US3422781A - Variably damped passive tank stabilizer - Google Patents

Variably damped passive tank stabilizer Download PDF

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Publication number
US3422781A
US3422781A US636780A US3422781DA US3422781A US 3422781 A US3422781 A US 3422781A US 636780 A US636780 A US 636780A US 3422781D A US3422781D A US 3422781DA US 3422781 A US3422781 A US 3422781A
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Prior art keywords
tank
frequency
ship
roll
liquid
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Expired - Lifetime
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US636780A
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English (en)
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Sheldon B Field
Frans V A Pangalila
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FLUME STABILIZATION SYSTEMS Inc
FLUME STABILIZATION SYST
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FLUME STABILIZATION SYST
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/08—Control of attitude, i.e. control of roll, pitch, or yaw
    • G05D1/0875—Control of attitude, i.e. control of roll, pitch, or yaw specially adapted to water vehicles

Definitions

  • VARIABLY DAMPED PASSIVE TANK STABILIZER Filed May 8,1967 Sheet of 4 GYROSCOPIC CONTROL UNIT INVENTORS.
  • a passive tank stabilizer for ships including an elongated tank partially filled with a body of liquid in a free surface condition, and a gyroscopically controlled door operative between open, closed and intermediate positions so as to variably and selectively control the amount of damping imparted to transferring liquid, said door operatively permitting maximum liquid passage when the vessel rolls near natural frequency and closing by degrees as the ship rolls at frequencies further away from resonancy and being closed to deactivate the tank when the ship is forced rolled above at frequencies at which the stabilizer would otherwise destabilize the ship.
  • the present invention relates to passive tank stabilizers and more particularly to substabilizers of the free surface type in which by virtue of the tank geometry and the liquid level of the stabilizin medium therein the tank liquid oscillates with a natural frequency matched to the roll of the ship.
  • Frahms stabilizer commonly known as a U-tube type passive tank, was characterized by a pair of opposite wing tanks interconnected by a narrow duct which extended from the bottom of the wing tanks down around the bottom of the ship to the bottom of the opposite tank. In later designs, the entire tank was confined between decks of a ship but the interconnecting duct continued to have a height to confine the liquid in the crossover duct. With this arrangement, the Frahm tanks oscillated at a frequency tuned to the roll of the ship so that the stabilizing moment was applied first in one direction and then in another depending upon the angular position of the ship.
  • the present invention improves on the conventional free surface tank by providing for the first time variable damped, free surface tank which senses the roll frequency and amplitude of the ship and automatically controls damping so that damping is reduced when the ship rolls near resonance and the damping is maximized to completely deactivate the tank when the ship rolls beyond a frequency limit.
  • the damping may be variably set to intermediate degrees at specified frequency ranges between the frequency limit and resonance.
  • the present invention provides a passive free surface tank with a motor control valve or door movable between fully opened and fully closed positions.
  • An automatic sensing and control unit preferably a gyroscopic type, senses the rolling of the ship and produces signals of predetermined magnitude corresponding to the rolling frequency and, in some cases, amplitude.
  • the Ship rolls near resonance which for the purpose of this disclosure is synonymous with natural roll frequency
  • the unit controls the motor to open the door as wide as possible so as to impart minimum damping and to permit maximum liquid passage therethrough resulting in the greatest stabilizing moment.
  • the unit controls the motor to fully close the door thus deactivating the tank preventing the tank from destablizing the ship. At this time, the ship is stablized by virtue of its inherent static stability.
  • the control unit operatively moves the door to intermediate positions so as to impart controlled and predetermined amounts of damping depending upon the sensed rolling frequency.
  • FIGURE 1 is a horizontal section of a tank in accordance with the present invention and part of the ships hull.
  • FIGURE 2 is a transverse vertical section taken along line 22 of FIGURE 1.
  • FIGURE 3 is a longitudinal vertical section taken along line 33 of FIGURE 1.
  • FIGURES 4 and 5 are charts illustrating the amplitudefrequency characteristics of an unsta blized ship, and ships stablized with various stablizer configurations including the present invention.
  • FIGURE 6 is a typical block diagram schematic of one example of the sensing and control apparatus for the invention.
  • a preferred embodiment of the invention includes a passive tank stablizer generally indicated as 10 arranged between adjacent decks 12 and 14 of ship 16 and extending from one side of the hull to the other.
  • the hight of tank 10 is generally uniform throughout and a body of liquid 18 partially fills tank 12 to a level adjusted so that the natural frequency of the tank liquid oscillation is matched to the roll frequency of the ship.
  • the breadth (fore and aft) of tank 10 is determined by the particular volume capacity and geometry selected to best suit the particular ship being stabilized.
  • the liquid can be of any suitable kind such as fresh 'water, sea water, bunker oil, fuel or the like.
  • tank 10 is divided into two wing tanks 11 and an interconnecting channel 13 by four upstanding members 32 aligned in pairs and spaced from the center and ends of the tank.
  • Members 32 extend from the bottom of the tank up to a height well above the static surface of body 18 and have mutually facing ends 34 spaced from each other to form passageways 36 and turned outward for hydrodynamic purposes.
  • the cross section area of opening 36 is designed so that members 32 impart some damping to the passage of liquid therethrough. For reasons made clear below, the damping provided by members 32 should be less than that provided by the tanks of U8. Patent No. 3,054,373.
  • a damping and cut-off control assembly 20 is arranged in the center of the tank.
  • the assembly can have any suitable form such as sliding doors, rotating horizontal or vertical flaps, or the like.
  • One preferred assembly is formed by a pair of upstanding plates 22 extending from the floor of tank 10 up the fore and aft walls thereof to a height suitably above the expected static liquid level within the tank.
  • a valve plate or door 24 supported for rotation about a vertical shaft 26 between plates 22 is operatively movable between perpendicular and generally parallel positions relative to plates 22, i.e., open and closed positions, respectively.
  • the distance D should be selected so that door 24 when in a partially opened position cooperates with members 32 to impart damping to liquid passage.
  • Door 24 is operated by a reversible motor 28 receiving control signals from a gyroscopic control unit 3 1 which senses the frequency of the rolling of the ship and generates a control signal which operates motor 28 to effect rotation of door 24 to the fully opened, fully closed, or one of a number of intermediate positions.
  • the assembly 20 operates to vary the damping imparted to the tank liquid and in some instances serves to de-activate the tank completely. It will be appreciated that more than one such assembly 20 and control motor therefor can be provided throughout the tank as desired.
  • Mechanical means may be provided to bias the door toward the closed position so that the tank halves are isolated in the event of power failure.
  • Motor 28 is housed within a space formed in the top of the tank by a flat plate 30 supported by the tops of plates 22 and 32 and joined rigid with the top of the tank by transverse diaphrams 38 and longitudinal plates 40, the latter of which are provided with openings 42 to permit a free passage of air and to reduce the weight of the assembly.
  • unit 31 average the frequency of the previous ten (or other suitable number) roll cycles and generate control signals accordingly. 'In this way, the stabilizer will avoid hunting and will not be adversely affected by transients as would be the case if assembly 20 responded solely to the frequency of each roll cycle.
  • Unit 31 may comprise any suitable mechanical or electrical arrangement, one example of which is illustrated in FIGURE 6.
  • Power supply 71 applies operating power to the system.
  • a sensing transducer stage 72 senses the roll rate and magnitude and develops a sinusoidal signal accordingly.
  • the transducer feeds this signal to the computer stage 74 which is programmed by the manually adjusted switches of the control panel 76 which has override switching capability.
  • the computer automatically develops the door control signals in accordance with the control switch settings and receives transducer signals and applies the same to motor 28. In response thereto, motor 28 opens, closes, or moves door 24 to one of a number of intermediate positions.
  • computer 7-4 can also generate a hold signal to fix the door 24 in position whenever the sensed roll magnitude is below a predetermined value regardless of roll frequency.
  • FIGURE 4 In that figure there is illustrated the typical amplitude-frequency characteristic curve for the unstabilized ship. Roll amplitude is maximum at resonance, F that is, when the frequency of oncoming waves is matched to the natural roll frequency of the ship. It can be seen that because of the static stability of the ship the amplitude of roll at frequencies well above and below F drops off to only a fraction of that at resonance. Also illustrated in the figure is the curve for the typical Frahm type stabilizer with its characteristic double hump bridging the resonant frequency. It is thus clearly seen that the Frahm type stabilizer introduces more roll amplitude at the high and low frequency regions than for the case of the unstabilized ship, However, the Frahm type stabilizer does achieve good results near resonance.
  • curve A for a typical passive free surface tank of the type disclosed in US. Patent No. 3,054,373 which provides a generally flat response curve A showing adequate roll reduction near resonance and much better results at :high and low frequencies than in the case of the Frahm type stabilizer.
  • the amplitude-frequency roll characteristics of a ship stabilized is represented by curve B.
  • F control unit 31 operates motor 20 to open door 24 to the fullest extent. With door 24 fully opened, the tank imparts a minimum damping to the liquid passage so that a maximum stabilizing moment is developed in op position to roll. Because of the operation of the invention at high and low frequencies as described below, the magnitude of this minimum damping (developed by all internal members 32, 22, 24) is less than that developed by the conventional free surface tank of US. Patent No. 3,054,373. Therefore, for frequencies near F curve B has a lower magnitude than curve A.
  • the invention is designed so that the tank liquid oscillates at a substantial phase lag relative to the ships roll, i.e., up to a theoretical 90 lag.
  • the gyroscopic control unit 31 When the gyroscopic control unit 31 senses that the ship is rolling below F or above F it generates a signal sufficient to close door 24 an amount which corresponds to the extent said frequency is removed from F or F Thus, as the ship rolls at decreasing frequencies below and relative to F or at increasing frequencies above and relative to F door 24 is rotated to more closed positions to correspondingly block liquid passage. As evident from FIGURE 4, the effect of closing door 24 in the regions of F -F and i -F is to change the response curve toward that for the unstablized ship at the frequency limits. Examples of the door position-roll frequency are:
  • Another mode of operation for the invention involves stabilizing short period ships. For these ships a greater volume of tank liquid may be placed in the tank than is required for tuning the tank liquid and ship roll. Normally, such a step would be detrimental to tank operation at low frequencies but beneficial to tank performance near F and high frequencies. See curve C, FIGURE 5. But with the invention good results are obtained over the entire frequency range by effecting curve D at frequencies below F To develop curve D, the invention operates as follows:
  • variable damped free surface passive tank stabilizer which is designed for optimum performance near resonant frequency without consequence to the destabilization effect it might have at high or low frequency forced roll conditions.
  • the invention provides means to impart variable amounts of damping to the tank liquid at prescribed frequency ranges so that the ship operates with improved stability.
  • a roll stabilization system for ships comprising an elongated tank extending from one side of the hull to the other, a body of free surface liquid distributed generally throughout the tank and partially filling the tank to a level at which the tank liquid imparts to the ship an oscillating, timed stabilizing moment near the natural frequency of the ship at a phase lag significantly near closure means including a closure assembly located within the tank and spaced from the ends thereof to selectively isolate and permit liquid communication along the liquid path within the tank, and sensing and control means for sensing the roll frequency of the ship and closing the closure assembly to effectively deactivate the tank when the average of a predetermined number of roll cycles is at a first frequency away from its natural frequency and at which the tank liquid would destabilize the ship so that the ship rolling characteristic is primarily dependent upon the ships static stability.
  • sensing and control means elfects a first opening of said closure means when the ship rolls at a second frequency between the ships natural roll frequency and said first frequency in order to permit liquid passage in the tank with a first degree of hydraulic damping.
  • sensing and control unit effects a second opening of the closure assembly greater than the first opening when the ship rolls at a third frequency between the ships natural roll frequency and said second frequency in order to permit liquid passage in the tank with a second degree of hydraulic damping less than said first degree.
  • liquid level is set so that the natural tank liquid oscillation is tuned to the ships roll with the closure assembly full open and minimum damping being imparted to liquid passage.
  • liquid level is selected above that required for tuning the tank liquid oscillation frequency with the ships roll and said first and second frequency are below the ships natural roll frequency.

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  • Engineering & Computer Science (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Automation & Control Theory (AREA)
  • Vibration Prevention Devices (AREA)
  • Vehicle Body Suspensions (AREA)
  • Filling Or Discharging Of Gas Storage Vessels (AREA)
US636780A 1967-05-08 1967-05-08 Variably damped passive tank stabilizer Expired - Lifetime US3422781A (en)

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US63678067A 1967-05-08 1967-05-08

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US (1) US3422781A (enrdf_load_stackoverflow)
JP (1) JPS527639B1 (enrdf_load_stackoverflow)
DE (1) DE1756326B2 (enrdf_load_stackoverflow)
ES (1) ES353658A1 (enrdf_load_stackoverflow)
FR (1) FR1587877A (enrdf_load_stackoverflow)
GB (1) GB1199213A (enrdf_load_stackoverflow)
NL (1) NL6806522A (enrdf_load_stackoverflow)
NO (1) NO127291B (enrdf_load_stackoverflow)
PL (1) PL79302B1 (enrdf_load_stackoverflow)
SE (1) SE347923B (enrdf_load_stackoverflow)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3516377A (en) * 1968-07-03 1970-06-23 Flume Stabilization Syst Variably damped passive tank stabilizer
WO2008076168A1 (en) * 2006-12-15 2008-06-26 Exxonmobil Upstream Research Company Long tank fsru/flsv/lngc
WO2011016730A1 (en) * 2009-08-06 2011-02-10 Eirik Hellesvik Roll dampening apparatus
US8915203B2 (en) 2011-05-18 2014-12-23 Exxonmobil Upstream Research Company Transporting liquefied natural gas (LNG)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3192888A (en) * 1963-09-19 1965-07-06 Mcmullen Ass John J Combination stabilization and heeling system for ice breakers
US3269346A (en) * 1964-03-02 1966-08-30 Muirhead & Co Ltd Passive tank stabilizers for floating bodies

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3192888A (en) * 1963-09-19 1965-07-06 Mcmullen Ass John J Combination stabilization and heeling system for ice breakers
US3269346A (en) * 1964-03-02 1966-08-30 Muirhead & Co Ltd Passive tank stabilizers for floating bodies

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3516377A (en) * 1968-07-03 1970-06-23 Flume Stabilization Syst Variably damped passive tank stabilizer
WO2008076168A1 (en) * 2006-12-15 2008-06-26 Exxonmobil Upstream Research Company Long tank fsru/flsv/lngc
US8079321B2 (en) 2006-12-15 2011-12-20 Exxonmobil Upstream Research Company Long tank FSRU/FLSV/LNGC
KR101502793B1 (ko) 2006-12-15 2015-03-16 엑손모빌 업스트림 리서치 캄파니 액체 수송을 위한 해양 선박, 상기 선박에 의해 유체를 수입하는 방법 및 상기 선박의 저장 탱크를 설계하는 방법
WO2011016730A1 (en) * 2009-08-06 2011-02-10 Eirik Hellesvik Roll dampening apparatus
US8915203B2 (en) 2011-05-18 2014-12-23 Exxonmobil Upstream Research Company Transporting liquefied natural gas (LNG)

Also Published As

Publication number Publication date
NO127291B (enrdf_load_stackoverflow) 1973-06-04
DE1756326B2 (de) 1976-07-22
JPS527639B1 (enrdf_load_stackoverflow) 1977-03-03
PL79302B1 (enrdf_load_stackoverflow) 1975-06-30
GB1199213A (en) 1970-07-15
FR1587877A (enrdf_load_stackoverflow) 1970-04-03
ES353658A1 (es) 1969-11-01
SE347923B (enrdf_load_stackoverflow) 1972-08-21
DE1756326A1 (de) 1970-04-02
NL6806522A (enrdf_load_stackoverflow) 1968-11-11

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