Comparing Two Implementations of a Micromixing Model. Part II: Canopy Flow     

John?V.?PostmaEmail author  John?D.?Wilson  Eugene?Yee 《Boundary-Layer Meteorology》2011,140(2):225-241

The sequential particle micromixing model (SPMMM) is used to estimate concentration fluctuations in plumes dispersing into a canopy flow. SPMMM uses the familiar single-particle Lagrangian stochastic (LS) trajectory framework to pre-calculate the required conditional mean concentrations, which are then used by an interaction by exchange with the conditional mean (IECM) micromixing model to predict the higher-order fluctuations of the scalar concentration field. The predictions are compared with experimental wind-tunnel dispersion data for a neutrally stratified canopy flow, and with a previously reported implementation using simultaneous particle trajectories. The two implementations of the LS–IECM model are shown to be largely consistent with one another and are able to simulate dispersion in a canopy flow with fair to good accuracy.  相似文献   

Effects of environmental stresses on the responses of mangrove plants to spent lubricating oil     

Ke L  Zhang C  Guo C  Lin GH  Tam NF 《Marine pollution bulletin》2011,63(5-12):385-395

The influence of different environmental stresses, including salinity (5-35‰), tidal cycle (6/6, 12/12 and 24/24 h of high/low tidal regimes) and nutrient addition (1-6 times background nitrogen and phosphorus content) on Bruguiera gymnorrhiza and Aegiceras corniculatum grown in sediment contaminated with spent lubricating oil (7.5 L m(-2)) were investigated. The oil-treated 1-year-old mangrove seedlings subject to low (5‰) and high (35‰) salinity had significantly more reduction in growth, more release of superoxide radical (O2·-) and higher activity of superoxide dismutase (SOD) than those subject to moderate salinity (15‰). Extended flooding (24/24 h of high/low tidal regime) enhanced O2·- release and malondialdehyde (MDA) content in both oil-treated species but had little negative effects on biomass production (P>0.05) except the stem of A. corniculatum (P=0.012). The addition of nutrients had no beneficial or even posed harmful effects on the growth and cellular responses of the oil-treated seedlings.  相似文献   

Seasonal variations of imposex indices and butyltin concentrations in the rock shell Thais clavigera collected from Hong Kong waters     

Qiu JW  Chan KM  Leung KM 《Marine pollution bulletin》2011,63(5-12):482-488

This study investigated butyltin contamination in Hong Kong waters using the rock shell Thais clavigera as a biomonitor. We collected rock shells from nine coastal sites in both winter 2005 and summer 2006 to examine the spatial and seasonal patterns. The relative penis size index (RPSI) and vas deferens sequence index (VDSI) were determined following a standard protocol, while the tissue concentrations of butyltins (i.e., mono-, di- and tri-butyltin) were measured using gas chromatography. The results showed that imposex was particularly severe in T. clavigera collected from Victoria Harbour, Pak Sha Wan and Sai Kung Pier where shipping activities were frequent. Both imposex indices had a positive correlation with tissue concentration of tributyltin in T. clavigera. While VDSI exhibited little seasonal variation, RPSI of winter specimens was significantly higher than that of summer specimens. Thus, sampling season should be standardised when using RPSI as a biomarker.  相似文献   

Electro-Osmotic Consolidation Studies on Peat and Clayey Silt Using Electric Vertical Drain   总被引：2，自引：1，他引：1  

Shenbaga R. Kaniraj  H. L. Huong  J. H. S. Yee 《Geotechnical and Geological Engineering》2011,29(3):277-295

Peat and soft soil deposits are abundant in Malaysia. Studies using electrokinetic geosynthetics (EKG) such as prefabricated electric vertical drains (EVD or ePVD) have shown the potential for the application of these materials in electrokinetic strengthening of soft clays and increasing solids content in mining tailings and sludges. There are no studies reported on the effectiveness of electro-osmosis using EVD in peat. Laboratory experiments were carried out to investigate the effectiveness of electro-osmotic stabilization of two peat samples and a slightly organic clayey silt sample, from the North Sarawak region. Commercially available EVD was used to induce electro-osmosis and drainage of pore water. The influence of voltage gradient, organic content, initial water content, anode–cathode configuration and presence of roots on electro-osmotic consolidation was investigated. Electro-osmotic consolidation using EVDs was effective in the improvement of peat, over a large range of initial water contents. An increase in the voltage gradient generally improved consolidation. The maximum voltage gradient for optimum results appeared to be in the region 120 V/m. The 2anodes-1cathode configuration performed better than the 1anode-1cathode configuration. The presence of roots reduced the electro-osmosis effect.  相似文献   

Variations of methane induced pyrite formation in the accretionary wedge sediments offshore southwestern Taiwan   总被引：4，自引：0，他引：4  

Yee Cheng Lim  Saulwood Lin  Tsanyao Frank Yang  Yue-Gau Chen  Char-Shine Liu 《Marine and Petroleum Geology》2011,28(10):1829-1837

The accretionary wedge of offshore southwestern Taiwan contains abundant deposits of gas hydrate beneath the sea floor. High concentrations of methane in pore waters are observed at several locations with little data concerning historical methane venting available. To understand temporal variation of methane venting in sediments over geologic time, a 23-m-long Calypso piston core (MD05-2911) was collected on the flank of the Yung-An Ridge. Pore water sulfate, dissolved sulfide, dissolved iron, methane, sedimentary pyrite, acid volatile sulfide, reactive iron, organic carbon and nitrogen as well as carbonate δ¹³C were analyzed.Three zones with markedly different pyrite concentration were found at the study site. Unit I sediments (>20 mbsf) were characterized with a high amount of pyrite (251–380 μmol/g) and a δ¹³C-depleted carbonate, Unit II sediments (15–20 mbsf) with a low pyrite (15–43 μmol/g) and a high content of iron oxide mineral and Unit III sediments (<10 mbsf) by a present-day sulfate–methane interface (SMI) at 5 m with a high amount of pyrite (84–221 μmol/g) and a high concentration of dissolved sulfide.The oscillation records of pyrite concentrations are controlled by temporal variations of methane flux. With an abundant supply of methane to Unit I and III, anaerobic methane oxidation and associated sulfate reduction favor diagenetic conditions conducive for significant pyrite formation. No AOM signal was found in Unit II, characterized by typical organically-limited normal marine sediments with little pyrite formation. The AOM induced pyrite formation near the SMI generates a marked pyrite signature, rendering such formation of pyrite as a useful proxy in identifying methane flux oscillation in a methane flux fluctuate environment.  相似文献   

CFD simulations of the effects of fouling and antifouling   总被引：1，自引：0，他引：1  

Yee Shin Khor 《Ocean Engineering》2011,38(10):1065-1079

Biofouling is a global problem in the marine industry though its effects on lift and drag are rarely discussed. This paper seeks to employ Computational Fluid Dynamics (CFD) method to quantify the effects of this problem based on the obtained flow field information. The simulation is carried out on a NACA 4424 airfoil and Defence Research Establishment Atlantic (DREA) Submarine Hull. Different levels of fouling are studied with quantified fouling height and density. As an extension, the effects of two common antifouling methods, i.e. tin-free Self-Polishing Copolymer (SPC) and Foul Release on the drag of NACA 4424 foil and the submarine hull is investigated. For NACA 4424 airfoil, fouling reduces lift-drag ratio (C_L/C_D) by up to 80% in maximum and therefore result in the significant increase in fuel consumption. Predicted flow data shows this is related to the increased flow separation region caused by the fouling. It is found that pressure gradient gradually increases from the smallest fouling height to the largest but does not vary that much for fouling of varying densities. The general trend of C_L/C_D varies with angle of attack agrees well with others experimental data. Computed results also show good agreement with experimental data for the DREA bare hull. As to antifouling, Foul Release, despite being 30% more expensive than SPC, exhibits 10-40% higher C_L/C_D as compared to SPC for NACA foil and submarine hull.  相似文献   

Exploring the influence of interparticle friction on critical state behaviour using DEM   总被引：1，自引：0，他引：1  

Xin Huang  Kevin J. Hanley  Catherine O'Sullivan  Chung Yee Kwok 《国际地质力学数值与分析法杂志》2014,38(12):1276-1297

Understanding the extent to which discrete element method (DEM) simulations can capture the critical state characteristics of granular materials is important to legitimize the use of DEM in geomechanics. This paper documents a DEM study that considered the sensitivity of the critical state response characteristics to the coefficient of interparticle friction (μ) using samples with gradings that are representative of a real soil. Most of the features that are typically associated with sand behaviour at the critical state were seen to emerge from the DEM simulation data. An important deviation occurs when high μ values (μ ≥ 0.5) are used, as has been the case in a number of prior DEM studies. While there is a systematic variation in the critical state behaviour with μ for μ < 0.5, when μ ≥ 0.5, the behaviour at the critical state seems to be insensitive to further increases in μ. In contrast to observations of conventional soil response, when μ ≥ 0.5, the void ratio at the critical state initially increases with increasing mean effective stress (p′). Analysis of the DEM data and use of simple models of isolated force chains enabled some key observations. When ‘floating’ particles that do not transmit stress are eliminated from the void ratio calculation, the void ratio at the critical state decreases consistently with increasing p′. There is a transition from sliding to rolling behaviour at the contact points as μ increases. Beyond a limiting value of μ, further increases in μ do not increase the buckling resistance of individual strong force chains. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Hydrogeochemical evolution of the shallow and deep basaltic aquifers in Tamborine Mountain,Queensland (Australia)     

Catania  Sabrina T.  Reading  Lucy 《Hydrogeology Journal》2023,31(4):1083-1100

Tamborine Mountain, Queensland (Australia), is a prime example of a basalt fractured-rock aquifer. Yet very little is known about the hydrochemistry of this groundwater system. Both analytical (major ions and stable isotopes) and multivariate (hierarchical cluster analysis, principal component analysis and factor analysis) analyses were used in this study to investigate the factors that interact within this aquifer system, in order to determine groundwater hydrogeochemistry. A new approach was applied to the data by classifying hydrographs by water type to clearly identify differing aquifer zones. Three distinct groundwater chemistry types were identified, and they were differentiated by variations in depth. Shallow bores were dominated by Na–Cl waters, deep bores were dominated by Na–HCO₃ and Ca–HCO₃ waters, and the two deepest bores were dominated by mixed water types. The evaluation of hydrogeochemical data has determined that both mineral weathering processes and groundwater/surface-water interaction had a strong influence on the hydrogeochemistry. Seasonal effects were minimal in the study area based on physicochemical parameters and ion chemistry. However, stable isotopic data show temporal trends. Increased rainfall events during the wet season produced a depletion in δ¹⁸O and increased d-excess values. The opposite is found during the dry season as a result of higher evaporation rates that are not hindered by intense rainfall events.

  相似文献   

Homological relations: A methodology for the certification of irregular tessellations     

Eliseo Clementini  Brahim Lejdel  Sabrina Mazzagufo  Robert Laurini 《Transactions in GIS》2021,25(1):491-515

In GIS, spatial analysis is based on the use of spatial operations such as testing the spatial relations between features. Often, such tests are invalidated by errors in datasets. It is a very common experience that two bordering regions which should obey the topological relation “meet” fall instead in the “overlap” category. The situation is exacerbated when applying topological operators to regions that come from different datasets, where resolution and error sources are different. Despite the problem being quite common, up to now no standard approach has been defined to deal with spatial relations affected by errors of various origins. Referring to topological relations, we define a model to extend the eight Egenhofer relations between two simple regions: we call them homological relations (H‐relations). We discuss how exact topological relations can be extracted from observed relations and discuss the case of irregular tessellations, where errors have the most impact on vector data. In the proposed case study within the domain of geographic crowdsourced data, we propose algorithms for identifying homological regions and obtaining a corrected tessellation. This methodology can be considered as a step for quality control and the certification of irregular tessellations.  相似文献   

Imaging polarimetry of Comet 9P/Tempel before and after the Deep Impact     

Reiko Furusho  Yuji Ikeda  Wing-Huen Ip  Toshihiro Kasuga  Yusuke Sato  Ming-Shin Chang  Jun-ichi Watanabe 《Icarus》2007,190(2):454-458

The NASA's Deep Impact mission was the first impact experiment to a cometary nucleus. The target of the mission was Comet 9P/Tempel, one of the Jupiter family comets. The impact was performed on July 4th, 2005. Imaging polarimetric observations were carried out by Polarimetric Imager for COmets (PICO) mounted on the Lulin One-meter Telescope (LOT) at Lulin Observatory, Taiwan. Intensity and linear polarization degree maps were obtained on July 3-5, 2005. Impact ejecta plume was clearly recognized in the enhanced intensity map. Furthermore, arc-shaped region of high polarization was recognized in the polarization map. Dust grains in this region had larger expansion velocity than the grains which provided the brightest area in the intensity map. comparing our results with the MIR spectroscopy obtained by Subaru Telescope we conclude that very small carbonaceous grains might be responsible for the region of high polarization.  相似文献