Comparison of wind turbine tower failure modes under seismic and wind loads

This paper studies the structural responses and failure modes of a 1.5-MW horizontal-axis wind turbine under strong ground motions and wind loading. Ground motions were selected and scaled to match the two design response spectra given by the seismic code, and wind loads were generated considering tropical cyclone scenarios. Nonlinear dynamic time-history analyses were conducted and structural performances under wind loads as well as short- and long-period ground motions compared. The results show that under strong wind loads the collapse of the wind turbine tower is driven by the formation of a plastic hinge at the lower section of the tower. This area is also critical when the tower is subject to most ground motions. However, some short-period earthquakes trigger the collapse of the middle and upper parts of the tower due to the increased contribution of high-order vibration modes. Although long-period ground motions tend to result in greater structural responses, short-period earthquakes may cause brittle failure modes in which the full plastic hinge develops quickly in regions of the tower with only a moderate energy dissipation capacity. Based on these results, recommendations for future turbine designs are proposed

NDM-558: COMPUTATIONAL MODELING OF TORNADIC LOAD ON A TALL BUILDING

Numerical simulations are carried out to analyse the impact of tornadic load on a tall building. For the present study a one-celled tornado replicating a real EF-2 scale has adopted. A standard tall building based on the Commonwealth Advisory Aeronautical Research Council (CAARC) is used. For detail analysis, the tornado is placed in three different locations with respect to the center of the building. These locations are at the tornado center, at the core radii and outside core radii. As the building has rectangular cross section (plan wise), two different orientation of the building with respect to the center of the buildings are considered. Irrespective of the orientation of the building, higher suction obtains when the center of the building coincides with the center of the tornado and it started to decrease as the tornado center moves away from the building center. This happens due to the ground pressure distribution which dominates the overall pressure distribution along the faces of the building. After comparing the pressure distribution on the roof it obtains that, suction is higher for short building than tall building

NDM-557: COMPUTATIONAL MODELING OF HILL EFFECTS ON TORNADO LIKE VORTEX

Tornado is a complex flow structure, where high swirling flow closer to the ground converges to the center and then moves upward. As a result, it creates a high suction pressure at the ground near the center of the tornado. The main objective of this study is to analyse the impact over flow structure and ground pressure by implementing topographical changes. For the present study a one-celled tornado replicating a real EF-2 scale has been chosen. Previous study suggests that suction ground pressure is highest at the tornado core center, also it changes more sharply near the core center. As a result, the authors decided to raise the surface in the form of a hill at the tornado core center. In this study, two different types of hill based on their slope are implemented for analysing the impact of two different types of topographical changes. It has obtained that as the slope becomes steeper the peak speed up value increases. Also, unlike the synoptic flow case, maximum speed up does not occur at the crest of the hill. Presence of the hill hardly has any impact on the overall pressure distribution at the ground

Evaluating the effect of topographic elements on wind flow : a combined numerical simulation-neutral network approach

Wind pressures on buildings and other structures, pedestrian level winds, and wind-induced dispersion of pollutants in urban locations depend, among other factors, on the velocity profile and turbulence characteristics of the upcoming wind. These, in turn, depend on the roughness and general configuration of the upstream topography. Consequently, wind standards and codes of practice typically assume simplified upstream topography conditions of homogeneous roughness or provide explicit corrections only for a limited number of specific topographies such as single hills, valleys, or escarpments. For all other more complex situations, the practitioner is referred to physical simulations in a boundary layer wind tunnel (BLWT). This thesis evaluates the effect of upstream topography on wind flow using two mathematical approaches: Computational Fluid Dynamics (CFD) and Neural Network (NN) chosen in lieu of traditional BLWT test. CFD-based numerical simulation usually consists of discretizing and solving a set of partial differential equations (the so called Reynolds-averaged Navier-Stokes equations and standard k-[varepsilon] turbulence model) describing the wind flow over a number of different topographic elements. For this purpose a robust Grid Generator, suitable for geometries characterized by curves and slopes, and a specialized CFD tool have been designed using an object-oriented approach and implemented in C++ programming language. Emphasis has been given to several numerical details and to the incorporation of influential parameters such as ground roughness. The associated accuracy of the proposed CFD tool has been quantified and validated against the results of the extensive review carried out. Despite continuous progress in hardware/software technology resulting in fewer resource requirements, the practical utilization of CFD-based numerical simulations to predict design wind load parameters is rather limited. To address this issue, a new combined CFD-NN approach in which the NN model is trained with CFD-generated data has been proposed and developed. Since the NN approach is defined on the basis of connections between system state variables (input, internal and output variables) with only limited knowledge of the "physical" behavior of the system, output variable values (speed-up ratio in the present case) are produced following input of simple geometrical parameters describing the topography and roughness of the ground. In this combined approach, the domain expert first carries out the complex numerical simulations and validations, then trains the NN model and makes it available for use by the end user who avoids therefore dealing with complex numerical simulations. (Abstract shortened by UMI.

NDM-514: LARGE EDDY SIMULATION OF WIND INDUCED LOADS ON A LOW RISE BUILDING WITH COMPLEX ROOF GEOMETRY

Wind induced damage on low-rise buildings with complex roof geometry is common in coastal areas of USA, such as Florida and Louisiana. Available design codes provide information about the design of regular roof geometries (e.g. hip/gable roofs), but refer to wind tunnel modelling for complex roof geometries. Due to time and financial constraints physical modelling may not always be possible to carry out. Computational modelling through Large Eddy Simulation (LES) has been used successfully for several wind engineering applications. This paper presents comparisons between LES and previously obtained wind tunnel data of mean and peak pressure coefficients on a low rise building with complex roof geometry. Two different cases, namely: isolated building and the effect of neighbouring buildings have been considered for the most critical wind direction of 135 degrees. Results show that the mean pressure coefficients on the low rise building roof for the case with adjacent buildings were somewhat lower in magnitude (less suction) than the isolated case. In general, excellent matching was obtained within a factor of 1.1 between wind tunnel and LES for all roof locations except at the roof ridge, where the latter predicted somewhat lower mean and peak pressure coefficient values than wind tunnel data. The velocity streamlines obtained from LES provide an excellent overview of the airflow around the buildings. This study shows the efficacy of LES for assessing wind loads on building roofs with complex geometry, since existing codes do not provide any quantitative assessment methods for such problems

Predicting Residential Energy Consumption Using Wavelet Decomposition With Deep Neural Network

Electricity consumption is accelerating due to economic and population growth. Hence, energy consumption prediction is becoming vital for overall consumption management and infrastructure planning. Recent advances in smart electric meter technology are making high-resolution energy consumption data available. However, many parameters influencing energy consumption are not typically monitored for residential buildings. Therefore, this study’s main objective is to develop a data-driven energy consumption forecasting model (next-hour consumption) for residential houses solely based on analyzing electricity consumption data. This research proposes a deep neural network architecture that combines stationary wavelet transform features and convolutional neural networks. The proposed approach utilizes automatically extracted features from smart-meter readings by applying wavelet decomposition, convolution, and pooling operations. This study’s findings have demonstrated the advantage of integrating wavelet features with convolutional neural networks to improve forecasting accuracy while automating feature extraction

NDM-538: WIND TUNNEL TESTING OF A MULTIPLE SPAN AEROELASTIC TRANSMISSION LINE SUBJECTED TO DOWNBURST WIN

A 1:50 scale aeroelastic wind tunnel test for a multi-span transmission line system is conducted at the WindEEE dome under downburst wind. WindEEE is a novel three-dimensional wind testing facility capable of simulating downbursts and tornadoes. This test simulates a transmission line consisting of v-shaped guyed towers holding three conductor bundles. Details about the model design, the wind field and the test setup are provided. A downburst loading case that is critical for the line design and causes unbalanced tension load on the conductors is investigated in the current study. Resulting line responses obtained from the test are compared with a previously developed finite element model by the research group at the University of Western Ontario. The comparison shows a good agreement which validates the finite element models. Results obtained from this test will be very useful to understand the behavior of the lines under downburst wind

NDM-530: AERODYNAMIC OPTIMIZATION TO REDUCE WIND LOADS ON TALL BUILDINGS

Wind is one of the governing load cases for tall building design, which produces high level of straining actions, deflections and lateral and transverse vibrations. Keeping those vibrations within the comfort limits is becoming a key aspect in tall building design, especially for buildings with high aspect ratio. Improving the aerodynamic performance of the tall building by modifying its shape can lower building motions, which reduces the additional expenses for external damping systems and alleviate the high cost associated with lateral support systems. In the present study, an aerodynamic shape optimization procedure is developed by combining Computational Fluid Dynamics (CFD), optimization algorithm and Artificial Neural Network (ANN). The developed procedure utilizes ANN as a surrogate model for evaluating aerodynamic properties, which is pre-trained using two-dimensional CFD analysis. The current study investigates the validity of the developed procedure by conducting a high accuracy, three-dimensional Large Eddy Simulation (LES) based analysis on the optimal building shapes. It was observed that utilizing two-dimensional CFD simulations in the optimization procedure can help identify effective cross-sections of tall buildings

NDM-529: NUMERICAL EVALUATION OF WIND LOADS ON A TALL BUILDING LOCATED IN A CITY CENTRE

Estimation of wind-induced loads and responses is an essential step in tall building design process. Wind load for super tall buildings is commonly evaluated using boundary layer wind tunnel (BLWT) tests. However, the recent development in computational power and techniques is encouraging designers to explore numerical wind load evaluations using a Computational Fluid Dynamics (CFD) approaches. CFD can provide a faster estimation for building loads and responses with lower cost and satisfactory accuracy for preliminary design stages. The current study investigates the accuracy of evaluating wind pressure and building responses of a typical tall building (CAARC building). Two configurations are investigated, which are (1) standalone building and (2) located in a city center. Large Eddy Simulation (LES) numerical model is utilized adopting a newly developed synthesizing turbulence generator named Consistent Discrete Random Flow Generator (CDRFG). The adopted inflow technique is believed to provide good representation of wind statistics (i.e. velocity and turbulence profiles, spectra and coherency). Pressure distributions and building responses from the current study match with those obtained from boundary layer wind tunnel tests. The average difference between the pressure values between the current model and the BLWT is 4%. While the difference in building responses resulted from the LES model to those from BLWT is 6%. It was found that utilizing CDRFG in LES models provides an accurate estimation for building aerodynamic performance in an efficient computational time owing to its capability of supporting parallel processing

Nonlinear response history analysis and collapse mode study of a wind turbine tower subjected to tropical cyclonic winds

The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases