Instantaneous velocity of multiphase flow is an important parameter in scientific and industrial applications such as fluid mechanics modeling and flow measurement and monitoring. Ultrasound Doppler ...provides the spatial-temporal distribution of multiphase flow velocity in a non-intrusive manner. This technique can be used to uncover the fluid dynamics by measuring the flow structures, detecting the gas–liquid interface position, measuring the multiphase rheology, and providing an online sensing solution for flowrate metering and flow status monitoring. These functions facilitate fluid dynamics investigations and modeling, industrial safety assurance and reliability, production estimation, and process control and optimization. This review focuses on the principle and the state-of-art development of the ultrasonic Doppler technique for measuring gas–liquid two-phase flow, liquid–liquid two-phase flow, and three-phase flow, and provides insights into the advantages, limitations, and future trends of this technique.
Quarter-wavelength (QWL) velocity refers to the S-wave velocity at a depth equal to one-fourth of the wavelength of the seismic waves. It provides valuable information about the characteristics of ...the subsurface material properties affecting seismic waves propagation. The Swiss Seismological Service (SED) network, with over 200 stations across different lithologies, offers a rich dataset to implement correlation between site properties and site amplification factors. The current study is based on a subset of 113 selected SED seismic stations for which shear-wave velocity (Vs) profiles from geophysical measurements are available. We first meticulously analyzed and adjusted them to accurately determine the bedrock depth of the sites they are located on. Using empirical spectral modelling (ESM), we computed amplification functions from recorded earthquakes, referenced to the Swiss standard rock profile with a VS30 of 1100 m/s. Then we performed a bivariate analysis between empirical amplification functions, QWL velocity and QWL velocity contrast. The resulting coefficients are used to predict elastic amplification at frequencies between 0.5 and 10 Hz, with predictions generally being within 20–28% of observed values. We also developed an empirical equation relating VS30 (time-averaged Vs to 30 m depth) and κ0 (high-frequency attenuation parameter), to incorporate the anelastic term in the amplification. Applying our method to a 3D geophysical model of Visp, a high seismic hazard zone in Switzerland, we found it effective in predicting 1D site amplification, but noted caution in areas susceptible of 2D/3D resonance effects. A calibration function based on observed vs. predicted amplification and the frequencies of estimation normalized by the expected 2D resonance frequency improved predictions for Visp. Our study demonstrates that QWL velocity profiles offer a straightforward approach for characterizing site effects, which can be used in seismic hazard assessment to evaluate the potential amplification of ground motions.
•Correlation analysis between amplification functions, quarter-wavelength velocity and impedance contrast.•The aim of the correlation is to test a strategy to predict amplification using the site velocity profile.•Test at local scale highlights that the proposed method is powerful especially in 1D context.•The method represents a valid interpolation scheme to infer amplification maps.
This study aimed (i) to explore the relationship between vertical (jumping) and horizontal (sprinting) force-velocity-power (FVP) mechanical profiles in a large range of sports and levels of ...practice, and (ii) to provide a large database to serve as a reference of the FVP profile for all sports and levels tested. A total of 553 participants (333 men, 220 women) from 14 sport disciplines and all levels of practice participated in this study. Participants performed squat jumps (SJ) against multiple external loads (vertical) and linear 30-40 m sprints (horizontal). The vertical and horizontal FVP profile (i.e., theoretical maximal values of force (
), velocity (
), and power (
)) as well as main performance variables (unloaded SJ height in jumping and 20-m sprint time) were measured. Correlations coefficient between the same mechanical variables obtained from the vertical and horizontal modalities ranged from -0.12 to 0.58 for
, -0.31 to 0.71 for
, -0.10 to 0.67 for
, and -0.92 to -0.23 for the performance variables (i.e, SJ height and sprint time). Overall, results showed a decrease in the magnitude of the correlations for higher-level athletes. The low correlations generally observed between jumping and sprinting mechanical outputs suggest that both tasks provide distinctive information regarding the FVP profile of lower-body muscles. Therefore, we recommend the assessment of the FVP profile both in jumping and sprinting to gain a deeper insight into the maximal mechanical capacities of lower-body muscles, especially at high and elite levels.
AbstractSince the existence of dunes in fluvial channels significantly alters near-bed flow structures, the related velocity profile is complex and different from that over a plane bed. To understand ...its average characteristics over a dune length, velocity distribution is analyzed preferably in a spatiotemporal or double-averaging manner. In this study, turbulent flow velocities over two-dimensional fixed dunes with smooth and rough surfaces are measured using particle image velocimetry (PIV). The data analysis shows that the double-averaged velocity profile generally comprises two layers, the first being linear near the bed and the second being logarithmic away from the bed. The two-layer velocity profile can be described using a unified formula, which is proposed by combining the linear and logarithmic laws in a power-sum fashion. The new formula is finally validated using the experimental data.
Practical ApplicationsAs a prevalent bedform in fluvial and coastal environments, dunes have been a subject of research for decades. To appreciate the average characteristics of the flow over a dune-covered bed, it would be better to perform a proper average of measurements of flow fields in both time and space domains. Such an effort was made in the present study. With the measured data, we are able to develop a new approach for unifying the velocity distribution from the dune trough to the free water surface. This is done by combining logarithmic and linear laws in a power-sum form. Although conducting fine-scale field measurements of flows over dunes is still not easy at present, the formula proposed in this paper would be of great significance in estimating dune-affected flow velocity distributions, and thus helpful for understanding flow resistance, sediment transport, and river and coastal management.
This project aims to determine the Coefficient of Variation (CV) and Correlation Length (CL) of the soil at site. The methodology involves data acquisition through seismometers, analysis of ...horizontal to vertical spectral ratios (HVSR), inversion analyses to obtain shear wave velocity (VS) profiles, and subsequent calculations of CV and CL. The site consists of a dense array of 14 seismometers, complemented by additional borehole tests. HVSR were computed for both surface and subsurface recordings, and the resulting inversed VS profiles were utilized to derive a representative profile for the site. CV was computed for each layer of the representative profile, and CL was determined from spatial autocorrelation coefficients. The analysis revealed that CV varies with depth, with higher values in shallow layers and a decrease with depth. The CL also exhibited depth-dependent behavior, increasing up to 150 m and decreasing beyond that depth. This comprehensive investigation provides valuable insights into the soil properties at site, which are essential for seismic hazard assessments and engineering considerations.
The definition of simple and accurate methods to estimate flow resistance in vegetated channels is still a challenging issue in soil bioengineering practices and programming riparian vegetation ...management to control channel conveyance capacity, sediment deposition, and flooding propensity. In this paper, measurements collected by Errico et al. (2018, 2019) in drainage channels colonized by common reed (Phragmites australis) were used to study the effect of flexible vegetation and its management in flow resistance estimate. At first, a theoretical flow resistance equation, obtained applying dimensional analysis and incomplete self‐similarity condition for the velocity distribution of an open channel flow, was briefly summarized. Then, this flow resistance equation was calibrated and tested by open‐field hydraulic experiments carried out by Errico et al. (2018, 2019) at the real scale of existing vegetated drainage channels. In particular, the Γ function of the power velocity profile was empirically related to the slope energy and the flow Froude number by using the available measurements. Taking into account the hydrological regime of the flow in the investigated channels, the original data set was divided into two sub‐data sets (calibrating and testing data set) exploring the same range of measured discharges. The calibration and testing of the flow resistance equation were carried out without distinguishing measurements corresponding to different vegetation conditions (full‐vegetated, half‐vegetated, non‐vegetated, central vegetation cut, extensive vegetation cut). The analysis demonstrated that the theoretical flow resistance equation allows an accurate estimate of the Darcy‐Weisbach friction factor which is characterized by errors that are always less than 10% and less than or equal to 5% for 90.9% of the investigated cases. The finding of this study also allowed to evaluate the effects of different vegetation management scenarios on flow resistance.
A flow resistance law was verified by measurements performed in real scale channels investigating the effect of three different vegetation management scenarios. The calibrated equations allowed an accurate estimate of Darcy‐Weisbach factor f and the presented approach considers the effect of the cutting management in the estimate of f.
•We analyzed three regimes of boundary layers: sub-, trans-, and supercritical.•Theoretical profiles are computed by self-similar solution.•Two-phase transcritical boundary layers have the ...sub-layer.•There is no transcritical boundary layer at small Mach number.•Wall temperature may be greater than inflow total temperature.
Boundary layers can be defined as sub-, trans-, and supercritical regime according to whether their temperature profiles cross the Widom line. The transcritical boundary layers which contain liquid and supercritical phases are hard to solve. In this paper, adiabatic flat plate laminar boundary layers of supercritical carbon dioxide (SCO2) are preliminarily explored by the self-similar solution. We analyze the difference of boundary layer profiles at 8 MPa - inflow pressure by varying inflow temperature Te and Mach number Ma. The influence of Te and Ma on the velocity profiles exhibits complex diversity at three boundary layer regimes. Compared with subcritical and supercritical boundary layers, transcritical boundary layers with smaller skin friction coefficients are the most special, and they include the “sub-layer”. Notably, there is no transcritical boundary layer when Te increases to pseudo-critical temperature Tpc at small Ma. The wall temperature Tw of transcritical boundary layers may be greater than inflow total temperature T0 at larger Ma.
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•A method to predict velocity profile in rod bundle has been proposed.•Gas velocity distribution can be simplified to turbulent velocity distribution.•Liquid velocity distribution can be derived by ...interfacial shear stress correlation.•The predictions show reasonable agreement with data.
Annular flow in rod bundle occurs frequently in boiling water reactor (BWR) under normal operation and in pressurized water reactor (PWR) under accident conditions. When annular flow occurs, rod film thickness is one of the most important parameters for safety concern. In order to calculate rod film thickness distribution inside rod bundle, both gas and liquid velocity distribution inside rod bundle is necessary. Also, flow distribution inside rod bundle is of importance for calculation of interfacial shear stress and other parameters in each sub-channel. However, entrained droplets in gas core can sharpen the gas velocity profile while existing rods can flatten the gas velocity profile, making it different from that of single phase flow. The liquid velocity distribution inside rod bundle is hard to obtain from experiment because of the complex structure of its geometry. Due to these reasons, this paper deducts gas and liquid velocity profiles from existing adiabatic rod film thickness data. Even the gas velocity profiles for different flow conditions are different, there exists a gas velocity profile that can be applied to all current flow conditions with minimum uncertainties. Based on that gas velocity profile, liquid velocity profile can be calculated. From these flow velocity profiles, film thickness on each rod and interfacial shear stress in each sub-channel can be calculated.
AbstractThe mean velocity distribution of open channel flows with fully submerged two-layered vegetation can be divided into three zones. Zone 1 represents the lower region of short vegetation, where ...the flow has high drag because of highly dense vegetation, Zone 2 represents the middle flow zone from the edge of the short vegetation to the top of the tall one, and Zone 3 denotes the upper region with the free surface flow. A new analytical model is developed based on the momentum equation of vegetated flow, where turbulent eddy viscosity is approximated as a linear relationship with local velocity. The analytical model was evaluated using seven experimental data sets under different flow conditions with distinctive densities and formations of vegetation. Three sets of data available from other researchers were also used to check the applicability of the proposed model. An agreement between the analytical model and experimental data indicates the validity and robustness of the model.
Rill erosion is considered one of the most important soil processes because of the large amount of soil loss due to the development of a rill network able to promote an efficient transport of both ...rill flow‐detached particles and those delivered from the inter‐rill areas. Rill flow experiments are useful to overcome the gap in rill hydraulics knowledge and to test the reliability of currently applied uniform open channel flow equations for mobile bed rills. In this paper the applicability of a theoretical flow resistance equation, based on a power‐velocity profile, to rill channels shaped on soils having different textures was investigated. The measurements (437 runs) of water depth, cross‐section area, wetted perimeter, bed slope and flow velocity carried out in rill reaches shaped on experimental plots, having different slope values (9–26%) and soil texture (clay fraction range of 32.7–73%), were carried out. These measurements were jointly examined with 35 experimental runs carried out by other authors in a rill flume having a slope range of 18–84% and a clay content of 3%. The main aim of this paper is to deduce a relationship between the velocity profile parameter Γ, the channel slope and the flow Froude number using a database characterized by a wide range of slope (9–84%) and textural classes (clay ranging from 3 to 73%). The obtained relationship was also verified using 117 experimental runs carried out in this investigation by sloping plots (slope equal to 9 and 15%) with a soil having a clay content of 32.7%. The analysis demonstrated that the applicability of the theoretical flow resistance law is experimentally supported and that the effect of soil grain‐size distribution is represented by silt and clay fractions which take into account the influence of the detachability and transportability properties of the soil particles.
Highlights
Rill flow resistance is affected by interaction between flow, bed morphology and sediment transport.
A new theoretical flow resistance law is tested for rills shaped on different textured soils.
The velocity profile is related to the channel slope, the flow Froude number and the soil texture.
The Darcy‐Weisbach friction factor can be accurately estimated by the proposed theoretical approach.
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