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Irwin P.A.,RWDI
Structures Congress 2010 | Year: 2010

Buildings need to be designed to withstand wind loads regardless of where they are located and the laws of physics governing wind loads do not change when crossing political boundaries, nor do basic statistical principles. Likewise in the colder regions of the world snow loads need to be designed for and design values should again be governed by the laws of physics and statistics. However, as any designer working internationally knows, the requirements of building codes can be very different in different parts of the world. Part of this is understandable due to the geographic dependence of climate. Some is also due to historically different approaches to risk and different rates of advancement technically. However, the largest cause is the large gaps in knowledge that still exist in many aspects of wind and snow loads, and these gaps will continue to exist, making international consensus difficult, unless some of the advanced countries decide to increase considerably the research funding directed to these topics. This presentation will discuss some of the differences and similarities of wind and snow provisions in the codes of various countries and discuss approaches to improving consistency and uniformity of methods. © 2010 American Society of Civil Engineers.

Cook N.J.,RWDI
Wind and Structures, An International Journal | Year: 2014

The impact of artefacts in archived wind observations on the design wind speed obtained by extreme value analysis is demonstrated using case studies. A signpost protocol for detecting candidate artefacts is described and its performance assessed by comparing results against previously validated data. The protocol targets artefacts by exploiting the serial correlation between observations. Additional "sieve" algorithms are proposed to identify types of correctable artefact from their "signature" in the data. In extreme value analysis, artefacts displace valid observations only when they are larger, hence always increase the design wind speed. Care must be taken not identify large valid values as artefacts, since their removal will tend to underestimate the design wind speed. Copyright © 2014 Techno-Press, Ltd.

Sanderson R.S.,Trent University | McKenna Neuman C.,Trent University | Boulton J.W.,RWDI
Aeolian Research | Year: 2014

The waste products of mining and smelter operations contain fine particles that, when stored in stockpiles and tailings ponds, are subject to aerodynamic forces that may result in their suspension and transport within boundary layer air flows. The accuracy of atmospheric dispersion models such as AERMOD depends strongly upon suitable inputs for the emission rate that generally must be either measured or estimated from suitable analogues. Measurements of the emission rate of PM10 from smelter slag, based on wind tunnel experiments using the control volume method, are reported in this study and compared with vertical flux values obtained using a finite difference approximation. As compared to natural soils, the dust coatings on slag fragments are rapidly depleted during wind events so that the temporal aspect is important to capture in any consideration of the emission rate. At low wind speeds, vertical flux measurements underestimate the emission rate, but otherwise the agreement is excellent. Comparison with field measurements obtained at the smelter site reveals a degree of overlap with the laboratory data. As a general rule, PM10 emission from smelter slag by aerodynamic entrainment alone is several orders of magnitude lower than published fluxes of total suspended particulate (TSP) emitted from natural soil surfaces for which saltation bombardment is recognized to play a key role in the ejection of dust. © 2014 Elsevier B.V.

Cook N.J.,RWDI
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2013

This paper uses Bootstrapping methods to calibrate the accuracy of estimating the design once in 50 year wind speed, V50, from peak-over-threshold wind speed observations. It confirms previous studies showing that the generalised Pareto distribution is not a satisfactory model for extreme wind speeds. It demonstrates that when n-day maxima are used the value of the total population of independent events is known. This allows the peak-over-threshold observations to be represented by a left-censored probability distribution, eliminating mean bias and greatly reducing the standard error in the V50 estimates. © 2013 Elsevier Ltd.

Cook N.J.,RWDI
Meteorological Applications | Year: 2014

This paper consolidates recent advances in methodologies in extreme-value analysis of wind speeds by using sub-annual maxima in conjunction with exact and penultimate extreme-value models. By avoiding asymptotic models and the associated issues of asymptotic convergence, the consolidated methodology is able to extend analysis further into the lower tail, greatly increasing the statistical confidence. The standard error in design predictions of dynamic pressure is reduced to less than a third of the corresponding standard error from annual maxima. The methodology is demonstrated by re-analysing wind speed data from previously published studies at sites in simple and in various mixed-mechanism climates. © 2013 Royal Meteorological Society.

Harris R.I.,RWDI | Cook N.J.,RWDI
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2014

Part 1: The Weibull distribution has been used for many years to fit parent wind data. It is a particularly good fit to mean wind speed data arising from a wind climate dominated by temperate depressions. This good fit is practically useful, but intellectually not very satisfactory, because the familiar or Forward Weibull distribution is a purely empirical construct and there have seemed to be no reasons, grounded in either atmospheric physics or probability theory, why wind speeds should conform to this model. This paper introduces another distribution, the Offset Elliptical Normal (OEN) model, which has some justification in terms of probability theory and appears to form a more plausible model for mean wind speeds. It is shown that, over the entire practical range from everyday values to 1:10,000 year extremes and beyond, this new distribution matches a Weibull distribution so closely, that the Weibull can be regarded as not just empirical, but as an effective surrogate for the new distribution. One Weibull distribution corresponds to a whole family of the new distribution.Part 2: The assumptions of Harris' Offset Elliptical Normal (OEN) model are verified using direct vector analysis of hourly wind observations at two, widely separated UK stations. The Jenkinson-Lamb index is found not to be effective in separating UK wind observations by causal mechanism for individual analysis. Fitting to the marginal distributions of wind speed and direction is shown not to be practicable owing to the information on their joint action that has been lost. Instead, an optimisation methodology is used to fit multiple disjoint OEN models to the joint PDF of the observed wind vectors, without prior separation of the observations. For Marham, Norfolk, a single OEN is sufficient, but two is marginally better. For Tiree, Inner Hebrides, two disjoint OENs are sufficient, but three is marginally better. For Changi, Singapore, three disjoint OENs correspond well with the three seasonal climates (inter-monsoon, "wet" NE monsoon and "dry" SW monsoon). For Rome (Ciampino) the component that dominates in the upper tail is shown to include downbursts from thunderstorms or other strong convective events. © 2014 Elsevier Ltd.

Ian Harris R.,RWDI
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2014

This paper provides a contribution to the testing of existing methods of analysis of extreme wind speeds and to the development of better alternatives. A method is developed for synthesising a correlated random time series with a Rayleigh amplitude distribution and an arbitrary auto-correlation. The auto-correlation is selected to be the Von Karman model because the method is then used to generate 20,000 years of simulated hourly mean wind speeds. Annual maxima are extracted and exhibited on Gumbel plots. Familiar problems with convergence to asymptotic forms are confirmed and a new problem is revealed in that the annual rate parameter, previously believed to be constant, is found to vary significantly in the range of the measured data encountered in practical extreme value analyses. With the exception of newly developed penultimate methods, all the existing methods of analysis depend implicitly on either convergence to an asymptotic form, or invariance of the annual rate parameter, or both. This has serious implications for the accuracy of these methods, not only for the analysis of annual maxima, but also for extensions of these methods developed to use more data from each year. © 2013 Elsevier Ltd.

Dorigatti F.,RWDI | Sterling M.,University of Birmingham | Baker C.J.,University of Birmingham | Quinn A.D.,University of Birmingham
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2015

This paper explores the results obtained from an innovative physical model study which examined wind induced forces and pressures on a 1:25 scale model of a Class 390 Pendolino at a 30° yaw angle. For the first time, the work considers in detail the differences between moving model experiments and static experiments. Differences between the static and moving experiments are observed in the pressure distribution on the nose region of the train, however over the rest of the train the differences between the two sets of experiments are within the experimental uncertainty. The overall side, lift and rolling moment coefficients acting on the train are also shown to agree. This paper provides the scientific underpinning embedded within the current industrial guidelines and once and for all, demonstrates that in terms of the overall mean aerodynamic side and lift forces and rolling moment coefficients, static experiments are sufficient. © 2014 Elsevier Ltd.

Cook N.J.,RWDI | Harris R.I.,RWDI
Wind and Structures, An International Journal | Year: 2013

The Gringorten estimator has been extensively used in extreme value analysis of wind speed records to obtain unbiased estimates of design wind speeds. This paper reviews the derivation of the Gringorten estimator for the mean plotting position of extremes drawn from parents of the exponential type and demonstrates how it eliminates most of the bias caused by the classical Weibull estimator. It is shown that the coefficients in the Gringorten estimator are the asymptotic values for infinite sample sizes, whereas the estimator is most often used for small sample sizes. The principles used by Gringorten are used to derive a new Consistent Linear Unbiased Estimator (CLUE) for the mean plotting positions for the Fisher Tippett Type 1, Exponential and Weibull distributions and for the associated standard deviations. Analytical and Bootstrap methods are used to calibrate the bias error in each of the estimators and to show that the CLUE are accurate to better than 1%. Copyright © 2013 Techno Press.

Wu H.,RWDI | Kriksic F.,RWDI
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2012

The paper describes methodologies for microclimate assessment and provides strategies for master planners and building designers to create pedestrian comfort conditions that are more responsive to the local climate. The development of these strategies always starts with a detailed analysis of local meteorological data, focusing on the correlation between wind and other weather parameters. The influences of wind conditions on other microclimate issues are illustrated by selected case studies. In these case studies, scale-model wind tunnel testing and CFD modeling are used to predict the wind flow fields around the built environment, as well as the associated outdoor thermal comfort, air ventilation, snow accumulation, rain infiltration and other microclimate conditions. © 2012 Elsevier Ltd.

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