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Nozzle geometry-induced vortices in supersonic wind tunnels
No full textStreamwise-coherent structures were observed in schlieren images of a Mach 2.5 flow in an empty supersonic wind tunnel with a rectangular cross section. These features are studied using Reynolds-averaged Navier–Stokes computations in combination with wind-tunnel experiments. The structures are identified as regions of streamwise vorticity embedded in the sidewall boundary layers. These vortices locally perturb the sidewall boundary layers, and they can increase their thickness by as much as 37%. The vortices are caused by a region of separation upstream of the nozzle where there is a sharp geometry change, which is typical in supersonic wind tunnels with interchangeable nozzle blocks. Despite originating in the corners, the vortices are transported by secondary flows in the sidewall boundary layers so they end up near the tunnel center height, well away from any corners. The successful elimination of these sidewall vortices from the flow is achieved by replacing the sharp corner with a more rounded geometry so that the flow here remains attached
Introducing platform ecosystem resilience: leveraging mobility platforms and their ecosystems for the new normal during COVID-19
No full textCOVID-19 has created many constraint-related challenges for humans in general and organisations in particular. Specifically, businesses that require physical contact, such as mobility providers, have been severely impacted by the crisis. This paper reveals how mobility platforms and their ecosystem of actors have adapted faster than their non-platform competitors to become resilient. Whereas current research on resilience explicitly deals with the concept of organisational resilience, community resilience, or IT resilience, socio-technical characteristics of digital platforms have not been investigated. We build on a case survey approach, including heterogeneous qualitative evidence of 266 actions of 171 analysed mobility platforms. The results show five archetypes of how mobility platforms leverage their platform-based nature and the ecosystem to build resilience. Based on this, we develop the concept of platform ecosystem resilience as leveraging socio-technical factors of digital platforms and ecosystems frugally to design, deploy and use situation-specific responses to prepare for, endure and adapt by capturing new opportunities and engaging in transformative activities to cope with exogenous shocks and become resilient for future disruptions. Our results emphasise the importance of platform ecosystems for practitioners and policy planners to develop the “new normal” rather than resuming existing practices
Fuel Effects on Turbulent Premixed Jet Flame Topology as Resolved by CH PLIF Imaging
No full textThe current study focuses on flame topology and curvature measurements of prevaporized premixed liquid fuel jet flames using CH PLIF. Flames fueled by n-heptane, n-dodecane, and methane are tested in a piloted McKenna burner operating at Re=10,000. CH PLIF experiments are performed using the (v’=0, v’’=0) band and a new image processing technique with topology tracking is employed to assign the detected flame edges as reactant or product stream-oriented. Curvature statistics for both streams and all liquid fuels are obtained and compared with data from a premixed methane-air flame generated by the same burner. The comparison allows for the investigation of non-unity Lewis number (Le ≠ 1) effects on the flame structure and curvature probability density functions while focusing on different regions of the reaction zones. Results indicate differences in the curvature between reactant and product sides of the flame. The curvature of the reactant side reported being higher compared to the product side, which suggests the CH layer edges on the reactant side are more corrugated. The effect of the Le number is investigated by signal-curvature correlation. The correlation of signal and curvature is compared for methane and n-dodecane. It indicates that the n-dodecane fluorescence signal value is higher for negative curvature compared to positive curvature. But for the methane, the positive and negative curvature contains a similar range of fluorescence signal values
Exploring gestural input for engineering surveys of real-life structures in virtual reality using photogrammetric 3D models
No full textPhotogrammetry is a promising set of methods for generating photorealistic 3D models of physical objects and structures. Such methods may rely solely on camera-captured photographs or include additional sensor data. Digital twins are digital replicas of physical objects and structures. Photogrammetry is an opportune approach for generating 3D models for the purpose of preparing digital twins. At a sufficiently high level of quality, digital twins provide effective archival representations of physical objects and structures and become effective substitutes for engineering inspections and surveying. While photogrammetric techniques are well-established, insights about effective methods for interacting with such models in virtual reality remain underexplored. We report the results of a qualitative engineering case study in which we asked six domain experts to carry out engineering measurement tasks in an immersive environment using bimanual gestural input coupled with gaze-tracking. The qualitative case study revealed that gaze-supported bimanual interaction of photogrammetric 3D models is a promising modality for domain experts. It allows the experts to efficiently manipulate and measure elements of the 3D model. To better allow designers to support this modality, we report design implications distilled from the feedback from the domain experts
Surfactant-free synthesis of copper nanoparticles and gas phase integration in CNT-composite materials
No full textCopper nanoparticles (Cu-NPs) represent a viable low-cost alternative to replace bulk copper or other more expensive NPs (e.g.gold or silver) in various applications such as electronics for electrical contact materials or high conductivity materials. This study deals with the synthesis of well dispersed Cu-NPs by using an Ar + H2microplasma using a solid copper precursor. The morphological analysis is carried out by electron microscopy showing particles with a mean diameter of 8 nm. Crystallinity and chemical analyses were also carried out by X-ray diffraction and X-ray photoelectron spectroscopy, respectively. In the second step, the Cu-NPs were successfully deposited onto porous carbon nanotube ribbons; surface coverage and the penetration depth of the Cu-NPs inside the CNT ribbon structure were investigated as these can be beneficial for a number of applications. The oxidation state of the Cu-NPs was also studied in detail under different conditions
A Time-Division-Multiplexed Clocked-Analog Low-Dropout Regulator
No full textThis paper presents a time-division-multiplexed (TDM) clocked-analog low-dropout regulator (CLDO) that shares one controller between multiple output channels. Clocked-analog operation is introduced to create idle periods that enable the shared controller to independently regulate different output channels through time-division multiplexing. Furthermore, an asynchronous transient enhancing technique is presented. Thanks to the controller sharing, the TDM CLDO is more area-efficient than conventional designs for supplying multiple outputs, especially when power stages and on-chip loads are small. To verify the effectiveness of the TDM CLDO, a dual-channel version is fabricated in a 130 nm CMOS process. Measurement results show that it can independently track two 100 kHz 0.3~\rm V{pp} sinusoidal signals with 4 mV average output error at 100~\Omega load and 6 MHz clock frequency. For load transient responses, it can independently regulate two output channels to 1.05 V and 0.95 V with 41 mV/88 mV and 67 mV/39 mV overshoot/undershoot when both channels experience 5 mA current steps at 1.2~\rm V{dd}. To the best of our knowledge, this is the first time that hardware sharing is implemented for continuous closed-loop systems
An experimental exploration of the properties of random frequency response functions
No full textThe vibro-acoustic analysis of complex structures over a broadband frequency range is an extremely challenging problem that may often require the use of a hybrid deterministic-statistical approach. Due to manufacturing imperfections, the frequency response functions (FRFs) of an ensemble of nominally identical systems can be considered to be random. These FRFs, however, have statistical properties that can be potentially used in vibro-acoustic models. This work explores some of these fundamental properties by using measured FRFs from an ensemble of nominally identical structures, obtained by randomising a thin rectangular plate using point masses. It is first shown that the measured ensemble of FRFs satisfies the analyticity-ergodicity condition, experimentally verifying this recently demonstrated fundamental property. Then, the ensemble is used to explore whether the direct field dynamic stiffness, a key parameter in a well-established hybrid deterministic-statistical formulation, can be obtained experimentally. The results are compared against those computed using numerical techniques, showing that measured data may be a suitable alternative provided that an ensemble of systems can be measured. Finally, an alternative method, based on the use of virtual point masses, opposed to physical ones, is proposed for those cases where experimental randomisation is particularly challenging. It has been found, however, that the method may be extremely sensitive to measurement imprecisions, specially when applied to lightly damped structures. It is concluded that the statistical properties of random causal FRFs are not only interesting in themselves, but can enhance and extend vibro-acoustic prediction models
Capturing the value in printed pharmaceuticals – A study of inkjet droplets released from a polymer matrix
No full textThe future of personalised combination dosages will rely on the programming and delivery of multiple, separate APIs, their carrier fluids and excipients to a stable matrix, where each will remain separate until it is needed to be released. A recent technique has demonstrated how to print, capture and release materials from a polymer matrix using inkjet printing, a low cost and customisable technique. Droplets of a formulation are delivered to a fluid polymer matrix, where they are imbibed and remain pinned just under the upper surface, held in place by a balance of interfacial energies. Once the surrounding matrix cures and solidifies, the coating or matrix has trapped the formulation, but each drop has a small opening or pore to the outside that will allow delivery through diffusion. However, while the trapping mechanism has been explored in detail, to-date the release involved in this delivery has never been studied or quantified to the same level. Here we show a first study to quantify the release of a model system from a polymer matrix. An aqueous fluorescein solution is delivered and trapped, with release demonstrated to an agarose gel and aqueous environments. The work reveals that the balance of interfacial tensions prevents a reliable release until low concentrations of surfactant are included. This provides a route forward to further explore stabilising combinations of drugs within one material using a digitally controlled and affordable technique
Charge transport physics of a unique class of rigid-rod conjugated polymers with fused ring conjugated units linked by double carbon-carbon bonds
No full textWe investigate the charge transport physics of a novel class of electron deficient conjugated polymers that do not contain any single bonds linking monomer units along the backbone, but only double bond linkages. Such polymers would be expected to behave as rigid rods but little is known about their actual chain conformations and electronic structure. Here we present a detailed study of the structural and charge transport properties of a family of four such polymers. Small angle neutron scattering provides evidence for a highly rigid chain conformation. By adopting a copolymer design we achieve high electron mobilities up to 0.5 cm2V-1s-1. Field-induced ESR measurements of charge dynamics provide evidence for relatively slow hopping over, however, long distances. Our work provides important insights into the factors that limit charge transport in this unique class of polymers and allow us to identify molecular design strategies for achieving even higher levels of performance