Embodiments of the present invention are directed toward mooring systems for vessels, and more specifically, towards mooring systems that compensate for motion of the moored vessel and/or in response to the load or tension on the ropes, mooring lines, and/or hawsers connected to the vessel.
This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present techniques. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present techniques. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Mooring systems for marine vessels have not changed in principle since the early days of sail. A vessel is moored when it is fastened to a fixed object such as a bollard, pier, terminal, quay or the seabed, or to a floating object such as an anchor buoy. Mooring is often accomplished using thick ropes called mooring lines or hawsers. The lines may be constructed of fiber, natural or synthetic, or metal wire, or a combination of both wire and fiber. The lines are fixed to deck fittings on the vessel at one end, and fittings on the shore, such as bollards, rings, or cleats, on the other end. Once the lines are passed between the vessel and mooring hooks mounted on the pier or shore, they are heaved tight. On large ships, this tightening can be accomplished with the help of heavy machinery called mooring winches or capstans. For the heaviest cargo ships, more than a dozen mooring lines can be required.
As noted above, mooring lines are usually made out of synthetic materials such as nylon. Nylon has a property of being elastic. This elasticity has its advantages and disadvantages. The main advantage is that during an event, such as a high wind or the close passing of another ship, excess stress can be spread among several lines. On the other hand, if a highly-stressed nylon line does break, or part, it causes a very dangerous phenomenon called “snapback” which can cause fatal injuries.
Typical mooring systems work well when forces are relatively small and/or constant in force and direction. When the forces are varied, the vessel starts to sway and surge on its moorings. When the forces are large or their frequency approaches the natural frequency of the mooring system, the vessel can move enough to render brakes (i.e. exceed the capacity of the brakes on the mooring line winches on the vessel) or part the mooring lines.
Existing vessel-mooring systems manage these wave load issues in several ways:
Limiting the size of waves (and thus wave loads) that the vessel-mooring system can be exposed to. This is a minor issue for terminals in protected waters, such as harbors, but can have a significant effect on the ability to moor a vessel at an offshore terminal, such as the Adriatic LNG terminal.
Increasing the size and number of mooring lines. This makes the system stronger and able to work in larger waves, at a cost. There is still a wave limit, for example in long period waves, such as those longer than 10 seconds, ships can only be moored in wave heights of one meter or less. Most vessels are limited in the number of mooring lines they can handle.
Adjusting the stiffness of the mooring lines. Adding stretchable tails to the mooring lines changes the stiffness of the system, which in turn changes the natural period, which in turn changes the extent of resonance and dynamic amplification. At least one company has proposed the addition of mechanical springs. While these systems reduce the chance of a line breaking they can result in even more pronounced surge motions.
With the presently available technologies, vessel-mooring systems can reach their limits when the swell has a significant wave height of about one meter.
The need still exists for new approaches to the mooring of a vessel. In particular, there is a need for new approaches due to unsafe conditions created when wave heights increase beyond one meter, which is frequently encountered at offshore terminals.
Embodiments herein relate to a mooring apparatus that includes an actuator connected to a mooring hook and the mooring base. The actuator provides translational movement of the mooring hook towards the mooring base. The mooring apparatus also includes a vessel motion detection system and a mooring apparatus control system. The mooring apparatus may include a mooring line tension gauge. The vessel motion detection system provides an input indicative of vessel motion to the mooring apparatus control system. The mooring apparatus control system then provides an output signal to the appropriate mooring system(s) which results in adjustment of the mooring line tension in the appropriate mooring system(s).
Embodiments herein relate to a method of controlling a mooring system which includes mooring a vessel to a terminal using one or more mooring lines and one or more mooring hooks connected to a terminal. A vessel motion detection system detects motion of the vessel and provides a signal to a mooring control system which can control the movement of the mooring hooks of the mooring system. The mooring control system can then let out or retract the appropriate mooring hooks in response to the input from the vessel motion detection system to oppose the detected motion of the vessel. The vessel motion detection system can provide a signal to the mooring control system which is indicative of vessel direction, rotation, speed, and/or acceleration. The mooring control system can also determine which mooring lines may be aiding the detected direction of the motion of the vessel and decrease the tension in those lines by letting out the appropriate mooring hooks. Embodiments herein also may include a mooring line tension system which provides a signal to the mooring control system. The mooring control system may control the mooring hooks such that mooring line tension is minimized or optimized. The mooring control system may therefore provide a method of avoiding excessive mooring line tension and damaging mooring lines or mooring equipment and provide a safer work environment. The mooring control system may also minimize motion of a vessel alongside a terminal and keep the vessel-based manifold system in approximate alignment with the terminal's unloading or loading facilities. Thus, the mooring control system may allow safer and continued operations in conditions that were previously unsafe or prevented unloading or loading operations.
Methods for use thereof and methods of manufacture thereof are also disclosed.
The foregoing and other advantages of the present techniques may become apparent upon reviewing the following detailed description and drawings of non-limiting examples of embodiments in which:
In the following detailed description section, the specific embodiments of the present techniques are described in connection with preferred embodiments. However, to the extent that the following description is specific to a particular embodiment or a particular use of the present techniques, this is intended to be for exemplary purposes only and simply provides a description of the exemplary embodiments. Accordingly, the invention is not limited to the specific embodiments described below, but rather, it includes all alternatives, modifications, and equivalents falling within the true spirit and scope of the appended claims.
As used herein, “control system” typically comprises one or more physical system components employing logic circuits that cooperate to achieve a set of common process results. In an operation of a load-compensation mooring system, the objectives can be to maintain a particular vessel location and optimize line mooring line tension during challenging weather conditions. The control system can be designed to reliably control the physical system components in the presence of external disturbances, variations among physical components due to manufacturing tolerances, and changes in inputted set-point values for controlled output values. Control systems usually have at least one measuring device, which provides a reading of a process variable, which can be fed to a controller, which then can provide a control signal to an actuator, which then drives a final control element acting on, for example, a mooring hook or the base of a mooring hook system. The control system can be designed to remain stable and avoid oscillations within a range of specific operating conditions. A well-designed control system can significantly reduce the need for human intervention, even during upset conditions in an operating process.
Embodiments herein relate to a mooring apparatus that includes an actuator connected to a mooring hook and the mooring base. The actuator provides translational movement of the mooring hook away from and towards the mooring base. The mooring apparatus also includes a vessel motion detection system and a mooring apparatus control system. The mooring apparatus may include a mooring line tension gauge. The vessel motion detection system provides an input indicative of vessel motion to the mooring apparatus control system. The mooring apparatus control system then provides an output signal to the appropriate mooring system(s) which results in adjustment of the mooring line tension in the appropriate mooring system(s).
Embodiments herein relate to a method of controlling a mooring system which includes mooring a vessel to a terminal using one or more mooring lines and one or more mooring hooks connected to a terminal. A vessel motion detection system detects motion of the vessel and provides a signal to a mooring control system which can control the movement of the mooring hooks of the mooring system. The mooring control system can then let out or retract the appropriate mooring hooks in response to the input from the vessel motion detection system to oppose the detected motion of the vessel. The vessel motion detection system can provide a signal to the mooring control system which is indicative of vessel direction, rotation, speed, and/or acceleration. The mooring control system can also determine which mooring lines may be aiding the detected direction of the motion of the vessel and decrease the tension in those lines by letting out the appropriate mooring hooks. Embodiments herein also may include a mooring line tension system which provides a signal to the mooring control system. The mooring control system may control the mooring hooks such that mooring line tension is minimized or optimized. The mooring control system may therefore provide a method of avoiding excessive mooring line tension and damaging mooring lines or mooring equipment and provide a safer work environment. The mooring control system may be designed to act dynamically to alter the natural period of the moored vessel, thus reducing the likelihood of resonant response and dynamic amplification of loads in the mooring lines. The mooring control system may also minimize motion of a vessel alongside a terminal and keep the vessel based manifold system in approximate alignment with the terminal's unloading or loading facilities. Thus, the mooring control system may allow safer and continued operations in conditions that were previously unsafe or prevented unloading or loading operations.
Referring to
Referring to
Sway motions of a vessel and loads in its mooring lines are affected by wind, wave, and current acting on the vessel. Wind and current loads are essentially static. Wave loads, however, act at many frequencies and the wave loads that are near the natural period of the vessel-mooring system in sway can cause dynamic response, including resonance and amplification. The mooring lines which have some degree of elasticity act provide a spring-like effect in the mooring system. The six degree of freedom vessel-mooring system can be considered a lightly damped, spring mass system that will have natural resonance and amplification frequencies. Wave loads at resonance with the surge period can lead to excessive mooring line loads that may damage or break mooring lines and other mooring equipment and result in large vessel motions. One-time, or impulsive, wave loads can be amplified when they occur with a rise time that relates to the natural period of the vessel-mooring system.
Referring to
Referring to
In the illustrated embodiment of
In the embodiment shown in
The base 402 would move on the primary axis of the mooring lines that attach to the base. That is in the surge direction for spring lines, and in the sway direction for breast, head and stern lines.
Referring to
The embodiment of
An embodiment of the control system for the load compensating mooring system will be based on the motion of the vessel, similar to a Dynamic Positioning (DP) system. Primary input would come from vessel position tracking equipment such as MDL's Fanbeam® system. When motion of the vessel is detected, the appropriate mooring base will be driven to quickly increase the mooring line tension. As the movement of the vessel is slowed by the increased mooring line tension, the direction of the driven mooring base may be changed to decrease mooring line tension and to minimize spring back of the vessel. The computer will drive the mooring base to softly return the vessel to its original position, not exceed the recommended limits on mooring line tension, and minimize overshoot of the vessel.
For example, the breast hooks can be adjusted to compensate for external forces and maintain contact with the fenders while reducing fender compression and spring off. When motion of the vessel is detected towards the fenders the moorings would be rendered, i.e., let out to reduce the mooring breast line tension. Conversely, motion away from the fenders will cause the motion bases to be driven to quickly increase mooring breast line tension. The control system will control the bases to softly maintain the vessel on the fenders.
In some embodiments, the mooring control system may be designed to actuate the load compensating mooring system dynamically in order to alter the natural period of the moored vessel. For example, continuous changing of the mooring system stiffness reduces the magnitude of resonant response and dynamic amplification of loads in the mooring lines.
Referring to
In step 606, the tension in the appropriate mooring lines that oppose the detected motion of the vessel from step 604 is increased by a retraction of the appropriate load compensating mooring system. In optional step 608, the tension in the appropriate mooring lines that aid, i.e. are pulling in the motion of the vessel from step 604 is decreased by letting out the appropriate load compensating mooring system. In step 610, the tension in the retracted mooring lines may be decreased to avoid over-compensating or having a spring-back effect by the vessel. Step 610 may require the measurement of the mooring line tension, detection of a change in the vessel's motion in response to the retraction of the mooring system, such as a deceleration of the vessel's motion, or a combination of both. In an embodiment, the retraction of the mooring lines in step 606 may be controlled to minimize any spikes in tension of the lines.
The control logic will include controls to limit overload of mooring lines to the extent possible, up to the limit of motion of the base. The load compensating mooring system may have a locking mechanism to facilitate personnel working the mooring lines and also to save energy when conditions are benign and load compensating mooring system is not required. The load compensating mooring system may allow a vessel to safely maintain position alongside a terminal in 2 to 3 meter significant wave height, or approximately 2 to 3 times the present limit. It should also result in fewer broken lines and increase the safety of personnel working near mooring lines.
The computer system 700 may also include computer components such as computer-readable storage media. Examples of computer-readable storage media include a random access memory (RAM) 706, which may be SRAM, DRAM, SDRAM, or the like. The computer system 700 may also include additional computer-readable storage media such as a read-only memory (ROM) 708, which may be PROM, EPROM, EEPROM, or the like. RAM 706 and ROM 708 hold user and system data and programs, as is known in the art. The computer system 700 may also include an input/output (I/O) adapter 710, a communications adapter 722, a user interface adapter 724, and a display adapter 718.
The I/O adapter 710 preferably connects a storage device(s) 712, such as one or more of hard drive, compact disc (CD) drive, floppy disk drive, tape drive, etc. to computer system 700. The storage device(s) may be used when RAM 706 is insufficient for the memory requirements associated with storing data for operations of embodiments of the present techniques. The data storage of the computer system 700 may be used for storing information and/or other data used or generated as disclosed herein.
The computer system 700 may comprise one or more graphics processing units (GPU(s)) 714 to perform graphics processing. Moreover, the GPU(s) 714 may be adapted to provide a visualization useful in monitoring vessel motions and mooring line tensions according to the present techniques. The GPU(s) 714 may communicate via a display driver 716 with a display adapter 718. The display adapter 718 may produce a visualization on a display device 720. Moreover, the display device 720 may be used to display information or a representation pertaining to a mooring line tension, mooring system movement, vessel motion data including direction, speed, acceleration, etc., according to certain exemplary embodiments. Moreover, an exemplary embodiment of the display adapter 718 may comprise a visualization engine that is adapted to provide a visualization of such communication data. The I/O adapter 710, the user interface adapter 724, and/or communications adapter 722 may, in certain embodiments, enable a user to interact with computer system 700 in order to input information.
A user interface adapter 724 may be used to couple user input devices. For example, the user interface adapter 724 may connect devices such as a pointing device 726, a keyboard 728, and/or output devices to the computer system 700.
The architecture of system 700 may be varied as desired. For example, any suitable processor-based device may be used, including without limitation personal computers, laptop computers, computer workstations, and multi-processor servers. Moreover, embodiments may be implemented on application specific integrated circuits (ASICs) or very large scale integrated (VLSI) circuits. In fact, persons of ordinary skill in the art may use any number of suitable structures capable of executing logical operations according to the embodiments.
While the present techniques of the invention may be susceptible to various modifications and alternative forms, the exemplary embodiments discussed above have been shown by way of example. However, it should again be understood that the invention is not intended to be limited to the particular embodiments disclosed herein. Indeed, the present techniques of the invention are to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
This application is the National Stage of International Application No. PCT/US2013/021238, filed 11 Jan. 2013, which claims the priority benefit of U.S. Provisional Patent Application 61/592,928, filed 31 Jan. 2012 entitled LOAD COMPENSATING MOORING HOOKS, the entirety of which is incorporated by reference herein.
Filing Document | Filing Date | Country | Kind |
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PCT/US2013/021238 | 1/11/2013 | WO | 00 |
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WO2013/115958 | 8/8/2013 | WO | A |
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