Modeling Flutter-Based Microgenerators

2012 ◽  
Author(s):  
Raed Kafafy ◽  
Abdulhakeem Javeed ◽  
Moumen Idres ◽  
Sany Ihsan
Keyword(s):  
Power Output ◽  
Design Parameters ◽  
Maximum Speed ◽  
Wind Speeds ◽  
Plane Analysis ◽  
Wind Structure ◽  
Wide Range ◽  
Different Dimensions ◽  
Electromagnetic Transduction ◽  
Low Wind Speeds

Flutter-based micro generators have been successfully demonstrated to power wireless sensors. Since environmental wind speeds vary widely, flutter-based micro generators which are designed to operate within particular range of wind speeds will underperform elsewhere. At low wind speeds, magnets embedded near the ends of the belt will not move the desired distance between the coils, thereby reducing the energy conversion. A broadband flutter-based micro generator will have pick-up coils embedded on several vibrating elements with different dimensions. The coils are particularly concentrated near the point of maximum speed to maximize power output. The variation in fluttering element dimensions allows the microgenerator to generate considerable power at a wide range of wind speeds. In this work, we develop a mathematical model for the flutter-based micro generator, which addresses the wind – structure interaction, induced vibrations and electromagnetic transduction. The model primarily makes use of equations from bridge deck and thin plane analysis of flutter due to their similarities, and they are formulated to provide the velocity. This is later fed into electromagnetic transduction equations to calculate the output power. The model is useful to determine the significant design parameters of a flutter-based micro generator. The dynamic response and power output of a broadband micro generator with coils embedded on a set of cantilever films vibrating with respect to an external permanent magnetic field are calculated.

Stability-Dependent Exchange Coefficients for Air–Sea Fluxes*

2005 ◽  
Vol 22 (7) ◽  
pp. 1080-1094 ◽  
Author(s):  
A. Birol Kara ◽  
Harley E. Hurlburt ◽  
Alan J. Wallcraft
Keyword(s):  
Heat Flux ◽  
Water Vapor ◽  
Wind Stress ◽  
General Circulation ◽  
Global Ocean ◽  
Polynomial Functions ◽  
Substantial Impact ◽  
Wind Speeds ◽  
Wide Range ◽  
Low Wind Speeds

Abstract This study introduces exchange coefficients for wind stress (CD), latent heat flux (CL), and sensible heat flux (CS) over the global ocean. They are obtained from the state-of-the-art Coupled Ocean–Atmosphere Response Experiment (COARE) bulk algorithm (version 3.0). Using the exchange coefficients from this bulk scheme, CD, CL, and CS are then expressed as simple polynomial functions of air–sea temperature difference (Ta − Ts)—where air temperature (Ta) is at 10 m, wind speed (Va) is at 10 m, and relative humidity (RH) is at the air–sea interface—to parameterize stability. The advantage of using polynomial-based exchange coefficients is that they do not require any iterations for stability. In addition, they agree with results from the COARE algorithm but at ≈5 times lower computation cost, an advantage that is particularly needed for ocean general circulation models (OGCMs) and climate models running at high horizontal resolution and short time steps. The effects of any water vapor flux in calculating the exchange coefficients are taken into account in the polynomial functions, a feature that is especially important at low wind speeds (e.g., Va < 5 m s−1) because air–sea mixing ratio difference can have a major effect on the stability, particularly in tropical regions. Analyses of exchange coefficients demonstrate the fact that water vapor can have substantial impact on air–sea exchange coefficients at low wind speeds. An example application of the exchange coefficients from the polynomial approach is the recalculation of climatological mean wind stress magnitude from 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) data in the North Pacific Ocean over 1979–2002. Using ECMWF 10-m winds and the authors’ methodology provides accurate surface stresses while largely eliminating the orographically induced Gibb’s waves found in the original ERA-40 surface wind stresses. These can have a large amplitude near mountainous regions and can extend far into the ocean interior. This study introduces exchange coefficients of air–sea fluxes, which are applicable to the wide range of conditions occurring over the global ocean, including the air–sea stability differences across the Gulf Stream and Kuroshio, regions which have been the subject of many climate model studies. This versatility results because CD, CL, and CS are determined for Va values of 1 to 40 m s−1, (Ta − Ts), intervals of −8° to 7°C, and RH values of 0% to 100%. Exchange coefficients presented here are called the Naval Research Laboratory (NRL) Air–Sea Exchange Coefficients (NASEC) and they are suitable for a wide range of air–sea interaction studies and model applications.

scholarly journals An LES-based airborne Doppler lidar simulator for investigation of wind profiling in inhomogeneous flow conditions

2019 ◽  
Author(s):  
Philipp Gasch ◽  
Andreas Wieser ◽  
Julie K. Lundquist ◽  
Norbert Kalthoff
Keyword(s):  
Laser System ◽  
Doppler Lidar ◽  
Flow Conditions ◽  
Acceptable Error ◽  
Wind Speeds ◽  
Spatially Resolved ◽  
Future System ◽  
Wide Range ◽  
Inhomogeneous Flow ◽  
Low Wind Speeds

Abstract. Wind profiling by Doppler lidar is common practice and highly useful in a wide range of applications. Airborne observations can provide additional insights to ground-based systems by allowing for spatially resolved and targeted measurements. This study prepares the ground for an upcoming airborne Doppler lidar system by investigating the measurement process theoretically. To evaluate the future system characteristics and measurement accuracy, a first LES-based airborne Doppler lidar simulator (ADLS) has been developed. The accuracy of retrieved wind profiles under inhomogeneous flow conditions in the boundary layer is investigated. In general, when using reasonable system setups, wind profiling is possible with acceptable error margins. Results allow for determination of preferential system setups and wind profiling strategies. Under the conditions considered, flow inhomogeneities exert the dominant influence on wind profiling error. In comparison, both the errors caused by random radial velocity fluctuations due to laser system noise and beam pointing inaccuracy due to system vibrations are of smaller magnitude. Airborne Doppler lidar wind profiling at low wind speeds (

Parametrically Excited Nonlinear Piezoelectric Wind Energy Harvester

2011 ◽  
Author(s):  
M. Amin Karami ◽  
Justin R. Farmer ◽  
Scott Bressers ◽  
Shashank Priya ◽  
Daniel J. Inman
Keyword(s):  
Wind Energy ◽  
Electric Power ◽  
Axial Force ◽  
Power Output ◽  
Permanent Magnets ◽  
Energy Harvester ◽  
Power Production ◽  
Experimental Investigations ◽  
Wind Speeds ◽  
Low Wind Speeds

A nonlinear piezoelectric wind energy harvester is proposed which operates at low wind speeds and is not sensitive to the speed of the gusts. The piezoelectric transduction mechanism is used instead of DC generators to eliminate the gearbox in the windmill and thus reduces the friction. The reduced friction facilitates operation of the windmill at low wind speeds. Permanent magnets have been placed in the blade part of the windmill. The magnets axially repel another set of magnets which are positioned at the tip of the piezoelectric beams. As a result, when the rotating magnets pass over the piezoelectric beams they excite the beams and affect the type of their vibrations. The nature of excitations in the proposed design is therefore both parametric excitations and ordinary excitations. The nonlinear magnetic axial force makes the vibrations of the beams nonlinear and can make the beams bi-stable. This phenomenon is utilized to enhance the power output and to improve the robustness of the power production. Two designs are presented which incorporate parametric and ordinary excitations to generate electric power. The performance of each design is examined through experimental investigations.

Analysis of a Concept for a Low Wind Speed Tolerant Axial Wind Turbine

2011 ◽  
Author(s):  
Ali A. Ameri ◽  
Majid Rashidi
Keyword(s):  
Wind Speed ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Power Output ◽  
Turbine Rotor ◽  
Navier Stokes ◽  
Ambient Wind ◽  
Wind Speeds ◽  
Low Wind Speed ◽  
Low Wind Speeds

In this paper, the authors analyze a design for a wind tower intended for areas of low wind speeds. The wind tower consists of a combination of several rooftop size turbines arranged alongside a cylindrical structure that acts as a Wind Deflecting Structure (WDS). The WDS amplifies the effective wind speed thus allowing the turbine rotors to operate under lower ambient wind speeds. Analyses were performed using simple models as well as more sophisticated CFD methods employing Steady and Unsteady Reynolds Averaged Navier-Stokes methodology. The effect of the wind amplification was shown on a commercial small wind turbine power output map. Also, a wind turbine rotor flow was computed as operating alongside the WDS and compared to the computed operation of isolated turbines at equal effective and ambient wind velocities. The computational analyses of this work suggest that the power output of isolated rooftop wind turbines deployed at low to moderate wind speed may be matched by installing wind turbines alongside a cylindrical wind deflecting structure operating at lower wind speeds. Other benefits of the arrangement are also enumerated.

scholarly journals Canard optimization for enhancing the performance of small horizontal axis wind turbine at low wind speeds

2020 ◽  
Vol 37 ◽  
pp. 63-71
Author(s):  
Yui-Chuin Shiah ◽  
Chia Hsiang Chang ◽  
Yu-Jen Chen ◽  
Ankam Vinod Kumar Reddy
Keyword(s):  
Wind Turbine ◽  
Urban Areas ◽  
Horizontal Axis ◽  
Power Coefficient ◽  
Peak Performance ◽  
Small Scale ◽  
Horizontal Axis Wind Turbine ◽  
Wind Speeds ◽  
Optimum Parameters ◽  
Low Wind Speeds

ABSTRACT Generally, the environmental wind speeds in urban areas are relatively low due to clustered buildings. At low wind speeds, an aerodynamic stall occurs near the blade roots of a horizontal axis wind turbine (HAWT), leading to decay of the power coefficient. The research targets to design canards with optimal parameters for a small-scale HAWT system operated at variable rotational speeds. The design was to enhance the performance by delaying the aerodynamic stall near blade roots of the HAWT to be operated at low wind speeds. For the optimal design of canards, flow fields of the sample blades with and without canards were both simulated and compared with the experimental data. With the verification of our simulations, Taguchi analyses were performed to seek the optimum parameters of canards. This study revealed that the peak performance of the optimized canard system operated at 540 rpm might be improved by ∼35%.

scholarly journals Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine

Entropy ◽  
2021 ◽  
Vol 23 (4) ◽  
pp. 419
Author(s):  
Congzheng Qi ◽  
Zemin Ding ◽  
Lingen Chen ◽  
Yanlin Ge ◽  
Huijun Feng
Keyword(s):  
Power Output ◽  
Performance Optimization ◽  
External Load ◽  
Thermal Contact ◽  
Heat Engine ◽  
Design Parameters ◽  
Load Effect ◽  
Heat Engines ◽  
Heat Leakage ◽  
Steady Current

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.

scholarly journals Dependence of Power Characteristics on Savonius Rotor Segmentation

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2912
Author(s):  
Krzysztof Doerffer ◽  
Janusz Telega ◽  
Piotr Doerffer ◽  
Paulina Hercel ◽  
Andrzej Tomporowski
Keyword(s):  
High Wind ◽  
Horizontal Axis Wind Turbine ◽  
Savonius Rotor ◽  
Power Characteristics ◽  
Wind Speeds ◽  
Single Segment ◽  
High Elongation ◽  
Low Wind Speeds ◽  
Number Of Segments ◽  
Rotor Type

Savonius rotors are large and heavy because they use drag force for propulsion. This leads to a larger investment in comparison to horizontal axis wind turbine (HAWT) rotors using lift forces. A simple construction of the Savonius rotor is preferred to reduce the production effort. Therefore, it is proposed here to use single-segment rotors of high elongation. Nevertheless, this rotor type must be compared with a multi-segment rotor to prove that the simplification does not deteriorate the effectiveness. The number of segments affects the aerodynamic performance of the rotor, however, the results shown in the literature are inconsistent. The paper presents a new observation that the relation between the effectiveness of single- and multi-segment rotors depends on the wind velocity. A single-segment rotor becomes significantly more effective than a four-segment rotor at low wind speeds. At high wind speeds, the effectiveness of both rotors becomes similar.

scholarly journals Evaluating Usability of Academic Websites through a Fuzzy Analytical Hierarchical Process

2021 ◽  
Vol 13 (4) ◽  
pp. 2040
Author(s):  
AbdulHafeez Muhammad ◽  
Ansar Siddique ◽  
Quadri Noorulhasan Naveed ◽  
Uzma Khaliq ◽  
Ali M. Aseere ◽  
...  
Keyword(s):  
Evaluation Framework ◽  
Analytic Hierarchy ◽  
Academic Tasks ◽  
Frequency Of Use ◽  
Wide Range ◽  
Different Dimensions ◽  
Academic Websites ◽  
Academic Information ◽  
Hierarchy Process ◽  
Usability Criteria

In the higher education sector, there is a growing trend to offer academic information to users through websites. Contemporarily, the users (i.e., students/teachers, parents, and administrative staff) greatly rely on these websites to perform various academic tasks, including admission, access to learning management systems (LMS), and links to other relevant resources. These users vary from each other in terms of their technological competence, objectives, and frequency of use. Therefore, academic websites should be designed considering different dimensions, so that everybody can be accommodated. Knowing the different dimensions with respect to the usability of academic websites is a multi-criteria decision-making (MCDM) problem. The fuzzy analytic hierarchy process (FAHP) approach has been considered to be a significant method to deal with the uncertainty that is involved in subjective judgment. Although a wide range of usability factors for academic websites have already been identified, most of them are based on the judgment of experts who have never used these websites. This study identified important factors through a detailed literature review, classified them, and prioritized the most critical among them through the FAHP methodology, involving relevant users to propose a usability evaluation framework for academic websites. To validate the proposed framework, five websites of renowned higher educational institutes (HEIs) were evaluated and ranked according to the usability criteria. As the proposed framework was created methodically, the authors believe that it would be helpful for detecting real usability issues that currently exist in academic websites.

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