US3425384A

US3425384A - Stabilizing arrangements for floating bodies

Info

Publication number: US3425384A
Application number: US666866A
Authority: US
Inventors: John Bell
Original assignee: Muirhead and Co Ltd
Current assignee: Muirhead and Co Ltd
Priority date: 1966-10-20
Filing date: 1967-09-11
Publication date: 1969-02-04
Anticipated expiration: 1986-02-04
Also published as: GB1167547A

Description

Feb. 4, 1969 J. BELL 3,

STABILIZING ARRANGEMENTS FOR FLOATING BODIES Filed Sept. 11,. 1967 Sheet 1 of 2 Feb. 4, 1969 J. BELL 3,425,384

STABILIZING ARRANGEMENTS FOR FLOATING BODIES Filed Sept. 11, 1967 She et 2 of 2 United States Patent 46,950/ 66 US. Cl. 114-125 Int. Cl. B63b 43/06 Claims ABSTRACT OF THE DISCLOSURE A floating member in the liquid in a tank moves from side to side of the tank with the ships roll and by displacing the liquid in the tank stabilizes the ship. The floating member is free to move from side to side and moves in a path of pronounced curvature.

This invention relates to stabilizing arrangements for bodies floating in liquids e.g. ships floating in Water, by which the body is stabilized against periodic rolling action.

It is known to do this by incorporating tanks in the body so that liquid flows from one side to the other under the periodic rolling motion of the body but out of phase therewith so as to dampen the rolling motion.

Tan-k systems are normally constituted of two tanks approximately the same size, on either side of the vessel, connected by a channel and partly filled with liquid so that the stabilizing liquid will flow from one tank to the other under the influence of the movement of the ship.

Various designs of tanks are known and the shape of the tank may be varied, as also the connecting channel between; for example, some channels have restrictive features causing resistance to the flow of the liquid, and others may have valves which control according to a sensing device the flow of the liquid. But in all the hitherto known designs the configuration of the tank and its connecting channel are fixed, or semi-permanent; in other words, the size of the tanks and channel does not change with the rolling motion of the vessel.

In one aspect the present invention consists in a tank system for stabilizing a floating body against periodic rolling motion, comprising a tank containing liquid, and a member floating therein and free to move over a range within the tank to vary the distribution of the liquid along the tank, i.e. athwartships in the vessel to be stabilized.

For an efficient system of this type the floating member would ideally have no mass, but the efliciency of the system is such that a mass of up to say 30% or thereabouts of the equivalent volume of the liquid in the tank can be accepted.

The floating member may be constrained to move in accordance with the designed features of the tank or otherwise and in accordance with any desired law, and the shape of the floating member may be designed either for simplicity or high efiiciency; for example, the simplest form of floating member would be a sphere or cylinder.

Preferably the tank system is contained in a compartment or portion of the vessel which is roughly rectangular in shape, although variations from this shape can readily be accommodated without affecting the operation of the system.

In the event the tank system is a closed one, an air or gas-filled space is generally provided above the liquid surface. The air or gas pressure may be near, or above or below atmospheric pressure.

The level of liquid surface in the tank system may be varied or alternatively the tank system may be completely filled and if desired may be arranged to be open, or openable to the liquid surrounding the body to be stabilized, e.g. the sea.

The variation in level may be used to regulate the oscillation period.

Also, the period and power may be regulated by filling the float partially with liquid, e.g. by means of flexible pipes attached thereto.

The invention will be further described with reference to the accompanying drawings, in which:

FIGURE la is a cross-section of a tank system according to the invention when the floating body containing it is in a neutral position;

FIGURE lb is a similar view with tilted to one side.

FIGURE 2a is a view similar to FIGURE 1a 'with an alternative form of floating or buoyancy member;

FIGURE 2b shows the tank system of FIGURE 2a in the position in which the associated floating body is tilted to one side.

FIGURE 3a is a view showing a variation of the tank arrangement of FIGURE 2a; and

FIGURE 3b shows the same arrangement in the tilted position of the floating body;

FIGURE 4a is a similar view to FIGURE la showing another form of floating member, and

FIGURE 4b is another view of the same corresponding to the tilted position of the associated floating body.

FIGURE 5a shows a variation of the FIGURE 4a system, and

FIGURE 5 b is the same in the tilted position.

FIGURE 6 is a cross-section of a tank stabilizing system according to the invention;

FIGURE 7 is a similar view of a modified system;

FIGURE 8 is a similar view of an alternative system;

FIGURE 9 is a similar view of a still further system.

Referring to FIGURES la and 1b, a tank 1 of rectangular shape substantially full of water having a free surface and containing a sphere 2, which is buoyant and presses up against the top of the tank due to the buoyancy of the liquid, the roof or top 1a of the tank is of barrel vault shape. With the vessel in which the tank is mounted on an even keel the sphere will be in the centre. With a heel or movement of the vessel the sphere 2 will move to one side or the other as shown in FIGURE lb, and in doing so will displace the stabilizing liquid in the opposite direction. This movement of the liquid in a known tuned periodic manner 'will therefore cause a stabilizing moment to be exerted on the vessel.

In the arrangement shown in FIGURES 2a and 2b, the sphere 2 has been replaced by a rectangular body 3, supported by a system of wheels or rollers 4 within or attached to the rectangular body, the said wheels or rollers 4 being pressed against the curved roof of the tank.

As shown in FIGURES 3a and 3b, the roof of the tank or part thereof is made in an alternative form consisting of two cam or curved surfaces against which the wheels or rollers 4 bear, the position of the rectangular body being controlled by the tilt of the vessel and the contour of the cam surfaces.

FIGURES 4a and 4b show a similar rectangular member 3 which in this case is secured to the bottom of tank 1 by two sets of parallel spaced links 5.

the floating body As shown in FIGURES a and 5b the links 5 instead of being parallel would be inclined towards each other from top to bottom.

The cross section of the tank system only is shown in the drawings; the length in the fore and aft direction will depend on the value of the stabilizing moment required in any given application.

This novel tank system has been called a Buoyant Passive Tank because of the movable floating or buoyant member.

In common with previously known tanks, the Buoyant Passive Tank is tunable and will resonate at a given periodic time depending on a number of design features. For example, in FIGURES 1a and 1b the tuning will depend on the density of the fluid, the density of the sphere, the dimensions of the tank and sphere and the radius of curvature of the upper part of the tank. A much wider scope for tuning is thus provided than in previously known passive tank system.

Referring to FIGURE 6, there is a tank system 1 containing a float 3 having wheels 4 and oscillating from side to side on a suitably shaped cam system 6 the height of which may be adjusted from a motor 7 operating over gears 8 and threaded members 9 passing through the top of the tank 1 to engage the cam system 6.

A stop pin 10 is provided to engage in a recess in the upper surface of the float for the purpose of locking the float centrally (or in any other predetermined position).

In FIGURE 7 there is shown a similar arrangement but with a single threaded member control centrally located instead of the two spaced threaded members of FIGURE 6. Also the cam system 6 is formed of two members hinged together, the threaded member 9 operating on the hinge pin 6a.

In FIGURE 8 is shown a system similar to that of FIGURES 2a and 2b but in this case with the tank system shown completely filled and provided with slide doors or valves 11 at the side for passage of liquid from surrounding sea.

The floating member may be arranged (although not shown on diagram) to be held closely to the tank bottom, so that the amount of water not contributing to stabilization is reduced to a minimum and water flows in and out through the open slide doors 11.

According to the use of various cams or linkages, the floating member may be moved in any way desired, ie. it can be moved parallel to tank bottom or tilted with respect to it.

The sea openings may be positioned as desired and the openings fitted with slide doors or valves. The slide doors or valves may be adjustable to regulate the flow of water in any desired manner.

The tank will thus be tunable by adjustment of the controls or cam shape or by adjustment of the sea opening. A combination of two or more of these methods may be used if so desired.

The loss of metacentric height due to the free surface eflect compounded in this system with the movement of the buoyant member is controlled by the design of cam as is also the sensitivity of the stabilizer. In this respect, sensitivity is defined as the moment generated for a given heel of the vessel.

Provision may also be made for controlling the movement of the floating member by braking means.

In an alternative arrangement shown in FIGURE 9, the cam surface may be provided for example with gear teeth to engage the rollers of the float which would take the form of pinions 4a, and suitable brakes 12 may be fitted to brake the pinions and controlled from roll sensing means '13 of known type. Alternatively, gears as described may be fitted in addition to rollers which would carry the loading forces.

Variations in the tuning with amplitude can also be achieved; for example, in FIGURE In, if instead of a uniform radius, a curve be substituted in which the eflective radius at the centre portion is greater or less than the radius at the sides then the periodic responses will change with amplitude.

This feature and other features inherent in this novel tank design can be used to alter the resonance curve and produce a resonance system having a controllable band width of resonance.

Various other modifications may be made within the scope of the invention. Thus, for example, under excessive seas, to prevent the floating member violently striking the end of the tank in its movement, the curvature may be increased rapidly to provide a greater re-centering force for the buoyant member.

Again, the variations shown in FIGURES 3a and 5a allow for the buoyant member to tilt as well as move in the translational sense across the tank, and this can be used to promote higher efliciency by forcing the bulk of the liquid to one'end and so achieve a greater stabilizing moment. The buoyant member may also be suitably shaped to achieve the same objectives.

For smooth operation of the floating member, it may also be fitted with rollers or wheels on the sides to guide it in the tank.

Variations can also be made in the shape of the tank system. For efiicient stabilization of a given vessel a certain volume is required and this volume can be disposed either as a deep tank with small dimensions in the fore and aft direction of the vessel, or alternatively, a shallow tank with correspondingly longer fore and aft dimensions, the law of movement required of the floating member being made the same in either case by suitably arranging the linkages or cam and roller arrangement which guide and control the floating member.

The construction of the floating member may be of a rigid type utilising metal or such lighter material as fibre glass; alternatively, it may be of wholly flexible material such as rubber or plastic or constructed with a combination of plastic and rigid members. The floating member may in a further variant in construction be designed to keep its desired shape by means of internal gas pressure.

In a further variation of the invention the movement of the floating member may be controlled either by positive means or by means of a system such as a brake for dissipating energy or for holding the member stationary, such action being initiated or controlled by a suitable sensor responsive to the movement of the vessel being stabilized.

I claim:

1. A tank system stabilizing a vessel against periodic rolling motion comprising a tank containing a liquid; a buoyant member in said liquid and dividing said tank internally into two volumes which vary inversely in dependence on the displacement of said buoyant member from a mid position in said tank; a passageway interconnecting said tank volumes and formed between said buoyant member and said tank; and tank tuning means in said tank partially determined by the height of said passageway between said buoyant member and said tank and by guide means which define a path of pronounced curvature along which said buoyant member is freely movable during rolling motion of the vessel, said guide means varying the movement of said member from said mid position as a function of the roll angle of the vessel.

2. A tank system as set forth in claim 1 in which said guide means comprise a track disposed above said buoyant member which is held by its buoyancy against said track.

3. A tank system as set forth in claim 2 further comprising vertical adjustment means controllably operable to vary the height of said buoyant member in said tank.

4. A tank system as set forth in claim 3 in which said vertical adjustment means produce vertical displacement of said track.

5. A tank system as set forth in claim 4 further comprising means controllably operable to alter said pronounced curvature of said track.

6. A tank system as claimed in claim 1 in which said buoyant member is a sphere.

7. A tank system as claimed in claim 1 in which said buoyant member is a cylinder.

8. A tank system as claimed in claim 1 in which said tank is of generally rectangular shape.

9. A tank system as claimed in claim 1 in which said buoyant member is constrained by a curved roof on the tank.

10. A tank system as claimed in claim 1 in which said buoyant member is secured by at least one link to said tank.

11. A tank system as claimed in claim 10 in which said buoyant member is secured by parallel links to the bottom of said tank.

12. A tank system as claimed in claim 10 in which said buoyant member is secured by inclined links to the bottom of said tank.

13. A tank system as claimed in claim 1 in which said liquid has a free surface.

14. A tank system as claimed in claim 1 in which the tank system is filled.

15. A tank system as claimed in claim 14 in which the tank system is open to the surrounding sea.

References Cited UNITED STATES PATENTS 3,083,671 4/1963 Ripley 114-124 FQREIGN PATENTS 20,711 1914 Great Britain. 1,039,992 5/1953 France.

TRYGVE M. BLIX, Primary Examiner.