Computational simulation of thunderstorm downbursts and associated wind turbine loads

textWind turbines operate in a constantly changing wind environment. This requires modeling and simulation of extreme events in which the wind turbine operates and a study of associated turbine loads as part of the design practice and/or site assessment. Thunderstorms are transient atmospheric events that occur frequently in some regions of the world and can influence the design of a wind turbine. Downbursts are extreme surface winds that are produced during a thunderstorm. They are both complex to model and their damaging effect on wind turbines has been noted in recent years. In the last few decades, downbursts have been the subject of studies in various fields--- most notably, in aviation. Despite their complexity, generally only empirical models based on observational data have been developed for practical uses. Based on such field data as well as laboratory tests, it is common to model a downburst as a jet impingement on a flat plate. The actual buoyancy-driven flow has been commonly modeled as an equivalent momentum flux-driven flow resulting from the impinging jet. The use of computational fluid dynamics (CFD) to model a downburst based on the idea of an impinging jet offers an alternative approach to experimental and analytical approaches. Simulation of "downburst"' wind fields using a computational model and analysis of associated loads on a wind turbine operating during such events is the subject of this study. Although downburst-like events have been simulated using commercial CFD software, the resulting wind fields from such simulations have not been used as inflow fields for wind turbine loads analysis. In this study, the commercial CFD software, ANSYS FLUENT 12.0, is used to simulate downburst events and the output wind fields are used as input to loads analysis for a utility-scale 5-MW wind turbine. The inflow wind fields are represented by both non-turbulent and turbulent components---the former are simulated using FLUENT while the latter are simulated as stochastic processes using Fourier techniques together with standard turbulence power spectral density functions and coherence functions. The CFD-based non-turbulent wind fields are compared with those from empirical/analytical approaches; turbine loads are also compared for the two approaches. The study suggests that a CFD-based approach can capture similar wind field characteristics as are modeled in the alternative approach; associated turbine loads are as well not noticeably different with the two approaches.Civil, Architectural, and Environmental Engineerin

A Comprehensive X-Ray Diffraction Study On Anatase-To-Rutile Transformation Utilising Mechanical And Thermal Approaches

A comprehensive investigation using x-ray diffractometry has been conducted to study the optimum mechanical and thermal conditions for the transformation of anatase-to-rutile from a titanium dioxide (TiOl) powder. Milling was applied by employing a conventional ball milling instrument and a quasi-high-energy pulveriser and varying the milling period. Heat treatment was performed by calcination at 850, 900, 950, 975, 1000, 1050 and 1100°C for 1 hour, being the predicted optimum temperature to obtain fidly rutile powder was 975°C. Each powder was milled and then calcined prior to the x-ray difiaction investigation. X-ray diffraction data were analysed using (1) standard identification and peak characterisation and (2) Mozulx, an own-developed software to provide strain, crystallite size and size distribution of phases. Results showed that milling speed and milling up to 24 hours does not significantly change the phases' composition, but enhances the transformation temperature. Conventional milling gives better results than pulverising. Conventional milling at 100 rprn for 3 hours reduces the transformation temperature from 1100°C to 1000°C. Longer milling, however, does not improve the transformation temperature. The optimum process is discussed and SEM micrographs are used to support the argumen

Modeling and analysis of radial flux toroidally wound twin rotor permanent magnet motor

The main objective of current thesis is the study of Radial Flux Twin Rotor Permanent Magnet (RFTWTRPM) motor. The tasks were to review the literature about RFTWTPM motors and model the motor using Finite Element Method Magnetics (FEMM 4.0). Later the performance of RFTWTRPM motor as a brushless dc motor was analyzed by using MATLAB/SIMULINK package. To find the electrical and mechanical parameters of the RFTWTRPM motor, the rotor and stator dimensions of the motor were firstly optimized using linear FEMM model of the motor. The optimized dimensions were used to construct the cylindrical FEMM model. This model was later used to determine electrical and mechanical parameters. The electro-mechanical parameters were used in the construction of motor block diagram in SIMULINK. This block diagram was used to test the performance of the motor as Brushless DC motor was analyzed for various dynamic and steady state conditions. It was observed that the RFTWTRPM motor was highly suitable to operate as Brushless DC motor

Heat and Mass Transfer On MHD Flow Problems with Hall and Ion Slip Effects On Exponentially Accelerated Plate

We in this paper intended to investigate heat and mass transfer for MHD free convective flow for exponentially accelerated plate. The effects of Ion slip and Hall are studied considering variable temperatures, concentration, and angle of inclination. We applied finite element analysis for solving governing equations. Flow velocity, concentration and temperature’s graphical profiles are examined for non-dimensional parameters. Flow reversal is prevented due to magnetic field, is observed. Velocity experiences retarding effect due to angle of inclination, this helps in acknowledging drag force in seepage flow

Sintesis MgTiO3 dengan Variasi Temperatur Kalsinasi Menggunakan Metode Pencampuran Larutan

Telah dilakukan sintesis MT (magnesium titanat) dengan metode pencampuran larutan. Prekursor dibuat dengan melarutkan serbuk logam ke dalam HCl 37% dan dikeringkan di udara pada temperatur 110oC dilanjutkan dengan kalsinasi. Dalam penelitian ini digunakan variasi temperatur kalsinasi yaitu 600°C, 700°C, 800°C dengan waktu tahan yaitu 1 jam untuk mengetahui pengaruhnya terhadap sintesis MT. Hasil sintesis dikarakterisasi dengan XRD (X-Ray Diffraction), kemudian dianalisis menggunakan software rietica dan MAUD. Hasil analisis menunjukkan bahwa temperatur dan waktu tahan kalsinasi mempengaruhi hasil dari sintesis. Berdasarkan metode Rietveld untuk fraksi berat relatif komposisi fase, pembentukan MT yang paling optimal adalah pada temperatur 800 oC,waktu tahan 1 jam dengan fraksi berat 95,1%. Dengan analisis menggunakan MAUD diperoleh nanokristal MgTiO3 pada pemanasan 600oC dengan ukuran kristal 75nm

Sintesis Zn0.5Mg0.5TiO3 dengan Variasi Rasio Mol Serbuk (Zn+Mg):Ti Menggunakan Metode Pencampuran Larutan pada Suhu 600ºC

Dalam penelitian ini telah dilakukan sintesis serbuk larutan padat Zn0.5Mg0.5TiO3 dengan metode pencampuran larutan dalam jumlah yang relatif tinggi (>90 % berat). Bahan dasar yang digunakan dalam sintesis adalah serbuk-serbuk Mg dan Ti, sedangkan Zn digunakan sebagai bahan aditif dengan variasi rasio mol serbuk yang digunakan antara 1,03:1 ≤ (Zn+Mg):Ti ≤ 1,18:1. Prekursor dibuat dengan melarutkan masing-masing serbuk Mg, Zn, dan Ti ke dalam HCl 37%, mencampurkan ketiga larutan dan mengeringkan campuran di udara pada suhu 110ºC serta terakhir mengkalsinasi serbuk hasil pengeringan pada suhu 600ºC selama ½ jam. Uji komposisi serbuk hasil sintesis tersebut dilakukan dengan difraksi sinar-x. Identifikasi fasa pada serbuk hasil sintesis menunjukkan bahwa seluruh variasi rasio mol menghasilkan fasa Zn0.5Mg0.5TiO3 dan rutil. Ukuran kristal fasa Zn0.5Mg0.5TiO3 dengan rasio mol 1,03:1 dan 1,05:1 berturut-turut adalah 20 dan 29 nm. Variasi mol yang menghasilkan fraksi berat Zn0.5Mg0.5TiO3 terbesar adalah 1,12:1, yaitu sebesar 91%

Heat and Mass Transfer On MHD Flow Problems with Hall and Ion Slip Effects On Exponentially Accelerated Plate

We in this paper intended to investigate heat and mass transfer for MHD free convective flow for exponentially accelerated plate. The effects of Ion slip and Hall are studied considering variable temperatures, concentration, and angle of inclination. We applied finite element analysis for solving governing equations. Flow velocity, concentration and temperature’s graphical profiles are examined for non-dimensional parameters. Flow reversal is prevented due to magnetic field, is observed. Velocity experiences retarding effect due to angle of inclination, this helps in acknowledging drag force in seepage flow

Analisis Kristalinitas Serbuk Magnesium Oksida Hasil Sintesis Metode Logam-Terlarut Asam

Telah dilakukan sintesis magnesium oksida (MgO) dengan metode logam terlarut asam dengan penambahan 2 jenis polietilen glikol (PEG), yaitu PEG400 dan PEG1000, Tujuan dari sintesis ini yaitu untuk mengetahui seberapa efektif metode pencampuran logam-terlarut asam dalam menghasilkan serbuk magnesium oksida dengan kemurnian tinggi dan untuk mengetahui derajat kristalinitas pada masing-masing sampel. Serbuk murni Mg digunakan sebagai bahan dasar yang dilarutkan dalam larutan HCl 37% untuk menyiapkan sampel tanpa PEG (MgONP) dan dua sampel lain disiapkan dengan menambahkan PEG400 (MgOP4) dan PEG1000 (MgOP10). Bahan–bahan dasar dicampur dengan cara diaduk selama 1 jam pada temperatur kamar, lalu dikeringkan pada temperatur 80°C. Serbuk yang telah dikeringkan diuji dengan DTA-TGA untuk mengetahui fenomena termal dari sampel yang digunakan sebagai dasar memilih temperatur kalsinasi. Temperatur kalsinasi yang digunakan adalah 400, 500  600, dan 700°C. Serbuk-serbuk terkalsinasi dikarakterisasi menggunakan XRD dan, secara umum, diketahui bahwa fasa-fasa yang terbentuk adalah periklas dan bikosfit. Analisis kekristalan dari data difraksi menegaskan bahwa tingkat kekristalan sampel meningkat dengan temperatur kalsinasi. Kalsinasi pada temperatur 700°C menghasilkan sampel dengan derajat kekristalan tertinggi, yaitu antara 78-79% (berat), dan semuanya adalah periklas, untuk ketiga sampel