Sliding mode self-adaptation-based multi-point mooring system positioning control method
1. A multi-point mooring system positioning control method based on sliding mode self-adaptation is characterized by comprising the following steps:
s1, establishing a multi-point mooring system dynamic model;
s2, deriving a multi-point mooring motion equation based on the low-frequency motion model of the semi-submersible platform;
s3, defining an error variable and constructing a sliding modal surface of the system;
s4, designing a self-adaptive law of the weight of the neural network, and realizing the online approximation of the nonlinear term;
and S5, verifying the global stability of the system by adopting a Lyapunov function.
2. The sliding-mode adaptive multi-point mooring system positioning control method according to claim 1, wherein the step S2 further comprises:
the nonlinear coupling low-frequency motion equation of the multi-point mooring system is as follows:
wherein eta is [ x y psi ═ n]TAs a fixed coordinate system (X)E YE ZE) The lower multi-point mooring system surging displacement, swaying displacement and yawing angle; v ═ u vr]TThe velocity vectors of a multi-point mooring system in three directions of surging, swaying and yawing in a motion coordinate system (X Y Z); j (n) is a rotation matrix between the fixed coordinate system and the moving coordinate system; m is the superposition of an additional mass matrix and an inertia matrix of the multi-point mooring system; c (V) is an obliquely symmetrical Coriolis centripetal force matrix of the multi-point mooring system; d is a damping matrix of the multipoint mooring system; tau ismIs the control moment generated by the mooring line; tau iseEnvironmental moments imposed by wind, waves and ocean currents.
3. The sliding-mode adaptive multi-point mooring system positioning control method according to claim 2, wherein the step S3 further comprises:
defining a position error function of the multi-point mooring system to obtain a sliding modal surface of the system:
e=ηd-η (3),
and (3) obtaining a derivative of the sliding mode surface s, and substituting the nonlinear coupling low-frequency motion equation to obtain:
sliding mode control law tau of multipoint mooring systemmSelecting:
p, Q, F in equations (5) and (6) is calculated as follows:
wherein e represents a platform position deviation, ηdDenotes the target position of the stage, κ denotes a position error coefficient and κ > 0, ε denotes the rate at which the motion approaches the switching plane s ═ 0 and ε > 0, λ denotes an exponential approach law coefficient and λ > 0.
4. The sliding-mode adaptive multi-point mooring system positioning control method according to claim 3, wherein the step S4 further comprises:
using a gaussian function h (σ):
F(σ)=W*Th(σ)+δ (9)
network input fetching of RBF neural networkThe network output is then:
wherein j is a hidden node of the neural network, and j is 1,2, 3.σ is the vector of the network input layer; | | · | | represents the euclidean norm; h isjIs a gaussian function of node j in the neural network; c. CjIs the central vector; bjIs the gaussian spread width; f (σ) is the expected value of the neural network output; w*Is an ideal weight for the neural network; delta is the approximation error of the neural network, delta is less than or equal to deltaN,δNIs the error bound.
5. The sliding-mode adaptive multi-point mooring system positioning control method according to claim 4, wherein the step S4 further comprises:
using saturation function sat(s) instead of sign function sgn(s), i.e.Wherein delta is a boundary layer, and the unknown term F in the formula (6) is subjected to self-adaptive approximation by using the RBF neural network of the formula (10) to obtain a final control law taumComprises the following steps:
based on the control law design and the requirement of satisfying stability analysis, the corresponding self-adaptive law is designedComprises the following steps:
wherein γ represents a normal number.
6. The sliding-mode adaptive multi-point mooring system positioning control method according to claim 5, wherein in step S5, the global stability uses Lyapunov function direct method, which includes the following processes:
wherein
Defining the Lyapunov function as:
wherein gamma is greater than 0(14)
From formulas (13) and (14):
formula (12) can be substituted for formula (15):
because the approximation error delta of the RBF neural network is a small positive real number, if epsilon is more than delta, then
When in useAnd s ≡ 0, according to the Lasalel invariant set principle, the closed-loop system is gradually stable, and when the time t → ∞, the sliding mode surface s → 0.
Background
The semi-submersible platform has no restoring force for the swaying, surging and yawing motion in the horizontal plane, and a positioning system is required to be installed to resist the disturbance influence of the marine environment, so that the horizontal motion of the platform is reduced, and the normal operation of oil-gas production is ensured. Therefore, various marine structures, such as mooring positioning systems, dynamic positioning systems, anchor auxiliary dynamic positioning systems, and the like, are widely applied to semi-submersible production platforms. In these positioning modes, the mooring system has low initial installation, use and maintenance costs, and the routine maintenance and inspection are convenient, so that the mooring system has a dominant position in the positioning system.
The semi-submersible platform is positioned by adopting a multi-point mooring system, and a multi-point mooring system control algorithm is a core technology influencing the positioning performance. The existing various control algorithms generally have the problems of low positioning precision, limited positioning effect, complex algorithm and the like.
Disclosure of Invention
The invention aims to provide a sliding mode self-adaptive multi-point mooring system positioning control method, which overcomes the defect of low mooring positioning accuracy caused by factors such as strong external interference, system nonlinearity, model uncertainty and the like when a semi-submersible production platform works on the sea surface, and improves the positioning accuracy of a multi-point mooring system.
In order to achieve the above purpose, the invention is realized by the following technical scheme:
a sliding mode self-adaptation-based positioning control method for a multipoint mooring system comprises the following steps:
s1, establishing a multi-point mooring system dynamic model;
s2, deriving a multi-point mooring motion equation based on the low-frequency motion model of the semi-submersible platform;
s3, defining an error variable and constructing a sliding modal surface of the system;
s4, designing a self-adaptive law of the weight of the neural network, and realizing the online approximation of the nonlinear term;
and S5, verifying the global stability of the system by adopting a Lyapunov function.
The step S2 further includes:
the nonlinear coupling low-frequency motion equation of the multi-point mooring system is as follows:
wherein eta is [ x y psi ═ n]TAs a fixed coordinate system (X)E YE ZE) The lower multi-point mooring system surging displacement, swaying displacement and yawing angle; v ═ u vr]TThe velocity vectors of a multi-point mooring system in three directions of surging, swaying and yawing in a motion coordinate system (X Y Z); j (n) is a rotation matrix between the fixed coordinate system and the moving coordinate system; m is the superposition of an additional mass matrix and an inertia matrix of the multi-point mooring system; c (V) is an obliquely symmetrical Coriolis centripetal force matrix of the multi-point mooring system; d is a damping matrix of the multipoint mooring system; tau ismIs the control moment generated by the mooring line; tau iseEnvironmental moments imposed by wind, waves and ocean currents.
The step S3 further includes:
defining a position error function of the multi-point mooring system to obtain a sliding modal surface of the system:
e=ηd-η (3),
and (3) obtaining a derivative of the sliding mode surface s, and substituting the nonlinear coupling low-frequency motion equation to obtain:
sliding mode control law tau of multipoint mooring systemmSelecting:
p, Q, F in equations (5) and (6) is calculated as follows:
wherein e represents a platform position deviation, ηdDenotes the target position of the stage, κ denotes a position error coefficient and κ > 0, ε denotes the rate at which the motion approaches the switching plane s ═ 0 and ε > 0, λ denotes an exponential approach law coefficient and λ > 0.
The step S4 further includes:
using a gaussian function h (σ):
F(σ)=W*Th(σ)+δ (9)
network input fetching of RBF neural networkThe network output is then:
wherein j is a hidden node of the neural network, and j is 1,2, 3.σ is the vector of the network input layer; | | · | | represents the euclidean norm; h isjIs a gaussian function of node j in the neural network; c. CjIs the central vector; bjIs the gaussian spread width; f (σ) is the expected value of the neural network output; w*Is an ideal weight for the neural network; delta is the approximation error of the neural network, delta is less than or equal to deltaN,δNIs the error bound.
The step S4 further includes:
using saturation function sat(s) instead of sign function sgn(s), i.e.Wherein delta is a boundary layer, and the unknown term F in the formula (6) is subjected to self-adaptive approximation by using the RBF neural network of the formula (10) to obtain a final control law taumComprises the following steps:
based on the control law design and the requirement of satisfying stability analysis, the corresponding self-adaptive law is designedComprises the following steps:
wherein γ represents a normal number.
In step S5, the global stability is based on the Lyapunov function direct method, and the method includes the following steps:
wherein
Defining the Lyapunov function as:
wherein gamma is greater than 0(14)
From formulas (13) and (14):
formula (12) can be substituted for formula (15):
because the approximation error delta of the RBF neural network is a small positive real number, if epsilon is more than delta, then
When in useAnd s ≡ 0, according to the Lasalel invariant set principle, a closed-loop system is gradually stable, and when the time t → ∞ is reached, a sliding mode surface s → 0.
Compared with the prior art, the invention has the following advantages:
(1) the method establishes a control model of the multi-point mooring system, utilizes the characteristic that a neural network approximates to any function, carries out online estimation on uncertain factors and optimizes a model algorithm of the multi-point mooring system;
(2) the multi-point mooring model has strong robustness, can meet the requirement that the semi-submersible platform effectively positions an expected operation place under the conditions of external interference and model uncertainty, and has good popularization value and application prospect.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings used in the description will be briefly introduced, and it is obvious that the drawings in the following description are an embodiment of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts according to the drawings:
fig. 1 is a flowchart of a positioning control method of a sliding-mode adaptive based multi-point mooring system according to an embodiment of the present invention;
FIG. 2 is a multi-point mooring system dynamics model provided by the present invention;
fig. 3 is a structural diagram of a multi-point mooring control algorithm provided by the present invention.
Detailed Description
The invention is described in further detail below with reference to the figures and the detailed description. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are all used in a non-precise scale for the purpose of facilitating and distinctly aiding in the description of the embodiments of the present invention. To make the objects, features and advantages of the present invention comprehensible, reference is made to the accompanying drawings. It should be understood that the structures, ratios, sizes, and the like shown in the drawings and described in the specification are only used for matching with the disclosure of the specification, so as to be understood and read by those skilled in the art, and are not used to limit the implementation conditions of the present invention, so that the present invention has no technical significance, and any structural modification, ratio relationship change or size adjustment should still fall within the scope of the present invention without affecting the efficacy and the achievable purpose of the present invention.
As shown in fig. 1, the method for controlling positioning of a sliding-mode adaptive based multi-point mooring system provided by the invention is characterized by comprising the following steps:
s1, establishing a multi-point mooring system dynamic model;
s2, deriving a multi-point mooring motion equation based on the low-frequency motion model of the semi-submersible platform;
s3, defining an error variable and constructing a sliding modal surface of the system;
s4, designing a self-adaptive law of the weight of the neural network, and realizing the online approximation of the nonlinear term;
and S5, verifying the global stability of the system by adopting a Lyapunov function.
The present invention will be described in detail with reference to fig. 2 and 3.
In step S1, the multi-point mooring system dynamic model established by the present invention is divided into surging, transom and yawing motions in the horizontal direction of the platform, the model is a three-degree-of-freedom nonlinear system under only wave excitation, and the model structure is shown in fig. 2.
In step S2, the multi-point mooring equation of motion of the present invention is derived based on the low frequency slow drifting motion, as follows:
wherein eta is [ x y psi ═ n]TAs a fixed coordinate system (X)E YE ZE) The lower multi-point mooring system surging displacement, swaying displacement and yawing angle; v ═ u vr]TThe velocity vectors of a multi-point mooring system in three directions of surging, swaying and yawing in a motion coordinate system (X Y Z); j (n) is a rotation matrix between the fixed coordinate system and the moving coordinate system; m is the superposition of an additional mass matrix and an inertia matrix of the multi-point mooring system; c (V) is an obliquely symmetrical Coriolis centripetal force matrix of the multi-point mooring system; d is a damping matrix of the multipoint mooring system; tau ismFor control forces (moments) generated by the mooring lines; tau iseEnvironmental forces (moments) applied to wind, waves and ocean currents.
In step S3, defining a position error function of the multi-point mooring system, and obtaining a sliding mode surface of the system:
e=ηd-η (3),
and (3) derivation is carried out on a sliding mode surface (switching function) s, and the nonlinear coupling low-frequency motion equation is substituted to obtain:
sliding mode control law tau of multipoint mooring systemmSelecting:
p, Q, F in equations (5) and (6) is calculated as follows:
wherein e represents a platform position deviation, ηdDenotes the target position of the stage, κ denotes a position error coefficient and κ > 0, ε denotes the rate at which the motion approaches the switching plane s ═ 0 and ε > 0, λ denotes an exponential approach law coefficient and λ > 0.
It can be understood that the mooring platform is in an unbalanced state in the marine environment due to the external environmental acting force, so that the tension of the cable is required to maintain the system in a balanced state, and the tension of the cable is time-varying and is realized by the cable retracting and releasing of the anchor machine. Control law τmIt is representative of the cable tension derived by the control algorithm.
In step S4, a gaussian function h (σ) is adopted:
F(σ)=W*Th(σ)+δ (9)
network input fetching of RBF neural networkThe network output is then:
wherein j is a hidden node of the neural network, and j is 1,2, 3.σ is the vector of the network input layer; | | · | | represents the euclidean norm; h isjIs a gaussian function of node j in the neural network; c. CjIs the central vector; bjIs the gaussian spread width; f (σ) is the expected value of the neural network output; w*Is an ideal weight for the neural network; delta is the approximation error of the neural network, delta is less than or equal to deltaN,δNIs the error bound.
Further, to avoid or reduce vibration problems, it is desirable to useThe sign function sgn(s) is replaced by a saturation function sat(s), i.e.Wherein delta is a boundary layer, and the unknown term F in the formula (6) is subjected to self-adaptive approximation by using the RBF neural network of the formula (10) to obtain a final control law taumComprises the following steps:
based on the control law design and the requirement of satisfying stability analysis, the corresponding self-adaptive law is designedComprises the following steps:
wherein γ represents a normal number.
In step S5, the global stability is based on the Lyapunov function direct method, which includes the following steps:
wherein
Defining the Lyapunov function as:
wherein gamma is greater than 0(14)
From formulas (13) and (14):
formula (12) can be substituted for formula (15):
because the approximation error delta of the RBF neural network is a small positive real number, taking epsilon > delta, the approximation error delta is obtained byThus, it is possible to provide
When in useAnd s ≡ 0, according to the Lasalel invariant set principle, a closed-loop system is gradually stable, and when the time t → ∞ is reached, a sliding mode surface s → 0.
Therefore, the control algorithm provided by the invention can finally make the system globally stable.
While the present invention has been described in detail with reference to the preferred embodiments, it should be understood that the above description should not be taken as limiting the invention. Various modifications and alterations to this invention will become apparent to those skilled in the art upon reading the foregoing description. Accordingly, the scope of the invention should be determined from the following claims.
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