CN114940237B - Control method for heave compensation of offshore platform and tensioner device thereof - Google Patents

Abstract

The invention relates to a control method for heave compensation of an offshore platform and a tensioner device thereof, which comprises the following steps: setting input sea wave parameters, and constructing a sea wave motion equation; step two: analyzing the motion state of the offshore floating platform; step three: calculating the displacement change of the hydraulic cylinder connecting point of the heave compensation device; step four: analyzing the motion of the heave compensation system, and calculating the pose change of the upper platform in the motion process; step five: the simultaneous equations calculate the motion of the hydraulic cylinders to keep the offshore floating platform level. According to the invention, the complete active control model of the top-tensioned riser tensioner with heave compensation is established by calculating the motion relation between sea waves and the floating platform, so that the tensioner has strong anti-interference capability, high tensioning control precision, stable performance and no time delay in compensation, and the offshore floating platform is more stable.

Description

Control method and tensioner device for offshore platform heave compensation

Technical Field

The present application relates to the technical field of hydraulic system simulation, and in particular to a control method and a tensioner device thereof for heave compensation of an offshore platform.

Background technique

Based on today's mature hydraulic simulation technology and the use of complete simulation software, simulating the hydraulic system is helpful to understand the performance of the hydraulic system in advance. By optimizing the design parameters, the design of the hydraulic system becomes more reasonable and convenient, shortening the hydraulic system design and development cycle and reducing development costs.

In the offshore oil and gas industry, floating vessels such as tension leg platforms (TLPs) for drilling and/or production are common. TLPs are platforms used for drilling and production in relatively deep waters. Limited by the harsh marine environment of float-over installation, a heave compensation device is built to solve the problem of excessive impact of waves on the floating platform by actively controlling the tensioner. The hydraulic control system of the device is studied to improve the accuracy and stability of active control.

When large floating platforms are subjected to complex environmental effects such as wind, waves, currents, and tides in the deep sea, it has a serious impact on offshore operations and poses serious safety hazards to workers. The passive tensioner widely used in actual operations has slightly poor performance stability and tensioning lag. It is very necessary to propose an active tensioner method to ensure safe and efficient operations.

Summary of the invention

In order to overcome the shortcomings of the prior art, the present invention calculates the motion relationship between waves and floating platforms and establishes a complete active control model of top-tensioned riser tensioners with heave compensation, so that the tensioner has strong anti-interference ability and high tensioning control accuracy, making the offshore floating platform more stable.

To achieve the above purpose, the solution adopted by the present invention is:

A control method for heave compensation of an offshore platform, comprising the following steps:

Step 1: Given the input wave parameters, construct the wave motion equation;

An absolute coordinate system based on the sea level is established, where O is any point on the sea level, O-XY represents the sea level, and O-Z represents the direction perpendicular to the sea level; the wave motion equation is as follows:

Where: Γ(x,z,t) represents the wave motion equation; x represents the displacement coordinate of the wave on the X-axis; z represents the displacement coordinate of the wave on the Z-axis; t represents time; A represents the wave height; λ represents the wave wavelength; θ represents the average inclination angle of the wave; ω represents the frequency of the wave; It represents the initial phase angle of the wave acting on the floating platform;

The speed of the wave is determined based on the partial derivative of the wave motion equation with respect to time as follows:

Where: V represents the speed of the wave; represents the partial derivative of the wave motion equation with respect to time;

Step 2: Analyze the motion state of the offshore floating platform;

Calculate the roll angle change curve of the offshore floating platform under the action of waves and the heave motion curve at the center of mass. According to the platform size parameters, calculate the motion curve of the platform under wave conditions, and finally calculate the motion state of each node of the platform;

Obtain the wave motion speed calculated in step 1, and the calculation method of the vertical force and longitudinal moment of the floating platform under the action of waves is as follows:

Where: F represents the force of the waves; T represents the theoretical moment of the waves; V represents the speed of the waves;

Furthermore, the method for obtaining the heave displacement and roll motion offset angle of the offshore floating platform is as follows:

Where: m represents the overall mass of the floating platform; The second derivative of the heave motion displacement is:/> represents the second derivative of the roll motion offset angle; J _θ represents the moment of inertia; B represents the platform width;

Step 3: Calculate the displacement change of the connection point of the hydraulic cylinder of the heave compensation device;

Obtain the heave displacement and roll offset angle calculated in step 2; connect the hydraulic cylinder of the heave compensation device to the offshore floating platform, use four hydraulic cylinders to connect to the upper platform, and determine the calculation formulas of the displacement change curves at the connection points of the four hydraulic cylinders of the heave compensation device as follows:

Where: z0(t) represents the displacement change of the connection point between the floating platform and the heave compensation hydraulic cylinder under the action of waves; L represents the distance between the two longitudinal connection points; h(t) represents the heave motion displacement; θ(t) represents the roll motion offset angle;

Step 4: Analyze the movement of the heave compensation system and calculate the change in the upper platform posture during the movement;

During the heave compensation movement, the motion state of the floating platform and the motion of the compensation platform are analyzed, and the force balance and moment balance equations are established. The center of mass theorem is used to list equations for the entire system, and the force balance equations and moment balance equations including T ₁ (t), T ₂ (t), T ₃ (t) and T ₄ (t) of the hydraulic cylinder are established. In order to further calculate the angular acceleration of the platform around the X-axis and Y-axis during the heave compensation movement, the calculation formula used for the moment of inertia of the floating platform system is as follows:

Where: M _l represents the rolling moment of the floating platform under the action of waves; I _X and I _Y represent the moment of inertia of the floating platform about the X and Y axes; B represents the platform width; L _p represents the length between the vertical lines of the platform;

The displacement change curve at the connection point between the upper floating platform and the heave compensation actuator hydraulic cylinder is obtained according to the following formula:

Where: Z ₁ (t) represents the displacement change curve at the connection point between the upper floating platform and the heave compensation actuator hydraulic cylinder; l ₁ represents the distance between the two longitudinal connection points; l ₂ represents the distance between the two lateral connection points; θ _X (t) and θ _Y (t) represent the angle change in the rolling direction and the pitch direction of the floating platform, respectively;

Step 5: Combine equations to calculate the motion of the hydraulic cylinder to keep the offshore floating platform level;

According to the equation relationship established in step 4, T ₁ (t), T ₂ (t), T ₃ (t) and T ₄ (t) are solved simultaneously to control the movement of the hydraulic cylinder to keep the floating platform level.

Preferably, the control method is specifically:

After the electronic control unit of the hydraulic system gives an input signal, the electronic control system converts the signal into an electric current to control the opening size and direction of the electro-hydraulic proportional directional valve, thereby controlling the extension and retraction of the hydraulic cylinder; with the help of a displacement sensor, the heave compensation device executes the extension and retraction displacement of the hydraulic cylinder and feeds it back to the input end to form a closed-loop control, thereby controlling the motion device of the offshore platform.

Preferably, the force balance equation and moment balance equation of T ₁ (t), T ₂ (t), T ₃ (t) and T ₄ (t) of the hydraulic cylinder in step 4 are specifically:

The force balance equation is as follows:

∑F＝ _Fh- (mg+ _T1 (t)+ _T2 (t)+ _T3 (t)+ _T4 (t))＝ma

Where: _Fh represents the resultant force of the buoyancy of the floating platform and the vertical force of the platform under the action of waves at the center of mass; g represents the acceleration of gravity; _T1 (t), _T2 (t), _T3 (t) and _T4 (t) represent the reaction forces of the first, second, third and fourth hydraulic cylinders on the upper platform respectively; a represents the resultant acceleration;

The moment balance equation is as follows:

Wherein: Σm _x (F) and Σm _y (F) represent the projections of the external torque acting on the floating platform during the heave compensation movement on the X-axis and Y-axis respectively; ε _X (t) and ε _Y (t) represent the projections of the angular acceleration of the floating platform during the heave compensation movement on the X-axis and Y-axis respectively.

Preferably, the control of the hydraulic cylinder movement in step 5 is:

After the platform hydraulic cylinder action signal is given, the displacement at the connection point between the upper platform and the executing hydraulic cylinder changes due to the influence of the reaction force on the platform movement during the hydraulic cylinder movement and the existence of the system's own errors; the reaction force T of the executing hydraulic cylinder on the upper platform during the heave compensation movement is solved by the simultaneous force equations; compared with the initial measurement value of the pressure sensor, the hydraulic cylinder is made to reduce/increase the displacement in the original direction to achieve the compensation effect; the obtained reaction force is used as the floating platform motion signal input during the heave compensation movement; the displacement change at the connection point between the floating platform and the executing hydraulic cylinder of the heave compensation device during the heave compensation movement is solved; the calculated displacement change at the connection point of the floating platform is used as the input of the executing hydraulic cylinder of the heave compensation device; the displacement change at the connection point of the heave compensation upper platform and the executing hydraulic cylinder of the heave compensation device is calculated.

A second aspect of the present invention provides a tensioner device for a control method for heave compensation of an offshore platform, wherein the tensioner device, an upper platform and a lower platform together form an offshore floating platform; the lower platform is in direct contact with the sea surface, and the upper platform is kept relatively horizontal by the movement of the tensioner device;

The tensioner device comprises: a hydraulic cylinder, a tensioning ring, a nitrogen bottle and a bracket;

The bottom of the cylinder body of the hydraulic cylinder is connected to the bracket through a connecting piece for fixing the hydraulic cylinder. One end of the hydraulic cylinder is connected to the tensioning ring through a connecting piece. The tensioning ring is fixed on the riser. The riser is tensioned by realizing the contraction of the hydraulic cylinder through this connection mode. The rod end of the hydraulic cylinder is connected to the hydraulic oil, and the rodless end is connected to the low-pressure nitrogen bottle. The hydraulic cylinder adopts a single-acting hydraulic cylinder with a tensile piston rod. The rod chamber of the hydraulic cylinder is tensioned by oil inlet, and the rod chamber is connected to a gas-liquid accumulator.

The tensioner can adjust the structural type of the tensioning hydraulic cylinder and the connecting piece according to the size of the top tensioning force.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The active control method of the top-tensioned riser tensioner with heave compensation for offshore platforms proposed in the present invention establishes a complete active control model of the top-tensioned riser tensioner with heave compensation by calculating the motion relationship between the waves and the floating platform, thereby improving the accuracy and efficiency of the mathematical model. It is also very convenient to assemble the established mathematical model into a standard module and form a complex hydraulic system model with other mature hydraulic component modules;

(2) The active control method of the top-tensioned riser tensioner for offshore platform heave compensation proposed in the present invention significantly enhances the anti-interference ability of the tensioner tensioning, greatly improves the tensioner tensioning control accuracy, improves the performance stability, reduces the compensation delay, and greatly improves the stability of the offshore floating platform;

(3) The active control method of the top-tensioned riser tensioner for heave compensation of offshore platforms proposed in the present invention uses a heave compensation execution hydraulic cylinder device for feedback compensation. The entire platform is supported by four hydraulic cylinders. The weight of the entire working module and the platform is distributed on the four hydraulic cylinders. The stroke of the hydraulic cylinder piston is the tensioning stroke. The overall structure is compact and the tensioning work is well controlled. Modular construction can solve problems such as the difficulties in offshore platform construction and reduce construction time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a block diagram of active control of a top-tensioned riser tensioner for an offshore platform according to an embodiment of the present invention;

FIG2 is a flow chart of a module model for establishing simulation according to an embodiment of the present invention;

FIG3 is a schematic diagram of the overall structural layout of an actively controlled riser tensioner according to an embodiment of the present invention;

FIG4 is an overall model of a hydraulic cylinder according to an embodiment of the present invention;

FIG5 is a schematic diagram of a hydraulic system according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of overall modeling of a platform motion device and a heave compensation motion device according to an embodiment of the present invention.

1. Centering device; 2. Bracket; 3. Low-pressure nitrogen bottle; 4. Accumulator; 5. Hydraulic cylinder; 6. Tensioning ring; 7. Standpipe; 8. Hydraulic cylinder; 9. Displacement sensor; 10. Adjustable throttle valve; 11. Oil tank; 12. Liquid level thermometer; 13. Air filter; 14. Temperature relay; 15. Oil suction filter; 16. Stop valve; 17. Rubber pipe; 18. Axial piston variable pump; 19. Motor; 20. Overflow valve; 21. Check valve; 22. Pressure gauge switch; 23. Pressure gauge; 24. Normally open stop valve; 25. Accumulator; 26. Servo valve; 27. Hydraulic cylinder; 28. Displacement sensor; 29. One-way throttle valve; 30. Balance valve; 31. Cooler; 32. Return oil filter; 33. Heater.

Detailed ways

The following is an explanation of the embodiments of the present invention with reference to the accompanying drawings. In this case, by calculating the motion relationship between the waves and the floating platform, a complete active control model of the top-tensioned riser tensioner with heave compensation is established, so that the tensioner has strong anti-interference ability and high tensioning control accuracy, making the offshore floating platform more stable. As shown in Figure 1, it is a block diagram of the active control of the top-tensioned riser tensioner for an offshore platform according to an embodiment of the present invention;

The embodiment of the present invention provides an active control method for a top-tensioned riser tensioner for an offshore platform. In order to prove the applicability of the present invention, it is applied to an example. FIG2 is a flowchart of a module model for establishing a simulation in the embodiment of the present invention, which specifically includes the following steps:

S1: Given the input wave parameters, construct the wave motion equation;

Establish an absolute coordinate system based on the sea level, where O is any point on the sea level, O-XY represents the sea level, and OZ represents the direction perpendicular to the sea level; the wave parameters include the wave height A, wavelength λ, average inclination θ, frequency ω and initial phase angle The method for obtaining the wave motion equation is as follows:

Where: Γ(x,z,t) represents the wave motion equation; x represents the displacement coordinate of the wave on the X-axis; z represents the displacement coordinate of the wave on the Z-axis; t represents time; A represents the wave height; λ represents the wave wavelength; θ represents the average inclination angle of the wave; ω represents the frequency of the wave; It represents the initial phase angle of the wave acting on the floating platform;

The speed of the wave is determined based on the partial derivative of the wave motion equation with respect to time as follows:

Where: V represents the speed of the wave; represents the partial derivative of the wave motion equation with respect to time.

S2: Analyze the motion status of offshore floating platforms;

The roll angle variation curve of the offshore floating platform under the action of waves and the heave motion curve at the center of mass are calculated. According to the platform size parameters, the motion curve of the platform under wave conditions is calculated, and finally the motion state of each node of the platform is calculated.

Obtain the wave motion speed calculated by S1, and the calculation method of the vertical force and longitudinal moment of the floating platform under the action of waves is as follows:

Where: F represents the force of the waves; T represents the theoretical moment of the waves; V represents the speed of the waves;

Furthermore, the method for obtaining the heave displacement and roll motion offset angle of the offshore floating platform is as follows:

Where: m represents the overall mass of the floating platform; The second derivative of the heave motion displacement is:/> represents the second derivative of the roll motion offset angle; J _θ represents the moment of inertia; B represents the platform width;

S3: Calculate the displacement change of the connection point of the hydraulic cylinder of the heave compensation device;

Obtain the heave displacement and roll offset angle calculated by S2; connect the hydraulic cylinder of the heave compensation device to the offshore floating platform. Here, the overall structure uses four hydraulic cylinders to connect to the upper platform. The calculation formulas for the displacement change curves at the connection points of the four hydraulic cylinders of the heave compensation device are as follows:

Where: z0(t) represents the displacement change at the connection point between the floating platform and the heave compensation hydraulic cylinder under the action of waves; L represents the distance between the two longitudinal connection points;

S4: Analyze the movement of the heave compensation system and calculate the changes in the upper platform posture during the movement;

During the heave compensation process, the motion state of the floating platform and the compensation platform are analyzed to establish the force balance and moment balance equations. The center of mass theorem is used to list the equations for the entire system, and the force balance equation is derived as follows:

∑F＝ _Fh- (mg+ _T1 (t)+ _T2 (t)+ _T3 (t)+ _T4 (t))＝ma

Where: _Fh represents the resultant force of the buoyancy of the floating platform and the vertical force of the platform under the action of waves at the center of mass; g represents the acceleration of gravity; _T1 (t), _T2 (t), _T3 (t) and _T4 (t) represent the reaction forces of the first, second, third and fourth hydraulic cylinders on the upper platform respectively; a represents the resultant acceleration;

The moment balance equation is as follows:

Wherein, ∑m _X (F) and ∑m _Y (F) represent the projections of the external torque on the floating platform during the heave compensation movement on the X-axis and Y-axis respectively; ε _X (t) and ε _Y (t) represent the projections of the angular acceleration of the floating platform during the heave compensation movement on the X-axis and Y-axis respectively.

The angular acceleration of the platform around the X-axis and Y-axis during the heave compensation movement is further calculated. The calculation formula used for the moment of inertia of the floating platform system is as follows:

Where: M _l represents the rolling moment of the floating platform under the action of waves; I _X and I _Y represent the moment of inertia of the floating platform about the X and Y axes; B represents the platform width; L _p represents the length between the vertical lines of the platform;

In summary, the displacement change curve at the connection point between the upper floating platform and the heave compensation hydraulic cylinder is obtained according to the following formula:

Where: Z ₁ (t) represents the displacement change curve at the connection point between the upper floating platform and the heave compensation actuator hydraulic cylinder; l ₁ represents the distance between the two longitudinal connection points; l ₂ represents the distance between the two lateral connection points; θ _X (t) and θ _Y (t) represent the angle change in the rolling direction and the pitch direction of the floating platform, respectively;

S5: Simultaneous equations to calculate the motion of the hydraulic cylinder to keep the offshore floating platform level;

According to the equation relationship established in S4, T ₁ (t), T ₂ (t), T ₃ (t) and T ₄ (t) are solved simultaneously to control the movement of the hydraulic cylinder to keep the floating platform level.

The specific steps of controlling the movement of the hydraulic cylinder are as follows: after the platform hydraulic cylinder action signal is given, the displacement at the connection point between the upper platform and the executing hydraulic cylinder changes due to the influence of the reaction force on the platform movement during the movement of the hydraulic cylinder and the existence of the system's own errors; the reaction force T of the executing hydraulic cylinder on the upper platform during the heave compensation movement is solved by the simultaneous force equations; the reaction force T is compared with the initial measurement value of the pressure sensor so that the hydraulic cylinder reduces/increases the displacement in the original direction to achieve the compensation effect; the obtained reaction force is used as the floating platform movement signal input during the heave compensation movement; the displacement change at the connection point between the floating platform and the executing hydraulic cylinder of the heave compensation device during the heave compensation movement is solved; the calculated displacement change at the connection point of the floating platform is used as the input of the executing hydraulic cylinder of the heave compensation device; and the displacement change at the connection point between the upper platform of the heave compensation and the executing hydraulic cylinder of the heave compensation device is calculated.

A second aspect of the present invention provides a tensioner device for a control method for heave compensation of an offshore platform. The tensioner device, the upper platform and the lower platform together constitute an offshore floating platform; the lower platform is in direct contact with the sea surface, and the upper platform is kept relatively horizontal through the movement of the tensioner device; Figure 6 is a schematic diagram of the overall modeling of the platform motion device and the heave compensation motion device of an embodiment of the present invention.

The tensioner device includes: a hydraulic cylinder, a tensioning ring, a nitrogen bottle and a bracket.

FIG3 is a schematic diagram of the overall structural layout of the active control riser tensioner of the embodiment of the present invention. The upper part of the tensioning bracket is connected to the working platform so that the entire tensioning hydraulic cylinder can be located at the lower part of the platform, saving space on the working platform and lowering the center of gravity of the platform. The hydraulic cylinders of the tensioner system will be used in pairs symmetrically. Due to the required tension and the specifications of the hydraulic cylinders, four hydraulic cylinders are used here. The angle between the hydraulic cylinder and the riser should be as small as possible to reduce the radial force on the hydraulic rod and increase the service life. For the convenience of control, sensors are installed on the hydraulic cylinders to monitor the position, direction and speed of the hydraulic cylinder piston movement in real time. The complete measurement system can provide timely feedback on the actual working status of the tensioning system. The bottom of the hydraulic cylinder body is connected to the bracket through a connecting piece to fix the hydraulic cylinder, and one end of the piston cylinder is connected to the tensioning ring through a connecting piece. The tensioning ring is fixed on the riser. Through this connection method, the hydraulic cylinder can be contracted to tension the riser; the rod end of the hydraulic cylinder is connected to the hydraulic oil, and the rodless end is connected to the low-pressure nitrogen bottle. The stability of nitrogen can maintain continuous pressure on the piston end of the hydraulic cylinder and prevent corrosion; the hydraulic cylinder adopts a single-acting hydraulic cylinder with a tensile piston rod, the rod cavity of the hydraulic cylinder is tensioned by oil, and the rod cavity is connected to the gas-liquid accumulator; the tensioning ring is connected to the riser by friction tensioning, the tensioning force can be adjusted, maintenance is convenient, and it is easy to disengage when the riser fails.

Amesim is a multidisciplinary complex system simulation platform. According to the above analysis results, a simulation model is built, parameters are defined, and the simulation structure is improved. A simulation standard module is established in the Amesim simulation platform for joint simulation. As shown in Figure 4, the overall model of the hydraulic cylinder in the embodiment of the present invention is shown.

According to the design principles of hydraulic system, combined with the actual situation of this example, the principle diagram of the hydraulic system of the heave compensation device is designed, as shown in Figure 5. This system uses a three-position four-way electro-hydraulic servo valve as the control valve of the hydraulic cylinder. The extension and retraction speed of the hydraulic cylinder is adjusted by the opening size of the hydraulic servo valve, and the extension and retraction of the hydraulic cylinder is adjusted by reversing, so as to further realize the adjustment of the heave compensation displacement of the floating platform. At the same time, a servo hydraulic cylinder is used as the driving rod of the hydraulic system, and a displacement sensor is installed to record the extension and retraction amount of the hydraulic cylinder, and the collected displacement signal is input into the computer stroke hydraulic cylinder displacement closed-loop control to improve the control accuracy of the extension and retraction displacement. Due to the randomness of the wave changes, the response speed of the hydraulic control system must be agile. Adding an accumulator to the main oil circuit can effectively overcome the shortcomings of the slow response of the constant pressure variable system.

The structural design and analysis of the tensioner requires the establishment of a suitable mathematical model to determine the size of the top tensioning force and to design the tensioning hydraulic cylinder and connecting parts. Table 1 shows the characteristics of the system components.

Table 1 is the system component information table

Using the standardized modules of the simulation software, a model of the active control tensioner hydraulic system is built, including: hydraulic cylinder, displacement sensor, connector and adjustable throttle. The displacement sensor collects the displacement signal of the piston in the hydraulic cylinder by connecting to the hydraulic cylinder, and the displacement sensor transmits the input displacement signal parameters to the simulation control module. The simulation control module calculates the output signal of each stage and transmits it to the adjustable throttle valve for throttling. The parameters of the heave compensation execution structure are optimized.

The complete simulation model of S5 is connected to the hydraulic system, and its geometric parameters are debugged and optimized. The specific parameters involved in the simulation control module are shown in Table 2;

Table 2 Parameter setting comparison table

The displacement curve is obtained by simulation, analyzed, and the above parameters are continuously adjusted to obtain the optimal compensation feedback effect and optimize the structure of the tensioner active control.

In summary, the results of the active control method of the top-tensioned riser tensioner used for heave compensation of offshore platforms in this case proved to be very effective.

(1) The method proposed in this application calculates the motion relationship between the waves and the floating platform to establish a complete active control model of the top-tensioned riser tensioner with heave compensation, thereby improving the accuracy and efficiency of the mathematical model. It is also very convenient to assemble the established mathematical model into a standard module and form a complex hydraulic system model with other mature hydraulic component modules;

(2) The data listed in this example show that the anti-interference ability of the tensioner is significantly enhanced, the tensioner tensioning control accuracy is greatly improved, the performance stability is improved, the compensation delay is reduced, and the stability of the offshore floating platform is greatly improved;

(3) The attached drawings in this example illustrate the structure of the device in detail. A hydraulic cylinder device is used to perform feedback compensation for heave compensation. The entire platform is supported by four hydraulic cylinders. The weight of the entire working module and the platform is distributed on the four hydraulic cylinders. The stroke of the hydraulic cylinder piston is the tensioning stroke. The overall structure is compact and the tensioning work is easy. Modular construction can solve the difficulties in the construction of offshore platforms and greatly reduce construction time.

The embodiments described above are only descriptions of the preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims (5)

1. A control method for heave compensation of an offshore platform, characterized in that it comprises the steps of:

step 1: setting input sea wave parameters, and constructing a sea wave motion equation;

establishing an absolute coordinate system taking the sea level as a reference, wherein O is any point on the sea level, O-XY represents the sea level, and O-Z represents the direction perpendicular to the sea level; the sea wave motion equation is as follows:

Wherein: Γ (x, z, t) represents the sea wave equation of motion; x represents the displacement coordinate of the wave on the X axis; z represents the displacement coordinate of the wave on the Z axis; t represents time; a represents wave height of sea wave; lambda represents the wave length; θ represents the average dip angle of the ocean wave; ω represents the frequency of the ocean wave; indicating the initial phase angle of the sea wave acting on the floating platform;

and determining the sea wave movement speed according to the partial derivative of the sea wave movement equation with respect to time, wherein the sea wave movement speed is as follows:

Wherein: v represents the sea wave movement speed; Representing the partial derivative of the sea wave equation of motion with respect to time;

Step 2: analyzing the motion state of the offshore floating platform;

Calculating a roll angle change curve of the offshore floating platform under the action of sea waves and a heave motion curve at a centroid point, calculating a motion curve of the platform under the condition of the sea waves according to the size parameters of the platform, and finally calculating to obtain the motion state of each node of the platform;

The method for calculating the vertical stress and the longitudinal moment of the floating platform under the action of the sea wave is as follows when the sea wave movement speed calculated in the step 1 is obtained:

Wherein: f represents the wave acting force; t represents the theoretical moment of the wave; v represents the sea wave movement speed;

Further, the heave motion displacement and roll motion offset angle of the offshore floating platform are obtained as follows:

wherein: m represents the whole mass of the floating platform; the second derivative representing heave motion displacement: /(I) A second derivative representing the roll motion offset angle; j _θ denotes moment of inertia; b represents a platform type width;

Step 3: calculating the displacement change of the hydraulic cylinder connecting point of the heave compensation device;

Acquiring heave motion displacement and roll motion offset angles calculated in the step 2; the hydraulic cylinders of the heave compensation device are connected with the offshore floating platform, 4 hydraulic cylinders are connected with the upper platform, and the calculation formulas for respectively determining displacement change curves obtained at the connection points of the 4 hydraulic cylinders of the heave compensation device are as follows:

Wherein: z0 (t) represents the displacement change of the connection point of the floating platform and the heave compensation hydraulic cylinder under the action of sea waves; l represents the distance between two longitudinal connecting points; h (t) represents heave motion displacement: θ (t) represents the roll motion offset angle;

Step 4: analyzing the motion of the heave compensation system, and calculating the pose change of the upper platform in the motion process;

during the heave compensation movement process, the motion state of the floating platform and the motion of the compensation platform are analyzed, and a force balance equation and a moment balance equation are established; the whole system adopts the centroid theorem to list equations, and establishes a force balance equation and a moment balance equation comprising T ₁(t)、T₂(t)、T₃ (T) and T ₄ (T) of the stress of the hydraulic cylinder; in order to further calculate the angular acceleration of the platform around the X axis and the Y axis in the heave compensation motion process, the calculation formula adopted for calculating the rotational inertia of the floating platform system is as follows:

Wherein: m _l represents the rolling moment of the floating platform under the action of sea waves; i _X and I _Y represent the moment of inertia of the floating platform to the X and Y axes; b represents a platform type width; l _p represents the platform catenary length;

the displacement change curve at the connection point of the upper floating platform and the heave compensation execution hydraulic cylinder is obtained according to the following formula:

wherein: z ₁ (t) represents a displacement change curve at the connection point of the upper floating platform and the heave compensation execution hydraulic cylinder; l ₁ denotes the distance between the two longitudinal connection points; l ₂ denotes the distance between the two lateral connection points; θ _X (t) and θ _Y (t) represent a floating platform roll direction angle change and a pitch direction angle change, respectively;

step 5: the simultaneous equation calculates the movement of the hydraulic cylinder to keep the offshore floating platform horizontal;

And (3) solving the equation relation established in the step (4) simultaneously to obtain the T ₁(t)、T₂(t)、T₃ (T) and the T ₄ (T), and controlling the hydraulic cylinders to move so as to keep the floating platform horizontal.

2. The control method for heave compensation of an offshore platform according to claim 1, characterised in that the control method is in particular:

after an input signal is given to an electric control unit of the hydraulic system, the electric control system converts the signal into current to control the opening size and direction of the electro-hydraulic proportional directional valve, and then the expansion and contraction of the hydraulic cylinder are controlled; the hydraulic cylinder telescopic displacement is fed back to the input end by means of the displacement sensor acquisition heave compensation device, closed-loop control is formed, and further the offshore platform movement device is controlled.

3. The control method for heave compensation of an offshore platform according to claim 1, wherein the establishing of the force balance equation and the moment balance equation in step 4 comprising the T ₁(t)、T₂(t)、T₃ (T) and the T ₄ (T) of the hydraulic cylinder forces is specifically:

the force balance equation is as follows:

∑F＝F_h-(mg+T₁(t)+T₂(t)+T₃(t)+T₄(t))＝ma

Wherein: f _h represents the resultant force of the vertical force of the floating platform at the centroid under the action of the buoyancy and waves; g represents gravitational acceleration; t ₁(t)、T₂(t)、T₃ (T) and T ₄ (T) represent the reaction forces of the first, second, third and fourth hydraulic cylinders, respectively, to the upper platform; a represents resultant acceleration;

The moment balance equation is as follows:

Wherein: Σm _x (F) and Σm _y (F) represent projections of external moments applied to the floating platform on the X axis and the Y axis respectively during heave compensation motion; epsilon _X (t) and epsilon _Y (t) represent projections of the angular acceleration of the floating platform on the X-axis and Y-axis during heave compensation motions.

4. The control method for heave compensation of an offshore platform according to claim 1, wherein the control cylinder movement in step 5 is:

after the action signal of the hydraulic cylinder of the platform is given, the displacement at the connection point of the upper platform and the execution hydraulic cylinder changes because of the influence of the reaction force on the movement of the platform and the error of the system in the movement process of the hydraulic cylinder; solving a reaction force T of the hydraulic cylinder on the upper platform in the heave compensation motion process through a simultaneous force equation; comparing with the initial measurement value of the pressure sensor, so that the displacement of the hydraulic cylinder in the original direction is reduced/increased, and the compensation effect is achieved; inputting the obtained reaction force as a motion signal of the floating platform in the heave compensation motion process; solving displacement change of the connection point of the hydraulic cylinder of the floating platform and the heave compensation device in the heave compensation motion process; taking the calculated displacement variation at the connecting point of the floating platform as the input quantity of the hydraulic cylinder executed by the heave compensation device; and calculating the displacement variation of the connection point of the heave compensation upper platform and the hydraulic cylinder of the heave compensation device.

5. Tensioner means for implementing the control method for heave compensation of an offshore platform according to any of claims 1 to 4, characterised in that the tensioner means together with the upper platform and the lower platform form an offshore floating platform; the lower platform is in direct contact with the sea surface, and the upper platform is kept relatively horizontal through the movement of the tensioner device;

The tensioner device includes: the device comprises a hydraulic cylinder, a tensioning ring, a nitrogen cylinder and a bracket;

The bottom of the cylinder body of the hydraulic cylinder is connected with the bracket through a connecting piece and used for fixing the hydraulic cylinder, the first end of the hydraulic cylinder is connected with the tensioning ring through the connecting piece, and the tensioning ring is fixed on the vertical pipe, so that the shrinkage of the hydraulic cylinder is realized to tension the vertical pipe; the rod end of the hydraulic cylinder is connected with hydraulic oil, and the rod end of the hydraulic cylinder is connected with a low-pressure nitrogen cylinder; the hydraulic cylinder adopts a single-acting hydraulic cylinder with a piston rod pulled, a rod cavity of the hydraulic cylinder is used for tensioning oil inlet, and the rod cavity is connected with a gas-liquid accumulator;

the tensioner can adjust the structural style of the tensioning hydraulic cylinder and the connecting piece according to the magnitude of the top tensioning force.