A method for modeling and numerical simulation of maneuverability of azimuth propulsion ships

Abstract

The present invention discloses a modeling and numerical simulation method for maneuverability of an omni-rotation propulsion ship, and relates to the technical field of virtual simulation experiments. Compared with the previous omni-rotation propulsion ship maneuvering model, the present invention solves the problem that due to its unique maneuverability, the omni-rotation propulsion ship is prone to large-angle heeling during driving, which may cause the stability of the ship to decrease; the ship model hydrodynamic derivatives are obtained by simulating the ship constraint model test through CFD technology, and a four-degree-of-freedom MMG maneuvering motion mathematical model suitable for omni-rotation twin-propeller propulsion ships is proposed. Numerical simulation prediction is performed for the rotation motion and Z-shaped maneuvering motion of the ship in still water, and compared with the actual ship test data, the feasibility of the proposed omni-rotation propulsion ship maneuvering motion model is verified, and an effective solution is provided for the accurate prediction of maneuverability in the ship design stage.

Description

Technical Field

[0001] The invention relates to the technical field of virtual simulation test, and in particular to a maneuverability modeling and numerical simulation method for an azimuth propulsion ship. Background Art

[0002] As the focus of ship performance research, ship maneuverability has always been one of the important factors affecting the safe navigation of ships. Generally speaking, people will choose simple, efficient and economical maneuverability evaluation methods, such as regression formulas or database methods based on characteristic parameters, free self-propelled model test methods, and numerical calculation methods based on mathematical models. Existing technicians have established a complete six-degree-of-freedom maneuvering motion model for ship motion in waves based on the MMG equation; combined the long short-term memory neural network model with the attention mechanism to complete the online prediction of ship maneuverability motion; used full-scale test data to carry out gray box modeling of relevant parameters in the mathematical model of ship motion to predict the ship's motion state. However, the above methods have a high dependence on data basis and time and material costs, and are not suitable for the initial stage of ship design. With the development of computer technology, prediction methods based on computational fluid dynamics (CFD) have been increasingly used. Existing technicians have also studied the hydrodynamic characteristics of the ORNT twin-propeller twin-rudder ship under maneuvering state based on the CFD method, and carried out simulation verification for the turning and Z-type maneuvering motions; they have also carried out oblique towing tests and plane motion mechanism tests on the KCS ship model to obtain hydrodynamic derivatives, which have better predicted the ship's maneuvering performance; they have also calculated the hydrodynamic force of the maneuvering motion of inland ships through numerical simulation of viscous flow based on the CFD method. Its excellent simulation accuracy provides a new method for quickly predicting the maneuvering performance during the ship design stage.

[0003] Compared with the traditional rudder propeller combination, the azimuth propeller has stronger maneuverability and can easily cope with special and complex situations such as rotation in place and lateral movement. Existing technicians have carried out maneuvering motion analysis of such ships through model tests and data, and compared the maneuverability with that of traditional propulsion ships; they have also further verified the effectiveness of the mathematical model by establishing a three-degree-of-freedom MMG maneuvering motion mathematical model suitable for azimuth ships, or solving related hydrodynamic derivatives through model tests. However, due to its unique maneuverability, azimuth propulsion ships are prone to large-angle heeling during driving, which may reduce the stability of the ship. In order to solve the above problems, the present invention proposes a maneuverability modeling and numerical simulation method for azimuth propulsion ships. Summary of the invention

[0004] The purpose of the present invention is to propose a method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship to solve the problems raised in the background technology:

[0005] Due to its unique maneuverability, azimuth propulsion ships are prone to large-angle heeling during navigation, which may reduce the stability of the ship.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship comprises the following steps:

[0008] S1: CFD method is used to simulate all the hydrodynamics of the ship, RANS equation is used to deal with the viscous flow field, VOF method is applied to capture the free liquid surface, and the steel body motion module is used to perform numerical simulation of the constrained model test;

[0009] S2: Carry out oblique towing test and circular motion test on the model ship, and fit the numerical simulation results of the test by the least squares regression method to obtain various hydrodynamic derivatives;

[0010] S3: A four-degree-of-freedom MMG maneuvering motion model for fully rotating propulsion ships is proposed, the rotation and Z-type maneuvering motions are simulated, and actual ship tests are carried out for comparative verification.

[0011] Preferably, in S1, a CFD method is used to simulate all the hydrodynamic forces of the ship, and various forces and moments acting on the ship are divided into forces and moments of the bare hull and propeller for calculation; wherein, the hull fluid dynamics of the bare hull are divided into fluid inertia force and fluid viscosity force, and the hull fluid inertia force is analyzed based on the Guidao model:

[0012] Based on the Guidao model, the hull hydrodynamic model is summarized by considering the rolling viscous moment caused by the ship motion:

[0013]

[0014] Among them, X H , Y H , K H and N H are the longitudinal force, transverse force, rolling moment and yaw moment of all external forces acting on the ship except the propeller; X(u) is the straight-line resistance of the bare hull; X vv , X vr , X rr , Y v , Y r , Y v|v| , Y r|r| , Y vvr , Y vrr , N v , N r , N v|v| , N r|r| , N vvr , Nvrr All are hydrodynamic derivatives; To consider the swaying viscous moment caused by the ship motion; is the viscous moment of the bow caused by the ship's motion; u and v are the velocity components in the x and y directions respectively; r is the angular velocity of the bow; is the roll angle; is the roll damping moment; is the roll restoring moment; Y H z H is the hull fluid dynamics Y H Roll moment about the x-axis; z H Y H The z coordinate of the point of action;

[0015] Analysis of fluid viscosity based on RANS equations:

[0016] The RANS equation is obtained by time averaging the random pulsation term in the viscous flow field. The continuity equation of the viscous flow in the viscous flow field is as follows:

[0017]

[0018]

[0019] Among them, x i 、x j represents the time-averaged value of the variable component; t represents the time; ρ represents the density of seawater; μ represents the dynamic viscosity coefficient; P represents the time-averaged value of pressure; is the Reynolds stress term; is the pulsating velocity component; u i 、u j is the time-averaged value of the velocity component;

[0020] Let’s analyze the propeller again:

[0021] The ship is a fully rotating twin-propeller ship, and the left and right propellers of the fully rotating twin-propeller ship are symmetrically distributed, and the longitudinal distance from the center of gravity of the ship is L op , the lateral distance between the two propellers is L ps ;

[0022] In the propulsion of a fully rotating twin-propeller ship, the forward and turning motion of the ship is achieved by the propeller's own steering and the speed difference between them. The axial thrust of the propeller generated in still water is obtained as follows:

[0023]

[0024] Among them, T p and T s are propeller thrust components respectively; t pis the propeller thrust reduction coefficient; p and s represent the left and right propellers respectively; D is the propeller disk diameter; n p and n s are the left and right propeller speeds respectively; k T(p) and k T(s) are the thrust coefficients of the left and right propellers respectively;

[0025] When the left and right propellers are p , δ s When the rotation angle works at the same time, the axial thrust generated is decomposed along the attached coordinate system GX and GY, and the combined thrust and torque generated are:

[0026]

[0027] Among them, X p , Y p , K p and N p are respectively the propeller's longitudinal surge force, transverse surge force, rolling moment and yaw moment; z p It is the distance between the horizontal center axis of the propeller and the baseline.

[0028] Preferably, in S1, the calculation domain is taken as a cuboid, and the cutting body is used for grid division, and the grid of the area around the hull and the free liquid surface in the cuboid is encrypted to capture the flow characteristics of the surrounding fluid during the movement of the ship; the bow and stern are meshed; the hull surface adopts a no-slip wall condition, the k-ε turbulence model is selected and combined with the two-layer full y+Wall Treatment wall treatment method, the fluid volume method is used to capture the free liquid surface, and the rigid body motion DFBI module is used to numerically simulate the constrained motion of the ship model.

[0029] Preferably, the boundary layer region of the hull is encrypted using four layers of prismatic grids.

[0030] Preferably, in S1, the grid size and time step of the ship's straight-line motion are subjected to convergence analysis, and the convergence parameter R G Determine the stability of the calculation results:

[0031]

[0032] Among them, S1, S2 and S3 are the calculation results of fine, moderate and coarse levels respectively.

[0033] Preferably, in S3, based on the analysis of the forces and moments of the bare hull and the propeller in S1, the four-degree-of-freedom MMG maneuvering motion equation of the full-turn propulsion ship is constructed as follows:

[0034]

[0035] Among them, X P , Y P , K P and N P are the longitudinal surge force, transverse surge force, rolling moment and yaw moment of the azimuth thruster acting on the ship; m is the mass of the ship; m x and m y are the additional masses of the ship on the x-axis and y-axis respectively; q is the rolling angular velocity; and are the corresponding moduli respectively; I zz and J zz are the moment of inertia and additional moment of inertia of the ship around the z axis respectively; I xx and J xx are the ship's moment of inertia and additional moment of inertia around the x-axis respectively.

[0036] Preferably, in S3, based on the four-degree-of-freedom MMG maneuvering motion equation of the full-turn propulsion ship, various hydrodynamic derivatives are solved through a series of empirical formulas and CFD numerical simulation, and then the time domain differential equation is solved to realize the simulation of the dynamic characteristics of the ship's maneuvering motion, and the ship's motion track and maneuvering motion characteristic parameters are obtained.

[0037] Compared with the prior art, the present invention provides a method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship, which has the following beneficial effects:

[0038] The present invention obtains the hydrodynamic derivatives of the ship model by simulating the ship constraint model test through CFD technology, proposes a four-degree-of-freedom MMG maneuvering motion mathematical model suitable for fully rotating twin-propeller propulsion ships, performs numerical simulation predictions on the rotational motion and Z-shaped maneuvering motion of the ship in still water, and compares them with the actual ship test data, verifying the feasibility of the proposed fully rotating propulsion ship maneuvering motion model, and providing an effective solution for the accurate prediction of maneuverability in the ship design stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of the method mentioned in Example 1 of the present invention;

[0040] Figure 2 This is a schematic diagram of the calculation basin and boundary conditions of the ship model mentioned in Example 1 of the present invention;

[0041] Figure 3 This is a schematic diagram of the grid division scheme mentioned in Example 1 of the present invention;

[0042] Figure 4 It is a schematic diagram of free liquid surface waveforms for direct navigation simulation at different speeds mentioned in Example 1 of the present invention;

[0043] Figure 5The calculated resistance value and the fitting curve diagram mentioned in Example 1 of the present invention;

[0044] Figure 6 It is a free liquid surface waveform diagram under different test conditions mentioned in Example 1 of the present invention;

[0045] Figure 7 This is a schematic diagram of the bow waterline at different drift angles mentioned in Example 1 of the present invention;

[0046] Figure 8 This is the pressure distribution diagram of the hull bottom mentioned in Example 1 of the present invention;

[0047] Fig. 9 This is a diagram showing the simulation results of the oblique drag test mentioned in Example 1 of the present invention;

[0048] Fig.10 This is a simulation result diagram of the circular motion test when β=0° mentioned in Example 1 of the present invention;

[0049] Fig.11 The simulation result diagram of the circular motion test when r'=-2, -4, -6 mentioned in Example 1 of the present invention;

[0050] Fig.12 The control motion simulation results and comparison diagrams mentioned in Example 1 of the present invention are shown. DETAILED DESCRIPTION

[0051] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0052] The present invention uses CFD technology to simulate ship constraint model tests to obtain the hydrodynamic derivatives of the ship model, proposes a four-degree-of-freedom MMG maneuvering motion mathematical model suitable for fully rotating twin-propeller propulsion ships, performs numerical simulation predictions on the rotational motion and Z-shaped maneuvering motion of ships in still water, and compares them with actual ship test data to verify the feasibility of the proposed fully rotating propulsion ship maneuvering motion model, providing an effective solution for the accurate prediction of maneuverability in the ship design stage. Specifically, it includes the following contents.

[0053] Embodiment 1:

[0054] See also Figure 1-12 The present invention provides a method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship, comprising:

[0055] S1: CFD method is used to simulate all the hydrodynamics of the ship, RANS equation is used to deal with the viscous flow field, VOF method is used to capture the free liquid surface, and the steel body motion module is used to perform numerical simulation of the constrained model test; the details are as follows:

[0056] The CFD method is used to simulate all the hydrodynamic forces of the ship, and the various forces and moments acting on the ship are divided into the forces and moments of the bare hull and propeller for calculation; among them, the hull fluid dynamics of the bare hull are divided into fluid inertia force and fluid viscosity force. On the basis of the Guidao model, according to the consideration of the rolling viscosity moment caused by the ship movement, the hull fluid dynamic model is summarized and constructed, and then the fluid viscosity force is analyzed based on the RANS equation. The RANS equation averages the random pulsation terms in the viscous flow field over time, and then converts the unsteady problem into a steady problem for solution. This embodiment takes the fully rotating twin-propeller ship as the research object. In the propulsion of the fully rotating twin-propeller ship, the forward and turning movements of the ship can be achieved by the propeller's own steering and the speed difference between each other, and the propeller is analyzed to build a combined thrust and torque model.

[0057] The computational domain is taken as a cuboid. Figure 2 As shown, its inlet, side, top and bottom are set as velocity inlet, and the outlet is set as pressure outlet. The size is -4L pp <x<2L pp 、-2.5L pp <y<2.5L pp 、-2.5L pp <z<1.0L pp The computational flow domain is meshed by cutting bodies, and the mesh is encrypted in the area around the hull and the free surface to accurately capture the flow characteristics of the surrounding fluid during the ship's motion; the mesh is encrypted at the bow and stern to improve the precision of flow field capture. A 4-layer prismatic mesh is used in the boundary layer area to maintain the dimensionless wall distance Y in most areas. + The k-ε turbulence model is selected and combined with two layers of full y+Wall Treatment wall treatment. The free liquid surface is captured by the fluid volume method, and the rigid body motion DFBI module is used to simulate the constrained motion of the ship model. The total number of grids in the computational domain is about 2.55×10 6 The number of numerical simulation grids under different working conditions is slightly different. The grid division of the hull surface and the computational domain is as follows: Figure 3 shown.

[0058] In order to determine the influence of grid size and time step on the calculation results and verify the effectiveness of the calculation scheme, The convergence analysis of the ship's straight-line motion when Fr = 0.226 is carried out according to the grid size and time step, and can be referred to Table 1. G Determine the stability of the calculation results:

[0059]

[0060] Among them, S1, S2 and S3 are the calculation results of fine, moderate and coarse levels respectively. <R G <1, the results converge uniformly.

[0061] Table 1 Convergence analysis of mesh size and time step

[0062]

[0063] The calculation results show that both the grid size and the time step are convergent, and as the grid size or time step decreases, the calculation result error is further reduced, and the calculation results of different working conditions are in good agreement with the test results. After ensuring the calculation accuracy and time cost, this embodiment uses a medium grid and a medium time step for simulation.

[0064] By carrying out numerical simulation of straight-line resistance, the accuracy of the numerical model calculation method can be further verified, and the resistance function X(u) of the ship model at different speeds can be fitted. The calculation cases and results are shown in Table 2. The ship model resistance is compared with the actual ship test value after Froude resistance transformation. The error is about 5%, and the overall trend is consistent; the free surface waveform at different speeds is shown in Figure 4 As shown, the two symmetrical Kelvin waveforms formed by the bow and stern are accurately captured, and the contours of the crests and troughs are also clear, indicating that the simulation effect is good.

[0065] Table 2 Comparison of straight-line resistance calculation conditions and results

[0066]

[0067] Draw the calculated resistance values ​​in the table into a resistance curve, such as Figure 5 As shown, the resistance function of the "Zhifei" ship model is fitted as: X(u) = 29.5635u 2 -53.6771u+28.5869.

[0068] The free liquid surface waveforms under different test conditions are as follows: Figure 6 In the simulation of oblique towing motion, when β = 0°, two symmetrical Kelvin waves will be generated at the bow and stern of the ship. Conversely, asymmetrical waves will be generated on both sides of the hull, and as the β value increases, it becomes more obvious. The bow wave and stern wave on the windward side gradually approach each other, while the waves on the leeward side gradually move away from each other. Figure 7 The bow waterline diagram under different drift angles is shown. As the drift angle increases, the asymmetry of the bow wave crest distribution becomes more and more obvious, with the wave crest on one side becoming larger and larger, while the opposite is true for the other side.

[0069] S2: Carry out oblique towing test and circular motion test on the model ship, and fit the numerical simulation results of the test by the least squares regression method to obtain various hydrodynamic derivatives; the details are as follows:

[0070] The 300TEU intelligent container ship "Zhifei" is taken as the research object, and the main parameters of its hull, propeller and numerical calculation scale model are shown in Table 3. In order to obtain the hydrodynamic derivatives of the hull, the oblique towing test (OTT) and circular motion test (CMT) were carried out on the model ship, and the calculation conditions are shown in Table 4.

[0071] Table 3 Main parameters of hull and propeller

[0072]

[0073] Table 4 Calculation conditions

[0074]

[0075] In the circular motion simulation, when β = 0°, as r' increases, the bow wave crest gradually shifts to the starboard side, and the stern wave bends to the starboard side as the ship moves. When β>0°, the hull wave amplitude is small and the main distribution area of ​​the bow wave and stern wave is located on the port side. When β<0°, the hull wave amplitude is significantly increased, and the main distribution area of ​​the bow wave and stern wave is located on the starboard side. The bow and stern waves gradually approach from the port side and gradually spread to the starboard side. Figure 8 is the distribution diagram of the pressure coefficient at the bottom of the hull. In general, the pressure on the starboard side of the bow increases with the increase of r'. When β<0°, the pressure on the bow side is more concentrated and its high-pressure area continues to expand with the increase of r', and the pressure amplitude continues to grow. When β>0°, the pressure on the port side of the bow is more concentrated, and the high-pressure area gradually shifts to the starboard side as r' increases. When the pressure on the starboard side of the bow gradually increases, negative pressure appears on the port side and the starboard side of the stern.

[0076] The dimensionless longitudinal force, transverse force and bow moment acting on the hull in the oblique towing test and circular motion test are as follows: Figure 9-11As shown in the figure, it can be found that all three tend to increase with the increase of drift angle, and the calculation results are consistent with the test results of other ships of the same type in the overall trend. Within the drift angle range given by the oblique towing test, the transverse force and the bow turning moment approximately show a linear change relationship, but the longitudinal force is relatively slightly affected by the drift angle change. When β=0°, the longitudinal force on the hull can be expressed as X=X(u). Similarly, when β is small, the longitudinal force on the hull can be regarded as a constant. When β continues to increase, the transverse force is also increasing, and its growth rate is also increasing with the increase. In the circular motion test, the transverse force and the bow turning moment are significantly affected by the changes in the drift angle and the bow turning angular velocity. When β=0°, the development trend of the longitudinal force is basically similar to that in the oblique towing test, while the transverse force and the bow turning moment show greater sensitivity to the change of the bow turning angular velocity. As the bow turning angular velocity increases, the transverse force on the hull gradually increases and the increase is getting larger and larger, while the bow turning moment gradually decreases and the amplitude decreases slightly. In the simulation of different bow angular velocities, it can be found that the smaller the bow angular velocity, the smoother the changes of the three curves, the smaller the influence of the drift angle, and the longitudinal force on the hull reaches the minimum value somewhere when β>0°.

[0077] By performing least squares regression analysis on the simulation results, the hydrodynamic derivatives are shown in Table 5.

[0078] Table 5 Calculation results and comparison of hydrodynamic derivatives

[0079]

[0080] By comparing the numerical values ​​calculated with the empirical formula, it can be found that there are certain errors in the CFD calculation results. Among them, the calculated values ​​of various linear hydrodynamic derivatives are in good agreement with the empirical formula and are basically in the same order of magnitude, while the errors of some nonlinear hydrodynamic derivatives are large. This may be because the numerical simulation does not accurately predict the hydrodynamics under conditions with large drift angles. In addition, the predictions of the lateral hydrodynamic derivatives are underestimated to a certain extent. The reason may be that in some conditions, the drift angle and the bow angular velocity are large, and there is a flow separation phenomenon around the hull that is difficult to capture. In general, the hydrodynamic derivatives calculated by CFD are similar to the results calculated by the empirical formula, and some high-order hydrodynamic derivatives and cross-coupled hydrodynamic derivatives have certain errors.

[0081] S3: A four-degree-of-freedom MMG maneuvering motion model for fully rotating propulsion ships is proposed, the rotation and Z-type maneuvering motions are simulated, and actual ship tests are carried out for comparative verification. The details are as follows:

[0082] Based on the four-degree-of-freedom MMG maneuvering motion equation of the full-turn propulsion ship, various hydrodynamic derivatives are solved through a series of empirical formulas and CFD numerical simulations, and then the time-domain differential equations are solved to realize the computer simulation of the dynamic characteristics of the ship's maneuvering motion, and the ship's motion track and maneuvering motion characteristic parameters are obtained. Assuming that the speed of the left and right propellers does not change during the calculation process and has exactly the same motion instructions, the ship's 10° rotation motion and ±10° Z-type maneuvering motion are numerically simulated. At the same time, a real ship test with the same instructions was carried out in calm waters, and the results of the two simulation tests were compared with the real ship test results. Fig.12 As shown in Table 6, the characteristic parameter comparison of its rotational motion and Z-type manipulation motion is shown in Table 6.

[0083] Table 6 Comparison of characteristic parameters between simulated motion and actual ship test

[0084]

[0085] It can be seen from the chart that the simulated motion obtained by CFD test of various hydrodynamic derivatives of the ship is consistent with the various parameter data of the actual ship test, and its turning performance and heading stability performance meet the IMO maneuverability standards. Among them, the simulation effect of tactical diameter in the turning motion is basically consistent, and the overall motion trajectory has a certain deviation from the actual ship test. The reason may be that the slight wind and wave flow during the actual ship test causes the ship's track to shift to one side. The errors of the remaining characteristic parameters are basically within 15%, which is within an acceptable range. In the Z-type maneuvering motion test, the simulation of the bow angle is generally consistent with the test curve, and the error of the first overtaking angle is small. However, with the continuous iteration of the calculation time, the error caused by time accumulation will gradually increase. Overall, the error of the simulated Z-type maneuvering motion parameters is within 10%, which is basically consistent with the actual data. Compared with the results calculated by the empirical formula, the method used in this paper can greatly reduce the simulation error when simulating various characteristic parameters of ship maneuvering motion, improve the accuracy of ship maneuvering prediction at an acceptable calculation cost, and is more suitable for the verification and optimization of maneuverability in the ship design stage.

[0086] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship, characterized in that: The steps include: S1: CFD method is used to simulate all the hydrodynamics of the ship, RANS equation is used to deal with the viscous flow field, VOF method is applied to capture the free liquid surface, and rigid body motion module is used to perform numerical simulation of constrained model tests; In S1, the CFD method is used to simulate all the hydrodynamic forces of the ship, and the various forces and moments acting on the ship are divided into the forces and moments of the bare hull and the propeller for calculation; among them, the hull fluid dynamics of the bare hull are divided into fluid inertia force and fluid viscosity force, and the hull fluid inertia force is analyzed based on the Guidao model: Based on the Guidao model, the hull hydrodynamic model is summarized by considering the rolling viscous moment caused by the ship motion: Among them, X H , Y H , K H and N H are the longitudinal force, transverse force, rolling moment and yaw moment of all external forces acting on the ship except the propeller; X(u) is the straight-line resistance of the bare hull; X vv , X vr , X rr , Y v , Y r , Y vv , Y rr , Y vvr , Y vrr , N v , N r , N vv , N rr , N vvr , N vrr All are hydrodynamic derivatives; To consider the swaying viscous moment caused by the ship motion; is the viscous moment of the bow caused by the ship's motion; u and v are the velocity components in the x and y directions respectively; r is the angular velocity of the bow; is the roll angle; is the roll damping moment; is the roll restoring moment; Y H z H is the hull fluid dynamics Y H Roll moment about the x-axis; z H Y H The z coordinate of the point of action; Analysis of fluid viscosity based on RANS equations: The RANS equation is obtained by time averaging the random pulsation term in the viscous flow field. The continuity equation and RANS equation of the viscous flow in the viscous flow field are as follows: Among them, x i 、x j represents the time-averaged value of the variable component; t represents the time; ρ represents the density of seawater; μ represents the dynamic viscosity coefficient; P represents the time-averaged value of pressure; is the Reynolds stress term; is the pulsating velocity component; u i 、u j is the time-averaged value of the velocity component; Let’s analyze the propeller again: The ship is a fully rotating twin-propeller ship, and the left and right propellers of the fully rotating twin-propeller ship are symmetrically distributed, and the longitudinal distance from the center of gravity of the ship is L op , the lateral distance between the two propellers is L ps ; In the propulsion of a fully rotating twin-propeller ship, the forward and turning motion of the ship is achieved by the propeller's own steering and the speed difference between them. The axial thrust of the propeller generated in still water is obtained as follows: Among them, T p and T s are propeller thrust components respectively; t p is the propeller thrust reduction coefficient; p and s represent the left and right propellers respectively; D is the propeller disk diameter; n p and n s are the left and right propeller speeds respectively; k T(p) and k T(s) are the thrust coefficients of the left and right propellers respectively; When the left and right propellers are p , δ s When the rotation angle works at the same time, the axial thrust generated is decomposed along the attached coordinate system GX and GY, and the combined thrust and torque generated are: Among them, X p , Y p , K p and N p are respectively the propeller's longitudinal surge force, transverse surge force, rolling moment and yaw moment; z p is the distance between the horizontal center axis of the propeller and the baseline; S2: Carry out oblique towing test and circular motion test on the model ship, and fit the numerical simulation results of the test by the least squares regression method to obtain various hydrodynamic derivatives; S3: A four-degree-of-freedom MMG maneuvering motion model for fully rotating propulsion ships is proposed, the rotation and Z-type maneuvering motions are simulated, and actual ship tests are carried out for comparative verification.

2. The method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship according to claim 1, characterized in that: In S1, the computational flow domain is taken as a cuboid, and the cutting body is used for meshing, and the area around the hull and the free liquid surface in the cuboid are meshed to capture the flow characteristics of the surrounding fluid during the movement of the ship; The grids of the bow and stern are encrypted; the no-slip wall condition is adopted on the hull surface, the k-ε turbulence model is selected and combined with the two-layer full y+WallTreatment wall treatment method, the fluid volume method is used to capture the free liquid surface, and the rigid body motion DFBI module is used to numerically simulate the constrained motion of the ship model.

3. The method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship according to claim 2, characterized in that: The boundary layer region of the hull is encrypted using a four-layer prismatic grid.

4. The method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship according to claim 3 is characterized in that: In S1, the grid size and time step of the ship's straight-line motion are analyzed for convergence, and the convergence parameter R G Determine the stability of the calculation results: Among them, S1, S2 and S3 are the calculation results of fine, moderate and coarse levels respectively.

5. The method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship according to claim 4, characterized in that: In S3, based on the analysis of the forces and moments of the bare hull and the propeller in S1, the four-degree-of-freedom MMG maneuvering motion equation of the full-turn propulsion ship is constructed as follows: Among them, X P , Y P , K P and N P are the longitudinal surge force, transverse surge force, rolling moment and yaw moment of the azimuth thruster acting on the ship; m is the mass of the ship; m x and m y are the additional masses of the ship on the x-axis and y-axis respectively; q is the rolling angular velocity; and are the corresponding moduli respectively; I zz and J zz are the moment of inertia and additional moment of inertia of the ship around the z axis respectively; I xx and J xx are the ship's moment of inertia and additional moment of inertia around the x-axis respectively.

6. The method for modeling and numerical simulation of maneuverability of an azimuth propulsion ship according to claim 5, characterized in that: In S3, based on the four-degree-of-freedom MMG maneuvering motion equation of the full-turn propulsion ship, various hydrodynamic derivatives are solved through a series of empirical formulas and CFD numerical simulation, and then the time domain differential equation is solved to realize the simulation of the dynamic characteristics of the ship's maneuvering motion, and the ship's motion track and maneuvering motion characteristic parameters are obtained.

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