Real-sea real-time trajectory forecasting method for double-propeller double-rudder ship

Abstract

The invention provides a real-sea real-time trajectory forecasting method for a double-propeller double-rudder ship, and relates to the field of ship real-sea data processing methods and ship control motion forecasting, and the method comprises the following steps: constructing a separated ship control motion equation; a wave force database of the target ship is constructed based on the generation intervals of the route, the sea condition and the navigational speed, and the ship control motion equation and the wave force database form a separated ship control motion model; reading a real sea navigation track and a navigation state, obtaining a ship motion state under a body coordinate at a forecast initial moment through processing and decomposition, and realizing latitude and longitude position information output through processing and conversion; a ship control motion equation is solved, the motion state and track prediction of the ship in the future time period is achieved in a time stepping mode, and the control precision and maneuverability can be improved by independently controlling propellers and rudders through double-propeller and double-rudder configuration.

Description

Technical Field

[0001] The present invention relates to the technical fields of ship real-sea data processing methods and ship maneuvering motion prediction technologies, and particularly relates to a real-sea real-time trajectory prediction method for a twin-screw and twin-rudder ship. Background Art

[0002] In modern marine shipping, navigation safety and efficiency are of crucial importance. Especially for twin-screw and twin-rudder ships, although this design has advantages in terms of maneuverability and stability, in a complex marine environment, it also faces more complex maneuvering and trajectory prediction problems. The advantage of this configuration is that it can improve the maneuvering accuracy and mobility by independently controlling the propellers and rudders. Compared with the traditional single-screw and single-rudder system, twin-screw and twin-rudder can provide higher thrust and more flexible maneuvering response. In a twin-screw and twin-rudder ship, mechanism modeling needs to take into account the independent control characteristics of the twin-screws and twin-rudders. An accurate mechanism model can predict the motion trajectory of the ship under different maneuvering commands, thus providing accurate trajectory prediction. Real-sea data refers to the data collected in the actual marine environment, and these data include many element data such as longitude, latitude, course, combined speed, rudder angle, main engine speed, wind speed, water depth, etc. By using the real-sea data as the initial moment value of the trajectory prediction model, the performance of the ship in the real environment can be more realistically simulated. When the ship is actually sailing, it will be affected by complex environmental factors, and the most significant one is the wave. These wave environmental forces can significantly change the motion trajectory of the ship. The change of the wave will cause irregular forces (moments) in the longitudinal and transverse directions of the ship, thus affecting its motion prediction. To improve the accuracy of trajectory prediction, it is necessary to incorporate the wave environmental forces into the model. Usually, marine sensors are used to obtain real-sea data, such as significant wave height, frequency, and wave direction information.

[0003] Generally speaking, the "real-sea real-time trajectory prediction method for twin-screw and twin-rudder ships" combines mechanism modeling, wave environmental forces, and real-sea data, providing strong support for the real-sea real-time trajectory prediction of ships. Through this comprehensive method, the ship can perform relatively accurate motion trajectory prediction under complex marine conditions, improving safety and operation efficiency. The application of this technology not only helps to understand the maneuvering performance of the ship, but also has important significance for fields such as shipping and military.

[0004] In the prior art, CN 118445980 A discloses a virtual-real data fusion visual display system for ship maneuvering motion. A virtual-real data fusion visual display system for ship maneuvering motion, which relates to the field of ship maneuvering simulation technology, proposes a virtual-real data fusion visual display system for ship maneuvering motion. First, multiple different real-time online prediction calculation units related to ship maneuvering are integrated to initially form a relatively complete virtual test system for ship motion performance. Secondly, a data processing unit and a simulation scene display unit for visual simulation data conversion, transmission, and driving are established. Finally, an integrated research and application development system for ship maneuvering is formed with the integrated ship performance prediction unit as the core module, data conversion, transmission, and driving as the interaction channels, and connecting the motion analysis visual display of the ship maneuvering physical model. The system disclosed in this invention reduces the difficulty of interdisciplinary research. The application of visual simulation technology is beneficial to shortening the test and research cycle and solving the scale effect problem between the test ship model and the actual ship. The deficiencies of this patent are as follows: (1) The system proposed in this patent has a high degree of integration, and it is difficult to implement the specific technical details and the interaction of each module; (2) It can achieve convenient and fast scale conversion between the ship model and the actual ship data, but the scale effect between the ship model and the actual ship is difficult to eliminate; (3) Scene rendering and storage require large computer resources and network conditions, which will be restricted to a certain extent in real sea shipping.

[0005] In the prior art, CN 116720363 A discloses a virtual sea trial simulation platform for ship maneuvering and its implementation method, which relates to a virtual sea trial simulation platform for ship maneuvering and its implementation method. The simulation platform includes: a parameter setting module, a simulation calculation module, a virtual reality visualization module, and a result saving and analysis module; the parameter setting module is used to set ship parameters; the simulation calculation module is used to perform real-time virtual simulation on the motion and trajectory during the ship maneuvering sea trial based on ship parameters, the professional knowledge of the simulation calculation module, and the knowledge related to the construction of the virtual sea trial platform to obtain the ship motion results; the virtual reality visualization module is used to intuitively display and real-time render the motion and trajectory of the ship through the ship motion results; the result saving and analysis module is used to store and call the ship motion results and perform maneuvering criteria based on relevant specifications. The purpose of this invention is to improve the user's understanding and mastery level of the knowledge related to the ship maneuvering sea trial prediction method and result analysis. The deficiencies of this patent are as follows: (1) The empirical formula method for calculating ship hydrodynamic derivatives is difficult to apply to special ship types; (2) It is designed for single-screw and single-rudder ship types; (3) The sea trial simulation does not consider environmental impacts such as waves; (4) It fails to achieve the input and output of real sea data.

[0006] It can be seen that there are relatively few real-time trajectory prediction methods for the actual sea based on ship maneuvering motion prediction methods. Ship maneuverability involves aspects such as the construction of ship simulation systems, the design of simulation sea trial platforms, and the modeling methods of the maneuvering motions of special ship types, which are quite different from the real-time trajectory prediction method for the actual sea of twin-screw and twin-rudder ships. Therefore, the following technical problems exist in the existing technology:

[0007] 1. The virtual-real fusion system of ship maneuvering motion is relatively conceptual, and it is difficult to coordinate the calling of specific embedded modules, algorithms, and modules;

[0008] 2. Most of the ship maneuvering motion prediction or modeling methods are in still water, without considering environmental factors such as waves, and it is difficult to use them in actual sea trials or voyages;

[0009] 3. The use of real-sea data and environmental acquisition information of ship navigation is insufficient. If these information can be used as the input at the initial moment for future maneuvering motion prediction, it may be possible to predict the navigation trajectory of the ship in the next short two minutes, which has important application significance for ship collision avoidance, obstacle avoidance, etc.;

[0010] 4. The advantage of the twin-screw and twin-rudder configuration is that it can improve the control accuracy and maneuverability by independently controlling the propellers and rudders. Compared with the traditional single-screw and single-rudder system, in twin-screw and twin-rudder ships, mechanism modeling needs to consider the independent control characteristics of the twin-screws and twin-rudders. Summary of the Invention

[0011] To solve the above technical problems, the present invention proposes a real-time trajectory prediction method for the actual sea of twin-screw and twin-rudder ships, including the following steps:

[0012] Step 1: Construct a separated ship maneuvering motion equation;

[0013] Step 2: Based on the route, sea conditions, and the interval where the ship speed occurs, construct a wave force database for the target ship. The ship maneuvering motion equation and the wave force database constitute a separated ship maneuvering motion model;

[0014] Step 3: Read the real-sea navigation trajectory and navigation state, and obtain the ship motion state in the body coordinates at the prediction initial moment through processing and decomposition, and realize the output of longitude and latitude position information through processing and conversion;

[0015] Step 4: Solve the ship maneuvering motion equation, and adopt a time-stepping method to further realize the prediction of the ship's motion state and trajectory in the future time period.

[0016] In a preferred embodiment, in Step 1, the ship maneuvering motion equation is shown as follows:

[0017]

[0018] Wherein, m and I zzare the ship mass and the moment of inertia about the yaw direction, respectively, m x 、m y 、J zz are the added mass in the longitudinal and lateral directions of the ship and the added moment of inertia about the yaw direction, respectively; the unknowns are u, v, and r, which are the longitudinal velocity u, the lateral velocity v, and the yaw angular velocity r, respectively; the right-hand side terms X and Y represent the longitudinal and lateral forces on the hull, and N represents the moment acting on the hull in the direction of the bow rotation, where the terms with subscripts H, R, P, and W represent the hydrodynamic forces and moments acting on the hull, propeller, rudder, and waves, respectively, and the lateral force caused by the rotation of the propeller and its moment about the center of gravity are ignored.

[0019] In the preferred embodiment, in step 3, the longitude, latitude, resultant velocity, course angle, rudder angle, and rotational speed at the previous moment and the current moment are read, the geographical coordinates are converted into plane coordinates, the course angle is obtained by decomposing using the plane coordinates and velocity information, and then the drift angle is obtained. The longitudinal and lateral velocities in the body coordinate system are decomposed for ship motion prediction, and the plane coordinates are inversely converted into geographical coordinates during the prediction process.

[0020] In the preferred embodiment, the real-time longitude, latitude, resultant velocity, and course angle information of the ship and the wave period, wavelength, and significant wave height of the current sea state level are used as inputs. The obtained longitude and latitude position information is converted into plane coordinates through geographical coordinate conversion. The conversion formula is as follows:

[0021]

[0022] where R is the average radius of the earth; x and y represent the longitudinal and lateral coordinate axes of the plane coordinates, respectively.

[0023] In the preferred embodiment, the direction of the resultant velocity U is calculated, and the angle α between the resultant velocity and the y0 axis is used to represent it:

[0024]

[0025] The resultant velocity is decomposed into the geodetic coordinate system:

[0026]

[0027] In the preferred embodiment, the course angle θ is calculated:

[0028]

[0029] The drift angle β is calculated:

[0030]

[0031] where ψ represents the course angle.

[0032] In a preferred embodiment, the initial values of the velocities u m and v m in the body coordinates at the current moment of the ship maneuvering motion prediction are calculated as follows:

[0033]

[0034] In a preferred embodiment, the viscous hydrodynamic forces acting on the hull are calculated by the following formula:

[0035]

[0036] The non-dimensional longitudinal viscous hydrodynamic force X′ H acting on the hull is expressed as the sum of the non-dimensional still water resistance R′0 and the quadratic and quartic terms of the non-dimensional lateral velocity v′ and the non-dimensional yaw angular velocity r′. X' vv 、X' vr 、X' rr and X' vvvv are the longitudinal non-dimensional hydrodynamic derivatives; the non-dimensional lateral viscous hydrodynamic force Y′ H and the non-dimensional yaw viscous hydrodynamic moment N′ H are expressed as the sum of the linear and cubic terms of the non-dimensional lateral velocity v′ and the non-dimensional yaw angular velocity r′. Y' v 、Y' r 、Y' vvv 、Y' vvr 、Y' vrr and Y' rrr are the lateral non-dimensional hydrodynamic derivatives; N' v 、N' r 、N' vvv 、N' vvr 、N' vrr and N' rrr are the non-dimensional moment derivatives about the heading.

[0037] In a preferred embodiment, the forces and moments generated by the propeller are calculated by the following formula:

[0038]

[0039] In the formula, X P 、Y P 、N p on the left side of the equal sign respectively represent the longitudinal thrust of the propeller, the acting force generated laterally, and the turning moment about the heading. The subscripts p and s in the curly brackets represent the left and right propellers respectively; n p 、D p 、t P 、K T are the rotational speed, diameter, thrust deduction coefficient, and propeller thrust coefficient of the propeller respectively. ρ represents the density of seawater, and l p′ is the correction factor for the lateral velocity caused by the yawing motion, r′ is the yaw angular velocity, and c yp is the propeller side force coefficient, L is the ship length, d is the draft, and the advance coefficient is J P .

[0040] In the preferred embodiment, the hydrodynamic force caused by the rudder is calculated by the following formula:

[0041]

[0042] In the formula, X on the left side of the equal sign R , Y R , N R respectively represent the longitudinal force, lateral force, and yaw moment generated by the rudder. The subscripts p and s in the curly brackets respectively represent the left and right rudders. The longitudinal position of the rudder is x R , the correction factor for the lateral force induced by the steering on the hull is a H , the rudder angle is δ, and the rudder resistance reduction coefficient is t R .

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] Design a real-time sea trajectory prediction method for twin-screw and twin-rudder ships. Based on the separated ship maneuvering motion mechanism modeling method, a ship maneuvering motion mathematical model is constructed. Independent mechanism modeling is carried out for the twin-screw and twin-rudder to achieve the effect of independent control respectively. According to the ship speed range and the wind and wave levels of the route, a wave force database is constructed in advance. By using the real-time longitude, latitude, ship speed and other real-time navigation states and real-time wave information in the real sea as the initial maneuvering motion prediction values at the current moment, a short-term trajectory prediction for the next two minutes is carried out, and the trajectory and navigation states in the next two minutes can be visually displayed.

[0045] This method is a real-time sea trajectory prediction method for twin-screw and twin-rudder ships, providing a simulation platform for ship maneuvering motion simulation prediction teaching, providing a prediction means and an auxiliary decision-making basis for ship collision avoidance and obstacle avoidance in actual sea trials of ships, and promoting the integration and application of ship maneuvering motion prediction virtual simulation and actual sea trials and navigation. The present invention is a method driven purely by physics, does not involve neural networks, and only considers the wave force model without adding wind and current models. Description of the Drawings

[0046] Figure 1 is a schematic diagram of the geodetic coordinate system and the body-fixed coordinate system;

[0047] Figure 2 is a schematic diagram of the working conditions for obtaining hydrodynamic derivatives by captive ship simulation;

[0048] Figure 3 is a schematic diagram of the wave encounter frequency of the ship turning in waves;

[0049] Figure 4 It is a diagram for the calculation method of the second-order drift force of a ship in irregular waves;

[0050] Figure 5 It is a diagram for the acquisition results of the ship trajectory and navigation state information of a partial shipborne inertial navigation system;

[0051] Figure 6 It is a diagram for the acquisition results of the wave environment information collected by a shipborne radar;

[0052] Figure 7 It is a flowchart for the implementation of the inventive method. Detailed implementation manners

[0053] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0054] In the accompanying drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the components in the system and show the connection relationships of the various parts in the device, only the relative positional relationships between the components are clearly distinguished, and it does not constitute a limitation on the signal transmission direction, connection sequence, and the sizes, sizes, and shapes of the various parts of the structure within the component or structure.

[0055] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that may be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not all refer to the same embodiment, nor is it a separate or selectively mutually exclusive embodiment with other embodiments.

[0056] The present invention provides a real-sea real-time trajectory prediction method for a twin-screw and twin-rudder ship, including a separated ship maneuvering motion modeling, constructing a wave force database based on the ship speed and sea condition intervals of the shipping route, processing and using the real-sea real-time trajectory navigation state data and wave acquisition data, setting the ship type parameters, and solving the ship maneuvering motion equation.

[0057] Step 1: Construct a separated ship maneuvering motion equation.

[0058] The separated ship maneuvering motion modeling is based on the first principles, and a physical or mathematical model is constructed for the target problem. The forces acting on the ship are decomposed into three parts: the ship, the propeller, and the rudder, and the interference hydrodynamic coefficients among the three are added, and on this basis, the influence of the environmental acting forces is added to obtain the ship maneuvering motion model.

[0059] When predicting ship maneuvering motion using a separated ship maneuvering motion model, it is necessary to clarify two coordinate systems used: the earth coordinate system x0y0z0 and the body translation coordinate system xyz, as Figure 1 shown.

[0060] The ship maneuvering motion equation is established in the body translation coordinate system and is shown as follows:

[0061] The above equation is the ship maneuvering motion equation to be solved. m and I zz are the ship mass and the moment of inertia about the yaw axis respectively. m x , m y , J zz are the added mass in the longitudinal and lateral directions and the added moment of inertia about the yaw axis of the ship respectively. The unknowns are u, v, and r, which are the longitudinal velocity u, the lateral velocity v, and the yaw angular velocity r respectively. The right-hand terms X and Y represent the longitudinal and lateral forces on the hull respectively, and N represents the moment on the hull about the direction of turning the bow. The terms with subscripts H, R, P, and W represent the hydrodynamic forces and moments acting on the hull, propeller, rudder, and waves respectively. The lateral force caused by the rotation of the propeller and its moment about the center of gravity are ignored.

[0062] To facilitate subsequent calculations and comparisons, a dimensionless method is further introduced. All types of variables are made dimensionless according to the following equations and marked with a prime (′).

[0063]

[0064] In the equations: ρ represents the seawater density with the unit of kg / m 3 ; L represents the ship length with the unit of m; U represents the ship speed at the center of gravity with the unit of m / s.

[0065] The viscous hydrodynamic force acting on the hull is calculated by the following formula:

[0066]

[0067] The dimensionless longitudinal viscous hydrodynamic force X′ H can be expressed as the sum of the dimensionless static water resistance R0′ and the quadratic and quartic terms of the dimensionless lateral velocity v′ and the dimensionless yaw angular velocity r′. X' vv , X' vr , X' rr and X' vvvv are the longitudinal dimensionless hydrodynamic force derivatives; the dimensionless lateral viscous hydrodynamic force Y′ H and the dimensionless yaw viscous hydrodynamic moment N′ HExpressed as the sum of the first and third order terms of the non-dimensional lateral velocity v′ and yaw angular velocity r′, Y' v 、Y' r 、Y' vvv 、Y' vvr 、Y' vrr and Y' rrr are the non-dimensional lateral hydrodynamic derivatives; N' v 、N' r 、N' vvv 、N' vvr 、N' vrr and N' rrr are the non-dimensional moment derivatives about the heading.

[0068] Among them, many hydrodynamic derivatives are obtained by simulating captive model tests using captive model tests or CFD methods, including oblique towing motion tests and turning motion tests as Figure 2 shown, and the specific working conditions of the tests are shown in Table 1:

[0069] Table 1 Simulated working conditions of captive model tests

[0070]

[0071] The external force of the propeller is mainly reflected in generating the propulsive force. In addition, under maneuvering conditions, the lateral force of the propeller shows a relatively high magnitude, so its influence on the ship motion response cannot be ignored. The forces and moments generated by the propeller are calculated by the following formula:

[0072]

[0073] In the formula, X P 、Y P 、N p respectively represent the longitudinal thrust of the propeller, the lateral force generated, and the yaw moment about the heading. The subscripts p and s in the curly brackets represent the left and right propellers respectively. n p 、D p 、t P 、K T are the rotational speed, diameter, thrust deduction coefficient, and propeller thrust coefficient of the propeller respectively. The propeller thrust deduction coefficient t P is calculated using the Hankel formula t P = 0.50C P - 0.18; The propeller thrust coefficient K T can be expressed as a cubic polynomial of the advance coefficient J P , and is calculated according to . Among them, J P is the advance coefficient, and is calculated according to J P = [Ucosβ(1 - w P )] / (n P DP ) Calculation, where w p is the wake fraction at the propeller, and the Hirano model is adopted The wake fraction w of the propeller when the ship is going straight P0 Adopt w P0 = 0.55C B - 0.2 for calculation; β′ P is the drift angle at the propeller, calculated according to β′ P = β - x′ P r′, where x′ P is the longitudinal position of the propeller, take x′ P = - 0.48. L is the ship length, d is the draft, c yp is the lateral force coefficient of the propeller, β is the drift angle, l p ′ is the correction factor for the lateral velocity caused by the yawing motion.

[0074] The hydrodynamic force caused by the rudder is calculated by the following formula:

[0075]

[0076] In the formula, X on the left side of the equal sign R , Y R , N R respectively represent the longitudinal force, lateral force and yawing moment in the bow direction generated by the rudder. The subscripts p and s in the curly brackets represent the left and right rudders respectively. The rudder resistance reduction coefficient t R is calculated approximately using ; the correction factor a for the lateral force induced by steering on the hull H is calculated approximately using ; the distance x′ between the acting point of the lateral force on the hull caused by steering and the center of gravity of the ship H is calculated using x′ H = -(0.4 + 0.1C b ) for calculation; the longitudinal position x of the rudder R is taken as - 0.5. F Np , F Ns respectively represent the normal pressures of the left and right rudders. The normal pressure F of the rudder N can be calculated using to calculate the normal pressures of the left and right rudders respectively. f a represents the lift gradient coefficient of the rudder. f a = 6.13Λ / (Λ + 2.25), where Λ represents the aspect ratio of the rudder; A R represents the rudder area; α R represents the effective angle of attack. α R = δ - v R / u R ; U R represents the resultant velocity flowing into the rudder u R and vR They respectively represent the longitudinal velocity component and the lateral velocity component of the rudder.

[0077] For the calculation of added mass and added moment of inertia, from the perspective of convenience and practicality, the added mass and added moment of inertia of the ship can be calculated using regression formulas:

[0078]

[0079] So far, in this step, mechanism modeling is carried out separately for the twin propellers and twin rudders, enabling the propellers and rudders to be controlled separately. By separately considering the establishment mechanism models of individual propellers and rudders, and then by separately reading the respective control parameters of each propeller and rudder, mainly including parameters such as rudder angle, rate of turning the rudder, target rudder angle, rotational speed, and open water efficiency of the propeller, separate control of any propeller and rudder can be achieved when predicting the ship's maneuvering motion trajectory.

[0080] Step 2: Construct a wave force database of the target ship based on the route, sea conditions, and the interval where the ship speed occurs. The ship maneuvering motion equation and the wave force database constitute a separated ship maneuvering motion model.

[0081] Specifically, a wave force database containing a sufficient number of working conditions is constructed in advance. When reading the corresponding sea condition information, interpolation calculation is performed to obtain wave forces closer to the real sea conditions as the environmental wave force terms for ship maneuvering motion prediction. For the wave forces affected by the environment, the average wave drift force and moment acting on the target ship need to be calculated based on the potential flow method, considering the wave direction, ship speed, and wave frequency. The calculation working conditions are shown in Table 2:

[0082] Table 2 Calculation working conditions of the wave force database

[0083]

[0084] The average wave drift force of the ship in waves is calculated based on the near-field method in the potential flow calculation software. Among them, the longitudinal force The lateral force And the yaw moment For the force and moment, according to The non-dimensional average wave force coefficient is obtained. In the formula, ρ and g are respectively the water density and the acceleration due to gravity, L and B are respectively the ship length and the ship width, and h is the wave amplitude of the incident wave. The obtained non-dimensional average wave force coefficient is sorted into the wave force database according to the wavelength-to-ship-length ratio, wave direction, and ship speed.

[0085] So far, a complete separated ship maneuvering motion model has been constructed, that is Figure 7 The sub-module of the system of equations to be solved in the real-time motion prediction module based on the ship maneuvering motion equation. In this step, a wave force database of the target ship is constructed in advance based on the route, sea conditions, and the interval where the ship speed occurs, realizing the real-time prediction of the ship's maneuvering motion in the wave environment.

[0086] Specifically, based on the potential flow theory, a wave force calculation software is used to construct a wave force database in advance according to the longitudinal, lateral, and bow mean wave drift forces at different ship speeds in the main shipping routes of the ship and the sea state occurrence intervals. After reading the real-time wave force data, wave force interpolation is performed according to the ship speed to provide wave force information for the real-time prediction of ship maneuvering motions in real seas.

[0087] The specific wave force interpolation is explained in detail as follows: When the ship makes a turning maneuver in waves, after a given wave direction, due to the changes in the ship speed and heading angle during the movement process, the wave frequencies and wave directions encountered also change. As Figure 4 shown, taking regular waves as an example, it is assumed that the waves propagate along the -x0 direction of the earth coordinate system, and the initial state of the ship (position A) is head-on to the waves. The actual encounter frequency is greater than the wave frequency observed in the earth-fixed coordinate system; when the ship moves to a heading angle of 90° (position B) and 270° (position D), it is beam-on to the waves, and the encounter frequency is equal to the frequency in the earth coordinate system; when the heading angle is 180° (position C), it is following the waves, and the encounter frequency is less than the frequency in the earth coordinate system.

[0088] For the maneuvering motions in irregular waves, according to the sea state information, the irregular waves in the ship's navigation area are discretized to obtain a series of regular waves. The average wave drift forces on the ship under each regular wave condition have been calculated and formed a database before. As Figure 5 shown, for the time series of irregular waves, the method of equivalent half-wavelength regular waves can be adopted, which is regarded as being composed of half-wavelength regular waves with different periods and wave amplitudes spliced together. The time interval between adjacent wave crests and wave troughs is the half-period T i / 2 of the regular wave, and the height difference between the wave crest and the wave trough is twice the wave amplitude of the regular wave. Within this half-wave that the ship has experienced, the corresponding wave drift force is found from the database and added to the right end of the MMG equation, and then the equation is solved to obtain the simulation results of the turning motion in irregular waves. During the interpolation process of the wave drift force, a time delay processing method is adopted, that is, the wave drift force is included after a short period of time at the beginning of the simulation, about one average period, to ensure that the wave period and wave amplitude within the current time step are known.

[0089] Step 3: Read the real-sea navigation trajectory and navigation state, and obtain the ship motion state in the body coordinate system at the initial moment of prediction through processing and decomposition, and realize the output of the longitude and latitude position information through processing and conversion.

[0090] This step provides the initial values and the longitude and latitude information of the trajectory for the real-time prediction of ship maneuvering motions in real seas for use and output. Specifically, it includes: setting control parameters and reading real-time ship motion and environmental information, measuring and calculating real-sea data parameters such as the ship's position, speed, heading, and attitude through the shipborne inertial navigation system, corresponding Figure 7There are two modules: the acquisition information input module and the control parameter input module.

[0091] The control parameters include: simulation start time, simulation end time, simulation time step. The real-time ship motion and environmental information readings include: previous moment latitude coordinate, current moment latitude coordinate, previous moment longitude coordinate, current moment longitude coordinate, previous moment heading angle, current moment heading angle, current moment resultant velocity, rudder rate, current moment left rudder angle, current moment right rudder angle, target rudder angle, left propeller speed, right propeller speed, significant wave height, frequency and wave direction of the current sea state level.

[0092] The real sea data parameters such as ship position, speed, heading and attitude are measured and calculated through the shipborne inertial navigation system as Figure 3 shown; the marine environmental information is measured by the shipborne radar as Figure 6 shown, and the wave environmental information is obtained through the spectral analysis of the Fourier transform. The information such as the real-time longitude, latitude, resultant velocity, and heading angle of the ship and the wave period, wavelength, and significant wave height of the current sea state level are used as inputs. The geographical coordinates (i.e., longitude and latitude information) obtained from the real sea acquisition are converted into plane coordinates (i.e., metric coordinates) through the coordinate transformation method. The plane coordinates are used in the calculation throughout the prediction process. In order to obtain the geographical coordinates as the output result, the plane coordinates need to be converted into geographical coordinates through the inverse transformation formula after each time step calculation is completed. The transformation formula is as follows:

[0093]

[0094] In the formula, R is the average radius of the earth, R = 6.378×10 6 m; x and y represent the longitudinal and transverse coordinate axes of the plane coordinates respectively.

[0095] The resultant velocity is decomposed to obtain the longitudinal velocity u m = 0.5144Ucos(β) and the transverse velocity v m = -0.5144Usin(β) in the body coordinate system of the ship, where U is the resultant velocity with the unit of kn; β is the drift angle.

[0096] Since the drift angle is difficult to measure with instruments, it needs to be obtained by decomposing the resultant velocity vector in combination with the heading angle. The decomposition method is expressed by the following formula:

[0097] Calculate the direction of the resultant velocity, and use the α angle to represent the angle between the resultant velocity and the y0 axis:

[0098]

[0099] Decompose the resultant velocity into the geodetic coordinate system:

[0100]

[0101] Calculate the course angle θ:

[0102]

[0103] Calculate the drift angle β:

[0104]

[0105] In the formula, ψ represents the course angle, and the unit is °.

[0106] Since the ship real sea information collector cannot directly collect the longitudinal and lateral speeds of the ship in the body coordinates, in order to make the prediction results more accurate, it is necessary to add the state of the ship at the moment when the prediction starts, that is, the initial values of the speeds u m and v m in the body coordinates at the initial moment of ship maneuvering motion prediction, which are calculated using the following formula:

[0107]

[0108] This step reads information such as the real sea navigation track and navigation state of the ship, decomposes and obtains the ship motion state in the body coordinates at the prediction initial moment through program processing, and converts and outputs the longitude and latitude position information through program processing, providing the initial values and longitude and latitude information of the track for real-time real sea ship maneuvering motion prediction. Specifically, this key point reads information such as longitude, latitude, resultant velocity, course angle, rudder angle, and rotational speed at the previous moment and the current moment, converts the geographic coordinates into plane coordinates, uses the plane coordinates and speed and other information to decompose to obtain the course angle and then calculate the drift angle, decomposes to obtain the longitudinal and lateral speeds in the body coordinates for ship motion prediction, and performs the inverse conversion of the plane coordinates into geographic coordinates during the prediction process.

[0109] Step 4, solve the ship maneuvering motion equation, and adopt the time-stepping method to further realize the prediction of the motion state and track of the ship in the future time period.

[0110] The ship type parameter setting and the solution of the ship maneuvering motion equation correspond to Figure 5 the ship type parameter input module and the solution method sub-module in the real-time motion prediction module based on the ship maneuvering motion equation in

[0111] The ship parameters include: ship parameters: length between perpendiculars, molded breadth, forward draft, after draft, block coefficient, prismatic coefficient, displacement; propeller parameters: propeller diameter, open water curve coefficient of propeller, propeller pitch, distance of propeller pitch center from midship longitudinal section, longitudinal position of propeller; rudder parameters: rudder height, aspect ratio of rudder, rudder area, distance of rudder from midship longitudinal section, longitudinal position of rudder.

[0112] The fourth-order Runge-Kutta numerical solution technique is adopted to solve the differential equation set, namely the ship maneuvering motion equation set, and the time-stepping method is used to realize the prediction of the ship's motion state and trajectory in the next two minutes.

[0113] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0114] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A real-time trajectory prediction method for a double-propeller double-rudder ship in real sea, characterized in that: The following steps are involved: Step 1: Construct the separated ship maneuvering motion equations; Step 2: Construct a wave force database of the target ship based on the route, sea conditions and speed interval. The ship maneuvering motion equation and the wave force database constitute a separate ship maneuvering motion model. Step 3: Read the actual sea navigation track and navigation state, obtain the ship's motion state in the body coordinates at the initial moment of the forecast by processing and decomposition, and output the longitude and latitude position information by processing and conversion; Step 4: Solve the ship maneuvering motion equations and use the time stepping method to predict the ship's motion state and trajectory in the future time period.

2. The real-time trajectory prediction method for a double-propeller and double-rudder ship in real sea according to claim 1 is characterized in that: In step 1, the ship maneuvering motion equation is as follows: Among them, m and I zz are respectively the ship mass and the moment of inertia in the yaw direction, m x 、m y , J zz are the additional masses in the longitudinal and transverse directions and the additional moments of inertia in the yaw direction of the ship respectively; the unknown quantities are u, v and r, which are the longitudinal velocity u, the transverse velocity v, and the yaw angular velocity r respectively; the terms X and Y on the right side represent the longitudinal and transverse forces on the hull respectively, and N represents the moment on the bow direction of the hull, among which the terms with subscripts H, R, P and W represent the hydrodynamic forces and moments acting on the hull, propeller, rudder and waves respectively, and the lateral force caused by the rotation of the propeller and its moment on the center of gravity are neglected.

3. The real-time trajectory prediction method for a double-propeller double-rudder ship in real sea according to claim 1 is characterized in that: In step 3, the longitude, latitude, combined speed, heading angle, rudder angle, and rotation speed of the previous moment and the current moment are read, the geographic coordinates are converted into plane coordinates, the plane coordinates and speed information are used to decompose the speed angle, and then the drift angle is obtained, and the longitudinal and lateral speeds of the body coordinates are decomposed to predict the ship motion, and the plane coordinates are reversely converted into geographic coordinates during the prediction process.

4. The real-time trajectory prediction method for a double-propeller and double-rudder ship in real sea according to claim 3 is characterized in that: The ship's real-time longitude, latitude, combined speed, heading angle information and the wave period, wavelength, and significant wave height of the current sea condition level are used as input, and the obtained longitude and latitude position information is converted into plane coordinates through geographic coordinates. The conversion formula is as follows: Where R is the average radius of the earth; x and y represent the longitudinal and transverse axes of the plane coordinates, respectively.

5. The real-time sea trajectory prediction method for a double-propeller double-rudder ship according to claim 4 is characterized in that: Calculate the direction of the resultant velocity U, and use angle α to represent the angle between the resultant velocity and the y0 axis: The total velocity is decomposed into the geodetic coordinate system:

6. The real-time track prediction method for a double-propeller double-rudder ship in real sea according to claim 5, characterized in that: Calculate the speed angle θ: Calculate the drift angle β: Where ψ represents the heading angle.

7. The real-time sea trajectory prediction method for a double-propeller double-rudder ship according to claim 6 is characterized in that: Calculate the initial velocity u in the body coordinates at the current moment of the ship maneuvering motion forecast m and v m :

8. The real-time sea trajectory prediction method for a double-propeller double-rudder ship according to claim 1 is characterized in that: The viscous hydrodynamic force acting on the hull is calculated using the following formula: The longitudinal dimensionless viscous hydrodynamic force X′ acting on the hull H It is expressed as the sum of the dimensionless hydrostatic resistance R′0 and the quadratic and quartic terms of the dimensionless lateral velocity v′ and the dimensionless yaw angular velocity r′, X′ vv , X' vr , X' rr With X' vvvv is the longitudinal dimensionless hydrodynamic derivative; the transverse dimensionless viscous hydrodynamic Y′ H and the dimensionless viscous hydrodynamic moment N′ H It is expressed as the sum of the first and third terms of the dimensionless lateral velocity v′ and the yaw angular velocity r′, Y′ v , Y' r , Y' vvv , Y' vvr , Y' vrr With Y' rrr is the lateral dimensionless hydrodynamic derivative; N' v 、N' r 、N' vvv 、N' vvr 、N' vrr With N' rrr is the dimensionless moment derivative toward the heading.

9. The real-time sea trajectory prediction method for a double-propeller double-rudder ship according to claim 8, characterized in that: The forces and moments generated by the propeller are calculated using the following formula: In the formula, the X on the left side of the equal sign is P , Y P 、N p They represent the longitudinal thrust of the propeller, the lateral force and the bow moment of the bow, respectively. The p and s in the subscript brackets represent the left and right propellers respectively. p , D p ,t P , K T are propeller speed, diameter, thrust reduction coefficient and propeller thrust coefficient respectively, ρ represents the seawater density, l p ′ is the correction factor of the lateral velocity caused by the turning motion, r′ is the heading angular velocity, c yp is the propeller side force coefficient, L is the ship length, d is the draft, and the speed coefficient is J P .

10. The real-time track prediction method for a double-propeller double-rudder ship in real sea according to claim 9, characterized in that: The hydrodynamic force caused by the rudder is calculated using the following formula: In the formula, the X on the left side of the equal sign is R , Y R 、N R The p and s in the brackets represent the left and right rudders, respectively. The longitudinal position of the rudder is x. R , the correction factor of the steering-induced hull transverse force is a H , the rudder angle is δ, and the rudder resistance reduction coefficient is t R .

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