The development of new aerospace systems has become increasingly fraught with delays, cost overruns and abject programme failures. There is a substantial body of evidence that suggests that as these systems become more complex the ability to achieve even moderate success decreases rapidly. Currently aerospace programmes typically run several years late and significantly overbudget. The Boeing 787 was delivered more than three years late, on a 5 year development programme, and is likely to cost Boeing more than twice their initial estimate. Research shows that common organisational and systems engineering methods, when faced with technology uncertainty are a significant part of this problem. Serving to increase cycle time, reduce performance and increase cost. This talk demonstrate that even small organisations with relatively simple products can fall into this trap and show a path forward for the development of possible new systems engineering approaches.
Semi-flexible polymers (actin filaments) subject to hydrodynamic forcing play an important role in cytoskeletal dynamics in the cell. Giant vesicles are mimicking the cell membrane, therefore further helping to understand the rheological response of the cell. The non-equilibrium problem of vesicle and semi-flexible polymer dynamics is highly challenging due to the coupling between the objects deformations and the flow. This leads to a free-boundary hydrodynamic problem, where the object shape is not given a priori, but determined by an interplay between flow, bending energy and the surface area and volume constraints in the case of the vesicles and the arc-length conservation in the case of the actin filaments. We have investigated experimentally dynamics of giant vesicles and actin filaments in different types of flow. Near hyperbolic stagnation points of the elongational flow filaments and vesicles experience a competition between bending elasticity and tension induced by the flow, and are predicted to display suppressed thermal fluctuations in the steady regime and a buckling instability under sudden change of the velocity gradient. Subject to a flow with vorticity, vesicles undergo tank-treading motion, trembling or tumbling, depending on the control parameters of the experiment.
In the last few years, we have investigated several turbulent flows, characterized by different ratios of classical (large-scale) and quantum (small-scale) kinetic energy in cold superfluid 4He: (i) a cloud of polarized quantized vortex rings in which rare binary collisions of rings trigger an onset of turbulence; (ii) a compact tangle of quantized vortex loops in which trapped electron bubbles in an applied electric field exert body force on the liquid resulting in a propagating giant classical vortex ring; (iii) space-filling turbulence continuously pumped by a jet of injected electrons; (iv) inertial waves and turbulence produced by perturbing the rectilinear vortex lines present during steady rotation; (v) the free decay of all the flows mentioned. All experiments were in a cubic container and the characterization of the density, polarization and spread of the vortex tangle was done through measurements of the transport of electron bubbles either trapped by the tangle or propagating on probe vortex rings. These experiments were performed at T < 0.5 K (when there is no normal fluid component). Numerical simulations of short-range interactions of individual quantized vortex rings and of large-scale flows forced by injected electrons have also been performed.
For many years, the transition to turbulence in pipe flow has been investigated by using a transverse jet to perturb fully developed Hagen-Poisueille flow. However, the vortical structures, which result from the interaction of the jet and the crossflow in the confined geometry of a pipe, have received little attention. The resultant flow features, in the near- and far-field, will be discussed and characterised using flow visualisation and experimental results from a constant mass-flux facility. The consequences of these findings will be related to the enigmatic problem of the transition from laminar to turbulent pipe flow.
Refreshments will be provided in the basement social area of the Schuster Lab. from 2.30pm. If you have any suggestions for future speakers, please contact Dr Draga Pihler-Puzovic.