A friction resistance change test evaluation method suitable for pools

Abstract

The present invention relates to a friction resistance change test evaluation method suitable for a water pool, comprising the following steps: S1, assembling a test tool; S2, making the immersion depth of the axis of a test ring greater than 1.5 times the outer diameter of the test ring; S3, driving the test ring to rotate at a fixed speed using an open water dynamometer, and measuring the rotation speed and the rotation torque of the test ring at this time; S4, measuring the torque at different rotation speeds; S5, measuring the average friction resistance of the surface of the test ring at each rotation speed and the corresponding friction resistance coefficient; S6, adhering a friction reduction material to the test ring, and measuring the torque of the test ring rotation at different rotation speeds; S7, comparing the test ring torque with the torque without the friction reduction material. The evaluation method provided by the present invention can realize the qualitative test evaluation in the process of studying the friction reduction scheme and the quantitative test evaluation after the friction reduction scheme is determined, and provides an efficient and convenient qualitative-quantitative evaluation approach for evaluating the friction reduction effect of new materials.

Description

Technical Field

[0001] The present invention relates to the technical field of ship resistance detection, and in particular to a friction resistance change test and evaluation method applicable to a water tank. Background Art

[0002] A ship's resistance performance directly impacts its operating costs and is a crucial component of its performance. For typical ships, navigational resistance primarily consists of frictional resistance and wave-making resistance. For low-speed vessels, frictional resistance accounts for 70% to 80% of the total resistance, while for high-speed vessels, it accounts for approximately 50%. Therefore, reducing frictional resistance has become a constant pursuit in ship performance design.

[0003] Microbubble friction reduction technology, wall vibration friction reduction technology, and biomimetic coating friction reduction technology are all major current research areas. With the development of polymer chemistry and nanomaterials science, biomimetic coating friction reduction technology is gaining increasing attention. The first challenge faced after the successful development of new materials is to verify their friction reduction effectiveness, and water tank model testing is the most effective method for this verification.

[0004] In the study of ship friction resistance, we generally introduce the equivalent plate assumption: the friction resistance of a real ship or ship model is equal to the turbulent friction resistance of a smooth plate with the same speed, length, and wetted area. In this way, by using the equivalent plate assumption, we can simplify the ship friction resistance to the friction resistance of a plate. From the classical knowledge of fluid mechanics, we know that the flow in the plate boundary layer can be divided into three states: laminar flow ( <3.5~5.0×10 5 ), transition flow (3.5~5.0×10 5 < <3.0×10 6 ) and turbulence ( >3.0×10 6 ). Due to the large difference in friction resistance coefficient between the laminar section and the turbulent section, experience shows that when the model length Reynolds number reaches 2.0×10 7 At this time, the length of the laminar section is less than 2.5%, and its influence on the resistance is small enough to be negligible. Direct extrapolation of the test results will not cause large deviations. This is the Reynolds number requirement for domestic underwater resistance tests.

[0005] The flatbed drag method is a commonly used evaluation method. Different biomimetic coatings are attached to a flatbed. A trailer drives the flatbed forward at a constant speed in a pool of water. The drag value is measured during navigation. By comparing the drag values ​​of different biomimetic coatings, the change in frictional resistance is evaluated. Assuming a towing speed of 5m / s~6m / s (10kN~12kN), the specimen length should not be less than 3m~4m. This ensures that the Reynolds number within the range is greater than 2.0×107 However, such a large plate brings a series of installation difficulties, especially when towing or when the water speed is high, the vibration of the plate is difficult to control, and the repeatability and accuracy of the test are difficult to guarantee.

[0006] To this end, we propose a friction resistance change test evaluation method suitable for water pools. Summary of the Invention

[0007] In response to the shortcomings of the above-mentioned existing production technology, the applicant provides a friction resistance change test evaluation method suitable for water pools, thereby realizing qualitative test evaluation during the friction reduction scheme research process and quantitative test evaluation after the friction reduction scheme is determined, providing an efficient and convenient qualitative-quantitative evaluation approach for the friction reduction effect evaluation of new materials.

[0008] The technical solutions adopted in the present invention are as follows:

[0009] 1. A method for evaluating the change in friction resistance of a pool, comprising a first test fixture comprising:

[0010] An open water dynamometer is arranged perpendicular to the water plane, one end of which is connected to a guide cap and inserted into the water, and the other end is suspended above the water plane;

[0011] A test ring, which is installed in the open water dynamometer and immersed in water;

[0012] The qualitative evaluation test using the test tool 1 includes the following steps:

[0013] S1. Assemble the test tool 1;

[0014] S2. Fix the open water dynamometer on the trailer lifting platform and adjust the lifting platform to change the immersion depth of the test ring so that the immersion depth of the test ring axis is greater than 1.5 times the outer diameter of the test ring. D ;

[0015] S3. The open water dynamometer drives the test ring to rotate at a constant speed, and the open water dynamometer measures the speed at this time. n and the rotational torque of the test ring Q 0;

[0016] S4. Change the speed of the open water dynamometer and measure different speeds n Torque when

[0017] S5, average friction resistance of the test ring surface at each speed and the corresponding friction resistance coefficient;

[0018] S6. Attach the friction-reducing material to the test ring and measure different rotation speeds. n The torque of the test ring when rotatingQ mi ;

[0019] S7. Compare the torque of the test ring with the friction reducing material attached to it with the torque of the test ring without the friction reducing material to determine the friction reducing effect of the material.

[0020] It is further characterized by:

[0021] The test ring comprises a connecting sleeve, which is connected to the downstream section of the open water dynamometer, and the connecting sleeve is connected to the test ring through a plurality of connecting rods.

[0022] The diameter of the test ring is between 400 mm and 500 mm, and the rotation speed is between 6 rps and 20 rps.

[0023] The angle of the downstream section does not exceed 20°, and the length of the guide cap is greater than 1.5 times the diameter of the test ring hub.

[0024] In S4, the speed n Critical Reynolds number for covering with friction-reducing material R e range, i.e. ,in is the kinematic viscosity coefficient, and its value varies with the test water temperature.

[0025] In S5, the average friction resistance is:

[0026]

[0027] The corresponding friction resistance coefficient is:

[0028]

[0029] In the above formula, h represents the width of the test ring, represents the density of pool water, Vm represents the linear velocity of the test ring, and Sm represents the external surface area of ​​the test ring.

[0030] In S6, the friction resistance coefficient of the friction-reducing material is:

[0031]

[0032] Where: ρm represents the pool water density, h represents the width of the test ring, and δmi represents the thickness of the drag reduction material.

[0033] The quantitative test evaluation includes a second test fixture, which includes a rotating body and an underwater resistance meter. The rotating body is horizontally arranged in water, and the number of underwater resistance meters is two and they are vertically connected to the upper end of the rotating body.

[0034] The quantitative test evaluation method includes:

[0035] SS1, assemble test fixture 2, and use the trailer to drive the rotating body to accelerate to the target speed V Then, measure the resistance of the rotating body when sailing at a constant speed. R 0, the total drag coefficient, the corresponding friction drag coefficient and the residual drag coefficient at each speed of the model tend to be approximately constant viscous pressure drag coefficient;

[0036] SS2, evenly cover the surface of the rotating body with anti-friction material and measure the speed at different speeds V Resistance R i , then:

[0037]

[0038] The friction coefficient when adhering to the friction-reducing material is:

[0039]

[0040] SS3, the friction coefficient of the rotating body with the friction-reducing material C fi Friction resistance coefficient of rotating body without friction reducing material C f0 Make comparisons to determine the friction reduction effect of the material when used on ships;

[0041] .

[0042] In the SS1, the test vehicle speed V The Reynolds number requirements of the friction reduction material must be met. ,in L is the characteristic length of the body of revolution;

[0043] At this time, the total drag coefficient of the model at each speed is:

[0044]

[0045] in is the density of water, which varies with the test water temperature. S is the wet surface area of ​​the rotating body;

[0046] The corresponding friction resistance coefficient is:

[0047]

[0048] The residual drag coefficient tends to be approximately constant viscous pressure drag coefficient:

[0049] ;

[0050] Assuming that the drag reduction measures do not affect the residual drag coefficient (viscosity-pressure drag coefficient):

[0051] .

[0052] The beneficial effects of the present invention are as follows:

[0053] The present invention has a compact and reasonable structure and is easy to operate. In response to the shortcomings of existing testing methods, the present invention provides a friction resistance change test evaluation method suitable for a water pool, which can realize qualitative test evaluation in the friction reduction scheme research process and quantitative test evaluation after the friction reduction scheme is determined, providing an efficient and convenient qualitative-quantitative evaluation approach for the friction reduction effect evaluation of new materials.

[0054] At the same time, the present invention also has the following advantages:

[0055] During the qualitative test evaluation in the present invention, the open water dynamometer is vertically immersed in water. Compared with conventional horizontal immersion, there is no water pressure difference in the test ring at this time, and the test is more stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a structural diagram of the test tool 1 in the present invention.

[0057] Figure 2 for Figure 1 A partial enlarged view of part A in the middle.

[0058] Figure 3 for Figure 1 A magnified schematic diagram of the test ring.

[0059] Figure 4 This is a schematic structural diagram of the test tool 2 in the present invention.

[0060] In the figure, 1. open water dynamic instrument; 2. downstream section; 3. test ring; 4. guide cap; 5. rotating body; 6. underwater resistance meter; 301. connecting sleeve; 302. connecting rod; 303. ring body. DETAILED DESCRIPTION

[0061] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0062] In response to the shortcomings of existing testing methods, the present invention provides a friction resistance change test evaluation method suitable for water pools, which can realize qualitative test evaluation during the friction reduction scheme research process and quantitative test evaluation after the friction reduction scheme is determined, providing an efficient and convenient qualitative-quantitative evaluation approach for the friction reduction effect evaluation of new materials.

[0063] The present invention adopts the following technical solutions:

[0064] The present invention is applicable to a water pool laboratory environment and comprises two parts: qualitative evaluation and quantitative evaluation.

[0065] The qualitative evaluation component of the present invention was developed based on this requirement. Different friction-reducing materials were attached to the outer wall of the test ring 3. The torque at different rotational speeds was compared between the test ring with and without the friction-reducing materials to determine the optimal friction reduction solution.

[0066] The present invention provides a friction resistance change test evaluation method applicable to a water pool, which includes two parts: a qualitative evaluation method and a quantitative evaluation method.

[0067] Example 1

[0068] In order to meet the Reynolds number greater than 2.0×10 7 , reducing the laminar flow area to a negligible less than 3%. For qualitative evaluation, the diameter of test ring 3 should be between 400mm and 500mm, and the rotational speed should be between 6rps and 20rps. For quantitative evaluation, the length of the rotating model is recommended to be 3500mm, with a submerged depth of at least 1 / 3 of its length. The test vehicle speed is 6m / s.

[0069] The test steps for the qualitative evaluation test are as follows:

[0070] S1, such as Figure 1-Figure 3 As shown, assemble the test fixture 1, which includes:

[0071] An open water dynamometer 1 is arranged perpendicular to the water plane, one end of the open water dynamometer 1 is connected to a guide cap 4 and inserted into the water, and the other end is suspended above the water plane;

[0072] The test ring 3 is mounted on a side wall of the open water dynamometer 1 in the water.

[0073] The test ring 3 includes a connecting sleeve 301, which is connected to the downstream section 2 of the open water dynamic instrument 1. The connecting sleeve 301 is connected to the ring body 303 through a plurality of connecting rods 302;

[0074] Install the test ring 3 on the vertical open water dynamometer 1. Install the downstream section 2 in front of the test ring 3 and the open water dynamometer 1 to transition. Install the guide cap 4 behind the test ring 3. Screw the test ring 3 and the open water dynamometer 1 together. The angle of the downstream section 2 does not exceed 20 degrees, and the length of the guide cap 4 is greater than 1.5 times the diameter of the hub of the test ring 3.

[0075] S2. Fix the open water dynamometer 1 on the trailer lifting platform, and adjust the lifting platform to change the immersion depth of the test ring 3 so that the immersion depth of the axis of the test ring 3 is greater than 1.5 times the outer diameter of the test ring 3. D ;

[0076] S3, open water dynamometer 1 drives the test ring 3 to rotate at a constant speed, and the open water dynamometer 1 measures the speed at this time n and the rotational torque of the test ring 3 Q 0;

[0077] S4. Change the speed of open water dynamometer 1 and measure different speeds n Torque at speed n Critical Reynolds number for covering with friction-reducing material R e Range, i.e. ,in is the kinematic viscosity coefficient, and its value varies with the test water temperature;

[0078] S5. The average friction resistance of the test ring 3 surface at each speed is:

[0079] ;

[0080] The corresponding friction resistance coefficient is:

[0081] ;

[0082] Where: h represents the width of the test ring, represents the density of pool water, Vm represents the linear velocity of the test ring, and Sm represents the external surface area of ​​the test ring.

[0083] S6. Attach the friction-reducing material to the test ring 3 and measure different rotation speeds. n The torque of the test ring 3 is Q mi , considering the thickness of the friction reducing material , then the friction resistance coefficient of the friction-reducing material is:

[0084]

[0085] Where: ρm represents the pool water density, h represents the width of the test ring, and δmi represents the thickness of the drag reduction material.

[0086] S7, compare the torque of the test ring 3 with the torque of the test ring without friction reducing material to determine the friction reducing effect of the material. For comparison purposes, the friction reduction effects of different friction reduction coatings are analyzed.

[0087] Qualitative evaluation: The research and development of new friction-reducing materials generally involves the evaluation of a large number of different friction-reducing solutions. The qualitative evaluation technology in this application is mature, reliable, simple, easy to implement, and low-cost.

[0088] Example 2

[0089] Slender rotating bodies often have low form resistance, with frictional resistance accounting for approximately 90% of the total resistance. This high frictional component of total resistance makes it easier to discern the effectiveness of friction reduction in comparative tests. Therefore, rotating bodies are often used as research subjects for quantitative evaluation tests.

[0090] The test steps for the quantitative evaluation test are as follows:

[0091] SS1, such as Figure 4 As shown, the test fixture 2 includes a rotator 5 and an underwater resistance meter 6. The rotator 5 is horizontally arranged in the water. There are two underwater resistance meters 6 and they are vertically connected to the upper end of the rotator 5.

[0092] Assemble the second test fixture, which includes a rotating body 5 and an underwater resistance meter 6;

[0093] The rotating body 5 is installed on the underwater resistance meter 6, and the trailer drives the rotating body 5 to accelerate to the target speed. V Then, measure the resistance of the rotating body 5 when sailing at a constant speed. R 0. Test speed V The Reynolds number requirements of the friction reduction material must be met. ,in L is the characteristic length of the body of revolution.

[0094] At this time, the total drag coefficient of the model at each speed is:

[0095]

[0096] in is the density of water, which varies with the test water temperature. S is the wet surface area of ​​the rotating body.

[0097] The corresponding friction resistance coefficient is:

[0098]

[0099] The residual drag coefficient tends to be approximately constant viscous pressure drag coefficient:

[0100] ;

[0101] Assuming that the drag reduction measures do not affect the residual drag coefficient (viscosity-pressure drag coefficient):

[0102]

[0103] SS2, evenly cover the surface of the rotating body 5 with the friction-reducing material and measure the speed at different speeds V Resistance R i , then:

[0104]

[0105] The friction coefficient when adhering to the friction-reducing material is:

[0106]

[0107] SS3, the friction resistance coefficient of the rotating body 5 to which the friction reducing material is adhered C fi Friction resistance coefficient of rotating body without friction reducing material C f0 Compare and determine the friction reduction effect of the material when applied to ships.

[0108]

[0109] Quantitative evaluation: After the optimal friction reduction solution is determined through qualitative evaluation, the material can be applied to the surface of a ship model to conduct quantitative evaluation tests to determine the friction reduction effect of the material when applied to the ship.

[0110] In summary, the present invention provides a friction resistance change test evaluation method suitable for water pools, which can realize qualitative test evaluation during the friction reduction scheme research process and quantitative test evaluation after the friction reduction scheme is determined, providing an efficient and convenient qualitative-quantitative evaluation approach for the friction reduction effect evaluation of new materials.

[0111] The above description is an explanation of the present invention, not a limitation of the present invention. The scope of the present invention is defined in the claims. Any modifications may be made within the scope of protection of the present invention.

Claims

1. A friction resistance change test evaluation method suitable for a pool, characterized in that: A test tool 1 is used, and the test tool 1 includes: An open water dynamometer is arranged perpendicular to the water plane, one end of which is connected to a guide cap and inserted into the water, and the other end of which is suspended above the water plane; A test ring is installed at the bottom of the open water dynamometer and immersed in water together; the test ring includes a connecting sleeve, a connecting rod and a ring body, the connecting sleeve is connected to the downstream section of the open water dynamometer, and the connecting sleeve is connected to the ring body through a plurality of connecting rods; The diameter of the test ring is between 400mm and 500mm, and the rotation speed is between 6rps and 20rps; The angle of the downstream section does not exceed 20°, and the length of the guide cap is greater than 1.5 times the diameter of the test ring hub; The qualitative evaluation test conducted by the test tool 1 includes the following steps: S1. Assemble the test tool 1; S2. Fix the open water dynamometer on the trailer lifting platform, and change the immersion depth of the test ring by adjusting the lifting platform, so that the immersion depth of the test ring axis is greater than 1.5 times the outer diameter of the test ring D ; S3. The open water dynamometer drives the test ring to rotate at a fixed speed, and the open water dynamometer measures the speed at this time. n and the rotational torque of the test ring Q 0; S4. Change the speed of the open water dynamometer and measure different speeds n Torque when S5. Calculate the average friction resistance of the test ring surface at each rotation speed and the corresponding friction resistance coefficient; S6. Attach the friction-reducing material to the test ring and measure different rotation speeds n The torque of the test ring when rotating Q mi ; S7. Compare the torque of the test ring with the friction reducing material attached to it with the torque of the test ring without the friction reducing material to determine the friction reducing effect of the material.

2. A friction resistance change test and evaluation method suitable for a pool as claimed in claim 1, characterized in that: In S4, the speed n needs to cover the critical Reynolds number Re range of the friction reducing material, that is, ,in is the kinematic viscosity coefficient, and its value varies with the test water temperature.

3. A friction resistance change test and evaluation method suitable for a pool as claimed in claim 1, characterized in that: In S5, the average friction resistance is: ； The corresponding friction coefficient is: In the above formula, h represents the width of the test ring, represents the density of pool water, Vm represents the linear velocity of the test ring, and Sm represents the external surface area of ​​the test ring.

4. A friction resistance change test and evaluation method suitable for a pool as claimed in claim 1, characterized in that: In S6, the friction coefficient of the friction-reducing material is: Where: ρm represents the pool water density, h represents the width of the test ring, and δmi represents the thickness of the drag reduction material.

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