Computer simulation of flow through a lattice flow-cell model

For single-phase flow through a network model of a porous medium, we report (1) solutions of the Navier–Stokes equation for the flow, (2) micro-particle imaging velocimetry (PIV) measurements of local flow velocity vectors in the “pores throats” and “pore bodies,” and (3) comparisons of the computed and measured velocity vectors. A “two-dimensional” network of cylindrical pores and parallelepiped connecting throats was constructed and used for the measurements. All pore bodies had the same dimensions, but three-different (square cross-section) pore-throat sizes were randomly distributed throughout the network. An unstructured computational grid for flow through an identical network was developed and used to compute the local pressure gradients and flow vectors for several different (macroscopic) flow rates. Numerical solution results were compared with the experimental data, and good agreement was found. Cross-over from Darcy flow to inertial flow was observed in the computational results, and the permeability and inertia coefficients of the network were estimated. The development of inertial flow was seen as a “two-step” process: (1) recirculation zones appeared in more and more pore bodies as the flow rate was increased, and (2) the strengths of individual recirculation zones increased with flow rate. Because each pore-throat and pore-body dimension is known, in this approach an experimental (and/or computed) local Reynolds number is known for every location in the porous medium at which the velocity has been measured (and/or computed).     

Responses of Ras El Bar seafloor characteristics to the protective engineering structures, Nile delta, Egypt

Bathymetry of the seafloor in the area in front of Ras El Bar coast, the characters of the seafloor sediments and the effects of protective structures on seafloor bathymetry were examined. Seafloor depths in front of Ras El Bar seawall ranged between 2 and 4 m. These depths, coupled with wave climate, result in waves breaking directly onto the wall and exerting high, dynamic pressures on the area at the structure’s toe. The sandy seafloor in front of the wall has been scoured. Sea water has undermined the wall causing removal of sediment, destabilization of its slope and the whole face of the wall has slipped. Toe protection in the form of a rocky apron is required to prevent such damage. West of the seawall, the constructed breakwater system has affected the bathymetry of the seafloor in the area. Shoaling and submerged spits have been formed in the shadow of each breakwater unit. The gaps between the breakwater units have attained deep depths and steep slopes. Scours and steep slopes adjacent to the head of the breakwater units have been recorded. Seaward of the breakwater system, deeper depths and gentle slopes characterize the seafloor. Offshore–onshore current and sediment movements toward the northeast is inferred from the configuration of the bottom contour lines.     

Application of the single point measurement in discharge estimation

The fluid flow system can be described by an equivalent electromagnetic system. In this paper a successful application of the Biot–Savart law in hydraulics is presented. Similarity between the magnetic field of a current wire and the isovel contours in a channel cross-section is used to derive the isovel patterns in an open or closed channel. Having obtained the normalized isovel contours, one can easily obtain the discharge using a single point of velocity measurement at the conduit cross-section. The estimated discharge, based on measured points and the predicted isovels on the upper half of the flow depth away from the boundaries was within ±5% of the measured and much better in comparison to the prediction of one- and two-point methods. Furthermore, the model was applied to real life channels. The prediction of the water surface velocity for the River Unon in Japan and depth-averaged velocity for the Severn River in UK show a good agreement with the measured data and analytical results.     

Les manifestations tectono-sédimentaires d'âge Campanien–Maastrichtien en Tunisie : implications sur l'évolution géodynamique de la marge Nord-AfricaineThe Campanian–Maastrichtian synsedimentary tectonic activity: implication in the geodynamic evolution of the North African Margin

The synsedimentary tectonic activity evidenced in central and northern Tunisia points out the fact that the Campanian–Maastrichtian deposits are associated with several NW–SE and east–west normal faults. These results suggest that the east–west transform fault of North African Margin is still active during this stage. These data allow us to discuss a new geodynamic model for the North African Margin. To cite this article: M. Dlala, C. R. Geoscience 334 (2002) 135–140.     

Attitude determination by integration of MEMS inertial sensors and GPS for autonomous agriculture applications

Integration of Global Positioning System (GPS) and Inertial Navigation System (INS) technologies, which has widespread usage in industry, is also regarded as an ideal solution for automated agriculture because it fulfils the accuracy, reliability and availability requirements of industrial and agricultural applications. Agriculture applications use position, velocity and heading information for automated vehicle guidance and control to enhance the yield and quality of the crop, and in order to vary the application of fertilizer and herbicides according to soil heterogeneity at sub-field level. A loosely coupled GPS/INS integration algorithm known as “AhrsKf” is introduced for automated agriculture vehicle guidance and control utilizing MEMS inertial sensors and GPS. The AhrsKf can produce high-frequency attitude solutions for the vehicle’s guidance and control system, by using inputs from a single survey grade L1/L2 antenna, eliminating the need for the previous two antenna solutions. Given its agricultural application, the AhrsKf has been implemented with some specific design features to improve the accuracy of the attitude solution including, temperature compensation of the inertial sensors, and the aid of plough lines of farm lands. To evaluate the AhrsKf solution, two benchmarking tests have been conducted by using a three-antenna GPS system and NovAtel’s SPAN-CPT. The results have demonstrated that the AhrsKf solution is stable and can correctly track the movement of the farming vehicle.     

Seismic performance of high-rise buildings in selected regions in Saudi Arabia according to different seismic codes

The design code for each country is revised and updated based on an expected zone’s seismic intensities,geotechnical site classifications,structural systems,construction materials and methods of construction in order to provide more realistic considerations of seismic demand,seismic response,and seismic capacity.Based on the aforementioned provisions,structures designed according to different seismic codes may yield different performances for the same level of hazard.This study aims to investigate and compare the induced responses related to the earthquake-resistant design of reinforced concrete(RC)buildings according to the Saudi building code(SBC-301),American code(ASCE-7),uniform building code(UBC-97),and European code(EC-8).In order to account for the provision regarding the hazard specification and its effect on the induced seismic responses,four regions in the Kingdom of Saudi Arabia with different seismic levels are selected.The code provisions related to the specification of site classification and its effect on the induced design base shear are investigated as well.Significant differences are observed in the induced responses with the variation in seismic design codes for the considered seismic hazards and site classifications.     

Revisiting hydrological drought propagation and recovery considering water quantity and quality

Climate extremes, in particular droughts, are significant driving forces towards riverine ecosystem disturbance. Drought impacts on stream ecosystems include losses that can be either direct (e.g., destruction of habitat for aquatic species) or indirect (e.g., deterioration of water quality, soil quality, and increased chance of wildfires). This paper combines hydrologic drought and water quality changes during droughts and represents a multistage framework to detect and characterize hydrological droughts while considering water quality parameters. This method is applied to 52 streamflow stations in the state of California, USA, over the study period of 1950–2010. The framework is assessed and validated based on two drought events declared by the state in 2002 and 2008. Results show that there are two opposite drought propagation patterns in northern and southern California. In general, northern California indicates more frequent droughts with shorter time to recover. Chronology of drought shows that stations located in southern California have not followed a specific pattern but they experienced longer drought episodes with prolonged drought recovery. When considering water quality, results show that droughts either deteriorate or enhance water systems, depending on the parameter of interest. Undesirable changes (e.g., increased temperature and decreased dissolved oxygen) are observed during droughts. In contrast, decreased turbidity is detected in rivers during drought episodes, which is desirable in water systems. Nevertheless, water quality deteriorates during drought recovery, even after drought termination. Depending on climatic and streamflow characteristics of the watersheds, it was found that it would take nearly 2 months on average for water quality to recover after drought termination.     

Physical properties of three short period close binaries:KIC 2715417,KIC 6050116 and KIC 6287172

We present the physical parameters of three short period close binaries using data observed from the Kepler Space Telescope. All of these observations were taken in a single bandpass(which approximates the Johnson V-band). Our three systems are KIC 2715417, KIC 6050116 and KIC 6287172. The first system, KIC 2715417, is considered a semi-detached system with the secondary component filling its Roche lobe. The second system, KIC 6050116, is an overcontact system, while the third system, KIC 6287172, belongs to ellipsoidal variables as deduced from the Roche lobe geometry. For photometric analysis, we used the PHOEBE software package, which is based on the Wilson-Devinney code. Due to lack of spectroscopic data, the photometric mass ratios are determined from the analyses of light curves using the q-search method. The absolute parameters are determined using three different methods(Harmanec, Maceroni Van'tVeer and Gazeas Niarchos).     

Geotectonic significance of the Neoproterozoic ophiolitic metagabbros of Muiswirab area,South Eastern Desert,Egypt: constraints from their mineralogical and geochemical characteristics

Acta Geochimica - Petrological and geochemical studies of Neoproterozoic metagabbros were carried out in the Muiswirab area, South Eastern Desert of Egypt. The Muiswirab area comprises of...     

Effect of electrode contact impedance on A.C. electrical properties of a wet hematite sample

Electrode polarization is a major problem in the determination of dielectric properties of samples, particularly at low frequencies. Understanding of these interfacial phenomena is essential in order to measure correctly the electrical properties of a sample of interest. This paper presents a comparative study of the effect of electrode contact impedance on A.C. electrical properties of a partially and fully saturated hematitic sandstone sample. The electrical properties of the sample were first measured using stainless steel electrodes with high contact impedance, and measured again with a four terminal Cu–CuSO₄ electrode of low contact impedance. Complex impedance measurements at room temperature (~16°C) were performed in the frequency range from 1 Hz to 100 kHz. Measured electrical spectra vary strongly with the electrode type. The difference in the electrical properties between the two electrode types (stainless steel and Cu–CuSO₄) may be attributed to the surface contact impedance between the sample and the electrode. Experimental data indicate that the electrical properties vary strongly with water saturation. The dielectric constant decreases with frequency and increases with saturation up to a certain saturation limit then decreases. Charge transport can occur either through the bulk of the solid matrix (hematite or sand) or along the grain boundaries of aggregates (water). When soil minerals are exposed to water, exchangeable ions go into solution. Most of the ionic or covalent bonded rock forming minerals such as quartz, mica, and feldspars are nonconductors. When the surfaces of these minerals come into contact with liquid water, electrolytes are formed and ionic drift associated with the electrical field causes electrical conduction. The anomalous dielectric properties of partially saturated rocks can be interpreted using percolation theory. This theory predicts that when the conductive fraction (water) increases, clustering of conductive inclusions develops, and the thickness of insulating gaps between conductive clusters decreases, causing a large increment in the capacitance of the sample. Further increases in the conductive component causes the shunting of insulating capacitive gaps.