US3054373A

US3054373A - Flume type heeling tank stabilizer

Info

Publication number: US3054373A
Application number: US9144A
Authority: US
Inventors: Kenneth C Ripley
Original assignee: John J Mcmullen Associates Inc
Current assignee: John J Mcmullen Associates Inc
Priority date: 1960-02-16
Filing date: 1960-02-16
Publication date: 1962-09-18
Anticipated expiration: 1979-09-18
Also published as: NL6816201A; GB962343A; BE598596A

Description

Sept. 18, 1962 K. c. RIPLEY 3,054,373

FLUME TYPE HEELING TANK STABILIZER Filed Feb. 16, 1960 5 Sheets-Sheet 1 i \CENTER OF ROTATION FIG. 1.

FIG. 2.

INVENTOR KENNETH C. RIPLEY ATTORNEYS Sept. 18, 1962 K. c. RIPLEY 3,

FLUME TYPE HEELING TANK STABILIZER Filed Feb. 16, 1960 3 Sheets-Sheet 2 Sept. 18, 1962 K. c. RIPLEY FLUME TYPE HEELING TANK STABILIZER 5 SheetsSheet 3 Filed Feb. 16, 1960 Ill/l l/ll/ II] ///I Ill/III l/ll/I/I/ I/II/l/II KENNETH c. RIPLEY FIG. 5.

ATTORNEYS 3,fi54,373 Patented Sept. 18, 1962 3,054,373 FLUNE TYPE I-EELTNG TANK STABILIZER Kenneth C. Ripiey, Washington, D.C., assignor to John 5.

McMullen Associates, Inc, New York, N.Y., a corporation of New York Filed Feb. 16, 1960, Ser. No. 9,144 12 Claims. (Cl. 114-125) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to ship stabilization systems and more particularly to ship stabilization systems wherein passive antirolling tanks are utilized.

In oceangoing vessels the need for combating ship motion due to wave action has long been realized. There have been a variety of devices and designs directed at reducing undesirable motion in a seaway. Roll stabilization, the aim of the present invention, has continued to be a problem to be reckoned with although various devices for reducing roll are in operation today on many types of craft.

Many vessels use one type or another of antiroll fins projecting from the sides of the vessel to create large resistances to rolling action. Some of these fins are fixed; others are controllable, but all fail to prevent roll in heavy seas at speeds below about 15 knots. On ships designed for low speeds, such as missile tracking vessels while on station, antirolling fins are ineffective.

In icebreaking vessels, a very severe rolling action is encountered in heavy seas due to the inherent design of the ship. The ship must be capable of heeling to break itself free from ice. This is accomplished by designing the ship with a great metacentric height and a round bottom to facilitate heel by use of heeling tanks. These qualities however make the ship very unsteady in heavy seas and it will be realized that any projections from the side of the hull are prohibited due to the stresses exerted by ice. Therefore antiroll fins and bilge heels are impractical on icebreaking vessels.

A system of tanks for shifting the center of gravity of a vessel to create a righting moment to rolling or heeling action has also been tried. These systems utilized, generally, a pair of closed tanks, one located on each side of the ship and connected by a U-shaped crossover tube which was completely filled with water while in operation and also by an air duct connected between the tops of the tanks and having a valve for controlling the flow of air between the tanks.

These stabilizers were tried on a number of vessels but were found to suffer from several serious disadvantages. One disadvantage was the excessively noisy operation. The controllable air flow between the tanks acted as a damping system to prevent too rapid an exchange of Water between the tanks. To sustain sufiicien-t pressure in the line for adequate damping, the flow of air through the constricted portion attained very high velocities and was exceptionally noisy.

The system required that the lowest level of water in a tank during transfer could not fall below the top of the crossover duct otherwise the damping of the system would not be operable. At the same time, arrangement considerations usually dictate that the stabilizer be kept to one deck height, whenever the installation is to be below the main deck. These requirements severely limit what the designer may do to get best use of the weight and space that reasonably can be allowed for passive antirolling tanks. When the designer chooses a conventional U-tube type stabilizer he is confronted with the difficulty that of the water in the tank the portion between the bottom of the tank and the level corresponding to the top of the cross-over duct is water which serves no really useful purpose. This water that adds nothing to the effectiveness of the stabilizer does, however, add to the required weight and space of the installation,

The method of designing the system for optimum operation consisted in proportioning the tanks and crossover ducts to give the correct computed value for the ratio of the horizontal sectional area of the tanks to the vertical sectional area of the cross-over duct. A tuning once established could not be changed since the duct cross-section was fixed. This gave a lack of control to the system since only by changing the damping of the air throttling system could the tanks system be made less critical for passing through resonance. Changing the damping of the air throttling system quite often meant that the system was too well damped to allow suflicient water transfer between the tanks. Thus, although the system was occasionally well adjusted for a particular type of see, it failed in others.

The present invention utilizes a type of construction which eliminates the disadvantages of the conventional U tube type of system described above. In this invention, all need to have a separate connection for air is eliminated. This elimination is accomplished by extending the cross over ducts to substantially the level of the tank tops and making the transfer duct into a flu'me. With this arrangement, the air space above the water surface in the duct is so large that air throttling effects no longer exist. Thus both the natural frequency and the damping of the stabilizer are functions of the geometry of the hydrodynamic portion of the stabilizer alone. A nozzle with a throat extending the full height of the duct is provided in the duct to produce additional damping into the system. This system is adjustable merely by changing the level of liquid in the tanks to vary the natural frequency of the system. Once the system is adjusted, no attendance by ship personnel is needed, and the system will perform satisfactorily irrespective of sea conditions.

The system may be fitted on one deck and carries only liquid which serves a useful purpose thus lowering the space and weight requirements needed for the conventional U-tube type of system. Since there are no air throttling valves, the noise is reduced considerably.

An object of the present invention is to provide a ship stabilizing system which is economical in cost, weight, and space.

Another object of this invention is the provision of a passive antiroll tank system which is relatively quiet in operation in comparison with known devices of kind.

Still another object of the present invention is to provide an antiroll system which requires a of attendance but which can be adjusted for tuning if the need arises.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a sectional view in elevation of an embodiment of the invention mounted in a ship hull;

FIG. 2 is a top view of the tank system of FIG. 1;

i FIG. 3 is an isometric view of the tank system of FIG. 1; a

FIG. 4 is a sectional view in elevation of a second embodiment of the invention;

FIG. Sis a sectional view taken on line 55 of FIG. 4; and

-FIG.. 6 is an enlarged view of one of the nozzles of the embodiment shown in FIG. 4.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a hull 11 of a surface vessel. It will be realized that the hull shape shown is for illustrative purposes only andthat the hull may have any desired configuration. V

Mounted inside hull 11 at each side thereof are a pair of storage tanks 12 interconnected by a flume or duct 13 which as can be seen from the figures has substantially the same height as the tanks and both the tanks and the duct are open to air at approximately atmospheric pressure. As can be seen from the figures, the duct 13 is relatively wide at its center portion and has a restriction or nozzle 14 at each end at the point where it enters each tank. Inside each tankat the point of entry of the duct are a pair of semi-cylindrical members 16 which serve to smooth the flow of liquid and eliminate stresses at these points. The nozzles or restrictions 14 as shown have a constant width dimension from top to bottom at,

the points where they enter the tanks, but it will be realized thatthe width dimension may vary from top to bottom. a

The tanks and duct normally contain arpredetermined levelof liquid, such as water or fuel oil, as can be seen in FIGS. 1 and 3. The initial tuning of the system for roll reduction is by properly proportioning of the eifective horizontal sectional area of the tanks to the vertical sectional area of water in the crossover duct. With this system it is possible to vary the sectional area of water in the duct simply by raising or lowering the initial level of liquid of the system. Thus, change of water level provides a means for adjustment of-the damping and a tuning of the system throughout the service life of the stabilizer A r i To be well designed, a flume type stabilizer must deliberately be overdesigned as regardscapacity, for ca pacity expressed asso many feet of possible transfer of water between tanks. This allows a margin within which to make changes in initial level of water of the systeml as a means for keeping the stabilizer correctly tuned to the ship. In one embodiment which is now in operation, a change of liquid level by only one foot, upor down, is sufficient to correct for a change of metacentric height of 09 foot up or down from the design value of metacentric height. f V

The restrictions or nozzles provide additional damping to the system and the dimensions of nozzle must be determined along with those of the tanks and ducts in ac-' cordance with the design of the particular ship on which the system is to be installed. r p

i In one embodiment of the invention which is now in operation, the following characteristics apply:

, Ship Length, overall, f t s 455 Length at waterline, feet"; 444 Beam, maximum,feet V 62 Displacement, full load, tons "10,680 Center of gravity aboveba'seline, feet 2-1.83 Center of buoyancy above baseline, feet 11.00 Transverse metacenter above baseline, feet 25.60 Metacentric height, feet"; 3.70 Draft, fee 21.00

. Naturalperiod in roll, seconds 14.20

4 Antirolling Tank System Number of tan 4 Width of one tank at free surface. level, feet 16.27 Length, fore and aft, each tank, feet 12.00 Weighted length of tank, feet 16.23 Area of free surface of one tank, square feet 191.40 Total free surface area of tanks, square feet 765.60 Width of one duct, feet 6.00 Axial length, feet 28.33 Plan area per duct, square feet 141.27 Wetted cross-section area per duct at centerline plane of ship with six foot depth of water, square feet 36.00 Tank moment arm, feet n 22.30 Height of center of rotation above baseline, feet... 21.83 Height of bottom of duct above baseline, feet 28.00

The results obtained with this system show that the average roll in a middle state 5 sea is reduced to between one degree, for a quarter head sea, and two degrees, for a quarter following sea. When only the one-tenth greatest rolls are used to get an average roll, the value for roll is doubled. The occasional roll of 4 degrees in the quarter following sea case compares with an occasional roll of'approximately 15 degrees for the same quarter following sea, but with the tanks'drained. The improvement given to roll reduction by this invention can be seen.

In operation as'the ship rolls due to wave action, water is transferred between the tanks by force of gravity and local sway'but is damped by the restrictions in the ducts.'.

Due to the damping to water transfer provided by the ducts as the ship rolls about its center of rotation (FIG. 1) -a righting moment is applied, thereby causing a shift of the center of gravity to aid the force due to buoyancy in restoring the ship to the vertical position.

A second embodiment of the invention is illustrated in FIGS. 4-6. This embodiment'is' designed for installation in an existing reserve fuel tank.- As shown in FIG. 4, the hull 11 has disposed therein, between

decks

21 and 22, a tank 23 which may contain fuel oil as shown or alternatively may contain water or other liquids. tank 23 extends transversely across the ship substantially the entire width thereof.

Disposed the tank 23 at each side thereof are a plurality of

parallel pipes

25, 26 extending from top to bottom inside the tank; Each of the pipes has welded thereto a pair of fins 27, along the plane of the array of pipes. The pipes with the attached fins act as restrictions to the transfer of liquid from one heeling tank to the other as the ship rolls. As shown in FIG. 6 the flow is broken away by the fins to form 'a throat of constant width independently of the amount of roll. Round pipes of larger diameter without fins could be substituted but the flow rate would tend to cause variation of the effective throat diameter due to change in Reynolds number with change of flow velocity. The' attached fins correct for this possibility and allow more accurate tuning than would be possible without the fins.

The arrays of 'parallelpipes' are shown as being inclined inward at the top. This allows storage of a maximum amount of liquid during roll' and thereby gives a maximum righting moment to counteract the roll. It will be realized, however, that the inclination of the array is not necessary for the device to be operable. The pipes may be arranged vertically or'inclined at a different angle from that shown in FIG. 4. e

The initial tuning in this embodiment is again governed In place of the pipe array of the embodiment of FIG. 4 or the single nozzle restriction as shown in FIG. 2,:it will be, realizedthat many variations of restrictions may be The utilized without departing from the scope of this invenown.

The invention described herein provides a means of roll reduction in situations where conventional roll reducing techniques fail. It has been found that in addition to roll reduction there are also substantial reductions in both yaw and sway. Additional advantages are the inherent quietness of the system, economy of space, adjustable tuning merely by varying liquid level, and the minimum of attendance required for operation of the device. Although the system has been described for roll reduction in ships or boats it will be realized that it may be useful in other vehicles as well and that the principles may be applied for example to pitch reduction as Well as roll reduction.

It will be realized that many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. The combination of a vessel and a stabilization system therefor comprising an elongated enclosure extending transversely across said vessel, wall means compartmenting said enclosure to define a wing tank on each end of said enclosure and an interconnecting central compartment, said wall means defining restricted vertically elongated openings communicating said wing tanks and said central compartment with the openings being shaped to cause substantial jet loss of head from liquid passing therethrough, and a body of liquid in said enclosure having a liquid level such that in a repose horizontal condition the openings defined in said wall means extend substantially above and below the level of the liquid to provide unrestricted passage for air and restricted passage for liquid.

2. The combination recited in claim 1 wherein the vertical edges of the openings are rounded.

3. The combination recited in claim 1 wherein the openings extend from the bottom to the top of said enclosure.

4. The combination recited in claim 1 wherein the openings are of uniform width from top to bottom.

5. The combination recited in claim 1 wherein the enclosure is substantially of uniform height for its entire length.

6. The combination recited in claim 1 wherein said Wall means comprises a plurality of pipes extending from top to bottom in said enclosure.

7. The combination recited in claim 6 wherein a pair or fins are attached to each pipe along its length.

8. The combination of a vessel and a stabilization system therefore comprising, a pair of wing tanks mounted in spaced relation on opposite sides of the vessel centerline, a crossover duct interconnecting said wing tanks, said duct and said wing tanks mutually defining restricted communicating vertically elongated openings to produce a substantial jet loss of head from liquid passing therethrough, liquid in said wing tanks and said duct at a uniform level throughout said system which level is spaced substantially below the top of said wing tanks and said duct when the system is in a repose horizontal condition, and said wing tanks and said duct defining a continuous airspace, including the upper portion of said restricted communicating openings, above the level of liquid which allows for the free unrestricted exchange and equalization of air as between said wing tanks and said duct.

9. The combination recited in claim 8 wherein the vertical edges of said restricted openings are rounded.

10. The combination recited in claim 8 wherein the restricted openings extend from top to bottom of the wing tanks and the duct.

11. The combination recited in claim 8 wherein the restricted openings are of uniform width top to bottom.

12. The combination recited in claim 8 wherein the wing tanks and the duct are of substantially the same height.

References Cited in the file of this patent UNITED STATES PATENTS 1,023,477 Oldham Apr. 16, 1912 FOREIGN PATENTS 13,784 Great Britain of 1908 435,100 Great Britain Sept. 13, 1935 675,003 Germany Apr. 27, 1939 OTHER REFERENCES Ser. No. 132,695, Hort (A.P.C.), published May 11, 1943.