Bankfull Regional Curves for the Alleghany Plateau/Valley and Ridge,Piedmont, and Coastal Plain Regions of Maryland

Regional curves are empirical relationships that can help identify the bankfull stage in ungaged watersheds and aid in designing the riffle dimension in stream restoration projects. Bankfull regional curves were developed from gage stations with drainage areas less than 102 mi² (264.2 km²) for the Alleghany Plateau/Valley and Ridge (AP/VR), Piedmont, and Coastal Plain regions of Maryland. The AP/VR regions were combined into one region for this project. These curves relate bankfull discharge, cross‐sectional area, width, and mean depth to drainage area within the same hydro‐physiographic region (region with similar rainfall/runoff relationship). The bankfull discharge curve for the Coastal Plain region was further subdivided into the Western Coastal Plain (WCP) and Eastern Coastal Plain (ECP) region due to differences in topography and runoff. Results show that the Maryland Piedmont yields the highest bankfull discharge rate per unit drainage area, followed by the AP/VR, WCP, and ECP. Likewise, the Coastal Plain and AP/VR streams have less bankfull cross‐sectional area per unit drainage area than the Piedmont. The average bankfull discharge return interval across the three hydro‐physiographic regions was 1.4 years. The Maryland regional curves were compared to other curves in the eastern United States. The average bankfull discharge return interval for the other studies ranged from 1.1 to 1.8 years.     

Dynamic analysis of a one-prey multi-predator impulsive system with Ivlev-type functional

Considering the Ivlev-type functional response, we develop and analyze a class of one-prey multi-predator system with impulsive effect at different fixed times. Some sufficient conditions ensuring the prey to be extinct are obtained via the Floquent theory and small amplitude perturbation skill. Using the method of comparison involving multiple Laypunov functions, we derive some conditions for the permanence of the system. Numerical simulations of the impulsive system exhibit the rich complex dynamics for the key parameters, such as symmetry-breaking pitchfork bifurcation, periodic doubling bifurcation, chaos, periodic halving cascade and crisis.     

含缺陷油套管的抗弯曲特性研究

本研究选用J55油套管，用人工缺陷法在外径为73mm的油套管外表面预制了缺陷，通过三点弯曲对称加载试验，研究了缺陷管的抗弯强度，对改进的NSC准则进行实验检验。结果表明，在缺陷角较小时，改进的NSC准则能给出与试验数据接近的预测结果，但对于在缺陷角较大的情形，预测结果却不理想。根据试验结果，本文进一步提出了一个含有缺陷几何参量的新公式。新公式能很好地预测含缺陷管的抗弯曲能力。     

高强箍筋混凝土简支梁斜裂缝分形理论研究

通过对8根集中荷载作用下高强箍筋T形截面简支梁的试验研究，运用分形理论对试件中斜裂缝的出现、发育及分布特征进行了分析。结果表明：分形理论对斜裂缝自相似性有很好的量化关系。     

HYDRAULIC GEOMETRY AND STREAM CHANNEL BEHAVIOR: A UNCERTAIN LINK1

ABSTRACT: The at-a-station hydraulic geometry of stream channels can serve as a predictor of alluvial stream channel behavior. This geometry is the empirical relations describing changes in water surface width, mean depth, and mean velocity with changing discharge. The exponent values are correlated with channel morphology and behavior such as scour and fill, flow resistance, bank resistance, and competence. Channel behavior and morphology are apparently related, but some causes for effects are uncertain. Several studies, using empirical and theoretical bases, are reviewed here to illustrate the relation between hydraulic geometry and channel behavior, but the relations are not always consistent. Hydraulic geometry variables are easy to measure and readily available, but they do not always reflect what may be more important ones such as turbulence, the velocity distribution profile, and distribution and cohesion of sediment particles. This paper illustrates some of these problems, provides some solutions, and addresses need for more work to better predict stream channel behavior from hydraulic geometry     

基于污染物临界粘附力的超滤动态过程的CFD模拟

针对膜污染的动态变化问题,通过计算流体力学(CFD)手段建立了中空纤维膜的二维轴对称模型,综合考虑了污染物间粘附力及水流剪切力的影响,提出有效剪切应力的概念,在模型中耦合了变形几何、自由多孔介质流动及稀物质传递3种物理场,将污染物法向积累、切向有效剪切与污染物界面处的网格速度相关联,建立了膜面污染物截留的动态模型.依据死端过滤与错流过滤的实验数据,确定出模型的匹配参数.在此基础上,研究了不同进给方式(连续流与脉冲流)对膜面污染物的影响.模拟结果表明,当水流剪切力足以克服污染物的临界粘附力时,可对膜面污染物起冲刷作用;与连续流相比,脉冲流具有更高的有效剪切速率,在对膜面污染物的冲刷作用方面更具优势.     

BANKFULL HYDRAULIC GEOMETRY RELATIONSHIPS AND RECURRENCE INTERVALS FOR NORTH CAROLINA'S COASTAL PLAIN1

ABSTRACT: Bank full hydraulic geometry relationships relate stream channel geometry to watershed size for specific physiographic regions. This paper presents bank full hydraulic geometry relationships and recurrence intervals for the Southeastern Plain coercion and the flat woods subtype of the Middle Atlantic Coastal Plain ecoregion found within North Carolina's Coastal Plain physiographic province. Cross‐sectional and longitudinal survey data from gated and unpaged streams were used to compute channel dimension and profile information. Power functions were developed, relating drainage area to bank full discharge, cross‐sectional area, width, and mean depth. Recurrence intervals of bank full events were estimated from gagged streams using both a Log‐Pearson Type III distribution of peak annual discharge and a partial‐duration series of average daily discharge. Results from both methods indicate that average bank full recurrence intervals for the study area are below one year. Determinations of recurrence intervals by the Log‐Pearson Type III distribution were for the most part inconclusive (less than one year), while a partial duration series estimated a 0.19 year average, ranging from 0.11 to 0.31 years.     

Path selection and foraging efficiency in Argentine ant transport networks

We experimentally investigated both individual and collective behavior of the Argentine ant Linepithema humile as they crossed symmetrical and asymmetrical bifurcations in gallery networks. Ants preferentially followed the branch that deviated the least from their current direction and their probability to perform a U-turn after a bifurcation increased with the turning angle at the bifurcation. At the collective level, colonies were better able to find the shortest path that linked the nest to a food source in a polarized network where bifurcations were symmetrical from one direction and asymmetrical from the other than in a network where all bifurcations were symmetrical. We constructed a model of individual behavior and showed that an individual’s preference for the least deviating path will be amplified via the ants’ mass recruitment mechanism thus explaining the difference found between polarized and non-polarized networks. The foraging efficiency measured in the simulations was three times higher in polarized than in non-polarized networks after only 15 min. We conclude that measures of transport network efficiency must incorporate both the structural properties of the network and the behavior of the network users.     

Effect of injection timing,injector opening pressure and nozzle geometry on the performance of a compression ignition engine operated on non-edible oil methyl esters from different sources

Increasing cost of fossil fuels, environmental threats from exhaust emissions and their depleting nature have generated intense international interest in developing renewable and alternative fuels for internal combustion engines. This study investigates the suitability of different non-edible-derived biodiesels such as cottonseed oil methyl ester (COME), honne oil methyl ester (HnOME) and honge oil methyl ester (HOME) to four-stroke, single-cylinder compression ignition (CI) engine. Engine tests were conducted to study the effect of fuel injection timing (IT), fuel injector opening pressure (IOP) and injector nozzle geometry on the performance, combustion and emission characteristics of COME, HnOME and HOME in the modified CI engine. IT was varied from 19° to 27° before top dead centre (bTDC) in steps of 4° bTDC; IOP was varied from 205 to 240 bar in steps of 10 bar. Nozzle injectors of three to five holes, each of 0.3 mm size, were selected for the study. It was concluded that a retarded IT of 19° bTDC increased IOP of 230 bar, and four-hole nozzle injector of 0.3 mm size resulted in overall better engine performance with increased brake thermal efficiency and reduced hydrocarbon and carbon monoxide smoke emissions for the fuels tested.     

BANKFULL DISCHARGE RECURRENCE INTERVALS AND REGIONAL HYDRAULIC GEOMETRY RELATIONSHIPS: PATTERNS IN THE PACIFIC NORTHWEST,USA1

ABSTRACT: The model bankfull discharge recurrence interval (annual series) (T_a) in streams has been approximated at a 1.5‐year flow event. This study tests the linkage between regional factors (climate, physiography, and ecoregion) and the frequency of bank‐full discharge events in the Pacific Northwest (PNW). Patterns of Ta were found to be significant when stratified by EPA Ecoregion. The mean value for T_a in the PNW is 1.4 years; however, when the data is stratified by ecoregion, the humid areas of western Oregon and Washington have a mean value of 1.2 years, while the dryer areas of Idaho and eastern Oregon and Washington have a mean value of 1.4 to 1.5 years. Among the four factors evaluated, vegetation association and average annual precipitation are the primary factors related to channel form and T_a. Based on the results of the T_a analyses, regional hydraulic geometry relationships of streams were developed for the PNW, which relate variables, such as bank‐full cross‐sectional area, width, depth, and velocity, to bankfull discharge and drainage area. The verification of T_a values, combined with the development of regional hydraulic geometry relationships, provides geographically relevant information that will result in more accurate estimates of hydraulic geometry variables in the PNW.