WO2000078606A1

WO2000078606A1 - Oscillatory motion propulsion system

Info

Publication number: WO2000078606A1
Application number: PCT/IT1999/000179
Authority: WO
Inventors: Giuseppe Pollastri
Original assignee: Giuseppe Pollastri
Priority date: 1999-06-21
Filing date: 1999-06-21
Publication date: 2000-12-28

Abstract

An oscillatory motion propulsion system is made up by two elements oscillating in phase opposition, whereof the first element is a solid body (A) while the second element is a laminar structure (B).

Description

OSCILLATORY MOTION PROPULSION SYSTEM

This invention relates to a marine oscillatory motion propulsion system wherein the propulsive action is generated by cavitational forces.

As known, on the surface of a body moving in a fluid take place both compression and cavitation phenomena, originating in turn forces which oppose motion and tend to restore the surrounding medium's balance in the shortest possible time.

The differentiated action developing on the opposed faces of a laminar structure (wing) is well known and widely exploited in aircraft flight, but heretofore little was known about the differentiated action developed in oscillatory motion.

With reference to Fig. 1 herewith attached, on the surface of an elongated solid body A oscillating around a vertical axis O at one of its ends, the action of the cavitational forces increases with the distance from the axis of oscillation and the body is imparted a centrifugal thrust. This thrust also develops in orbital oscillations, as in the case of a rotating eccentric mass housed in an elongated container at one of its ends.

On the opposed faces of a plano-convex laminar structure B attached to the end of an oscillating arm /^*, as shown in Fig.2, a difference in pressure is generated, which impels the foil to move radially towards the center of oscillation (centripetal force).

It should be stressed that the lower pressure is found on the plane face, rather than on the convex one as in a wing. The contradiction is but apparent, since in both cases the fluid impinging on the convex face of the wing section and on the plane face of the foil is subject to identical stresses, as indicated in Fig.2. In fact, if the rectilinear section MN is rotated around O by an angle a, so as to bring N in M, a particle of the fluid lying in M will be compelled to move as if the dotted convex section shown in the figure - a virtual or hydrodynamic section - were sliding under it.

The value of thrust depends on the average weight of water displaced by the oscillating body in the unit of time; this weight represents the potential capacity of an oscillating body and is expressed by the following formula:

Pc = c (S r a j) where:

Pc = potential capacity

2πδ c = conversion factor =

360 S = active surface (area of the figure projected by the oscillating body on the oscillation median plane) r = distance from the active surface figure-center from the axis of oscillation a = oscillation amplitude = oscillation frequency δ = density of the fluid.

As indicated, the formula parameters include the oscillating body's active surface, which can be easily increased for solid bodies A, but not for laminar structures B, where, being the projection of a foil on a plane perpendicular to itself, it is always of a rather negligible extent. This makes it necessary to act on the position of the foil with respect to the translation plane; when the foil's angle of attack remains unchanged tliroughout the oscillation, the thrust is linked to its value and therefore to the craft's advancement speed, just as the angle of pull-up is linked to an aircraft's rate of climb.

To keep the angle of attack unaltered throughout an oscillation, the foil, as shown in Fig.3, is hinged at a point P on an arm r, with freedom to move within a sector of predetermined width (twice the required angle of attack).

In this arrangement, the foil's opposed faces alternatively exchange functions. But, as previously indicated, this does not alter the thrust's direction, since the resulting effect is due to a hydrodynamic - not a geometric - profile, and therefore the foil can operate properly and effectively even with symmetrical opposed faces. An oscillatory motion propulsion system and a jet of the type currently used in aircraft basically perform the same operations - compression and expansion.

In either case, thrust is originated in the expansion stage, but there is a paramount difference: a jet operates in a closed space, i.e. in a highly pressurized container, while an oscillatory motion propulsion system operates in the open and at lower pressures than the environment's. In both cases, maximum efficiency is attained when the surrounding medium is by no means perturbed: in the former instance, when the fluid is discharged in a state of rest, in the latter, when the fluid thread of the surrounding medium consistently follows the hydrodynamic profile of the oscillating body, without ever deflecting off it. The problem of keeping a fluid thread adherent to a body's surface is widely discussed with reference to wing lift. A wing is linearly translated in space on a plane which keeps parallel to itself, while an oscillating laminar structure is translated in space on a plane which keeps tangent to a circumference whose radius equals the distance of the foil from its oscillation axis.

It is clear that, in order to avoid any perturbation to the surrounding medium, a structure's section must have the same course as motion: rectilinear, in the case of a wing, and circular in the case of an oscillating foil (see dotted line in Fig.3).

But since the opposed faces of a foil hinged at one end of an aπn alternatively perform the same function, they must have an identical section. This condition does not alter the thrust's value, as it results from a virtual profile depending on the characteristics of motion.

Motion is characterized by several elements, including path, speed, and also, if present, acceleration or deceleration.

Fig.2 shows how it is possible to obtain the effect of a geometrically convex section with a rectilinear section through rotary motion.

Obviously, an increase in speed enhances this effect on the surrounding fluid and, accordingly, the hydrodynamic camber, while a decrease in speed reduces it.

With an oscillating body, speed has a sinusoidal course; as a result, the hydrodynamic camber is enhanced by the body's acceleration, and flattened by its deceleration.

Thus, a body with identical leading and trailing edges of the type shown in Fig. l generates, when oscillating, a hydrodynamic profile with the same characteristics and the same effects as a wing profile linearly translated in space at a constant speed.

The foil shape giving the best perfonnance is the triangle, since, like in a modem aircraft wing, the absence of connecting elements between leading and trailing edge eliminates any environmental perturbation.

For the laminar structure propulsion system, it was deemed advisable to select a V-shape very similar to the tailfin of a shark.

On the trailing edge, however well-designed, there are always efficiency losses due to stall, whose effects can be reduced by a flexible appendix, i.e. a tail for an elongated body, a thin membrane for a laminar structure.

The above mentioned energy losses relate to the fluid surrounding a body. But an oscillating body, due also to the inherent characteristics of motion, brings about energy losses on its own support, when it is not counterbalanced by a body of the same potential capacity oscillating around the same axis, or around an axis parallel and in phase opposition to it.

In nature, a fish progressing in water through oscillatory motion could not attain maximum efficiency if its motive mechanism were not foπned by one or more pairs of segments which oscillate in series and in phase opposition, with each segment generating its own thrust and all thrusts having the same direction and sense.

This invention purports to provide an oscillatory motion pulsehydrojet system based on cavitation phenomena, which is made up by two parts

(pair of elements) of the same potential capacity, oscillating in series on opposed fronts and in phase opposition. In accordance with this invention, the first part is a solid body A, and the second is a laminar structure B, as shown in Fig. 4.

The couplings in parallel of the first two elements or the second two elements, and the coupling in series of a first with a second element, make it possible to obtain three propulsion systems of different types, all based on cavitational phenomena, which in model tests gave excellent results in every respect.

This invention is described in more detail hereafter, with the accompanying drawings illustrating some of its practical implementations.

Figs. 4-5 are a side view and a cross section of a pulsehydrojet made up by two parts (pair of elements) A and B, of the same potential capacity, oscillating in series on opposed fronts and in phase opposition.

Fig. 6 shows a pulsehydrojet made up by two parts (pair of elements)

A, oscillating in parallel and in phase opposition.

Fig. 7 shows a pulsehydrojet made up by two parts B, oscillating in parallel and in phase opposition.

Fig. 8 shows a system of gears C, designed to impart an oscillatory motion to the bodies A-B, starting from the rotary motion generated by a power source.

The figures illustrate a marine oscillatory motion propulsion system, wherein the propulsive action is generated by cavitational phenomena.

The system concept envisages two parts.

Part A is an elongated solid structure, whose design is based on tests performed with type-/, bodies. Part B, whose design results from performed with -5-type bodies, is a V-shaped symmetrical structure, hinged in P on an oscillating aπn r and free to move within a sector of predeteπnined width. In the cross section at Fig. 5, / designates the angle of attack of the laminar structure on the translation plane Z, and a designates the span of the sector of predeteπnined width.

Fig. 5 clearly illustrates the system's operation: when point P on aπn r is oscillated from Pi to P2. the laminar structure hinged in P, under the forces acting on it, freely moves within the sector of predeteπnined width, as indicated in the figure at 1 , and when point P on aπn r goes from P2 to Pi, it moves as indicated in same figure at 2. The asymmetry of the dotted drawings of the laminar structure in 1 and 2 is due to the fact that they reproduce its hydrodynamic, and not its geometric, profile.

This propulsion system, like a jet in an aircraft, may embody in structure A a power source, and, in an outboard type configuration, provide a thrust in every direction.

It is therefore the ideal propulsion system, being the most self- contained, the most widely applicable, and altogether the simplest of all.

Claims

1 ) System for marine oscillatory motion propulsion, wherein the propulsive action is generated by cavitational phenomena, characterized by two parts, or pairs of elements, of the same potential capacity, oscillating in series on opposed fronts and in phase opposition, whereof the first part is a solid body (A), while the second part is a laminar structure (B), by couplings in parallel of the said first two elements or of the second two elements, and by couplings in series of a first with a second element.

2) System for marine propulsion according to claim 1 , characterized in an elongated body oscillating around an axis situated at one of its ends in order to provide a centrifugal thrust.

3) System for marine propulsion according to claim 1 , characterized in a foil transversally attached to the end of an oscillating aπn in order to provide a centripetal thrust.

4) System for marine propulsion according to claims 1 and 3, characterized in a foil hinged at the end of an oscillating aπn and free to move, under the forces acting on it, within a sector of predeteπnined width.

5) System for marine propulsion according to claim 1 , characterized in an element consisting in a symmetrical V-shaped laminar structure (B) hinged in a point (P) on an oscillating arm (r) with freedom of movement within a sector of predetermined width.

6) System for marine propulsion according to claim 1 , characterized in a pulsehydrojet foπned by two solid bodies (A), oscillating in parallel and in phase opposition. 7) System for marine propulsion according to claim 1 , characterized in a pulsehydrojet formed by two laminar structures (B), oscillating in parallel and in phase opposition.

8) System for marine propulsion according to claim 1 , characterized in gears (G) which impart an oscillatory motion to the bodies (solid body-laminar structure) (A-B), starting from the rotary motion generated by a power source.