System for stabilizing a ship

Abstract

 Control system for controlling the propulsion installation of a ship which during operation is propelled by at least two waterjets. The installation comprises actuators for controlling the direction of the waterjets in response to control signals, and a control unit for generating said control signals to said acutaors. The system comprises furthermore means for detecting the momentaneous roll angle of the ship and/or means for detecting the momentaneous pitch angle of the ship. Detection signals from said means are supplied to the control unit which modifies the control signals such that the roll movement and/or pitch movement of the ship is counteracted.

Description

[0001] The invention relates to a control system for controlling the propulsion installation of a ship which during operation is propelled by at least two waterjets, the installation comprising:
- actuators for controlling the direction of the waterjets in response to control signals, and
- a control unit which during operation receives setpoint signals and ship condition signals, which signals are processed according to a predetermined algorithm to generate control signals which are supplied to said acutators.

[0002] Such a control system is for instance known from the German Offenlegungsschrift DE 3 420 541. Both waterjets, which are controlled by this control system, are destined to propel the ship in various directions. In the situation in which both waterjets are directed mainly backwards by the corresponding actuators then the ship is propelled in forward direction. If both waterjets are directed by the respective actuators mainly in forward direction, then the ship will be propelled in backwards direction. If one of the waterjets by the respective actuator is directed forwards and the other jet is directed by the respective actuator backwards then the ship will start to move mainly in sidewards direction.

[0003] In general influencing the direction in which a ship moves by controlling the direction of the waterjets in relation to the length direction of the ship, in other words controlling the course of the ship by means of the waterjets, is considered as known. The control of the waterjets is carried out in principle by varying the angle between the direction vector of each waterjet and the vertical longitudinal cross-sectional plane through the ship.

[0004] In general the speed of a ship will be controlled by controlling the number of revolutions per minute of the motor driving the pumps which in turn are generating the waterjets. It is furthermore known to influence the speed of a ship by varying the angle between the waterjet direction vector and the horizontal plane. An increase of said angle will lead to a decrease of the horizontal vector component and therewith to a decrease of the propulsion force.

[0005] Varying the vertical angle between the direction vectors of the waterjets and the horizontal plane can also be used for trimming the ship. A system in which this feature is applied is for instance described in the US patent 3,756.185. As is described in this US patent, directing the waterjet somewhat downwards can be applied for tuning the vessel, in other words for influencing the average position of the vessel in relation to the horizontal plane in a speed dependent manner.

[0006] The object of the invention is now to develop the prior art system further such that the system is not only suited to propel a ship with predetermined speed in a predetermined direction, but is also suited to stabilize a ship, especially to diminish roll angle movements and pitch angle movements of the vessel.

[0007] According to the invention said object is fulfilled by a system of the type described in the heading paragraph, which is characterized in that the system comprises furthermore
- means for detecting the momentaneous roll angle of the ship or a parameter related therewith, and for generating corresponding roll angle signals, and that
- the control system receives said roll angle signals from said detection means, interpretes these roll angle signals as one of the possible ship condition signal and processes said signals according to said algorithm and supplies control signals to the actuators for controlling the direction of the waterjets such that the roll angle will be decreased.

[0008] During operation of this control system the directions of the waterjets are controlled out-of-phase (in counter phase) which means that from a reference position one of the waterjets is directed more downwards whereas the other waterjet is directed more upwards. It will be clear that therewith a roll movement of the ship is counteracted.

[0009] The above-mentioned object is also fulfilled with a control system of the type mentioned in the heading paragraph in that the system comprises furthermore
- means for detecting the momentaneous pitch angle of the ship or a parameter related therewith, and for generating corresponding pitch angle signals, and that
- the control system receives said pitch angle signals from said detection means, interpretes these pitch angle signals as one of the possible ship condition signal and processes said signals according to said algorithm and supplies control signals to the actuators for controlling the direction of the waterjets such that the pitch angle will be decreased.

[0010] During operation of this control system the directions of the waterjets are controlled in-phase, which means that from a certain reference position both waterjets are directed either more downwards or more upwards. It will be clear that therewith a pitch movement of the ship will be counteracted.

[0011] Preferably the control system is embodied such that both the roll movement as well as the pitch movement will be counteracted. An embodiment designed for this purpose is according to the invention characterized in that the system comprises
- means for detecting the momentaneous roll angle of the ship or a parameter related therewith, and for generating corresponding roll angle signals,
- means for detecting the momentaneous pitch angle of the ship or a parameter related therewith, and for generating corresponding pitch angle signals, and that
- the control system receives said roll angle signals and pitch angle signals from said respective detection means, interpretes these roll angle signals and pitch angle signals as possible ship condition signal and processes said signals according to said algorithm and supplies control signals to the actuators for controlling the direction of the waterjets such that both the roll angle and the pitch angle will be decreased.

[0012] Because in this embodiment the angle between the direction vectors of both waterjets and the horizontal plane can be varied under the influence of suitable control signals which comprise in-­phase components as well as out-of-phase (counter phase) components, both the roll movement and the pitch movement can be counteracted.

[0013] The invention will be explained in more detail with reference to the attached drawings.

Figure 1 illustrates very schematically a control system which is known from the state of the art.

Figure 2 illustrates a control system which is in agreement with the invention further developed and is especially destined for decreasing the roll movement of a ship.

Figure 3 illustrates a control system which is in agreement with the invention further developed and is especially destined for decreasing both the roll movement as well as the pitch movement of the ship.

Figure 4 illustrates a possible realization of a control unit in the system according to the invention using analog components.

Figure 5 illustrates a possible realization of the control unit in the system according to the invention using a computer system.

[0014] Figure 1 illustrates in the form of a schematic control diagram the components of a control system which is known as such. The ship, which is propelled by means of at least two waterjets is in general indicated by the reference number 1. The waterjets take care that the ship is propel led with a predetermined speed, registered or measured by the detector 2. The direction of the waterjets is determined for the port side by the PS-actuator 3 and for the starboard side by the SS-actuator 4. Both actuators 3 and 4 are controlled by means of an adjustment signal or setpoint signal which determines the desired speed and which is supplied to the input 6. This setpoint signal at the input 6 is in a comparator 5 compared with the momentaneous speed signal at the output 2 and as a result of this comparison an error signal is generated which is supplied to the actuators 3 and 4 to control said actuators 3 and 4 such that the desired speed is obtained and maintained. Especially the vertical angle between the waterjets and the horizontal plane is for this purpose increased if the speed has to be decreased or is decreased if the speed has to be increased.

[0015] It is remarked that the feedback from the output 2 to the comparator 5 is not present in all known applications. In simpler embodiments the setpoint signal 6 is directly supplied to the actuators 3 and 4.

[0016] Figure 2 illustrates a system which is further developed in agreement with the invention. The ship 1, which comprises the waterjet generators for generating the waterjets to propel the ship, is unchanged and so are both actuators 3 and 4 for controlling the direction of both waterjets. Apart from the relocation movement with a preset speed, determined by the setpoint signal at the input 6, the ship will move in some other ways. Especially the ship will carry out pitch and roll movements. The roll movement of the ship is in the embodiment of figure 2 detected by a detector 8 supplying a signal to the input 9 of the control unit 10. The control unit 10 receives furthermore a speed setpoint signal at the input 6.

[0017] The roll movement of the ship is preferably detected by determining the roll angle velocity because detectors suitable for that purpose are easily obtainable at reasonable prices. However, within the scope of the invention is also possible to detect the roll angle itself or another parameter which is related to the roll angle.

[0018] In the control unit 10 the input signal at the input 6, by means of which a predetermined speed is set, is converted into control signals for the actuators 3 and 4 in such a manner that the desired speed of the ship is obtained and maintained. Under the influence of these control signals the waterjets will simultaneously be directed somewhat more downwards if the speed has to be decreased or somewhat more upwards if the speed has to be increased.

[0019] The roll angle information at the input 9 is converted by the control unit 10 in further control signals for both actuators 3 and 4 which on the basis of these signals take care that the waterjets from the position, determined by the speed setpoint will move in vertical direction such that the roll movement of the ship is counteracted. If during this roll movement the port side of the ship is heading downwards and the starboard side of the ship is in agreement therewith heading upwards, then the actuators 3 and 4 will, under control of the control unit 10, change the vertical angle of both waterjets such that the starboard jet will be directed more downwards so that the downwards movement of the starboard side of the ship is counteracted. Simultaneously the starboard jet is moved somewhat upwards so that the average vertical angle of both waterjets and therewith the speed of the ship is not or hardly influenced.

[0020] In the same way a downwards movement of the port side of the ship in relation to the starboard side can be corrected by direction the port side jet somewhat more downwards and simultaneously moving the starboard jet somewhat more upwards.

[0021] In figure 2 the feedback of the speed information from the detector 2 to the comparator 5 in which said information is compared with the setpoint signal at the input 6 is omitted to obtain a more clearly readable drawing. However, it will be clear that such a feedback can be present in the embodiment of figure 2. Such a feedback can be realized separately but can also be implemented in the control unit.

[0022] Figure 3 illustrates a further development of a system according to the invention. The components 1 until 9 are already present in figure 2 and are functioning in exactly the same manner as described with reference to figure 2. Furthermore the system according to figure 3 comprises a second detector 11 for detecting pitch movements of the ship. The pitch movement of the ship is preferably detected by the determining the pitch angle velocity because suitable detectors for this purpose are easily obtainable at reasonable prices. However, within the scope of the invention it is also possible to detect the pitch angle itself.

[0023] The detector 11 supplies in this embodiment a signal corresponding to the pitch angle to the input 12 of the adapted control unit 10′. In the adapted control unit 10′ the setpoint signal at the input 6 is processed in such a manner that on the basis of this setpoint signal (and eventually on the basis of the feedback velocity signal derived from the detector 2, which feedback connection is also not illustrated separately in this figure) control signals are generated for the actuators 3 and 4 to adjust the average vertical angle of the waterjets in relation to the horizontal plane in such a manner that the desired speed of the ship is maintained.

[0024] The pitch movement of the ship is detected again by means of the detector 8 and the corresponding signal at the input 9 is processed by the control unit 10′ in such a manner that therewith both waterjets are in the above described manner moved in counter phase such that the roll movement of the ship is counteracted.

[0025] As already said furthermore in this embodiment the pitch movement of the ship is detected by means of the detector 11 and a signal, corresponding especially to the pitch angle velocity of the ship, is supplied to the input 12 of the control unit 10′. This signal is converted by the control unit 10′ in control signals for the actuators 3 and 4 to change the vertical angle between both waterjets and the horizontal plane in-phase, such that the roll movement is counteracted. If during such a roll movement the stern of the ship is moving downwards and the bow of the ship is moving upwards then this movement can be counteracted by directing both waterjets more downwards. If on the other hand the stern of the ship is moving upwards and the bow of the ship is moving upwards then this movement can be corrected by directing both waterjets more upwards. During this in-phase movement of both waterjets the control unit takes care that the average vertical angle between both waterjets and the horizontal plane does not change so that this roll angle correction does not have any influence on the average speed of the ship.

[0026] As a result of the combination of the signals on the inputs 9 and 12 the vertical movement vectors of both waterjets will on the one hand comprise an in-phase component, which takes care for the simultaneous movement of the waterjets upwards or downwards dependent on the roll movement of the ship, and will comprise on the other hand an out-of-phase component which takes care that both waterjets are in counterphase moved upwards or downwards dependent on the roll movement of this ship.

[0027] In a combined circuit, as is described above with reference to figure 3, the vertical movements of the waterjets are influenced by the actuators 3 and 4 in such a manner that dependent on the speed, roll angle or pitch angle the following adjustments will be obtained.
- speed adjustment:
To set a lower speed than the maximum speed both waterjets can be directed under a certain angle downwards. The angle is fixed dependent on the setpoint signal and corresponds with a predetermined speed.
- roll angle compensation:
To eliminate the roll angle movement of the ship both waterjets are, in the rithm of the pitch movement, simultaneously or in-phase moved upwards or downwards in such a manner that the pitch movement of the ship is counteracted. In combination with the speed setting, this rithmical upwards or downwards in-phase movement of both waterjets will take place with respect to a selected vertical reference angle which correspond to the desired speed setting.
- roll angle correction:
For correcting the roll angle the vertical angles between both waterjets are changed in counter phase in the rithm of the roll movement to direct both waterjets more or less downwards such that the roll movement is counteracted. In combination with the speed setting this modulation of the waterjet directions will take place with respect to the vertical reference angle which corresponds to the desired speed setting. If furthermore the pitch angle correction is applied than the in-phase control for pitch angle correction and the out-of-phase control for roll anlge correction are carried out in combination with respect to the reference angle corresponding to the desired speed setting.

[0028] It will be clear that the combination of speed setting, roll angle compensation and pitch angle compensation will result into a complicated movement pattern, however, tests have indicated that the desired effect can be obtained, i.e. a suppression of the pitch and roll movement of the ship and thereby simultaneously maintaining the preset speed of the ship.

[0029] Figure 4 illustrates in more detail a possible realization of the control unit 10′ by means of analog components. In figure 4 are illustrated again the ship 1, the PS-actuator 3, the SS-actuator 4, the detector 8 for detecting the roll angle velocity of the ship 1, the detector 11 for detecting the pitch angle velocity of the ship 1 and the speed detector 2 for detecting the speed of the ship 1. The speed setpoint signal 6 will be compared in the comparator 5 with the momentaneous speed and an error signal will be supplied to the control unit 10˝. As is illustrated this control unit 10˝ comprises two amplifiers 13 and 14 for amplifying the signals of the detectors 8 and 11 with a predetermined factor. The amplified signals are supplied to the respective summing means 15 and 16 in which the various signals are combined. Especially in the summing means 15 the speed error signal and the pitch angle signal are added and from the resulting sum signal the roll angle signal is subtracted. In the summing means 16 all three signals are added together. It will be clear that figure 4 describes only the principle of an analog embodiment of the system and that in practice other components can be added such as for instance an amplifier between the detector 2 and the summing means 5.

[0030] Figure 5 illustrates the principle diagram of an embodiment in which the control unit is implemented by means of a computer 10‴. It is assumed in this figure that when eventual analog to digital conversion of the signals delivered by the detectors 2, 8 and 11 is carried out in the computer 10‴. The computer 10‴ is preferably programmed such that a combination of PID-controllers is simulated by means of which controllers the sensor signals are converted into control signals for the actuators 3 and 4. The implementation of such an embodiment based on the data found in this description is considered within reach of an expert in this field.

[0031] It is finally pointed out that the control does not operate if the ship has to be propelled with maximum speed. In that case a vertical angle between the waterjets and the horizontal plane will result into a decrease of the horizontal propelling force of the waterjet. Under circumstances it might therefore be preferable to restrict the maximum settable speed in such a manner that it is possible to direct the waterjets with a sufficient angle in vertical direction to obtain the desired compensation of roll movement and/or pitch movement. Eventually such a restriction can be made dependent on the actual local circumstances. If the ship is subjected to strong roll movements then a stronger vertical swaying movement of the waterjets will be necessary to obtain a desired level of compensation which leads to a larger restriction of the maximum speed than in case of minor roll movements.

[0032] Above nothing is said about changing the direction of the waterjets under control of the actuators to influence the direction in which the ship moves, in other words those waterjet movements which are destined to bring the ship on a predetermined course and to maintain the ship thereon. The steering of the course of a ship by means of the waterjets is considered as generally known. As such furthermore control systems are known in which sideward movements of the waterjets are used not only for course correction, but also for counteracting roll movements of the ship. Such control systems are generally indicated by the term "rudder/roll" systems and are considered as known to the expert in this field.

[0033] It is possible to combine the system according to the invention with such a rudder/roll system in such a manner that an integral control system is obtained for controlling the speed and the course on the basis of setpoint signals and for obtaining a stabilization with reference to pitch and roll movements. In an application of such a control system the actuators for pitch and roll angle correction can be controlled such that the waterjets are not only moved in vertical direction but are simultaneously moved in horizontal direction. Especially in such a case the vertical movements can be restricted because part of the desired compensation can also be realized with the horizontal components of the movement vector.

[0034] Above the general term "ship" is used, however it will be clear that the term "ship" includes not only a conventional ship or vessel which is propelled by two waterjets, but includes for instance also a floating platform which can be propelled and manoeuvred eventually by means of more than two waterjets. In such a case the invention can be applied for a combined control of the vertical angles between the various waterjets and the horizontal plane. If desired, and if the configuration of waterjets does allow it then in such an embodiment it is possible to maintain the platform at a desired position, in other words to maintain a zero speed and to stabilize simultaneously the against roll or pitch movements.

Claims

1. Control system for controlling the propulsion installation of a ship which during operation is propelled by at least two waterjets, the installation comprising:
- actuators for controlling the direction of the waterjets in response to control signals, and
- a control unit which during operation receives setpoint signals and ship condition signals, which signals are processed according to a predetermined algorithm to generate control signals which are supplied to said acutators, characterized in that the system comprises furthermore
- means for detecting the momentaneous roll angle of the ship or a parameter related therewith, and for generating corresponding roll angle signals, and that
- the control system receives said roll angle signals from said detection means, interpretes these roll angle signals as one of the possible ship condition signal and processes said signals according to said algorithm and supplies control signals to the actuators for controlling the direction of the waterjets such that the roll angle will be decreased.

2. Control system for controlling the propulsion installation of a ship which during operation is propelled by at least two waterjets, the installation comprising:
- actuators for controlling the direction of the waterjets in response to control signals, and
- a control unit which during operation receives setpoint signals and ship condition signals, which signals are processed according to a predetermined algorithm to generate control signals which are supplied to said acutators, characterized in that the system comprises furthermore
- means for detecting the momentaneous pitch angle of the ship or a parameter related therewith, and for generating corresponding pitch angle signals, and that
- the control system receives said pitch angle signals from said detection means, interpretes these pitch angle signals as one of the possible ship condition signal and processes said signals according to said algorithm and supplies control signals to the actuators for controlling the direction of the waterjets such that the pitch angle will be decreased.

3. Control system for controlling the propulsion installation of a ship which during operation is propelled by at least two waterjets, the installation comprising:
- actuators for controlling the direction of the waterjets in response to control signals, and
- a control unit which during operation receives setpoint signals and ship condition signals, which signals are processed according to a predetermined algorithm to generate control signals which are supplied to said acutators, characterized in that the system comprises furthermore
- means for detecting the momentaneous roll angle of the ship or a parameter related therewith, and for generating corresponding roll angle signals,
- means for detecting the momentaneous pitch angle of the ship or a parameter related therewith, and for generating corresponding pitch angle signals, and that
- the control system receives said roll angle signals and pitch angle signals from said respective detection means, interpretes these roll angle signals and pitch angle signals as possible ship condition signal and processes said signals according to said algorithm and supplies control signals to the actuators for controlling the direction of the waterjets such that both the roll angle and the pitch angle will be decreased.

4. Control system according to one of the preceding claims, characterized in that the control system furthermore comprises
- means for detecting the momentaneous speed of the ship and for generating a corresponding speed signal and that
- the control system during operation receives said speed system from said detection means, interpretes said speed system as one of the possible ship condition signals and processes said signal according to said algorithm and supplies control signals to the actuators for controlling said actuators such that not only the roll angle and/or the pitch angle will be decreased but furthermore the speed is maintained and a speed value corresponding to the thereto related setpoint signals.

5. Control unit for applying a system according to one of the claims 1 to 4, characterized in that the control unit comprises means for amplifying the row angle signal and for combining the amplified roll angle signal with the setpoint signal such that during operation control signals will be generated which, when they are supplied to the actuators, will result into an out-of-phase (counter phase) control of the waterjets.

6. Control unit to be applied in a system according to one of the claim 2 to 4, characterized in that the control unit comprises means for amplifying the pitch angle signal and for combining said amplified pitch angle signal with the setpoint signal such that during operation control signals will be generated which, when they are applied to the actuators, will result in an in-phase control of the waterjets.

7. Control unit to be applied in a system according to one of the preceding claims 3 or 4, characterized in that the control unit comprises
- means for amplifying the roll angle signal
- means for amplifying the pitch angle signal and
- means for combining the amplified pitch angle signal and the amplified roll angle signal with the setpoint signals such that during operation control signals will be generated with in-fase components and out-of-phase components, which in­phase components will, when they are supplied to the actuators, result into a control of the waterjets mainly in the same direction whereas the out-of-phase components will, when they are supplied to the actuators, result in a control of the waterjets mainly in opposite direction.

8. Control unit to be applied in a control system according to one of the claims 1 to 4, characterized in that the control unit comprises a computer which is programmed such that a suitable number of PID-controllers is simulated, destined to process the ship condition signals and setpoint signals into control signals for the actuators.

9. Ship comprising a control system according to one of the preceding claims 1 to 4.

Drawing