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Reduced-order model prediction of far-field mixing noise from internally-notched nozzles
Get PDFThis work presents a numerical investigation of the effect of internal notches on the reduction of jet mixing noise from round nozzles. The baseline jet is produced by the University of Southampton’s Doak Laboratory 40mm-diameter convergent, round nozzle. Numerical predictions of mixing noise for both round and internally-notched nozzles are conducted using a Generalized Acoustic Analogy that relies on Reynolds-Averaged Navier-Stokes (RANS) solutions of the nozzle flows, particularly the one proposed by Leib and Bridges. In this method, the RANS variables of interest, including mean axial velocity, Mach number, density, turbulence kinetic energy, and its dissipation rate, are interpolated onto a cylindrical structured grid suitable for aeroacoustic calculations. Subsequently, the respective Green’s function and a hybrid spectral-time source model are computed, and power spectral densities at various polar and azimuthal angles are predicted. Comparison between predictions and experiments demonstrates good qualitative agreement for both nozzles, although the inversion in trends at certain Strouhal numbers is not captured by the numerical model. Additionally, the significance of the numerical scheme’s order employed to solve the adjoint Green’s function is evaluated. To elucidate the noise reduction attributed to internal notches, distributions of turbulent kinetic energy are analyzed at different azimuthal cross-sections.This work is funded by the Innovate UK Research Programme FANTASIA - Future Aircraft Noise Technologies And Systems Integration Analytics (ref. 74217). The authors would like to acknowledge the support provided by the Rolls-Royce University Technology Centre for Propulsion Systems Noise, within the Institute of Sound and Vibration Research at the University of Southampton. Additionally, the first author would like to thank Stewart Leib (NASA Glenn Research Center) for valuable discussions on the GAA implementation, and the Federal University of Uberlandia.30th AIAA/CEAS Aeroacoustics Conference (2024
Investigating the influence of varying water regimes on the growth and development and nutritional water productivity of bush tea (Athrixia phylicoides DC.)
Get PDFBush tea (Athrixia phylicoides DC.) is an indigenous shrub of South Africa known for its medicinal properties. However, due to a lack of comprehensive information to develop suitable irrigation management strategies, the cultivation of bush tea is currently limited to small‐scale operations. Considering this limitation, the current research investigated the effect of water regimes on the growth and development, yield, and nutrient content along with its nutritional water productivity (NWP) under field conditions. The treatment consisted of a crop water requirement (ETa) of 100%, 30%, and the control (stress) in a complete randomized block design (CRBD). Each treatment was replicated three times to ensure robustness and accuracy of the findings. Results demonstrated that the highest gravimetric moisture content readings were found in the control treatment and the lowest in the 100% treatment. Conversely, the 30% ETa treatment significantly (p < 0.05) impacted bush tea's growth, development, productivity, and NWP. However, it was observed that the 100% ETa treatment resulted in a higher biomass yield (259.1 kg/ha) compared to the 30% ETa treatment (171.2 kg/ha) and control (stress) (68.2 kg/ha). The water productivity exhibited notable differences across the varying water regimes. These findings contribute valuable insights for developing appropriate irrigation management strategies to overcome existing limitations in the scale of bush tea production. The research lays the groundwork for future studies and practical applications aimed to foster the sustainable cultivation of bush tea in South Africa.Water Research Commission, Grant/Award Number: C2020/2021-00420Urban Agriculture & Regional Food System
Energy fluctuation of floating photovoltaic solar panel due to wave-induced motions
Get PDFSolar photovoltaic is predicted to be the most widely used energy method in the future. However, the expansion of solar panels is currently limited by scarce land and lake spaces. To meet the world’s future clean energy target, floating solar panels are expected to be deployed on abundant ocean space, but floating solar panels on the ocean will be subject to loads and motions induced by waves. In particular, a continuous rotation can cause the solar panel surface to constantly change its sunlight intake angle, which could lead to a loss of energy. To investigate this phenomenon, a novel interdisciplinary experimental facility has been established, where a solar simulator was installed on top of a wave tank. A floating solar unit is placed in high-concentration light beams and subject to wave-induced motions. Its motions are measured and related to the power output. It was found that the average power output oscillates due to the motions, and an evident power loss was shown by the rotational motion. For all the tested wave conditions, the highest pitch amplitude of 6.7° corresponds to a significant level of 12.7% average power loss. Overall, the work presents a novel experimental approach and results that can estimate power output for floating solar projects in wave environments. The results also highlight the importance of considering wave attenuation technologies to avoid direct wave interaction with floating solar units.L.H. acknowledges grants from Innovate UK (No. 10048187, 10079774, 10081314), and the Royal Society (IEC\NSFC\223253)ASME 2024 43rd International Conference on Ocean, Offshore and Arctic Engineerin
Comprehensive geophysical, geotechnical, and geochemical assessments of an offshore landfill in Singapore
Get PDFComprehensive site investigation techniques, including Electrical Resistivity Tomography (ERT), Induced Polarization (IP), Multichannel Analysis of Surface Waves (MASW), and Microtremor Array Method (MAM), were integrated with geotechnical and geochemical tests of retrieved waste samples from Singapore’s operational offshore landfill. The properties of landfill wastes vary widely, including shear-wave velocities 127–248 m/s, densities 1.2–2.1 Mg/m3, resistivity 3.0–25.3 Ω∙m, and chargeability 48–82 mV/V. The natural clay layer underneath was clearly delineated and effectively mitigated leachate leakage. K-means clustering of the geophysical data facilitates precise mapping of waste distribution and quantities of recoverable metals based on quantitative criteria. This study illustrates a thorough case study adopting the new site investigation and characterization paradigm for an offshore landfill, which provides insights into leachate leakage detection and evaluations of landfill mining and resource recovery.This research/project is supported by the National Research Foundation, Singapore, and the National Environment Agency, Singapore under its Closing the Waste Loop Funding Initiative (Award No. USS-IF-2021–4).Journal of Hazardous Material
Safe online learning for nonlinear dynamical systems using control contraction metrics
No full textThis thesis aims to develop an online learning framework for a military fixed-wing aircraft
that can adapt a control policy to unforeseen changes in the airframe’s flight dynamics.
This is an active area of research and a significant challenge for high dimensional non linear systems due to the inherent safety risks and computational challenges of solving
exponential time algorithms.
The research achieves this aim by providing an extensive survey of safe online learn ing approaches for nonlinear systems by assessing each technique with the aid of key
performance metrics. Two critical performance metrics are the reliability and time com plexity of the approach taken. To support the survey a benchmarking study of salient
techniques provides further evidence to support the findings of the literature survey to
identify promising avenues of research.
A generic safe learning process is defined and a convex optimisation learning pipeline
is developed to handle nonlinear system identification and online controller synthesis via
control contraction metrics. The developed pipeline is applied to a longitudinal simulation
of an F-16 aircraft using high-fidelity wind tunnel data. The gap in knowledge around the
application of control contraction metrics to aircraft designed to meet flying qualities
requirements based on linear time invariant theory is bridged.
A novel cascaded two loop algorithm is developed to explicitly place the eigenvalues
of the inner and outer loop of a differential feedback controller. Further a parameterisa tion of a robust controller is shown to better optimise the performance relative to flying
qualities specifications. Conditions for a hybrid linear sum of controllers is shown to
provide a stability guarantee for a mixed controller that enables a performance trade-off
of each approach. The performance of the developed controllers is demonstrated on six
damaged aircraft profiles to assess the robustness and transient characteristics for each
method based on a forty second flight trajectory.
The variation in nonlinear damage profiles illustrates the limitations of a linear ap proximating function for three nonlinear deviations. We show that the robust quadratic
regulator controller generates a smoother transient response compared to the exponential
contraction controllers. The two-loop contraction metric controller improves the rise-time
performance compared to a single loop but is less robust to damage variations. The out come of the research is a greater understanding of the application of contraction-based
controllers and the effect of tuning parameters for a robust controller with potential for
a reinforcement learning algorithm. Further a method to hybridise control policies is
proposed and a loop shaping method using contraction based linear matrix inequalities
developed with potential application to cascaded systems.Engineering and Physical Sciences Research Council (EPSRC)PhD in Manufacturin
Enhancing drought resilience and vulnerability assessment in small farms: A global expert survey on multidimensional indicators
No full textThe purpose of the paper is to evaluate drought vulnerability and resilience within the context of small-scale farms. Small-scale farms are distinguished by their family-oriented motives, which prioritize maintaining the stability of the household farm system. This type of farming is responsible for a significant part of the world's food production, thus identifying their vulnerability and resilience to drought is essential to avoid adverse socioeconomic impacts. The paper contributes to this issue by presenting the findings of a comprehensive global survey conducted among experts on drought risk analysis, focusing on indicators related to drought resilience and vulnerability in small-scale farming. An online questionnaire was sent to experts asking them to rate a list of 36 indicators in terms of five metrics: relevancy, accessibility, objectivity, understanding, and temporal consistency. Each indicator was rated on a three-point scale (low, medium, and high). The survey was entirely completed by 120 experts from 42 countries and different areas of expertise. The survey results offer a comprehensive evaluation of multiple indicators, contributing to future research by guiding the selection of indicators for composite drought resilience indexes and enhancing the understanding of farmers' and food systems' climate resilience. The survey results indicate that: i) government and institutional indicators are very relevant for drought resilience assessment; ii) there is an undefined role for social indicators in drought vulnerability assessment; iii) experts still do not perceive the importance of local engagement in drought risk management; iv) the use of relevant indicators in drought risk assessment can be limited because of a lack of accessibility and temporal consistency.Engineering and Physical Sciences Research Council (EPSRC)International Journal of Disaster Risk Reductio
Fabrication of Hi-Bi multi-core silica optical fibre preforms from dual-curing resins incorporating nano composites
Get PDFAdditive manufacturing (AM) or three-dimensional (3D) printing stands out for its remarkable ability to manufacture custom-designed preforms for specialty silica optical fibres (SOFs) featuring sophisticated structures and diverse material compositions. Here, a novel scheme for manufacturing preforms for highly birefringent multi-core silica optical fibres (Hi-Bi MC SOFs) is proposed and tested using specially formulated dual-curing resins with AM technologies. These resins, incorporating nano composites (NCs), are ultraviolet (UV) and thermally cured to form fibre preforms in respective AM processes. Sample silica fibre preforms are successfully fabricated with holey cladding (Ti-doped, UV cured), multiple cores (Ge-Ti co-doped, thermally cured) and stress applying parts (SAPs, B-Al co-doped, thermally cured). As confirmed by X-ray diffraction (XRD) tests, these preforms can be consolidated into clear amorphous silica with the required structure and strength, demonstrating the potential of the proposed scheme in developing preforms for specialty fibres with custom-designed structures and materials required for sensing applications.Engineering and Physical Sciences Research Council (EPSRC)Engineering and Physical Sciences Research Council, UK under Grant EP/H02252X/1Journal of Lightwave Technolog
Knowledge-based bidirectional thermal variable modelling for directed energy deposition additive manufacturing
Get PDFDirected energy deposition additive manufacturing (DED-AM) has gained significant interest in producing large-scale metallic structural components. In this paper, a knowledge-based machine learning (ML) approach, combining both physics-based simulation and data-driven modelling, is proposed for a study on thermal variables of DED-AM. This approach enables both forward and backward predictions, which breaks down the barriers between the basic process parameters and key process attributes. Process knowledge plays a critical role to enable the prediction and enhance the accuracy in both prediction directions. The proposed ML approach successfully predicted the thermal variables of wire arc based DED-AM for forward modelling and the process parameters for backward modelling, typically within 7% errors. This approach can be further generalised as a powerful modelling tool for design, control, and evaluation of DED-AM processes regarding build geometry and properties, as well as an essential constituent element in a digital twin of a DED-AM system.Engineering and Physical Sciences Research CouncilThe authors would like to express their gratitude to Engineering and Physical Sciences Research Council (EPSRC) (EP/ R027218/1, New Wire Additive Manufacturing) for supporting aspects of this research.Virtual and Physical Prototypin
Performance and CFD analyses for a novel and existing thrust reverser designs.
No full textThe landing phase of any flight is the most important one with respect to safety. For a high bypass ratio turbofan engine, aircraft deceleration can be achieved by the use of thrust reversers, lift spoilers and brakes. The use of thrust reversers naturally contributes to a reduction in engine life while the use of brakes has operational limitations with respect to aircraft “turn-around times”. With a drive towards improved engine efficiency and lower overall weight, research into novel thrust reverser concepts is imperative to identify designs which offer improved reverser effectiveness and lower weight as well as ease of installation and storage.
The main contributions to knowledge of this PhD research are related to feasibility assessments of the following two thrust reverser concepts:
A novel vane target type hybrid reverser (VTTHR) design concept has been conceived and evaluated (at a preliminary level) by the author. The design incorporates a target type thrust reverser with cascade vanes. This idea may be patentable.
NASA has developed and tested a core mounted target type thrust reverser (CMTTTR) for which experimental data is available in the public domain. The second contribution to knowledge of this PhD research is extensive studies of this design. These studies comprise 2D and 3D CFD analyses to assess design feasibility and provide an understanding of performance and flow physics of this thrust reverser for both static and landing conditions (not available in public domain).
In addition to these studies, comprehensive studies of the impact of thrust reverser deployment on overall engine and component performance (for both a mixed and a separate exhaust high bypass ratio turbofan engine) were performed.
The preliminary feasibility studies of the VTTHR, which were performed using 2D CFD, suggest that this new design may offer benefits in terms of greater reverser efficiency, weight and ease of storage, relative to conventional designs. Additionally, it was deduced from a large number of CFD investigations that this may be the only feasible “core mounted” thrust reverser design concept for future high bypass ratio engines. There are of course several additional studies (aerodynamic and structural) that need to be performed to mature this technology but the preliminary studies performed provide a good foundation for these. The use of a VTTHR reverser concept relocates reverser hardware to the core cowl, offering potential reductions in reverser and nacelle weight while allowing the nacelle lines to be optimized. Also, installation of VTTHR would benefit aircraft cruise performance, as during cruise flight there will be no losses due to flow leakage and pressure drops that normally occur across the stowed reverser hardware for conventional cascade type thrust reversers, thus, an improvement in specific fuel consumption and therefore mission fuel burn is expected.
The CMTTTR models developed were successfully validated using experimental data. However it was concluded that this design may not be feasible because of issues related to reverser effectiveness, mass flow compatibility and runway clearance.PhD in the School of Engineerin
Fundamental challenges and complexities of damage identification from dynamic response in plate structures
Get PDFFor many years, structural health monitoring (SHM) has held significant importance across diverse engineering sectors. The main aim of SHM is to assess the health status and understand distinct features of structures by analyzing real-time data from physical measurements. The dynamic response (DR) is a significant tool in SHM studies. This response is used primarily to detect variations or damage by examining the vibration signals of DR. Numerous scholarly articles and reviews have discussed the phenomenon and importance of using DR to predict damages in uniform thickness (UT) plate structures. However, previous reviews have predominantly focused on the UT plates, neglecting the equally important varying thickness (VT) plate structures. Given the significance of VT plates, especially for academic researchers, it is essential to compile a comprehensive review that covers the vibration of both the UT and VT cracked plate structures and their identification methods, with a special emphasis on VT plates. VT plates are particularly significant due to their application in critical components of various applications where optimizing the weight, aerodynamics, and dimensions is crucial to meet specific design specifications. Furthermore, this review critically evaluates the damage identification methods, focusing on their accuracy and applicability in real-world applications. This review revealed that current research studies are inadequate in describing crack path identification; they have primarily focused on predicting the quantification of cracks in terms of size or possible location. Identifying the crack path is crucial to avoid catastrophic failures, especially in scenarios where the crack may propagate in critical dimensions of the plate. Therefore, it can be concluded that an accurate analytical and empirical study of crack path and damage identification in these plates would be a novel and significant contribution to the academic field.Applied Science