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

Fluid-Structure Interaction

apport de recherch

Fatigue-Induced Failure in Horizontal-Axis Wind-Turbine (HAWT) Blades and HAWT Drivetrain Gears

Wind energy is one of the most promising and the fastest growing installed alternative-energy production technologies. In fact, it is anticipated that by 2030, at least 20% of the U.S. energy needs will be met by various onshore and offshore wind-farms [a collection of wind-turbines (converters of wind energy into electrical energy) at the same location]. A majority of wind turbines nowadays fall into the class of the so-called Horizontal Axis Wind Turbines (HAWTs). Turbine blades and the gearbox are perhaps the most critical components/subsystems in the present designs of HAWTs. The combination of high failure rates (particularly those associated with turbine-blades and gear-boxes), long downtimes and the high cost of repair remains one of the major problems to the wind-energy industry today. In the case of HAWT blades, one is typically concerned about the following two quasi-static structural-performance requirements: (a) sufficient \u27flap-wise\u27 bending strength to withstand highly-rare extreme static-loading conditions (e.g., 50-year return-period gust, a short strong blast of wind); and (b) sufficient turbine blade \u27flap-wise\u27 bending stiffness in order to ensure that a minimal clearance is maintained between blade tip and the turbine tower at all times during wind turbine operation. If these two structural requirements are not met, HAWT blades typically fail prematurely. In addition to the aforementioned quasi-static structural-performance requirements, one is also concerned about the premature-failure caused by inadequate fatigue-based durability of the HAWT blades. The durability requirement for the turbine blades is typically defined as a minimum of 20-year fatigue life (which corresponds roughly to ca. 108 cycles) when subjected to stochastic wind-loading conditions and cyclic gravity-induced edge-wise bending loads in the presence of thermally-fluctuating and environmentally challenging conditions. In the present work, a computational framework has been developed to address: (a) structural response of HAWT blades subjected to extreme loading conditions; (b) high-cycle-fatigue-controlled durability of the HAWT blades; and (c) methodology for HAWT-blade material selection. To validate the computational approach used, key results are compared with their experimental counterparts available in the public-domain literature. As far as the HAWT gear-boxes are concerned, while they are designed for the entire life (ca. 20 years) of the HAWT, in practice, most gear-boxes have to be repaired or even overhauled considerably earlier (3-5 years). Typically, a HAWT gear-box fails either due to the bending-fatigue-induced failure of its gears, or by tribo-chemical degradation and failure of its bearings. In the present work, a computational framework has been developed to predict HAWT service-life under extreme loading and unfavorable kinematic conditions, for the case when the gear-box service-life is controlled by gear-tooth bending-fatigue failure. In addition, a preliminary investigation of gear-box bearing kinematics, which can result in undesirable rolling-element skidding conditions, is conducted

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

Vibration issues in timber structures: A state-of-the-art review

The increasing use of timber structures worldwide has brought attention to the challenges posed by their lightweight nature, making them more prone to vibrations than more massive structures. Consequently, significant research efforts have been dedicated to understanding and mitigating vibrations in timber structures, while scientific committees strive to establish suitable design regulations. This study aims to classify and identify the main research themes related to timber structure vibrations and highlight future research needs and directions. A bibliometricbased selection process briefly introduces each research topic, presenting the latest findings and proposals for vibration design in timber structures. The paper emphasizes the key outcomes and significant contributions to understanding and addressing vibration issues in timber structures. These findings serve as valuable guidance for researchers, designers, and regulatory bodies involved in designing and assessing timber structures subjected to vibrations

Euromech Colloquium 509: Vehicle Aerodynamics. External Aerodynamics of Railway Vehicles, Trucks, Buses and Cars - Proceedings

During the 509th Colloquium of the Euromech society, held from March 24th & 25th at TU Berlin, fifty leading researchers from all over europe discussed various topics affecting both road vehicle as well as railway vehicle aerodynamics, especially drag reduction (with road vehicles), cross wind stability (with trains) and wake analysis (with both). With the increasing service speed of modern high-speed railway traffic, aerodynamic aspects are gaining importance. The aerodynamic research topics comprise both pure performance improvements, such as the continuous lowering of aerodynamic drag for energy efficiency, as well as safety relevant topics, such as cross-wind stability. The latter topic was most recently brought to attention when a swiss narrow-gauge train overturned during the severe storm Kyrill in january 2007. The shape of the train head usually has largest influence on cross wind stability. Slipstream effects of passing trains cause aerodynamic loads on objects and passengers waiting at platforms. The strength of the slipstream is determined by both the boundary layer development along the length of the train and the wake developing behind the tail of the train. Since high-speed trains can be considered to be as smooth as technically possible, attention is drawn to the wake region. The wake of the train again is also one important factor for the total drag of a train. Due to the fact that trains are bidirectional, optimisation of the leading car of a train with respect to drag and cross wind performance while simultaneously minimising the wake of the train for drag and slipstream performance is a great challenge. Modern optimisation tools are used to aid this multi-parameter multi-constraint design optimisation in conjunction with both CFD and wind tunnel investigations. Since many of the aerodynamic effects in the railway sector are of similar importance to road vehicles, the aim of the colloquium is to bridge the application of shape optimisation principles between rail- and road vehicles. Particular topics to be addressed in the colloquium are: Drag, Energy consumption and emissions: Due to increase in energy cost, drag reduction has gained focus in the past years and attention will grow in the future. Pressure induced drag is of common importance for both rail- and road vehicles. The optimisation of head- and tail shape for road vehicles as well as for bi-directional vehicles (trains) is in the focus. Interference drag between adjacent components shall also be treated. Slipstream Effects: Are a safety issue for high-train operation (Prams sucked into track due to train-induced draught flows) when trains passing platforms at high speeds. For Road vehicles, the ride stability of overtaking cars is influenced by the wake of the leading trucks and busses. Common interest is the minimisation of wake effects for both rail and road vehicles. Cross-Wind Safety, Ride stability under strong winds: Both are safety issues for rail- and road vehicles. Aerodynamic forces shall be minimised (roll moment for trains and also yaw moment for road vehicles). Strategies for Vehicle shape optimisation (head, tail and roof shape) in order to minimise aerodynamic moments. Possibilities of Flow control. Optimisation strategies: Parametrisation, analyses (CFD), Optimisation tools and methods, Application to Drag, Cross-Wind, Ride stability and Snow issue

Wind-induced vibration and equivalent wind load of double-layer cylindrical latticed shells

Previous studies have not comprehensively revealed the wind effects on the double-layer cylindrical latticed shell (DCLS). In the paper, the code considering cross spectra of wind and cross terms of modes is programmed and verified. All the nodes and elements are selected to study the characteristics of wind pressure and response spectra. Studies show that wind pressure energy at the top of the shell is higher than that at the windward or leeward side. The most unfavorable wind direction and the dangerous area is 90° and the middle top, not 120° and the end area as stated in the previous documents. Different orders of mode are excited in various responses, and the resonant component should not be ignored. Higher turbulence at the flow separation area leads to stronger structural amplification on wind effects and different ESWL distributions for various targets. The type of target of should be properly chosen according to the concerned structural performance. Under high wind velocity, structural material and geometric nonlinearities make the dynamic equilibrium positions of the shell jump with time

Coupling road vehicle aerodynamics and dynamics in simulation

A fully coupled system in which a vehicle s aerodynamic and handling responses can be simulated has been designed and evaluated using a severe crosswind test. Simulations of this type provide vehicle manufacturers with a useful alternative to on road tests, which are usually performed at a late stage in the development process with a proto- type vehicle. The proposed simulations could be performed much earlier and help to identify and resolve any aerodynamic sensitivities and safety concerns before significant resources are place in the design. It was shown that for the simulation of an artificial, on-track crosswind event, the use of the fully coupled system was unnecessary. A simplified, one-way coupled system, in which there is no feedback from the vehicle s dynamics to the aerodynamic simulation was sufficient in order to capture the vehicle s path deviation. The realistic properties of the vehicle and accurately calibrated driver model prevented any large attitude changes whilst immersed in the gust, from which variations to the aerodynamics could arise. It was suggested that this system may be more suited to other vehicle geometries more sensitive to yaw motions or applications where a high positional accuracy of the vehicle is required