CN114036646A - Electric propulsion engine propeller matching design method under ship bottom fouling resistance - Google Patents

Abstract

The invention relates to a matching design method of an electric propulsion engine propeller under ship bottom fouling resistance, which comprises the following steps: 1) making an effective resistance increasing scheme; 2) constructing a ship fouling numerical model and numerical simulation, modeling the full appendage of a target ship, performing real-scale resistance numerical simulation, establishing the ship fouling numerical model, and performing numerical simulation of the open water of stock paddles; 3) a matching storage method is established, an effective matching storage method is provided by combining the working characteristics that a propulsion motor has constant torque lower than a rated rotating speed and constant power higher than the rated rotating speed according to the change rule of a propeller matching point when the resistance of a ship body changes due to fouling, and the matching effect of the propellers in the whole life operation period of the ship is taken as a target, so that the propulsion motor, the propellers and a shaft system can stably run for a long time in a task working condition, the failure rate of equipment is reduced, and the normal sailing rate of the ship is ensured. The invention can shorten the design period of the target ship type, reduce the design cost and improve the design reliability of the target ship type.

Description

Electric propulsion engine propeller matching design method under ship bottom fouling resistance

Technical Field

The invention relates to a design method of a ship electric propulsion engine propeller, in particular to a matching design method of the electric propulsion engine propeller under ship bottom fouling resistance.

Background

The engine-propeller matching point of a ship is the matching point of the rated working conditions of the engine and the propeller, and is related to the characteristic curves of the engine and the propeller selected in the design, generally, the characteristic curves of the engine and the propeller are marked on the same power-rotating speed (or torque-rotating speed) characteristic diagram, and the intersection point of the characteristic curves is found, namely the matching point. When the ship propulsion system is designed, theoretically, a matching point is an MCR point of a prime motor with 100% load and 100% rotating speed, but after the ship operates for a period of time, the ship body resistance is increased due to the fact that marine organisms are attached to the surface of the ship body and the surface of a propeller and corrosion occurs, and the ship speed is reduced. Generally, only a newly-built new ship is in a running design point during pilot run, and in most cases, the ship runs in a non-design working condition point, so that the design of propeller matching storage needs to be carried out according to the resistance change rule of a real ship, and the matching problem of the propeller and a prime motor is directly influenced by the selection of a load point (the selection of the storage amount). The problems of unavailable navigational speed, excessive torque of a prime motor, unavailable power, low propeller efficiency, abnormal vibration and the like can be generally caused when the mechanical propeller is matched, faults and damages of key equipment of systems such as the prime motor, a shafting system, the propeller and the like occur in different degrees in the past for a long time, when the faults and the damages are serious, a ship needs to be docked for maintenance, a large amount of manpower and financial resources are consumed, and the normal operation of the ship is also influenced.

At present, the research on the matching of the ship and the engine propeller at home and abroad is mainly embodied in the fields of the matching design optimization research of the ship and the engine propeller, the working condition matching research of the ship and the engine propeller, the matching modeling simulation research of the ship and the engine propeller and the like in the fields of the propulsion of diesel engines and electric pod, the research and analysis of the engine propeller matching theory of an electric driving propulsion system for increasing the resistance due to the ship bottom pollution are few, and the relevant experimental research and data support are lacked.

Therefore, a method for researching a target ship propulsion system engine propeller matching storage method and recommending engine propeller matching points of a target ship under design conditions by modeling and simulating through CFD software and analyzing the trend of ship fouling resistance change and combining the characteristics that a propulsion motor has constant torque lower than a rated rotating speed and constant power higher than the rated rotating speed is needed, so that a good engine propeller matching effect can be obtained in the whole life operation period of a ship.

Disclosure of Invention

The invention aims to solve the problem of engine propeller matching under the condition of increasing the fouling resistance in the whole life operation period of a ship, and provides a method for designing the matching of an electric propulsion engine propeller under the condition of the fouling resistance of the ship.

In order to achieve the purpose, the technical scheme of the invention is as follows: a method for matching and designing an electric propulsion engine propeller under ship fouling resistance comprises the following steps:

1) making an effective resistance-increasing scheme

Aiming at the difficult problem of evaluating the ship fouling resistance, an effective resistance increasing scheme is formulated through the prior art documents and the fouling data of similar ships in combination with numerical simulation, and the matching accuracy of the engine propeller is improved;

2) building ship fouling numerical model and numerical simulation

Modeling the full appendage of a target ship, carrying out real-scale resistance numerical simulation, establishing a ship fouling numerical model, carrying out stock paddle open water numerical simulation, designing paddle open water numerical simulation and self-navigation numerical simulation of two pairs of paddles;

3) method for establishing matching reserve

According to the change rule of the propeller matching point when the resistance of the ship body changes due to the fouling, the working characteristics that the propulsion motor has constant torque lower than the rated rotating speed and constant power higher than the rated rotating speed are combined, the matching effect of the propellers in the whole life operation period of the ship is taken as a target, an effective matching storage method is provided, the propulsion motor, the propellers and the shafting can stably run for a long time in a task working condition, the failure rate of equipment is reduced, and the normal sailing rate of the ship is guaranteed.

Further, the specific method for formulating the effective resistance increase scheme by the numerical simulation comprises the following steps:

1) defining the pollution level;

2) finding out the corresponding relation between the bottom grade and the roughness;

3) and (4) calculating a stain bottom resistance increasing value.

Furthermore, the target ship adopts a numerical simulation method to carry out analysis research on propeller matching, the accuracy required by design analysis is met, and three-dimensional modeling is carried out through numerical analysis input data.

Further, the numerical simulation adopts numerical simulation to calculate a control equation, the equation is a continuity equation and a momentum equation, the control equation is subjected to finite volume method dispersion, and a Reynolds average method is adopted as a turbulence numerical simulation method.

Further, design oar open water numerical simulation adopts numerical value pond virtual test, and numerical value pond virtual test divide into open water, resistance, the triplex of navigating oneself, and the test result is handled unanimously with the physical pond of entity, includes:

1) propeller model design

Two propellers are respectively designed for comparing and considering the matching characteristics of the propellers after the rotating speed storage:

(1) conventional oar

The conventional propeller is a propeller with the motor power and the rotating speed running at a design point under the condition of considering the working condition of a new ship, and the conventional design pitch ratio is 1.32 according to resistance data of a ship body;

(2) optimized oar

Under the working condition of considering a new ship, the rotating speed of the motor under rated power is higher than the rated rotating speed by more than 5%, the design pitch of the optimized propeller is 1.22, and the pitch ratio of the optimized propeller is lower than that of a conventional propeller;

2) open water virtual test

The calculation domain of the cube is adopted, the paddle model 3D model is located in the middle of the calculation domain, and the boundary conditions are as follows: the inflow surface is set as a speed inlet, the outlet surface is set as a pressure outlet, the side surface is a symmetrical surface, the bottom and the top are sliding wall surfaces, and the other side is also set as a symmetrical surface. The water flow flows from the positive x direction to the negative x direction, a cylindrical area around the paddle die can rotate, and the rotating area exchanges numerical values with a large calculation area of a cube; respectively carrying out numerical simulation on the propeller of the conventional propeller and the propeller of the optimized propeller;

3) self-propelled virtual test

Similar to the resistance numerical simulation, the model scale resistance calculation domain is a cube, the whole ship model is positioned in the middle of the calculation domain, and the boundary conditions are as follows: the inflow surface is set as a speed inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetrical surfaces, the bottom and the top are sliding wall surfaces, and the other side surface is also set as a symmetrical surface. The water flow flows from the positive x direction to the negative x direction, and is similar to real-scale resistance numerical simulation, unstructured grids are adopted for grid division, the grids are cutting bodies and are encrypted near the free liquid level, grids around the ship body are dense, and the grids far away from the ship body are sparse.

The invention has the beneficial effects that:

the invention combines the engineering application requirements of a target ship, develops the research and analysis of the engine propeller matching theory of the electric propulsion system, grasps the key engine propeller matching technology of the multi-working-condition electric propulsion system, and improves the integrated design capability of the domestic electric propulsion system. The achievement of the invention can be directly applied to the design of the propulsion system and the propeller of the target ship, thereby shortening the design period of the target ship type, reducing the design cost and improving the design reliability of the target ship type; meanwhile, the achievement can be widely applied to various other electric propulsion and hybrid power ships.

Drawings

FIG. 1 is a flow chart of a method for designing a propeller matching of an electric propulsion engine under ship fouling resistance;

FIG. 2 is a schematic view of a full hull geometry;

FIG. 3 is a grid division diagram;

FIG. 4 is a calculation domain diagram of an open water virtual experiment;

FIG. 5 is a side view of a conventional paddle;

FIG. 6 is a side view of an optimizing paddle;

FIG. 7 is a graph of forward and aft speed change versus speed field for a conventional paddle at J-0.95;

FIG. 8 is a graph of forward and aft speed variation versus speed field for an optimized pitch at J0.95;

FIG. 9 is a grid partitioning diagram from time to time;

FIG. 10 is a speed-power diagram.

Detailed Description

The invention is further described with reference to the following figures and examples.

As shown in figure 1, the method for designing the matching of the electric propulsion engine propeller under the ship bottom-fouling resistance comprises the following steps

1. Determination of research methods

The traditional mechanical propeller matching analysis can adopt methods such as data regression, map calculation, model test and the like. The advantages of data regression and map calculation are low cost, fast calculation speed, the data regression requires to make the meaning of the parameter in the regression equation clear, the regression equation has limitation, and different equations are needed to calculate for different ship types and different water areas.

Similar problems also exist with atlas calculations: the ship body resistance, the wake flow fraction and the thrust reduction are estimated by an empirical formula, the open water performance of the propeller is obtained by a map, and the design accuracy is low.

The hydrodynamic model test can obtain more accurate results than methods such as a map and regression, but needs to process a ship model and use pool test equipment, so that the cost is high and the time consumption is long.

The target ship carries out analysis research on propeller matching by adopting a numerical simulation (numerical simulation) method, and compared with a data regression and map calculation method, the numerical simulation analysis result has higher accuracy. Compared with a numerical simulation method of a water tank test, the method has the advantages of lower cost, shorter analysis time and higher accuracy and can meet the design and analysis requirements.

The numerical simulation method is a variant of CFD Computational Fluid Dynamics (Computational Fluid Dynamics). The basic principle of CFD for calculating fluid mechanics is to approximately express integral and differential terms in a fluid mechanics control equation into discrete algebraic forms, so that the discrete algebraic forms become algebraic equation sets, and then the discrete algebraic equation sets are solved through a computer to obtain numerical solutions on discrete time/space points.

2. Numerical analysis input data and three-dimensional modeling

TABLE 1 Ship type Main parameters

Length m between vertical lines	90
		Shape width m	12
Design draft m	3.3
		Design of draft-type drainage volume m3	1550

TABLE 2 host principal parameters

Propulsion motor MCR	6875kW×2
		Common power CSR (90% MCR)	6187.5kW×2
Shafting efficiency	0.93

TABLE 3 Propeller Main parameters

Number and type of propellers	2 spacing paddles
		Diameter of propeller	2.8m
Number of blades	5 leaves/paddle

Note: the numerical simulation was carried out under the design conditions at an input condition of 6187.5X 2kW and a rotation speed of 280 rpm. The three-dimensional geometric model establishment of the ship body and the appendage is completed, and the formed full appendage model is shown in figure 2:

3. research on ship pollution resistance increase

A ship fouling numerical model construction method is established by looking up documents and researching relevant research documents of ship fouling and roughness at home and abroad.

1) Definition of soil class

The soft fouling is typically algae, mucilage, and grasses, with minimal impact on the coating system and ship performance. Hard fouling with calcareous structures is more recalcitrant and may impair the performance of ships and coating systems. Complex fouling, including hard fouling and soft fouling organisms, is extremely detrimental to ship performance, coatings and mechanical systems.

The formation of slime and slime is the first step in the fouling process of the fouling substrate. Almost all objects immersed in seawater rapidly accumulate a layer of slime consisting of bacteria, fungi, protozoa and algae. Bacteria usually attach within half an hour of wetting the surface and mucus is usually felt by hand within one hour. The slime coating is smooth and generally follows the contour of the hull.

Grasses are a form of multicellular green and brown algae. It is formed most near the waterline, which has enough light for photosynthesis. As the depth increases, this phenomenon becomes less pronounced, with the primary color changing from green to brown.

The main forms of hard biofouling are barnacles and sarcodictes. Certain subsea components may be subjected to harsh conditions under which a combination of biofouling (hard and soft) and calcareous deposits may form.

The fouling rating is defined by the reference WATERBORNE UNDERWATERWHOLLING CLEANING OF NAVYSHIPS SHIP SUBMERNAL SHIP. The dirty bottom can be classified into a dirty bottom grade of 0-100, and the larger the numerical value is, the more serious the dirty bottom condition is. Wherein, 0-30 is soft attachment, the length of the grass-shaped attachment is shorter than 76mm, the height is not more than 6.4mm, 40-90 is hard, and 100 is the most serious soft-hard composite attachment. The diameter or height of the calcified matter of 40-60 mm is less than 6.4 mm. 70-80 are higher than 6.4mm and overlapping growth occurs. Document [1] states that hull fouling should be periodically checked and that full cleaning is required when fouling is at a rate of 50, so the patent numerical simulation will only consider fouling levels between 0 and 50.

2) Correlation between stain level and roughness

The relationship between the fouling rating and the equivalent roughness can be found in the literature "Effects of coating roughness and biofouling on ship resistance":

TABLE 4 relationship between stain level and equivalent roughness

Grade of soil	State description	Equivalent roughness
				0	Smooth wall surface	0
0	Typical antifouling paint coatings	30
			10-20	Deteriorated coating or slight slime	100
30	Severe slime	300
			40-60	Mild calcareous bottom or seaweed	1000
70-80	Moderate calcium bottom with stain	3000

The numerical simulation of the invention only considers the dirty grade of 0-50, so the corresponding roughness considers 0-1000. And performing real-scale resistance calculation according to equivalent roughnesses 0, 30, 100, 300 and 1000 of the states and the soil grades corresponding to the documents, and performing numerical calculation under the navigational speeds of 24kn and 26kn respectively.

3) Calculation of the resistance-increasing value of the soil

The grid division adopts unstructured grids, as shown in fig. 3, the grids are cut bodies, the grids are encrypted near the free liquid level, the grids around the ship body are dense, and the grids far away from the ship body are sparse.

4. Numerical simulation setup

The numerical simulation calculation control equation is a continuity equation and a momentum equation, the control equation is subjected to finite volume method dispersion, and a Reynolds average method is adopted as a turbulence numerical simulation method; the calculation adopts a SIMPLE algorithm, a model capable of realizing turbulence is adopted, the fluid is incompressible constant-density fluid, and the free liquid level is captured by a VOF method.

Density of fluid: 1026.021kg/m ^3

Hydrodynamic viscosity: 12.20141E-4Pa-s

The calculation is carried out under the real ship scale.

TABLE 5 simulation calculation results of the soil increment values

Grade of soil	State description	Equivalent roughness	24kn	26kn
						0	Smooth wall surface	1	97.9％	97.6％
0	Typical antifouling paint coatings	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	Mild calcareous bottom or seaweed	1000	128.2％	125.4％

At a stain level of 50, the 26 knots had 25.4% more resistance than no stain, and the 24 knots had 28.2% more resistance.

At a stain level of 30, the resistance of 26 knots is increased by 15.6 percent compared with the resistance of no stain, and the resistance of 24 knots is increased by 17.3 percent.

Similar to the situation described in the publications "Effects of roughness of coating and biofouling on ship resistance and power", the increase in drag is greater at low speeds, probably because the friction drag is greater at low speeds and the wave drag is greater at high speeds.

5. Numerical pool virtual test

The numerical value pool virtual test is divided into three parts of open water, resistance and self-navigation, and the test result processing is consistent with the physical pool of an entity.

1) Design of propeller model

And two propellers are respectively designed for comparing and considering the matching characteristics of the propellers after the rotating speed storage.

1) Conventional oar

The conventional propeller (code 1711) is a propeller with the motor power and the rotating speed both running at the design point under the new ship working condition. This conventional design pitch ratio is 1.32 based on hull drag data.

2) Optimized oar

The optimized propeller (code 1711m) considers the working condition of a new ship, and the rotating speed of the motor is higher than the rated rotating speed by more than 5 percent under the rated power. The design pitch of the optimized propeller is 1.22, which is lower than the pitch ratio of the conventional propeller.

5.1 virtual test in open water

The calculation domain is a cube, and the paddle model 3D model is located in the middle of the calculation domain. The boundary conditions are as follows: the inflow surface is set as a speed inlet, the outlet surface is set as a pressure outlet, the side surface is a symmetrical surface, the bottom and the top are sliding wall surfaces, and the other side is also set as a symmetrical surface. The water flows from the positive x direction to the negative x direction.

The cylindrical area around the paddle die can be rotated and the rotated field is exchanged with the large computational field of the cube, as shown in figure 4. The outer boundary is sufficiently far from the propeller to be considered substantially unaffected. Numerical simulation was performed on the code 1711 propeller and the code 1711m propeller, respectively.

The calculation is carried out under the model scale, and the scaling is 16.3636. Open water characteristic numerical simulations were performed on the conventional paddle (see fig. 5) and optimized paddle (see fig. 6) models, respectively.

TABLE 6 open water characteristics of conventional paddle model

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

As shown in fig. 7 and 8, the speed vector arrows indicate the speed magnitude and direction, the arrow length indicates the speed magnitude, the conventional paddle (code 1711, P/D ═ 1.32) in fig. 7 and the optimized paddle (code 1711m, P/D ═ 1.22) in fig. 8 are adopted.

TABLE 7 optimized Paddle model open Water characteristics

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

5.2 virtual resistance test

Similar to the real-scale resistance numerical simulation, the model scale resistance calculation domain is a cube, and the half ship model is positioned in the middle of the calculation domain. The boundary conditions are as follows: the inflow surface is set as a speed inlet, the outlet surface is set as a pressure outlet, the side surface is a symmetrical surface, the bottom and the top are sliding wall surfaces, the symmetrical surface is also set as a symmetrical surface, and the symmetrical surface is positioned on a longitudinal section line in the ship body. The water flows from the positive x direction to the negative x direction. Similar to real-scale resistance numerical simulation, the grid division adopts unstructured grids which are cutting bodies, the grids are encrypted near the free liquid level, the grids around the ship body are dense, and the grids far away from the ship body are sparse.

The calculation is carried out under the model scale, and the scaling is 16.3636.

The results of the virtual trials are shown in the following table.

Table 8 model resistance virtual test results

5.3 self-propelled virtual test

Similar to the resistance numerical simulation, the model scale resistance calculation domain is a cube, and the whole ship model is positioned in the middle of the calculation domain. The boundary conditions are as follows: the inflow surface is set as a speed inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetrical surfaces, the bottom and the top are sliding wall surfaces, and the other side surface is also set as a symmetrical surface. The water flows from the positive x direction to the negative x direction.

Similar to the real-scale resistance numerical simulation, as shown in fig. 9, the grid division adopts unstructured grids, the grids are cut bodies, the grids are encrypted near the free liquid level, the grids around the ship body are dense, and the grids far away from the ship body are sparse.

The calculation is carried out under the model scale, and the scaling is 16.3636. And respectively carrying out self-propulsion characteristic numerical simulation on the conventional paddle model and the optimized paddle model. The results of the virtual tests are shown in Table 9.

TABLE 9 self-propulsion virtual test of conventional paddles

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

Table 10 optimized paddle self-propulsion virtual test

The optimized paddle speed is higher than that of the conventional paddle, and is consistent with the expectation, and the wake flow fraction and the thrust reduction rate of the optimized paddle are basically consistent.

6. Real ship forecast

The analysis method of numerical simulation is consistent with that of a physical pool.

The increase of the fouling resistance occurs on the scale of a real ship, so that the model value is unchanged in the forecasting process, and the increase of the fouling resistance is increased on the resistance coefficient of the real ship. The result of the forecast of the navigational speed is as follows:

TABLE 11 forecast results for conventional paddle boat

TABLE 12 forecast results of 20% drag-increasing conventional oar for real ship

TABLE 13 forecast results of 25% resistance-increasing conventional paddle on-board ship

TABLE 14 optimized oar actual ship forecast results

Table 15 forecast results of 20% optimized paddle drag-increasing real ship

Table 16 forecast results of 25% drag-increasing optimized propeller for real ship

The data of the tables are combined, the forecast result is analyzed and a rotating speed-power diagram is drawn (figure 10)

From fig. 10, we derive:

1) the conventional paddle (code 1711) sails at a speed of about 280rpm and 26.30kn without a dirty bottom; at 25% drag increase, the propulsion motor is run de-energized with propeller speed at about 266rpm and a conventional propeller speed of 24.45 kn.

2) The optimized paddle (code 1711m) has the rotating speed of about 294rpm and the sailing speed of 26.25kn when no bottom is polluted; at 25% drag, the propulsion motor is operated at constant power, the propeller speed is at about 286rpm, and the conventional propeller speed is 24.75 kn.

The analysis of the rotating speed power diagram shows that the speed reduction of the conventional paddle in the numerical simulation is 1.85kn and 1.5kn respectively, and the speed reduction of the optimized paddle is 0.35kn (0.35/1.5-23.33%). This is because the conventional paddle moves left in the curve after increasing the resistance, resulting in the propulsion motor not being able to operate at rated power, while the optimized paddle moves left in the curve and the propulsion motor can still operate at rated power.

7. Conclusion

The invention adopts the full appendage modeling of a certain ship, and carries out real-scale resistance numerical simulation, establishes a ship fouling numerical model construction method, carries out open water numerical simulation of stock paddles, and designs paddle open water numerical simulation and self-navigation numerical simulation of two pairs of paddles.

The present study can conclude the following:

1) and collecting and translating the standard of the dirty level, and obtaining the corresponding relation between the dirty level and the equivalent roughness. When the fouling level is 30, the 26kn speed of the ship increases the drag by about 15 percent. When the fouling level is 40-60, the 26kn speed of the ship increases the drag by about 25%.

2) The rotational speed reserve refers to the margin of the propeller rotational speed in view of the new vessel absorbing 100% of the main engine power under future use conditions. By reducing the pitch ratio of the fixed-pitch propeller in the design stage, the propeller of a new ship can run at a lighter load, and the rotating speed of the propeller is higher than the rated rotating speed of the main engine when 100% of the main engine power is absorbed.

3) In the numerical simulation, the conventional paddle contrasts the optimized paddle, the speed reduction is respectively 1.85kn and 1.5kn, and the optimized paddle reduces the flight speed to be 0.35kn (0.35/1.5-23.33%).

4) The rotational speed reserve allows the propeller to maintain the propulsion motor operating at the designed rated power in the event of increased hull drag due to fouling and the like. The characteristic of constant power after the motor exceeds the rated rotating speed can be utilized, and a larger light rotation margin is reserved when the motor is matched with the fixed-pitch propeller. Above 7% is recommended, but the excess is not suitable, and the excessive light rotation margin can reduce the open water efficiency of the designed propeller.

The invention adopts a numerical simulation method to analyze and research the ship fouling resistance increase and the engine propeller matching, and can also be replaced by a water tank test, the fouling resistance increase and the engine propeller matching of the ship fouling resistance increase and the engine propeller matching of the engine.

Claims (5)

1. A method for matching and designing an electric propulsion engine propeller under ship fouling resistance is characterized by comprising the following steps:

1) making an effective resistance-increasing scheme

Aiming at the difficult problem of evaluating the ship fouling resistance, an effective resistance increasing scheme is formulated through the prior art documents and the fouling data of similar ships in combination with numerical simulation, and the matching accuracy of the engine propeller is improved;

2) building ship fouling numerical model and numerical simulation

Modeling the full appendage of a target ship, carrying out real-scale resistance numerical simulation, establishing a ship fouling numerical model, carrying out stock paddle open water numerical simulation, designing paddle open water numerical simulation and self-navigation numerical simulation of two pairs of paddles;

3) method for establishing matching reserve

According to the change rule of the propeller matching point when the resistance of the ship body changes due to the fouling, the working characteristics that the propulsion motor has constant torque lower than the rated rotating speed and constant power higher than the rated rotating speed are combined, the matching effect of the propellers in the whole life operation period of the ship is taken as a target, an effective matching storage method is provided, the propulsion motor, the propellers and the shafting can stably run for a long time in a task working condition, the failure rate of equipment is reduced, and the normal sailing rate of the ship is guaranteed.

2. The method for designing matching of propeller of electric propulsion machine under ship resistance to fouling according to claim 1, characterized in that: the specific method for formulating the effective resistance increasing scheme by numerical simulation comprises the following steps:

1) defining the pollution level;

2) finding out the corresponding relation between the bottom grade and the roughness;

3) and (4) calculating a stain bottom resistance increasing value.

3. The method for designing matching of propeller of electric propulsion machine under ship resistance to fouling according to claim 1, characterized in that: the target ship adopts a numerical simulation method to carry out analysis research of propeller matching, meets the accuracy of design analysis requirements, and carries out three-dimensional modeling through numerical analysis input data.

4. The method for designing matching of propeller of electric propulsion machine under ship resistance to fouling according to claim 1, characterized in that: the numerical simulation adopts numerical simulation to calculate a control equation, the equation is a continuity equation and a momentum equation, the control equation is subjected to finite volume method dispersion, and a Reynolds average method is adopted as a turbulence numerical simulation method.

5. The method for designing matching of propeller of electric propulsion machine under ship resistance to fouling according to claim 1, characterized in that: design oar open water numerical simulation adopts numerical value pond virtual test, and numerical value pond virtual test divide into open water, resistance, self-propulsion triplex, and the test result is handled unanimously with the physical pond of entity, includes:

1) propeller model design

Two propellers are respectively designed for comparing and considering the matching characteristics of the propellers after the rotating speed storage:

(1) conventional oar

The conventional propeller is a propeller with the motor power and the rotating speed running at a design point under the condition of considering the working condition of a new ship, and the conventional design pitch ratio is 1.32 according to resistance data of a ship body;

(2) optimized oar

Under the working condition of considering a new ship, the rotating speed of the motor under rated power is higher than the rated rotating speed by more than 5%, the design pitch of the optimized propeller is 1.22, and the pitch ratio of the optimized propeller is lower than that of a conventional propeller;

2) open water virtual test

The calculation domain of the cube is adopted, the paddle model 3D model is located in the middle of the calculation domain, and the boundary conditions are as follows: the inflow surface is set as a speed inlet, the outlet surface is set as a pressure outlet, the side surface is a symmetrical surface, the bottom and the top are sliding wall surfaces, and the other side is also set as a symmetrical surface. The water flow flows from the positive x direction to the negative x direction, a cylindrical area around the paddle die can rotate, and the rotating area exchanges numerical values with a large calculation area of a cube; respectively carrying out numerical simulation on the propeller of the conventional propeller and the propeller of the optimized propeller;

3) self-propelled virtual test

Similar to the resistance numerical simulation, the model scale resistance calculation domain is a cube, the whole ship model is positioned in the middle of the calculation domain, and the boundary conditions are as follows: the inflow surface is set as a speed inlet, the outlet surface is set as a pressure outlet, the side surfaces are symmetrical surfaces, the bottom and the top are sliding wall surfaces, and the other side surface is also set as a symmetrical surface. The water flow flows from the positive x direction to the negative x direction, and is similar to real-scale resistance numerical simulation, unstructured grids are adopted for grid division, the grids are cutting bodies and are encrypted near the free liquid level, grids around the ship body are dense, and the grids far away from the ship body are sparse.

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