摘要：
The impact of the South China Sea (SCS) to the super typhoon Mangkhut (2018) and the air-sea interaction are evaluated through COAWST model in this study which fully coupled with the atmosphere model (WRF), the ocean model (ROMS), and the wave model (SWAN). A comparison of our modeled results with several buoys and tide stations revealed remarkable consistency, the minimum root mean square error (RMSE) for wind speed, significant wave height, and water level are 3.013 m/s, 0.641m, 0.007m. During the development and dissipation of super typhoon Mangkhut, the Coriolis force caused the typhoon wind field to exhibit a pronounced rightward deflection. The characteristics of the significant wave height field are generally similar to those of the wind field, although there is a temporal lag of several hours. Moreover, we researched on the spatiotemporal variations of sea surface temperature (SST) impact by the Mangkhut’s passage, and found that it exhibits two main characteristics: spatial asymmetry and temporal lag. The spatial asymmetry is primarily governed by typhoon-generated wind fields, while the temporal lag is mainly controlled by upwelling and vertical mixing processes during the typhoon’s passage, with Ekman pumping playing a pivotal role in these dynamics. This study mainly concentrates on investigating the dynamic and thermodynamic responses of the ocean during extreme weather conditions by using COAWST model.
通讯机构：
[Huang, ZY ] C;Changsha Univ Sci & Technol, Sch Hydraul & Ocean Engn, Changsha, Peoples R China.;Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha, Peoples R China.
关键词：
Dongting Lake Basin;extreme precipitation;large-scale climate teleconnections;spatiotemporal variability;surface air temperature;topography
摘要：
The intensification of global climate change and regional human activities has led to an increase in the frequency and intensity of extreme precipitation, posing significant challenges to regional sustainable development. Using daily precipitation observation data from 108 meteorological stations during 1960-2020, the spatiotemporal distribution characteristics of extreme precipitation in the Dongting Lake Basin (DLB) are revealed, and the mechanisms driving extreme precipitation variation in the DLB are investigated. The results showed that with the increase in the frequency, intensity and amount of extreme precipitation, the DLB is trending towards increased humidity. However, consecutive wet days have declined significantly at a rate of -0.015 days/year, indicating that more short-duration but high-intensity extreme precipitation are likely to occur in the future. These changes have intensified with the increase in regional average warming. In contrast, the weakening of the East Asian Summer Monsoon (EASM) amplifies changes in extreme precipitation through nonlinear enhancement mechanisms, particularly when interacting with other climate drivers. Additionally, extreme precipitation exhibits a sensitive response to elevation. Specifically, low-altitude areas tend to experience more frequent and intense extreme events, whereas high-altitude regions are more prone to short-duration heavy rainfall. The fastest growth in extreme precipitation was observed in the hilly-valley transition zone between the northern Xuefeng Mountains and southern Wuling Mountains. At the sub-basin level, the Lishui River Basin exhibits relatively minor variations in most extreme precipitation indices, while the Xiangjiang River Basin records the greatest increase in the frequency of extreme precipitation. These patterns may be explained by differences in the categories of dominant climate drivers and the strength of their associated impacts.
作者机构：
[Yuan, Shuai] Changsha Univ Sci & Technol, Sch Hydraul & Ocean Engn, Changsha 410114, Peoples R China.;[Jiang, Changbo; Yuan, Shuai] Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.;[Jiang, Changbo] Hunan Univ Technol, Sch Civil & Environm Engn, Zhuzhou 412007, Peoples R China.;[Ma, Yuan] Henan Water Conservancy Migrat Affairs Ctr, Zhengzhou 450000, Peoples R China.;[Li, Shanshan] Hunan City Univ, Coll Civil Engn, Yiyang 413002, Peoples R China.
通讯机构：
[Jiang, CB ] K;Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.;Hunan Univ Technol, Sch Civil & Environm Engn, Zhuzhou 412007, Peoples R China.
关键词：
West Dongting Lake;hydrological regime;degree of hydrologic alteration (DHA);IHA–RVA
摘要：
To quantitatively evaluate the hydrological regime dynamics in West Dongting Lake over the past seven decades, this study utilizes daily average water level series (1955-2024) from key control stations (Nanzui and Xiaohezui) to analyze variations in water level and discharge through change-point detection methods, adopting the water level difference between Xiaohezui and Nanzui as a pivotal indicator of hydrological changes; the IHA-RVA framework is then applied to comprehensively assess the degree of alteration in hydrological indicators before and after identifying change points, demonstrating the following: (1) declining trends in water level/discharge at both stations-primarily attributable to reduced inflows from the Songzi and Hudu Rivers-underwent abrupt shifts in 1983 and 2003, while the water level difference displayed an increasing trend with a change point in 1991; (2) the overall degree of hydrologic alteration (DHA) was moderate, with enhanced variability during T2 (2003-2024) relative to T1 (1983-2003), notably for discharge at Nanzui and water level at Xiaohezui; (3) reduced discharge in the Songzi and Hudu Rivers primarily drives the decreased outflow from West Dongting Lake. In the Li and Yuan basins during period T1, anthropogenic factors dominated runoff alterations. During T2, anthropogenic contributions accounted for 76.27% and 48.67% of runoff changes, respectively, resulting in reduced runoff volumes under equivalent precipitation inputs. (4) Under fixed water level differences, a significant positive correlation exists between discharges at Xiaohezui and Nanzui stations. Greater discharge flows downstream through the flow channel adjacent to NZ at West Dongting Lake's outlet. Collectively, these findings establish a technical foundation for assessing the impact of hydrological regimes and aquatic ecological security in Dongting Lake, thereby advancing sustainable water resource utilization across the basin.
摘要：
There has been significant interest in post-tsunami surveys regarding how effective fringing reefs are at protecting coastlines from inundation caused by tsunamis. Limited attention has been given to the wave transformation characteristics and wave run-up dynamics within a complex reef-lagoon-channel system compared to the extensively studied two-dimensional horizontal fringing reefs. In response to this research gap, a three-dimensional numerical wave tank has been created, incorporating the incompressible Reynolds-averaged Navier-Stokes equations accompanied with k-ω SST turbulence model. The volume of fluid (VOF) strategy is employed to track the free surface, accompanied by advanced grid cascading encryption technology. Laboratory measurements (Swigler, 2009; Briggs et al., 1995) of the waves are utilized for model validation. The influence of incident wave height, reef flat submergence, fore-reef slope, and channel width on wave propagation characteristics were examined. The results reveal that the relative run-up decreases with larger wave heights and decreases near channels as reef flat submergences rise. Initially, smaller channels reduce relative run-up, but it increases again with widening, shifting the maximum relative run-up location away from the channel, while fore-reef slope changes minimally affect run-up.
There has been significant interest in post-tsunami surveys regarding how effective fringing reefs are at protecting coastlines from inundation caused by tsunamis. Limited attention has been given to the wave transformation characteristics and wave run-up dynamics within a complex reef-lagoon-channel system compared to the extensively studied two-dimensional horizontal fringing reefs. In response to this research gap, a three-dimensional numerical wave tank has been created, incorporating the incompressible Reynolds-averaged Navier-Stokes equations accompanied with k-ω SST turbulence model. The volume of fluid (VOF) strategy is employed to track the free surface, accompanied by advanced grid cascading encryption technology. Laboratory measurements (Swigler, 2009; Briggs et al., 1995) of the waves are utilized for model validation. The influence of incident wave height, reef flat submergence, fore-reef slope, and channel width on wave propagation characteristics were examined. The results reveal that the relative run-up decreases with larger wave heights and decreases near channels as reef flat submergences rise. Initially, smaller channels reduce relative run-up, but it increases again with widening, shifting the maximum relative run-up location away from the channel, while fore-reef slope changes minimally affect run-up.
作者机构：
[Yin, Longbin; Yang, Kang; Rao, Han; Liu, Jiang; Deng, B; Xiong, Kai; Deng, Bin; Guan, Zhixing; Luo, Wei] Changsha Univ Sci & Technol, Sch Hydraul & Ocean Engn, Changsha 410114, Peoples R China.;[Jiang, Changbo; Deng, B; Deng, Bin] Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.;[Guan, Zhixing] Hunan Port Shipping & Water Resources Grp Co Ltd, Changsha 410004, Peoples R China.;[Lu, Weizhi] Natl Engn Lab Appl Technol Forestry & Ecol Souther, Changsha 410004, Peoples R China.;[Lu, Weizhi] Cent South Univ Forestry & Technol, Coll Ecol & Environm, Changsha 410004, Peoples R China.
通讯机构：
[Deng, B ] C;Changsha Univ Sci & Technol, Sch Hydraul & Ocean Engn, Changsha 410114, Peoples R China.;Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.
关键词：
Chlorophyll-a retrieval;Optical water types;Ensemble learning;Extreme drought;Remote sensing
摘要：
Accurate and robust retrieval of chlorophyll-a (Chl-a) concentrations in optically complex lakes is critical for effective water quality monitoring, especially under frequent extreme climatic conditions. This study proposes an integrated framework combining optical water type (OWTs) classification and ensemble learning algorithms to enhance the re- mote sensing retrieval accuracy of Chl-a in Dongting Lake and Poyang Lake during 2020–2023, particularly during the extreme drought event of 2022. Firstly, K-means clustering combined with spectral feature analysis was used to classify both lakes into four distinct OWTs. Dongting Lake classifications effectively separated phytoplankton-dominated waters (OWT1, OWT2, OWT4) from those dominated by non-algal suspended matter (OWT3). For Poyang Lake, classifications identified mixed water types (OWT1), frequent algal bloom areas (OWT2), high biomass phytoplankton areas (OWT3), and areas significantly masked by non-algal particles (OWT4). Further analysis indicated that OWT2 in Dongting Lake is prone to algal blooms, while OWT3 and OWT4 are dominated by non-algal particles. Secondly, the performance of ensemble learning methods (Bagging, Boosting, Stacking, and Voting) was evaluated against traditional single models (SVR and BPNN). The results demonstrated the superior stability and predictive accuracy of the Voting strategy under low Chl-a conditions in Dongting Lake, achieving a maximum MAPE reduction of 84.76 %. Meanwhile, the Stacking method exhibited outstanding robustness in Poyang Lake’s complex optical conditions, with RMSE reduced by up to 93.12 %. Additionally, hierarchical modeling based on OWT-specific ensemble methods significantly reduced errors compared to traditional global models, with decreases of 36 % in Dongting Lake and 42.19 % in Poyang Lake. Finally, this study revealed that the extreme drought event in the Yangtze River basin in 2022 significantly altered seasonal and interannual variations in the OWTs of Dongting Lake and Poyang Lake. The drought led to lake shrinkage and increased dominance of non-algal suspended particles, highlighting the vulnerability of these connected lake ecosystems under extreme climatic conditions. The research emphasizes the importance of combining a lake-specific OWTs classification and advanced ensemble learning techniques for precise water quality assessment under dynamic environmental conditions.
Accurate and robust retrieval of chlorophyll-a (Chl-a) concentrations in optically complex lakes is critical for effective water quality monitoring, especially under frequent extreme climatic conditions. This study proposes an integrated framework combining optical water type (OWTs) classification and ensemble learning algorithms to enhance the re- mote sensing retrieval accuracy of Chl-a in Dongting Lake and Poyang Lake during 2020–2023, particularly during the extreme drought event of 2022. Firstly, K-means clustering combined with spectral feature analysis was used to classify both lakes into four distinct OWTs. Dongting Lake classifications effectively separated phytoplankton-dominated waters (OWT1, OWT2, OWT4) from those dominated by non-algal suspended matter (OWT3). For Poyang Lake, classifications identified mixed water types (OWT1), frequent algal bloom areas (OWT2), high biomass phytoplankton areas (OWT3), and areas significantly masked by non-algal particles (OWT4). Further analysis indicated that OWT2 in Dongting Lake is prone to algal blooms, while OWT3 and OWT4 are dominated by non-algal particles. Secondly, the performance of ensemble learning methods (Bagging, Boosting, Stacking, and Voting) was evaluated against traditional single models (SVR and BPNN). The results demonstrated the superior stability and predictive accuracy of the Voting strategy under low Chl-a conditions in Dongting Lake, achieving a maximum MAPE reduction of 84.76 %. Meanwhile, the Stacking method exhibited outstanding robustness in Poyang Lake’s complex optical conditions, with RMSE reduced by up to 93.12 %. Additionally, hierarchical modeling based on OWT-specific ensemble methods significantly reduced errors compared to traditional global models, with decreases of 36 % in Dongting Lake and 42.19 % in Poyang Lake. Finally, this study revealed that the extreme drought event in the Yangtze River basin in 2022 significantly altered seasonal and interannual variations in the OWTs of Dongting Lake and Poyang Lake. The drought led to lake shrinkage and increased dominance of non-algal suspended particles, highlighting the vulnerability of these connected lake ecosystems under extreme climatic conditions. The research emphasizes the importance of combining a lake-specific OWTs classification and advanced ensemble learning techniques for precise water quality assessment under dynamic environmental conditions.
通讯机构：
[Zhou, T ] C;Changsha Univ Sci & Technol, Sch Hydraul & Ocean Engn, Changsha 410114, Hunan, Peoples R China.;Key Lab Water Sediment Sci & Water Disaster Preven, Changsha 410114, Peoples R China.
摘要：
The sand dredging activities on the reef flat to meet the material requirement of engineering construction are prevalent around some Asia-Pacific reef islands, and its potential impact on the coastal hazard mitigation raises growing attention in the community of coastal research. In contrast to the extensively studied spectral wave processes with reef-flat excavation pit over fringing reefs, limited investigations have focused on the wave transformation possesses over such an artificially modified reef profile under monochromatic waves. To remedy current research deficiency, a new set of physical experiments is conducted to investigate the propagation and runup of monochromatic waves over fringing reefs with a reef-flat excavation pit. A series of incident waves are tested in a wave tank, and the influences of the pit's width and location are examined. An empirical formula is also proposed for predicting the measured wave runups. Meanwhile, a Smooth Particle Hydrodynamics model is innovatively introduced in this study. The adopted model is first validated by the present experimental data in view of cross-shore variations of wave and current on the reef flat as well as wave runup on the back-reef slope. Subsequently, the adopted model is used to examine the impacts of such pit characteristics as pit side slope, pit depth, and pit number on the wave processes that are not addressed by present laboratory experiments.
摘要：
Repeatedly solving flow around structures with varying parameters using computational fluid dynamics (CFD) is often essential for structural design. This study proposes a boundary-assimilation Fourier neural operator (BAFNO) method to address the challenges of manually setting initial conditions for CFD. The focus of the BAFNO is on the generalization ability to predict initial flow fields without relying on observational data. BAFNO addresses the boundary constraint requirements of the existing physics-informed neural operator models in parametric geometries. Inspired by the ghost node method, the domain boundary conditions are assimilated into the loss function instead of adding penalty terms. Meanwhile, the structure boundaries are assimilated into a damping source term using a level set function. BAFNO can flexibly handle parametric geometries with different shapes and quantities. Subsequently, a series of numerical experiments for flow-around structures are conducted to confirm the performance of the BAFNO. The results indicate that the BAFNO has strong generalization capability, and the BAFNO + CFD can obtain dynamic stable fields faster than the direct CFD.
摘要：
Floods are one of the most destructive disasters and require a range of structural and non-structural measures to reduce their impacts. Evacuation is an effective non-structural measure to increase the resilience of flood-affected areas. This study aims to provide a systematic overview of evacuation planning for urban flood scenarios in terms of theories, methods, models, and techniques for both pedestrians and vehicles. The review addresses key components such as flood simulation modelling, flood hazard assessment methods, shelter identification, evacuation route development, and evacuee movement modelling. Among these, we highlight the comparison and analysis of flood hazard assessment methods, shelter optimisation and route optimisation. Additionally, a systematic analysis and comparison of evacuation shelters, evacuation route algorithms, and evacuee movement models are presented. Meta-heuristic algorithms have been shown to perform well for evacuation routes. Finally, the insights into four recent directions for enhancing evacuation plans include consideration of pedestrian and vehicle movement speeds, evacuee psychology, multimodal emergency evacuation, and the effect of overhead power lines on rescue operations.
Floods are one of the most destructive disasters and require a range of structural and non-structural measures to reduce their impacts. Evacuation is an effective non-structural measure to increase the resilience of flood-affected areas. This study aims to provide a systematic overview of evacuation planning for urban flood scenarios in terms of theories, methods, models, and techniques for both pedestrians and vehicles. The review addresses key components such as flood simulation modelling, flood hazard assessment methods, shelter identification, evacuation route development, and evacuee movement modelling. Among these, we highlight the comparison and analysis of flood hazard assessment methods, shelter optimisation and route optimisation. Additionally, a systematic analysis and comparison of evacuation shelters, evacuation route algorithms, and evacuee movement models are presented. Meta-heuristic algorithms have been shown to perform well for evacuation routes. Finally, the insights into four recent directions for enhancing evacuation plans include consideration of pedestrian and vehicle movement speeds, evacuee psychology, multimodal emergency evacuation, and the effect of overhead power lines on rescue operations.
摘要：
Extreme wave events induced by marine meteorological extremes such as storm surges and tsunamis have become a critical focus in contemporary coral reef hydrodynamics research. The synergistic forcing of strong winds and extreme wave regimes poses significant challenges to the structural safety of reef engineering systems. A high-resolution numerical model was established based on OpenFOAM. The reliability and accuracy of the model were verified by comparing with experimental data. Building upon this foundation, the effects of wind on the interaction processes between solitary waves and vertical walls on reef flats were investigated. The findings demonstrate that wind enhances vortex motions during solitary wave interactions with vertical walls while attenuating wave reflection effects. At low wind speeds, the maximum horizontal force experiences minor reductions compared to windless scenarios, whereas high wind speeds induce significant increases. The maximum vertical force at the wall crest exhibits monotonic growth with increasing wind intensity. Wind action also advances the initiation of overtopping processes relative to windless. Crucially, the maximum cumulative overtopping volume amplifies progressively with wind speed, reaching approximately 1.23–4.11 times the windless at U∗ = 4. This study provides theoretical references for the design of protective engineering structures on coral reefs.
Extreme wave events induced by marine meteorological extremes such as storm surges and tsunamis have become a critical focus in contemporary coral reef hydrodynamics research. The synergistic forcing of strong winds and extreme wave regimes poses significant challenges to the structural safety of reef engineering systems. A high-resolution numerical model was established based on OpenFOAM. The reliability and accuracy of the model were verified by comparing with experimental data. Building upon this foundation, the effects of wind on the interaction processes between solitary waves and vertical walls on reef flats were investigated. The findings demonstrate that wind enhances vortex motions during solitary wave interactions with vertical walls while attenuating wave reflection effects. At low wind speeds, the maximum horizontal force experiences minor reductions compared to windless scenarios, whereas high wind speeds induce significant increases. The maximum vertical force at the wall crest exhibits monotonic growth with increasing wind intensity. Wind action also advances the initiation of overtopping processes relative to windless. Crucially, the maximum cumulative overtopping volume amplifies progressively with wind speed, reaching approximately 1.23–4.11 times the windless at U∗ = 4. This study provides theoretical references for the design of protective engineering structures on coral reefs.
摘要：
洞庭湖水体面积动态变化监测对防洪、维系生态系统的稳定及生物多样性具有重要意义。以经典Unet网络模型和创新性HRNet网络模型为代表的深度学习技术已成为遥感图像信息获取的高效途径，实验以Sentinel-1A SAR影像为主要数据源，定性、定量地分析了Sentinel-1双极化水体指数法（Sentinel-1 Dual-Polarized Water Index，SDWI）、面向对象分类法、UNet网络模型和HRNet网络模型4种方法的水体提取效果，并基于最佳水体提取方法对洞庭湖2016~2021年汛期（4~10月）水体面积进行时空变化特征分析。结果表明：①HRNet和Unet网络模型较传统方法具有更优的水体提取效果，其中，HRNet网络模型在抑噪、抗阴影等方面表现更佳，F1分数、误判率和平均交并比分别为0.961 6、0.007 8和0.958 6；②汛期洞庭湖水体面积在月际变化上呈现出“涨—丰—退”的变化特征，湖面从4~5月份开始扩张，6~8月份水域面积维持在较高水平，此后由于来水减少，9~10月的水体面积逐步减小。研究期间所监测到的最大水体面积为2020年7月30日的2 263.90 km 2 ；③洞庭湖汛期的水体淹没频率从湖体中心和干流向外逐渐降低，不同湖区的淹没频率分布格局不同，东洞庭湖 “湖心高四周低”，南洞庭湖和西洞庭湖“南高北低”。综上所述，Sentinel-1A SAR影像与深度学习技术的结合应用可以实现洞庭湖水体信息高效获取与水面面积高频监测，为高动态湖泊水域监测提供了一种新思路。 您的浏览器不支持 audio 元素。 AI语音播报 Monitoring the dynamic changes of water area in Dongting Lake is of great significance for flood control， ecosystem stability and biodiversity. The deep learning algorithm represented by the classic Unet the innovative HRNet has become an efficient way to obtain remote sensing image information. Taking Sentinel-1A SAR image as the main data source， this paper qualitatively and quantitatively analyzes the water extraction results of SDWI index method （Sentinel-1 Dual-Polarized Water Index，SDWI）， object-oriented classification method， UNet network model and HRNet network model. Based on the best water extraction method， the temporal and spatial variation characteristics of water area in the flood season （April to October） of Dongting Lake from 2016 to 2021 are analyzed. The results show that ： ① The deep learning algorithm represented by HRNet and Unet has better water extraction effect than traditional methods. Among them， HRNet has superior performance in noise suppression and shadow resistance， and the F1 score， MRate and MIoU are 0.961 6， 0.007 8 and 0.958 6， respectively. ② During the flood season， the water area of Dongting Lake shows the characteristics of “ increase-full-decrease ” in the monthly variation. The lake surface begins to expand from April to May， and the water area maintained at a high level from June to August. Since then， due to the decrease of inflow， the water area gradually decreases from September to October. The 2 263.90 km 2 at July 30， 2020 is the largest water area monitored during the study period. ③ The submerged frequency of water body in flood season of Dongting Lake gradually decreases from the center of the lake body and the main stream. The distribution patterns of submerged frequency in different lake areas are different. The submerged frequency of East Dongting Lake is higher than that of South Dongting Lake and West Dongting Lake. In summary， the combination of Sentinel-1A SAR image and deep learning technology can realize the efficient acquisition of water information and high-frequency monitoring of the water surface area at Dongting Lake， providing a new idea for the high dynamic lake water monitoring.
通讯机构：
[Chen, J ] C;Changsha Univ Sci & Technol, Sch Hydraul & Environm Engn, Changsha 410114, Peoples R China.;Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.;Key Lab Water Sediment Sci & Water Disaster Preven, Changsha 410114, Peoples R China.
关键词：
reef islands;coral sand beach;equilibrium beach profile;coral sand bar
摘要：
This study utilized 50 laboratory experiments to document the evolution of coral beaches under varying regular wave conditions, including five distinct wave periods and ten wave heights. Both the type of equilibrium beach and the shape of sand bars were used to represent beach evolution. The evolution of coral sand beaches was then compared to quartz sand beaches. The experimental results show that the predicted (modeled) equilibrium profile of a quartz sand beach was not applicable to coral sand beaches. Compared to sand bars on quartz sand beaches, the distance from bar crests to the beach berm in coral sand beaches was greater, whereas the erosional depth of sand troughs was deeper. However, the grain size distribution of sand associated with the coral sand beach under wave action was consistent with Celikoglu’s law. Both an equilibrium beach profile classification model and a sand bar shape prediction model for coral sand beaches were developed based on the experimental data.
期刊：
Journal of Fluid Mechanics,2024年990:A15 ISSN：0022-1120
通讯作者：
He, F
作者机构：
[Yao, Zhen; Long, Yuannan; Bian, Cheng; Jiang, Changbo; Jiang, Chao; Wu, Zhiyuan; Deng, Bin; Chen, Jie] Changsha Univ Sci & Technol, Sch Hydraul & Environm Engn, Changsha 410114, Peoples R China.;[Long, Yuannan; Jiang, Changbo; Wu, Zhiyuan; Deng, Bin; Chen, Jie] Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.;[Long, Yuannan; Jiang, Changbo; Wu, Zhiyuan; Deng, Bin; Chen, Jie] Key Lab Water Sediment Sci & Water Disaster Preven, Changsha 410114, Peoples R China.;[He, Fei] Univ Western Australia, Sch Engn, 35 Stirling Highway, Crawley, WA 6009, Australia.
通讯机构：
[He, F ] U;Univ Western Australia, Sch Engn, 35 Stirling Highway, Crawley, WA 6009, Australia.
关键词：
sediment transport
摘要：
Understanding settling motion of coral grains is important in terms of protection of coral reef systems and resotoration of the associated ecosystems. In this paper, a series of laboratory experiments was conducted to investigate the settling motion, using optical microscopy to measure shape parameters of coral grains and the particle-filtering-based object tracking to reconstruct the three-dimensional trajectory. Three characteristic descent regimes, namely, tumbling, chaotic and fluttering, are classified based on the three-dimensional trajectory, the spiral radius variation and the velocity spectrum. It is demonstrated that if one randomly picks up one coral grain, then the probabilities of occurrence of the three regimes are approximately $26\,\%$ , $42\,\%$ and $32\,\%$ , respectively. We have shown that first, the dimensionless settling velocity generally increases with the non-dimensional diameter and Corey shape factor and second, the drag coefficient generally decreases with the Reynolds number and Corey shape factor. Based on this, the applicability of existing models on predicting settling velocity and drag coefficient for coral grains is demonstrated further. Finally, we have proposed extended models for predicting the settling velocity. This study contributes to better understanding of settling motion and improves our predictive capacity of settling velocity for coral grains with complex geometry.
期刊：
Journal of Marine Science and Engineering,2024年12(5):820- ISSN：2077-1312
通讯作者：
Chen, J
作者机构：
[Yao, Zhen; Bian, Cheng; Jiang, Changbo; Wu, Zhiyuan; Chen, Jie; Liu, Jiaxiang] Changsha Univ Sci & Technol, Sch Hydraul & Environm Engn, Changsha 410114, Peoples R China.;[Jiang, Changbo; Wu, Zhiyuan; Chen, Jie] Key Lab Water Sediment Sci & Water Disaster Preven, Changsha 410114, Peoples R China.;[Jiang, Changbo; Wu, Zhiyuan; Chen, Jie] Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.
通讯机构：
[Chen, J ] C;Changsha Univ Sci & Technol, Sch Hydraul & Environm Engn, Changsha 410114, Peoples R China.;Key Lab Water Sediment Sci & Water Disaster Preven, Changsha 410114, Peoples R China.;Key Lab Dongting Lake Aquat Ecoenvironm Control &, Changsha 410114, Peoples R China.
关键词：
bivalve shells;gastropod shells;final orientation;incipient mean velocity;motion thresholds
摘要：
Understanding the motion thresholds of shells is important, as shell motion allows the analysis of beach profiles, prevents excessive erosion of the coastline, and helps to resource the use of discarded shells, providing new ideas for the protection of beaches. In this study, the orientational motions and motion thresholds of two types of typical molluscan shells, bivalve and gastropod shells, were investigated by means of flume experiments. The final orientations with the statistically highest number of occurrences during the orientational motions of each shell were used as the initial orientations for the respective threshold flow velocity measurements. The critical Shields parameter and the incipient mean velocity of the flow were used to represent the critical threshold of the motion. The critical Shields parameters for bivalve shells in the convex upward position were overall higher on average than those for gastropod shells. The experimental data showed that the incipient mean flow velocities of bivalve shells in the convex upward position were about 1.4–2.8 times larger than those in the convex downward position. The incipient mean velocity data were regressed to obtain the motion threshold equations applicable to bivalve shells in the convex upward and convex downward positions as well as gastropod shells under different final orientations.
