Search results for "oceanic"
showing 10 items of 642 documents
A numerical model of the cloud-topped planetary boundary-layer: influence of the physico-chemical properties of aerosol particles on the effective ra…
2000
The present investigation deals with the impact of different aeorosol types on the value of the effective radius of stratiform clouds. In several numerical sensitivity studies with the microphysical stratus model MISTRA, the aerosol composition was linearly changed from pure maritime to pure rural aerosol particles. Numerical results show that in environments with pure maritime aerosols, the effective radius is usually much larger than in continental regions. Values of the effective radius are also time-dependent with minima and maxima during day and night, respectively. In precipitating clouds, the effective radius might achieve values larger than 30 μm. In continental regions, the effecti…
Linear relationship between effective radius and precipitation water content near the top of convective clouds: measurement results from ACRIDICON–CH…
2021
Quantifying the precipitation within clouds is a crucial challenge to improve our current understanding of the Earth's hydrological cycle. We have investigated the relationship between the effective radius of droplets and ice particles (re) and precipitation water content (PWC) measured by cloud probes near the top of growing convective cumuli. The data for this study were collected during the ACRIDICON–CHUVA campaign on the HALO research aircraft in clean and polluted conditions over the Amazon Basin and over the western tropical Atlantic in September 2014. Our results indicate a threshold of re∼13 µm for warm rain initiation in convective clouds, which is in agreement with previous studie…
A software for the evaluation of winding factor harmonic distribution in high efficiency electrical motors and generators
2013
In this paper a software developed for the determination of winding connections, the calculation of winding factors and the evaluation of their harmonic distribution of three and two phase windings is presented by using as input data simply the number of slots, pole pairs and phases. The software is implemented as a function in MATLAB environment. By means of some examples, covering the most relevant winding types, the capabilities of this software will be shown. Particularly, integer and fractional single and double layer winding can be treated. Some examples are presented and briefly discussed. The connections, the winding factor harmonic distribution, the electro-motive force (e.m.f) THD…
Winding loss analysis and optimization of an AC inductor for a galvanically isolated PV inverter
2012
This paper describes simple treatments for fringing fields of air gaps in the core and bypass fluxes in the winding window area of an existing high frequency AC inductor used by a commercial developer of PV inverters. For this purpose, Maxwell (ANSOFT) electromagnetic software package is used for winding eddy current loss analysis. It is displayed that air gaps cause high flux strength and, therefore, induce significantly high eddy currents to the surrounded windings. Proximity effect also causes non uniform current density in the winding. Altogether, the inductor is affected by fringing fields, and proximity effect produces a very high AC resistance, consequently resulting in undesirable h…
Multi-step ahead wind speed forecasting using an improved wavelet neural network combining variational mode decomposition and phase space reconstruct…
2017
Abstract Accurate wind speed forecasting is crucial to reliable and secure power generation system. However, the intermittent and unstable nature of wind speed makes it very difficult to be predicted accurately. This paper proposes a novel hybrid model based on variational mode decomposition (VMD), phase space reconstruction (PSR) and wavelet neural network optimized by genetic algorithm (GAWNN) for multi-step ahead wind speed forecasting. In the proposed model, VMD is firstly applied to disassemble the original wind speed series into a number of components in order to improve the overall prediction accuracy. Then, the multi-step ahead forecasting for each component is conducted using GAWNN…
Generalized feed-forward based method for wind energy prediction
2013
Abstract Even though a number of new mathematical functions have been proposed for modeling wind speed probability density distributions, still the Weibull function continues to be the most commonly used model in the literature. Therefore, the parameters of this function are still widely used to obtain typical wind probability density distributions for finding the wind energy potential by researchers, engineers and designers. Once long-term average of Weibull function’s parameters are known, then the probability density distributions can easily be obtained. Artificial neural network (ANN) can be used as alternative to analytical approach as ANN offers advantages such as no required knowledg…
Pitch controller modeling for wind turbine power regulation using feed forward control strategies
2015
In this work, pitch controlled power regulation of a horizontal axis wind turbine coupled with a fixed speed asynchronous generator is studied using SimulationX®. Wind turbines need to be operated as per specified power output vs wind speed characteristics of it. If the wind speed is between the cut-in wind speed and the rated wind speed, then the wind turbine needs to be operated constant Cp. If wind speed is between the rated speed and the cut-off wind speed, then the wind turbine needs to be operated for constant rated power. To extract rated power above rated wind speed a proper controller strategy is required. This work provides a simulation model for power regulation of a horizontal a…
Computer Aided Optimization Via Simulation Tools of Energy Generation Systems With Universal Small Wind Turbines
2012
This paper considers the general issues in the project and the optimization of energy generation systems using small universal wind turbines, suitable in Distributed Generation (DG) and computer aided optimization for a better exploitation of wind source. Optimization in this field reveal to be more and more important because the local generation and consumption of electrical power, even for grid connected generators can suffers for unevenness of wind source exploitation, also in terms of wrong directions and in not regular wind flows. Computer aided design and optimization of small plants may give significant improvements in the development of the wind source also in accordance with the pr…
A Model-Based Control Strategy for Wind Turbines with Asynchronous Generator
2007
In this paper a model based control methodology is described with reference to a wind turbine for production of alternative energy. The mathematical model of a 600 kW wind turbine is taken into account assuming a well defined profile of the rotor blades. A set of reference angular speeds of the asynchronous generator and a set of reference pitch angles of the blade wind turbine are obtained in order to maximize the extracted wind power and to reach equilibrium conditions between the wind-generated torque and the electric torque of the generator. Finally a PID model based controller is designed and then tested by means of simulation experiments.
GA-ANN for Short-Term Wind Energy Prediction
2011
Wind turbine power output is totally intermittent in the nature. For grid connected wind turbine generators, power system operators (transmission system operators) need reliable and robust wind power forecasting system. Rapid changes in the wind generation relative to the load require proper energy management system to maintain the power system stability and of course to balance the power generation, frequency, voltage regulation within the statutory limits. Accurate wind energy forecasting helps the power system transmission system operators in anticipating rapid changes in wind turbine power output with respect to load and helps in making decision not only for optimum energy management bu…