This paper puts forward two useful methods for self-adaptation of the mutation distribution - the concepts of derandomization and cumulation. Principle shortcomings of the concept of mutative strategy parameter control and two levels of derandomization are reviewed. Basic demands on the self-adaptation of arbitrary (normal) mutation distributions are developed. Applying arbitrary, normal mutation distributions is equivalent to applying a general, linear problem encoding. The underlying objective of mutative strategy parameter control is roughly to favor previously selected mutation steps in the future. If this objective is pursued rigorously, a completely derandomized self-adaptation scheme results, which adapts arbitrary normal mutation distributions. This scheme, called covariance matrix adaptation (CMA), meets the previously stated demands. It can still be considerably improved by cumulation - utilizing an evolution path rather than single search steps. Simulations on various test functions reveal local and global search properties of the evolution strategy with and without covariance matrix adaptation. Their performances are comparable only on perfectly scaled functions. On badly scaled, non-separable functions usually a speed up factor of several orders of magnitude is observed. On moderately mis-scaled functions a speed up factor of three to ten can be expected.

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Completely Derandomized Self-Adaptation in Evolution Strategies

Because of their ubiquitous presence in high-speed flight and their impact on vehicle and component performance, shock-wave/boundary-layer interactions have been studied for about 50 years. Despite truly remarkable progress in computational and measurement capabilities, there are still important quantities that cannot be predicted very accurately, that is, peak heating in strong interactions, or cannot be predicted at all, that is, unsteady pressure loads. There remain observations that cannot be satisfactorily explained and physical processes that are not well understood. Much work remains to be done. Based on the author's own views and those of colleagues, some suggestions are made as to where future efforts might be focused. Just as the first workers in the field could not have foreseen the capabilities generated by the computer/instrumentation revolution of the past 20 years, it is probably fair to assume that the extent of our vision and imagination in the year 2000 is equally limited. New simulation and measurement techniques will doubtlessly become available in the next 10 or 20 years, the results from which will render many of the current concerns moot

Fifty Years of Shock-Wave/Boundary-Layer Interaction Research: What Next?

The paper provides an overview of the historical development of wind energy technology and discusses the current world-wide status of grid-connected as well as stand-alone wind power generation. During the last decade of the twentieth century, grid-connected world-wide wind capacity has doubled approximately every three years. Due to the fast market development, wind turbine technology has experienced an important evolution over time. An overview of the different design approaches is given and issues like power grid integration, economics, environmental impact and special system applications, such as offshore wind energy, are discussed. Due to the complexity of the wind energy technology, however, this paper mainly aims at presenting a brief overview of the relevant wind turbine and wind project issues. Therefore, detailed information to further readings and related organisations is provided. This paper is an updated version of the article ‘Wind Energy Technology and Current Status: A Review’, published in Renewable and Sustainable Energy Reviews, 4/2000, pp. 315–374. This update was requested by Elsevier due to the large interest in wind power.

/pdf/an-overview-of-wind-energy-status-2002-1etdqpsmb8.pdf

An overview of wind energy-status 2002

Location and quantification of noise sources on a wind turbine

Installed global wind power increased by 26% during 2003, with U.S and Europe accounting for 90% of the cumulative capacity. Little is known about wind turbines’ impact on people living in their vicinity. The aims of this study were to evaluate the prevalence of annoyance due to wind turbine noise and to study dose–response relationships. Interrelationships between noise annoyance and sound characteristics, as well as the influence of subjective variables such as attitude and noise sensitivity, were also assessed. A cross-sectional study was performed in Sweden in 2000. Responses were obtained through questionnaires (n=351; response rate 68.4%), and doses were calculated as A-weighted sound pressure levels for each respondent. A statistically significant dose–response relationship was found, showing higher proportion of people reporting perception and annoyance than expected from the present dose–response relationships for transportation noise. The unexpected high proportion of annoyance could be due to visual interference, influencing noise annoyance, as well as the presence of intrusive sound characteristics. The respondents’ attitude to the visual impact of wind turbines on the landscape scenery was found to influence noise annoyance.

http://www.meganoisy.be/Documenten/Perception%20and%20annoyance%20due%20to%20wind%20turbine.pdf

Perception and annoyance due to wind turbine noise : a dose–response relationship

1 Introduction.- 1.1 Current Situation of Wind Energy and Perspectives.- 1.2 Advantages of Wind Energy.- 1.3 Current Problems of Wind Energy.- 1.4 Road Map of the Book.- 2 Noise and its Effects.- 2.1 Sound and Noise.- 2.2 Definitions.- 2.3 Noise Regulations.- 3 Introduction to Aeroacoustics.- 3.1 Introduction.- 3.2 Definitions.- 3.3 The Linear Wave Equation.- 3.4 Elementary Solutions of the Wave Equation.- 3.5 Lighthill's Acoustic Analogy.- 3.6 The Influence of Boundaries.- 3.7 Application of Aeroacoustic Theory.- 3.8 Conclusions.- 4 Noise Mechanisms of Wind Turbines.- 4.1 Classification of Noise Mechanisms.- 4.2 Low-Frequency Noise.- 4.3 Inflow-Turbulence Noise.- 4.4 Airfoil Self-Noise.- 4.5 Summary.- 5 Noise Prediction.- 5.1 Introduction.- 5.2 Low-Frequency Noise.- 5.3 High-Frequency Noise.- 5.4 Summary.- 6 Noise Propagation.- 6.1 Introduction.- 6.2 Mechanisms.- 6.3 Prediction.- 6.4 Results.- 6.5 Summary.- 7 Measurement of Noise and Flow Field.- 7.1 Acoustic Measurement in the Wind Tunnel.- 7.2 Acoustic Measurements on Operating Turbines.- 7.3 Flow Visualization on Operating Turbines.- 8 Noise Reduction.- 8.1 Introduction.- 8.2 Reduction of Tip Speed and Angle of Attack.- 8.3 Reduction of Trailing-Edge Noise.- 8.4 Reduction of Tip Noise.- 8.5 Reduction of Inflow-Turbulence Noise.- 8.6 Reduction of Blunt-Trailing-Edge Noise.- 8.7 Conclusions.- 9 Future Work.- 10 References.- 10.1 Recommended References.- 10.2 List of References.- Annex: Description of Tip Planform Shapes.

Wind Turbine Noise

When a laminar boundary layer separates be- cause of an adverse streamwise pressure gradient, the flow is subject to increased instability with respect to small- amplitude disturbances. Laminar-turbulent transition oc- curs under a rapid three-dimensional (3D) development within the separated shear layer. When the following tur- bulent boundary layer reattaches, a laminar separation bubble is formed. To allow controlled measurements, a small-amplitude Tollmien-Schlichting wave (TS wave) was introduced into the boundary layer without (case I) and with (case II) spanwise forcing of steady 3D disturbances. Combined application of laser-Doppler anemometry (LDA) and particle image velocimetry (PIV) demonstrates the suitability of both measurement techniques to capture the development of unsteady, periodic phenomena. The transition mechanism occurring in the flow field under consideration is discussed, and results obtained by con- trolled measurements are compared to direct numerical simulations (DNS) and predictions from linear stability theory (LST). Flow visualizations and stereoscopic PIV measurements give better insight into the 3D breakdown of the separated shear layer.

Investigations on controlled transition development in a laminar separation bubble by means of LDA and PIV

A laminar boundary layer separates in a region of adverse pressure gradient on a flat plate and undergoes transition. Finally the turbulent boundary layer reattaches, forming a laminar separation bubble (LSB). Laminar-turbulent transition within such a LSB is investigated by means of Laser-Doppler-Anemometry (LDA), Particle Image Velocimetry (PIV), and direct numerical simulation (DNS). The transition mechanism occurring in the flow-field under consideration is discussed in detail. Observations for the development of small disturbances are compared to predictions from viscous linear instability theory (Tollmien-Schlichting instability). Non-linear development of these disturbances and their role in final breakdown to turbulence is analyzed.

A Combined Experimental/Numerical Study of Unsteady Phenomena in a Laminar Separation Bubble

A tool for the numerical shape optimization of axisymmetric bodies submerged in incompressible flow at zero incidence has been developed. Contrary to the usual approach, the geometry of the body is not optimized in a direct way with this method. Instead, a source distribution on the body axis was chosen to model the body contour and the corresponding inviscid flowfield, with the source strengths being used as design variables for the optimization process. Boundary-layer calculation is performed by means of a proved integral method. To determine the transition location, a semiempirical method based on linear stability theory (e n method) was implemented. A commercially available hybrid optimizer as well as an evolution strategy with covariance matrix adaption of the mutation distribution are applied as optimization algorithms. Shape optimizations of airship hulls were performed for different Reynolds number regimes. The objective was to minimize the drag for a given volume of the envelope and a prescribed airspeed range

Drag Reduction and Shape Optimization of Airship Bodies

Reynolds-averaged compressible Navier ‐Stokes computations are presented for the hovering 7A model rotor and a low aspect ratio NACA0012 rotor in nonlifting forward e ight. For enhanced hover performance prediction, aeroelastic effects are taken into account by tightly coupling the e ow solver with a e nite element model of the blade based on Timoshenko beam theory. Good agreement between computed and measured rotor performance is achieved for three collective pitch settings on structured periodic grids featuring noncongruent cell faces along the periodicity planes. Results of a hybrid Navier ‐Stokes/Euler chimera hover computation are presented, in addition to the periodic grid analysis demonstrating the superiority of the overset grid approach with respect to tip vortex conservation. The unsteady Navier ‐Stokes computations for the nonlifting forward e ight test case show more sensitivity relative to time step size than comparable Euler analyses. Overall correlation of computed and experimental near-tip pressure distributions over blade azimuth is considered to be fair, and the strong transonic effects on the advancing blade are adequately captured by the numerical analysis.

Siegfried Wagner

Papers

Wind Turbine Noise

Investigations on controlled transition development in a laminar separation bubble by means of LDA and PIV

A Combined Experimental/Numerical Study of Unsteady Phenomena in a Laminar Separation Bubble

Drag Reduction and Shape Optimization of Airship Bodies

Navier-Stokes Analysis of Helicopter Rotor Aerodynamics in Hover and Forward Flight