Risk-based methodology for parameter calibration of a reservoir flood control model

Flash floods are of major relevance in natural disaster management in the Mediterranean region. In many cases, the damaging effects of flash floods can be mitigated by adequate management of flood control reservoirs. This requires the development of suitable models for optimal operation of reservoirs. A probabilistic methodology for calibrating the parameters of a reservoir flood control model (RFCM) that takes into account the stochastic variability of flood events is presented. This study addresses the crucial problem of operating reservoirs during flood events, considering downstream river damages and dam failure risk as conflicting operation criteria. These two criteria are aggregated into a single objective of total expected damages from both the maximum released flows and stored volumes (overall risk index). For each selected parameter set the RFCM is run under a wide range of hydrologic loads (determined through Monte Carlo simulation). The optimal parameter set is obtained through the overall risk index (balanced solution) and then compared with other solutions of the Pareto front. The proposed methodology is implemented at three different reservoirs in the southeast of Spain. The results obtained show that the balanced solution offers a good compromise between the two main objectives of reservoir flood control management

X-ray microtomography analysis of the damage micromechanisms in 3D woven composites under low-velocity impact

3D woven composites reinforced with either S2 glass, carbon or a hybrid combination of both and containing either polyethylene or carbon z-yarns were tested under low-velocity impact. Different impact energies (in the range of 21–316 J) were used and the mechanical response (in terms of the impact strength and energy dissipated) was compared with that measured in high-performance, albeit standard, 2D laminates. It was found that the impact strength in both 2D and 3D materials was mainly dependent on the in-plane fiber fracture. Conversely, the energy absorption capability was primarily influenced by the presence of z-yarns, having the 3D composites dissipated over twice the energy than the 2D laminates, irrespective of their individual characteristics (fiber type, compaction degree, porosity, etc.). X-ray microtomography revealed that this improvement was due to the z-yarns, which delayed delamination and maintained the structural integrity of the laminate, promoting energy dissipation by tow splitting, intensive fiber breakage under the tup and formation of a plug by out-of-plane shear.

Numerical and experimental study of overtopping and failure of rockfill dams

This paper aims to present and validate a numerical technique for the simulation of the overtopping and onset of failure in rockfill dams due to mass sliding. This goal is achieved by coupling a fluid dynamic model for the simulation of the free surface and through-flow problems, with a numerical technique for the calculation of the rockfill response and deformation. Both the flow within the dam body and in its surroundings are taken into account. An extensive validation of the resulting computational method is performed by solving several failure problems on physical models of rockfill dams for which experimental results have been obtained by the authors.

Analysis of the discharge capacity of radial-gated spillways using CFD and ANN - Oliana Dam case study.

The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana Dam is considered as a case study and the discharge capacity is predicted both by the application of a level-set-based free-surface solver and by the use of traditional empirical formulations. The results of the analysis are then used for training an artificial neural network to allow real-time predictions of the discharge in any situation of energy head and gate opening within the operation range of the reservoir. The comparison of the results obtained with the different methods shows that numerical models such as the FEM can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways.

Fracture micromechanisms and residual stresses of a highly resistant duplex stainless steel

The paper presents some preliminary results of an ongoing research intended to qualify a highly resistant duplex stainless steel wire as prestressing steel and, gets on insight on (he wires' fracture micromechanism and residual stresses field. SEM fractographic analysis of the stainless steel wires indicates an anisotropic fracture behavior in tension, in presence of surface flaws, attributed to the residual stresses generated through the fabrication process. The residual stresses magnitude influences the damage tolerance, its knowledge being a key issue in designating/qualifying the wires as prestressing steels.

Finite elastic deformations of transversely isotropic circular cylindrical tubes

We consider the finite radially symmetric deformation of a circular cylindrical tube of a homogeneous transversely isotropic elastic material subject to axial stretch, radial deformation and torsion, supported by axial load, internal pressure and end moment. Two different directions of transverse isotropy are considered: the radial direction and an arbitrary direction in planes normal locally to the radial direction, the only directions for which the considered deformation is admissible in general. In the absence of body forces, formulas are obtained for the internal pressure, and the resultant axial load and torsional moment on the ends of the tube in respect of a general strain-energy function. For a specific material model of transversely isotropic elasticity, and material and geometrical parameters, numerical results are used to illustrate the dependence of the pressure, (reduced) axial load and moment on the radial stretch and a measure of the torsional deformation for a fixed value of the axial stretch.

Simulación hidráulica de un tramo del río Tinguiririca (Chile): aplicación al diseño de la restauración fluvial

En el marco de SERELAREFA (Semillas REd LAtina Recuperación Ecosistemas Fluviales y Acuáticos) se ha propuesto el "Corredor fluvial río Tinguiririca". Esta iniciativa persigue llegar a definir una franja de territorio donde se le permita al río expresar su dinámica natural , pero controlándola con intervenciones de ingeniería integradas en el paisaje de manera que permita un desarrollo económico más seguro en las zonas aledañas y contar con los servicios ambientales brindados por un ecosistema en buen estado. Esta comunicación presenta la problemática del río Tinguiririca y la simulación hidráulica de un tramo del mismo río en la localidad de San Fernando en el marco del diseño del Corredor Fluvial Tinguririca. Se realizó un levantamiento topográfico de detalle del tramo y se simularon caudales crecientes en 2D con Infoworks ICM.

Simplified Finite Element Assessment of Beams With and Without Shear Deformation

This paper presents a simplified finite element (FE) methodology for solving accurately beam models with (Timoshenko) and without (Bernoulli-Euler) shear deformation. Special emphasis is made on showing how it is possible to obtain the exact solution on the nodes and a good accuracy inside the element. The proposed simplifying concept, denominated as the equivalent distributed load (EDL) of any order, is based on the use of Legendre orthogonal polynomials to approximate the original or acting load for computing the results between the nodes. The 1-span beam examples show that this is a promising procedure that allows the aim of using either one FE and an EDL of slightly higher order or by using an slightly larger number of FEs leaving the EDL in the lowest possible order assumed by definition to be equal to 4 independently of how irregular the beam is loaded.

Morphology and distribution of volcanic bombs in Caldera Quemada de Arriba (Lanzarote, Canary Islands): implications for volcanic hazard analysis

Análisis del riesgo volcánico. We show the preliminary results of the study of 561 volcanic bombs ejected from a pyroclastic cone during the 1730-1736 Timanfaya eruption (Lanzarote, Canary Islands). This cone displays the highest concentration of big bombs (major axis higher than 1 m) of Timanfaya. More than 560 bombs have been studied to calculate their reach. The results suggest that bombs of 1t have a reach of 409 m, while bombs up to 28 t have a reach of 248 m. These data may be used to define a security area once a vent has been opened, but also to calculate other data such the initial velocity of ejection. The geomorphological analysis and the study of the deposits also contribute to better understand an undocumented episode of the Timanfaya eruption and also provide important data for volcanic bombs modeling for volcanic hazard analysis.

Implicaciones geotécnicas de las sucesivas reactivaciones del deslizamiento de Pajonales-Rosiana (depresión de Tirajana, Gran Canaria)

Análisis geológico geotécnico de inestabilidades de ladera en terrenos volcánicos. En este trabajo se identifican los factores que han contribuido al desarrollo y reactivación del deslizamiento de Pajonales-Rosiana. Para ello, se ha reconstruido la paleotopografía previa al deslizamiento, se ha establecido un modelo geológico de la ladera en función de la observación directa y datos de los mapas geológicos, y se ha generado un modelo geotécnico con datos bibliográficos y datos propios obtenidos en ensayos de laboratorio. Las superficies de rotura del deslizamiento de Pajonales-Rosiana se han desarrollado a través de tobas piroclásticas e ignimbritas que, al ser meteorizadas, desarrollan niveles limo-arcillosos con ángulos de fricción bajos, alta plasticidad y comportamiento expansivo. Por otra parte, la presencia de agua constituyó un factor desencadenante del deslizamiento, ya que para que se produzca la inestabilidad es necesaria la saturación total de las ignimbritas del Grupo Mogán y la saturación parcial de las lavas y piroclastos del Grupo Roque Nublo.

Application of the agency theory for the analysis of performance-based mechanisms in road management

El WCTR es un congreso de reconocido prestigio internacional en el ámbito de la investigación del transporte, y aunque las actas publicadas están en formato digital y sin ISSN ni ISBN, lo consideramos lo suficientemente importante como para que se considere en los indicadores. This paper develops a model based on agency theory to analyze road management systems (under the different contract forms available today) that employ a mechanism of performance indicators to establish the payment of the agent. The base assumption is that of asymmetric information between the principal (Public Authorities) and the agent (contractor) and the risk aversion of this latter. It is assumed that the principal may only measure the agent?s performance indirectly and by means of certain performance indicators that may be verified by the authorities. In this model there is presumed to be a relation between the efforts made by the agent and the performance level measured by the corresponding indicators, though it is also considered that there may be dispersion between both variables that gives rise to a certain degree of randomness in the contract. An analysis of the optimal contract has been made on the basis of this model and in accordance with a series of parameters that characterize the economic environment and the particular conditions of road infrastructure. As a result of the analysis made, it is considered that an optimal contract should generally combine a fixed component and a payment in accordance with the performance level obtained. The higher the risk aversion of the agent and the greater the marginal cost of public funds, the lower the impact of this performance-based payment. By way of conclusion, the system of performance indicators should be as broad as possible but should not overweight those indicators that encompass greater randomness in their results.

Analysis of alternative tendering mechanisms for transportation Public-Private Partnerships

This paper describes a theoretical model based primarily on transaction costs, for comparing the various tendering mechanisms used for transportation Public-Private Partnership (PPP) projects. In particular, the model contrasts negotiated procedures with the open procedure, as defined by the current European Union legislation on public tendering. The model includes both ex ante transaction costs (borne during the tendering stage) and ex post transaction costs (such as enforcement costs, re-negotiation costs, and costs arising from litigation between partners), explaining the trade-off between them. Generally speaking, it is assumed that the open procedure implies lower transaction costs ex ante, while the negotiated procedure reduces the probability of the appearance of new contingencies not foreseen in the contract, hence diminishing the expected value of transaction costs ex post. Therefore, the balance between ex ante and ex post transaction costs is the main criterion for deciding whether the open or negotiated procedure would be optimal. Notwithstanding, empirical evidence currently exists only on ex ante transaction costs in transportation infrastructure projects. This evidence has shown a relevant difference between the two procedures as far as ex ante costs are concerned, favouring the open procedure. The model developed in this paper also demonstrates that a larger degree of complexity in a contract does not unequivocally favour the use of a negotiated procedure. Only in those cases dealing with very innovative projects, where important dimensions of the quality of the asset or service are not verifiable, may we observe an advantage in favour of the negotiated procedure. The bottom line is that we find it difficult to justify the employment of negotiated procedures in most transportation PPP contracts, especially in the field of roads. Nevertheless, the field remains open for future empirical work and research on the levels of transaction costs borne ex post in PPP contracts, as well as on the probabilities of such costs appearing under any of the procurement procedures.

Estudio mediante modelización numérica del efecto del estado tensional inicial del terreno en la carga de rotura de un ensayo trapdoor

Uno de los fenómenos que tiene más relevancia en la estabilidad de excavaciones subterráneas es el denominado efecto arco. Su estudio se puede llevar a cabo mediante el ensayo ?trapdoor?, conocido principalmente a partir de su presentación por Terzaghi en la primera ICSMFE en 1936 [1], aunque ya con alguna referencia en el siglo XIX. En este trabajo se lleva a cabo un estudio del ensayo "trapdoor", mediante modelización numérica, con el objetivo de analizar el efecto que tiene sobre la formación del arco estable el estado tensional inicial del terreno. Para ello se ha realizado un análisis paramétrico con el programa de diferencias finitas FLAC de ITASCA. La modelización numérica posibilita este tipo de estudios al poder fijar y variar cómodamente todos los parámetros que definen el ensayo. Pero, además, permite un exhaustivo seguimiento del proceso de rotura, por lo que se facilita el análisis de los resultados obtenidos. En un ensayo ?trapdoor? la carga última es función de la geometría del problema y de las propiedades del material, particularmente de su dilatancia. No obstante, los resultados de este trabajo muestran que el estado tensional del terreno determina, conjuntamente con el resto de parámetros del material, el proceso de rotura. Así, para situaciones con una relación entre la tensión horizontal y vertical superior a 0.5, se forma un primer arco estable de dimensiones reducidas que hace que se presente un mínimo en la carga de rotura, lo cual no ocurre en caso contrario. En consecuencia, se justifica que el estado tensional inicial del terreno incide claramente en la presión necesaria para estabilizar una excavación subterránea.

Statistical mechanics approaches to granular media: between micromechanics and macromechanics

The mechanical behavior of granular materials has been traditionally approached through two theoretical and computational frameworks: macromechanics and micromechanics. Macromechanics focuses on continuum based models. In consequence it is assumed that the matter in the granular material is homogeneous and continuously distributed over its volume so that the smallest element cut from the body possesses the same physical properties as the body. In particular, it has some equivalent mechanical properties, represented by complex and non-linear constitutive relationships. Engineering problems are usually solved using computational methods such as FEM or FDM. On the other hand, micromechanics is the analysis of heterogeneous materials on the level of their individual constituents. In granular materials, if the properties of particles are known, a micromechanical approach can lead to a predictive response of the whole heterogeneous material. Two classes of numerical techniques can be differentiated: computational micromechanics, which consists on applying continuum mechanics on each of the phases of a representative volume element and then solving numerically the equations, and atomistic methods (DEM), which consist on applying rigid body dynamics together with interaction potentials to the particles. Statistical mechanics approaches arise between micro and macromechanics. It tries to state which the expected macroscopic properties of a granular system are, by starting from a micromechanical analysis of the features of the particles and the interactions. The main objective of this paper is to introduce this approach.

Statistical distributions obtained from the compression of monodisperse, soft and frictionless particles

The cyclic compression of several granular systems has been simulated with a molecular dynamics code. All the samples consisted of bidimensional, soft, frictionless and equal-sized particles that were initially arranged according to a squared lattice and were compressed by randomly generated irregular walls. The compression protocols can be described by some control variables (volume or external force acting on the walls) and by some dimensionless factors, that relate stiffness, density, diameter, damping ratio and water surface tension to the external forces, displacements and periods. Each protocol, that is associated to a dynamic process, results in an arrangement with its own macroscopic features: volume (or packing ratio), coordination number, and stress; and the differences between packings can be highly significant. The statistical distribution of the force-moment state of the particles (i.e. the equivalent average stress multiplied by the volume) is analyzed. In spite of the lack of a theoretical framework based on statistical mechanics specific for these protocols, it is shown how the obtained distributions of mean and relative deviatoric force-moment are. Then it is discussed on the nature of these distributions and on their relation to specific protocols.