Flow resistance

River structures such as bridges and spur dykes cause water level rise during flood situations. Flood analysis considering this effect is very important for an accurate prediction of inundation flow. In this study, a numerical model is proposed and applied to a river channel with river structures and a river channel connected with floodplain. The numerical model is carried out on the unstructured meshes with finite volume method. The standard k-ε turbulence model and the volume of fluid (VOF) method are adopted for the turbulence closure and the free-surface modeling, respectively. The numerical simulations are carried out about the river channel with structures and the river connected with a floodplain. The proposed model is compared with the results of the experiment and another simulation. The results show tendencies of the overflow from the river and effects by the river structures with reasonable accuracy.

FLATModel is a two-dimensional shallow-water approximation code with corrections and modifications that create a simulation tool adapted to debris-flows behaviour. FLATModel uses the finite volume method with the numerical implementation ...

An acoustic reflectivity method is proposed for measuring flow resistivity of porous materials having rigid frame. The flow resistivity of porous material is defined as the ratio between the pressure difference across a sample and the velocity of flow of air through that sample per unit cube. It is important as one of the several parameters required by acoustical theory to characterize porous materials like plastic foams and fibrous or granular materials. The proposed method is based on a temporal model of the direct and inverse scattering problem for the diffusion of transient low-frequency waves in a homogeneous isotropic slab of porous material having a rigid frame. This time domain model of wave propagation was initially introduced by the authors [Z.E.A. Fellah and C. Depollier, J. Acoust. Soc. Am. 107, 683 (2000)]. The viscous losses of the medium are described by the model devised by Johnson et al. [D. L. Johnson, J. Koplik, and R. Dashen, J. Fluid. Mech. 176, 379 (1987)]. Ref...

The behaviour of wavefronts propagating in a tunnel with multiple, compact air chambers is investigated with particular reference to the suppression of unacceptable pressure disturbances radiating from exit portals. Attention is focussed primarily on chambers that respond in an over-damped manner to pressure variations in the tunnel. In the early part of the paper, comparisons are made between the qualitative behaviour of wavefront propagation in tunnels with and without air chambers. Thereafter, attention turns to a quantitative assessment of the influence of key design parameters, especially the chamber volume and properties of connectors between chambers and the tunnel. It is shown that the optimum type of connector depends upon the length of the tunnel along which the chambers exist. For short tunnels, relatively low-resistance connectors with linear pressure:flow rate characteristics are preferred, whereas for long tunnels, relatively high-resistance connectors with quadratic pressure:flow rate characteristics are likely to be more suitable. Brief attention is paid to the practical feasibility of creating suitable connectors.

The behavior of turbulent open channel flows over permeable surfaces is not well understood. In particular, it is not clear how the surface and the subsurface flow within the permeable bed interact and influence each other. In order to clarify this issue we carried out two sets of experiments, one involving velocity measurements in open channel flows over an impermeable bed composed of a single layer of spheres, and another one where velocities were measured over and within a permeable bed made of five such layers. Comparison of surface flow velocity statistics between the two sets of experiments confirmed that bed permeability can significantly affect flow resistance. It was also confirmed that even in the hydraulically rough regime, the friction factors for the permeable bed increase with increasing Reynolds number. Such an increase in flow resistance implies a different distribution of normal form-induced stress between the permeable and impermeable bed cases. Subsurface flow mea...

An attention for the effect of a post stenotic dilatation and multiple stenoses on an arterial blood flow is made through this work. The resistance to flow ratio is investigated with the different values of yield stress, viscosity, and the flux. For this study we consider fully developed, one-dimensional non-Newtonian fluid namely Bingham plastic fluid flow through a single vessel. The radius of vessel is varying. The formula for the resistance to flow is determined and the results are found for the yield stress, viscosity and flux. The numerical values of the resistance to flow ratio vary from maximum radii of the two abnormal segments to the minimum radii.

In the past years considerable research was done on stepped spillways. Investigations were conducted to understand the hydraulics on the stepped face of Roller Compacted Concrete (RCC) dams and overlays for embankment dams. Also a number of embankments were designed with concrete overtopping protection shaped in a stepped fashion. During large overflows on stepped chutes, there is no skin friction between mainstream and steps, and flow resistance is basically form drag. Significant energy losses occur along the stepped chute so that the energy dissipation structure, e.g. the stilling basin, becomes smaller and more economic. In addition, in design conditions when discharge, slope of the normal ground and the height of spillway are available, there are so many combinations of width and the number of steps, which leads to different head losses. In each feasible case the remained head should be dissipate by the energy dissipaters in down stream, which are much cost consuming. So the cost of project which is consist of spillway and it's down stream dissipaters should be minimized. In this study, the Genetic Algorithm has been applied to find the best combination of design variables to minimizing the total cost of both structures. The results show the efficiency of GA in this field of application. Furthermore, GA has a very rapid convergence to feasible and sufficient optimum.

Filter applications are important for the chemical, automotive and domestic appliances industries. DHCAE Tools developed a solver for the simulation of filters based on the open source CFD library OpenFOAM®. In this presentation DHCAE Tools presents two major approaches for filtration process modelling, a meso scale and a macro scale model. Furthermore, the deformation of filter media can be considered by iterative Fluid-structure interaction coupling (FSI) with the open-source structural solver CalculiX. The numeric models describe the interactions of discrete particles in a continuous flow with thin-walled, porous media on a macroscopic scale. An iterative algorithm was implemented to simulate the filter loading. Particles are injected as Lagrangian particles and tracked with a local time stepping (LTS) approach. With the local particle concentration, the non-uniform resistance of the filter is calculated. The pressure drop caused by the filters is calculated with the Darcy-Forchh...

Advances in Geo-Energy Research and serves as an Associate/Guest Editor for other international journals. Dr. Cai focuses on the petrophysical characterization and micro-transport phenomena in porous media, as well as fractal theory and its application. He has published more than 110 peer-refereed journal articles, three books, and numerous book chapters. Zhien Zhang is currently a postdoctoral researcher in the William G. Lowrie Department of Chemical and Biomolecular Engineering at Ohio State University. His research interests include advanced processes and materials (i.e., membranes) for CO2 capture, CCUS processes, gas separation, and gas hydrates. Dr. Zhang has published 80+ journal papers and 10+ editorials in high-impact journals, including Renewable and Sustainable Energy Reviews. He has written three Hot Papers (top 0.1%) and 10 Highly Cited Papers (top 1%). He also serves as an Editor or Guest Editor for several international journals, including Applied Energy, Fuel, and Journal of Natural Gas Science and Engineering. He currently works as a Visiting Professor at the University of Cincinnati. Qinjun Kang is a senior scientist at the Earth and Environmental Sciences (EES) Division of Los Alamos National Laboratory (LANL). His current research focuses on the modeling and simulation of transport and interfacial processes in porous media at the pore (nano/meso) scale, and on multiscale models bridging different scales. His work is applied to problems in a broad range of engineering and science disciplines, including the geologic storage of carbon dioxide and nuclear waste, conventional and unconventional hydrocarbon exploration and production, the fate and transport of underground contaminants, and the engineering of energy storage and conversion devices (e.g., fuel cells and batteries). Dr. Kang has coauthored more than 100 publications, which have been cited nearly 6000 times. He has been invited to give 20+ talks at various international and national conferences, universities, national laboratories, and industries, and has organized/chaired sessions at numerous conferences. He is currently a member of the Editorial Board or an Associate Editor for multiple journals, and has served as a reviewer for over 50 journals and numerous funding agencies, including DOE and NSF. Dr. Kang has been a top publisher in the EES Division at LANL since 2010.

Previous studies of the hydraulic conductivity of connective tissues have failed to show a correspondence between ultrastructure and specific hydraulic conductivity. We used the technique of quick-freeze/deep-etch to examine the ultrastructure of the corneal stroma and then utilized morphometric studies to compute the specific hydraulic conductivity of the corneal stroma. Our studies demonstrated ultrastructural elements of the extracellular matrix of the corneal stroma that are not seen using conventional electron microscopic techniques. Furthermore, we found that these structures may be responsible for generating the high flow resistance characteristic of connective tissues. From analysis of micrographs corrected for depth-of-field effects, we used Carmen-Kozeny theory to bound a morphometrically determined specific hydraulic conductivity of the corneal stroma between 0.46×10−14 and 10.3×10−14 cm2. These bounds encompass experimentally measured values in the literature of 0.5×10−1...

Previous research has shown that wash-out in bovine and primate eyes can be greatly reduced by perfusing with buffer containing 5-15 % serum. It was suggested that protein diffusion from the iris root might raise the in vivo protein concentration in the trabecular meshwork to a level much higher than in the anterior chamber. In this study, we investigated the protein concentration in effluent from the outflow pathways in bovine and human eyes, its possible relationship to wash-out, and whether the reduction of wash-out was caused by a bulk protein effect. Bovine and human eyes were placed under silicone oil and perfused with buffer. Outflow facility was continuously determined while effluent was periodically collected from the surface of the eye, and the soluble protein concentration in the effluent was determined. Separate studies were conducted perfusing either albumin or γ-globulin through bovine eyes. Theoretical models were developed to study the transport of protein into the perfusion fluid. In the bovine eyes, the initial protein concentration in the collected effluent was approximately 1 % that of serum, much lower than the 10-15 % buffer in serum required to prevent wash-out. Furthermore, the rate of change of outflow facility showed a different dependence on perfused volume than did the protein concentration. Human eyes showed a much higher level of protein in the perfusate, that decayed over a much longer time period. A statistically significant correlation existed between outflow resistance and soluble protein concentration in both bovine and human eyes. However, modelling studies suggested that this correlation might be due to flow resistance setting the flowrate which then determines the protein concentration of the effluent. Separate experiments indicated that the decreased rate of wash-out caused by perfusion of 10-15 % serum in buffer was not due to either albumin or γ-globulin alone. These results suggest that the reduction of wash-out observed in previous studies when serum proteins were perfused through bovine and monkey eyes was not due to the general level of serum proteins but may instead be due to interactions of a particular protein(s).

Vegetation can contribute to coastal defence by damping incoming waves. However, prior studies have shown that attenuation varies greatly among plant species. Plant flexibility is a mechanical property that is commonly omitted, but varies considerably between shrubs and grasses on salt marshes. Therefore, we present an experimental study in a laboratory wave flume with artificial vegetation that differs in flexibility only. We measured wave attenuation and water particle velocities around rigid and flexible salt marsh vegetation. Waves were measured using a series of gauges and Particle Image Velocimetry (PIV) was used to measure spatio-temporal variations of water particle velocities in the x-z plane around the vegetation. Our results show that flexible vegetation attenuates waves up to 70% less than rigid vegetation due to swaying of flexible plants. Furthermore, we find that rigid vegetation modifies the velocity structure, whereas flexible vegetation does not. Specifically, a mean current in the direction of wave propagation develops around the canopy and the horizontal particle velocities are amplified directly above the canopy. These results indicate that plant flexibility is a key parameter in the wave-vegetation interaction that controls wave damping and velocity structure.

Vegetation plays a vital role in the flow characteristics of natural open channels, such as rivers. Typically, vegetation density is higher in the lower layer and sparser in the upper layer of these channels. In this research, Ansys Fluent and the k–ϵ model have been employed to simulate various vegetation configurations to capture intricate flow complexities within vegetation regions. Numerical analysis demonstrated that the numerical results align with anticipated Turbulence Kinetic Energy data obtained from analytical and experimental studies. Our findings revealed that double-layer vegetation induces a more intricate flow distribution. In the spaces between vegetation zones, Turbulence Kinetic Energy decreases due to the resistance imposed by the vegetation patches. This resistance has positive implications for sustaining aquatic life and facilitating sediment deposition, promoting a more environmentally sustainable outcome.

The main objective of this work is to investigate, by means of numerical simulation, the effects of the surface roughness on the laminar fluid flow through annular microchannels, and to propose a method to take into account the surface roughness effects in the calculation or simulation of the fluid flow through these microchannels. This method is based on the classical viscous flow equations, and consists in building an equivalent smooth channel with the same flow resistance as the ''rough" one.

The air blood barrier phenotype can be reasonably described by the ratio of lung capillary blood volume to the diffusion capacity of the alveolar membrane (Vc/Dm), which can be determined at rest in normoxia. The distribution of the Vc/Dm ratio in the population is normal; Vc/Dm shifts from ∼1, reflecting a higher number of alveoli of smaller radius, providing a high alveolar surface and a limited extension of the capillary network, to just opposite features on increasing Vc/Dm up to ∼6. We studied the kinetics of alveolar-capillary equilibration on exposure to edemagenic conditions (work at ∼60% maximum aerobic power) in hypoxia (HA) (PIO2 90 mmHg), based on an estimate of time constant of equilibration (τ) and blood capillary transit time (Tt). A shunt-like effect was described for subjects having a high Vc/Dm ratio, reflecting a longer τ (>0.5 s) and a shorter Tt (<0.8 s) due to pulmonary vasoconstriction and a larger increase in cardiac output (>3-fold). The tendency to...

The mechanics of blood flow in microvessels and microvessel permeability are reviewed. In the first part, characteristics of blood flow in vivo and in vitro are described from a fluid-mechanical point of view, and mathematical models for blood flow in microvessels are presented. Possible causes of the increased flow resistance obtained in vivo compared to in vitro are examined, including the effects of irregularities of vessel lumen, the presence of endothelial surface glycocalyx and white blood cells. In the second part, the ultrastructural pathways and mechanisms whereby endothelial cells and the clefts between the cells modulate microvessel permeability to water and solutes are introduced. Previous and current models for microvessel permeability to water and solutes are reviewed. These models examine the role of structural components of interendothelial cleft, such as junction strands and surface glycocalyx, in the determination of water and solute transport across the microvessel walls. Transport models in the tissue space surrounding the microvessel are also described.

In the study, a formula for predicting fatigue crack tip opening displacement is deduced firstly. And then, due to comparing actual crack growth rate with the deduced formula, the crack tip configuration factor is defined to figure out the crack tip opening configuration that is useful to clarify the behavior of fatigue crack tip formation apparently. Applying the concept, the crack growth of 7/3 brass and 6/4 brass is predicted from the formula, by replacing material properties such as plastic flow resistance, Young modulus, the Poisson ratio, and fatigue toughness, and fatigue test conditions such as the stress intensity factor range, the load ratio, and cycle frequency. Furthermore, the theoretically expected results are verified with the fatigue tests which were carried out on CT specimens under different load conditions of load ratio, cycle frequency, and cyclic peak load, in different environments of air or corrosive ammonia atmosphere, for various brasses. And by comparing and discussing the calculated crack growth rate with attained experimental results, the apparent configuration factor at the crack tip is determined. And through the attained factor which changes along with crack growth, the behaviors of fatigue crack tip formation under different test conditions have been found out.

The diffraction of a spherical acoustic wave by a half plane in an infinite plane, porous barrier is considered. The barrier is modeled as a rigid material filled with narrow pores, more or less normal to the plane, that provide sound damping. However, the compressibility of the gas in the pores is also considered so that some sound transmission takes place. An approximate boundary condition is derived that models both these effects. The principal purpose of the barrier is to reduce the transmitted sound so that the flow resistance of the pores is large. This consideration is important in the sense that point sources are also regarded as reasonable substitutes for real sources. The far field is calculated using integral transforms, the Wiener-Hopf technique and asymptotic methods.

In order to experimentally investigate the flow dynamics around a 3D barchan dune, herein we adopt a new experimental approach that enables us to quantify flow around complex morphologies using a refractive index matching (RIM) flume. This technique allows the model barchan to be rendered invisible, thus permitting use of standard optical techniques for flow-field quantification. Here, we present full details of this unique new RIM facility and detail its use to investigate flow around a model barchan dune. These results are compared to past experimental and numerical models of barchan dune flow dynamics.

We measured minute ventilation (~rE), tidal volume (Vr), mean inspiratory flow (Vr/T0, and occlusion pressure (P.~) in I0 resting subjects breathing room air, in sitting, supine, right and left lateral positions, and compared them with corresponding data on static lung compliance [Cst(1)], dynamic lung compliance [Cdyn(l)], and pulmonary flow resistance JR(l)]. Highest values for Vv, VE, VT/Tb P.~, and effective inspiratory impedance [P.1/(VT/Ti)] were observed in the supine posture. Values for P~ and P.I/(VT/ T~ in lateral decubitus were intermediate to those obtained when seated and supine. While the increases in P.1 and P.j/(Va-/TI) in recumbent postures were qualitatively similar to the decrease in Cdyn(/) and increase in R(/), there was no significant correlation between them, probably reflecting the complex relationship between P.J(Vr/T~) and lung compliance and resistance, as the former, in addition to lung mechanics, also depends on the shape of the inspiratory driving pressure wave, the active inspiratory impedance, the mechanics of the chest wall, and the duration of inspiration.

Nozzles are used in industry for several different purposes ranging from cooling, painting, and mixing to dosing or flow seeding. When multiple nozzles should be used alongside with each other at equal rates, flowrate of feeding lines should be carefully controlled with precision. This task can be undertaken by means of expensive and sophisticated instruments. However, application constraints may necessitate simpler and cost effective solutions. One of the such solutions is adopting a common-rail type fluid distribution nozzle. The nozzle should ensure equal flowrate distribution to the target nozzles while several other parameters should be maintained. One such parameter is static pressure that is also responsible for equal flowrate distribution. In the present study, an illustration case of nozzles is aimed to be simulated via Computational Fluid Dynamics (CFD). Also, the CFD methodology by the recent tools is evaluated in terms of multiple outlets. A three dimensional investigation domain was created instead of axisymmetric two dimensional numerical domains. The tree dimensional domain was then divided to finite volumes by meshing feature of the adopted software. Three different mesh densities were tried to have a favorable mesh setting. Laminar flow governing equations were selected for the solver since the target nozzle applications generally remain in the laminar regime. A nondimensionalization approach by modifying thermo-physical properties to obtain desired Reynolds number in the laminar interval was utilized. Viscous dissipation was ignored, and energy equation was disabled. It is seen that up to five times the nozzle feeding line diameter of the manifold diameter can be deemed sufficient for one percent mass flow rate difference between the nozzle feeding line mass flow rates. However, nozzle feeding line inlet effects considering their connection to the manifold create a fluctuation in the static pressure at the proximity and downstream. The fluctuations spatially diminish in about two to three nozzle feeding line diameters. The mass flow rate change is not monolithic through the inline nozzles.

Pulp screens remove fibre bundles, plastic specks and other oversize contaminants from pulp suspensions before the pulp is made into paper. Removal efficiency increases as the size of the apertures in the screen plate is reduced. Smaller apertures do, however, increase the hydraulic resistance of the screen plate and may cause an excessive loss of screen capacity. There is considerable incentive to reduce hydraulic resistance so that smaller, more efficient, apertures can be used. The objective of this study was to learn what determines the hydraulic resistance of screen plate apertures, and how resistance can be reduced. Hydraulic resistance was assessed using the nondimensional pressure drop coefficient (K) across the screen plate, and K was studied by three methods. Computational fluid dynamics (CFD) was used to predict how flow variables and aperture geometry affect K in an idealized screening configuration. Experiments with a flow channel were used to confirm the theoretical CF...

The mean flow in a nature-like fishpass can be highly modified by the Froude number. It is important to understand this evolution to correctly design the structure. The studied configuration is an emergent staggered arrangement of obstacles. The hydraulic resistance of a fishpass is experimentally investigated that depends on several geometric parameters: block shape, ramp slope, block density, and bed roughness. An analytical model based on the balance momentum allows one to quantify the influence of each hydraulic parameter. The bed roughness has a weak influence, whereas the block shape and the Froude number are significant. The variation of the drag coefficient was analyzed to improve the stage-discharge relationship. To this end, a correlation with the block diameter and water level is proposed. The maximal velocity reached in the fishpass can also be estimated. These results have to be compared with the fish swimming ability to assess the fishpass passability.

To fulfil the increasing demand for faster and more complex separations, modern HPLC separations are performed at ever higher pressures and temperatures. Under these operating conditions, it is no longer possible to safely assume the mobile phase fluid properties to be invariable of the governing pressures and temperatures, without this resulting in significantly deficient results. A detailed insight in the influence of pressure and temperature on the physico-chemical properties of the most commonly used liquid mobile phases: water-methanol and water-acetonitrile mixtures, therefore becomes very timely. Viscosity, isothermal compressibility and density were measured for pressures up to 1000 bar and temperatures up to 100 • C for the entire range of water-methanol and water-acetonitrile mixtures. The paper reports on two different viscosity values: apparent and real viscosities. The apparent viscosities represent the apparent flow resistance under high pressure referred to by the flow rates measured at atmospheric pressure. They are of great practical use, because the flow rates at atmospheric pressure are commonly stable and more easily measurable in a chromatographic setup. The real viscosities are those complying with the physical definition of viscosity and they are important from a fundamental point of view. By measuring the isothermal compressibility, the actual volumetric flow rates at elevated pressures and temperatures can be calculated. The viscosities corresponding to these flow rates are the real viscosities of the solvent under the given elevated pressure and temperature. The measurements agree very well with existing literature data, which mainly focus on pure water, methanol and acetonitrile and are only available for a limited range of temperatures and pressures. As a consequence, the physico-chemical properties reported on in this paper provide a significant extension to the range of data available, hereby providing useful data to practical as well as theoretical chromatographers investigating the limits of modern day HPLC.

The pressure-drop characteristics of six sub-2 m columns of three different manufacturers but with the same surface chemistry (C 18 ) have been studied using the recently introduced total pore blocking method for the determination of the external porosity and by using scanning electron microscopy pictures to measure the actual size of the particles. Having used the Sauter-mean particle size to correctly account for the particle size spread, and having corrected for the influence of the intra-particle porosity, it was found that all columns yielded Kozeny-Carman constant (f KC ) values close to 180, in agreement with the theory. This agreement could subsequently be used to quantify how the different system parameters such as mean particle size, packing density and intra-particle porosity (all tending to vary significantly from manufacturer to manufacturer) each contributes to the observed total bed permeability. Small (upward) deviations from the f KC = 180-value could be correlated to a larger width of the particle size distribution, and more notably to the existence of a high size ratio of the largest to the smallest particles present in the particle batches.

To study the influence of the particle size distribution (PSD), we measured the chromatographic performance of a series of sub-2 m particle high performance liquid chromatography (HPLC) columns packed with four different particle mixtures having a purposely imposed different size distribution. Using the reduced kinetic plot representation by plotting the separation impedance (E 0 ) versus the plate number ratio (N opt /N), the different columns could be classified according to their chromatographic performance without the need to specify a mean particle diameter or a molecular diffusion coefficient, as is needed in the classical reduced plate height and flow resistance analysis. The present analysis shows that it is not so much the width or span of the particle size distribution, but rather the presence of fines that greatly determines the chromatographic performance of particulate columns.

Subglacial bed conditions are key to understanding ice stream behaviour and evolution, with bed roughness reflecting substrate composition and flow resistance. Here we present an analysis of bed roughness in the Siple Coast region of West Antarctica from airborne radio-echo sounding data. The ice streams are associated generally with low bed roughness values, which decrease downstream. The bed of the slow-flowing Ice Stream C (~10 000 km 2 ) is also characterized by being smooth at all scales (wavelengths ranging from 5 km to in excess of 40 km). Furthermore, the bed is smooth either side of Ice Stream C. This suggests the location of the ice stream is controlled by internal ice sheet dynamics rather than by bed morphology. If the ice stream were encouraged to migrate laterally, when active, there would be little resistance offered by the subglacial morphology. Other inter-ice stream regions are rough, however, indicating a subglacial topographic influence on ice stream position. Bed roughness increases up-flow of ice streams, which, unless the bed is modified, may limit the inland migration of these systems.

To assess and compare changes in pulmonary functions before and after exercise in young healthy adults. The case-control study was carried out from January to March 2010 on 292 medical students aged 18-24 years at Bahria University Medical and Dental College, Karachi. Baseline values for forced expiratory volume (FEV1) and forced vital capacity (FVC) were measured with a digital spirometer, and the FEV1: FVC ratio was calculated. The lung functions of group I comprising 192 volunteers after aerobic exercise of 30 minutes daily, for five days over eight weeks, was compared with group II having 100 controls who did not participate in any physical activity. SPSS 15 was used for statistical analysis. At the end of eight weeks, there was a significant rise in FEV1 (2.49 +/- 0.82 to 2.59 +/- 0.79 liters), decline in FVC (2.80 +/- 0.92 to 2.7 +/- 0.87 liters) and an increase in the FEV1: FVC ratio (89.52 +/-12.66 to 95.56 +/- 13.42) in group I students. Improvement in pulmonary functions w...

We recently measured the flow resistance and flow inductance of inertance tubes at high acoustic amplitudes for four different inner diameters of 0.6, 1.0, 1.5 and 2.0mm at various tube length ranging from 100 to 1500mm, at frequencies of 30, 40, 50, 60 and 70 Hz. The experimental data were compared with the explicit solution to the linear momentum equation for small acoustic amplitudes and were fitted with the modification coefficients in terms of the operating frequency and Reynolds numbers characterized by the amplitude of gas velocities.

The problem of non-Newtonian and non-linear blood flow through a stenosed artery is solved numerically where the non-Newtonian rheology of the flowing blood is characterized by the generalized Power-law and Herschel-Bulkley fluid models. The equations governing the flow of the proposed model are solved and closed form expressions for the blood flow characteristics, namely, velocity profile, volumetric flow rate, pressure gradient, resistance to flow, wall shear stress and apparent viscosity are derived. The effects of various parameters entering into problem are discussed with the help of graphs. It has been found that the wall shear stress and resistance to flow increases with the non-Newtonian behavior index of the blood as well as tube radius for constant value of the stenosis height for both fluid models but these increases are comparatively small in Power-law fluid model. Hence, it appears that Herschel-Bulkley fluid model would be more helpful in the functioning of diseased arterial circulation.

To determine if improvements in ventilatory strength with chronic inspiratory muscle training (IMT) improves 20km cycling time trial (TT) performance in hypoxia (F I O 2 = 16.1%). METHODS: Ten highly-trained men were pair-matched based on pre-exercise values of maximal inspiratory pressure (MIP) and randomly placed into either a sham (n = 5, VO 2 max = 61.7 ± 4.1 ml•kg-1 •min-1) or an IMT (n = 5, VO 2 max = 61.5 ± 6.8 ml•kg-1 •min-1) group. Subjects completed 6 weeks of flow resistive IMT (80% of MIP) or a sham protocol (30% of MIP), with each session consisting of up to 6 sets of 8 MIP maneuvers performed to failure with descending rest intervals 3 times per week. Pre-and posttraining, subjects performed tests of pulmonary function, lung volume, MIP, maximal expiratory pressure (MEP), lung diffusion capacity (DLCO), and a 20km cycling TT in hypoxia (FIO 2 = 16.1%). RESULTS: After 6 weeks of IMT or sham, the IMT group significantly improved MIP (145.3 ± 27.9 cmH 2 O vs 171.7 ± 38.7 cmH 2 O, p < 0.05), while MIP in the sham group remained unchanged. MEP, DLCO, lung volumes, and pulmonary function values remained unchanged in both groups post-training. 20km TT mean ventilation was higher post-IMT (98.9 ± 15.9 l•min-1 vs 109.3 ± 22.4 l•min-1 , p = 0.055) and unchanged in sham (p = 0.65). 20km TT mean breathing frequency was also higher post-IMT (43.5 ± 6.4 b•min-1 vs 47.8 ± 8.0 b•min-1 , p < 0.01) and unchanged in sham (p = 0.46). 20km TT mean VO 2 was higher post-IMT (45.5 ± 6.4 ml•kg-1 •min-1 vs 47.5 ± 7.1 ml•kg-1 •min-1 , p = 0.05) and unchanged in sham (p = 0.65). In the IMT group, 20km TT performance time pre-training was 37:46 ± 4:39 min:sec and post-training was 37:16 ± 4:02 min:sec (-1.2 ± 2.2%, p = 0.14). 20km TT performance time was unchanged in the sham group (+0.2 ± 2.1%, p = 0.90). 20km TT heart rate and SpO 2 were unchanged in both groups posttraining. CONCLUSION: In a small cohort, IMT-induced improvements respiratory muscle strength resulted in greater ventilation and oxygen uptake during a 20km time trial in hypoxia. IMT should be explored as a useful strategy for improving the quality of cycle exercise training and/or endurance exercise performance at altitude. PURPOSE: To determine the effects of adding different levels of inspiratory resistance to submaximal and maximal exercise performance in normobaric hypoxia on blood lactate (Lac) and hemoglobin (Hb) values. METHODS: Nine apparently healthy, male adults (mean ± SD; age = 25 ± 2 yr, height = 1.81 ± 0.06 m, mass = 92.5 ± 21.6 kg, BMI = 28.0 ± 5.3 kg•m 2 , VO 2 = 46.32 ± 9.01 ml/kg/min 2) were analyzed. The participants visited the laboratory on four separate visits in a counterbalanced design. The four conditions consisted of a normoxic (21% O 2)

The development of vegetation in the river bed and in the banks can affect the hydrodynamic conditions and the flow behavior of a watercourse. This can increase the risk of flooding and sediment transport. Therefore, it is important to develop analytical approaches to predict the resistance caused by vegetation and model its effect on the flow. This is the objective of this work which investigates the ability of different analytical models to predict the vertical velocity profile as well as the resistance induced by flexible submerged vegetation in open channels. Then it is possible to select the appropriate model that will be applied in the real case of rivers. The model validation is determined after a comparison between the data measured in the different experiments carried out and those from literature. For dense vegetation, the role of the Reynolds number is emphasized in particular with a model using the Darcy-Brinkman equation in the canopy. With a simple permeability, this model is relevant to estimate friction. However, for larger Reynolds number, models based on the fully turbulent flow assumption provide better results.

The development of vegetation in the river bed and in the banks can affect the hydrodynamic conditions and the flow behavior of a watercourse. This can increase the risk of flooding and sediment transport. Therefore, it is important to develop analytical approaches to predict the resistance caused by vegetation and model its effect on the flow. This is the objective of this work which investigates the ability of different analytical models to predict the vertical velocity profile as well as the resistance induced by flexible submerged vegetation in open channels. Then it is possible to select the appropriate model that will be applied in the real case of rivers. The model validation is determined after a comparison between the data measured in the different experiments carried out and those from literature. For dense vegetation, the role of the Reynolds number is emphasized in particular with a model using the Darcy-Brinkman equation in the canopy. With a simple permeability, this model is relevant to estimate friction. However, for larger Reynolds number, models based on the fully turbulent flow assumption provide better results.

Removal of volatile organic compounds (VOCs) from water/wastewater by membrane air stripping (MAS) was studied using microporous polypropylene hollow fiber membrane modules. Chloroform was used as model organic compound. The mass transfer of organic compound from feed solution to air stream was studied with liquid cross-flow on the shell side and airflow in the lumen of hollow fibers. The Graetz numbers for airflows in the lumen of the fibers in this study ranged from 3.1 × 10 −3 to 6.9 × 10 −3. For such low Graetz numbers, the widely used Lévéque's [Annales de Mines 12 (13/14) (1928) 201] model was found to be inapplicable. An alternative model is presented to predict the mass transfer resistance. This model was found to be useful, particularly when the airflow rate on the lumen side of the hollow fiber is very low.

Although Manning&#39;s roughness coefficient is known to vary with river stage, information on this aspect is limited, and practitioners have to resort to trial-and-error approaches or rely on their judgment to quantify the variation. This research was aimed at investigating the variation patterns of Manning&#39;s roughness coefficient over depth. Investigators conducted an extensive laboratory experiment using a fairly long and large channel, in the shape of half of a compound cross section, to simulate natural rivers. This experimental channel allowed a comprehensive investigation of both uniform and composite roughness elements along the channel&#39;s wetted perimeter. Data were taken from both cases: when flow was restricted in the main channel ( to simulated a prismatic channel) and when it covered the floodplain. In addition, the investigators converted data from other researchers to verify factors not covered in this study. The researchers found that while geometry and roughn...

Increasing the performance of heat exchangers is one of the main objectives of researchers and engineers in the industry. In this paper an experimental work is carried out aiming at modeling the efficiency of shell and tube heat exchanger under the influence of the most contributing factors on performance as fouling resistance, the inlet temperatures and the flow rate of the fluids. An experimental design method of type 3 1 .2 4 was used for the studies, requiring 48 tests with three repeats. The following factors are taken into account: the inlet temperature and flow rate of crude oil fluid and TEG fluid on two levels, and the fouling resistance on three levels. Regression analysis was produced a mathematical model for the efficiency based on the influential variables. The response surface and contour plots were allowed the selected from the optimum and predicted the behaviors of parameters. The effectiveness decreases considerably with the increase in fouling resistance and the decrease of inlet temperatures and flow rates.

The removal of bed material from active river channels usually affects the bed profile of the streambed, causing progressive degradation upstream and downstream of the extraction site. These effects can extend for kilometers affecting hydraulic structures located in the vicinity of the river reach. In this paper, the geomorphic effects of gravel mining are reviewed and summarized. Some cases in Venezuelan streams are presented to illustrate the problem. To describe the processes of erosion and sedimentation in a gravel extraction pit, a recent developed mathematical model for the simulation of flow and sediment transport in gravel-cobble bed streams is applied to a hypothetical case of gravel mining in a river channel. A simple rectangular dredge pit is imposed as initial condition in the channel bed, and changes in bed elevations and grain size distribution of bed material are calculated by using the numerical model. The process of deposition within the pit, and the downstream and upstream migration of the erosion wave are well simulated by the model and closely resemble the phenomena observed in laboratory experiments. The response of the friction coefficient to the changes in flow and bed elevations shows the importance in modeling adequately flow resistance and sediment transport in gravel-cobble bed streams.

A two-axis tiltmeter installed at the summit of Semeru volcano, Indonesia, reveals two different modes of deformation, short-term and longer-term. The short-term variations are inflations precursory to the occurrence of summit explosions. The time intervals between the explosions range from several minutes to several tens of minutes, and the maximum precursory tilt change observed is about 0.1-0.2 μrad. This change in tilt is interpreted to reflect a shallow pressurization source, just beneath the active crater. The longer-term tilt changes are displayed over a period of several days to weeks, and a steady inflation during a period of nearly 2 weeks preceded the occurrence of pyroclastic flows on December 22, 2005. Both short-term and longer-term changes are confined to the radial tilt component, pointing toward the active crater and conduit. To explain both of these tilt changes we propose relatively shallow conduit pressurization, although at somewhat deeper levels in the case of longer-term deformation. The causative mechanisms involve gas exsolution, microlite crystallization, and rheological stiffening, which results in greater flow resistance and dynamic pressure in the upper conduit, thus causing the edifice tilts observed. The gas pore pressure in the magma builds until the threshold required to trigger explosive fragmentation is reached.

A two-axis tiltmeter installed at the summit of Semeru volcano, Indonesia, reveals two different modes of deformation, short-term and longer-term. The short-term variations are inflations precursory to the occurrence of summit explosions. The time intervals between the explosions range from several minutes to several tens of minutes, and the maximum precursory tilt change observed is about 0.1–0.2 μrad. This change in tilt is interpreted to reflect a shallow pressurization source, just beneath the active crater. The longer-term tilt changes are displayed over a period of several days to weeks, and a steady inflation during a period of nearly 2 weeks preceded the occurrence of pyroclastic flows on December 22, 2005. Both short-term and longer-term changes are confined to the radial tilt component, pointing toward the active crater and conduit. To explain both of these tilt changes we propose relatively shallow conduit pressurization, although at somewhat deeper levels in the case of ...

Increasing the performance of heat exchangers is one of the main objectives of researchers and engineers in the industry. In this paper an experimental work is carried out aiming at modeling the efficiency of shell and tube heat exchanger under the influence of the most contributing factors on performance as fouling resistance, the inlet temperatures and the flow rate of the fluids. An experimental design method of type 3 1 .2 4 was used for the studies, requiring 48 tests with three repeats. The following factors are taken into account: the inlet temperature and flow rate of crude oil fluid and TEG fluid on two levels, and the fouling resistance on three levels. Regression analysis was produced a mathematical model for the efficiency based on the influential variables. The response surface and contour plots were allowed the selected from the optimum and predicted the behaviors of parameters. The effectiveness decreases considerably with the increase in fouling resistance and the decrease of inlet temperatures and flow rates.

Finding the critical factors that influence the pressure during pumping of concrete has been investigated for years. From fluid mechanics, the relationship between pressure and flow rate, radius or viscosity is known. In the practical guidelines for pumping of conventional vibrated concrete (CVC) the viscosity term is replaced by the concrete yield stress. However, recently, the influence of viscosity on pumping pressure has been reevaluated for self-consolidating concrete (SCC). In this paper, the influence of concrete rheology, tribology, flow rate and pipe radius on pumping pressure are discussed, based on full-scale pumping tests. The concrete mixtures varied from pumpable CVC to segregating SCC. The influence of flow rate and viscosity on pumping of concrete has been confirmed. It is also shown that with a 20% decrease in pipe radius (from 125 to 100 mm), the pumping pressure can be roughly doubled. An increase in yield stress also increases the pumping pressure, but its influence is only visible when the viscosity is approximately constant. The total flow resistance in the tribometer also appears to correlate well with the pumping pressure, proving that the developed tribometer mimics quite well the flow of concrete in a pipe.

El presente estudio pretende caracterizar la propagación de las ondas ultrasónicas en medios heterogéneos, prestando especial atención a la dispersión temporal de la onda. Los tejidos vegetales, y en concreto la piel de la naranja, son básicamente medios acuosos pero repletos de estructuras de diferente densidad y elasticidad, de ácidos y sustancias grasas, así como de zonas aéreas intercelulares. Se pretende por tanto obtener un modelo de predicción de la propagación de los ultrasonidos en dichos medios mediante técnicas de simulación numérica FDTD (Finite Difference Time Domain). Para validar los resultados de las simulaciones se contrastarán éstas con medidas obtenidas a partir de un dispositivo experimental. Desde el punto de vista aplicado, la validación de un modelo de propagación de ondas mecánicas en medios heterogéneos posee un gran interés, ya que permitirá profundizar en la comprensión y el desarrollo de nuevas técnicas de caracterización de materiales complejos, proporcionando herramientas para la predicción de los procesos de propagación en dichos medios.