Ship navigation risk assessment method based on reachable domain

Abstract

The invention discloses a reachable domain-based ship navigation risk assessment method, which comprises the following steps of: constructing kinematics and dynamics equations of a ship, and considering environmental interference factors; discretizing the model, and determining the state of the ship and a discrete motion model with limited control; calculating the reachable domain of the ship at the future moment; obtaining the position and geometric parameters of the island reef, and determining the safety domain of the island reef; and based on the reachable domain, carrying out navigation risk assessment between the ships and between the ship and the island reef. According to the method, through modeling and reachable set calculation, the future state uncertainty of the ship in a complex environment can be effectively predicted, a potential navigation risk area is identified, and a reliable theoretical basis is provided for safe navigation. Compared with a traditional method, the method can more comprehensively consider ship dynamic characteristics, environmental interference and multi-target navigation safety requirements, and the navigation safety is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ship navigation and control, and in particular to a ship navigation risk assessment method based on reachable domain. Background Art

[0002] As global maritime traffic becomes increasingly congested, the issue of ship navigation safety is becoming increasingly prominent. Traditional navigation safety assessment methods, which rely primarily on radar detection, AIS systems, and manual judgment, struggle to accurately predict a ship's motion and potential risks in complex environments. In particular, under the influence of environmental factors such as waves and wind currents, the trajectory of a ship is subject to significant uncertainty, leading to practical limitations in existing risk assessment methods.

[0003] Existing methods for ship safety risk analysis primarily include rule-based methods, artificial intelligence methods, and model-based prediction methods. While rule-based methods are simple and intuitive, they lack adaptability to complex environments. While artificial intelligence methods can handle complex situations, they lack interpretability and reliability. While theoretically sound, model-based prediction methods often employ simplified safety domain models, failing to accurately characterize the motion characteristics of ships under varying sea and environmental conditions. This results in inaccurate and unreliable risk assessment results.

[0004] As a system theory tool, the reachable domain can describe all possible states a system can reach within a given time. In recent years, it has been widely used in fields such as unmanned driving and aircraft safety analysis. However, there are relatively few studies on the calculation and application of the reachable domain for ship navigation safety, especially the research on the reachable domain of ships considering environmental interference. The reachable domain analysis can comprehensively consider the dynamic characteristics of ships and environmental uncertainties, providing a more reliable theoretical basis for navigation safety risk assessment. In complex sea scenarios, ships need to deal with multiple types of obstacles and environmental restrictions at the same time. How to accurately calculate the reachable domain of ships under these conditions and assess navigation risks based on the reachable domain information is a key technical issue to ensure the safe navigation of ships. At present, research on ship navigation risk analysis methods for complex sea scenarios is still insufficient, especially the comprehensive risk assessment method that combines ship dynamic characteristics, environmental impacts and multi-dimensional safety constraints has not yet been formed.

[0005] Therefore, developing a navigation safety risk analysis method for complex maritime scenarios based on accessible domains has important theoretical and practical implications for improving navigation safety and reducing the incidence of maritime accidents. By calculating and characterizing a ship's accessible domain, we can more comprehensively assess safety risks under different navigation environments and operating conditions, providing a scientific basis for navigation decision-making. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention discloses a ship navigation risk assessment method based on reachable domain, which is characterized by comprising the following steps:

[0007] S1: Construct a mathematical model of ship motion based on environmental interference factors;

[0008] S2: Discretize the mathematical model of ship motion to determine the discrete motion model of the ship's state and control constraints;

[0009] S3: Calculate the reachable area of the ship at the future moment;

[0010] S4: Obtain the location and geometric parameter information of islands and reefs, and determine the safety zone of the islands and reefs;

[0011] S5: Conduct navigation risk assessment between ships and between ships and islands and reefs based on the accessible domain.

[0012] Furthermore, the mathematical model of ship motion is as follows:

[0013]

[0014] Where (x,y)∈R 3 They represent the north and east positions in the inertial coordinate system respectively, ψ∈[-π,π] represents the heading angle of the unmanned boat, where is the system inertia matrix, is the linear damping coefficient matrix, τ=[τ u ,0,τ r ] T is the control input of the unmanned boat, where τ u and τ r are the longitudinal thrust and bow moment, τ wave =[τ waveu ,τ wavev ,τ waver ] T Interference from the external environment.

[0015] Furthermore, the mathematical model of ship motion is discretized as follows:

[0016]

[0017] Where k represents the time step, Δt is the size of the time step, and u k ,v k ,ψ k ,r k is the value at step k, and τ u,k ,τ waveu,k ,τ wavev,k ,τ r,k ,τ waver,kis the external torque at step k.

[0018] Furthermore, the calculation of the reachable area of a ship at a future time includes:

[0019] Assume that the initial condition of the mathematical model of ship motion is (t0, x0), and calculate the N The state variable x(t N ) The value range of each component;

[0020] Construct a polyhedron to represent the reachable area of the ship;

[0021] By calculating and projecting the boundary points of the polyhedron, the accurate reachable domain is obtained.

[0022] Furthermore, for islands and reefs with complex shapes and their safety zones, a combination of multiple basic geometric bodies is used to represent them:

[0023] εr=∪i=1 n ε r,i

[0024] where ε r,i represents the i-th basic geometric shape, which is an ellipsoid or a convex polygon, and n represents the number of combined geometric shapes.

[0025] Furthermore, the navigation risk assessment between ships and between ships and islands and reefs based on the accessible domain includes:

[0026] Represent the reachable domain of each ship as an ellipsoid;

[0027] Establish conditions for determining intersections between ships and between ships and island and reef safety zones;

[0028] Based on the intersection judgment results, potential navigation risk areas are identified.

[0029] Furthermore, the condition for determining whether the reachable domains of two ships intersect is as follows: for the reachable domain ellipsoids of two ships i and j, the two ellipsoids do not intersect when the following conditions are met:

[0030]

[0031] Among them, c i and c j Represent the centers of the two ellipsoids, M i and M j are their respective shape matrices.

[0032] Furthermore, the condition for determining whether the ship and the island safety zone intersect is as follows: for the reachable domain ellipsoid of ship i and the safety zone representation of island r, the two zones do not intersect when the following conditions are met:

[0033]

[0034] Among them, c i represents the center of the ship's reachable area ellipsoid, c r Indicates the center of the island and reef safety area, M i is the shape matrix of the ship, M r It is the shape matrix of the island and reef safety area.

[0035] This paper proposes a method for assessing ship navigation risk based on reachable domains. By constructing a ship dynamics model, the reachable domain of a ship under environmental interference is calculated. Combined with the safe zone representation of islands and reefs, this method enables navigation risk assessment between ships and between ships and islands and reefs based on reachable domains. This method comprehensively assesses the uncertainty of a ship's future state in complex environments, effectively identifies potential navigation risk areas, and provides a reliable theoretical basis for subsequent navigation decisions. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments recorded in this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 is a flow chart of the method of the present invention;

[0038] Figure 2 Schematic diagram of navigation risk assessment between ships and between ships and islands and reefs based on accessible areas. DETAILED DESCRIPTION

[0039] To make the technical solutions and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention:

[0040] like Figure 1 and Figure 2 A ship navigation risk assessment method based on reachable domain is shown, comprising the following steps:

[0041] S1: Construct the kinematic and dynamic equations of the ship and consider environmental interference factors;

[0042] S2: Discretize the model to determine the discrete motion model of the ship's state and control constraints;

[0043] S3: Calculate the reachable area of the ship at the future moment;

[0044] S4: Obtain the location and geometric parameters of islands and reefs, and determine their safe areas;

[0045] S5: Conduct navigation risk assessment between ships and between ships and islands and reefs based on the accessible area;

[0046] S1: Constructing the kinematic and dynamic equations of the ship

[0047] S11: The ship model and kinematic model used are as follows:

[0048]

[0049] where η = [x, y, ψ] T ∈R 3 is the inertial coordinate system O e X e Y e Z e The position state variable of the unmanned boat, (x, y)∈R 3 Respectively represent the north and east positions in the inertial coordinate system; ψ∈[-π,π] represents the heading angle of the unmanned vehicle, that is, the angle between the bow and the north direction. υ=[u,v,r] T ∈R 3 , is the attached coordinate system o b x b y b z b where u, v, and r represent the longitudinal, lateral, and bow angular velocities, respectively.

[0050] R(ψ)∈R 3 is the rotation matrix, which is defined as:

[0051]

[0052] The dynamic equation of the unmanned surface vehicle is as follows:

[0053]

[0054] in is the system inertia matrix; is the Coriolis centripetal force matrix; is the hydrodynamic damping coefficient matrix, τ=[τ u ,0,τ r ] T is the control input of the actuator, where τ u and τ r are longitudinal thrust and bow moment respectively; τ w =[τ wu ,τ wv ,τ wr ] T is the external time-varying disturbance such as wind, waves, and current, c 13=-c 31 =-m 22 v, c 23 =-c 32 =m 11 u.

[0055] S12: After adding real wave interference, the motion model is organized as follows:

[0056]

[0057] where τ wave =[τ waveu ,τ wavev ,τ waver ] T Interference from the external environment.

[0058] S2: Discretize the model to determine the discrete motion model of the ship's state and control constraints;

[0059] S21: The discrete linear motion model for determining the state and control constraints of the target object is obtained based on the state constraints, control constraints and motion characteristics of the target object. The discretized motion model is:

[0060]

[0061] Where k represents the time step, Δt is the size of the time step, and u k ,v k ,ψ k ,r k is the value at step k, and τ u,k ,τ waveu,k ,τ wavev,k ,τ r,k ,τ waver,k is the external torque at step k.

[0062] S3: Calculate the reachable area of the ship at the future time:

[0063] S31: Given the initial conditions (t0, x0) of the system, at t N The reachable set at a moment can be defined as follows:

[0064]

[0065] in, represents n-dimensional Euclidean space, represents a control input sequence or control strategy, Indicates that at time t N The state of the system at t0 is the initial time, x0 is the initial state, t N The target moment.

[0066] S32: Use polyhedron approximation method to calculate the reachable set:

[0067] First, calculate the components of the state variables at t N The minimum and maximum possible values for a moment

[0068]

[0069] S33: Construct a polyhedron S to approximate the reachable set:

[0070]

[0071] in Obviously

[0072] S4: Obtain the location and geometric parameters of islands and reefs, and determine their safe areas:

[0073] S41: Get the geometric parameters of islands and reefs, such as location, shape, and size:

[0074] For fixed obstacles such as islands and reefs, as they are static geographical entities, obtaining their precise geometric parameters, such as position, shape, and size, is fundamental to collision risk analysis. Geometric representations of islands and reefs can be obtained from nautical charts, electronic nautical charts, or survey data.

[0075] S42: Consider environmental factors such as tidal changes and shoal distribution

[0076] When determining the safe areas around islands and reefs, it is necessary to consider environmental factors such as tidal changes, shoal distribution, and seasonal changes. These factors will affect the safety of the waters around the islands and reefs, and in turn affect the area where ships can safely pass.

[0077] S43: Expand the safety boundary outside the geometric boundary of the islands and reefs to form an island and reef safety zone

[0078] Based on the geometric characteristics of the islands and reefs and environmental factors, a certain safety boundary is extended beyond the actual boundaries of the islands and reefs to form an island and reef safety zone. This safety zone can be represented by an ellipsoid or a polygon:

[0079] ε r =x:(xc r ) T M r (xc r )≤1

[0080] Among them, c r Indicates the center of the island and reef safety area, M r It is a positive definite matrix that determines the shape and direction of the safe area.

[0081] S44: For islands and reefs with complex shapes, a combination of multiple basic geometric bodies is used to represent them.

[0082] For islands and reefs with complex shapes and their safety zones, a combination of multiple ellipsoids or polygonal representation methods can be used:

[0083] εr=∪i=1 n ε r,i

[0084] where ε r,i represents the i-th basic geometric shape (ellipsoid or polygon), and n represents the number of combined geometric shapes. This representation method can more accurately describe the shape and distribution of complex islands and reefs, improving the accuracy of risk assessment.

[0085] S5: Ship navigation risk analysis based on reachable domain

[0086] S51: Express the reachable area of each ship as an ellipsoid:

[0087] ε i =x:(xc i ) T M i (xc i )≤1

[0088] Among them, c i represents the center of the ellipsoid, M i is a positive definite matrix that determines the shape and orientation of the ellipsoid. Representing the ship’s reachable domain with an ellipsoid can more accurately reflect the ship’s motion characteristics and state uncertainty in different directions.

[0089] S52: Establish the intersection judgment conditions between ships and between ships and island and reef safety areas:

[0090] The necessary and sufficient conditions for two regions to be disjoint are:

[0091]

[0092] This condition applies to the intersection judgment of the reachable areas between ships, and the intersection judgment of the reachable areas of ships and the safe areas of islands and reefs.

[0093] For complex-shaped island and reef safety areas, if multiple geometric bodies are used to represent them, the judgment conditions are:

[0094]

[0095] That is, the ship's reachable area does not intersect with any component of the island and reef safety area.

[0096] S53: Based on this condition, determine whether the reachable areas of any two ships and the safety areas of ships and islands and reefs intersect, thereby determining the safety risk.

[0097] By examining the intersections between ship-accessible zones and between ship-accessible zones and island-reef safety zones, we can identify ship pairs and ship-reef combinations that present potential navigation risks. Intersecting areas indicate the potential for navigation conflicts or safety threats within a specific time window.

[0098] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A ship navigation risk assessment method based on reachable domain, characterized by: The following steps are involved: S1: Construct a mathematical model of ship motion based on environmental interference factors; S2: Discretize the mathematical model of ship motion to determine the discrete motion model of the ship's state and control constraints; S3: Calculate the reachable area of the ship at the future moment; S4: Obtain the location and geometric parameter information of islands and reefs, and determine the safety zone of the islands and reefs; S5: Conduct navigation risk assessment between ships and between ships and islands and reefs based on the accessible domain.

2. A ship navigation risk assessment method based on reachable domain according to claim 1, characterized in that: The mathematical model of ship motion is as follows: Where (x,y)∈R 3 They represent the north and east positions in the inertial coordinate system respectively, ψ∈[-π,π] represents the heading angle of the unmanned boat, where is the system inertia matrix, is the linear damping coefficient matrix, τ=[τ u ,0,τ r ] T is the control input of the unmanned boat, where τ u and τ r are the longitudinal thrust and bow moment, τ wave =[τ waveu ,τ wavev ,τ waver ] T Interference from the external environment.

3. The method for ship navigation risk assessment based on reachable domain according to claim 2, characterized in that: The mathematical model of ship motion is discretized as follows: Where k represents the time step, Δt is the size of the time step, and u k ,v k ,ψ k ,r k is the value at step k, and τ u,k ,τ waveu,k ,τ wavev,k ,τ r,k ,τ waver,k is the external torque at step k.

4. The method for assessing ship navigation risk based on reachable domain according to claim 1, characterized in that: The calculation of the reachable area of a ship at a future time includes: Assume that the initial condition of the mathematical model of ship motion is (t0, x0), and calculate the N The state variable x(t N ) The value range of each component; Construct a polyhedron to represent the reachable area of the ship; By calculating and projecting the boundary points of the polyhedron, the accurate reachable domain is obtained.

5. The method for assessing ship navigation risk based on reachable domain according to claim 4, characterized in that: For islands and reefs with complex shapes and their safety zones, a combination of multiple basic geometric bodies is used to represent them: εr=∪i=1 n e r,i where ε r,i represents the i-th basic geometric shape, which is an ellipsoid or a convex polygon, and n represents the number of combined geometric shapes.

6. The method for ship navigation risk assessment based on reachable domain according to claim 1, characterized in that: Navigation risk assessment between ships and between ships and islands and reefs based on accessible areas includes: Represent the reachable domain of each ship as an ellipsoid; Establish conditions for determining intersections between ships and between ships and island and reef safety zones; Based on the intersection judgment results, potential navigation risk areas are identified.

7. The method for assessing ship navigation risk based on reachable domain according to claim 6, characterized in that: The condition for determining whether the reachable domains of two ships intersect is: for the reachable domain ellipsoids of two ships i and j, the two ellipsoids do not intersect when the following conditions are met: Among them, c i and c j Represent the centers of the two ellipsoids, M i and M j are their respective shape matrices.

8. The method according to claim 6, wherein: The conditions for determining whether the ship and the island safety zone intersect are as follows: for the reachable domain ellipsoid of ship i and the safety zone representation of island r, the two zones do not intersect when the following conditions are met: Among them, c i represents the center of the ship's reachable area ellipsoid, c r Indicates the center of the island and reef safety area, M i is the shape matrix of the ship, M r It is the shape matrix of the island and reef safety area.

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