US3270703A

US3270703A - Ship stabilizer comprising surface covering means

Info

Publication number: US3270703A
Application number: US386285A
Authority: US
Inventors: Sheldon B Field
Original assignee: John J Mcmullen Associates Inc
Current assignee: John J Mcmullen Associates Inc
Priority date: 1964-07-30
Filing date: 1964-07-30
Publication date: 1966-09-06
Anticipated expiration: 1983-09-06
Also published as: GB1045517A

Description

Sept. 6, 1966 s. B. FIELD 3,

SHIP STABILIZER COMPRISING SURFACE COVERING MEANS Filed July 30, 1964 2 Sheets-Sheet l INVENTOR She/don 8. Field A ORNEYS Se t. 6, 1966 s. a. FIELD 3,270,703

SHIP STABILIZER COMPRISING SURFACE COVERING MEANS Filed July 50, 1964 2 Sheets-Sheet 2 V E" a 9: m E E g k Q INVENTOR She/don 5. Field ATTORNEYS United States Patent 3,270,703 SHIP STABILIZER COMPRISING SURFACE COVERING MEANS Sheldon B. Field, Floral Park, N.Y., assignor to John J.

The present invention relates to a ship stabilizer and more particularly an improved apparatus for applying a restoring moment by a movement of the fluid within a tank,

Ships of practically every type encounter the problem of undesirable ship motion caused by the surface condition of water. Depending upon the type and size of the ship and the operating conditions to which the ship is to be subjected, various hull designs are selected to counteract the tendency of the water to impart motion to the ship. Due to the great number of variables present, such cyclic motion can cause a gradual increase in the motion of the ship, and hull design provides only a limited effect in controlling the ship motion. Other attempts to minimize ship motion in response to wave action include the provision of stabilization systems which are capable of applying a restoring moment to the ship when it is subjected to the motion. Particular emphasis has been made with respect to improving systems for minimizing roll. Ballast tanks connected by piping and the like have been applied in order to transfer water in a manner to generate a restoring moment. Such systems encounter the difficulty of maintaining a proper phasing between the restoring moment and motion imparted to the ship. Efforts to employ volumes of air above liquid ballast for controlling the ballast have resulted in massive systems which are uncertain as well as excessively noisy in operation. Efforts also have been directed to providing the ship with fin members extending from the hull beneath the water line and adapted to generate a restoring moment from the hydrodynamic forces on the fins accompanying a motion ofthe ship. In certain applications controlled fins have been effective in controlling the roll of the ship but only with the expense of complex systems employing massive fin members and operating machinery. Furthermore, control fins are generally effective only when the ship is under way and therefore said fins cause drag resulting in a loss of speed.

Accordingly, it is the primary object of the invention to provide a ship stabilizer which is capable of applying a restoring moment to the ship whether the ship is under way or stationary. I

More particularly, it is an object of the invention to provide a ship stabilizer which is passive, that is, a stabilizer which applies the restoring moment directly in response to the movement of the ship about the axis about which the ship is to be stabilized without the need of control equipment. Furthermore, it is an object of the invention to provide a ship stabilizer in which the movement of the fluid in response to the movement of a ship is sufficiently dampened in order that the fluid can apply a restoring moment to the ship.

Another object of the invention is to provide a ship stabilizer which is passive in operation but which is adapted to be conveniently positioned to compensate for changes in the condition of the ship or the sea.

A still further object of the invention is to provide a ship stabilizer which is relatively compact and of reasonable weight.

A further object of the invention is to provide a ship stabilizer which damps the movement of fluid therein so that better stability can be imparted and the degree of roll of the ship is held to a minimum.

"ice

In an embodiment of the invention the stabilizer comprises an elongated fluid containing means or tank disposed substantially horizontally and substantially at right angles to the axis about which the ship is to be stabilized. Thus, if the ship is to be stabilized against roll, the tank is disposed in a substantially athwartship direction along one of the decks of the ship. The tank is filled to a desired level with a heavy liquid, such as water, the surface of which is covered with a desired amount of a lighter liquid, such as oil. The lighter liquid and heavier liquid should have the properties of being immiscible, so that the lighter liquid always floats on top or completely blankets the heavier liquid.

Further and other objects of the invention will be understood from the following description with respect to the drawings in which:

FIGURE 1 is a vertical sectional view of a ship showing the arrangement of the ship stabilizer;

FIGURE 2 is an enlarged plan view of one embodiment of the invention;

FIGURES 3, 4 and 5 are vertical section views of the invention taken along lines 3-3 of FIGURE 2;

Referring to the FIGURES 1-5 in detail, there is shown in FIGURE 1 a ship stabilizer generally indicated as stabilizer 10 mounted athwartship below decks 12 of the ship 14. It can be seen, when the stabilizer 10 is partially filled with fluid, said stabilizer can perform passive stabilization whenever roll forces are applied to ship 14. The stabilizer comprises a tank 16 formed by

sides

18 and 20 and

ends

22 and 24. The tank 16 can have a top or cover to prevent fluid spill or the sides could extend between two decks, thus using the upper deck as a top. By extending the stabilizer across the hull of the ship 14 the maximum moment arm of the liquid can be obtained. The stabilizer is proportioned in a manner such that the weight of the liquid which is displaced in a position adjacent an end portion thereof is sufiicient to generate a restoring moment capable of restoring the motion of the ship for a range of sea conditions. The fluid within the tank has a free surface and can move in,-response to the motion of the ship. It can be seen, however, that once the moment force is created by the liquid to oppose the roll of the ship, the fluid mass velocity increases so that the fluid mass begins to move across the tank to the opposite end thereof. As will be described below, a portion of the kinetic energy of the moving mass will be absorbed and the movement of said mass will be impeded or dampened by the layer of oil riding on the surface of the water.

The fluid to be employed within the stabilizer tank can be any liquid or the like having sufficient density and with a sufficient viscosity whereby flow can readily take place within tank 16. Qnce the stabilizer has been designed in the ship, the depth of the fluid Within the stabilizer tank can be varied for tuning the stabilizer to various conditions of the ship and the sea. Furthermore, the amount of damping or fluid movement impedance can be varied to some degree by varying the depth of the oil layer on top of the water surface.

In order for a restoring moment to be generated, it is necessary that the moment be substantially out of phase with the forces applied to the ship by the sea. Thus in the case of roll, as the crest of the wave strikes along one side of the ship, the force resulting from the moment must be applied in opposition to the force of the wave. After the wave causes the ship to roll, it is necessary that the moment be reversed so that the force is applied to the opposite side of the ship.

The operation of the stabilizer will now be described It is known that a fluid containing tank when tilted first in one direction and then in another in an oscillatory manner creates a wave or a moving fluid mass within the tank. It is also known that the waves within fluid of a certain density, for example, water, can be quieted or impeded by covering the entire surface of said fluid with another fluid, for example, oil. It is believed that the creation of the wave or fluid mass expands in surface area in the vicinity of said forming mass, and therefore, the forces creating said wave must overcome the surface tension forces tending to hold the oil layer together, Due to the molecular structure of the oil layer, these surface tension forces are relatively great with respect to the weight of the oil layer. Therefore, when the wave is forming and said wave tends to break through the oil layer and the surface area increases to force a separation in the oil layer, the surface tension forces inherent in the oil act to suppress or impede the movement of the wave or fluid mass. In the same manner, it is believed when a wave is moving within the tank, it must overcome the surface tension forces as well as the weight of the displaced oil layer, and therefore, fluid motion is impeded and kinetic energy is dampened or dissipated.

Another theory for the resulting dampening is that the lighter fluid is of greater viscosity than the heavier fluid and the turbulent energy of the heavier fluid is absorbed by tending to create a like turbulence in the more viscous fluid.

Let it be assumed that a wave strikes the ship such that the ship rolls to elevate side 30 and lower side 32. As side 30 rises and approaches its maximum point of upward movement, a hydrostatic head is formed within the stabilizer so that flow of fluid takes place and the fluid mass flows toward end 36. The potential energy of the fluid is maximum at the maximum elevation of side 30 and the weight of the hydrostatic head imparts a restoring moment force to the ship. The potential energy of the fluid in end portion 34 is converted into kinetic energy as the fluid mass begins to flow toward end portion 36. After side 30 is lowered and the ship passes through a level position, the fluid continues to flow in the direction of end portion 36 due to its kinetic energy. In this way, it is seen that there is an accumulation of fluid in end portion 36 as the portion of the hull adjacent thereto attempts to be elevated by the sea or rolling forces. As the mass of fluid arrives at end portion 36, a portion of the kinetic energy thereof is absorbed by the oil layer due to the local turbulence and rising of the arriving fluid mass. Hence, it can be seen that the motion of the moving fluid mass within tank 16 is impeded by the inherent forces and weight of the oil layer located at the surface of the water within the tank. This process then continues so long as sea forces are applied to the hull to cause it to move about or roll about the axis of the ship.

It should be understood that any desired liquids or fluids can be used as long as they have the properties as described above without departing from the scope of the invention.

While there has been disclosed what at present are considered to be preferred embodiments of the invention, it is to be understood that changes and modifications can be made therein without departing from the essential spirit of the invention. The scope of the present invention should only be limited by the scope of the appended claims.

What is claimed is:

1. A stabilization system for a vessel comprising an elongated tank having its longitudinal axis arranged perpendicular to the roll axis of the vessel, a first liquid body partially filling said tank to a predetermined level which is spaced below the top of said tank, said tank being substantially free of liquid transfer damping structure, said first liquid body having a distributed mass which when alone in said tank oscillates at a natural fundamental frequency substantially removed from a phase lag of the vessel rolling frequency, a second liquid body which is immiscible with said first liquid body floating on the top, exposed surface thereof, the upper surface of said second liquid body being spaced below said top of said tank, said second liquid body being viscous and having a mass suflicient to dampen the fundamental transfer of said first liquid body so that the first and second liquid body combination collectively transfers in oscillation with a fundamental frequency equal to the fundamental frequency of said ship roll and the phase oscillation of said first and second liquid body combination being such that there is as successive accumulation of liquid at that end region of said tank which is rising, each accumulation being suflicient to oppose the rise so that the vessel is stabilized.

2. A stabilizer as set forth in claim 1 wherein the weight of said first liquid body is greater than the weight of said second liquid body.

3. A stabilizer as set forth in claim 2 wherein said second liquid is oil.

4-. A stabilizer as set forth in claim 3 wherein said first liquid is water.

5. A stabilizer as set forth in claim 2 wherein said tank has a substantially constant cross-sectional area throughout its length.

References Cited by the Examiner UNITED STATES PATENTS 1,098,977 6/1914 Rouse 114 209 1,133,154 3/1915 Kahnweiler "114-209 1,575,134 3/1926 Stocking 114 209 3,083,672 4/1963 Ripley 114 OTHER REFERENCES Ser. No. 132,695, Hort (A.P.C.), published May 11, 1943.

5 MILTON BUCHLER, Primary Examiner.

T. M. BLIX, Assistant Examiner.

Claims

1. A STABILIZATION SYSTEM FOR A VESSEL COMPRISING AN ELONGATED TANK HAVING ITS LONGITUDINAL AXIS ARRANGED PERPENDICULAR TO THE ROLL AXIS OF THE VESSEL, A FIRST LIQUID BODY PARTIALLY FILLING SAID TANK TO A PREDETERMINED LEVEL WHICH IS SPACED BELOW THE TOP OF SAID TANK, SAID TANK BEING SUBSTANTIALLY FREE OF LIQUID TRANSFER DAMPING STRUCTURE, SAID FIRST LIQUID BODY HAVING A DISTRIBUTED MASS WHICH WHEN ALONE IN SAID TANK OSCILLATES AT A NATURAL FUNDAMENTAL FREQUENCY SUBSTANTIALLY MOVED FROM A 90* PHASE LEG OF THE VESSEL ROLLING FREQUENCY, A SECOND LIQUID BODY WHICH IS IMMISCIBLE WITH SAID FIRST LIQUID BODY FLOATING ON THE TOP, EXPOSED SURFACE THEREOF, THE UPPER SURFACE OF SAID SECOND LIQUID BODY BEING SPACED BELOW SAID TOP OF SAID TANK, SAID SECOND LIQUID BODY BEING VISCOUS AND HAVING A MASS SUFFICIENT TO DAMPEN THE FUNDAMENTAL TRANSFER OF SAID FIRST LIQUID BODY SO THAT THE FIRST AND SECOND LIQUID