Journal articles on the topic 'Swept-fluid technique'

Silk-Screen Print Technique was used to print roughness elements at the leading edge of a swept wing for crossflow (CF) dominated Laminar Flow control (LFC) in fluid dynamics. Crossflow was studied to be sensitive to the spacing and height of the roughness elements, as well as the density of the metal ink. Experiments in our research showed silk-screen print technique can precisely print the elements to dominate to delay transition.

The partial differential equations describing compressible fluid flows can be notoriously difficult to resolve on a pragmatic scale and often require the use of high-performance computing systems and/or accelerators. However, these systems face scaling issues such as latency, the fixed cost of communicating information between devices in the system. The swept rule is a technique designed to minimize these costs by obtaining a solution to unsteady equations at as many possible spatial locations and times prior to communicating. In this study, we implemented and tested the swept rule for solving two-dimensional problems on heterogeneous computing systems across two distinct systems and three key parameters: problem size, GPU block size, and work distribution. Our solver showed a speedup range of 0.22–2.69 for the heat diffusion equation and 0.52–1.46 for the compressible Euler equations. We can conclude from this study that the swept rule offers both potential for speedups and slowdowns and that care should be taken when designing such a solver to maximize benefits. These results can help make decisions to maximize these benefits and inform designs.

Molecular film displacement is a new nanofilm EOR technique. A large number of experiments show that the mechanism of molecular film displacement is different from conventional chemical displacement (polymer, surfactant, alkali and ASP displacement etc). With water solution acting as transfer medium, molecules of the filming agent develop the force to form films through electrostatic interaction, with efficient molecules deposited on the negatively charged rock surface to form ultrathin films at nanometer scale. This change the properties of reservoir surface and the interaction condition with crude oil, making the oil easily be displaced as the pores swept by the injected fluid. Thus oil recovery is enhanced. The mechanism of molecular filming agent mainly includes absorption, wettability alteration, diffusion and capillary imbibition etc.

AbstractOne of the aerospace design engineer’s goals aims to reduce drag for increased aircraft performance, in terms of range, endurance, or speed in the various flight regimes. To accomplish this, the designer must have rapid and accurate techniques for computing drag. At subsonic Mach numbers drag is primarily a sum of lift-induced drag and zero-lift drag. While lift-induced drag is easily and efficiently determined by a far field method, using the Trefftz plane analysis, the same cannot be said of zero-lift drag. Zero-lift drag (CD,0) usually requires consideration of the Navier-Stokes equations, the solution of which is as yet unknown except by using approximate numerical techniques with computational fluid dynamics (CFD). The approximate calculation of zero-lift drag from CFD is normally computed with so-called near-field techniques, which can be inaccurate and too time consuming for consideration in the design environment. This paper presents a technique to calculate zero-lift and boundary-layer drag in the subsonic regime that includes aeroelastic effects and is suitable for the design environment. The technique loosely couples a two-dimensional aerofoil boundary-layer model with a 3D aeroelastic solver to compute zero-lift drag. We show results for a rectangular wing (baseline), a swept wing, and a tapered wing. Then compare with a rectangular wing with variable thickness and camber, thinning out from the root to tip (spanwise direction), thus demonstrating the practicality of the technique and its utility for rapid conceptual design.

Wind tunnel models are traditionally machined from high-quality metal material; this condition reduces the possibility to test different geometric variations or models as it corresponds to incremental cost. In the last decade, the quality of additive manufacturing techniques has been progressively increasing, while the cost has been decreasing. The utilization of 3D-printing techniques suggests the possibility to improve the cost, time, and flexibility of a wind tunnel model production. Possible disadvantages in terms of quality of the model finishing, stiffness, and geometric accuracy are investigated, to understand if the production technique is capable of providing a suitable test device. Additionally, pressure taps for steady surface pressure measurements are integrated during the printing procedure and the production of complex three-dimensional highly swept wings have been selected as targets. Computational fluid dynamics tools are exploited to confirm the experimental results in accordance with the best practice approaches characterizing flow patterns dominated by leading-edge vortices. The fidelity level of the experimental data for scientific research of the described flow fields is investigated. An insight of the most important guidelines and the possible improvements is provided as well as the main features of the approach.

Summary The fluid-flow mechanism of enhanced oil recovery (EOR) in porous media by alkali/surfactant/polymer (ASP) flooding is investigated by measuring the production performance, pressure, and saturation distributions through the installed differential-pressure transducers and saturation-measurement probes in a physical model of a vertical heterogeneous reservoir. The fluid-flow variation in the reservoir is one of the main mechanisms of EOR of ASP flooding, and the nonlinear coupling and interaction between pressure and saturation fields results in the fluid-flow variation in the reservoir. In the vertical heterogeneous reservoir, the ASP agents flow initially in the high-permeability layer. Later, the flow direction changes toward the low- and middle-permeability layers because the resistance in the high-permeability layer increases on physical and chemical reactions such as adsorption, retention, and emulsion. ASP flooding displaces not only the residual oil in the high-permeability layer but also the remaining oil in the low- and middle-permeability layers by increasing both swept volume and displacement efficiency. Introduction Currently, most oil fields in China are in the later production period and the water cut increases rapidly, even to more than 80%. Waterflooding no longer meets the demands of oilfield production. Thus, it is inevitable that a new technology will replace waterflooding. The new technique of ASP flooding has been developed on the basis of alkali-, surfactant-, and polymer-flooding research in the late 1980s. ASP flooding uses the benefits of the three flooding methods simultaneously, and oil recovery is greatly enhanced by decreasing interfacial tension (IFT), increasing the capillary number, enhancing microscopic displacing efficiency, improving the mobility ratio, and increasing macroscopic sweeping efficiency (Shen and Yu 2002; Wang et al. 2000; Wang et al. 2002; Sui et al. 2000). Recently, much intensive research has been done on ASP flooding both in China and worldwide, achieving some important accomplishments that lay a solid foundation for the extension of this technique to practical application in oil fields (Baviere et al. 1995; Thomas 2005; Yang et al. 2003; Li et al. 2003). In previous work, the ASP-flooding mechanism was studied visually by using a microscopic-scale model and double-pane glass models with sand (Liu et al. 2003; Zhang 1991). In these experiments, the water-viscosity finger, the residual-oil distribution after waterflooding, and the oil bank formed by microscopic emulsion flooding were observed. In Tong et al. (1998) and Guo (1990), deformation, threading, emulsion (oil/water), and strapping were observed as the main mechanisms of ASP flooding in a water-wetting reservoir, while the interface-producing emulsion (oil/water), bridging between inner pore and outer pore, is the main mechanism of ASP flooding in an oil-wetting reservoir. For a vertical heterogeneous reservoir, ASP flooding increases displacement efficiency by displacing residual oil through decreased IFT, simultaneously improving sweep efficiency by extending the swept area in both vertical and horizontal directions. Some physical and chemical phenomena, such as emulsion, scale deposition, and chromatographic separation, occur during ASP flooding (Arihara et al. 1999; Guo 1999). Because ASP flooding in porous media involves many complicated physicochemical properties, many oil-recovery mechanisms still need to be investigated. Most research has been performed on the microscopic displacement mechanism of ASP flooding, while the fluid-flow mechanism in porous media at the macroscopic scale lacks sufficient study. In this paper, a vertical-heterogeneous-reservoir model is established, and differential-pressure transducers and saturation-measuring probes are installed. The fluid-flow mechanism of increasing both macroscopic sweep efficiency and microscopic displacement efficiency is studied by measuring the production performance and the variation of pressure and saturation distributions in the ASP-flooding experiment. An experimental database of ASP flooding also is set up and provides an experimental base for numerical simulation.

Summary We present an efficient history-matching technique that simultaneously integrates 4D repeat seismic surveys with well-production data. This approach is particularly well-suited for the calibration of the reservoir properties of high-resolution geologic models because the seismic data are areally dense but sparse in time, whereas the production data are finely sampled in time but spatially averaged. The joint history matching is performed by use of streamline-based sensitivities derived from either finite-difference or streamline-based flow simulation. For the most part, earlier approaches have focused on the role of saturation changes, but the effects of pressure have largely been ignored. Here, we present a streamline-based semianalytic approach for computing model-parameter sensitivities, accounting for both pressure and saturation effects. The novelty of the method lies in the semianalytic sensitivity computations, making it computationally efficient for high-resolution geologic models. The approach is implemented by use of a finite-difference simulator incorporating the detailed physics. Its efficacy is demonstrated by use of both synthetic and field applications. For both the synthetic and the field cases, the advantages of incorporating the time-lapse variations are clear, seen through the improved estimation of the permeability distribution, the pressure profile, the evolution of the fluid saturation, and the swept volumes.

AbstractIn recent years, much progress has been made to quantify the momentum exchange between the atmosphere and the oceans. The role of surface waves on the airflow dynamics is known to be significant, but our physical understanding remains incomplete. The authors present detailed airflow measurements taken in the laboratory for 17 different wind wave conditions with wave ages [determined by the ratio of the speed of the peak waves Cp to the air friction velocity u* (Cp/u*)] ranging from 1.4 to 66.7. For these experiments, a combined particle image velocimetry (PIV) and laser-induced fluorescence (LIF) technique was developed. Two-dimensional airflow velocity fields were obtained as low as 100 μm above the air–water interface. Temporal and spatial wave field characteristics were also obtained. When the wind stress is too weak to generate surface waves, the mean velocity profile follows the law of the wall. With waves present, turbulent structures are directly observed in the airflow, whereby low-horizontal-velocity air is ejected away from the surface and high-velocity fluid is swept downward. Quadrant analysis shows that such downward turbulent momentum flux events dominate the turbulent boundary layer. Airflow separation is observed above young wind waves (Cp/u*< 3.7), and the resulting spanwise vorticity layers detached from the surface produce intense wave-coherent turbulence. On average, the airflow over young waves (with Cp/u* = 3.7 and 6.5) is sheltered downwind of wave crests, above the height of the critical layer zc [defined by 〈u(zc)〉 = Cp]. Near the surface, the coupling of the airflow with the waves causes a reversed, upwind sheltering effect.

Summary Time-lapse three-dimensional (3D) seismic, which geophysicists often abbreviate to four-dimensional (4D) seismic, has the ability to image fluid flow in the interwell volume by repeating a series of 3D seismic surveys over time. Four-dimensional seismic shows great potential in reservoir monitoring and management for mapping bypassed oil, monitoring fluid contacts and injection fronts, identifying pressure compartmentalization, and characterizing the fluid-flow properties of faults. However, many practical issues can complicate the simple underlying concept of a 4D project. We address these practical issues from the perspective of a reservoir engineer on an asset team by asking a series of practical questions and discussing them with examples from several of Chevron's ongoing 4D projects. We discuss feasibility tests, technical risks, and the cost of doing 4D seismic. A 4D project must pass three critical tests to be successful in a particular reservoir: Is the reservoir rock highly compressible and porous? Is there a large compressibility contrast and sufficient saturation changes over time between the monitored fluids? and Is it possible to obtain high-quality 3D seismic data in the area with clear reservoir images and highly repeatable seismic acquisition? The risks associated with a 4D seismic project include false anomalies caused by artifacts of time-lapse seismic acquisition and processing and the ambiguity of seismic interpretation in trying to relate time-lapse changes in seismic data to changes in saturation, pressure, temperature, or rock properties. The cost of 4D seismic can be viewed as a surcharge on anticipated well work and expressed as a cost ratio (seismic/wells), which our analysis shows ranges from 5 to 35% on land, 10 to 50% on marine shelf properties, and 5 to 10% in deepwater fields. Four-dimensional seismic is an emerging technology that holds great promise for reservoir management applications, but the significant practical issues involved can make or break any 4D project and need to be carefully considered. Introduction Four-dimensional seismic reservoir monitoring is the process of repeating a series of 3D seismic surveys over a producing reservoir in time-lapse mode. It has a potentially huge impact in reservoir management because it is the first technique that may allow engineers to image dynamic reservoir processes1 such as fluid movement,2 pressure build-up,3 and heat flow4,5 in a reservoir in a true volumetric sense. However, we demonstrate that practical operational issues easily can complicate the simple underlying concept. These issues include requiring the right mix of business drivers, a favorable technical risk assessment and feasibility study, a highly repeatable seismic acquisition survey design, careful high-resolution amplitude-preserved seismic data processing, and an ultimate reconciliation of 4D seismic images with independent reservoir borehole data and history-matched flow simulations. The practical issues associated with 4D seismic suggest that it is not a panacea. Four-dimensional seismic is an exciting new emerging technology that requires careful analysis and integration with traditional engineering data and workflows to be successful. Our objective in this paper is to provide an overview of the 4D seismic method and illuminate the practical issues important to an asset team reservoir engineer. For this reason, we do not present a comprehensive case study of a single 4D project here, but instead draw examples from several Chevron 4D projects to illustrate each of our points. We have structured this paper as a series of questions an engineer should ask before undertaking any 4D seismic project: What is 4D seismic? What can 4D seismic do for me? Will 4D seismic work in my reservoir? What are the risks with 4D seismic? What does 4D seismic cost? We answer these questions, highlight important issues, and offer lessons learned, rules of thumb, and general words of advice. What Is 4D Seismic? To describe the basic concepts underlying 4D seismic, we briefly review the seismic method in general6 and then consider the advantages of the time-lapse aspect of 4D seismic. In a single 3D seismic survey, seismic sources (dynamite, airguns, vibrators, etc.) generate seismic waves at or near the earth's surface. These source waves reflect off subsurface seismic impedance contrasts that are a function of rock and fluid compressibility, shear modulus, and bulk density. Arrays of receivers (geophones or hydrophones) record the reflected seismic waves as they arrive back at the earth's surface. Applying a wave-equation-imaging algorithm7 to the recorded wavefield creates a 3D seismic image of the reservoir rock and fluid property contrasts that are responsible for the reflections. Four-dimensional seismic analysis involves simply repeating the 3D seismic surveys, such that the fourth dimension is calendar time,8 to construct and compare seismic images in time-lapse mode to monitor time-varying processes in the subsurface during reservoir production. The term 4D seismic is usually reserved for time-lapse 3D seismic, as opposed to other time-lapse seismic techniques that do not have 3D volumetric coverage [e.g., two dimensional (2D) surface seismic, and the borehole seismic methods of vertical seismic profiling and crosswell seismic9,10]. Four-dimensional seismic has all the traditional reservoir characterization benefits of 3D seismic,11 plus the major additional benefit that fluid-flow features may be imaged directly. To first order, seismic images are sensitive to spatial contrasts in two distinct types of reservoir properties: time-invariant static geology properties such as lithology, porosity, and shale content; and time-varying dynamic fluid-flow properties such as fluid saturation, pore pressure, and temperature. Fig. 1 shows how the seismic impedance of rock samples with varying porosity changes as the pore saturation changes from oil-full to water-swept conditions. Given a single 3D seismic survey, representing a single snapshot in time of the reservoir, the static geology and dynamic fluid-flow contributions to the seismic image couple nonuniquely and are, therefore, difficult to separate unambiguously. For example, it may be impossible to distinguish a fluid contact from a lithologic boundary in a single seismic image, as shown in Frames 1 and 2 of Fig. 2. Examining the difference between time-lapse 3D seismic images (i.e., 4D seismic) allows the time-invariant geologic contributions to cancel, resulting in a direct image of the time-varying changes caused by reservoir fluid flow (Frame 3 of Fig. 2). In this way, the 4D seismic technique has the potential to image reservoir scale changes in fluid saturation, pore pressure, and temperature during production.

We use numerical and asymptotic techniques to study the stability of a two-phase air/water flow above a flat porous plate. This flow is a model of the boundary layer which forms on a yawed cylinder and can be used as a useful approximation to the air flow over swept wings. The air and water form an immiscible interface which can destabilize the flow, leading to travelling wave disturbances which move along the attachment line. This instability occurs for lower Reynolds numbers than is the case in the absence of a water layer. The two-fluid flow can be used as a crude model of the effect of heavy rain on the leading edge of a swept wing.We also investigate the instability of inviscid stationary modes. We calculate the effective wavenumber and orientation of the stationary disturbance when the fluids have identical physical properties. Using perturbation methods we obtain corrections due to a small stratification in viscosity, thus quantifying the interfacial effects. Our analytical results are in agreement with the numerical solution which we obtain for arbitrary fluid properties.

The Hammerstein model identification technique based on swept sine excitation signals proved in numerous applications to be particularly effective for the definition of a model for nonlinear systems. In this paper we address the problem of the robustness of this model parameter estimation procedure in the presence of noise in the measurement step. The relationship between the different functions that enter the identification procedure is analyzed to assess how the presence of additive noise affects model parameters estimation. This analysis allows us to propose an original technique to mitigate the effects of additive noise in order to improve the accuracy of model parameters estimation. The different aspects addressed in the paper and the technique for mitigating the effects of noise on the accuracy of parameter estimation are verified on both synthetic and experimental data acquired with an ultrasonic system. The results of both simulations and experiments on laboratory data confirm the correctness of the assumptions made and the effectiveness of the proposed mitigation methodology.

Summary Foam is used in the oil industry in a variety of applications, and polymer is sometimes added to increase foam's stability and effectiveness. A variety of surfactant and polymer combinations have been employed to generate polymer-enhanced foam (PEF), typically anionic surfactants and anionic polymers, to reduce their adsorption in reservoir rock. While addition of polymer to bulk foam is known to increase its viscosity and apparent stability, polymer addition to foams for use in porous media has not been as effective. In this pore-level modeling study, we develop an apparent viscosity expression for PEF at fixed bubble size, as a preliminary step to interpret the available laboratory coreflood data. To derive the apparent viscosity, the pressure-drop calculation of Hirasaki and Lawson (1985) for gas bubbles in a circular tube is extended to include the effects of shear-thinning polymer in water, employing the Bretherton's asymptotic matching technique. For polymer rheology, the Ellis model is employed, which predicts a limiting Newtonian viscosity at the low-shear limit and the well-known power-law relation at high shear rates. While the pressure drop caused by foam can be characterized fully with only the capillary number for Newtonian liquid, the shear-thinning liquid requires one additional grouping of the Ellis-model parameters and bubble velocity. The model predicts that the apparent viscosity for PEF shows behavior more shear-thinning than that for polymer-free foam, because the polymer solution being displaced by gas bubbles in pores tends to experience a high shear rate. Foam apparent viscosity scales with gas velocity (Ug) with an exponent [-a/(a+2)], where a, the Ellis-model exponent, is greater than 1 for shear-thinning fluids. With a Newtonian fluid, for which a = 1, foam apparent viscosity is proportional to the (-1/3) power of Ug, as derived by Hirasaki and Lawson. A simplified capillary-bundle model study shows that the thin-film flow around a moving foam bubble is generally in the high-shear, power-law regime. Because the flow of polymer solution in narrower, water-filled tubes is also governed by shear-thinning rheology, it affects foam mobility as revealed by plot of pressure gradient as a function of water and gas superficial velocities. The relation between the rheology of the liquid phase and that of the foam is not simple, however. The apparent rheology of the foam depends on the rheology of the liquid, the trapping and mobilization of gas as a function of pressure gradient, and capillary pressure, which affects the apparent viscosity of the flowing gas even at fixed bubble size. Introduction When a gas such as CO2 or N2 is injected into a mature oil reservoir for improved oil recovery, its sweep efficiency is usually very poor because of gravity segregation, reservoir heterogeneity, and viscous fingering of gas, and foam is employed to improve sweep efficiency with better mobility control (Shi and Rossen 1998; Zeilinger et al. 1996). When oil is produced from a thin oil reservoir overlain with a gas zone, a rapid coning of gas can drastically reduce oil production rate, and foam is used to delay the gas coning (Aarra et al. 1997; Chukwueke et al. 1998; Dalland and Hanssen 1997; Thach et al. 1996). During a well stimulation operation with acid, a selective placement of acid into a low-permeability zone from which oil has not been swept is desired, which can be accomplished with use of foam (Cheng et al. 2002). For environmental remediation of subsurface soil using surfactant, foam is used to improve displacement of contaminant, such as DNAPL, from heterogeneous soil (Mamun et al. 2002).

We have developed an efficient approach of petroleum reservoir model calibration that integrates 4D seismic surveys together with well-production data. The approach is particularly well-suited for the calibration of high-resolution reservoir properties (permeability) because the field-scale seismic data are areally dense, whereas the production data are effectively averaged over interwell spacing. The joint calibration procedure is performed using streamline-based sensitivities derived from finite-difference flow simulation. The inverted seismic data (i.e., changes in elastic impedance or fluid saturations) are distributed as a 3D high-resolution grid cell property. The sensitivities of the seismic and production surveillance data to perturbations in absolute permeability at individual grid cells are efficiently computed via semianalytical streamline techniques. We generalize previous formulations of streamline-based seismic inversion to incorporate realistic field situations such as changing boundary conditions due to infill drilling, pattern conversion, etc. A commercial finite-difference flow simulator is used for reservoir simulation and to generate the time-dependent velocity fields through which streamlines are traced and the sensitivity coefficients are computed. The commercial simulator allows us to incorporate detailed physical processes including compressibility and nonconvective forces, e.g., capillary pressure effects, while the streamline trajectories provide a rapid evaluation of the sensitivities. The efficacy of our proposed approach was tested with synthetic and field applications. The synthetic example was the Society of Petroleum Engineers benchmark Brugge field case. The field example involves waterflooding of a North Sea reservoir with multiple seismic surveys. In both cases, the advantages of incorporating the time-lapse variations were clearly demonstrated through improved estimation of the permeability heterogeneity, fluid saturation evolution, and swept and drained volumes. The value of the seismic data integration was in particular proven through the identification of the continuity in reservoir sands and barriers, and by the preservation of geologic realism in the calibrated model.

In recent years, a constant increase of oil prices and declining reserves of coventional crude oils have produced those deposits of lights to be considered economically unattractive to be produced as an alternative way to keep the world´s oil supply volume. Heavy oil deposits are mainly characterized by having high resistance to flow (high viscosity), which makes them diffi-cult to produce. Since oil viscosity is a property that is reduced by increasing the temperature, thermal recovery techniques -such as steam injection or in-situ combustion- have become over the years the main tool for tertiary recovery of these oils. Composite reservoirs can occur naturally or may be artificially created. Changes in reservoir width, facies or type of fluid (hydraulic contact) forming two different regions are examples of two-zone composite reservoirs occurring naturally. On the other hand, such enhanced oil recovery projects as waterflooding, polymer floods, gas injection, in-situ combustion, steam drive, and CO2 miscible artificially create conditions where the reservoir can be considered as a composite system. A reservoir undergoing a thermal recovery process is typically idealized as a two-zone composite reservoir, in which, the inner region represents the swept region surrounding the injection well and the outer region represents the larger portion of the reservoir. Additionally, there is a great contrast between the mobilities of the two zones and the storativity ratio being different to one. In this work, the models and techniques developed and implemented by other authors have been enhanced. Therefore, the interpretations of the well tests can be done in an easier way, without using type-curve matching. A methodology which utilizes a pressure and pressure derivative plot is developed for reservoirs subjected to thermal recovery so that mobilities, storativity ratio, distance to the radial discontinuity or thermal front and the drainage area can be estimated. The precedence of the heat source (in-situ combustion or hot injected fluids) does not really matter for the application of this methodology; however, this was successfully verified by its application to synthetic and field examples of in-situ combustion. The point of comparison was the input data used for simulation for the synthetic case and the results from simulation matching and from previous studies for the field cases.

Summary Foam performance was evaluated by several experimental methods (corefloods, bulk foam stability, micromodel observations, interfacial parameters) using three commercial surfactants, either by themselves or mixed with a fluorinated surfactant. The presence of oil reduced foam mobility reduction factors (Fmr) to different degrees; excellent Fmr were still attained with some surfactants in the presence of residual oil. Using the fluorinated surfactant as additive enhanced the oil tolerance of some, but not all, foams. The tested foams exhibited oil transporting properties. Each foam adjusted to its own residual oil saturation and corresponding level of mobility reduction. Foam performance in corefloods did not correlate in general with predictions based on the other experimental methods. Introduction Foams have been considered for mobility control in solvent, gas, or vapor injection improved oil recovery (IOR) processes, for blocking and diverting using either conventional or gelled foams, and for gas/oil ratio control at production wells. In a diverse range of applications, a foam encounters a range of oil saturations, which necessitates designing a foam with the required stability to oil. In applications where it is desirable to place a foam into swept (low oil saturation) zones, a foam with intermediate or low stability to oil may be adequate. If a foam is to be used as an oil displacing fluid or for gas/oil ratio control in producing wells, foam stability to oil is essential. Coreflood experiments by different investigators suggest that oil becomes detrimental to foam at oil saturations above 5 to 20%. 1 Among a number of mechanisms of foam/oil interaction suggested in the literature,1–5 three main models have emerged in attempts to predict foam stability to oil: spreading and entering coefficients, lamella number, and pseudoemulsion film models. The classical spreading and entering coefficients, based on interfacial tensions measured with bulk liquids, have been used with some success,6,7 but do not correlate with foam stability to oil in general.2-5,8,9 A geometry-dependent spreading coefficient,10 a "generalized entering coefficient,"4 and a "film excess energy,"5 have been defined in order to take into account thin-film forces important in foam/oil encounters in porous media. The lamella number attempts to quantify the observation that oil can become emulsified and imbibed into foam lamellae, which tends to destabilize a foam to various degrees.2,11,12 Pseudoemulsion film models state that a foam can only be stable in the presence of oil if the oil is wetted by the aqueous phase, i.e., if oil and gas phases remain separated by a film of aqueous phase (the pseudoemulsion film).3-5,13 Although different models have been successfully applied to different situations, translating the fundamental mechanisms of foam/oil interaction into generally applicable rules for field application remains difficult. The objective of this work was to evaluate the performance of six foams in the absence and presence of crude oil using different experimental techniques: corefloods in Berea and North Sea reservoir sandstone, bulk foam heights in a blender and in a high-pressure cell, lamella breakage frequency in an etched-glass micromodel, and interfacial parameters. The purpose of the corefloods was to screen a series of promising surfactant candidates for the application of foam in the North Sea. A large amount of experimental 14 and simulation15 work was simultaneously carried out by Norsk Hydro, and has led to a successful field test.16 The other experimental techniques have been used by others as screening tools or to evaluate foam/oil interactions. They were used in this work to study possible correlations with coreflood performance. Some fluorinated surfactants form foams that are very stable in the presence of oil.2,4,8,17 They are, however, more costly than hydrocarbon surfactants by one to two orders of magnitude. In this study, a fluorinated surfactant was used as an additive at relatively low concentration to improve the oil tolerance of three conventional surfactants. Experiment Materials. Cores were either Berea sandstone (length 30 cm, diameter 3.8 cm, porosity 23%, and absolute permeability to air 940 to 1,200 md), or reservoir sandstone (length 17 cm, diameter 3.7 cm, porosity 26%, and absolute permeability to air 3,400 to 3,900 md) from the Oseberg field (North Sea), supplied by Norsk Hydro. The reservoir cores were extracted in a chloroform/methanol mixture and dried before use. Four commercial surfactants were used: Chaser GR-1080 (Chaser International, proprietary blend containing mostly alpha olefin sulfonates), Enordet X-2001 (Shell Chemical Company, alcohol ethoxyglycerylsulfonate), Dow XSS-84321.05 (Dow Chemical, mixture of C10 diphenyletherdisulfonate and C 14-16 alpha olefin sulfonate), and Fluorad FC-751 (3M Company, fluoroalkylsulfobetaine). They will be referred to as Chaser, Enordet, Dow, and Fluorad in this paper. Cited concentrations are active concentrations in %w/v in sea water. The three hydrocarbon-based surfactants (Chaser, Enordet, and Dow) were used either by themselves or mixed with Fluorad (1:9 by mass Fluorad to Chaser, Enordet, or Dow). The brine was filtered (0.45 ?m) synthetic sea water (density 1.004 g/cm 3 and viscosity 0.38 mPa's, at 75°C and 13.8 MPa), and the gas was methane (CP grade, 99 vol% and density 0.0835 g/cm3 viscosity 0.0160 mPa's, at 75°C and 13.8 MPa). Crude oil (Oseberg Field, North Sea) was supplied by Norsk Hydro and cleaned by centrifugation and filtration (0.22 ?m). The viscosity and density of the dead oil at 23°C and ambient pressure were 9.5 mPa's and 0.87 g/cm3 respectively. Methane-saturated oil had a gas/oil ratio of 70 and a density of 0.75 g/cm 3 at 75°C and 13.8 MPa. Corefloods. The core was contained in a stainless-steel core holder within a lead sleeve to which confining pressure (24 MPa) was applied. Liquids were injected by displacement from floating piston vessels using HPLC pumps. Methane was supplied either from a cylinder, its flow rate being controlled by a mass flow controller, or from a Ruska pump. System pressure was controlled by a gas dome-type backpressure regulator. Pressure drops across the whole core and across the outlet half were monitored by differential pressure transducers. The half-core pressure drops were consistently about 70% of the full-core pressure drops, possibly because of capillary end effects or changing flow rates and foam qualities caused by gas expansion during flow through the core. Materials. Cores were either Berea sandstone (length 30 cm, diameter 3.8 cm, porosity 23%, and absolute permeability to air 940 to 1,200 md), or reservoir sandstone (length 17 cm, diameter 3.7 cm, porosity 26%, and absolute permeability to air 3,400 to 3,900 md) from the Oseberg field (North Sea), supplied by Norsk Hydro. The reservoir cores were extracted in a chloroform/methanol mixture and dried before use. Four commercial surfactants were used: Chaser GR-1080 (Chaser International, proprietary blend containing mostly alpha olefin sulfonates), Enordet X-2001 (Shell Chemical Company, alcohol ethoxyglycerylsulfonate), Dow XSS-84321.05 (Dow Chemical, mixture of C10 diphenyletherdisulfonate and C 14-16 alpha olefin sulfonate), and Fluorad FC-751 (3M Company, fluoroalkylsulfobetaine). They will be referred to as Chaser, Enordet, Dow, and Fluorad in this paper. Cited concentrations are active concentrations in %w/v in sea water. The three hydrocarbon-based surfactants (Chaser, Enordet, and Dow) were used either by themselves or mixed with Fluorad (1:9 by mass Fluorad to Chaser, Enordet, or Dow). The brine was filtered (0.45 ?m) synthetic sea water (density 1.004 g/cm 3 and viscosity 0.38 mPa's, at 75°C and 13.8 MPa), and the gas was methane (CP grade, 99 vol% and density 0.0835 g/cm3 viscosity 0.0160 mPa's, at 75°C and 13.8 MPa). Crude oil (Oseberg Field, North Sea) was supplied by Norsk Hydro and cleaned by centrifugation and filtration (0.22 ?m). The viscosity and density of the dead oil at 23°C and ambient pressure were 9.5 mPa's and 0.87 g/cm3 respectively. Methane-saturated oil had a gas/oil ratio of 70 and a density of 0.75 g/cm 3 at 75°C and 13.8 MPa.

Abstract The aerodynamic shapes of the blades are still of high importance and various aerodynamic designs have been developed in order to increase the amount of energy production. In this study, a swept horizontal axis wind turbine blade has been optimized to increase the aerodynamic efficiency using the computational fluid dynamics method. To illustrate the technique, a wind turbine with a rotor diameter of 0.94 m has been used as the baseline turbine, and the most appropriate swept blade design parameters, namely the sweep start-up section, tip displacement, and mode of the sweep have been investigated to obtain the maximum power coefficient at the design tip speed ratio. At this stage, a new equation that allows all three swept blade design parameters to be changed independently has been used to design swept blades, and the response surface method has been used to find out the optimum swept blade parameters. According to the results obtained, a significant increase of 4.28% in the power coefficient was achieved at the design tip speed ratio with the newly designed optimum swept wind turbine blade. Finally, baseline and optimum swept blades have been compared in terms of power coefficients at different tip speed ratios, force distributions, pressure distributions, and tip vortices.

Control of laminar-to-turbulent transition on a swept-wing is achieved by base-flow modification in an experimental framework, up to a chord Reynolds number of 2.5 million. This technique is based on the control strategy used in the numerical simulation by Dörr & Kloker (J. Phys. D: Appl. Phys., vol. 48, 2015b, 285205). A spanwise uniform body force is introduced using dielectric barrier discharge plasma actuators, to either force against or along the local cross-flow component of the boundary layer. The effect of forcing on the stability of the boundary layer is analysed using a simplified model proposed by Serpieri et al. (J. Fluid Mech., vol. 833, 2017, pp. 164–205). A minimal thickness plasma actuator is fabricated using spray-on techniques and positioned near the leading edge of the swept-wing, while infrared thermography is used to detect and quantify transition location. Results from both the simplified model and experiment indicate that forcing along the local cross-flow component promotes transition while forcing against successfully delays transition. This is the first experimental demonstration of swept-wing transition delay via base-flow modification using plasma actuators.

We present a computational fluid mechanics technique for modeling of wave-energy air turbines, specifically the Wells turbine. In this type of energy conversion, the wave motion is converted to an oscillating airflow in a duct with the turbine. This is a self-rectifying turbine in the sense that it maintains the same direction of rotation as the airflow changes direction. The blades of the turbine are symmetrical, and here we consider straight and swept blades, both with constant chord. The turbulent flow physics involved in the complex, unsteady flow is governed by nonequilibrium behavior, and we use a stabilized formulation to address the related challenges in the context of RANS modeling. The formulation is based on the streamline-upwind/Petrov-Galerkin and pressure-stabilizing/Petrov-Galerkin methods, supplemented with the DRDJ stabilization. Judicious determination of the stabilization parameters involved is also a part of our computational technique and is described for each component of the stabilized formulation. We compare the numerical performance of the formulation with and without the DRDJ stabilization and present the computational results obtained for the two blade configurations with realistic airflow data.

This study proposes a comparison between CFD (Computational Fluid Dynamics) and experimental results for a cylindrical stirred tank reactor. The stirred tank reactor considered here is 0.7 m high, 0.4 m in diameter, baffled and has four impeller blades on a single shaft, placed at the symmetry axis. The tank is filled with water and serves as a model for molten aluminium purifying reactors.The experimental part of the study compares the use of PIV and LDV techniques to determine the flow field inside the tank. We use PIV to get a complete picture of the flow field in two vertical sections of the tank (one radial and one eccentric). LDV is then used to check and compare the velocities obtained by PIV along horizontal lines belonging to the two vertical sections considered under the PIV-measurements. Good overall agreement between the two methods is obtained.The experimental results are compared to simulation of the tank using an alternative model that we have implemented in the commercial CFD software Fluent. The modeling approach we propose here avoids the classical sliding mesh technique and its tedious use (especially for pre- and post-processing). Our model does not physically represent the impeller blades. It rather introduces them as a time-dependent source term in the momentum equation. This term is only accounted for at the cells that would have been swept by a blade if the blades were present. The modeling of the tank and the set-up of the case are faster and easier. The computation of the flow field using this modeling approach is compared to the sliding mesh approach and to the experimental results discussed above. Results show good agreement between experimental data and both modeling approaches (sliding mesh technique and no impeller model). The model we propose does not bring more accuracy but more convenience in the modeling work.

Background/aimsMicroperimetry is a technique that is increasingly used to assess visual function in age-related macular degeneration (AMD). In this study, we aimed to evaluate the relationship between retinal sensitivity measured with macular integrity assessment (MAIA) microperimetry and optical coherence tomography (OCT)-based macular morphology in AMD.MethodsProspective, cross-sectional study. All participants were imaged with colour fundus photographs used for AMD staging (Age-Related Eye Disease Study scale), spectral-domain OCT (Spectralis, Heidelberg, Germany) and swept-source OCT (Topcon, Japan). Threshold retinal sensitivity of the central 10° diameter circle was assessed with the full-threshold, 37-point protocol of the MAIA microperimetry device (Centervue, Italy). Univariable and multivariable multilevel mixed-effect linear regression models were used for analysis.ResultsWe included 102 eyes with AMD and 46 control eyes. Multivariable analysis revealed that older age (p<0.0001), advanced AMD stage (p<0.0001) and reduced retinal thickness (p<0.0001) were associated with decreased mean retinal sensitivity. No associations were found between choroidal thickness and retinal sensitivity within the macula. Within the 10° diameter circle of the macula, the presence of ellipsoid disruption, subretinal fluid, atrophy and fibrosis, and outer retinal tubulation on OCT images was also associated with decreased retinal sensitivity (all p<0.05).ConclusionsThere is an association between TRS as determined by MAIA microperimetry and several OCT structural parameters across various stages of AMD. This study highlights the relevance of microperimetry as a functional outcome measure for AMD.

: The Preformed Particle gels (PPGs) has been widely used and injected in low permeability rich oil zones as di-verting agent to solve the conformance issues, distract displacing fluid into out of sorts swept zones and reduce the perme-ability of thief zones and high permeability fractured zones. However, the PPG propagation and plugging mechanism is still remain unpredictable and sporadic in manifold void space passages. PPGs have two main abilities, first, it increases the sweep efficiency and second, it decreases the water production in mature oilfields. But the success or failure of PPG treatment largely depends on whether it efficiently decreases the permeability of the fluid paths to an expected target or not. In this study, the different factors were studied that affecting the performance of PPG in such reservoirs. PPGs were treated in different ways; treated with brine, low salinity, and high salinity brine and then their impacts were investigated in low/high permeability and fractured reservoirs and void space conduit models as well. From the literature, it was revealed that the sweep efficiency can be improved through PPG but not displacement efficiency and little impact of PPG were found on displacement efficiency. Similarly, on the other hand, Low salinity water flooding (LSWF) can increase the displacement efficiency but not sweep efficiency. Hence, based on above issues, few new techniques and directions were introduced in this work for better treatment of PPG to decrease water cut and increase oil recovery.

Background information Sandscript was programmed with the web application « Tchat-scene », created by Carol-Ann Braun and the computer services company Timsoft (). It organizes a data-base of raw material into compositions and sequences allowing to build larger episodes. Multimedia resources are thus attributed to frames surrounding the chat space or to the chat space itself, thus “augmented” to include pre-written texts and graphics. Sandscript works best on a PC, with Internet Explorer. On Mac, use 0S9 and Internet Explorer. You will have to download a chat application for the site to function. Coded conversation General opinion would have it that chat space is a conversational space, facilitating rather than complicating communication. Writing in a chat space is very much influenced by the current ideological stance which sees collaborative spaces as places to make friends, speak freely, flip from one “channel” to another, link with a simple click into related themes, etc. Moreover, chat users tend to think of the chat screen in terms of a white page, an essentially neutral environment. A quick analysis of chat practices reveals a different scenario: chat spaces are highly coded typographical writing spaces, quick to exclude those who don’t abide by the technical and procedural constraints associated with computer reading/writing tools (Despret-Lonné, Gentès). Chatters seek to belong to a “community;” conversely, every chat has “codes” which restrict its membership to the like-minded. The patterns of exchange characteristic of chats are phatic (Jakobson), and their primary purpose is to get and maintain a social link. It is no surprise then that chatters should emphasize two skills: one related to rhetorical ingenuity, the other to dexterity and speed of writing. To belong, one first has to grasp the banter, then manage very quickly the rules and rituals of the group, then answer by mastering the intricacies of the keyboard and its shortcuts. Speed is compulsory if your answers are to follow the communal chat; as a result, sentences tend to be very short, truncated bits, dispatched in a continuous flow. Sandscript attempts to play with the limits of this often hermetic writing process (and the underlying questions of affinity, participation and reciprocity). It opens up a social space to an artistic and fictional space, each with rules of its own. Hyper-linked dialogue Sandscript is not just about people chatting, it is also about influencing the course of these exchanges. The site weaves pre-scripted poetic content into the spontaneous, real-time dialogue of chatters. Smileys and the plethora of abbreviations, punctuations and icons characteristic of chat rooms are mixed in with typographical games that develop the idea of text as image and text as sound — using Morse Code to make text resonate, CB code to evoke its spoken use, and graphic elements within the chat space itself to oppose keyboard text and handwritten graffiti. The web site encourages chatters to broaden the scope of their “net-speak,” and take a playfully conscious stance towards their own familiar practices. Actually, most of the writing in this web-site is buried in the database. Two hundred or so “key words” — expressions typical of phatic exchanges, in addition to other words linked to the idea of sandstorms and archeology — lie dormant, inactive and unseen until a chatter inadvertently types one in. These keywords bridge the gap between spontaneous exchange and multimedia content: if someone types in “hi,” an image of a face, half buried in sand, pops up in a floating window and welcomes you, silently; if someone types in the word “wind,” a typewritten “wind” floats out into the graphic environment and oscillates between the left and right edges of the frames; typing the word “no” “magically” triggers the intervention of an anarchist who says something provocative*. *Sandscript works like a game of ping-pong among chatters who are intermittently surprised by a comment “out of nowhere.” The chat space, augmented by a database, forms an ever-evolving, fluid “back-bone” around which artistic content is articulated. Present in the form of programs who participate in their stead, artists share the spot light, adding another level of mediation to a collective writing process. Individual and collective identities Not only does Sandscript accentuate the multimedia aspects of typed chat dialogues, it also seeks to give a “ shape” to the community of assembled chatters. This shape is musical: along with typing in a nickname of her choice, each chatter is attributed a sound. Like crickets in a field, each sound adds to the next to create a collective presence, modified with every new arrival and departure. For example, if your nick is “yoyo-mama,” your presence will be associated with a low, electronic purr. When “pillX” shows up, his nick will be associated with a sharp violin chord. When “mojo” pitches in, she adds her sound profile to the lot, and the overall environment changes again. Chatters can’t hear the clatter of each other’s keyboards, but they hear the different rhythms of their musical identities. The repeated pings of people present in the same “scape” reinforce the idea of community in a world where everything typed is swept away by the next bit of text, soon to be pushed off-screen in turn. The nature of this orchestrated collective presence is determined by the artists and their programs, not by the chatters themselves, whose freedom is limited to switching from one nick to another to test the various sounds associated with each. Here, identity is both given and built, both individual and collective, both a matter of choice and pre-defined rules. (Goffman) Real or fictitious characters The authors introduce simulated bits of dialogue within the flow of written conversation. Some of these fake dialogues simply echo whatever keywords chatters might type. Others, however, point else where, suggesting a hyper-link to a more elaborate fictionalized drama among “characters.” Sandscript also hides a plot. Once chatters realize that there are strange goings on in their midst, they become caught in the shifting sands of this web site’s inherent duality. They can completely lose their footing: not only do they have to position themselves in relation to other, real people (however disguised…) but they also have to find their bearings in the midst of a database of fake interlocutors. Not only are they expected to “write” in order to belong, they are also expected to unearth content in order to be “in the know.” A hybridized writing is required to maintain this ambivalence in place. Sandscript’s fake dialogue straddles two worlds: it melds in with the real-time small talk of chatters all while pointing to elements in a fictional narrative. For example, “mojo” will say: “silting up here ”, and “zano” will answer “10-4, what now? ” These two characters could be banal chatters, inviting others to join in their sarcastic banter… But they are also specifically referring to incidents in their fictional world. The “chat code” not only addresses its audience, it implies that something else is going on that merits a “click” or a question. “Clicking” at this juncture means more than just quickly responding to what another chatter might have typed. It implies stopping the banter and delving into the details of a character developed at greater length elsewhere. Indeed, in Sandscript, each fictional dialogue is linked to a blog that reinforces each character’s personality traits and provides insights into the web-site’s wind-swept, self-erasing world. Interestingly enough, Sandscript then reverses this movement towards a closed fictional space by having each character not only write about himself, but relate her immediate preoccupations to the larger world. Each blog entry mentions a character’s favorite URL at that particular moment. One character might evoke a web site about romantic poetry, another one on anarchist political theory, a third a web-site on Morse code, etc… Chatters click on the URL and open up an entirely new web-site, directly related to the questions being discussed in Sandscript. Thus, each character represents himself as well as a point of view on the larger world of the web. Fiction opens onto a “real” slice of cyber-space and the work of other authors and programmers. Sandscript mixes up different types of on-line identities, emphasizing that representations of people on the web are neither “true” nor “false.” They are simply artificial and staged, simple facets of identities which shift in style and rhetoric depending on the platform available to them. Again, identity is both closed by our social integration and opened to singular “play.” Conclusion: looking at and looking through One could argue that since the futurists staged their “electrical theater” in the streets of Turin close to a hundred years ago, artists have worked on the blurry edge between recognizable formal structures and their dissolution into life itself. And after a century of avant-gardes, self-referential appropriations of mass media are also second nature. Juxtaposing one “use” along another reveals how different frames of reference include or exclude each other in unexpected ways. For the past twenty years much artwork has which fallen in between genres, and most recently in the realm of what Nicolas Bourriaud calls “relational aesthetics.” Such work is designed not only to draw attention to itself but also to the spectator’s relation to it and the broader artistic context which infuses the work with additional meaning. By having dialogue serve as a hyper-link to multimedia content, Sandscript, however, does more. Even though some changes in the web site are pre-programmed to occur automatically, not much happens without the chatters, who occupy center-stage and trigger the appearance of a latent content. Chatters are the driving force, they are the ones who make text appear and flow off-screen, who explore links, who exchange information, and who decide what pops up and doesn’t. Here, the art “object” reveals its different facets around a multi-layered, on-going conversation, subjected to the “flux” of an un-formulated present. Secondly, Sandscript demands that we constantly vary our posture towards the work: getting involved in conversation to look through the device, all while taking some distance to consider the object and look at its content and artistic “mediations.” (Bolster and Grusin, Manovitch). This tension is at the heart of Sandscript, which insists on being both a communication device “transparent” to its user, and an artistic device that imposes an opaque and reflexive quality. The former is supposed to disappear behind its task; the latter attracts the viewer’s attention over and over again, ever open to new interpretations. This approach is not without pitfalls. One Sandscript chatter wondered if as the authors of the web-site were not disappointed when conversation took the upper hand, and chatters ignored the graphics. On the other hand, the web site’s explicit status as a chat space was quickly compromised when users stopped being interested in each other and turned to explore the different layers hidden within the interface. In the end, Sandscript chatters are not bound to any single one of these modes. They can experience one and then other, and —why not —both simultaneously. This hybrid posture brings to mind Herman’s metaphor of a door that cannot be closed entirely: “la porte joue” —the door “gives.” It is not perfectly fitted and closed — there is room for “play.” Such openness requires that the artistic device provide two seemingly contradictory ways of relating to it: a desire to communicate seamlessly all while being fascinated by every seam in the representational space projected on-screen. Sandscript is supposed to “run” and “not run” at the same time; it exemplifies the technico-semiotic logic of speed and resists it full stop. Here, openness is not ontological; it is experiential, shifting. About the Authors Carol-Ann Braun is multimedia artist, at the Ecole Nationale Superieure des Telecomunications, Paris, France. EmaiL: carol-ann.braun@wanadoo.fr Annie Gentes is media theorist and professor at the Ecole Nationale Superieure des Telecomunications, Paris, France. Email: Annie.Gentes@enst.fr Works Cited Adamowicz, Elza. Surrealist Collage in Text and Image, Dissecting the Exquisite Corpse. Cambridge: Cambridge University Press, 1998. Augé, Marc. Non-lieux, Introduction à une Anthropologie de la Surmodernité. Paris: Seuil, 1992. Bolter, Jay David and Richard Grusin. Remediation, Understanding New Media. Cambridge: MIT Press, 2000. Bourriaud, Nicholas. Esthétique Relationnelle. Paris: Les Presses du Réel, 1998. Despret-Lonnet, Marie and Annie Gentes, Lire, Ecrire, Réécrire. Paris: Bibliothèque Centre Pompidou, 2003. Goffman, Irving. Interaction Ritual. New York: Pantheon, 1967. Habermas, Jürgen. Théorie de l’Agir Communicationnel, Vol.1. Paris: Fayard, 1987. Herman, Jacques. “Jeux et Rationalité.” Encyclopedia Universalis, 1997. Jakobson, Roman.“Linguistics and Poetics: Closing statements,” in Thomas Sebeok. Style in Language. Cambridge: MIT Press, 1960. Latzko-Toth, Guillaume. “L’Internet Relay Chat, Un Cas Exemplaire de Dispositif Socio-technique,” in Composite. Montreal: Université du Québec à Montréal, 2001. Lyotard, Jean-François. La Condition Post-Moderne. Paris: les Editions de Minuit, 1979. Manovitch, Lev. The Language of New Media. Cambridge: MIT Press, 2001. Michaud, Yves. L’Art à l’Etat Gazeux. Essai sur le Triomphe de l’Esthétique, Les essais. Paris: Stock, 2003. Citation reference for this article MLA Style Braun, Carol-Ann & Gentes, Annie. "Dialogue: a hyper-link to multimedia content." M/C: A Journal of Media and Culture <http://www.media-culture.org.au/0406/05_Braun-Gentes.php>. APA Style Braun, C. & Gentes, A. (2004, Jul1). Dialogue: a hyper-link to multimedia content.. M/C: A Journal of Media and Culture, 7, <http://www.media-culture.org.au/0406/05_Braun-Gentes.php>