Search results for "Environmental engineering"
showing 10 items of 2674 documents
Spatial coherence of monsoon onset over Western and Central Sahel (1950-2000)
2009
Abstract The spatial coherence of boreal monsoon onset over the western and central Sahel (Senegal, Mali, Burkina Faso) is studied through the analysis of daily rainfall data for 103 stations from 1950 to 2000. Onset date is defined using a local agronomic definition, that is, the first wet day (>1 mm) of 1 or 2 consecutive days receiving at least 20 mm without a 7-day dry spell receiving less than 5 mm in the following 20 days. Changing either the length or the amplitude of the initial wet spell, or both, or the length of the following dry spell modifies the long-term mean of local-scale onset date but has only a weak impact either on its interannual variability or its spatial coher…
On the projected increase of Sahel rainfall during the late rainy season
2016
Thirteen CMIP5 models are used to analyse changes in climate over the West African monsoon region between the near future (2031–2070 under the RCP4.5 emission scenario), and a control period (1960–1999 under the historical emission scenario), with a focus on the late rainy season. The monsoon circulation is projected to strengthen and to shift northward leading to more rainfall during the Sahelian season. The results show an increase of the Rainfall amounts in September–October and a delay in the monsoon withdrawal. The increased moisture that fuels the rainfall anomalies is associated with an increase in moisture flux convergence and with local moisture recycling. The moisture transport do…
Extreme dry spell detection and climatology over the Mediterranean Basin during the wet season
2016
The E-OBS precipitation gridded data set v.10.0 is used to detect very long dry spell (VLDS) events over the entire Mediterranean Basin for the 1957–2013 period, during the wet season (September to April). The main objective is to characterize these events as climatic objects, in terms of location, spatial extent, duration, and temporal variability. In this study, 76 VLDS events were detected in the Mediterranean Basin and grouped into four spatial patterns: scattered localized (with 25 events), northeast Mediterranean (11 events), West Mediterranean (15 events), and southeast Mediterranean (25 events). Each pattern shows seasonality in events. Most of the scattered localized, northeast, an…
Droughts Over Amazonia in 2005, 2010, and 2015: A Cloud Cover Perspective
2018
Amazon forests experienced recent severe droughts in an anomalous short period induced by different mechanisms and had different length periods and spatial patterns. Droughts of 2005 and 2010 were attributed to anomalous Sea Surface Temperature (SST) over the Tropical North Atlantic (TNA) during the dry season, but the 2010 drought was more severe and remained for a longer period because it was also induced in late 2009 by a moderate to strong El Niño (EN). Drought in 2015 led to unprecedented warming and extreme soil moisture deficits over some regions, and it was attributed to a very strong EN. Several studies analyzed these drought events regarding different climatic factors such as anom…
Applying Numerical Weather Prediction Models to the Production of New European Wind Atlas : Sensitivity studies of the wind climate to the planetary …
2018
Reliable and precise information about the wind speed climate is crucial for the development of wind energy. Meteorological processes in the mesoscale (2 – 200 km) can be represented using Numerical Weather Prediction (NWP) models such as the Weather Research and Forecast model (WRF), but before their application for creating wind energy atlases, their results and sensitivity to modelling parameters should be investigated. Here the WRF model wind speed results for the year 2015 for the Baltic Sea region are investigated, and the effect of the planetary boundary layer parametrization scheme is analyzed.
A comparative study on the dynamic response of three semisubmersible floating offshore wind turbines
2019
Abstract Currently, there is a great interest to globally develop offshore wind energy due to the greenhouse effect and energy crisis. Great efforts have been devoted to develop reliable floating offshore wind energy technology to exploit the wind energy resources in deep seas. This paper presents a comparative study of the dynamic response of three different semisubmersible floating wind turbine structures. All the three platforms support the same 5MW wind turbine. The platforms examined are: a V-shaped Semi, an OC4-DeepCwind Semi and a Braceless Semi at 200 m water depth. A dynamic analysis is carried out in order to calculate and compare the performance of these platforms. The comparison…
Performance improvement of a Savonius water rotor with novel blade shapes
2021
Abstract Savonius water rotor is a prominent drag based turbine able to extract energy available in flowing water with low velocity like river streams, tidal currents or other man made water canals. However, in view of its low performance, an enhanced design of the rotor blades is necessary to better its efficiency. Therefore, the present study aims to improve the efficiency of Savonius rotor by changing the blade design. Different blade shapes were investigated numerically using computational fluid dynamics (CFD). Using conventional design, the peak power coefficient was found to be 0.166 at tip-speed ratio of 0.78. However, the peak power coefficient reaches 0.184 using the optimal blade …
Effect of Hot Drawing on the Mechanical Properties of Biodegradable Fibers
2016
The use of biodegradable polymers is increasingly attracting interest over the last years, since they can reduce the environmental effects related to disposal of traditional plastics and, in general, the use of fossil, non-renewable resources. One of the most promising applications is represented by fibers production. However, the orientation and the crystallinity degrees can significantly affect the mechanical properties. Therefore, it is of interest to investigate on the optimum processing conditions, in order to improve the mechanical properties. In particular, while crystallinity can be slightly modified by the processing, orientation can be significantly improved. In this work, the eff…
Calibration and simulation of ASM2d at different temperatures in a phosphorous removal pilot plant
2006
In this work, an organic and nutrient removal pilot plant was used to study the temperature influence on phosphorus accumulating organisms. Three experiments were carried out at 13, 20 and 24.5 degrees C, achieving a high phosphorus removal percentage in all cases. The ASM2d model was calibrated at 13 and 20 degrees C and the Arrhenius equation constant was obtained for phosphorus removal processes showing that the temperature influences on the biological phosphorus removal subprocesses in a different degree. The 24.5 degrees C experiment was simulated using the model parameters obtained by means of the Arrhenius equation. The simulation results for the three experiments showed good corresp…
Process intensification in a photocatalytic membrane reactor: Analysis of the techniques to integrate reaction and separation
2017
Abstract Different methods to integrate reaction and separation in a membrane reactor are studied in the present work, with the aim being to highlight the pros and cons of the different alternatives and the effects of the intervening parameters. The coupling of the two processes can take place inside a single apparatus or using separate units. If a single apparatus is utilized, the coupling is more direct, but separate units offer higher degrees of freedom for the design with more opportunities to optimize the system without constraints. However, when using separate units, the integration of the two unit operations depends largely on the parameters intervening in the coupling procedure. The…