Do the Volume-of-Fluid and the Two-Phase Euler Compete for Modeling a Spillway Aerator?

ABSTRACT: Spillway design is key to the effective and safe operation of dams. Typically, the flow is characterized by high velocity, high levels of turbulence, and aeration. In the last two decades, advances in computational fluid dynamics (CFD) made available several numerical tools to aid hydraulic structures engineers. The most frequent approach is to solve the Reynolds-averaged Navier?Stokes equations using an Euler type model combined with the volume-of-fluid (VoF) method. Regardless of a few applications, the complete two-phase Euler is still considered to demand exorbitant computational resources. An assessment is performed in a spillway offset aerator, comparing the two-phase volume-of-fluid (TPVoF) with the complete two-phase Euler (CTPE). Both models are included in the OpenFOAM® toolbox. As expected, the TPVoF results depend highly on the mesh, not showing convergence in the maximum chute bottom pressure and the lower-nappe aeration, tending to null aeration as resolution increases. The CTPE combined with the k?? SST Sato turbulence model exhibits the most accurate results and mesh convergence in the lower-nappe aeration. Surprisingly, intermediate mesh resolutions are sufficient to surpass the TPVoF performance with reasonable calculation efforts. Moreover, compressibility, flow bulking, and several entrained air effects in the flow are comprehended. Despite not reproducing all aspects of the flow with acceptable accuracy, the complete two-phase Euler demonstrated an efficient cost-benefit performance and high value in spillway aerated flows. Nonetheless, further developments are expected to enhance the efficiency and stability of this model

Unfolding kinetics of beta-lactoglobulin induced by surfactant and denaturant: a stopped-flow/fluorescence study

The beta ->alpha transition of beta-lactoglobulin, a globular protein abundant in the milk of several mammals, is investigated in this work. This transition, induced by the cationic surfactant dodecyltrimethylammonium chloride (DTAC), is accompanied by partial unfolding of the protein. In this work, unfolding of bovine beta-lactoglobulin in DTAC is compared with its unfolding induced by the chemical denaturant guanidine hydrochloride (GnHCl). The final protein states attained in the two media have quite different secondary structure: in DTAC the alpha-helical content increases, leading to the so-called alpha-state; in GnHCl the amount of ordered secondary-structure decreases, resulting in a random coil-rich final state (denatured, or D, state). To obtain information on both mechanistic routes, in DTAC and GnHCl, and to characterize intermediates, the kinetics of unfolding were investigated in the two media. Equilibrium and kinetic data show the partial accumulation of an on-pathway intermediate in each unfolding route: in DTAC, an intermediate (I-1) with mostly native secondary structure but loose tertiary structure appears between the native (beta) and alpha-states; in GnHCl, another intermediate (I-2) appears between states beta and D. Kinetic rate constants follow a linear Chevron-plot representation in GnHCl, but show a more complex mechanism in DTAC, which acts like a stronger binding species.info:eu-repo/semantics/publishedVersio

Three-Dimensional Characterization of Laboratory Scour Holes Around Bridge Piers

The presence of a bridge foundation leads to the formation of a scour hole, from which entrainment and transport of sediments are controlled by the turbulent structures therein developed. Hence, once formed, these scour holes interfere significantly with the scouring process in several ways, for instance, by modifying the incoming flow patterns. Therefore, a three-dimensional survey of the scour hole and the characterization of the deposition features is essential for prevention and safety control purposes. To investigate this, scouring experiments around two oblong bridge piers were performed in a tilting flume of the Portuguese National Laboratory of Civil Engineering (LNEC), under live bed flow conditions. A comprehensive characterization of laboratory scour holes was performed using two advanced image-based measuring techniques, namely close-range photogrammetry and the Kinect V2 sensor. The produced 3D bed morphology models provided detailed measurements, with significant accuracy, with quite similar results between the characterization approaches. A database for calibration and validation of numerical models is thus provided

Despedimento coletivo : combate à sindicabilidade mínima ou reapreciação do procedimento vigente?

Pretende-se com esta análise discutir se o despedimento coletivo é, pela sua natureza e complexidade, um mecanismo insuscetível de representar uma tutela efetiva e adequada dos trabalhadores abrangidos pelo mesmo ou se, pelo contrário, essa é uma realidade alcançável, mas simplesmente não atingida no sistema jurídico português. Para obter essa resposta, dividiuse a presente dissertação em três partes estruturais. Uma primeira, em que se foca na figura do despedimento coletivo e na sua vertente procedimental; uma segunda, em que se analisa a sindicabilidade judicial da decisão de despedimento; e uma última, que reflete sobre os problemas que podem advir da sua aplicação prática. Verifica-se que a solução pretendida não passa pelo alargamento dos poderes de cognição do tribunal, sendo que essa solução representaria uma violação dos princípios estruturantes do nosso ordenamento jurídico e um retrocesso na “liberalização” dos despedimentos coletivos, que alguns sistemas jurídicos, incluindo o português, têm procurado alcançar. Conclui-se que se deve, antes, defender a necessidade de aperfeiçoamento de um regime que se considera incompleto e deficiente, que não faz justiça aos direitos de participação e informação legalmente previstos, afastando-se o entendimento de que é o controlo judicial mínimo que torna este despedimento um mecanismo pouco ou não garantísticoThe aim of this analysis is to discuss whether collective dismissal is, by its nature and complexity, a mechanism that cannot adequately protect the workers involved, or whether this reality is attainable, but simply not achieved in the Portuguese regulatory framework. To achieve this answer, we decided to split our dissertation into three structural pillars. A first one, that focuses on collective dismissal and its procedural aspects; a second one, which studies the judicial review of the dismissal decision; and a final one, that makes us reflect about the problems that may arise in practical reality. Our analysis will show that the intended solution does not involve extending the court's powers of cognition, since this solution would represent a violation of structuring principles and a step backwards in the "liberation" of collective dismissals, which some regulated legal systems, including the Portuguese, are trying to achieve. It should rather focus on the improvement of an incomplete and deficient regime, which does not do justice to the worker's legal rights to participation and information, and the understanding that it is the minimum judicial control that makes collective dismissal a poor or non-guaranteed mechanism should be set aside

Investigative activities for statistics learning with 1st grade Portuguese students

The relevance of data exploration in mathematics programmes at all levels of education led us to develop a learning experience with 1st grade students with the aim of investigating the contribution of investigative activities in the learning of statistics. To achieve this objective, the following research questions were outlined: How do students implement investigative activities when learning statistics? What difficulties do students have in carrying out investigative activities when learning statistics? Adopting a qualitative and interpretative approach, data were collected through students’ written records, the reflections of the teacher, and a written test applied before and after the learning experience. The results obtained suggest that students were able to carry out investigative activities when learning statistics although with some weaknesses, namely defining the topic and research questions, and analysing the data due to the greater complexity of the research proposed by them. Students were able to formulate conclusions, although in some groups the conclusions were underdeveloped. Students were most confident in data collection, organization, and representation activities, with limitations typical of their young age (e.g., written communication). Students also showed difficulties in managing group work and knowledge of statistics, notably concerning strategies of data organization and representation and statistical measures

Computational fluid dynamics for sub-atmospheric pressure analysis in pipe drainage

[EN] The occurrence of sub-atmospheric pressure in the drainage of pipelines containing an air pocket has been known as a major cause of several serious problems. Accordingly, some system malfunction and pipe buckling events have been reported in the literature. This case has been studied experimentally and numerically in the current research considering objectives for a better understanding of: (i) the emptying process, (ii) the main parameters influencing the drainage, and (iii) the air-water interface deformation. Also, this research demonstrates the ability of a computational fluid dynamic (CFD) model in the simulation of this event. The effects of the air pocket size, the percentage and the time of valve opening on the pressure variation have been studied. Results show the pipeline drainage mostly occurs due to backflow air intrusion. The worst case scenario is associated with a fast valve opening when a tiny air pocket exists in the pipeline.This work is supported by Fundacao para a Ciencia e Tecnologia (FCT), Portugal [grant number PD/BD/114459/2016].Besharat, M.; Coronado-Hernández, OE.; Fuertes-Miquel, VS.; Viseu, MT.; Ramos, HM. (2019). Computational fluid dynamics for sub-atmospheric pressure analysis in pipe drainage. Journal of Hydraulic Research. 58(4):553-565. https://doi.org/10.1080/00221686.2019.1625819S553565584ANSYS FLUENT R19.0 academic [Computer software]. ANSYS, Canonsburg, PA. Retrieved from https://www.ansys.com/academic/free-student-productsApollonio, C., Balacco, G., Fontana, N., Giugni, M., Marini, G., & Piccinni, A. (2016). Hydraulic Transients Caused by Air Expulsion During Rapid Filling of Undulating Pipelines. Water, 8(1), 25. doi:10.3390/w8010025Benjamin, T. B. (1968). Gravity currents and related phenomena. Journal of Fluid Mechanics, 31(2), 209-248. doi:10.1017/s0022112068000133Besharat, M., Coronado-Hernández, O. E., Fuertes-Miquel, V. S., Viseu, M. T., & Ramos, H. M. (2018). Backflow air and pressure analysis in emptying a pipeline containing an entrapped air pocket. Urban Water Journal, 15(8), 769-779. doi:10.1080/1573062x.2018.1540711Besharat, M., Tarinejad, R., Aalami, M. T., & Ramos, H. M. (2016). Study of a Compressed Air Vessel for Controlling the Pressure Surge in Water Networks: CFD and Experimental Analysis. Water Resources Management, 30(8), 2687-2702. doi:10.1007/s11269-016-1310-1Besharat, M., Tarinejad, R., & Ramos, H. M. (2015). The effect of water hammer on a confined air pocket towards flow energy storage system. Journal of Water Supply: Research and Technology-Aqua, 65(2), 116-126. doi:10.2166/aqua.2015.081Besharat, M., Teresa Viseu, M., & Ramos, H. (2017). Experimental Study of Air Vessel Behavior for Energy Storage or System Protection in Water Hammer Events. Water, 9(1), 63. doi:10.3390/w9010063Collins, R. P., Boxall, J. B., Karney, B. W., Brunone, B., & Meniconi, S. (2012). How severe can transients be after a sudden depressurization? Journal - American Water Works Association, 104(4), E243-E251. doi:10.5942/jawwa.2012.104.0055Coronado-Hernández, O., Fuertes-Miquel, V., Besharat, M., & Ramos, H. (2017). Experimental and Numerical Analysis of a Water Emptying Pipeline Using Different Air Valves. Water, 9(2), 98. doi:10.3390/w9020098Coronado-Hernández, O. E., Fuertes-Miquel, V. S., Besharat, M., & Ramos, H. M. (2018). Subatmospheric pressure in a water draining pipeline with an air pocket. Urban Water Journal, 15(4), 346-352. doi:10.1080/1573062x.2018.1475578Coronado-Hernández, O. E., Fuertes-Miquel, V. S., Iglesias-Rey, P. L., & Martínez-Solano, F. J. (2018). Rigid Water Column Model for Simulating the Emptying Process in a Pipeline Using Pressurized Air. Journal of Hydraulic Engineering, 144(4), 06018004. doi:10.1061/(asce)hy.1943-7900.0001446Ding, H., Visser, F. C., Jiang, Y., & Furmanczyk, M. (2011). Demonstration and Validation of a 3D CFD Simulation Tool Predicting Pump Performance and Cavitation for Industrial Applications. Journal of Fluids Engineering, 133(1). doi:10.1115/1.4003196Fuertes-Miquel, V. S., Coronado-Hernández, O. E., Iglesias-Rey, P. L., & Mora-Meliá, D. (2018). Transient phenomena during the emptying process of a single pipe with water–air interaction. Journal of Hydraulic Research, 57(3), 318-326. doi:10.1080/00221686.2018.1492465Izquierdo, J., Fuertes, V. S., Cabrera, E., Iglesias, P. L., & Garcia-Serra, J. (1999). Pipeline start-up with entrapped air. Journal of Hydraulic Research, 37(5), 579-590. doi:10.1080/00221689909498518Laanearu, J., Annus, I., Koppel, T., Bergant, A., Vučković, S., Hou, Q., … van’t Westende, J. M. C. (2012). Emptying of Large-Scale Pipeline by Pressurized Air. Journal of Hydraulic Engineering, 138(12), 1090-1100. doi:10.1061/(asce)hy.1943-7900.0000631Liu, D., & Zhou, L. (2009). Numerical Simulation of Transient Flow in Pressurized Water Pipeline with Trapped Air Mass. 2009 Asia-Pacific Power and Energy Engineering Conference. doi:10.1109/appeec.2009.4918544Martinoia, T., Barreto, C. V., da Rocha, J. C. D. C., Lavoura, J., & Henriques, F. M. P. (2012). Simulation and Planning of Pipeline Emptying Operations. Volume 1: Upstream Pipelines; Project Management; Design and Construction; Environment; Facilities Integrity Management; Operations and Maintenance; Pipeline Automation and Measurement. doi:10.1115/ipc2012-90432Martins, N. M. C., Delgado, J. N., Ramos, H. M., & Covas, D. I. C. (2017). Maximum transient pressures in a rapidly filling pipeline with entrapped air using a CFD model. Journal of Hydraulic Research, 55(4), 506-519. doi:10.1080/00221686.2016.1275046Tijsseling, A. S., Hou, Q., Bozkuş, Z., & Laanearu, J. (2015). Improved One-Dimensional Models for Rapid Emptying and Filling of Pipelines. Journal of Pressure Vessel Technology, 138(3). doi:10.1115/1.4031508Trindade, B. C., & Vasconcelos, J. G. (2013). Modeling of Water Pipeline Filling Events Accounting for Air Phase Interactions. Journal of Hydraulic Engineering, 139(9), 921-934. doi:10.1061/(asce)hy.1943-7900.0000757Vasconcelos, J. G., & Wright, S. J. (2008). Rapid Flow Startup in Filled Horizontal Pipelines. Journal of Hydraulic Engineering, 134(7), 984-992. doi:10.1061/(asce)0733-9429(2008)134:7(984)Wang, L., Wang, F., Karney, B., & Malekpour, A. (2017). Numerical investigation of rapid filling in bypass pipelines. Journal of Hydraulic Research, 55(5), 647-656. doi:10.1080/00221686.2017.1300193Zhou, L., & Liu, D. (2013). Experimental investigation of entrapped air pocket in a partially full water pipe. Journal of Hydraulic Research, 51(4), 469-474. doi:10.1080/00221686.2013.785985Zhou, L., Liu, D., Karney, B., & Wang, P. (2013). 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Experimental characterization of the flow field around oblong bridge piers

The prediction of scour evolution at bridge foundations is of utmost importance for engineering design and infrastructures’ safety. The complexity of the scouring inherent flow field is the result of separation and generation of multiple vortices and further magnified due to the dynamic interaction between the flow and the movable bed throughout the development of a scour hole. In experimental environments, the current approaches for scour characterization rely mainly on measurements of the evolution of movable beds rather than on flow field characterization. This paper investigates the turbulent flow field around oblong bridge pier models in a well-controlled laboratory environment, for understanding the mechanisms of flow responsible for current-induced scour. This study was based on an experimental campaign planned for velocity measurements of the flow around oblong bridge pier models, of different widths, carried out in a large-scale tilting flume. Measurements of stream-wise, cross-wise and vertical velocity distributions, as well as of the Reynolds shear stresses, were performed at both the flat and eroded bed stages of scouring development with a high-resolution acoustic velocimeter. The time-averaged values of velocity and shear stress are larger in the presence of a developed scour hole than in the corresponding flat bed configuration

Debating the rules: an experimental approach to assess cyprinid passage performance thresholds in vertical slot fishways

Producción CientíficaThroughout the world, emerging barriers in river systems block longitudinal connectivity for migrating fish, causing significant impacts by precluding them from carrying out vital life cycle activities. Fishways are still the main mitigation solution implemented, where barrier removal is not feasible. Within the multiple technical fish passage devices, the vertical slot fishway (VSF) is considered the most reliable. Early design guidelines, established for cyprinids, indicate that the volumetric dissipation power (Pv) in the pools should be Pv < 150 Wm−3, while most frequent slope values range from 10 to 12%. In this study, an experimental approach was conducted to question and debate the validity of these recommendations. For this, the Iberian barbel (Luciobarbus bocagei, Steindachner, 1864) passage performance was assessed in a full-scale fishway that exceeded Pv design guidelines, under different configurations. These varied in discharge (Q) and mean pool water depth (hm): VSF1 (Q = 81 Ls−1; hm = 0.55 m); VSF2 (Q = 110 Ls−1; hm = 0.80 m); and the same design was equipped with a deep notch: DN1 (Q = 71 Ls−1; hm = 0.55 m); DN2 (Q = 99 Ls−1; hm = 0.80 m). The slope was set to 15.2% while the head drop per pool was Δh = 0.28 m, which generated a Pv that ranged from 222 in VSF1 to 187 Wm−3 in DN2. Passage behaviour was assessed using PIT telemetry and time-to-event analysis to evaluate the barbel upstream passage using standardized metrics: (i) motivation (ii) ascend success, and (iii) transit time. The hydrodynamic scenarios experienced by fish were characterized through a numerical model using computational fluid dynamics (CFD). The results, contrary to what was expected, showed a higher performance in VSF1 confirmed by the ascent analysis and transit time. Although no differences were found in fish motivation, the results indicate that larger fish displayed lower times to perform the first passage attempt. The CFD results show that, although maximum velocities and turbulence (turbulent kinetic energy (TKE) and Reynolds shear stress (RSS)) do not change significantly between configurations, their distribution in the pools is quite different. Regarding TKE, larger volumes with magnitudes higher than 0.05 m2s−2 were notorious in both DN1 and DN2 configurations compared to VSF1, influencing passage efficiency which is in line with the ascent and transit time metrics results. Overall, the present research undeniably debates the literature design guidelines and reinforces the need to jointly assess species-specific fish passage criteria and fishway hydrodynamics, whereas precaution should be taken when using very general recommendations.Fundación Portuguesa para la Ciencia y la Tecnología (FCT), Centro de Investigación e Innovación en Ingeniería Civil para la Sostenibilidad (CERIS) - (grantUIDB/04625/2020)Fundación Portuguesa para la Ciencia y la Tecnología (FCT), Centro de Investigación Forestal (CEF) - (grant UIDB/00239/2020)Fundación Portuguesa para la Ciencia y la Tecnología (FCT) - (grant PD/BD/142883/2018