Macroscopic Flow Behavior Research Articles

Iterative Learning Identification Method for the Macroscopic Traffic Flow Model

By transforming the macroscopic traffic flow model into a more general discrete-time nonlinear system model,an iterative learning identification method is developed to estimate the parameters of the more general discrete- time nonlinear system,so the macroscopic traffic flow parameters as well,based on the repeatability of the macroscopic traffic flow behavior in a freeway.With rigorous analysis,it is shown that the proposed learning identification scheme can guarantee the convergence and robustness.A number of simulation results are provided to demonstrate the efficacy of the proposed approach.

Hydrodynamics of a liquid–solid circulating fluidized bed: Effect of dynamic leak

Abstract Experiments were conducted in a liquid–solid circulating fluidized bed (LSCFB) of 80 mm i.d. and 2.8 m high to study the macroscopic flow structure over a wide range of liquid velocity and solids inventory in the storage vessel. The results indicate that the valve configuration (i.e. lift pot and the angle made by the solids feed pipe with the riser), solids inventory in the storage vessel and location of the primary liquid distributor were found to play an important role on the macroscopic properties of LSCFB. Dynamic leak, flow of solids from the return leg into the riser in the absence of auxiliary liquid flow, has been noticed at very high liquid velocities when the primary liquid distributor inlet (positioned at the bottom of the riser) is near to the solids feed pipe from the storage vessel. The dynamic leak was prevented by changing the position of the primary distributor inlet and the macroscopic flow behavior with and without dynamic leak was compared. The transitional liquid velocity that demarcates the conventional fluidization from the circulating fluidization was determined by three different methods and was found to be independent of solids inventory and dynamic leak.

Analysis of flow behaviour of an aluminium containing austenitic steel

Experimental true stress–true strain data, at both ambient and elevated temperatures, of an Fe–Ni–Cr–Al alloy in solution treated as well as aged conditions have been analysed using different flow relationships. Ludwigson relationship provides the best fit of the data for all the conditions investigated, though all the relationships, except Voce, describe the flow behaviour well at a high temperature of 673 K. The transition in macroscopic flow behaviour of the alloy with strain, in solution treated condition, can be correlated with the transition in dislocation mechanism from planar slip in low strain regime to slip plus deformation twinning in the high strain regime. Although ageing does not appear to alter the macroscopic flow behaviour, it causes considerable change in flow parameters of the Ludwigson relationship and substructural evolution. The flow data of the aged alloys fitted according to Ludwigson model not only yield a unique set of flow parameters for each ageing condition but also exhibit a systematic trend with ageing time. The transition in macroscopic flow behaviour of the alloy with strain, in aged conditions, can be correlated with a change in dislocation mechanism from dislocation–precipitate interaction at lower strains to dislocation–dislocation interaction at higher strains leading to formation of a dense dislocation tangled networks in the matrix regions surrounding the precipitates.

Network model of fluid flow in semi-solid aluminum alloys

A network model is presented to simulate solidification and fluid flow within a semi-solid aluminum alloy. The model consists of a set of connected channels representing the interdendritic liquid and its possible flow directions at high solid fractions (>0.7). The individual channels react according to solidification rules upon liquid solute convection and changes of the local temperature. This dynamic network model has been designed in such a way that a qualitative study of the interaction between the channels is possible. The simulations of the alloys considered show good agreement with the expected macroscopic fluid flow behavior. The simulations indicate a possible reason for deviations from the Kozeny–Carman relationship in measurements of semi-solid alloys.

Proteinaceous bubble and nanoparticle flows in microchannels

Proteinaceous bubbles of 185 nm average diameter were synthesized by a sonochemical treatment of bovine serum albumin (BSA) in an aqueous solution and the nanoparticles (TiO2) solution was made by ultrasonic irradiation. To study the macroscopic flow behavior associated with the changes in the state of the microparticles, a flow test of these solutions in microchannels was done. Also, the size distributions of the proteinaceous bubbles in solution before and after the flow test were measured by a light scattering method. Test results show that the air-filled proteinaceous bubbles in solution adjust their size to reduce the shear stress encountered in the flow through the microchannel. On the other hand, the mass flow rate of the solution with nanoparticle suspensions becomes smaller than that of deionized water in a microchannel of dimension 100×100 μm2.

Comparative analysis of CFD models of dense gas–solid systems

AbstractMany gas–solid CFD models have been put forth by academic researchers, government laboratories, and commercial vendors. These models often differ in terms of both the form of the governing equations and the closure relations, resulting in much confusion in the literature. These various forms in the literature and in commercial codes are reviewed and the resulting hydrodynamics through CFD simulations of fluidized beds compared. Experimental data on fluidized beds of Hilligardt and Werther (1986), Kehoe and Davidson (1971), Darton et al.(1977), and Kuipers (1990) are used to quantitatively assess the various treatments. Predictions based on the commonly used governing equations of Ishii (1975) do not differ from those of Anderson and Jackson (1967) in terms of macroscopic flow behavior, but differ on a local scale. Flow predictions are not sensitive to the use of different solid stress models or radial distribution functions, as different approaches are very similar in dense flow regimes. The application of a different drag model, however, significantly impacts the flow of the solids phase. A simplified algebraic granular energy‐balance equation is proposed for determining the granular temperature, instead of solving the full granular energy balance. This simplification does not lead to significantly different results, but it does reduce the computational effort of the simulations by about 20%.

FLUID–FLUID AND SOLID–FLUID INTERFACIAL INTERACTIONS IN PETROLEUM RESERVOIRS

The distribution and flow behavior of crude oil, gas and brine in the porous rock medium of petroleum reservoirs are controlled largely by the interactions occurring at the interfaces within the various fluids and by the interactions between the fluids and the rock surface. With an objective to correlate the macroscopic multiphase flow behavior with fundamental interfacial interactions, the recent developments in the field of fluid–fluid and solid–fluid interactions and their applications in petroleum engineering are presented in this contribution. A computerized drop shape analysis technique and its application to the measurement of fluid–fluid interfacial tension at elevated pressures and temperatures are discussed. A recently developed technique that is capable of measuring dynamic (advancing and receding) contact angles at realistic conditions encountered in petroleum reservoirs is presented. Its effectiveness in making reproducible and rapid measurements relative to the conventional techniques is demonstrated with several reservoir case studies. Attempts are made to correlate the interfacial phenomena of adhesion and spreading in solid–liquid–liquid systems with dynamic contact angles as well as to extend the applicability of the critical surface tension concept from the conventional solid-liquid-vapor systems to the rock-oil-brine systems of interest in petroleum engineering. These interfacial concepts have been applied to the practical problems of asphaltene destabilization from crude oils and the effect of temperature on wettability alteration in heavy oil fields. A simple procedure is outlined to enable the estimation of interfacial adhesion forces and to demonstrate the significant role they play relative to the capillary forces in retaining the fluids within the porous rock medium.

Upscaling of anisotropy in unsaturated Miller‐similar porous media

Geological and pedological processes rarely form isotropic media as is usually assumed in transport studies. Anisotropy at the Darcy or field scale may be detected directly by measuring flow parameters or may become indirectly evident from movement and shape of solute plumes. Anisotropic behavior of a soil at one scale may, in many cases, be related to the presence of lower‐scale directional structures. Miller similitude with different pore‐scale geometries of the basic element is used to model macroscopic flow and transport behavior. Analytical expressions for the anisotropic conductivity tensor are derived based on the dynamic law that governs the flow problem at the pore scale. The effects of anisotropy on transport parameters are estimated by numerical modeling.

Stochastic Aspects of Bridging Bonds of Induced Structure of Electro-Rheological Fluids in Shear Flow

The bridging of electrodes by clusters of polarizable elements occurs to be a dominant feature of the response of certain electrorheological fluid suspensions and liquid polymeric blends to the imposed electric field. The evolution of the bridging structure in deformation and flow is described as a stochastic process and identified with the macroscopic flow behavior. The effect of structure is introduced into the rheological equation providing its non-linear modification. The comparisons are presented showing how the proposed rheological equation describes rheological characteristics measured at steady shearing flow and start-up shearing flow.

The shear-flow properties of electro-rheological liquid polymeric blends

The bridging of the electrodes by the induced columnar structure of urethane-modified polypropylene glycol (UPPG) is a dominant feature of the response of electro-rheological UPPG/dimethylsiloxane polymeric blends to the imposed electric field. The breaking up and formation of the bridging columns in flow is described as a stochastic process affecting the macroscopic flow behaviour of blends modelled by the Maxwell-like rheological equation. The results show that the proposed rheological equation describes well the rheological characteristics measured at steady and transient shear-flows.

Macroscopic flow behaviour of smectic C and smectic C* liquid crystals

The equations governing the macroscopic flow behaviour of smectic C and smectic C* liquid crystals are written down and it is demonstrated that the viscoelastic behaviour of these systems demands 20 viscous coefficients and 9 elastic constants for a complete treatment. With the smectic C stress tensor as a starting point, different aspects of the flow behaviour of the system are treated. Among the topics discussed are the concepts of torques and countertorques in smectic C and smectic C* liquid crystals as well as flow alignment in shear and backflow effects in the switching dynamics of a surface stabilized ferroelectric liquid crystal cell.

循環流動層ライザー内の巨視的な流動特性

A review on the macroscopic flow behavior such as bed-density distribution and change in flow regime, as well as mixing and heat transfer, in risers of circulating fluidized beds is briefly made in the paper. It is usually found that formation of dense bed at the bottom or so-called S-shaped bed-density distribution in riser is usually observed in operation at relatively low gas velocity. Such density distribution, however, is easy to disappear with decreasing and/or increasing of solids circulation rate. Thus, it should be noted that the flow behavior and axial bed-density distribution in riser of circulating fluidized bed have wide variety with changing in gas velocity and solids circulation rate. For future work, it will be needed to take account of solid property for better understanding of solids and gas behavior as well as classification of flow regime.

Determination of collagen-proteoglycan interactions in vitro

The objective of this study was to characterize the physical interactions of the molecular networks formed by mixtures of collagen and proteoglycan in vitro. Pure proteoglycan aggrecan solutions, collagen (type II) suspensions and mixtures of these molecules in varying proportions and concentrations were subjected to viscometric flow measurements using a cone-on-plate viscometer. Linear viscoelastic and non-Newtonian flow properties of these solutions and suspensions were described using a second-order statistical network theory for polymeric fluids (Zhu et al., 1991, J. Biomechanics 24, 1007–1018). This theory provides a set of material coefficients which relate the macroscopic flow behavior of the fluid to an idealized molecular network structure. The results indicated distinct differences between the flow properties of pure collagen suspensions and those of pure proteoglycan solutions. The collagen network showed much greater shear stiffness and more effective energy storage capability than the proteoglycan network. The relative proportion of collagen to proteoglycan is the dominant factor in determining the flow behavior of the mixtures. Analysis of the statistical network theory indicated that the collagen in a collagen-proteoglycan mixture enhances molecular interactions by increasing the amount of entanglement interactions and/or the strength of interaction, while aggrecan acts to reduce the number and/or strength of molecular interactions. These results characterize the physical interactions between type II collagen and aggrecan and provide some insight into their potential roles in giving articular cartilage its mechanical behavior.

FLOW BEHAVIORS OF RIVER EFFLUX INTO ESTUARY

The aim of this study is to disclose the characteristics of river efflux into a estuary by means of three-dimensional numerical analysis. The flow behaviors in estuary are governed by river efflux momentum and buoyancy force due to density difference between fresh and salt waters. The flow obtained by test simulation in a model estuary shows the plume or turbulent jets characteristics according to discharge and density. The increase of river discharge has similar effect with the decrease of density difference, in which the flow behavior resembles turbulent jets. On the contrary, the decrease of discharge or the increase of density difference causes the flow similar to a plume. Internal Froude number, the ratio of kinematic energy flux to density-deficit potential energy flux, is found to play an important role to macroscopic flow behaviors.

Deformation of Diffusion-Bonded Bi-Pst and Directionally Solidified Crystals of TiAl

ABSTRACTWith a data base now available on the microstructural characteristics and the deformation, fracture and macroscopic flow behavior of polysynthetically twinned (PST) crystals of γ/α2 TiAl-base alloys, an approach to achieve a good combination of strength, ductility and toughness in γ/α2 TiAl-base alloys was proposed using directional solidification (DS) techniques to produce a columnar grain material with the lamellar orientation aligned parallel to the growth direction. Such alignment of the lamellar microstructure was recently accomplished in γ/α2 TiAl-base alloys of near equiatomic compositions using an appropriately oriented seed crystal from the Ti-Al-Si system.At the same time, bi-PST crystals, each containing a planar boundary parallel to the loading axis were prepared by directional solidification and diffusion bonding of two PST crystals. Such bi-PST crystals were deformed in tension at room temperature and their deformation behavior was examined in terms of the compatibility requirements imposed at the grain boundary and the interaction of the two component PST crystals.In this paper, (i) the current status of our DS processing efforts, (ii) some results of microscopic characterization of grain boundaries in diffusion bonded bi-PST crystals and (iii) results of deformation experiments of bi-PST crystals prepared by DS processing and diffusion bonding, will be reported.

Permeability characterization. Part 1: A proposed standard reference fabric for permeability

AbstractA three‐dimensionally woven fabric is proposed as a standard reference material for permeability characterization. The 3‐D woven fabric requires care in cutting and handling, although it is more robust than 2‐D woven or braided fabrics. If prepared carefully, the permeability of the 3‐D woven fabric can be measured reproducibly within 15% in either radial flow or saturated 1‐D flow geometries. The material was characterized for permeability in radial, unsaturated and saturated 1‐D, and through‐thickness flow geometries. The transient results demonstrated the importance of structural heterogeneity on the unsaturated flow behavior, and agree qualitatively with a simplistic model of flow in heterogeneous unsaturated porous media. The effects of heterogeneity were manifested in the proposed SRM by an increasing trend in the “unsaturated permeability.” Experiments were also conducted with a random mat that displayed transient flows dominated by wicking. The effects of wicking on the macroscopic flow behavior were manifested by transients in the “unsaturated permeability” in which a decreasing trend was observed.

Transmissivity of a heterogeneous formation

The objective of this paper is to derive the transmissivity of an equivalent homogeneous medium having the same macroscopic flow behavior as the actual heterogeneous formation. We apply generalized Taylor‐Ans moment analysis in order to determine the phenomenological coefficient of transmissivity for the case of saturated flow confined in a heterogeneous permeable formation with variable thickness. The generalized Taylor‐Aris moment analysis yields a two‐step procedure for determining the constant two‐dimensional transmissivity tensor from the three‐dimensional spatially variable conductivity tensor: solve a flow problem and then perform an integration. For the special case that the conductivity is locally isotropic and the impermeable confining surfaces are parallel, the equations governing transmissivity are discretized using a pseudospectral Fourier‐Galerkin scheme. The resultant system of linear algebraic equations is solved efficiently, using preconditioned conjugate gradients, in order Nt In (Nt) operations, where Nt is the number of spatial discretization points. The numerical method is used in several examples to compute the transmissivity of lognormally distributed hydraulic conductivity, and the results are compared with the transmissivity found using the usual depth‐averaging approach and another method suggested in the literature. The numerical results show that the averaging volume required to obtain an effective value of transmissivity is about 10 horizontal integral scales. When the flow field has a significant three‐dimensional character, the standard method of finding transmissivities by depth averaging can lead to significant errors in the prediction of global scale flows. It is shown that depth averaging consistently overestimates transmissivities. An example illustrates how in the case of tilted strata, anisotropic transmissivities arise and how the degree of transmissivity anisotropy depends on the angle of the dip and the horizontal to vertical integral scale ratio.

Science of Multiphase Interface

The phenomena occurring at a nanoscopic scale on the very surface of solid substrates are discussed, as one particular aspect of multiphase flow studies. The STM (scanning tunneling microscopy) observation as well as the newly developed total reflection X-ray diffractometry experiments revealed the nanoscopic behavior of organic molecules from vapor to solid phases (crystallization process), whichd epends greatly on the nature of the substrates, namely on the interaction between the molecules and the substrate atoms. It is suggested that such interactions, including the electrostatic intermolecular interaction, play an essential role in the aggregation process of molecules above solid surfaces, as indeed simulated by a computer calculation. Moreover, the possible correlation of these nanoscopic mechanisms to the macroscopic multiphase flow behavior is discussed.

The structure of a〈100〉 and a〈110〉 dislocation cores in NiAl

High resolution TEM has been used to observe the core structures of a〈100〉 and a〈110〉 edge dislocations in stoichiometric NiAl. The images indicate that the a〈100〉 edge dislocations have large elastic strain fields but the cores are non-dissociated. Two core structure for the a〈100〉 edge dislocations have been observed. One configuration is climb dissociated into two a 2 〈111〉 partial dislocations which are about 1.0 nm apart. These partial dislocations are linked by an anti-phase boundary (APB) which lies normal to the glide plane. In the second configuration, the a〈110〉 core is decomposed into two a〈100〉 dislocations. The implications of these observed core configurations are discussed with respect to dislocation mobility and the macroscopic flow behavior of NiAl.

Correlation between microscopic structural parameters and macroscopic flow behaviour of some polymer‐surfactant systems suitable for tertiary oil recovery

AbstractSome materials, suitable for application in polymer‐surfactant flooding used in tertiary oil recovery (EOR), have been characterized by static and dynamic light scattering and studied in respect to their suitability in various model brines by measuring their rheological and dynamic‐rheological behaviour. Xanthan and polyacrylamides of different degree of hydrolysis have been used as polymers, an ethylene glycol sulfonate as surfactant.Correlations have been established between microscopic structural parameters (Hydrodynamic radius, radius of gyration, molar mass, shape of the polymers) and the macroscopic behaviour, such as viscosity and elasticity, being important rheological parameters for EOR application. Additional investigations on surface tension and long term viscosity study lead then to a judgement for the efficiency and long term stability of polymer‐surfactant slugs in various reservoirs of different salinity.