Rapid manufacturing- state of the art, analysis and future perspectives

Layer based manufacturing system often referred to as Rapid Prototyping (RP) have been in existence for 22 years, in the past 5 years Rapid Manufacturing (RM) has emerged from these RP systems to produce functional and structural customer focused end use components and products. This keynote paper will review the current range of technologies for metallic systems, it will also evaluate the operating principles, features, potential and limitations of current commercially available systems. Rapid Manufacture is increasingly being used for high value difficult to manufacture components with a new set of design rules required to fully exploit the RM systems inherent characteristics. A case studies approach will be used to show the benefits and pitfalls this new design freedom can provide designers

Low-angle dunes in the Changjiang (Yangtze) Estuary: Flow and sediment dynamics under tidal influence

It has long been highlighted that important feedbacks exist between river bed morphology, sediment transport and the turbulent flow field and that these feedbacks change in response to forcing mechanisms. However, our current understanding of bedform dynamics is largely based on studies of steady flow environments and cohesionless bed conditions. Few investigations have been made under rapidly changing flows. Here, we examine flow and sediment dynamics over low-angle dunes in unsteady flows in the Changjiang (Yangtze) Estuary, China. Topography, flow and sediment data were collected over a reach ca 1.8 km long through a semi-diurnal tidal cycle in a moderate tide of flood season. The results show that: (1) roughness length derived from the upper flow changes little with the flow reversing and displays the same value on both the ebb and flood tide. Moreover, the variability of individual bedform features plays an important role in roughness length variation. (2) Shear stress over the crest of low-angle dunes roughly represents the total spatially averaged stress over dunes in this study area, which has significant implications for advancing numerical models. (3) Changes in morphology, flow and sediment dynamics over dunes through time reveal how low-angle dunes evolve within a tidal cycle. (4) The clockwise hysteresis loops between flow dynamics and bedform features (height and aspect ratio) are also observed. The combination of suspended sediment transport and bedload transport on dune transformation and migration attributes to the clockwise hysteresis. The specific sediment composition of the riverbed, in some extent, affects the mechanism of sediment transport related to the exchange between suspended sediment and riverbed, but further investigation is needed to figure out the mechanism behind this for extended series of tides, such as spring/neap tide and tides in flooding and dry season

The influence of flow discharge variations on the morphodynamics of a diffluence-confluence unit on a large river: Impacts of discharge variation on a diffluence-confluence unit

© 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. Bifurcations are key geomorphological nodes in anabranching and braided fluvial channels, controlling local bed morphology, the routing of sediment and water, and ultimately defining the stability of their associated diffluence–confluence unit. Recently, numerical modelling of bifurcations has focused on the relationship between flow conditions and the partitioning of sediment between the bifurcate channels. Herein, we report on field observations spanning September 2013 to July 2014 of the three-dimensional flow structure, bed morphological change and partitioning of both flow discharge and suspended sediment through a large diffluence–confluence unit on the Mekong River, Cambodia, across a range of flow stages (from 13 500 to 27 000 m 3 s −1 ). Analysis of discharge and sediment load throughout the diffluence–confluence unit reveals that during the highest flows (Q = 27 000 m 3 s −1 ), the downstream island complex is a net sink of sediment (losing 2600 ± 2000 kg s −1 between the diffluence and confluence), whereas during the rising limb (Q = 19 500 m 3 s −1 ) and falling limb flows (Q = 13 500 m 3 s −1 ) the sediment balance is in quasi-equilibrium. We show that the discharge asymmetry of the bifurcation varies with discharge and highlight that the influence of upstream curvature-induced water surface slope and bed morphological change may be first-order controls on bifurcation configuration. Comparison of our field data to existing bifurcation stability diagrams reveals that during lower (rising and falling limb) flow the bifurcation may be classified as unstable, yet transitions to a stable condition at high flows. However, over the long term (1959–2013) aerial imagery reveals the diffluence–confluence unit to be fairly stable. We propose, therefore, that the long-term stability of the bifurcation, as well as the larger channel planform and morphology of the diffluence–confluence unit, may be controlled by the dominant sediment transport regime of the system. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Extreme flood-driven fluvial bank erosion and sediment loads: direct process measurements using integrated Mobile Laser Scanning (MLS) and hydro-acoustic techniques: Direct measurement of flood-driven erosion using MLS and MBES

Copyright © 2016 John Wiley & Sons, Ltd. This methods paper details the first attempt at monitoring bank erosion, flow and suspended sediment at a site during flooding on the Mekong River induced by the passage of tropical cyclones. We deployed integrated mobile laser scanning (MLS) and multibeam echo sounding (MBES), alongside acoustic Doppler current profiling (aDcp), to directly measure changes in river bank and bed at high (~0.05 m) spatial resolution, in conjunction with measurements of flow and suspended sediment dynamics. We outline the methodological steps used to collect and process this complex point cloud data, and detail the procedures used to process and calibrate the aDcp flow and sediment flux data. A comparison with conventional remote sensing methods of estimating bank erosion, using aerial images and Landsat imagery, reveals that traditional techniques are error prone at the high temporal resolutions required to quantify the patterns and volumes of bank erosion induced by the passage of individual flood events. Our analysis reveals the importance of cyclone-driven flood events in causing high rates of erosion and suspended sediment transport, with a c. twofold increase in bank erosion volumes and a fourfold increase in suspended sediment volumes in the cyclone-affected wet season. Copyright © 2016 John Wiley & Sons, Ltd

Microplastic trapping efficiency and hydrodynamics in model coral reefs: A physical experimental investigation.

Coastal ecosystems, such as coral reefs, are vulnerable to microplastic pollution input from proximal riverine and shoreline sources. However, deposition, retention, and transport processes are largely unevaluated, especially in relation to hydrodynamics. For the first time, we experimentally investigate the retention of biofilmed microplastic by branching 3D printed corals (staghorn coral Acropora genus) under various unidirectional flows (U = {0.15, 0.20, 0.25, 0.30} ms ) and canopy densities (15 and 48 corals m ). These variables are found to drive trapping efficiency, with 79-98% of microplastics retained in coral canopies across the experimental duration at high flow velocities (U = 0.25-0.30 ms ), compared to 10-13% for the bare bed, with denser canopies retaining only 15% more microplastics than the sparse canopy at highest flow conditions (U = 0.30 ms ). Three fundamental trapping mechanisms were identified: (a) particle interception, (b) settlement on branches or within coral, and (c) accumulation in the downstream wake region of the coral. Corresponding hydrodynamics reveal that microplastic retention and spatial distribution is modulated by the energy-dissipative effects of corals due to flow-structure interactions reducing in-canopy velocities and generating localised turbulence. The wider ecological implications for coral systems are discussed in light of the findings, particularly in terms of concentrations and locations of plastic accumulation. [Abstract copyright: Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.

Sustainable rice cultivation in the deep flooded zones of the Vietnamese Mekong Delta

This paper explains how the management of the full-dyke system in the deep flooded zones of the Vietnamese Mekong Delta affects rice cultivation, and outlines how alternative dyke management strategies could offer more sustainable adaptations in the face of future environmental threats. The current management of the ‘full-dyke’ network has been successful in promoting triple-cropping rice cultivation, but this practice has prevented sediment deposition on the land surface. River-borne sediments deposited on the delta land surface have high economic value because they are (i) rich in nutrients (potentially 26 million USD/yr of free fertiliser to An Giang Province) and can (ii) help to maintain the Mekong Delta land above sealevel. Without a continuing supply of sediment to the delta, triple-cropping paddies may not continue to be sustainable or profitable for the majority of rice farmers over the next 10 to 20 years. The economic value of sediment as a free fertiliser is particularly important to poor farmers, as without sediment, they run a significant risk of debt due to fluctuations in rice, fertiliser, and other input prices. With incoming loads now declining, sediment must be managed carefully as a resource. Our projections show that the best use of the remaining sediment resource can be achieved by allowing full paddy flooding only in years of high sediment potential, and this would greatly increase the sustainability of rice agriculture in the face of future environmental change. This recommended policy is an option with few regrets, in that its other benefits include maximising groundwater replenishment, ensuring freshwater availability during drought periods (including countering salt water intrusion), cleansing rice paddies of pests and disease, and tempering downstream flooding. If triple-rice-cropping continues to have priority, financial support will particularly be needed to provide help to poorer farmers coping with increases in artificial fertiliser prices

Non-buoyant microplastic settling velocity varies with biofilm growth and ambient water salinity

Rivers are the major conveyor of plastics to the marine environment, but the mechanisms that impact microplastic (<5 mm) aquatic transport, and thus govern fate are largely unknown. This prevents progress in understanding microplastic dynamics and identifying zones of high accumulation, along with taking representative environmental samples and developing effective mitigation measures. Using a suite of settling experiments we show that non-buoyant microplastic settling is influenced by a combination of biofilm growth, water salinity and suspended clay concentrations typically seen across fluvial to marine environments. Results indicate that biofilms significantly increased settling velocity of three different polymer types of non-buoyant microplastics (fragments and fibres, size range 0.02–4.94 mm) by up to 130% and significant increases in settling velocity were observable within hours. Impacts were both polymer and shape specific and settling regimes differed according to both salinity and sediment concentrations. Our results further validate previous statements that existing transport formula are inadequate to capture microplastic settling and highlight the importance of considering the combination of these processes within the next generation of predictive frameworks. This will allow more robust predictions of transport, fate and impact of microplastic pollution within aquatic environments

Long-term outcomes of patients undergoing endovascular infrainguinal interventions with single-vessel peroneal artery runoff

ObjectivesRecent reports have shown promising early results after endovascular revascularization (percutaneous transluminal angioplasty [PTA]/stent) of patients with peroneal artery-only runoff (PAOR), although the long-term durability is unclear. This study evaluated long-term primary patency and limb salvage of PTA/stent in patients with single-vessel runoff and critical limb ischemia to determine if the peroneal artery yields inferior results.MethodsFrom January 2002 to December 2007, 1075 infrainguinal PTA/stent procedures were performed in 920 patients. The study cohort comprised 201 limbs in 187 patients with single-vessel runoff and critical limb ischemia. End points included primary patency, assisted patency, limb salvage, and survival. Long-term outcomes were determined by Kaplan-Meier life-table and multivariate Cox regression analyses.ResultsThere were 104 PAOR and 97 limbs with single-vessel posterior or anterior tibial artery runoff (non-PAOR). Median follow-up was 25 months (range, 0-75 months). PAOR patients tended to be older (77.36 ± 0.92 vs 72.65 ± 1.18 years, P = .002) and were more likely to be taking clopidogrel at presentation (88% vs 76%; P = .04). There were no statistically significant differences in 5-year primary patency (26% ± 6.8% vs 30% ± 7.6%; P = .79), assisted patency (75% ± 8.8% vs 81% ± 7.0%; P = .77), limb salvage (74% ± 8.0% vs 75% ± 7.1%; P = .47), and survival (38% ± 7.7% vs 47% ± 6.6%; P = .99) between the PAOR and the non-PAOR groups, respectively. On Cox regression multivariate analysis, total occlusions predicted decreased assisted patency (hazard ratio, 2.99; 95% confidence interval, 1.21-7.41; P = .02), whereas younger age predicted poor limb salvage (hazard ratio, 0.97; 95% confidence interval, 0.94-0.99; P = .04). PAOR was not an independent predictor of any outcome on multivariate analysis.ConclusionsPatients with PAOR have similar long-term outcomes to patients with non-PAOR. Thus, infrainguinal endovascular revascularization can be considered a first-line therapy for patients with PAOR and critical limb ischemia