System and method for measuring entry of lifeboat into water based on trajectory tracking algorithm

Abstract

The invention discloses a lifeboat water entry measurement system and method based on a trajectory tracking algorithm, the system comprises a wind wave flow coupling test pool, a throwing type lifeboat release platform and a throwing type lifeboat water entry test measurement module, the wind wave flow coupling test pool is used for simulating marine environments under different working conditions; the throwing type lifeboat releasing platform is used for simulating the releasing process of the throwing type lifeboat under different working conditions; the throwing type lifeboat water entry test measurement module solves and obtains the movement track, speed and attitude angle change of the lifeboat based on a trajectory tracking algorithm, and obtains the movement response mechanism of the lifeboat; according to the invention, a complex marine environment can be simulated, multi-degree-of-freedom motion response can be captured in real time, and test measurement of a key load can be quantitatively measured.

Description

Technical Field

[0001] This invention relates to a lifeboat entry measurement system and method, specifically to a lifeboat entry measurement system and method based on a trajectory tracking algorithm. Background Technology

[0002] In marine engineering, ship design, and lifesaving equipment development, the water entry problem of structures has always been an important research direction. However, most current water entry tests focus on slender bodies and bodies of revolution, primarily concerned with changes in the water flow field and stress characteristics, while research on bluff body water entry is relatively limited. Drop-off lifeboats, as a typical bluff body structure, have attracted widespread attention in the field of marine lifesaving. The process of a lifeboat sliding down a ramp, being dropped from the air, entering the water, and surfacing is simple and reliable, but the strong nonlinear loads generated during water entry can potentially cause injury to personnel inside the lifeboat. Therefore, research on the water entry characteristics of drop-off lifeboats has significant practical implications.

[0003] In the current field of marine engineering testing technology, water entry tests are mostly limited to single flow environments, such as still water or regular wave conditions, making it difficult to accurately characterize the real dynamic response under the coupling of multiple physical fields such as wind, waves, and currents in actual complex sea conditions. Existing test methods have significant shortcomings in simulating real sea surface fluctuations with random characteristics, and in particular, there is a lack of effective test systems that can systematically study the motion response and load distribution of objects (such as lifeboats) under the combined excitation of wind, waves, and currents.

[0004] On the other hand, although existing motion tracking technologies have been applied to dynamic response capture to some extent, there is still a lack of an integrated testing system with high spatiotemporal synchronization and multi-dimensional measurement capabilities for the six-degree-of-freedom strong nonlinear motion characteristics exhibited by drop-out lifeboats. Traditional methods have limitations in measurement accuracy, system integration, and parameter correlation, making it difficult to achieve coordinated capture and unified analysis of motion trajectories, structural loads, and sea state parameters. This restricts a deeper understanding of the lifeboat's full-process motion and safety status in complex environments. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a lifeboat entry measurement system based on a trajectory tracking algorithm to simulate complex marine environments and capture multi-degree-of-freedom motion responses in real time. On the other hand, it also provides a lifeboat entry measurement method based on a trajectory tracking algorithm.

[0006] Technical solution: The lifeboat entry measurement system of the present invention includes a wind-wave-current coupling test pool, a drop-type lifeboat release platform, and a drop-type lifeboat entry test measurement module, wherein: The wind-wave-current coupling test pool is used to simulate the marine environment under different working conditions; the drop-type lifeboat release platform is used to simulate the release process of the drop-type lifeboat under different working conditions. The drop-type lifeboat water entry test measurement module is equipped with several high-speed cameras, which capture the circular color blocks of the lifeboat from different perspectives, record the six degrees of freedom changes of the lifeboat, and solve the motion trajectory, velocity and attitude angle changes of the lifeboat based on the trajectory tracking algorithm, so as to obtain the motion response mechanism of the lifeboat.

[0007] Preferably, the drop-type lifeboat release platform consists of a swaying platform connected to the bottom of the lifeboat release rack and a lifting system fixed to the bottom of the swaying platform.

[0008] Preferably, the swaying platform includes a top-opening platform connected to the lifeboat release rack. The top-opening platform is connected to one end of a coupling via a universal hinge, and the other end of the coupling is connected to a bottom platform via the universal hinge. The central control system is located on the bottom platform.

[0009] Preferably, a circulating water tank is placed next to the lifting system.

[0010] Preferably, the plurality of high-speed cameras are respectively installed above, beside, and in front of the circulating water pool.

[0011] Preferably, the drop-type lifeboat water entry test measurement module includes a lifeboat hull, a wireless data acquisition device is installed at the bottom of the lifeboat hull, and a gyroscope is installed between the wireless data acquisition devices.

[0012] Preferably, a plurality of pressure sensors are installed on one side of the bow of the lifeboat hull, arranged at equal intervals.

[0013] The lifeboat entry measurement method of the present invention includes the following steps: The wind-wave-current coupling test pool simulates steady flow, wind, and wave fields under different working conditions; The drop-type lifeboat release platform simulates different drop heights, slide angles, and slide lengths of the lifeboat; High-speed cameras from different perspectives captured the lifeboat's trajectory, its drop into the air, its entry into the water, and its ascent, collecting data throughout the entire motion process to obtain the lifeboat's six degrees of freedom angular changes. Based on the trajectory tracking algorithm, the motion trajectory of the circular colored blocks at different positions of the lifeboat is identified, and the motion trajectory, velocity and attitude angle changes of the lifeboat are obtained, thus revealing the motion response mechanism of the lifeboat.

[0014] Preferably, the actual lifeboat's image is obtained based on the image distortion correction method, and the binarized frame is obtained through the threshold segmentation method. The centroid position of the color block is obtained using the principles of image morphology and the median denoising method. The centroid motion response of the color block in the experiment is obtained by converting the pixel value to its true size and iteratively solving. The motion trajectory, speed and attitude angle changes of the lifeboat during the experiment are obtained from the centroid motion response based on the trigonometric function relationship.

[0015] Preferably, the lifting legs of the lifting system are linked with the hinge to simulate different drop heights of the lifeboat; the hydraulic extension and retraction of the coupling is controlled by the central control system, and the universal hinge drives the angle of the top open platform to change, thereby changing the angle of the lifeboat release frame and simulating the lifeboat sliding from different slide angles; the release system changes its own rotation angle to control the release or fixation of the lifeboat hull, simulating the control of the lifeboat hull sliding length.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: Through trajectory tracking algorithm and image recognition technology, it can capture the multi-degree-of-freedom motion response and slam load of the entire process of the drop-type lifeboat entering the water under different sensitivity parameters in real time. Furthermore, it proposes an experimental method for measuring key motion response and load, and forms a high-precision integrated measurement system for the complex motion and slam characteristics of drop-type lifeboats in complex marine environments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the system appearance of the present invention; Figure 3 This is a schematic diagram of the overall structural design of the test and measurement system of the present invention; Figure 4 This is a side view schematic diagram showing the installation position of the testing instruments inside the hull of the drop-type lifeboat of the present invention; Figure 5 This is a top view of the installation location of the testing instruments inside the hull of the drop-type lifeboat of the present invention, and a schematic diagram of the location of the circular colored block on the top of the hull. Figure 6 A front view of the position of the pressure sensor at the bow of the drop-type lifeboat and a schematic diagram of the position of the circular color block at the bow in this invention; Figure 7 This is a schematic diagram of the boat frame design and release system structure of the present invention; Figure 8 This is a schematic diagram of the swaying platform and lifting system of the present invention; Figure 9 This is a schematic diagram showing the cooperation between the bottom platform of the swaying platform and the top shaft of the lifting system of the present invention; Figure 10 This is a schematic diagram of the overall layout of the components of the circulating water tank of the present invention; Figure 11 The image shows a comparison between the angle change calculated by the trajectory tracking algorithm of this invention and the result from the gyroscope; the red line represents the result of the trajectory tracking algorithm, and the blue dashed line represents the result from the gyroscope. Detailed Implementation

[0018] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings.

[0019] The lifeboat entry measurement system based on trajectory tracking algorithm consists of three parts: a wind-wave-current coupling test pool, a drop-type lifeboat release platform, and a drop-type lifeboat entry test measurement module.

[0020] The wind-wave-current coupling test pool consists of a circulating water pool 5, which is used to simulate marine environments under different working conditions, including still water, regular waves, different wind speeds, different current velocities, or their coupling environments, to comprehensively reflect the motion response and load changes of the drop-type lifeboat throughout the entire process of entering the water under different working conditions.

[0021] The drop-out lifeboat release platform consists of a lifeboat release frame 2, a swaying platform 3, and a lifting system 4. It is used to simulate the release process of the drop-out lifeboat under different working conditions, including adjusting the release height, drop height, and release angle to simulate different initial postures and realistically reflect the motion characteristics of the drop-out lifeboat in different initial states.

[0022] The drop-type lifeboat water entry test measurement module consists of the lifeboat hull 1, a top-view high-speed camera 6, a front-view high-speed camera 7, and a side-view high-speed camera 8. It is used to capture the dynamic response and load changes of the drop-type lifeboat in real time during the entire water entry process. The high-speed camera records the six degrees of freedom motion of the hull, and the trajectory, velocity, and attitude angle changes of the hull are obtained based on the trajectory tracking algorithm. The motion changes and impact load characteristics of the lifeboat from the track gliding, air drop, water entry and floating stages are comprehensively analyzed.

[0023] The lifeboat hull 1 is equipped with a lifeboat release rack 2 at the bottom. The release rack 2 is connected to a swaying platform 3 below it. The bottom of the swaying platform 3 is fixed to the lifting system 4. A circulating water pool 5 is placed next to the lifting system 4. A high-speed camera 6 with a top view, a high-speed camera 7 with a front view, and a high-speed camera 8 with a side view are installed above, to the side, and in front of the circulating water pool 5, respectively.

[0024] The lifeboat hull 1 includes a watertight hatch 11, an acceleration sensor 12, a gyroscope 13, a wireless data acquisition device 14, a pressure sensor 15, a rigid strut 16, a rigid base 17, a circular color block on the side of the boat 18, a circular color block on the top of the boat 19, and a circular color block on the bow 20.

[0025] The lifeboat hull 1 has two watertight hatches 11 on its top, located above the parallel midbody of the lifeboat hull 1. These hatches are open for easy installation of internal testing instruments and closed during testing to prevent water leakage from the lifeboat hull 1. Six rigid bases 17 are installed at the bottom inside the lifeboat hull 1 for securing testing instruments. Six rigid support rods 16, proportionally corresponding to the seats inside a real drop-in lifeboat, are mounted on the six rigid bases 17. Six acceleration sensors 12 are installed on the six rigid support rods 16 to measure the acceleration of the seats inside the lifeboat throughout its descent into the water. Acceleration in the X, Y, and Z directions was measured to simulate the acceleration values ​​at the seats inside the lifeboat when it enters the water. The results of all test conditions were compared to determine the optimal solution that minimizes harm to the human body during actual lifeboat entry. Six rigid bases 17, six rigid struts 16, and six acceleration sensors 12 were arranged in pairs at the front, middle, and rear of the lifeboat hull 1, with equal spacing and symmetrical positions. Two wireless data acquisition devices 14 were installed at the bottom of the lifeboat hull 1, positioned in the gaps between the six rigid bases 17, to transmit the measured data. For easy storage at the terminal; the gyroscope 13 is arranged in the middle of the inner bottom of the lifeboat hull 1, between the two wireless data acquisition devices 14, to measure the attitude angle time-history changes of the lifeboat hull 1 throughout the test; seventeen pressure sensors 15 are installed on one side of the bow of the lifeboat hull 1, arranged at equal intervals, to measure the slamming pressure generated when the lifeboat hull 1 enters the water. The arrangement of the pressure sensors 15 is reasonable according to the bow profile of the lifeboat hull 1. This arrangement is for conditions where the hull is not rolling. For other conditions, the other side of the bow of the lifeboat hull can be used. Pressure sensor 15 is installed as the preferred solution to the problem. Circular colored blocks 18 are affixed to the sides of the lifeboat hull 1, circular colored blocks 19 are affixed to the top, and circular colored blocks 18, 19, and 20 of the same size and color are affixed to the bow. These are placed on the sides, top, and bow of the lifeboat hull 1, respectively, with three blocks at each location, arranged in a triangle, and their colors are distinct from the overall test environment. The circular colored blocks facilitate the implementation of the trajectory tracking algorithm, and their motion changes are equivalent to the six degrees of freedom changes of the lifeboat hull 1. The motion of the circular colored block 18 on the side represents the hull's pitch, heave, and roll; the motion of the circular colored block 19 on the top represents the hull's sway and bow roll; and the motion of the circular colored block 20 on the bow represents the hull's roll.

[0026] The lifeboat release frame 2 includes symmetrically arranged side pulleys 21, bottom pulleys 23, and a release system 22. The lifeboat release frame 2 is a steel frame structure used for the launching lifeboat to complete the track-sliding phase. The side pulleys 21 are installed on both sides of the upper part of the lifeboat frame 2, with a number adjusted according to the frame length, to fix the lifeboat's sliding movement and prevent bow rolling. The bottom pulleys 23 are arranged on both sides of the bottom of the lifeboat frame 2, with a number adjusted according to the frame length, to assist the lifeboat's sliding. The release system 22 is located between the bottom pulleys 23, and is a slender block structure with a number of components. Its cross-sectional size is lower than the cross-sectional height of the frame structure. When the lifeboat is in the sliding preparation phase, it needs to fix the position of the lifeboat hull 1 by rotating to lock the hull and restrict its movement. When the lifeboat needs to slide, the rotation of the release system 22 is turned off, allowing the lifeboat hull 1 to slide. By controlling the working state of the release system 22, the movement distance of the lifeboat during the sliding phase can be changed, effectively changing the track length.

[0027] The swaying platform 3 includes a top open platform 31, a coupling 32, a universal hinge 33, a central control system 34, and a bottom platform 35. The top open platform 31 is connected and fixed to the lifeboat frame 2, and the opening prevents the lifeboat hull 1 from contacting the platform; the two ends of the coupling 32 are connected to the universal hinge 33, and the central control system 34 controls the movement of the coupling 32 and the universal hinge 33 to achieve the angle of the top open platform 31, thereby directly affecting the angle of the slide; the bottom platform 35, in addition to supporting the above components, is connected to the top shaft 41.

[0028] The lifting system 4 includes a top shaft 41, a hinge 42, lifting legs 43, a lifting platform main unit 44, and a fixing frame 45. The lifting system 4 is used to change the drop height of the lifeboat; the top shaft 41 is connected to the bottom platform 35 and can slide within the bottom platform 35, preventing the bottom platform 35 from tilting and affecting the test when changing the lifting height; the hinge 42 is connected to the lifting legs 43, and the two are controlled to rotate relative to each other by the lifting platform main unit 44; the fixing frame 45 is used to fix the position of the lifting system and reduce the error caused by resonance during the test.

[0029] The circulating water tank 5 includes a wind speed monitor 51, a wind direction monitor 52, a water level gauge 55, a flow meter 57, a wave damper 53, a fan 54, a wave generator 59, a suction pump 58, and a drainage pump 56. The wind speed monitor 51 and the wind direction monitor 52 are arranged at appropriate locations in the wind field generated by the fan 54 to monitor wind speed and direction; the water level gauge 55 is located above the free surface to monitor water depth; the flow meter 57 is located below the free surface to extract flow field data; the suction pump 58 and the drainage pump 56 are located at the bottom of the circulating water tank 5 and work together to change the flow field; the wave generator 59 and the wave damper 53 are located at both ends of the circulating water tank 5 to generate and dampen waves respectively, preventing reflected waves from interfering with the test results.

[0030] The lifeboat entry measurement method based on trajectory tracking algorithm includes the following steps: In the circulating water tank 5, the suction pump 58 and the drainage pump 56 are activated simultaneously to regulate the flow rate and generate a stable flow field; the flow velocity meter 57 is activated to measure and adjust the flow velocity to the target value; the water depth is adjusted by the water level gauge 55 to meet the test requirements; the fan 54 is activated to generate a stable wind field, and the wind speed and wind direction angle are detected and adjusted by the wind speed monitor 51 and the wind direction monitor 52 to meet the test requirements; the wave generator 59 is operated to adjust the wave parameters to achieve the target wave state; the position of the wave damping plate 53 is fixed to reduce interference.

[0031] By controlling the lifting platform host 44, the movement state of the lifting legs 43 and hinges 42 of the lifting system 4 is adjusted to change the drop height of the lifeboat to meet the test conditions; the fixed frame 45 is opened to reduce additional vibration during the test; the hydraulic extension and retraction of the coupling 32 is adjusted by the central control system 34 to change the angle of the top open platform 31 and adjust it to the required slide angle; the lifeboat hull 1 is controlled to reach the target slide length position by the release system 22.

[0032] The lifeboat hull 1's sliding-dropping process was captured using cameras. High-speed cameras 6 (top-view), 7 (front-view), and 8 (side-view) were calibrated to obtain lens distortion parameters. Video data streams were obtained from circular color blocks 18 on the side, 19 on the top, and 20 on the bow, and the actual captured images were derived using image distortion correction methods. Intrinsic distortion parameters were obtained based on calibration, and radial / tangential distortion correction and homography perspective correction were performed to achieve accurate pixel-to-actual-scale mapping. Binarization after pixel thresholding and morphological opening / closing operations followed by median filtering denoising effectively separated the target area from the background, resulting in the center location of the target area. The velocity, trajectory, and attitude angle changes of lifeboat hull 1 during the experiment were obtained from the centroid motion response based on trigonometric relationships, using the time difference between consecutive video frames and the position difference of the center point. Furthermore, the angle history changes were obtained by combining the angle changes between the point and the Earth's coordinate system with the time difference.

[0033] The test instruments are installed inside the lifeboat hull 1 and the watertight hatch 11 is closed; the lifeboat hull 1 is released through the lifeboat release rack 2, and three high-speed cameras (6, 7, 8) are activated to take pictures at the same time, and the wireless data acquisition instrument 14 records the data in real time; the accelerometer 12 measures the acceleration in the X, Y, and Z directions inside the hull, the gyroscope 13 records the entire process of the six-degree-of-freedom angle change, and the pressure sensor 15 monitors the slam load when the hull enters the water.

[0034] Comparing the angle changes calculated by the trajectory tracking algorithm with the results from the gyroscope 13 inside the lifeboat hull 8, it can be seen that the algorithm and the instrument measurement results are highly consistent. The central control system 34 controls the movement of the coupling 32 and the universal hinge 33 to realize the angle of the top open platform 31, which directly affects the slide angle. The trajectory, total speed, lateral speed, and vertical speed results under different working conditions are compared. After the experiment, the actual captured image is restored using the image distortion correction method. The trajectory tracking algorithm is used to identify the movement trajectory of the circular color block 18 on the side of the boat, the circular color block 19 on the top of the boat, and the circular color block 20 on the bow of the boat, and calculate their movement speed and angle changes to analyze the motion response mechanism of the lifeboat hull 1. At the same time, the analysis results are compared with the data recorded by the gyroscope 13 to verify the accuracy and reliability of the trajectory tracking algorithm.

Claims

1. A lifeboat water entry measuring system based on a trajectory tracking algorithm, characterized in that, The wind wave flow coupling test pool, the drop-type lifeboat release platform, and the drop-type lifeboat water entry test measurement module are included, wherein: The wind wave flow coupling test pool is used for simulating the ocean environment under different working conditions; the drop-type lifeboat release platform is used for simulating the release process of the drop-type lifeboat under different working conditions; The drop-type lifeboat water entry test measurement module is provided with a plurality of high-speed cameras, which respectively shoot the circular color blocks of the lifeboat under different visual angles, record the six-degree-of-freedom changes of the lifeboat, and solve the motion trajectory, speed and attitude angle changes of the lifeboat based on a trajectory tracking algorithm to obtain the motion response mechanism of the lifeboat.

2. The system of claim 1, wherein, The drop-type lifeboat release platform is composed of a swaying platform (3) connected with the lower part of a lifeboat release frame (2) and a lifting system (4) fixed to the bottom of the swaying platform (3).

3. The system of claim 2, wherein, The swaying platform (3) includes a top open platform (31) connected with the lifeboat release frame (2), the top open platform (31) is connected with a coupling (32) through a universal hinge (33) at one end, the other end of the coupling (32) is connected with a bottom platform (35) through the universal hinge (33), and a central control system (34) is located on the bottom platform (35).

4. The system of claim 2, wherein, The lifting system (4) is placed beside a circulating pool (5).

5. The system of claims 1-4, wherein, The plurality of high-speed cameras are respectively arranged above, beside and in front of the circulating pool (5).

6. The system of claim 1, wherein, The drop-type lifeboat water entry test measurement module includes a lifeboat body (1), the bottom of the lifeboat body (1) is provided with a wireless data acquisition instrument (14), and a gyroscope (13) is arranged between the wireless data acquisition instruments (14).

7. The system of claim 6, wherein, A plurality of pressure sensors (15) are arranged in equidistant arrangement on one side of the bow of the lifeboat body (1).

8. A method for measuring the water entry of a lifeboat based on a trajectory tracking algorithm, characterized in that, The method comprises the following steps: The wind wave flow coupling test pool simulates the steady flow field, wind field and wave field environment under different working conditions; The drop-type lifeboat release platform simulates different drop heights, slide angles and slide lengths of the lifeboat; The high-speed cameras under different visual angles respectively shoot the track sliding, air dropping, water entry and floating process of the lifeboat, collect the data in the whole motion process, and obtain the six-degree-of-freedom angle changes of the lifeboat; Based on the trajectory tracking algorithm, the motion trajectory of the circular color block at different positions of the lifeboat is identified, the motion trajectory, speed and attitude angle changes of the lifeboat are solved, and the motion response mechanism of the lifeboat is obtained.

9. The method of claim 8, wherein, Based on the image distortion correction method, the actual shooting picture of the lifeboat is obtained, the threshold segmentation method is used to obtain the binary frame picture, the image morphology principle and the median noise reduction method are used to obtain the color block centroid position; the color block centroid motion response in the test is obtained through the real size conversion of the pixel value and the cyclic solution; based on the trigonometric function relationship, the motion trajectory, speed and attitude angle changes of the lifeboat in the test process are obtained.

10. The method of claim 8, wherein, The lifting leg (43) of the lifting system (4) is linked with the hinge (42) to simulate different falling heights of the lifeboat; the central control system (34) controls the hydraulic expansion of the coupling (32), the universal hinge (33) drives the angle change of the top open platform (31), so as to change the angle of the lifeboat release frame (2), simulate the sliding process of the lifeboat from different slide angles; the release system (22) changes the rotation angle to control the release or fixation of the lifeboat body (1), and simulate the sliding length of the lifeboat body (1).

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