A Design Method for Matching of Electric Propulsion Machine and Propeller under Hull Fouling Resistance

Abstract

The present invention relates to a method for matching design of a motor and a propeller for a ship under fouling resistance, including: 1) formulating an effective resistance increase scheme; 2) constructing a numerical model of ship fouling and numerical simulation, adopting full-appendage modeling of the target ship, conducting full-scale resistance numerical simulation, establishing a numerical model of ship fouling, and conducting open-water numerical simulation of the stock propeller; 3) establishing a matching reserve method, through the variation law of the matching point of the engine and the propeller when the hull resistance changes due to fouling, combined with the working characteristics of the propulsion motor having constant torque below the rated speed and constant power above the rated speed, aiming at the matching effect of the engine and the propeller during the whole-life operation cycle of the ship, an effective matching reserve method is proposed to enable the propulsion motor, the propeller, and the shafting to operate efficiently and stably for a long time in the mission working conditions, reduce the equipment failure rate, and ensure the normal departure rate of the ship. The present invention can shorten the design cycle of the target ship type, reduce the design cost, and improve the design reliability of the target ship type.

Description

Technical Field

[0001] The present invention relates to a design method for a ship's electric propulsion engine and propeller, in particular to a matching design method for an electric propulsion engine and propeller under the fouling resistance of a ship. Background Art

[0002] The matching point of the engine and propeller of a ship refers to the matching point of the rated working conditions of the engine and the propeller. It is related to the characteristic curves of the engine and the propeller selected during design. Generally, the characteristic curves of the two are marked on the same power - speed (or torque - speed) characteristic diagram and the intersection point is found, and this intersection point is the matching point. When designing a ship propulsion system, theoretically the matching point is the MCR point of the prime mover at 100% load and 100% speed. However, after a ship has been in operation for some time, the resistance of the ship will increase due to the attachment of marine organisms and corrosion on the hull surface and the propeller surface, and the ship speed will decrease. Generally, only newly built ships during sea trials are at the designed operating point. In most cases, the ship is operating at a non - designed operating condition point. This requires a reserve design for the matching of the engine and propeller according to the resistance change law of the actual ship. The selection of the load point (the selection of the reserve amount) directly affects the matching problem between the propeller and the prime mover. Problems in the matching of the engine and propeller usually result in issues such as the ship speed not reaching the required value, the prime mover exceeding the torque, the power not being generated, low propeller efficiency, and abnormal vibration. In the long run, it will lead to varying degrees of failures and damages to key equipment in systems such as the prime mover, shafting, and propeller. Seriously, the ship needs to enter the dry dock for repair, consuming a large amount of manpower and financial resources while also affecting the normal operation of the ship.

[0003] Currently, the research on the matching of ship engines, propellers, and pods at home and abroad mainly focuses on the research and optimization of the matching design of ship engines, propellers, and pods in the fields of diesel engine propulsion and electric pod propulsion, the research on the working condition matching of ship engines, propellers, and pods, and the research on the modeling and simulation of ship engine, propeller, and pod matching. There is very little theoretical research and analysis on the matching of the electric drive propulsion system with increased resistance due to ship fouling, and there is a lack of relevant experimental research and data support.

[0004] Therefore, there is a need to use CFD software for modeling and simulation, analyze the trend of the change in ship fouling resistance, and combine the characteristics of the propulsion motor with constant torque below the rated speed and constant power above the rated speed to study the reserve method for the matching of the propulsion system of the target ship, recommend the matching point of the engine and propeller for the designed operating condition of the target ship, so as to achieve a good matching effect of the engine and propeller throughout the life cycle of the ship's operation. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of the matching between the engine and the propeller under the increased fouling resistance during the whole life cycle of a ship. A design method for the matching between the electric propulsion engine and the propeller under the fouling resistance of a ship is provided. This method simulates the trend of the ship's resistance change caused by hull fouling through a numerical and simulation system, combines the rotational speed-power characteristics of the propulsion motor, analyzes and compares the matching between the ship, the engine and the propeller, and proposes a power reserve method applicable to the electric propulsion system, providing a new design idea for the matching design of the ship, the engine and the propeller under the fouling resistance.

[0006] To achieve the above object, the technical solution of the present invention is: A design method for the matching between the electric propulsion engine and the propeller under the fouling resistance of a ship, including:

[0007] 1) Formulate an effective resistance increase plan

[0008] In view of the evaluation problem of the fouling resistance of a ship, through the existing technical literature and the fouling data of similar ships, combined with numerical simulation, an effective resistance increase plan is formulated to improve the accuracy of the matching between the engine and the propeller;

[0009] 2) Construct a numerical model of ship fouling and numerical simulation

[0010] Full appendage modeling of the target ship is adopted, and full-scale resistance numerical simulation is carried out to establish a numerical model of ship fouling. Open-water numerical simulation of the stock propeller is carried out, and open-water numerical simulation of the designed propeller and self-propulsion numerical simulation of two pairs of propellers are carried out;

[0011] 3) Establish a matching reserve method

[0012] Based on the variation law of the matching point between the engine and the propeller when the hull resistance changes due to fouling, combined with the working characteristics of the propulsion motor with constant torque below the rated speed and constant power above the rated speed, an effective matching reserve method is proposed with the goal of the matching effect between the engine and the propeller during the whole life cycle of the ship, enabling the propulsion motor, the propeller and the shafting to operate efficiently and stably for a long time under the mission conditions, reducing the equipment failure rate, and ensuring the normal departure rate of the ship.

[0013] Furthermore, the specific method for formulating an effective resistance increase plan by the numerical simulation includes:

[0014] 1) Definition of fouling level;

[0015] 2) Find the corresponding relationship between the fouling level and the roughness;

[0016] 3) Calculation of the fouling resistance increase value.

[0017] Furthermore, the target ship uses the numerical simulation method to conduct the analysis and research on the matching between the engine and the propeller, meets the accuracy requirements of the design analysis, and conducts three-dimensional modeling through the input data of the numerical analysis.

[0018] Further, the numerical simulation uses the control equations for numerical simulation calculation, which are the continuity equation and the momentum equation. The control equations are discretized by the finite volume method, and the Reynolds-averaged method is used as the turbulence numerical simulation method.

[0019] Further, the open-water numerical simulation of the designed propeller uses virtual tests in a numerical tank. The virtual tests in the numerical tank are divided into three parts: open water, resistance, and self-propulsion. The processing of the test results is the same as that of the physical tank of the entity, including:

[0020] 1) Propeller model design

[0021] Two types of propellers are designed respectively to compare the matching characteristics of the engine and propeller considering the rotational speed reserve:

[0022] (1) Conventional propeller

[0023] The conventional propeller is the one that considers the motor power and rotational speed both operating at the design point under the new ship conditions. According to the hull resistance data, the pitch ratio of this conventional design is 1.32;

[0024] (2) Optimized propeller

[0025] The optimized propeller is the one that considers the rotational speed being more than 5% higher than the rated speed under the rated power of the motor under the new ship conditions. The designed pitch of the optimized propeller is 1.22, which is lower than the pitch ratio of the conventional propeller;

[0026] 2) Open-water virtual test

[0027] A cubic computational domain is adopted. The 3D model of the propeller model is located in the middle of the computational domain. The boundary conditions are as follows: the incoming flow surface is set as the velocity inlet, the outlet surface is set as the pressure outlet, the side surfaces are symmetric surfaces, the bottom and top are slip walls, and the other side is also set as a symmetric surface. The water flow moves from the positive x direction to the negative x direction, and it can rotate in the cylindrical region around the propeller model. The rotating domain exchanges numerically with the large computational domain of the cube; numerical simulations are carried out on the propellers of the conventional propeller and the optimized propeller respectively;

[0028] 3) Self-propulsion virtual test

[0029] Similar to the resistance numerical simulation, the computational domain for the model-scale resistance is a cube, and the full-ship model is located in the middle of the computational domain. The boundary conditions are as follows: the incoming flow surface is set as the velocity inlet, the outlet surface is set as the pressure outlet, the side surfaces are symmetric surfaces, the bottom and top are slip walls, and the other side surface is also set as a symmetric surface. The water flow moves from the positive x direction to the negative x direction. Similar to the real-scale resistance numerical simulation, unstructured grids are used for grid division. The grids are cut bodies, which are encrypted near the free surface, and the grids are dense around the hull and sparse in the direction far from the hull.

[0030] The beneficial effects of the present invention are:

[0031] Combined with the engineering application requirements of the target ship, this invention conducts theoretical research and analysis on the matching of the power propulsion system's engine and propeller, masters the key technologies of engine-propeller matching for the multi-condition power propulsion system, and improves the domestic integrated design ability of the power propulsion system. The results of this invention can be directly applied to the propulsion system of the target ship and the design of the propeller, shortening the design cycle of the target ship type, reducing the design cost, and improving the design reliability of the target ship type. At the same time, the results can be widely applied to various types of ships with other power propulsion and hybrid power. Brief Description of the Drawings

[0032] Figure 1 is the flow chart of the design method for the power propulsion engine-propeller matching under the fouling resistance of the ship;

[0033] Figure 2 is the schematic diagram of the geometric shape of the fully appended hull;

[0034] Figure 3 is the mesh division diagram;

[0035] Figure 4 is the open water virtual test calculation domain diagram;

[0036] Figure 5 is the side view of the conventional propeller;

[0037] Figure 6 is the side view of the optimized propeller;

[0038] Figure 7 is the front and rear speed change and speed field diagram of the conventional propeller when J = 0.95;

[0039] Figure 8 is the front and rear speed change and speed field diagram of the optimized propeller when J = 0.95;

[0040] Figure 9 is the mesh division diagram during self-propulsion;

[0041] Figure 10 is the rotational speed-power diagram. Detailed Implementation Manner

[0042] The present invention will be further described below in conjunction with the drawings and embodiments.

[0043] As Figure 1 shown, the design method for the power propulsion engine-propeller matching under the fouling resistance of the ship of the present invention includes

[0044] 1. Determine the research method

[0045] Traditional propeller-hull matching analysis can adopt methods such as data regression, atlas calculation, and model tests. The advantages of data regression and atlas calculation are low cost and fast calculation speed. Data regression requires a clear understanding of the meaning of the parameters in the regression equation, and the regression equation has limitations. For different ship types and different waters, different equations need to be used for calculation.

[0046] Similar problems also exist in atlas calculation: hull resistance, wake fraction, and thrust deduction are estimated by empirical formulas, and the open-water performance of the propeller is obtained from atlases, resulting in relatively low design accuracy.

[0047] Hydrodynamic model tests can obtain more accurate results than methods such as atlases and regression, but they require the fabrication of ship models and the use of pool test equipment, so the cost is high and the time consumption is long.

[0048] For the target ship, numerical simulation (numerical simulation) methods are used for the analysis and research of propeller-hull matching. Compared with data regression and atlas calculation methods, the numerical simulation analysis results have higher accuracy. Compared with pool tests, the numerical simulation method has lower costs and can shorten the analysis time, and the accuracy can also meet the design analysis requirements.

[0049] The numerical simulation method is another name for CFD (Computational Fluid Dynamics). The basic principle of CFD is to approximately represent the integral and differential terms in the control equations of fluid mechanics as discrete algebraic forms, making them into algebraic equation systems, and then solving these discrete algebraic equation systems through a computer to obtain the numerical solutions at discrete time / space points.

[0050] 2. Numerical analysis input data and 3D modeling

[0051] Table 1 Main parameters of the ship type

[0052] Length between perpendiculars m 90 Moulded breadth m 12 Design draft m 3.3 <![CDATA[Design draft displacement volume m 3 > 1550

[0053] Table 2 Main parameters of the main engine

[0054] Propulsion motor MCR 6875kW×2 Service power CSR(90%MCR) 6187.5kW×2 Shafting efficiency 0.93

[0055] Table 3 Main parameters of the propeller

[0056] Number and type of propellers 2 fixed pitch propellers Propeller diameter 2.8m Number of blades 5 blades / propeller

[0057] Note: The numerical simulation is carried out under the input conditions of 6187.5×2kW and a rotational speed of 280 rpm, which is the design condition. The establishment of the 3D geometric model of the hull and appendages is completed, and the full-appendage model formed is as Figure 2 shown:

[0058] 3. Research on ship fouling resistance increase

[0059] By consulting the literature and researching relevant domestic and foreign research literature on ship fouling and roughness, a method for constructing a numerical model of ship fouling was established.

[0060] 1) Definition of fouling level

[0061] Soft fouling is usually algae, viscous mucus, and grass, which have the least impact on the coating system and ship performance. Hard fouling with a calcareous structure is more tenacious and may damage the performance of the ship and the coating system. Composite fouling includes both hard and soft fouling organisms, which is extremely detrimental to the performance, coating, and mechanical systems of the ship.

[0062] The formation of viscous substances and mucus is the first step in the fouling and scaling process. Almost all objects immersed in seawater will quickly accumulate a layer of mucus, which consists of bacteria, fungi, protozoa, and algae. Bacteria usually attach within half an hour of wetting the surface and can usually be felt by hand within an hour. The mucus coating is smooth and usually follows the hull contour.

[0063] Grass is a form of multicellular green and brown algae. It forms most abundantly near the waterline, where there is sufficient light for photosynthesis. As the depth increases, this phenomenon becomes less obvious, and the main color changes from green to brown.

[0064] The main forms of hard biofouling are barnacles and tubeworms. Some underwater components may experience severe conditions under which a combination of biofouling (hard and soft) and calcareous deposits forms.

[0065] The fouling level was defined by referring to the literature "WATERBORNE UNDERWATERHULL CLEANING OF NAVYSHIPS Ship Underwater Hull Attached Aquatic Organisms Cleaning". The fouling can be divided into a fouling level of 0 - 100. The larger the value, the more serious the fouling situation. Among them, 0 - 30 is soft attachments, the length of the grass-like attachments is less than 76 mm and the height does not exceed 6.4 mm, 40 - 90 is hard, and 100 is the most serious with a combination of hard and soft attachments. The diameter or height of the calcified substances in the range of 40 - 60 is less than 6.4 mm. For 70 - 80, it is higher than 6.4 mm and overlapping growth occurs. It is introduced in the literature [1] that the hull fouling should be inspected periodically, and when the fouling level is 50, it is necessary to dry dock for a full cleaning. Therefore, this patent's numerical simulation will only consider the situation between the fouling levels of 0 - 50.

[0066] 2) Corresponding relationship between fouling level and roughness

[0067] From the literature "Effects of coating roughness and biofouling on ship resistance and powering", the relationship between fouling bottom grade and equivalent roughness can be obtained:

[0068] Table 4 Relationship between fouling bottom grade and equivalent roughness

[0069] Fouling level Condition description Equivalent roughness 0 Smooth wall 0 0 Typical anti-fouling paint coating 30 10-20 Deteriorated coating or slight slime 100 30 Severe slime 300 40-60 Slight calcareous fouling or seagrass 1000 70-80 Moderate calcareous fouling 3000

[0070] In the numerical simulation of the present invention, only fouling bottom grades 0 - 50 are considered, so the corresponding roughness considers 0 - 1000. According to the corresponding states and fouling bottom grades in the literature, full-scale resistance calculations are carried out for equivalent roughnesses of 0, 30, 100, 300, and 1000. The numerical calculations are carried out at ship speeds of 24 kn and 26 kn respectively.

[0071] 3) Numerical calculation of fouling-induced resistance increase

[0072] Unstructured grids are used for grid division. As Figure 3 shown, the grids are cut bodies, which are densified near the free liquid surface, the grids around the hull are dense, and the grids are sparser in the direction away from the hull.

[0073] 4. Numerical simulation settings

[0074] The control equations for this numerical simulation calculation are the continuity equation and the momentum equation. The control equations are discretized by the finite volume method, and the Reynolds-averaged method is used as the turbulence numerical simulation method; the SIMPLE algorithm is used in this calculation, the realizable turbulence model is adopted, the fluid is an incompressible constant-density fluid, and the free liquid surface is captured by the VOF method.

[0075] Fluid density: 1026.021 kg / m^3

[0076] Fluid dynamic viscosity: 12.20141E - 4 Pa·s

[0077] This calculation is carried out at the full-scale of the actual ship.

[0078] Table 5 Numerical simulation calculation results of fouling-induced resistance increase

[0079] Fouling level Condition description Equivalent roughness 24kn 26kn 0 Smooth wall 1 97.9％ 97.6％ 0 Typical anti-fouling paint coating 30 100.0％ 100.0％ 10-20 Deteriorated coating or slight slime 100 107.9％ 106.8％ 30 Severe slime 300 117.3％ 115.6％ 40-60 Slight calcareous fouling or seagrass 1000 128.2％ 125.4％

[0080] When the fouling bottom grade is 50, the resistance increase at 26 knots is 25.4% compared to no fouling, while the resistance increase at 24 knots is 28.2%.

[0081] When the fouling bottom grade is 30, the resistance increase at 26 knots is 15.6% compared to no fouling, while the resistance increase at 24 knots is 17.3%.

[0082] Similar to the situation described in the literature "Effects of coating roughness and biofouling on ship resistance and powering", the increase in resistance is more significant at low speeds. The reason may be that the frictional resistance accounts for a larger proportion at low speeds while the wave-making resistance accounts for a larger proportion at high speeds.

[0083] 5. Numerical tank virtual test

[0084] The numerical tank virtual test is divided into three parts: open water, resistance, and self-propulsion. The processing of test results is the same as that of a physical tank.

[0085] 1) Regarding the design of propeller models

[0086] Two types of propellers are designed respectively to compare the propeller-engine matching characteristics considering the rotational speed reserve.

[0087] 1) Conventional propeller

[0088] The conventional propeller (code 1711) is the propeller that considers the motor power and rotational speed both operating at the design point under the conditions of a new ship. According to the hull resistance data, the pitch ratio of this conventional design is 1.32.

[0089] 2) Optimized propeller

[0090] The optimized propeller (code 1711m) is the propeller that considers the rotational speed being more than 5% higher than the rated rotational speed under the rated power of the motor under the conditions of a new ship. The designed pitch of the optimized propeller is 1.22, which is lower than the pitch ratio of the conventional propeller.

[0091] 5.1 Open water virtual test

[0092] The computational domain is a cube, and the 3D model of the propeller model is located in the middle of the computational domain. The boundary conditions are: the incoming flow surface is set as a velocity inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetric surfaces, the bottom and top are sliding wall surfaces, and the other side is also set as a symmetric surface. The water flow moves from the positive x direction to the negative x direction.

[0093] The cylindrical area around the propeller model can rotate, and the rotating domain exchanges numerical values with the large computational domain of the cube, as Figure 4 shown. The external boundary is far enough from the propeller that it can be considered that there is basically no influence. Numerical simulations are carried out on the propeller with code 1711 and the propeller with code 1711m respectively.

[0094] This calculation is carried out at the model scale, and the scale ratio is 16.3636. Numerical simulations of the open water characteristics are carried out on the conventional propeller (see Figure 5 ) and the optimized propeller (see Figure 6 ) models respectively.

[0095] Table 6 Open-water characteristics of the conventional propeller model

[0096] J Kt 10Kq Rn*E+6 Etao 0.850 0.2972 0.6315 0.44426 0.6368 0.900 0.2662 0.5803 0.44774 0.6570 0.950 0.2358 0.5300 0.45139 0.6727 1.000 0.2057 0.4796 0.45521 0.6826 1.050 0.1756 0.4284 0.45919 0.6850 1.100 0.1451 0.3756 0.46333 0.6764 1.150 0.1139 0.3205 0.46762 0.6506

[0097] As Figure 7 shown in Figure 8, the velocity vector arrows represent the magnitude and direction of the velocity. Longer arrows indicate a higher velocity, while shorter arrows indicate a lower velocity. Figure 7 For the conventional propeller (code number 1711, P / D = 1.32) in Figure 8 and the optimized propeller (code number 1711m, P / D = 1.22) in

[0098] Table 7 Open-water characteristics of the optimized propeller model

[0099] J Kt 10Kq Rn*E+6 Etao 0.850 0.2396 0.4940 0.44426 0.6561 0.900 0.2099 0.4481 0.44774 0.6708 0.950 0.1799 0.4012 0.45139 0.6780 1.000 0.1497 0.3532 0.45521 0.6748 1.050 0.1194 0.3039 0.45919 0.6564 1.100 0.0888 0.2532 0.46333 0.6140

[0100] 5.2 Virtual resistance test

[0101] Similar to the full-scale resistance numerical simulation, the computational domain for the model-scale resistance is a cube, and the half-ship model is located in the middle of the computational domain. The boundary conditions are as follows: the incoming flow surface is set as a velocity inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetry planes, the bottom and top surfaces are slip walls, and the symmetry plane is also set as a symmetry plane, which is located at the mid-longitudinal section of the hull. The water flow moves from the positive x-direction to the negative x-direction. Similar to the full-scale resistance numerical simulation, unstructured grids are used for grid division. The grids are cutting bodies, which are densified near the free surface, dense around the hull, and sparse in the direction away from the hull.

[0102] This calculation is carried out at the model scale with a scale ratio of 16.3636.

[0103] The results of the virtual test are shown in the following table.

[0104] Table 8 Results of the virtual resistance test of the model

[0105]

[0106]

[0107] 5.3 Self-propulsion virtual test

[0108] Similar to the resistance numerical simulation, the computational domain for the model-scale resistance is a cube, and the full-ship model is located in the middle of the computational domain. The boundary conditions are as follows: the incoming flow surface is set as a velocity inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetry planes, the bottom and top surfaces are slip walls, and the other side surface is also set as a symmetry plane. The water flow moves from the positive x-direction to the negative x-direction.

[0109] Similar to the full-scale resistance numerical simulation, as Figure 9 shown, unstructured grids are used for grid division. The grids are cutting bodies, which are densified near the free surface, dense around the hull, and sparse in the direction away from the hull.

[0110] This calculation is carried out at the model scale, with a scale ratio of 16.3636. Numerical simulations of the self-propulsion characteristics are respectively conducted on the conventional propeller and optimized propeller models. The results of the virtual tests are shown in Table 9.

[0111] Table 9 Virtual Self-Propulsion Tests of Conventional Propeller

[0112] Vs Vm Nm Rtm Fd Tm Qm Jm kn m / s r / s N N N N*m - 24.00 3.052 16.512 105.956 14.266 102.20 4.1329 0.9781 24.50 3.116 17.062 113.304 14.761 110.66 4.4413 0.9729 25.00 3.179 17.591 121.439 15.264 118.84 4.7436 0.9691 25.50 3.243 18.100 129.834 15.772 126.74 5.0397 0.9664 26.00 3.307 18.589 137.962 16.288 134.36 5.3292 0.9645 26.50 3.370 19.057 145.417 16.809 141.71 5.6119 0.9632 27.00 3.434 19.505 152.262 17.337 148.77 5.8877 0.9623 27.50 3.497 19.933 158.676 17.872 155.55 6.1563 0.9619 28.00 3.561 20.340 164.839 18.412 162.04 6.4175 0.9617 Vs wtm t Etar kn - - - 24.00 0.0946 0.1029 0.9699 24.50 0.0884 0.1095 0.9736 25.00 0.0825 0.1066 0.9762 25.50 0.0771 0.1000 0.9781 26.00 0.0723 0.0944 0.9793 26.50 0.0681 0.0924 0.9799 27.00 0.0647 0.0931 0.9799 27.50 0.0620 0.0948 0.9796 28.00 0.0601 0.0964 0.9788

[0113] Table 10 Virtual Self-Propulsion Tests of Optimized Propeller

[0114]

[0115]

[0116] The rotational speed of the optimized propeller is higher than that of the conventional propeller, which is consistent with the expectation. The wake fraction and thrust deduction of the two are basically the same.

[0117] 6. Full-Scale Ship Prediction

[0118] The analysis method of the numerical simulation is the same as that of the physical towing tank.

[0119] The fouling resistance increment occurs at the full-scale ship level. Therefore, the model value remains unchanged during the prediction process, and the resistance increment is added to the resistance coefficient of the full-scale ship. The predicted ship speeds are as follows:

[0120] Table 11 Full-Scale Ship Prediction Results of Conventional Propeller

[0121]

[0122] Table 12 Full-Scale Ship Prediction Results of Conventional Propeller with 20% Resistance Increment

[0123]

[0124]

[0125] Table 13 Full-Scale Ship Prediction Results of Conventional Propeller with 25% Resistance Increment

[0126]

[0127] Table 14 Full-Scale Ship Prediction Results of Optimized Propeller

[0128]

[0129] Table 15 Full-Scale Ship Prediction Results of Optimized Propeller with 20% Resistance Increment

[0130]

[0131] Table 16 Full-Scale Ship Prediction Results of Optimized Propeller with 25% Resistance Increment

[0132]

[0133]

[0134] Based on the data in the above tables, analyze the prediction results and draw a rotational speed - power diagram ( Figure 10 )

[0135] From Figure 10 it is obtained that:

[0136] 1) For the conventional propeller (code 1711), at a rotational speed of approximately 280 rpm, the ship speed is 26.30 kn without fouling on the bottom; in the case of a 25% increase in resistance, the propulsion motor operates at a reduced power, the propeller rotational speed is approximately 266 rpm, and the ship speed of the conventional propeller is 24.45 kn.

[0137] 2) For the optimized propeller (code 1711m), at a rotational speed of approximately 294 rpm, the ship speed is 26.25 kn without fouling on the bottom; in the case of a 25% increase in resistance, the propulsion motor operates at a constant power, the propeller rotational speed is approximately 286 rpm, and the ship speed of the conventional propeller is 24.75 kn.

[0138] Analysis of the rotational speed - power diagram shows that in this numerical simulation, compared with the optimized propeller, the speed drops of the conventional propeller are 1.85 kn and 1.5 kn respectively, and the optimized propeller reduces the speed drop to 0.35 kn (0.35 / 1.5 = 23.33%). This is because after the increase in resistance, the curve of the conventional propeller moves to the left, resulting in the propulsion motor being unable to operate at the rated power, while the propulsion motor of the optimized propeller can still operate at the rated power when the curve moves to the left.

[0139] 7. Conclusions

[0140] The present invention adopts full - appendage modeling of a certain ship, conducts full - scale resistance numerical simulation, establishes a method for constructing a ship fouling numerical model, conducts open - water numerical simulation of stock propellers, open - water numerical simulation of designed propellers, and self - propulsion numerical simulation of two pairs of propellers.

[0141] The following conclusions can be obtained from the research of the present invention:

[0142] 1) Collected and translated the standards of fouling grades, and obtained the corresponding relationship between fouling grades and equivalent roughness. When the fouling grade is 30, the resistance of the ship at a speed of 26 kn increases by about 15%. When the fouling grade is 40 - 60, the resistance of the ship at a speed of 26 kn increases by about 25%.

[0143] 2) Rotational speed reserve refers to the margin of the propeller rotational speed when the new ship absorbs 100% of the main engine power under future operating conditions. By reducing the pitch ratio of the fixed - pitch propeller in the design stage, the propeller of the new ship can operate with a lighter load, and the propeller rotational speed when absorbing 100% of the main engine power is higher than the rated rotational speed of the main engine.

[0144] 3) In the numerical simulation, when comparing the conventional propeller with the optimized propeller, the speed reductions are 1.85 kn and 1.5 kn respectively. The speed reduction of the optimized propeller is reduced to 0.35 kn (0.35 / 1.5 = 23.33%).

[0145] 4) The rotational speed reserve enables the propeller to keep the propulsion motor still operating at the designed rated power when the hull resistance increases due to reasons such as fouling. The characteristic of constant power after the motor exceeds the rated speed can be utilized, and a relatively large light-load rotational speed margin can be reserved when the motor is matched with a fixed-pitch propeller. It is recommended to be above 7%, but it should not be too large. An overly large light-load rotational speed margin will cause the open-water efficiency of the designed propeller to decline.

[0146] The present invention uses the numerical simulation method to analyze and study the increased resistance due to hull fouling and the matching of the engine and the propeller. It can also be replaced by a tank test. The design ideas of the increased resistance due to hull fouling and the matching of the engine and the propeller are the same for both. The tank test uses a scaled-down physical hull and propeller model to conduct resistance, open-water, and self-propulsion tests in a test tank. Its accuracy is relatively high, but the analysis time is long and the cost is expensive.

Claims

1. A method for designing the matching of a marine electric propulsion machine and propeller under the resistance of fouled hull bottom, characterized in that, it includes: Step 1: Formulate a resistance increase plan In view of the evaluation problem of the resistance of fouled hull bottom, through existing technical literature and the fouled hull bottom data of the ship, combined with numerical simulation, a resistance increase plan is formulated to improve the accuracy of the matching of the machine and propeller; Step 2: Construct a numerical model of fouled hull bottom and numerical simulation Full appendage modeling of the target ship is adopted, and full-scale resistance numerical simulation is carried out to establish a numerical model of fouled hull bottom, and open water numerical simulation of the stock propeller is carried out, and open water numerical simulation of the designed propeller and self-propulsion numerical simulation of two pairs of propellers are designed; The numerical simulation adopts the control equations of numerical simulation calculation, which are the continuity equation and the momentum equation. The control equations are discretized by the finite volume method, and the Reynolds-averaged method is used as the turbulent numerical simulation method; The open water numerical simulation of the designed propeller adopts the virtual test of the numerical tank. The virtual test of the numerical tank is divided into three parts: open water, resistance, and self-propulsion. The processing of the test results is the same as that of the physical tank of the entity; Step 3: Establish a matching reserve method Based on the variation law of the matching point of the machine and propeller when the hull resistance changes due to fouling, combined with the working characteristics of the propulsion motor with constant torque below the rated speed and constant power above the rated speed, an effective matching reserve method is proposed with the goal of the matching effect of the machine and propeller during the entire life cycle of the ship, so that the propulsion motor, propeller, and shafting can all operate efficiently and stably in the mission conditions, reduce the equipment failure rate, and ensure the normal departure rate of the ship.

2. The method for designing the matching of a marine electric propulsion machine and propeller under the resistance of fouled hull bottom according to claim 1, characterized in that: The specific method for formulating the resistance increase plan by numerical simulation includes: Step 1.1: Definition of fouled hull bottom grade; Step 1.2: Find out the corresponding relationship between the fouled hull bottom grade and roughness; Step 1.3: Calculation of the resistance increase value of fouled hull bottom: Unstructured grid division is adopted, the grid is a cut body, which is encrypted near the free surface, the grid around the hull is dense, and the grid is relatively sparse in the direction away from the hull. A virtual test of the numerical tank for the resistance increase of fouled hull bottom is carried out to obtain the specific resistance increase value.

3. The method for designing the matching of a marine electric propulsion machine and propeller under the resistance of fouled hull bottom according to claim 1, characterized in that: The target ship uses numerical simulation methods for the analysis and research of the matching of the machine and propeller, meets the accuracy requirements of design analysis, and conducts three-dimensional modeling through the input data of numerical analysis.

4. The method for designing the matching of a marine electric propulsion machine and propeller under the resistance of fouled hull bottom according to claim 1, characterized in that: The open water numerical simulation of the designed propeller includes: Step 2.1: Propeller model design Two kinds of propellers are designed respectively to compare the matching characteristics of the machine and propeller considering the speed reserve: Step 2.1.1: Conventional propeller The conventional propeller is the propeller that considers that both the motor power and speed operate at the design point under the condition of a new ship. According to the hull resistance data, the pitch ratio of this conventional design is 1.32; Step 2.1.2: Optimized propeller The optimized propeller is the propeller that considers that the speed is more than 5% higher than the rated speed under the rated power of the motor under the condition of a new ship. The pitch of the optimized propeller design is 1.22, which is lower than the pitch ratio of the conventional propeller; Step 2.2: Open water virtual test A cubic computational domain is adopted, and the propeller 3D model is located in the middle of the computational domain. The boundary conditions are as follows: the incoming flow surface is set as a velocity inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetry planes, the bottom and top are slip walls, and the other side is also set as a symmetry plane; the water flow moves from the positive x-direction to the negative x-direction, and the cylindrical area around the propeller model can rotate, and the rotating domain exchanges numerical values with the large cubic computational domain; numerical simulations are carried out on the propellers of the conventional propeller and the optimized propeller respectively. Step 2.3: Virtual resistance test The virtual resistance test is the numerical simulation of resistance, which is carried out at the model scale and the full scale. The computational domains of the model scale and the full scale resistance are cubes, and the full ship model is located in the middle of the computational domain. The boundary conditions are as follows: the incoming flow surface is set as a velocity inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetry planes, the bottom and top are slip walls, and the other side surface is also set as a symmetry plane. The water flow moves from the positive x-direction to the negative x-direction. Unstructured grids are used for grid division, and the grids are cutting bodies, which are encrypted near the free liquid surface, the grids around the hull are dense, and the grids are sparser in the direction away from the hull. Step 2.4: Self-propulsion virtual test Similar to the numerical simulation of resistance, the computational domain of the model scale resistance is a cube, and the full ship model is located in the middle of the computational domain. The boundary conditions are as follows: the incoming flow surface is set as a velocity inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetry planes, the bottom and top are slip walls, and the other side is also set as a symmetry plane; the water flow moves from the positive x-direction to the negative x-direction. Similar to the numerical simulation of the full scale resistance, unstructured grids are used for grid division, and the grids are cutting bodies, which are encrypted near the free liquid surface, the grids around the hull are dense, and the grids are sparser in the direction away from the hull.

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