A ship rolling air column drag reduction device and method

Abstract

This invention discloses a drag-reducing device for a ship's rolling air column, comprising an air compressor, a compressed air tank, a rolling air column generator, and a control module, all disposed within the ship's hull. The lower surface of the rolling air column generator is flush with the outer surface of the bow hull, while the outer surface of the aft hull is higher than the lower surface of the rolling air column generator, forming a step. The rolling air column generator has three channels, numbered 1, 2, and 3, arranged sequentially from bottom to top on the vertical surface of the step. Channels 1 and 2 are connected to the compressed air tank via gas channels, and channel 3 is connected to the ship's liquid system via a liquid channel. The control module controls the opening and closing of the gas channel solenoid valve and the liquid channel solenoid valve. The air column generated by this invention has an internal rotating flow to achieve a rolling effect, stabilizing the air column for long-distance propagation. Intermittent ventilation continuously refreshes the near-wall flow structure, stabilizing the drag reduction effect and effectively reducing ventilation power consumption.

Description

Technical Field

[0001] This invention relates to the field of ship drag reduction and range extension technology, and in particular to a ship rolling air column drag reduction device and method. Background Technology

[0002] Existing methods for reducing drag during ship navigation involve introducing a large amount of gas into the hull-liquid interface to form a continuous gas film or microbubble cluster, thereby reducing direct contact between the liquid and the hull and reducing frictional drag. However, due to buoyancy and fluid shear, the gas film or microbubble cluster is difficult to maintain a complete and continuous coverage under the hull, quickly breaking up and floating to the sides of the hull. This uncontrollable coverage position leads to a loss of drag reduction effect and may even increase drag. This problem is particularly pronounced for drag reduction in low-speed, large ships, severely limiting the application of these methods.

[0003] Chinese patent CN106564562A discloses a method for reducing ship resistance and a ship that generates air columns on both sides and forward of the bow. Its high-pressure air supply system continuously ejects high-pressure air through air supply pipes into jet holes, generating air columns on both sides and forward of the bow, thereby reducing the ship's resistance and increasing speed or saving energy. However, this patent still has the following drawbacks: 1) Continuous jetting requires a large amount of gas, increasing ventilation power consumption. 2) There is no rotating internal flow within the air column; once generated, the air column is left to flow freely, resulting in uncontrolled gas coverage and limited drag reduction. Due to these two drawbacks, the net power saving may even be negative. Summary of the Invention

[0004] This invention addresses the problems of poor drag reduction stability and high energy consumption in traditional ventilation drag reduction methods by proposing a ship rolling air column drag reduction device and method. The device generates a ventilation air column with internal rotating flow to achieve a rolling effect, which can stabilize the air column for long-distance propagation. The method achieves continuous refresh of the near-wall flow structure through intermittent ventilation, stabilizes the drag reduction effect, and effectively reduces ventilation power consumption.

[0005] The technical solution adopted in this invention is: A ship rolling air column drag reduction device includes an air compressor, a compressed air tank, and a rolling air column generating device disposed inside the hull. The air compressor is connected to the compressed air tank. The lower surface of the rolling air column generating device is flush with the outer surface of the bow hull, while the outer surface of the hull aft of the rolling air column generating device is higher than the lower surface of the rolling air column generating device, forming a step. The rolling air column generating device has three channels, namely channel 1, channel 2, and channel 3, arranged sequentially from bottom to top on the vertical surface of the step. Channels 1 and 2 are connected to the compressed air tank through gas channels, and channel 3 is connected to the ship's liquid system through a liquid channel. The ship rolling air column drag reduction device also includes a control module, a gas channel solenoid valve disposed on the gas channel, and a liquid channel solenoid valve disposed on the liquid channel. The gas channel solenoid valve and the liquid channel solenoid valve are respectively signal-connected to the control module, and the control module controls the opening or closing of the gas channel solenoid valve and the liquid channel solenoid valve.

[0006] In the above scheme, channel 1 is a horizontal channel along the length of the ship; channel 2 includes a horizontal section and a downward-sloping section arranged sequentially along the length of the ship, and the airflow is ejected after passing through the horizontal section and the downward-sloping section in sequence.

[0007] In the above scheme, the No. 3 channel is set along the length of the ship, and the width of the exit end gradually increases.

[0008] In the above scheme, the control module first controls the gas flow channel solenoid valve to open, and uses the high-pressure gas in the compressed gas tank to spray high-speed airflow from channel 1 and channel 2 to form a rolling air column with rotating internal flow at the rear; then the control module closes the gas flow channel solenoid valve and opens the liquid flow channel solenoid valve, so that channel 3 sprays out low-speed fluid, pushing the rolling air column away from the step and rolling towards the stern.

[0009] In the above scheme, the ship's liquid system is the ship's own seawater system.

[0010] In the above scheme, the ship rolling air column drag reduction device is suitable for flat-bottomed boats.

[0011] In the above scheme, the control module is also connected to the compressed air tank signal to monitor the pressure data of the compressed air tank.

[0012] This invention also proposes a method for reducing drag from a ship's rolling air column, which employs the aforementioned device and includes the following steps: S1. High-pressure air is injected into the compressed air tank by the air compressor. The control module monitors the ship's draft, speed and compressed air tank pressure data, and calculates the required ventilation volume and ventilation interval. S2. The control module sends an opening signal to the gas flow channel solenoid valve and holds it for a certain period of time. The high-pressure gas in the compressed gas tank is ejected from the No. 1 and No. 2 channels at high speed. When the air flow reaches the set value, a rolling air column is formed at the rear. The control module closes the gas flow channel solenoid valve. Then, the liquid flow channel solenoid valve is opened, so that the No. 3 channel ejects a low-speed fluid, pushing the rolling air column away from the step. Under the action of internal rotational flow and surface tension, the rolling air column gradually evolves into a smoother rolling air column and rolls towards the stern. S3. When the rolling air column moves away from the step by a certain distance, close the liquid flow channel solenoid valve. Repeat S2 after the set ventilation interval time is reached, thereby generating rolling air columns with equal intervals.

[0013] In the above method, the required ventilation rate in S1 is calculated according to the following formula:

[0014] In the formula, Due to environmental pressures, For the required air column volume, To compress the air tank pressure, This refers to ventilation volume.

[0015] In the above method, in S1, the ventilation interval is calculated according to the following formula:

[0016] In the formula, For ventilation intervals, The required distance between the rolling air columns. This represents the displacement velocity of the ship relative to the seawater.

[0017] The beneficial effects of this invention are: 1. This invention utilizes a specially designed flow channel inside the rolling air column generator to form a rolling air column with internal rotating flow at the flow channel outlet. The rotation direction inside the air column is tangential to the ship's movement direction and the direction of the liquid flow, which can effectively reduce the disruption of airflow shape and gas volume loss caused by fluid shearing, entrainment and other effects. It can achieve the propagation and coverage of the rolling air column along the ship's length under the hull, making the drag reduction effect more stable and effectively reducing the required ventilation volume.

[0018] 2. This invention achieves intermittent, stable air column rolling propagation, thus requiring only a smaller ventilation volume per unit time to achieve a better air column coverage effect. In addition, intermittent ventilation also proportionally reduces the ventilation time, thus significantly reducing the total ventilation power consumption. The ventilation power consumption is expected to be about 1 / 10 of that of the direct ventilation drag reduction method. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the structure of the ship rolling air column drag reduction device of the present invention; Figure 2 yes Figure 1 The diagram shows the principle of rolling air column generation in the ship rolling air column drag reduction device.

[0021] In the diagram: 10, air compressor; 20, compressed air tank; 30, rolling air column generator; 31, channel 1; 32, channel 2; 33, channel 3; 40, rolling air column; 50, control module; 60, gas flow solenoid valve; 70, liquid flow solenoid valve. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0024] In this invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0025] Furthermore, it should be noted that the features of the various embodiments of the present invention can be combined or integrated in whole or in part, and as those skilled in the art will understand, they can interact and operate in different ways. Each embodiment can be implemented independently of each other or in association with one another.

[0026] like Figure 1 As shown, a ship rolling air column drag reduction device includes an air compressor 10, a compressed air tank 20, a rolling air column generator 30, a control module 50, a gas flow solenoid valve 60, and a liquid flow solenoid valve 70, all installed in the ship's hull. The lower surface of the rolling air column generator 30 is flush with the outer surface of the bow hull, while the outer surface of the rear hull is higher than the lower surface of the rolling air column generator 30, forming a step. The rolling air column generator 30 has three channels, numbered 1 (31), 2 (32), and 3 (33), arranged sequentially from bottom to top on the vertical surface of the step. Channels 1 and 2 are connected to the compressed air tank 20 via gas flow channels, and the gas flow solenoid valve 60 is installed on the gas flow channels. The compressed air tank 20 is connected to the air compressor 10. Channel 3 (33) is connected to the ship's liquid system via a liquid flow channel, and the liquid flow solenoid valve 70 is installed on the liquid flow channel. The gas flow solenoid valve 60 and the liquid flow solenoid valve 70 are respectively connected to the control module 50 for signal connection. The control module 50 controls the opening or closing of the gas flow solenoid valve 60 and the liquid flow solenoid valve 70.

[0027] During operation, high-pressure air is injected into the compressed air tank 20 by the air compressor 10. The control module 50 monitors data such as the ship's draft, speed, and pressure in the compressed air tank 20, and calculates the required ventilation volume and ventilation interval. After determining the ventilation volume and ventilation interval, the control module 50 first controls the gas flow channel solenoid valve 60 to open and maintain it for a certain period of time to ensure the ventilation volume parameter is achieved. High-pressure gas from the compressed air tank 20 is ejected at high speed from channels 1 31 and 2 32, mixing at the channel outlet to form a rolling air column 40 with a rotating internal flow. When the ventilation volume reaches the set value, the control module 50 closes the gas flow channel solenoid valve 60 and opens the liquid flow channel solenoid valve 70, causing low-speed fluid to be ejected from channel 3 33, pushing the rolling air column 40 away from the step and rolling it towards the stern. After the set ventilation interval time is reached, a signal is sent to the gas flow channel solenoid valve 60 to open it again.

[0028] This invention introduces gas from a compressed gas tank 20 into a rolling air column generator 30. The gas passes through a specially designed flow channel within the generator 30, where it mixes at the channel outlet to form a rolling air column 40 with internal rotating flow. The rotation direction within the air column is tangential to both the ship's movement direction and the liquid's incoming flow direction. This effectively reduces the disruption of airflow shape and gas volume loss caused by fluid shearing and entrainment, allowing the rolling air column 40 to propagate and cover a greater distance beneath the ship's hull. This effect is analogous to the vortex ring phenomenon. Because the internal rotating flow direction of the vortex ring is opposite to the external fluid movement direction, sliding friction is converted into rolling friction, greatly reducing the loss of vortex ring kinetic energy due to fluid friction, enabling the vortex ring to propagate over greater distances. For example, underwater vortex rings or smoke rings in the air can achieve greater propagation due to their internal rotating flow.

[0029] The specific generation method of the rolling air column 40 with rotating internal flow is as follows: Figure 2 As shown, the lower surface of the rolling air column generator 30 is flush with the outer surface of the bow hull, while the outer surface of the hull behind the rolling air column generator 30 is higher than its lower surface, forming a step. The step's function is that after the liquid flow passes over the step, it continues to flow to the left (i.e., towards the stern) due to inertia. A low-pressure zone is generated to the left of the step. If air is injected into this low-pressure zone, protected by the step, the air mass is less affected by the water flow and can persist for a long time behind the step. This method is used in many papers on ventilation drag reduction. This invention also borrows the aft step flow method to protect the rolling air column 40.

[0030] Channel 1 (31) is a horizontal channel along the ship's length; Channel 2 (32) includes a horizontal section and a downward-sloping section arranged sequentially along the ship's length; Channel 3 (33) is arranged along the ship's length, and its width gradually increases at the outlet end, causing the seawater to disperse and flow at a low speed, pushing the air column backward and away from the generating device. The specific principle of generating the rolling air column 40 is as follows: In the first stage - the generation stage of the rolling air column 40, Channel 1 (31) and Channel 2 (32) are controlled by the gas flow solenoid valve 60 to use the high-pressure gas in the compressed gas tank 20 to eject a high-speed airflow. After the high-speed airflow from Channel 2 (32) is ejected obliquely downward, due to the inertia of the gas, the obliquely downward ejected high-speed airflow will cause a low-pressure area to be generated in the space above the nozzle, while a high-pressure area will be generated in the space obliquely below the nozzle. Driven by the pressure difference, the high-speed airflow will change direction towards the low-pressure area, ultimately forming an airflow rotating around the low-pressure area. The high-speed airflow in channel 1 (31) serves two purposes: first, it converges with the airflow in channel 2 (32) to create a high-pressure zone, forcing the high-speed airflow in channel 2 (32) to rotate; second, it isolates the incoming liquid flow, protecting the high-speed airflow in channel 2 (32) from disturbance. In the second stage – the pushing-away stage of the rolling air column 40 – after the rolling air column 40 is generated and has internal rotational flow, the gas flow channel solenoid valve 60 is closed, eliminating airflow in channels 1 (31) and 2 (32). The liquid flow channel solenoid valve 70 is opened, causing a low-speed liquid (seawater in this embodiment) to spray from channel 3 (33), pushing the rolling air column 40 away from the step. Under the influence of internal rotational flow and surface tension, the rolling air column 40 gradually evolves into a smoother shape and propagates to the left in the diagram, thus entering the third stage – the propagation stage of the rolling air column 40. When the rolling air column 40 moves a certain distance away from the step, it repeats the first stage of the next rolling air column 40. The repeated operation of these three stages generates rolling air columns 40 at equal intervals.

[0031] In a further optimization, in this embodiment, the ship's liquid system is the ship's own seawater system.

[0032] In a further optimization, in this embodiment, the ship rolling air column 40 drag reduction device is suitable for flat-bottomed boats.

[0033] In a further optimization, in this embodiment, the control module 50 is also connected to the compressed air tank 20 via a signal to monitor the pressure data of the compressed air tank 20.

[0034] Accordingly, the present invention also proposes a method for reducing drag of a ship's rolling air column 40, which employs the above-mentioned device and includes: S1. High-pressure air is injected into the compressed air tank 20 by the air compressor 10. The control module 50 monitors the ship's draft, speed and the pressure data of the compressed air tank 20, and calculates the required ventilation volume and ventilation interval.

[0035] Among the data monitored by the control module 50, the ship's draft primarily affects the ambient pressure at which the rolling air column 40 is located. This data is used to calculate the ventilation volume required for the rolling air column 40 to maintain a certain volume below the hull. The pressure data from the compressed air tank 20 can assist in calculating the available ventilation volume. and required air column volume It can be solved by the ideal gas law Converted to 20 bar of compressed air pressure and ventilation ventilation This determines the opening time of the solenoid valve; the required air column volume. The distance between the rolling air columns is determined based on the ship's beam and the air column diameter, which is approximately 5cm. The diameter can be adjusted appropriately based on the drag reduction effect. Ship speed affects the spacing of the rolling air columns 40, which is used to correct for the optimal ventilation interval. This is the required distance between the rolling air columns 40. Divide by the ship's displacement velocity relative to the seawater This allows the airflow interval of the rolling air column generator 30 to be determined. When a ship travels at a higher speed, the time interval for achieving optimal drag reduction is shorter; when the speed is lower, the time interval is relatively longer.

[0036] S2. The control module 50 sends an opening signal to the gas flow channel solenoid valve 60 and maintains it for a certain period of time to ensure the realization of the ventilation parameters. The high-pressure gas in the compressed gas tank 20 is ejected from the No. 1 channel 31 and the No. 2 channel 32 to the rear at a high speed. When the ventilation reaches the set value, a rolling air column 40 is formed at the rear. The control module 50 closes the gas flow channel solenoid valve 60. Then, the liquid flow channel solenoid valve 70 is opened, so that the No. 3 channel 33 ejects a low-speed fluid, pushing the rolling air column 40 away from the step. Under the action of internal rotational flow and surface tension, the rolling air column 40 gradually evolves into a more smoothly shaped rolling air column 40 and moves towards the stern of the ship. S3. When the rolling air column 40 moves away from the step by a certain distance, the liquid flow channel solenoid valve 70 is closed. After the set ventilation interval time is reached, S2 is repeated to generate rolling air columns 40 with equal intervals.

[0037] The mechanism of drag reduction through ventilation is to use a lower viscosity gas to replace the liquid in contact with the hull, thereby reducing or even eliminating the frictional resistance caused by the liquid flow. Traditional direct ventilation drag reduction methods suffer from significant gas escape due to gas buoyancy and fluid entrainment. To achieve a good air film coverage at the bottom of the hull, a large amount of air needs to be introduced, thus using excessive air to achieve a good air film coverage effect. In contrast, the drag reduction method of this invention uses intermittent introduction of a rolling air column 40, which allows the rolling air column 40 to propagate more stably rearward under the hull without breaking, effectively reducing the required ventilation volume. Compared to the direct ventilation drag reduction method, this invention achieves intermittent, stable rolling propagation of the air column, thus requiring only a smaller ventilation volume per unit time to achieve a better air column coverage effect. Furthermore, intermittent ventilation proportionally reduces the ventilation time, resulting in a significant reduction in total ventilation power consumption, which is estimated to be approximately 1 / 10 of that of the direct ventilation drag reduction method. Although the gas from intermittent ventilation cannot completely cover the hull, the area covered still provides a significant drag reduction effect, while the required ventilation volume is greatly reduced. The energy efficiency ratio (drag reduction effect / ventilation power consumption) is significantly improved compared to direct ventilation. For example, the currently mature application of direct ventilation drag reduction methods can reduce the frictional resistance of commercial cargo ships by about 60% at economic speeds (frictional resistance accounts for about 70% of the total ship resistance). Considering the large ventilation power consumption, the final overall energy saving effect is approximately 5% to 10%. In one embodiment of the method of this invention, intermittent ventilation with a 50% duty cycle can achieve a 30% reduction in frictional resistance, but the ventilation power consumption is about 1 / 10 of that of the direct ventilation drag reduction method, resulting in a final overall energy saving effect of approximately 5% to 10%.

[0038] It should be noted that, compared to traditional aeration drag reduction methods, the method of this invention increases the energy consumption of seawater. However, since the ship itself has its own seawater system, the seawater pump usually operates at a constant speed in a steady state, and the amount of seawater provided is already greater than the user's demand. The seawater used in this invention is not for cooling, but only to push the air column away from the device outlet. The water consumption is far lower than the water consumption of the original seawater system user, and the impact on the original seawater system is minimal. It can operate without increasing additional power consumption.

[0039] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0040] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0041] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A drag reduction device for a ship's rolling air column, comprising an air compressor, a compressed air tank, and a rolling air column generating device disposed inside the ship's hull, wherein the air compressor is connected to the compressed air tank; characterized in that, The lower surface of the rolling air column generator is flush with the outer surface of the bow hull, while the outer surface of the hull behind the rolling air column generator is higher than the lower surface of the rolling air column generator, forming a step. The rolling air column generator is provided with three channels, namely channel 1, channel 2 and channel 3, arranged from bottom to top on the vertical surface of the step. Channel 1 and channel 2 are connected to the compressed air tank through gas channels, and channel 3 is connected to the ship's liquid system through a liquid channel. The ship rolling air column drag reduction device also includes a control module, a gas flow solenoid valve disposed on the gas flow channel, and a liquid flow solenoid valve disposed on the liquid flow channel; the gas flow solenoid valve and the liquid flow solenoid valve are respectively signal connected to the control module, and the control module controls the opening or closing of the gas flow solenoid valve and the liquid flow solenoid valve.

2. The ship rolling air column drag reduction device according to claim 1, characterized in that, Channel 1 is a horizontal channel along the length of the ship; Channel 2 includes a horizontal section and a downward-sloping section arranged sequentially along the length of the ship, and the airflow is ejected after passing through the horizontal section and the downward-sloping section in sequence.

3. The ship rolling air column drag reduction device according to claim 1, characterized in that, The No. 3 channel is set along the length of the ship, and the width of the exit end gradually increases.

4. The ship rolling air column drag reduction device according to claim 1, characterized in that, The control module first controls the gas flow channel solenoid valve to open, using the high-pressure gas in the compressed gas tank to spray high-speed airflow from channel 1 and channel 2 to the rear, forming a rolling air column with rotating internal flow at the rear; then the control module closes the gas flow channel solenoid valve and opens the liquid flow channel solenoid valve, causing channel 3 to spray low-speed fluid, pushing the rolling air column away from the step and rolling towards the stern.

5. The ship rolling air column drag reduction device according to claim 1, characterized in that, The ship's liquid system is a built-in seawater system.

6. The ship rolling air column drag reduction device according to claim 1, characterized in that, The aforementioned ship rolling air column drag reduction device is suitable for flat-bottomed ships.

7. The ship rolling air column drag reduction device according to claim 1, characterized in that, The control module is also connected to the compressed air tank for monitoring the pressure data of the compressed air tank.

8. A method for reducing drag from a ship's rolling air column, characterized in that, The method employs the apparatus of any one of claims 1-7, comprising: S1. High-pressure air is injected into the compressed air tank by the air compressor. The control module monitors the ship's draft, speed and compressed air tank pressure data, and calculates the required ventilation volume and ventilation interval. S2. The control module sends an opening signal to the gas flow channel solenoid valve and holds it for a certain period of time. The high-pressure gas in the compressed gas tank is ejected from the No. 1 and No. 2 channels at high speed. When the air flow reaches the set value, a rolling air column is formed at the rear. The control module closes the gas flow channel solenoid valve. Then, the liquid flow channel solenoid valve is opened, so that the No. 3 channel ejects a low-speed fluid, pushing the rolling air column away from the step. Under the action of internal rotational flow and surface tension, the rolling air column gradually evolves into a smoother rolling air column and rolls towards the stern. S3. When the rolling air column moves away from the step by a certain distance, close the liquid flow channel solenoid valve. Repeat S2 after the set ventilation interval time is reached, thereby generating rolling air columns with equal intervals.

9. The method for reducing drag from a ship's rolling air column according to claim 8, characterized in that, In S1, the required ventilation volume is calculated according to the following formula: In the formula, Due to environmental pressures, For the required air column volume, To compress the air tank pressure, This refers to ventilation volume.

10. The method for reducing drag from a ship's rolling air column according to claim 8, characterized in that, In S1, the ventilation interval is calculated according to the following formula: In the formula, For ventilation intervals, The required distance between the rolling air columns. This represents the displacement velocity of the ship relative to the seawater.

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