Non-synoptic Wind Research Articles

Generation and characterization of a non-stationary flow field in a small-scale wind tunnel using a multi-blade flow device

Physical experimentation for non-stationary wind phenomena has been the focal point of much research. Replication of transient, non-synoptic wind events such as thunderstorm downbursts and tornadoes require innovative means that break from traditional boundary-layer wind tunnel experiments. This paper examines the feasibility of a multi-blade flow device capable of reproducing the gust front of a non-stationary outflow. The device is inserted into the test chamber of the small-scale, closed-circuit wind tunnel at Northeastern University. Replication of spatial and temporal features of a non-stationary gust front (slowly-varying flow and turbulence fluctuations) is investigated through velocity measurements at various elevations. The wind velocity record from the Andrews Air Force Base downburst is employed for verification of the experimental procedure; its physical effects on a tall building model are recorded. The results suggest that this device may be used to simulate the main features of simplified non-stationary gust fronts in a conventional wind tunnel without significant modifications to the test chamber.

A first characterization of high winds that affect the energy distribution system of Uruguay and their related effects

UTE is the company that delivers electric power to all Uruguay, serving almost a million and a half clients and 99.3% of Uruguayan homes.When direct wind effects on energy distribution systems are simulated, usually studying the action of wind on sections of these systems, it is generally assumed that high winds are of synoptic type, as e.g. those generated by hurricanes or winter storms. In Uruguay, high wind events are sometimes generated by synoptic winds, usually due to the passage of intense extratropical cyclones, but non-synoptic winds generated by severe convective activity are more frequent and intense in comparison, and are the cause of many incidences and damage to different economic sectors in the country.This paper presents results from the first academic research conducted on wind effects on the energy distribution system of Uruguay. Its aims were to characterize the main outages that occur in this system at national and management levels and their associated meteorological conditions, to explore the relative importance of synoptic and non-synoptic winds as causes of these incidences, and the possibility that different regions of the country exhibit different behavior in relation to the related weather conditions.

A time-domain method for predicting wind-induced buffeting response of tall buildings

• Experimental extraction of aerodynamicload parameters foratall building. • New method for prediction of wind-induced loads and response of a tall building. • Suggested time-domain method can be used even for non-synoptic wind events. • Parametric study showing the effect of increasing building height on the response.

Comparative study of tall building response to synoptic and non-synoptic wind action

Abstract Until the beginning of the 21st Century, the characteristics of wind for purposes of structural analysis and design, as reflected in wind codes worldwide, were based on the behavior of wind currents in the vicinity of the ground surface observed in so-called synoptic events. It was only recently recognized that the latter are not the only cause of wind damage to buildings and structures, not even its main cause. In view of the absence of any reference to non-synoptic winds in most South American wind codes, their urgent revision to include the effects on non-synoptic winds is badly needed. The downburst is a relevant meteorological phenomenon that causes extreme winds in the lower atmospheric boundary layer. The present article briefly describes an introduction to an simplified approach recently proposed by the second author to describe the wind velocity field in this type of meteorological phenomenon, that is, downbursts within instability lines. The method is examined by a comparative study of tall building response to synoptic and non-synoptic wind action.

Downburst-induced transient response of a long-span bridge: A CFD-CSD-based hybrid approach

The long-span bridges, frequently located in the coastline and mountainous areas, are prone to suffering from the transient downburst winds associated with the thunderstorms. Therefore, it is important to examine the behaviors of long-span bridges under such wind events. In this study, the time history of non-turbulent downburst wind field is modeled using the impinging jet-based computational fluid dynamics (CFD) approach. It has demonstrated high-fidelity simulations of the downburst wind field, especially for the near-surface radial winds that are particularly significant for present investigation of bridge aerodynamics and aeroelasticity, with a reasonable computational cost. The simulated time-varying mean wind velocity field of a typical downburst event is validated using available field measurements. The correlated nonstationary fluctuations of the downburst are stochastically simulated by the Hilbert-wavelet scheme based on full-scale data, and then superimposed onto the CFD-based transient mean wind field. The obtained turbulent downburst wind field is employed as the dynamic inputs to the line-element-based three-dimensional (3-D) finite element model of the long-span bridge, and its downburst-induced transient response is acquired using the computational structural dynamics (CSD) approach. The aerodynamic and aeroelastic couplings between the downburst winds and the long-span bridge are modeled using the two-dimensional (2-D) indicial response functions that could well represent the transient bridge aerodynamics under non-synoptic winds. The time-domain buffeting response analysis of a long-span suspension bridge under the traveling downburst has been carried out utilizing the CFD-CSD-based hybrid methodology. The results highlight the importance of the transient and nonstationary effects on the non-synoptic wind-induced structural dynamic response.

Assessment of downburst wind loading on tall structures

Wind features for purposes of structural analysis and design, implicit in wind codes worldwide until the end of last century, were based on the behavior of synoptic winds in the vicinity of the ground surface. Afterwards it was finally recognized that synoptic storms are not the only cause of wind damage to buildings and structures, not even its main cause. In spite of this evidence, non-synoptic winds are still far from being considered as standard loading in structural design. A simplified approach recently proposed by one of the authors to describe the wind velocity field in this type of meteorological phenomenon, more specifically, in downbursts within instability lines, is herein examined, including an assessment of dynamic and size effects not previously addressed. The predictions of the proposed method in applications to tall and slender structures are determined in the paper, assuming that available aerodynamic coefficients, obtained assuming synoptic wind, may be still applied with negligible error.

Novel techniques in wind engineering

While the Alan Davenport Wind Engineering Chain is still valid today, the wind engineering techniques and methodologies have evolved. These changes relate to methods of collecting full scale data, physical and numerical modeling techniques, analysis techniques and wind-structure interaction approaches. These methodologies allow us to look at a more diverse spectrum of wind events including non-stationary, non-synoptic winds and their impact on buildings and structures. Spatially distributed full scale data combined with mesoscale and microscale simulations are more fitted today to characterize the local climatic scales associated to these complex wind events. These wind fields are three-dimensional, non-stationary and sometimes non-Gaussian in nature. However, our well-established Boundary Layer Wind Tunnels produce straight and steady wind and are limited in Reynolds number.The development of larger, multi-fan and sometimes three-dimensional wind facilities has now enabled more realistic laboratory simulations of surface flows for these events. Also, it invites new insight in data analysis and the way we treat the wind-structure interaction problems in a non-stationary context.In view of all this, we provide a review of new emerging technologies and examples of their applicability in the context of new experiments conducted at the WindEEE Research Institute at Western.

Computer-based model for the transient dynamics of a tall building during digitally simulated Andrews AFB thunderstorm

Thunderstorm downbursts are near ground-level meteorological hazards, exhibiting transient, non-synoptic, short-duration and high intensity wind velocities. Winds can induce nonstationary loads and large-amplitude dynamic response in a slender vertical structure. The thunderstorm-induced response against non-synoptic wind loads is extremely complex and cannot be investigated by conventional wind analysis approaches. This study examines the thunderstorm-induced dynamic response of tall buildings. The wind load is based on the observation of the Andrews Air Force Base (AFB) thunderstorm. The main objectives are to: (i) reconstruct the Andrews thunderstorm wind speed record and replicate structure, lifecycle and the fundamental wind parameters, (ii) digitally synthesize the non-turbulent and turbulent velocities to derive aerodynamic loads on a reference tall building, (iii) formulate the thunderstorm-induced dynamics of the tall building subjected to the Andrews thunderstorm-induced downburst loads, and (iv) investigate the response of a tall building by considering two different plausible scenarios. Some unanswered scientific questions are investigated: uncertainty in vertical wind velocity profiles, abrupt change of wind direction angles and influence of crosswind velocities. Three amplitude modulation functions are employed to simulate the transient turbulent field observed during the Andrews thunderstorm. Numerical simulations analyze the dynamic response of the 183-m CAARC tall building.

Field Data Analysis and Weather Scenario of a Downburst Event in Livorno, Italy, on 1 October 2012

AbstractThe Mediterranean is a “hot spot” for the genesis of different types of severe weather events, including potentially damaging wind phenomena like downbursts, whose occurrence and evolution in this geographical region have not been documented in the literature. This paper is part of an interdisciplinary collaboration between atmospheric scientists and wind engineers with the objective of conducting a comprehensive analysis of the field measurements and weather scenarios related to nonsynoptic wind systems in this area. The downburst that struck the Livorno coast of Italy at about 1310 local time 1 October 2012 is investigated as a relevant test case for such severe wind events. The wind velocity records detected by ultrasonic anemometers, part of a monitoring network created for the European “Wind and Ports” and “Wind, Ports and Sea” projects, are analyzed and decomposed in order to inspect the main statistical features of this transient event. The analysis of the meteorological precursors to this event is carried out making use of model analyses, standard in situ measurements, remote sensing techniques, proxy data, and direct observations. The results obtained bring new insights into a downburst’s onset and detection in the Mediterranean, its evolution at the local scale, and possible connections to specific synoptic-scale weather conditions like secondary cyclogenesis in the lee of the Alps.

Modeling vortex-shedding effects for the stochastic response of tall buildings in non-synoptic winds

This study derives a model for the vortex-induced vibration and the stochastic response of a tall building in strong non-synoptic wind regimes. The vortex-induced stochastic dynamics is obtained by combining turbulent-induced buffeting force, aeroelastic force and vortex-induced force. The governing equations of motion in non-synoptic winds account for the coupled motion with nonlinear aerodynamic damping and non-stationary wind loading. An engineering model, replicating the features of thunderstorm downbursts, is employed to simulate strong non-synoptic winds and non-stationary wind loading. This study also aims to examine the effectiveness of the wavelet-Galerkin (WG) approximation method to numerically solve the vortex-induced stochastic dynamics of a tall building with complex wind loading and coupled equations of motions. In the WG approximation method, the compactly supported Daubechies wavelets are used as orthonormal basis functions for the Galerkin projection, which transforms the time-dependent coupled, nonlinear, non-stationary stochastic dynamic equations into random algebraic equations in the wavelet space. An equivalent single-degree-of-freedom building model and a multi-degree-of-freedom model of the benchmark Commonwealth Advisory Aeronautical Research Council (CAARC) tall building are employed for the formulation and numerical analyses. Preliminary parametric investigations on the vortex-shedding effects and the stochastic dynamics of the two building models in non-synoptic downburst winds are discussed. The proposed WG approximation method proves to be very powerful and promising to approximately solve various cases of stochastic dynamics and the associated equations of motion accounting for vortex shedding effects, complex wind loads, coupling, nonlinearity and non-stationarity.

Numerical simulation of dynamic response of a long-span bridge to assess its vulnerability to non-synoptic wind

Winds generated by non-synoptic events such as those from tornadoes, microbursts or gust fronts, that are non-stationary or transient in nature and extreme in magnitude, can cause major damage to flexible structures. In this paper, a time-domain method is used to simulate the response of a long-span bridge subject to winds generated by a particular type of non-synoptic wind phenomenon such as a microburst to assess the vulnerability of the bridge to such winds. The self-excited or motion-induced and buffeting or turbulence-induced wind loads on the structure were modeled and simulated by Rational Functions and buffeting indicial functions, respectively. Wind from a translating microburst was simulated using empirical relationships that were derived from measurements of a laboratory-simulated microburst and the bridge response calculated to compare it with those induced by an equivalent straight-line wind that is used for structural design. It is shown that microburst induced structural vibration could be larger or smaller than the vibration induced by straight-line wind of equivalent magnitude depending on the relative size of the microburst with respect to the bridge span.

Wind engineering challenges of the new generation of super-tall buildings

The new generation of tall buildings is going much higher than before. This poses new challenges for wind engineering. The boundary layer models in many building codes and standards have served well for buildings less than about 300 m but more realistic models need to be used above 300 m. The statistics of upper level winds need also to be known with better certainty. New tools such as the archived global re-analysis data coming from weather forecast models can help shed more light on the upper level wind statistics. There are also questions to be answered about the effects on all tall buildings of non-synoptic wind profiles such as occur in thunderstorm downbursts and the Shamal winds of the Middle East. For the super-tall buildings wind tunnel testing is often commenced much earlier in the design than for lesser buildings. This permits the results to be used in a pro-active way to shape both the architectural design and structural design. The wind tunnel methods used include the force balance technique, aeroelastic modeling, high frequency pressure integration tests, as well as the traditional pressure model and pedestrian wind studies. A super-tall building pushes the limits of the force balance method due to difficulties in maintaining sufficient model stiffness and in accounting for the influence of higher modes of vibration. Since the impact of wind on people using terraces and balconies increases with building height, it is an issue needing particular attention for super-tall buildings.