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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%. [ABSTRACT FROM AUTHOR]

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%.

Cracks are one of the most common defects in underwater structures. Failure to repair them in time may end anger the safety of the overall structure and cause major accidents. Traditional crack detection method consumes a lot of man power and material resources with low efficiency. Therefore, an underwater crack detection method based on the target detection algorithm of underwater robot deployment is proposed. Based on YOLOX model, self-attention mechanism and ASPP structure were introduced into the detection network, activation function was improved, and an underwater crack data set was made. The algorithm is tested on the underwater crack data set. The results show that the improved algorithm has lower training loss and faster model convergence. The AP value is increased by 2.07% compared with the original YOLOX model, which is 4.35%higher than YOLOv5. Experiments with data sets of different sizes show that the detection performance of the improved algorithm improves faster with the increase of data sets, and it is more suitable for large-scale data sets. Finally, the algorithm is applied to the detection of underwater cracks and obtains relatively good recognition results. [ABSTRACT FROM AUTHOR]

Due to the functions of a water intake structure, its underwater structure has to be located relatively deep in water. In the silty coastal environment with limited construction water area and unclear sight under the water, it is necessary to optimize the scheme selection and the construction technology according to the geological conditions of the construction site and the construction experience in similar projects around. The technology for underwater pile installation, underwater welding of steel brackets, underwater construction of prefabricated beams and pile cores and underwater installation of prefabricated culverts is emphatically controlled by means of field practice and summary of data of the project, and necessary key measures were formulated for relevant supporting pre-tightening and post-tightening procedures. Reliable quality and safety control of the construction of the underwater structure of water intakes have been finally achieved. [ABSTRACT FROM AUTHOR]

To detect the underwater structure of hydraulic engineerings, conventional approaches usually require manual diving or underwater optical visualization techniques, which however have some inherent shortcomings, such as low efficiency, poor safety, or susceptibility to operational environment interference. To address these limitations, a deep learning-assisted high resolution sonar detection method is presented. Specifically, on-site experiments were first conducted using multi-beam, forward looking sonar, where a deep learning dataset containing various structural apparent damages was then established. Then, a segmentation network incorporating both channel attention mechanism and spatial attention mechanism was proposed. The comparative experimental results indicate that the proposed network exhibits satisfactory segmentation performance while maintaining a relatively fast inference speed. In addition, based on the proposed quantitative size estimation method, dynamic quantitative estimation of the geometric size of the target damage can be further carried out, which is highly beneficial for assessing the extent of damage to the structure. • Observation parameters notably affects sonar results of underwater structures. • Deep learning enables efficient analysis of sonar data of underwater structures. • Geometric information of target damages can be estimated by pixel analysis. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Fuzhou University is the property of Journal of Fuzhou University, Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Coral reefs support a biologically rich ecosystem and are economically invaluable. Unfortunately, due to several reasons including, but not limited to, human activities, global warming effects, and both biotic and abiotic stressors, coral reefs are gradually disappearing from Hawaii’s shorelines. This study introduces novel coral husbandry techniques to help restore injured coral reef habitats. The techniques presented in this work are focused on saving whole coral colonies detached from their bases (via wave action or other physical disturbances) instead of fragmenting existing colonies. Design, fabrication, assembly, and installation details of an in-water Fiberglass Reinforced Plastic (FRP) coral nursery structure are discussed in this work. Material selection and novel design of the coral nursery were specifically adapted to physical ocean conditions of the south shore of O’ahu, Hawaii. Factors such as safety, practicality, cost efficiency, transportation, installation, and attachment of coral colonies for systematic restoration efforts, while maintaining minimal environmental impact, were considered to design and build the coral nursery. Structural fatigue was investigated via finite element methods considering underwater loading and boundary conditions. FRP was chosen for the material by a trade-off comparison method. This structure was built, assembled, and deployed in south shore O’ahu, Hawaii, in April 2018. This study demonstrated the design, engineering, and build of a durable coral nursery structure.

The local cylindrical acoustic holography technology is introduced, and its application in identifying and locating the column is introduced. The implementation algorithm of local cylindrical holographic reconstruction is given. In engineering operations, columnar sound sources such as electric motors, water pipes, and underwater structures are common noise sources in engineering. Therefore, this paper is of great significance for the location identification and control of such sound sources. The simulation results show that the proposed local cylindrical acoustic holography algorithm is useful to identify the noise source and reconstruct the sound field correctly. [ABSTRACT FROM AUTHOR]

Recently, the demand for higher performing underwater structures under diverse conditions has increased. Examples include improved precision and speed of the position control of robot manipulators. To prevent the control spillover problems when active controls are used, a control system is typically constituted with a low-pass filter to eliminate all modes except for the target modes. However, experimentally measuring the dynamic properties of an underwater structure in an environment where the structure and a fluid continuously influence each other is difficult. We have recently proposed a noncontact vibration testing method for dynamic characterizations of underwater structures in which the response to a laser ablation excitation force is measured by laser Doppler vibrometer. Integrating passive control using a vibration-damping material affixed onto the underwater structure and active control constituted with the low-pass filter may realize a more cost-effective system. To develop this combined control into a practical method, the reliability of the measured frequency response function must be validated. Additionally, the applicable frequency range must be expanded to encompass the high-frequency region (several tens of kHz) so that the vibration suppression quality of underwater structures can be evaluated. Herein we quantify the effect of random measurement errors on the measured frequency response function with a reliability factor based on the concept of coherence functions. Using the measured frequency response function with a reliability factor, we demonstrated that our method can evaluate passive vibration suppression effect of an underwater structure with a damping material in high-frequency ranges up to 20 kHz. [ABSTRACT FROM AUTHOR]

Hydraulic factors account for a large part of the causes of bridge collapse. Due to the nature of the underwater environment, quick and accurate inspection is required when damage occurs. In this study, we developed a 2 MHz side scan sonar sensor module and effective operation technique by improving the limitations of existing sonar. Through field tests, we analyzed the correlation of factors affecting the resolution of the sonar data such as the angle of survey, the distance from the underwater structure and the water depth. The effect of the distance and the water depth and the structure on the survey angle was 66~82%. We also derived the relationship between these factors as a regression model for effective operating techniques. It is considered that application of the developed 2 MHz side scan sonar and its operation method could contribute to prevention of bridge collapses and disasters by quickly and accurately checking the damage of bridge substructures due to hydraulic factors. [ABSTRACT FROM AUTHOR]

Guided waves can propagate along the surface of a solid structure at a large distance with little attenuation. Hidden defects within the structure can be detected based on the abnormal reflection or transmission of guided waves. The distance between the defect and the transducer can be calculated according to the arrival time of the wave package and wave speed. Therefore, the guided wave speed should be known prior. However, existing analytical models can only predict the guided wave speed along the surface of a horizontal solid covered by a liquid layer. These models are not suited for the characterization of ultrasonic nondestructive testing of ship hulls, sluice gates, water dams, bridge piers, etc. In this study, an analytical model is proposed for the guided wave propagation along a vertical solid partially inserted into a horizontal liquid layer. A secular equation is derived and solved to predict the guided wave speed at the vertical solid–liquid interface. Twenty finite element simulations and thirty-three physical experiments are conducted on different materials with different dimensions by using varying incident frequencies. The results demonstrate that the proposed model can provide accurate analytical wave speeds to guide the nondestructive testing and structural health monitoring of underwater structures. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this paper, an underwater structure is modeled as a cylindrical shell with internal bulkheads, and closed by a truncated conical shell, and it consists of metal substrate and sound absorbing coating, whose FGM core is considered. Suppose the inner cavity and outer space of the structure are filled with air and fluid mediums, the mechanical response of the underwater structure is calculated with Galerkin method while the acoustic response is investigated by means of the Helmholtz integral. Some numerical examples are given and the effect of geometrical size and material parameters on mechanical and acoustic response is discussed. [ABSTRACT FROM AUTHOR]

Noise reduction by means of applying decoupling coating on underwater structures is commonly used in the marine field. Assuming decoupling coating as viscoelastic fluid, a vibration and acoustics model of a simply supported rectangular plate covered by decoupling coating is presented. The model simulates the vibration and acoustic response of the structure which is water-loaded on one side and air backed on the other. The characteristics of vibration and acoustics reduction by the decoupling coating are analyzed, and the influences of the physical parameters of decoupling coating to vibration velocity of base plate and sound radiation power are researched. The results show that: for single flexural mode of plate, 'plate-decoupling coating-water layer' is similar to two-freedom degree system, which has two resonant frequencies and an anti-resonant frequency, and dynamic absorber characteristics are introduced by decoupling coating. Dynamic absorber characteristics could be used to reduce the low-frequency vibration and underwater radiation noise by selecting suitable parameters of decoupling coating. [ABSTRACT FROM AUTHOR]

Abstract: The maintenance and repair of reinforced concrete structures, especially those submerged in the sea-water require effective inspection and monitoring techniques for assessing the state of corrosion in the reinforcement material. An underwater inspection system was developed which is able to monitor the corrosion of the reinforcement. The system is composed of a remotely operating vehicle (ROV) equipped with the sealed tube neutron generator (NG). By rotating the NG and by using the associated alpha particle technique it is possible to measure the concrete cover thickness together with the reinforcing bar diameter. The possibility of estimating the carbon and chloride contents in the concrete was investigated. Iron plates of different thickness, covered by 6 cm thick concrete block, were successfully detected and the thickness of the concrete cover was estimated. In addition, reinforcing bar of one and 3 cm in diameter were identified and measured. All measurements could be performed without cleaning the concrete surface from fouling material. [Copyright &y& Elsevier]

In order to conduct an effective and reasonable heat transfer analysis, a real-time thermal test platform was established, which consists of two flow loops, the heating system, the data acquisition system, the automatic data processing software and the relative piping system. Based on this platform, a typical T-type deadleg and a gate valve assembly are adopted to investigate their heat transfer characteristics. The experiment data are compared with the numerical calculation with great good agreements. For further application, this real-time thermal test platform could be used for cool down analysis and thermal insulation assessment. Ultimately, promotional values for similar and even much larger scale complex underwater structures could be found in this study. [ABSTRACT FROM AUTHOR]

Underwater cylindrical shell structures have been found a wide of application in many engineering fields, such as the element of marine, oil platforms, etc. The coupled vibration analysis is a hot issue for these underwater structures. The vibration characteristics of underwater structures are influenced not only by hydrodynamic pressure but also by hydrostatic pressure corresponding to different water depths. In this study, an acoustic finite element method was used to evaluate the underwater structures. Taken the hydrostatic pressure into account in terms of initial stress stiffness, an acoustical fluid-structure coupled analysis of underwater cylindrical shells has been made to study the effect of hydrodynamic pressures on natural frequency and sound radiation. By comparing with the frequencies obtained by the acoustic finite element method and by the added mass method based on the Bessel function, the validity of present analysis was checked. Finally, test samples of the sound radiation of stiffened cylindrical shells were acquired by a harmonic acoustic analysis. The results showed that hydrostatic pressure plays an important role in determining a large submerged body motion, and the characteristics of sound radiation change with water depth. Furthermore, the analysis methods and the results are of significant reference value for studies of other complicated submarine structures. [ABSTRACT FROM AUTHOR]

In ocean engineering and coastal environmental studies, local scour around a submerged structure is a typical issue, which is affected by the inclination of the structure. To investigate the effect of inclination directions and angles on flow structure and the bed morphology, a three-dimensional numerical model of a submerged inclined cylinder was established. In this model, the hydrodynamics are solved from the RANS (Reynolds-averaged Navier–Stokes) equations closed with the RNG k-ε turbulence model, while the bed morphology evolution is captured by the sediment transport model. In the case of vertical-cylinder scour, the simulation results agree well with existing laboratory experiments. In the cases of inclined-cylinder scour, the results show that the inclination direction not only changes the intensity and the location of the downflow but also modulates the pattern of the horseshoe vortex in front of the cylinder, thus influencing the local scour depth and the morphology of the bed. Compared with the case of vertical cylinder, the scour around an upstream-inclined cylinder is deeper, mainly due to the enhancement of downflow in front of the cylinder. The scour around a downstream-inclined cylinder is shallower and broader due to the weakened downflow and accelerated incoming flow. The maximum scour depth decreases with the inclination angle in the downstream-inclination case. In the upstream-inclination case, the maximum scour depth does not vary monotonously with the inclination angle, which results from a competitive effect of the horseshoe vortex and downflow in the front of the cylinder. [ABSTRACT FROM AUTHOR]

Hydraulic factors account for a large part of the causes of bridge collapse. Due to the nature of the underwater environment, quick and accurate inspection is required when damage occurs. In this study, we developed a 2 MHz side scan sonar sensor module and effective operation technique by improving the limitations of existing sonar. Through field tests, we analyzed the correlation of factors affecting the resolution of the sonar data such as the angle of survey, the distance from the underwater structure and the water depth. The effect of the distance and the water depth and the structure on the survey angle was 66~82%. We also derived the relationship between these factors as a regression model for effective operating techniques. It is considered that application of the developed 2 MHz side scan sonar and its operation method could contribute to prevention of bridge collapses and disasters by quickly and accurately checking the damage of bridge substructures due to hydraulic factors.