Effects of oscillation amplitude on motion-induced forces for 5:1 rectangular cylinders

While the 5:1 rectangular cylinder is a benchmark section, studied extensively, there are limited experimental studies commenting on any amplitude-dependence of its motion-induced forces. To this goal, such a cylinder is tested in wind tunnel through a forced vibration protocol for extracting distributed simultaneous pressure measurements under smooth flow conditions and for different heaving, pitching and coupled motion amplitudes. Ordinary flutter derivatives are extracted, and discrepancies due to oscillation amplitude are scrutinized. Spectral analysis is performed for the developing motion-induced forces, and it is found that torsional amplitudes above a threshold would increase higher harmonic frequency content. The phenomenon was also confirmed by means of Probability Density Functions and (PDFs) the Proper Orthogonal Decomposition (POD) of the unsteady wind force. In order to understand the link between the observed amplitude dependence and the flow field variation, the movement of the reattachment point on the cylinder surface is investigated by interpreting statistics of the recorded pressure measurements. The response in terms of instantaneous angle of attack is proven to be incompatible with respect to observations, since equal amplitudes of this variable result to different motion-induced forces

Aeroelastic Phenomena and Pedestrian-Structure Dynamic Interaction on Non-Conventional Bridges and Footbridges

Fluid-structure and pedestrian-structure interaction phenomena are extremely important for non-conventional bridges. The results presented in this volume concern: simplified formulas for flutter assessment; innovative structural solutions to increase the aeroelastic stability of long-span bridges; numerical simulations of the flow around a benchmark rectangular cylinder; examples of designs of large structures assisted by wind-tunnel tests; analytical, computational and experimental investigation of the synchronisation mechanisms between pedestrians and footbridge structures. The present book is addressed to a wide audience including professionals, doctoral students and researchers, aiming to increase their know-how in the field of wind engineering, bluff-body aerodynamics and bridge dynamics

Typhoon Wind Modeling and Flutter Fragility Analysis of Long-Span Bridges in Coastal Regions of China

Typhoon or hurricane or tropical cyclone, which is a large-scale air rotating system around a low atmospheric pressure center, frequently causing devastating economic loss and human casualties along coastal regions due to violent winds, heavy rainfall, massive storm surges, flash flooding or even landslides in mountainous areas. The coastal region of China, which is characterized by high population densities and well-developed cities, is always exposed to typhoon threats with 7~8 landfall typhoons every year since Western Pacific Basin is the most active typhoon basin on earth, accounting for almost one-third of global annual storms. With more long-span bridges are being constructed along this coastal area, it is of great importance to perform the risk assessments on these flexible or wind-sensitive structures subjected to typhoon winds. To reconstruct the mean typhoon wind speed field, a semi-analytical height-resolving typhoon boundary layer wind field model, including a parametric pressure model and an analytical wind model was first developed in Chapter 2 using a scale analysis technique. Some basic characteristics of the inner structure of typhoon wind field, such as the logarithmic vertical wind profile near the ground and super-gradient winds were reproduced. Then, Chapter 3 develops a dataset of two wind field parameters, i.e. the radius to maximum wind speed, R_(max,s) and the Holland pressure profile parameter, B_s in Western Pacific Ocean using the wind data information from best track dataset archived by the Japan Meteorological Agency (JMA) coupled with the present wind field model. The proposed dataset of R_(max,s) and B_s is able to reproduce the JMA wind observations as closely as possible, which allows performing more accurate typhoon wind hazard estimation. On this basis, the maximum wind hazard footprints for over-water, roughness only and roughness and topography combined conditions of 184 observed landed or offshore typhoon-scale storms are generated and archived for risk assessment. Moreover, this supplementary dataset of R_(max,s) and B_s enables the development of recursive models to facilitate both sub-region typhoon simulations and full track simulations. Since the present wind field model can only generate long-time-duration speed, say 10-min mean wind speed, Chapter 4 develops an algorithm to compute the gust factor curve by taking the non-stationary and non-Gaussian characteristics of typhoon winds into account. The real wind data of nine typhoons captured by the structural health monitoring system (SHMS) installed in Xihoumen Bridge were utilized to validate the proposed model. Then, the probability distributions of gust factor associated with any gust time duration of interest can be readily achieved after introducing the statistical models of skewness and kurtosis of typhoon winds. To predict the typhoon wind hazard along the coastal region of China, a geographically-weighted-regression (GWR) -based subregion model was proposed in Chapter 5. The storm genesis model was first applied to a circular boundary around the site of interest. Then, the typhoon forward model including the tracking model, intensity model, and wind field parameter model was developed utilizing the GWR method. A series of performance assessments were performed on the present subregion model before it was employed to predict the typhoon wind hazards around the coastal regions of China. Chapter 6 develops a framework to investigate the probabilistic solutions of flutter instability in terms of critical wind speed accounting for multiple resources of uncertainty to facilitate the development of the fragility curve of flutter issue of long-span bridges. The quantifications of structural uncertainties, as well as aerodynamic uncertainties or the randomness of flutter derivatives, were conducted using both literature survey and experimental methods. A number of probabilistic solutions of flutter critical wind speed for two bridges, say a simply supported beam bridge and the Jiangyin Suspension Bridge were achieved by introducing different sources of uncertainty utilizing both 2D step-by-step analysis and 3D multimode techniques. To examine the flutter failure probability of long-span bridge due to typhoon winds, a case study of a 1666-m-main-span suspension bridge located in the typhoon-prone region was performed. The fragility curves of this bridge in terms of critical wind speed and the typhoon wind hazards curves of the bridge site as the probability of occurrence with respect to any years of interest were developed, respectively by exploiting the techniques achieved in previous chapters. Then a limit state function accounting for the bridge-specific flutter capacity and the site-specific mean typhoon wind hazard as well as the gust factor effects was employed to determine the flutter failure probabilities utilizing Monte Carlo simulation approach

New Advances in Fluid Structure Interaction

Fluid–structure interactions (FSIs) play a crucial role in the design, construction, service and maintenance of many engineering applications, e.g., aircraft, towers, pipes, offshore platforms and long-span bridges. The old Tacoma Narrows Bridge (1940) is probably one of the most infamous examples of serious accidents due to the action of FSIs. Aircraft wings and wind-turbine blades can be broken because of FSI-induced oscillations. To alleviate or eliminate these unfavorable effects, FSIs must be dealt with in ocean, coastal, offshore and marine engineering to design safe and sustainable engineering structures. In addition, the wind effects on plants and the resultant wind-induced motions are examples of FSIs in nature. To meet the objectives of progress and innovation in FSIs in various scenarios of engineering applications and control schemes, this book includes 15 research studies and collects the most recent and cutting-edge developments on these relevant issues. The topics cover different areas associated with FSIs, including wind loads, flow control, energy harvesting, buffeting and flutter, complex flow characteristics, train–bridge interactions and the application of neural networks in related fields. In summary, these complementary contributions in this publication provide a volume of recent knowledge in the growing field of FSIs

The application of parallel computer technology to the dynamic analysis of suspension bridges

This research is concerned with the application of distributed computer technology to the solution of non-linear structural dynamic problems, in particular the onset of aerodynamic instabilities in long span suspension bridge structures, such as flutter which is a catastrophic aeroelastic phenomena. The thesis is set out in two distinct parts:- Part I, presents the theoretical background of the main forms of aerodynamic instabilities, presenting in detail the main solution techniques used to solve the flutter problem. The previously written analysis package ANSUSP is presented which has been specifically developed to predict numerically the onset of flutter instability. The various solution techniques which were employed to predict the onset of flutter for the Severn Bridge are discussed. All the results presented in Part I were obtained using a 486DX2 66MHz serial personal computer. Part II, examines the main solution techniques in detail and goes on to apply them to a large distributed supercomputer, which allows the solution of the problem to be achieved considerably faster than is possible using the serial computer system. The solutions presented in Part II are represented as Performance Indices (PI) which quote the ratio of time to performing a specific calculation using a serial algorithm compared to a parallel algorithm running on the same computer system

Aerodynamic Flutter and Buffeting of Long-span Bridges under Wind Load

With the continuous increase of span lengths, the aerodynamic characteristics of long-span bridges under external wind excitation have become much more complex and wind-induced vibration has always been a problem of great concern. The present research targets on the aerodynamic performance of long-span bridges under wind load with an emphasis on bridge flutter and buffeting. For the aerodynamic flutter analysis of long-span bridges, the present research investigated the effects of the wind turbulence on flutter stability. The characterizations of the self-excited forces are presented in both the frequency-domain and in the time-domain, and the flutter analysis is conducted under both uniform and turbulent flows. The effect of wind turbulence is directly modeled in time-domain to avoid the complicated random parametric excitation analysis of the equation of motion used in previous studies. It is found that turbulence has a stabilizing effect on bridge aerodynamic flutter. A probabilistic flutter analysis of long-span bridges involving random and uncertain variables is also conducted, which can provide more accurate and adequate information than the critical flutter velocity for wind resistance design of long-span bridges. For the buffeting analysis of long-span bridges, the stress-level buffeting analysis of the bridge under spatial distributed forces is conducted to investigate the effects of wind turbulence on the fatigue damage of long-span bridges. It is found that the increase of the turbulence intensity has a strengthening effect on the buffeting-induced fatigue damage of long-span bridges. For buffeting control, a lever-type TMD system is proposed for suppressing excessive buffeting responses of long-span bridges. The lever-type TMD with an adjustable frequency can overcome the drawback of excessive static stretch of the spring of traditional hanging-type TMD and be adaptive to the change of the environment and the structure itself. To effectively apply the lever-type TMD to future feedback control design, the control performance of the lever-type TMD for excessive buffeting responses of long-span bridges has been studied. The effects of wind velocity and attack angle and the stiffness reduction of bridge girder on the control efficiency have also been investigated to determine the adjustment strategy of the lever-type TMD. It is found that the control efficiency of the lever-type TMD varies greatly with the change of the location of the mass block. The lever-type TMD should be adjusted accordingly based on comprehensive consideration of the environment change and specific control objectives

5 European & African Conference on Wind Engineering

The 5th European-African Conference of Wind Engineering is hosted in Florence, Tuscany, the city and the region where, in the early 15th century, pioneers moved the first steps, laying down the foundation stones of Mechanics and Applied Sciences (including fluid mechanics). These origins are well reflected by the astonishing visionary and revolutionary studies of Leonardo Da Vinci, whose kaleidoscopic genius intended the human being to become able to fly even 500 years ago… This is why the Organising Committee has decided to pay tribute to such a Genius by choosing Leonardo's "flying sphere" as the brand of 5th EACWE

Assessment of Numerical Prediction Models for Aeroelastic Instabilities of Bridges

The phenomenon of aerodynamic instability caused by the wind is usually a major design criterion for long-span cable-supported bridges. If the wind speed exceeds the critical flutter speed of the bridge, this constitutes an Ultimate Limit State. The prediction of the flutter boundary, therefore, requires accurate and robust models. The complexity and uncertainty of models for such engineering problems demand strategies for model assessment. This study is an attempt to use the concepts of sensitivity and uncertainty analyses to assess the aeroelastic instability prediction models for long-span bridges. The state-of-the-art theory concerning the determination of the flutter stability limit is presented. Since flutter is a coupling of aerodynamic forcing with a structural dynamics problem, different types and classes of structural and aerodynamic models can be combined to study the interaction. Here, both numerical approaches and analytical models are utilised and coupled in different ways to assess the prediction quality of the coupled model