Usama Kadri

A methodology for the generation of biomimetic design concepts

Systems found in nature provide a large database of strategies and mechanisms that can be implemented in biomimetic designs. Although several biomimetic design strategies are currently available, the generation of a successful design concept is still challenging. A major challenge is the absence of a systematic selective design methodology that is capable of identifying the relevant systems and then abstracting their strategies and mechanisms. In this paper, some existing biomimetic design strategies applied for nature emulation are analysed. As an outcome, a methodology for the generation of biomimetic design concepts is developed. The design methodology selects dominant strategies that function simultaneously in nature and provides selective user-friendly tools, which facilitate the generation of preliminary design concepts. An example for the generation process of a design concept is presented.

Deep ocean water transport by acoustic‐gravity waves

Acoustic-gravity waves are compression-type waves propagating with amplitudes governed by the restoring force of gravity. They are generated, among others, by wind-wave interactions, surface waves interactions, and submarine earthquakes. We show that acoustic-gravity waves contribute to deep ocean currents and circulation; they cause chaotic flow trajectories of individual water parcels, which can be transported up to a few centimeters per second.

Pressure field induced in the water column by acoustic‐gravity waves generated from sea bottom motion

An uplift of the ocean bottom caused by a submarine earthquake can trigger acoustic-gravity waves that travel at near the speed of sound in water and thus may act as early tsunami precursors. We study the spatiotemporal evolution of the pressure field induced by acoustic-gravity modes during submarine earthquakes, analytically. We show that these modes may all induce comparable temporal variations in pressure at different water depths in regions far from the epicenter, though the pressure field depends on the presence of a leading acoustic-gravity wave mode. Practically, this can assist in the implementation of an early tsunami detection system by identifying the pressure and frequency ranges of measurement equipment and appropriate installation locations.

Tsunami mitigation by resonant triad interaction with acoustic–gravity waves

Tsunamis have been responsible for the loss of almost a half million lives, widespread long lasting destruction, profound environmental effects, and global financial crisis, within the last two decades. The main tsunami properties that determine the size of impact at the shoreline are its wavelength and amplitude in the ocean. Here, we show that it is in principle possible to reduce the amplitude of a tsunami, and redistribute its energy over a larger space, through forcing it to interact with resonating acoustic–gravity waves. In practice, generating the appropriate acoustic–gravity modes introduces serious challenges due to the high energy required for an effective interaction. However, if the findings are extended to realistic tsunami properties and geometries, we might be able to mitigate tsunamis and so save lives and properties. Moreover, such a mitigation technique would allow for the harnessing of the tsunamis energy.

Generation of Hydroacoustic Waves by an Oscillating Ice Block in Arctic Zones

The time harmonic problem of propagating hydroacoustic waves generated in the ocean by a vertically oscillating ice block in arctic zones is discussed. The generated acoustic modes can result in orbital displacements of fluid parcels sufficiently high that may contribute to deep ocean currents and circulation. This mechanism adds to current efforts for explaining ocean circulation from a snowball earth Neoproterozoic Era to greenhouse earth arctic conditions and raises a challenge as the extent of ice blocks shrinks towards an ice-free sea. Surprisingly, unlike the free-surface setting, here it is found that the higher acoustic modes exhibit a larger contribution.

Acoustic-Gravity Waves Interacting with a Rectangular Trench

A mathematical solution of the two-dimensional linear problem of an acoustic-gravity wave interacting with a rectangular trench, in a compressible ocean, is presented. Expressions for the flow field on both sides of the trench are derived. The dynamic bottom pressure produced by the acoustic-gravity waves on both sides of the trench is measurable, though on the transmission side it decreases with the trench depth. A successful recording of the bottom pressures could assist in the early detection of tsunami.

Rewinding the waves: tracking underwater signals to their source

Analysis of data, recorded on March 8th 2014 at the Comprehensive Nuclear-Test-Ban Treaty Organisation’s hydroacoustic stations off Cape Leeuwin Western Australia, and at Diego Garcia, reveal unique pressure signatures that could be associated with objects impacting at the sea surface, such as falling meteorites, or the missing Malaysian Aeroplane MH370. To examine the recorded signatures, we carried out experiments with spheres impacting at the surface of a water tank, where we observed almost identical pressure signature structures. While the pressure structure is unique to impacting objects, the evolution of the radiated acoustic waves carries information on the source. Employing acoustic–gravity wave theory we present an analytical inverse method to retrieve the impact time and location. The solution was validated using field observations of recent earthquakes, where we were able to calculate the eruption time and location to a satisfactory degree of accuracy. Moreover, numerical validations confirm an error below 0.02% for events at relatively large distances of over 1000 km. The method can be developed to calculate other essential properties such as impact duration and geometry. Besides impacting objects and earthquakes, the method could help in identifying the location of underwater explosions and landslides.

Random patterns in fish schooling enhance alertness: a hydrodynamic perspective

One of the most highly debated questions in the field of animal swarming and social behaviour, is the collective random patterns and chaotic behaviour formed by some animal species, in particular if there is a danger. Is such a behaviour beneficial or unfavourable for survival? Here we report on one of the most remarkable forms of animal swarming and social behaviour - fish schooling - from a hydrodynamic point of view. We found that some fish species do not have preferred orientation and they swarm in a random pattern mode, despite the excess of energy consumed. Our analyses, which includes calculations of the hydrodynamic forces between slender bodies, show that such a behaviour enhances the transfer of hydrodynamic information, and thus enhances the survivability of the school. These findings support the general hypothesis that a disordered and non-trivial collective behaviour of individuals within a nonlinear dynamical system is essential for optimising transfer of information - an optimisation that might be crucial for survival.

Prediction of gas-pulsation frequency to reduce slug length in gas/liquid horizontal-pipe flow

Very long slugs reaching several hundreds of pipe diameters may appear when transporting gas and liquid in horizontal pipes. Such slugs may cause serious operational and system failures. One could avoid the long slugs by pulsating the gas phase at the inlet at a specific range of frequencies. The present paper provides a simplified mathematical expression for the optimum gas-pulsation frequency. Predictions of the pulsation frequency for different flow conditions and pipe diameters are presented. Comparisons with available experiments are satisfactory.