System and method for controlling rolling motion of a marine vessel

Abstract

A system for countering the rolling motion of a marine vessel, includes one or more sensors adapted to characterize a sea condition approaching the vessel, one or more control systems, a computer, and one or more active stabilizers. The computer is adapted to receive the characterized sea condition data, is further adapted to generate one or more control signals in dependence on the characterized sea condition data, and is still further adapted to transmit the or each control signal to the or each control system. The or each control system is in turn adapted to actuate the or each active stabilizer in response to receipt of the or each control signal, to counter the rolling motion of the marine vessel.

Claims

1. A method of countering a rolling motion of a marine vessel, the marine vessel comprising one or more active stabilizers, the method comprising the steps of: sensing a speed and a heading for the marine vessel relative to an approaching wave; characterizing a first surface profile of a wave field approaching the marine vessel, using one or more sensors; predicting a first impingement time being the time at which the approaching wave field will impinge on the marine vessel; applying a harmonic analysis technique to decompose the first surface profile into constituent simple sinusoidal wave components of known amplitude and length; predicting a wave celerity of the constituent sine waves; determining a relative phase shift of the sinusoidal wave components; and phase shift the component waves for a future impingement of the wave field on the marine vessel for the time involved and then recombine the constituent wave components in their shifted relationship to derive a second surface profile corresponding to the future impingement of the wave field on the marine vessel; computing one or more control signals, using the second surface profile; and transmitting the one or more control signals to the one or more active stabilizers, to cause the one or more active stabilizers to apply a heeling moment to the marine vessel to counter a roll moment produced by an impingement of the wave field on the marine vessel.

2. The method as claimed in claim 1, wherein the or each active stabilizer is selected from the group comprising rudders, fins, foils and trim tabs, propellers, steerable water jets, internal stabilizers, movable weights, and anti-roll tanks.

3. The method as claimed in claim 1, wherein the step of: characterizing a first surface profile of a wave field approaching the marine vessel, using one or more sensors, comprises the step of: measuring characteristics of a wave field approaching the marine vessel to thereby generate a first sea surface profile.

4. The method as claimed in claim 3, wherein the characteristics are selected from the group comprising wave height, wave length, wave surface slope, wave roughness and wave grouping.

5. The method as claimed in claim 1, wherein, for a sea depth being greater than half of the wave length, the wave celerity of the constituent sine waves is predicted by: $\left({\mathrm{celerity}}_{d>\frac{L}{2}}=\sqrt{\frac{\mathrm{gL}}{2\pi }}\right)$ where: g=acceleration due to gravity (m/s.sup.2); L=wave length (m); and d=sea depth (m).

6. The method as claimed in claim 1, wherein, for a sea depth being greater than 0.05 times the wave length but less than half of the wave length, the wave celerity of the constituent sine waves is predicted by: $\left({\mathrm{celerity}}_{\frac{L}{20}<d<\frac{L}{2}}=\sqrt{\frac{\mathrm{gL}}{2\pi }}\tanh \left(2\pi \frac{d}{L}\right)\right)$ where: g=acceleration due to gravity (m/s.sup.2); L=wave length (m); and d=sea depth (m).

7. The method as claimed in claim 1, wherein the step of: the control system automatically acting on at least one of the one or more control signals in advance of the predicted sea surface profile to actuate one or more active stabilizers to thereby control the rolling motion of the marine vessel, comprises the step of: calculating the degree of actuation required to be fed into the active stabilizer at what instant so that a stabilization effort is deployed as the marine vessel encounters the sea condition corresponding to the predicted sea surface profile, so as to prevent roll of the marine vessel.

8. The method as claimed in claim 1, wherein the step of: determining a predicted sea surface profile using the detected actual sea surface profile, comprises the additional initial step of: calculating an allowance for spreading.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) There now follows a description of an embodiment of the disclosure, by way of non-limiting example, with reference being made to the accompanying drawings in which:

(2) FIG. 1 shows a perspective view of a marine vessel illustrating roll of the vessel;

(3) FIG. 2 shows a perspective view of a marine vessel according to an embodiment of the disclosure; and

(4) FIG. 3 shows a perspective view of the vessel of FIG. 2 showing the sensing geometry.

(5) It is noted that the drawings may not be to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION

(6) Referring to FIG. 2, a system for countering the rolling motion of a marine vessel according to an embodiment of the disclosure is designated generally by the reference numeral 100.

(7) The system 100 is shown installed on a marine vessel 10. The marine vessel 10 is provided with one or more (two, in the embodiment shown in the figures) active stabilizers 140.

(8) In the present embodiment, the two active stabilizers 140 take the form of steerable pod thrusters 140.

(9) The system 100 comprises one or more sensors 110, one or more control systems 120, a computer 130, and one or more active stabilizers 140.

(10) The present embodiment comprises three sensor arrays 110, a first sensor array 110 directed forwards along the longitudinal axis 30 of the marine vessel 10, a second sensor array 110 directed outwardly across the port beam 60, and a third sensor array 110 directed outwardly across the starboard beam 70.

(11) These sensor arrays 110 are radar sensors. However, in another arrangement of the system the sensor arrays 110 may take the form of another sensor such as, for example, microwave or ultrasonic sensors.

(12) In another arrangement, the marine vessel may also be equipped with a sensor array directed forward over the bow, or an existing sensor array may be realignable to look forward, and the same technique of analysis, decomposition, phase shift and subsequent recombination for ahead seas to generate an approximation to a future wave form will be used to form a prediction of heave and pitch response at specific instances in the future. Other than in the case of SWATH type vessels and some types of catamarans and hydrofoils, there is currently no practicable means of control over pitch response. In these cases therefore, the system would be intended primarily to provide an estimate of the predicted motion for use by independent but linked control systems embedded in other vessels, platforms or structures, such as Landing Systems, docking systems, replenishment at sea systems of heave compensated cranes or winches. Such systems may or may not be autonomous in nature, but it is anticipated that the primary beneficiaries of providing such information would be systems capable of autonomous decision making.

(13) The sensor arrays 110 are connected to the computer 130. The computer 130 is then connected to the or each control system 120. The or each control system 120 is then connected to each of the active stabilizers 140.

(14) In use, as shown in FIG. 3, the sensor arrays 110 scan an area of sea 112 extending from the vessel through a near field area 114 to a far field area 116. The sensor arrays 110 generate a dataset that characterizes the sea condition approaching the vessel 10.

(15) As illustrated in FIG. 3, the sensor array 110 scans in both the horizontal plane 117 and the vertical plane 118. Horizontally, the scan area 112 is defined by a horizontal field angle 113, while vertically the scan area 112 is defined by a vertical field angle 115.

(16) In the example illustrated in FIG. 3, the scan area 112 encompasses four wavefronts, or wave crests, 80.

(17) The characterized sea condition data defines a first surface profile 82 of the approaching wave field 80. This characterized sea condition data in the form of the first surface profile 82 is transmitted to the computer 130.

(18) The computer 130 receives the first surface profile 82 from the sensor arrays 110, processes this data, in conjunction with a real-time data stream relating to the speed and heading of the vessel 10, to produce a predicted second surface profile 84 of the wave field at some point in the future when it will impinge on the vessel 10.

(19) The computer 130 then goes on to generate one or more control signals in dependence on the relationship between the predicted second surface profile 84 and the vessel 10. The or each control signal is then transmitted to the active stabilizers 140 to cause the active stabilizers 140 to generate a stabilizing moment 142.

(20) This stabilizing moment 142 is determined to be sufficient to exactly counter the rolling moment resulting from the interaction between the predicted second surface profile 84 of the approaching wave field and the vessel 10. In this way, the stabilizing moment 142 counters the rolling moment and maintains the vessel 10 in an athwardtships level configuration.

(21) Referring to FIG. 3, a landing system for landing an unmanned aerial vehicle (UAV) 160 on a marine vessel 10 is designated generally by the reference numeral 200. The UAV 160 comprises a landing control system 161.

(22) The landing system 200 comprises a system 100 for countering the rolling motion of a marine vessel 10, as described above, together with a communications module 166.

(23) The communications module 166 is adapted to communicate bidirectionally between the system 100 and the landing control system 161 of the UAV 160.

(24) In use, the communications module 166 transmits positional data relating to the position and orientation of the vessel 10. This positional data is then used by the landing control system 161 of the UAV 160 to navigate a landing path 164 onto a deck of the vessel 10.

(25) The foregoing description of various aspects of the disclosure has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and obviously, many modifications and variations are possible. Such modifications and variations that may be apparent to a person of skill in the art are included within the scope of the disclosure as defined by the accompanying claims.