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CONTENTS
Volume 13, Number 2, March 2010
 

Abstract


Key Words


Address


Abstract
This review paper discusses research from the last few years relating to windborne debris risk models and the essential elements of engineering damage prediction models. Generic types of windborne debris are discussed. The results of studies of debris trajectories that are relevant to damage models are described ? in particular the horizontal component of debris velocity as a function of distance travelled. The merits of impact momentum versus impact kinetic energy as a relevant parameter for predicting damage are considered, and how published data from generic cannon impact tests can be used in risk models. The quantitative variation of debris impact damage with wind speed is also discussed. Finally the main elements of previously-proposed debris damage models are described.

Key Words
hurricane; risk; trajectory; tropical cyclone; windborne debris.

Address
J.D. Holmes; JDH Consulting, P.O. Box 269, Mentone, Victoria, 3194, Australia

Abstract
This work presents some analytical and numerical results of a dynamic analysis of the dimensionless 2-D sheet flight equations. Two empirical models for aerodynamic forces and moments are used and compared. Results show that the initial condition of rest is always unstable, and for long times three distinct flight regimes are possible, depending on the initial angle of attack, the Tachikawa number, Ta (in fact, the parameter chosen was its inverse), and a mass ratio. The final orbits in the velocity space and their maximum kinetic energy are compared with a theoretical asymptotic state of the motion equations, and some design considerations are proposed.

Key Words
sheet debris; stability; aerodynamic forces.

Address
A. Scarabino and P. Giacopinelli; Departamento Aeronautica, Universidad Nacional de La Plata,
Calle 116 e/ 47 y 48, 1900 La Plata, Argentina

Abstract
Pressure measurements on static and autorotating flat plates have been recently reported by Lin et al. (2006), Holmes, et al. (2006), and Richards, et al. (2008), amongst others. In general, the variation of the normal force with respect to the angle of attack appears to stall in the mid attack angle range with a large scale separation in the wake. To date however, no surface pressures have been measured on auto-rotating plates that are typical of a certain class of debris. This paper presents the results of an experiment to measure the aerodynamic forces on a flat plate held stationary at different angles to the flow and allowing the plate to auto-rotate. The forces were determined through the measurement of differential pressures on either side of the plate with internally mounted pressure transducers and data logging systems. Results are presented for surface pressure distributions and overall integrated forces and moments on the plates in coefficient form. Computed static force coefficients show the stall effect at the mid range angle of attack and some variation for different Reynolds numbers. Normal forces determined from autorotational experiments are higher than the static values at most pitch angles over a cycle. The resulting moment coefficient does not compare well with current analytical formulations which suggest the existence of a flow mechanism that cannot be completely described through static tests.

Key Words
aerodynamic force coefficients; wind effects; debris.

Address
P. Martinez-Vazquez; School of Civil Engineering, University of Birmingham, UK
C.J. Baker; School of Civil Engineering, University of Birmingham, UK
M. Sterling; School of Civil Engineering, University of Birmingham, UK
A. Quinn; School of Civil Engineering, University of Birmingham, UK
P.J. Richards; Department of Mechanical Engineering University of Auckland, New Zealand

Abstract
By using the \'failure\' model approach, the effects of wind direction on the flight of sheathing panels from the roof of a model house in extreme winds was investigated. A complex relationship between the initial conditions, failure velocities, flight trajectories and speeds was observed. It was found that the local flow field above the roof and in the wake of the house have important effects on the flight of the panels. For example, when the initial panel location is oblique to the wind direction and in the region of separated flow near the roof edge, the panels do not fly from the roof since the resultant aerodynamic forces are small, even though the pressure coefficients at failure are high. For panels that do fly, wake effects from the building are a source of significant variation of flight trajectories and speeds. It was observed that the horizontal velocities of the panels span a range of about 20% ? 95% of the roof height gust speed at failure. Numerical calculations assuming uniform, smooth flow appear to be useful for determining panel speeds; in particular, using the mean roof height, 3 sec gust speed provides a useful upper bound for determining panel speeds for the configuration examined. However, there are significant challenges for estimating trajectories using this method.

Key Words
wind borne debris; low-rise buildings; bluff body aerodynamics; hurricanes.

Address
Bahareh Kordi, Gabriel Traczuk and Gregory A. Kopp; Boundary Layer Wind Tunnel Laboratory, Faculty of Engineering,
University of Western Ontario, London, ON, N6A 5B9, Canada

Abstract
This paper describes the use of coupled Computational Fluid Dynamics (CFD) and Rigid Body Dynamics (RBD) in modelling the aerodynamic behaviour of wind-borne plate type objects. Unsteady 2D and 3D Reynolds Averaged Navier-Stokes (RANS) CFD models are used to simulate the unsteady and non-uniform flow field surrounding static, forced rotating, auto-rotating and free-flying plates. The auto-rotation phenomenon itself is strongly influenced by vortex shedding, and the realisable k-epsilon turbulence modelling approach is used, with a second order implicit time advancement scheme and equal or higher order advection schemes for the flow variables. Sequentially coupling the CFD code with a RBD solver allows a more detailed modelling of the Fluid-Structure Interaction (FSI) behaviour of the plate and how this influences plate motion. The results are compared against wind tunnel experiments on auto-rotating plates and an existing 3D analytical model.

Key Words
CFD; autorotation; windborne debris; fluid-structure interaction.

Address
B. Kakimpa; Department of Civil Engineering, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK
D.M. Hargreaves; Department of Civil Engineering, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK
J.S. Owen; Department of Civil Engineering, The University of Nottingham, University Park, Nottingham, NG7 2RD, UK
P. Martinez-Vazquez; School of Civil Engineering, The University of Birmingham,Edgbaston, Birmingham, B15 2TT, UK
C.J. Baker; School of Civil Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
M. Sterling; School of Civil Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
A.D. Quinn; School of Civil Engineering, The University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK



Abstract
Windborne debris is a major cause of structural damage during severe windstorms and hurricanes owing to its direct impact on building envelopes as well as to the \'chain reaction\' failure mechanism it induces by interacting with wind pressure damage. Estimation of debris risk is an important component in evaluating wind damage risk to residential developments. A debris risk model developed by the authors enables one to analytically aggregate damage threats to a building from different types of debris originating from neighboring buildings. This model is extended herein to a general debris risk analysis methodology that is then incorporated into a vulnerability model accounting for the temporal evolution of the interaction between pressure damage and debris damage during storm passage. The current paper (Part I) introduces the debris risk analysis methodology, establishing the mathematical modeling framework. Stochastic models are proposed to estimate the probability distributions of debris trajectory parameters used in the method. It is shown that model statistics can be estimated from available information from wind-tunnel experiments and post-damage surveys. The incorporation of the methodology into vulnerability modeling is described in Part II.

Key Words
windborne debris; risk analysis; probabilistic modeling; hurricane

Address
Ning Lin and Erik Vanmarcke; Department of Civil and
Environmental Engineering, Princeton University, Princeton, NJ, 08544, USA


Abstract
The \'chain reaction\' effect of the interaction between wind pressure and windborne debris is likely to be a major cause of damage to residential buildings during severe wind events. The current paper (Part II) concerns the quantification of such pressure-debris interaction in an advanced vulnerability model that integrates the debris risk model developed in Part I and a component-based wind-pressure damage model. This vulnerability model may be applied to predict the cumulative wind damage during the passage of particular hurricanes, to estimate annual hurricane losses, or to conduct system reliability analysis for residential developments, with the effect of windborne debris fully considered.

Key Words
windborne debris; risk; vulnerability; hurricane.

Address
Ning Lin, Erik Vanmarcke and Siu-Chung Yau; Department of Civil and Environmental Engineering, Princeton University, Princeton, New Jersey, USA


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