Underwater pipeline inspection plays a vital role in the proactive maintenance and management of critical marine infrastructure and subaquatic systems.However,the inspection of underwater pipelines presents a challeng...Underwater pipeline inspection plays a vital role in the proactive maintenance and management of critical marine infrastructure and subaquatic systems.However,the inspection of underwater pipelines presents a challenge due to factors such as light scattering,absorption,restricted visibility,and ambient noise.The advancement of deep learning has introduced powerful techniques for processing large amounts of unstructured and imperfect data collected from underwater environments.This study evaluated the efficacy of the You Only Look Once(YOLO)algorithm,a real-time object detection and localization model based on convolutional neural networks,in identifying and classifying various types of pipeline defects in underwater settings.YOLOv8,the latest evolution in the YOLO family,integrates advanced capabilities,such as anchor-free detection,a cross-stage partial network backbone for efficient feature extraction,and a feature pyramid network+path aggregation network neck for robust multi-scale object detection,which make it particularly well-suited for complex underwater environments.Due to the lack of suitable open-access datasets for underwater pipeline defects,a custom dataset was captured using a remotely operated vehicle in a controlled environment.This application has the following assets available for use.Extensive experimentation demonstrated that YOLOv8 X-Large consistently outperformed other models in terms of pipe defect detection and classification and achieved a strong balance between precision and recall in identifying pipeline cracks,rust,corners,defective welds,flanges,tapes,and holes.This research establishes the baseline performance of YOLOv8 for underwater defect detection and showcases its potential to enhance the reliability and efficiency of pipeline inspection tasks in challenging underwater environments.展开更多
In this investigation,a hybrid approach integrating the IDDES turbulence model and FW-H is employed to forecast the hydroacoustic of the rim driven thruster(RDT)under non-cavitation and uniform flow conditions at vary...In this investigation,a hybrid approach integrating the IDDES turbulence model and FW-H is employed to forecast the hydroacoustic of the rim driven thruster(RDT)under non-cavitation and uniform flow conditions at varying loading conditions(J=0.3 and J=0.6).It is revealed that the quadrupole term contribution in the P-FWH method significantly affects the monopole term in the low-frequency region,while it mainly affects the dipole term in the high-frequency region.Specifically,the overall sound pressure levels(SPL)of the RDT using the P-FWH method are 2.27 dB,10.03 dB,and 16.73 dB at the receiving points from R1 to R3 under the heavy-loaded condition,while they increase by 0.67 dB at R1,and decrease by 14.93 dB at R2,and 22.20 dB at R3,for the light-loaded condition.The study also utilizes the pressure-time derivatives to visualize the numerical noise and to pinpoint the dynamics of the vortex cores,and the optimization of the grid design can significantly reduce the numerical noise.The computational accuracy of the P-FWH method can meet the noise requirements for the preliminary design of rim driven thrusters.展开更多
Vortex-induced vibration(VIV)of an underwater manipulator in pulsating flow presents a notable engineering problem in precise control due to the velocity variation in the flow.This study investigates the VIV response ...Vortex-induced vibration(VIV)of an underwater manipulator in pulsating flow presents a notable engineering problem in precise control due to the velocity variation in the flow.This study investigates the VIV response of an underwater manipulator subjected to pulsating flow,focusing on how different postures affect the behavior of the system.The effects of pulsating parameters and manipulator arrangement on the hydrodynamic coefficient,vibration response,motion trajectory,and vortex shedding behaviors were analyzed.Results indicated that the cross flow vibration displacement in pulsating flow increased by 32.14%compared to uniform flow,inducing a shift in the motion trajectory from a crescent shape to a sideward vase shape.In the absence of interference between the upper and lower arms,the lift coefficient of the manipulator substantially increased with rising pulsating frequency,reaching a maximum increment of 67.0%.This increase in the lift coefficient led to a 67.05%rise in the vibration frequency of the manipulator in the in-line direction.As the pulsating amplitude increased,the drag coefficient of the underwater manipulator rose by 36.79%,but the vibration frequency in the cross-flow direction decreased by 56.26%.Additionally,when the upper and lower arms remained in a state of mutual interference,the cross-flow vibration amplitudes of the upper and lower arms were approximately 1.84 and 4.82 times higher in a circular-elliptical arrangement compared to an elliptical-circular arrangement,respectively.Consequently,the flow field shifted from a P+S pattern to a disordered pattern,disrupting the regularity of the motion trajectory.展开更多
The phenomenon of attenuation and scattering of light propagating in water leads to such problems as color deviation and blur in underwater imaging.These problems bring great challenges to the subsequent feature match...The phenomenon of attenuation and scattering of light propagating in water leads to such problems as color deviation and blur in underwater imaging.These problems bring great challenges to the subsequent feature matching,target recognition and other tasks.Therefore,this paper proposes an underwater image enhancement method by double compensation with comparative adjustment or edge reinforcement.The experiments have found that the proposed method has good underwater color image quality evaluation(UCIQE)value,underwater image quality measures(UIQM)value,and the number of feature matching points.This demonstrates that the proposed method has good color correction ability for underwater images with different attenuation levels,where the processed images have more details suitable for feature matching.展开更多
Underwater imaging is frequently influenced by factors such as illumination,scattering,and refraction,which can result in low image contrast and blurriness.Moreover,the presence of numerous small,overlapping targets r...Underwater imaging is frequently influenced by factors such as illumination,scattering,and refraction,which can result in low image contrast and blurriness.Moreover,the presence of numerous small,overlapping targets reduces detection accuracy.To address these challenges,first,green channel images are preprocessed to rectify color bias while improving contrast and clarity.Se-cond,the YOLO-DBS network that employs deformable convolution is proposed to enhance feature learning from underwater blurry images.The ECA attention mechanism is also introduced to strengthen feature focus.Moreover,a bidirectional feature pyramid net-work is utilized for efficient multilayer feature fusion while removing nodes that contribute minimally to detection performance.In addition,the SIoU loss function that considers factors such as angular error and distance deviation is incorporated into the network.Validation on the RUOD dataset demonstrates that YOLO-DBS achieves approximately 3.1%improvement in mAP@0.5 compared with YOLOv8n and surpasses YOLOv9-tiny by 1.3%.YOLO-DBS reduces parameter count by 32%relative to YOLOv8n,thereby demonstrating superior performance in real-time detection on underwater observation platforms.展开更多
Unlike conventional spherical charges,a shaped charge generates not only a strong shock wave and a pulsating bubble,but also a high strain rate metal jet and a ballistic wave during the underwater explosion.They show ...Unlike conventional spherical charges,a shaped charge generates not only a strong shock wave and a pulsating bubble,but also a high strain rate metal jet and a ballistic wave during the underwater explosion.They show significant characteristic differences and couple each other.This paper designs and conducts experiments with shaped charges to analyze the complicated process.The effects of liner angle and weight of shaped charge on the characteristics of metal jets,waves,and bubbles are discussed.It is found that in underwater explosions,the shaped charge generates the metal jet accompanied by the ballistic wave.Then,the shock wave propagates and superimposes with the ballistic wave,and the generated bubble pulsates periodically.It is revealed that the maximum head velocity of the metal jet versus the liner angle a and length-to-diameter ratio k of the shaped charge follows the laws of 1/(α/180°)^(0.55)andλ^(0.16),respectively.The head shape and velocity of the metal jet determine the curvature and propagation speed of the initial ballistic wave,thus impacting the superposition time and region with the shock wave.Our findings also reveal that the metal jet carries away some explosion products,which hinders the bubble development,causing an inward depression of the bubble wall near the metal jet.Therefore,the maximum bubble radius and pulsation period are 5.2%and 3.9%smaller than the spherical charge with the same weight.In addition,the uneven axial energy distribution of the shaped charge leads to an oblique bubble jet formation.展开更多
Researchers have achieved notable advancements over the years in exploring ship damage and stability resulting from underwater explosions(UNDEX).However,numerous challenges and open questions remain in this field.In t...Researchers have achieved notable advancements over the years in exploring ship damage and stability resulting from underwater explosions(UNDEX).However,numerous challenges and open questions remain in this field.In this study,the research progress of UNDEX load is first reviewed,which covers the explosion load during the shock wave and bubble pulsation stages.Subsequently,the research progress of ship damage caused by UNDEX is reviewed from two aspects:contact explosion and noncontact explosion.Finally,the research progress of ship navigation stability caused by UNDEX is reviewed from three aspects:natural factors,ship’s internal factors,and explosion factors.Analysis reveals that most existing research has focused on the damage to displacement ships caused by UNDEX.Meanwhile,less attention has been paid to the damage and stability of non-displacement ships caused by UNDEX,which are worthy of discussion.展开更多
Bubbles play crucial roles in various fields,including naval and ocean engineering,chemical engineering,and biochemical engineering.Numerous theoretical analyses,numerical simulations,and experimental studies have bee...Bubbles play crucial roles in various fields,including naval and ocean engineering,chemical engineering,and biochemical engineering.Numerous theoretical analyses,numerical simulations,and experimental studies have been conducted to reveal the mysteries of bubble motion and its mechanisms.These efforts have significantly advanced research in bubble dynamics,where theoretical study is an efficient method for bubble motion prediction.Since Lord Rayleigh introduced the theoretical model of single-bubble motion in incompressible fluid in 1917,theoretical studies have been pivotal in understanding bubble dynamics.This study provides a comprehensive review of the development and applicability of theoretical studies in bubble dynamics using typical theoretical bubble models across different periods as a focal point and an overview of bubble theory applications in underwater explosion,marine cavitation,and seismic exploration.This study aims to serve as a reference and catalyst for further advancements in theoretical analysis and practical applications of bubble theory across marine fields.展开更多
Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of sh...Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.展开更多
It is difficult to improve both energy consumption and detection accuracy simultaneously,and even to obtain the trade-off between them,when detecting and tracking moving targets,especially for Underwater Wireless Sens...It is difficult to improve both energy consumption and detection accuracy simultaneously,and even to obtain the trade-off between them,when detecting and tracking moving targets,especially for Underwater Wireless Sensor Networks(UWSNs).To this end,this paper investigates the relationship between the Degree of Target Change(DoTC)and the detection period,as well as the impact of individual nodes.A Hierarchical Detection and Tracking Approach(HDTA)is proposed.Firstly,the network detection period is determined according to DoTC,which reflects the variation of target motion.Secondly,during the network detection period,each detection node calculates its own node detection period based on the detection mutual information.Taking DoTC as pheromone,an ant colony algorithm is proposed to adaptively adjust the network detection period.The simulation results show that the proposed HDTA with the optimizations of network level and node level significantly improves the detection accuracy by 25%and the network energy consumption by 10%simultaneously,compared to the traditional adaptive period detection schemes.展开更多
Underwater target detection is extensively applied in domains such as underwater search and rescue,environmental monitoring,and marine resource surveys.It is crucial in enabling autonomous underwater robot operations ...Underwater target detection is extensively applied in domains such as underwater search and rescue,environmental monitoring,and marine resource surveys.It is crucial in enabling autonomous underwater robot operations and promoting ocean exploration.Nevertheless,low imaging quality,harsh underwater environments,and obscured objects considerably increase the difficulty of detecting underwater targets,making it difficult for current detection methods to achieve optimal performance.In order to enhance underwater object perception and improve target detection precision,we propose a lightweight underwater target detection method using You Only Look Once(YOLO)v8 with multi-scale cross-channel attention(MSCCA),named YOLOv8-UOD.In the proposed multiscale cross-channel attention module,multi-scale attention(MSA)augments the variety of attentional perception by extracting information from innately diverse sensory fields.The cross-channel strategy utilizes RepVGGbased channel shuffling(RCS)and one-shot aggregation(OSA)to rearrange feature map channels according to specific rules.It aggregates all features only once in the final feature mapping,resulting in the extraction of more comprehensive and valuable feature information.The experimental results show that the proposed YOLOv8-UOD achieves a mAP50 of 95.67%and FLOPs of 23.8 G on the Underwater Robot Picking Contest 2017(URPC2017)dataset,outperforming other methods in terms of detection precision and computational cost-efficiency.展开更多
Cu/Al composite plates were fabricated using rolling and underwater explosive welding techniques,separately,to compare their interfacial microstructures and mechanical performance.Interface morphology,grain orientatio...Cu/Al composite plates were fabricated using rolling and underwater explosive welding techniques,separately,to compare their interfacial microstructures and mechanical performance.Interface morphology,grain orientation,grain boundary characteristics,and phase distribution were analyzed through optical microscope,scanning electron microscope,and electron backscattered diffractometer.Mechanical properties were assessed using tensile shear tests,90°bending tests,and hardness measurements.Vickers hardness and nanoindentation test results further provided information on the hardness distributions.Results indicate that the diffusion layer in rolled Cu/Al composites is relatively fragile,while that produced by underwater explosive welding features a diffusion layer of approximately 18μm in thickness,which is metallurgically bonded through atomic diffusion.The tensile shear strength of these composites ranges from 64.45 MPa to 70.84 MPa,and in the 90°three-point bending test,the underwater-explosive-welded samples exhibit superior flexural performance.This study elucidates the effects of different manufacturing methods on the interfacial properties and mechanical performance of Cu/Al composites,offering essential insights for the selection of manufacturing methods and applications.展开更多
The Underwater Acoustic(UWA)channel is bandwidth-constrained and experiences doubly selective fading.It is challenging to acquire perfect channel knowledge for Orthogonal Frequency Division Multiplexing(OFDM)communica...The Underwater Acoustic(UWA)channel is bandwidth-constrained and experiences doubly selective fading.It is challenging to acquire perfect channel knowledge for Orthogonal Frequency Division Multiplexing(OFDM)communications using a finite number of pilots.On the other hand,Deep Learning(DL)approaches have been very successful in wireless OFDM communications.However,whether they will work underwater is still a mystery.For the first time,this paper compares two categories of DL-based UWA OFDM receivers:the DataDriven(DD)method,which performs as an end-to-end black box,and the Model-Driven(MD)method,also known as the model-based data-driven method,which combines DL and expert OFDM receiver knowledge.The encoder-decoder framework and Convolutional Neural Network(CNN)structure are employed to establish the DD receiver.On the other hand,an unfolding-based Minimum Mean Square Error(MMSE)structure is adopted for the MD receiver.We analyze the characteristics of different receivers by Monte Carlo simulations under diverse communications conditions and propose a strategy for selecting a proper receiver under different communication scenarios.Field trials in the pool and sea are also conducted to verify the feasibility and advantages of the DL receivers.It is observed that DL receivers perform better than conventional receivers in terms of bit error rate.展开更多
Underwater Wireless Sensor Networks(UWSNs)are gaining popularity because of their potential uses in oceanography,seismic activity monitoring,environmental preservation,and underwater mapping.Yet,these networks are fac...Underwater Wireless Sensor Networks(UWSNs)are gaining popularity because of their potential uses in oceanography,seismic activity monitoring,environmental preservation,and underwater mapping.Yet,these networks are faced with challenges such as self-interference,long propagation delays,limited bandwidth,and changing network topologies.These challenges are coped with by designing advanced routing protocols.In this work,we present Under Water Fuzzy-Routing Protocol for Low power and Lossy networks(UWF-RPL),an enhanced fuzzy-based protocol that improves decision-making during path selection and traffic distribution over different network nodes.Our method extends RPL with the aid of fuzzy logic to optimize depth,energy,Received Signal Strength Indicator(RSSI)to Expected Transmission Count(ETX)ratio,and latency.Theproposed protocol outperforms other techniques in that it offersmore energy efficiency,better packet delivery,lowdelay,and no queue overflow.It also exhibits better scalability and reliability in dynamic underwater networks,which is of very high importance in maintaining the network operations efficiency and the lifetime of UWSNs optimized.Compared to other recent methods,it offers improved network convergence time(10%–23%),energy efficiency(15%),packet delivery(17%),and delay(24%).展开更多
Given the challenges of underwater garbage detection,including insufficient lighting,low visibility,high noise levels,and high misclassification rates,this paper proposes a model named CSC-YOLO.CSC-YOLO for detecting ...Given the challenges of underwater garbage detection,including insufficient lighting,low visibility,high noise levels,and high misclassification rates,this paper proposes a model named CSC-YOLO.CSC-YOLO for detecting garbage in complex un-derwater environments characterized by murky water and strong hydrodynamic conditions.The model incorporates the Content-Guid-ed Attention(CGA)attention mechanism into the SPPF module of the YOLOv8 backbone network to enhance dehazing,reduce noise interference,and fuse multi-scale feature information.Additionally,a Single-Head Self-Attention(SHSA)mechanism is introduced in the final layer of the backbone network to achieve local and global feature fusion in a lightweight manner,improving the accuracy of garbage detection.In the detection head,the CBAM attention mechanism is added to further enhance feature representation,increase the model’s target localization,and improve robustness against complex backgrounds and noise.Furthermore,the anchor box coordi-nates from CSC-YOLO are fed into Mobile_SAM to achieve precise segmentation of underwater garbage.Experimental results show that CSC-YOLO achieves a Precision of 0.962,Recall of 0.898,F1-score of 0.929,and mAP0.5 of 0.960 on the ICRA19 trash dataset,representing improvements of 2.9%,1.7%,2.3%,and 2.0%over YOLOv8n,respectively.The combination of CSC-YOLO and Mo-bile_SAM not only enables garbage detection in complex underwater environments but also achieves segmentation.This approach generates additional garbage segmentation masks without manual annotations,facilitating rapid expansion of labeled underwater garbage datasets for training.As an emerging model for intelligent underwater garbage detection,the proposed method holds signifi-cant potential for practical applications and academic research,offering an effective solution to the challenges of intelligent garbage detection in complex underwater environments.展开更多
Health monitoring of underwater concrete facility systems is important in civil engineering. Unlike conventional manual inspection techniques, digital image processing offers a more convenient and effective approach, ...Health monitoring of underwater concrete facility systems is important in civil engineering. Unlike conventional manual inspection techniques, digital image processing offers a more convenient and effective approach, becoming an indispensable tool for structural inspection. Cracks, which are pervasive defects, are a central focus of structural deterioration research. However, the complexity of the marine environment poses challenges to underwater visibility.In this study, the underwater environment under controlled laboratory conditions is replicated, where varying turbidity and illumination conditions and images of concrete cracks are captured. An approach combining a defogging algorithm with guided and fast guided filtering techniques is proposed to enhance both natural underwater images and crack images captured through experimental photography. When applied to turbid crack images captured under two different suspension conditions, the method increases the information entropy(IE) by 32.92% and 17.92% and the underwater color image quality evaluation(UCIQE) by 35.76% and 18.36%, respectively. These results demonstrate its efficiency in enhancing image definition. The findings of this study could significantly impact the practical applications of image visualization and evaluation for underwater concrete cracks.展开更多
A multi-resolution smoothed particle hydrodynamics and peridynamics(SPH-PD)coupling model is proposed in this study for simulating the fracture characteristics of ice plates exposed to underwater blast loads.The SPH m...A multi-resolution smoothed particle hydrodynamics and peridynamics(SPH-PD)coupling model is proposed in this study for simulating the fracture characteristics of ice plates exposed to underwater blast loads.The SPH model employs a volume adaptive scheme(VAS)and a multi-resolution particle technique to accurately simulate explosive charge detonation and shock wave propagation.This approach addresses numerical challenges from charge expansion and significant size disparity between the charge and the fluid particles.The model captures the full underwater explosion process,covering both the shock wave phase and the bubble expansion stage,by applying appropriate equations of state for each respective phase.To analyze ice plate damage and crack propagation influenced by temperature changes,an ordinary state-based PD(OSB-PD)formulation with coupled mechanical and thermodynamic models is used.Numerical results show that the proposed coupling method demonstrates good agreement with reference solutions and experimental data.展开更多
Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater mani...Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater manipulator with different postures using the user-defined function (UDF) method. The lift coefficient (C_(L)), drag coefficient (C_(D)), and vortex shedding of the underwater manipulator in single-and dualarm forms were obtained. Results indicated that the maximum increase in the lift and drag coefficients subjected to the pulsation parameters was 24.45%and 28%, respectively, when the fluid flowed past a single arm. Compared with the single arm, the lift and drag coefficients of the arms were higher than those of the single arm when arm 2 was located upstream. Additionally, the pulsation frequency had no obvious effect on the manipulator, but the C_(L) and C_(D) of arm 2 showed an obvious increasing trend with an increase in pulsation amplitude. Meanwhile, when arm 2 was located downstream, the C_(L) and C_(D) of arm 2 were reduced by 16.38%and 1.15%, respectively, with an increase in the pulse frequency,and the maximum increase in the lift and dragcoefficients was 33.33%and 16.78%,respectively,with increasing pulsation amplitude.Moreover, the downstream wake morphology changed significantly, and a combined vortex phenomenon appeared. Finally, a theoretical basis for examining the hydrodynamic characteristics of marine engineering equipment was established to aid future marine resource exploitation.展开更多
The underwater anechoic coating technology,which considers pressure resistance and low-frequency broadband sound absorption,has become a research hotspot in underwater acoustics and has received wide attention to addr...The underwater anechoic coating technology,which considers pressure resistance and low-frequency broadband sound absorption,has become a research hotspot in underwater acoustics and has received wide attention to address the increasingly advanced low-frequency sonar detection technology and adapt to the working environment of underwater vehicles in deep submergence.One the one hand,controlling low-frequency sound waves in water is more challenging than in air.On the other hand,in addition to initiating structural deformation,hydrostatic pressure also changes material parameters,both of which have a major effect on the sound absorption performance of the anechoic coating.Therefore,resolving the pressure resistance and acoustic performance of underwater acoustic coatings is difficult.Particularly,a bottleneck problem that must be addressed in this field is the acoustic structure design with low-frequency broadband sound absorption under high hydrostatic pressure.Based on the influence of hydrostatic pressure on underwater anechoic coatings,the research status of underwater acoustic structures under hydrostatic pressure from the aspects of sound absorption mechanisms,analysis methods,and structural designs is reviewed in this paper.Finally,the challenges and research trends encountered by underwater anechoic coating technology under hydrostatic pressure are summarized,providing a reference for the design and research of low-frequency broadband anechoic coating.展开更多
The position deviation of the underwater manipulator generated by vortex-induced vibration(VIV)in the shear flow increases relative to that in the uniform flow.Thus,this study established an experimental platform to i...The position deviation of the underwater manipulator generated by vortex-induced vibration(VIV)in the shear flow increases relative to that in the uniform flow.Thus,this study established an experimental platform to investigate the vibration characteristics of the underwater manipulator under shear flow.The vibration response along the manipulator was obtained and compared with that in the uniform flow.Results indicated that the velocity,test height,and flow field were the main factors affecting the VIV of the underwater manipulator.With the increase in the reduced velocity(U_(r)),the dimensionless amplitudes increased rapidly in the in-line(IL)direction with a maximum of 0.13D.The vibration responses in the cross-flow(CF)and IL directions were concentrated at positions 2,3 and positions 1,2,with peak values of 0.46 and 0.54 mm under U_(r)=1.54,respectively.In addition,the vibration frequency increased with the reduction of velocity.The dimensionless dominant frequency in the CF and IL directions varied from 0.39-0.80 and 0.35-0.64,respectively.Moreover,the ratio of the CF and IL directions was close to 1 at a lower U_(r).The standard deviation of displacement initially increased and then decreased as the height of the test location increased.The single peak value of the standard deviation showed that VIV presented a single mode.Compared with the uniform flow,the maximum and average values of VIV displacement increased by 104%and 110%under the shear flow,respectively.展开更多
文摘Underwater pipeline inspection plays a vital role in the proactive maintenance and management of critical marine infrastructure and subaquatic systems.However,the inspection of underwater pipelines presents a challenge due to factors such as light scattering,absorption,restricted visibility,and ambient noise.The advancement of deep learning has introduced powerful techniques for processing large amounts of unstructured and imperfect data collected from underwater environments.This study evaluated the efficacy of the You Only Look Once(YOLO)algorithm,a real-time object detection and localization model based on convolutional neural networks,in identifying and classifying various types of pipeline defects in underwater settings.YOLOv8,the latest evolution in the YOLO family,integrates advanced capabilities,such as anchor-free detection,a cross-stage partial network backbone for efficient feature extraction,and a feature pyramid network+path aggregation network neck for robust multi-scale object detection,which make it particularly well-suited for complex underwater environments.Due to the lack of suitable open-access datasets for underwater pipeline defects,a custom dataset was captured using a remotely operated vehicle in a controlled environment.This application has the following assets available for use.Extensive experimentation demonstrated that YOLOv8 X-Large consistently outperformed other models in terms of pipe defect detection and classification and achieved a strong balance between precision and recall in identifying pipeline cracks,rust,corners,defective welds,flanges,tapes,and holes.This research establishes the baseline performance of YOLOv8 for underwater defect detection and showcases its potential to enhance the reliability and efficiency of pipeline inspection tasks in challenging underwater environments.
基金The National Natural Science Foundation of China(Grant No.52201376)the Natural Science Foundation of Hubei Province,China(Grant No.2023AFB683).
文摘In this investigation,a hybrid approach integrating the IDDES turbulence model and FW-H is employed to forecast the hydroacoustic of the rim driven thruster(RDT)under non-cavitation and uniform flow conditions at varying loading conditions(J=0.3 and J=0.6).It is revealed that the quadrupole term contribution in the P-FWH method significantly affects the monopole term in the low-frequency region,while it mainly affects the dipole term in the high-frequency region.Specifically,the overall sound pressure levels(SPL)of the RDT using the P-FWH method are 2.27 dB,10.03 dB,and 16.73 dB at the receiving points from R1 to R3 under the heavy-loaded condition,while they increase by 0.67 dB at R1,and decrease by 14.93 dB at R2,and 22.20 dB at R3,for the light-loaded condition.The study also utilizes the pressure-time derivatives to visualize the numerical noise and to pinpoint the dynamics of the vortex cores,and the optimization of the grid design can significantly reduce the numerical noise.The computational accuracy of the P-FWH method can meet the noise requirements for the preliminary design of rim driven thrusters.
基金Supported by the National Natural Science Foundation of China(No.51905211)A Project of the“20 Regulations for New Universities”Funding Program of Jinan(No.202228116).
文摘Vortex-induced vibration(VIV)of an underwater manipulator in pulsating flow presents a notable engineering problem in precise control due to the velocity variation in the flow.This study investigates the VIV response of an underwater manipulator subjected to pulsating flow,focusing on how different postures affect the behavior of the system.The effects of pulsating parameters and manipulator arrangement on the hydrodynamic coefficient,vibration response,motion trajectory,and vortex shedding behaviors were analyzed.Results indicated that the cross flow vibration displacement in pulsating flow increased by 32.14%compared to uniform flow,inducing a shift in the motion trajectory from a crescent shape to a sideward vase shape.In the absence of interference between the upper and lower arms,the lift coefficient of the manipulator substantially increased with rising pulsating frequency,reaching a maximum increment of 67.0%.This increase in the lift coefficient led to a 67.05%rise in the vibration frequency of the manipulator in the in-line direction.As the pulsating amplitude increased,the drag coefficient of the underwater manipulator rose by 36.79%,but the vibration frequency in the cross-flow direction decreased by 56.26%.Additionally,when the upper and lower arms remained in a state of mutual interference,the cross-flow vibration amplitudes of the upper and lower arms were approximately 1.84 and 4.82 times higher in a circular-elliptical arrangement compared to an elliptical-circular arrangement,respectively.Consequently,the flow field shifted from a P+S pattern to a disordered pattern,disrupting the regularity of the motion trajectory.
基金supported by the National Natural Science Foundation of China(Nos.62372100 and 6237118)。
文摘The phenomenon of attenuation and scattering of light propagating in water leads to such problems as color deviation and blur in underwater imaging.These problems bring great challenges to the subsequent feature matching,target recognition and other tasks.Therefore,this paper proposes an underwater image enhancement method by double compensation with comparative adjustment or edge reinforcement.The experiments have found that the proposed method has good underwater color image quality evaluation(UCIQE)value,underwater image quality measures(UIQM)value,and the number of feature matching points.This demonstrates that the proposed method has good color correction ability for underwater images with different attenuation levels,where the processed images have more details suitable for feature matching.
基金funded by the Jilin City Science and Technology Innovation Development Plan Project(No.20240302014)the Jilin Provincial Department of Educa-tion Science and Technology Research Project(No.JJKH 20250879KJ)the Jilin Province Science and Tech-nology Development Plan Project(No.YDZJ202401640 ZYTS).
文摘Underwater imaging is frequently influenced by factors such as illumination,scattering,and refraction,which can result in low image contrast and blurriness.Moreover,the presence of numerous small,overlapping targets reduces detection accuracy.To address these challenges,first,green channel images are preprocessed to rectify color bias while improving contrast and clarity.Se-cond,the YOLO-DBS network that employs deformable convolution is proposed to enhance feature learning from underwater blurry images.The ECA attention mechanism is also introduced to strengthen feature focus.Moreover,a bidirectional feature pyramid net-work is utilized for efficient multilayer feature fusion while removing nodes that contribute minimally to detection performance.In addition,the SIoU loss function that considers factors such as angular error and distance deviation is incorporated into the network.Validation on the RUOD dataset demonstrates that YOLO-DBS achieves approximately 3.1%improvement in mAP@0.5 compared with YOLOv8n and surpasses YOLOv9-tiny by 1.3%.YOLO-DBS reduces parameter count by 32%relative to YOLOv8n,thereby demonstrating superior performance in real-time detection on underwater observation platforms.
基金funded by the National Natural Science Founda-tion of China(52071109).
文摘Unlike conventional spherical charges,a shaped charge generates not only a strong shock wave and a pulsating bubble,but also a high strain rate metal jet and a ballistic wave during the underwater explosion.They show significant characteristic differences and couple each other.This paper designs and conducts experiments with shaped charges to analyze the complicated process.The effects of liner angle and weight of shaped charge on the characteristics of metal jets,waves,and bubbles are discussed.It is found that in underwater explosions,the shaped charge generates the metal jet accompanied by the ballistic wave.Then,the shock wave propagates and superimposes with the ballistic wave,and the generated bubble pulsates periodically.It is revealed that the maximum head velocity of the metal jet versus the liner angle a and length-to-diameter ratio k of the shaped charge follows the laws of 1/(α/180°)^(0.55)andλ^(0.16),respectively.The head shape and velocity of the metal jet determine the curvature and propagation speed of the initial ballistic wave,thus impacting the superposition time and region with the shock wave.Our findings also reveal that the metal jet carries away some explosion products,which hinders the bubble development,causing an inward depression of the bubble wall near the metal jet.Therefore,the maximum bubble radius and pulsation period are 5.2%and 3.9%smaller than the spherical charge with the same weight.In addition,the uneven axial energy distribution of the shaped charge leads to an oblique bubble jet formation.
基金Supported by the Key R&D Program of Heilongjiang Province(Grant No.JD22A024)the Science Fund for Excellent Youth Foundation of Heilongjiang Province of China(Grant No.YQ2021E010).
文摘Researchers have achieved notable advancements over the years in exploring ship damage and stability resulting from underwater explosions(UNDEX).However,numerous challenges and open questions remain in this field.In this study,the research progress of UNDEX load is first reviewed,which covers the explosion load during the shock wave and bubble pulsation stages.Subsequently,the research progress of ship damage caused by UNDEX is reviewed from two aspects:contact explosion and noncontact explosion.Finally,the research progress of ship navigation stability caused by UNDEX is reviewed from three aspects:natural factors,ship’s internal factors,and explosion factors.Analysis reveals that most existing research has focused on the damage to displacement ships caused by UNDEX.Meanwhile,less attention has been paid to the damage and stability of non-displacement ships caused by UNDEX,which are worthy of discussion.
文摘Bubbles play crucial roles in various fields,including naval and ocean engineering,chemical engineering,and biochemical engineering.Numerous theoretical analyses,numerical simulations,and experimental studies have been conducted to reveal the mysteries of bubble motion and its mechanisms.These efforts have significantly advanced research in bubble dynamics,where theoretical study is an efficient method for bubble motion prediction.Since Lord Rayleigh introduced the theoretical model of single-bubble motion in incompressible fluid in 1917,theoretical studies have been pivotal in understanding bubble dynamics.This study provides a comprehensive review of the development and applicability of theoretical studies in bubble dynamics using typical theoretical bubble models across different periods as a focal point and an overview of bubble theory applications in underwater explosion,marine cavitation,and seismic exploration.This study aims to serve as a reference and catalyst for further advancements in theoretical analysis and practical applications of bubble theory across marine fields.
基金supported by the National Science Foundation of China(Grant Nos.12372361,12102427,12372335 and 12102202)the Fundamental Research Funds for the Central Universities(Grant No.30923010908)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX23_0520).
文摘Shaped charge has been widely used for penetrating concrete.However,due to the obvious difference between the propagation of shock waves and explosion products in water and air,the theory governing the formation of shaped charge jets in water as well as the underwater penetration effect of concrete need to be studied.In this paper,we introduced a modified forming theory of an underwater hemispherical shaped charge,and investigated the behavior of jet formation and concrete penetration in both air and water experimentally and numerically.The results show that the modified jet forming theory predicts the jet velocity of the hemispherical liner with an error of less than 10%.The underwater jets exhibit at least 3%faster and 11%longer than those in air.Concrete shows different failure modes after penetration in air and water.The depth of penetration deepens at least 18.75%after underwater penetration,accompanied by deeper crater with 65%smaller radius.Moreover,cracks throughout the entire target are formed,whereas cracks exist only near the penetration hole in air.This comprehensive study provides guidance for optimizing the structure of shaped charge and improves the understanding of the permeability effect of concrete in water.
文摘It is difficult to improve both energy consumption and detection accuracy simultaneously,and even to obtain the trade-off between them,when detecting and tracking moving targets,especially for Underwater Wireless Sensor Networks(UWSNs).To this end,this paper investigates the relationship between the Degree of Target Change(DoTC)and the detection period,as well as the impact of individual nodes.A Hierarchical Detection and Tracking Approach(HDTA)is proposed.Firstly,the network detection period is determined according to DoTC,which reflects the variation of target motion.Secondly,during the network detection period,each detection node calculates its own node detection period based on the detection mutual information.Taking DoTC as pheromone,an ant colony algorithm is proposed to adaptively adjust the network detection period.The simulation results show that the proposed HDTA with the optimizations of network level and node level significantly improves the detection accuracy by 25%and the network energy consumption by 10%simultaneously,compared to the traditional adaptive period detection schemes.
基金supported in part by the National Natural Science Foundation of China Grants 62402085,61972062,62306060the Liaoning Doctoral Research Start-Up Fund 2023-BS-078+1 种基金the Dalian Youth Science and Technology Star Project 2023RQ023the Liaoning Basic Research Project 2023JH2/101300191.
文摘Underwater target detection is extensively applied in domains such as underwater search and rescue,environmental monitoring,and marine resource surveys.It is crucial in enabling autonomous underwater robot operations and promoting ocean exploration.Nevertheless,low imaging quality,harsh underwater environments,and obscured objects considerably increase the difficulty of detecting underwater targets,making it difficult for current detection methods to achieve optimal performance.In order to enhance underwater object perception and improve target detection precision,we propose a lightweight underwater target detection method using You Only Look Once(YOLO)v8 with multi-scale cross-channel attention(MSCCA),named YOLOv8-UOD.In the proposed multiscale cross-channel attention module,multi-scale attention(MSA)augments the variety of attentional perception by extracting information from innately diverse sensory fields.The cross-channel strategy utilizes RepVGGbased channel shuffling(RCS)and one-shot aggregation(OSA)to rearrange feature map channels according to specific rules.It aggregates all features only once in the final feature mapping,resulting in the extraction of more comprehensive and valuable feature information.The experimental results show that the proposed YOLOv8-UOD achieves a mAP50 of 95.67%and FLOPs of 23.8 G on the Underwater Robot Picking Contest 2017(URPC2017)dataset,outperforming other methods in terms of detection precision and computational cost-efficiency.
基金Anhui Province Key Research and Development Plan(2022a05020021)China Coal Science and Industry Group Chongqing Research Institute Independent Research and Development Project(2023YBXM58)。
文摘Cu/Al composite plates were fabricated using rolling and underwater explosive welding techniques,separately,to compare their interfacial microstructures and mechanical performance.Interface morphology,grain orientation,grain boundary characteristics,and phase distribution were analyzed through optical microscope,scanning electron microscope,and electron backscattered diffractometer.Mechanical properties were assessed using tensile shear tests,90°bending tests,and hardness measurements.Vickers hardness and nanoindentation test results further provided information on the hardness distributions.Results indicate that the diffusion layer in rolled Cu/Al composites is relatively fragile,while that produced by underwater explosive welding features a diffusion layer of approximately 18μm in thickness,which is metallurgically bonded through atomic diffusion.The tensile shear strength of these composites ranges from 64.45 MPa to 70.84 MPa,and in the 90°three-point bending test,the underwater-explosive-welded samples exhibit superior flexural performance.This study elucidates the effects of different manufacturing methods on the interfacial properties and mechanical performance of Cu/Al composites,offering essential insights for the selection of manufacturing methods and applications.
基金funded in part by the National Natural Science Foundation of China under Grant 62401167 and 62192712in part by the Key Laboratory of Marine Environmental Survey Technology and Application,Ministry of Natural Resources,P.R.China under Grant MESTA-2023-B001in part by the Stable Supporting Fund of National Key Laboratory of Underwater Acoustic Technology under Grant JCKYS2022604SSJS007.
文摘The Underwater Acoustic(UWA)channel is bandwidth-constrained and experiences doubly selective fading.It is challenging to acquire perfect channel knowledge for Orthogonal Frequency Division Multiplexing(OFDM)communications using a finite number of pilots.On the other hand,Deep Learning(DL)approaches have been very successful in wireless OFDM communications.However,whether they will work underwater is still a mystery.For the first time,this paper compares two categories of DL-based UWA OFDM receivers:the DataDriven(DD)method,which performs as an end-to-end black box,and the Model-Driven(MD)method,also known as the model-based data-driven method,which combines DL and expert OFDM receiver knowledge.The encoder-decoder framework and Convolutional Neural Network(CNN)structure are employed to establish the DD receiver.On the other hand,an unfolding-based Minimum Mean Square Error(MMSE)structure is adopted for the MD receiver.We analyze the characteristics of different receivers by Monte Carlo simulations under diverse communications conditions and propose a strategy for selecting a proper receiver under different communication scenarios.Field trials in the pool and sea are also conducted to verify the feasibility and advantages of the DL receivers.It is observed that DL receivers perform better than conventional receivers in terms of bit error rate.
文摘Underwater Wireless Sensor Networks(UWSNs)are gaining popularity because of their potential uses in oceanography,seismic activity monitoring,environmental preservation,and underwater mapping.Yet,these networks are faced with challenges such as self-interference,long propagation delays,limited bandwidth,and changing network topologies.These challenges are coped with by designing advanced routing protocols.In this work,we present Under Water Fuzzy-Routing Protocol for Low power and Lossy networks(UWF-RPL),an enhanced fuzzy-based protocol that improves decision-making during path selection and traffic distribution over different network nodes.Our method extends RPL with the aid of fuzzy logic to optimize depth,energy,Received Signal Strength Indicator(RSSI)to Expected Transmission Count(ETX)ratio,and latency.Theproposed protocol outperforms other techniques in that it offersmore energy efficiency,better packet delivery,lowdelay,and no queue overflow.It also exhibits better scalability and reliability in dynamic underwater networks,which is of very high importance in maintaining the network operations efficiency and the lifetime of UWSNs optimized.Compared to other recent methods,it offers improved network convergence time(10%–23%),energy efficiency(15%),packet delivery(17%),and delay(24%).
基金support of this research from the National Natural Science Foundation of China(No.12174085)the Key Research and Devel-opment Project of Changzhou,Jiangsu Province(No.CE 20235054).
文摘Given the challenges of underwater garbage detection,including insufficient lighting,low visibility,high noise levels,and high misclassification rates,this paper proposes a model named CSC-YOLO.CSC-YOLO for detecting garbage in complex un-derwater environments characterized by murky water and strong hydrodynamic conditions.The model incorporates the Content-Guid-ed Attention(CGA)attention mechanism into the SPPF module of the YOLOv8 backbone network to enhance dehazing,reduce noise interference,and fuse multi-scale feature information.Additionally,a Single-Head Self-Attention(SHSA)mechanism is introduced in the final layer of the backbone network to achieve local and global feature fusion in a lightweight manner,improving the accuracy of garbage detection.In the detection head,the CBAM attention mechanism is added to further enhance feature representation,increase the model’s target localization,and improve robustness against complex backgrounds and noise.Furthermore,the anchor box coordi-nates from CSC-YOLO are fed into Mobile_SAM to achieve precise segmentation of underwater garbage.Experimental results show that CSC-YOLO achieves a Precision of 0.962,Recall of 0.898,F1-score of 0.929,and mAP0.5 of 0.960 on the ICRA19 trash dataset,representing improvements of 2.9%,1.7%,2.3%,and 2.0%over YOLOv8n,respectively.The combination of CSC-YOLO and Mo-bile_SAM not only enables garbage detection in complex underwater environments but also achieves segmentation.This approach generates additional garbage segmentation masks without manual annotations,facilitating rapid expansion of labeled underwater garbage datasets for training.As an emerging model for intelligent underwater garbage detection,the proposed method holds signifi-cant potential for practical applications and academic research,offering an effective solution to the challenges of intelligent garbage detection in complex underwater environments.
基金financially supported by the National Natural Science Foundation of China (Grant No. 52175245)the Natural Science Foundation of Hubei Province (Grant No. 2021CFB462)。
文摘Health monitoring of underwater concrete facility systems is important in civil engineering. Unlike conventional manual inspection techniques, digital image processing offers a more convenient and effective approach, becoming an indispensable tool for structural inspection. Cracks, which are pervasive defects, are a central focus of structural deterioration research. However, the complexity of the marine environment poses challenges to underwater visibility.In this study, the underwater environment under controlled laboratory conditions is replicated, where varying turbidity and illumination conditions and images of concrete cracks are captured. An approach combining a defogging algorithm with guided and fast guided filtering techniques is proposed to enhance both natural underwater images and crack images captured through experimental photography. When applied to turbid crack images captured under two different suspension conditions, the method increases the information entropy(IE) by 32.92% and 17.92% and the underwater color image quality evaluation(UCIQE) by 35.76% and 18.36%, respectively. These results demonstrate its efficiency in enhancing image definition. The findings of this study could significantly impact the practical applications of image visualization and evaluation for underwater concrete cracks.
基金partially funded by the National Natural Science Foundation of China(Grant No.52171329)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2024B1515020107)+1 种基金the Young Elite Scientist Sponsorship Program by CAST(Grant No.2022QNRC001)Characteristic Innovation Project of Universities in Guangdong Province(Grant No.2023KTSCX005).
文摘A multi-resolution smoothed particle hydrodynamics and peridynamics(SPH-PD)coupling model is proposed in this study for simulating the fracture characteristics of ice plates exposed to underwater blast loads.The SPH model employs a volume adaptive scheme(VAS)and a multi-resolution particle technique to accurately simulate explosive charge detonation and shock wave propagation.This approach addresses numerical challenges from charge expansion and significant size disparity between the charge and the fluid particles.The model captures the full underwater explosion process,covering both the shock wave phase and the bubble expansion stage,by applying appropriate equations of state for each respective phase.To analyze ice plate damage and crack propagation influenced by temperature changes,an ordinary state-based PD(OSB-PD)formulation with coupled mechanical and thermodynamic models is used.Numerical results show that the proposed coupling method demonstrates good agreement with reference solutions and experimental data.
基金the National Natural Science Foundation of China (No. 51905211)China Postdoctoral Science Foundation (Grant No. 2020M672128)+1 种基金University of Jinan Research Startup and Discipline Construction Fund (Grant No.1009435)a Project of the “20 Regulations for New Universities” funding program of Jinan (No.202228116)。
文摘Pulsating flow is a common condition for under water manipulators in Bohai Bay.This study aimed to investigate the effects of pulsation frequency and amplitude on the hydrodynamic characteristics of an underwater manipulator with different postures using the user-defined function (UDF) method. The lift coefficient (C_(L)), drag coefficient (C_(D)), and vortex shedding of the underwater manipulator in single-and dualarm forms were obtained. Results indicated that the maximum increase in the lift and drag coefficients subjected to the pulsation parameters was 24.45%and 28%, respectively, when the fluid flowed past a single arm. Compared with the single arm, the lift and drag coefficients of the arms were higher than those of the single arm when arm 2 was located upstream. Additionally, the pulsation frequency had no obvious effect on the manipulator, but the C_(L) and C_(D) of arm 2 showed an obvious increasing trend with an increase in pulsation amplitude. Meanwhile, when arm 2 was located downstream, the C_(L) and C_(D) of arm 2 were reduced by 16.38%and 1.15%, respectively, with an increase in the pulse frequency,and the maximum increase in the lift and dragcoefficients was 33.33%and 16.78%,respectively,with increasing pulsation amplitude.Moreover, the downstream wake morphology changed significantly, and a combined vortex phenomenon appeared. Finally, a theoretical basis for examining the hydrodynamic characteristics of marine engineering equipment was established to aid future marine resource exploitation.
基金Supported by the National Natural Science Foundation of China(Grant No.52271309)Natural Science Foundation of Heilongjiang Province of China(Grant No.YQ2022E104)Doctoral Science and Technology Innovation Fund of Harbin Engineering University(Grant No.3072023GIP0302).
文摘The underwater anechoic coating technology,which considers pressure resistance and low-frequency broadband sound absorption,has become a research hotspot in underwater acoustics and has received wide attention to address the increasingly advanced low-frequency sonar detection technology and adapt to the working environment of underwater vehicles in deep submergence.One the one hand,controlling low-frequency sound waves in water is more challenging than in air.On the other hand,in addition to initiating structural deformation,hydrostatic pressure also changes material parameters,both of which have a major effect on the sound absorption performance of the anechoic coating.Therefore,resolving the pressure resistance and acoustic performance of underwater acoustic coatings is difficult.Particularly,a bottleneck problem that must be addressed in this field is the acoustic structure design with low-frequency broadband sound absorption under high hydrostatic pressure.Based on the influence of hydrostatic pressure on underwater anechoic coatings,the research status of underwater acoustic structures under hydrostatic pressure from the aspects of sound absorption mechanisms,analysis methods,and structural designs is reviewed in this paper.Finally,the challenges and research trends encountered by underwater anechoic coating technology under hydrostatic pressure are summarized,providing a reference for the design and research of low-frequency broadband anechoic coating.
基金Supported by the National Natural Science Foundation of China(No.51905211)the“20 Regulations for New Universities”of Jinan(No.202228116).
文摘The position deviation of the underwater manipulator generated by vortex-induced vibration(VIV)in the shear flow increases relative to that in the uniform flow.Thus,this study established an experimental platform to investigate the vibration characteristics of the underwater manipulator under shear flow.The vibration response along the manipulator was obtained and compared with that in the uniform flow.Results indicated that the velocity,test height,and flow field were the main factors affecting the VIV of the underwater manipulator.With the increase in the reduced velocity(U_(r)),the dimensionless amplitudes increased rapidly in the in-line(IL)direction with a maximum of 0.13D.The vibration responses in the cross-flow(CF)and IL directions were concentrated at positions 2,3 and positions 1,2,with peak values of 0.46 and 0.54 mm under U_(r)=1.54,respectively.In addition,the vibration frequency increased with the reduction of velocity.The dimensionless dominant frequency in the CF and IL directions varied from 0.39-0.80 and 0.35-0.64,respectively.Moreover,the ratio of the CF and IL directions was close to 1 at a lower U_(r).The standard deviation of displacement initially increased and then decreased as the height of the test location increased.The single peak value of the standard deviation showed that VIV presented a single mode.Compared with the uniform flow,the maximum and average values of VIV displacement increased by 104%and 110%under the shear flow,respectively.
