Analysis of the performance of a hybrid CPU/GPU 1D2D coupled model for real flood cases

Coupled 1D2D models emerged as an efficient solution for a two-dimensional (2D) representation of the floodplain combined with a fast one-dimensional (1D) schematization of the main channel. At the same time, high-performance computing (HPC) has appeared as an efficient tool for model acceleration. In this work, a previously validated 1D2D Central Processing Unit (CPU) model is combined with an HPC technique for fast and accurate flood simulation. Due to the speed of 1D schemes, a hybrid CPU/GPU model that runs the 1D main channel on CPU and accelerates the 2D floodplain with a Graphics Processing Unit (GPU) is presented. Since the data transfer between sub-domains and devices (CPU/GPU) may be the main potential drawback of this architecture, the test cases are selected to carry out a careful time analysis. The results reveal the speed-up dependency on the 2D mesh, the event to be solved and the 1D discretization of the main channel. Additionally, special attention must be paid to the time step size computation shared between sub-models. In spite of the use of a hybrid CPU/GPU implementation, high speed-ups are accomplished in some cases

Use of internal boundary conditions for levees representation: application to river flood management

River floods can be simulated with the 2D shallow water system of equations using finite volume methods, where the terrain is discretized in cells that form the computational mesh. Usually a proper treatment of wet/dry fronts is required. River levees can be modelled as part of the topography by means of sufficiently small cells of higher elevation than the rest of the bed level in locally refined meshes. This procedure is associated with a large computational time since the time step depends directly on the cell size. The alternative proposed in this work includes the levees as internal boundary conditions in the 2D numerical scheme. In particular, levees have been defined by a weir law that, depending on the relative values of water surface levels on both sides, can formulate the discharge for different situations (i.e. free flow and submerged flow). In addition, having identified numerical difficulties in cases of low discharge under free flow conditions, a novel procedure to avoid oscillations has been developed and called volume transport method. The validation and comparison between methods has been carried out with benchmark test cases and, in addition, with a real flood event in the Ebro River (Spain)

Simulation of PID control applied to irrigation channels

Open-channel flow usually includes many hydraulic elements to help with the regulation of water supply in terms of automatic control. On the other hand, the one-dimensional Shallow Water Equations (SWE) are widely used to model and predict the flow dynamics in this kind of configurations. In this work, the unsteady SWE are used to model the water motion and they are solved using a finite volume upwind scheme able to cope with all flow regimes. Furthermore, the regulation of hydraulic structures at channels is frequently based on the PID controller. In this work, the implementation and coupling of the channel flow simulation with hydraulic elements and PID regulation is performed

A Riemann coupled edge (RCE) 1D–2D finite volume inundation and solute transport model

A novel 1D–2D shallow water model based on the resolution of the Riemann problem at the coupled grid edges is presented in this work. Both the 1D and the 2D shallow water models are implemented in a finite volume framework using approximate Roe’s solvers that are able to deal correctly with wet/dry fronts. After an appropriate geometric link between the models, it is possible to define local Riemann problems at each coupled interface and estimate the contributions that update the cell solutions from the interfaces. The solute transport equation is also incorporated into the proposed procedure. The numerical results achieved by the 1D–2D coupled model are compared against a complete 2D model, which is considered the reference solution. The computational time is also examined

A model for computing thermally-driven shallow flows

In many natural disasters such as overland oil spills or lava flows, physical fluid properties as density change when considering non-homogeneous spatial and time variable distributions of the temperature. This effect is even more remarkable when these flows show a non-Newtonian behaviour due to the sensitivity of their rheological properties as viscosity or yield stress to temperature. In these cases, temperature becomes a significant variable that drives the fluid behaviour, which must be solved using an energy equation coupled with the free surface flow system. Special attention is devoted to thermal source terms which must include all the heat fluid exchanges, and their modelling sometimes can govern the complete flow behaviour. Fluid density, viscosity and yield stress, also affected by temperature, must be recomputed every time step. Summarizing, this work presents a 2D free surface flow model considering density and temperature variations, which could even modify viscosity and yield stress, with heat transfer mechanisms. The model is applied to oil spill overland simulations and heating/cooling test cases are carried out to ensure the system energy balance. As conclusions, it can be said that the numerical results demonstrate the importance of the heat exchange effects and those of the density, viscosity and yield stress variations

Validation and simulation of a regulated survey system through Monte Carlo techniques

[EN] Channel flow covers long distances and obeys to variable temporal behaviour. It is usually regulated by hydraulic elements as lateral gates to provide a correct of water supply. The dynamics of this kind of flow is governed by a partial differential equations system named shallow water model. They have to be complemented with a simplified formulation for the gates. All the set of equations form a non-linear system that can only be solved numerically. Here, an explicit upwind numerical scheme in finite volumes able to solve all type of flow regimes is used. Hydraulic structures (lateral gates) formulation introduces parameters with some uncertainty. Hence, these parameters will be calibrated with a Monte Carlo algorithm obtaining associated coefficients to each gate. Then, they will be checked, using real cases provided by the monitorizing equipment of the Pina de Ebro channel located in Zaragoza.[ES] El flujo en canales se caracteriza por cubrir largas distancias y obedecer a patrones temporales variables. Suele estar regulado por elementos hidráulicos, como compuertas laterales, para asegurar un correcto abastecimiento de agua. La dinámica de este flujo viene gobernada por un sistema de ecuaciones diferenciales en derivadas parciales llamado de aguas poco profundas. Junto a ellas es necesario establecer una formulación simplificada del funcionamiento de las compuertas. El conjunto forma un sistema no lineal que sólo se puede resolver numéricamente. Aquí se propone un esquema descentrado explícito de volúmenes finitos con el fin de resolver todo tipo de regímenes. La modelización de las estructuras hidráulicas (compuertas laterales) introduce parámetros con incertidumbre. Por ello, serán calibradas mediante el algoritmo de Monte Carlo, obteniendo como resultado unos coeficientes asociados a cada una de ellas. Posteriormente serán verificadas utilizando casos reales proporcionados por el equipo de monitorización del canal de Pina de Ebro (Zaragoza).Los autores de este trabajo agradecen la financiación del Ministerio de Ciencia e Innovación (BIA2011-30192-C02-01), a D. Angel Usón, gestor la Comunidad de Regantes de Pina de Ebro y a la empresa Riegosalz, S.LLacasta Soto, A.; Morales-Hernández, M.; Tejero-Juste, M.; Burguete, J.; Brufau, P.; García-Navarro, P. (2015). Calibración y simulación de un sistema regulado de suministro de agua a través de técnicas de Monte Carlo. Ingeniería del Agua. 19(3):117-133. https://doi.org/10.4995/ia.2015.3350SWORD117133193Albertson, M. L., Dai, Y., Jensen, R. A., Rouse, H. (1950). Diffusion of submerged jets. Transactions of the American Society of Civil Engineers, 115(1), 639-664.Burguete, J., García-Navarro, P. (2004). Improving simple explicit methods for unsteady open channel and river flow. International Journal for Numerical Methods in Fluids 45, 125-156. doi:10.1002/fld.619Burguete, J., Calibrator, https://github.com/jburguete/calibrator.Ferro, V. (2000). Simultaneous flow over and under a gate. Journal of irrigation and drainage engineering, 126(3), 190-193. doi:10.1061/(ASCE)0733-9437(2000)126:3(190)García-Navarro, P., Brufau, P., Murillo, J., Zorraquino, C. (2003). Estudio hidráulico del riesgo de inundación en el meandro de Ranillas: Modelos de simulación numérica. Ingeniería del Agua, 10, 115-125.Habibzadeh, A., Vatankhah, A. R., Rajaratnam, N. (2011). Role of energy loss on discharge characteristics of sluice gates. Journal of Hydraulic engineering, 137(9), 1079-1084. doi:10.1061/(ASCE)HY.1943-7900.0000406Henderson, F. M. (1996). Open channel flow. Macmillan. ISO 690 .Lozano, D., Mateos, L., Merkley, G. P., Clemmens, A. J. (2009). Field calibration of submerged sluice gates in irrigation canals. Journal of irrigation and drainage engineering, 135(6), 763-772. doi:10.1061/(ASCE)IR.1943-4774.0000085Lacasta, A., Morales-Hernández, M., Brufau, P., García-Navarro, P. (2014). A simulation based tool for PID control in canals: application to the Pina de Ebro irrigation community. En Proc. Cong. On Industrial & Agricultural Canals, septiembre 2-5, Lleida, España.Li, Y., Cantoni, M., Weyer, E. (2005). On water-level error propagation in controlled irrigation channels. En Proc. 44th IEEE Conf. on Decidion and Control, and the Europ. Control Conf., Diciembre 12-15, Sevilla, España.Lin, C., Yen, J., Tsai, C. (2002). Influence of Sluice Gate Contraction Coefficient on Distinguishing Condition. Journal of Irrigation and Drainage Engineering, 128(4), 249-252. doi:10.1061/(ASCE)0733-9437(2002)128:4(249)Morales-Hernández, M., García-Navarro, P., Burguete, J., Brufau, P. (2013a). A conservative strategy to couple 1D and 2D models for shallow water flow simulation. Computers & Fluids, 81, 26-44. doi:10.1016/j.compfluid.2013.04.001Morales-Hernández, M., Murillo, J., García-Navarro, P. (2013b). The formulation of internal boundary conditions in unsteady 2-D shallow water flows: application to flood regulation. Water Resources Research, 49(1), 471-487. doi:10.1002/wrcr.20062Pongput K., Merkley G. P., (1997). Comparison and calibration of canal gate automation algorithms. Journal of irrigation and drainage engineering, 123(3), 222-225. doi:10.1061/(ASCE)0733-9437(1997)123:3(222)Rajaratnam, N., Subramanya, K. (1967). Flow equation for the sluice gate. Journal of Irrigation and Drainage Engineering, 93(3), 167-186.Shamir, U., Howard, C. D. D. (1968). Water Distribution Systems Analysis, En Proc ASCE, Vol. 94, No. HY1, 219-234Skogerboe, G. V., Merkley, G. P. (1996). Irrigation maintenance and operations learning process. Water Resources Publication.Swamee, P. K. (1992). Sluice-gate discharge equations. Journal of Irrigation and Drainage Engineering, 118(1), 56-60. doi:10.1061/(ASCE)0733-9437(1992)118:1(56

Plasma bile acids are not associated with energy metabolism in humans

Bile acids (BA) have recently been shown to increase energy expenditure in mice, but this concept has not been tested in humans. Therefore, we investigated the relationship between plasma BA levels and energy expenditure in humans. Type 2 diabetic (T2DM) patients (n = 12) and gender, age and BMI-matched healthy controls (n = 12) were studied before and after 8 weeks of treatment with a BA sequestrant. In addition, patients with liver cirrhosis (n = 46) were investigated, since these display elevated plasma BA together with increased energy expenditure. This group was compared to gender-, age- and BMI-matched healthy controls (n = 20). Fasting plasma levels of total BA and individual BA species as well as resting energy expenditure were determined. In response to treatment with the BA sequestrant, plasma deoxycholic acid (DCA) levels decreased in controls (-60%, p &lt;0.05) and T2DM (-32%, p &lt;0.05), while chenodeoxycholic acid (CDCA) decreased in controls only (-33%, p &lt;0.05). Energy expenditure did not differ between T2DM and controls at baseline and, in contrast to plasma BA levels, was unaffected by treatment with the BA sequestrant. Total BA as well as individual BA species did not correlate with energy expenditure at any time throughout the study. Patients with cirrhosis displayed on average an increase in energy expenditure of 18% compared to values predicted by the Harris-Benedict equation, and plasma levels of total BA (up to 12-fold) and individual BA (up to 20-fold) were increased over a wide range. However, neither total nor individual plasma BA levels correlated with energy expenditure. In addition, energy expenditure was identical in patients with a cholestatic versus a non-cholestatic origin of liver disease while plasma total BA levels differed four-fold between the groups. In conclusion, in the various (patho) physiological conditions studied, plasma BA levels were not associated with changes in energy expenditure. Therefore, our data do not support an important role of circulating BA in the control of human energy metabolism.</p

Efficient numerical computation and experimental study of temporally long equilibrium scour development around abutment

YesFor the abutment bed scour to reach its equilibrium state, a long flow time is needed. Hence, the employment of usual strategy of simulating such scouring event using the 3D numerical model is very time consuming and less practical. In order to develop an applicable model to consider temporally long abutment scouring process, this study modifies the common approach of 2D shallow water equations (SWEs) model to account for the sediment transport and turbulence, and provides a realistic approach to simulate the long scouring process to reach the full scour equilibrium. Due to the high demand of the 2D SWEs numerical scheme performance to simulate the abutment bed scouring, a recently proposed surface gradient upwind method (SGUM) was also used to improve the simulation of the numerical source terms. The abutment scour experiments of this study were conducted using the facility of Hydraulics Laboratory at Nanyang Technological University, Singapore to compare with the presented 2D SGUM-SWEs model. Fifteen experiments were conducted over a total period of 3059.7 hours experimental time (over 4.2 months). The comparison shows that the 2D SGUM-SWEs model gives good representation to the experimental results with the practical advantage

Flow structure in a compound channel: benchmarking 2D and 3D numerical models

The benchmarking test of 2D and 3D numerical models on a compound channel flow with a rectangular-shaped main channel and a rectangular-shaped floodplain was carried out by the IAHR Working Group on Compound Channels. The selected test case is the flume experiment by Nezu and Tominaga (1991). Nine depth-averaged 2D models and four 3D models participated in the benchmark. In the 2D models, the depth-averaged streamwise velocity profiles in the lateral direction were compared. In the 3D models, velocity components in three directions as well as the distribution of the turbulence kinetic energy in a cross-section were compared. Through the comparison, the applicability and limitations of each model are highlighted and discussed with regard to the model characteristics.Konferencija je održana na daljinu (on-line), bez fizičkog prisustva i sav materijal se nalazi na web-stranici organizatora skupa

Leaching material from Antarctic seaweeds and penguin guano affects cloud-relevant aerosol production

Within the Southern Ocean, the greatest warming is occurring on the Antarctic Peninsula (AP) where clear cryospheric and biological consequences are being observed. Antarctic coastal systems harbour a high diversity of marine and terrestrial ecosystems heavily influenced by Antarctic seaweeds (benthonic macroalgae) and bird colonies (mainly penguins). Primary sea spray aerosols (SSA) formed by the outburst of bubbles via the sea-surface microlayer depend on the organic composition of the sea water surface. In order to gain insight into the influence of ocean biology and bio-geochemistry on atmospheric aerosol, we performed in situ laboratory aerosol bubble chamber experiments to study the effect of different leachates of biogenic material - obtained from common Antarctic seaweeds as well as penguin guano - on primary SSA. The addition of different leachate materials on a seawater sample showed a dichotomous effect depending on the leachate material added - either suppressing (up to 52%) or enhancing (22–88%) aerosol particle production. We found high ice nucleating particle number concentrations resulting from addition of guano leachate material. Given the evolution of upper marine polar coastal ecosystems in the AP, further studies on ocean-atmosphere coupling are needed in order to represent the currently poorly understood climate feedback processes.The study was further supported by the Spanish Ministry of Economy through project PI-ICE (no. CTM 2017–89117-R) and the Ramon y Cajal fellowship (no. RYC-2012-11922). This work acknowledges the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). The National Centre for Atmospheric Science (NCAS) Birmingham group is funded by the UK Natural Environment Research Council. We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation, Projektnummer 268020496–TRR 172) within the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3” in subproject B04.Peer reviewe