ANALITICAL AND ARTIFICIAL NEURAL NETWORK MODELS OF DISCHARGE VALUE PASSING OVER OGEE SPILLWAY

In this study, analytical and Artificial Neural Network (ANN) models’ output of the discharge value, passing over Ogee Spillways, were compared. For this aim, a flume having 7.5 cm width, 15 cm depth and 5 m length, was used in the laboratory. Discharge values above the spillway were measured for different heads. Discharge values were also computed by the formula for the measured heads. An ANN model was set by using the experimental results in order to estimate the discharge value. So, the performance of the ANN model was investigated. As the result, it was seen that ANN model produced very successful output

Numerical analysis of air-water flows in hydraulic structures using computational fluid dynamics (CFD)

Tesis por compendioThe new legal regulations derived from climate change dictate that hydraulic structures must be designed to handle flood events associated with return periods up to 10,000 years. This obviously involves adapting the existing infrastructure to meet such requirements. In order to avoid risks in the restitution of the flow discharged to rivers, such as bank overflows or streambed erosion and scour processes, hydraulic design must be supported by reliable tools capable of reproducing the behavior of hydraulic structures. In the work presented herein, a fully three-dimensional CFD model to reproduce the behavior of different types of air-water flow in hydraulic structures is presented. The flow is assumed to be turbulent, isotropic and incompressible. Several RANS turbulence models are tested and structured rectangular meshes are employed to discretize the analyzed domain. The presence of two fluids is modeled using different VOF approaches and simulations are run using the PIMPLE algorithm. The model is implemented using the open-source platform OpenFOAM and its performance is compared to the commercial code FLOW-3D. The analysis is conducted separately on two different parts of hydraulic structures, namely: the spillway and the stilling basin. Additionally, a case of practical application, where the model reproduces the flow of a real-life case, is also presented in order to prove the suitability of the model to actual design cases. Mesh independence and model validation using experimental data are checked in the results of all the case studies. The sensitivity of the presented model to certain parameters is extensively discussed using different indicator variables. Among these parameters are turbulence closure, discretization scheme, surface tracking approach, CFD code or boundary conditions. Pros and contras of each of them are addressed. The analyzed turbulence models are the Standard k ¿ ¿, the Realizable k ¿ ¿, the RNG k ¿ ¿, and the SST k ¿ ¿. The discretization schemes under study are: a first-order upwind method, the second-order limited Van Leer method, and a second-order limited central difference method. The VOF approaches analyzed are the Partial VOF, as implemented in OpenFOAM, and the TruVOF, as implemented in FLOW-3D. In most cases, the Standard k ¿ ¿ model provides the most accurate estimations of water free surface profiles, although the rest of variables, with few exceptions, are better predicted by the RNG k ¿ ¿. The latter model generally requires slightly longer computation times. The SST k ¿ ¿ reproduces correctly the phenomena under study, although it generally turned out to be less accurate than its k ¿ ¿ counterparts. As regards the comparison among VOF approaches and codes, it is impossible to determine which one performs best. E.g. OpenFOAM, using the Partial VOF, managed to reproduce the in- ternal hydraulic jump structure and all derived variables better than FLOW-3D, using the TruVOF, although the latter seems to capture better the momentum transfer and so all derived variables. In the case of flow in stepped spillways, OpenFOAM captures better the velocity profiles, although FLOW-3D is more accurate when estimating the water free surface profile. It is worth remark- ing that not even their response to certain model parameters is comparable. E.g. FLOW-3D is significantly less sensitive to mesh refinement than OpenFOAM. Given the result accuracy achieved in all cases, the proposed model is fully applicable to more complex design cases, where stilling basins, stepped spillways and hydraulic structures in general must be investigated.Las nuevas disposiciones legales derivadas del cambio climático dictaminan que las estructuras hidráulicas sean capaces de funcionar correctamente con eventos de inundación asociados a periodos de retorno de hasta 10,000 años. Esto, obviamente, implica adaptar la infraestructura existente para satisfacer dichos requerimientos. A fin de evitar riesgos en la restitución de los caudales vertidos al río, como desbordamientos o procesos erosivos y de socavación, el diseño hidráulico ha de sustentarse en herramientas fiables capaces de reproducir el comportamiento de las estructuras hidráulicas. En este trabajo, se presenta un modelo numérico CFD completamente tridimensional para reproducir el comportamiento de diferentes tipos de flujo aire-agua en estructuras hidráulicas. Se asume que el flujo es turbulento, isotrópico e incompresible. Diversos modelos de turbulencia RANS son contrastados y se emplean mallas estructuradas rectanuglares para discretizar el dominio analizado. La presencia de dos fluidos es modelada utilizando diferentes enfoques VOF y las simulaciones son ejecutadas empleando el algoritmo PIMPLE. El modelo es implementado mediante la plataforma de código abierto OpenFOAM y su respuesta es comparada con la del modelo comercial FLOW-3D. El análisis se lleva a cabo sobre dos partes diferentes de una estructura hidráulica, a saber, el aliviadero y el cuenco amortiguador, de forma separada. Además, un caso de aplicación práctica, donde el modelo reproduce el flujo en una estructura real, es presentado también a fin de probar la adecuación del modelo a casos de diseño aplicado. Se comprueban la independencia de la malla y la validación con datos experimentales de los resultados de todos los casos de estudio. La sensibilidad del modelo presentado a ciertos parámetros es analizada de forma exhaustiva empleando diferentes variables indicadoras. Los pros y contras de cada uno de éstos son planteados. Los modelos de turbulencia analizados son el Standard k-epsilon, el Realizable k-epsilon, el RNG k-epsilon y el SST k-omega. Los esquemas de discretización estudiados son: un método de primer orden upwind, uno de Van Leer de segundo orden y un esquema de segundo orden limitado de diferencias centradas. Los enfoques VOF analizados son el Partial VOF, implementado en OpenFOAM, y el TruVOF, implementado en FLOW-3D. En la mayoría de casos, el modelo k-epsilon aporta las estimaciones más precisas de perfiles de lámina libre de agua, pese a que el resto de variables, con alguna excepción, son mejor predichas por el RNG k-epsilon. Este modelo generalmente requiere mayores tiempos de cálculo. El k-omega reproduce correctamente los fenómenos bajo estudio, pese a que su precisión es generalmente más baja que la de los modelos k-epsilon. En lo que respecta a la comparación entre enfoques VOF y códigos, es imposible determinar cuál es el mejor. Por ejemplo, OpenFOAM, empleando el Partial VOF, logra reproducir la estructura interna del resalto hidráulico y todas las variables derivadas mejor que FLOW-3D, empleando el TruVOF, a pesar de que este último parece capturar mejor la transferencia de cantidad de movimiento y, por tanto, todas las variables derivadas. En el caso del flujo en aliviaderos escalonados, OpenFOAM captura mejor los perfiles de velocidad, pese a que FLOW-3D es más preciso en la estimación de los perfiles de lámina libre de agua. Conviene recalcar que ni tan sólo su respuesta a ciertos parámetros del modelo es comparable. Por ejemplo, FLOW-3D es significativamente menos sensible al refinado de malla que OpenFOAM. A la luz de la precisión de los resultados obtenidos en todos los casos, el modelo propuesto es completamente aplicable a casos de diseño más complejos, donde cuencos amortiguadores, aliviaderos escalonados y estructuras hidráulicas en general han de ser investigadas.Les noves disposicions legals derivades del canvi climàtic dictaminen que cal que les estructures hidràuliques siguen capaces de funcionar correctament amb esdeveniments d'inundació associats a períodes de retorn de fins a 10,000 anys. Això, òbviament, implica adaptar la infraestrctura existent per satisfer aquests requeriments. A fi d'evitar riscs en la restitució dels cabals vessats al riu, com desbordaments o processos erosius i de socavació, el disseny hidràulic ha de recolzar-se en ferramentes fiables capaces de reproduir el comportament de les estructures hidràuliques. En aquest treball, es prsenta un model numèric CFD completament tridimensional per a reproduir el comportament de diferents tipus de flux aire-aigua en estructures hidràuliques. S'assumeix que el flux és turbulent, isotròpic i incompressible. Diferents models de turbulència RANS són contrastats i s'empren malles estructurades rectangulars per discretitzar el domini analitzat. La presència de dos fluids és modelada utilitzant diferents enfocaments VOF i les simulacions són executades emprant l'algorisme PIMPLE. El model és implementat mitjançant la plataforma de codi obert OpenFOAM i la seua resposta és comparada amb la del codi comercial FLOW-3D. L'anàlisi es du a terme sobre les diferents parts d'una estructura hidràulica, a saber, sobreeixidors esgraonats i vas esmorteïdor, de forma separada. A més, un cas d'aplicació pràctica, on el model reprodueix el flux a una estructura real, és presentat també a fi de provar l'adequació del model a casos de disseny aplicat. Es comproven la independència de la malla i la validació amb dades experimentals dels resultats de tots els casos d'estudi. La sensibilitat del model presentat a certs paràmetres és analitzada de forma exhaustiva emprant diferents variables indicadores. Els pros i contres de cadascun d'aquests són plantejats. Els models de turbulència analitzats són l'Standard k-epsilon, el Realizable k-epsilon, el RNG k-epsilon i l'SST k-omega. Els esquemes de discretització estudiats són: un mètode de primer ordre upwind, un de Van Leer de segon ordre i un esquema de segon ordre limitat de diferències centrades. Els enfocaments VOF analitzats són el Partial VOF, implementat en OpenFOAM, i el TruVOF, implementat en FLOW-3D. En la majoria de casos, el model Standard k-epsilon aporta les estimacions més precises de perfils de làmina lliure d'aigua, tot i que la resta de variables, amb alguna excepció, són millor predites pel RNG k-epsilon. Aquest model generalment requereix majors temps de càlcul. El k-omega reprodueix correctament els fenòmens sota estudi, tot i que la seua precisió és generalment més baixa que la dels models k-epsilon. Pel que fa la comparació entre enfocaments VOF i codis, és impossible determinar quin és el millor. Per exemple, OpenFOAM, emprant el Partial VOF, aconsegueix reproduir l'estructura interna del ressalt hidràulic i totes les variables derivades millor que FLOW-3D, emprant el TruVOF, tot i que aquest últim pareix capturar millor la transferència de quantitat de moviment i, per tant, totes les variables derivades. En el cas del flux en sobreeixidors esgraonats, OpenFOAM captura millor els perfils de velocitat, tot i que FLOW-3D és més precís en estimar els perfils de làmina lliure d'aigua. Cal deixar palès que ni tan sols la seua resposta a certs paràmetres del model és comparable. Per exemple, FLOW-3D és significativament menys sensible al refinament de malla que OpenFOAM. En base a la precisió dels resultats obtinguts en tots els casos, el model proposat és completament aplicable a casos de disseny més complexos, on vassos esmorteïdors, sobreeixidors esgraonats i estructures hidràuliques en general han de ser investigades.Bayón Barrachina, A. (2017). Numerical analysis of air-water flows in hydraulic structures using computational fluid dynamics (CFD) [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/90440TESISCompendi

Proceedings of the International Workshop on Hydraulic Design of Low-Head Structures - IWLHS 2013

Scientific standards applicable to publication of BAWProceedings: http://izw.baw.de/publikationen/vzb_dokumente_oeffentlich/0/2020_07_BAW_Scientific_standards_conference_proceedings.pd

Advanced Characterization of Hydraulic Structures for Flow Regime Control: Experimental Developement

A good understanding of flow in a number of hydraulic structures, such as energy dissipators, among others, is needed to effectively control upstream and downstream flow conditions, for instance, high water depth and velocity to ensure, scouring, flow stability and control scouring, which is thus crucial to ensuring safe acceptable operation. Although some previous research exists on minimizing scouring and flow fluctuations after hydraulic structures, none of this research can fully resolve all issues of concern. In this research, three types of structures were studied, as follows: a) a vertical gate; b) a vertical gate with an expansion; and c) a vertical gate with a contraction. A Stability Concept was introduced and defined to characterize the conditions downstream of gated structures. When established criteria for stability are met, erosion is prevented. This research then investigated and evaluated two methods to classify the flow downstream of a gated vii structure to easily determine stability. The two classification methods are: the Flow Stability Factor and the Flow Stability Number. The Flow Stability Factor, which is developed based on the Fuzzy Concept, is defined in the range of 0 to 1; the maximum value is one and indicates that the flow is completely stable; and the minimum value is zero and indicates that the flow is completely unstable. The Flow Stability Number is defined as the ratio of total energy at two channel sections with a maximum value of one, and it allows flow conditions to be classified for various hydraulic structures; the number is dimensionless and quantitatively defines the flow stability downstream of a hydraulic structure under critical and subcritical flow conditions herein studied, also allowing for an estimate of the downstream stable condition for operation of a hydraulic structure. This research also implemented an Artificial Neural Network to determine the optimal gate opening that ensures a downstream stable condition. A post-processing method (regression-based) was also introduced to reduce the differences in the amount of the gate openings between experimental results and artificial intelligence estimates. The results indicate that the differences were reduced approximately 2% when the post-processing method was implemented on the Artificial Neural Network estimates. This method provides reasonable results when few data values are available and the Artificial Neural Network cannot be well trained. Experiments were conducted in two laboratories, for two different scales, to investigate any possible scale effect. Results indicate, for instance, that the case of the vertical gate with an expansion performs better in producing a downstream stable condition than the other two studied structures. Moreover, it was found that smaller changes caused by expansions and contractions on the channel width show better performance in ensuring a viii downstream stable condition in the cases of a vertical gate with an expansion and a vertical gate with a contraction over a wide range of structures. Moreover, upstream flow depths in the gate with expansion are higher than in the cases of a gate and a gate with a contraction, suggesting that it may be more appropriate for agriculture applications. This research also applied Game Theory and the Nash Equilibrium Concept in selecting the best choice among various structures, under different flow expectations. In addition, the accuracy of the Flow Stability Factor and the Flow Stability number were compared. This showed that the Flow Stability Factor and the Flow Stability number had good agreement in stable conditions. Hence, the Flow Stability Factor can then be used instead of the Flow Stability number to define stable conditions, as a visual method that does not need any measurement. Importantly, a Fuzzy-based Efficiency Index, a method based on an image processing technique, was also innovatively tested to estimate the hydraulic efficiency of the hydraulic structures. The method was tested and validated using laboratory data with an average agreement of 96.45%, and then demonstrated for prototype case situations in Florida and California. These cases yielded overall efficiencies of 96% and 97.87% in Spillway Park, FL and Oroville Dam, CA, respectively. Statistical assessment was also done on the image, determining an Efficiency Index. Specifically, an image histogram was extracted from the grayscale image, then the mean and standard deviation of the histogram was used to calculate the Index. The method uses the darkness and whiteness of the image to estimate the Efficiency Index; it is easy to use, quick, low cost, and trustworthy

Dam Safety. Overtopping and Geostructural Risks

This reprintshows recent advances in dam safety related to overtopping and the prevention, detection, and risk assessment of geostructural risks. Related to overtopping, the issues treated are: the throughflow and failure process of rockfill dams; the protection of embankment dams against overtopping by means of a rockfill toe or wedge-shaped blocks; and the protection of concrete dams with highly convergent chutes. In the area of geostructural threats, the detection of anomalies in dam behavior from monitoring data using a combination of machine learning techniques, the numerical modeling of seismic behavior of concrete dams, and the determination of the impact area downstream of ski-jump spillways are also studied and discussed. In relation to risk assessment, three chapters deal with the development of fragility curves for dikes and dams in relation to various failure mechanisms

Advances in Hydraulics and Hydroinformatics Volume 2

This Special Issue reports on recent research trends in hydraulics, hydrodynamics, and hydroinformatics, and their novel applications in practical engineering. The Issue covers a wide range of topics, including open channel flows, sediment transport dynamics, two-phase flows, flow-induced vibration and water quality. The collected papers provide insight into new developments in physical, mathematical, and numerical modelling of important problems in hydraulics and hydroinformatics, and include demonstrations of the application of such models in water resources engineering

Calibrating saturated conductivity and soil cohesion in rainfall-triggered landslides in the Langhe area (1994)

In this work we have analyzed a “cold case”, i.e., the prolonged rainfall and flood event occurred in the Piedmont region (Northern Italy) in November 1994, causing several hundred of shallow landslides. The research aim is to put some focus on the possibility to calibrate soil parameters by means of the combined use of a simple hydrological model (Rosso et al. 2006) and post-event geotechnical surveys. For this purpose, a database of geometries and soil characteristics for 238 observed landslides has been used. To address the calibration of the cohesion and hydraulic conductivity parameters, the safety factor expression from the Limit Equilibrium Analysis has been targeted to assume a maximum value of 1 for all the slopes made unstable by the actual (measured) rainfall. Significant reduction of the cohesion parameter was observed after calibration, suggesting caution in the use of literature values, typically obtained on mechanically undisturbed soil sample