A physically-based approach for evaluating the hydraulic invariance in urban transformations

Transformation of urban areas satisfies hydraulic invariance (HI) if the maximum flow rate outgoing the area stays unchanged. The HI can be respected by dimensioning appropriate water storage volumes or low impact developments (LID) to balance the soil sealing and ground levelling effects. In order to comply with HI, some Italian regional legislation and river basin authority provide for the creation of storage tanks whose volume must be estimated through simple conceptual rainfallrunoff models. In this work a physically based approach for evaluating HI is proposed. It is based on interpolating the results from a large number of hydraulic simulations conducted using FullSWOF, which is an open source code developed by the University of Orléans. In this software the shallow water equations are solved using a finite volume scheme and friction laws and infiltration models are included. Simulations have been carried out considering the effect of three properties of the area, that is: the saturated hydraulic conductivity of soil, the slope of ground surface and the standard deviation of ground elevation around the mean level. Using the results, interpolating laws for the peak discharge and the critical rainfall duration as function of the three basin parameters have been derived. A parametric hydrograph as a function of the basin parameters and rainfall duration is defined and a HI evaluation method based on routing the parametric hydrograph is proposed. The results from this approach have been compared with those from non-physically based methods currently used, such as the direct rainfall approach and the linear reservoir approach. The comparison shows that the difference between these conceptual methods with that one proposed here is strongly dependent on the runoff coefficient value. It is also not possible to predict whether they are conservative or not

Demand uncertainty In modelling WDS: scaling laws and scenario generation

Water distribution systems (WDS) are critical infrastructures that should be designed to work properly in different conditions. The design and management of WDS should take into account the uncertain nature of some system parameters affecting the overall reliability of these infrastructures. In this context, water demand represents the major source of uncertainty. Thus, uncertain demand should be either modelled as a stochastic process or characterized using statistical tools. In this paper, we extend to the 3rd and 4th order moments the analytical equations (namely scaling laws) expressing the dependency of the statistical moments of demand signals on the sampling time resolution and on the number of served users. Also, we describe how the probability density function (pdf) of the demand signal changes with both the increase of the user’s number and the sampling rate variation. With this aim, synthetic data and real indoor water demand data are used. The scaling laws of the water demand statistics are a powerful tool which allows us to incorporate the demand uncertainty in the optimization models for a sustainable management of WDS. Specifically, in the stochastic/robust optimization, solutions close to the optimum in different working conditions should be considered. Obviously, the results of these optimization models are strongly dependent on the conditions that are taken into consideration (i.e. the scenarios). Among the approaches for the definition of demand scenarios and their probability-weight of occurrence, the moment-matching method is based on matching a set of statistical properties, e.g. moments from the 1st (mean) to the 4th (kurtosis) order

Water Demand Uncertainty: The Scaling Laws Approach

The robust design of WDS has gained popularity over the last years. Researchers have been focusing on methods and algorithms to solve the stochastic optimization problems, and great improvements have been made in this aspect. However, the quantification of the uncertainty itself has not been addressed. Values for the variance and correlation of nodal demands are always assumed and no attention is being paid in properly quantifying these parameters. The optimization problems could be significantly improved if more realistic values for the uncertainty would be taken into account. This work addresses the need to understand in which measure the statistical parameters depend on the number of aggregated users and on the temporal resolution in which they are estimated. It intends to describe these dependencies through scaling laws, in order to derive the statistical properties of the total demand of a group of users from the features (mean, variance and correlation) of the demand process of a single-user. In future stages the results of this work will be incorporated in decision models for design purpose or scenario evaluation. Through this approach, we hope to develop more realistic and reliable WDS design and management solutions

SPH simulation of periodic wave breaking in the surf zone. A detailed fluid dynamic validation

The estimation of wave breaking and run-up on sloped beaches is a relevant issue in different coastal engineering applications. The present study stresses on the capabilities of a Smoothed Particle Hydrodynamics (SPH) solver, with optimal numerical and physical parameters, to accurately simulate the complex flow field in the surf zone and run-up region. Numerical results are compared with high quality experimental measurements of the local flow field in terms of instantaneous and phase averaged values. The selected test case regards the propagation and breaking of regular non-linear waves on a smooth impermeable plane slope. The comparison is based on a complete set of 128 consecutive non-linear regular waves. The level of accuracy of the numerical results and the ability of the model to reproduce the periodic flow in the surf-zone is provided. Current limitations and uncertainty sources are identified and discussed to guide future developments

Condotte in materiali lapidei: calcestruzzo ordinario, armato e precompresso, fibrocemento, grès

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