Improved Dark Channel Defogging Algorithm for Defect Detection in Underwater Structures

In order to flexibly monitor the underwater structure in the complex underwater environments, a small multi-thrusters AUV (Autonomous Underwater vehicle) has been designed with the attitude fusions of monocular vision and IMU (Inertial Measurement Unit). The tasks for detecting the surface faults of the underwater structures in designated area, such as large vessel propellers and offshore oil rig, determine the functional requirements of underwater image processing, flexible attitude control and autonomous navigation for AUV. In this paper, we present a novel design scheme of AUV, including the AUV hardware platform, the corresponding hydrodynamic model for “SAIL”, and the modified attitude fusion algorithm based on monocular vision and IMU. Finally, the experiments are carried out to evaluate the performances of the AUV.

A pulsed-laser ablation method for non-contact experimental vibration analysis of completely submerged underwater structures is proposed. Although impact testing with an impulse hammer is commonly used for vibration analysis due to its simplicity, impact testing has limited use in underwater conditions. An input-detection-free frequency response function measurement in water will greatly contribute to the development of high-precision and high-speed positioning autonomous underwater vehicles, underwater vehicle-manipulators, underwater robots, submarines, etc., which are used in dangerous conditions (e.g., deep oceans, under ice, and nuclear reactor plants). To achieve these high-performance underwater systems, vibrations due to hydrodynamic parameters (such as added mass, buoyant force, drag force, and damping coefficient) should be suppressed, and vibration tests should be conducted on the actual equipment submerged in water. The proposed method yields the frequency response function by applying a pulsed-laser-ablation excitation force to an underwater structure and measuring the output using a laser Doppler vibrometer. Because the direction, strength, and effective duration of the pulsed-laser-ablation force are essentially constant, this force can be estimated by measuring these properties in advance. Hence, the proposed method realizes input-detection-free frequency response function measurements in underwater conditions.

Diver and submersible navigation using acoustic techniques in and around complex underwater structures such as drilling and production platforms is complicated by the effects of multipath acoustic propagation. The research described in this paper is concerned with the investigation of techniques to overcome such effects, thereby leading to navigation systems which yield accurate locations of divers and submersibles operating within the core of the underwater structure. Several strategies are being studied including fixed transponder systems placed at prescribed locations in the structure and systems with tracking pencil-beams. The paper describes a computer simulation of a representative underwater structure which was developed for the study of the interaction between structural members and propagating acoustic beams generated by transponders mounted on and around the structure. It evaluates the detection probability of a diver or submersible operating within the structure as a function of acoustic source coordinates and yields information on optimal placement of acoustic sources and gives additional insight into the nature of the multipath transmission effect. INTRODUCTION A requirement exists for systems which can facilitate accurate navigation and location of divers or RCVs within the vicinity of offshore structures to allow routine inspection and maintenance. 1,2 Currently available short base-line or long base-line transponder oriented navigational systems 3 cannot be directly employed as they rely entirely on line of sight communication Transponder navigation systems compute locations on the basis of time-elapse measurements which are only valid along straight line paths. Within an off-shore structure, with its multiple structural members, signals to and from omni-directional transponders will be heavily corrupted by multipath transmission effects due to multiple reflections from various members, as well as by additive acoustic noise interference which may be both random and impulsive in nature, and will lead to ambiguous computations of distance based purely on time elapse measurements. A system which can be considered as more reliable in the underwater environment of the offshore structure than an omni-directional transponder system is an Inertial Navigation System. However two factors militate against such a system being employed for diver/RCV support. The first is cost, the second is gyroscopic drift which requires frequent compensation, and is particularly critical in the Azimuth gyroscope. This paper presents details of research being conducted at Strathclyde University towards the development of an accurate and reliable acoustic navigation system which employs some novel techniques of analysis, signal processing, and simulation to overcome the disadvantages outlined above. Several different strategies for system configuration and diver location are being currently pursued. After a discussion of some of these strategies, which are based on the location of sensors, results on the optimisation of these locations for representative offshore structures will be covered, and an ensuing measure of performance probability of detection for varying numbers of sensors-will be developed. The work on optimisation of sensor location and the attendant detection probabilities is extremely important as it leads to a reliable and robust system configuration for any specified offshore structure.

The integrate of underwater structure of dams and bridges are very important for the safety of the projects. However, due to the complex flow field near the underwater structure, it is a challenge for the underwater robot to maintain stable near the underwater structures when performing inspection tasks. Moreover, it is difficult for underwater robots to absorb on the surface of underwater structures due to rough surface. This paper proposes a design of an adsorption track wheel for underwater wall-climbing robot, which combines the swirl suction cup and track wheel. The relationship between the water flow velocity, the wall gap and the suction cup adsorption force are analyzed. The influence of the surface curvature diameter of the structure and the diameter of the suction cup on the suction force is explored, and the structure of the suction cup is optimized to resist the influence of the water flow on the suction cup as much as possible while considering the flow velocity. After the suction cup improved, a prototype is designed and built. The final experiment demonstrates that the track wheel can provide sufficient adsorption force and friction force, which helps the structure to resist the water flow velocity up to 2.5m/s. Finally, it proposes the track wheel prototype can provide stable adsorption on the surface of underwater buildings for complex flow field.

This paper comprehensively summarizes and discusses the latest research progress in the underwater concrete structure damage repair technology of infrastructures. The prompt application of underwater concrete structure repair technology can effectively deal with the damaged parts of underwater concrete structures, and it can ensure the safe and stable operation of infrastructure and extend its service life. Firstly, this study uses bibliometric methods to analyze the characteristics of the literature on research into underwater concrete repair in the past 30 years (1993–2023), and expounds the research status and hotspots of this field. Then, we conduct a comprehensive classification and discussion of the underwater concrete structure damage repair technologies at the current stage. This technology can be divided into two major types: direct underwater type and dry environment type. Further, the development history of these technologies is systematically sorted out and, combined with practical engineering application cases, the operation processes, applicability, limitations, and economy of these technologies are analyzed. Finally, the challenges and future development trends of the current underwater concrete structure damage repair technology are pointed out, which provides a direction for future research on the intelligent maintenance of underwater concrete structures.

Abstract: In recent years, a potential interest has been developed in exploring and enhancing the quality of underwater images. The captured underwater images often experience scattering and high levels of noise due to the properties of light transit within the water and the biotic movement that occurs inside the ocean bottom. Underwater cameras or devices were fitted inside the unmanned underwater vehicles (UUVs), autonomous underwater vehicles (AUVs), remotely operated vehicles (ROVs), ocean detector networks, etc to see the ocean bottom. Despite being a crucial detector for keeping an eye on underwater landscapes, modern underwater camera sensors or detectors contain a number of problems. Numerous solutions to the issues with conventional underwater photography have been put out during the last five years. With the help of the number of contributions and difficulties reported by more than 40 researchers in their research article, this study focused to mention the current underwater image processing methods. This article represents an overview of numerous underwater image-processing techniques utilized, including underwater picture de-scattering, underwater image colour refurbishment, and underwater image aspect evaluations. Also, the latest trends, problems, and challenges for creating and processing underwater image sensors were discussed.

Recently, the demand for atypical structures with functions and sculptural beauty is increasing in the construction industry. Existing mold-based structure production methods have many advantages, but building complex atypical structures represents limitations due to the cost and technical characteristics. Production methods using molding are suitable for mass production systems, but production cost, construction period, construction cost, and environmental pollution can occur in small quantity batch production. The recent trend in the construction industry calls for new construction methods of customized small quantity batch production methods that can produce various types of sophisticated structures. In addition to the economic effects of developing related technologies of 3D Concrete Printers (3DCP), it can enhance national image through the image of future technology, the international status of the construction civil engineering industry, self-reliance, and technology export. Until now, 3DCP technology has been carried out in producing and utilizing residential houses, structures, etc., on land or manufacturing on land and installing them underwater. The final purpose of this research project is to produce marine structures by directly printing various marine structures underwater with 3DCP equipment. Compared to current underwater structure construction techniques, constructing structures directly underwater using 3DCP equipment has the following advantages: 1) cost reduction effects: 2) reduction of construct time, 3) ease of manufacturing amorphous underwater structures, 4) disaster prevention effects. The core element technology of the 3DCP equipment is to extrude the transferred composite materials at a constant quantitative speed and control the printing flow of the materials smoothly while printing the output. In this study, the extruding module of the 3DCP equipment operates underwater while developing an extruding module that can control the printing flow of the material while extruding it at a constant quantitative speed and minimizing the external force that can occur during underwater printing. The research on the development of 3DCP equipment for printing concrete structures underwater and the preliminary experiment of printing concrete structures using high viscosity low-flow concrete composite materials is explained.

This paper presents an approach of predicting the vibration and acoustic response of ring-stiffened cylindrical shell in infinite underwater domain using the so-called acoustic transfer vector (ATV) technique. It is verified that the ATV is efficient in solving the vibration and acoustic response of the underwater structures by comparing with the results obtained from standard boundary element method (BEM). Furthermore, the influence of the number of measurements is also discussed in the acoustic computation according three different schemes, then the optimal scheme can be obtained and it is very meaningful in acoustic response prediction for underwater structure.

In certain precision work scenarios, underwater robots require the ability to adhere to surfaces in order to perform tasks effectively. An efficient and stable suction device plays a pivotal role in the functionality of such underwater robots. The vortex suction cup, distinguished by its uncomplicated design, high suction efficiency, and capability for non-contact adhesion, holds significant promise for integration into underwater robotic systems. This paper presents a novel design for a vortex suction cup and investigates its suction force and torque when encountering surfaces with varying curvature radii using Computational Fluid Dynamics (CFD) simulations and experimental testing. These findings offer valuable insights for the development of robots capable of adapting to underwater structures of different dimensions. Results from both experiments and simulations indicate that reducing the curvature radius of the adhered surface results in a decrease in suction force and an increase in torque exerted on the suction cup. As the adhered surface transitions from flat to a curvature radius of 150 mm, the adhesion force of our proposed vortex suction cup decreases by approximately 10%, while the torque increases by approximately 20% to 30%. Consequently, the adhesion efficiency of the suction cup decreases by about 25% to 30%.

Pose Estimation Considering an Uncertainty Model of Stereo Vision for In-Water Ship Hull Inspection

A turbulent boundary layer develops on the surface of submerged bodies in motion; these layers consist of complex flows and interact with the structure causing turbulent boundary layer induced noise due to fluid-structure interaction. Recently, although the research on such noise has attracted great interest in the naval fields, owing to the focus on the competitive development of low-noise naval ships, the limitations corresponding to the application of methods developed in aeroacoustics for underwater structures having lower convection speed of turbulence and faster sound speed along with insufficient environments to conduct experiments restrained to subjects of simple structures at high frequency. To overcome the abovementioned limitations and study the noise characteristics for ship hull design, in this research, methods to analyze the noise radiated due to turbulent flow on the complex underwater structure are developed using energy flow analysis methods for vibro-acoustic calculations. For estimation of the input hydrodynamic forces, wall pressure fluctuation spectrum on the surface is obtained from turbulent boundary layer properties to acquire sufficient resolutions. The vibrational response of the structure is calculated using energy flow analysis incorporating the finite element method for structural forces estimated as input power. The acoustical response coupled with the vibrational response is obtained using the calculated vibrational energy density with the boundary element method in combination with the energy flow analysis, taking advantages of the fact that the methods share the common energy variables. Developed methods are validated with a case of broadband noise radiated from a plate. Using the procedures, numerical estimation and analysis of acoustic performance are performed for trimaran ship hull designs with steady-state computational fluid dynamics to demonstrate the method’s usability as an assessment tool in the early design stage.

Taking an underwater shell structure as engineering background, the Improved Genetic Algorithms (IGAs) is applied to detect the structural damage by static response data acquisition in the paper. Firstly, region water-level and finite point strains of the underwater shell structure are measured. Then, the Genetic Algorithms (GAs) are optimized. Finally, the structural damage location and degree are identified by comparison between measurement strains and calculation ones. When the measured strains are approached most close to the one among all the calculation strains, the structural damage condition is determined. In order to diagnose the large-scale structural damage by GAs, the decoding the damage location and damage index at same time is proposed, as well as, fine-tuning of variables and niche technique are also introduced to improve the convergence efficiency of GAs.

Crack detection is an important issue in the health monitoring and performance evaluation of concrete structures. Based on the heat transfer theory, a temperature tracer method and a monitoring system for crack detection in underwater concrete structures are presented in this paper. The system is composed of an integrated sensing and heating system, a monitoring tube, and multiple casing tubes. The inner diameter of the casing tube should be larger than the outer diameter of the monitoring tube so that there is a certain gap between the casing tube and the monitoring tube to form a cavity. Water fills the cavity along the crack face when the underwater concrete structure cracks, resulting in a change in the surrounding medium at the cracked site. Thus, the cooling rate of the heat source in the monitoring tube corresponding to the cracked site will be accelerated. Crack identification can be done based on a comparative analysis of the cooling curves of the heat source in the uncracked and cracked states. The effects of cavity geometry size and intensity of heat source on crack identification are studied using numerical simulations and crack detection tests. Both simulations and test results confirm the feasibility of the proposed crack detection method.

Region-specialized underwater image restoration in inhomogeneous optical environments

The paper explores the problems of restoring underwater images exposed to distortions in the form of color and contrast deformations, the presence of haze, etc., arising from the interaction of optical radiation with the aquatic environment. Restoring underwater images is a non-trivial task due to the large variability of the parameters of the aquatic environment and photography conditions. The proposed method, unlike other underwater image recovery algorithms based on an imaging model, is not based on a simplified exponential Beer-Lambert law for estimating optical radiation attenuation in water, but on a more accurate physical approach that simulates the propagation of optical rays in water using the Monte Carlo method, taking into account the main parameters the water environment and the camera. The results of numerical simulation of optical ray propagation in an aquatic environment are used for image processing in the spatial domain by editing the histograms of each image channel in the RGB color space. To test the developed algorithm, 6 real underwater images were selected obtained under various lighting conditions (natural and artificial) and various parameters of the aquatic environment (clear ocean and turbid coastal water). For the purpose of qualitative and quantitative analysis of the obtained results, the following similar underwater image processing methods were used: Fusion, UDCP IATP, Retinex, HE, and UWB VCSE. The Underwater Colour Image Quality Evaluation Metric (UCIQE) and Underwater Image Quality Measure (UIQM) indicators were used to quantify the results obtained. The results of the qualitative assessment demonstrate the high efficiency of the proposed method: regardless of the conditions of the initial image parameters, the application of the developed method improves visual perception and does not lead to excessive contrast enhancement, color distortion, loss of detail, the appearance of artifacts, etc. Quantification of underwater image processing results demonstrates comparable and superior results when comparing the efficiency of the algorithm with similar methods. For the UCIQE parameter, the developed method provided an improvement from 9 % to 51 % relative to the parameter value for the original image, while similar methods demonstrated results from minus 10 % to 82 %. For the UIQM parameter, the developed method provided an improvement from 24 % to 99 % relative to the parameter value for the original image, while similar methods demonstrated results from minus 10 % to 123 %. Unlike analogues, the developed method did not demonstrate the worst values of the UCIQE and UIQM parameters for any processed image, which indicates the stability of the method regardless of the parameters of the aquatic environment and shooting conditions. By dividing the developed method into preliminary and main stages, high image processing speed is ensured: 0.073 seconds for images with a resolution of 400 × 300 pixels and from 8.02 to 8.23 seconds for images with a resolution of 5184 × 3456 pixels. Similar methods demonstrated values from 0.19 to 10.81 seconds for an image with a resolution of 400 × 300 pixels and from 7.65 to 937.83 seconds for an image with a resolution of 5184 × 3456 pixels. The introduction of the proposed method into the geological exploration will increase their efficiency and reliability, and will provide more accurate data for further exploration of solid mineral deposits. Such technique integrated into the machine vision system of underwater vehicles will significantly expand their functionality by enabling automation of operations and improving the efficiency of recognition systems.