Dangerous ship-wave coupling avoidance route planning method based on reachable set

Abstract

The invention discloses a dangerous ship-wave coupling avoidance route planning method based on a reachable set, and the method comprises a dangerous navigation state recognition method based on a ship-wave coupling effect, i.e., the inherent frequency of a ship is estimated through the basic parameters of the ship, the encounter frequency of the ship and a wave field is analyzed according to the navigation state of the ship and the information of the nearby wave field, and the ship-wave coupling avoidance route planning method based on the ship-wave coupling effect is obtained. Further determining a dangerous sailing state according to the proportional relation; dangerous sailing state avoidance decision based on sailing safety specifications, namely, an optimal operation mode for departing from a dangerous sailing state is calculated according to a plurality of operation processes recommended by international maritime organization safety specifications (MSC.1 / Circ.1228) and control motion characteristics of a ship; according to the homeward voyage route planning method based on reachable set calculation, when a ship is out of a dangerous sailing state and deviates from an original global route, a reachable set calculation tool is started to calculate the time optimal route of the ship returning to the original global route under the condition that the ship does not enter the dangerous sailing state again.

Description

Technical Field

[0001] The present invention relates to the technical field of ship intelligent navigation, and in particular to a dangerous ship-wave coupling avoidance track planning method based on a reachable set. Background Art

[0002] When a ship is sailing in high sea conditions, it may encounter ship-wave coupling phenomena that threaten navigation safety, such as parametric roll and parametric harmonic roll. These dangerous phenomena may lead to a sharp decrease in the stability of ships at sea that comply with relevant IS ship design regulations in a short period of time. In order to help ships at sea avoid such dangerous ship-wave coupling phenomena and provide captains with a basis for decision-making during navigation, the Maritime Safety Committee (MSC) of the International Maritime Organization (IMO) issued MSC.1 / -Circ.1228 and MSC.1 / Circ.1627, which stipulate dangerous heading-speed combinations that ships at sea should not enter.

[0003] Although the trajectory planning techniques developed by researchers in the past have made some contributions to avoiding dangerous ship-wave coupling phenomena for ships at sea, they often rely on accurate global weather forecast assumptions and ignore the potential risks brought by sudden changes in local sea conditions. In other words, sudden changes in sea conditions (such as changes in wave direction and wave period) may still make the original safe navigation state on the originally planned global route dangerous. A practical strategy to deal with these unpredictable weather changes is to re-run the trajectory planning algorithm and find a new route. The re-planned route should guide the ship at sea to avoid the detected dangerous ship-wave coupling risks while still tracking the original global route. This requires the local trajectory planning algorithm to have the ability to plan the ship's heading and speed at the same time and ensure the shortest response time. However, most existing planning algorithms regard the speed as constant during the planning process, or adopt a two-stage optimization method. This destroys the global time optimality of the local trajectory planning algorithm when facing dangerous conditions. Summary of the invention

[0004] In order to solve these problems, the present invention proposes a trajectory planning technology based on reachable set calculation to reduce the risk of parametric rolling of ships at sea, which is used to plan the optimal time trajectory to avoid dangerous ship-wave coupling phenomena when the sea conditions suddenly change. The developed trajectory planning algorithm can be divided into two stages, in which the danger escape stage guides the ship away from the dangerous course-speed combination after detecting the danger, and the return stage helps the ship return to the original global route while staying away from the dangerous area. Specifically, in the danger escape stage, the framework will compare the reaction times of the three recommended operations given by IMO to determine the shortest evacuation time and trajectory. Then, in the return stage, we first calculate the forward propagation process of the reachable set by solving the variational inequality (VI) until it reaches the target point of the return for the first time. Then, by inversely solving the motion equation, the intermediate track points are traced back step by step to calculate the return path. If the algorithm framework proposed in this chapter is used in conjunction with the shipboard wave-measuring radar, it can provide warnings and suggestions to the captain and be integrated into a driving assistance system for manned ships; if the algorithm is combined with an autonomous navigation control module, it can become a key component of the autonomous driving system to cope with local adverse weather changes.

[0005] The present invention discloses a dangerous ship-wave coupling avoidance trajectory planning method based on a reachable set, and the dangerous ship-wave coupling avoidance trajectory planning method based on a reachable set comprises the following steps:

[0006] Step 1, determining whether the current ship is in a dangerous navigation state under severe weather conditions;

[0007] The dangerous navigation state includes a heading-speed combination that may cause wave riding / rolling, continuous high wave impact and parametric roll / harmonic roll;

[0008] Step 2: Plan two routes: the danger escape phase and the path return phase to get the ship out of danger.

[0009] Furthermore, in step 1, the dangerous navigation state is a state set including a heading-speed dangerous combination:

[0010] A obst ≡{x=[xyθF] T |(θ,F)}

[0011] x=[xyθF] T is a state variable, (x, y) represents the position, F represents its nominal speed, and θ represents the heading of the ship in the ENU coordinate system. The dangerous heading and speed combination specified in the wave riding / rolling phenomenon, continuous high wave impact phenomenon and parametric rolling / harmonic rolling phenomenon is used to judge whether it is in a dangerous navigation state.

[0012] Going one step further, in step 1, the wave angle in the wave riding / shuffling phenomenon is defined as:

[0013] α=θ wave -θ,α∈(0,360°)

[0014] where θ wave is the wave direction, θ is the heading; the dangerous heading and speed combination in the wave riding / bowling phenomenon is:

[0015] 135°<α<225°,

[0016] Among them, V is the speed of the ship and L represents the length of the ship.

[0017] Furthermore, in step 1, when the wave encounter period is within the preset multiple wave field period range, continuous high wave impact phenomenon will occur:

[0018] 1.8T W <T E <3.0T W ,

[0019] T W is the wave field period, T E is the wave encounter period, V is the ship’s speed, and α is the wave angle.

[0020] Furthermore, in step 1, the dangerous heading-speed combination is determined by the following judgment criteria for the parametric roll / harmonic roll phenomenon:

[0021] |T R -T E |<∈T E

[0022] |T R -2T E |<∈T E ∧(0°≤α≤30°∨150°≤α≤210°∨330°≤α<360°)

[0023] T R is the ship’s inherent rolling period, T E is the encounter period of the wave field, α is the wave head angle, and ∈ is a constant used to specify the width of the safety buffer zone.

[0024] Furthermore, in step 2, the danger escape phase also includes:

[0025] Step 211, calculating the escape time of the three operations, and selecting the route with the shortest escape time as the recommended evacuation route;

[0026] The three operations include: ω(t) = F(t) / R min and a constant speed turn to the left;

[0027] ω(t)=-F(t) / R min and a constant speed turn to the right;

[0028] Take a(t)=-a max and constant heading deceleration;

[0029] ω(t) represents the ship's bow turning rate, R min represents the minimum turning radius allowed by the ship, F(t) represents the speed of the ship, a(t) represents the acceleration of the ship, and a max Indicates the maximum acceleration allowed for the ship;

[0030] Step 212, in the evacuation path, continue to loop to determine whether it is in a dangerous speed and heading combination; if it is still in a dangerous state, go to step 1, otherwise enter the path return stage.

[0031] Furthermore, in step 2, the path return phase includes the following steps:

[0032] Step 221, determining the end point of the return path according to the end point of the dangerous escape path and the global path point to be tracked;

[0033] Step 222, define the level set function φ(x,t) used to represent the reachable set position, and its initial value is:

[0034] φ(x,0)=|xx s |2-ζ

[0035] x represents the ship state variable, x s represents the initial state of the ship's path return phase, ζ represents an arbitrary small constant;

[0036] Construct a value function for representing dangerous states, whose value is

[0037]

[0038] y represents any state on the boundary of the reachable set, and inf represents an operator that minimizes the right-hand expression in the state defined by its subscript;

[0039] Step 223, using the ENO-Godunov format to solve the control equation of the evolution of the control value function, obtain the value of the value function at each time and the position of the reachable set R0[t]:

[0040]

[0041] θ(t) represents the heading angle variable, φt represents the partial derivative of the value function with respect to time, φ x represents the partial derivative of the value function with respect to x, φ y represents the partial derivative of the value function with respect to y, φ θ represents the partial derivative of the value function with respect to θ, φ F represents the partial derivative of the value function with respect to F;

[0042] The solution process will continue until the reachable set R0[t] contains the target state x for the first time. f , can be judged by:

[0043]

[0044] F max Indicates the maximum speed allowed for the ship, x f Indicates the value of the return path end point in the x direction, y f Indicates the value of the end point of the return path in the y direction, θ f represents the heading of the ship at the end of the return path, and F represents the speed of the ship at the end of the return path;

[0045] Step 224, once it is determined The forward reachable set R0[t] of f to x s Best destinations According to the current track point P * (t n ) Determine the previous track point P * (t n-1 ), which is achieved by solving the following ODE:

[0046]

[0047] Δt represents the time step used in the path backtracking phase, x(t n-1 ) indicates that the ship is at time t n-1 The value of the state in the x direction, x(t n ) indicates that the ship is at time t n The value of the state in the x direction, y(t n-1 ) indicates that the ship is at time t n-1 The value of the state in the y direction, y(t n ) indicates that the ship is at time t n The value of the state in the y direction, F(t n ) indicates that the ship is at time t n The speed that should be maintained, F(t n-1 ) indicates that the ship is at time t n-1 The speed that should be maintained, θ(t n ) indicates that the ship is at time tn The heading to be taken, θ(t n-1 ) indicates that the ship is at time t n-1 the heading to be taken;

[0048] The optimal control ω * (t n ) and a * (t n )for:

[0049]

[0050] Step 225, push the trajectory composed of the path points and the matching speed to the control console.

[0051] The beneficial effects achieved by the present invention are:

[0052] The track planning method provided by the present invention can be combined with existing wave measurement technology and auxiliary navigation systems to provide safety warnings for large ocean-going ships (such as car roll-on / roll-off ships and container ships) during transoceanic voyages and push corresponding risk avoidance and return suggestions, thereby improving their safety when sailing under adverse weather conditions. In addition, since the ship's maneuvering motion constraints are taken into account, the present invention can also be directly integrated into the ship's automatic driving system to provide support for the navigation of unmanned ships in high sea conditions.

[0053] The track planning method provided by the present invention takes into account the impact of sudden changes in local sea conditions on navigation safety, and optimizes the speed and heading synchronously through the reachable set tool, thereby ensuring the time optimality of risk avoidance operations. This improvement can determine dangerous areas based on local sea conditions, provide operational suggestions, consider the impact of short-term risks on navigation, and optimize the ship's risk avoidance operations to ensure that the ship's control constraints are met, thereby improving the timeliness and feasibility of responding to dangerous waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 A flowchart of a dangerous ship-wave coupling avoidance trajectory planning method based on a reachable set provided by the present invention;

[0055] Figure 2 A polar coordinate schematic diagram of the dangerous ship heading and speed combination provided by the present invention;

[0056] Figure 3 A schematic diagram illustrating the occurrence of a dangerous navigation state provided by the present invention;

[0057] Figure 4 A schematic diagram of the left rudder return track planning problem after escaping danger provided by the present invention;

[0058] Figure 5 A schematic diagram of sea condition changes in a test case provided by the present invention;

[0059] Figure 6 This is a schematic diagram of the results of the planning method provided by the present invention in a test case. DETAILED DESCRIPTION

[0060] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0061] like Figure 1 As shown, the present invention proposes a dangerous ship-wave coupling avoidance trajectory planning method based on a reachable set, comprising the following steps:

[0062] Step 1, determining whether the current ship is in a dangerous navigation state under severe weather conditions;

[0063] In the framework of the proposed planning method, the ship is regarded as a particle moving on a two-dimensional (2D) plane, and its navigation state is completely determined by the state variable x = [xyθF] T Description, where (x, y) represents the position and F represents its nominal speed. In addition, θ represents the heading of the ship in the ENU (East-North Up) coordinate system. The state trajectory of the ship in motion is represented by P(t) and satisfies the following kinematic relationship

[0064]

[0065] Among them, the control inputs ω(t) and a(t) are the bow angular velocity and acceleration of the ship underway, respectively.

[0066] The maneuverability of a ship underway is affected by its minimum turning radius R min , maximum acceleration a max and maximum speed F max In the framework of the present invention, these parameters are set to the values ​​obtained by the maximum capability of the ship under operation within the design conditions, so as to ensure that its maneuvering capability is estimated with a safety margin.

[0067]

[0068] When sailing in adverse weather conditions, ships may encounter various dangerous ship-wave coupling phenomena, including i) wave riding / rolling; ii) continuous high wave impact; iii) parametric rolling / harmonic rolling. These phenomena may cause cargo damage and casualties on board. The present invention follows the safety criteria outlined in MSC.1 / Circ.1228 and classifies the areas that may cause dangerous ship-wave coupling into a series of heading-speed combinations under specific wave fields.

[0069] i) Wave riding / swinging phenomenon

[0070] In the case of a trailing wave or a quarter-slope trailing wave, a ship may travel on the crest of the wave (called riding and swinging). In this case, the ship may face the risk of capsizing due to a sudden change in heading and an unforeseen large tilt. Here, the present invention defines the wave angle as:

[0071] α=θ wave -θ,α∈(0,360°) (3)

[0072] where θ wave is the wave direction, and θ is the heading. To avoid riding waves and swinging sideways, ships should be prevented from entering the following heading-speed combination areas:

[0073]

[0074] Where V(knot) is the speed of the ship and L(m) represents the length of the ship.

[0075] ii) Continuous high wave impact

[0076] When the average wavelength ( T W The average wave period is greater than 0.8L and the nearby sea area has a significant wave height H s When the wave velocity is greater than 0.04L, ships at sea should pay attention to another dangerous ship-wave coupling phenomenon, namely, continuous high wave impact. Specifically, when the wave encounters a period T E Nearly twice (about 1.8 to 3.0 times) the wave field period T W This phenomenon occurs when:

[0077]

[0078] Therefore, for a given wave field, the unsafe state caused by continuous high wave impact can also be represented by certain specific combination areas of heading-speed in a specific wave field of the ship at sea.

[0079] iii) Parametric roll and parametric harmonic roll

[0080] When the ship's inherent rolling period T REncounter period with nearby wave fields T E When the ship's stability is reduced, the ship may experience a large rolling motion in a short period of time. Similarly, the change in stability between the crest and trough of the wave will also cause parametric rolling. This phenomenon can be further divided into asymmetric parametric rolling (T R / T E ≈1) and the symmetric parameter roll (T R / T E ≈2). It is worth noting that for the second parameter roll mode, the present invention only considers the impact of waves from the bow or stern at 60° to the left and right, so as to analyze the main risks. Specifically, the above-mentioned dangerous area can be determined by the following criteria to determine the dangerous heading-speed combination:

[0081] |T R -T E |<∈T E

[0082] |T R -2T E |<∈T E ∧(0°≤α≤30°∨150°≤α≤210°∨330°≤α<360°) (6)

[0083] where ∈ is a constant used to specify the width of the safety buffer.

[0084] In order to estimate the natural rolling period T of a ship underway R , the present invention adopts the method given in the "Regulations on Intact Stability of Ships" issued by IMO, that is,

[0085]

[0086] GM(m) represents the initial stability height of the ship. B(m) is the ship's molded breadth and d(m) represents the ship's average draft. Figure 2 A polar coordinate example diagram containing all the dangerous heading-speed combinations mentioned above is shown. It intuitively shows the wave = -30° and wave period T w = 10(s)) is a safety limit for the heading and speed of a ship at sea. The present invention refers to the state set containing the heading-speed dangerous combination as the dangerous state set, that is,

[0087] A obst ≡{x=[xy θ F] T |(θ,F)} (8)

[0088] (θ, F) is the dangerous course speed combination specified in (3)-(7);

[0089] Step 2: planning two routes, namely, the danger escape phase and the path return phase, to get the ship out of danger;

[0090] As mentioned in the technical background, due to the inherent uncertainty of weather forecasts, when sailing on pre-planned global routes according to weather forecasts, the course and speed of ships may be at risk of dangerous phenomena due to slight weather changes. For example, Figure 3 Shows the wave direction from θ wave =-35° becomes θ wave =-10°, which makes the original safe heading-speed state of the ship (i.e., θ=0° and F=10 (knot)) become dangerous.

[0091] Step 21, Dangerous Escape Phase

[0092] Step 211.

[0093] According to the guidelines of MSC.1 / Circ.1228, when a ship is in the aforementioned dangerous heading-speed combination, it should reduce its speed or change its heading to prevent the occurrence of dangerous phenomena. Therefore, once such a danger is detected, the method framework proposed in the present invention will first calculate the operation of evacuating from the dangerous heading-speed combination. Specifically, the proposed framework will calculate the escape time of three different operations to guide the ship out of the dangerous area, including: i) ω(t)=F(t) / R min and turn left at a constant speed (i.e. a(t) = 0); ii) with ω(t) = -F(t) / R min and turn right at a constant speed (i.e. a(t) = 0); iii) turn right at a(t) = -a max and constant heading deceleration (ie ω(t) = 0). Then, the operation with the shortest escape time is selected, and the corresponding route is selected as the recommended evacuation path.

[0094] Step 212.

[0095] During the above disengagement action, the ship is judged whether it is in a dangerous speed and heading combination according to MSC 1228. If it is still in a dangerous state, it goes to step 1, otherwise it enters the path return stage.

[0096] Step 22: Path return phase

[0097] Steps: After completing stage A, the ship has left the dangerous navigation state. At this time, if the ship deviates from the original global route (for example, by turning to leave the dangerous state), it is necessary to return to the original global route without re-entering the dangerous course-speed combination.

[0098] Assume that the ship is at ts To complete the escape process at any time, without loss of generality, we can set t s =0, and the state is x s =[x s y s θ s F s ] T The present invention takes the original global route as a reference and adopts a track point (x f ,y f ) as the return position. Let θ f For global routes in (x f ,y f ) at the heading angle, t f The time it takes for the ship to complete the return process. The goal of the return trajectory planning algorithm proposed in this invention is to determine

[0099]

[0100] And the corresponding return time optimal path P * (τ).

[0101] The present invention applies the reachable set theory to solve the defined return trajectory planning problem. That is, the set R0[t] of all control states that the ship can reach at different times under the conditions of satisfying kinematic constraints and safety constraints is calculated.

[0102]

[0103] So that: i) ii) P(τ) satisfies (1), iii) P(0) = x s}.

[0104] The present invention will reach the boundary of the set First time reaching the destination x f The time is the shortest return time after the ship escapes from danger. By planning the state trajectory P(t), the ship is always kept at the boundary of the reachable set superior Find the connection start state x through the track backtracking method s and the terminal state x f The state trajectory P * (t). Since the forward reachable set does not contain the dangerous set, the obtained trajectory will not enter the dangerous navigation state. The specific implementation steps are as follows:

[0105] Step 221.

[0106] According to the end point of the dangerous escape path (such as Figure 4The end point of the red curve in the middle) and the global path point to be tracked determine the end point of the return path (such as Figure 4 and the end point of the blue curve)

[0107] Step 222:

[0108] Define the level set function φ(x,t) used to represent the reachable set position, and its initial value is

[0109] φ(x,0)=|xx s |2-ζ (12)

[0110] Construct a value function for representing dangerous states, whose value is

[0111]

[0112] Step 223:

[0113] The ENO-Godunov format is used to solve the control equation of the evolution of the control value function, as shown in Equation (14), to obtain the value of the value function at each moment and the position of the reachable set R0[t].

[0114]

[0115] The solution process will continue until the reachable set R0[t] contains the target state x for the first time. f , can be determined by the following formula (15):

[0116]

[0117] Step 224:

[0118] Once it is determined The forward reachable set R0[t] of x f to x s Best destinations The key calculation of this process is based on the current track point P * (t n ) Determine the previous track point P * (t n-1 ), which is achieved by solving the following ODE:

[0119]

[0120] The optimal control ω * (t n ) and a * (t n ) is determined according to formula (14), that is,

[0121]

[0122] and

[0123]

[0124] Step 225.

[0125] Will be composed as Figure 4 The path points (position, heading) of the yellow and blue curves and the matching speed are pushed to the console.

[0126] Finally, this note gives a specific application case. In this case, the initial heading angle of the ship in the ENU coordinate system is θ init =0°, in F s = 10 (knot) to track the global route. Figure 5 As shown in the figure, the wave period monitored during navigation is becomes Waves from becomes The method proposed in the present invention is triggered. In this example, the time when the weather change is detected is regarded as t=0, and a local coordinate system is established, and its origin is set as the location where the change occurs.

[0127] First, the proposed method calculates the escape time of the three suggested operations, and their reaction times are 0.0219h (ω(t)=F init / R min ), 0.0219h(ω(t)=-F init / R min ) and 0.0260h (ω(t)=0, a(t)=-a max ). On this basis, the algorithm proposed in the present invention suggests that the ship passes ω(t)=F init / R min And a(t)=0, turn left to escape from the dangerous navigation state.

[0128] After the ship leaves the danger zone, the algorithm proposed in the present invention determines the initial point of the return path (i.e., the end point of the escape path) and the target point (i.e., (2,0)(nm)).

[0129] Then, using the developed reachability calculation, the path back to the global route is calculated, such as Figure 6 As shown by the cyan line in the figure.

[0130] The above are only specific steps of the present invention and do not constitute any limitation to the protection scope of the present invention; any technical solutions formed by equivalent transformation or equivalent replacement shall fall within the protection scope of the present invention; some parts not elaborated in detail in the present invention belong to the known technologies of those skilled in the art.

Claims

1. A dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets, characterized in that: The dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets comprises the following steps: Step 1, determining whether the current ship is in a dangerous navigation state under severe weather conditions; The dangerous navigation state includes a heading-speed combination that may cause wave riding / rolling, continuous high wave impact and parametric roll / harmonic roll; Step 2: Plan two routes: the danger escape phase and the path return phase to get the ship out of danger.

2. According to claim 1, the dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets is characterized in that: In step 1, the dangerous navigation state is a state set including a heading-speed dangerous combination: A obst ≡{x=[xyθF] T |(θ,F)} x=[xyθF] T is a state variable, (x, y) represents the position, F represents its nominal speed, and θ represents the heading of the ship in the ENU coordinate system. The dangerous heading and speed combination specified in the wave riding / rolling phenomenon, continuous high wave impact phenomenon and parametric rolling / harmonic rolling phenomenon is used to judge whether it is in a dangerous navigation state.

3. The dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets according to claim 2 is characterized in that: In step 1, the wave angle in the wave riding / swinging phenomenon is defined as: a=θ wave -θ,α∈(0.360°) where θ wave is the wave direction, θ is the heading; the dangerous heading and speed combination in the wave riding / bowling phenomenon is: Among them, V is the speed of the ship and L represents the length of the ship.

4. The dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets according to claim 2 is characterized in that: In step 1, when the wave encounter period is within the preset multiple wave field period range, continuous high wave impact phenomenon will occur: T W is the wave field period, T E is the wave encounter period, V is the ship’s speed, and α is the wave angle.

5. The dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets according to claim 2 is characterized in that: In step 1, for parametric roll / harmonic roll phenomena, the dangerous heading-speed combination is determined by the following criteria: |T R -T E |<∈T E |T R -2T E |<∈T E ∧(0°≤α≤30°∨150°≤α≤210°∨330°≤α<360°) T R is the ship’s inherent rolling period, T E is the encounter period of the wave field, α is the wave head angle, and ∈ is a constant used to specify the width of the safety buffer zone.

6. The dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets according to claim 1 is characterized in that: In step 2, the danger escape phase also includes: Step 211, calculating the escape time of the three operations, and selecting the route with the shortest escape time as the recommended evacuation route; The three operations include: ω(t) = F(t) / R min and a constant speed turn to the left; ω(t)=-F(t) / R min and a constant speed turn to the right; Take a(t)=-a max and constant heading deceleration; ω(t) represents the ship's bow turning rate, R min represents the minimum turning radius allowed by the ship, F(t) represents the speed of the ship, a(t) represents the acceleration of the ship, and a max Indicates the maximum acceleration allowed for the ship; Step 212, in the evacuation path, continue to loop to determine whether it is in a dangerous speed and heading combination; if it is still in a dangerous state, go to step 1, otherwise enter the path return stage.

7. The dangerous ship-wave coupling avoidance trajectory planning method based on reachable sets according to claim 1 is characterized in that: In step 2, the path return phase includes the following steps: Step 221, determining the end point of the return path according to the end point of the dangerous escape path and the global path point to be tracked; Step 222, define the level set function φ(x,t) used to represent the reachable set position, and its initial value is: φ(x,0)=|xx s |2-g x represents the ship state variable, x s represents the initial state of the ship's path return phase, ζ represents an arbitrary small constant; Construct a value function for representing dangerous states, whose value is y represents any state on the boundary of the reachable set, and inf represents an operator that minimizes the right-hand expression in the state defined by its subscript; Step 223, using the ENO-Godunov format to solve the control equation of the evolution of the control value function, obtain the value of the value function at each time and the position of the reachable set R0[t]: θ(t) represents the heading angle variable, φ t represents the partial derivative of the value function with respect to time, φ x represents the partial derivative of the value function with respect to x, φ Y represents the partial derivative of the value function with respect to y, φ θ represents the partial derivative of the value function with respect to θ, φ F represents the partial derivative of the value function with respect to F; The solution process will continue until the reachable set R0[t] contains the target state x for the first time. f , can be judged by: F max Indicates the maximum speed allowed for the ship, x f Indicates the value of the return path end point in the x direction, y f Indicates the value of the end point of the return path in the y direction, θ f represents the heading of the ship at the end of the return path, and F represents the speed of the ship at the end of the return path; Step 224, once it is determined The forward reachable set R0[t] of f to x s Best destinations According to the current track point P * (t n ) Determine the previous track point P * (t n-1 ), which is achieved by solving the following ODE: Δt represents the time step used in the path backtracking phase, x(t n-1 ) indicates that the ship is at time t n-1 The value of the state in the x direction, x(t n ) indicates that the ship is at time t n The value of the state in the x direction, y(t n-1 ) indicates that the ship is at time t n-1 The value of the state in the y direction, y(t n ) indicates that the ship is at time t n The value of the state in the y direction, F(t n ) indicates that the ship is at time t n The speed that should be maintained, F(t n-1 ) indicates that the ship is at time t n-1 The speed that should be maintained, θ(t n ) indicates that the ship is at time t n The heading to be taken, θ(t n-1 ) indicates that the ship is at time t n-1 the heading to be taken; The optimal control ω * (t n ) and a * (t n )for: Step 225, push the trajectory composed of the path points and the matching speed to the control console.

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