Search results for " losses"

Nonlinear droop control for minimum power losses operation in islanded microgrids

2017

In this work, a modified primary regulation technique is proposed to control one of the inverter interfaced units feeding an islanded microgrid. The proposed approach employs an off-line minimum losses Optimal Power Flow, OPF, to extract a lookup table for the composition of the droop curve. Simulations prove that generators reach an operating point that corresponds to a minimum loss operation for the relevant power flow distribution. Since OPF has been implemented with frequency and voltage dependent models, the results of the modified droop are stable and also energy efficient. Further studies will address further analysis on systems showing different R/X ratio and modeling of more genera…

Discussion of “Analysis of Geometrical Relationships and Friction Losses in Small-Diameter Lay-Flat Polyethylene Pipes” by Giuseppe Provenzano, Vince…

2016

For a lay-flat drip line with an inner nominal diameter dn = 16 mm, characterized by three different pipe wall thicknesses, WT, 6, 8 and 10 mil, the Authors of the original paper very accurately investigated the geometrical expansion of the cross-sectional diameter as a function of different pressure head values, ranging in between 0.84-17.55 m. Results obtained by the Authors, for pressure heads not exceeding a threshold pressure value, showed significant d variations, in a very narrow range of pressure heads, which however is seldom considered in practice (less than 3 m). The Authors experimentally evaluated a modified Blasius’ law friction coefficient, c, equal to 0.285, corresponding to…

Assessing a Local Losses Evaluation Procedure for Low-Pressure Lay-Flat Drip Laterals

2014

In the past, several research experiments have focused on the hydraulic characterization of traditional drip irrigation systems, and different design methodologies have been proposed with the aim of achieving very high emitter discharge uniformity (EU). The increasing use of low-pressure lay-flat drip laterals, characterized by a thin-walled polyethylene pipe, makes necessary a specific determination of their hydraulic properties, aimed to a correct design of such systems. Here, the validity of an empirical local losses estimation model was assessed for five different commercial lay-flat drip tapes. Moreover, the errors in the maximum lateral lengths obtained for a fixed emitter uniformity,…

An optimal dimensioning method of a green wall structure for noise pollution reduction

2021

International audience; This paper concern the optimization of a multilayered green wall structure including substrate and foliage in order to reduce as much as possible backward noise reflection and forward transmission from the wall. Each component involved in the wall structure is fully characterized experimentally to get its transfer matrix. Simulation demonstrated that foliage layer superimposed to substrate layer doesn’t affect the transmission losses but contributes greatly to the increase of return losses of the green wall structure. To achieve the best perfor­mances in terms of return and forward losses as well as frequency bandwidth, the methods of optimization are discussed inclu…

Eupelmus spermophilus Silvestri (Hymenoptera: Chalcidoidea), an Indigenous Olive Seed Wasp Potentially Harmful to Olive Growing in the Western Cape, …

2021

The objectives of this study were the specific taxonomic confirmation of the main olive seed wasp (OSW) attacking commercial olives in the Western Cape, to investigate monitoring methods and seasonal occurrence of OSW, to determine the potential economic damage of infestations, and to ascertain the geographic distribution of OSW in the regions where olives are cultivated in the Western Cape. Morphological and molecular methods were used to identify all the species obtained from cultivated olives at two trial sites near Stellenbosch and Agter-Paarl. Eupelmus spermophilus Silvestri (Hymenoptera: Chalcidoidea) was by far the most frequent and widespread olive seed wasp. Monitoring with yellow …

Analysis of Geometrical Relationships and Friction Losses in Small-Diameter Lay-Flat Polyethylene Pipes

2016

[EN] The use of lay-flat polyethylene pipes to irrigate horticultural crops has been receiving widespread attention in the last decade, due to the significant improvements in their hydraulic performance, their potentially high application efficiency, and their limited installation costs. However, even if hydraulic design procedures for conventional microirrigation systems are fairly well established, there is still the need to know how different pipe-wall thicknesses of lay-flat pipes can affect the pipe geometry under different operating pressures as well as the related consequences on friction losses. This paper, after comparing two different procedures (caliper and photographic) to asses…

Evidence of nonthermal particles in coronal loops heated impulsively by nanoflares

2014

The physical processes causing energy exchange between the Sun's hot corona and its cool lower atmosphere remain poorly understood. The chromosphere and transition region (TR) form an interface region between the surface and the corona that is highly sensitive to the coronal heating mechanism. High resolution observations with the Interface Region Imaging Spectrograph (IRIS) reveal rapid variability (about 20 to 60 seconds) of intensity and velocity on small spatial scales at the footpoints of hot dynamic coronal loops. The observations are consistent with numerical simulations of heating by beams of non-thermal electrons, which are generated in small impulsive heating events called "corona…

Sampling of Residential Water Use for Leak Control via Water Budgets

2009

Testing the long term applicability of USLE-M equation at a olive orchard microcatchment in Spain

2016

Abstract Universal Soil Loss Equation USLE-based erosion models have been used extensively to complement erosion measurements, to understand the interactions of the different geophysical features into erosion processes and to assess adequate alternative management practices and scenarios analyses. Despite its proved usefulness on different land-uses around the world, there is an urgent need to set up simple tools which do not require an advanced management expertise in terms of both choose of model parameters and calculation ability and which are accurate particularly at the event scale. In this paper the suitability of the Modified USLE (USLE-M) model at the event and the annual scale were…

Characterization of inductors in partial saturation including thermal effects for DC/DC converters

2018

Modern switching power electronic converters are widely used in many industrial and consumer applications, especially in step-up and step-down configurations. The optimization of the inductor in the converter design gives advantages in terms of power density increase and cost reduction; therefore, to properly design the converters, it is necessary to improve the knowledge of magnetic material behaviour as the current changes. The development of new models is becoming crucial in the design of modern power converters and there are some recent papers dealing with the use of inductors working in partial saturation [1-5]. This issue is of great interest for scientists and industry due to economi…