A series of scaled model aircraft ditching tests are performed by launch facility system in Hydraulics Laboratory.According to the measured pitch angle,acceleration and pressure history,research on the impact characte...A series of scaled model aircraft ditching tests are performed by launch facility system in Hydraulics Laboratory.According to the measured pitch angle,acceleration and pressure history,research on the impact characteristic of ditching is conducted.To solve the problem of cavitation effect which may occur in full scale aircraft,the action mechanism and effect of cavitation are studied,and an innovative experimental simulation measure is taken.It is shown that the cavitation bar directly and effectively separates aircraft bottom from water surface and therefore reduces negative pressure,thus enhancing the authenticity of the test results.The dynamic responses including stability and overload after impacting water at different initial pitch angles are analyzed to find the optimum one,which turns out to be heavily dependent on the bottom curvature of fuselage,and rebound phenomenon occurs when pitch angle exceeds a certain value because of the huge positive pressure acting at the spray root on rear fuselage.In addition,the influences of descent rate and horizontal velocity are analyzed.The results show that the descent rate mainly affects the overall load,which is of higher level of importance,while the horizontal velocity mainly affects the load of local structure.展开更多
Stubble-breaking device is a key working part of no-tillage seeder in stub land,and directly affects planting quality of seeder.Based on the current domestic used stubble-breaking device,a new kind of stubble-breaking...Stubble-breaking device is a key working part of no-tillage seeder in stub land,and directly affects planting quality of seeder.Based on the current domestic used stubble-breaking device,a new kind of stubble-breaking ditching colter was designed.To study its strength property and reduce trouble in work,the three-dimensional model of stubble-breaking ditching colter was established based on SolidWorks.By using Cosmos,it was carried out the finite element analysis.The distortion and stress of stubble-breaking ditching colter in work were obtained,and the weak link of strength was found.The result showed that the maximum stress of stubble-breaking ditching colter was 5.862×108 N/m2,and the maximum twisted displacement was 2.648 mm.The stubble-breaking ditching colter was carried out improved design.Based on Cosmos,the static analysis was carried out.It showed that the strength and rigidity of improved stubble-breaking ditching colter were obviously improved.The research provided reference basis for optimal design of the stubble-breaking ditching colter.展开更多
To understand the effect of attitude angle on helicopter water ditching,a finite element model(FEM)of helicopter water ditching was established via the nonlinear finite element method.Based on the LS-DYNA software,the...To understand the effect of attitude angle on helicopter water ditching,a finite element model(FEM)of helicopter water ditching was established via the nonlinear finite element method.Based on the LS-DYNA software,the finite element model of the helicopter was established.Different attitude of helicopter water ditching was simulated and analysed.Three pressure measuring points were arranged in the aircraft belly area.The pressure curves were provided seperately.Finally,the effects of attitude on helicopter water ditching was discussed,particularly the stability and the overload of helicopter.Through the contours of stress,it can be figured out that the maximum pressure locates at the position of aircraft belly where stiffness is larger.Then simulation and experimental results were compared.The difference of peak acceleration along the Z direction was small.Therefore,this method is feasible and helpful for the design of helicopter water ditching.展开更多
The large eddy simulation(LES)method combined with the global dynamic grid strategy is used to numerically study the influence of pitch angles on cavitation and ventilation phenomena in the rear of fuselage during dit...The large eddy simulation(LES)method combined with the global dynamic grid strategy is used to numerically study the influence of pitch angles on cavitation and ventilation phenomena in the rear of fuselage during ditching.The volume of fluid(VOF)method is used to capture the interface.By analyzing the normal force,moment,pressure distribution and nephograms,we find that the pitch angle has a great influence on the total load,the cavitation occurrence time and its transition to ventilation,thus affects the longitudinal load distribution and the controlling of aircraft dynamics.展开更多
To solve the difficulty in ditching for the deep fertilization in tea gardens caused by the high quantity of tea branches and stubbles,a new ditching device combined with a kind of rotary tillage and chisel shovel was...To solve the difficulty in ditching for the deep fertilization in tea gardens caused by the high quantity of tea branches and stubbles,a new ditching device combined with a kind of rotary tillage and chisel shovel was designed.The combined ditching device worked by the following steps:Firstly,the stubble,such as fallen leaves and weeds between the rows,was cleaned up and thrown away by the rotary tillage.Then,the chisel-shaped fertilizing shovel forcefully dug into the soil,realizing the deep fertilization groove.The parameters of the rotary tillage and stubble-throwing device and the chisel-shaped fertilizing shovel were optimized by single factor test and quadratic regression orthogonal rotation test,respectively.The optimization results showed that when the number of stubble-throwing blades of the rotary tillage and stubble-throwing device was five,and the blade installation inclination angle was 16°,the stubble removal rate was the highest at the high speed of the cutter(300 r/min),which was 91.64%.When the entry angle of the chisel-shaped fertilizing shovel was 30°,the entry clearance angle was 8°,and the operating speed was 0.7 m/s,the stability coefficient of the groove depth was 94.9%,which was the optimal parameter of the chisel-shaped fertilizing shovel.The field experiment showed that the average width of the ditching was 224 mm(between 202-248 mm),the average depth of the groove was 194.9 mm(between 173-218 mm),and the stability coefficient of the groove depth could reach 92.78%,realizing stable lateral deep fertilization in the tea garden.展开更多
Ditching is considered as one of the important aspects of safety performances of airplanes. It is related primarily with the fluid-solid interaction, whose studies mainly depend on experiments at the present time. Num...Ditching is considered as one of the important aspects of safety performances of airplanes. It is related primarily with the fluid-solid interaction, whose studies mainly depend on experiments at the present time. Numerical and analytical methods for fluid-solid interaction by using 3-D full scale airplane＇s model will reduce the dependence on the expensive model tests. Numerical studies can be used to estimate the safety of ditching and provide a reference for the crashworthiness design. This article proposes a 3-D dynamical structural model after the real shape of an airplane and an Arbitrary Lagrange-Euler （ALE） fluid-field model, to simulate the fluid-solid interactions caused by low speed ditching. The simulation is based on interaction computational methods, within LS-DYNA nonlinear finite-element code. The results of pressure distributions and accelerating time histories of the airplane＇s subfloor are discussed in the context of the safety of ditching, and the simulation results and the analytical methods are verified.展开更多
The research on ditching is indispensable for civil airplanes made in China to obtain the airworthiness certificates.The suction force effect in the ditching process is a hot and difficult research topic.In this paper...The research on ditching is indispensable for civil airplanes made in China to obtain the airworthiness certificates.The suction force effect in the ditching process is a hot and difficult research topic.In this paper,the explicit method is employed to solve the discrete Lagrangian finite element equations.The Eulerian finite volume method(FVM) is used to solve the Eulerian control equations;the fluid-solid coupling is realized through the general coupling method.The model of large civil airplane ditching is simulated by Dytran and the model test in tank is carried out in the same condition.Based on the analysis on the impacts and generation of the suction force and a numerical example,we obtain the accurate ditching pressure and pitch angle,as well as the results from the simulation and test.The estimated pressure and pitch angles are consistent with the results in the test.In the simulation,where the suction force is considered,the attitude-time history curve is very similar to the one of the tests,whereas the attitudes in the calculation without suction force is far different from the test.It can be concluded from the results that the suction force is the key impact in ditching calculation and can be simulated by general coupling method.In addition,different weight characteristics and different initial pitch angles both result in different pressures of ditching.展开更多
The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian（ALE） smoothed particle hydrodynamics（SPH） model. The test conditions are of interest for problems related to air...The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian（ALE） smoothed particle hydrodynamics（SPH） model. The test conditions are of interest for problems related to aircraft and helicopter emergency landing in water. Three main parameters are considered： the horizontal velocity, the approach angle（i.e., vertical to horizontal velocity ratio） and the pitch angle, a. Regarding the latter, small angles are considered in this study. As described in the theoretical work by Zhao and Faltinsen（1993）, for small a a very thin, high-speed jet of water is formed, and the time-spatial gradients of the pressure field are extremely high. These test conditions are very challenging for numerical solvers. In the present study an enhanced SPH model is firstly tested on a purely vertical impact with deadrise angle α=4°. An in-depth validation against analytical solutions and experimental results is carried out, highlighting the several critical aspects of the numerical modelling of this kind of flow, especially when pressure peaks are to be captured. A discussion on the main difficulties when comparing to model scale experiments is also provided. Then, the more realistic case of a plate with both horizontal and vertical velocity components is discussed and compared to ditching experiments recently carried out at CNR-INSEAN. In the latter case both 2-D and 3-D simulations are considered and the importance of 3-D effects on the pressure peak is discussed for α=4° and α=10°.展开更多
The present work has been performed in the context of the European H2020 project increased SAfety and Robust certification for ditching of Aircrafts and Helicopters(SARAH)dedicated to improving the safety during aircr...The present work has been performed in the context of the European H2020 project increased SAfety and Robust certification for ditching of Aircrafts and Helicopters(SARAH)dedicated to improving the safety during aircraft ditching,together with a better understanding of the physics involved during those crucial events.Both numerical and experimental aspects are explored during this project.The present study focuses on the application of the smoothed particle hydrodynamics(SPH)method to the simulation of helicopter ditching,as this method has proved to be particularly adapted to free surface impact cases.Simulations are performed for three different impact configurations,for which the numerical solutions are compared with the experimental results(forces and kinematics)obtained at the wave basin of Ecole Centrale Nantes on a mock-up shape provided by Airbus Helicopters.Elements of sensitivity analysis are also provided when needed,to assess the role of some parameters involved in the helicopter behavior and the fluid pressure forces exerted during the impact.展开更多
Agricultural drainage ditches(ADDs)are widespread and serve as critical zones,playing a vital role in mitigating non-point source nitrogen(N)and phosphorus(P)pollution in farmland.However,limited information is known ...Agricultural drainage ditches(ADDs)are widespread and serve as critical zones,playing a vital role in mitigating non-point source nitrogen(N)and phosphorus(P)pollution in farmland.However,limited information is known about the interaction relationship between multiple factors and nutrient release in multistage ADDs.Here,a comprehensive five-level agricultural drainage system(comprising field,sublateral,head,branch,and trunk ditches)was selected as the study model.We developed a simulation setup and applied the Box-Behnken Design(BBD)model to systematically examine the influence of various environmental factors on nutrient release dynamics.The results demonstrated that the developed regression model(p<0.0001)reliably predicted total nitrogen(TN)and total phosphorus(TP)concentrations in multistage ADDs.Based on the response surface plots and contour lines,optimal release conditions for nutrients in multistage ADDs(5 days,296 K,1.03 mg/L N,0.10 mg/L P)were determined through multi-objective optimization.We found that nutrient application exerted the most substantial influence on the release conditions.As field water was discharged into the ditches,the nutrient levels were decreased progressively.Overall,the N and P release processes in multistage ADDs were jointly influenced by environmental factors and ditch scale.These findings offer a solid theory for studying nutrient release and deposition in multistage ADDs,providing key insights for managing farmland ditches to reduce agricultural pollution.展开更多
Japan overtook China as the largest foreign holder of U.S. Treasury securities at the end of 2009 after China sold $34.2 billion in American securities last December. China had previously surpassed Japan as the larges...Japan overtook China as the largest foreign holder of U.S. Treasury securities at the end of 2009 after China sold $34.2 billion in American securities last December. China had previously surpassed Japan as the largest holder in September 2008. Since then, China has increased and reduced its holding from time to time. The latest amount, however, accounted for 4 percent of all Chinese holdings and was the biggest single month reduction in years. Some analysts attributed the reduction to intensifying bilateral trade disputes and political threats from the United States. Three scholars recently shared their views with Xinhua News Agency. Edited excerpts follow展开更多
The Yellow River(YR),China’s second-longest river,remains understudied regarding its greenhouse gases(GHGs)emissions,particularly the impacts of urban drainage ditches and wastewater treatment facilities on regional ...The Yellow River(YR),China’s second-longest river,remains understudied regarding its greenhouse gases(GHGs)emissions,particularly the impacts of urban drainage ditches and wastewater treatment facilities on regional GHGs dynamics.This study investigated methane(CH_(4))and carbon dioxide(CO_(2))concentrations,fluxes and stable carbon isotopes(δ^(13)C-CH_(4)and δ^(13)C-CO_(2))across six main stream,three ditches,and one wastewater treatment site along the upper Lanzhou section of the YR,spanning from the urban entrance(36.176°N,103.449°E)to the exit of Lanzhou city(36.056°N,104.020°E).Measured CH_(4)diffusion fluxes in mainstem sites ranged from 0.01 to 2.58 mmol·m^(−2)·d^(−1)(mean:0.36 mmol·m^(−2)·d^(−1)),while ebullitive fluxes(gas bubbles)ranged from 0.01 to 18.89 mmol·m^(−2)·d^(−1)(mean:0.90 mmol·m^(−2)·d^(−1)).CO_(2)diffusion fluxes varied between 9.16–92.80 mmol·m^(−2)·d^(−1)(averaged:39.11 mmol·m^(−2)·d^(−1))at these locations.Ebullition(bubble)fluxes accounted for 53.1%±22.4%(range:9.0%to 98.4%)to total CH_(4)emissions(diffusion plus ebullition),with peak fluxes occurring during summer,indicating its significance as a CH_(4)transport mechanism.Notably,both diffusion CH_(4)and CO_(2)fluxes and ebullitive CH_(4)rates at ditch sites substantially exceeded those in mainstream reaches.The lowest CH_(4)and highest CO_(2)concentrations were observed at a wastewater treatment site,likely resulting from the removal of high organic loads.Acetoclastic methanogenesis—the process converting acetate-derived methyl groups to CH_(4)—was identified as the dominant production pathway in both mainstream and ditch environments.CH_(4)and CO_(2)flux magnitudes in the upper YR(Lanzhou section)were comparable to those observed in subtropical Yangtze River tributaries.These results demonstrate that anthropogenic influences significantly enhance CO_(2)/CH_(4)emissions,and the lateral exports of dissolved carbon(DIC and DOC)in the main stream site was quantified.,which cannot be overlooked.The findings emphasize the critical need to account for pronounced spatiotemporal variations in arid-region GHG fluxes to improve basin-scale estimates for the YR.展开更多
In recent years,the ecological quality of ditches became worse and worse with the degradation of its ecological functioning.It was necessary to apply a multi-disciplinary and multi-scale approach to study ditches base...In recent years,the ecological quality of ditches became worse and worse with the degradation of its ecological functioning.It was necessary to apply a multi-disciplinary and multi-scale approach to study ditches based on landscape ecology theory.Spatial and network features of agricultural ditches in Lake Dianchi Basin were analyzed by geographic information system technology.The results indicated that the ditches at high level were made by concrete or block stones,the coverage of vegetation of buffer zones and width ratio between ditch sections and vegetation zones were very low;The network of agricultural ditches in Lake Dianchi basin had similar characteristics,the connectivity and circuitry were low,and the fractal dimension index of ditch network were larger in southeastern and southern banks.展开更多
According to the annual variation of water discharge and water quality of Xidagou in Lingwu in Ningxia,combining local cropping system,the influence degree of ditch water recharge on soil and crop was studied,and the ...According to the annual variation of water discharge and water quality of Xidagou in Lingwu in Ningxia,combining local cropping system,the influence degree of ditch water recharge on soil and crop was studied,and the feasibility of ditch water recharge was analyzed in our paper,which could provide scientific basis for the utilization of ditch water recharge in local area.展开更多
In this study, the shallow dish cross-section roadside ditch was designed, based on highway 304 line from Yanchi to Hongjing of Ningxia Province. The hy- draulic calculation of the shallow ditch obtained the correspon...In this study, the shallow dish cross-section roadside ditch was designed, based on highway 304 line from Yanchi to Hongjing of Ningxia Province. The hy- draulic calculation of the shallow ditch obtained the corresponding water outlet dis- tance of the ditch with the width of 1.5 m or 2 m suitable for local use under dif- ferent groove longitudinal slope conditions. And the key roadside ditch construction techniques and suitable grass species were introduced.展开更多
To achieve high efficiency of nitrogen and phosphorus removal and to investigate the rule of simultaneous nitrification and denitrification phosphorus removal （SNDPR）, a whole course of SNDPR damage and recovery was...To achieve high efficiency of nitrogen and phosphorus removal and to investigate the rule of simultaneous nitrification and denitrification phosphorus removal （SNDPR）, a whole course of SNDPR damage and recovery was studied in a pilot-scale, anaerobicanoxic oxidation ditch （OD）, where the volumes of anaerobic zone, anoxic zone, and ditches zone of the OD system were 7, 21, and 280 L, respectively. The reactor was fed with municipal wastewater with a flow rate of 336 L/d. The concept of simultaneous nitrification and denitrification （SND） rate （rSND） was put forward to quantify SND. The results indicate that： （1） high nitrogen and phosphorus removal efficiencies were achieved during the stable SND phase, total nitrogen （TN） and total phosphate （TP） removal rates were 80% and 85%, respectively; （2） when the system was aerated excessively, the stability of SND was damaged, and rSND dropped from 80% to 20% or less; （3） the natural logarithm of the ratio of NOx to NH4^＋ in the effluent had a linear correlation to oxidation-reduction potential （ORP）; （4） when NO3^- was less than 6 mg/L, high phosphorus removal efficiency could be achieved; （5） denitrifying phosphorus removal （DNPR） could take place in the anaerobic-anoxic OD system. The major innovation was that the SND rate was devised and quantified.展开更多
The oxidation ditch process is economic and efficient for wastewater treatment, but its application is limited in case where land is costly due to its large land area required. An innovative integrated oxidation ditch...The oxidation ditch process is economic and efficient for wastewater treatment, but its application is limited in case where land is costly due to its large land area required. An innovative integrated oxidation ditch with vertical circle(IODVC) system was developed to treat domestic and industrial wastewater aiming to save land area. The new system consists of a single channel divided into two ditches(the top one and the bottom one by a plate), a brush, and an innovative integral clarifier. Different from the horizontal circle of the conventional oxidation ditch, the flow of IODVC system recycles from the top zone to the bottom zone in the vertical circle as the brush is running, and then the IODVC saved land area required by about 50% compared with a conventional oxidation ditch with an intrachannel clarifier. The innovative integral clarifier is effective for separation of liquid and solids, and is preferably positioned at the opposite end of the brush in the ditch. It does not affect the hydrodynamic characteristics of the mixed liquor in the ditch, and the sludge can automatically return to the down ditch without any pump. In this study, experiments of domestic and dye wastewater treatment were carried out in bench scale and in full scale, respectively. Results clearly showed that the IODVC efficiently removed pollutants in the wastewaters, i.e., the average of COD removals for domestic and dye wastewater treatment were 95% and 90%, respectively, and that the IODVC process may provide a cost effective way for full scale dye wastewater treatment.展开更多
Bioaerosol emissions from wastewater and wastewater treatment processes are a significant subgroup of atmospheric aerosols. Most previous work has focused on the evaluation of their biological risks. In this study, ho...Bioaerosol emissions from wastewater and wastewater treatment processes are a significant subgroup of atmospheric aerosols. Most previous work has focused on the evaluation of their biological risks. In this study, however, the adsorption method was applied to reduce airborne microorganisms generated from a pilot scale wastewater treatment facility with oxidation ditch. Results showed adsorption on granule activated carbon （GAC） was an efficient method for the purification of airborne microorganisms. The GAC itself had a maximum adsorption capacity of 2217 CFU/g for airborne bacteria and 225 CFU/g for fungi with a flow rate of 1.50 m^3/hr. Over 85% of airborne bacteria and fungi emitted from the oxidation ditch were adsorbed within 80 hr of continuous operation mode. Most of them had a particle size of 0.65-4.7 μm. Those airborne microorganisms with small particle size were apt to be adsorbed. The SEM/EDAX, BET and Boehm＇s titration methods were applied to analyse the physicochemical characteristics of the GAC. Relationships between GAC surface characteristics and its adsorption performance demonstrated that porous structure, large surface area, and hydrophobicity rendered GAC an effective absorber of airborne microorganisms. Two regenerate methods, ultraviolet irradiation and high pressure vapor, were compared for the regeneration of used activated carbon. High pressure vapor was an effective technique as it totally destroyed the microorganisms adhered to the activated carbon. Microscopic observation was also carried out to investigate original and used adsorbents.展开更多
An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finit...An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finite-element method(FEM)-based models. The results show that the reactivation of old landslide deposit was triggered by the long-term leakage of diversion ditch before October 2012, and the reactivation was triggered again by the intense rainfall on 7-9 October 2012. The old cracks, which formed in the earlier reactivation of landslide, played a key role for the rainfall infiltration. They offered a preferential path for much more rainfall to infiltrate fast into deep soil, and caused wetting front to move down faster in landslide. The old slip zone with lower permeability was another important factor to cause the infiltrated water to accumulate and form a high pore water pressure above slip zone. Then the high pore water pressure decreased the shear strength of slip zone and triggered the reactivation of the old landslide deposit again.展开更多
Bioaerosols from wastewater treatment processes are a significant subgroup of atmospheric aerosols. In the present study,airborne microorganisms generated from a wastewater treatment station（WWTS） that uses an oxida...Bioaerosols from wastewater treatment processes are a significant subgroup of atmospheric aerosols. In the present study,airborne microorganisms generated from a wastewater treatment station（WWTS） that uses an oxidation ditch process were diminished by ventilation.Conventional sampling and detection methods combined with cloning/sequencing techniques were applied to determine the groups,concentrations,size distributions,and species diversity of airborne microorganisms before and after ventilation. There were 3021 ± 537 CFU/m3 of airborne bacteria and 926 ± 132 CFU/m3 of airborne fungi present in the WWTS bioaerosol.Results showed that the ventilation reduced airborne microorganisms significantly compared to the air in the WWTS. Over 60% of airborne bacteria and airborne fungi could be reduced after4 hr of air exchange. The highest removal（92.1% for airborne bacteria and 89.1% for fungi） was achieved for 0.65–1.1 μm sized particles. The bioaerosol particles over 4.7 μm were also reduced effectively. Large particles tended to be lost by gravitational settling and small particles were generally carried away,which led to the relatively easy reduction of bioaerosol particles0.65–1.1 μm and over 4.7 μm in size. An obvious variation occurred in the structure of the bacterial communities when ventilation was applied to control the airborne microorganisms in enclosed spaces.展开更多
基金supported by the National Project for Large Aircraft of China。
文摘A series of scaled model aircraft ditching tests are performed by launch facility system in Hydraulics Laboratory.According to the measured pitch angle,acceleration and pressure history,research on the impact characteristic of ditching is conducted.To solve the problem of cavitation effect which may occur in full scale aircraft,the action mechanism and effect of cavitation are studied,and an innovative experimental simulation measure is taken.It is shown that the cavitation bar directly and effectively separates aircraft bottom from water surface and therefore reduces negative pressure,thus enhancing the authenticity of the test results.The dynamic responses including stability and overload after impacting water at different initial pitch angles are analyzed to find the optimum one,which turns out to be heavily dependent on the bottom curvature of fuselage,and rebound phenomenon occurs when pitch angle exceeds a certain value because of the huge positive pressure acting at the spray root on rear fuselage.In addition,the influences of descent rate and horizontal velocity are analyzed.The results show that the descent rate mainly affects the overall load,which is of higher level of importance,while the horizontal velocity mainly affects the load of local structure.
基金Supported by National Science and Technology Support Plan of China(2011BAF07B01)~~
文摘Stubble-breaking device is a key working part of no-tillage seeder in stub land,and directly affects planting quality of seeder.Based on the current domestic used stubble-breaking device,a new kind of stubble-breaking ditching colter was designed.To study its strength property and reduce trouble in work,the three-dimensional model of stubble-breaking ditching colter was established based on SolidWorks.By using Cosmos,it was carried out the finite element analysis.The distortion and stress of stubble-breaking ditching colter in work were obtained,and the weak link of strength was found.The result showed that the maximum stress of stubble-breaking ditching colter was 5.862×108 N/m2,and the maximum twisted displacement was 2.648 mm.The stubble-breaking ditching colter was carried out improved design.Based on Cosmos,the static analysis was carried out.It showed that the strength and rigidity of improved stubble-breaking ditching colter were obviously improved.The research provided reference basis for optimal design of the stubble-breaking ditching colter.
基金funded by the International S&T Cooperation Program of China(No.2011DFR80210)the National Natural Science Foundation of China(No.11302105)
文摘To understand the effect of attitude angle on helicopter water ditching,a finite element model(FEM)of helicopter water ditching was established via the nonlinear finite element method.Based on the LS-DYNA software,the finite element model of the helicopter was established.Different attitude of helicopter water ditching was simulated and analysed.Three pressure measuring points were arranged in the aircraft belly area.The pressure curves were provided seperately.Finally,the effects of attitude on helicopter water ditching was discussed,particularly the stability and the overload of helicopter.Through the contours of stress,it can be figured out that the maximum pressure locates at the position of aircraft belly where stiffness is larger.Then simulation and experimental results were compared.The difference of peak acceleration along the Z direction was small.Therefore,this method is feasible and helpful for the design of helicopter water ditching.
文摘The large eddy simulation(LES)method combined with the global dynamic grid strategy is used to numerically study the influence of pitch angles on cavitation and ventilation phenomena in the rear of fuselage during ditching.The volume of fluid(VOF)method is used to capture the interface.By analyzing the normal force,moment,pressure distribution and nephograms,we find that the pitch angle has a great influence on the total load,the cavitation occurrence time and its transition to ventilation,thus affects the longitudinal load distribution and the controlling of aircraft dynamics.
基金supported by the National Natural Science Foundation of China(Grant No.52175233).
文摘To solve the difficulty in ditching for the deep fertilization in tea gardens caused by the high quantity of tea branches and stubbles,a new ditching device combined with a kind of rotary tillage and chisel shovel was designed.The combined ditching device worked by the following steps:Firstly,the stubble,such as fallen leaves and weeds between the rows,was cleaned up and thrown away by the rotary tillage.Then,the chisel-shaped fertilizing shovel forcefully dug into the soil,realizing the deep fertilization groove.The parameters of the rotary tillage and stubble-throwing device and the chisel-shaped fertilizing shovel were optimized by single factor test and quadratic regression orthogonal rotation test,respectively.The optimization results showed that when the number of stubble-throwing blades of the rotary tillage and stubble-throwing device was five,and the blade installation inclination angle was 16°,the stubble removal rate was the highest at the high speed of the cutter(300 r/min),which was 91.64%.When the entry angle of the chisel-shaped fertilizing shovel was 30°,the entry clearance angle was 8°,and the operating speed was 0.7 m/s,the stability coefficient of the groove depth was 94.9%,which was the optimal parameter of the chisel-shaped fertilizing shovel.The field experiment showed that the average width of the ditching was 224 mm(between 202-248 mm),the average depth of the groove was 194.9 mm(between 173-218 mm),and the stability coefficient of the groove depth could reach 92.78%,realizing stable lateral deep fertilization in the tea garden.
基金supported by the Shanghai Key Basic Research Program of China (Grant No. 07JC14001)
文摘Ditching is considered as one of the important aspects of safety performances of airplanes. It is related primarily with the fluid-solid interaction, whose studies mainly depend on experiments at the present time. Numerical and analytical methods for fluid-solid interaction by using 3-D full scale airplane＇s model will reduce the dependence on the expensive model tests. Numerical studies can be used to estimate the safety of ditching and provide a reference for the crashworthiness design. This article proposes a 3-D dynamical structural model after the real shape of an airplane and an Arbitrary Lagrange-Euler （ALE） fluid-field model, to simulate the fluid-solid interactions caused by low speed ditching. The simulation is based on interaction computational methods, within LS-DYNA nonlinear finite-element code. The results of pressure distributions and accelerating time histories of the airplane＇s subfloor are discussed in the context of the safety of ditching, and the simulation results and the analytical methods are verified.
基金supported by the National Natural Science Foundation of China (Grant No. 10772013)the National Technology Research and Development Program of China (Grant No. 2012AA112201)the Aeronautical Science Foundation of China (Grant No. 20100251007)
文摘The research on ditching is indispensable for civil airplanes made in China to obtain the airworthiness certificates.The suction force effect in the ditching process is a hot and difficult research topic.In this paper,the explicit method is employed to solve the discrete Lagrangian finite element equations.The Eulerian finite volume method(FVM) is used to solve the Eulerian control equations;the fluid-solid coupling is realized through the general coupling method.The model of large civil airplane ditching is simulated by Dytran and the model test in tank is carried out in the same condition.Based on the analysis on the impacts and generation of the suction force and a numerical example,we obtain the accurate ditching pressure and pitch angle,as well as the results from the simulation and test.The estimated pressure and pitch angles are consistent with the results in the test.In the simulation,where the suction force is considered,the attitude-time history curve is very similar to the one of the tests,whereas the attitudes in the calculation without suction force is far different from the test.It can be concluded from the results that the suction force is the key impact in ditching calculation and can be simulated by general coupling method.In addition,different weight characteristics and different initial pitch angles both result in different pressures of ditching.
基金partially received funding from the European Union's Horizon 2020 Research and Innovation Programme (Grant No. 724139)
文摘The violent water entry of flat plates is investigated using a Riemann-arbitrary Eulerian-Lagrangian（ALE） smoothed particle hydrodynamics（SPH） model. The test conditions are of interest for problems related to aircraft and helicopter emergency landing in water. Three main parameters are considered： the horizontal velocity, the approach angle（i.e., vertical to horizontal velocity ratio） and the pitch angle, a. Regarding the latter, small angles are considered in this study. As described in the theoretical work by Zhao and Faltinsen（1993）, for small a a very thin, high-speed jet of water is formed, and the time-spatial gradients of the pressure field are extremely high. These test conditions are very challenging for numerical solvers. In the present study an enhanced SPH model is firstly tested on a purely vertical impact with deadrise angle α=4°. An in-depth validation against analytical solutions and experimental results is carried out, highlighting the several critical aspects of the numerical modelling of this kind of flow, especially when pressure peaks are to be captured. A discussion on the main difficulties when comparing to model scale experiments is also provided. Then, the more realistic case of a plate with both horizontal and vertical velocity components is discussed and compared to ditching experiments recently carried out at CNR-INSEAN. In the latter case both 2-D and 3-D simulations are considered and the importance of 3-D effects on the pressure peak is discussed for α=4° and α=10°.
基金Supported by the European Union Horizon 2020 Research and Innovation Program(Grant No.724139)The authors thank the Pole de Calcul et de Donnees Marines(PCDM)for providing DATARMOR storage and computational resources(http://www.ifremer.fr/pcdm),and the Institut de Calcul Intensif(ICI)(Grant No.2018-P1804060).
文摘The present work has been performed in the context of the European H2020 project increased SAfety and Robust certification for ditching of Aircrafts and Helicopters(SARAH)dedicated to improving the safety during aircraft ditching,together with a better understanding of the physics involved during those crucial events.Both numerical and experimental aspects are explored during this project.The present study focuses on the application of the smoothed particle hydrodynamics(SPH)method to the simulation of helicopter ditching,as this method has proved to be particularly adapted to free surface impact cases.Simulations are performed for three different impact configurations,for which the numerical solutions are compared with the experimental results(forces and kinematics)obtained at the wave basin of Ecole Centrale Nantes on a mock-up shape provided by Airbus Helicopters.Elements of sensitivity analysis are also provided when needed,to assess the role of some parameters involved in the helicopter behavior and the fluid pressure forces exerted during the impact.
基金supported by the National Science Funds for Creative Research Groups of China(No.51421006)the National Key Research and Development Program of China(No.2021YFD1700600)the National Major Projects of Water Pollution Control and Management Technology(No.2017ZX07204003)。
文摘Agricultural drainage ditches(ADDs)are widespread and serve as critical zones,playing a vital role in mitigating non-point source nitrogen(N)and phosphorus(P)pollution in farmland.However,limited information is known about the interaction relationship between multiple factors and nutrient release in multistage ADDs.Here,a comprehensive five-level agricultural drainage system(comprising field,sublateral,head,branch,and trunk ditches)was selected as the study model.We developed a simulation setup and applied the Box-Behnken Design(BBD)model to systematically examine the influence of various environmental factors on nutrient release dynamics.The results demonstrated that the developed regression model(p<0.0001)reliably predicted total nitrogen(TN)and total phosphorus(TP)concentrations in multistage ADDs.Based on the response surface plots and contour lines,optimal release conditions for nutrients in multistage ADDs(5 days,296 K,1.03 mg/L N,0.10 mg/L P)were determined through multi-objective optimization.We found that nutrient application exerted the most substantial influence on the release conditions.As field water was discharged into the ditches,the nutrient levels were decreased progressively.Overall,the N and P release processes in multistage ADDs were jointly influenced by environmental factors and ditch scale.These findings offer a solid theory for studying nutrient release and deposition in multistage ADDs,providing key insights for managing farmland ditches to reduce agricultural pollution.
文摘Japan overtook China as the largest foreign holder of U.S. Treasury securities at the end of 2009 after China sold $34.2 billion in American securities last December. China had previously surpassed Japan as the largest holder in September 2008. Since then, China has increased and reduced its holding from time to time. The latest amount, however, accounted for 4 percent of all Chinese holdings and was the biggest single month reduction in years. Some analysts attributed the reduction to intensifying bilateral trade disputes and political threats from the United States. Three scholars recently shared their views with Xinhua News Agency. Edited excerpts follow
基金funded by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0950000)the NSFC(Grant No.42201155+2 种基金4240114742201137)the State Key Laboratory of Cryospheric Science and Frozen Soil Engineering(CSFSE-ZQ-2410).
文摘The Yellow River(YR),China’s second-longest river,remains understudied regarding its greenhouse gases(GHGs)emissions,particularly the impacts of urban drainage ditches and wastewater treatment facilities on regional GHGs dynamics.This study investigated methane(CH_(4))and carbon dioxide(CO_(2))concentrations,fluxes and stable carbon isotopes(δ^(13)C-CH_(4)and δ^(13)C-CO_(2))across six main stream,three ditches,and one wastewater treatment site along the upper Lanzhou section of the YR,spanning from the urban entrance(36.176°N,103.449°E)to the exit of Lanzhou city(36.056°N,104.020°E).Measured CH_(4)diffusion fluxes in mainstem sites ranged from 0.01 to 2.58 mmol·m^(−2)·d^(−1)(mean:0.36 mmol·m^(−2)·d^(−1)),while ebullitive fluxes(gas bubbles)ranged from 0.01 to 18.89 mmol·m^(−2)·d^(−1)(mean:0.90 mmol·m^(−2)·d^(−1)).CO_(2)diffusion fluxes varied between 9.16–92.80 mmol·m^(−2)·d^(−1)(averaged:39.11 mmol·m^(−2)·d^(−1))at these locations.Ebullition(bubble)fluxes accounted for 53.1%±22.4%(range:9.0%to 98.4%)to total CH_(4)emissions(diffusion plus ebullition),with peak fluxes occurring during summer,indicating its significance as a CH_(4)transport mechanism.Notably,both diffusion CH_(4)and CO_(2)fluxes and ebullitive CH_(4)rates at ditch sites substantially exceeded those in mainstream reaches.The lowest CH_(4)and highest CO_(2)concentrations were observed at a wastewater treatment site,likely resulting from the removal of high organic loads.Acetoclastic methanogenesis—the process converting acetate-derived methyl groups to CH_(4)—was identified as the dominant production pathway in both mainstream and ditch environments.CH_(4)and CO_(2)flux magnitudes in the upper YR(Lanzhou section)were comparable to those observed in subtropical Yangtze River tributaries.These results demonstrate that anthropogenic influences significantly enhance CO_(2)/CH_(4)emissions,and the lateral exports of dissolved carbon(DIC and DOC)in the main stream site was quantified.,which cannot be overlooked.The findings emphasize the critical need to account for pronounced spatiotemporal variations in arid-region GHG fluxes to improve basin-scale estimates for the YR.
基金Supported by National Key Sciences and Technology Program for Water Solutions (2008ZX07102-004) ~~
文摘In recent years,the ecological quality of ditches became worse and worse with the degradation of its ecological functioning.It was necessary to apply a multi-disciplinary and multi-scale approach to study ditches based on landscape ecology theory.Spatial and network features of agricultural ditches in Lake Dianchi Basin were analyzed by geographic information system technology.The results indicated that the ditches at high level were made by concrete or block stones,the coverage of vegetation of buffer zones and width ratio between ditch sections and vegetation zones were very low;The network of agricultural ditches in Lake Dianchi basin had similar characteristics,the connectivity and circuitry were low,and the fractal dimension index of ditch network were larger in southeastern and southern banks.
基金Supported by National Science and Technology Major Program of Water Pollution Control and Management in China(2009ZX07212-004-2)~~
文摘According to the annual variation of water discharge and water quality of Xidagou in Lingwu in Ningxia,combining local cropping system,the influence degree of ditch water recharge on soil and crop was studied,and the feasibility of ditch water recharge was analyzed in our paper,which could provide scientific basis for the utilization of ditch water recharge in local area.
基金Supported by the Science and Technology Project of the Communication and Transportation Construction~~
文摘In this study, the shallow dish cross-section roadside ditch was designed, based on highway 304 line from Yanchi to Hongjing of Ningxia Province. The hy- draulic calculation of the shallow ditch obtained the corresponding water outlet dis- tance of the ditch with the width of 1.5 m or 2 m suitable for local use under dif- ferent groove longitudinal slope conditions. And the key roadside ditch construction techniques and suitable grass species were introduced.
文摘To achieve high efficiency of nitrogen and phosphorus removal and to investigate the rule of simultaneous nitrification and denitrification phosphorus removal （SNDPR）, a whole course of SNDPR damage and recovery was studied in a pilot-scale, anaerobicanoxic oxidation ditch （OD）, where the volumes of anaerobic zone, anoxic zone, and ditches zone of the OD system were 7, 21, and 280 L, respectively. The reactor was fed with municipal wastewater with a flow rate of 336 L/d. The concept of simultaneous nitrification and denitrification （SND） rate （rSND） was put forward to quantify SND. The results indicate that： （1） high nitrogen and phosphorus removal efficiencies were achieved during the stable SND phase, total nitrogen （TN） and total phosphate （TP） removal rates were 80% and 85%, respectively; （2） when the system was aerated excessively, the stability of SND was damaged, and rSND dropped from 80% to 20% or less; （3） the natural logarithm of the ratio of NOx to NH4^＋ in the effluent had a linear correlation to oxidation-reduction potential （ORP）; （4） when NO3^- was less than 6 mg/L, high phosphorus removal efficiency could be achieved; （5） denitrifying phosphorus removal （DNPR） could take place in the anaerobic-anoxic OD system. The major innovation was that the SND rate was devised and quantified.
文摘The oxidation ditch process is economic and efficient for wastewater treatment, but its application is limited in case where land is costly due to its large land area required. An innovative integrated oxidation ditch with vertical circle(IODVC) system was developed to treat domestic and industrial wastewater aiming to save land area. The new system consists of a single channel divided into two ditches(the top one and the bottom one by a plate), a brush, and an innovative integral clarifier. Different from the horizontal circle of the conventional oxidation ditch, the flow of IODVC system recycles from the top zone to the bottom zone in the vertical circle as the brush is running, and then the IODVC saved land area required by about 50% compared with a conventional oxidation ditch with an intrachannel clarifier. The innovative integral clarifier is effective for separation of liquid and solids, and is preferably positioned at the opposite end of the brush in the ditch. It does not affect the hydrodynamic characteristics of the mixed liquor in the ditch, and the sludge can automatically return to the down ditch without any pump. In this study, experiments of domestic and dye wastewater treatment were carried out in bench scale and in full scale, respectively. Results clearly showed that the IODVC efficiently removed pollutants in the wastewaters, i.e., the average of COD removals for domestic and dye wastewater treatment were 95% and 90%, respectively, and that the IODVC process may provide a cost effective way for full scale dye wastewater treatment.
基金supported by the National Natural Science Foundation of China (No.50921064, 50978249)
文摘Bioaerosol emissions from wastewater and wastewater treatment processes are a significant subgroup of atmospheric aerosols. Most previous work has focused on the evaluation of their biological risks. In this study, however, the adsorption method was applied to reduce airborne microorganisms generated from a pilot scale wastewater treatment facility with oxidation ditch. Results showed adsorption on granule activated carbon （GAC） was an efficient method for the purification of airborne microorganisms. The GAC itself had a maximum adsorption capacity of 2217 CFU/g for airborne bacteria and 225 CFU/g for fungi with a flow rate of 1.50 m^3/hr. Over 85% of airborne bacteria and fungi emitted from the oxidation ditch were adsorbed within 80 hr of continuous operation mode. Most of them had a particle size of 0.65-4.7 μm. Those airborne microorganisms with small particle size were apt to be adsorbed. The SEM/EDAX, BET and Boehm＇s titration methods were applied to analyse the physicochemical characteristics of the GAC. Relationships between GAC surface characteristics and its adsorption performance demonstrated that porous structure, large surface area, and hydrophobicity rendered GAC an effective absorber of airborne microorganisms. Two regenerate methods, ultraviolet irradiation and high pressure vapor, were compared for the regeneration of used activated carbon. High pressure vapor was an effective technique as it totally destroyed the microorganisms adhered to the activated carbon. Microscopic observation was also carried out to investigate original and used adsorbents.
基金supported by the National Natural Science Foundation of China (Grant Nos. 41472274, 41672300)Independent Subject Foundation of SKLGP (SKLGP2017Z010)
文摘An ancient landslide, situated in Deqin County, Yunnan Province, China, was used to investigate the reactivation by water infiltration. This study considers the infiltration process and landslide stability using finite-element method(FEM)-based models. The results show that the reactivation of old landslide deposit was triggered by the long-term leakage of diversion ditch before October 2012, and the reactivation was triggered again by the intense rainfall on 7-9 October 2012. The old cracks, which formed in the earlier reactivation of landslide, played a key role for the rainfall infiltration. They offered a preferential path for much more rainfall to infiltrate fast into deep soil, and caused wetting front to move down faster in landslide. The old slip zone with lower permeability was another important factor to cause the infiltrated water to accumulate and form a high pore water pressure above slip zone. Then the high pore water pressure decreased the shear strength of slip zone and triggered the reactivation of the old landslide deposit again.
基金financially supported by the National Key Technology R & D Program of China (No.2012BAC13B04-08)the National Natural Science Foundation of China (Nos.51178451 and 51221892)
文摘Bioaerosols from wastewater treatment processes are a significant subgroup of atmospheric aerosols. In the present study,airborne microorganisms generated from a wastewater treatment station（WWTS） that uses an oxidation ditch process were diminished by ventilation.Conventional sampling and detection methods combined with cloning/sequencing techniques were applied to determine the groups,concentrations,size distributions,and species diversity of airborne microorganisms before and after ventilation. There were 3021 ± 537 CFU/m3 of airborne bacteria and 926 ± 132 CFU/m3 of airborne fungi present in the WWTS bioaerosol.Results showed that the ventilation reduced airborne microorganisms significantly compared to the air in the WWTS. Over 60% of airborne bacteria and airborne fungi could be reduced after4 hr of air exchange. The highest removal（92.1% for airborne bacteria and 89.1% for fungi） was achieved for 0.65–1.1 μm sized particles. The bioaerosol particles over 4.7 μm were also reduced effectively. Large particles tended to be lost by gravitational settling and small particles were generally carried away,which led to the relatively easy reduction of bioaerosol particles0.65–1.1 μm and over 4.7 μm in size. An obvious variation occurred in the structure of the bacterial communities when ventilation was applied to control the airborne microorganisms in enclosed spaces.
