The present invention relates to a method of damping the motion of a vessel. The present invention further relates to a method of damping the motion of a mass suspended from a suspension point on a support structure of a vessel. The present invention further relates to a vessel comprising a damping device.
In the field of marine operations, operations at sea are often carried out with vessels. An operation may be a lifting operation, a pipeline laying operation, an installation operation or a removal operation of a structure such as a wind turbine or a drilling platform, a rescue or salvage operation, a drilling operation for drilling hydrocarbons. Other operations may be a loading or unloading operation of a vessel at sea. Other operations may include the collecting and processing of hydrocarbons on an FPSO or other kind of vessel, or the unloading of the collected hydrocarbons from the FPSO to a shuttle tanker.
Other operations may include the launch of a space rocket from a marine platform or the collecting of data with a research vessel. Many other operations are performed at sea in the field of the art.
Generally, wind, waves and currents exert forces on the vessel, which forces cause movements of the vessel. In some cases, the natural period of the waves approximates or equals the natural period of a vessel. In that case, the vessel may tend to roll to substantial roll angles and have motions which are undesirable.
In some cases, these motions hinder the execution of the operation itself. It may be desirable to reduce the motions of the vessel at certain times.
The invention relates to a vessel comprising:
In an embodiment, the trajectory is curved.
In an embodiment, the support structure extends over a vertical distance from a centre of gravity of the vessel, providing a suspension point at a vertical distance from the centre of gravity of said hull, the damping device further comprising an elongate suspension organ via which the mass is suspended as a pendulum from the suspension point, the mass being able to make a pendular movement relative to said hull, wherein the damping device is configured to dampen the pendular movement of the mass relative to the hull.
In an embodiment, the damping device comprises an energy dissipation device constructed to dissipate energy from the moving mass.
In an embodiment, the damping device comprises at least one elongate damping organ which connects at least one support point on the hull with the mass and which is constructed to apply a damping force on the mass. The elongate damping organ will generally be a cable or line.
In an embodiment, the elongate damping organ is extendable and constructed to:
The extension may be provided by extending the elongate damping organ itself or by providing extra length.
In an embodiment, the elongate organ is a line, and the damping device comprises:
In an embodiment, the energy dissipation device comprises a generator which is coupled to the winch and which is constructed to operate as:
In an embodiment, the damping device is a passive device, requiring substantially no energy for damping the movement of the mass relative to said hull. If a generator is used, the spooling of the line onto the winch requires some energy, but relatively little in comparison with the amount of electrical energy which is generated when the mass moves away from the support point and pulls the line off the winch, thereby driving the generator which works as a dynamo.
In an embodiment, the support structure extends upwards from the hull, and wherein the mass is provided above the water level. In an embodiment, the support structure extends upwards from the hull, and wherein the mass is supported higher than the upper deck of the hull, wherein at least a part of the trajectory extends above the upper deck. The free space above the deck allows a substantial freedom of movement for the mass.
In an embodiment—when seen in top view—the trajectory is located eccentric to a longitudinal plane of symmetry of said hull.
In an embodiment—when seen in top view—the suspension point is located outboard of the perimeter of the hull, in particular on the right side or left side of the vessel. The suspension point is located at a horizontal distance from the center of gravity of the vessel.
In an embodiment, the support structure is a crane. A crane may already be present on a vessel for other reasons, and can be used for stabilizing the vessel as well.
In an embodiment, the support structure is positioned near the bow or stern of the vessel, in particular at a distance of less than 15 percent of a total length of the vessel.
In an embodiment, the damping device comprises:
In another embodiment, the damping device does not comprise a sensor for measuring the speed or tension but only provides a direct relationship between the payout speed of the line and the tension. This allows a relatively simple damping device.
In an embodiment, the damping device is constructed and arranged to provide a damping force which is:
In an embodiment, the damping device is constructed to provide a damping force on the mass which is maximized, i.e. if the speed of the mass exceeds a certain value, the damping force does not exceed a predetermined maximum value.
In an embodiment, the damping device is constructed to provide a damping force on the mass which is minimized for a maximum speed of the mass in a direction toward the support point, i.e. if the speed of the mass in a direction toward the support point on the hull exceeds a certain value, the damping force on the line does not fall below a predetermined minimum, in order to ensure that the line remains taut.
In an embodiment, the elongate damping organ comprises a piston with a dampener. With this embodiment, a direct dampening of the movement of the mass is possible.
In an embodiment, the vessel does not comprise a rail constructed for guiding the moving mass. The leaving out of a rail results in a relatively simple construction
In an embodiment, the moment of inertia of the vessel without the mass about a roll axis of the vessel is less than a factor 10, preferably less than a factor 5 greater than the moment of inertia of the mass about the suspension point.
In an embodiment, the support point is provided at a distance of less than 30% of the width of the vessel above a center of gravity of the vessel.
In an embodiment, the damping device comprises at least a first and second elongate damping organ, and at least a first and second support point, wherein the first support point and second support point are spaced apart in a direction perpendicular to the trajectory.
With this embodiment, it is relatively easy to control the movements of the mass, and it is in particular possible to control the orientation of the mass.
In an embodiment, the damping device comprises:
In an embodiment, the support structure extends over a horizontal distance from the hull and is constructed and arranged to support the mass at a substantial depth under water via the elongate suspension organ, wherein the elongate suspension organ has an elasticity and is constructed to act as a spring which allows an up-and-down oscillation of the mass when the vessel makes a rolling movement, wherein the damping device comprises a line which extends substantially vertically from the vessel to the mass, the line being coupled to an energy dissipation device and being constructed to apply a damping force on the mass.
The invention further relates to a damping device constructed and arranged for damping the movement of a vessel or of a mass, the damping device comprising:
The present invention further relates to a method of stabilizing a mass or a vessel, the method comprising:
In an embodiment, the method comprises:
In an embodiment, the method comprises dampening the roll motion of the vessel about at least one axis.
In an embodiment, the method comprises:
In an embodiment, the vessel comprises a reeling device for laying pipeline, the method comprising transferring a reel with pipeline spooled onto the reel to the vessel, 10 wherein the damping device is used to dampen the motion of the reel and/or the vessel during the transfer of the reel.
In an embodiment, the method comprises:
The above mentioned aspects and other aspects of the invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying figures in which like reference symbols designate like parts.
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The vessel 12 has a bow 13 and a stern 15. The vessel has an upper deck 21. The vessel has a moonpool 29 for pipe lay operations.
The natural roll period of the vessel may be 13 seconds or between 10 and 20 seconds.
The vessel may comprise a pipeline laying installation 19, as is diagrammatically shown in
In operation, multiple reels 34 may be positioned on the deck 21 of the vessel 12 for pipeline laying operations. For this end, the vessel comprises one or more reel supports on deck.
A support structure 16 in the form of a crane 16 is provided on the vessel 12. The crane comprises 16 a base 18 via which the crane 16 is connected to the hull 14. The crane further comprises a column 20 which extends upward over a vertical distance. The column 20 is connected to the base 18. Further, the crane 16 comprises a beam 22 which is pivotally connected to the column 20 at a pivot 24 and which extends over a horizontal distance. At least one line 26 extends from an upper part of the column 20 to the beam 22 for maintaining the beam in the desired angle a. The line is connected to a winch (not shown) and allows the beam to be pivoted relative to the column 20 over an angle a.
The column 20 and beam 22 are rotatable relative to the hull about a vertical axis 28 of rotation in the direction of arrow 30 over an angle β (shown in
A suspension point 32 is provided on the beam 22 from which a load 34 can be suspended via a line 36. The line 36 is typically connected to a winch 38 on the crane 16 or on the hull 14
The crane is positioned at one end 15 of the vessel 12, in this case the stern. This allows a relatively large portion of a working range of the crane to be located outboard of a perimeter of the vessel, when seen in top view. In use, the suspension point 32 is located outboard of the perimeter of the hull, when seen in top view, in particular on the right side or left side of the vessel.
It also allows a heavy load to be supported aft of the vessel, such that the entire length of the vessel can contribute in supporting the heavy load, in particular in preventing large rotations of the vessel 12 due to the weight of the load 34. The crane may also be positioned on the bow 15, with a similar effect on the working range.
The crane is positioned at a side of the vessel, in this case the right side. This further increases the outboard working range of the crane.
Cranes of this type are known in the field of the art and a skilled person will understand that different types of cranes exist which have a different construction but similar capabilities.
A damping device 37 comprises two winches 40, 42 which are mounted to the hull of the vessel. The winches 40, 42 define respective support points 41, 43. One winch 40 is located aft of the suspension point 32 and one winch 42 is located forward of the suspension point 32. This provides the benefit that the rotation of the mass 34 can be controlled.
A line 70, 72 extends from each winch 40, 42 to the mass 34. The lines 70, 72 may also be connected to the line 36 at a distance above the mass 34. The lines 70, 72 can be a cable, a chain, a dyneema line or another type of line or a combination of different materials.
The winches 40, 42 are mounted to the deck 21 of the hull. The winches 40, 42 are connected to respective generators 44, 46 via respective axes 45, 47.
The winches 40, 42 are located on an opposite side of a vertical plane 55 as the support construction 16 and the support point 32, wherein the longitudinal plane extends longitudinally and divides the vessel in a left half and a right half, see
In one embodiment, the damping device 37 comprises at least one first speed sensor 120 which is configured to measure a payout speed of the line 70, 72 from the winch 44, 46. The speed sensor 120 is coupled via line 124 to a control unit 122 which controls the energy dissipation device, so that in use a speed signal is transmitted from the sensor to the control unit. The signal represents the payout speed of the line 70, 72.
A second sensor 121, i.e. a tension sensor 121 is provided which is configured to measure the tension in the line 70, 72 and to generate a tension signal on the basis of the measured tension. The second sensor is coupled to the control unit 122 via a line 125.
Each winch 40, 42 is equipped with a speed sensor 120 and a tension sensor 121, and the control unit 122 is constructed to control both generators 44, 46.
The generators 44, 46 can be switched between two modes:
1. Energy dissipation mode, in which the line 70, 72 is spooled from the winch 40, 42 and the rotating motion of axis 45, 47 is converted into electric energy by the dynamos 44, 46. The damping force applied by the dynamos 44, 46 is adjustable, for instance in dependence of the weight of the mass 34. In energy dissipation mode, the generators 44, 46 act as energy dissipation devices. The tension in the line 70, 72, i.e. the brake torque exerted by the dynamo, for a given speed may be varied by varying the resistance over the dynamo. To this end, the dynamos 44, 46 are equipped with a variable resistor 126, shown in
2. Motor mode, in which the generators operate as electric motors and spool the lines 70, 72 onto the winch by a rotary movement. The electric motors 70, 72 use little energy because only energy is required for taking in the excessive line in order to keep the lines 70, 72 taut. The mass 34 itself is substantially not pulled in motor mode.
The load (or mass) 34 is shown as being suspended from the suspension point 32 via a line 36. The load 34 is a reel 34. The load can also be a different kind of load. For the invention, the mass of the load 34 relative to the mass (or water displacement) of the vessel 12 is relevant.
Instead of using dynamos, it is also possible to use controlled disc brakes to control the tension. It is also possible to use the disc brakes in addition to the dynamos, for instance at higher loads. Instead of an electric winch 40, 42, it is also possible to use a hydraulic winch having a hydraulic motor. The hydraulic motor can be use to drive the winch in motor mode and to brake the winch in energy dissipation mode.
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The suspension point 32 is provided at a horizontal distance 59 from a vertical axis 61 extending through the centre of gravity 54.
The first spring is defined by the hull characteristics. i.e. the relation between an angular rotation γ of the hull 14 and a roll moment 57 which is created by the forces of the water on the hull as a result of the rotation.
The first damper is defined by the damping action of the water, i.e. the rotating hull moves the water, and energy is dissipated in the water as a result of the moving water. This dampens the rotating movement of the hull 14. The water line is shown as line 53.
The second spring is determined by the pendular mass 34, i.e. a moment is created on the hull by a horizontal force 56 which is exerted on the suspension point 34 by the line 36 which carries the mass. The horizontal force 56 on the suspension point 34 is determined by the angle of deflection ε and the weight of the mass 34 itself. The moment on the hull 14 is determined by the horizontal force 56 on the suspension point (crane tip) 32 multiplied by the vertical distance 58 between the crane tip 32 and the center of gravity 54 of the hull.
The second damper is determined by the line 70, 72 extending between the mass and the winch, and the characteristics of the winch 40, 42 and the generators 45, 47. The damping force 52 is a function of the speed 60 of the mass relative to the support point, i.e. a function of the rotational speed of the generators 45, 47.
Operation
The present system may be used to dampen the motions of a vessel at sea, for instance when there are substantial waves. The motions of the vessel may cause operations to be halted, and the present system can dampen the motions to such an extent that the working conditions of the vessel are extended, i.e. a same vessel can operate in higher waves, and/or greater wind forces.
The system may also be used to dampen the motions of a load which is suspended from the crane, for instance when the load is transferred onto the vessel or from the vessel onto a barge or other delivery point.
In operation, a preference angle a and a preference angle β will be chosen for the crane, such that the position of the suspension point 32, i.e. the vertical distance 58 and the horizontal distance 59, relative to the hull is known. A mass 34 is suspended from the crane 16, for instance by picking the mass 34 up from the deck with the crane. It is also possible to pick up the mass from a barge as is shown in
The mass 34 is capable of making a pendulum movement along a curved trajectory 110 relative to the vessel, while forming angle ε with the vertical axis
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The setpoint 64 is compared at 131 with an actually measured tension F in the line 70, 72. This actual tension F is measured with tension sensor 121 which is mounted on the winch 40, 42. Box 132 depicts the control algorithm in which the difference between the desired tension 64 and the measured tension F in the line 70, 72 is used in a PID algorithm. With the PID algorithm a desired resistance R of the dynamo 44, 46 is calculated. This desired resistance R is fed to the dynamo 44, 46 in box 134. The variable resistor 126 of dynamo 44, 46 is adjusted accordingly. This results in a tension F of the line 70, 72 which is paid out by the winch 40, 42. The tension F is measured by the tension sensor 121.
The tension force F is exerted on the swaying mass 34 and dampens the motions of the swaying mass 34, which is shown in box 136. This results in a speed of the mass 34, 35 which directly results in a payout speed of the lines 70, 72. The payout speed of the lines is measured by speed sensor 120 which is mounted on each winch 40, 42. The measured speed 60 is fed back to control box 130.
The control diagram is a cascaded control loop, wherein the measured parameter in an outer control loop, i.e. the speed 60, is used to determine the set point, i.e. the force, of an inner control loop.
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The payout speed 60 can be positive or negative (i.e. taking in line). The tension 67 is maintained at a certain minimum to keep the line taut. This is carried out by switching the generators 44, 46 to motor mode and taking in the lines 70, 72.
When the pay-out speed 60 is positive, the generators are switched to energy dissipation mode and kinetic energy is converted to electric energy by breaking the winches 40, 42 with the dynamos 44, 46.
In use, a signal is transmitted from the speed sensor 120 to the control unit 122. The signal represents the payout speed of the line. The control unit 122 determines a desired tension, i.e. a setpoint of the tension in the line 70, 72, on the basis of the measured speed and a predetermined speed-tension relationship.
The control unit 122 further receives the tension signal from the tension sensor 121 and compares the measured tension with the setpoint. If the measured tension is lower than the desired tension, the control unit increases the resistance of the variable resistor 126 of the dynamos 44, 46. This is performed via a PID control algorithm. Other algorithms are possible. If the measured tension is greater than the desired tension, the control unit 122 decreases the resistance of the variable resistor 126 of the dynamos 44, 46 via the PID algorithm. In this way the tension in the line 70, 72 is controlled.
Between the minimum tension 67 and the maximum tension 66, the tension 64 is a linear function of the speed 60.
It is also possible that the relation between the speed 60 and the line tension 64 is carried out as a step function or a substantial step function. Such a relationship is also stored in a memory of the control unit 122. This implies that when the mass 34 is moving away from the winch, i.e. at a positive speed 60, the line tension is maintained at a maximum, and when the mass is moving toward the winch, i.e. at a negative speed 60, the line tension is maintained at a minimum.
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It can be seen in
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Further embodiment
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A second line 102 extends between a second suspension point 33 and the mass 34. The second line 102 extends substantially alongside and parallel to the first line 36. The second line 102 is reeved via the suspension point 33 to a winch 40 mounted on the deck 21 of the vessel. The second line 102 is configured and arranged to in use act as a damper for damping the vertical oscillation of the mass 34. The winch is coupled to a generator 44.
In use, the vessel rolls about its roll axis as a result of waves. The suspension point 32 makes a movement along a part of a circular arc 105 with the center of gravity 54 as the center of the circle. The movement of the suspension point 32 comprises both a horizontal component and a vertical component. The vertical component causes a vertical oscillation of the mass. The mass moves up and down (i.e. back and forth) along trajectory 110.
A length of the line 36, i.e. a depth of the mass 34, may be varied in order to vary the spring constant, if required. Multiple cables 36 may be provided.
When the mass 34 moves upwards relative to the suspension point 33, the generator acts as a motor to haul in excessive line 102. When the mass 34 moves downwards relative to the suspension point 32, the generator 44 acts as a brake which dampens the downward movement of the mass.
The action of the dampening line 102 works in addition to a dampening effect of the 20 water itself, which dampens the vertical oscillating of the mass 34.
In this way, the rolling motion of the vessel is dampened. This embodiment can do without a heavy weight which moves above the deck of the vessel.
It will be understood by a person skilled in the art, that the scope of the invention is not limited to the embodiments shown in the figures. Many variants and combinations are possible and are also envisaged, and the scope of the invention is only limited by the claims.
Number | Date | Country | Kind |
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2007165 | Jul 2011 | NL | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/NL2012/050517 | 7/19/2012 | WO | 00 | 5/13/2014 |
Number | Date | Country | |
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61510699 | Jul 2011 | US | |
61545668 | Oct 2011 | US |