A Method for Establishing an Automatic Berthing Model for Underactuated Ships

Abstract

This invention discloses a method for establishing an automatic berthing model for underactuated ships, relating to automatic berthing and unberthing of ships. The method includes: establishing a three-dimensional geometric model of the ship based on its linesform, propeller linesform, and rudder linesform; establishing a numerical simulation environment for the three-dimensional geometric model using computational fluid dynamics (CFD) software, and conducting numerical simulation experiments on the three-dimensional geometric model within the numerical simulation environment; establishing a mathematical model of the ship's berthing process based on the numerical simulation experiments; and identifying the ship's hydrodynamic parameters using the constrained least squares algorithm based on the mathematical model of the ship's berthing process. This invention, based on ship CFD virtual numerical simulation and constrained least squares algorithm for identifying hydrodynamic coefficients, effectively solves the problems of difficult acquisition of actual ship test data and high test costs. Furthermore, the use of CFD software allows for simultaneous execution of multiple sets and types of tests, effectively improving the efficiency of model establishment.

Description

Technical Field

[0001] This invention relates to the field of automated berthing and unberthing of ships, and more specifically to the establishment of a mathematical model for the automated berthing process of underactuated ships. Background Technology

[0002] In military and marine engineering fields, researching mathematical models for automated berthing processes is increasingly important to improve the maneuverability and control of large ships, enhance operational efficiency, prevent berthing and unberthing safety accidents, and reduce berthing and unberthing costs. During automated berthing of underactuated vessels, the motion environment involves shallow water, low speed, ship suction effect, and shore wall effect, coupled with wind, waves, and current interference, making traditional modeling methods less adaptable. Inaccurate mathematical models significantly increase the difficulty of designing automated control algorithms, and simulation verification before actual ship trials cannot be guaranteed, failing to meet the requirements of automated control during berthing.

[0003] Therefore, how to adapt to the automatic berthing environment of ships and accurately establish an automatic berthing model of ships is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a method for establishing an automatic berthing model for underactuated ships, which at least partially solves the technical problems existing in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for establishing an automatic berthing model for underactuated ships includes the following steps:

[0007] Based on the ship's lines diagram, propeller lines diagram, and rudder lines diagram, establish a three-dimensional geometric model of the ship;

[0008] A numerical simulation environment for the three-dimensional geometric model of the ship was established based on computational fluid dynamics (CFD) software, and a numerical simulation test of the three-dimensional geometric model of the ship was conducted in the numerical simulation environment.

[0009] A mathematical model of the ship berthing process was established based on numerical simulation experiments.

[0010] Based on the mathematical model of the ship berthing process, the constrained least squares algorithm is used to identify the ship's hydrodynamic parameters.

[0011] Preferably, the numerical simulation environment for establishing the three-dimensional geometric model of the ship based on computational fluid dynamics (CFD) software specifically includes:

[0012] In the CFD software, the hull length of the ship's three-dimensional geometric model is set to L, and the hull surface is set as a no-slip wall.

[0013] Using the intersection of the ship's hull baseline and stern in the three-dimensional geometric model of the ship as the origin of the coordinate system, inflow boundaries are established at a distance of 1L from the bow and 2L from the left and right sides of the ship, outflow boundaries are established at a distance of 2L from the stern, upper interface is established at a distance of 1L from above the ship, and lower interface is established at a distance of 2L from below the ship.

[0014] Preferably, the numerical simulation test of the three-dimensional geometric model of the ship is a specific ship drift angle oblique navigation test.

[0015] Preferably, a mathematical model of the ship berthing process is established, specifically including:

[0016] Establish a mathematical model of the ship's 4-DOF nonlinear motion:

[0017]

[0018] Where m is the ship's mass; m x m y These represent the longitudinal attachment mass and the lateral additional mass of the ship in the attachment coordinate system, respectively. Let represent the ship's longitudinal acceleration, lateral acceleration, and bow angle acceleration in the attached coordinate system, respectively; u, v, and r represent the ship's speed, lateral velocity, and bow angle velocity, respectively; I z J z These represent the ship's additional moment of inertia due to rolling and the ship's own moment of inertia due to rolling, respectively.

[0019] X, Y, and N represent the longitudinal force, lateral force, and bow roll moment acting on the hull, respectively.

[0020] Preferably, X, Y, and N are represented by the following expressions:

[0021] X = X H +T+X R +R

[0022] Y = Y H +Y R

[0023] N = N H +N R

[0024] In the formula, X H T, X R R represents the longitudinal hydrodynamic viscous force of the hull, the propeller thrust, the longitudinal component of the rudder force, and the hull resistance, respectively; Y H Y R N represents the lateral hydroviscous force of the hull and the lateral component of the rudder force, respectively; H N RThese are the bow roll moment generated by the hull fluid viscosity force and the bow roll moment generated by the rudder force, respectively.

[0025] Preferably, it also includes further supplementation of the hull viscous hydrodynamic parameters under low-speed and large drift angle motions, specifically including:

[0026] X H =X uu u|u|+X uvv UV 2 +X uuvv u 2 v 2 +X vv v 2

[0027] Y H =Y uuv u 2 v+Y uuvvv u 2 v 3 +Y vvv v 3

[0028] N H =N uv uv+N uuv u 2 v+N uuvvv u 2 v 3 +N vvv v 3

[0029] Among them, X H Y H N H represents the longitudinal fluid viscous force, the transverse fluid viscous force, and the bow moment generated by the fluid viscous force of the hull, respectively; u, v, and r represent the ship's speed, transverse velocity, and bow angular velocity, respectively; X uu X is the drag coefficient for straight-line flight; uvv X uuvv X vv respectively uv 2 u 2 v 2 v 2 The longitudinal viscous hydrodynamic coefficient generated by the term; Y uuv Y uuvvv Y vvv u 2 v、u 2 v 3 v 3 The transverse viscous hydrodynamic coefficient generated by the term; N uv N uuv N uuvvvN vvv They are uv and u respectively 2 v、u 2 v 3 v 3 The viscous hydrodynamic coefficient in the heading direction generated by the term.

[0030] Preferably, the constrained least squares algorithm is used to identify the ship's hydrodynamic parameters. The constrained least squares algorithm specifically includes the following formulas:

[0031]

[0032] In the formula: y(k) represents the variable to be optimized; t represents the identification process time; t max Indicates the time when the identification process ended; X out X represents the sum of forces acting on the hull calculated by CFD software. est (x) represents the hull force model that needs to be identified, and x represents the parameter that needs to be identified.

[0033] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a method for establishing an automatic berthing model for underactuated ships, which has the following beneficial effects:

[0034] (1) This invention proposes a model building method based on ship CFD virtual numerical simulation and constrained least squares algorithm to identify hydrodynamic coefficients without over-reliance on actual ship tests. This effectively solves the problems of difficult acquisition of actual ship test data and high test costs. Furthermore, CFD software can be used to conduct multiple sets and types of tests simultaneously, which effectively improves the efficiency of model building.

[0035] (2) This invention uses the constrained least squares algorithm to identify the hydrodynamic parameters of a ship. The constrained least squares algorithm can identify hydrodynamic parameters based on the state variables of the ship during its self-propulsion process, the hydrodynamic / torque components acting on the hull, and the acceleration term as inputs. Under the condition that a real ship test cannot be carried out, the self-propulsion test simulation using CFD can obtain the force / torque and acceleration information of the hull in various directions based on numerical calculation. Using the constrained least squares method for parameter identification is a relatively advantageous method. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0037] Figure 1 A schematic diagram illustrating the technical approach to underactuated ship modeling provided in this embodiment of the invention.

[0038] Figure 2 A three-dimensional geometric model diagram of a ship provided in an embodiment of the present invention;

[0039] Figure 3 A schematic diagram of the virtual numerical simulation environment provided in the embodiments of the present invention;

[0040] Figure 4 A schematic diagram of a ship virtual numerical simulation test provided in an embodiment of the present invention;

[0041] Figure 5 A schematic diagram illustrating the principle of the constrained least squares algorithm for identifying hydrodynamic coefficients provided in this embodiment of the invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] This invention discloses a method for establishing an automatic berthing model for underactuated ships. The method establishes a ship model expression structure based on a separable ship maneuvering motion model (MMG). Based on this model structure, a virtual numerical simulation environment for the self-propulsion process of the underactuated ship is established using computational fluid dynamics (CFD) software. The constrained least squares algorithm is used to identify parameters in the navigation data generated by the ship's motion in the virtual numerical tank, thereby obtaining the hydrodynamic coefficients in the model structure. Once the hydrodynamic coefficients are obtained, the mathematical model expression for the ship's motion is also established.

[0044] like Figure 1 As shown, the method for establishing an automatic berthing model for underactuated ships includes the following steps;

[0045] Step 1: Geometric Model Establishment

[0046] Reference Figure 2 Based on 3D modeling software, a 3D geometric model of the ship under study is drawn according to the ship's lines, propeller lines, and rudder lines, which serves as the research object for CFD simulation.

[0047] Step 2: Establish a numerical simulation environment based on computational fluid dynamics (CFD) software.

[0048] See attached document Figure 3Using the intersection of the hull baseline and the stern as the origin, in the CFD software, the inflow boundary is established at 1L in the bow direction (the length of the ship is L), and the outflow boundary is established at 2L in the stern direction. The upper interface is set at 1L above the ship model, the lower interface is set at 2L below the ship model, and the inflow boundary is set at 2L on both the left and right sides of the ship model. All hull surfaces are set as non-slip walls.

[0049] In numerical simulations of ship maneuvering, the ship moves relative to the watershed with a significant amplitude of motion. Traditional meshes suffer from decreased mesh quality and reduced computational accuracy during such large-amplitude movements. Therefore, traditional deformable meshes are ill-suited for numerical calculations of ship maneuvering. Overlapping meshes ensure that the mesh remains undeformed during relative motion calculations, guaranteeing mesh quality and solution accuracy. Therefore, overlapping mesh technology is used to construct the mesh elements for moving components such as the rudder and propeller in numerical simulations of ship maneuvering. The background mesh is based on the attached... Figure 3 The grid cells of the established computational space.

[0050] Based on the dynamic fluid-solid interaction model using CFD software, the numerical values ​​of forces and moments acting on the hull under different experimental conditions can be directly obtained. These values ​​serve as input to the identification algorithm. (See attached document) Figure 4 The numerical simulation test will adopt a variable drift angle slant test to obtain the hydrodynamic forces acting on the hull through numerical simulation at different drift angles.

[0051] Step 3: Establish the mathematical model structure for the ship berthing process

[0052] Based on the hydrodynamic data obtained from the slant navigation tests with different drift angles, an appendage coordinate system was established with the ship's center of gravity as the origin. The X-axis is along the ship's length, pointing towards the bow as positive, and the Y-axis is along the ship's width, pointing towards the port side of the ship as positive. The Z-axis forms a right-handed coordinate system with the X-axis and Y-axis.

[0053] The following mathematical model structure for the ship berthing process is established:

[0054]

[0055] m is the mass of the ship. x m y These represent the longitudinal and transverse additional mass and additional moment of inertia of the ship in the attached coordinate system, respectively. Let be the longitudinal acceleration, lateral acceleration, and bow angle acceleration of the ship in the attached coordinate system, respectively; u, v, and r be the ship's speed, lateral velocity, and bow angle velocity, respectively; and I be the ship's speed. z J z These are the ship's additional moment of inertia due to rolling and the ship's own moment of inertia due to rolling, respectively.

[0056] X, Y, and N represent the longitudinal force, transverse force, and bow roll moment acting on the hull, respectively, and their expressions are further expressed as:

[0057]

[0058] X on the right side of the equation H T, X R R represents the longitudinal hydrodynamic viscous force of the hull, the propeller thrust, the longitudinal component of the rudder force, and the hull resistance, respectively; Y H Y R N represents the lateral hydroviscous force of the hull and the lateral component of the rudder force, respectively; H N R These are the bow roll moment generated by the hull fluid viscosity force and the bow roll moment generated by the rudder force, respectively; where T is obtained from the propeller open-water test performance curve, and the rudder force is directly obtained from CFD software.

[0059] Based on the hydrodynamic analysis of the ship's hull, the viscous forces acting on the hull include, on the one hand, u 2 v 2 v 3 On the one hand, there are nonlinear terms of this type, and on the other hand, there are coupled terms where u and v form a product. According to the mathematical model of ship slant motion given by Karuno (a scholar in the field of ship maneuverability research), X in the ship's low-speed domain and large drift angle motion H Y H Z H The expression is as follows:

[0060]

[0061] Among them, X uu X is the drag coefficient for straight-line flight; uvv X uuvv X vv UV respectively 2 u 2 v 2 v 2 The longitudinal viscous hydrodynamic coefficient generated by the term; Y uuv Y uuvvv Y vvv u 2 v、u 2 v 3 v 3 The transverse viscous hydrodynamic coefficient generated by the term; N uv N uuv N uuvvv N vvv They are uv and u respectively 2 v、u 2 v 3 v 3The viscous hydrodynamic coefficient in the heading direction generated by the term.

[0062] Step 4: Identification of hydrodynamic parameters for the mathematical model of the ship berthing process

[0063] Implementation of the constrained least squares algorithm for ship parameter identification:

[0064]

[0065] In the formula: y(k) represents the variable to be optimized; t represents the identification process time; t max Indicates the time when the identification process ended; X out X represents the sum of forces acting on the hull calculated by CFD software. est (x) represents the hull force model that needs to be identified, and x represents the parameters that need to be identified. Specifically:

[0066]

[0067]

[0068]

[0069] X out1 X tot X out2 X represents the axial, lateral, and torque values ​​in the steering direction, respectively, provided by the CFD software. est1 (χ1), X est2 (χ2), X est3 (χ3) represents the expressions for axial force, lateral force and turning torque in the identification process, respectively. x1, x2 and x3 are the sets of parameters that need to be identified in the expressions for axial force, lateral force and turning torque.

[0070] Since actual ship trials are generally arranged after all technical conditions have been completed, the modeling process is affected. This invention, based on the principles of computational fluid dynamics, uses CFD software to establish a virtual numerical simulation environment corresponding to the actual ship trials, thereby obtaining ship navigation test data. This is an effective method that can obtain an accurate ship berthing model.

[0071] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0072] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for establishing an automatic berthing model for underactuated ships, characterized in that, The method includes the following steps: Based on the ship's lines diagram, propeller lines diagram, and rudder lines diagram, establish a three-dimensional geometric model of the ship; A numerical simulation environment for the three-dimensional geometric model of the ship was established based on computational fluid dynamics (CFD) software, and a numerical simulation test of the three-dimensional geometric model of the ship was conducted in the numerical simulation environment. A mathematical model of the ship berthing process is established based on numerical simulation experiments; specifically including: Establish a mathematical model of the ship's motion with four degrees of freedom nonlinearity: Where m is the ship's mass; m x m y These represent the longitudinal attachment mass and the lateral additional mass of the ship in the attachment coordinate system, respectively. Let represent the ship's longitudinal acceleration, lateral acceleration, and bow angle acceleration in the attached coordinate system, respectively; u, v, and r represent the ship's speed, lateral velocity, and bow angle velocity, respectively; I z J z These represent the ship's additional moment of inertia due to rolling and the ship's own moment of inertia due to rolling, respectively. X, Y, and N represent the longitudinal force, lateral force, and bow moment acting on the hull, respectively. X, Y, and N are represented by the following expressions: X=X H +T+X R +R Y / Y H +And R N=N H +N R In the formula, X H T, X R R represents the longitudinal hydrodynamic viscous force of the hull, the propeller thrust, the longitudinal component of the rudder force, and the hull resistance, respectively; Y H Y R N represents the lateral hydroviscous force of the hull and the lateral component of the rudder force, respectively; H N R These are the bow roll moment generated by the hull fluid viscosity force and the bow roll moment generated by the rudder force, respectively. This also includes further supplementation of the viscous hydrodynamic parameters of the ship hull under low-speed and large drift angle motion, specifically including: X H =X uu u|u|+X uvv uv 2 +X uuvv u 2 v 2 +X vv v 2 AND H =Y uuv or 2 v+Y uuvvv or 2 v 3 +And vvv v 3 N H =N uv uv+N uuv u 2 v+N uuvvv u 2 v 3 +N vvv v 3 Among them, X H Y H N H represents the longitudinal fluid viscous force, the transverse fluid viscous force, and the bow moment generated by the fluid viscous force of the hull, respectively; u, v, and r represent the ship's speed, transverse velocity, and bow angular velocity, respectively; X uu X is the drag coefficient for straight-line flight; uvv X uuvv X vv respectively uv 2 u 2 v 2 v 2 The longitudinal viscous hydrodynamic coefficient generated by the term; Y uuv Y uuvvv Y vvv u 2 v、u 2 v 3 v 3 The transverse viscous hydrodynamic coefficient generated by the term; N uv N uuv N uuvvv N vvv They are uv and u respectively 2 v、u 2 v 3 v 3 The viscous hydrodynamic coefficient in the bow direction generated by the term; Based on the mathematical model of the ship berthing process, the constrained least squares algorithm is used to identify the ship's hydrodynamic parameters.

2. The method for establishing an automatic berthing model for underactuated ships according to claim 1, characterized in that, The numerical simulation environment for establishing the three-dimensional geometric model of the ship based on computational fluid dynamics (CFD) software specifically includes: In the CFD software, the hull length of the ship's three-dimensional geometric model is set to L, and the hull surface is set as a no-slip wall. Using the intersection of the ship's hull baseline and stern in the three-dimensional geometric model of the ship as the origin of the coordinate system, inflow boundaries are established at a distance of 1L from the bow and 2L from the left and right sides of the ship, outflow boundaries are established at a distance of 2L from the stern, upper interface is established at a distance of 1L from above the ship, and lower interface is established at a distance of 2L from below the ship.

3. The method for establishing an automatic berthing model for underactuated ships according to claim 1, characterized in that, The numerical simulation test of the ship's three-dimensional geometric model specifically includes the ship's slant course test with varying drift angle.

4. The method for establishing an automatic berthing model for underactuated ships according to claim 1, characterized in that, The constrained least squares algorithm is used to identify ship hydrodynamic parameters. The constrained least squares algorithm specifically includes the following formulas: In the formula: y(k) represents the variable to be optimized; t represents the identification process time; t max Indicates the time when the identification process ended; X out X represents the sum of forces acting on the hull calculated by CFD software. est (x) represents the hull force model that needs to be identified, and x represents the parameter that needs to be identified.

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