A method for determining the total main engine power of a multi-propeller ship based on full-scale numerical simulation

Abstract

The application discloses a method for determining the total main engine power of a multi-propeller ship based on full-scale numerical simulation technology; the method comprises the following steps: obtaining an open water characteristic curve of a propeller, calculating the bare hull resistance, calculating the self-propelling resistance of the hull, the thrust and torque of each propeller and the total thrust under a certain speed and propeller rotating speed; determining the propeller rotating speed corresponding to the self-propelling point of the hull, the total thrust, the self-propelling resistance of the hull, the thrust and torque of each propeller, calculating the post-hull thrust and torque coefficient of each propeller and the total thrust reduction fraction; in the open water characteristic curve of the propeller, the open water parameters of each propeller are calculated by using the equal-thrust method; the post-hull propeller parameters are calculated by using the determined parameters, the average parameters of the post-hull propeller are calculated by using the thrust weighted average method, the propelling efficiency is calculated, and finally the main engine power required by the multi-propeller ship under the designed speed is obtained. The method has the advantages of significantly simplifying the experimental data collection steps, greatly reducing the fund investment and time investment, and high accuracy.

Description

Technical Field

[0001] This invention relates to the determination of main engine power in ship design, specifically to a method for determining the total main engine power of a multi-propeller ship based on full-scale numerical simulation; the multi-propeller ship has two to four propellers. Background Technology

[0002] During the ship design phase, it is necessary to select an appropriate main engine power based on requirements such as speed and economy. The accuracy of the predicted main engine power is crucial for ensuring that the ship's performance meets design requirements. To calculate the required main engine power, it is necessary to analyze the interaction between the hull and the propeller to determine the various power transfer coefficients between the propeller's open-water power and the power received by the propeller at the stern. The interaction between the hull and the propeller can be approximated in two aspects: firstly, the influence of the propeller, installed at the stern, on the hull. The presence of the propeller alters the pressure distribution of the flow field around the hull, leading to an increase in hull drag, i.e., thrust deduction; secondly, the influence of the hull on the propeller. During navigation, the hull drives the surrounding water flow, causing the flow velocity at the propeller to differ from the ship's speed, i.e., the wake effect.

[0003] For multi-propeller ships, the flow field conditions of each propeller installed at different locations on the stern are not the same. Therefore, current research on the interaction between the hull and propellers, as well as the estimation of main engine power, is mainly carried out through self-propulsion tests on ship models. However, due to the complex structure and time-consuming nature of the test mechanism for self-propulsion tests on multi-propeller ships, the economic and time costs are high. Furthermore, when determining the average relative rotational efficiency, average wake fraction, average open water efficiency, total thrust deduction fraction, and hull efficiency of each propeller at the stern, and their influence coefficients on the interaction between the hull and propellers, limitations in test equipment often require separate testing of each propeller at the stern, collecting data separately, and then combining these data for calculation. Clearly, this approach fragments the hydrodynamic data of these propellers, which should be operating under the same conditions, resulting in a significant difference from the actual operating conditions of multiple propellers operating simultaneously at the stern of a real ship. Therefore, the self-propulsion test of this multi-propeller ship model and its corresponding data processing methods are not entirely rigorous, and the data results converted to actual ships cannot be guaranteed to be completely reliable. Summary of the Invention:

[0004] The purpose of this invention is to provide a method for determining the total main engine power of a multi-propeller ship based on full-scale numerical simulation technology that significantly simplifies the experimental data acquisition process, greatly reduces financial and time investment, overcomes the inherent theoretical defects caused by the scaling conversion between the real and model in the self-propulsion test of multi-propeller ship models, and achieves high accuracy.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation technology includes the following steps:

[0007] S1. Input the computational domain of a single propeller into the computational fluid dynamics analysis software STAR-CCM+, set the propeller speed n, and obtain the results of a single propeller at different advance speeds V. A Given the thrust T and torque Q, the thrust coefficient K of a single propeller at the advance coefficient J can be obtained using the formula. T Torque coefficient K Q With open water efficiency η0; with advance coefficient J as the abscissa and thrust coefficient K as the ordinate. T Torque coefficient K Q With the open water efficiency η0 as the ordinate, we obtain JK T Curves, JK Q Curve and J-η0 curve: Propeller open-water performance curve diagram;

[0008] S2. Input the bare hull calculation domain into the computational fluid dynamics analysis software STAR-CCM+ to obtain the bare hull hydrostatic resistance R0 at the given design speed V.

[0009] S3. Input the computational domain of X propellers and hull combinations into the computational fluid dynamics analysis software STAR-CCM+, where X is any integer from 2 to 4; obtain the hull resistance R at the design speed V and propeller speed n. c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b The total thrust of the propeller, T b According to formula (3-1) The calculation is performed, where x is the propeller number;

[0010] S4. Change the set propeller speed n and repeat step S3 to obtain the hull resistance R at different propeller speeds n. c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b The aft thrust coefficient K of each propeller is determined using a graphical method according to the following formula. Tbsx , Ship rear torque coefficient K Qbsx and the total ship thrust reduction fraction t cs Plot the propeller speed n on the x-axis and the hull resistance nR. c Curve, Rotational Speed ​​- Total Propeller Thrust nT b Curve, Rotational Speed-Thrust nT of the Same Propeller Groupbx Curve and the speed-torque nQ of the same propeller group bx Curve, when nR c Curve and nT b When the curves intersect, stop repeating step S3; the x-axis corresponding to the intersection point is the propeller speed n under self-propulsion conditions. bs Passing through the propeller at a rotational speed of n bs Draw a vertical line perpendicular to the x-coordinate from the point of value nR. c Curve, nT b Curve, nT bx Curve and nQ bx The intersection points of the curves yield the ship's self-propulsion resistance R under self-propulsion conditions. cs The thrust T of each propeller bsx With torque Q bsx and the total thrust T of the propeller bs Value:

[0011]

[0012] S5. Draw X horizontal lines on the propeller open-water performance curve obtained in step S1. The vertical axis corresponding to each horizontal line is the stern thrust coefficient K of each propeller under the ship's self-propulsion state obtained in step S4. Tbsx ; X horizontal lines and JK in the propeller open-water characteristic curve diagram T The curve has X intersection points. At each intersection point, a vertical line perpendicular to the horizontal axis is drawn. The advance coefficient J of each propeller under the ship's self-propelled state is obtained from the intersection of the vertical line and the horizontal axis. sx According to the vertical line and JK Q The intersection of the curve and the J-η0 curve yields the open-water torque coefficient K for each propeller under the ship's self-propulsion state, with the ordinate value being... Q0sx With open water efficiency η 0sx ;

[0013] S6. The propeller speed n under the self-propulsion state of the ship, as determined in step S4. bs With the aft torque coefficient K Qbsx and the advance coefficient J of each propeller determined in step S5 sx Open water torque coefficient K Q0sx With open water efficiency η 0sx Determine the stern advance speed V of each propeller at the design speed V using formulas 6-1 to 6-3. Abx Relative rotational efficiency η Rx With the fraction of the accompanying flow ω bx ;

[0014]

[0015] S7. Determine the average relative rotational efficiency η of the stern propeller using the thrust-weighted average method according to the following formula. R-aver Average wake fraction ω b-aver and average open water efficiency η 0s-aver :

[0016]

[0017] S8. Determine the hull efficiency η according to the following formula. H With propulsion efficiency η D This leads to the determination of the total main engine power P required for a multi-rotor ship at its design speed V. S :

[0018]

[0019] To further achieve the objectives of this invention, preferably, the computational domain of a single propeller is a cylinder containing the geometric shape of a single propeller, formed after the geometric spatial coordinates of the single propeller are input into the 3D geometric modeling software Rhino, with the rotational axis of the cylinder coinciding with the propeller shaft; the advance velocity V A The average velocity of the flow along the axis in front of the propeller disk;

[0020] The thrust coefficient K of a single propeller at the advance coefficient J is obtained according to the formula. T Torque coefficient K Q The formula related to the open water efficiency η0 is:

[0021]

[0022] Where D is the propeller diameter, ρ is the fluid density, and π is pi.

[0023] Preferably, the diameter of the cylinder is 6-10 times the propeller diameter D, the distance from the cylinder inlet boundary surface to the leading edge of the propeller hub is 1-3 times the propeller diameter D, and the distance from the cylinder outlet boundary surface to the trailing edge of the propeller hub is 4-8 times the propeller diameter D.

[0024] Preferably, the bare hull computational domain is a cuboid formed by inputting the spatial coordinates of the geometric shape of the bare hull without a propeller into the 3D geometric modeling software Rhino, which includes the shape of the bare hull without a propeller.

[0025] Preferably, the length of the cuboid's inlet boundary surface from the hull surface is 1-3 times the waterline length, and the length of the cylindrical outlet boundary surface from the hull surface is 4-8 times the waterline length; the top boundary surface is parallel to the hull's waterline and is 0.25-1.5 times the waterline length from it; the bottom boundary surface is parallel to the hull's waterline and is 0.5-2 times the waterline length from it; the length of the two side boundary surfaces from the widest point of the hull is 1-4 times the waterline length; and the two side boundary surfaces are symmetrical about the longitudinal section of the hull.

[0026] Preferably, the computational domain for the X propellers and the hull combination is a cylinder containing the geometric shape of each propeller and a cuboid containing the hull shape, formed by inputting the spatial coordinates of the geometric shape of each of the X propellers and the spatial coordinates of the geometric shape of the bare hull into the 3D geometric modeling software Rhino. Each cylinder is within the cuboid, and there is no overlap between the cylinders or between the cylinders and the hull. The rotation center axis of each cylinder coincides with the corresponding propeller shaft.

[0027] Preferably, in the X propeller and hull combination calculation domains, the inlet boundary surface of the cuboid is 1-3 times the waterline length from the hull surface, the outlet boundary surface is 4-8 times the waterline length from the hull surface, the top boundary surface is parallel to the hull waterline and is 0.25-1.5 times the waterline length from the hull waterline, the bottom boundary surface is parallel to the hull waterline and is 0.5-2 times the waterline length from the hull waterline, and the two side boundary surfaces are 1-4 times the waterline length from the widest point of the hull.

[0028] Preferably, in the X propeller and hull combination calculation domains, the diameter of each cylinder is 1.001-1.05 times the corresponding propeller diameter, the distance from the inlet boundary surface of each cylinder to the leading edge of the corresponding propeller hub is 0.05-1.5 times the propeller diameter, and the distance from the outlet boundary surface of each cylinder to the trailing edge of the corresponding propeller hub is 0.05-4 times the propeller diameter.

[0029] Preferably, the geometry and dimensions of the bare hull or propeller are consistent with the geometry and dimensions of the actual hull or propeller.

[0030] Preferably, the propeller is a conventional propeller or a ducted propeller.

[0031] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0032] 1) This invention places the hull and multiple simultaneously operating propellers in a unified computing platform for synchronous processing, truly realizing synchronous prediction of the state of multi-propeller ships under real-world operating environmental conditions, and the processing method is more accurate.

[0033] 2) Traditional self-propulsion testing methods for multi-propeller ships require addressing the interaction parameters between propellers at different positions on the hull and between different propellers, which involves complex issues related to propeller torque and thrust data acquisition. This invention utilizes computational fluid dynamics technology to successfully solve the problem of asynchronous and uncoordinated interaction parameters between propellers at different positions on the hull during self-propulsion testing of multi-propeller ships.

[0034] 3) This invention uses full-scale numerical simulation technology to analyze the interaction parameters between the propeller and the hull of a multi-propeller ship, overcoming the theoretical shortcomings caused by the need for scale conversion between the real and model in the self-propulsion test of traditional multi-propeller ship models.

[0035] 4) The method adopted in this invention overcomes the defects in data processing and testing technology caused by the need to separate devices that are originally working simultaneously in the same system in the self-propulsion test method of multi-propeller ship model, which is time-consuming and laborious. It provides a practical and reliable solution for determining the interaction parameters between the propeller and the hull at different positions in a multi-propeller ship using numerical methods.

[0036] 5) Even ignoring the inherent defects of traditional multi-propeller ship model self-propulsion test methods in scaled physical model tests, existing physical model ship model self-propulsion tests require a lot of money in model making, test equipment investment and preparation, as well as a long test preparation period. In contrast, the method of determining the total main engine power of multi-propeller ships based on full-scale numerical simulation of the present invention has obvious advantages in terms of investment and time, and can significantly reduce economic costs and save a lot of time.

[0037] 6) This invention also allows technicians to better understand the flow field information around the hull and each propeller, thereby gaining a clearer understanding of the interaction parameters between the propeller and the hull of a multi-propeller ship. Attached image description:

[0038] Figure 1 This is a flowchart of the method for calculating the total main engine power of a multi-propeller ship according to the present invention.

[0039] Figure 2 This is a schematic diagram of the propeller distribution and numbering provided in Embodiment 1 of the present invention.

[0040] Figure 3 This is a model diagram of a single propeller provided in Embodiment 1 of the present invention.

[0041] Figure 4 This is a model diagram of a bare hull without a propeller, as provided in Embodiment 1 of the present invention.

[0042] Figure 5 This is a model diagram of four propeller and hull combinations provided in Embodiment 1 of the present invention.

[0043] Figure 6 This is a schematic diagram of a cylindrical computational domain for analyzing the open-water characteristics of a propeller, as provided in Embodiment 1 of the present invention.

[0044] Figure 7 This is a curve showing the open-water performance characteristics of a propeller provided in Embodiment 1 of the present invention.

[0045] Figure 8 This is a schematic diagram of a cuboid computational domain for analyzing the hydrostatic resistance of a bare ship hull, provided in Embodiment 1 of the present invention.

[0046] Figure 9 This is a graph provided in Embodiment 1 of the present invention for calculating the self-navigation point parameters.

[0047] Figure 10 This is a curve showing the open-water performance characteristics of a propeller provided in Embodiment 2 of the present invention.

[0048] Figure 11 This is a graph provided in Embodiment 2 of the present invention for calculating the self-navigation point parameters. Detailed Implementation

[0049] To better understand the present invention, the invention will be further described below with reference to the accompanying drawings and embodiments, but the implementation of the invention is not limited thereto.

[0050] The existing methods for determining the total main engine power of multi-rotor ships have the following main drawbacks:

[0051] First, when converting the results of conventional ship model self-propulsion tests to actual ships, a series of defects in test methods and conversion theories arise because it is impossible to achieve full similarity between the test conditions of the model and the actual ship.

[0052] Secondly, obtaining the interaction parameters between the propeller and the hull through traditional self-propulsion testing methods for multi-propeller ships requires using a scaled-down model for physical model testing. Then, based on the principle of similarity, the test results from the scaled-down physical model are converted to data corresponding to the full-scale model under operating conditions. However, since self-propulsion testing methods for multi-propeller ships cannot achieve full similarity between the full-scale model and the model, artificial means such as frictional resistance correction are usually used to mitigate the impact of scale effects. This scaled-down model testing method is not rigorous in terms of meeting the similarity theory requirements of the physical model, and it also introduces significant conversion errors in data processing.

[0053] Third, for the acquisition of torque and thrust data of different propellers under the same operating conditions, due to the lack of testing equipment, the traditional self-propulsion test method of multi-propeller ship model often requires testing each propeller separately. This physical model test method not only requires a lot of testing costs and a long testing time, but also introduces a lot of testing errors due to the separate treatment of different propellers working at the same time. There are obvious theoretical and technical deficiencies in testing methods and data processing.

[0054] To address the above problems, the technical solution adopted by the present invention is as follows: Figure 1 As shown, a method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation technology includes the following steps:

[0055] S1. Input the computational domain of a single propeller into the computational fluid dynamics analysis software STAR-CCM+, set the propeller speed n, and obtain the results of a single propeller at different advance speeds V. A Given the thrust T and torque Q, the thrust coefficient K of a single propeller at the advance coefficient J can be obtained using the formula. T Torque coefficient K Q With open water efficiency η0; with advance coefficient J as the abscissa and thrust coefficient K as the ordinate. T Torque coefficient K Q With the open water efficiency η0 as the ordinate, we obtain JK T Curves, JK Q Curve and J-η0 curve: Propeller open-water performance curve diagram;

[0056] The preferred formulas involved in this step are as follows:

[0057]

[0058] Where D is the propeller diameter, ρ is the fluid density, and π is pi.

[0059] S2. Input the bare hull calculation domain into the computational fluid dynamics analysis software STAR-CCM+ to obtain the bare hull hydrostatic resistance R0 at the given design speed V.

[0060] S3. Input the computational domain of X propellers and hull combinations into the computational fluid dynamics analysis software STAR-CCM+, where X is any integer from 2 to 4; obtain the hull resistance R at the design speed V and propeller speed n. c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b The total thrust of the propeller, T b Calculate using the following formula, where x is the propeller serial number;

[0061] S4. Change the set propeller speed n and repeat step S3 to obtain the hull resistance R at different propeller speeds n. c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b The aft thrust coefficient K of each propeller is determined using a graphical method according to the following formula. Tbsx , Ship rear torque coefficient K Qbsx and the total ship thrust reduction fraction t cs Plot the propeller speed n on the x-axis and the hull resistance nR. c Curve, Rotational Speed ​​- Total Propeller Thrust nT b Curve, Rotational Speed-Thrust nT of the Same Propeller Group bx Curve and the speed-torque nQ of the same propeller group bx Curve, when nR c Curve and nT b When the curves intersect, stop repeating step S3; the x-axis corresponding to the intersection point is the propeller speed n under self-propulsion conditions. bs Passing through the propeller at a rotational speed of n bs Draw a vertical line perpendicular to the x-coordinate from the point of value nR. c Curve, nT b Curve, nT bx Curve and nQ bx The intersection points of the curves yield the ship's self-propulsion resistance R under self-propulsion conditions. cs The thrust T of each propeller bsx With torque Q bsx and the total thrust T of the propeller bs Value:

[0062]

[0063] S5. Draw X horizontal lines on the propeller open-water performance curve obtained in step S1. The vertical axis corresponding to each horizontal line is the stern thrust coefficient K of each propeller under the ship's self-propulsion state obtained in step S4. Tbsx ; X horizontal lines and JK in the propeller open-water characteristic curve diagram T The curve has X intersection points. At each intersection point, a vertical line perpendicular to the horizontal axis is drawn. The advance coefficient J of each propeller under the ship's self-propelled state is obtained from the intersection of the vertical line and the horizontal axis. sx According to the vertical line and JK Q The intersection of the curve and the J-η0 curve yields the open-water torque coefficient K for each propeller under the ship's self-propulsion state, with the ordinate value being... Q0sxWith open water efficiency η 0sx ;

[0064] S6. The propeller speed n under the self-propulsion state of the ship, as determined in step S4. bs With the aft torque coefficient K Qbsx and the advance coefficient J of each propeller determined in step S5 sx Open water torque coefficient K Q0sx With open water efficiency η 0sx Determine the stern advance speed V of each propeller at the design speed V using formulas 6-1 to 6-3. Abx Relative rotational efficiency η Rx With the fraction of the accompanying flow ω bx ;

[0065]

[0066] S7. Determine the average relative rotational efficiency η of the stern propeller using the thrust-weighted average method according to the following formula. R-aver Average wake fraction ω b-aver and average open water efficiency η 0s-aver :

[0067]

[0068] S8. Determine the hull efficiency η according to the following formula. H With propulsion efficiency η D This leads to the determination of the total main engine power P required for a multi-rotor ship at its design speed V. S :

[0069]

[0070] The above-mentioned technical solution of the present invention has the following characteristics:

[0071] 1) This invention utilizes STAR-CCM+, a highly integrated commercial multiphysics computational fluid dynamics simulation software developed by CD-adapco. Users define the computational domain and boundary conditions for a moving object in the flow field. Automatic mesh generation technology discretizes the fluid motion control equations of the moving object, thereby obtaining various physical field information such as velocity, acceleration, pressure, force, and torque around the moving object using computational fluid dynamics methods. This software is currently widely used in various computational fluid dynamics analyses and calculations in ship engineering fields such as ship resistance and propulsion. The computational domains defined using this software—a single propeller, a bare hull, and a combination of X propellers and the hull—have similar definitions in the field. "Single propeller," "bare hull," and "propeller-hull combination" are commonly used terms in this field. The thrust coefficient K of a single propeller at the advance coefficient J is...T Torque coefficient K Q The formulas related to the open-water efficiency η0 are also existing in this field. The specific parameters of the computational domain involving cylinders and cuboids are empirical parameters.

[0072] 2) The method for determining the total main engine power of a multi-propeller ship in this invention is based on a single propeller computational domain, a bare hull computational domain, and a combined computational domain of X propellers and the hull. This invention places the hull and multiple simultaneously operating propellers in a unified computing platform for synchronous processing, using the true scale of a real ship and actual propellers for numerical simulation. In this computational environment, the mutual dynamics between the hull and propellers, and between different propellers, and their mutual influences are fully and realistically reflected, thus revealing the true state of interaction between the hull and each propeller more accurately. Therefore, the interaction parameters between the propellers and the hull obtained using the method of this invention have higher prediction accuracy than the asynchronous, fragmented processing method used in traditional physical model experiments for different propellers.

[0073] 3) This invention calculates the relative rotational efficiency η of different propellers by having them operate simultaneously at different locations on the stern of the ship, interacting with the flow field generated by the ship's movement in the same scenario. Rx , co-current fraction ω x With open water efficiency η 0x Simultaneously, based on the thrust generated by each propeller, the average relative rotational efficiency η, which reflects the overall effect of each propeller, is calculated according to the thrust weighted average principle. mR Average wake fraction ω m Average open water efficiency η m0 The invention simulates the interaction parameters between the propeller and the hull in a multi-propeller ship. By placing the hull and multiple simultaneously operating propellers on a unified computational platform, it performs numerical simulations using the true scale of a real ship and actual propellers. In this computational environment, the dynamic interactions between the hull and propellers, as well as between different propellers, are fully and realistically represented, conforming to objective conditions.

[0074] 4) In this invention, the geometric model is 1:1 in size with the actual hull and propeller; that is, the geometric shape of the bare hull and propeller is consistent with the actual hull and propeller dimensions. The calculation method proposed in this invention is a numerical simulation method based on computational fluid dynamics, conducted under conditions consistent with the actual ship dimensions, overcoming the inherent defects of traditional multi-propeller ship model self-propulsion tests in scaled-down physical model tests.

[0075] 5) This invention utilizes the thrust weighted average method to obtain the average relative rotational efficiency, average wake fraction, and average open water efficiency of each propeller at the stern of the ship, making the obtained comprehensive interaction influence coefficients between the hull and each propeller more accurate and reasonable.

[0076] 6) This invention sets a uniform incoming flow into the computational domain from the inlet: For a single propeller, the incoming flow is a single-phase flow, the fluid is seawater, and its magnitude is equal to the propeller's advance velocity; For a bare hull without a propeller or an assembly of X propellers and a hull, the incoming flow is a multiphase flow. The fluid properties are set at the inlet boundary, and the fluids are air and seawater. The boundary conditions between the two phases satisfy the dynamic and kinematic boundary conditions of a free surface, and the magnitude of each phase velocity is equal to the ship's speed.

[0077] 7) When calculating the hydrodynamic characteristics of a ship's self-propulsion under the combined propulsion of multiple propellers, this invention employs a sliding mesh hybrid technique to construct the computational domain. The composite computational domain is formed by coupling cylindrical and cuboid sub-computational domains constructed for each propeller and hull respectively. These sub-computational domains are constructed according to the different computational functions required. The flow field information between the sub-computational domains and the hull computational domain is achieved by arranging sliding meshes on the surface of each cylindrical sub-computational domain.

[0078] 8) When calculating the hydrodynamic characteristics of a ship's self-propulsion under the combined propulsion of multiple propellers, this invention uses a moving reference frame method to simulate the rotation of the X propellers. That is, during the calculation process, the relative rotational displacement between the geometric models of the X propellers and the hull model is maintained. By defining the rotational motion of the corresponding reference coordinate system of the sub-computation domain corresponding to the X propellers and making the rotational speed of the reference coordinate system equal to the rotational speed of the propellers, the numerical simulation of the rotating flow field near the propellers is realized.

[0079] It should be noted that, in this invention, the inlet boundary refers to the surface in which fluid flows into the computational domain; the outlet boundary refers to the surface in which fluid flows out of the computational domain; the waterline length refers to the horizontal distance between the waterline surface and the intersection of the bow and stern ends of the hull surface; Boolean subtraction is a three-dimensional graphics operation method, which refers to obtaining a new geometric shape by performing a difference operation on two or more geometric shapes during the generation of the computational domain.

[0080] A ducted propeller is constructed by adding a guide tube to the outside of a regular propeller. In the calculation method used in this invention, there is essentially no difference between the two; choosing either a ducted propeller or a regular propeller as the calculation object will not affect the effectiveness of the method. In this invention, the propeller can be either a ducted propeller or a regular propeller; this embodiment uses a ducted propeller as an example only.

[0081] The present invention is based on propulsion efficiency η D Determine the total main engine power P required by a multi-propeller ship at its design speed V by using the still water bare hull resistance R0 at a given speed V. S When frictional losses in the propeller shaft system are neglected, that is, the shaft system efficiency η is assumed to be... S =1.0.

[0082] Example 1

[0083] This embodiment 1 takes a shallow-draft, high-power, multi-functional marine platform supply vessel as an example. This vessel has multiple ducted propellers installed at the stern, with these propellers arranged substantially parallel to each other at the stern (see [link]). Figure 2 In this embodiment, the number of duct propellers is specifically four, with four main units driving the four duct propellers respectively, such as... Figure 2 The propellers shown in Figures 2-1 to 2-4 are numbered 1 to 4 from port to starboard, with a diameter of 1.9m. The four ducted propellers rotate at the same speed and are symmetrically arranged on both port and starboard sides. The hull is a single-hull displacement vessel with a design speed of V = 10 knots. The corresponding main dimensions of the actual hull are: waterline length 68.6m, beam 19m, average draft 3.1m, and displacement 3500t.

[0084] like Figure 1 As shown, a method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation includes the following steps:

[0085] S1. Input the spatial coordinates of the geometric shape of a single propeller into the 3D geometric modeling software Rhino to construct... Figure 3 The image shows a single propeller geometry model. This single propeller geometry model is then imported into the computational fluid dynamics analysis software STAR-CCM+, and the single propeller geometry model is set as follows: Figure 6 Inside the cylinder 6-1 shown, the cylinder's rotational axis coincides with the propeller shaft. The cylinder's diameter is 15.2 meters. The distance from the cylinder's inlet boundary 6-2 to the leading edge of the propeller hub is 3.8 meters, and the distance from the cylinder's outlet boundary 6-3 to the trailing edge of the propeller hub is 11.4 meters. By performing Boolean subtraction operations between the cylinder and the geometric model, a cylindrical computational domain with a hollow cavity (6-4) is formed for a single propeller. Using this cylindrical computational domain, the fluid flow range during the calculation process is defined in the computational fluid dynamics analysis software STAR-CCM+. The propeller's computational rotational speed n is set to 300 rpm. The software is then used to output data for a single propeller at different advance speeds V. A Thrust T and torque Q (precession speed V) under the given conditions A The average velocity of the flow along the axis in front of the propeller disk is used to calculate the thrust coefficient K of a single propeller in the range of advance coefficient J = 0 to 1. T Torque coefficient KQ With open water efficiency η0, the advance coefficient J is plotted on the x-axis, and the thrust coefficient K is plotted on the y-axis. T Torque coefficient K Q The value of open water efficiency η0 is obtained as follows: Figure 7 The diagram shows JK. T Curve (7-1), JK Q The propeller open-water characteristic curves include curve (7-2) and the J-η0 curve (7-3). The advance coefficient J and thrust coefficient K are also mentioned. T Torque coefficient K Q The propeller open-water efficiency η0 is calculated using the following formula:

[0086]

[0087] In the formula, V A ρ is the advance velocity, ρ is the fluid density, n is the propeller speed, D is the propeller diameter, T is the propeller open-water thrust, and Q is the propeller open-water torque.

[0088] S2. Input the spatial coordinates of the bare hull geometry (without propeller) into the 3D modeling software Rhino to construct... Figure 4 The bare hull geometry model is shown. The bare hull geometry model is placed on... Figure 8 Inside the cuboid 8-1 shown, the inlet boundary 8-2 is 140 meters from the hull surface, the outlet boundary 8-3 is 350 meters from the hull surface, the top edge 8-4 is parallel to the waterline 8-5 and is 35 meters above it, the bottom boundary is parallel to the waterline 8-5 and is 70 meters above it, and the side boundary is 140 meters from the widest point of the hull. By performing Boolean subtraction between the cuboid and the bare hull geometric model, a cuboid computational domain with a hollow hull shape 8-6 is formed. Using this cuboid computational domain, the fluid flow range during the calculation process is defined in the computational fluid dynamics analysis software STAR-CCM+, and the analysis software outputs the still water resistance R0 experienced by the bare hull at the design speed V. In this embodiment, the calculated static water resistance R0 of the bare hull without a propeller at the design speed V = 10kn is 251584N.

[0089] As a verification of the effectiveness of the calculation method described in this invention, the inventors conducted a ship model towing resistance test in a towing tank using a laboratory physical scale model test method on the bare hull of step S2. The ship model test results were converted into the static water resistance of the actual bare hull at the design speed V, which is R. 0(test)=240260N, and the relative error between the static water resistance of the bare hull obtained in step S2 and the result is 4.713%, which proves that the numerical simulation results calculated by the computational fluid dynamics analysis software STAR-CCM+ meet the accuracy requirements required for engineering applications.

[0090] S3. Input the geometric spatial coordinates of the propeller and hull into the 3D modeling software Rhino to construct... Figure 5 The four propeller and hull combination geometric models shown are placed inside a cuboid. The dimensions and positions of the cuboid are defined the same as those of the cuboid used in step S2 to analyze the hydrostatic resistance R0 of the bare hull. A cylinder is placed at the location of each propeller, with its axis centered on the corresponding propeller shaft. The radius of each cylinder is 1.0015 times the propeller diameter D. The distance from the cylinder's inlet boundary surface to the leading edge of the propeller hub is 0.5 times the propeller diameter D, and the distance from the cylinder's outlet boundary surface to the trailing edge of the propeller hub is... The length is one times the propeller diameter D. Boolean subtraction operations are performed between each cylinder and its corresponding propeller model. Boolean subtraction operations are also performed between the cuboid and the hull model, as well as the cylindrical sub-computation domains, forming a cylindrical computational domain containing the geometry of each propeller and a cuboid computational domain containing the hull shape. All cylinders are within the cuboid. The propeller shaft coincides with the rotation center axis of the corresponding cylinder. The cylinders in the combined computational domain of the four propellers and the hull do not overlap; that is, the difference set of each cylinder is empty. The fluid flow range during the calculation process is defined in the computational fluid dynamics analysis software STAR-CCM+ using the cuboid computational domain. The boundary conditions of the cylindrical sub-computation domain surface and the surface contacting the cuboid and cylindrical sub-computation domains are all set as sliding mesh boundary conditions. The rotation of the four propellers is simulated using a moving reference frame method, i.e., maintaining no relative rotational displacement between the X propeller geometric models and the hull model during the calculation process. This is achieved by subtracting the cylindrical computational domains I corresponding to the four propellers. x The rotational motion is defined using a corresponding reference coordinate system, and the rotational speed of the reference coordinate system is made equal to the propeller speed, thus enabling numerical simulation of the rotating flow field near the propeller. The analysis software STAR-CCM+ outputs the ship's self-propulsion resistance R at the design speed V and propeller speed n. c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b In this embodiment, the designed speed V is 10 knots, and the initial propeller speed n is set to 248 rpm. The self-propulsion resistance R of the hull under self-propulsion conditions is obtained using computational fluid dynamics. c The thrust is 275839 N, and the thrust of each propeller is T. b1 =T b4 =63536N,Tb2 =T b3 =63536N, torque is Q b1 =Q b4 =17642 N·m, Q b2 =Q b3 =14205 N·m, total propeller thrust T b The calculation is performed using the following formula, where x is the propeller number. In this embodiment, the total propeller thrust T corresponds to a propeller speed n = 248 rpm. b It is 210744N;

[0091]

[0092] S4, the ship's self-propulsion resistance R calculated in step S3 c Greater than the total propeller thrust T b Therefore, the propeller speed n is increased to 254 rpm, and the calculation in step S3 is repeated. At this time, the ship's self-propulsion resistance R is obtained. c The total thrust of the propeller is 272,903 N. b The resistance is 233,782 N, and the self-propulsion resistance R of the hull is... c Still greater than the total propeller thrust T b Continue increasing the propeller speed n to 273 rpm, and repeat the calculation in step S3 to obtain the ship's self-propulsion resistance R. c The total thrust of the propeller is 277,650 N. b The resistance is 286238 N, at which point the ship's self-propulsion resistance R is... c Less than the total propeller thrust T b Stop repeating step S3. Using a graphical method, determine the aft thrust coefficient K of each propeller according to the following formulas (4-1), (4-2), and (4-3). Tbsx , Ship rear torque coefficient K Qbsx and the total ship thrust reduction fraction t cs ;

[0093]

[0094] The specific drawing method is as follows: Figure 9 As shown, the propeller speed n is plotted on the horizontal axis, and the hull resistance R is... c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b Using the vertical axis as the ordinate, plot the rotational speed versus the hull resistance nR. c Curve, Rotational Speed ​​- Total Propeller Thrust nT b Curve, Rotational Speed-Thrust nT of the Same Propeller Group bx Curve and the speed-torque nQ of the same propeller groupbx curve. Figure 9 In the middle, nR c Curve and nT b The intersection point 9-1 of the curves is the ship's self-propulsion point, and the x-coordinate corresponding to the intersection point 9-1 is the propeller speed n under self-propulsion conditions. bs =269.5 rpm, the vertical axis represents the ship's self-propulsion resistance R under self-propulsion conditions. cs With the total thrust T of the propeller bs In this embodiment, R cs =T bs = 276491N. The rotational speed n of the propeller. bs Draw a vertical line 9-2 perpendicular to the horizontal axis from the point value. Line 9-2 intersects the speed-torque curves of propellers 1 and 4 at point 9-3, the speed-torque curves of propellers 2 and 3 at point 9-4, the speed-thrust curves of propellers 1 and 4 at point 9-5, and the speed-thrust curves of propellers 2 and 3 at point 9-6. This yields the thrust T of each propeller under self-propulsion conditions. bs1 =T bs4 =81053N,T bs2 =T bs3 =57193N, torque Q bs1 =Q bs4 = 21821 N·m, Q bs2 =Q bs3 =18121 N·m; then the stern thrust coefficient K of each propeller was calculated according to formulas (4-1), (4-2), and (4-3). Tbsx K Tbs1 =K Tbs4 =0.3004, K Tbs2 =K Tbs3 =0.2120, stern torque coefficient K Qbsx K Qbs1 =K Qbs4 =0.04257, K Qbs2 =K Qbs3 =0.03535, total ship thrust reduction fraction t cs =0.0901.

[0095] S5, such as Figure 7 As shown, the propeller open-water performance curve obtained in step S1 (JK) T Curve 7-1, JK Q Draw four horizontal lines on curves 7-2 and J-η0 (7-3). The vertical coordinate of each horizontal line corresponds to the stern thrust coefficient K of each propeller under the ship's self-propulsion state obtained in step S4. TbsxIn this embodiment, since the four ducted propellers rotate at the same speed and are symmetrically arranged on the port and starboard sides, the data for propeller 1 and propeller 4 are the same, and the data for propeller 2 and propeller 3 are the same. The four horizontal lines are simplified as follows: Figure 7 The middle horizontal lines 7-4 and 7-5, where horizontal line 7-4 refers to the stern thrust coefficient K of propellers 1 and 4. Tbs1 The vertical axis is denoted by y, and the horizontal line 7-5 represents the stern thrust coefficient K of propellers 2 and 3. Tbs2 The vertical axis is used as the coordinate.

[0096] Horizontal lines 7-4 and JK T Curve 7-1 intersects at point 7-6, and the horizontal line 7-5 intersects with JK. T Curve 7-1 has an intersection point 7-7. At the intersection point 7-6, draw a vertical line 7-8 perpendicular to the horizontal axis. At the intersection point 7-7, draw a vertical line 7-9 perpendicular to the horizontal axis. The intersection point of vertical line 7-8 and the horizontal axis is 7-10, and the intersection point of vertical line 7-9 and the horizontal axis is 7-11.

[0097] Based on the position of intersection point 7-10 on the horizontal axis, read the advance coefficient J corresponding to propellers 1 and 4 under the ship's self-propulsion state. sx For J s1 =J s4 =0.397; Based on the position of intersection point 7-11 on the horizontal axis, read the advance coefficient J corresponding to propellers No. 2 and No. 3 under the ship's self-propulsion state. sx For J s2 =J s3 =0.547.

[0098] Based on vertical lines 7-8 and JK Q The ordinate of the intersection point 7-12 of curve 7-2 can be used to read the open-water torque coefficient K of propellers 1 and 4 under the ship's self-propulsion condition. Q0sx For K Q0s1 =K Q0s4 =0.0413; The open-water efficiency η of propellers 1 and 4 under self-propulsion conditions is obtained from the ordinate of the intersection point 7-13 of the vertical line 7-8 and the J-η0 curve 7-3. 0sx For η 0s1 =η 0s4 =0.46.

[0099] Based on vertical lines 7-9 and JK Q The ordinate of the intersection point 7-14 of curve 7-2 is used to read the open-water torque coefficient K of propellers 2 and 3 under the ship's self-propulsion state. Q0sx For K Q0s2 =K Q0s3=0.0360. Based on the ordinate of the intersection point 7-15 of the vertical line 7-9 and the J-η0 curve 7-3, the open-water efficiency η of propellers No. 2 and No. 3 under the ship's self-propulsion state is read. 0sx For η 0s2 =η 0s3 =0.513.

[0100] S6. The propeller speed n under the self-propulsion state of the ship, as determined in step S4. bs With the aft torque coefficient K Qbsx and the advance coefficient J of each propeller determined in step S5 sx Open water torque coefficient K Q0sx With open water efficiency η 0sx Determine the stern advance speed V of each propeller at the design speed V using the following formulas (6-1), (6-2), and (6-3). Abx Relative rotational efficiency η Rx and the fraction of the accompanying flow ω bx The calculated stern velocity of propellers 1 and 4 is V. Ab1 =V Ab4 = 3.774 m / s, the backward speed of propellers 2 and 3 is V Ab2 =V Ab3 = 5.195 m / s, the relative rotational efficiency of propeller No. 1 and propeller No. 4 is η R1 =η R4 =0.972, the relative rotational efficiency of propellers 2 and 3 is η. R2 =η R3 =1.017, the wake fraction of propellers 1 and 4 is ω b1 =ω b4 =0.267, the wake fraction of propellers 2 and 3 is ω b2 =ω b3 = -0.010.

[0101]

[0102] S7. Calculate the average relative rotational efficiency η of the stern propeller using the thrust-weighted average method according to the following formula. R-aver Average wake fraction ω b-aver and average open water efficiency η 0s-aver As shown in formulas (7-1), (7-2), and (7-3), the principle of the thrust weighted average method is to combine the hydrodynamic parameters (relative rotational efficiency η) of each propeller. Rx , co-current fraction ω bx and open water efficiency η 0sx Multiply by the corresponding propeller thrust T at the rear of the ship under self-propulsion conditions. bsxWith the total thrust T of the propeller bs The ratios are then summed to obtain the average hydrodynamic parameters of the propeller (average relative rotational efficiency η). R-aver Average wake fraction ω b-aver and average open water efficiency η 0s-aver The average relative rotational efficiency η of the propeller at the stern was calculated. R-aver =0.9906, average wake fraction ω b-aver =0.1525, average open water efficiency η 0s-aver =0.5025;

[0103]

[0104] S8. Determine the hull efficiency η according to the following formula. H =1.074 and propulsion efficiency η D =0.535, based on propulsion efficiency η D The total main engine power P required for the multi-propeller ship at the design speed V = 10 knots is determined by using the still water bare hull resistance R0 obtained in step S2. S =2422kW:

[0105]

[0106] Example 2

[0107] Based on Example 1, Example 2 is designed with a cruising speed of 8 knots and uses the same ducted propeller. Figure 10 JK is shown in the open-water performance curve of the propeller in Example 2. T Curve (10-1), JK Q Curve (10-2) and J-η0 curve (10-3) and Example 1 Figure 7 same.

[0108] Step S1 is the same as in Example 1.

[0109] S2. Similar to step S2 in Example 1, the spatial coordinates of the geometric shape of the bare hull without a propeller are input into the 3D modeling software Rhino to construct the computational domain of the bare hull. The size and location of the computational domain are defined the same as in Example 1. Using the computational fluid dynamics analysis software STAR-CCM+, the hydrostatic resistance R0 of the bare hull without a propeller at the design speed V = 8 knots is calculated to be 138526 N.

[0110] S3. Similar to step S3 in Example 1, the geometric spatial coordinates of the propeller and hull are input into the 3D modeling software Rhino to construct four combined propeller and hull computational domains. The size and position of the cuboid computational domain and the cylindrical sub-computational domain are defined the same as in Example 1. In this example, the designed speed V is 8 knots, and the initial propeller speed n is set to 211 rpm. The self-propulsion resistance R of the hull under self-propulsion conditions is calculated using the computational fluid dynamics analysis software STAR-CCM+. c The thrust is 146706 N, and the thrust of each propeller is T. b1 =T b4 =35168N,T b2 =T b3 =16639N, torque is Q b1 =Q b4 =10817 N·m, Q b2 =Q b3 = 7718 N·m, total propeller thrust T b The calculation is performed according to formula (3-1), where x is the propeller number. In this embodiment, the total propeller thrust T corresponds to a propeller speed n = 211 rpm. b It is 103614N.

[0111] S4, the ship's self-propulsion resistance R calculated in step S3 c Greater than the total propeller thrust T b Therefore, the propeller speed n is increased to 220 rpm, and the calculation in step S3 is repeated. At this time, the self-propulsion resistance R of the hull is obtained. c The total thrust of the propeller is 148,123 N. b The resistance is 131229 N, and the self-propulsion resistance R of the hull is... c Still greater than the total propeller thrust T b Continue increasing the propeller speed n to 238 rpm, and repeat the calculation in step S3 to obtain the ship's self-propulsion resistance R. c The total thrust of the propeller is 149682 N. b The resistance is 183459 N, at which point the ship's self-propulsion resistance R is... c Less than the total propeller thrust T b Stop repeating step S3. Use the graphical method to determine the aft thrust coefficient K of each propeller according to formulas (4-1), (4-2), and (4-3). Tbsx , Ship rear torque coefficient K Qbsx and the total ship thrust reduction fraction t cs ;

[0112] Using the plotting method in step S4 of Example 1, such as Figure 11 As shown, nR c Curve and nT bThe intersection point 11-1 of the curves represents the self-propulsion point of the hull at its design speed of V = 8kn. The x-axis corresponding to the intersection point 11-1 is the propeller speed n during the self-propulsion state. bs =226rpm, from the vertical axis we obtain the ship's self-propulsion resistance and the total propeller thrust R under self-propulsion conditions. cs =T bs =147449N. Draw vertical line 11-2, and obtain the thrust T of each propeller under self-propulsion conditions from the intersection points 11-5 and 11-6 respectively. bs1 =T bs4 =46958N,T bs2 =T bs3 =26757N, torque Q is obtained from intersections 11-3 and 11-4. bs1 =Q bs4 =13619 N·m, Q bs2 =Q bs3 =10371 N·m; The stern thrust coefficient K of each propeller is calculated according to formulas (4-1), (4-2), and (4-3). Tbsx K Tbs1 =K Tbs4 =0.2476, K Tbs2 =K Tbs3 =0.1411, stern torque coefficient K Qbsx K Qbs1 =K Qbs4 =0.03779, K Qbs2 =K Qbs3 =0.02877, total ship thrust reduction fraction t cs =0.0605.

[0113] S5, similar to step S5 in Example 1, such as Figure 10 As shown in the open-water performance curve diagram of the propeller, two horizontal lines are drawn, with the horizontal line 10-4 representing the stern thrust coefficient K of propellers No. 1 and No. 4. Tbs1 The vertical axis is denoted by y, and the horizontal line 10-5 represents the stern thrust coefficient K of propellers 2 and 3. Tbs2 The vertical axis is used as the coordinate.

[0114] Horizontal line 10-4 and JK T Curve 10-1 intersects at point 10-6, and the horizontal line 10-5 intersects with JK. T Curve 10-1 has an intersection point 10-7. At intersection point 10-6, draw a vertical line 10-8 perpendicular to the horizontal axis. At intersection point 7-7, draw a vertical line 10-9 perpendicular to the horizontal axis. The intersection point of vertical line 10-8 and the horizontal axis is 10-10, and the intersection point of vertical line 10-9 and the horizontal axis is 10-11.

[0115] Based on the position of intersection point 10-10 on the horizontal axis, read the advance coefficient J corresponding to propellers 1 and 4 under the ship's self-propulsion state. sx For J s1 =J s4 =0.484; Based on the position of intersection point 10-11 on the horizontal axis, read the advance coefficient J corresponding to propellers 2 and 3 under the ship's self-propulsion state. sx For J s2 =J s3 =0.673.

[0116] Based on vertical line 10-8 and JK Q The ordinate of the intersection point 10-12 of curve 7-2 is used to read the open-water torque coefficient K of propellers 1 and 4 under the self-propulsion state of the ship. Q0sx For K Q0s1 =K Q0s4 =0.0385; The open-water efficiency η of propellers 1 and 4 under self-propulsion is obtained from the ordinate of the intersection point 10-13 of the vertical line 10-8 and the J-η0 curve 10-3. 0sx For η 0s1 =η 0s4 =0.501.

[0117] Based on vertical line 10-9 and JK Q The ordinate of the intersection point 10-14 of curve 10-2 is used to read the open-water torque coefficient K of propellers 2 and 3 under the self-propulsion state of the ship. Q0sx For K Q0s2 =K Q0s3 =0.0305. The open-water efficiency η of propellers 2 and 3 under self-propulsion conditions is obtained from the ordinate of the intersection point 10-15 of the vertical line 10-9 and the J-η0 curve 10-3. 0sx For η 0s2 =η 0s3 =0.494.

[0118] S6. Similar to step S6 in Example 1, the stern advance speed of propellers 1 and 4 is calculated as V according to formulas (6-1), (6-2), and (6-3). Ab1 =V Ab4 = 3.464 m / s, the backward speed of propellers 2 and 3 is V. Ab2 =V Ab3 = 4.814 m / s, the relative rotational efficiency of propellers 1 and 4 is η R1 =η R4 =1.018, the relative rotational efficiency of propellers 2 and 3 is η R2 =η R3 =1.059, the wake fraction of propellers 1 and 4 is ω b1 =ω b4=0.158, the wake fraction of propellers 2 and 3 is ω b2 =ω b3 = -0.170.

[0119] S7. Similar to step S7 in Example 1, the average relative rotational efficiency η of the stern propeller is calculated using the thrust weighted average method according to the following formulas (7-1), (7-2), and (7-3). R-aver =1.0329, average wake fraction ω b-aver =0.0393, average open water efficiency η 0s-aver =0.4987;

[0120] S8. Determine the hull efficiency η according to formulas (8-1), (8-2), and (8-3). H =0.9779 and propulsion efficiency η D =0.5037, based on propulsion efficiency η D The total main engine power P required for the multi-propeller ship at the design speed V = 8 knots is determined by using the still water bare hull resistance R0 obtained in step S2. S =1415kW.

[0121] This invention uses numerical simulation to determine the propulsion efficiency η of a multi-propeller ship. D This allows for the prediction of the total main engine power of the designed vessel at its design speed. Specifically, Examples 1 and 2 calculate the propulsion efficiency η at design speeds V = 10 knots and V = 8 knots. D The values ​​are 0.5345 and 0.5037 respectively, and their values ​​are both within the range of 0.50 to 0.65, which is common for propulsion efficiencies of conventional four-propeller ships (Ding Xiaoqiang. Research on ship-engine-propeller matching of large four-propeller ships [D]. Heilongjiang: Harbin Engineering University, 2009. DOI:10.7666 / d.y1655361.). This proves that the propulsion efficiency results calculated in Example 1 and Example 2 are reasonable and reliable.

[0122] In Example 1, the hydrostatic resistance R0 of the bare hull calculated using the method of the present invention is 251584 N, which is converted to the hydrostatic resistance R obtained by the method of laboratory physical scale model test. 0(test) =240260N, and the relative error between them is 4.713%. This proves that the calculations of the various embodiments of the present invention performed using the computational fluid dynamics analysis software STAR-CCM+ meet the accuracy requirements.

[0123] The calculated total main engine power required for a multi-propeller ship can be used to select a suitable main engine, predict the ship's speed and economy, and provide important reference for ship design. Compared with traditional self-propelled test methods for multi-propeller ships, this invention uses numerical simulation to calculate the total main engine power of a multi-propeller ship, simplifying the experimental data acquisition steps and significantly reducing the cost and time required to obtain the same prediction effect. It also overcomes the inherent theoretical defects caused by the scaling conversion between the actual and model versions in self-propelled tests of multi-propeller ships, realistically revealing the flow field state near the hull and each propeller, as well as their mutual influence and interaction, thus improving the accuracy of the prediction.

[0124] The multi-propeller ship power calculation method based on full-scale numerical simulation shown in this invention may have other embodiments rather than being limited thereto. Without departing from the spirit and essence of this invention, those skilled in the art can make various corresponding changes and modifications according to this invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation, characterized in that... Includes the following steps: S1. Input the computational domain of a single propeller into the computational fluid dynamics analysis software STAR-CCM+, set the propeller speed n, and obtain the results of a single propeller at different advance speeds V. A Given the thrust T and torque Q, the thrust coefficient K of a single propeller at the advance coefficient J can be obtained using the formula. T Torque coefficient K Q With open water efficiency η0; with advance coefficient J as the abscissa and thrust coefficient K as the ordinate. T Torque coefficient K Q With the open water efficiency η0 as the ordinate, we obtain JK T Curves, JK Q Curve and J-η0 curve: Propeller open-water performance curve diagram; S2. Input the bare hull calculation domain into the computational fluid dynamics analysis software STAR-CCM+ to obtain the bare hull hydrostatic resistance R0 at the given design speed V. S3. Input the computational domain of X propellers and hull combinations into the computational fluid dynamics analysis software STAR-CCM+, where X is any integer from 2 to 4; obtain the hull resistance R at the design speed V and propeller speed n. c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b The total thrust of the propeller, T b According to formula (3-1) The calculation is performed, where x is the propeller number; S4. Change the set propeller speed n and repeat step S3 to obtain the hull resistance R at different propeller speeds n. c The thrust T of each propeller bx and torque Q bx and the total thrust T of the propeller b The aft thrust coefficient K of each propeller is determined using a graphical method according to the following formula. Tbsx , Ship rear torque coefficient K Qbsx and the total ship thrust reduction fraction t cs Plot the propeller speed n on the x-axis and the hull resistance nR. c Curve, Rotational Speed ​​- Total Propeller Thrust nT b Curve, Rotational Speed-Thrust nT of the Same Propeller Group bx The curve and the speed-torque nQ of the same propeller group bx Curve, when nR c Curve and nT b When the curves intersect, stop repeating step S3; the x-axis corresponding to the intersection point is the propeller speed n under self-propulsion conditions. bs Passing through the propeller at a rotational speed of n bs Draw a vertical line perpendicular to the x-coordinate from the point of value nR. c Curve, nT b Curve, nT bx Curve and nQ bx The intersection points of the curves yield the ship's self-propulsion resistance R under self-propulsion conditions. cs The thrust T of each propeller bsx With torque Q bsx and the total thrust T of the propeller bs Value: （4-1） ；（4-2） ； （4-3） ； （4-4） S5. Draw X horizontal lines on the propeller open-water performance curve obtained in step S1. The vertical axis corresponding to each horizontal line is the stern thrust coefficient K of each propeller under the ship's self-propulsion state obtained in step S4. Tbsx ; X horizontal lines and JK in the propeller open-water characteristic curve diagram T The curve has X intersection points. At each intersection point, a vertical line perpendicular to the horizontal axis is drawn. The advance coefficient J of each propeller under the ship's self-propelled state is obtained from the intersection of the vertical line and the horizontal axis. sx According to the vertical line and JK Q The intersection of the curve and the J-η0 curve yields the open-water torque coefficient K for each propeller under the ship's self-propulsion state, with the ordinate value being... Q0sx With open water efficiency η 0sx ; S6. The propeller speed n under the self-propulsion state of the ship, as determined in step S4. bs With the aft torque coefficient K Qbsx and the advance coefficient J of each propeller determined in step S5 sx Open water torque coefficient K Q0sx With open water efficiency η 0sx Determine the stern advance velocity V of each propeller at the design speed V using formulas 6-1 to 6-3. Abx Relative rotational efficiency η Rx With the fraction of the accompanying flow ω bx ; （6-1） ； （6-2） ； （6-3） S7. Determine the average relative rotational efficiency η of the stern propeller using the thrust-weighted average method according to the following formula. R-aver Average wake fraction ω b-aver and average open water efficiency η 0s-aver : （7-1） ； （7-2） ； （7-3） S8. Determine the hull efficiency η according to the following formula. H With propulsion efficiency η D This leads to the determination of the total main engine power P required for a multi-rotor ship at its design speed V. S : （8-1） ； （8-2） ； （8-3） 。 2. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 1, characterized in that, The computational domain of a single propeller is a cylinder containing the geometric shape of the single propeller, formed after the geometric spatial coordinates of the single propeller are input into the 3D geometric modeling software Rhino. The rotational axis of the cylinder coincides with the propeller shaft; the advance velocity V... A The average velocity of the flow along the axis in front of the propeller disk; The thrust coefficient K of a single propeller at the advance coefficient J is obtained according to the formula. T Torque coefficient K Q The formula related to the open water efficiency η0 is: （1-1） ； （1-2） ；（1-3） ； （1-4） Where D is the propeller diameter, ρ is the fluid density, and π is pi.

3. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 2, characterized in that, The cylinder has a diameter of 6-10 times the propeller diameter D, the distance from the cylinder's inlet boundary surface to the leading edge of the propeller hub is 1-3 times the propeller diameter D, and the distance from the cylinder's outlet boundary surface to the trailing edge of the propeller hub is 4-8 times the propeller diameter D.

4. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 1, characterized in that, The bare hull computational domain is a cuboid formed by inputting the spatial coordinates of the geometric shape of the bare hull without a propeller into the 3D geometric modeling software Rhino, which includes the shape of the bare hull without a propeller.

5. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 4, characterized in that, The length of the cuboid's inlet boundary surface from the hull surface is 1-3 times the waterline length, and the length of the cylindrical outlet boundary surface from the hull surface is 4-8 times the waterline length; the top boundary surface is parallel to the hull's waterline surface and is 0.25-1.5 times the waterline length from it; the bottom boundary surface is parallel to the hull's waterline surface and is 0.5-2 times the waterline length from it; the length of the two side boundary surfaces from the widest point of the hull is 1-4 times the waterline length; and the two side boundary surfaces are symmetrical about the mid-longitudinal section of the hull.

6. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 1, characterized in that, The computational domain for the X propellers and the hull combination consists of a cylinder containing the geometric shape of each propeller and a cuboid containing the hull shape, formed by inputting the spatial coordinates of the geometric shape of each of the X propellers and the spatial coordinates of the geometric shape of the bare hull into the 3D geometric modeling software Rhino. Each cylinder is within a cuboid, and there is no overlap between the cylinders or between the cylinders and the hull. The rotation center axis of each cylinder coincides with the corresponding propeller shaft.

7. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 6, characterized in that, In the computational domain of X propeller and hull combinations, the inlet boundary surface of the cuboid is 1-3 times the waterline length from the hull surface, the outlet boundary surface is 4-8 times the waterline length from the hull surface, the top boundary surface is parallel to the hull waterline and is 0.25-1.5 times the waterline length from the hull waterline, the bottom boundary surface is parallel to the hull waterline and is 0.5-2 times the waterline length from the hull waterline, and the two side boundary surfaces are 1-4 times the waterline length from the widest point of the hull.

8. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 6, characterized in that, In the computational domain of X propeller and hull combinations, the diameter of each cylinder is 1.001-1.05 times the corresponding propeller diameter, the distance from the inlet boundary surface of each cylinder to the leading edge of the corresponding propeller hub is 0.05-1.5 times the propeller diameter, and the distance from the outlet boundary surface of each cylinder to the trailing edge of the corresponding propeller hub is 0.05-4 times the propeller diameter.

9. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to claim 2, 4, or 6, characterized in that, The geometry and dimensions of the bare hull or propeller are consistent with those of the actual hull or propeller.

10. The method for determining the total main engine power of a multi-rotor ship based on full-scale numerical simulation according to any one of claims 1-8, characterized in that, The propeller is a conventional propeller or a ducted propeller.

Images