Comparison under controlled conditions between multi-frequency ADCPs and LISST-SL for investigating suspended sand in rivers

This paper aims to investigate the possibility and limits of using the laser device LISST-SL to calibrate and validate the multi-frequency acoustic method for assessing the concentration and grain size of suspended sand in rivers by using Acoustic Doppler Current Profilers (ADCPs). Over the last few decades, the methods for investigating suspended sediment using Acoustic Backscattering (ABS) have been gaining increasing acceptance for riverine applications. ABS allows indirect quantification of the suspended sediment using non-intrusive measurements with high temporal and spatial resolution from a moving boat, with a range of several metres. Despite the advancement of these techniques, the use of ABS usually implies calibration and validation in the field, which can be performed by comparing echo recording by ADCP to data from water samples. Sampling and analysis of water samples noticeably increase the campaign cost and limits the reliability of the calibration because of the time and spatial averaging involved in physical sampling. In the present work, the LISST-SL suited to river applications was tested to provide matching data in one point for the validation of ADCP methods in future field work. To this end, laboratory tests were conducted utilising two ADCPs working at 1200 and 600. kHz frequencies and studying the same water volume that was concurrently being analysed by the laser device. Rapid injections of sand (median grain size: 130-250 \u3bcm) produced average concentrations of 100-1000. mg/L in a 0.25-m/s-fast and 1.7-m-deep flow. Echo records at the two frequencies were compared to the mean grain size and concentration measured via laser diffraction. Although noticeable differences between the acoustic and laser assessments of concentration were due to (1) inappropriate sampling of LISST-SL at low flow velocity and (2) investigation scarce resolution with respect to actual gradients, the corresponding mean sizes were well correlated. \ua9 2014 Elsevier Ltd

A detailed microstructural and corrosion analysis of magnesium alloy WE43 manufactured by selective laser melting

The production of magnesium alloy WE43 was achieved by selective laser melting (SLM). The alloy was investigated after SLM, hot isostatic pressing (HIP), and solutionising heat treatment. The microstructure and corrosion behaviour of the specimens were carefully characterised, whilst assessed and contrast relative to the conventionally cast alloy counterpart. The SLM prepared specimens possess a unique microstructure comprising fine grains growing with a strong [0001] texture along the building direction with a low fraction of process-induced and metallurgical defects, reaching < 0.1 %, after optimising the SLM parameters and the HIP treatment. Electrochemical measurements demonstrated that the SLM prepared WE43 is cathodically more active as compared with its cast counterpart. It is proposed that this behaviour is due to a high density of zirconium-rich oxide particles uniformly distributed throughout the alloy microstructure as well as the alterations in the chemical composition of the solid-solution matrix originating from the high cooling rates of SLM. It was also noted that the oxide particles are mainly sourced by powder. The present results suggest that the corrosion of SLM prepared Mg alloys could be greatly improved once the influence of powder characteristics is further understood and controlled