Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
  • B63B35/003—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for for transporting very large loads, e.g. offshore structure modules
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B77/00—Transporting or installing offshore structures on site using buoyancy forces, e.g. using semi-submersible barges, ballasting the structure or transporting of oil-and-gas platforms
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B1/00—Installations or systems with accumulators; Supply reservoir or sump assemblies
  • F15B1/02—Installations or systems with accumulators
  • F15B1/021—Installations or systems with accumulators used for damping
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
  • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
  • F15B9/00—Servomotors with follow-up action, e.g. obtained by feed-back control, i.e. in which the position of the actuated member conforms with that of the controlling member
  • F15B9/02—Servomotors with follow-up action, e.g. obtained by feed-back control, i.e. in which the position of the actuated member conforms with that of the controlling member with servomotors of the reciprocatable or oscillatable type
  • F15B9/03—Servomotors with follow-up action, e.g. obtained by feed-back control, i.e. in which the position of the actuated member conforms with that of the controlling member with servomotors of the reciprocatable or oscillatable type with electrical control means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
  • F16F9/00—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium
  • F16F9/10—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium using liquid only; using a fluid of which the nature is immaterial
  • F16F9/14—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect
  • F16F9/16—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts
  • F16F9/18—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts with a closed cylinder and a piston separating two or more working spaces therein
  • F16F9/20—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts with a closed cylinder and a piston separating two or more working spaces therein with the piston-rod extending through both ends of the cylinder, e.g. constant-volume dampers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16F—SPRINGS; SHOCK-ABSORBERS; MEANS FOR DAMPING VIBRATION
  • F16F9/00—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium
  • F16F9/10—Springs, vibration-dampers, shock-absorbers, or similarly-constructed movement-dampers using a fluid or the equivalent as damping medium using liquid only; using a fluid of which the nature is immaterial
  • F16F9/14—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect
  • F16F9/16—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts
  • F16F9/22—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts with one or more cylinders each having a single working space closed by a piston or plunger
  • F16F9/26—Devices with one or more members, e.g. pistons, vanes, moving to and fro in chambers and using throttling effect involving only straight-line movement of the effective parts with one or more cylinders each having a single working space closed by a piston or plunger with two cylinders in line and with the two pistons or plungers connected together
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63H—MARINE PROPULSION OR STEERING
  • B63H25/00—Steering; Slowing-down otherwise than by use of propulsive elements; Dynamic anchoring, i.e. positioning vessels by means of main or auxiliary propulsive elements

Definitions

• the invention relates to a method for use in offshore load transfer, wherein a floater is taken to a transfer site at sea and loads are transferred between the floater and the transfer site, the floater being positioned horizontally relative to a marine structure at the transfer site before and during the load transfer operation.
• the invention relates to a floater having adjustable buoyancy for offshore transport, installation and removal of structural elements.
• the invention has been especially developed in connection with the need for the mounting and dismantling of large structural elements offshore, in particular in connection with the removal of existing fixed platform installations at sea.
• the floater may have any form that is adapted to or suitable for offshore transport, installation and removal of structural elements.
• the floater may, for example, be of the type taught in US Patent No. 6,244,786 Bl, which illustrates and describes a column stabilised floater, or it may be a catamaran-like floater, for instance, as taught in US Patent No. 3,078,680.
• Other embodiments of suitable floaters can be found in EP 000 462 Al, FR 247 992, NO 160424, NO 171495 and NO 135056.
• the floater will be deployed for transport and installation (or removal) of large structural elements (hereinafter referred to as "loads") to (from) fixed structures or a floating structure (hereinafter referred to as “marine structures”) offshore, in open sea where the floater will be exposed to waves.
• loads large structural elements
• marine structures floating structure
• the load is preferably supported from underneath by means of beam elements (load- transfer beams) projecting from the floater.
• beam elements load- transfer beams
• the weight of the load is transferred from the floater to the marine structure by ballasting the floater (filling ballast into the ballast tanks of the floater).
• the said methods for load transfer of large structural elements to/from marine structures could introduce huge dynamic horizontal loads from the floater onto the marine structure when such an operation is carried out offshore, in open sea (where the floater is exposed to waves) if the floater is not designed to absorb horizontal motions, especially wave frequency motions, relative to the marine structure during the load transfer operation. This could result in damage to the marine structure, especially to old, corroded oil and gas platforms where the upper parts have to be removed from the platform substructure (jackets).
• the horizontal dynamic load from the floater could introduce a large bending moment at the bottom of the substructure (that is fixed to the seabed), large shear forces in the substructure as well as large horizontal forces at the contact point between the so-called topsides of the platform and the load-carrying point on the load-transfer beams.
• Fig. 1 shows an example of such a structure, where hinged beams are used.
• One of the main objects of the present invention is to be able to reduce the horizontal motions of the floater caused by waves, without thereby introducing large dynamic horizontal loads on the marine structure, and to keep the vessel in a target position, within a horizontal frame, relative to the marine structure.
• the purpose is to simplify the design of the load transfer system, to reduce the weight and the costs of the load transfer system and to avoid collisions between the floater and the marine structure during the preparations for and the execution of the load transfer operation.
• Another feature of the invention is that it will stabilise the load (removed from the marine structure) and secure it horizontally (sea securing) relative to the floater at so- called lift off (after the load transfer operation has been completed).
• the inventive idea resides in the use of a floater which is provided with a horizontal positioning system.
• the system consists of at least three hydraulic jacks with drive and control systems and supporting structures.
• the jacks are mounted on the floater by cardanic suspension, which allows the jacks to tilt in the vertical and horizontal plane.
• Pistons in the hydraulic jacks, or extension beams fitted to the pistons, are connected to the load (or the marine structure).
• One or more hydraulic jacks regulate the longitudinal position and motions (surge) of the floater relative to the load (or the marine structure), and one or more hydraulic jacks regulate the transverse position and motions (sway) of the floater relative to the load (or the marine structure).
• a minimum of two jacks control the orientation and the yaw motion relative to the load (or the marine structure).
• the horizontal motions of the floater consist of wave frequency motion and low frequency motion. Small forces are required to stop the low frequency motion compared to those required to stop the wave frequency motion (the low frequency forces will only constitute about 10% of the force required to stop wave frequency motions). By eliminating the low frequency motions, the amplitude of the floater's horizontal motions (oscillation) could be reduced by more than 50%.
• the drive and control systems for the hydraulic jacks will be such that they virtually eliminate the low frequency motion and thus reduce the horizontal motions of the floater considerably, whilst allowing wave frequency motions and preventing a substantial dynamic load from the floater from acting on the load or the marine structure.
• each positioning system must first be activated, which means that it has to be coupled between the floater and the load (or the marine structure), whereupon certain operational characteristics have to be activated.
• the horizontal positioning system will include one or more spring elements which will constantly try to pull the floater back to its target position, and this will be done with or without damping elements.
• the spring elements may be in the form of a linear or non-linear spring.
• the spring characteristic force/deflection
• the spring characteristic may have different stiffness in different deflection ranges.
• this element may have a speed-independent or speed-dependent force.
• a combination of these two dependencies may help to obtain an optimal horizontal positioning system.
• Fig. 1 shows a known floater with hinged beams
• Fig. 2 is a graph showing the spring characteristic of the new system
• Fig. 3 is a schematic top view of a U-shaped floater
• Fig. 4 shows a hydraulic system according to the invention
• Fig. 5 shows a variant of the hydraulic system, with a special damping effect
• Fig. 6 is a more artistic presentation of a floater during a load transfer operation.
• the U-shaped floater 1 in Fig. 1, see also Fig. 6, is provided with a plurality of hinged beams 2 for supporting a load 3, see also Fig. 6 which shows a load in the form of a superstructure placed on a tower 4.
• the required function of the horizontal positioning system can be achieved by means of electric drive solutions or by means of hydraulic drive solutions, and here a hydraulic drive solution is presented.
• the object of the invention is to provide a system having the aforementioned properties and of the passive type.
• Fig. 3 is a top view of a U-shaped floater 1, which floater 1 is positioned around a load 3, mounted on top of a marine structure 4 (Fig. 6).
• the floater 1 can make horizontal movements in three different directions (degrees of freedom). These are motions known as surge, sway and yaw. The first two are linear motions, one in the longitudinal direction and the other in the lateral direction of the floater 1. The last-mentioned motion is rotation about a vertical axis.
• HPS 1 is mounted in the longitudinal direction and affects the surge motion
• HPS 2 and HPS 3 are mounted in the lateral direction and affect the sway and yaw motions. These systems are also shown in Fig. 1.
• Each HPS system has the same mode of operation, but the dimensions and the absolute values of the force deflection characteristics may be different.
• a hydraulic cylinder 5 with two piston rods 6 and 7 and with a piston 16 is connected to the floater 1 by means of a cardanic suspension 8 (or other device that allows the hydraulic cylinder 5 to tilt horizontally and vertically), and the piston 7 is connected to the load 3 (or the marine structure).
• a cardanic suspension 8 or other device that allows the hydraulic cylinder 5 to tilt horizontally and vertically
• the piston 7 is connected to the load 3 (or the marine structure).
• Other types of cylinders and fixing means may also be used.
• a hydraulic pump/motor 9 with variable displacement is used for the transfer of hydraulic oil from one side of the cylinder to the other.
• This pump/motor is advantageously driven by an electric motor (m), and this combination is suitable for 4- quadrant operation, which means that all force directions and speed directions are possible. By means of this arrangement, it is possible to move the piston rods 6, 7 in a controlled manner at all times.
• Each cylinder side is connected to a set of (at least) three hydro-pneumatic accumulators 10, 11 and 12.
• the number of accumulators is related to the number of the different spring characteristics.
• the accumulator 10 is a low-pressure piston accumulator with a built-in mechanical end stop 14. In Fig. 4, the low-pressure piston 15 has been shifted into a position resting against the mechanical end stop 14.
• the accumulator 11 is used for a low to medium pressure range, and may be of the membrane or piston type.
• the accumulator 12 is for the medium to high pressure range and is of the piston type. These are the preferred accumulator types. Other types may be used providing they have the same properties.
• a movement of the piston 16 to the right will cause the left-hand chamber of the cylinder 5 to increase in volume and the required volume of oil will then flow out of the accumulator 10.
• the pressure in the right-hand chamber of the cylinder 5 will increase, whilst the pressure in the left-hand chamber will fall.
• the force F on the piston rod 7 thus increases when the movement is to the right.
• the desired spring stiffness in the first part of the deflection range (0 - x ⁇ can be obtained. Beyond this range, the force F will change from 0 to Fi.
• the pressure in the accumulator 11 will be practically identical to the pre-fill pressure in the accumulator 12, and now (at deflection x > x ) the oil will flow into this last-mentioned accumulator from the right-hand cylinder chamber in the cylinder 5.
• the size and the pre-fill pressure of the accumulator 12 are chosen so that the spring stiffness (force deflection curve) will have a different, lower value than the value in the small deflection range (here reference is being made to "one" stiffness related to the accumulator 12).
• the maximum stroke length of the cylinder 5 is greater than the maximum stroke length required by the motions of the floater.
• the oil on one side of the system can be transferred to the other side, and in this way the position of the spring characteristic can be shifted to the extent required, without the piston 16 reaching its end positions in the cylinder 5.
• FIG. 4 also shows two (remotely) adjustable safety relief valves 17. These have a number of functions:
• the hydraulic elements 18 will include stop valves (manually or electrically operated) to enable the cylinder position to be “frozen” when the system is out of operation.
• the box 19 represents standard hydraulic equipment, which is used for filling the system, for pressurising the system, flushing, filtering and cooling. This equipment is not described in more detail because it does not constitute essential elements of the invention.
• a solution is described that has a certain spring characteristic, without a special damping effect.
• a cylinder configuration as shown in Fig. 5 may be used.
• This configuration includes an "inner" cylinder 20 with two pistons 21 and 22 which are connected to the rod 31, and four oil chambers or sub-chambers 23, 24, 25 and 26.
• the two central sub-chambers 24, 25 are connected to a hydraulic system with multiple hydro-pneumatic accumulators, as shown in Fig. 4. In this figure only one accumulator 27, 28 is shown symbolically for each sub-chamber.
• the two outer sub-chambers 23 and 26 in the "inner" cylinder 20 are connected to each other via a fixed or (proportionally controlled) adjustable flow restrictor 29. This serves as a damping element in the system.
• the damping characteristic is "freely programmable".
• An important advantage that is obtained with the invention is the possibility of dampening the relative motions between the floater and the load from the time of the so- called lift off of the load from the marine structure and until the moment this phase is complete (on condition that the piston rod is connected to the load and not the marine structure).
• the horizontal motion of the structural element relative to the floater will then be dampened by the spring characteristics of the hydraulic jacks.
• the structural element can then be fastened to the floater (sea secured) by closing the valves 18. When these valves are closed, possible high loads are limited by the pressure relief valves 17.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Transportation (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Ocean & Marine Engineering (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Earth Drilling (AREA)
• Ship Loading And Unloading (AREA)

Applications Claiming Priority (3)

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• 2002
  • 2002-02-08 NO NO20020630A patent/NO317430B1/no not_active IP Right Cessation
• 2003
  • 2003-02-07 WO PCT/NO2003/000047 patent/WO2003066425A1/en not_active Application Discontinuation
  • 2003-02-07 AU AU2003244392A patent/AU2003244392A1/en not_active Abandoned
  • 2003-02-07 EP EP03737521A patent/EP1478568A1/de not_active Withdrawn
  • 2003-02-07 US US10/503,879 patent/US20050095069A1/en not_active Abandoned

Non-Patent Citations (1)

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