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This is a treatment of a number of aspects of the theory of hydrody
namic propulsion. It has been written with in mind technical
propulsion systems generally based on lift producing profiles. We
assume the fluid, which is admitted in conventional hydrody namics,
to be incompressible. Further we assume the occurring Reynolds
numbers to be sufficiently high such that the inertia forces
dominate by far the viscous forces, therefore we take the fluid to
be inviscid. Of course it must be realized that viscosity plays an
important part in a number of phenomena displayed in real flows,
such as flow separation at the nose of a profile and the
entrainment of fluid by a ship's hull. Another ap proximation which
will be used in general is that the problems are linearized. In
other words it is assumed that the induced disturbance velocities
are sufficiently small, such that their squares can be neglected
with respect to these velocities themselves. Hence it is necessary
to evaluate the domain of validity of the results with respect to
these two a priori assumptions. Anyhow it seems advisable to have
first a good understanding of the linearized non-viscous theory
before embarking on complicated theories which describe more or
less realistic situations. For elaborations of the theory to
realistic situations we will refer to current literature. In low
Reynolds number flow, singular external forces and moments are very
useful.
HYDRODYNAMIC PROPULSION AND ITS OPTIMIZATION ANALYTIC THEORY
Hydrodynamic propulsion has been of major interest ever since craft
took to the water. In the course of time, many attempts have been
made to invent, develop, or to improve hydrodynamic propulsion
devices. Remarkable achievements in this field were made
essentially by experienced individuals, who were in need of
reliable propulsion units such as paddle wheels, sculling devices,
screw propellers, and of course, sails. The problem of minimizing
the amount of input energy for a prescribed effective output was
first investigated seriously at the beginning of this century. In
1919, BETZ presented a paper on air-screw propellers with minimum
consumption of energy which could be applied to ship-screw
propellers also. Next, attempts were made to optimize hydrodynamic
propulsion units. Ensuing investigations concerned the optimization
of the hydrodynamic system: ship-propeller. The first simple theory
of ship propulsion which was presented considered more or less only
thrust augmentation, wake processing and modification of propeller
characteristics when operating behind the ships hull. This theory
has been little improved meanwhile and is still useful,
particularly with regard to practical ship design and for
evaluating results of ship model tests. However, this theory is not
adequate for optimization procedures necessary for high-technology
propulsion, particularly for ship propellers utilizing propulsion
improving devices such as tip end plates or tip fins at the
propeller blades, spoilers in front of the propeller, asymmetrical
stern etc.
HYDRODYNAMIC PROPULSION AND ITS OPTIMIZATION ANALYTIC THEORY
Hydrodynamic propulsion has been of major interest ever since craft
took to the water. In the course of time, many attempts have been
made to invent, develop, or to improve hydrodynamic propulsion
devices. Remarkable achievements in this field were made
essentially by experienced individuals, who were in need of
reliable propulsion units such as paddle wheels, sculling devices,
screw propellers, and of course, sails. The problem of minimizing
the amount of input energy for a prescribed effective output was
first investigated seriously at the beginning of this century. In
1919, BETZ presented a paper on air-screw propellers with minimum
consumption of energy which could be applied to ship-screw
propellers also. Next, attempts were made to optimize hydrodynamic
propulsion units. Ensuing investigations concerned the optimization
of the hydrodynamic system: ship-propeller. The first simple theory
of ship propulsion which was presented considered more or less only
thrust augmentation, wake processing and modification of propeller
characteristics when operating behind the ships hull. This theory
has been little improved meanwhile and is still useful,
particularly with regard to practical ship design and for
evaluating results of ship model tests. However, this theory is not
adequate for optimization procedures necessary for high-technology
propulsion, particularly for ship propellers utilizing propulsion
improving devices such as tip end plates or tip fins at the
propeller blades, spoilers in front of the propeller, asymmetrical
stern etc.
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