end to the other of the beam. When the scarming is complete it is saved on diskette and can then be evaluated on a PC. The scanner is controlled by the P-scan system, which enables the results to be presented in three dimensions (Top, Side and End view). 

Gup and Vane Anemometers. A number of flow meter designs use a rotating element kept in motion by the kinetic energy of the flowing stream such that the speed is a measure of fluid velocity. In general, these meters, if used to measure wind velocity, are called anemometers if used for open-channel Hquids, current meters and if used for closed pipes, turbine flow meters. 

Cup anemometers have shaped cups mounted on the spokes of a wheel. The cups, under the action of the fluid forces, spin in a horizontal plane about a vertical shaft mounted in bearings. Vane or propeller types use a multibladed rotor, the axis of which is parallel to the flow direction as the rotating member. Both designs are commonly used for wind speed measurement or similar appHcations such as the velocity in ventilation ducts. Because of inertia, anemometers are most accurate under steady conditions. Velocity fluctuations cause readings that are too high. 

The use of wind as a renewable energy source involves the conversion of power contained in moving air masses to rotating shaft power. These air masses represent the complex circulation of winds near the surface of Earth caused by Earth s rotation and by convective heating from the sun. The actual conversion process utilizes basic aerodynamic forces, ie, lift or drag, to produce a net positive torque on a rotating shaft, resulting in the production of mechanical power, which can then be used directly or converted to electrical power. 

The winding that is static is termed a stator and that which rotates is a rotor. If l is the rotor current and 0 the instantaneous flux, then the force in terms of torque, T, produced by these parameters can be expressed by... 

A constant field rotating at synchronous speed Ns Figure 1.4 Production ol magnetic field in a 3-0 winding... 

The current in the copper ring opposes the main flux in that area of the pole and behaves like an artificial second winding, and develops a rotating field. Although the torque so developed is extremely low, it is enough to rotate such small drives, requiring an extremely low starting torque, of the order of 40-50% of the full load torque. 

Since there is only one winding and the poles are already shaded at one particular end, the direction of the rotating flux is fixed and so is the direction of rotation of the rotor. The direction of rotation cannot be altered as in the earlier cases. Since there is only one winding and no need of a speed-operated centrifugal switch, these motors require almost no operational maintenance. 

The electricity generated depends primarily on the speed of the wind at the site of installation. A conventional formula to determine the wind energy, based on the design of the rotor (rotating blades) and the site conditions is given by... 

Shutdown speed = 20 m/s Rotor diameter including hub = 39.35 m Rotational speed of the rotor at the rated wind speed = 38 r.p.m. 

Cut-in wind speed is the minimum wind speed at which the generator commences the generation of power. At this speed the brakes release and the prime mover (blades) starts rotating. 

Cut-oul wind speed is the maximum w ind speed beyond which the prime mover may overspeed above its permissible limits. As the structure and the blades are designed for a particular maximum speed, a wind speed higher than this may exceed their mechanical endurance and become unsafe. At this speed the brakes apply and the machine is disconnected from the grid. The cut-in and cut-out speeds define the wind speed limits within which the turbine will work safely through the generator. Rated wind speed is the speed at which the prime mover rotates at the rated negative slip and generates the rated power. 

If the motor is switched on, in a single phasing condition, it will not rotate in the absence of a rotating field, similar to a single-phase motor without a start winding. 

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