Enhancing PIV image and fractal descriptor for velocity and shear stresses propagation around a circular pier

© 2016 China University of Geosciences (Beijing) and Peking University In this study, the fractal dimensions of velocity fluctuations and the Reynolds shear stresses propagation for flow around a circular bridge pier are presented. In the study reported herein, the fractal dimension of velocity fluctuations (u′, v′, w′) and the Reynolds shear stresses (u′v′ and u′w′) of flow around a bridge pier were computed using a Fractal Interpolation Function (FIF) algorithm. The velocity fluctuations of flow along a horizontal plane above the bed were measured using Acoustic Doppler Velocity meter (ADV) and Particle Image Velocimetry (PIV). The PIV is a powerful technique which enables us to attain high resolution spatial and temporal information of turbulent flow using instantaneous time snapshots. In this study, PIV was used for detection of high resolution fractal scaling around a bridge pier. The results showed that the fractal dimension of flow fluctuated significantly in the longitudinal and transverse directions in the vicinity of the pier. It was also found that the fractal dimension of velocity fluctuations and shear stresses increased rapidly at vicinity of pier at downstream whereas it remained approximately unchanged far downstream of the pier. The higher value of fractal dimension was found at a distance equal to one times of the pier diameter in the back of the pier. Furthermore, the average fractal dimension for the streamwise and transverse velocity fluctuations decreased from the centreline to the side wall of the flume. Finally, the results from ADV measurement were consistent with the result from PIV, therefore, the ADV enables to detect turbulent characteristics of flow around a circular bridge pier

Scour at partially blocked box-culverts under steady flow

© 2016, Thomas Telford Services Ltd. All rights reserved. Culverts are built at locations where a waterway crosses a road or railway and creates a limitation to flow passage. Furthermore, blockage commonly occurs during flood events with accumulation of debris at the culvert inlet. The inlet blockage changes the flow structure at the outlet and may result in culvert failure. Despite this, the impacts of blockage on culvert hydraulics and downstream waterways have not received consideration in the literature. The purpose of this paper is to mitigate this deficiency by reporting on an investigation into scouring at the outlet of partially blocked culverts. Experimental tests were conducted under steady flow to investigate a relationship between the maximum scour depth, blockage ratio of the culvert and the flow characteristics. Both non-blocked and partially blocked conditions were considered. Consideration of the results obtained showed that the scoured area and maximum scour depth increased with partially blocked culverts conditions compared with equivalent non-blocked culverts

Location of the maximum scouring depth at the outlet of partially-blocked and non-blocked box culvert

Among various hydraulic structures, culvert is the most likely one which usually blocks by the debris that are carrying by flow during large flood events. The size of the structure and its location where a waterway crosses a road or railway increases the possibility of clogging. The blockage of culvert accelerates bed scouring at the outlet hence affects bed scouring profile. This leads to increase the risk of culvert collapsed and produce different kinds of damages to the society. The present study concerns the effect of upstream blockage on the scouring profile at the outlet of a box culvert. Therefore, the experimental program was designed to investigate the relationship between the scouring geometry and blockage ratio. The experimental tests were carried out under non-blocked and partially blocked conditions. The sediment material used in this study was uniform non-cohesive sand material. Results showed that the scouring bed profile is different in partially blocked condition when compared to the non-blocked condition. Additionally it was found that the maximum scouring depth in a partially blocked culvert occurred at a distance very close to the outlet of the box culvert. © 2014 Taylor & Francis Group, London

The muon g-2: the hadronic vacuum polarisation contributions

The anomalous magnetic moment of the muon stands as an enduring test of the Standard Model (SM), where the 3:5 (or higher) discrepancy between the experimental measurement and the SM prediction could be an indication of the existence of new physics beyond the SM. This work presents a complete re-evaluation of the hadronic vacuum polarisation contributions to the anomalous magnetic moment of the muon from a combination of available electron-positron to hadrons cross section data as input in a predominantly data driven analysis. Focus has been placed on the development of a new data combination method, that has been advocated to be free of bias and allows for the full use of any available correlated statistical and systematic uncertainties into the determination of both the resulting mean value and corresponding error. In a related work, the three precision measurements of the two-pion cross section using initial state radiation by the KLOE collaboration provide an important input for the prediction of the hadronic contribution to the anomalous magnetic moment of the muon. These measurements are correlated for both statistical and systematic uncertainties and, therefore, the simultaneous use of these measurements requires covariance matrices that fully describe the correlations. The construction of these matrices has allowed for the determination of a combined KLOE measurement of the two-pion cross section. For the full calculation of the leading order and next-to-leading order hadronic vacuum polarisation contributions, all available electron-positron to hadrons cross section data have been analysed and included, where the new data compilation has yielded the full hadronic R-ratio and its covariance matrix from threshold to 11.2 GeV. Using these combined data and pQCD above that range results in estimates of the hadronic vacuum polarisation contributions to g-2 of the muon that yields a new determination for the SM prediction which is 3.7 standard deviations below the current experimental measurement. Detailed comparisons with results from similar related works are given, as well as discussions of the prospects for improving the calculation of these contributions in the future