Ship bubble drag reduction system and using method

Abstract

The ship bubble resistance reduction system comprises an air compressor, a bubble adjusting cylinder and an adjusting mechanism, the bubble adjusting cylinder comprises an inner cylinder body and an outer cylinder body which are sleeved inside and outside, air holes are evenly distributed in the peripheral face of the inner cylinder body, and an air injection opening is formed in the peripheral face of the bottom of the outer cylinder body; the adjusting mechanism is connected with the end face of one end of the inner cylinder body and drives the inner cylinder body to rotate relative to the outer cylinder body, and the air compressor is communicated with the end face of the other end of the inner cylinder body through a breather pipe. And a more accurate and automatic drag reduction solution is provided for the river-sea direct ship.

Description

Technical Field

[0001] The present invention belongs to the technical field of green intelligent ship navigation, and particularly relates to a ship bubble drag reduction system and a using method thereof. Background Art

[0002] The technology of reducing frictional resistance by injecting bubbles into the turbulent boundary layer under a ship, i.e., the bubble drag reduction technology, is applied to reduce the energy consumption of a vehicle. This technology is particularly suitable for large ships sailing at low speeds, such as oil tankers, because most of their propulsion force is used to counteract the frictional resistance, and the frictional resistance accounts for about 70% of their total resistance. Bubble drag reduction can significantly reduce the sailing resistance under suitable conditions.

[0003] The bubble drag reduction technology has been tested or applied on some high-end ships, and bubble drag reduction systems have been installed on some commercial ships such as some cargo ships, oil tankers or container ships to reduce the operating costs. On some special ships, such as high-speed ships and experimental ships, their performance improvements have been verified through the bubble drag reduction technology. In the ship model tests under laboratory conditions, the bubble drag reduction effect is remarkable, and the reduction range of frictional resistance can reach 5% to 20%.

[0004] Currently, most of the practices related to bubble drag reduction are mainly carried out in a fresh water environment, and such a single condition is difficult to truly reflect the actual effect of bubble drag reduction in a complex water environment. In practical applications, ships sail in diverse environments, and factors such as the salt concentration and pollution degree of different waters will significantly affect the physical behavior of bubbles, such as the merging process, distribution state and stability of bubbles. These changes are directly related to the change of flow resistance. If the corresponding gas injection volume and bubble size cannot be changed in time, it is difficult to obtain an ideal drag reduction effect, which makes it difficult for the existing drag reduction technology to achieve an ideal drag reduction effect in a complex environment.

[0005] On the other hand, there are significant differences between the actual operating conditions of a ship and traditional ship model tests or simplified flat plate tests. During actual sailing, the states of a ship such as speed, load and route will constantly change, and these factors will all affect the bubble drag reduction effect. Specifically, when the ship speed changes, the optimal injection flow rate and size of bubbles will also change accordingly. Therefore, in practical applications, how to determine the optimal gas injection flow rate and bubble size, and dynamically adjust and control the gas injection flow rate based on the real-time sailing state is the key means to improve the micro-bubble drag reduction efficiency.

[0006] At present, in the field of ship bubble drag reduction, the method of manually adjusting the bubble injection volume is still widely used. This method relies too much on manual experience, lacks a precise correction mechanism and rapid response ability, and is particularly difficult to adapt to complex and changeable environments. More importantly, this method cannot adjust the bubble diameter to adapt to the influence of water salinity changes on bubble coalescence characteristics. In actual operation, this deficiency not only greatly reduces the drag reduction effect and makes it difficult to approach the ideal state in the laboratory and simulation tests, but even in some cases, the resistance may increase due to changes in the flow field.

[0007] There is an urgent need to propose a ship bubble drag reduction system to meet the diverse needs in the actual navigation environment. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a ship bubble drag reduction system and its usage method in view of the above problems, which can adapt to different water environments (such as salinity changes) and ship operating states (such as speed changes) in real time, dynamically adjust the bubble size and gas injection volume, and ensure that the drag reduction effect is always in the optimal state.

[0009] The embodiments of the present application are implemented as follows: The embodiments of the present application provide a ship bubble drag reduction system, which is characterized in that it includes an air compressor, a bubble adjusting cylinder and an adjusting mechanism. The bubble adjusting cylinder includes an inner cylinder and an outer cylinder sleeved inside and outside. The outer peripheral surface of the inner cylinder is evenly distributed with air holes, and the outer peripheral surface of the bottom of the outer cylinder is provided with a jet opening. The adjusting mechanism is connected to one end face of the inner cylinder and drives the inner cylinder to rotate relative to the outer cylinder. The air compressor is connected to the other end face of the inner cylinder through a ventilation pipe.

[0010] In some optional implementation schemes, the outer peripheral surface of the inner cylinder is divided into multiple air hole blocks, and the pore diameters of the air holes in each air hole block are not the same.

[0011] In some optional implementation schemes, the adjusting mechanism includes a rotating motor and a rotating shaft. The inner end of the rotating shaft passes through the outer cylinder and is connected to the inner cylinder, and the outer end of the rotating shaft is connected to the rotating motor to drive the rotating shaft to drive the inner cylinder to rotate.

[0012] In some optional implementation schemes, sealing members are provided at both ends of the inner cylinder corresponding to the positions of the jet openings.

[0013] In some alternative embodiments, an automatic control system is further included. The automatic control system includes a central processing unit, a water salinity sensor, and a ship speed sensor. The input end of the central processing unit is electrically connected to the water salinity sensor and the ship speed sensor, and the output end of the central processing unit is electrically connected to the air compressor and the rotary motor.

[0014] A method for using a ship bubble drag reduction system, characterized by comprising the following steps: Step a, equipment installation: Align the jet opening of the bubble adjustment cylinder with the bottom opening of the ship and weld it firmly. Install the air compressor and the adjustment mechanism. The ship speed sensor is installed on the hull, and the water salinity sensor is installed at a position where the bottom of the ship is in direct contact with the water body. Step b, dynamic adjustment of bubble drag reduction: The central processing unit determines the optimal bubble size based on the sensing data of the water salinity sensor, calculates the optimal gas injection volume according to the sensing data of the ship speed sensor, and transmits electrical signals to the adjustment mechanism and the air compressor respectively. The rotary motor drives the inner cylinder to rotate, so that the pore block with a suitable aperture is aligned with the jet opening. At the same time, the gas injection volume of the air compressor is adjusted to achieve the adjustment of the jet speed, generate a stable bubble layer, set the interval duration of each adjustment, and dynamically optimize the drag reduction effect.

[0015] In some alternative embodiments, the water salinity is divided into four types, including fresh water with a salinity <0.05%, brackish water with a salinity of 0.05% - 3%, saline water with a salinity of 3% - 5%, and brine with a salinity > 5%.

[0016] In some alternative embodiments, the pore blocks are divided into four blocks, and the pore diameters of the four blocks are 0.2 mm, 1 mm, 2 mm, and 4 mm respectively.

[0017] In some alternative embodiments, the gas injection volume is dimensionless, and its calculation formula is as follows:

[0018]

[0019]

[0020]

[0021] In the formula, is the gas jet flow rate, is the liquid flow rate in the boundary layer, is the ship speed, is the ship width, is the boundary layer thickness, is the boundary layer displacement thickness.

[0022] In some alternative embodiments, the interval duration for each adjustment is 15 - 25 s.

[0023] The beneficial effects of the present application are as follows: A ship bubble drag reduction system and its usage method provided by the present application can, by integrating salt concentration sensing, ship speed monitoring, and intelligent control technologies, perceive in real time the changes in the water area environment and the ship's operating state, dynamically adjust the gas injection volume of the bubbles through the ant colony algorithm, and adjust the bubble adjustment cylinder to match the gas injection volume to obtain the optimal bubble size, so as to comprehensively obtain the optimal bubble drag reduction level; it can achieve a higher level of automation, and can also significantly improve the drag reduction effect under complex water area conditions, with the maximum increase reaching 20%, meeting the diverse needs in the actual navigation environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other relevant drawings can also be obtained based on these drawings.

[0025] Figure 1 is the structural schematic diagram of the embodiment of the present application; Figure 2 is the perspective view of the bubble adjustment cylinder of the embodiment of the present application; Figure 3 is the construction diagram of the geometric model numerical calculation domain of the embodiment of the present application; Figure 4 is the model grid distribution diagram of the embodiment of the present application; Figure 5 is the test diagram of the influence of the gas injection volume on the drag reduction effect of the embodiment of the present application; Figure 6 is the change diagram of the resistance with the increase of the gas injection volume of the embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. Usually, the components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0028] It should be understood that the magnitudes of the sequence numbers of the steps in the embodiments do not imply the order of execution. The order of execution of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

[0029] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0030] In the description of the present application, it should also be noted that, unless otherwise clearly specified and limited, the terms "arranged", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0031] The features and performance of the present application will be further described in detail below in conjunction with the embodiments.

[0032] Embodiment 1 As Figure 1 , Figure 2 shown, a ship bubble drag reduction system is disclosed in this embodiment, including an air compressor 1, a bubble adjusting cylinder 2 and an adjusting mechanism. The bubble adjusting cylinder includes an inner cylinder 3 and an outer cylinder 4 which are sleeved inside and outside. Air holes 5 are evenly distributed on the outer peripheral surface of the inner cylinder, and a jet opening 6 is provided on the outer peripheral surface of the bottom of the outer cylinder. The adjusting mechanism is connected to one end face of the inner cylinder, driving the inner cylinder to rotate relative to the outer cylinder. The air compressor is connected to the other end face of the inner cylinder through an air pipe 7.

[0033] The adjusting mechanism includes a rotary motor 8 and a rotary shaft 9. The inner end of the rotary shaft passes through the outer cylinder and is connected to the inner cylinder, and the outer end of the rotary shaft is connected to the rotary motor, driving the rotary shaft to drive the inner cylinder to rotate.

[0034] It further includes an automatic control system, which includes a central processor, a water salinity sensor and a ship speed sensor. The input end of the central processor is electrically connected to the water salinity sensor and the ship speed sensor, and the output end of the central processor is electrically connected to the air compressor and the rotary motor.

[0035] Salt concentration monitoring: The salinity information of the water in the navigation area is detected in real time through the water salt concentration sensor. The system divides the water area into four types: fresh water (water salt concentration is less than 0.05%), brackish water (water salt concentration is 0.05%-3%), salt water (water salt concentration is 3%-5%) and brine (water salt concentration is greater than 5%).

[0036] The two ends of the inner cylinder body are provided with sealing members 10 at positions corresponding to the air jet openings. The outer peripheral surface of the inner cylinder body is divided into a plurality of air hole blocks, and the air hole diameters of each air hole block are different.

[0037] Study on the correlation between salt concentration and bubble diameter: The latest related research found that there is a non-monotonic relationship between salt concentration and bubble pore size: in the low concentration range (M less than 0.04 mol / L), salt forms micron-sized bubbles through a stable liquid film; while at high concentrations (M greater than 0.06 mol / L), the charge screening effect caused by ion supersaturation promotes bubble selective aggregation to form millimeter-sized large-pore bubbles. This two-way regulation characteristic provides a new idea for optimizing drag reduction strategies.

[0038] When the salinity is high, the high salinity of the water body will cause the microbubbles to form a gel-like layer in the near-wall area, the effective viscosity will increase by 50%, the Weber number (We) will decrease to 0.3, the bubbles will become rigid, and the turbulence modulation will be weakened. This means that although the diameter of the bubbles is suppressed, the deformation ability is suppressed, the ion supersaturation induces a charge screen and suppresses coalescence, which in turn increases the roughness of the gas-water mixing area and reduces the drag reduction effect. At this time, large-aperture bubbles should be used to increase the air film coverage to 85% (compared to 45% of microbubbles) and reduce the wall shear stress to 60% of the salt-free conditions (when α=0.13) to obtain better drag reduction effects. In the experiment, we proposed optimized bubble pore sizes under four typical conditions, namely 0.2mm, 1mm, 2mm, and 4mm. In freshwater environments (salinity <0.05%), the pore size needs to be reduced by 10–15% (to compensate for the tendency of aggregation caused by ion loss), so the original design is optimized from 0.3mm to 0.2mm; in slightly brackish water environments (salinity 0.05%-3%), the pore size can be increased and the design is optimized to 1mm. For salt water environments (water body salt concentration of 3%-5%), the design is 2mm pore size. For brine environments (water body salt concentration greater than 5%). In the extreme salinity gradient area of ​​bubble diameter, it is recommended to use 4mm pore bubbles and increase the jet volume, which can increase the air film coverage by 12% in the experiment.

[0039] This application calculates the optimal jet volume based on the ant colony algorithm. It is dimensionless and its calculation formula is as follows:

[0040]

[0041]

[0042]

[0043] In the formula, is the gas jet flow rate, is the liquid flow rate in the boundary layer, is the ship speed, is the ship width, is the boundary layer thickness, is the boundary layer displacement thickness.

[0044] The value range of the dimensionless gas injection volume is 0 to 0.05, and the interval is 0.01.

[0045] When this drag reduction system is in use, it includes three aspects: 1. Intelligent adjustment of the bubble aperture: In different water salinity environments, the system selects the best bubble aperture gear according to the experimentally fitted data. The central processor controls the mechanical device of the bubble control barrel through electrical signals to adjust the sleeve gear, thereby generating bubbles that match the characteristics of the current water area.

[0046] 2. Gas injection volume control: Real-time monitoring of ship speed: The ship speed sensor records the current ship speed and transmits the data to the central processor.

[0047] Adjustment of gas injection volume: If the current ship speed is the design condition, the system calls the best jet speed in the experimental data and directly adjusts the jet control module.

[0048] If it is not the design condition, the system uses the ant colony algorithm to calculate the most suitable gas injection volume and dynamically adjusts the gas injection volume of the air compressor.

[0049] 3. Generation of the bubble layer: The air compressor transports the gas to the bubble control cylinder, and generates qualified bubble diameters through the adjustment of different pore blocks. These bubbles form a bubble covering layer on the hull surface, effectively reducing the frictional resistance between the water flow and the hull. Example 1 In this embodiment, the geometric model for the simulation test is a bulk carrier with a deadweight tonnage of 95,000 DWT, and the scale ratio is set to 1:50. The length between perpendiculars of the actual ship is 231 meters, the molded breadth is 38 meters, the molded depth is 20.7 meters, the designed draft is 12.5 meters, the displacement volume reaches 91,893.0 cubic meters, the wetted surface area is 12,543.0 square meters, and the ship speed is set to 14.5 knots. In particular, a rectangular jet device is installed at the 17th station of the ship model. The length of this device is 400 mm and the width is 90 mm.

[0050] The construction of the numerical calculation domain is as Figure 3 shown. The overlapping model modeling method that ignores the influence of the free surface is adopted, and the free surface is simplified to a symmetric slip wall surface. To improve the calculation efficiency, only the half-ship model is used for the simulation. The velocity inlet boundary is one ship length away from the bow, the outlet boundary is three ship lengths away from the stern, and the bottom and side boundaries are both one ship length away from the hull. The cutting body grid technology is used for grid generation. For the specific distribution, see Figure 4 . The maximum grid size in the whole domain is 231 mm. The near-wall area of the hull is encrypted, and the minimum grid reaches 7.2 mm. Three layers of boundary layer grids are set on the hull surface. The thickness of the first layer of grid is optimized to meet the requirement of turbulent simulation with y + >30.

[0051] The simulation conditions are based on the designed ship speed (1.055 m / s). The verification process is divided into two stages: First, compare the calculated result of the ship's frictional resistance in the non-jet state with the result of the frictional resistance coefficient formula recommended by the ITTC specification; if the error meets the accuracy requirement, then carry out the second stage of the analysis of the drag reduction effect of flat plate microbubbles in the jet state. The specific form of the ITTC frictional resistance coefficient formula is:

[0052] The calculated frictional resistance is compared with the model calculation result as shown in the following table:

[0053] The gap between the error of the resistance and the result obtained according to the empirical formula is only 0.3%. Based on this, we have reason to believe that the calculation accuracy of this model can provide strong support for subsequent in-depth research. Next, we will carry out detailed calculations for the working conditions of bubble drag reduction.

[0054] In this simulation test, we specifically selected the designed ship speed condition and set the condition of traveling in a straight line throughout the whole process. To comprehensively explore the influence of the jet volume on the drag reduction effect, we carefully set 5 gears for the jet volume and carried out drag reduction effect tests for a total of 5 working conditions with the dimensionless jet volume in the range of 0.01 - 0.05.

[0055] As Figure 5As shown, this figure presents the distribution of the gas volume fraction near the bottom of the ship during the operation of the ship at the designed speed under specific conditions of a freshwater environment, when the dimensionless gas injection volume is set to 0.05 and the bubble diameter is 0.2 mm. Through careful analysis of this figure, we can clearly observe that in the case of the smallest bubbles (d = 0.2 mm), the gas distribution at the bottom of the ship is relatively uniform. After calculation, the average value of the surface gas volume fraction at this time is 0.327, and the drag reduction rate is also relatively large at this time.

[0056] When the pore diameter is 0.2 mm, the drag under freshwater (salt concentration less than 0.05%) and saltwater (water body salt concentration set to 5%) conditions is divided by the drag obtained in the case of no bubbles before, and the drag reduction ratio is obtained and plotted as the ordinate to compare the influence of water body salinity on the bubble drag reduction ability of 0.2 mm diameter bubbles. Then, the bubble diameter is enlarged to the designed 2 mm diameter and a secondary simulation is carried out in saltwater to compare the influence of the change in bubble diameter on the bubble drag reduction ability in saltwater. Finally, a graph of the change in drag with the increase in gas injection volume is obtained (see Figure 6 )

[0057] During the simulation process, we clearly and intuitively observed that the change in water body salt concentration had a relatively significant impact on bubble drag reduction.

[0058] At the same time, we carried out an optimized design for the bubble diameter and compared the optimized scheme with the original scheme under the same simulation conditions. The results showed that the optimized bubble diameter parameters significantly improved the bubble drag reduction effect compared with the original scheme.

[0059] A series of data and results obtained from this simulation experiment provided strong support for this patent. These detailed simulation data fully confirmed that the design involved in this patent could effectively improve the bubble drag reduction ability, further highlighting the innovation and practicality of this patent in the relevant field and effectively improving the bubble drag reduction ability.

[0060] This drag reduction system can collect the salt concentration information of the water area where the vehicle is located in real time, as well as the current speed information, match the appropriate bubble pore size and calculate the jet flow rate using the ant colony algorithm. Since the salt concentration directly affects the generation and coalescence process of bubbles, through precise calculation and control of the jet parameters, the system can adapt to the changes in the water area environment with higher precision. By transmitting adjustment instructions through electrical signals, the system realizes automatic adjustment of the gas injection volume, thus solving the problems of low precision and response lag caused by relying on experience in the process of manually adjusting the bubble flow rate in the past, and greatly improving the real-time performance and operation precision.

[0061] Secondly, this patent innovatively adds a matching mechanism for bubble size. This is because the size of the bubbles has a direct impact on the drag reduction effect, and appropriate bubble sizes can optimize the stability and coverage effect of the bubble layer. Compared with the limitations of traditional systems that ignore this factor, the present invention realizes further improvement in drag reduction performance through precise control of bubble size, making the overall drag reduction effect more efficient and stable.

[0062] This patent provides an innovative ship bubble drag reduction solution through the integration of intelligent perception, algorithm optimization, and automated control, breaking through the applicability bottleneck of traditional technologies in complex environments. This system not only conforms to the concept of sustainable development but also shows broad market application prospects in the field of green intelligent ships, providing strong technical support for the energy conservation and emission reduction goals of the shipping industry.

Claims

1. A ship bubble drag reduction system, characterized in that: It includes an air compressor, a bubble regulating cylinder and a regulating mechanism. The bubble regulating cylinder includes an inner cylinder and an outer cylinder arranged inside and outside. Air holes are evenly distributed on the outer circumference of the inner cylinder. The outer circumference of the bottom of the outer cylinder is provided with an air jet opening. The regulating mechanism is connected to one end surface of the inner cylinder to drive the inner cylinder to rotate relative to the outer cylinder. The air compressor is connected to the other end surface of the inner cylinder through a ventilation pipe.

2. A ship bubble drag reduction system according to claim 1, characterized in that: The outer peripheral surface of the inner cylinder is divided into a plurality of pore blocks, and the pore diameters of the pore blocks are different.

3. A ship bubble drag reduction system according to claim 2, characterized in that: The adjusting mechanism comprises a rotating motor and a rotating shaft. The inner end of the rotating shaft passes through the outer cylinder and is connected to the inner cylinder. The outer end of the rotating shaft is connected to the rotating motor to drive the rotating shaft to rotate the inner cylinder.

4. A ship bubble drag reduction system according to claim 2 or 3, characterized in that: Sealing parts are arranged at the two ends of the inner cylinder at positions corresponding to the jet openings.

5. A ship bubble drag reduction system according to claim 4, characterized in that: It also includes an automatic control system, which includes a central processing unit, a water salinity sensor and a speed sensor. The input end of the central processing unit is electrically connected to the water salinity sensor and the speed sensor, and the output end of the central processing unit is electrically connected to the air compressor and the rotating motor.

6. A method for using the ship bubble drag reduction system according to claim 4, characterized in that: The steps include: Step a, equipment installation: Align the air jet opening of the bubble regulating cylinder with the opening on the bottom of the ship and weld and fasten it, install the air compressor and regulating mechanism, install the speed sensor on the hull, and install the water salinity sensor at the position where the bottom of the ship is in direct contact with the water; Step b, dynamic adjustment of air bubble drag reduction: The central processing unit determines the optimal bubble size based on the sensor data of the water salinity sensor, calculates the optimal jet volume according to the sensor data of the speed sensor, and transmits electrical signals to the adjustment mechanism and the air compressor respectively. The rotary motor drives the inner cylinder to rotate so that the air hole block with appropriate aperture is aligned with the jet opening. At the same time, the jet volume of the air compressor is adjusted to achieve the adjustment of the jet speed, generate a stable bubble layer, set the interval time of each adjustment, and dynamically optimize the drag reduction effect.

7. The method for using the ship bubble drag reduction system according to claim 6, characterized in that: The water salinity is divided into four types, including fresh water with a salinity of <0.05%, brackish water with a salinity of 0.05%-3%, salt water with a salinity of 3%-5%, and brine with a salinity of >5%.

8. The method for using the ship bubble drag reduction system according to claim 7, characterized in that: The pore block is divided into four blocks, and the pore diameters of the four blocks are 0.2mm, 1mm, 2mm, and 4mm respectively.

9. A method for using a ship bubble drag reduction system according to claim 6 or 8, characterized in that: The jet volume It is dimensionless and its calculation formula is as follows: In the formula, is the gas jet flow rate, is the liquid flow rate in the boundary layer, is the ship speed, The width of the ship. is the boundary layer thickness, is the boundary layer exclusion thickness.

10. The method for using the ship bubble drag reduction system according to claim 9, characterized in that: The interval duration of each adjustment is 15 to 25 seconds.

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