7/26/2019 Biomimicry Structure

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Biomimicry in Structural Engineering: A Load Bearing Duct

Francesco Ciriello,1Dr. M. A. Wadee,1Prof. G. R. Hunt,2

1Department of Civil & Environmental Engineering, Imperial College London,

2Department of Engineering, University of Cambridge

Integrating Structural & Ventilation Strategies

Biomimicry is an emerging science that seeks technological inspiration

via analogies to the behaviour of living systems (Yiatros et al. 2007). The

review and application of the philosophical aspects that pertain to the

field of biomimicry, as applied to the context of sustainable architecture,

has made us, among other things, decide to explore an innovative idea:that of taking advantage of the typically hollow form and stack height of

columns to provide natural ventilation services to a building.

The Tall Emptying Box Model

The upper limit to the optimal number of stack ventilation systems was

found to be provided by the dynamics via which buoyant fluid enters the

duct. A model was proposed based on an extension of Linden et al. s

(1990) classical displacement flow model and Barnetts(1990) work on tall

filling boxes. The modelling framework was set out via analysing the effectof container aspect ratio on filling box processes containing a central

buoyant source (see Figure 3). For boxes of low aspect ratio, successive

levels of stratification are formed in the upper regions. Upon increasing the

slenderness of the container, overturning of buoyant fluid is observed owing

to the increase in momentum flux as the spreading flow hits the sidewalls.

For sufficiently tall boxes, the radius of the plume will eventually approach

that of the container, resulting in a complete breakdown of its structure.

FIGURE 1

The breaking regime

The breakdown of the plume forms a uniformly mixed layer of constantthickness, which in turn convects buoyant fluid in the upper regions of the

container. At steady state, for a vented box, the upper regions fills with

buoyant fluid of reduced gravity corresponding to the plumes reduced

gravity at breakdown level (see Figure 4). For a range of opening areas, thetemperature in the interior does not respond; and opening or closing vents

has no influence on the internal temperature.

An appreciation of the connection

between form (geometry) and

function (behaviour regimes) for a

multifunctional component wasidentified as a good starting place

for an exploration in integrated

structural and ventilation strategies.

An elemental study was performed

upon cylindrical hollow shells to

understand, via simple models, how

buoyancy driven flows behaved

within them. To address issues ofresource allocation, a thought

experiment was proposed where the

performance of equal amounts of

material is assessed by dividing a

single duct into multiple segments,

resulting in a variation of aspect

ratio upon comparison.

FIGURE 4The breaking regime translates to the

implication that, for a sufficiently tall

box containing a heat source at floorlevel, the temperatures within the

upper regions will depend solely on the

buoyancy flux that the heat source

generates; suggesting that designerscan achieve better control of

environmental conditions by

constricting the flow geometrically.

The result provides future grounds for

more resilient and controllable naturalventilation systems; and highlights the

potential role biomimicry can have in

the development of new technologies

in engineering disciplines.

FIGURE 2

ACKNOWLEDGEMENTS

Special thanks to Dr. M.A. Wadee (Imperial College London) and

Professor G.R. Hunt (University of Cambridge) for their valuable help

during the supervision of this dissertation. I would also like to thank

friends and family for their support throughout these past few years.

REFERENCES

Barnett, J. S. (1990) The Dynamics of Buoyant Releases in Confined

Spaces. PhD Thesis. University of Cambridge.

Linden, P., Lane-Serff, G. & Smeed, D. (1990) Emptying filling boxes: thefluid mechanics of natural ventilation. Journal of Fluid Mechanics. 212, 309-

335.

Yiatros, S., Wadee, M. A. & Hunt, G. R. (2007) The load-bearing duct:

Biomimicry in structural design. Proceedings of the Institution of CivilEngineers: Engineering Sustainability. 160 (4), 179-188.

Preliminary Analysis

A series of idealised cases of natural convection within the load bearing

duct element were examined. Initially, a simple model was examined of a

vertical circular pipe, full of buoyant fluid and surrounded by cooler,

denser ambient fluid, with an opening at each end (see Figure 2). The

results of the study showed that:

1. Using a larger number of independent stack ventilation systems

results in higher total volume fluxes for a fixed amount of material.

2. Modelling minor head losses via the Darcy Weisbach formula,

= / /2, showed that the variation of friction with aspect

ratio had little influence on total volume fluxes.

FIGURE 3

overturning plume breakdownstable stratifications

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S17 Francesco Ciriello