With the increase of petroleum and gas production in deep ocean, marine risers of circular cylinder shape are widely used in the offshore oil and gas platform. In order to research the hydrodynamic performance of mari...With the increase of petroleum and gas production in deep ocean, marine risers of circular cylinder shape are widely used in the offshore oil and gas platform. In order to research the hydrodynamic performance of marine risers, the dynamic mesh technique and User-Defined Function(UDF) are used to simulate the circular cylinder motion. The motion of a transversely oscillating circular cylinder in combination of uniform flow and oscillating flow is simulated. The uniform flow and oscillating flow both are in x direction. SIMPLE algorithm is used to solve the Navier-Stokes equations. The User-Defined Function is used to control the cylinder transverse vibration and the inlet flow. The lift and drag coefficient changing with time and the map of vorticity isolines at different phase angle are obtained. Force time histories are shown for uniform flow at Reynolds number(Re) of 200 and for the combination of uniform and oscillating flows. With the increase of amplitude of oscillating flow in combined flow, the change of lift amplitude is not sensitive to the the change of cylinder oscillating frequency. Lift amplitude increases with the increase of oscillating flow amplitude in the combined flow, but there is no definite periodicity of the lift coefficient. The drag and inertia force coefficients change when the maximum velocity of the oscillating flow increases in the combined flow. The vortex shedding near the circular cylinder shows different characteristics.展开更多
Marine gas hydrates,one of the largest methane reservoirs on Earth,may greatly affect the deep sea sedimentary environment and biogeochemistry;however,the carbon geochemistry in gas hydrate-bearing sediments is poorly...Marine gas hydrates,one of the largest methane reservoirs on Earth,may greatly affect the deep sea sedimentary environment and biogeochemistry;however,the carbon geochemistry in gas hydrate-bearing sediments is poorly understood.In this study,we investigated the carbon variables in sediment core 973-3 from the southwestern Taiwan Basin in the South China Sea to understand the effect of environmental factors and archaeal communities on carbon geochemistry.The carbon profiles suggest the methanogenesis with the incerase of dissolved inorganic carbon(DIC)and high total organic carbon(TOC)(mean=0.46%)originated from terrigenous organic matter(mean j13CToc value of-23.6%0)driven by the abundant methanogen'Methanosaeta and Methanomicrobiales'.The active anaerobic oxidation of methane is characterized by the increase of DIC and inorganic carbon(IC),and the depletedδ13CIC,coupled with the increase of TOC and the decrease ofδ13Croc values owing to the methanotroph'Methanosarcinales/ANME'in 430-840 cm.Environmental factors and archaeal communities in core 973-3 are significantly correlated to carbon variables owing to methane production and oxidation.Our results indicate that the carbon geochemical characteristics are obviously responding to the formation and decomposition of gas hydrates.Furthermore,pH,Eh and grain size,and Methanosaeta greatly affect the carbon geochemistry in gas hydrate-associated sediments.展开更多
The development of microchannels with open flow for use in irrigation and rainy areas is challenged by electricity generation via hydrokinetic devices in shallow and low velocity flows.Conventional hydrokinetic turbin...The development of microchannels with open flow for use in irrigation and rainy areas is challenged by electricity generation via hydrokinetic devices in shallow and low velocity flows.Conventional hydrokinetic turbines are known to be highly dependent on current speed and water depth.Another drawback of conventional turbines is their low efficiency.These shortcomings lead to the need to accelerate the flow in the channel system to enhance the extracted power.The method of deploying a novel turbine configuration in irrigation channels can help overcome the low performance of conventional hydrokinetic turbines.Therefore,this study experimentally presents a bidirectional diffuser-augmented channel that includes dual cross flow/Banki turbines.Results show that the maximum efficiency of the overall system with two turbines is nearly 55.7%.The efficiency is low relative to that of hydraulic turbines.Nevertheless,the result can be considered satisfactory given the low head of the present system.The use of this system will contribute to a highly efficient utilization of flows in rivers and channels for electrical energy generation in rural areas.展开更多
Development and application of offshore wind turbine farms have been increasing, particularly in the developed countries,because of their high power rating, high yield energy, high offshore wind, and unlimited space i...Development and application of offshore wind turbine farms have been increasing, particularly in the developed countries,because of their high power rating, high yield energy, high offshore wind, and unlimited space in the offshore. However, the poor data and simplistic methodologies of the previous assessments result in insufficient estimates of the wind energy potential.Thus, this study provides an assessment of the offshore wind energy resources in Malaysia using multi-mission satellite altimetry data. The satellite altimetry data was extracted from Radar Altimeter Database Systems located at GNSS and Geodynamics Laboratory, Universiti Teknologi Malaysia. The data were validated by buoy measurements from two offshore sites, as indicated by the high correlation coefficient of 0.88. Further, the offshore wind energy resource mapping data in Malaysia identified three areas in Peninsular Malaysia and Borneo as potential areas for offshore wind energy development.展开更多
Underwater data collection is an importance part in the process of network monitoring,network management and intrusion detection.However,the limited-energy of nodes is a major challenge to collect underwater data.The ...Underwater data collection is an importance part in the process of network monitoring,network management and intrusion detection.However,the limited-energy of nodes is a major challenge to collect underwater data.The solution of this problem are not only in the hands of network topology but in the hands of path of autonomous underwater vehicle(AUV).With the problem in hand,an energy-efficient data collection scheme is designed for mobile underwater network.Especially,the data collection scheme is divided into two phases,i.e.,routing algorithm design for sensor nodes and path planing for AUV.With consideration of limited-energy and network robustness,Q-learning based dynamic routing algorithm is designed in the first phase to optimize the routing selection of nodes,through which a potential-game based optimal rigid graph method is proposed to balance the trade-off between the energy consumption and the network robustness.With the collected data,Q-learning based path planning strategy is proposed for AUV in the second phase to find the desired path to gather the data from data collector,then a mode-free tracking controller is developed to track the desired path accurately.Finally,the performance analysis and simulation results reveal that the proposed approach can guarantee energy-efficient and improve network stability.展开更多
This study uses a numerical method to analyze the proposed model structure. Before the parametric analysis, a pre-analysis to make sure the analytical results are accountable, a verification analysis was performed. Th...This study uses a numerical method to analyze the proposed model structure. Before the parametric analysis, a pre-analysis to make sure the analytical results are accountable, a verification analysis was performed. The results found are compared well with the limited experimental findings of Goda et al. and it is very encouraging to find that for the proposed method as an alternative for green energy developments, as long as an appropriate design is performed, an OWC combined with breakwater structure may provide an alternative for green energy system utilized in a harbor area. From the results of the first stage of parameter analysis that the size of the openings of the cell of converting system is variable, a traditional full opened cell is not necessary the most efficient design for the wave power conversion in terms of the variations of air pressure inside the cell and air speed through the outlet orifice that will drive the electricity power generator.展开更多
A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses fr...A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses from experiments are, tound to differ from theoretical resuhs. The response of p0 in permeable seabed has a small decay and phase shift to the nonlinear wave actions, and the dynamic stresses, σs/p0, σh/p0 and u/p0, contain different phase shift characteristics. Such phenomena will strongly affect the dynamic stress path in seabed. If the phase shifts of σs. and σh are neglected, the stress path will become a straight line; otherwise, it will become an elliptical curve. In phase shift cases, the long axis of the p - q diagram will be shortened when the depth increases, and the short axis will become longer when the phase shift increases. For the p＇ - q＇ diagram, the larger the phase lag of u, the longer the short axis. Relative results offer useful information for the analysis of seabed stability.展开更多
Resistance analysis is an important analytical method used to evaluate the hydrodynamic performance of High Speed Craft (HSC). Analysis of multihull resistance in shallow water is essential to the performance evaluati...Resistance analysis is an important analytical method used to evaluate the hydrodynamic performance of High Speed Craft (HSC). Analysis of multihull resistance in shallow water is essential to the performance evaluation of any type of HSC. Ships operating in shallow water experience increases in resistance because of changes in pressure distribution and wave pattern. In this paper, the shallow water performance of an HSC design concept, the semi-Small Waterplane Area Twin Hull (semi-SWATH) form, is studied. The hull is installed with fin stabilizers to reduce dynamic motion effects, and the resistance components of the hull, hull trim condition, and maximum wave amplitude around the hull are determined via calm water resistance tests in shallow water. These criteria are important in analyzing semi-SWATH resistance in shallow water and its relation to flow around hull. The fore fin angle is fixed to zero degrees, while the aft fin angle is varied to 0o, 5o, 10o, and 15o. For each configuration, investigations are conducted with depth Froude numbers (FrH) ranging from 0.65 to 1.2, and the resistance tests are performed in shallow water at the towing tank of UTM. Analysis results indicate that the resistance, wave pattern, and trim of the semi-SWATH hull form are affected by the fin angle. The resistance is amplified whereas the trim and sinkage are reduced as the fin angle increases. Increases in fin angle contribute to seakeeping and stability but affect the hull resistance of HSCs.展开更多
The flow interference of multiple cylinders subjected to vortex-induced vibration(VIV)is a complex response that is not fully understood.This paper investigates the fluid-dynamic behaviour of elastically mounted rigid...The flow interference of multiple cylinders subjected to vortex-induced vibration(VIV)is a complex response that is not fully understood.This paper investigates the fluid-dynamic behaviour of elastically mounted rigid cylinders where both cylinders were free to oscillate in the cross-flow direction.The cylinders were subjected to uniform water flow at various separation distances of 3.5,4.0,and 4.5 D(D is the diameter of the cylinder)in a tandem arrangement.Based on the observation,the interference between the cylinders and the unsteady wake from the leading cylinder caused a continuous vibration with no lower branch in amplitude response.While as found in the cases of the single cylinder,there was a lower branch in amplitude response.The results also revealed that the cylinders experienced the VIV and wake-induced vibration(WIV)at each separation distance.Moreover,the leading cylinder oscillated at a larger amplitude at a separation distance of 3.5 D,indicating a critical distance for cylinders in the tandem arrangement due to the existence of a bistable regime.Hence,it is reasonable to conclude that the flow interference between the leading and trailing cylinders significantly impacts the cylinders’dynamic behaviour.展开更多
Atmospheric Kármán vortex streets,which frequently emerge on the leeward side of isolated islands under specific atmospheric conditions,play a critical role in large-scale atmospheric dynamics.However,their ...Atmospheric Kármán vortex streets,which frequently emerge on the leeward side of isolated islands under specific atmospheric conditions,play a critical role in large-scale atmospheric dynamics.However,their automated detection and the influence of atmospheric variables on their formation remain insufficiently explored.Here,we firstly developed an object detection dataset utilizing 20 years of cloud imagery from the MODIS aboard the Terra and Aqua satellites,facilitating the application of artificial intelligence algorithms for the automated detection of Kármán vortex streets.Given that these vortex streets can manifest under both cloudy and cloudfree conditions,we further assessed the contribution of various spectral bands to vortex detection by implying a multi-channel classification network.This network,built upon a custom-designed miniResNet dual-level classification network and trained on MODls HDFformat sensor data,demonstrates that the dataset is particularly suited for detecting Kármán vortex streets in cloudy conditions.Different types of advanced algorithms were applied on the dataset,yielding baseline performance metrics and potential detection methods.Additionally,we proposed two optimization strategies tailored to Kármán vortex streets detection.First,leveraging the intrinsic properties of vortex structures,we introduced a Gamma loss optimization for bounding box aspect ratios,which significantly enhanced performance across six YoLO-based models.Second,we investigated the role of atmospheric variables in vortex formation and incorporated an auxiliary-task-enhanced learning approach to further refine detection accuracy,drawing upon findings from our recently published work.In summary,this study provides a novel dataset that supports meteorological and climatological research,addressing a critical gap in atmospheric data.Furthermore,the proposed auxiliary optimization strategies highlight the distinct challenges of Kármán vortex streets detection compared to conventional object detection,underscoring the unique structural and atmospheric characteristics of these phenomena.展开更多
There are still fundamental problems lying in the basic research of bulk nanobubbles.Are the bulk nanobubbles reported in the literature nano scale bubbles or contaminants in fact?At present,there is not yet sufficien...There are still fundamental problems lying in the basic research of bulk nanobubbles.Are the bulk nanobubbles reported in the literature nano scale bubbles or contaminants in fact?At present,there is not yet sufficient experimental evidence to show that the bulk nanoparticles are only gas bubbles but not other nano scale contaminants.If they are indeed nanobubbles,what causes the bulk nanobubbles observed in the literature to be much more stable than being predicted by the Epstein-Plesset theory?This paper firstly discusses the contradiction between the traditional theory prediction and the observed lifetime of the bulk nanobubbles,and then discusses whether the so-called nanobubbles are gas aggregates.We review the existing typical models,and the influence of different conditions on the stability of bulk nanobubbles,for paving the road to a clear understanding of the stability mechanism of bulk nanobubbles.In addition,the representative production methods and characterization methods of bulk nanobubbles are discussed in order to offer some guidance to their wide range of commercial applications.展开更多
Water entry problems represent complex multiphase flows involving air,water,and structure interaction,occurring rapidly in rough seas,and potentially effecting structural integrity of floating structures.This paper ex...Water entry problems represent complex multiphase flows involving air,water,and structure interaction,occurring rapidly in rough seas,and potentially effecting structural integrity of floating structures.This paper experimentally investigates asymmetric slamming loads acting on a 3-D elastic wedge section.The specimen,featuring two different bottom plates(stiffened and unstiffened),each 4 mm thick,aims to assess the effect of structural stiffness on dynamic loads.The experiments are conducted at different drop heights of 25 cm and 50 cm and varying heel angles from 5°to 25°.The paper describes the experimental conditions,including wedge geometry,material properties,and the test plan.The study explores the influence of heel angle on impact acceleration,revealing an increase in peak acceleration with a higher inclination angle,particularly in the vertical direction.Additionally,the hydrodynamic pressure resulting from asymmetric slamming is presented.The pressure results analyzed and compared at different locations along the length of the wedge.The experimental findings indicate that,despite the leeward side(stiffened)experiencing a smaller hydrodynamic load,the heel angle significantly affects pressure results on the windward side(unstiffened),leading to a more pronounced dynamic response.The time history of pressure results emphasizes the effect of elastic vibrations,particularly noticeable on the unstiffened bottom plate.This study contributes to a deeper understanding of asymmetric slamming on aluminum structures,facilitating the enhancement of mathematical models and the validation of numerical simulations.展开更多
基金supported financially by the Natural Science Foundation of China (No. 51079136/51179179/51239008)
文摘With the increase of petroleum and gas production in deep ocean, marine risers of circular cylinder shape are widely used in the offshore oil and gas platform. In order to research the hydrodynamic performance of marine risers, the dynamic mesh technique and User-Defined Function(UDF) are used to simulate the circular cylinder motion. The motion of a transversely oscillating circular cylinder in combination of uniform flow and oscillating flow is simulated. The uniform flow and oscillating flow both are in x direction. SIMPLE algorithm is used to solve the Navier-Stokes equations. The User-Defined Function is used to control the cylinder transverse vibration and the inlet flow. The lift and drag coefficient changing with time and the map of vorticity isolines at different phase angle are obtained. Force time histories are shown for uniform flow at Reynolds number(Re) of 200 and for the combination of uniform and oscillating flows. With the increase of amplitude of oscillating flow in combined flow, the change of lift amplitude is not sensitive to the the change of cylinder oscillating frequency. Lift amplitude increases with the increase of oscillating flow amplitude in the combined flow, but there is no definite periodicity of the lift coefficient. The drag and inertia force coefficients change when the maximum velocity of the oscillating flow increases in the combined flow. The vortex shedding near the circular cylinder shows different characteristics.
基金supported by grants from the National Natural Science Foundation of China(No.41276046 and 41773078)
文摘Marine gas hydrates,one of the largest methane reservoirs on Earth,may greatly affect the deep sea sedimentary environment and biogeochemistry;however,the carbon geochemistry in gas hydrate-bearing sediments is poorly understood.In this study,we investigated the carbon variables in sediment core 973-3 from the southwestern Taiwan Basin in the South China Sea to understand the effect of environmental factors and archaeal communities on carbon geochemistry.The carbon profiles suggest the methanogenesis with the incerase of dissolved inorganic carbon(DIC)and high total organic carbon(TOC)(mean=0.46%)originated from terrigenous organic matter(mean j13CToc value of-23.6%0)driven by the abundant methanogen'Methanosaeta and Methanomicrobiales'.The active anaerobic oxidation of methane is characterized by the increase of DIC and inorganic carbon(IC),and the depletedδ13CIC,coupled with the increase of TOC and the decrease ofδ13Croc values owing to the methanotroph'Methanosarcinales/ANME'in 430-840 cm.Environmental factors and archaeal communities in core 973-3 are significantly correlated to carbon variables owing to methane production and oxidation.Our results indicate that the carbon geochemical characteristics are obviously responding to the formation and decomposition of gas hydrates.Furthermore,pH,Eh and grain size,and Methanosaeta greatly affect the carbon geochemistry in gas hydrate-associated sediments.
基金This project is sponsored by the Ministry of Education Malaysia under ERGS Fund No.4 L.125.
文摘The development of microchannels with open flow for use in irrigation and rainy areas is challenged by electricity generation via hydrokinetic devices in shallow and low velocity flows.Conventional hydrokinetic turbines are known to be highly dependent on current speed and water depth.Another drawback of conventional turbines is their low efficiency.These shortcomings lead to the need to accelerate the flow in the channel system to enhance the extracted power.The method of deploying a novel turbine configuration in irrigation channels can help overcome the low performance of conventional hydrokinetic turbines.Therefore,this study experimentally presents a bidirectional diffuser-augmented channel that includes dual cross flow/Banki turbines.Results show that the maximum efficiency of the overall system with two turbines is nearly 55.7%.The efficiency is low relative to that of hydraulic turbines.Nevertheless,the result can be considered satisfactory given the low head of the present system.The use of this system will contribute to a highly efficient utilization of flows in rivers and channels for electrical energy generation in rural areas.
文摘Development and application of offshore wind turbine farms have been increasing, particularly in the developed countries,because of their high power rating, high yield energy, high offshore wind, and unlimited space in the offshore. However, the poor data and simplistic methodologies of the previous assessments result in insufficient estimates of the wind energy potential.Thus, this study provides an assessment of the offshore wind energy resources in Malaysia using multi-mission satellite altimetry data. The satellite altimetry data was extracted from Radar Altimeter Database Systems located at GNSS and Geodynamics Laboratory, Universiti Teknologi Malaysia. The data were validated by buoy measurements from two offshore sites, as indicated by the high correlation coefficient of 0.88. Further, the offshore wind energy resource mapping data in Malaysia identified three areas in Peninsular Malaysia and Borneo as potential areas for offshore wind energy development.
基金Supported by the National Natural Science Foundation of China(61873345,62222314)the Distinguished Young Foundation of Hebei Province(F2022203001)+2 种基金the Central Guidance Local Foundation of Hebei Province(226Z3201G)the three-three-three Foundation of Hebei Province(C20221019)the Open Fund Project of Key Laboratory of Ocean Observation Technology,MNR(2021klootA02).
文摘Underwater data collection is an importance part in the process of network monitoring,network management and intrusion detection.However,the limited-energy of nodes is a major challenge to collect underwater data.The solution of this problem are not only in the hands of network topology but in the hands of path of autonomous underwater vehicle(AUV).With the problem in hand,an energy-efficient data collection scheme is designed for mobile underwater network.Especially,the data collection scheme is divided into two phases,i.e.,routing algorithm design for sensor nodes and path planing for AUV.With consideration of limited-energy and network robustness,Q-learning based dynamic routing algorithm is designed in the first phase to optimize the routing selection of nodes,through which a potential-game based optimal rigid graph method is proposed to balance the trade-off between the energy consumption and the network robustness.With the collected data,Q-learning based path planning strategy is proposed for AUV in the second phase to find the desired path to gather the data from data collector,then a mode-free tracking controller is developed to track the desired path accurately.Finally,the performance analysis and simulation results reveal that the proposed approach can guarantee energy-efficient and improve network stability.
文摘This study uses a numerical method to analyze the proposed model structure. Before the parametric analysis, a pre-analysis to make sure the analytical results are accountable, a verification analysis was performed. The results found are compared well with the limited experimental findings of Goda et al. and it is very encouraging to find that for the proposed method as an alternative for green energy developments, as long as an appropriate design is performed, an OWC combined with breakwater structure may provide an alternative for green energy system utilized in a harbor area. From the results of the first stage of parameter analysis that the size of the openings of the cell of converting system is variable, a traditional full opened cell is not necessary the most efficient design for the wave power conversion in terms of the variations of air pressure inside the cell and air speed through the outlet orifice that will drive the electricity power generator.
基金This research was financially supported by the National Science Council , Taiwan under the project entitled"TheStudy of the Dynamic Behavior of Foundation Soil beneath Nearshore structures under Wave Loading Action (I)"withthe project number of NSC-91-2211-E-019-013
文摘A series of hydraulic model tests with horizontal movable seabed under regular wave actions have been carried out to investigate the dynamic interactions between water waves and seabed soil. Seabed dynamic stresses from experiments are, tound to differ from theoretical resuhs. The response of p0 in permeable seabed has a small decay and phase shift to the nonlinear wave actions, and the dynamic stresses, σs/p0, σh/p0 and u/p0, contain different phase shift characteristics. Such phenomena will strongly affect the dynamic stress path in seabed. If the phase shifts of σs. and σh are neglected, the stress path will become a straight line; otherwise, it will become an elliptical curve. In phase shift cases, the long axis of the p - q diagram will be shortened when the depth increases, and the short axis will become longer when the phase shift increases. For the p＇ - q＇ diagram, the larger the phase lag of u, the longer the short axis. Relative results offer useful information for the analysis of seabed stability.
文摘Resistance analysis is an important analytical method used to evaluate the hydrodynamic performance of High Speed Craft (HSC). Analysis of multihull resistance in shallow water is essential to the performance evaluation of any type of HSC. Ships operating in shallow water experience increases in resistance because of changes in pressure distribution and wave pattern. In this paper, the shallow water performance of an HSC design concept, the semi-Small Waterplane Area Twin Hull (semi-SWATH) form, is studied. The hull is installed with fin stabilizers to reduce dynamic motion effects, and the resistance components of the hull, hull trim condition, and maximum wave amplitude around the hull are determined via calm water resistance tests in shallow water. These criteria are important in analyzing semi-SWATH resistance in shallow water and its relation to flow around hull. The fore fin angle is fixed to zero degrees, while the aft fin angle is varied to 0o, 5o, 10o, and 15o. For each configuration, investigations are conducted with depth Froude numbers (FrH) ranging from 0.65 to 1.2, and the resistance tests are performed in shallow water at the towing tank of UTM. Analysis results indicate that the resistance, wave pattern, and trim of the semi-SWATH hull form are affected by the fin angle. The resistance is amplified whereas the trim and sinkage are reduced as the fin angle increases. Increases in fin angle contribute to seakeeping and stability but affect the hull resistance of HSCs.
基金supported by the Malaysian government under FRGS grants R.K130000.7843.5F297 and FRGS/1/2020/TK0/UTM/02/78.
文摘The flow interference of multiple cylinders subjected to vortex-induced vibration(VIV)is a complex response that is not fully understood.This paper investigates the fluid-dynamic behaviour of elastically mounted rigid cylinders where both cylinders were free to oscillate in the cross-flow direction.The cylinders were subjected to uniform water flow at various separation distances of 3.5,4.0,and 4.5 D(D is the diameter of the cylinder)in a tandem arrangement.Based on the observation,the interference between the cylinders and the unsteady wake from the leading cylinder caused a continuous vibration with no lower branch in amplitude response.While as found in the cases of the single cylinder,there was a lower branch in amplitude response.The results also revealed that the cylinders experienced the VIV and wake-induced vibration(WIV)at each separation distance.Moreover,the leading cylinder oscillated at a larger amplitude at a separation distance of 3.5 D,indicating a critical distance for cylinders in the tandem arrangement due to the existence of a bistable regime.Hence,it is reasonable to conclude that the flow interference between the leading and trailing cylinders significantly impacts the cylinders’dynamic behaviour.
基金supported by the Institute for Ocean Engineering,Shenzhen International Graduate School,Tsinghua University.
文摘Atmospheric Kármán vortex streets,which frequently emerge on the leeward side of isolated islands under specific atmospheric conditions,play a critical role in large-scale atmospheric dynamics.However,their automated detection and the influence of atmospheric variables on their formation remain insufficiently explored.Here,we firstly developed an object detection dataset utilizing 20 years of cloud imagery from the MODIS aboard the Terra and Aqua satellites,facilitating the application of artificial intelligence algorithms for the automated detection of Kármán vortex streets.Given that these vortex streets can manifest under both cloudy and cloudfree conditions,we further assessed the contribution of various spectral bands to vortex detection by implying a multi-channel classification network.This network,built upon a custom-designed miniResNet dual-level classification network and trained on MODls HDFformat sensor data,demonstrates that the dataset is particularly suited for detecting Kármán vortex streets in cloudy conditions.Different types of advanced algorithms were applied on the dataset,yielding baseline performance metrics and potential detection methods.Additionally,we proposed two optimization strategies tailored to Kármán vortex streets detection.First,leveraging the intrinsic properties of vortex structures,we introduced a Gamma loss optimization for bounding box aspect ratios,which significantly enhanced performance across six YoLO-based models.Second,we investigated the role of atmospheric variables in vortex formation and incorporated an auxiliary-task-enhanced learning approach to further refine detection accuracy,drawing upon findings from our recently published work.In summary,this study provides a novel dataset that supports meteorological and climatological research,addressing a critical gap in atmospheric data.Furthermore,the proposed auxiliary optimization strategies highlight the distinct challenges of Kármán vortex streets detection compared to conventional object detection,underscoring the unique structural and atmospheric characteristics of these phenomena.
基金Financial support from the Ministry of Science and Technology,China(No.ZK20210004)the Department of Science and Technology of Shandong Province,China(No.ZK20200026),are gratefully acknowledged.
文摘There are still fundamental problems lying in the basic research of bulk nanobubbles.Are the bulk nanobubbles reported in the literature nano scale bubbles or contaminants in fact?At present,there is not yet sufficient experimental evidence to show that the bulk nanoparticles are only gas bubbles but not other nano scale contaminants.If they are indeed nanobubbles,what causes the bulk nanobubbles observed in the literature to be much more stable than being predicted by the Epstein-Plesset theory?This paper firstly discusses the contradiction between the traditional theory prediction and the observed lifetime of the bulk nanobubbles,and then discusses whether the so-called nanobubbles are gas aggregates.We review the existing typical models,and the influence of different conditions on the stability of bulk nanobubbles,for paving the road to a clear understanding of the stability mechanism of bulk nanobubbles.In addition,the representative production methods and characterization methods of bulk nanobubbles are discussed in order to offer some guidance to their wide range of commercial applications.
基金supported by the Estonian Research Council (Grant No.PRG1820).
文摘Water entry problems represent complex multiphase flows involving air,water,and structure interaction,occurring rapidly in rough seas,and potentially effecting structural integrity of floating structures.This paper experimentally investigates asymmetric slamming loads acting on a 3-D elastic wedge section.The specimen,featuring two different bottom plates(stiffened and unstiffened),each 4 mm thick,aims to assess the effect of structural stiffness on dynamic loads.The experiments are conducted at different drop heights of 25 cm and 50 cm and varying heel angles from 5°to 25°.The paper describes the experimental conditions,including wedge geometry,material properties,and the test plan.The study explores the influence of heel angle on impact acceleration,revealing an increase in peak acceleration with a higher inclination angle,particularly in the vertical direction.Additionally,the hydrodynamic pressure resulting from asymmetric slamming is presented.The pressure results analyzed and compared at different locations along the length of the wedge.The experimental findings indicate that,despite the leeward side(stiffened)experiencing a smaller hydrodynamic load,the heel angle significantly affects pressure results on the windward side(unstiffened),leading to a more pronounced dynamic response.The time history of pressure results emphasizes the effect of elastic vibrations,particularly noticeable on the unstiffened bottom plate.This study contributes to a deeper understanding of asymmetric slamming on aluminum structures,facilitating the enhancement of mathematical models and the validation of numerical simulations.
