Autonomous anchoring method and system for foundations of offshore structures

Abstract

A method for the autonomous anchoring of foundations for offshore structures consisting of a self-floating concrete caisson manufactured in a floating dock, capable of being towed to their final location, provided with internal vertical cells, which are divided into cells that are interconnected with each other and equipped with emptying and filling devices that allow the regulation of the ballast level for anchoring when they are filled with seawater. This method comprises the following stages: constraining the foundation, fastening and mooring by at least three tugboats pulling radially on the foundation to be anchored from at least 3 different directions; connecting the different sensors needed for controlling the operation with a control unit; gradual and controlled sinking of the foundation until it reaches its position of installation on the seabed; and final ballasting of the foundation.

Claims

1. A method for autonomous anchoring of foundations for offshore structures, built on a floating dock and capable of being towed to a final location, consisting of a self-floating concrete caisson, provided with internal vertical cells, closed at a top by means of a slab that covers all or almost all cells in which the caisson is divided, which are interconnected with each other and equipped with emptying and filling devices that allow the regulation of the ballast level for anchoring when they are filled with seawater, comprising the following steps: a) constraining the foundation, fastening and mooring with at least three tugboats pulling radially on the foundation to be anchored from at least 3 different directions, spaced apart at a similar angle, so that once the foundation is vertically located on its final installation site, it is kept in the same vertical position throughout the entire anchoring process; b) connecting the different sensors needed for controlling the operation with a control unit receiving the information from said sensors, preferably located on the emerged platform of the foundation that remains above sea level once the foundation has been totally anchored, said control unit integrating means of communication with the directional system between the tugboats, and means of communication between a GPS station and a fixed GPS reference base located at a fixed point next to the installation location of the foundation; as well as the implementation of a decision-making support system, which enables visualizing and controlling the progress of the anchoring process; c) gradual and controlled sinking of the foundation until it is slowly submerged, remaining in a neutral position under the water and subsequent anchoring of the same in a next to neutral seaworthy condition until it reaches its position of installation on the seabed; d) final ballasting of the foundation, flooding of all the cells that the foundation incorporates and disengaging the tugboat lines.

2. The method, of claim 1, in which a filling of the cells of the foundation is carried out gradually, in groups of cells that are next to each other, in a controlled manner, either through control software or manually, using the greater or lesser filing of an area or areas of the foundation to achieve tilting and in this way controlling the heel and/or maximum trim of the structure during each stage of anchoring.

3. The method of claim 1, in which a tension of the tug lines of the different tugboats is controlled in order to cause displacement and thereby control a heel and/or maximum trim of the structure during each stage of anchoring.

4. The method of claim 1, in which a speed and a maximum acceleration of the sinking of the foundation is controlled by modifying a filling rate of the cells of the foundation with seawater.

5. A system for autonomous anchoring of foundations for offshore structures having automatic control and operation of gravity foundations, powered by an electric energy generating system and a compressor, comprising: an assembly of sensors that measure different variables that affect the foundation, enabling to determine movements, a degree of filling of the cells that make up the foundation, as well as a position of the foundation with respect to what will be a final anchoring site of the foundation; a control unit which receives signals from the sensors and from a position of a caisson at all times, the caisson conforming the foundation with respect to the location the control unit controlling a valve and other means of filling the caisson and the necessary corrections of said means of filling as well as the direction and the tension with which a tugboat pulls radially on the foundation to be anchored from at least 3 different directions spaced apart at a similar angle; such that the foundation gradually sinks until the foundation lies on a seabed in the final anchoring site; a means of communication between different pieces of equipment receiving information from the sensors, from a GPS station located on the foundation and from a fixed GPS reference station located at a fixed point next to the final anchoring site of the foundation, the different pieces of equipment, the GPS station, and the fixed GPS reference station communicating information to the control unit; and a user interface for decision-making support and the execution of different control instructions to said control unit, including means for visualizing the variables and progress of the operation, software in which sequence programming actions are implemented, and means that enable manual intervention in the operation.

6. The system according to claim 5, in which the sensors of the system fulfill the following functions: measuring the level of ballast in cell groups; measuring the interior air pressure in the cells; measuring the rotations of a structure that take place; determining the absolute position of the structure; determining the relative position of the structure with respect to the surface on which it is installed; measuring the vertical heave on the structure and the inertial response of the structure; recording the accelerations and speed rates that structural elements undergo; detecting contact of the structure with the seabed, as well as possible impacts on other structures; and measuring local conditions of a marine environment.

7. The system of claim 5 in which the control unit directs and regulates the following variables through the elements that integrate it: input and output of the liquid ballast in groups of cells; interior pressure in the cells; horizontal position of the structure (on a ground plan); dynamic control of trim and heel (rotations); dynamic control of structure installation on the seabed; relative position with respect to the installation surface (distance to the seabed); vertical heave and its inertial response; inertial response of the structural elements that it may transport or carry; possible impacts on other structures, marine environments or the seabed; and contact of the structure with the seabed.

8. The system of claim 5, further comprising: a receiver unit for information from the sensors located on the emerged platform of the foundation; a wireless intercommunication unit (Wi-Fi) between the vessels intended as control centers and the receiver and control unit for information from the sensors located on the foundation; a UHF communication system between GPS stations and the GPS-RTK base (fixed reference point); and a means of communication between a sensoring and control units.

9. The system of claim 5, in which the user interface comprises: means for a visualization of sensory variables and control (status) and of the progress of each of the operational status variables recorded by the sensoring and control subsystem during stages of anchoring; software in which a sequence of operational actions (opening of valves and voltages in the winches of the vessels) and of operational threshold by stages of anchoring, as well as automatic correction of thresholds are implemented; means that enable manual intervention on the operation; means of warning for exceedances of operational threshold and system operations status; and a status cross check for starting a new stage or restarting after operational shutdowns.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In order to complement the description presented herein, and with the aim of gaining a better understanding of the characteristics of the invention, a set of drawings is attached to this specification, wherein, by way of non-limiting examples, the following has been represented:

(2) FIG. 1 shows the tugboat system (2) arranged in a layout for the installation of any given foundation (1).

(3) FIG. 2 shows the elements involved in the anchoring system, wherein the following can be distinguished: The foundation to be anchored (1). The tugboats (2). The positioning system (3). The platform or fixed point of reference for the reference system (4).

(4) FIG. 3 shows an elevation of a foundation with a structure in whose upper area the wind turbine or the meteorological station will be fixed and on which the most important sensoring and control elements, arranged on the object to be anchored, have been pointed out: Valves (5) Filling level sensors (pressure sensors) (6) Submersible pumps (7) Accelerometer-gyroscope (8) GPS-RTK antennas (9)

(5) FIG. 4 shows a general flowchart of the autonomous anchoring system.

(6) FIG. 5 offers a schematic representation of the main stages of anchoring operations.

DETAILED DESCRIPTION OF THE INVENTION

(7) The proposed system for anchoring integrates its different elements into the equipment comprising the assembly of the same: tugboats (2), foundation to be anchored (1), base platform or fixed point of reference (4) and positioning network (3): see FIG. 2).

(8) The user interface consisting of a command control server or SCADA (Supervisory Control And Data Acquisition) system is installed in the tugboats (2), which system enables remote visualization, monitoring and control of the process. It is a closed loop system, i.e., it adjusts the control through feedback of the output signal. An 8-port switch, two modems for wireless communication and at least two CPUs and auxiliary screens are also installed in the tugboats (2), which enable the visualization of the status of the process variables by means of an interface. This interface has particular tabs for visualizing the position of the element to be installed, filling level of the cells, alarms, electrical parameters, tension in the mooring lines, etc. It also enables visualizing the status of the instrumentation such as the valves (5), pumps (7) and filling (6) and movement (accelerometer-gyroscope) sensors (8).

(9) The control unit, preferably consisting of a PLC (Programmable Logic Controller) is installed in an electric cabinet on the foundation platform (1) that remains emerged, which in turn communicates with the command control system in the vessels by means of Wi-Fi modems.

(10) The positioning equipment is be made up of an RTK reference base installed at a fixed reference point (3), a GPS-RTK antenna (9) installed on the foundation platform (1) that remains emerged and the accelerometer-gyroscope (8) also installed on the foundation platform (1).

(11) The system controls the measurements carried out by the sensoring subsystem, analyzes movement frequencies and filters them so that it can respond to them by setting new reference thresholds. Thus, it becomes independent from external factors: it turns into an autonomous anchoring system.

(12) The system for autonomous anchoring is susceptible of industrial application in the offshore wind power and civil engineering sectors. While foundation construction may be more or less industrialized for mass production, the process of laying the foundation is largely depends on the capabilities of the operator due to the large number of variables involved in the operations and the uniqueness of the stages of anchoring.

(13) FIG. 5 shows several stages of anchoring operations: Constraint of the foundation, attaching, and connection to tugboats (FIG. 5.1) Submerging (FIG. 5.2) Sinking (FIG. 5.3) Installation on the seabed (FIG. 5.4) Final ballasting (FIG. 5.5)

(14) In the stage of constraint of the foundation (1) at least three tugboats (2) are fastened and moored, which pull radially on the foundation to be anchored from at least 3 different directions, spaced apart at a similar angle, so that once it is located vertically on its final installation site, it is kept in the same position throughout the entire anchoring process. See FIG. 1.

(15) Before or after the previous stage, the following connections are carried out: The different sensors needed for controlling the operation. The control unit, located above sea level on the emerged platform of the foundation. The different communication equipment: with the directional system between the tugboats, between the GPS stations and with a fixed GPS reference base located at a fixed point next to the installation location of the foundation. And the implementation of a decision-making support system, which enables visualizing and controlling the progress of the anchoring process.

(16) Once all the instrumentation is installed and operating, and the tugboats (2) keep the cables that are pulling on the foundation (1) under tension, so that it is floating vertically on the point of the seabed on which it is to be installed, anchoring is carried out by gradually sinking the foundation, the whole process being controlled by the described system, until the foundation is slowly submerged (FIG. 5.2), remaining in neutral position below the water. Subsequently, the foundation continues to be anchored in a next to neutral seaworthy condition (FIG. 5.3) until it reaches its position of installation on the seabed (FIG. 5.4).

(17) Finally the foundation is ballasted, all the cells contained in the foundation are flooded and the tugboat lines are disengaged (FIG. 5.5).

(18) Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.