Device and method for acquiring wave water rolling area in water tank

Abstract

The invention provides a device and method for acquiring the water rolling area of waves in a water tank, and the method comprises the steps: a non-reflection wave maker is disposed at one end of the wave tank, an experiment section of the wave tank is provided with a terrain model, and a camera is disposed at one side of the wave tank and is used for shooting the water rolling process on the terrain model at a fixed point; the planar soft light box is arranged on the non-shooting side of the wave water tank and used for forming a bubble shadow contour, and the spherical soft light cover is arranged on the shooting side of the wave water tank and used for enabling a generated bubble area to form light and shade contrast; the computer is connected with the camera and is used for storing images and videos shot by the camera, identifying the water rolling body and acquiring the water rolling area; the wave height meter is used for calibrating parameters of incident waves. According to the application, the water rolling areas of different positions under different wave types and conditions can be efficiently and accurately measured, so that a comprehensive and systematic data basis is provided for wave surface water rolling theory and model research.

Description

Technical Field

[0001] The present application belongs to the field of coastal engineering experimental technology, and in particular relates to a device for obtaining wave water rolling area in a water tank and a method for obtaining the same. Background Art

[0002] When waves break near the shore, turbulent water that moves with the waves is generated at the front of the wave crest, which is called wave surface water roll. The wave surface water roll is generated as the wave breaks, grows by absorbing part of the energy dissipated by the wave breaking, and finally gradually dissipates due to the shear energy between the water roll and the wave surface. Numerous studies have shown that the water roll energy generated by the wave surface water roll on the surface of the water body has an important impact on the hydrodynamic movement in the nearshore wave-breaking zone. Accurately describing the change law of water roll energy is a prerequisite for establishing a reasonable water roll evolution model, and is also the basis for a deep understanding of the nearshore wave-current coupled movement mechanism.

[0003] Theoretical studies have shown that water rolling energy is positively correlated with water rolling area. Therefore, obtaining comprehensive and systematic water rolling area data is the key to solving the above problems. Since wave breaking is often accompanied by complex gas-liquid mixing and water turbulence, it is very difficult to obtain water rolling area data. The existing water rolling area data is extremely scarce, which restricts the perfection and versatility of water rolling theory and models.

[0004] Experiments on nearshore wave breaking based on wave flumes are an important technical means to study the evolution of wave surface water roll. However, there is currently a lack of experimental devices and methods that can quickly and accurately identify water rolls and obtain water roll areas. Summary of the invention

[0005] In view of this, the present application aims to propose a device and method for obtaining the wave water roll area in a water tank, so as to solve the current problems of lack of water roll area data and difficulty in measurement.

[0006] To achieve the above purpose, the technical solution of this application is implemented as follows:

[0007] In a first aspect, the present application provides a device for obtaining the rolling area of ​​waves in a water tank, comprising a wave tank, a non-reflective wave maker, a camera, a flat soft box with a built-in light source, a spherical soft cover with a built-in light source, a wave height meter, and a computer;

[0008] The non-reflective wave maker is arranged at one end of the wave tank, the middle of the wave tank is an experimental section, a terrain model is provided in the experimental section, and the camera is placed on one side of the wave tank and is used to shoot the water rolling process on the terrain model at a fixed point;

[0009] The flat soft box is placed on the non-shooting side of the wave tank to provide soft and uniform background light during shooting to form the shadow outline of the bubble. The spherical soft cover is placed on the shooting side of the wave tank to form a light and dark contrast in the generated bubble area.

[0010] The computer is connected to the camera and is used to store images and videos taken by the camera, identify the water rolling body and obtain the water rolling area;

[0011] The number of the wave height meters is no less than 3, and they are respectively arranged in the horizontal section between the experimental section and the non-reflection wave maker, and are used to calibrate the parameters of the incident waves.

[0012] In the second aspect, based on the same inventive concept, the present application further provides a method for obtaining the wave water rolling area in the water tank based on the device for obtaining the wave water rolling area in the water tank according to the first aspect, comprising:

[0013] Extracting pixel columns of the measuring station positions in all frames of the captured water rolling video, and sequentially sorting the extracted pixel columns in chronological order to form a time stack image;

[0014] The cumulative distribution function result H corresponding to the time stack image is obtained according to the cumulative distribution function calculation g and its derivative H′ g , and select H′ g The pixel intensity value corresponding to the leftmost peak within the given range is used as the threshold, and the pixels with pixel intensity less than the threshold are defined as water rolling pixels;

[0015] Based on the calculated water roll pixels, the water roll area at the measuring station location is calculated using the water roll area formula.

[0016] Compared with the prior art, the device and method for obtaining the rolling area of ​​waves in a water tank described in the present application have the following beneficial effects:

[0017] The device and method for acquiring the water roll area of ​​waves in a water tank described in the present application can obtain high-quality images with clear light and dark of water rolls of different wave types (regular waves, irregular waves) and conditions, can automatically process water roll images, and efficiently, accurately and objectively identify water rolls in multiple experimental groups and multiple positions and calculate the corresponding water roll areas, thereby providing a comprehensive and systematic data basis for the study of wave surface water roll theory and models. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1This is a schematic diagram of the structure of the acquisition device described in the embodiment of the present application;

[0020] Figure 2 This is an example diagram of water rolling image acquisition described in the embodiment of the present application;

[0021] Figure 3 This is a flowchart of the acquisition method described in the embodiment of the present application;

[0022] Figure 4 This is a schematic diagram of a method for generating a time stack image according to an embodiment of the present application;

[0023] Figure 5 This is an example diagram of a time stack image of decomposing irregular waves using the lower zero crossing method described in an embodiment of the present application;

[0024] Figure 6 This is a schematic diagram of selecting an intensity threshold using CDF according to an embodiment of the present application;

[0025] Figure 7 A sensitivity analysis diagram of the intensity threshold described in the embodiment of the present application;

[0026] Figure 8 This is a comparison diagram of different thresholds obtained by using the CDF method described in the embodiment of the present application and the actual thresholds observed manually;

[0027] Fig. 9 This is an example diagram of the distribution of water rolling area along the regular wave experiment described in the embodiment of the present application;

[0028] Fig.10 This is an example diagram of the distribution of water rolling area along the irregular wave experiment described in the embodiment of the present application.

[0029] Description of reference numerals:

[0030] 1- wave tank; 2- non-reflection wave maker; 3- terrain model; 4- camera; 5- flat soft box with built-in light source; 6- spherical soft cover with built-in light source; 7- computer; 8- wave height meter. DETAILED DESCRIPTION

[0031] In order to make the objectives, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0032] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application should be the usual meanings understood by people with ordinary skills in the field to which the present application belongs. The "first", "second" and similar words used in the embodiments of the present application do not represent any order, quantity or importance, but are only used to distinguish different components. "Including" or "comprising" and similar words mean that the elements or objects appearing in front of the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0033] See also Figure 1 As shown, this embodiment provides a device for obtaining the rolling area of ​​waves in a water tank, comprising a wave tank 1, a non-reflective wave maker 2, a camera 4, a flat soft box 5 with a built-in light source, a spherical soft cover 6 with a built-in light source, a wave height meter 8 and a computer 7;

[0034] The side wall of the wave tank 1 is made of tempered glass or other transparent materials. The non-reflective wave maker 2 is arranged at one end of the wave tank 1. The middle part of the wave tank 1 is an experimental section. The experimental section is provided with a terrain model 3. The terrain model 3 is made of a steel frame and an engineering plastic plate. The distance between the experimental section and the non-reflective wave maker 2 is 10.4 m. The camera 4 is placed on one side of the wave tank 1 and is used to shoot the water rolling process on the terrain model 3 at a fixed point. The shooting angle of the camera 4 is always perpendicular to the glass wall of the wave tank 1. The camera 4 adopts a Revealer 5KF20 high-speed camera. The camera 4 is equipped with a Nikon 50mm f / 1.8D zoom lens, and the zoom lens is equipped with a neutral density film.

[0035] A flat soft light box 5 with a built-in light source (an LED light is installed in the box, and the LED light model is Godox M600D) is placed on the non-shooting side of the wave tank 1 to provide soft and uniform background light during shooting to form the bubble shadow outline. A spherical soft light cover 6 with a built-in light source (an LED light is installed in the cover, and the LED light model is Godox SL200Ⅲ) is placed on the shooting side of the wave tank 1, forming an angle of 60° with the normal of the glass wall of the tank, to form a clearer light and dark contrast in the bubble area, thereby obtaining a higher quality image.

[0036] The computer 7 is connected to the camera 4 and is used to store images and videos taken by the camera 4, identify the water rolling body and obtain the water rolling area;

[0037] The number of the wave height meters 8 is not less than 3 (this embodiment uses 3 wave height meters 8), and they are respectively arranged in the horizontal section between the experimental section and the non-reflection wave maker 2, for calibrating the parameters of the incident waves.

[0038] Based on the device described in the above embodiment, the present application provides another embodiment, a wave surface water rolling test method, which specifically includes:

[0039] Step 1: Before the experiment, stick a ruler on the glass wall of the water tank to calibrate the size of the high-speed camera, and obtain the relationship between the actual size of the pixel point and the distance l between the high-speed camera lens and the focal plane. During the experiment, the actual size of the pixel point in the captured image is obtained based on l.

[0040] Step 2: Design the experimental groups and wave conditions, and use the wave height meter arranged in the horizontal section to calibrate the parameters of the incident waves.

[0041] Step 3: Adjust the power of the LED light and the angle of the neutral density filter on the zoom lens so that the high-speed camera can capture a high-quality water rolling image with clear light and dark. Figure 2 As shown, (a) and (b) are the situations before and after the wave breaking, respectively.

[0042] Step 4: Generate waves according to the results of step 2. For regular wave experiments, image acquisition starts from the 30th wave cycle after the first wave reaches the shoreline and continues for the following 30 wave cycles. For irregular wave experiments, image acquisition starts from the 30th average cycle after the first wave reaches the shoreline and continues for the following 100 average cycles.

[0043] Step 5: Use a high-speed camera to shoot the water rolling image at a specific location, and import the video into a computer. The resolution of the image acquisition is 1920×1080 and the frame rate is 50fps.

[0044] Step 6: Move the high-speed camera to shoot water rolling images at different positions and store them on a computer. During the movement of the high-speed camera, ensure that its shooting angle is always perpendicular to the glass wall of the water tank.

[0045] Step 7. Repeat steps 4 to 6 to conduct water rolling experiments under different wave and terrain conditions.

[0046] Based on the same inventive concept, corresponding to any of the above-mentioned embodiments, the embodiment of the present application further provides a method for obtaining the wave water rolling area based on a device for obtaining the wave water rolling area in a water tank, such as Figure 3 As shown, the method specifically comprises the following steps:

[0047] Step S101: extract pixel columns of the measuring station positions in all frames of the captured water rolling video, and sort the extracted pixel columns in chronological order to form a time stack image.

[0048] Specifically, in this embodiment, the pixel columns of the measuring station positions are extracted from all frames of the captured water rolling video, such as Figure 4 As shown by the vertical solid line in ; these pixel columns are arranged from left to right in the time sequence of each frame to form a time stack image, as shown in Figure 4 For the irregular wave experiment, the time stack image of 100 average cycles is decomposed into the time stack image of a single wave cycle using the lower zero crossing method, as shown in Figure 5 shown.

[0049] Step S102: Obtain the cumulative distribution function result H corresponding to the time stack image according to the cumulative distribution function calculation. g and its derivative H′ g , and select H′ g The pixel intensity value corresponding to the leftmost peak within the given range is used as the threshold, and the pixels with pixel intensity less than the threshold are defined as water rolling pixels;

[0050] Specifically, in this embodiment, for the time stack image obtained by processing in step S101, the H corresponding to the time stack image is calculated according to the Cumulative Distribution Function (CDF) formula. g and its derivative H′ g , the specific formula is:

[0051]

[0052] Where i represents the pixel intensity, ranging from 0 (black) to 1 (white); H g (i) represents the cumulative distribution function result of the pixel intensity; h g represents the normalized intensity histogram. White background (defined as pixels with i>0.9) is excluded from the pixel statistics of the CDF.

[0053] Select H′ g The pixel intensity value corresponding to 80% of the leftmost peak is used as the threshold, such as Figure 6 As shown in the figure, (a) is a time stack image of a wave cycle, and (b) is the H corresponding to the time stack image. g , (c) is H g The first-order derivative H′ g .

[0054] It should be noted that the present embodiment provides the following explanations for determining the set threshold:

[0055] According to the function H′ g Five threshold choices were explored (thresholds A to E, marked in Figure 6 (c)), this is because H′ g It usually shows relatively obvious peaks and relatively less random noise. Among these thresholds, threshold E corresponds to H' g The leftmost peak of threshold A to D is H′ g The values ​​correspond to the threshold E' g 20%, 40%, 60% and 80% of the value.

[0056] The choice of intensity threshold has a great influence on the statistics of water roll pixels and therefore Figure 6 The thresholds marked A to E in (c) were subjected to sensitivity analysis and performance analysis.

[0057] Figure 7 An example is given to illustrate the sensitivity of the statistics of water roll pixels to the intensity threshold. Figure 7 (a) shows the pixels segmented using threshold A in a periodic segment of the time stack image. It can be found that the pixels segmented by threshold A are very few, and only a few pixels are captured in one frame of the image at the peak. Figure 7 (b) shows the pixels segmented using threshold B. Compared with threshold A, threshold B corresponds to a higher brightness intensity and captures more pixels, but it is still far from meeting the requirements for quantifying the water rolling area. Similarly, the pixel range segmented by threshold C is further expanded to cover most of the area at the front of the wave crest, but there is still a certain discontinuity (see Figure 7 (c)). Compared with threshold C, threshold D further expands the pixel range and basically covers the entire crest front, which is the generally recognized water rolling area (see Figure 7 (d)). As the brightness intensity corresponding to the threshold increases further, the pixel range corresponding to threshold E has expanded to the deep water area and the back of the wave crest, and even captured some pixels outside the wave crest (see Figure 7 (e)). This shows that the pixels segmented by threshold E obviously include pixels other than water rolling pixels. Finally, Figure 7 (f) shows the water rolling area measurement values ​​determined at the station corresponding to this embodiment using thresholds A to E. The results show that the measured water rolling area is very sensitive to the brightness intensity threshold, and the measurement value increases with the increase of the brightness intensity of the threshold.

[0058] The automatic recognition algorithm described in this embodiment has the advantage of being more efficient in selecting thresholds, but it cannot distinguish the waves and water rolls in each image as carefully as manual observation. Therefore, the performance of the algorithm is usually evaluated by comparing the threshold predicted by the algorithm with the threshold observed manually. Figure 8The scatter plots between the predicted thresholds (thresholds A to E) and the manually observed true thresholds for 45 time stack images are shown. It can be found that there is a high positive correlation between the thresholds predicted by the CDF algorithm and the manually observed true thresholds.

[0059] The statistical parameters root mean square error (RMSE) and determination coefficient (R 2 )Evaluate the performance of thresholds A to E:

[0060]

[0061] In the formula, y i and They represent the true threshold value observed manually and the threshold value predicted by CDF, respectively. It represents the average value of the true threshold, and n is the number of samples.

[0062] The calculation results of statistical parameters are shown in Table 1. It can be seen that the determination coefficient (R 2 ) are all above 0.95, indicating that the predicted threshold is well correlated with the true threshold. Threshold D has the highest consistency with the observed value, and its RMSE is the smallest among the five predicted thresholds, which is 0.011. In contrast, although thresholds B, C, or E are closer to the manual observation threshold in a few images, they generally show a trend of being smaller or larger than the manual observation threshold, and their RMSEs are 0.023, 0.015, and 0.025, respectively. Threshold A deviates greatly from the manual observation threshold. Figure 8 These results are consistent with Figure 7 The threshold D (corresponding to the first-order derivative of the CDF (H′) g ) peak value of 80%) is quite close to the manually selected threshold and shows good performance in water rolling pixel statistics.

[0063] Table 1 Root mean square error (RMSE) and determination coefficient (R) of thresholds A to E 2 )

[0064] Threshold A B C D E RMSE 0.033 0.023 0.015 0.011 0.025 <![CDATA[R 2 ]]> 0.954 0.973 0.979 0.976 0.956

[0065] Step S103: Based on the calculated water roll pixels, the water roll area at the measuring station position is calculated using a water roll area formula.

[0066] Specifically, in this embodiment, after the water rolling pixel is determined, the water rolling area is calculated by the following formula:

[0067]

[0068] In the formula, A r represents the water rolling area; c represents the wave speed; T represents the wave period; It represents the time-averaged water roll thickness and is calculated by the following formula:

[0069]

[0070] Where N is the total number of frames of a single image acquisition. The duration of a single image acquisition is an integer multiple of the wave period. For irregular waves, it is a single wave period. p Represents the actual height corresponding to a unit pixel in the time stack image; P represents the number of water rolling pixels in a column of pixels corresponding to a certain frame.

[0071] Among them, the regular wave uses the above method to obtain the average water roll area of ​​multiple wave periods at the measuring station location, and the irregular wave obtains the water roll area of ​​each wave period based on the image of the period, and then obtains the characteristic value of the water roll area.

[0072] The distribution of water rolling area along the regular wave experiment with an incident wave height of 0.075m, a period of 1.1s, and a terrain with a uniform slope of 1:20 is shown in the following figure: Fig. 9 As shown in the figure, the water rolling area along the irregular wave experiment with an incident effective wave height of 0.075m, an average period of 1.1s, and a terrain with a uniform slope of 1:20 is obtained as shown in the figure. Fig.10 As shown, is the average water rolling area, A r,1％ It means that the cumulative frequency of exceeding this water rolling area is 1%, A r,5％ It means that the cumulative frequency of exceeding this water rolling area is 5%, A r,13％ This means that the cumulative frequency of exceeding this water rolling area is 13%.

[0073] The results show that the water roll experimental device and water roll area acquisition method proposed in this embodiment can efficiently and accurately measure the water roll areas at different positions under different wave types and conditions, thereby providing a comprehensive and systematic data basis for the study of wave surface water roll theory and models.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

[0075] The embodiments of the present application are intended to cover all such substitutions, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present application should be included in the scope of protection of the present application.

Claims

1. A device for obtaining the rolling area of ​​waves in a water tank, characterized in that: It includes a wave tank, a non-reflective wave maker, a camera, a flat soft box with a built-in light source, a spherical soft cover with a built-in light source, a wave height meter and a computer; The non-reflective wave maker is arranged at one end of the wave tank, the middle of the wave tank is an experimental section, a terrain model is provided in the experimental section, and the camera is placed on one side of the wave tank and is used to shoot the water rolling process on the terrain model at a fixed point; The flat soft box is placed on the non-shooting side of the wave tank to provide soft and uniform background light during shooting to form the shadow outline of the bubble. The spherical soft cover is placed on the shooting side of the wave tank to form a light and dark contrast in the generated bubble area. The computer is connected to the camera and is used to store images and videos taken by the camera, identify the water rolling body and obtain the water rolling area; The number of the wave height meters is no less than 3, and they are respectively arranged in the horizontal section between the experimental section and the non-reflection wave maker, and are used to calibrate the parameters of the incident waves.

2. The device according to claim 1, characterized in that: The distance between the experimental section and the reflectionless wave maker is not less than 10m.

3. The device according to claim 1, characterized in that: The shooting angle of the camera is perpendicular to the side wall of the wave tank. The camera is provided with a zoom lens for adjusting the focal length, and the zoom lens is provided with a dimming film for adjusting the amount of light entering the lens.

4. A method for obtaining the wave water roll area in a water tank based on the device for obtaining the wave water roll area in a water tank according to any one of claims 1 to 3, characterized in that: include: Extracting pixel columns of the measuring station positions in all frames of the captured water rolling video, and sequentially sorting the extracted pixel columns in chronological order to form a time stack image; The cumulative distribution function result H corresponding to the time stack image is obtained according to the cumulative distribution function calculation g and its derivative H′ g , and select H′ g The pixel intensity value corresponding to the leftmost peak within the given range is used as the threshold, and the pixels with pixel intensity less than the threshold are defined as water rolling pixels; Based on the calculated water roll pixels, the water roll area at the measuring station location is calculated using the water roll area formula.

5. The method according to claim 4, characterized in that The cumulative distribution function formula is: Where i represents pixel intensity, ranging from 0 to 1; H g (i) represents the cumulative distribution function result of the pixel intensity; h g Represents the normalized intensity histogram.

6. The method according to claim 4, characterized in that The water rolling area formula is: In the formula, A r represents the water rolling area; c represents the wave speed; T represents the wave period; Indicates the time-averaged water roll thickness; in, Where N is the total number of frames of a single image acquisition; Z p Represents the actual height corresponding to a unit pixel in the time stack image; P represents the number of water rolling pixels in a column of pixels corresponding to a certain frame.

7. The method according to claim 4, characterized in that The threshold is evaluated by the statistical parameters root mean square error and determination coefficient, specifically: In the formula, y i and They represent the true threshold value observed manually and the threshold value predicted by the cumulative distribution function, It represents the average value of the true threshold, and n is the number of samples.

8. The method according to claim 4, characterized in that: Set the pixel intensity less than 80% H′ g The pixels are defined as water rolling pixels.

Images