A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibrati...A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.展开更多
Mathematical models of propellers were created that investigate the influence of periodic boundary conditions on predictions of a propeller's performance.Thrust and torque coefficients corresponding to different a...Mathematical models of propellers were created that investigate the influence of periodic boundary conditions on predictions of a propeller's performance.Thrust and torque coefficients corresponding to different advance coefficients of DTMB 4119, 4382, and 4384 propellers were calculated.The pressure coefficient distribution of the DTMB 4119 propeller at different sections was also physically tested.Comparisons indicated good agreement between the results of experiments and the simulation.It showed that the periodic boundary condition can be used to rationally predict the open water performance of a propeller.By analyzing the three established modes for the computation, it was shown that using the spline curve method to divide the grids can meet the calculation's demands for precision better than using the rake cutting method.展开更多
The sea ice conditions in the Kara Sea have important impacts on Arctic shipping,oil and gas production,and marine environmental changes.In this study,sea ice coverage(C_(R))less than 30%is considered as open water,it...The sea ice conditions in the Kara Sea have important impacts on Arctic shipping,oil and gas production,and marine environmental changes.In this study,sea ice coverage(C_(R))less than 30%is considered as open water,its onset and end dates are defined as T_(open)and T_(close),respectively.The sea ice melt onset(T_(melt))is defined as the date when ice-sea freshwater flux initially changes from ice into the ocean.Satellite-based sea ice concentration(SIC)from 1989 to 2019 shows a negative correlation between T_(open)and T_(close)(r=-0.77,p<0.01)in the Kara Sea.This phenomenon is also obtained through analyzing the hindcast simulation from 1994 to 2015 by a coupled ocean and sea-ice model(NAPA1/4).The model results reveal that thermodynamics dominate the sea ice variations,and ice basal melt is greater than the ice surface melt.Heat budget estimation suggests that the heat flux is significant correlated with T_(open)(r=-0.95,p<0.01)during the melt period(the duration of multi-year averaged T_(melt)to T_(open))influenced by the sea ice conditions.Additionally,this heat flux is also suggested to dominate the interannual variation of the heat input during the whole heat absorption process(r=0.81,p<0.01).The more heat input during this process leads to later T_(close)(r=0.77,p<0.01).This is the physical basis of the negative correlation between T_(open)and T_(close).Therefore,the duration of open water can be predicted by T_(open)and thence support earlier planning of marine activities.展开更多
The persistent rise in concentrations of greenhouse gases (GHGs) in the earth’s atmosphere is responsible for global warming and climate change. Besides the known source of GHGs emissions like energy, industry, and a...The persistent rise in concentrations of greenhouse gases (GHGs) in the earth’s atmosphere is responsible for global warming and climate change. Besides the known source of GHGs emissions like energy, industry, and agriculture, intrinsic emissions from natural inland water bodies like wetland, rivers, reservoirs, estuaries, etc. have also been identified as other hotspots of GHGs emission and gaining the attention of the scientific communities in recent times. Inland fisheries in India are threatened by climate changes such as a change in temperature, precipitation, droughts, storm, sea-level rise, saltwater intrusion, floods that affect mostly the production, productivity and ultimately affect the fishers’ livelihood. There are, however, different mitigation and adaptation strategies to cope with the effects of climate change. Carbon sequestration and other related management interventions are one of the options available minimizing GHGs emissions from inland open waters, particularly the wetlands and coastal mangroves which are well known worldwide for their significant role in the storage of carbon. Assessment of C efflux from exposed sediments in dry streams, reservoirs, lakes, rivers, and ponds into the atmosphere can be considered imperative for a better understanding of their role as a C-sink or as a C-source to the atmosphere.展开更多
In view of the situation of excavation of should carry out simulation studies for the numerical open coal mine for the underground water disaster, we value of the water lowering project and improve the accuracy and th...In view of the situation of excavation of should carry out simulation studies for the numerical open coal mine for the underground water disaster, we value of the water lowering project and improve the accuracy and the level of the water lowering project. On the basis of the hydrological geological conditions of certain open mine digging, a more reasonable seepage numerical model was built according to MODFLOW. It was simulated in advance that the process of the confined water level descending with the time, and combining with the actual observations to test the correctness of the model. The calculation showed that the results coincided well with the results of actual measurement. Based on this, different water lowering numerical simulations were built for the open coal mine digging. It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit, and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process, which provide an important basis for the actual water lowering project and the possible project disposal.展开更多
The marine propeller typically functions within thefilowfiield generated by a water vehicle.Investigations into the geometric parameters of the propeller are commonly conducted under open‑water conditions as simultane...The marine propeller typically functions within thefilowfiield generated by a water vehicle.Investigations into the geometric parameters of the propeller are commonly conducted under open‑water conditions as simultaneously simulating both vehicle and propeller holds several computational challenges.While during operation,this propellant device must face several forces like gravity,hydrodynamic load,and centrifugal force,which cause different problems like cavitation and structural failure,etc.Since these issues affect performance,it necessitates comprehensive analysis.In this study,hydrodynamic analysis is performed by using commercial software STAR CCM+.In hydrodynamic analysis,the effect of the rake angles–5°,5°,10°and 15°on hydrodynamic coeffiicients and effiiciency of the DTMB 4119 in the open water is analyzed using Computational Fluid Dynamics(CFD)and the control volume approach.The Shear Stress Transport(SST)k‑ωturbulence model is used in Computational Fluid Dynamics(CFD)simulation.Hydrodynamic analysis reveals that the rake angles 5°and 10°cause the open water effiiciency of David Taylor Model Basin(DTMB)4119 to improve by 0.4 to 1.32%with exception of the rake angles–5°and 15°,which possess different effects on effiiciency.The angle–5°causes a decrease in propeller effiiciency under heavy loading situations(low advance coeffiicient)apart from a minorfiluctuation at light loading conditions(high advance coeffiicient),while the angle 15°produces a drop in effiiciency by higher advance ratios but little variation at lower advance ratios.展开更多
In this study,a series of numerical calculations are carried out in ANSYS Workbench based on the unidirectional fluid–solid coupling theory.Using the DTMB 4119 propeller as the research object,a numerical simulation ...In this study,a series of numerical calculations are carried out in ANSYS Workbench based on the unidirectional fluid–solid coupling theory.Using the DTMB 4119 propeller as the research object,a numerical simulation is set up to analyze the open water performance of the propeller,and the equivalent stress distribution of the propeller acting in the flow field and the axial strain of the blade are analyzed.The results show that FLUENT calculations can provide accurate and reliable calculations of the hydrodynamic load for the propeller structure.The maximum equivalent stress was observed in the blade near the hub,and the tip position of the blade had the largest stress.With the increase in speed,the stress and deformation showed a decreasing trend.展开更多
Numerical simulation is investigated to disclose how propeller boss cap fins （PBCF） operate utilizing Reynolds-averaged Navier-Stokes （RANS） method. In addition, exploration of the influencing mechanism of PBCF on...Numerical simulation is investigated to disclose how propeller boss cap fins （PBCF） operate utilizing Reynolds-averaged Navier-Stokes （RANS） method. In addition, exploration of the influencing mechanism of PBCF on the open water efficiency of one controllable-pitch propeller is analyzed through the open water characteristic curves, blade surface pressure distribution and hub streamline distribution. On this basis, the influence of parameters including airfoil profile, diameter, axial position of installation and circumferential installation angle on the open water efficiency of the controllable-pitch propeller is investigated. Numerical results show： for the controllable-pitch propeller, the thrust generated is at the optimum when the radius of boss cap fins is 1.5 times of propeller hub with an optimal installation position in the axial direction, and its optimal circumferential installation position is the midpoint of the extension line of the front and back ends of two adjacent propeller roots in the front of fin root. Under these optimal parameters, the gain of open water efficiency of the controllable-pitch propeller with different advance velocity coefficients is greater than 0.01, which accounts for approximately an increase of 1%-5% of open water efficiency.展开更多
The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This ...The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This paper is based on the numerical simulation and experimental research of hydrodynamics performance when the propeller is under wave conditions. Open-water propeller performance in calm water is calculated by commercial codes and the results are compared to experimental values to evaluate the accuracy of the numerical simulation method. The first-order Volume of Fluid(VOF) wave method in STAR CCM+ is utilized to simulate the three-dimensional numerical wave. According to the above prerequisite, the numerical calculation of hydrodynamic performance of the propeller under wave conditions is conducted, and the results reveal that both thrust and torque of the propeller under wave conditions reveal intense unsteady behavior. With the periodic variation of waves, ventilation, and even an effluent phenomenon appears on the propeller. Calculation results indicate, when ventilation or effluent appears, the numerical calculation model can capture the dynamic characteristics of the propeller accurately, thus providing a significant theory foundation forfurther studying the hydrodynamic performance of a propeller in waves.展开更多
In this paper,the scale effect of Kappel tip-rake propellers with different end plate designs was studied using computational fluid dynamics.Given the base size of the mesh and the appropriate numerical model for the ...In this paper,the scale effect of Kappel tip-rake propellers with different end plate designs was studied using computational fluid dynamics.Given the base size of the mesh and the appropriate numerical model for the determined simulation,the open-water performance of three Kappel propellers with different bending degrees of the end plate at different scales was calculated.Comparing the scale effect of these propellers,the scale effect of the torque coefficient of a Kappel propeller is more intense than that of the conventional propeller.In addition,the scale effect of the torque coefficient is strong when the bending degree of the end plate increases,dwarfing the scale effect on the thrust coefficient.Following the research on the scale effect of the wake field for the Kappel propeller,the laws that reveal the influence of the scale on the wake field were summarized;that is,the high-speed zone in the wake relatively expands with the increase of the scale in company with a trend of tip cross flow.The research reveals the basic variation trend and rule of the open-water performance and wake distribution for the Kappel propeller under different scales within the Reynolds number range of 4.665×10^(5)-8.666×10^(7)consideringγtransition,as well as the characteristic differences between the Kappel propellers with different end plate designs,which will be of great significance to its optimization design and application to marine vehicles of different scales.展开更多
Background:The Eurasian Spoonbill(Platalea leucorodia)occurs throughout Eurasia and North and sub-Saharan Africa,with three recognized subspecies and six geographically distributed populations.However,in China,we knew...Background:The Eurasian Spoonbill(Platalea leucorodia)occurs throughout Eurasia and North and sub-Saharan Africa,with three recognized subspecies and six geographically distributed populations.However,in China,we knew almost nothing about migration routes,habitat use and effectiveness of current site protection measures for this species.Methods:We deployed Global Positioning System/Global System for Mobile Communications(GPS/GSM)satellite trackers on 29 Eurasian Spoonbills captured in summer in Mongolia and northeastern China,to obtain complete migration routes data from 10 individuals from 19 complete migration episodes.Results:Tracking data showed no geographical overlap during the annual cycle in Eurasian Spoonbills marked in the two main summering areas.Birds marked in the Naoli River Basin in Heilongjiang Province,China,wintered along the Jiangsu coastline in China,while Eurasian Spoonbills from two discrete summering areas(in Inner and western Mon-golia)overwintered inland in the Yangtze River floodplain of China.Excluding the single Inner Mongolian bird,spring migration was significantly faster than autumn migration in the other two groups of birds.Eurasian Spoonbills mainly used water,wetland and grassland habitats in summer,but almost exclusively water in winter.Lack of protection of staging sites used by all the birds in spring and poor levels of protection throughout the annual cycle for western Mongolian birds(5-22%)gives considerable cause for concern,although sites used in other time by East Mongolian and Naoli River birds in the rest of their annual life cycle enjoyed good levels of protection(49-95%).Conclusions:These results revealed previously unknown relationships between summering and wintering areas,migration routes and stopover sites for Eurasian Spoonbills wintering in China,suggesting the existence of discrete biogeographical population units.They also identified winter habitat use of Eurasian Spoonbills in China,confirming open water habitats as being critical throughout the annual cycle,although based on small sample size,gaps in cur-rent site safeguard networks for these populations.展开更多
Background:Small coastal wetlands are vital sites for wintering waterbirds.Identifying important habitats is critical for managing waterbirds effectively.The Vourkari inlet is a small coastal wetland located near the ...Background:Small coastal wetlands are vital sites for wintering waterbirds.Identifying important habitats is critical for managing waterbirds effectively.The Vourkari inlet is a small coastal wetland located near the capital Athens,within the most urbanized and industrialized area of Greece.We aimed at identifying the most important habitats for waterbirds at the Vourkari inlet during winter.Methods:Data about habitat use and availability were collected for 14 waterbird species and for seven habitat classes.Habitat selection(Manly’s selection ratio),overlap indices(Pianka’s niche overlap index)and null models were calculated.Results:All the studied waterbird species selected available habitats nonrandomly.Shallow waters(0–2 m),were used by 13 waterbirds and selected by five waterbirds.Pools and channels were used and selected by 10 species.Mud was used by nine species and selected by six species.Mud with rocky substrate was used by nine species and selected by eight species.Medium(2–4 m)and deep(4–6 m)open water habitats were used by seven species and selected by four species.Halophytic vegetation was used by six species and selected by two species.Several habitats were selected by nationally important populations:mudflat habitats(i.e.,mud,mud with rocky substrate and pools and channels)by Common Redshanks(Tringa totanus),halophytic vegetation by Little Egrets(Egretta garzetta),shallow waters by Common Shelducks(Tadorna tadorna)and medium and deep waters by Sandwich Terns(Thalasseus sandvicencis),whilst shallow waters and mudflat habitats were preferred by a possibly internationally important population of Mediterranean Gulls(Ichthyaetus melanocephalus).Although overlap in habitat use between species was generally low,null models indicated habitat sharing and a lack of competition.Conclusions:Waterbirds coexisted in the absence of competition for habitats at Vourkari,where they mostly used and preferred shallow water and mudflats.Small coastal wetlands are numerous,both in Greece and worldwide,therefore our findings would be useful as a basis for comparisons,both temporal at the inlet and spatial with other sites,that would help assess the importance of habitats and improve management strategies to benefit waterbirds,especially in areas with similar Mediterranean-type habitats and climate.展开更多
The objective of marine propeller design optimization study is to obtain a propeller with minimum power absorption, maximum efficiency and good materials resistance. In this study, results of numerical simulation carr...The objective of marine propeller design optimization study is to obtain a propeller with minimum power absorption, maximum efficiency and good materials resistance. In this study, results of numerical simulation carried out on the flow around a conventional marine propeller are presented. The investigation focused on the aspects related to the influence of skew magnitude, thickness and blade number on the propeller performances. First, open water performances of a conventional propeller model DTMB 4148 was estimated using RANS （Reynolds Averaged Navier-Stokes） method. The flow around rotating propeller model was analyzed in the steady state using RANS approach of the commercial CFD （computational fluid dynamics） code fluent. The results provide good agreement with literature data. Numerical results show that the number of blades has an influence on the open water performances of marine propellers. It＇s noticed that the best propeller has four or five blades from only the hydrodynamic aspect. The thickness blade effect has been studied for the same propeller model and compared to the blade with three different thickness values. Results of the calculation show that the blade thickness increases moderately the propeller efficiency. Finally, numerical simulation is performed to study the magnitude skew effect on the propeller blade performance, so three different models were generated. The results of the simulation show that the skew distribution has a positive effect on the open water performances of the marine propellers.展开更多
Sea ice velocity impacts the distribution of sea ice,and the flux of exported sea ice through the Fram Strait increases with increasing ice velocity.Therefore,improving the accuracy of estimates of the sea ice velocit...Sea ice velocity impacts the distribution of sea ice,and the flux of exported sea ice through the Fram Strait increases with increasing ice velocity.Therefore,improving the accuracy of estimates of the sea ice velocity is important.We introduce a pyramid algorithm into the Horn-Schunck optical flow(HS-OF)method(to develop the PHS-OF method).Before calculating the sea ice velocity,we generate multilayer pyramid images from an original brightness temperature image.Then,the sea ice velocity of the pyramid layer is calculated,and the ice velocity in the original image is calculated by layer iteration.Winter Arctic sea ice velocities from 2014 to 2016 are obtained and used to discuss the accuracy of the HS-OF method and PHS-OF(specifically the 2-layer PHS-OF(2 LPHS-OF)and 4-layer PHS-OF(4 LPHS-OF))methods.The results prove that the PHS-OF method indeed improves the accuracy of sea ice velocity estimates,and the 2 LPHS-OF scheme is more appropriate for estimating ice velocity.The error is smaller for the 2 LPHS-OF velocity estimates than values from the Ocean and Sea Ice Satellite Application Facility and the Copernicus Marine Environment Monitoring Service,and estimates of changes in velocity by the 2 LPHS-OF method are consistent with those from the National Snow and Ice Data Center.Sea ice undergoes two main motion patterns,i.e.,transpolar drift and the Beaufort Gyre.In addition,cyclonic and anticyclonic ice drift occurred during winter 2016.Variations in sea ice velocity are related to the open water area,sea ice retreat time and length of the open water season.展开更多
This research is the summary of the results of the environmental damage assessment and rehabilitation cost estimation works carried out involving in total, 242 gold-placers’ licensed areas, within the framework of im...This research is the summary of the results of the environmental damage assessment and rehabilitation cost estimation works carried out involving in total, 242 gold-placers’ licensed areas, within the framework of implementation of the “Law on Prohibiting Exploration and Mining of Minerals at Sources of Rivers and Streams, within Protected zones of Water basins and Forest funds”, adopted by the Parliament of Mongolia, in 2009.展开更多
This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,tog...This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,together with fine prism grids to resolve the viscous sub-layer.At full scale,standard wall function is adopted.The scale-effect corrections yielded by our RANS simulations are compared with those obtained from the ITTC method.To explain the CFD results,an analysis of sectional forces is performed.To investigate how the tip rake influences propeller scale effects,the geometry of PPTC-II is modified by removing the tip rake only,and the RANS-predicted scale effects for the modified propeller,PPTC-II-m,are compared with those for the PPTC-II.The study indicates that the scale effect on propeller thrust can be as important as that on the torque;somehow the RANS-and ITTC-based predictions for full-scale efficiency agree quite well;the tip-rake reduces tip loading and tip vortex strength,and brings about large differences in the scale effects as compared with the propeller without tip-rake.展开更多
An inauguration ceremony was held to mark the opening of the Center for International Transboundary Water and Eco-Security, Tsinghua University （CITWES） on December 10, 2006. Zhai Haohui, Vice Minister of MWR, Tsing...An inauguration ceremony was held to mark the opening of the Center for International Transboundary Water and Eco-Security, Tsinghua University （CITWES） on December 10, 2006. Zhai Haohui, Vice Minister of MWR, Tsinghua Vice President Hu Heping and vips and representatives from some research institutions and universities in China participated in the event.展开更多
Numerical simulations of the flow around two bidirectional staggered propellers are conducted in uniform flow. The computed open water performance of the fore-propeller is compared with the corresponding experimental ...Numerical simulations of the flow around two bidirectional staggered propellers are conducted in uniform flow. The computed open water performance of the fore-propeller is compared with the corresponding experimental results, and the influence of the fore-propeller on the aft one is carefully investigated. It is found that the inflow around the aft propeller close to the side of the fore is especially affected by the fore one, leading to abnormal circumferential distribution of force on the blade in the shade region. For either forces or velocity distributions, the abnormal changes behave contrarily for cases with the rotating speed larger or smaller than the idle. Moreover, the more the rotating speed of the fore differs from the idle, the larger the abnormal values become.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51079157)
文摘A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.
基金Supported by the National Natural Science Foundation of China under Grant No.10702016
文摘Mathematical models of propellers were created that investigate the influence of periodic boundary conditions on predictions of a propeller's performance.Thrust and torque coefficients corresponding to different advance coefficients of DTMB 4119, 4382, and 4384 propellers were calculated.The pressure coefficient distribution of the DTMB 4119 propeller at different sections was also physically tested.Comparisons indicated good agreement between the results of experiments and the simulation.It showed that the periodic boundary condition can be used to rationally predict the open water performance of a propeller.By analyzing the three established modes for the computation, it was shown that using the spline curve method to divide the grids can meet the calculation's demands for precision better than using the rake cutting method.
基金The National Key Research and Development Program of China under contract No.2016YFC1401401the National Natural Science Foundation of China under contract Nos 41630969,41941013 and 41806225。
文摘The sea ice conditions in the Kara Sea have important impacts on Arctic shipping,oil and gas production,and marine environmental changes.In this study,sea ice coverage(C_(R))less than 30%is considered as open water,its onset and end dates are defined as T_(open)and T_(close),respectively.The sea ice melt onset(T_(melt))is defined as the date when ice-sea freshwater flux initially changes from ice into the ocean.Satellite-based sea ice concentration(SIC)from 1989 to 2019 shows a negative correlation between T_(open)and T_(close)(r=-0.77,p<0.01)in the Kara Sea.This phenomenon is also obtained through analyzing the hindcast simulation from 1994 to 2015 by a coupled ocean and sea-ice model(NAPA1/4).The model results reveal that thermodynamics dominate the sea ice variations,and ice basal melt is greater than the ice surface melt.Heat budget estimation suggests that the heat flux is significant correlated with T_(open)(r=-0.95,p<0.01)during the melt period(the duration of multi-year averaged T_(melt)to T_(open))influenced by the sea ice conditions.Additionally,this heat flux is also suggested to dominate the interannual variation of the heat input during the whole heat absorption process(r=0.81,p<0.01).The more heat input during this process leads to later T_(close)(r=0.77,p<0.01).This is the physical basis of the negative correlation between T_(open)and T_(close).Therefore,the duration of open water can be predicted by T_(open)and thence support earlier planning of marine activities.
文摘The persistent rise in concentrations of greenhouse gases (GHGs) in the earth’s atmosphere is responsible for global warming and climate change. Besides the known source of GHGs emissions like energy, industry, and agriculture, intrinsic emissions from natural inland water bodies like wetland, rivers, reservoirs, estuaries, etc. have also been identified as other hotspots of GHGs emission and gaining the attention of the scientific communities in recent times. Inland fisheries in India are threatened by climate changes such as a change in temperature, precipitation, droughts, storm, sea-level rise, saltwater intrusion, floods that affect mostly the production, productivity and ultimately affect the fishers’ livelihood. There are, however, different mitigation and adaptation strategies to cope with the effects of climate change. Carbon sequestration and other related management interventions are one of the options available minimizing GHGs emissions from inland open waters, particularly the wetlands and coastal mangroves which are well known worldwide for their significant role in the storage of carbon. Assessment of C efflux from exposed sediments in dry streams, reservoirs, lakes, rivers, and ponds into the atmosphere can be considered imperative for a better understanding of their role as a C-sink or as a C-source to the atmosphere.
文摘In view of the situation of excavation of should carry out simulation studies for the numerical open coal mine for the underground water disaster, we value of the water lowering project and improve the accuracy and the level of the water lowering project. On the basis of the hydrological geological conditions of certain open mine digging, a more reasonable seepage numerical model was built according to MODFLOW. It was simulated in advance that the process of the confined water level descending with the time, and combining with the actual observations to test the correctness of the model. The calculation showed that the results coincided well with the results of actual measurement. Based on this, different water lowering numerical simulations were built for the open coal mine digging. It could be simulated and forecast that the changes of the groundwater level in drainage process within and outside the mine pit, and it was quantitatively assessed that the possible water lowering result of the opencast water drainage process, which provide an important basis for the actual water lowering project and the possible project disposal.
文摘The marine propeller typically functions within thefilowfiield generated by a water vehicle.Investigations into the geometric parameters of the propeller are commonly conducted under open‑water conditions as simultaneously simulating both vehicle and propeller holds several computational challenges.While during operation,this propellant device must face several forces like gravity,hydrodynamic load,and centrifugal force,which cause different problems like cavitation and structural failure,etc.Since these issues affect performance,it necessitates comprehensive analysis.In this study,hydrodynamic analysis is performed by using commercial software STAR CCM+.In hydrodynamic analysis,the effect of the rake angles–5°,5°,10°and 15°on hydrodynamic coeffiicients and effiiciency of the DTMB 4119 in the open water is analyzed using Computational Fluid Dynamics(CFD)and the control volume approach.The Shear Stress Transport(SST)k‑ωturbulence model is used in Computational Fluid Dynamics(CFD)simulation.Hydrodynamic analysis reveals that the rake angles 5°and 10°cause the open water effiiciency of David Taylor Model Basin(DTMB)4119 to improve by 0.4 to 1.32%with exception of the rake angles–5°and 15°,which possess different effects on effiiciency.The angle–5°causes a decrease in propeller effiiciency under heavy loading situations(low advance coeffiicient)apart from a minorfiluctuation at light loading conditions(high advance coeffiicient),while the angle 15°produces a drop in effiiciency by higher advance ratios but little variation at lower advance ratios.
文摘In this study,a series of numerical calculations are carried out in ANSYS Workbench based on the unidirectional fluid–solid coupling theory.Using the DTMB 4119 propeller as the research object,a numerical simulation is set up to analyze the open water performance of the propeller,and the equivalent stress distribution of the propeller acting in the flow field and the axial strain of the blade are analyzed.The results show that FLUENT calculations can provide accurate and reliable calculations of the hydrodynamic load for the propeller structure.The maximum equivalent stress was observed in the blade near the hub,and the tip position of the blade had the largest stress.With the increase in speed,the stress and deformation showed a decreasing trend.
基金Supported by the National Natural Science Foundation of China under Grant No.51079157
文摘Numerical simulation is investigated to disclose how propeller boss cap fins （PBCF） operate utilizing Reynolds-averaged Navier-Stokes （RANS） method. In addition, exploration of the influencing mechanism of PBCF on the open water efficiency of one controllable-pitch propeller is analyzed through the open water characteristic curves, blade surface pressure distribution and hub streamline distribution. On this basis, the influence of parameters including airfoil profile, diameter, axial position of installation and circumferential installation angle on the open water efficiency of the controllable-pitch propeller is investigated. Numerical results show： for the controllable-pitch propeller, the thrust generated is at the optimum when the radius of boss cap fins is 1.5 times of propeller hub with an optimal installation position in the axial direction, and its optimal circumferential installation position is the midpoint of the extension line of the front and back ends of two adjacent propeller roots in the front of fin root. Under these optimal parameters, the gain of open water efficiency of the controllable-pitch propeller with different advance velocity coefficients is greater than 0.01, which accounts for approximately an increase of 1%-5% of open water efficiency.
基金Supported by the National Natural Science Foundation of China （51379043, 41176074, 51209048, 51409063）, High Tech Ship Research Project of Ministry of Industry and Technology （G014613002）, and the Support Plan for Youth Backbone Teachers of Harbin Engineering University （HEUCFQ 1408）
文摘The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This paper is based on the numerical simulation and experimental research of hydrodynamics performance when the propeller is under wave conditions. Open-water propeller performance in calm water is calculated by commercial codes and the results are compared to experimental values to evaluate the accuracy of the numerical simulation method. The first-order Volume of Fluid(VOF) wave method in STAR CCM+ is utilized to simulate the three-dimensional numerical wave. According to the above prerequisite, the numerical calculation of hydrodynamic performance of the propeller under wave conditions is conducted, and the results reveal that both thrust and torque of the propeller under wave conditions reveal intense unsteady behavior. With the periodic variation of waves, ventilation, and even an effluent phenomenon appears on the propeller. Calculation results indicate, when ventilation or effluent appears, the numerical calculation model can capture the dynamic characteristics of the propeller accurately, thus providing a significant theory foundation forfurther studying the hydrodynamic performance of a propeller in waves.
基金Supported by the Ningbo Institute of Materials Technology and Engineering affiliated to Chinese Academy of Sciences(Grant No.829203-I22101)TXC(Ningbo)Co.,Ltd.(Grant No.529203-I22004).
文摘In this paper,the scale effect of Kappel tip-rake propellers with different end plate designs was studied using computational fluid dynamics.Given the base size of the mesh and the appropriate numerical model for the determined simulation,the open-water performance of three Kappel propellers with different bending degrees of the end plate at different scales was calculated.Comparing the scale effect of these propellers,the scale effect of the torque coefficient of a Kappel propeller is more intense than that of the conventional propeller.In addition,the scale effect of the torque coefficient is strong when the bending degree of the end plate increases,dwarfing the scale effect on the thrust coefficient.Following the research on the scale effect of the wake field for the Kappel propeller,the laws that reveal the influence of the scale on the wake field were summarized;that is,the high-speed zone in the wake relatively expands with the increase of the scale in company with a trend of tip cross flow.The research reveals the basic variation trend and rule of the open-water performance and wake distribution for the Kappel propeller under different scales within the Reynolds number range of 4.665×10^(5)-8.666×10^(7)consideringγtransition,as well as the characteristic differences between the Kappel propellers with different end plate designs,which will be of great significance to its optimization design and application to marine vehicles of different scales.
基金supported by the National Natural Science Foundation of China(Grant No.31970433)Youth Innovation Promotion Association+1 种基金Chinese Academy of Sciences(Grant No.2020046)China Biodiversity Observation Networks(Sino BON)。
文摘Background:The Eurasian Spoonbill(Platalea leucorodia)occurs throughout Eurasia and North and sub-Saharan Africa,with three recognized subspecies and six geographically distributed populations.However,in China,we knew almost nothing about migration routes,habitat use and effectiveness of current site protection measures for this species.Methods:We deployed Global Positioning System/Global System for Mobile Communications(GPS/GSM)satellite trackers on 29 Eurasian Spoonbills captured in summer in Mongolia and northeastern China,to obtain complete migration routes data from 10 individuals from 19 complete migration episodes.Results:Tracking data showed no geographical overlap during the annual cycle in Eurasian Spoonbills marked in the two main summering areas.Birds marked in the Naoli River Basin in Heilongjiang Province,China,wintered along the Jiangsu coastline in China,while Eurasian Spoonbills from two discrete summering areas(in Inner and western Mon-golia)overwintered inland in the Yangtze River floodplain of China.Excluding the single Inner Mongolian bird,spring migration was significantly faster than autumn migration in the other two groups of birds.Eurasian Spoonbills mainly used water,wetland and grassland habitats in summer,but almost exclusively water in winter.Lack of protection of staging sites used by all the birds in spring and poor levels of protection throughout the annual cycle for western Mongolian birds(5-22%)gives considerable cause for concern,although sites used in other time by East Mongolian and Naoli River birds in the rest of their annual life cycle enjoyed good levels of protection(49-95%).Conclusions:These results revealed previously unknown relationships between summering and wintering areas,migration routes and stopover sites for Eurasian Spoonbills wintering in China,suggesting the existence of discrete biogeographical population units.They also identified winter habitat use of Eurasian Spoonbills in China,confirming open water habitats as being critical throughout the annual cycle,although based on small sample size,gaps in cur-rent site safeguard networks for these populations.
文摘Background:Small coastal wetlands are vital sites for wintering waterbirds.Identifying important habitats is critical for managing waterbirds effectively.The Vourkari inlet is a small coastal wetland located near the capital Athens,within the most urbanized and industrialized area of Greece.We aimed at identifying the most important habitats for waterbirds at the Vourkari inlet during winter.Methods:Data about habitat use and availability were collected for 14 waterbird species and for seven habitat classes.Habitat selection(Manly’s selection ratio),overlap indices(Pianka’s niche overlap index)and null models were calculated.Results:All the studied waterbird species selected available habitats nonrandomly.Shallow waters(0–2 m),were used by 13 waterbirds and selected by five waterbirds.Pools and channels were used and selected by 10 species.Mud was used by nine species and selected by six species.Mud with rocky substrate was used by nine species and selected by eight species.Medium(2–4 m)and deep(4–6 m)open water habitats were used by seven species and selected by four species.Halophytic vegetation was used by six species and selected by two species.Several habitats were selected by nationally important populations:mudflat habitats(i.e.,mud,mud with rocky substrate and pools and channels)by Common Redshanks(Tringa totanus),halophytic vegetation by Little Egrets(Egretta garzetta),shallow waters by Common Shelducks(Tadorna tadorna)and medium and deep waters by Sandwich Terns(Thalasseus sandvicencis),whilst shallow waters and mudflat habitats were preferred by a possibly internationally important population of Mediterranean Gulls(Ichthyaetus melanocephalus).Although overlap in habitat use between species was generally low,null models indicated habitat sharing and a lack of competition.Conclusions:Waterbirds coexisted in the absence of competition for habitats at Vourkari,where they mostly used and preferred shallow water and mudflats.Small coastal wetlands are numerous,both in Greece and worldwide,therefore our findings would be useful as a basis for comparisons,both temporal at the inlet and spatial with other sites,that would help assess the importance of habitats and improve management strategies to benefit waterbirds,especially in areas with similar Mediterranean-type habitats and climate.
文摘The objective of marine propeller design optimization study is to obtain a propeller with minimum power absorption, maximum efficiency and good materials resistance. In this study, results of numerical simulation carried out on the flow around a conventional marine propeller are presented. The investigation focused on the aspects related to the influence of skew magnitude, thickness and blade number on the propeller performances. First, open water performances of a conventional propeller model DTMB 4148 was estimated using RANS （Reynolds Averaged Navier-Stokes） method. The flow around rotating propeller model was analyzed in the steady state using RANS approach of the commercial CFD （computational fluid dynamics） code fluent. The results provide good agreement with literature data. Numerical results show that the number of blades has an influence on the open water performances of marine propellers. It＇s noticed that the best propeller has four or five blades from only the hydrodynamic aspect. The thickness blade effect has been studied for the same propeller model and compared to the blade with three different thickness values. Results of the calculation show that the blade thickness increases moderately the propeller efficiency. Finally, numerical simulation is performed to study the magnitude skew effect on the propeller blade performance, so three different models were generated. The results of the simulation show that the skew distribution has a positive effect on the open water performances of the marine propellers.
基金The National Key Research and Development Program of China under contract Nos 2018YFC1407200 and 2018YFC1407203the National Natural Science Foundation of China under contract No.41976212
文摘Sea ice velocity impacts the distribution of sea ice,and the flux of exported sea ice through the Fram Strait increases with increasing ice velocity.Therefore,improving the accuracy of estimates of the sea ice velocity is important.We introduce a pyramid algorithm into the Horn-Schunck optical flow(HS-OF)method(to develop the PHS-OF method).Before calculating the sea ice velocity,we generate multilayer pyramid images from an original brightness temperature image.Then,the sea ice velocity of the pyramid layer is calculated,and the ice velocity in the original image is calculated by layer iteration.Winter Arctic sea ice velocities from 2014 to 2016 are obtained and used to discuss the accuracy of the HS-OF method and PHS-OF(specifically the 2-layer PHS-OF(2 LPHS-OF)and 4-layer PHS-OF(4 LPHS-OF))methods.The results prove that the PHS-OF method indeed improves the accuracy of sea ice velocity estimates,and the 2 LPHS-OF scheme is more appropriate for estimating ice velocity.The error is smaller for the 2 LPHS-OF velocity estimates than values from the Ocean and Sea Ice Satellite Application Facility and the Copernicus Marine Environment Monitoring Service,and estimates of changes in velocity by the 2 LPHS-OF method are consistent with those from the National Snow and Ice Data Center.Sea ice undergoes two main motion patterns,i.e.,transpolar drift and the Beaufort Gyre.In addition,cyclonic and anticyclonic ice drift occurred during winter 2016.Variations in sea ice velocity are related to the open water area,sea ice retreat time and length of the open water season.
文摘This research is the summary of the results of the environmental damage assessment and rehabilitation cost estimation works carried out involving in total, 242 gold-placers’ licensed areas, within the framework of implementation of the “Law on Prohibiting Exploration and Mining of Minerals at Sources of Rivers and Streams, within Protected zones of Water basins and Forest funds”, adopted by the Parliament of Mongolia, in 2009.
文摘This paper presents our numerical study of the scale effects on a tip-rake propeller,the PPTC-II,based on the RANS simulations using software FLUENT 6.3.The low Re option in SST k-ωmodel is adopted at model scale,together with fine prism grids to resolve the viscous sub-layer.At full scale,standard wall function is adopted.The scale-effect corrections yielded by our RANS simulations are compared with those obtained from the ITTC method.To explain the CFD results,an analysis of sectional forces is performed.To investigate how the tip rake influences propeller scale effects,the geometry of PPTC-II is modified by removing the tip rake only,and the RANS-predicted scale effects for the modified propeller,PPTC-II-m,are compared with those for the PPTC-II.The study indicates that the scale effect on propeller thrust can be as important as that on the torque;somehow the RANS-and ITTC-based predictions for full-scale efficiency agree quite well;the tip-rake reduces tip loading and tip vortex strength,and brings about large differences in the scale effects as compared with the propeller without tip-rake.
文摘An inauguration ceremony was held to mark the opening of the Center for International Transboundary Water and Eco-Security, Tsinghua University （CITWES） on December 10, 2006. Zhai Haohui, Vice Minister of MWR, Tsinghua Vice President Hu Heping and vips and representatives from some research institutions and universities in China participated in the event.
文摘Numerical simulations of the flow around two bidirectional staggered propellers are conducted in uniform flow. The computed open water performance of the fore-propeller is compared with the corresponding experimental results, and the influence of the fore-propeller on the aft one is carefully investigated. It is found that the inflow around the aft propeller close to the side of the fore is especially affected by the fore one, leading to abnormal circumferential distribution of force on the blade in the shade region. For either forces or velocity distributions, the abnormal changes behave contrarily for cases with the rotating speed larger or smaller than the idle. Moreover, the more the rotating speed of the fore differs from the idle, the larger the abnormal values become.
