WO2024087996A1

WO2024087996A1 - Compliant offshore wind turbine foundation structure system

Info

Publication number: WO2024087996A1
Application number: PCT/CN2023/121560
Authority: WO
Inventors: 袁小荣; 杨宇婷
Original assignee: 袁小荣
Priority date: 2022-10-26
Filing date: 2023-09-26
Publication date: 2024-05-02
Also published as: CN115467356A

Abstract

A compliant foundation structure system for an offshore wind turbine, utilizing a structure comprising: a support system, having linear springs formed by a stay cable system; and a mass body formed by a floating hinged bottom-supported pile leg; and formed having a constrained two-degree-of-freedom rigid body motion system, thereby constructing an offshore wind turbine compliant "super-flexible" foundation structure support system. Under the action of an external load, the support system of the offshore wind turbine compliant foundation structure causes the floating pile leg to generate a compliant simple rocking about a hinge point at the bottom of the pile leg, with a certain amplitude of pitch and roll; this rocking motion allows inertial forces to balance the huge environmental load on the floating pile leg, thereby greatly reducing the balancing generally needing to be carried out by internal forces of the structure. The invention expands an applicable range of water depths, simplifies the structure of the pile body, reduces the environmental load response of the support system, reduces dependence on geological conditions, optimizes the inherent modes of vibration of the pile body system, simplifies turbine control policy, and significantly reduces costs related to aspects such as not using dynamic cables, etc.

Description

A compliant offshore wind turbine foundation structure system

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims priority to a Chinese patent application with application number 202211319129.X filed with the State Intellectual Property Office of China on October 26, 2022, entitled “A compliant offshore wind turbine foundation structure system,” the entire contents of which are incorporated by reference in this disclosure.

Technical Field

The present disclosure belongs to the field of marine engineering, and in particular to the field of a compliant offshore wind turbine foundation structure system.

Background technique

Offshore wind power generation is developing at a very rapid pace. At present, in my country's offshore wind power field, fixed foundations such as monopiles are still the most economical foundation schemes for offshore wind power projects. The cost of water depths below 40 meters is close to parity. It is an inevitable trend for wind farm resources to be developed in deep seas. However, with the increase of water depth, since monopiles and various fixed foundation structures are cantilever structures in principle, they have typical lever characteristics. When the water depth increases, which is equivalent to the cantilever extension, the various loads acting on the foundation will increase sharply, and the pile legs must be inserted into the deeper seabed. The cost of the pile legs will be greatly increased due to factors such as pile length, pile diameter, and wall thickness. The water depth of 40 meters for single pile foundations (the length of the pile legs may exceed 100 meters at a water depth of 40 meters) and the water depth of 60 meters for jacket foundations are the dividing lines between engineering adaptability and economy. Conventional fixed foundations have the limitation that they cannot remain economical in areas with a water depth of more than 50 meters, resulting in a sharp increase in the comprehensive cost of offshore wind power fixed foundation wind turbines. Usually, when the water depth is greater than 50 meters, the use of floating foundations will be considered. Compared with fixed foundations, floating foundations for offshore wind turbines can be moved, are not restricted by water depth, and are easy to dismantle. They can be installed in deep sea areas with richer wind energy resources. However, the development of offshore floating foundation wind power generation is not yet mature at this stage. For example, the biggest feature of the floating foundation of offshore wind turbines is that they have a large swing at sea. Due to their huge size and mass, complex structure, and complex motion characteristics in wind and waves, there are still many technical difficulties in their motion prediction, load analysis, mooring positioning, structural strength, and integrated design. There are still many unresolved problems in structural optimization, and the wind power conversion efficiency will also be affected, requiring complex control strategies to deal with it. In addition, the floating foundation wind turbine will have to use dynamic cable layout for cable connection due to the shaking of the platform, which will cause structural fatigue and seriously affect the reliability of the system. All of these will directly lead to a significant increase in the comprehensive cost of floating wind turbines. Although floating wind turbines are an important research direction for replacing and upgrading fixed wind turbines, they will not be able to achieve a similar level of economic efficiency as fixed offshore wind power within at least 10 years. There is also a semi-fixed offshore wind power foundation theory, that is, when the water depth exceeds 40 meters, the bottom of the wind turbine pile legs are connected to the seabed by hinges and fixed by cables. However, this semi-fixed wind power foundation is still pursuing the characteristics of fixed piles (the deflection of the pile leg structure is about 100 mm) to limit the movement of the wind turbine pile legs, resulting in its cables being subjected to huge tension. According to the level of existing engineering materials, it is impossible to achieve engineering with the capacity of inclined cables alone. Therefore, the development of an "excessive water depth" The low-cost offshore wind turbine foundation structure system (60-150 meters level) has very important practical significance.

Summary of the invention

A compliant foundation structure system for an offshore wind turbine generator adopts a support system of a linear spring formed by a cable system and a mass body structure formed by a floating hinged bottom pile leg to form a rigid body motion system with two degrees of freedom (pitch and roll) constrained, thereby constructing a compliant "super-flexible" foundation structure support system for an offshore wind turbine generator. Under the action of external loads, the support system of the compliant foundation structure of the offshore wind turbine generator will cause the floating pile leg to produce a simple swing of pitch and roll compliance of a certain amplitude around the bottom hinge point of the pile leg. Through this swinging motion, the inertial force balances the huge environmental load on the floating pile leg, greatly reducing the balance that usually needs to be performed through the internal force (extremely high stiffness and strength) of the structure. The applicable range of water depth is expanded, the pile structure is simplified, the environmental load response of the support system is reduced, the dependence on geological conditions is reduced, the natural vibration mode of the pile system is optimized, the wind turbine control strategy is simplified, and the dynamic cable is eliminated. The relevant costs are significantly reduced.

A compliant foundation structure system for an offshore wind turbine generator comprises a floating pile leg system at the bottom of the wind turbine generator and a cable system with a linear extension characteristic, wherein the upper mooring connection point of the floating pile leg system is connected to the wind turbine generator system; the floating pile leg system comprises a floating pile leg, an articulated connection device, a pile leg anchoring device and a mooring connection point, the floating pile leg is an inverted cone-shaped cylindrical steel structure, the mooring connection point is located near the sea surface or above the sea surface and does not interfere with the fan blades of the wind turbine, the pile leg anchoring device is fixedly connected to the seabed, the articulated connection device arranged at the bottom of the floating pile leg is connected to the pile leg anchoring device The cable system with linear extension characteristics includes more than 3 high-strength cables (cables) with linear extension characteristics that are evenly arranged radially with the mooring connection point as the center. Each cable is equipped with a cable anchoring device and a tensioning connection device. The lower end of the cable is fixed to the seabed through the cable anchoring device, and the upper end of the cable is connected to the mooring connection point through the tensioning connection device. The elongation of the cable is not more than 4% at the usable load (30% of the breaking strength), thereby controlling the amplitude of the compliant rigid body motion swing of the floating leg system around the hinged connection device. The cable is equipped with a buoyancy system that eliminates its own weight, so that the cable can reduce the amount of deadweight sagging as much as possible.

The mooring connection point is provided with a cable tensioning connection device having the same number as the cable, one end of which is connected to the floating pile leg and the other end is connected to the cable. The cable bears the horizontal load generated by the wind acting on the wind turbine and the tower and the waves and currents acting on the pile leg, and by adjusting the cable stiffness (elongation), the pile leg has a certain "flexible" swinging motion in the horizontal direction.

The articulated connection of the articulated connection device does not transmit bending moment. Compared with the rigid connection (such as deep pile insertion), the amount of structural steel used is greatly reduced, and the requirements of the floating pile legs on the seabed geological conditions can be reduced. Compared with the fixed form of the bottom rigidly connected (pile insertion) cantilever beam pile leg structure system, the present invention is a compliant structural form because the inclined cable has a certain elasticity and the pile leg is fixed by a cross connection. It is equivalent to having a certain flexibility. The internal force distribution generated by the same external load, such as bending moment and shear force, will change greatly. The energy of the external force will be balanced by the inertial force through a certain range of movement, and the force transmitted to the cable structure will be reduced accordingly. In addition, the connection between the pile leg and the seabed adopts an articulated connection method, so that the support structure system of the wind turbine can only move in limited directions (pitch and roll), simplifying the difficulty of predicting the movement trajectory and attitude of the wind turbine (relative to the floating wind turbine support structure), and reducing the impact of movement on the applicability and power generation efficiency of the wind turbine. The horizontal movement of the wind turbine support structure system is limited by the tensioned cable to control the movement amplitude of the wind turbine within the adaptable range of the wind turbine, ensuring the safe and effective operation of the wind turbine. Under the wind, wave and current environmental load and working load, the structural system composed of the wind turbine and the support structure exhibits a small-amplitude rigid body movement mode, so that the huge energy of the wind, wave and current load acting on the pile leg can be transferred and released, and is transferred to the upper mooring connection point, which is mainly borne by the cable. Different from the traditional fixed rigid pile foundation structure system that generates a huge concentrated bending moment at the root of the pile leg, the new system greatly reduces the concentrated bending moment load on the pile leg structure and optimizes the pile leg structure design. In addition, the cable-stayed cable can also adjust the inherent motion cycle of the entire system through the configuration of tension and mooring stiffness, combined with ballast water adjustment (total mass), thereby greatly improving the adaptability to wind turbines and the adaptability to the environment. Furthermore, the cable-stayed cable can reduce the amount of sag due to its own weight as much as possible. When the cable-stayed cable is in the initial tensioned state, the sag caused by its own weight can be reduced as much as possible. This is conducive to improving the linearity of the elongation of the cable-stayed cable by reducing the additional elongation of the cable-stayed cable. This compliant swinging motion is simple, slight, and controlled, and has strong adaptability to the wind turbines carried, reducing complex control strategies (relative to floating platform foundations). The present disclosure has pioneered a principle of an offshore wind power generation foundation structure system, which greatly optimizes the response of various components of the offshore wind power generation foundation structure system to environmental loads, thereby greatly reducing the amount of steel used in the structure. The use of a structural integration method can achieve self-installation of the foundation structure, which can greatly reduce the installation cost. Under excessive water depth conditions (60 meters to 150 meters), it is estimated that the comprehensive cost of the wind power foundation structure using this principle system can be reduced by 50% compared with the fixed pile legs.

As mentioned above, further, a floating structure is provided in a certain range above the floating legs, the interior of the floating structure is a ballast water tank, and the buoyancy of the floating structure is equal to the sum of 60% to 80% of the total mass of the wind turbine and the total mass of the floating legs.

The pile legs are equipped with floating structures and ballast water functions to adjust the buoyancy and deadweight of the pile legs, reduce and control the gravity load acting on the pile legs, make the structure lightweight, and reduce the structural cost. It is also helpful to prevent the vertical direction of the pile legs from overloading and instability. In addition, the reduction in the total mass of the wind turbine and the foundation structure also significantly reduces the requirements of the entire wind turbine system on the bearing capacity of the seabed foundation.

As mentioned above, further, the floating pile legs are provided with counterweights within a certain height range at their roots, so that the center of gravity of the floating pile legs is located below the center of buoyancy. Adding counterweights to lower the center of gravity of the pile leg structure allows the pile legs to float vertically before installation, which is convenient for subsequent installation. As for the pile leg foundation itself, its floating capacity is much greater than its own gravity. Before the wind turbine is installed, it is necessary to inject ballast water to achieve the gravity required for the pile legs to connect to the seabed. After the wind turbine is installed, the ballast water is discharged to restore buoyancy and minimize the gravity load on the pile legs, but at least the static gravity required for the pile legs to connect to the seabed must be maintained.

As mentioned above, further, the pile leg structure can adopt a closed column structure or a spatial structure combined column structure composed of several small-section columns, which is convenient for pile leg assembly and reduces costs.

As mentioned above, further, the length of the lower half is not less than the length of the upper half. Taking the mooring connection point as the boundary, the length of the lower half is greater than or equal to the upper half to maintain the stability of the system.

As mentioned above, further, the floating pile leg system is suitable for a water depth of 60-150 meters. Compared with the traditional fixed pile legs, the present disclosure can be used in deeper water depths, and the cost is lower than that of the traditional fixed pile legs. Compared with the floating wind turbine, the compliant wind turbine foundation structure system (relative floating structure) will not have a large-scale six-degree-of-freedom motion state. The pile leg pitch and roll motion characteristics caused by the extension characteristics of the inclined cable are relatively simple, and the relative motion amplitude is relatively small, which does not constitute a large additional load on the wind turbine structure and does not have much impact on the power generation efficiency. In addition, the output cable connected to the wind turbine does not need to adopt the dynamic cable arrangement adopted by the floating wind turbine, and can adopt the same fixed cable arrangement as the fixed pile foundation, avoiding the fatigue and reliability problem analysis test process of the dynamic cable, and reducing the cost of the external transmission cable. The present disclosure provides a low-cost compliant wind turbine foundation structure system solution within the applicable water depth range, significantly reducing the pile leg load and cost, overcoming the adaptability and economic problems of the fixed pile legs in the transitional deep water area, and greatly improving the utilization rate of offshore resource development.

As mentioned above, further, the wind turbine is a vertical axis wind turbine.

A method for reducing the overall cost of an offshore wind turbine generator, wherein a floating leg at the bottom of the wind turbine generator is fixed to the seabed by an articulated connection device, an articulated connection device at the bottom of the floating leg is fixedly connected to the seabed so that the floating leg does not undergo lateral and longitudinal displacement, a linearly extending inclined cable system is arranged around a mooring connection point on the floating leg to fix the floating leg to the seabed, a constrained support system of a linear spring formed by the inclined cable system and a mass body formed by the floating articulated bottom-seated leg are formed into a two-degree-of-freedom quasi-oscillator system, and an offshore wind turbine generator is formed. The supporting system of the offshore wind turbine compliant foundation structure will produce a simple sway of pitch and roll compliance of a certain amplitude under the action of external loads. Through this swaying motion, the huge environmental load on the floating pile legs is balanced by inertial force, which greatly reduces the balance that usually needs to be achieved through the internal force of the structure; the inclined cables of the inclined cable system are connected to the floating pile legs through a tensioning connection device, and the deadweight of the inclined cables is eliminated through the floating system, so that the deadweight sag of the inclined cables is reduced as much as possible.

The floating pile legs fixedly connected to the lower part of the wind turbine are fixed to the seabed by an articulated connection device, and the articulated connection device at the bottom of the floating pile legs is fixedly connected to the seabed, so that the floating pile legs will not undergo lateral and longitudinal displacements. The linearly extended inclined cable system fixes the floating pile legs to the seabed through the mooring connection points on the floating pile legs, and the inclined cables of the inclined cable system are connected to the floating pile legs by tensioning connection devices. The dead weight of the inclined cables is eliminated by the buoyancy system, so that the dead weight sag of the inclined cables is reduced as much as possible; the linear spring-like constraint support system formed by the inclined cable system and the mass body formed by the floating articulated bottom-seated pile legs form a two-degree-of-freedom oscillator-like system, forming a compliant foundation structure of the offshore wind power support system. Under the action of external loads, the support system of the offshore wind power compliant foundation structure will produce a simple swing of two degrees of freedom (pitch and roll) with a certain amplitude of compliance. The rocking motion balances the huge environmental loads on the floating legs by inertial forces, greatly reducing the balance that is usually required to be achieved through the internal forces of the structure.

An offshore aquaculture space constructed by an offshore wind turbine compliant foundation structure system comprises the compliant foundation structure system, and deep-sea aquaculture fences are fixed on at least three inclined cables of the compliant foundation structure system. Each fence fixed on the inclined cable is used to create a closed space for sea aquaculture activities.

Beneficial Effects

Offshore wind power will inevitably develop from near shallow waters to deep seas. With the increase of water depth, especially when the water depth exceeds 50 meters, the cost of the original fixed single pile foundation increases sharply, making it almost impossible to achieve "grid parity". In the case of using floating wind power foundations in deeper waters, it is even more impossible to achieve a level similar to that of shallow water fixed pile foundations in terms of economy at this stage. These current situations mean that there is no technical solution with good economic efficiency for wind power development in deeper waters (40 to 150 meters) at this stage.

The present invention starts with the concept of "compliant" basic principle, and uses a linear telescopic cable (spring) + floating bottom-mounted articulated tower (mass body) to form an offshore wind turbine foundation structure system with certain swing characteristics. The load-bearing structure is optimized and the load is reduced as much as possible from the vertical direction, horizontal direction, motion characteristics, pile leg bottom connection structure and linear telescopic cable mooring device. Under the premise of ensuring the structural rigidity and strength, the deadweight of the structure can be greatly reduced. The present invention adopts a hinged method to fix the pile legs because the cable has a certain elasticity. Therefore, it is a compliant structural form for environmental loads, which is equivalent to a certain range of flexible follow-up and produces corresponding swinging motion. It should be emphasized that this simple limited motion form is relatively easy to accept for offshore wind turbines compared to the complex motion characteristics of floating foundation structures. The internal force distribution generated by the same external load, such as bending moment and shear force, will change greatly. The energy of the external force will be balanced by the inertial force through a certain amplitude of rigid body motion, and the load transmitted to the cable-stayed structure will be reduced accordingly, thereby reducing the construction cost of the structure and greatly reducing the restrictions of geological conditions. The present disclosure enables the cable-stayed compliant single pile foundation system to achieve a cost equivalent to that of the original 40-meter fixed single pile foundation at a water depth of about 100 meters, achieving affordable and economical development at a water depth of about 100 meters, which is impossible with various existing technologies.

First, in the vertical direction, the pile legs have a floating structure, which can effectively offset the force exerted on the pile legs by most of the deadweight of the wind turbine and the pile legs, and reduce the gravity load in the vertical direction. Therefore, the wall thickness of the pile legs can be reduced, and the diameter of the pile legs can be reduced to reduce costs.

Secondly, in the horizontal direction, by setting up inclined cable mooring points, the cantilever beam structure of the conventional single pile foundation inserted into the seabed (usually the length of the single pile foundation is about 100 meters at a water depth of 40 meters) is transformed into an articulated simply supported beam structure fixedly standing on the seabed. On the one hand, the part of the traditional single pile inserted into the seabed is completely eliminated, the length of the pile leg is greatly reduced (more than 50%), the amount of steel used is greatly reduced, and the huge costs associated with renting large pile-driving ships for pile driving operations are eliminated.

Secondly, the wind turbine support structure system has the characteristics of a compliant structural system under wind, wave and flow environmental loads and working loads. It manifests as a small-amplitude rigid body swaying motion, so that the huge energy of wind, wave and current loads acting on the pile legs can be transferred and balanced through the action of inertial force. Different from the traditional fixed rigid pile foundation structure system that will produce a huge concentrated bending moment at the root of the pile leg, this new structure system greatly reduces the concentrated bending moment load on the pile leg structure, optimizes the pile leg structure design, and greatly reduces the amount of steel used in the structure itself.

Fourth, the bottom of the pile leg is hinged and fixed to the seabed, which limits the vertical, longitudinal and lateral displacement of the wind turbine support structure. More than three tensioned inclined cables limit the yaw displacement of the wind turbine support structure. The wind turbine support structure system only has two degrees of freedom, namely, longitudinal and lateral motion, which simplifies the difficulty of predicting the wind turbine's motion trajectory and attitude (relative to floating wind turbines), reduces the complexity of the wind turbine control strategy, increases the effectiveness of wind turbine operation control, and improves the applicability and power generation efficiency of the wind turbine.

Fifth, the horizontal movement of the wind turbine support structure system is restricted by tensioned cable-stayed cables. Through the design of the mooring system and the use of cable-stayed cables with controllable stiffness, the movement amplitude of the wind turbine can be controlled within a safe range that the wind turbine can adapt to, thereby ensuring safe and efficient operation of the wind turbine.

Sixth, compared with floating wind turbines, the foundation structure system of compliant wind turbines will not have large-scale six-degree-of-freedom motion. The bottom is hinged to the fixed support structure on the seabed. The output cable connected to the wind turbine does not need to use the dynamic cable used by floating wind turbines. Instead, it can use the same fixed cable arrangement as the fixed pile foundation, avoiding the fatigue and reliability problems of dynamic cables and greatly reducing the cost of cable arrangement.

Seventh, the buoyancy system of the cable configuration has a buoyancy force equivalent to the deadweight of the cable, which can eliminate the gravity sag of the cable as much as possible and reduce the additional elongation of the cable. The tensioning connection device can adjust the tension of the cable and pre-tension the cable, which can effectively eliminate the nonlinearity of the structural elongation of the cable or steel cable.

Eighth, the combined effect of the bottom hinge of the pile leg and the fixed connection with the seabed, the pre-tensioning of the inclined cable, the configuration of the inclined cable with a buoyancy system, and the fixed connection between the inclined cable and the seabed makes the pile leg only have roll or pitch, eliminating the sway, vertical swing, vertical swing and bow swing movement, and the roll and pitch movement under the action of the inclined cable and its buoyancy system is equivalent to setting a spring on the pile leg, so that the pile leg performs simple harmonic motion, that is, linear motion. Further, taking the water depth of 100 meters as an example, the angle between the inclined cable and the seabed is 45°, then the length of the inclined cable is about 140 meters, and the elongation rate of the inclined cable material (the elongation rate of the material cannot be avoided no matter what material is used) is 2%-3%, then the elongation of the inclined cable is about 2.8 meters-4.2 meters, and the movement range of the pile leg is about ±2.8 meters-4.2 meters. The simple movement of a rigid body of this magnitude is easy for wind turbines to withstand. Taking this as an example, if the bottom of the pile leg is only hinged and restrained by a cable, and the wind turbine pile leg is to be kept as rigid as a fixed pile leg and not move, the cross-sectional area of the cable will increase by an order of magnitude, which is not feasible in engineering.

Ninth, the present invention combines the simplicity and stability of fixed structure foundations with the advantages of floating structure foundations that can adapt to greater water depths, and constructs a unique low-cost composite foundation system that can adapt to greater water depths. Under water depths of 40 to 180 meters, compared with various existing fixed foundations and various existing floating structure foundations, it has obvious applicability and cost advantages. In addition, compared with floating wind turbine systems, the present invention, like conventional fixed foundations, does not require Conducting ultra-long-term offshore experimental verification will also help to further reduce costs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the structure of an offshore wind turbine foundation system.

FIG. 2 is a schematic top view of the structure of the offshore wind turbine foundation system.

FIG3 is a schematic diagram of the structure of an offshore aquaculture space constructed by an offshore wind turbine foundation structure system.

FIG. 4 is a top view of FIG. 3 .

Description of labels:

1. Wind turbines

2. Floating legs

3. Handover connection mechanism

4. Pile leg anchoring device

5. Mooring connection point

6. Stay Cable

7. Cable anchoring device

8.Tension connection device

9. Sea surface

10. Seabed

11. Fence

Detailed ways

As shown in Figure 1-2, a compliant offshore wind turbine foundation structure system that can adapt to a water depth of 100 meters is composed of a mass body structure formed by a floating articulated bottom pile leg system and a support system using linear springs formed by a cable system to form a constrained two-degree-of-freedom (pitch and roll) rigid body motion system, constructing a compliant "super-flexible" foundation structure support system for offshore wind turbines.

The "super-flexible" foundation structure support system includes (with the mooring connection point as the dividing point) an upper wind turbine system (with a certain model with a total mass of 1,100 tons as a reference) and a lower compliant wind turbine foundation structure system.

The wind turbine system comprises a wind turbine 1 and a tower structure.

The compliant wind turbine foundation structure system mainly includes two major systems: the floating articulated leg system and the inclined cable system.

The floating leg system specifically includes:

1. A floating pile leg 2 with a length of about 130 meters, of which about 100 meters are below the water surface and about 30 meters are above the water surface. The specific form is a steel inverted cone tower structure with a ballast tank inside.

2. The mooring connection point 5, the specific structure of which is composed of a flange device, a cable connection point and a tensioning connection device 8, and the pile leg anchoring device 4, the specific form of which is a flat-plate gravity anchor.

3. The pile leg articulated connection device 3 is specifically in the form of a spherical universal joint.

The mooring connection point 5 is the dividing point of the overall system, responsible for the connection between the floating leg 3 and the tower of the offshore wind turbine 1 and the connection between the floating leg 2 and the cable system.

The floating pile leg 2 has an internal space provided with a ballast tank capable of accommodating seawater, and the buoyancy of the floating pile leg 2 can be adjusted by injecting and discharging ballast water.

As shown in FIG1 , the floating pile leg 2 has a pile leg anchoring device 4 at the bottom, which is a thousand-ton reinforced concrete flat-plate gravity anchor. It is not only a counterweight system for the floating pile leg 2, but also a load-bearing pad for the floating pile leg 2 to reduce the pressure on the seabed 10. A hinged connection device 3 is arranged at the center of the flat-plate gravity anchor, which is connected to the floating pile leg 2 as a whole. Before the wind turbine 1 is installed, the main structure of the floating pile leg 2 has a large reserve buoyancy, but because the floating pile leg 2 has a pile leg anchoring device 4 at the bottom, the center of gravity of the floating pile leg 2 is located below the buoyancy center, so the floating pile leg 2 can stand vertically and float on the sea surface 9. With the cooperation of the inclined cable system, the draft depth of the floating pile leg 2 is adjusted by injecting ballast water into the ballast tank. Since the ballast water gathers in the lower part of the ballast tank, the center of gravity of the floating pile leg 2 is always lower than the buoyancy center. Since the length of the floating pile leg 2 is greater than the water depth, the floating pile leg 2 can maintain a vertical upright state and gradually sink until it touches the bottom. The ballast water is continuously injected to make the net buoyancy of the floating leg 2 disappear, and the leg anchoring device 4 at the bottom is fixed to the seabed 10 under the action of gravity and friction.

After the wind turbine 1 is installed and connected with the floating pile leg 2, the weight of the wind turbine 1 will act on the floating pile leg 2, generating a large gravity load. At this time, part of the ballast water is discharged to increase the net buoyancy of the floating pile leg 2, which can effectively offset the weight of the wind turbine 1 and greatly reduce the support reaction force on the floating pile leg 2, which is conducive to the lightweight structure of the floating pile leg 2. The flat counterweight anchor, i.e., the pile leg anchoring device 4, has a large ground contact area, which can greatly reduce the pressure of the whole system mass of the wind turbine 1 on the seabed 10. At the same time, it has sufficient gravity and friction to fix with the seabed 10, and bear the static load and alternating load of the floating pile leg 2 in the longitudinal and lateral directions. The articulated connection mode of the articulated connection device 3 does not transmit bending moment. Compared with the conventional single pile rigid connection (requires deep pile insertion), the amount of structural steel is greatly reduced, and at the same time, the requirements of the floating pile leg 2 on the geological conditions of the seabed 10 can be reduced.

The top of the floating leg 2 is connected to the stay cable system.

The cable-stayed system specifically includes:

1. The specific structure of the stay cable anchoring device 7 is a flat-plate type gravity anchor.

2. The cable-stayed cable 6 is a high-strength steel cable.

3. The tensioning connection device 8, the specific structure of which is a spiral screw.

4. Mooring connection point 5, the specific structure is a strong connection ring.

The stay cables 6 are made of high-strength steel cables, and there are 8 of them (6-1 to 6-8) in total, which are evenly distributed radially around the floating pile legs 2, and the angle between two adjacent stay cables 6 is 45 degrees.

The upper end of the inclined cable 6 is connected to the floating pile leg 2 through the mooring connection point 5 at about 30 meters above the water surface. Point 5 is mainly composed of a flange device and a tensioning connection device 8. The flange device is used to connect the offshore wind turbine 1; the tensioning connection device 8 is a spiral screw, which is used to connect the inclined cable 6 to the mooring connection point 5 and adjust the pre-tensioning degree of the inclined cable 6. The tensioning connection device 8 can also be a mechanical device such as a winch.

The lower end of the stay cable 6 is fixed to the seabed 10 via a stay cable anchoring device 7. The stay cable anchoring device 7 adopts a thousand-ton-level flat-plate gravity anchor (or pile anchor).

The cable 6 is made of high-strength galvanized steel wire rope with a breaking strength of 1,000 tons. The braided structural elongation of the cable 6 can be greatly reduced by a strong pre-stretching process in advance, and the resulting elongation is mainly material stretching. In the design working condition of the present disclosure, the breaking tension of each cable 6 is about 3 times the maximum possible external load.

According to preliminary calculations, when the wind, waves and current are in the same direction, the maximum total horizontal load (once in a hundred years) of the wind turbine 1 and the floating pile leg 2 acting on the connection point with the inclined cable 6, i.e., the mooring connection point 5, is about 800 tons, and the breaking strength of a single inclined cable 6 is greater than 1,000 tons. The eight inclined cables 6 are distributed around the floating pile leg 2 at intervals of 45 degrees, which can ensure that at least three inclined cables 6 are simultaneously loaded and stressed in any direction of wind and wave flow. The one in the middle front is the most loaded, with a load of about 400 tons, which is about 1/3 of the breaking tension of the inclined cable 6. The other two inclined cables 6 each bear about 200 tons. Under this tension state, the high-strength galvanized steel wire rope inclined cable 6 has a linear elongation of no more than 3%. This is equivalent to setting 8 strong springs with a linear elongation of 3% under a tension of 300-400 tons around the floating pile leg 2.

The stay cable 6 is connected to the stay cable anchoring device 7 on the seabed. The stay cable anchoring device 7 adopts a thousand-ton-level flat reinforced concrete gravity anchor, or a pile anchor, etc. It can not only ensure the effectiveness and reliability of the anchoring of the stay cable 6 under the maximum load in the horizontal and vertical directions, but also reduce the pressure on the seabed 10 as much as possible to prevent it from sinking naturally.

As shown in Fig. 1-2, the present disclosure provides a method for reducing the overall cost of an offshore wind turbine generator. The floating leg 2 at the bottom of the wind turbine generator 1 is fixed to the seabed 10 by an articulated connection device 3. The articulated connection device 3 at the bottom of the floating leg 2 is fixedly connected to the seabed 10, so that the floating leg 2 will not be displaced laterally and longitudinally. A linearly extending inclined cable system is arranged around the mooring connection point 5 on the floating leg 2 to fix the floating leg 2 to the seabed 10. The constrained support system of the linear spring formed by the inclined cable system and the mass body formed by the floating articulated bottom leg form a two-free A vibrator-like system of degrees is formed to form a support system for the compliant foundation structure of an offshore wind turbine. Under the action of external loads, the support system of the offshore wind turbine compliant foundation structure will produce a simple sway of pitch and roll compliance of a certain amplitude. Through this swaying motion, the huge environmental load on the floating pile leg 2 is balanced by the inertial force, which greatly reduces the balance that usually needs to be achieved through the internal force of the structure; the inclined cable 6 of the inclined cable system is connected to the floating pile leg 2 through the tensioning connection device 8, and the dead weight of the inclined cable is eliminated through the buoyancy system, so that the dead weight sag of the inclined cable 6 is reduced as much as possible.

As shown in FIG3 , the present disclosure provides an offshore aquaculture space constructed by an offshore wind turbine compliant foundation structure system, comprising the compliant foundation structure system, a fence 11 for deep-sea aquaculture is fixed on 8 inclined cables 6 of the compliant foundation structure system, and the fences 11 fixed on the inclined cables 6 of each compliant foundation structure system are connected end to end. The enclosed space is used for deep-sea aquaculture. After the basic structure is set up, the present invention can use one end of the inclined cable 6 to be fixedly connected to the seabed, and the other end to be connected to the upper position of the pile leg (near the sea surface), which can be used to fix the fence of deep-sea aquaculture. That is, the fence 11 for deep-sea aquaculture is set on the inclined cable 6. On the one hand, there is no need to set up a fence separately, and on the other hand, one thing has multiple uses, which increases the scope of deep-sea aquaculture and reduces the cost of deep-sea aquaculture infrastructure.

It should be noted that, in the above embodiments, horizontal wind turbines are taken as examples, and the present disclosure is also applicable to vertical axis wind turbines.

The present disclosure is described in detail above through specific and preferred embodiments, but those skilled in the art should understand that the present disclosure is not limited to the embodiments described above, and any modifications, equivalent substitutions, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Industrial Applicability

The present disclosure provides a compliant foundation structure system for an offshore wind turbine generator, which adopts a support system of a linear spring formed by a cable system and a mass body structure formed by a floating hinged bottom pile leg to form a constrained two-degree-of-freedom rigid body motion system, thereby constructing a compliant "super-flexible" foundation structure support system for an offshore wind turbine generator. Under the action of external loads, the support system of the compliant foundation structure of the offshore wind turbine generator will cause the floating pile leg to produce a simple swing of a certain amplitude of pitch and roll compliance around the hinge point at the bottom of the pile leg. Through this swinging motion, the inertial force balances the huge environmental load on the floating pile leg, greatly reducing the balance that usually needs to be performed through the internal force of the structure. The applicable range of water depth is expanded, the pile structure is simplified, the environmental load response of the support system is reduced, the dependence on geological conditions is reduced, the natural vibration mode of the pile system is optimized, the wind turbine control strategy is simplified, and the dynamic cable is eliminated, which significantly reduces the relevant costs.

In addition, it can be understood that the offshore wind turbine compliant foundation structure system of the present disclosure is reproducible and can be used in a variety of industrial applications. For example, the offshore wind turbine compliant foundation structure system of the present disclosure can be used in the marine engineering field.

Claims

A compliant offshore wind turbine foundation structure system, characterized by comprising a floating pile leg system at the bottom of the wind turbine and a stay cable system with linear extension characteristics, wherein the upper mooring connection point of the floating pile leg system is connected to the wind turbine system;

The floating leg system comprises a floating leg, an articulated connection device, a leg anchoring device and a mooring connection point, wherein the floating leg is an inverted cone-shaped cylindrical steel structure, the mooring connection point is located near the sea surface or above the sea surface and does not interfere with the fan blades of the wind turbine, the leg anchoring device is fixedly connected to the seabed, and the articulated connection device arranged at the lower part of the floating leg is connected to the leg anchoring device;

The cable-stayed system with linear extension characteristics comprises more than three high-strength cables with linear extension characteristics which are radially and evenly arranged with a mooring connection point as the center, each cable being equipped with a cable anchoring device and a tensioning connection device, the lower end of the cable being fixed to the seabed via the cable anchoring device, the upper end of the cable being connected to the mooring connection point via the tensioning connection device, the elongation of the cable being no greater than 4% at the usable load, and the cable being equipped with a buoyancy system for eliminating its own weight so as to minimize the amount of sagging due to its own weight.
The compliant offshore wind turbine foundation structure system according to claim 1 is characterized in that a floating structure is provided in a certain range above the floating legs, the interior of the floating structure is a ballast water tank, and the buoyancy of the floating structure is equal to the sum of 60% to 80% of the total mass of the wind turbine and the total mass of the floating legs.
According to the compliant offshore wind turbine foundation structure system of claim 1, it is characterized in that the floating pile legs are provided with counterweights within a certain height range at their roots so that the center of gravity of the floating pile legs is located below the center of buoyancy.
The offshore wind turbine compliant foundation structure system according to claim 1 is characterized in that the length of the lower half is not less than the length of the upper half.
The compliant offshore wind turbine foundation structure system according to any one of claims 1-4 is characterized in that the floating leg system is suitable for a water depth of 60-150 meters.
The compliant offshore wind turbine foundation structure system according to any one of claims 1 to 4 is characterized in that the wind turbine is a vertical axis wind turbine.
A method for reducing the comprehensive cost of an offshore wind turbine system, characterized in that the floating pile legs at the bottom of the wind turbine are fixed to the seabed by an articulated connection device, the articulated connection device at the bottom of the floating pile legs is fixedly connected to the seabed so that the floating pile legs will not undergo lateral and longitudinal displacements, a linearly extending inclined cable system is arranged around the mooring connection points on the floating pile legs to fix the floating pile legs to the seabed, a constrained support system of linear springs formed by the inclined cable system and a mass body formed by the floating articulated bottom-seated pile legs are formed into a two-degree-of-freedom oscillator-like system to form a support system for a compliant foundation structure of an offshore wind turbine, and under the action of external loads, the support system of the offshore wind power compliant foundation structure will generate certain amplitudes of pitch and roll compliance. Simple rocking, through which the huge environmental loads on the floating legs are balanced by inertial forces, greatly reducing the balance that is usually required through the internal forces of the structure.

The stay cables of the stay cable system are connected to the floating pile legs through a tensioning connection device, and the deadweight of the stay cables is eliminated through a buoyancy system, so that the deadweight sagging of the stay cables is reduced as much as possible.
An offshore aquaculture space constructed using the compliant offshore wind turbine foundation structure system described in any one of claims 1-6 is characterized in that it includes the compliant foundation structure system, and deep-sea aquaculture fences are fixed on at least three inclined cables of the compliant foundation structure system, and each fence fixed on the inclined cable is used to create an enclosed space for marine aquaculture activities.