A combined CFD-experimental method for abrasive erosion testing of concrete

Serious damage may occur to concrete hydraulic structures, such as water galleries, spillways, and stilling basins, due to the abrasive erosion caused by the presence of solid particles in the flow. This underlines the importance of being capable in providing characterization of the concrete from the point of view of its vulnerability to abrasive erosion, in order to improve the design of the structure and the material selection. Nevertheless, the existing apparatus for concrete abrasive erosion testing are either far from allowing realistic simulation of the actual environment in which this phenomenon occurs, or show a large degree of complexity and cost. An alternative method has been developed with the aid of Computational Fluid Dynamics (CFD). CFD was first employed to verify the effectiveness of a new laboratory equipment. Afterwards, a parameter has been introduced which, by successful comparison against preliminary experiments, proved suitable to quantify the effect of the fluid dynamic conditions on the concrete abrasive erosion, thereby opening the way to CFD-based customization of the apparatus. In the future, the synergy of numerical and physical modelling will allow developing predictive models for concrete erosion, making it possible to reliably simulate real structures

The Importance of Erosion Concrete Tests for Hydraulic Surfaces

The population growth requires improvements in water availability for consumption, food and energy. There are many challenges to achieve this. However, in many cases, one solution resolves all needs: reserving the water for supply, irrigation of crops and energy generation. In particular, the current demand for clean energy generation has encouraged some governments to invest in the construction of new hydropower plants. This scenario results in building a dam and its appurtenances. The concept of accumulating water for human use dates back to antiquity, but it was only during the 19th century that the technological development allowed the advent of hydropower plants. Since then, ongoing efforts on this field have developed technologies and the systematic construction of dams. More recently, there has been an increasing concern regarding the safety of dams. In Brazil, the safety legislation began to operate only in 2010. Malfunctioning of dams can lead to failure and even to catastrophic consequences. When an accident occurs, not only are the costs for repairing high, but it also compromises operation and the environment. A dam failure may be related to a poor performance of the spillway. Erosion is one of the main causes of spillways failure. In this sense, it is essential to characterize the composition and resistance of the concrete to be used in the spillway. Cavitation and water solid mixture are among the main causes of erosion that put spillways into risk. Cavitation is the formation of bubbles within the liquid, if the vapor pressure is reached. Once the pressure rises, the bubbles implode and eventually cause damage, noise, vibration and pressure fluctuation. Water solid mixture causes erosion by the impact of particles. The particles are carried in the flow, and it is especially important, because the damage is irreversible and progressive. The objective of this paper is to show the importance of testing concrete samples to erosion before using them in prototype. The concrete samples are submitted to erosion due to cavitation and water-solid mixture. The tests were performed at the Laboratory of Hydraulics and Fluid Mechanics at Unicamp, Brazil. The method for evaluating cavitation erosion resistance is based on the use of a high velocity cavitating jet. The other method, for evaluating water solid mixture erosion resistance, is based on the use of a mixing tank, where an impeller propels solid particles in the water over the sample. In both cases, the erosion resistance is associated with the mass loss of the sample through time. The results highlight the erosion that can occur in prototypes and the importance of testing concretes before construction or repairing of concrete spillways

Assessing the performance of near real-time rainfall products to represent spatiotemporal characteristics of extreme events: case study of a subtropical catchment in south-eastern Brazil

This study evaluates the performance of four Near Real-Time (NRT) satellite rainfall products in estimating the spatiotemporal characteristics of different extreme rainfall events in a subtropical catchment in south-eastern Brazil. The Climate Prediction Centre Morphing algorithm (CMORPH), Tropical Rainfall Measuring Mission, Multisatellite Precipitation Analysis in real time (TMPA-RT), the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Global Cloud Classification System (PERSIANN-GCCS), and the Hydro-Estimator are evaluated for monsoon seasons, based on their capability to represent four types of rainfall events distinguished for: (1) local and short duration, (2) long-lasting event, (3) short and spatial extent, and (4) spatial extent and long lasting. Since the events are defined relative to a percentile, the relative performance variation at different threshold levels (75th, 90th, and 95th) is also evaluated. The data from the 13 Automatic Weather Stations (AWSs) for the period from 2007 to 2014 are used as the reference. The results show that the product performance highly depends on the spatiotemporal characteristics of rainfall events. All four products tend to overestimate intense rainfall in the study area, especially in high altitude zones. CMORPH had the best overall performance to estimate different types of extreme spatiotemporal events. The results allow for developing a better understanding of the accuracy of the NRT products for the estimation of different types of rainfall events.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Water Resource