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In the present investigation, the roughness characteristics of the gravel bed is tested and modelled for the no-load condition. A straight trapezoidal channel having gravel bed surface of grain size D50 as 13.5 mm for no-load condition is used to carry out the investigation. Depth averaged velocity (DAV) and boundary shear stress (BSS) have been measured for five different depths. An improved model for prediction of friction factor is derived as the function of corresponding hydraulic radius and average diameter of the gravel. This improved model is validated with the models of past investigators. Furthermore, BSS is then calculated using Shiono and Knight Method (SKM), which is dependent on the following hydraulic parameters, such as friction factor f, coefficient of eddy viscosity λ and secondary flow term Г. Since friction factor is modelled for the given channel, same model is used to calculate the value of f over the bed, which tests the reliability of the model while using numerical method. The lateral distribution of DAV and BSS is shown for five different flow depths, which elaborate the bed friction due to the no-load condition. Finally, friction factor model is corroborated on two reaches of the natural river. [ABSTRACT FROM AUTHOR]

In this paper, the development of a solver for the Multi-Fluid and Multi-Pressure model (MFMP) is presented. MFMP is the extension of the two-fluid model. In this model, the number of fluids can be greater than or equal to two. The fluids are considered to be in mechanical nonequilibrium. The pressure across the interface is not considered to be equal. A pressure-based and semi-implicit numerical method is proposed. This is different from the method used for the two-fluid model or single-pressure model. The solver is verified by classical two-fluid benchmark problems and multifluid problems. The Multi-Fluid and Single-Pressure model (MFSP) and MFMP are used. Bestion's model is used in MFMP to consider the nonequilibrium effect of pressure. The computation shows that MFSP is unstable if the number of meshes is large enough, while MFMP is stable for the two-fluid problems and most cases of the multifluid problems. The results of MFMP are in agreement with the reference solution or analytical solution for the two-fluid problems and reasonable for most cases of the multifluid problems. [ABSTRACT FROM AUTHOR]

A hybrid-grid 3D non-hydrostatic model is developed and applied to predict nonlinear regular waves interacting with vertical circular cylinders. The model solves unsteady momentum and mass conservation equations by means of an explicit projection method. The 3D grid system is built from a 2D horizontal grid by adding several horizontal layers. The Perot’s scheme is used to treat horizontal advection terms in momentum equations. The 2D horizontal domain is discretized using a hybrid-grid system comprising rectangular and triangular cells to improve the model boundary-flexibility. The numerical model is validated against the experimental data of Stokes wave and cnoidal wave interacting with a vertical circular cylinder, respectively. Good agreement between model results and the experimental data are achieved, demonstrating the capability of the model on resolving interactions between nonlinear regular waves and vertical circular cylinders. [ABSTRACT FROM PUBLISHER]

The heat transfer and fluid flow characteristics of a new type of fin with built-in interrupted delta winglets is studied in this paper by three-dimensional numerical simulation. In order to ensure reliability of numerical model, plate fin with common-flow-up delta winglets is firstly simulated. The comparison of numerical and experimental results shows a maximum deviation of 11.4% within the entire range of Reynolds number. The computational results show that heat transfer capacity and overall performance increase by 35–60% and 19–64%, respectively. The flow field visualization shows that the interrupted delta winglets can produce longitudinal vortices at the rear of delta winglets and reduce the wake zone behind the tube, so the proposed fin can enhance heat transfer accompanied by low pressure loss. The field synergy theory and entransy dissipation extremum principle are employed on analyzing the mechanism of heat transfer enhancement. The results indicate that enhancement heat transfer mechanism of interrupted delta winglets can be explained as the result of the decrease of synergy angle and reduction of the entransy dissipation. [ABSTRACT FROM PUBLISHER]

The film cooling effectiveness and the jet exit conditions and the associated vortex structure downstream of the injection hole for both a circular exit shaped hole and an elliptical exit shaped holes were numerically investigated for the blowing ratios of 0.25, 0.5, 1, and 1.5. Four turbulence models, including the standard, RNG, realizable k − ϵ, and Reynolds-stress model, in combination with three near-wall approaches, were used for the present simulations. It was found that the predicted results using the realizable k − ϵ model combined with the standard wall function were in better agreement with the available experimental data from the literature. Further, the results indicate that the circular exit shaped hole improved the centerline and laterally averaged adiabatic effectiveness, particularly at high blowing ratios. Finally, adding the sister holes provided a notable decrease in the strength of the counterrotating vortex pairs, where the highest effectiveness was achieved for the circular exit shaped hole case with sister holes. [ABSTRACT FROM AUTHOR]

The specific objective of this work is to develop an empirical model to predict the existence of stratified flow in horizontal and downward inclined gas-liquid two-phase flow. The proposed model is in nondimensional form and attempts to emulate the qualitative trend of the Taitel and Dukler mechanistic model. The key advantage of the proposed method is that it is explicit in nature and, unlike Taitel and Dukler, it does not require use of a graphical or iterative solution. The empirical parameters used in the proposed model account for the effect of pipe diameter, pipe orientation, and the liquid density on the transition line between stratified and nonstratified flow. The accuracy of the proposed model is verified against the flow visualization data collected from more than 16 data sources consisting of 8 fluid combinations, pipe diameter in a range of 8.9 to 300 mm, liquid density in a range of 780 to 1420 kg/m3, and all downward pipe inclinations including horizontal. [ABSTRACT FROM AUTHOR]

Potentially powerful pipe flow models of container terminal logistics processes have been neglected to date. Despite phenomenal recent growth in container traffic in Egypt, modelling of terminals handling this traffic has remained rare. A case application in Alexandria, Egypt, collated empirical container and information flows using interviews and company records to develop a dynamic operational perspective. Using these data, operational-level model simulation of the entire logistical processes of both import and export flows was undertaken. Following successful validation of a base simulation model, scenario testing has empowered the case company to proactively design and test the impact of operational changes on the entire logistics process. [ABSTRACT FROM AUTHOR]

FORGE (Fate of Repository Gases) is an international research project supported by funding under the European Commission FP7 Euratom program and lasting four years from 2009 to 2013. The project is dedicated to understanding gas generation and migration as part of the quantitative assessment of a geological repository for radioactive waste. Within the FORGE project, Work Package 1 is dedicated to numerical modeling of a two-phase flow system (hydrogen gas due to corrosion and groundwater) in a geological repository for radioactive waste. Several benchmark exercises were proposed that cover the modeling of a deep geological repository from the disposal cell scale to the repository scale with different codes. During the definition of the exercises, special emphasis was given to the roles of the excavation-disturbed zone and of the inter faces between materials, which could act as a conduit for preferential flow. Some changes were made in the TOUGH2 code to enable the implementation of the prescribed conditions, models, and parameters of the benchmark. The results of the calculations performed with different codes show that TOUGH2 gives comparable results under the numerically challenging conditions defined in the exercise. Some differences were observed resulting from the use of different codes and also from some simplifications in the parameters and models adopted by the participating teams. In this paper, the cell-scale benchmark exercise and the results obtained by the Swiss Federal Nuclear Safety Inspectorate {ENSI) with TOUGH2 will be described, together with some difficulties encountered during the simulation, e.g., convergence problems. The results of other teams participating in the benchmark are in good agreement with the ENSI results. [ABSTRACT FROM AUTHOR]

The demand for medical treatment of casualties in mass casualty events (MCEs) exceeds resource supply. A key requirement in the management of such tragic but frequent events is thus the efficient allocation of scarce resources. This article develops a mathematical fluid model that captures the operational performance of a hospital during an MCE. The problem is how to allocate the surgeons—the scarcest of resources—between two treatment stations in order to minimize mortality. A focus is placed on casualties in need of immediate care. To this end, optimization problems are developed that are solved by combining theory with numerical analysis. This approach yields structural results that create optimal or near-optimal resource allocation policies. The results give rise to two types of policies, one that prioritizes a single treatment station throughout the MCE and a second policy in which the allocation priority changes. The approach can be implemented when preparing for MCEs and also during their real-time management when future decisions are based on current available information. The results of experiments, based on the outline of real MCEs, demonstrate that the proposed approach provides decision support tools, which are both useful and implementable. [ABSTRACT FROM PUBLISHER]

The author studied effects of immobile water saturation on hydraulic fracture design. So the effect of immobile water saturation on the non-Darcy flow coefficient characterizing the flow of gas in the reservoir and in the hydraulic fracture was considered. There is single-phase gas flow in both subsystems, but the immobile water saturation affects the actual value of the non-Darcy coefficient. An additional simplification often used in the literature is that in the hydraulic fracture there is no immobile water saturation. The goal of this work was to develop a consistent fracture design procedure taking into account non-Darcy effects on the flow of gas both in the reservoir and in the fracture, but affected by the immobile water saturation only in the reservoir. [ABSTRACT FROM AUTHOR]

A quasi-implicit time-marching scheme for solving unsteady incompressible three-dimensional flows on cell-centered unstructured meshes is developed. The finite-volume formulation is used for the spatial derivatives, and the flow variables at the cell face are obtained using the pressure correction. The nonlinear equations resulting from the fully implicit scheme are linearized without deterioration of the overall super-linear time accuracy. The system matrices are solved using the CG iterative method, known as the P-BiCGSTAB method for the momentum equation and the P-CG method for the pressure Poisson equation. The model is applied to simulate fully developed laminar flow in both a 90° curved 3-D circular duct and a 90° curved 3-D square duct. Steady solution is obtained in an unsteady time-marching manner. Computed results compare well with experimental data and other numerical results. It is demonstrated that the present method can be applied to unsteady incompressible laminar 3-D flow with a complex geometry on the unstructured grid system. [ABSTRACT FROM PUBLISHER]

An optical measurement system was used to investigate the effect of microchannel length and inlet geometery on adiabatic gas–liquid two-phase flow. Experiments were conducted with 146-mm- and 1571-mm-long, circular microchannels of 100 μm diameter. Void fraction and gas and liquid plug/slug lengths and their velocities were measured for two inlet configurations for gas–liquid mixing: (a) reducer and (b) T-junction. The superficial gas velocity was varied from 0.03 to 14 m/s, and superficial liquid velocity from 0.04 to 0.7 m/s. The test section length was found to have a significant effect on the two-phase flow characteristics measured at the same axial location (37 mm from the inlet) in both microchannels. The mean void fraction data for the short (146 mm) microchannel with the reducer inlet agreed well with the equation previously proposed by Kawahara et al. (2002). On the other hand, the mean void fraction data for the long (1571 mm) microchannel obeyed the homogeneous flow model and Armand's equation for both the reducer and T-junction inlet configurations. Many long and rapidly moving gas plugs/slugs and long, slowly moving liquid plugs/slugs were observed in the short microchannel compared to the long microchannel, leading to the differences in the time-averaged void fraction data. The mean velocity of liquid plugs/slugs generally agreed well with Hughmark's equation and the homogeneous flow model predictions, regardless of the inlet configurations and microchannel lengths. Thus, both the microchannel length and inlet geometry were found to significantly affect the two-phase flow characteristics in a microchannel. [ABSTRACT FROM AUTHOR]

Accurate assessment of the potential of a nonisothermal polymer flood process requires a model on the viscosities of reservoir fluids as a function of temperature. A three-dimensional numerical model for fluid flow, mass transport, and energy balance is used to analyze the performance of the reservoir in a five-spot pattern operating under polymer flood followed by waterflood. The nonisothermal scheme can be used as a quantitative tool to evaluate the comparative studies of different polymer flooding scenarios with respect to temperature dependence of fluids' viscosities. Results of cumulative recovery and water-oil ratio at the production well are presented for various types of temperature dependencies, reservoir temperatures, and oil viscosities. Significant improvement in predicted oil recovery and reduction in water-oil ratio is obtained for the case of including temperature dependencies of both water and oil because the reduction of oil viscosity is larger than that of brine viscosity. The inclusion of heat loss to over/underburden formations had little effect on the oil recovery because of the relatively small temperature difference under the conditions considered in this study. More rapid reduction of oil viscosity results in the considerable reduction in mobility ratio and significant increase of oil recovery at a higher temperature. [ABSTRACT FROM AUTHOR]

The theoretical derivation of the cuttings transport problem for a two-region system composed of a fluid bed and a stationary bed of drill cuttings, which was considered as a porous medium, was presented in part 1 of this article. The aim of this article is to derive the momentum and mass flux interregion conditions (jump conditions) that contain terms representing the excess surface due to accumulation, convection, stress, and bulk in addition to a term representing the exchange with the surrounding regions. The averaged equations obtained in part 1 of this article and the interregion conditions obtained in this work allow modeling the two-region system described above. [ABSTRACT FROM AUTHOR]

The aim of this article is to derive a mathematical model without length-scale restrictions for cuttings transport in horizontal wellbores using the non-local forms of the volume averaging method, which is a technique used to derive transport equations for multiphase systems and one of the main approaches in two-phase flow modeling. The theoretical derivation of the cuttings transport problem is for a two-region system composed of a fluid bed (ω region) and a stationary bed (η region) of drill cuttings that it is considered as a porous medium. The volume-averaged mathematical model obtained in this work consists of the mass and momentum equations for the ω and η regions. The model was the starting point to obtain one-equation models for both regions. The one-equation models together with adequate jump conditions can be used to predict the hydrodynamics of the ω and η regions. The mathematical derivations of the momentum and mass flux transfer jump conditions are presented in Part II of this article. [ABSTRACT FROM AUTHOR]

Based on solid-liquid flow mechanics, considering the interaction between layers, the slip between solid and liquid phase, and the effect of drillpipe rotation, a dynamic three-layer cutting transport model was developed. By orthogonal experiment regression, a formula for calculating the thickness of the cutting bed was developed that is suitable for field application. The dynamic thickness of the cutting bed can be predicted by measured equivalent circulating density (ECD). Research has shown that the field equipment cannot attain the capability to keep the borehole clean, and when the thickness of the cutting bed exceeds 10%, a flushing method must be used to keep the borehole clean. [ABSTRACT FROM AUTHOR]

We present a flux-based wave decomposition (FBWD) scheme for numerical computation of isentropic two-fluid two-phase flows. We use Tait's equation of state for both the gas and the liquid phases. Extension of the scheme to the second order is made by the MUSCL-Hancock approach. The solutions of several two-phase shock tube problems resulting from the present scheme are compared with the solutions obtained by the earlier HLL scheme. Investigation of the effect of the interfacial pressure models and the drag coefficient are also included. It is concluded that the present FBWD scheme is robust and accurate for computation of isentropic two-fluid models. [ABSTRACT FROM AUTHOR]

In this paper, we consider a class of perturbed risk processes that have an underlying Markov structure, including Markov-modulated risk processes, and Sparre-Andersen risk processes when both inter-claim times and claim sizes are phase-type. We apply the Erlangization method to the risk process in the class in order to obtain an accurate approximation of the finite time ruin probability. In addition, we develop an efficient recursive procedure by recognizing a repeating structure in the probability matrices we work with. We believe the present work is among the first to either compute or approximate finite time ruin probabilities in the perturbed risk model. [ABSTRACT FROM AUTHOR]

In this work, an improved smoothed particle hydrodynamics (IMSPH) method is presented to simulate a polymer-free surface based on XPP model. The IMSPH is a coupled approach between smoothed particle hydrodynamics (SPH) method and the finite particle method (FPM), which possesses higher accuracy and better stability than SPH, especially on boundary. An artificial stress term is added to IMSPH for removing the unphysical phenomenon. The examples of impacting drop and jet buckling are investigated, and the influence of the physical parameters on moving free surface with high Weissenberg number is considered. All the numerical results agree well with the available data. [ABSTRACT FROM AUTHOR]

A numerical investigation of the two-dimensional laminar flow around side-by-side rotating circular cylinders using Lattice Boltzmann method is conducted. The effects of variation of rotational speed ratio β and different gap spacings g* at Reynolds number of 100 are studied. A various range of rotational speed ratio 0 ≤ β ≤ 2 for four different gap spacings of 3, 1.5, 0.7 and 0.2 are investigated. Flow conditions and its characteristics, such as lift and drag coefficients and Strouhal number, is studied. The results indicated that as β increases, the flow changes its condition from periodic to steady after a critical rotational speed. Results also indicated that variation of the gap spacing and rotational speed has significant effect on wake pattern. Wake pattern in turn has significant effect on the Strouhal number. Finally, the result is compared with experimental and other numerical data. [ABSTRACT FROM AUTHOR]

Laboratory experiments conducted in a rectangular open channel on passive mixing of pollutants in longitudinal and vertical directions due to a transverse line source on the flow surface are reported. A finite numerical difference scheme developed by the authors was extended to determine optimum values of longitudinal and vertical mixing coefficients from the observed concentration versus time curves. The vertical mixing coefficient was also computed from the measured velocity distribution and compared with the derived optimum. The velocity distribution-based values of vertical mixing coefficient corresponds well with the optimum derived using the numerical scheme. Through a sensitivity analysis, the errors in the predicted concentration versus time curves are quantified by using the numerical scheme proposed by the authors for two-dimensional dispersion in streams. The sensitivity analysis indicated that predictions of concentration versus time curves can be made with a maximum error of about ±30% if a ±100% error is contained in the values of longitudinal and vertical mixing coefficients. [ABSTRACT FROM AUTHOR]

In this article, we present a unified phase-type approach for calculating ruin probabilities for a class of perturbed risk processes, which includes the perturbed Sparre-Andersen process with phase-type interclaim time and claim size distributions, the perturbed Markov-modulated risk process, and the MAP/PH risk process as well. The key to the solution method is the identification for a given risk process of a parallel Markov-modulated fluid flow. The resulting group of perturbed risk processes amenable to this approach we refer to as the Markov-modulated fluid-flow equivalent (MFE) class, as the ability to find an equivalent fluid flow is the only limiting factor in our analysis. The primary contributions of this work are 1) the unified, tractable, phase-type structures for the maximal aggregate loss and ladder height distributions for all variants of perturbed risk processes belonging to the MFE class, and 2) the explicit formulas for the ruin probability for all variants in this class. The full breadth of the models is illustrated through a diverse range of examples. [ABSTRACT FROM AUTHOR]

The article discusses the effect of baffle spacing on the hydrodynamics and transport performance in a scaled contact tank with variable baffle spacing. Topics discussed include use of Large-Eddy Simulation (LES) for solving the filtered Navier–Stokes equations, assessment of solute transport capacity by a three dimensional model and serpentine flow contact tanks resulting in advection.

The discharge of circular sharp-crested orifices is commonly obtained by using experimental data of the discharge coefficient. This procedure is subjected to errors in graph reading. Further, such a procedure also cannot be used for analytical purposes. Presented herein is a high-accuracy explicit equation of the orifice discharge. The equation unifies viscous and potential flows. [ABSTRACT FROM AUTHOR]

A correction to the article "Modelling and Numerical Simulation of Baffles Height Affect on a Von Karman Turbulent Flow," that appeared in the 2014 issue is presented.

We investigate numerically the mixing of freshwater with ambient saltwater in a model estuary along with associated particle settling processes. We first discuss and specify two numerical setups that consider several relevant features to study the particle settling. The first configuration is a large rectangular basin with a small inlet for the (particle-laden) freshwater; the second is geometrically identical to the first except that the flow is laterally confined to the narrow inlet width. The two flows are computed until a statistically stationary solution is reached. We perform highly resolved direct numerical simulations using a high-order finite difference approach to yield reliable and accurate results. Accordingly, all relevant turbulent scales are resolved and turbulence modeling is not needed. The main target of this study is to describe and illustrate the fluid dynamics and the particle settling processes under the influence of turbulence arising in the freshwater/saltwater-stratified mixing layer. To this end we analyze and compare the two simulations with respect to different aspects of the freshwater/saltwater interaction and to the transport and settling processes of the particles. We investigate the spatial structure as well as the temporal evolution of the flows and the particle suspensions. Generally, we find a qualitatively good agreement of both numerical simulations with pertinent laboratory experiments. Particularly, the results confirm a significant enhancement of the particle settling speeds compared to pure Stokes settling in the presence of turbulence. However, we also demonstrate that the results for the two configurations differ fundamentally in several aspects: stability of the freshwater/saltwater interface, degree of turbulent mixing, particle plume expansion and particle settling enhancement. Using these two simulations we explain the observed settling enhancement, which is not related to the particle inertia (as it is not considered in the numerical model) but rather to the buoyancy velocity of the particle suspension and the geometry of the estuary mouth configuration. [ABSTRACT FROM AUTHOR]