Metodología numérica y experimental para el diseño de los cuencos de disipación en el sobrevertido de presas de fábrica

[SPA] El incremento en la magnitud de las avenidas de diseño por efecto del cambio climático han promovido a nivel mundial, la revaluación de la capacidad de los aliviaderos y de los escenarios de operación de las grandes presas. Diversas investigaciones han demostrado que la capacidad actual de muchos aliviaderos es inadecuada, surgiendo la posibilidad de que las presas lleguen a desbordarse durante los eventos extremos. El aumento de la capacidad de los aliviaderos resulta con frecuencia caro y en ocasiones técnicamente inviable. En estos casos, los responsables de las presas se podrían plantear el desbordamiento como una estrategia adicional de operación durante estos eventos extremos. Esta situación crea nuevos escenarios en las acciones sobre la presa, surgiendo interrogantes sobre los problemas de erosión y socavación aguas abajo. En el caso específico de las presas de fábrica, la socavación en los estribos y/o en el cauce del río puede ocurrir cuando el caudal que desborda impacta sobre los diferentes materiales que constituyen la cimentación de la presa (Wahl et al., 2008). Para evaluar los requerimientos de protección de estas áreas afectadas, se requiere hacer una comparación entre el potencial hidráulico erosivo y la resistencia a la erosión de los diferentes materiales (Castillo, 2011). En este contexto, las principales agencias de gestión del agua de Estados Unidos (Bureau of Reclamation, Cuerpo de Ingenieros, etc.) vienen estudiando desde hace algunos años los efectos que los eventos extremos pueden producir en la infraestructura de regulación y evacuación de avenidas, con el objeto de reforzar adecuadamente las presas existentes y, así, evitar su destrucción (Annandale, 2006; Wahl et al., 2008). Las formulaciones existentes que cuantifican las acciones hidrodinámicas por efecto del desbordamiento de presas han sido obtenidas principalmente a partir de medidas sistematizadas de presiones instantáneas en diferentes laboratorios de hidráulica. Destacan las investigaciones en la Universidad de Glasgow (Reino Unido) (Ervine y Falvey, 1987; Ervine et al., 1997), la Escuela Técnica Federal de Lausanne (Bollaert, 2002, Bollaert y Schleiss, 2003; Manso et al., 2005; y Felderspiel, 2011); así como en la Universidad Politécnica de Cataluña y Universidad Politécnica de Cartagena (Castillo, 1989, 1990, 2002, 2006, 2007; Armengou, 1991; Castillo et al., 1991, 1996, 1999, 2007; Puertas, 1994; Puertas y Dolz, 2002, 2005; y Castillo y Carrillo, 2011, 2012, 2013). Sin embargo, la caracterización del potencial hidráulico erosivo (acciones debidas a los chorros turbulentos bifásicos) no está suficientemente analizada. Se considera necesario avanzar en su conocimiento con más estudios, tanto en modelos (físicos y numéricos) como en prototipos, caracterizando simultáneamente presiones, velocidades y fenómenos de aireación. En esta Tesis se ha llevado a cabo una investigación sobre la localización y la cuantificación de la energía residual del chorro incidente durante el desbordamiento por coronación en las presas de fábrica. En la investigación se ha utilizado tecnología tanto de tipo experimental como numérico para definir la trayectoria del chorro vertiente, caracterizar la zona de impacto, determinar la disipación de energía en el aire por fenómenos de aireación y atomización, así como la disipación de energía por los fenómenos de difusión e impacto del chorro en el cuenco disipador o zona de recepción.[ENG] The increase of the design floods due to climate change has promoted the revaluation of the spillways capacity and the operation scenarios of large dams throughout the world. Various research have shown that the current capacity of some spillways is inadequate. The studies show that many dams could overflow during extreme events. Increasing the capacity of the spillways is difficult and expensive. Sometimes, the increase is technically impossible. In these cases, dam owners may consider acceptable when their dam overflows as it is a strategy to obtain additional discharge during extreme events. This creates new scenarios for actions related to the discharge. There are questions about the scour downstream from the dam. In the specific case of concrete dams, scour at the abutments and/or the riverbed can occur when the jet overflowing over the dam impacts on the foundation of the dam (Wahl et al., 2008). To evaluate the protection requirements of these affected areas, it is required to make a comparison between the hydraulic potential of scour of the water and the erosion resistance of the materials (Castillo, 2011). In this context, the main water management agencies of the United States (Bureau of Reclamation, Corps of Engineers, etc.) have been studying for some years the effects that extreme events may generate in both, the regulatory infrastructures and the flood evacuation. The objective is to strengthen existing dams and, thus, to prevent their destruction (Annandale, 2006, Wahl et al., 2008.).The formulae that quantify hydrodynamic actions of dam overflow have mainly been obtained from systematic measurements of instantaneous pressures in different hydraulic laboratories. This is highlighted in research done at the University of Glasgow (UK) (Ervine and Falvey, 1987; Ervine et al., 1997), the Federal School of Lausanne (Bollaert, 2002, Bollaert and Schleiss, 2003; Manso et al., 2005; and Felderspiel, 2011), as well as at the Universidad Politécnica de Cataluña and Universidad Politécnica Cartagena (Castillo, 1989, 1990, 2002, 2006, 2007; Armengou, 1991; Castillo et al., 1991, 1996, 1999, 2007; Puertas, 1994; Puertas and Dolz, 2002, 2005; and Castillo and Carrillo, 2011, 2012, 2013). Nevertheless, the hydraulic potential of scour (actions due to the two-phase turbulent jets) has not been sufficiently analysed. Further studies in models (physical and numerical) and in prototypes should be done simultaneously characterising pressures, velocity and air entrainment. In this Thesis, an investigation has been carried out about the localisation and the quantification of the residual energy of the incident jet during the overflow of concrete dams. During the research, technology experimental and numerical, was used to define the trajectory of the falling jet, characterize the impact zone, determine the energy dissipation in the air due to aeration and spray phenomena, the dissipation energy for diffusion phenomena, and the impact of the jet on the stilling basin.Universidad Politécnica de CartagenaPrograma de doctorado en Medio Ambiente y Minería Sostenibl

Influence of surfactants on the electrospinnability of lignin‑PVP solutions and subsequent oil structuring properties of nanofiber mats

This work focuses on the improvement of the electrospinnability of low-sulfonate lignin (LSL)/polyvinylpyrrolidone (PVP) solutions by the addition of surfactants (SDS, CTAB and Tween-20) as well as on the ability of resulting nanofibers to structure castor oil. Solutions with two LSL/PVP weight ratios (70:30 and 90:10) in DMF were prepared by adding variable surfactant concentrations (0–1 wt.%), and physicochemically characterized. Electrical conductivity, surface tension and rheological measurements were performed. Variations of these physicochemical properties were explained on the basis of surfactant-polymer interactions. The addition of surfactants to LSL/PVP solutions improves electrospinnability, producing more compact and uniform fiber mats in 70:30 LSL/PVP systems, generally reducing the average diameter of the nanofibers and the number of beads. In contrast, nanofiber mats were not obtained with 90:10 LSL/PVP solutions, but different nanostructures composed of particle clusters. Dispersions of nanofiber mats obtained by electrospinning from 70:30 LSL/PVP solutions in castor oil were able to generate physically stable strong oleogels. In general, linear viscoelastic functions of oleogels increased with surfactant concentration. In addition, these oleogels exhibited excellent lubrication performance in a tribological contact, with extremely low values of the friction coefficient and wear diameters, which may lead to potential applications as lubricants.Research project (RTI2018-096080-B-C21) funded by MCIN/ AEI/10. 13039/ 501100011033 and by “ERDF A way of making Europe.” Funding for open access charge Universidad de Huelva/CBU

Electrospun lignin-PVP nanofibers and their ability for structuring oil

This work explores the electrospinnability of low-sulfonate Kraft lignin (LSL)/polyvinylpyrrolidone (PVP) solutions in N,N-dimethylformamide (DMF) and the ability of the different micro- and nano-architectures generated to structure castor oil. LSL/PVP solutionswere prepared at different concentrations (8–15wt%) and LSL:PVP ratios (90:10–0:100) and physico-chemically and rheologically characterized. The morphology of electrospun nanostructures mainly depends on the rheological properties of the solution. Electrosprayed nanoparticles or micro-sized particles connected by thin filamentswere obtained fromsolutionswith lowLSL/PVP concentrations and/or high LSL:PVP ratios,whereas beaded or bead-free nanofibers were produced by increasing concentration and/or decreasing LSL:PVP ratio, due to enhanced extensional viscoelastic properties and non-Newtonian characteristics. Electrospun LSL/PVP nanofibers are able to form oleogels by simply dispersing them into castor oil at concentrations between 10 and 30 wt%. The rheological properties of the oleogels may be tailored bymodifying the LSL:PVP ratio and nanofibers content. The potential application of these oleogels as bio-based lubricants was also explored in a tribological cell. Satisfactory friction and wear results are achieved when using oleogels structured by nanofibers mats with enhanced gel-like properties as lubricants. Overall, electrospinning of lignin/ PVP solutions can be proposed as a simple and effective method to produce nanofibers for oil structuringThis work is part of a research project (RTI2018-096080-B-C21) sponsored by the MICINN-FEDER I+D+i Spanish ProgrammeFunding for open access charge: Universidad de Huelva / CBU

Impact of the Morphology of Electrospun Lignin/Ethylcellulose Nanostructures on Their Capacity to Thicken Castor Oil

This study reports on a novel strategy for manufacturing thickened gel-like castor oil formulations by dispersing electrospun lignin/ethylcellulose nanostructures. These thickened formulations were rheologically and tribologically evaluated with the aim of being proposed as alternative ecofriendly lubricating greases. Low-sulfonate kraft lignin (LSL) and ethylcellulose (EC) were dissolved in a DMAc:THF mixture at different concentrations (8, 10, and 15 wt.%) and LSL:EC ratios (50:50, 70:30, and 90:10) and subjected to electrospinning. The resulting electrospun nanostructures were morphologically characterized. EC acting as the cospinning polymer improved both LSL spinnability and the oil structuring ability. Solutions with a high lignin content achieved microsized particles connected by fibrils, whereas solutions with a high EC content (50:50 ratio) and LSL/EC total concentration (10 and 15 wt.%) yielded beaded or bead-free nanofibers, due to enhanced extensional viscoelastic properties and nonNewtonian characteristics. The gel-like properties of electrospun nanostructure dispersions in castor oil were strengthened with the nanostructure concentration and the EC:LSL ratio, as a result of the formation of a more interconnected fiber network. The oleodispersions studied exhibited a satisfactory frictional response in a tribological contact, with friction coefficient values that were comparable to those achieved with traditional lithium-lubricating greases: This work was supported by MCIN/AEI/10.13039/501100011033, by “ERDF—A way of making Europe” (grant number: RTI2018-096080-BC21) and by Junta de Andalucía/EPIT2020-UHU (grant numbers: PY20_00751 and UHU202029) by the FEDER European Programm

Impact of acetylation process of kraft lignin in development of environment-friendly semisolid lubricants

The aim of this work was to study the influence of the acetylation process of kraft lignin on developing dispersions potentially applicable as new bio-based semisolid lubricants. Lignin was functionalized with acetic anhydride and pyridine as a catalyst by modifying different reaction variables (temperature, ratio of pyridine/acetic anhydride and time). Acetylated lignin was analyzed using FTIR, 1H and 13C NMR techniques, TGA, DSC and SEM to evaluate the chemical, morphological and thermal changes induced by the acetylation process. The influence of the acetylation process on the rheological and tribological properties of dispersions was related to the development of different microstructures, which depend on chemical and morphological properties of acetylated lignin. In this sense, two different rheological behaviours (gel-like or fluid-like) were found to depend on the reaction time. From the experimental results obtained, it can be concluded that the acetylation process is a key issue to modulate rheological and morphological properties of dispersions, resulting in an effective method to improve the compatibility of lignin and castor oil. Acetylated lignin with medium degrees of substitution with adequate morphological properties can be potentially used as an effective thickening agent to develop semisolid lubricants.This work is part of two research projects, RTI2018-096080-B-C21 and 802C1800001, funded by a Ministerio de Ciencia e Innovación and Junta de Andalucía Spanish programmes, respectively. The authors gratefully acknowledge the financial support.Departamento de Ingeniería Química, Química Física y Ciencias de los Materiale

Importance of physical activity in preventing and coping with stress

Uno de los factores fundamentales implicados en el proceso del estrés, y que ha demostrado determinar significativamente sus consecuencias, es el afrontamiento. El concepto de afrontamiento del estrés hace referencia a los esfuerzos conductuales y cognitivos que lleva a cabo la persona para afrontar al estrés, o lo que es lo mismo, a la habilidad para manejar tanto las demandas externas como las internas generadoras del estrés, así como al malestar psicológico que suele acompañar al mismo.One of the key factors involved in the stress process, and it has been shown to significantly determine its consequences, is coping. The concept of coping refers to the behavioral and cognitive efforts holding the person manage with stress or what it is the same, the ability to handle both, external demands as generating internal stress as well as psychological distress that often carry on with it...

Electrohydrodynamic Processing of PVP-Doped Kraft Lignin Micro- and Nano-Structures and Application of Electrospun Nanofiber Templates to Produce Oleogels

The present work focuses on the development of lignin micro- and nano-structures obtained by means of electrohydrodynamic techniques aimed to be potentially applicable as thickening or structuring agents in vegetable oils. The micro- and nano-structures used were mainly composed of eucalyptus kraft lignin (EKL), which were doped to some extent with polyvinylpyrrolidone (PVP). EKL/PVP solutions were prepared at different concentrations (10–40 wt.%) and EKL:PVP ratios (95:5–100:0) in N, N-dimethylformamide (DMF) and further physico-chemically and rheologically characterized. Electrosprayed micro-sized particles were obtained from solutions with low EKL/PVP concentrations (10 and 20 wt.%) and/or high EKL:PVP ratios, whereas beaded nanofiber mats were produced by increasing the solution concentration and/or decreasing EKL:PVP ratio, as a consequence of improved extensional viscoelastic properties. EKL/PVP electrospun nanofibers were able to form oleogels by simply dispersing them into castor oil at nanofiber concentrations higher than 15 wt.%. The rheological properties of these oleogels were assessed by means of small-amplitude oscillatory shear (SAOS) and viscous flow tests. The values of SAOS functions and viscosity depended on both the nanofiber concentration and the morphology of nanofiber templates and resemble those exhibited by commercial lubricating greases made from traditional metallic soaps and mineral oilsThis work is part of a research project (Ref. RTI2018-096080-B-C21) sponsored by the MICINN-FEDER I+D+i Spanish Programme. The authors gratefully acknowledge their financial support. J.F.R.-V. acknowledges receiving the Ph.D. Research Grant PRE2019-090632 from MICINN (Spain

Oil structuring properties of electrospun Kraft lignin/ cellulose acetate nanofibers for lubricating applications: influence of lignin source and lignin/cellulose acetate ratio

In the present work, electrospun Kraft lignin/cellulose acetate nanostructures were produced, assessed and proposed as structuring or thickening agents of castor oil for lubricating applications. Solutions of Kraft lignins (KL) derived from different sources (eucalyptus, poplar and olive tree pruning) and cellulose acetate (CA) were prepared and used as feed for electrospinning. The rheological properties (shear and extensional viscosity), electrical conductivity and surface tension of KL/CA solutions influence the morphology of the electrospun nanofibers, which in turn is affected by the chemical structure and composition of the Kraft lignins. Electrospun KL/CA nanostructures consisting of filament-interconnected nanoparticles, beaded nanofibers or uniform nanofiber mats were able to form gel-like homogeneous fine dispersions by simply mechanically dispersing them into castor oil. The swelling of KL/ CA nanofibers in the percolation network was demonstrated. The rheological, tribological and microstructural properties of these oleogels are essentially governed by the morphological characteristics of the electrospun nanostructures, i.e. fiber diameter, number of beads and porosity. Rheological properties of the resulting oleogels may be tailored by modifying the lignin source and KL:CA weight ratio. According to their rheological and tribological properties, KL/ CA electrospun nanostructures-based oleogels can be proposed as a sustainable alternative to conventional lubricating greases.This work is part of a research project (RTI2018-096080-B-C21) funded by MCIN/AEI/10. 13039/501100011033 and by “ERDF A way of making Europe”. J.F. Rubio-Valle has also received a Ph.D. Research Grant PRE2019-090632 from Ministerio de Ciencia e Innovación (Spain). The financial support is gratefully acknowledged. Universidad de Huelva/CBUA thanks to the CRUE-CSIC agreement with Springer Nature

Production of lignin/cellulose acetate fiber-bead structures by electrospinning and exploration of their potential as green structuring agents for vegetable lubricating oils

In this work we developed electrospun lignin/cellulose acetate fiber-bead nanostructures and explored their potential as structuring agents for vegetable oils to be used as eco-friendly lubricating oleogels. A variety of nanostructures were obtained from solutions containing 20 or 30 wt. % eucalyptus Kraft lignin (EKL) and cellulose acetate (CA) in variable weight ratios from 100:0 to 60:40 in an N,N-dimethylformamide/acetone mixture. The EKL/CA solutions were characterized in physicochemical terms from viscosity, surface tension and electrical conductivity measurements. Also, the electrospun nanostructures were characterized morphologically by scanning electron microscopy. Their morphology was found to be strongly dependent on the rheological properties of the biopolymer solution. Electrospun EKL/CA beaded nanofibers and well-developed uniform nanofiber mats allowed oleogels to be easily obtained by simply dispersing them in castor oil whilst nanoparticle clusters gave rise to unstable dispersions. The rheological properties of these gel-like dispersions can be tailored through the membrane concentration and/or EKL/CA ratio and depend to a large extent on the morphology of the electrospun nanostructures. The rheological and tribological properties of the oleogels were comparable to those previously reported for conventional and other bio-based lubricating greases. Overall, electrospun EKL/CA nanofibers allow easy, efficient structuring of vegetable oils to obtain oleogels holding potential for use as lubricants.Research Project RTI2018–096080-B-C21, funded by MCIN/AEI/10.13039/501100011033 and “ERDF A way of making Europe”. PhD Research Grant PRE2019–090632 from Spain’s Ministry of Science and Innovation. Funding for open access charge: Universidad de Huelva / CBU