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Über dieses Buch

This volume gathers the latest advances, innovations, and applications in the field of wind engineering, as presented by leading international researchers and engineers at the XV Conference of the Italian Association for Wind Engineering (IN-VENTO 2018), held in Naples, Italy on September 9-12, 2018. It covers highly diverse topics, including aeroelasticity, bluff-body aerodynamics, boundary layer wind tunnel testing, computational wind engineering, structural dynamics and reliability, wind-structure interaction, flow-induced vibrations, wind modeling and forecast, wind disaster mitigation, and wind climate assessment. The contributions, which were selected by means of a rigorous international peer-review process, highlight numerous exciting ideas that will spur novel research directions and foster multidisciplinary collaboration among different specialists.

Inhaltsverzeichnis

Frontmatter

Invited Lectures

Frontmatter

Urban Wind Energy: A Wind Engineering and Wind Energy Cross-Roads

Renewable energy reliance and the need to exploit renewable energy resources become an important focus of society. Wind engineering has developed significantly and has contributed to the study of significant aspects of wind energy, particularly in the area of the so-called urban wind energy. This review paper seeks to correlate the characteristics of wind engineering field and wind energy technology by analysing the contributions made in the areas of wind resource assessment in urban areas; examining the current practices in the utilization of wind turbine technologies and future prospects; as well as discussing the attempts to optimize the performance of microgeneration in the urban environment.

T. Stathopoulos, H. Alrawashdeh

Mixed Climatology, Non-synoptic Phenomena and Downburst Wind Loading of Structures

Modern wind engineering was born in 1961, when Davenport published a paper in which meteorology, micrometeorology, climatology, bluff-body aerodynamics and structural dynamics were embedded within a homogeneous framework of the wind loading of structures called today “Davenport chain”. Idealizing the wind with a synoptic extra-tropical cyclone, this model was so simple and elegant as to become a sort of axiom. Between 1976 and 1977 Gomes and Vickery separated thunderstorm from non-thunderstorm winds, determined their disjoint extreme distributions and derived a mixed model later extended to other Aeolian phenomena; this study, which represents a milestone in mixed climatology, proved the impossibility of labelling a heterogeneous range of events by the generic term “wind”. This paper provides an overview of this matter, with particular regard to the studies conducted at the University of Genova on thunderstorm downbursts.

G. Solari

Technical Papers

Frontmatter

Comparison of High-Resolution Pressure Peaks in Closed and Open-Section Wind Tunnels

Wind tunnel testing represents an established technique for the assessment of wind-induced pressure on cladding systems. Nonetheless, some physical events, such as the strong negative peaks of pressure that occur on a building’s lateral facades, are not fully understood. These events can be catastrophic for cladding systems, which motivates their further investigation. The objective of the present work is to study the nature of extreme suction events, by comparing high-resolution pressure tap measurements on a high-rise building collected at two different facilities: the closed-circuit wind tunnel of Politecnico di Milano, and the open-circuit Wall of Wind facility at Florida International University. We first compare the statistics of the two atmospheric boundary layers, and subsequently present results for the mean and root mean square pressure distributions and negative peak pressure events. The experiments provide consistent results, and they both exhibit two types of negative peak pressure events: one is characterized by an extremely short duration and spatial extension, while the other impacts a larger portion of the facade.

L. Amerio, G. Lamberti, G. Pomaranzi, A. Zasso, C. Gorlé

Aerodynamic Tailoring of a Bluff Deck Section Subjected to Inclined Winds Due to the Complex Orography of the Construction Site

Bridges crossing steep valleys in mountainous regions may be subjected to large angles of attack of the incoming wind flow, because of the complex orography of the region where the structure is located. Therefore, the aerodynamic analysis of bridges in this kind of regions should account for this peculiarity. In this paper, the aerodynamic characterization of a bluff deck section of a railway bridge, with angles of attack ranging from −6 to +6° is discussed. It is shown that standard analyses that consider only angles of attack near 0° only are not sufficient to ensure optimal aerodynamic performances. Indeed, with such large angles of attack the flow field near the deck may change consistently, also leading to aeroelastic instabilities or strong vortex-induced vibrations. To mitigate the aeroelastic issues, without an abrupt change of the deck section, several aerodynamic appendices were tested, and a tailored section with acceptable behavior was selected.

T. Argentini, S. Omarini, A. Zasso, M. Petrangeli

A SCADA-Based Method for Estimating the Energy Improvement from Wind Turbine Retrofitting

Retrofitting of operating wind turbines has been spreading in the recent years in the wind energy industry, at the aim of optimizing the efficiency of wind kinetic energy conversion. This kind of interventions has material and labor costs and it is therefore fundamental to estimate realistically the production improvement. Further, the retrofitting of wind turbines sited in harsh environments, as for example complex terrain, might exacerbate the stressing conditions and therefore affect the residue lifetime. This work deals with a case of retrofitting: the testing ground is a multi-megawatt wind turbine from a wind farm sited in a very complex terrain. The blades have been optimized by installing vortex generators and passive flow control devices. A general method is proposed for estimating production upgrades from wind turbine retrofitting, basing on multivariate linear modeling of the power output of the upgraded wind turbine. Applying the model to the test case of interest, it arises that the upgrade increases the annual energy production of the wind turbine of an amount of the order of the 2%.

D. Astolfi, F. Castellani, M. L. Fravolini, S. Cascianelli, L. Terzi

Wind Effects on Containers Stability

Due to their natural location, ports are very exposed to extreme weather conditions. Considering in particular terminal containers, the piled containers can fall and get damaged under strong wind. This paper describes a wide research activity aimed at the evaluation of wind effects on containers stability. The analytical formulation of stability conditions shows that they depend on three groups of parameters: the local wind field and turbulence parameters, the friction coefficient between the containers surface and the aerodynamic coefficients of piled containers. The friction coefficient has been analysed by means of in situ tests on the piled containers. The aerodynamic coefficients have been studied by means of wind tunnel tests on scaled models. The main results are shown and discussed.

A. Balbi, M. P. Repetto, G. Solari, A. Freda, G. Riotto

Mooring System Optimization for a Spar-Buoy Wind Turbine in Rough Wind and Sea Conditions

In this paper the dynamic response of a spar-buoy floating offshore wind turbine (FOWT) is investigated in order to optimize the design of the deep water mooring system. Several mooring system design parameters are considered respecting the assigned constraints with the aim to minimize the platform motions, the normal stress in the mooring lines and the fatigue estimation for harsh environmental conditions. The influence of mooring line ballasting positioning and their amount along the cables is investigated and compared to the reference case.

G. Barbanti, E. Marino, C. Borri

Hybrid HIL Testing of Floating Wind Turbines Within LIFES50+ Project

This paper describes the innovative experimental approach, introduced by the authors in the framework of the EU H2020 project LIFES50+, to perform scale model tests on floating offshore wind turbines (FOWTs). A 6-DOFs hardware-in-the-loop (HIL) system was designed and realized to reproduce the global FOWT response to wind and waves in the atmospheric boundary layer (ABL) of the Politecnico di Milano (PoliMi) wind tunnel. A 2-DOFs (surge and pitch) HIL system was used to perform preliminary tests, assessing the capabilities of the hybrid experimental methodology, and to gather data for the finalization of the 6-DOFs setup. Results from the first experimental campaign are discussed, showing the effect of aerodynamic loads on the coupled FOWT response.

I. Bayati, L. Bernini, A. Facchinetti, A. Fontanella, H. Giberti, A. Zasso, M. Belloli

Wind-Tunnel Experiments on a Large-Scale Flettner Rotor

Experiments on a large-scale Flettner rotor were carried out in the boundary-layer test section of Politecnico di Milano wind tunnel. The rotating cylinder used in the experimental campaign (referred to as Delft Rotor) had a diameter of 1.0 m and span of 3.73 m. The Delft Rotor was equipped with two purpose-built force balances and two different systems to measure the pressure on the rotor’s outer skin. The goal of the experiments was to study the influence of different Reynolds numbers on the aerodynamic forces generated by the spinning cylinder. The highest Reynolds number achieved during the experiments was $$ {\text{Re}} = 1.0 \cdot 10^{6} $$ .

G. Bordogna, S. Muggiasca, S. Giappino, M. Belloli, J. A. Keuning, R. H. M. Huijsmans, A. P. van‘t Veer

Self-excited Vibrations of a Bridge Deck with Single and Double Wind Barriers

Wind-tunnel experiments were carried out to study the influence of wind barriers on the flutter susceptibility of a bridge-deck section. This was performed on the model of a streamlined bridge-deck section equipped with various wind barriers. The wind barriers of various heights and constant porosity of 30% were placed at the (a) windward bridge-deck edge, (b) leeward bridge-deck edge, (c) both windward and leeward bridge-deck edges. The results indicate that the studied bridge deck remains dynamically stable with respect to the heave motion for all configurations of wind barriers. The configurations with wind barriers at both edges are more sensitive to torsional flutter when compared to configurations with single wind barriers placed either at the windward or at the leeward bridge-deck edge.

A. Buljac, H. Kozmar, M. Macháček, S. Pospíšil

Wind Tunnel Experimentation on Stationary Downbursts at WindEEE Dome

In the context of the European Project THUNDERR a scientific collaboration between the Wind Engineering and Structural Dynamics (Windyn) Research Group of the University of Genoa (Italy) and the Wind Engineering, Energy and Environment (WindEEE) Research Institute of Western University (Canada) has been established to study experimentally at the WindEEE Dome facility how the main geometrical and mechanical properties of downbursts are affected by different cloud base outflows of stationary thunderstorms. At present, the analysis of the downbursts simulated experimentally is ongoing and some preliminary elaborations have been obtained concerning the qualitative and quantitative interpretation of the corresponding signals. Classical signal decomposition was applied to experimentally produced downbursts in the WindEEE Dome in order to study transient features of the time series. This study presents the results for two radial positions from downdraft centre and for twenty repetitions per radial position. Several prospects for further research are also discussed.

M. Burlando, D. Romanić, H. Hangan, G. Solari

Damage from Recent Thunderstorms in Romania

The paper presents an overview of wind-induced damage to the natural and the built environment caused by thunderstorms that have occurred in Romania in the past five years (2013–2017). To this aim, a vast online search of mass-media reports is performed in order to identify the date, location and damage type produced by each storm. Due to the lack of measured data, a thunderstorm is identified by means of descriptions of the event provided by interviewed witnesses, by images posted online by the newspaper or by the pattern of damage caused by the storm. The types of damage associated with the identified events include damage to buildings and transmission towers produced by strong winds, damage produced by large hail to buildings, cars as well as crops and flooding produced by heavy rainfall.

I. Calotescu

Full-Scale Measurements of the Structural Response of a 63-Storey Mixed-Use High-Rise Under Wind Loading

Despite the hundreds of wind tunnel studies executed every year on tall- and super-tall buildings globally, the number of full-scale measurements conducted on these structures is still somewhat limited. Full-scale measurements, even for a short duration, have in fact tremendous value as they can be used to validate the structural frequencies predicted during the design stage through Finite Element Model (FEM) analysis and, at the same time, they can provide very valuable information on the level of damping these structures can inherently exhibit once built. In the assessment of the wind-induce response of tall- and super-tall buildings, damping does in fact constitute one of the most uncertain variables. In this technical paper, the findings of a 3-month full-scale monitoring campaign conducted on a 63-storey high-end residential tall building will be presented and discussed in detail.

S. Cammelli, H. Nguyen-Sinh, J. García Navarro

Mitigation of Structural Demand to Wind Turbines: Experimental Investigation of Three Control Strategies

The adoption of wind turbines to produce electric energy nowadays represents one of the most promising alternatives to the use of the exhausting fossil fuel stocks. The actual tendency is toward the design of taller towers that can produce more power because excited by stronger winds. There is the need of designing these structures in a cost effective way, aiming to reduce the wind induced growing structural demand. Three different control systems are investigated and compared herein to this aim, on the basis of the experimental results gathered at the Structural Dynamics Laboratory of the Denmark Technical University. Two of these are passive (tuned rolling-ball damper, spherical tuned liquid damper), while the third one is semi-active and aims at realizing a time-variant base restraint. The experimental comparison of the three strategies, tested against two types of wind loads, allow to draw interesting conclusions and to provide useful hints to give rise to further developments of the technologies investigated.

N. Caterino, C. T. Georgakis, M. Spizzuoco, J. Chen

Feasibility and Assessment of Real Time Monitoring Systems for Smart Structural Control of Wind Turbines

A semi-active (SA) control strategy has been proposed by the authors in the recent years to mitigate structural demand to high wind turbines against strong wind loads. Numerical as well as experimental analyses shown it is really promising and potentially useful to owners who want to optimize costs of realization and installation of such huge structures. The application to real cases of this technique, since based on the use of variable dissipative devices, requires the tower is instrumented for real time monitoring of structural response of the tower. This allows the control algorithm to make the decision about the optimal calibration, moment by moment, of the variable devices. Making reliable high frequency measurements of the horizontal displacement of points placed at a height of tens of meters can be not so trivial. With the aim of evaluating the efficiency and feasibility of Global Navigation Satellite System (GNSS)-based systems for structural control of wind turbines, this paper try to obtain insight into the characteristics (receiver type, type of observables, sampling data rate) and data processing techniques that can make the GNSS useful for such application. Finally, numerical investigations referred to a case study allow to discuss how the features of the measurement system may affect the performance of the proposed SA technique in reducing structural demand due to wind induced vibrations.

N. Caterino, G. Pugliano, M. Spizzuoco, U. Robustelli

Flow Distortion Recorded by Sonic Anemometers on a Long-Span Bridge

Eight months of sonic anemometer records, collected above the deck of a long-span suspension bridge in complex terrain, have been used to assess possible distortion effect of the bridge girder on the monitored flow. For the two main wind directions observed on the bridge site, the velocity records from the downwind side of the deck, in particular, the vertical wind component, are systematically affected by the bridge deck. More precisely, the friction velocity and the variance of the vertical wind fluctuating component are underestimated on the downstream side of the deck. For a deck height H, both the anemometers located on the downwind side, on the same hanger, at a height of 3.6H and 2.2H show a substantial level of flow distortion. This indicates that flow distortion issues can be mitigated more efficiently using anemometers on both sides of the bridge instead of mounting them as high as possible above the deck. The influence of terrain-induced flow distortion is also found to be non-negligible, such that turbulence characteristics significantly different than observed in flat and homogeneous terrains are found.

E. Cheynet, J. B. Jakobsen, J. Snæbjörnsson

Influence of the Measurement Height on the Vertical Coherence of Natural Wind

Two years of sonic anemometer records, collected on the offshore platform FINO1 in the North Sea are used to study the vertical coherence of the along-wind and vertical wind components under near-neutral conditions. The goal is to assess the influence of the measurement height on the coherence estimates. For the data set considered, a 3-parameter coherence model, which depends explicitly on the measurement height and accounts for the limited dimensions of the eddies, is found to be more appropriate than the Davenport model or the uniform shear model to describe the vertical coherence. This is partly because the latter two models do not take into account the blockage effect by the sea surface. The computation of the joint acceptance function of a line-like vertical structure with the Davenport model and the 3-parameter coherence model suggests that the use of the latter model may substantially improve the design of high-rise wind-sensitive structures such as wind turbines.

E. Cheynet

Modeling and Simulation of Non-stationary Thunderstorm Outflows

Wind action on structures is commonly estimated under the stationary assumption that is related to the phenomena that occur in neutral atmospheric conditions at the synoptic scale with velocity profiles in equilibrium with the atmospheric boundary layer. Nevertheless, when thunderstorm outflows are concerned the wind induced load description should take into account its inherent non-stationary features. In this paper a non-stationary model is proposed to describe wind velocity fluctuations of a typical thunderstorm in the northern Italian coast. This model can be obtained by modulating both amplitude and frequency of a stationary process. First, experimental time histories are used to calibrate the non-stationary model, then a parametric dynamic response study to stationary and non-stationary wind loads is finally investigated.

M. Ciano, M. Gioffrè, V. Gusella, M. Grigoriu

On the Aerostructural Design of Long-Span Cable-Stayed Bridges: The Contribution of Parameter Variation Studies with Focus on the Deck Design

The design of long-span bridges consists of dealing with a large number of design variables and it is conditioned by responses of structural and aeroelastic nature. A deep knowledge about the influence of these variables governing the bridge responses is crucial to achieve efficient and safe designs. Apart from heuristic rules, numerical approaches, such as parameter variation studies, sensitivity analysis and optimization algorithms, can provide reliable information to improve designs. This work studies the effects on the flutter and structural responses of a cable-stayed bridge when the mechanical, mass, aerodynamic and aeroelastic properties of a streamlined mono-box deck are modified. These results are used to understand qualitatively and quantitatively the effects caused by the variation of the deck plate thickness and cross-section shape on the bridge responses.

M. Cid Montoya, F. Nieto, S. Hernández, J. Á. Jurado

Structural Optimization of a Reduced-Scale Model of a Wind Mill Tower for Wind Tunnel Testing

This paper describes a research carried out for the design of a wind mill tower reduced-scale model to be built and tested in the boundary layer wind tunnel at the University of La Coruña. It is well known that one of the many requirement of a reduced-scale model is its capability of reproduce the natural frequencies and vibration modes of the real structure. In this research, this is achieved by using a technique developed by the authors in a previous work and adapted to this particular case. This technique is based on the use of optimization algorithms, allowing the minimization of the error between these dynamic properties of the reduced-scale model and the target values. The numerical results are presented.

M. Cid Montoya, S. Hernández, C. López, A. Álvarez, L. Romera, J. Á. Jurado

Probabilistic Assessment of the Galloping Stability of Ice-Accreted Bridge Hangers

Galloping vibrations have recently been identified as a potential problem for ice-accreted bridge hangers. In this study, starting from wind tunnel measurements of the aerodynamic coefficients of an ice accreted HDPE cable hanger, the nature of the ice-accretion aerodynamics is shown. Then, a framework based on Montecarlo simulations is applied for the probabilistic assessment of the minimum structural damping required to prevent galloping of bridge hangers based on the output of a 2-DoFs sectional quasi-steady aeroelastic model. All the variables required to define the hanger dynamics, the sheath aerodynamics and the local wind climate are considered. The results highlight the advantages of the probabilistic procedure in terms of reliability quantification, compared to the deterministic approach.

C. Demartino, F. Ricciardelli

Experimental and Numerical Study of the Wind Tunnel Blockage Effects on the Behaviour of a Horizontal Axis Wind Turbine

This study presents an experimental and numerical investigation of the effects of tunnel blockage, defined as the ratio of the free portion of a wind tunnel cross-section with and without the rotor of a small-size (diameter 2 m) horizontal-axis turbine (HAWT). Experimental measurements were performed on three rotors with different number of blades, namely three, five and six, and different tip speed ratios, in the closed-loop closed-test chamber wind tunnel of the University of Perugia. Numerical wind tunnel simulations were performed at the University of Genoa through a steady-RANS method with SST k-ω turbulence model by means of the CFD solver OpenFOAM. The wind turbine was represented numerically by the actuator disc method. Simulations have been compared to experimental results for validation.

A. Eltayesh, M. Burlando, F. Castellani, M. Becchetti

Wind Field Variability in Complex Terrain: Lessons from the Hardanger Bridge

Along the Coastal Highway E39 in the western coast of Norway, Norwegian Government is planning to build several extreme bridges spanning from 1.5 to 5 km. The region is typically mountainous with deep fjords seeping inland. Here, experience gained from a 5-year monitoring campaign on the Hardanger Bridge in Norway is summarized relating to this ambitious project. The analysis of data provided valuable knowledge on the wind characteristics, which can be generalized for the whole region. Insight has also been gained on the dynamic behaviour of the bridge and how it is influenced by the wind conditions. The results are presented and discussed here with the future bridges in mind.

A. Fenerci, O. Øiseth

Validated Numerical Simulation of Aerodynamic and Aeroelastic Characteristics of Rhein-Crossing Bridge in Leverkusen

This paper presents the results of numerical investigation of the aeroelastic characteristics of an aged bridge deck. The study is developed on the hand of the Rhein-crossing bridge in Leverkusen (Germany), which is undergoing major investigations and will be likely demolished after 53 years of service. Static coefficients and instationary flutter derivatives are determined by means of both forced vibration tests at WIST wind tunnel (Ruhr-Universität Bochum, Germany) and CFD analysis by performing this last as two-dimensional simulations. Pressure measurements in a cross-section in the middle of the bridge model are performed in the wind tunnel experiments, to analyse the wind flow pattern. The numerical model uses the Finite Volume discretization and the turbulence is simulated by the k-ω-SST model. Force and pressure measurements from wind tunnel tests are used for validating the numerical model. The main and original contribution of the study consists in assessing the aerodynamic, as well as aeroelastic, behaviour of an aged bridge deck (with rather unusual “old-fashion” profile) and to verify the performance of CFD-URANS method to determine the bridge flutter derivatives. The aeroelastic forces are obtained by calculating the vectoral difference between the two sets of measurements (Šarkić et al. 2017; Lupi et al. 2018).

G. Ferri, A. Chiaracane, C. Borri, R. Höffer, F. Lupi, U. Winkelmann

Full-Aeroelastic Model of CAARC Building: Iterative Design Procedure and Wind Tunnel Tests

A first step of a broader framework, concerning the investigation of tall buildings’ dynamic response to wind load, is presented. In order to accomplish this challenging task, a well-known benchmark has been selected: the CAARC (Commonwealth Advisory Aeronautical Research Council) standard tall building. Decades of literatures on the subject make it the perfect candidate to tackle the complexity of wind-structure interaction phenomena. The present work concerns the design of a full-aeroelastic multi degrees of freedom model. The configuration proposed by J. Holmes at International Conference on Wind Engineering (2007), accounting for both flexural and torsional decoupled modes of vibrations, is adopted. A design theory present in literature is re-proposed, from a different prospective, in a semi-automated fashion through a Python script. At last, preliminary results are shown, demonstrating the method’s efficiency and applicability, not only to tall buildings, but more generally to structures with continuous distribution of mass.

G. Frison, A. M. Marra, G. Bartoli, R. Scotta

Aerodynamic Instability of Cables with Circular Appendages

The present paper describes the aerodynamic study performed on a cable fitted with a circular tube (pipe) of comparable diameter. Experimental tests were carried out in the high velocity low turbulence test section of the Politecnico di Milano wind tunnel. Typical galloping instability was observed, due to asymmetry introduced by the fitting, but also a strong torsional instability occurred. This phenomenon is not generally significant for cables, but it can appear when fittings change substantially the shape of the cable: for this reason, the study included experimental tests on this instability.

S. Giappino, A. Manenti, S. Muggiasca

Cyclist Aerodynamics: A Comparison Between Wind Tunnel Tests and CFD Simulations for Helmet Design

During the last decades, a particular attention has been paid to the aerodynamic optimization of professional bike riders and their equipment, with a large use of experimental investigation as well as numerical simulations. Extensive studies have been carried out in wind tunnels all over the world by professional cycling teams to study the best set-up for time trial competitions. The standard approach is to compare different parts of the equipment or different positions and find out the optimized configuration by a trial and error procedure. This paper presents an attempt of helmet design based on CFD calculations and experimental validation of numerical results with a new experimental set-up able to measure the surface pressure on a real helmet.

S. Giappino, S. Omarini, P. Schito, S. Somaschini, M. Belloli, M. Tenni

Towards the Second Generation Eurocodes: Evolution of EN 1991-1-4 Wind Actions

In December 2012, through Mandate M/515, the European Commission asked CEN to develop new standards, or new parts of existing standards. This is to include the incorporation of new performance requirements and design methods, the introduction of a more user-friendly approach in several existing standards, and a technical report on how to adapt the existing Eurocodes and the new Eurocode for structural glass to take into account the relevant impacts of future climate change. Within Phase 2 of the Mandate, in 2017 Project Team SC1.T3 EN1991-1-4 was appointed to draft the new EN1991-1-4 on wind actions on structures. This paper summarises the first revised draft prepared in the first year of activity of the Project Team, providing preliminary information on the possible modifications that might appear in the second generation of the document, expected to be completed in 2020.

S. O. Hansen, R. Höffer, J. Rees, F. Ricciardelli, P. Spehl

Extreme Wind Prediction – The Australian Experience

The extreme wind climate of Australia is discussed with a description of the available historical data recorded by the Bureau of Meteorology. The necessity of correction of gusts for gust duration, and for terrain, and for separating the data into storm type is outlined. The ‘bootstrapping’ technique for assessing sampling errors and confidence limits is also discussed. As examples of the methods discussed, recent data from three locations in South Australia were processed. These illustrated the mixed climate near the southern coastline, and the dominance of non-synoptic downdraft winds at a northern station far from the coast.

J. D. Holmes

Life-Cycle Cost-Based Wind Design of Tall Buildings

An automated and computationally cost-effective procedure, designated Life-Cycle Cost Wind Design (LCCWD) and recently proposed by the authors, is presented for the design of wind-excited tall buildings. The LCCWD is based on the evaluation of the life-cycle cost associated with wind-induced damage through the PEER equation. The “best” design configuration is obtained by comparing the lifetime cost of different design alternatives. All the main peculiarities involved in the design of high-rise buildings can be included: uncertainties in the wind load characterization and in the damage estimation, wind directionality effects, modeling of the response (modal superposition accounting for power-law function mode shapes, torsional effects, etc.), comfort issues. Moreover, the long-term monetary benefits associated with the installation of a control system can be considered. The present work is aimed at enhancing the investigation of the potentialities of the LCCWD procedure by including direct and indirect losses, different fragility/cost models and various design strategies.

L. Ierimonti, I. Venanzi, L. Caracoglia, A. L. Materazzi

Motion-Dependent Forces on Streamlined Bridge Girders and Their Influencing Parameters – Observations from Wind Tunnel Buffeting Response Data

Aerodynamic stability of long-span bridges is most readily examined in the frequency domain, with self-excited forces modelled as linearized functions of the bridge velocities and displacements. The present paper briefly recalls the experimental approaches to characterize the motion-dependent forces, and further explores the validity of superposition of the linearized load components, in presence of various influencing parameters. Flutter derivatives obtained with section models of two streamlined bridge girders in ambient vibrations are revisited. Emphasis is placed on the influence of the twisting to vertical frequency ratio and the type of the participating degrees of freedom on the identified wind-structure interaction. A novel aspect of the analysis of the buffeting response data is also attempted, in order to isolate the significance of the twisting amplitude on the self-excited wind forces in ambient vibrations.

J. B. Jakobsen

Uncertainty Quantification for RANS Predictions of Wind Loads on Buildings

Computational fluid dynamics simulations to calculate wind pressure loads on buildings can be strongly influenced by uncertainty in the inflow boundary conditions and the turbulence model. In the present work we investigate these uncertainties in Reynolds-averaged Navier-Stokes predictions for wind pressure coefficients of a high-rise building, and compare the results to wind tunnel measurements. The uncertainty in the inflow boundary condition is characterized using three uncertain parameters, the reference velocity, roughness length and model orientation, and propagated to the quantities of interest using a non-intrusive polynomial chaos expansion approach. The results indicate that the uncertainty in the inflow conditions is non negligible, but insufficient to explain the discrepancy with the wind tunnel data, in particular where flow separation occurs. The uncertainty related to the turbulence model is investigated by introducing perturbations in the Reynolds stress tensor. The results confirm that the turbulence model form uncertainty is dominant near the separation region that forms downstream of the windward building edge.

G. Lamberti, C. Gorlé

A Model Extension for Vortex-Induced Vibrations

The paper presents free-vibration wind tunnel tests performed at WIST Boundary Layer Wind Tunnel at Ruhr-Universität Bochum (Germany) on a 3D aeroelastic cylindrical model with circular cross-section. The aim of the tests is to validate a model extension to the original spectral method developed by Vickery & Basu, able to calculate the maximum oscillation of a structure subjected to vortex-induced vibration in the lock-in region. The peculiarity of the extension is the implementation of an experimental curve for the negative aerodynamic damping. It was previously developed by the authors through forced vibration wind tunnel tests. The model extension is based on a linear differential equation. In fact, linear – in case iterative – approaches are usually preferred for the design of structures. However, limitations due to linearization of an intrinsically non-linear phenomenon are unavoidable. Strengths and weaknesses of the linear approach are discussed in the paper.

F. Lupi, H.-J. Niemann, R. Höffer

Aerodynamic Effect of Non-uniform Wind Profiles for Long-Span Bridges

Long-span bridges are often designed based on the assumption of wind field homogeneity. At the Hardanger Bridge, the wind field along the bridge span is monitored though 8 triaxial ultrasonic anemometers. Simultaneously recorded profiles for mean wind velocity and turbulence intensity along the span are used to investigate the effect of non-uniform wind profiles on the aerodynamic behaviour of the Hardanger Bridge. Extreme non-uniformity is considered using Monte Carlo simulations to generate extreme, but realistic wind profiles based on the variability of the measured wind field. When the buffeting response of the Hardanger Bridge is considered, significant effects on the behaviour is found.

T. M. Lystad, A. Fenerci, O. Øiseth

A Comparative Analysis of Construction Costs of Onshore and Shallow- and Deep-Water Offshore Wind Farms

Recent years have seen renewed effort in the technological development of wind energy industry, where alongside onshore and shallow water offshore turbines, deep water offshore turbines have made their appearance, which represent the next frontier. One of the main aspects while developing a wind energy project is the overall cost and its breakdown between the main components. A comparative analysis of the costs associated with the different solution, the assessment of the key parameters of the wind economy, is therefore crucial when evaluating the possible investments. The aim of this work is to compare typical costs of onshore, shallow- and deep-water offshore wind farms, through an analysis of the aspects that characterize the wind economy, such as the cost of capital and operation and maintenance, and of their subheadings.

C. Maienza, A. M. Avossa, F. Ricciardelli, F. Scherillo, C. T. Georgakis

Some Topics About Wind Engineering that Curtain Walling Design Might Be Longing for in Standards

Curtain walling is assuming more and more a leading role in tall building architectural design.From a structural standpoint, there is no doubt that the wind action is the main loading condition, governing all the dimensioning of any curtain wall single component. On the other hand, the wind action is sensitive to any curtain wall local shape discontinuity, or composition peculiarity, which may modify the load intensity on a micro-scale, but still important for structural safety.On such respect, the structural engineer may have to cope with some recurrent issues: to define wind loads during an initial tender phase, when no wind tunnel test has been developed yet; to define wind loads for the cladding of a building that will never have the aid of a wind tunnel test; to define wind loads on components that have not been simulated in the wind tunnel test, because their size was too small when scaled to the wind tunnel test model. Published standards are the main support to this activity, but this paper will show some frequent cases that are still missing, or just partially treated, in the international standards, like: Façade projections, i.e. canopies, balconies, sun-shadings, etc.; Buildings with curved surfaces but non-circular shape; Cladding elements with more than one skin. Examples from the everyday design work will be shown.

G. Manara

Flow Separation Delay and Drag Reduction Through Contoured Transverse Grooves

The results of several investigations aimed at assessing the performance of contoured transverse grooves as a method to delay flow separation are described. The physical mechanism at the basis of this passive technique is the local relaxation of the no-slip boundary condition, with a consequent reduction of the viscous losses and an increase of the downstream near-wall momentum. Numerical simulations and experiments showed that the application of one groove transverse to the flow direction may delay boundary layer separation both in laminar and turbulent conditions. As a consequence, significant increases of the pressure recovery in plane diffusers and decreases of the drag of boat-tailed axisymmetric and two-dimensional bluff bodies were obtained. It is shown that robust configurations may be devised provided the shape and dimension of the grooves are suitably chosen in order to assure the formation of steady and stable local flow recirculations.

A. Mariotti, G. Buresti, M. V. Salvetti

Experimental Study on the Effect of Secondary Vortices at the Trailing Edge on Motion-Induced Vortex Vibration

According to the results of conventional wind tunnel tests on rectangular cross sections with side ratios of B/D = 2–8 (B: along-wind length (m), D: cross-wind length (m)), motion-induced vortex vibration was confirmed. The generation of motion-induced vortex vibration is considered to be caused by the unification of separated vortices from the leading edge and secondary vortices at the trailing edge. Spring-supported tests and smoke flow visualization tests for B/D = 0.62, 0.75, 1.0, 1.18 and 1.50 were conducted in a wind tunnel at Kyushu Institute of Technology. As a result, it was considered that the secondary vortices at the trailing edge are not always essential for the generation of the motion-induced vortex vibration in heaving motion of each cross section. In this study, smoke flow visualizations were performed for side ratios of B/D = 2.0, 4.0, 6.0 in order to elucidate the role of secondary vortices at the trailing edge in motion-induced vortex vibration in heaving motion. Spring-supported tests were also carried out in order to obtain the response characteristics of the models.

K. Matsuda, K. Kato, N. Cao, R. Higashimura

Wind–Wave Loading and Response of OWT Monopiles in Rough Seas

Monopile-supported OWTs are prone to ringing – a dangerous nonlinear resonant phenomenon which is still not fully understood. Both wind and waves have a major influence on it, wind with its aerodynamic damping in the case of an operating wind turbine, and waves due to the fact that only in the case of fully nonlinear wave kinematics such phenomenon has been observed numerically. This study is interested in both of these influences, especially in the case of misaligned wind and waves – when the nonlinearities of waves are coming from a direction of reduced aerodynamic damping. However, for the influence of wave nonlinearities to be fully understood and the most accurate loading model to be used in the study, an intermediate investigation is conducted comparing the loading from combinations of six models for wave kinematics in increasing nonlinearity and three hydrodynamic loading models – Morison equation, slender-body theory in its two used formulations, and FNV perturbation theory on a fixed cylinder representative of an OWT monopile. It has been found that wave kinematics from fifth order could already be sufficient to capture the nonlinear loading in such steep waves as long as a suitable more sophisticated loading model is used. Moreover, none of the considered combinations in this two-dimensional study manage to capture the secondary load cycle, which used to be directly linked to ringing, therefore in the next phase a moving cylinder is to be considered to analyse the potential of capturing ringing in the most efficient manner before moving to the full dynamic OWT in wind and waves.

A. Mockute, C. Borri, E. Marino, C. Lugni

Transitional Shear Layers on Rectangular Sections

The present work implements 2D Particle Image Velocimetry measurements in an effort to study the transition process of the separated shear layer on rectangular sections. Inspection of the average and fluctuating vector fields enable quantitative definitions of important length scales such as transition lengths and reattachment lengths. The effect of free stream Reynolds number is examined in detail which, among other points, show clear trends of increasingly rapid transitions lengths over the wind speeds investigated. Additionally, transitional shear layer dynamics are discussed for sections exposed to inclined winds. It is shown that under small angles of attack, relatively large changes in shear layer trajectory result in significant alterations to the global loads felt by the body.

D. M. Moore, C. W. Letchford, M. Amitay

An Immersed Boundary CFD Code for Building and Environment Applications

We present a novel Computational Fluid Dynamics (CFD) software developed for the Building and Environment applications. The technical noveltries are represented by the use of the Immersed Boundary method which allows a fully automated and extremely quick Cartesian Grid generation process. The result is an easy work-flow that takes less than 10 min to prepare the application, no matter of the geometrical complexity of the object of the simulation. The software focuses on 4 outdoor wind applications: the evaluation of the wind load on constructions, the so called pedestrian comfort analysis on urban districts, the natural ventilation in buildings and the transport and diffusion of contaminants on cities and environmental sites, both in steady-state and transient modes.The equation for the contaminant is decoupled from the solution of the 5 thermo-fluid dynamic equations (conservation of mass, equation of motion and conservation of energy), and it can be solved on an available, previously computed solution, in frozen mode.A fully implicit solution algorithm drives the iterative method to the steady-state solution. In case a transient analysis is of interest, the same solution algorithm is used to follow the time evolution time-step after time-step.The software has been validated against available wind tunnel data.

M. Mulas, R. Zucca

Simultaneous Vibration Suppression and Energy Harvesting in Wind Excited Tall Buildings Equipped with the Tuned Mass Damper Inerter (TMDI)

This paper investigates the potential of tuned mass dampers (TMDs) coupled with inerter devices in different tuned mass dampers inerter (TMDI) topologies to dissipate oscillations in tall buildings due to vortex shedding in the across wind direction while generating electric energy. The TMDI is first optimized for minimizing peak accelerations for serviceability purposes in a 74 storey benchmark steel building under different wind intensity levels. It is seen that TMDI stiffness and damping optimal parameters are robust to design/reference wind velocity and, therefore, to potential climate change effects, while achieving same level of performance using significantly smaller attached mass compared to the classical TMD. Then, a regenerative electromagnetic motor (EM) is added to the TMDI allowing for varying the TMDI damping property as well as transforming part of the dissipated kinetic energy to electricity. It is shown that by increasing TMDI damping above the optimal value for vibration suppression and/or by reducing the inerter property increases the available energy for harvesting at the expense of larger floor accelerations. Therefore, it is concluded that by relaxing serviceability limit state requirements associated with occupancy considerations renders possible an increase in energy generation in wind-excited tall buildings.

F. Petrini, Z. Wang, A. Giaralis

Probabilistic Assessment of Windblown Sand Accumulation Around Railways

New ultra-long transnational railway megaprojects are currently being planned or under construction. Along their route, they increasingly cross arid and desert regions. In these regions, railways are vulnerable to windblown sand. Several failure cases recently occurred, e.g. along the Linhai-Ceke railway in China, or the Aus-Lüderitz railway in Namibia. We consider windblown sand as an environmental key factor, analogously to wind or snow drift. We categorize its effects into Sand Ultimate Limit States and Sand Serviceability Limit States. In the design perspective, the quantitative prediction of the windblown sand sedimented along the railway is mandatory. We propose a probabilistic approach to sedimented windblown sand modelling because of the inborn variability of the phenomenon. The proposed method allows evaluating the design value of the accumulated windblown sand volume for a given site.

L. Raffaele, L. Bruno

Wind-Induced Fatigue Verification Standard Methods

Wind-induced fatigue is a crucial topic in the design of slender structures. Based on a closed-form solution proposed by one of the authors, this paper reports an engineering approach developed to evaluate the buffeting-induced fatigue life of structures and structural elements. Two classes of formulas, referred to as detailed and simplified calculations, are shown. The detailed calculation provides refined approximations of the reference target solution, while the simplified calculation provides easy solutions on the safe side. The novelty of this paper is that it completes the formulation with analytical assessment of input parameters, fully coherent with standards format. Furthermore, the method has been applied to a turbulence-sensitive structural type of sign support structures. Large-scale inspections show that many of these structures suffer for fatigue damages. The comparison between the inspection outcomes and the proposed method results shows a very good agreement, while the European standard assessment provides unreliable results of fatigue life of this kind of structures.

M. P. Repetto, M. Damele

Experimental and Computational Analysis of Microscale Wind Conditions in the Port of Amsterdam

The present paper deals with on-site measurements and 3D steady RANS simulations performed on the “IJmuiden vault” which falls under the Port Authority of Amsterdam. The numerical results were validated, in terms of amplification factor and local wind direction, using on-site measurements carried out by four 2D ultrasonic anemometers for a period of nine months. To quantify the deviation between measured and simulated data, the metric FAC1.3 was used. In that respect, 90% of simulated data (in terms of amplification factor) was found to be within 30% of deviation from the measured data. In terms of local wind direction, 86% of simulated data were found within ±30° and only the 6% of the whole database showed a large deviation equal and greater than ±60°. Finally, a software application was developed to convert the macroscale wind conditions to the local wind conditions near and in the newly built vault.

A. Ricci, B. Blocken

Experimental Tests on the Wave-Induced Response of a Tension Leg Platform Supporting a 5 MW Wind Turbine

Floating offshore wind turbines are complex dynamic structures, and the analysis of their environmental loads requires experimental test investigations. This paper aims to provide the experience gained from wave basin experiments performed at the Danish Hydraulic Institute on a floating wind turbine Tension Leg Platform within the framework of the EU-Hydralab IV Integrated Infrastructure Initiative. Froude-scaled model was subjected to regular waves and steady wind loads. Measurements were taken of hydrodynamics, displacements and wave induced forces at the mooring lines. First, free vibration and hammer tests were performed to obtain the natural frequencies of the floating motions and tower elastic behaviour, respectively. Then, displacements, rotations, and forces were measured under regular waves and parked and rated wind conditions. Spectral analyses were carried out to investigate the dynamic response of TLP wind turbine. The results show that most of the dynamic response occurs at the wave frequency and natural frequencies.

L. Riefolo, M. Vardaroglu, A. M. Avossa

Mixture Model in High-Order Statistics for Peak Factor Estimation on Low-Rise Building

To design reliable structures, extreme pressures and peak factors are required. In many applications of Wind Engineering, their statistical analysis has to be performed considering the non-Gaussianity of the wind pressures. With the increasing precision and sampling frequency of pressure sensors, short and local peak events of large amplitude are more usually captured. Their relevance is naturally questioned in the context of a structural design. Furthermore, the increasing computational power allows for accumulation and analysis of larger data sets revealing the detailed nature of wind flows around bluff bodies. In particular, in the shear layers and where local vortices form, it is commonly admitted that the Probability Density Function (PDF) of measured pressures might exhibit two or more significant components. These mixed flows can be modelled with mixture models (Cook 2016). Whenever several processes coexist, and when one of them is leading in the tail of the statistical distribution, as will be seen next in the context of corner vortices over a flat roof, it is natural to construct the extreme value model with this leading process and not with the mixed observed pressures. It is therefore important to separate the different processes that can be observed in the pressure histories. Once this is done, specific analytical formulations of non-Gaussian peak factors can be used to evaluate the statistics of extreme values (Kareem and Zhao 1994; Chen and Huang 2009). The separation of mixed processes is usually done by means of the PDF of the signals (Cook 2016). This information is of course essential to perform an accurate decomposition, but it might be facilitated by considering higher rank information like auto-correlations and higher correlations like the triple or quadruple correlation. Indeed, the two phenomena that need to be separated and identified might be characterized by significantly different timescales, which are not reflected in the PDF. In this paper, the large negative pressures measured on a flat roof are analyzed and decomposed into two elementary processes, namely, the flapping corner vortex and the turbulent flow detaching from the sharp upstream edge. This paper will finally show that an accurate decomposition of the recorded pressures into their underlying modes provides a more meaningful evaluation of the extreme pressures.

F. Rigo, T. Andrianne, V. Denoël

Vortex Induced Vibrations of Rectangular Cylinders Arranged on a Grid

A grid arrangement made of one hundred rectangular cylinders fixed to the facade of a house generates strong and disturbing mono-harmonic noise. The cross-flow vibration of the rectangular cylinders is identified as the origin of the noise. The present article proposes a complete investigation of the Vortex Induced Vibration (VIV) combined with a grid effect. It is based on in situ measurements, numerical (finite elements and Computational Fluid Dynamics (CFD)) and extensive wind tunnel (WT) modelling. A comparison between unsteady pressure measurements and CFD results allows to understand the vortex shedding process and synchronization type depending on the wind incidence and spacing of the cylinders. On the basis of this multi- approach parametric investigation, a deep understanding of the VIV-grid phenomenon enables to propose two mitigation techniques. These techniques are tested and their effectiveness is reported in terms of vibration amplitude and acoustic intensity (Rigo et al. 2018).

F. Rigo, V. Denoël, T. Andrianne

The Interplay Between Background Atmospheric Boundary Layer Winds and Downburst Outflows. A First Physical Experiment

This paper studies the interaction between downburst outflows and the background atmospheric boundary layer (ABL) winds close to the surface. Downburst is a buoyancy-driven downdraft of cold air that emerges from cumuliform clouds and results in a vigorous starburst outflows upon reaching the surface. Currently, there are neither satisfactory analytical models nor experimental results on the highly complex interaction between these two wind systems. One of the advanced modes of the WindEEE Dome operation, at Western University in Canada, enables the simultaneous generation of downbursts and ABL winds. In accordance with the WindEEE Dome capabilities, an experiment is designed to address this long-standing question on the relationship between ABL winds and downbursts. This paper shows the interaction between downburst and ABL winds for seven azimuthal positions in respect to the incoming ABL wind direction and six heights. The results show that the traditional approach of adding ABL winds to downburst outflow as either vector or algebraic sum is inaccurate for all heights and azimuth angles. A new empirical relationship between downbursts with and without ABL winds is presented herein.

D. Romanic, H. Hangan

Field Measurement of Gas Dispersion in the Atsugi Area

The ability to predict the dispersion of gases is highly important for the environmental assessment of cities and industrial areas, where gaseous emissions have become a matter of global concern. Our study aims to understand the extent to which theoretical models of gaseous dispersion make accurate predictions when compared to actual measurements from real-world geographical areas and to investigate its limitations. With this in mind, we conducted a field study on gas dispersion in the urban area of Atsugi city in Japan. The release point for the gas was set on the rooftop of a building. The sampling points were located on the ground. We compared the distribution of dispersed gases in terms of concentration obtained from the field measurements with our calculations based on the plume model. Both sets of results were in good agreement with each other, except when there was atmospheric instability in an area where dispersion was measured. Meteorological parameters of wind direction fluctuation and vertical wind profile were studied to further understand the areas of atmospheric instability.

R. Sasaki, K. Miyashita, R. Yoshie

Definition of Wind Loads on the Riyadh Western Metro Station

Design of large modern structures can be strongly affected by wind actions, in terms of dynamic loading as well as peak façade cladding load. The wind forcing can be described by means of CFD analysis as well by wind tunnel tests using a scaled model instrumented with pressure taps. The density and the distribution of pressure taps on the building surface is critical, as well as the averaging of the surface pressure time history for the definition of the wind actions. Dynamic actions are calculated using a modal approach, while pressure excitation is computed according to time equivalent area averaging. The definition of the time equivalent area averaging is carefully analysed, in order to provide pressure values consistent with the forcing area.

P. Schito, L. Rosa, A. Zasso

Characterization of Mean Wind Profiles and Surface Roughness Assessment from Wind LIDAR Measurements

To evaluate wind loading on medium to high-rise structures, an accurate representation of the mean wind profile and of the structure of turbulence is required. Wind models are currently incorporated in Codes of Practice, which have been theoretically derived and experimentally calibrated. Nevertheless, the limited amount of data makes such calibration questionable at times. Wind LIDARS have recently appeared and are becoming more and more common for the assessment of wind power and for the monitoring of wind characteristics. They provide a direct measurement of the wind velocity at the site and at the height of interest and offer the possibility of analysing the spatial distribution of mean and fluctuating wind speed. In this paper, wind LIDAR measurements are used to characterize the vertical wind profile, to calibrate surface roughness to be used in wind models and to discuss their accuracy.

V. Sepe, F. Rizzo, F. Ricciardelli, A. M. Avossa

Design and Experimental Optimisation of a cm-Scale Wind Turbine for Energy Harvesting

Wind turbine is a good choice for energy harvesting on trains. The air flow is generated by the train movement and it is quite simple to find places with high flow speed near the wireless sensor nodes location which are typically mounted on bogies and wheelsets. The requested amount of energy is relatively small, in the order of 0.01–0.05 W, allowing for wind turbines with very small diameter, between 2 to 6 cm. In the present work a newly designed turbine is described. The turbine is placed in a duct with protection purposes and it has a symmetrical design that results in power production independently from the train movement direction.

G. Tomasini, D. Tarsitano, S. Giappino, L. Bernini

Experimental Study of Wind Loads on Domed Free Roofs

Design wind loads on domed free roofs have been investigated in a wind tunnel. Wind pressure distributions both on the top and bottom surfaces of the roof models were measured. The rise-to-span ratio, f/D, was varied from 0.1 to 0.4. First, the effect of the Reynolds number on the pressure distribution is examined. Then, the effects of f/D on the wind pressures and forces are made clear. The wind force coefficients for designing the main wind force resisting systems are proposed, in which focus is on the axial forces induced in the columns supporting the roof as the most important load effect, assuming that the roof is rigid and supported by four columns. Finally, the peak wind force coefficients for the design of cladding/components are proposed based on the maximum and minimum peak wind force coefficients irrespective of wind direction.

Y. Uematsu, R. Yamamura

Wind Pressure Distribution on a Porous Double Skin Façade System

Permeable double skin facades (permeable DSF) are part of modern architectural concepts. An accurate assessment of the wind loads and the porosity effects on this kind of facades is crucial for a correct design and performance evaluation. Measuring and predicting DSF airflow is not a straightforward task due to the interaction between the wind turbulence and the outer porous skin. Moreover, Eurocode and many other National Codes do not supply any prescription about such issue. In this paper the comprehensive experimental study of wind loads acting on the porous double skin facade of the New Bocconi Campus, currently under construction in Milan, is reported. Cladding loads assessment has been carried out performing wind tunnel tests on properly scaled rigid models able to reproduce the aerodynamic behaviour of the porous medium. Peak pressures for the inner facade have been estimated and compared to the ones expected forcing a standard glazed facade.

A. Zasso, F. Perotti, L. Rosa, P. Schito, G. Pomaranzi, N. Daniotti

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