Simulations of liquid metal flows over plasma-facing component edges and application to beryllium melt events in JET

Navier-Stokes simulations of liquid beryllium flows over the straight edge of plasma-facing components are carried out in conditions emulating upper dump plate melting observed experimentally in JET. The results demonstrate the existence of three main hydrodynamic regimes featuring various degrees of downstream flow attachment to the underlying solid surface. Transitions between these regimes are characterized by critical values of the Weber number, which quantifies the relative strength of fluid inertia and surface tension, thereby providing a general stability criterion that can be applied to any instance of transient melt events in fusion devices. The predictive capabilities of the model are tested by comparing numerical output with JET data regarding the morphology of the frozen melt layers and the location of beryllium droplets splashed onto nearby vacuum vessel surfaces as a result of disruption current quench plasmas interacting with the solid beryllium tiles protecting the upper main chamber regions. Simulations accounting for the coupling between fluid flow and heat transfer confirm the key role played by re-solidification as a stabilizing process, as previously found through macroscopic melt dynamics calculations performed with the MEMOS-U code. The favourable agreement found between the simulations and the general characteristics of the JET beryllium upper dump plate melt splashing give confidence that the same approach can be applied to estimate the possibility of such mechanisms occurring during disruptions on ITER.

Buoyancy-driven algebraic (localised) boundary-layer disturbances

We show that a new class of steady linear eigenmodes exist in the Falkner–Skan boundary layer, associated with an algebraically developing, thermally coupled three-dimensional perturbation that remains localised in the spanwise direction. The dominant mode has a weak temperature difference that decays (algebraically) downstream, but remains sufficient (for favourable pressure gradients that are below a critical level) to drive an algebraically growing disturbance in the velocity field. We determine the critical Prandtl number and pressure gradient parameter required for downstream algebraic growth. We also march the nonlinear boundary-region equations downstream, to demonstrate that growth of these modes eventually gives rise to streak-like structures of order-one aspect ratio in the cross-sectional plane. Furthermore, this downstream flow can ultimately become unstable to a two-dimensional Rayleigh instability at finite amplitudes.

The Impact of Variable Horizon Shade on the Growing Season Energy Budget of a Subalpine Headwater Wetland

Surface energy budgets are important to the ecohydrology of complex terrain, where land surfaces cycle in and out of shadows creating distinct microclimates. Shading in such environments can help regulate downstream flow over the course of a growing season, but our knowledge on how shadows impact the energy budget and consequently ecohydrology in montane ecosystems is very limited. We investigated the influence of horizon shade on the surface energy fluxes of a subalpine headwater wetland in the Canadian Rocky Mountains during the growing season. During the study, surface insolation decreased by 60% (32% due to evolving horizon shade and 28% from seasonality). The influence of shade on the energy budget varied between two distinct periods: (1) Stable Shade, when horizon shade was constant and reduced sunlight by 2 h per day; and (2) Dynamic Shade, when shade increased and reduced sunlight by 0.18 h more each day, equivalent to a 13% reduction in incoming shortwave radiation and 16% in net radiation. Latent heat flux, the dominant energy flux at our site, varied temporally because of changes in incoming radiation, atmospheric demand, soil moisture and shade. Horizon shade controlled soil moisture at our site by prolonging snowmelt and reducing evapotranspiration in the late growing season, resulting in increased water storage capacity compared to other mountain wetlands. With the mounting risk of climate-change-driven severe spring flooding and late season droughts downstream of mountain headwaters, shaded subalpine wetlands provide important ecohydrological and mitigation services that are worthy of further study and mapping. This will help us better understand and protect mountain and prairie water resources.

An Efficient Hybrid Grey Wolf Optimization Based KELM Approach for Prediction of the Discharge Coefficient of Submerged Radial Gates

Radial gates are widely used hydraulic structures for flow control in irrigation canals. Accurately prediction of discharge coefficient through radial gates is considered as a challenging hydraulic subject, particularly under highly submerged flow conditions. Incurring the advantages of Kernel-depend Extreme Learning Machine (KELM), this study offers a Grey Wolf Optimization-based KELM (GWO-KELM) for effective prediction of discharge coefficient through submerged radial gates. Additionally, Support Vector Machine (SVM), and Gaussian Process Regression (GPR) methods are also presented for comparative purposes. To build prediction models using GWO-KELM, GPR, and SVM an extensive experimental database was established, consisting of 2125 data samples gathered by the US Bureau of Reclamation. From simulation results, it is observed that the proposed GWO-KELM approach with input parameters of the ratio of the downstream flow depth to the gate opening (y3/w) and submergence ratio (y1-y3/w) provides the best performance with the correlation coefficient (R) of 0.983, the Determination Coefficient (DC) of 0.966 and the Root Mean Squared Error (RMSE) of 0.027. Furthermore, the obtained results showed that the employed kernel-depend methods are capable of a statistically predicting the discharge coefficient under varied submergence conditions with satisfactory level of accuracy.

Impacts of structural parameters of baffle plate on jetting pigging robot in the underwater oil and gas pipeline

During the operation of oil and gas transportation pipeline, condensate forms on the inner wall of the pipeline can lead to reduced transportation efficiency and potential safety hazards. Pigging is a widely used technology to remove deposition in pipelines. From the studies, it is found that the effect of pigging largely depends on the structure of the pig. The jetting pig is a new type of pigging device designed to prevent the blocking in the pigging process, and its baffles play an important role in guiding the jet fluid. In this paper, the impact of the structure of the baffle plate on the downstream flow field of the jetting pig is simulated and analyzed. The surface of the baffle plate is changed by using the curve of the contraction section of the water tunnel. It is found that the baffle plate structure has a great influence on the flow field at the outlet of the jet pig: (1) The increase of buffle area leads to the increase of turbulent kinetic energy and the decrease of velocity; (2) The rise of edge angle lead to the regular change of turbulent kinetic energy; (3) Different curved surfaces make the change of turbulent kinetic energy and velocity. The results in this study are helpful for a better understanding of mechanism of jetting pig and improved design of mechanical structure for improved pigging performance.

Improvement of Downstream Flow by Modifying SWAT Reservoir Operation Considering Irrigation Water and Environmental Flow from Agricultural Reservoirs in South Korea

This study aims to develop a reservoir operation rule adding downstream environmental flow release (EFR) to the exclusive use of irrigation water supply (IWS) from agricultural reservoirs through canals to rice paddy areas. A reservoir operation option was added in the Soil and Water Assessment Tool (SWAT) to handle both EFR and IWS. For a 366.5 km2 watershed including three agricultural reservoirs and a rice paddy irrigation area of 4744.7 ha, the SWAT was calibrated and validated using 21 years (1998–2018) of daily reservoir water levels and downstream flow data at Gongdo (GD) station. For reservoir water level and streamflow, the average root means square error (RMSE) ranged from 19.70 mm to 19.54 mm, and the coefficient of determination (R2) and Nash–Sutcliffe efficiency (NSE) had no effect on the improved SWAT. By applying the new reservoir option, the EFR amount for a day was controlled by keeping the reservoir water level up in order to ensure that the IWS was definitely satisfied in any case. The downstream mean wet streamflow (Q95) decreased to 5.70 m3/sec from 5.71 m3/sec and the mean minimum flow (Q355) increased to 1.05 m3/sec from 0.94 m3/sec. Through the development of a SWAT reservoir operation module that satisfies multiple water supply needs such as IWR and EFR, it is possible to manage agricultural water in the irrigation period and control the environmental flow in non-irrigation periods. This study provides useful information to evaluate and understand the future impacts of various changes in climate and environmental flows at other sites.

Changes in Ecosystems of Bodies of Water Resulting from of the Aaggregates Extraction

The evaluation issues on the aggregate’s extraction on the ecosystem of bodies of water has been considered. The dredgers' impact of various capacities on bodies of water of different capacities have been compared, as well as on food supply change of bodies of water for benthos eater. The research findings have showed the dragger's impact of a higher capacity is bigger on a large body of water than this of a lower capacity on a small body of water. The impact manifests itself in decreasing the number and biomass of macrozoobenthos in the area used for the oil and lubricants extraction and the downstream flow. It has been found that the complete destruction of macrozoobenthos at the site of hydraulic engineering activities has not been detected either in small rivers or in large reservoirs.

Design Parameter Influence on Losses and Downstream Flow Field Uniformity in Supersonic ORC Radial-Inflow Turbine Stators

The design of organic Rankine cycle (ORC) turbines often requires dealing with transonic flows due to the cycle efficiency requirements and the matching of the temperature profiles with heat sources and sinks, as well as the nature of organic fluids, often featuring high molecular weight. Consequently, the use of convergent–divergent turbine stators has been widely established as a solution in the published literature for use in both axial- and radial-inflow machines. With respect to the latter layout in particular, the available design guidelines are still limited. The present work shows the results of an investigation into a series of ORC radial-inflow convergent–divergent nozzles that differ with respect to the vane count and the designed metal angle of the outlet. These stators were designed by fitting the divergent portion of a sharp-edged minimum-length nozzle, designed by means of the method of characteristics (MoC) adapted to dense gases, into a radial-inflow turbine stator. The geometries were analysed by means of steady-state RANS CFD calculations, and the results were used to assess the influence of the design parameters on the nozzle losses and downstream flow field uniformity, showing that conflicting trends exist between optimum stator efficiency and optimum downstream flow field uniformity.

A laboratory study of the effect of asymmetric-lattice collar shape and placement on scour depth and flow pattern around the bridge pier

In this study, the effect of collar shape and its alignment on reducing scour depth in the front part of the structure, with the pier under clear water conditions, was investigated to determine changes in the flow pattern around the structure. The collars were examined in two asymmetrical shapes with dimensions of and at three levels of installation relative to the bed: bed level, 1 and 2 cm above the bed. The results revealed that the presence of the collar not only reduced the ultimate scouring depth but also delayed the formation of the scouring hole. This impact was observed to be greater as the size of the collar increased. In addition, reducing the alignment of the collars can lead to better performance of the collar and its efficiency in the cost of the design. Therefore, collars installed on the bed surface indicated good performance in controlling scour. On the other hand, once the flow characteristics around the bridge pier with and without collar were examined, it was determined that affecting the downstream flow reduces the strength of the vortices and changes the reciprocating behavior and the displacement of the vortices.

Venous activation of MEK/ERK drives development of arteriovenous malformation and blood 2 flow anomalies with loss of Rasa1

Vascular malformations develop when growth pathway signaling goes awry in the endothelial cells lining blood vessels. Arteriovenous malformations (AVMs) arise where arteries and veins abnormally connect in patients with loss of RASA1, a Ras GTPase activating protein, and, as we show here, in zebrafish rasa1 mutants. Mutant fish develop massively enlarged vessels at the connection between artery and vein in the tail vascular plexus. These AVMs progressively enlarge and become filled with slow-flowing blood and have a greater drop in pulsatility from the artery to the vein. Expression of the flow responsive transcription factor klf2a is diminished in rasa1 mutants, suggesting changes in flow velocity and pattern contribute to the progression of vessel malformations. Migration of endothelial cells is not affected in rasa1 mutants, nor is cell death or proliferation. Early developmental artery-vein patterning is also normal in rasa1 mutants, but we find that MEK/ERK signaling is ectopically activated in the vein as compared to high arterial activation seen in wildtype animals. MEK/ERK signaling inhibition prevents AVM development of rasa1 mutants, demonstrating venous MEK/ERK drives the initiation of rasa1 AVMs. Thus, rasa1 mutants show overactivation of MEK/ERK signaling causes AVM formation, altered blood flow and downstream flow responsive signaling.