# Ib Troen's research while affiliated with Roskilde University and other places

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## Publications (34)

A model has been derived for calculating the aggregate effects of stability and the finite height of the planetary boundary layer upon the long-term mean wind profile. A practical implementation of this probabilistic extended similarity-theory model is made, including its incorporation within the European Wind Atlas (EWA) methodology for site-to-si...

The Weibull distribution is commonly used to describe climatological wind-speed distributions in the atmospheric boundary layer. While vertical profiles of mean wind speed in the atmospheric boundary layer have received significant attention, the variation of the shape of the wind distribution with height is less understood. Previously we derived a...

Using the Wind Atlas methodology to predict the average wind speed at one location from measured climatological wind frequency distributions at another nearby location we analyse the relative prediction errors using a linearized flow model (IBZ) and a more physically correct fully non-linear 3D flow model (CFD) for a number of sites in very complex...

Planning and financing of wind power installations require very importantly accurate resource estimation in addition to a number of other considerations relating to environment and economy. Furthermore, individual wind energy installations cannot in general be seen in isolation.
It is well known that the spacing of turbines in wind farms is critica...

The development of wind power as a competitive energy source requires resource assessment of increasing accuracy and detail (including not only the long-term ‘raw’ wind resource, but also turbulence, shear, and extremes), and in areas of increasing complexity. This in turn requires the use of the most advanced large-scale meteorological models and...

The present work addresses the problem of establishing the necessary grid resolution to obtain a given level of numerical accuracy using a CFD model for prediction of flow over terrain. It is illustrated, that a very high resolution may be needed if the numerical difference between consecutive refinements should be of the order of one percent for a...

We propose a simple gust definition based on the theory of excursions by Rice (1944 and 1945). We discuss the relation to the distribution of extreme events and demonstrate theoretically and experimentally that the most probable extreme event is very close to being identical to the gust according to our definition. We demonstrate how it is possible...

Four models of surface boundary-layer flow in complex terrain are compared with observations made at Blashaval Hill, North Uist, Scotland. The field experiment is described by Mason and King (1985). Three of the models are derived from the two-dimensional theory of Jackson and Hunt (1975) and are described in Mason and King (1985), Walmsley et al....

When air blows across a change in surface roughness, an internal boundary layer (IBL) develops within which the wind adapts to the new surface. This process is well described for short fetches, > 1 km. However, few data exist for large fetches on how the IBL grows to become a new equilibrium boundary layer where again the drag laws can be used to e...

An operational hazard assessment technique has been developed to investigate impacts of high concentrations from pollutants emitted in complex terrain. In such environments, atmospheric dispersion is influenced, not only by turbulent mixing and diffusion of the cloud itself, but also by topographically induced wind shear, channeling, local slope fl...

This paper provides an overview of some aspects of atmospheric boundary-layer dispersion processes over homogeneous and complex terrain. Special emphasis is placed on a discussion of the boundarylayer scaling regimes over homogeneous terrain and the characteristics of the dispersion processes associated with each of these regimes. The paper points...

A simple formula for calculating dispersion from a continuous finite line source, placed at right angles to the mean wind direction, is derived on the basis of statistical theory. Comparison is made with the virtual source concept usually used and this is shown to be correct only in the limit where the virtual time lag T sub v is small compared to...

For many problems with turbulent dispersion the Lagrangian approach as introduced by Taylor (1921) is the most appropriate. Extension of this theory to atmospheric dispersion problems is, however, complicated by the inhomogeneity and instationarity of atmospheric turbulence. Here we first describe a method based on the Preferred Path Integration (P...

Some basic principles for a computational puff-model for prediction and simulation of atmospheric dispersion are dis-cussed. The constraints imposed by use of a single point measure-ment of the windfield for advection of puffs are examined. A simple scheme for simulation of a more realistic windfield is proposed. One example of the use of a puff-mo...

The diffusion equation with a wavenumber-dependent diffusivity is derived as an approximation to the statistical theory of plume dispersion from a continuous point source. The travel time explicitly appearing in the statistical theory is implicitly included in the wavenumber-dependent diffusivity K(k). By suitable choice of this function it is poss...

## Citations

... A1b. A domain height of only 3 km was found to be sufficient to ensure an undisturbed flow at the top of the domain, although this value is smaller than the one recommended bySørensen et al. (2012). ...

... WAsP CFD 24 is based on the EllipSys finite volume CFD solver 25,26 and is intended for use on atmospheric microscales; thus, the Coriolis effect is neglected. 27 The topographic (terrain) model is set up for neutral atmospheric stability, 28 and wind speed profiles are modified according to momentum fluxes generated by neutrally buoyant flow for surface roughness. 29 Simulations are run at 20 m by 20 m resolution for the 2 km by 2 km region (the inner box in Figure 2) from a much large grid (the outer domain shown in Figure 2). ...

... The long range model chain is established by nesting the outputs from the local scale model chain to the Eulerian long-range model MATCH , Robertson et al.,(1996). Rimpuff (Mikkelsen et al., 1984;Thykier-Nielsen et al., 1988;Thykier-Nielsen et al. (1993a) is a fast and operational puff diffusion code, developed for real-time simulation of atmospheric dispersion during accidents. It accounts for changes in meteorological conditions (in time and space) while the accident evolves. ...

... In typical preconstruction estimates many models, each treating different effects, are used together in order to predict long-term wind statistics. Each model carries its own (sub-)component uncertainties: e.g., flow modelling over terrain accounting for different mast and turbine positions [78,79], vertical extrapolation [80,81], and long-term correction [e.g. 82] contribute to statistical uncertainty in prediction of wind resources. ...

... The wind speed frequency distribution and turbine power curve are essential for calculating the power produced by wind turbines. The probability density function of the Weibull distribution is a widely reckoned resource for describing the wind speed frequency distribution via parametrization [54], which is given by: ...

... Aside from wind energy, the knowledge of the wind characteristics is important in other areas such as for the calculation of wind loads on buildings and for the planning of airport infrastructure and terminal flight procedures. The depiction of local winds is also essential as a boundary condition for the numerical mapping of wind resources and pollution dispersion (Petersen and Troen, 2012;Lin and Hildemann, 1996). Most current methods and models used in the prediction of wind characteristics were developed based on experiments conducted in extra-tropical locations (H€ ogstr€ om, 1988;Gryning et al., 2007;Sathe et al., 2011;Peña et al., 2014). ...

... The RIX (ruggedness index) is one of the major parameters in WAsP (Mortensen et al., 2004). It has the goal of quantifying the terrain complexity. ...

... More importantly, it is closely tied with the wave field, which in turn is determined by the wind speed, fetch distance, etc. Nevertheless, for ease of usage, a constant surface roughness length (z0) of about 0.2 mm has been widely used in existing literature, e.g., wind resource estimation program WAsP [28] and Charnok relation [29]. ...

... The ruggedness index (RIX) was calculated using WAsP and the result presented in Fig. 13 showed that the ruggedness index of the terrain varies from 0% to 35.7% with an average RIX value of 7.4%. The site could be classified as aflat site [27]. ...

... The detailed map of mean wind speed in the CR was recently computed at the Institute of Atmospheric Physics CAS (Hanslian et Hošek, 2015). It combines VAS interpolation method (Sokol et Štekl, 1995) with microscale model WAsP (Mortensen et al., 1993) and contains data from manned weather stations, unnamed weather stations, air pollution stations and special wind measurements. The resulting wind map shows wind frequency, mean wind speed and Weibull shape parameter for each of 12 evenly distributed directional sectors. ...