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Lance Manuel - One of the best experts on this subject based on the ideXlab platform.
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on wind turbine loads during thunderstorm Downbursts in contrasting atmospheric stability regimes
Energies, 2019Co-Authors: Patrick Hawbecker, Sukanta Basu, Lance ManuelAbstract:Severe winds produced by thunderstorm Downbursts pose a serious risk to the structural integrity of wind turbines. However, guidelines for wind turbine design (such as the International Electrotechnical Commission Standard, IEC 61400-1) do not describe the key physical characteristics of such events realistically. In this study, a large-eddy simulation model is employed to generate several idealized downburst events during contrasting atmospheric stability conditions that range from convective through neutral to stable. Wind and turbulence fields generated from this dataset are then used as inflow for a 5-MW land-based wind turbine model; associated turbine loads are estimated and compared for the different inflow conditions. We first discuss time-varying characteristics of the turbine-scale flow fields during the Downbursts; next, we investigate the relationship between the velocity time series and turbine loads as well as the influence and effectiveness of turbine control systems (for blade pitch and nacelle yaw). Finally, a statistical analysis is conducted to assess the distinct influences of the contrasting stability regimes on extreme and fatigue loads on the wind turbine.
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extreme and fatigue loads on wind turbines during thunderstorm Downbursts the influence of alternative turbulence models
Journal of Renewable and Sustainable Energy, 2015Co-Authors: Hieu H Nguyen, Lance ManuelAbstract:Downburst winds are inherently transient and non-stationary by nature. Field records have confirmed the often very rapid variation in time of both mean wind speed and wind direction during a downburst. Turbulence characteristics in a downburst are also different from those in the neutral boundary layer. Studies have indicated that turbulence power spectra during a downburst can deviate significantly from more traditional spectra used for the neutral boundary layer. Estimated power spectra from downburst records indicate additional turbulence energy in the mid-frequency range and often they do not follow the −5/3 slope in the inertial subrange. In this study, three turbulence models that can be combined with a non-turbulent downburst wind field model are presented. The influence of these three models on extreme and fatigue loads for a 5-MW wind turbine is investigated first. Then, a parametric study on the longitudinal turbulence length scale, turbulence intensity, and turbulence vertical component in downburst turbulence modeling is carried out. The influence of these various turbulence-related parameters on loads on the 5-MW wind turbine is discussed.
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transient thunderstorm Downbursts and their effects on wind turbines
Energies, 2014Co-Authors: Hieu H Nguyen, Lance ManuelAbstract:The International Electrotechnical Commission (IEC) Standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of off-standard atmospheric conditions include thunderstorm Downbursts, hurricanes, tornadoes, low-level jets, etc. The simulation of thunderstorm Downbursts and associated loads on a utility-scale wind turbine is the focus of this study. Since the problem has not received sufficient attention, especially in terms of design, we thus focus in this paper on practical aspects. A wind field model that incorporates component non-turbulent and turbulent parts is described and employed in inflow simulations. The non-turbulent part is based on an available analytical model with some modifications, while the turbulent part is simulated as a stochastic process using standard turbulence power spectral density functions and coherence functions whose defining parameters are related to the downburst characteristics such as the storm translation velocity. Available information on recorded Downbursts is used to define two storm scenarios that are studied. Rotor loads are generated using stochastic simulation of the aeroelastic response of a model of a utility-scale 5-MW turbine. An illustrative single storm simulation and the associated turbine response are used to discuss load characteristics and to highlight storm-related and environmental parameters of interest. Extensive simulations for two Downbursts are then conducted while varying the storm’s location and track relative to the turbine. Results suggest that wind turbine yaw and pitch control systems clearly influence overall system response. Results also highlight the important effects of both the turbulence as well as the downburst mean wind profiles on turbine extreme loads.
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simulation of thunderstorm Downbursts and associated wind turbine loads
Journal of Solar Energy Engineering-transactions of The Asme, 2013Co-Authors: Hieu H Nguyen, Lance Manuel, Jason Jonkman, Paul S VeersAbstract:This study is focused on simulation of thunderstorm Downbursts and associated wind turbine loads. We first present a thunderstorm downburst model, in which the wind field is assumed to result from the summation of an analytical mean field and stochastic turbulence. The structure and evolution of the downburst wind field based on the analytical model are discussed. Loads are generated using stochastic simulation of the aeroelastic response for a model of a utility-scale 5-MW turbine. With the help of a few assumptions, particularly regarding control strategies, we address the chief influences of wind velocity fields associated with Downbursts—namely, large wind speeds and large, rapid wind direction changes—by considering different storm scenarios and studying associated turbine loads. These scenarios include, first, an illustrative case to understand details related to the turbine response simulation; this is followed by a study involving a different storm touchdown location relative to the turbine as well as a critical case where a shutdown sequence is included. Results show that the availability of and assumptions in wind turbine control systems during a downburst clearly influence overall system response. Control system choices can significantly mitigate turbine loads during Downbursts. Results also show that different storm touchdown locations result in distinct characteristics in inflow wind fields and, hence, in contrasting turbine response.
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alternative procedures for the simulation of thunderstorm Downbursts and associated wind turbine loads
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2012Co-Authors: Phanisri P Pratapa, Hieu H Nguyen, Lance ManuelAbstract:This study is focused on the simulation of thunderstorm downburst wind fields defined separately from non-turbulent and turbulent parts and of associated loads on a 5-MW wind turbine. The non-turbulent part is simulated using computational fluid dynamics (CFD) tools as well as an alternative semi-empirical model; the turbulent part is simulated as additive stochastic processes using standard turbulence power spectral density functions and coherence functions. A generalized CFD based model—referred to as the Paused Downburst model—is developed to simulate a non-turbulent downburst wind field that is suitable for engineering applications. The CFD-based model also serves as an alternative to an available semi-empirical model that has been developed based on recorded downburst events. These models include as main parameters, the maximum radial velocity as well as the elevation above ground and the radial distance to the maximum radial velocity. Other storm parameters—such as the storm intensity, the storm translation velocity, and the direction of the storm path—are all added to both models in order to simulate the evolution of a downburst. A wind turbine response simulation during a thunderstorm downburst also takes into account ambient (environmental) winds and the storm touchdown point relative to the turbine. Turbine loads are generated using aeroelastic response simulation of a model of the selected utility-scale 5-MW turbine. Using a representative downburst scenario, turbine loads are compared based on wind fields generated using the two approaches. Based on the similarity in response predictions with the two models, it is concluded that the CFD-based Paused Downburst model can serve as an alternative to the semi-empirical one in evaluating thunderstorm downburst scenarios and their effects on wind farms.
Ashraf El A Damatty - One of the best experts on this subject based on the ideXlab platform.
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extensible catenary approach in analyzing transmission line s conductors under Downbursts
Engineering Structures, 2021Co-Authors: A Y Shehata, Ashraf El A DamattyAbstract:Abstract The objective of this paper is to develop a mathematical approach that can predict the structural performance of a cable with end points unaligned both vertically and horizontally. The approach takes into account the extensibility of the cable. Moreover, it considers the analysis of a multiple span cable, the flexibility of the cable’s supports and the effect of both in plane and out-plane loads. An important application of this model is related to the performance of transmission line conductors under High Intensity Wind (HIW) such as Downbursts. The localized nature of those events can lead to failure of one tower, which results in misalignment of the end points of the adjacent spans. The developed model can be used in predicting the performance of an entire line post the failure of one tower during a downburst event. The validation of this mathematical model is conducted by comparing its numerical predictions to the results of the analysis of multi-span conductors conducted using non-linear Finite Element Analysis (FEA). The main advantage of the mathematical model compared to FEA is the efficient computational time, which is very important for predicting the progressive failure of transmission lines under Downbursts as this requires conducting a large number of analyses by varying the location and size of the localized wind event.
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behaviour and design of guyed pre stressed concrete poles under Downbursts
Wind and Structures, 2019Co-Authors: Ahmed Ibrahim, Ashraf El A DamattyAbstract:Pre-stressed concrete poles are among the supporting systems used to support transmission lines. It is essential to protect transmission line systems from harsh environmental attacks such as downburst wind events. Typically, these poles are designed to resist synoptic wind loading as current codes do not address high wind events in the form of Downbursts. In the current study, the behavior of guyed pre-stressed concrete Transmission lines is studied under downburst loads. To the best of the authors\' knowledge, this study is the first investigation to assess the behaviour of guyed pre-stressed concrete poles under downburst events. Due to the localized nature of those events, identifying the critical locations and parameters leading to peak forces on the poles is a challenging task. To overcome this challenge, an in-house built numerical model is developed incorporating the following: (1) a three-dimensional downburst wind field previously developed and validated using computational fluid dynamics simulations; (2) a computationally efficient analytical technique previously developed and validated to predict the non-linear behaviour of the conductors including the effects of the pretension force, sagging, insulator\'s s stiffness and the non-uniform distribution of wind loads, and (3) a non-linear finite element model utilized to simulate the structural behaviour of the guyed pre-stressed concrete pole considering material nonlinearity. A parametric study is conducted by varying the Downbursts locations relative to the guyed pole while considering three different span values. The results of this parametric study are utilized to identify critical downburst configurations leading to peak straining actions on the pole and the guys. This is followed by comparing the obtained critical load cases to new load cases proposed to ASCE-74 loading committee. A non-linear failure analysis is then conducted for the three considered guyed pre-stressed concrete transmission line systems to determine the downburst jet velocity at which the pole systems fail.
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critical load cases for lattice transmission line structures subjected to Downbursts economic implications for design of transmission lines
Engineering Structures, 2018Co-Authors: Ashraf El A Damatty, Amal ElawadyAbstract:Abstract An extensive research program was recently conducted at The University of Western Ontario, Canada to investigate the load profiles that can be used in the analysis and the design of transmission towers subjected to Downbursts. This research was motivated by many transmission line failures that have occurred in different locations around the globe during downburst events. It was also triggered by the fact that the existing codes of practice and guidelines provide very limited information regarding the critical load profiles associated with Downbursts, which act on the towers and conductors of a transmission line system. One of the challenges in predicting the critical forces acting on the towers and conductors is that they are not only dependent on the magnitude of the event but also on its size and location relative to the center of the tower. This complexity results from the localized nature of such events. In the current study, an extensive parametric study is conducted on a number of transmission line systems to evaluate their critical response to downburst loads. The study considers the variations in the downburst location, angle of attack, and size to determine the effect of changing these parameters on the response of the transmission line systems. Based on the results obtained from this parametric study, three critical load cases are identified. The studied towers are then used to assess the economic impact of applying those load cases, expressed by the increase in the weight of the tower.
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finite element modelling of pre stressed concrete poles under Downbursts and tornadoes
Engineering Structures, 2017Co-Authors: Ahmed M Ibrahim, Ashraf El A Damatty, Ayman El M AnsaryAbstract:Abstract Among different types of electrical transmission line structures, pre-stressed concrete transmission poles have the advantages of low installation and maintenance cost, appropriate delivery time, and high corrosion resistivity. Typically, these concrete poles are designed to resist only synoptic wind loading as current codes do not consider high intensity wind events in the form of Downbursts and tornadoes. To the best of the authors’ knowledge, this study is the first investigation to assess the behaviour of pre-stressed concrete poles under High intensity wind events. Due to the localized nature of those events, identifying the critical locations and parameters leading to peak forces on the poles is a challenging task. To overcome this challenge, a built in-house numerical model is developed incorporating the following: (1) a three-dimensional downburst and tornado wind field previously developed and validated using computational fluid dynamics simulations; (2) A computationally efficient analytical technique previously developed and validated to predict the non-linear behaviour of the conductors under non-uniform loads resulting from those events (3) a non-linear finite element model developed in the current study to simulate the structural behaviour of pre-stressed concrete poles considering material nonlinearity. The non-linear finite element model, is validated using experimental data available in the literature. Extensive parametric studies are conducted using the numerical model to determine the critical downburst and tornado configurations leading to peak overturning moment acting on a pole which is designed to remain un-cracked under synoptic wind load. Failure studies are then conducted to assess the downburst and tornado velocities that would lead to a full collapse of the pole.
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aero elastic testing of multi spanned transmission line subjected to Downbursts
Journal of Wind Engineering and Industrial Aerodynamics, 2017Co-Authors: Amal Elawady, Ashraf El A Damatty, Haitham Aboshosha, Girma Bitsuamlak, Horia Hangan, Ahmed ElatarAbstract:Abstract This paper reports the first aero-elastic test conducted under a scaled downburst wind field at the WindEEE dome facility at the University of Western Ontario, Canada. The main purpose of the test is to assess the dynamic response of a multi-span transmission line. The study starts by providing a characterization of the downburst wind field produced in WindEEE including a comparison with results of previously conducted numerical simulations. A number of test configurations, involving different locations of the downburst relative to the line, is considered. A decomposition approach is developed to separate between the resonant and the background components of the response. The results are presented in the form of a dynamic magnification factor that relates the peak response including the dynamic effect to the maximum quasi-static response. The test results show that the resonance contribution ranges between 5% and 10% of the peak response for the tower. They also show that the dynamic response of the conductors can reach up to 30% and 12% of the peak response at low and high downburst speeds, respectively.
Hieu H Nguyen - One of the best experts on this subject based on the ideXlab platform.
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extreme and fatigue loads on wind turbines during thunderstorm Downbursts the influence of alternative turbulence models
Journal of Renewable and Sustainable Energy, 2015Co-Authors: Hieu H Nguyen, Lance ManuelAbstract:Downburst winds are inherently transient and non-stationary by nature. Field records have confirmed the often very rapid variation in time of both mean wind speed and wind direction during a downburst. Turbulence characteristics in a downburst are also different from those in the neutral boundary layer. Studies have indicated that turbulence power spectra during a downburst can deviate significantly from more traditional spectra used for the neutral boundary layer. Estimated power spectra from downburst records indicate additional turbulence energy in the mid-frequency range and often they do not follow the −5/3 slope in the inertial subrange. In this study, three turbulence models that can be combined with a non-turbulent downburst wind field model are presented. The influence of these three models on extreme and fatigue loads for a 5-MW wind turbine is investigated first. Then, a parametric study on the longitudinal turbulence length scale, turbulence intensity, and turbulence vertical component in downburst turbulence modeling is carried out. The influence of these various turbulence-related parameters on loads on the 5-MW wind turbine is discussed.
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transient thunderstorm Downbursts and their effects on wind turbines
Energies, 2014Co-Authors: Hieu H Nguyen, Lance ManuelAbstract:The International Electrotechnical Commission (IEC) Standard 61400-1 for the design of wind turbines does not explicitly address site-specific conditions associated with anomalous atmospheric events or conditions. Examples of off-standard atmospheric conditions include thunderstorm Downbursts, hurricanes, tornadoes, low-level jets, etc. The simulation of thunderstorm Downbursts and associated loads on a utility-scale wind turbine is the focus of this study. Since the problem has not received sufficient attention, especially in terms of design, we thus focus in this paper on practical aspects. A wind field model that incorporates component non-turbulent and turbulent parts is described and employed in inflow simulations. The non-turbulent part is based on an available analytical model with some modifications, while the turbulent part is simulated as a stochastic process using standard turbulence power spectral density functions and coherence functions whose defining parameters are related to the downburst characteristics such as the storm translation velocity. Available information on recorded Downbursts is used to define two storm scenarios that are studied. Rotor loads are generated using stochastic simulation of the aeroelastic response of a model of a utility-scale 5-MW turbine. An illustrative single storm simulation and the associated turbine response are used to discuss load characteristics and to highlight storm-related and environmental parameters of interest. Extensive simulations for two Downbursts are then conducted while varying the storm’s location and track relative to the turbine. Results suggest that wind turbine yaw and pitch control systems clearly influence overall system response. Results also highlight the important effects of both the turbulence as well as the downburst mean wind profiles on turbine extreme loads.
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simulation of thunderstorm Downbursts and associated wind turbine loads
Journal of Solar Energy Engineering-transactions of The Asme, 2013Co-Authors: Hieu H Nguyen, Lance Manuel, Jason Jonkman, Paul S VeersAbstract:This study is focused on simulation of thunderstorm Downbursts and associated wind turbine loads. We first present a thunderstorm downburst model, in which the wind field is assumed to result from the summation of an analytical mean field and stochastic turbulence. The structure and evolution of the downburst wind field based on the analytical model are discussed. Loads are generated using stochastic simulation of the aeroelastic response for a model of a utility-scale 5-MW turbine. With the help of a few assumptions, particularly regarding control strategies, we address the chief influences of wind velocity fields associated with Downbursts—namely, large wind speeds and large, rapid wind direction changes—by considering different storm scenarios and studying associated turbine loads. These scenarios include, first, an illustrative case to understand details related to the turbine response simulation; this is followed by a study involving a different storm touchdown location relative to the turbine as well as a critical case where a shutdown sequence is included. Results show that the availability of and assumptions in wind turbine control systems during a downburst clearly influence overall system response. Control system choices can significantly mitigate turbine loads during Downbursts. Results also show that different storm touchdown locations result in distinct characteristics in inflow wind fields and, hence, in contrasting turbine response.
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alternative procedures for the simulation of thunderstorm Downbursts and associated wind turbine loads
50th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2012Co-Authors: Phanisri P Pratapa, Hieu H Nguyen, Lance ManuelAbstract:This study is focused on the simulation of thunderstorm downburst wind fields defined separately from non-turbulent and turbulent parts and of associated loads on a 5-MW wind turbine. The non-turbulent part is simulated using computational fluid dynamics (CFD) tools as well as an alternative semi-empirical model; the turbulent part is simulated as additive stochastic processes using standard turbulence power spectral density functions and coherence functions. A generalized CFD based model—referred to as the Paused Downburst model—is developed to simulate a non-turbulent downburst wind field that is suitable for engineering applications. The CFD-based model also serves as an alternative to an available semi-empirical model that has been developed based on recorded downburst events. These models include as main parameters, the maximum radial velocity as well as the elevation above ground and the radial distance to the maximum radial velocity. Other storm parameters—such as the storm intensity, the storm translation velocity, and the direction of the storm path—are all added to both models in order to simulate the evolution of a downburst. A wind turbine response simulation during a thunderstorm downburst also takes into account ambient (environmental) winds and the storm touchdown point relative to the turbine. Turbine loads are generated using aeroelastic response simulation of a model of the selected utility-scale 5-MW turbine. Using a representative downburst scenario, turbine loads are compared based on wind fields generated using the two approaches. Based on the similarity in response predictions with the two models, it is concluded that the CFD-based Paused Downburst model can serve as an alternative to the semi-empirical one in evaluating thunderstorm downburst scenarios and their effects on wind farms.
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a monte carlo simulation study of wind turbine loads in thunderstorm Downbursts
52nd AIAA ASME ASCE AHS ASC Structures Structural Dynamics and Materials Conference, 2011Co-Authors: Hieu H Nguyen, Lance ManuelAbstract:The simulation of thunderstorm Downbursts and of associated loads on a utility-scale wind turbine loads are the focus of this study. Using a deterministic-stochastic hybrid model, downburst-related wind fields are generated separately from non-turbulent and turbulent parts. The non-turbulent part builds on available analytical models developed from data sets that include recorded downburst events; the turbulent part is simulated as a stochastic process using standard turbulence power spectral density functions and coherence functions adjusted by information on parameters such as the thunderstorm’s translation velocity. Key thunderstorm downburst-related parameters include the maximum radial velocity; the height and radial distance to the maximum radial velocity; the storm intensity; the storm translation velocity; and the storm translation direction. In addition, the ambient (environmental) winds, and the storm touchdown location relative to the wind turbine are also important in turbine load computation. A utility-scale 5MW wind turbine model is selected and loads are generated using stochastic simulation of the aeroelastic response. Information available in the literature on recorded Downbursts is used to define the cases studied. A single storm simulation and associated turbine response simulation is first discussed to illustrate loads computation and highlight storm-related parameters of interest. Next, a Monte Carlo simulation study is performed to investigate the influence of touchdown locations and translation direction on turbine extreme loads.
C W Letchford - One of the best experts on this subject based on the ideXlab platform.
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numerical simulation of extreme winds from thunderstorm Downbursts
Journal of Wind Engineering and Industrial Aerodynamics, 2007Co-Authors: Ling Chen, C W LetchfordAbstract:In (Chen, L., 2005. Vector time-varying autoregressive (TVAR) models and their application to downburst wind speeds. A PhD Dissertation, Texas Tech University, Lubbock, Texas.), a nonparametric deterministic–stochastic hybrid (NDESH) model was proposed for characterizing and simulating nonstationary thunderstorm downburst wind fields, and two sets of full-scale downburst wind speed records were fitted in this model. This paper aims to build an empirical numerical model for downburst wind fields according to the NDESH model and based on the results in (Chen, L., 2005; Chen, L., Letchford, C.W., 2005. Proper orthogonal decomposition of two vertical profiles of full-scale nonstationary downburst wind speeds. Journal of Wind Engineering and Industrial Aerodynamics 93(3), 187–216; Chen, L., Letchford, C.W., 2006. Multi-scale correlation analyses of two lateral profiles of full-scale downburst wind speeds, Journal of Wind Engineering and Industrial Aerodynamics 94(9), 675–696.), so that correlated downburst wind speeds can be synthesized from this empirical model.
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multi scale correlation analyses of two lateral profiles of full scale downburst wind speeds
Journal of Wind Engineering and Industrial Aerodynamics, 2006Co-Authors: L Chen, C W LetchfordAbstract:Abstract Lateral correlation analyses are carried out in different scales for two sets of full-scale thunderstorm downburst full wind speed time series. These two sets of data were recorded at the TTU field site, Texas, USA, on June 4 and 15, 2002, respectively. The same data sets were also used in the authors’ previous paper [L. Chen, C.W. Letchford, Proper orthogonal decomposition of two vertical profiles of full-scale nonstationary correlated downburst wind speeds, J. Wind Eng. Ind. Aerodyn., 93(3)(2005) 187–266.], which presents a methodology to model downburst vertical profiles. The statistical procedures utilized in [7], such as the POD technique, the wavelet shrinkage for time-varying mean inference, the two-stage weighted moving-average method for time-varying variance inference and the Priestley's EPSD estimator, are also employed in this paper and their details are thus omitted. While in [7] the authors employed the proper orthogonal decomposition (POD) to reduce the dimensions, POD in this article is employed to measure the degree of the correlation between two deterministic time series. Conventionally, wind speeds are decomposed to a time-varying mean speed and a nonstationary fluctuating speed by virtue of wavelet shrinkage [7]. Time-varying mean speeds are in the largest scale, which are essentially due to translations of storms and radial velocities of spreading flow. It was observed that the time-varying standard deviations [7] of fluctuating speeds are basically driven by time-varying mean speeds other than small-scale turbulence. Therefore, time-varying standard deviations are considered in the medium scale. Finally, the modulated fluctuating speeds are viewed in the smallest scale and due to small-scale turbulence. It is found that (1) the two lateral profiles are fully correlated and almost evenly spatially distributed in the largest and medium scales with more than 96% of the total energy; (2) they are uncorrelated in the smallest scale since the measurement locations are at least 263 m apart.
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proper orthogonal decomposition of two vertical profiles of full scale nonstationary downburst wind speeds lzcl
Journal of Wind Engineering and Industrial Aerodynamics, 2005Co-Authors: L Chen, C W LetchfordAbstract:Abstract The paper proposes a novel analysis framework for nonstationary wind speeds, from which accumulated results can potentially lead to or enhance empirical nonstationary wind speed models such as the hybrid one for Downbursts in (Eng. Struct. 26 (2004) 619). This framework is motivated by the proper orthogonal decomposition (POD) technique and consists of four major steps: separation, POD, approximation and property inference. In the first step, the original wind speed time histories are separated into their time-varying mean speeds and fluctuating speeds through wavelet shrinkage, which is a promising new tool for smoothing; fluctuating speeds are further expressed as the product of their time-varying standard deviations and normalized fluctuating speeds with unit variance. In the second step, the POD is applied to the time-varying means, standard deviations and normalized fluctuation. In the third step, by properly selecting the number of retained modes, the original time series can be approximated to a numerical model. Finally, wind properties such as velocity vertical profiles and turbulence vertical profiles can be calculated from the model. The POD employed herein is a specific POD for arbitrary multivariate data representation. The normalized fluctuations are characterized by both their power spectral densities (PSD) and evolutionary power spectral densities (EPSD). The concept of EPSD for nonstationary processes is briefly presented and one EPSD estimator is given. Specifically, the PSD/EPSD of an original process is related to the PSD/EPSD of the principal coordinate process obtained by the POD. This framework is applied to two sets of nonstationary full-scale thunderstorm downburst wind speed time series. Many appealing downburst properties are obtained and the benefit of the POD is demonstrated.
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parametric study on the along wind response of the caarc building to Downbursts in the time domain
Journal of Wind Engineering and Industrial Aerodynamics, 2004Co-Authors: L Chen, C W LetchfordAbstract:Abstract A primary investigation on the along-wind responses of tall buildings to thunderstorm Downbursts is presented in this paper. Related characteristics of Downbursts are first reviewed. By assuming that Downbursts are fully correlated over the building height, a simple model is applied for downburst wind speeds. As a representative, the CAARC building is modelled as a linear 2-D cantilever beam and a base-pivoted single degree of freedom rigid body as well, and subjected to non-stationary conceptual, actual, and wind tunnel-simulated downburst velocity time histories. For comparison, a typical stationary wind speed record is also applied to the building. The maximum dynamic magnification factor (MDMF) is introduced as a non-dimensional variable to measure and compare the effect of non-stationary Downbursts on the building. The definition of MDMF is the ratio of the maximum dynamic response to the corresponding maximum static response. Relationships between MDMF of the first normal coordinate and MDMFs of responses are derived. For the parametric study, MDMFs of the first normal coordinate for all the time histories are obtained as functions of the building first circular frequency and the first modal damping ratio. Effects of gust profiles and building characteristics on MDMFs and structural along-wind responses are observed theoretically and by the parametric study. The characterizing period for Downbursts could be 36 s . Differences between MDMFs from the Downbursts and those from the typical wind are noted. In practice, the procedure and the results presented here may be used to estimate the maximum dynamic response of a tall building subjected to severe downburst winds.
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a deterministic stochastic hybrid model of Downbursts and its impact on a cantilevered structure
Engineering Structures, 2004Co-Authors: Lizhong Chen, C W LetchfordAbstract:Abstract Thunderstorm Downbursts, which are sources of extreme wind loadings in nature, have caused numerous structural failures around the world. It is essential to build some applicable, though approximate, model for these loadings under which structures can be assessed. In this paper, a deterministic–stochastic hybrid model of Downbursts is presented. In this model, downburst winds are the summation of a deterministic mean and a stochastic fluctuation. Wood’s velocity profile for the vertical profile and Holmes’ empirical model for the time function are utilized to model the mean wind. The fluctuation is modeled as a uniformly modulated evolutionary vector stochastic process. Time histories of downburst wind speeds over slender structures, such as tall buildings, can be simulated by the spectral representation method. Using the simulated Downbursts as input, the dynamic responses of structures are obtained in the time domain. As a numerical example, the dynamic response of a cantilevered structure to simulated Downbursts is computed and their sensitivity to the coherence function is discussed.
Amal Elawady - One of the best experts on this subject based on the ideXlab platform.
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critical load cases for lattice transmission line structures subjected to Downbursts economic implications for design of transmission lines
Engineering Structures, 2018Co-Authors: Ashraf El A Damatty, Amal ElawadyAbstract:Abstract An extensive research program was recently conducted at The University of Western Ontario, Canada to investigate the load profiles that can be used in the analysis and the design of transmission towers subjected to Downbursts. This research was motivated by many transmission line failures that have occurred in different locations around the globe during downburst events. It was also triggered by the fact that the existing codes of practice and guidelines provide very limited information regarding the critical load profiles associated with Downbursts, which act on the towers and conductors of a transmission line system. One of the challenges in predicting the critical forces acting on the towers and conductors is that they are not only dependent on the magnitude of the event but also on its size and location relative to the center of the tower. This complexity results from the localized nature of such events. In the current study, an extensive parametric study is conducted on a number of transmission line systems to evaluate their critical response to downburst loads. The study considers the variations in the downburst location, angle of attack, and size to determine the effect of changing these parameters on the response of the transmission line systems. Based on the results obtained from this parametric study, three critical load cases are identified. The studied towers are then used to assess the economic impact of applying those load cases, expressed by the increase in the weight of the tower.
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aero elastic testing of multi spanned transmission line subjected to Downbursts
Journal of Wind Engineering and Industrial Aerodynamics, 2017Co-Authors: Amal Elawady, Ashraf El A Damatty, Haitham Aboshosha, Girma Bitsuamlak, Horia Hangan, Ahmed ElatarAbstract:Abstract This paper reports the first aero-elastic test conducted under a scaled downburst wind field at the WindEEE dome facility at the University of Western Ontario, Canada. The main purpose of the test is to assess the dynamic response of a multi-span transmission line. The study starts by providing a characterization of the downburst wind field produced in WindEEE including a comparison with results of previously conducted numerical simulations. A number of test configurations, involving different locations of the downburst relative to the line, is considered. A decomposition approach is developed to separate between the resonant and the background components of the response. The results are presented in the form of a dynamic magnification factor that relates the peak response including the dynamic effect to the maximum quasi-static response. The test results show that the resonance contribution ranges between 5% and 10% of the peak response for the tower. They also show that the dynamic response of the conductors can reach up to 30% and 12% of the peak response at low and high downburst speeds, respectively.
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longitudinal force on transmission towers due to non symmetric downburst conductor loads
Engineering Structures, 2016Co-Authors: Amal Elawady, Ashraf El A DamattyAbstract:Abstract Many failure incidents for transmission line structures have been observed in various locations around the globe as a result of downburst wind events. The localized nature of such Downbursts imposes a load case on transmission towers that does not exist under large-scale events such as hurricanes. This load case happens when the downburst location leads to an uneven and unequal distribution of wind velocity along the conductor spans located at opposite sides of a tower. Hence, a difference in the tension forces will develop between the two spans of the conductors attached to the left and right sides of the tower. This difference in tension forces will lead to a net longitudinal force acting on the tower cross arm, which is believed to be the reason for the failure of a number of towers during Downbursts. The estimation of this force requires conducting a nonlinear analysis of the conductors under the variable loading conditions resulting from the most critical downburst location, while taking into account a number of key parameters including the flexibility of the insulators and the conductor’s pretension force. The objective of this paper is to develop a simple procedure that can be used by practitioners to estimate such a force. A study is first conducted to determine the most critical downburst configuration expected to produce the highest values of the longitudinal forces. A parametric study is then conducted to assess the variations in the longitudinal forces with various geometric and material parameters influencing the behaviour of the conductors. Results of this parametric study are then used to develop a set of charts that can be used to estimate the longitudinal forces using three-dimensional linear interpolation. An example is provided to illustrate the application of the developed procedure.
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development of critical load cases simulating the effect of Downbursts and torndos on transmission line structures
Eighth Asia-Pacific Conference on Wind Engineering, 2013Co-Authors: Ashraf El A Damatty, Ahmed Hamada, Amal ElawadyAbstract:In the past decades, many failure incidents for transmission line structures were observed during High Intensity Wind (HIW) events, in the form of Downbursts and tornados, in North America, Australia, and other locations around the globe. Examining design codes pertaining to this type of structures reveals the lack of procedures to determine the wind loading acting on transmission tower systems due to High Intensity events. A major challenge in the analysis and design of structures under HIW is the localized nature of these events, which makes the forces acting on the towers and lines dependent on the location and characteristics of the event. Motivated by the failure of number of transmission towers in Canada, an extensive research program was initiated at the University of Western Ontario (UWO) a decade ago and is still progressing with final aim for developing knowledge and information for designing transmission line structures to sustain HIW events. The current paper covers the two types of HIW events: tornados and Downbursts. For each event, a literature review is provided followed by a summary of the outcomes of the research conducted at UWO and a description of the wind field. The main contribution in this paper is the introduction of procedures to account for the critical effects of HIW on transmission line structures. Using the knowledge gained from years of research on this subject, critical load cases and load profiles simulating the downburst and tornado configurations that are critical for transmission towers are identified and presented in a format that can be implemented in design codes and can be used by practitioners.