Search results for "technical"

Flow hydraulic characteristics determining the occurrence of either smooth or abrupt sewer pressurization

2014

Laboratory experiments showed that pipe pressurization consequent on a drastic reduction in the downstream discharge can occur either by a gradual rising of the free-surface (“smooth” pressurization) or by propagation of a front filling the whole cross-section (“abrupt” pressurization). This study examines the free-surface flow characteristics that determine smooth or abrupt pressurization pattern through a theoretical approach using dimensionless variables. A critical flow rate value, which separates the pressurization patterns, exists for any given pipe diameter. For flow rates higher than this specific value, only abrupt pressurization occurs. For lower flow rates, either smooth or abrup…

Bed Topography Reconstruction in a Large Amplitude Meandering Flume: Application of Close Range Photogrammetry

2014

Natural rivers are characterized by continuous variations in bed topography, especially along curved reaches. High resolution topographic data are necessary to analyze the mutual interactions between the downstream flow and the cross-stream flow, which determine the distribution of the bed-shear stress along the channel. Because of the difficulty in acquiring good and accurate data in rivers, the major part of studies have been conducted in laboratory flumes. This paper reports on a laboratory study in which the automatic digital photogrammetric survey was applied to derive the high-resolution Digital Surface Model (DSM) of the bed topography in a large amplitude meandering flume. In order …

Reverse and normal drag along a fault

2005

An analysis of the theoretical displacement field around a single dip-slip fault at depth reveals that normal and reverse fault drag develop by perturbation flow induced by fault slip. We analytically model the heterogeneous part of the instantaneous displacement field of an isolated two-dimensional mode II fault in an infinite, homogeneous elastic body in response to fault slip. Material on both sides of the fault is displaced and ‘opposing circulation cells’ arise on opposite sides of the fault, with displacement magnitudes increasing towards the center of the fault. Both normal and reverse drag can develop at the fault center depending on the angle between the markers and the fault; norm…

Experimental analysis of the effect of vegetation on flow and bed shear stress distribution in high-curvature bends

2016

The cross-sectional circulation, which develops in meandering bends, exerts an important role in velocity and the boundary shear stress redistributions. This paper considers the effect of vegetation on cross-sectional flow and bed shear distribution along a high-curvature bend. The analysis is conducted with the aid of data collected in a large-amplitude meandering flume during a reference experiment without vegetation and an experiment with vegetation on the bed. The results show that the presence of vegetation modifies the curvature-induced flow pattern and the directionality of turbulent structures. In fact, in the presence of vegetation, the turbulent structures tend to develop within a…

New Flow-Resistance Law for Steep Mountain Streams Based on Velocity Profile

2017

This paper deduces a new flow-resistance equation for open-channel flow applying dimensional analysis and self-similarity theory. The incomplete self-similarity hypothesis is used to establish the flow velocity distribution whose integration gives the theoretical expression of the Darcy-Weisbach friction factor. The theoretical resistance equation then is tested by the available field measurements of flow velocity, water depth, river width and bed slope carried out in 653 reaches of several Canadian mountain streams. A relationship between the G function of the velocity profile and the channel slope and the flow Froude number is also established. The analysis shows that the Darcy- Weisbach …

Discussion of “Modified Hazen–Williams and Darcy–Weisbach Equations for Friction and Local Head Losses along Irrigation Laterals” by John D. Valiantz…

2007

Closure to “Applying Hypothesis of Self-Similarity for Flow-Resistance Law in Calabrian Gravel-Bed Rivers” by Vito Ferro and Paolo Porto

2019

Flow resistance in gravel-bed channels with large-scale roughness

2003

A previously published mixing length (ML) model for evaluating the Darcy–Weisbach friction factor for a large-scale roughness condition (depth to sediment height ratio ranging from 1 to 4) is briefly reviewed and modified (MML). Then the MML model and a modified drag (MD) model are experimentally tested using laboratory measurements carried out for gravel-bed channels and large-scale roughness condition. This analysis showed that the MML gives accurate estimates of the Darcy–Weisbach coefficient and for Froude number values greater than 0·5 the MML model coincides with the ML one. Testing of the MD model shows limited accuracy in estimating flow resistance. Finally, the MML and MD models are com…

Testing a new rill flow resistance approach using the Water Erosion Prediction Project experimental database

2018

In this paper, a recently theoretically deduced rill flow resistance equation, based on a power‐velocity profile, was tested using the Water Erosion Prediction Project database. This database includes measurements of flow velocity, water depth, cross section area, wetted perimeter, and bed slope that were made in rills shaped on experimental sites distributed across the continental United States. In particular, three different experimental conditions (only rainfall, only flow, and rain with flow) were examined, and for each condition, the theoretically based relationship for estimating the Γ function of the power velocity profile was calibrated. The results established that (a) the Darcy‐We…

Flow Resistance Law in Channels with Flexible Submerged Vegetation

2005

In this paper, experimental data collected in a straight flume having a bed covered by grasslike vegetation have been used to analyze flow resistance for flexible submerged elements. At first, the measurements are used to test the applicability of Kouwen’s method. Then, a calibration of two coefficients appearing in the semilogarithmic flow resistance equation is carried out. Finally, applying the P-theorem and the incomplete self-similarity condition, a flow resistance equation linking the friction factor with the shear Reynolds number, the depth-vegetation height ratio and the inflection degree is deduced.