Total Flow Resistance Research Articles

Prediction of overland flow resistance and its components based on flow characteristics using support vector machine

Abstract Due to the significance of overland flow resistance (f) in hillslope hydrology and models of erosion, the present study peruses the capability of non-linear approaches to estimate the overland flow resistance and its components. For this purpose, numerous support vector machine (SVM) models were developed and tested using four series of flume experimental data sets. This study was divided into two parts; the first section aimed to model the total overland flow resistance and investigates the effect of the different parameters on the resistance. In the second section, the resistance was linearly divided into different types of resistance (namely, grain resistance (fg), form resistance (ff), wave resistance (fw), sediment transport resistance (fs)). Then the separated components (fw and fs) were estimated by SVM. The results revealed the importance of the Froude number (Fr) values as an input data in most of the estimated models. Also, it was concluded that the slope gradient has a stronger impact on the on the sediment transport resistance over plane beds than the other hydraulic properties do. The outcome of the models approved the capability of the proposed models based on SVM. Also, SVM outperformed the empirical approaches.

Flow through a filter plate backed by a packed bed of spheres

In this paper we perform direct numerical simulation (DNS) on the problem of fluid flow through a filter plate backed by a packed bed of spheres, resembling a cake layer on top of a membrane. For both the complete problem, and its single components (the filter plate and a bed of spheres of finite height) we have observed three flow regimes, depending on the Reynolds number. In each regime the flow resistance is showing a different scaling with the Reynolds number. In the Stokes flow regime the total flow resistance can be decomposed in linear independent components. The interior flows inside the filter holes and inside the packed bed follow the same correlations as hold for the single component. However, at the transition zone between filter plate and packed bed, there is a diverging flow in the first row of the packed bed, whose contribution in the flow resistance scales with the fractional hole to the power −1.5. Similar scaling exponent has been found earlier for the viscous-inertial regime with Reynolds numbers larger than 10, which has been modelled using the porous medium approach. Our findings suggest that also in the Stokes flow and the weakly flow regime the problem can also be solved with the same porous medium approach using the Navier-Stokes equation having Darcy–Brinkman terms incorporated. This investigation provides a good basis for developing more accurate analytical models for the flow resistance of membrane filters with a cake layer on top.

Particle selectivity of sediment deposited over grass barriers and the effect of rainfall

Particle selectivity of the sediment deposited over vegetative barriers is of importance to predict sediment transport and particulate pollutant load into surface waters. Grassed barriers with 20%, 40%, 60%, 70% and 90% covers at 15° slope were subjected to silt-laden inflows in the presence and absence of simulated rainfalls to investigate the sediment deposition processes. The results show that re-grass of steep croplands can effectively trap eroded sediment from upslope, and the rowed grass barriers can strengthen sediment deposition. The deposition order of sediment particle sizes (μm) follows (>50)> (25-50)>(10-25)=( (2-10), and the particle selectivity weakens with increasing grass covers. Clay particles had a similar deposition efficiency to overall sediment, implying the effectiveness of re-grass in controlling soil nutrient loss. The contribution of grass to total overland flow resistance is almost equivalent to the percentage of grass cover. For steep grassed slopes, raindrop impact significantly decreases sediment deposition, but limitedly affects particle selectivity of deposited sediment and overland flow hydraulics. Both raindrop kinetic energy and stream power available for surface soil contribute to sediment deposition in net deposition areas of grass barriers. These imply that rainfall effect on sediment delivery over vegetated barriers derives from the additional raindrop energy, rather than the variation in runoff hydraulics. These results can help to clarify the effect of raindrop impact on sediment transport and to evaluate the benefit of re-vegetation in decreasing sediment yield and its particulate nutrient load into surface waters. This article is protected by copyright. All rights reserved.

Pressure drop characteristics of vertically upward flow in inclined rod bundles

An experimental and theoretical research has been carried out for vertically upward two-phase flow of air–water across staggered rod bundles having inclination angles of 0°, 45° and 90°. New correlations for single-phase pressure drops in rod bundles for various inclination angles were developed. The single-phase frictional resistance in the vertical flow was found to have a minimal effect on the total flow resistance in the inclined flow. Based on the single-phase pressure drop data, a new superposition model was proposed and verified to be successful in predicting both the present data and the experimental data in previous experiments of other researchers. The two-phase friction multiplier in the inclined rod bundle, which decreased with increasing mass velocity at a given value of Martinelli parameter, could be fit well in terms of Martinelli parameter and the defined dimensionless mass velocity. In addition, the two-phase friction multiplier first increased and then decreased with increasing Martinelli parameter at a given value of mass velocity for G<200kgm−2s−1. The new correlations developed for two-phase friction multipliers were successful in predicting the two-phase pressure drop data in the inclined rod bundle.

Thermal Modeling of Extreme Heat Flux Microchannel Coolers for GaN-on-SiC Semiconductor Devices

Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) dissipate high power densities which generate hotspots and cause thermomechanical problems. Here, we propose and simulate GaN-based HEMT technologies that can remove power densities exceeding 30 kW/cm2 at relatively low mass flow rate and pressure drop. Thermal performance of the microcooler module is investigated by modeling both single- and two-phase flow conditions. A reduced-order modeling approach, based on an extensive literature review, is used to predict the appropriate range of heat transfer coefficients associated with the flow regimes for the flow conditions. Finite element simulations are performed to investigate the temperature distribution from GaN to parallel microchannels of the microcooler. Single- and two-phase conjugate computational fluid dynamics (CFD) simulations provide a lower bound of the total flow resistance in the microcooler as well as overall thermal resistance from GaN HEMT to working fluid. A parametric study is performed to optimize the thermal performance of the microcooler. The modeling results provide detailed flow conditions for the microcooler in order to investigate the required range of heat transfer coefficients for removal of heat fluxes up to 30 kW/cm2 and a junction temperature maintained below 250 °C. The detailed modeling results include local temperature and velocity fields in the microcooler module, which can help in identifying the approximate locations of the maximum velocity and recirculation regions that are susceptible to dryout conditions.

Power loss mechanisms in pathological tracheas

The effort required to inhale a breath of air is a critically important measure in assessing airway function. Although the contribution of the trachea to the total flow resistance of the airways is generally modest, pathological alterations in tracheal geometry can have a significant negative effect. This study investigates the mechanisms of flow energy loss in a healthy trachea and in four geometries affected by retrosternal goitre which can cause significant distortions of tracheal geometry including constriction and deviation with abnormal curvature. By separating out the component of energy loss related to the wall shear (frictional loss), striking differences are found between the patterns of energy dissipation in the normal and pathological tracheas. Furthermore the ratio of frictional to total loss is dramatically reduced in the pathological geometries.

How do concrete rheology, tribology, flow rate and pipe radius influence pumping pressure?

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.

Fluidic Flexible Matrix Composite Vibration Absorber for a Cantilever Beam

Fluidic flexible matrix composite (F2MC) tubes with resonant fluidic circuits can absorb vibration at a specific frequency when bonded to flexible structures. The transverse structural vibration applies cyclic axial strain to the F2MC tubes. The anisotropic elastic properties of the composite tube amplify the axial strain to produce large internal volume change. The volume change forces fluid through a flow port and into an external accumulator. The fluid inertance in the flow port (inertia track) and the stiffness of the accumulator are analogous to the vibration absorbing mass and stiffness in a conventional tuned vibration absorber. An analytical model of an F2MC-integrated cantilever beam is developed based on Euler–Bernoulli beam theory and Lekhnitskii's solution for anisotropic layered tubes. The collocated tip force to tip displacement analytical transfer function of the coupled system is derived. Experimental testing is conducted on a laboratory-scale F2MC beam structure that uses miniature tubes and fluidic components. The resonant peak becomes an absorber notch in the frequency response function (FRF) if the inertia track length is properly tuned. Tuning the fluid bulk modulus and total flow resistance in the theoretical model produces results that match the experiment well, predicting a magnitude reduction of 35 dB at the first resonance using an F2MC absorber. Based on the experimentally validated model, analysis results show that the cantilever beam vibration can be reduced by more than 99% with optimally designed tube attachment points and flow port geometry.

Subjective and objective assessments of seasonal effect in children with seasonal allergic rhinitis

BackgroundEpidemiological and clinical studies suggest a relationship between rhinitis and asthma. Upper and lower airways may be influenced by a common inflammatory process. ObjectiveThis study aimed to investigate the relationships between rhinitis symptom scores, and both nasal and bronchial airflow among children with seasonal allergic rhinitis (SAR) by means of spirometric and rhinomanometric measurement during and outside the pollen season. MethodsTwenty-nine children with both seasonal allergic rhinitis and asthma (AR+A), 30 children with SAR and no asthma (AR) and 36 non-allergic healthy children were evaluated prospectively during and outside the pollen season. Symptom severity was evaluated using both total symptom score and visual analog score (VAS). All participants also received rhinomanometric evaluation and pulmonary function testing. ResultsIn children with SAR the median total nasal flow, FEV1, FEF25–75 values were lower than control group during pollen season (p=0.01, p<0.001 and p<0.001 respectively). They had also higher total nasal resistance compared with control groups (p=0.01). Nasal symptom scores were higher among patients with concurrent asthma than patients who had only SAR out of pollen season (p<0.001). There was no significant difference between SAR participants with or without asthma and control group in terms of total nasal flow and total nasal resistance measured out of season (p=0.105 and p=0.19). FEF25–75 values of patients with and without asthma were significantly lower than those of controls out of season (p=0.022, p<0.001 respectively). ConclusionOur data suggests that as the presence of AR worsens asthma control, the presence of asthma may worsen symptoms of AR out of pollen season. We found that total nasal flow, FEV1, FEF25–75 values of patients with SAR were lower than those of controls out of season. FEF25–75 values of patients with asthma and without asthma were significantly lower than those of controls out of season. Thus, a careful evaluation of lower airways should be performed in even patients with seasonal allergic rhinitis alone.

Single Phase Natural Circulation Behaviors of the Integral Type Marine Reactor Simulator under Rolling Motion Condition

During operation in the sea the reactor natural circulation behaviors are affected by ship rolling motion. The development of an analysis code and the natural circulation behaviors of a reactor simulator under rolling motion are described in this paper. In the case of rolling motion, the primary coolant flow rates in the hot legs and heating channels oscillated periodically, and the amplitude of flow rate oscillation was in direct proportion to rolling amplitude, but in inverse proportion to rolling period. The total mass flow rate also oscillated with half the rolling period, and the average total mass flow rate was less than that in steady state. In the natural circulation under a rolling motion, the flow rate oscillations in the hot legs were controlled by the tangential force; however, the mass flow rate oscillations in the total natural circulation and the heating channels were a result of the combined action of the change of inclination angle, flow resistance, and the extra force arising from the rolling motion. The extra tangential force brought about intense flow rate oscillations in the hot legs, which resulted in increasing total flow resistance; however the extra centrifugal force played a role in increasing thermal driving head.

Development of a tribometer to characterize lubrication layer properties of self-consolidating concrete

The last decade, significant advances have been made in investigating, understanding and predicting the flow characteristics during pumping of concrete. Kaplan developed theoretical equations based on the rheological and tribological properties of concrete to predict pumping pressures. Several tribometers were developed to characterize the flow properties of concrete along a smooth wall, but none of them allows the use of highly-workable concretes. The main reason is that for the calculation of the yield stress and viscous constant of the lubrication layer, the concrete is not allowed to be sheared.In this paper, a new design for the concrete tribometer is presented, along with a calculation procedure to eliminate the contribution of concrete shearing from the rotational velocity. In this way, the viscous constant can be calculated in the same way as for the previously developed tribometers. The analysis of the data reveals that the total flow resistance in the tribometer (Itrib) is well related to the plastic viscosity for SCC and to the yield stress for the other concretes, which is in line with practical results on the influence of rheology on pumping pressure. The viscous constant of the lubrication layer appears related to the plastic viscosity of SCC, but the paper shows that many mix design parameters influence this relationship.

0808 規則的に配置した四角形リブ周りの速度分布と流体抵抗との関係についての実験的解析

Experimental analysis for determining the general relationship between surface roughness and flow resistance has been performed. In this study, we measured the actual flow resistance on the rough wall with regularly distributed rectangular ribs by using the concentric cylinder device and velocity distribution was also measured by LDV. Based on the present result, we proposed a simple equation for predicting flow resistance over rough wall. For making the equation, we evaluated the factional drag and pressure drag acting on the surface of ribs separately by the measured velocity distribution. Consequently, we can also estimate total flow resistance. Compared the estimated flow resistance by measured velocity distribution with the actual flow resistance measured by toque of the inner cylinder, these results had good agreement and validity of a simple prediction equation was confirmed.

Variable contribution of wood to the hydraulic resistance of headwater tropical streams

We investigated the relative contribution of wood to total flow resistance in a tropical setting by measuring wood load and hydraulic resistance in six forested headwater sites at a range of subformative discharges. We evaluated the effectiveness of wood in increasing resistance by comparing measured velocity with predicted velocity from nondimensional hydraulic geometry equations that include slope, unit discharge, and either bed grain size (D84) or bed elevation variation (σt). The predictive equation that uses D84 as the characteristic roughness length successfully predicts velocity in the steep, coarse‐bed study reaches, but greatly overpredicts velocity in the low‐energy, sand‐bed study reaches. The degree of overprediction correlates with a dimensionless wood load metric (α*), which incorporates projected area of wood per unit volume of flow in the reach (α) and average wood diameter (dave). We use this correlation to suggest a wood load adjustment factor for the D84‐based predictive equation. The equation that uses σt as the roughness length successfully predicted velocity in the sand‐bed reaches, where large wood pieces incorporated into the bed and oriented perpendicular to flow cause most bed elevation variation. In our study sites, frequent and flashy floods appear to reorganize the wood in high‐energy reaches, leaving wood that is concentrated in low‐velocity zones along the channel margins and streamlined to flow, thus reducing wood resistance compared to similar streams in snowmelt‐dominated or spring‐fed hydrologic settings. However, in our low‐energy, sand‐bed study reaches, wood contributes strongly to flow resistance by increasing channel bed and margin complexity.

Anterior Rhinomanometry and Determination of Nasal Mucociliary Clearance Time With the Saccharin Test in Children With Crimean-Congo Hemorrhagic Fever

Crimean-Congo hemorrhagic fever (CCHF), like other viral infections, may prolong mucociliary clearance time and increase nasal resistance in children. The aim of the present prospective case-control study was to study, using saccharin and anterior rhinomanometry tests, whether CCHF infections caused any change in nasal physiology. Overall, 40 subjects, 20 of whom had CCHF (group 1) and 20 of whom were healthy controls (group 2), were enrolled in this study. The definitive diagnosis of CCHF infection was made based on typical clinical and epidemiological findings and detection of CCHF virus-specific IgM by ELISA or of genomic segments of the CCHF virus by reverse transcription-polymerase chain reaction. Anterior rhinomanometry was performed in all participants according to current recommendations of the Committee Report on Standardization of Rhinomanometry. A saccharin test was used to evaluate mucociliary clearance, and nasal mucociliary clearance time was assessed with the saccharin test as described previously. In our patients, the mean time from the application of saccharin crystals to the first feeling of a sweet taste was 6.77 ± 3.25 minutes (range 2-16 min). In terms of the mean time from the application of saccharin crystals to the first feeling of a sweet taste, there was no difference between two groups. The mean total air flow was 637.60 ± 76.18 mL/s (range 490-760 mL/s). The mean total nasal airway resistance was 0.24 ± 0.03 Pa/mL s (range 0.20-0.31 Pa/mL s). In terms of the degree of nasal air flow and nasal airway resistance and the total air flow and total nasal airway resistance of each nostril, there was no difference between the 2 groups. The results obtained in anterior rhinomanometry and saccharin test showed that there was no statistically significant difference between CCHF (+) patients and controls. These results suggest us that CCHF virus infection does not affect nasal physiology. However, this is the first study performed on this issue and further studies on larger series need to be performed.

Experimental investigations on frictional resistance and velocity distribution of rough wall with regularly distributed triangular ribs

The relationship between the flow resistance of a turbulent flow over triangular ribs regularly distributed on a wall surface and the velocity distribution around the ribs was investigated experimentally. A concentric cylinder device composed of an inner test cylinder and an outer cylinder was employed to measure the flow resistance using the torque of the shaft of the inner cylinder and the velocity distribution of the flow around a rib by laser Doppler velocimetry (LDV) simultaneously. We prepared four inner test cylinders having 4, 8, 12 and 16 triangular ribs on the surface with the same interval between them. Each rib had an isosceles right triangle V-shape and a height of 2mm. To investigate the relationship between flow resistance and velocity distribution, we estimated the frictional drag and pressure drag acting on the surface of the ribs separately using the velocity distribution. Therefore, we could also estimate the total flow resistance using the velocity distribution. As a result of the experiment, the flow resistance and the attachment point downstream of the rib were shown to depend on the distance between ribs. Moreover, the flow resistance estimated using the velocity distribution had good agreement with the flow resistance measured using the torque of the inner cylinder.

A Mathematical Model for the Flow Resistance and the Related Hydrodynamic Dispersion Induced by River Dunes

Present work is aimed at the derivation of a simply usable equation for the total flow resistance associated with river bedforms, by a unifying approach allowing for bypassing some of the limiting restrictions usually adopted in similar types of studies. Specifically, we focused on the effect induced by the out-of-phase free surface undulations appearing in presence of sand dunes. The proposed expression, obtained by combining the balance of momentum referred to the control volume whose longitudinal dimension coincides with the dune wavelength and the energy balance integrated between its extreme sections, was tested by comparison with some laboratory experimental measurements available in the literature and referred to steady flow past fixed, variably rough bedforms. In terms of shear stress or friction factor, the proposed theory provides estimates in good agreement with the real data, especially if evaluated against the performances provided by other classical similar approaches. Moreover, when analyzed in terms of hydrodynamic dispersive properties as a function of the skin roughness on the basis of a previously derived analytical solution, the dune-covered beds seem to behave like meandering channels, responsible for a globally enhanced fluid particles longitudinal spreading, with a relatively reduced effect in the presence of less pronounced riverbed modelling.

Rinomanometria ed espansione palatale: studio clinico prospettico. Dati preliminari

ObjectivesTo evaluate the effect of palatal expansion on nasal airway resistance in patients with maxillary transversal constriction using rhinomanometry. Materials and methodsTwenty patients (12 females and 8 males) aged 7–11 years with monolateral or bilateral crossbite or with transversal maxillary constriction without crossbite, underwent rhinomanometric examination before (T0) and 9 months after rapid palatal expansion (T1). Total airway flow and nasal resistance were assessed during inspiration and expiration. ResultsNasal airway resistance decreased significantly after rapid maxillary expansion (P<.05). ConclusionsRhinomanometric examination detects an improvement in nasal resistance after rapid palatal expansion.

River channel slope, flow resistance, and gravel entrainment thresholds

River beds are traditionally assumed to become mobile at a fixed value of nondimensional shear stress, but several flume and field studies have found that the critical value is higher in steep shallow flows. Explanations for this have been proposed in terms of the force balance on individual grains. The trend can also be understood in bulk‐flow terms if total flow resistance has “base” and “additional” components, the latter due to protruding immobile grains as well as any bedforms, and the stress corresponding to “additional” resistance is not available for grain movement in threshold conditions. A quantitative model based on these assumptions predicts that critical Shields stress increases with slope, critical stream power is near‐invariant with slope, and each has a secondary dependence on bed sorting. The proposed slope dependence is similar to what force‐balance models predict and consistent with flume data and most field data. Possible explanations are considered for the inability of this and other models to match the very low critical values of width‐averaged stress and power reported for some low‐gradient gravel bed rivers.

Research on the Flow Characteristics of Forced Circulation Evaporative Cooling System of Stator in Turbo-Generator

The forced circulation evaporative cooling system of stator in turbo-generator is a new cooling system under study, with the advantages of high-security, high efficiency and energy-saving. In this paper, an experiment table of this new cooling system with single hollow conductor was established. The flow characteristics of coolant in hollow conductor were analyzed and discussed by theoretical simulating and experimental researching. The results show that with the volume flow of coolant increasing, the variation tendencies of total flow resistance in hollow conductor and Xe are not monotonic and the prediction precision of total flow resistance in hollow conductor is satisfying with maximum relative error less than 10%. The length of subcooled flow boiling region in hollow conductor is relative long and can not be ignored. The conclusions in this paper can provide the theoretical and experimental basis for the further study of this new cooling system.

粗度配置が異なる長方形断面開水路の抵抗特性とせん断応力分布に関する実験的研究

Experimental results of characteristics of flow resistance and boundary shear stress distribution along the wetted perimeter of rectangular cross-sectional channels are reported in order to discuss sidewall roughness effects on them. In the experiments, square cross-sectional acrylic bars are employed as artificial strip roughness elements. Three types of arrangement of roughness elements are examined, that is, on the channel bed, the side wall and both of them. Varying vertical slope and discharge, flow resistances are measured. In some selected runs, cross-sectional velocity distributions are measured and shear stresses on the boundary are determined by methods based on the logarithmic velocity law because the velocity profiles fit the law near the boundary. It has been found that effects of roughness elements on the sidewalls are restricted near them affecting slightly total flow resistance even in case with steep slopes and that shear distributions have very high non-uniformity suggesting influences of secondary flows.