09-04-2012, 02:30 PM
WATER JET PROPULSION DETERMINATION OF PRIMARY DESIGN CHARACTERISTICS
WATER JET PROPULSION DETERMINATION OF PRIMARY DESIGN CHARACTERISTICS.docx (Size: 97.57 KB / Downloads: 128)
INTRODUCTION
The desire to travel faster and further is probably as old as mankind itself. Over the passage of time, there has been a quantum of improvement in the mode of transport being used by mankind. The development of transportation over air, land and sea is perhaps rivaled only by the development of automation, controls and computers. At first, it was only over land, and later also over sea. And since about a century, it has been possible to ravel through air as well. Achievements in automotive and aerospace technology are widely and publicly recognized, but the public in general does not realize and recognize the substantial development which has taken place in high speed marine transportation.
Analysis of various propulsion systems
The table has been drawn up based upon various characteristics of common propulsion systems in vogue today. Attributes have been given to the various qualities/characteristics of the propulsion systems in order to objectively analyse them to arrive at an optimal propulsion solution. Table 1 shows the comparison of the operational characteristics of various propulsion systems.
Description of Concepts
A stern-mounted waterjet installation as used in commercial applications, can be divided into four components, namely, the inlet, the pump, the nozzle and the steering device. Figure 1 shows a drawing of a typical waterjet installation. A propeller is an external machine, whereas the waterjet installation is mainly an internal flow system. The thrust of a propeller is passed onto the ship’s structure only via the thrust block. In a waterjet installation, the forces can be transferred to the vessel via the shaft and of ship structure. In fact, it is possible to have higher thrust acting on the shaft than the net thrust of the installation. In that case, a negative force will act on the transom stern and the inlet ducting.
Wake Fraction
The water that is ingested into the waterjet inlet channel partly originates from the hull’s boundary layer. The mass averaged velocity of the ingested water (Vin) is lower than the ship speed due to this boundary layer. The velocity, In deficit is expressed as the momentum wake fraction (w), which is defined as
Conclusion
All the three rations have been defined in this paper in brief and all the ship and pump velocities revolves around these velocities.
Principle parameters of the water jet propulsion system are as follows.