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Improving the engineering design process by simulating iteration impact with ASM2.0
No full text© 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd. part of Springer Nature. Engineering design processes that are dependent on Computer-Aided Engineering (CAE) tools commonly involve complex patterns of tasks, including concurrency and intertwined iterations. There are often inefficiencies and improvement opportunities in such processes, but it can be difficult to identify and evaluate them—partly because of the complex iteration patterns, and partly because process knowledge is usually tacit and often distributed among process participants so that it is difficult to appreciate the causes and effects of iteration in an integrated way. The Applied Signposting Model (ASM) was developed to address these issues during more than a decade of research and case studies in the aerospace sector. This article describes an evolved version of the ASM, called ASM2.0, alongside a detailed case to demonstrate its application to improve CAE-driven, iteration-intensive engineering design processes. A review of applications is also provided. A differentiating feature of ASM2.0 is that it integrates visually-familiar flowchart mapping with quantitative analysis of process performance, to enable the modelling of complex iteration patterns that are typical of engineering design practice
Attention forcing for speech synthesis
No full textAuto-regressive sequence-to-sequence models with attention mechanisms have achieved state-of-the-art performance in various tasks including speech synthesis. Training these models can be difficult. The standard approach guides a model with the reference output history during training. However during synthesis the generated output history must be used. This mismatch can impact performance. Several approaches have been proposed to handle this, normally by selectively using the generated output history. To make training stable, these approaches often require a heuristic schedule or an auxiliary classifier. This paper introduces attention forcing, which guides the model with the generated output history and reference attention. This approach reduces the training-evaluation mismatch without the need for a schedule or a classifier. Additionally, for standard training approaches, the frame rate is often reduced to prevent models from copying the output history. As attention forcing does not feed the reference output history to the model, it allows using a higher frame rate, which improves the speech quality. Finally, attention forcing allows the model to generate output sequences aligned with the references, which is important for some down-stream tasks such as training neural vocoders. Experiments show that attention forcing allows doubling the frame rate, and yields significant gain in speech quality
Light-trapping Optimisation Framework Based on Fourier-space Grating Design for Coupling to Waveguide Modes in an Ultra-thin Solar Cell
No full textEver-thinner solar cells are currently of interest to the photovoltaics community and demand the introduction of light-trapping techniques to retain a competitive photovoltaic performance. This work presents a framework for a guided light-trapping design applied to an ultra-thin (< 100 nm) solar cell. The framework is based on a fundamental study of the waveguide modes supported by a realistic device architecture. Mode-coupling is ensured by introducing a scattering layer according to its Fourier spectrum. The framework can be applied to any device architecture and for single or multiple wavelength absorption enhancement, having the flexibility to attain high-efficiency in ever-thinner photovoltaics
Thermal response of energy soldier pile walls
No full textUtilising foundation systems as heat exchangers has received significant public interest worldwide, as these energy geo-structures can constitute a clean, renewable, and economical solution for space heating and cooling. Despite their potential, the thermal performance of energy retaining walls, especially soldier pile walls, has not been sufficiently studied and understood and thus further research is required. This work utilises the first ever energy soldier pile wall in the currently under-construction Melbourne CBD North metro station as a case study. A section of this wall has been instrumented and monitored by the University of Melbourne. Full scale thermal response tests (TRTs) have been conducted on a single thermo-active soldier pile at two different excavation levels. Thermal response testing field data results are presented in terms of mean fluid temperatures and further analysed to show the potential impact of the excavation level on the structure's thermal performance. To further explore this impact of excavation depth (or pile embedment depth) and the long-term thermal performance of energy pile walls, a detailed 3D finite element numerical model is developed in COMSOL Multiphysics and validated against the field-testing results. The simulation suggests that thermally activating all the soldier piles in the station can provide enough energy to fulfil the heating and cooling demand of the station and to satisfy partial heating demand to the surrounding buildings. Furthermore, results suggest that current energy pile design approaches may be adapted for designing energy pile walls
Large-eddy-simulation prediction of an installed jet flow and noise with experimental validation
No full textExtra noise is generated when jets are installed beneath solid surface. In this paper, large-eddy simulation (LES) has been used to investigate these jet installation effects. The simulations were performed on two jet configurations: An isolated jet and a jet installed below a horizontal flat plate. The LES is compared with experimental data from measurements using hot wires, unsteady surface pressure sensors, and far-field microphones. Good agreement has been achieved between LES and experimental measurements on flow statistics, space-time correlations, and both near-field and far-field sound spectra. The installed effects are discussed from the perspective of flows and acoustics in the validation process
A cascade-looped thermoacoustic driven cryocooler with different-diameter resonance tubes. Part: Experimental study and comparison
No full textA small-scale, heat-driven cooling system is required for on-site liquefaction of unconventional natural gas in a distributed station. To meet such demands, we propose a highly efficient heat-driven thermoacoustic cryocooler. This paper presents the experimental results of the proposed system, which is optimized based on previous theoretical analysis. Firstly, we compare two high-temperature heat exchangers with similar heat transfer effectiveness but different flow uniformity. The experimental results show that the heat exchanger with uniform flow can improve system efficiency by 28%. Experimental investigations are then carried out to understand the effect of operating temperatures on system performance. Later, the performance of the system operating at variable heating temperatures is studied. Finally, the reasons for the discrepancy between experiments and calculations are discussed. The experimental results show that the proposed thermoacoustically-driven cryocooler can achieve an exergy efficiency of 10 % and a cooling power of 378 W at a heating temperature of 730 K and a cooling temperature of 130 K. This represents a 25% improvement in efficiency compared to the previous record-holder thermoacoustic system
High-responsivity graphene photodetectors integrated on silicon microring resonators
No full textGraphene integrated photonics provides several advantages over conventional Si photonics. Single layer graphene (SLG) enables fast, broadband, and energy-efficient electro-optic modulators, optical switches and photodetectors (GPDs), and is compatible with any optical waveguide. The last major barrier to SLG-based optical receivers lies in the low responsivity - electrical output per optical input - of GPDs compared to conventional PDs. Here we overcome this shortfall by integrating a photo-thermoelectric GPD with a Si microring resonator. Under critical coupling, we achieve 90% light absorption in a 6 m SLG channel along the Si waveguide. Exploiting the cavity-enhanced light-matter interaction, causing carriers in SLG to reach 400 K for an input power of 0.6 mW, we get a voltage responsivity 90 V/W, demonstrating the feasibility of our approach. Our device is capable of detecting data rates up to 20 Gbit/s, with a receiver sensitivity enabling it to operate at a 10 bit-error rate, on par with mature semiconductor technology. The natural generation of a voltage rather than a current, removes the need for transimpedance amplification, with a reduction of the energy-per-bit cost and foot-print, when compared to a traditional semiconductor-based receiver
Microbial-induced carbonate precipitation applicability with the methane hydrate-bearing layer microbe
No full textProduction of methane gas from the methane-hydrate-bearing layer below the deep-ocean floor is expected to be crucial in the future of energy resources worldwide. During the methane gas-production phase from the methane hydrate with the depressurisation method, the depressurising zone around the production well will lose strength, causing a potential geohazard. In this study, a bio-mediated treatment to reinforce the methane hydrate layers is proposed. A urease-producing bacterium, Sporosarcina newyorkensis, was isolated for the first time from a pressure core sampled from the Nankai Trough seabed methane-hydrate-bearing layer in Japan. This newly isolated species can survive deep-seabed environments and also enhance the population under nutrient-rich conditions. In addition, it is uniquely characterised with higher urease activities under low-temperature conditions in comparison to the well-known bacterium S. pasteurii. The results of triaxial tests suggest that this bacterium can catalyse the precipitation of calcium carbonate through urea hydrolysis, which enhances the soil strength below the ocean floor and hence reinforces the production well. This will not only make methane gas extraction safer but may also reduce sand production in the well, making extraction operations more efficient and cost effective
Cathodoluminescence visualisation of local thickness variations of GaAs/AlGaAs quantum-well tubes on nanowires
No full textWe present spatially and spectrally resolved emission from nanowires with a thin radial layer of GaAs embedded in AlGaAs barriers, grown radially around taper-free GaAs cores. The GaAs layers are thin enough to show quantization, and are quantum wells. Due to their shape, they are referred to as quantum well tubes (QWTs). We have investigated three different nominal QWT thicknesses: 1.5, 2.0, and 6.0 nm. They all show average emission spectra from the QWT with an energy spread corresponding to a thickness variation of 30%. We observe no thickness gradient along the length of the nanowires. Individual NWs show a number of peaks, corresponding to different QW thicknesses. Apart from the thinnest QWT, the integrated emission from the QWTs shows homogeneous emission intensity along the NW. The thinnest QWTs show patchy emission patterns due to the incomplete coverage of the QWT. We observe a few NWs with larger diameters. The QWTs in these NWs show spatially resolved variations across the NW. An increase in the local thickness of the QWT at the corners blocks the diffusion of carriers from facet to facet, thereby enabling us to visualise the thickness variations of the radial quantum wells
Wigner function and photon number distribution of a superradiant state in semiconductor heterostructures
No full text© 2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaft. Advanced quantum technologies require sources of non-Gaussian and non-classical light. For the understanding of properties of quantum light it is necessary to reconstruct its quantum state. Here, we use time-domain optical homodyne tomography for the quantum state recognition and reconstruction of the femtosecond optical field from a nonequilibrium superradiant coherent electron-hole state formed in a semiconductor GaAs/AlGaAs heterostructure. We observe severe deviations from the Poissonian statistics of the photons associated with the coherent state when the transformation from lasing to superradiance occurs. The estimated Mandel parameter Q of the superradiant states is in the range of 1.08-1.89. The reconstructed Wigner functions show large areas of negative values, a characteristic sign of non-classicality, demonstrating the quantum nature of the generated superradiant emission. The photon number distribution and Wigner function of the superradiant state are very similar to those of the displaced Fock state