Hydraulic Flow Resistance Research Articles

Physical modelling of large wood (LW) processes relevant for river management: Perspectives from New Zealand and Switzerland

AbstractIn the last 30 years, work on large wood (LW) has expanded and matured considerably, and river scientists, managers and practitioners now have a better appreciation of the role of LW in maintaining ecosystems, forming or stabilizing riverine landforms, and interacting with river morphodynamics. We have gained a better understanding of the hazards posed by the recruitment and transport of LW in the river channel and associated infrastructure. While LW dynamics have traditionally been studied in the natural river environment, innovations in laboratory techniques have enabled important advances in understanding LW process dynamics, using physical scale models, new sensors, scanners and sophisticated model boundary conditions. Current trends in LW laboratory research focus on (1) mobilization and transport of logs, (2) trapping and deposition of sediment in the presence of LW and (3) LW contribution to hydraulic flow resistance. Ultimately, a combined process understanding is needed to assess impacts upon infrastructure with erodible boundaries, such as bridge piers and LW retention racks. In this review, we present a critical analysis of emerging experimental work on LW obtained through physical modelling studies. We put recent experimental work in context with global LW management challenges. In particular, we set our work in context with the present environmental and engineering issues that confront catchment and natural resource managers in Switzerland and New Zealand. We show how improved physical models incorporating LW transport, accumulation and scouring processes are needed to contribute to more reliable hazard and risk assessment and improved river management in LW‐prone systems.

The effect of asymmetric dune roughness on tidal asymmetry in the Weser estuary

AbstractThe bed of estuaries is often characterized by ripples and dunes of varying size. Whereas smaller bedforms adapt their morphological shape to the oscillating tidal currents, large compound dunes (here: asymmetric tidal dunes) remain stable for periods longer than a tidal cycle. Bedforms constitute a form roughness, that is, hydraulic flow resistance, which has a large‐scale effect on tidal asymmetry and, hence, on hydrodynamics, sediment transport, and morphodynamics of estuaries and coastal seas. Flow separation behind the dune crest and recirculation on the steep downstream side result in turbulence and energy loss. Since the energy dissipation can be related to the dune lee slope angle, asymmetric dune shapes induce variable flow resistance during ebb and flood phases. Here, a noncalibrated numerical model has been applied to analyze the large‐scale effect of symmetric and asymmetric dune shapes on estuarine tidal asymmetry evaluated by residual bed load sediment transport at the Weser estuary, Germany. Scenario simulations were performed with parameterized bed roughness of symmetric and asymmetric dune shapes and without dune roughness. The spatiotemporal interaction of distinct dune shapes with the main drivers of estuarine sediment and morphodynamics, that is, river discharge and tidal energy, is shown to be complex but substantial. The contrasting effects of flood‐ and ebb‐oriented asymmetric dunes on residual bed load transport rates and directions are estimated to be of a similar importance as the controls of seasonal changes of discharge on these net sediment fluxes at the Lower Weser estuary. This corroborates the need to consider dune‐induced directional bed roughness in numerical models of estuarine and tidal environments.

Hydraulic flow resistance of epigean and hypogean fish of the family Trichomycteridae (Ostariophysi, Siluriformes)

Critical swimming speeds of four trichomycterid fish species from epigean and hypogean environments were analyzed and compared: Trichomycterus itacarambiensis and Ituglanis passensis, both troglobitic from underground rivers; Trichomycterus brasiliensis, from epigean rivers; and Ituglanis sp., an undescribed troglophilic species from an underground stream. Swimming tests were conducted with a non-volitional apparatus in which fish swim against a progressive incremental water velocity until they longer resist the flow. Total length was significantly related to critical speed for only T. itacarambiensis. The critical speed obtained by each species, in decreasing order, with values in lengths per second (lengths/s), were: I. passensis (3.61), T. itacarambiensis (3.49), T. brasiliensis (3.11) and Ituglanis sp. (1.89). Swimming performance differed between the congeners T. itacarambiensis and T. brasiliensis, but did not differed between I. passensis and Ituglanis sp. The greater speed for the troglobitic species compared to that of the troglophilic and epigean species is probably related to seasonal flooding pulses that can be extremely severe in caves. Furthermore, during the tests, fish were observed using their mouth and/or barbels to fasten themselves to the substrate to avoid high flows.

Satellite remote sensing estimation of river discharge: Application to the Yukon River Alaska

A methodology based on general hydraulic relations for rivers has been developed to estimate the discharge (flow rate) of rivers using satellite remote sensing observations. The estimates of discharge, flow depth, and flow velocity are derived from remotely observed water surface area, water surface slope, and water surface height, and demonstrated for two reaches of the Yukon River in Alaska, at Eagle (reach length 34.7 km) and near Stevens Village (reach length 38.3 km). The method is based on fundamental equations of hydraulic flow resistance in rivers, including the Manning equation and the Prandtl-von Karman universal velocity distribution equation. The method employs some new hydraulic relations to help define flow resistance and height of the zero flow boundary in the channel. Estimates are made both with and without calibration. The water surface area of the river reach is measured by using a provisional version of the U.S. Geological Survey (USGS) Landsat based product named Dynamic Surface Water Extent (DSWE). The water surface height and slope measurements require a self-consistent datum, and are derived from observations from the Jason-2 satellite altimeter mission. At both reach locations, the Jason-2 radar altimeter non-winter heights consistently tracked the stage recorded at USGS streamgages with a standard deviation of differences (error) during the non-winter periods of less than 7%. Part of the error may be due to differences in the gage and altimeter crossing locations with respect to the range of stage change and the response to changes in discharge at the upstream and downstream locations. For the non-winter periods, the radar derived slope estimates (mean = 0.0003) were constant over the mission lifetime, and in agreement with previously measured USGS water surface slopes and slopes determined from USGS topographic maps. The accuracy of the mean of the uncalibrated daily estimates of discharge varied between reaches, ranging from 13% near Stevens Village (N = 90) to −21% at Eagle (N = 246) based on the absolute error, and 5% to −6% based on the error of the log of the estimates. Calibrating to the mean of USGS daily discharge estimates from the streamflow rating for the same period of record at each streamgage resulted in mean absolute errors ranging from 1% to 2%, and log errors ranging from 1% or less. The error pattern of the estimates shows that without calibration, even though the mean is well simulated, the high and low end values over the range of estimates may have significant bias.

Influence of deposition of fine plant debris in river floodplain shrubs on flood flow conditions – The Warta River case study

This paper presents problems caused by organic material transported by flowing water. This material is usually referred to as plant debris or organic debris. Its composition depends on the characteristic of the watercourse. For lowland rivers, the share of the so-called small organic matter in plant debris is considerable. This includes both various parts of water plants and floodplain vegetation (leaves, stems, blades of grass, twigs, etc.). During floods, larger woody debris poses a significant risk to bridges or other water engineering structures. It may cause river jams and may lead to damming of the flowing water. This, in turn, affects flood safety and increases flood risk in river valleys, both directly and indirectly. The importance of fine plant debris for the phenomenon being studied comes down to the hydrodynamic aspect (plant elements carried by water end up on trees and shrubs, increase hydraulic flow resistance and contribute to the nature of flow through vegetated areas changed from micro-to macro-structural). The key part of the research problem under analysis was to determine qualitative and quantitative debris parameters and to establish the relationship between the type of debris and the type of land use of river valleys (crop fields, meadows and forested river sections). Another problem was to identify parameters of plant debris for various flow conditions (e.g. for low, medium and flood flows). The research also included an analysis of the materials deposited on the structure of shrubs under flood flow conditions during the 2010 flood on the Warta River.

Flow and sediment suspension events over low‐angle dunes: Fraser Estuary, Canada

AbstractThe morphodynamics of large sand‐bedded rivers and estuaries are ultimately controlled by the way bed material is moved and the development of large, subaqueous sand dunes that control hydraulic flow resistance. It is widely thought that the primary mechanism for moving sandy bed material in these channels is large‐scale coherent flow structures that cause suspension events whose properties vary with flow, especially in tidally influenced environments. Here, we examine mean flow and sediment suspension events over low‐angle dunes (lee face angle <30°) in the unsteady flow of the Fraser Estuary, Canada. At high tide, flow nearly ceased and a salt wedge entered the channel, forcing salt water under the downstream‐moving fresh water. The salt wedge persisted in the channel until late in the falling tide, causing stratification in the water column and instabilities along the saline‐fresh water interface. At low tide, mean velocities peaked and forced the saline water out of the channel. Flow over the low‐angle dunes displayed topographically induced patterns previously observed over high‐angle dunes, but permanent flow separation was not observed. Large‐scale sediment suspension events dominated sediment flux during low tide and became larger scale, yet less frequent, as the tide began to rise. The suspension events appeared to form over the lower stoss of the dunes and grew up over the bed forms and, less commonly, emerged downstream of the crest. Suspension events move ~69% of the total sediment in the flow above low‐angle dunes when they are present.

About Fluids Structure in Microchannels

The paper deals with molecular dynamics simulation of fluid flow characteristics in nanochannels. A new MD algorithm is developed to simulate plane flow with a pressure drop along the channel. Fluids of hard spheres and Lennard-Jones molecules are considered. Emphasis is on the study of the dependence of the hydraulic flow resistance on the fluid structure. An analysis was made of (i) the density distribution across and along the channel; (ii) radial distribution function of the fluid near the channel wall and in bulk; (iii) influence of the interaction law of the molecules with the wall; (iv) the dependence of the flow resistance coefficient on the Reynolds and Knudsen numbers.

Gel layer formation and hollow fiber membrane filterability of polysaccharide dispersions

Gel layer formation on the membrane surface during filtration plays a significant role in membrane fouling that, in many instances, controls water production and energy consumption in the treatment of waters and wastewaters. In this study, alginate is selected as a model of the polysaccharides prevalent in wastewaters which, on membrane filtration, may form a gel on the membrane surface which subsequently limits filtrate throughput. We show that over the range of the applied pressures of 11.7–135 kPa considered here, constant pressure ultrafiltration of alginate follows the behavior of cake filtration. The material properties of the alginate are determined by the employment of the previously developed steady-state filtration approach. The consolidation of the gel layer is found to be controlled by the hydraulic flow resistance rather than the rearrangement of particles. Under these conditions, it is valid to apply the derived material properties for the quantification of both constant pressure and constant flux filtration. The gel layer formed from alginate is very compressible and far from uniform over its depth. Within the range of the applied pressures, the gel layer is very porous with a water content of more than 96% but very low Darcy permeability of less than 1 × 10 −17 m 2. During hollow fiber membrane filtration, the local flux is neither uniform nor constant along the fiber length, resulting in non-uniformity of the growth rate, the average porosity and the thickness of the gel layer. The non-uniformity is most apparent at the start of filtration and then gradually diminishes as the gel layer builds up with ongoing filtration.

In Vitro and in Vivo Evaluation of a New Polysulfone Membrane for Hemodialysis. Reference Methodology and Clinical Results: (Part 1: In Vitro Study)

Different high flux membranes have been recently developed. The present study is aimed at describing the technical features and the clinical performances of a new high flux polysulfone membrane (T-sulfone, Toray, Japan). The study has been carried out on two different dialyzers (surface area = 1.3 and 1.8 m2). The filters have been tested in vivo during hemodialysis and hemodiafiltration. The in vivo study was carried out on 12 ESRD patients on regular hemodialysis treatment. The protocol was reviewed and approved by the local ethical committee. The in vivo clearances (K) at 300 ml/min of blood flow are reported in the following Table: [Table in text]. Beta-2-m reduction ratio exceeded 50% in all sessions. Beta-2-m mass balance executed by collection of spent dialysate and elution from the used filters evidenced that removal is obtained mostly by filtration while absorption is negligible. Excellent tolerance and hemocompatibility was observed in all the studied sessions.

Evaluation of dead-end ultrafiltration properties by ultracentrifugation method.

In protein ultratiltration, solution environment factors such as pH and solvent density are important in controlling the filtration flux. Also, the properties of the filter cake of macromolecular solutes formed on the membrane surface play a vital role in determining the filtration flux in ultratiltration. On the basis of the sedimentation velocity technique and the high-speed sedimentation equilibrium technique using an analytical ultracentrifuge, the influence of the protein solution pH on the time variation of the filtration flux in unstirred dead-end ultrafiltration was accurately described. It was clearly demonstrated that the low filtration flux around the isoelectric point is mainly due to the build-up of compact filter cake, which causes a large hydraulic flow resistance. Furthermore, it was shown that the solvent density ρ has a large effect on the dynamically balanced filtration rate in upward ultrafiltration just as it does on the sedimentation coefficient in ultracentrifugation.

Mutual influence of hydraulic flow resistances in components of installations

When developing designs for applications in power engineering, chemical engineering, etc., the need arises to estimate the hydraulic flow resistances when the heat transfer fluid (coolant) is circulated through the flow passages in order that one may choose the characteristics of the pumps, ventilation equipment, etc. The recommendations and design formulas proposed in handbooks are mainly intended for determining the flow resistances of individual components. The handbooks almost never consider the influence exerted by the design of adjacent components. This results in the hydraulic characteristics of the coolant circuits being incorrectly determined. These are refined only after their construction and during commissioning. Thus, when nuclear power stations with BN-350 and BN-600 fast reactors were put into operation, it was established that the hydraulic flow resistance of the secondary coolant loop was considerably lower than that which was calculated. The work reported in this article was devoted to studying the influence of adjacent components on the hydraulic flow resistances in a flow passage for individual components and of the reactor system as a whole.

Diffusion of tritiated water in chondroitin sulfate solutions

Water transport processes, such as titriated water exchange diffusion and hydraulic flow resistance, show molecular weight independence in semi dilute solutions of chondroitin sulfate and other linear polysaccharides yet cannot be directly related through the Onsager reciprocal relationship. Relationships can be invoked, however, with the recognition that the critical segment lengths of the linear polymers determining frictional interaction with water are different. The relatively fast process of exchange diffusion is associated with small chain segments that are independent of the chemical nature and the higher order structure of the polymer. Transport with relatively longer relaxation time, such as hydraulic conductivity, is associated with longer chain segments that manifest specific secondary and tertiary structures. This is particularly the case with chondroitin sulfate as it is very effective at flow resistance because of its interresidue hydrogen bonding.

A unique left-right flow imbalance compensation scheme for an implantable total artificial heart.

A new method has been developed for accommodating the difference between pulmonary and arterial flows in a totally implantable, hydraulically actuated total artificial heart (TAH). The left and right sides are alternately pumped, with concurrent filling of one pump and ejection from the other. A small hydraulic fluid chamber is used to compensate for the higher left sided flow. This chamber is incorporated into the left inflow of the TAH, with the flexing bladder in contact with atrial blood, and the hydraulic fluid communicates with the right sided hydraulic chamber. The volume of hydraulic fluid that enters and exits the latter chamber constitutes a corresponding reduction in the right sided blood chamber stroke volume. Placement of this compensation chamber in the left side inflow provides a negative feedback of the right sided flow, based on the left atrial pressure (LAP). Higher LAP (indicating too much right sided flow) leads to higher fluid flow to and from the compensation chamber and a lower right sided blood flow and vice versa. The hydraulic flow resistance can be preadjusted to yield a 15% flow difference at an LAP of 15 mmHg.

Sequential Leaf Senescence and Correlatively Controlled Increases in Xylem Flow Resistance

In bean, Phaseolus vulgaris L. (Contender), the directly measured hydraulic resistance of the xylem pathway between roots and primary leaf pulvinal junctions increased rapidly and progressively from 21 to 28 days after planting. These increases in xylem resistance (+390%) were specifically located in the pulvinal junction of the primary leaf. Moreover, they occurred just prior to the onset of primary leaf yellowing. Developmental increases in xylem hydraulic flow resistance and stomatal resistance, as well as subsequent primary leaf yellowing, were completely prevented by detopping the shoots above the primary leaves at 21 days. Thus, the onset of these senescence-associated symptoms was correlatively controlled. In short-term investigations of the mechanisms involved, flow between petiole and cut tip of excised leaves was rapidly reduced by infiltration of 20 picomoles of soluble dextran into the xylem. Moreover, imbibition of approximately 120 picomoles of dextran by excised leaves increased stomatal resistances. A programmed secretion of hormonal concentrations of similar polysaccharides into specific xylem sections in vivo might provide a mechanism for regulating the partitioning of essential xylem supplies between leaves, thus inducing sequential leaf senescence.