Search results for "Low velocity"
showing 10 items of 231 documents
Duplexsonographie der normalen Pfortader
2008
In 50 normal subjects flow velocity and direction on the portal vein was measured by ultrasonic duplex system. The measurements revealed at a mean diameter of 9.7 mm, a mean flow velocity of 15.2 +/- 2.6 cm/s, corresponding to a volume flow of 693 +/- 235 ml/min. Postprandially this increased to 880 +/- 269 ml/min. Inter-observer and day to day measurements demonstrated good reproducibility. Thus, this simple non-invasive method is well suited for quantitative assessment of the portal vein system in portal hypertension, thrombosis or after shunt operations.
Experimental determination of viscous damper parameters in low velocity ranges
2017
In the last decades many strategies for seismic vulnerability mitigation of structures have been developed through analytical studies and experimental tests. Among these, energy dissipation by external devices assumes a great relevance for the relative design simplicity, even if applied to complex structures, and the effectiveness in reducing seismic demand. In particular, the use of fluid viscous dampers represents a very attractive solution because of their velocity-dependent behaviour and relatively low costs. The application on structures requires specific study under seismic excitation and a particular care of structural details. In this context the use of proper constitutive models fo…
Velocity and turbulence measurements: uncertainty in the application of the Image-based technique
2018
This work focuses on the application of image-based technique to estimate velocity and turbulent flow characteristics. In particular, in the present work digital imaging technique is used for performing surface velocity measurements of hyper-concentrated flows. The analysis is conducted with the aid of data collected in a scale laboratory flume constructed at the Hydraulic laboratory of the Department of Civil, Environmental, Aerospatial and of Materials Engineering (DICAM) – University of Palermo (Italy). In the present paper a brief summary of results obtained in previous works on the flow velocity estimation error and uncertainty related to the acquisition procedure is reported.
Flow velocity profile and turbulence characteristics in a vegetated straight flume
2008
Vegetation affects the hydrodynamic conditions of an open channel flow with direct implications in physical and biophysical processes. In this paper, the vertical flow velocity distribution of a vegetated flow has been analyzed using experimental data collected in a straight flume. The experimental velocity distributions are positively compared with the hyperbolic tangent profile of a pure mixing layer previously verified by Ghisalberti and Nepf (2002). Peculiarly, for different flow and vegetative conditions, fitting of the hyperbolic tangent profile to the experimental velocity distributions has allowed the localization of the inflection point of the velocity profile at a distance from th…
Roughness effect on the correction factor of surface velocity for rill flows
2021
Flow velocity is one of the most important hydrodynamic variables for both channelized (rill and gullies) and interrill erosive phenomena. The dye tracer technique to measure surface flow velocity Vs is based on the measurement of the travel time of a tracer needed to cover a known distance. The measured Vs must be corrected to obtain the mean flow velocity V using a factor αv = V/Vs which is generally empirically deduced. The Vs measurement can be influenced by the method applied to time the travel of the dye-tracer and αv can vary in different flow conditions. Experiments were performed by a fixed bed small flume simulating a rill channel for two roughness conditions (sieved soil, gravel)…
Dissipative scaling of step-pool features
2021
Abstract This paper focuses on the dissipative similarity of step-pool units at rill, flume and stream scale. This investigation is carried out using recent advances in open channel flow resistance, applications of close-range photogrammetry to rill erosion, available published data on step-pool features in flumes and streams and a new dataset of measurements in fixed bed step-pool rills. A theoretically-based equation for calculating the Darcy-Weisbach friction factor obtained by integration of a power velocity profile is presented. The scale factor Γ of this power velocity profile, which is included in the flow resistance equation, was previously calibrated (Eq. 10) for mobile bed rills w…
Assessing flow resistance law in vegetated channels by dimensional analysis and self-similarity
2019
Abstract In this paper experimental data collected by Kouwen et al., Wilson and Horrit, Raffaelli et al. and Carollo et al., using straight flumes having a bed covered by grass-like vegetation with different stem concentrations, were used to analyze flow resistance for flexible submerged elements. At first, the dimensional analysis and the incomplete self-similarity hypothesis was applied to deduce the flow velocity distribution and the resulting theoretical expression of the Darcy-Weisbach friction factor. Then, a relationship between the Γ function of the velocity profile and the biomechanical characteristics of vegetation, the channel slope, the Reynolds number and the flow Froude number…
Assessing theoretical flow velocity profile and resistance in gravel bed rivers by field measurements
2018
Previous studies showed that integrating a power velocity profile, deduced applying dimensional analysis and the incomplete self-similarity condition, the flow resistance equation for open channel flow can be obtained. At first, in this paper the relationship between the Gamma function of the power velocity profile, the channel slope and the Froude number, which was already empirically introduced in a previous paper, is now theoretically deduced. Then this relationship is calibrated using the field measurements of flow velocity, water depth and bed slope carried out in 101 reaches of gravel bed rivers available by literature. The proposed relationship for estimating Gamma function and the t…
On the variation of the correction factor of surface velocity with the measurement vertical for shallow flows over rough beds
2023
Considering that water flow energy affects the detachment of soil particles, the transport and deposit of the detached particles, the flow velocity is a key variable governing the soil erosion processes at the hillslope scale. The simple dye-tracer technique for measuring mean flow velocity can be applied in non-controlled field applications for which some measurement difficulties (e.g. due to sediment transport, and shallow flows) can occur. The correction factor is usually obtained as the ratio between the mean velocity, deriving from measurements of flow discharge and water depth, and surface velocity. Alternatively, the possibility of using the velocity profile in a given vertical to de…
Numerical experiments for defining criteria for the use of LS-PIV based techniques in river monitoring.
2019
The developing of new image-based techniques for environmental monitoring is opening new frontiers for remote streamflow measurements in natural environments, since they allow for non-intrusive measurements even in adverse circumstances, such as high flow conditions that often hinder the use of traditional approaches and instruments. Methods based on the acquisition, analysis and elaboration of images for streamflow observation, such as the large scale particle image velocimetry (LSPIV) and the particle tracking velocimetry (PTV) techniques, are rapidly evolving also in consideration of the growing availability of a new generation of optical sensors, digital cameras and methodologies. A num…