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1.
《中国海洋大学学报(英文版)》2021,(5)
Nettings are complex flexible structures used in various fisheries. Understanding the hydrodynamic characteristics, deformation, and the flow field around nettings is important to design successful fishing gear. This study investigated the hydrodynamic characteristics and deformation of five nettings made of polyethylene and nylon materials in different attack angles through numerical simulation and physical model experiment. The numerical model was based on the one-way coupling between computational fluid dynamics(CFD) and large deflection nonlinear structural models. Navier-Stokes equations were solved using the finite volume approach, the flow was described using the k-ω shear stress turbulent model, and the large deflection structural dynamic equation was derived using a finite element approach to understand the netting deformation and nodal displacement. The porous media model was chosen to model the nettings in the CFD solver. Numerical data were compared with the experimental results of the physical model to validate the numerical models. Results showed that the numerical data were compatible with the experimental data with an average relative error of 2.34%, 3.40%, 6.50%, and 5.80% in the normal drag coefficients, parallel drag coefficients, inclined drag coefficients,and inclined lift coefficients, respectively. The hydrodynamic forces of the polyethylene and nylon nettings decreased by approximately 52.56% and 66.66%, respectively, with decreasing net solidity. The drag and lift coefficients of the nylon netting were approximately 17.15% and 6.72% lower than those of the polyethylene netting. A spatial development of turbulent flow occurred around the netting because of the netting wake. However, the flow velocity reduction downstream from the netting in the wake region increased with increasing attack angle and net solidity. In addition, the deformation, stress, and strain on each netting increased with increasing solidity ratio. 相似文献
2.
Sea bottom stress is conventionally assumed to be directly proportional to the square of the verticallyaveraged velocity,and the drag coefficient to be dependent on the speed and direction of the wind on the sea surface,the depth and dimension of the sea,the period of the tide and so on. In this paper a three-dimensional numerical model is used to discuss the relation the dragcoefficient and the above-mentioned factors.It can be shown from calculation that the relation, is valid,that the drag coefficient is a constant in a major part of a sea as thought conventionally,andthat there is a small area near the coast where the drag coefficient is far greater.We call it singular area. A number of conclusions on the relation between the drag coefficient and the speed and direction ofthe wind,the sea depth and so on,were obtained. 相似文献
3.
Impacts of Climatic Factors on Runoff Coefficients in Source Regions of the Huanghe River 总被引：4，自引：0，他引：4
CHEN Liqun LIU Changming LI Yanping WANG Guoqiang 《中国地理科学(英文版)》2007,17(1):047-055
Runoff coefficients of the source regions of the Huanghe River in 1956–2000 were analyzed in this paper. In the 1990s runoff of Tangnaihai Hydrologic Station of the Huanghe River experienced a serious decrease, which had at- tracted considerable attention. Climate changes have important impact on the water resources availability. From the view of water cycling, runoff coefficients are important indexes of water resources in a particular catchment. Kalinin baseflow separation technique was improved based on the characteristics of precipitation and streamflow. After the separation of runoff coefficient (R/P), baseflow coefficient (Br/P) and direct runoff coefficient (Dr/P) were estimated. Statistic analyses were applied to assessing the impact of precipitation and temperature on runoff coefficients (including Dr/P, Br/P and R/P). The results show that in the source regions of the Huanghe River, mean annual baseflow coefficient was higher than mean annual direct runoff coefficient. Annual runoff coefficients were in direct proportion to annual pre- cipitation and in inverse proportion to annual mean temperature. The decrease of runoff coefficients in the 1990s was closely related to the decrease in precipitation and increase in temperature in the same period. Over different sub-basins of the source regions of the Huanghe River, runoff coefficients responded differently to precipitation and temperature. In the area above Jimai Hydrologic Station where annual mean temperature is –3.9oC, temperature is the main factor in- fluencing the runoff coefficients. Runoff coefficients were in inverse relation to temperature, and precipitation had nearly no impact on runoff coefficients. In subbasin between Jimai and Maqu Hydrologic Station Dr/P was mainly affected by precipitation while R/P and Br/P were both significantly influenced by precipitation and temperature. In the area be-tween Maqu and Tangnaihai hydrologic stations all the three runoff coefficients increased with the rising of annual precipitation, while direct runoff coefficient was inversely proportional to temperature. In the source regions of the Huanghe River with the increase of average annual temperature, the impacts of temperature on runoff coefficients be-come insignificant. 相似文献
4.
Black rockfish(Sebastes schlegeli) is an important species for culture; however, its reproductive characteristics have not been fully documented. In this study, we investigated the morphology and developmental process of germ cells in this ovoviviparous rockfish in reproductive season(October 2011–November 2012) with histological methods. We found that the gonad of mature fish showed notable seasonal changes in developmental characteristics and morphological structure. The sperm cells matured during a period lasting from October to December, significantly earlier than the oocytes did. A large number of spermatozoa and other cells occurred in testis at different developmental stages. Vitellogenesis in oocytes began in October, and gestation appeared in April next year. Spermatophores were discovered for the first time in Sebastes, which assembled in testis, main sperm duct, oviduct and genital tract, as well as ovarian cavity in October and April. These organs may serve either as production or hiding places for spermatophores and spermatozoa which were stored and transported in form of spermatophores. Testicular degeneration started from the distal part of testis in April, with spermatophores assembled in degenerating testis and waiting for transportation. The copulation probably lasted for a long period, during which the spermatozoa were discharged in batches as spermatophores. These spermatophores were coated with sticky materials secreted from the interstitial areas of testis and the main sperm duct, then transported into ovary. 相似文献
5.
Black rockfish（Sebastes schlegeli） is an important species for culture; however, its reproductive characteristics have not been fully documented. In this study, we investigated the morphology and developmental process of germ cells in this ovoviviparous rockfish in reproductive season（October 2011–November 2012） with histological methods. We found that the gonad of mature fish showed notable seasonal changes in developmental characteristics and morphological structure. The sperm cells matured during a period lasting from October to December, significantly earlier than the oocytes did. A large number of spermatozoa and other cells occurred in testis at different developmental stages. Vitellogenesis in oocytes began in October, and gestation appeared in April next year. Spermatophores were discovered for the first time in Sebastes, which assembled in testis, main sperm duct, oviduct and genital tract, as well as ovarian cavity in October and April. These organs may serve either as production or hiding places for spermatophores and spermatozoa which were stored and transported in form of spermatophores. Testicular degeneration started from the distal part of testis in April, with spermatophores assembled in degenerating testis and waiting for transportation. The copulation probably lasted for a long period, during which the spermatozoa were discharged in batches as spermatophores. These spermatophores were coated with sticky materials secreted from the interstitial areas of testis and the main sperm duct, then transported into ovary. 相似文献
6.
Flume experiments and numerical simulation were conducted to characterize the hydrodynamics of a trapezoid artificial reef. Measurements in particle image velocimetry were conducted to observe the formation of upwelling and vortices; and forces for the reef model were measured by load cell. The results of flume experiments agree well with the numerical data. In addition, the flow structure around a reef combining trapezoidal and cubic blocks was simulated numerically under two deployment schemes, showing a more complicated flow structure than that of a stand-alone reef. Relationship between drag coefficient and Reynolds number suggest that the degree of turbulence can be assessed from the value of drag coefficient downstream from the reef. The role of the reef in water flow is to reduce flow velocity and generate turbulence. 相似文献
7.
In this study, two common pollutants （benzo[a]pyrene and methamidophos） in marine environment were tested by comet assay for their inducement of in vivo genotoxic effect to the blood cells of black porgy （ Acanthopagrus schlegeli）. The fish was exposed to 2 μg/L of benzo[a]pyrene （BaP） and methamidophos, and their mixture. The assay was performed on whole blood at 2 h, 5 h, 24 h and 96 h exposure intervals. A significant increase in DNA damage was observed in each treatment with the pollutants. Additive effect of BaP and methamidophos was also found in the experiment. However, the decrease ratios of DNA damage for 5 h and 96 h exposure interals compared with 2 h and 24 h exposure ones, respectively, were noticed. This phenomenon may be explained by the function of repairing process via enzyme cytochrome P450 in the animal. Evidence of the genotoxicity of organophosphorus pesticides （OPs） and polynuclear aromatic hydrocarbons （PAHs） on marine fish are discussed in this paper. 相似文献
8.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献
9.
NUMERICAL STUDY OF THE INFLUENCE OF WAVES AND TIDE-SURGE INTERACTION ON TIDE-SURGES IN THE BOHAI SEA
Abstract The author‘s combined numerical model consisting of a third generation shallow water wave model and a 3-D tide-surge model with wave-dependent surface wind stress were used to study the influence of waves on fide-surge motion. For the typical weather case, in this study, the magnitude and mechanism of the influence of waves on tide-surges in the Bohai Sea were revealed for the first time. The results showed that although consideration of the wave-dependent surface wind stresses raise slightly the traditional surface wind stress, due to the accumulated effects, the computed results are improved on the whole. Storm level maximum modulation can reach 0.4 m. The results computed by the combined model agreed well with the measured data. 相似文献
10.
The Pearl River Delta is a unique and extremely complicated ecological system remarkably influenced by runoff. Investigation data obtained in March of 1987 were studied and used to calculate the transformation rate of carbon , the transformation coefficients of river water and sea water , and the flux coefficient of carbon in the reservoirs in the three estuarine bays (Lingdingyang , Modaomen and Yamen) of the Pearl River . 相似文献
11.
The Aral Sea was one of the largest lakes in the world before it started to shrink in the 1960s due to water withdrawal for agricultural irrigation.Precipitation decreased from 9.4 km3 in 1960 to 3.2 km3 in 2009,and annual river inflow into the Aral Sea decreased from 31.5 km3 in 1998 to 5.2 km3 in 2009.Comparison on the hydrological data of the Aral Sea between 1960 and 2009 showed the evaporation,water surface area,and water volume decreased by 90%,80%,and 88%,respectively.This study employs the observed values of water volume,precipitation,runoff,evaporation,and salinity to estimate water volume and salinity from 1960 to 2009,and the efficiency coefficients for predicted water volume and salinity are 0.975 and 0.974,respectively.Regression equations calculated from the observed data are used to predict precipitation,runoff,evaporation,and salinity from 2010 to 2021,and the results are then applied in the estimation of water volume and salinity.Our estimates suggest that salinity will increase to around 200 g/L and water volume will decrease to around 83 km3 in 2021. 相似文献
12.
Nitrogen balance method and nitrogen-free diet were used in this study to determine nitrogen maintenance requirement (NM) and nitrogen maintenance requirement per unit metabolism body weight (NM’) of black porgy Acanthopagrus schlegeli. Fish with body weight (BW) of 50, 80, 120, 160 and 200 g were fed by the diets containing three graded levels of crude protein (380, 420 and 460 g/kg). The results from nitrogen balance experiment showed that the amount of nitrogen deposition varied from 0.15 to 0.31 mg/g BW... 相似文献
13.
Three-stranded rope is widely used in fishing gear and mooring system. Results of numerical simulation are presented for flow around a three-stranded rope in uniform flow. The simulation was carried out to study the hydrodynamic characteristics of pressure and velocity fields of steady incompressible laminar and turbulent wakes behind a three-stranded rope. A three-cylinder configuration and single circular cylinder configuration are used to model the three-stranded rope in the two-dimensional simulation. The governing equations, Navier-Stokes equations, are solved by using two-dimensional finite volume method. The turbulence flow is simulated using Standard κ-ε model and Shear-Stress Transport κ-ω(SST) model. The drag of the three-cylinder model and single cylinder model is calculated for different Reynolds numbers by using control volume analysis method. The pressure coefficient is also calculated for the turbulent model and laminar model based on the control surface method. From the comparison of the drag coefficient and the pressure of the single cylinder and three-cylinder models, it is found that the drag coefficients of the three-cylinder model are generally 1.3–1.5 times those of the single circular cylinder for different Reynolds numbers. Comparing the numerical results with water tank test data, the results of the three-cylinder model are closer to the experiment results than the single cylinder model results. 相似文献
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15.
Linear wave theory and Longuet-Higgins and Steward's (1964) group-induced second-order longweve (GSLW) theory ware used in this study on the grouping effect on wave forces acting on a verticalbreakwater. The calculated variance of total wave pressure on the vertical breakwater was closer tothe measured value if the wave grouping effect was considered. 相似文献
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17.
Chitosan derived from crab shells,was used to prepare the graft polymer in aqueous solution with acrylamide (AM) and methacrylatoethyl trimethyl ammonium chloride (DMC) as raw materials and ceric ammonium nitrate (CAN) as initiator.The floc-culation ability of the resulting polymer (PCAD) was studied in waste water treatment experiments.Its properties were determined on the basis of the transmittance of waste water after flocculation.The effects of chitosan and DMC content on PCAD’s flocculation ability wer... 相似文献
18.
Quantifying the effects of forests on water and soil conservation helps further understanding of ecological functions and improving vegetation reconstruction in water-eroded areas.Studies on the effects of vegetation on water and soil conservation have generally focused on vegetation types or vegetation horizontal distribution densities.However,only a few studies have used indicators that consider the vegetation vertical distribution.This study used the leaf area index(LAI) to investigate the relationship between forests and water and soil conservation in experimental plots.From 2007 to 2010,rainfall characteristics,LAI,and water and soil loss in 144 natural erosive rainfall events were measured from five pure tree plots(Pinus massoniana).These tree plots were located in Hetian Town,Changting County,Fujian Province,which is a typical water-eroded area in Southern China.Quadratic polynomial regression models for LAI and water/soil conservation effects(RE/SE) were established for each plot.The RE and SE corresponded to the ratios of the runoff depth(RD) and the soil loss(SL) of each pure tree plot to those of the control plot under each rainfall event.The transformation LAIs of the LAI–RE and LAI–SE curves,as well as the rainfall characteristics for the different water/soil conservation effects,were computed.The increasing LAI resulted in descending,descending–ascending,ascending–descending,and ascending trends in the LAI–RE and LAI–SE curves.The rainfall frequencies corresponding to each trend of LAI–RE and LAI–SE were different,and the rainfall distributions were not uniform per year.The effects of soil conservation in the plots were superior to those of water conservation.Most of the RE and SE values presented a positive effect on water and soil conservation.The main factor that caused different effects was rainfall intensity.During heavy rains(e.g.,rainfall erosivity R = 145 MJ mm/ha h and maximum 30 min intensity I30 = 13 mm/h),the main effects were positive,whereas light rains(e.g.,R = 70 MJ mm/ha h and I30 = 8 mm/h) generally led to negative effects.When the rainfall erosivity was lower than that of the positive or the negative effects to a threshold and the tree LAI reached a transformation value,the relationships between LAI and RE or SE notably transformed.Results showed that the plottransformation LAIs for water and soil conservation during rainfall events were both approximately 1.0 in our study.These results could be used to come up with a more efficient way to alleviate water and soil loss in water-eroded areas. 相似文献
19.
We tested the utility of chemical marking techniques in the juvenile black rockfish Sebastes schlegelii. Juveniles(30–40 mm total length) were immersed in a range of tetracycline hydrochloride(TC) solutions at concentrations ranging from 300 to 500 mg/L, and alizarin complexone(ALC) solutions at concentrations ranging from 200 to 400 mg/L in filtered sea water(salinity of 30) for 24 h, respectively. Otoliths(sagittae, asteriscus), scales, fin rays(dorsal, pectoral, ventral, anal, and caudal fin rays), and fin spines(dorsal, ventral, and anal fin spines) were sampled and used to detect fl uorescent marks after a 60-day growth experiment. With the exception of 300 mg/L TC, acceptable marks were produced in the otoliths and fin spines by all concentrations of TC and ALC. In particular, we observed clearly visible marks in the sagittae, asteriscus, and fin spines under normal light at concentrations of 200–400 mg/L, 250–400 mg/L, and 250–400 mg/L ALC, respectively. Scales and fin rays had acceptable marks at much higher concentrations(≥350 mg/L TC, ≥250 mg/L ALC for scales and ≥350 mg/L TC, ≥300 mg/L ALC for fin rays). The best mark quality(i.e., acceptable marks were observed in all sampled structures after immersion marking) were obtained following immersion in TC at between 350–500 mg/L, and ALC between 300–400 mg/L. In addition, there was no significant difference in survival and growth of TC and ALC marked fish compared to their controls up to 60 days post-marking( P 0.05). 相似文献
20.
Soil carbon stock and flux in plantation forest and grassland ecosystems in Loess Plateau,China 总被引：1，自引：1，他引：0
Carbon sequestration occurs when cultivated soils are re-vegetated. In the hilly area of the Loess Plateau, China, black locust(Robinia pseudoacacia) plantation forest and grassland were the two main vegetation types used to mitigate soil and water loss after cultivation abandonment. The purpose of this study was to compare the soil carbon stock and flux of these two types of vegetation which restored for 25 years. The experiment was conducted in Yangjuangou catchment in Yan′an City, Shaanxi Province, China. Two adjacent slopes were chosen for this study. Six sample sites were spaced every 35–45 m from summit to toe slope along the hill slope, and each sample site contained three sampling plots. Soil organic carbon and related physicochemical properties in the surface soil layer(0–10 cm and 10–20 cm) were measured based on soil sampling and laboratory analysis, and the soil carbon dioxide(CO2) emissions and environmental factors were measured in the same sample sites simultaneously. Results indicated that in general, a higher soil carbon stock was found in the black locust plantation forest than that in grassland throughout the hill slope. Meanwhile, significant differences in the soil carbon stock were observed between these two vegetation types in the upper slope at soil depth 0–10 cm and lower slope at soil depth 10–20 cm. The average daily values of the soil CO2 emissions were 1.27 μmol/(m2·s) and 1.39 μmol/(m2·s) for forest and grassland, respectively. The soil carbon flux in forest covered areas was higher in spring and less variation was detected between different seasons, while the highest carbon flux was found in grassland in summer, which was about three times higher than that in autumn and spring. From the carbon sequestration point of view, black locust plantation forest on hill slopes might be better than grassland because of a higher soil carbon stock and lower carbon flux. 相似文献