Browsing by Author "Gray, Iain"

Now showing 1 - 6 of 6
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    Attitude control analysis of tethered de-orbiting
    (2018-03-12) Peters, T. V.; Briz Valero, José Francisco; Escorial Olmos, Diego; Lappas, V.; Jakowski, P.; Gray, Iain; Tsourdos, Antonios; Schaub, H.; Biesbroek, R.
    The increase of satellites and rocket upper stages in low earth orbit (LEO) has also increased substantially the danger of collisions in space. Studies have shown that the problem will continue to grow unless a number of debris are removed every year. A typical active debris removal (ADR) mission scenario includes launching an active spacecraft (chaser) which will rendezvous with the inactive target (debris), capture the debris and eventually deorbit both satellites. Many concepts for the capture of the debris while keeping a connection via a tether, between the target and chaser have been investigated, including harpoons, nets, grapples and robotic arms. The paper provides an analysis on the attitude control behaviour for a tethered de-orbiting mission based on the ESA e.Deorbit reference mission, where Envisat is the debris target to be captured by a chaser using a net which is connected to the chaser with a tether. The paper provides novel insight on the feasibility of tethered de-orbiting for the various mission phases such as stabilization after capture, de-orbit burn (plus stabilization), stabilization during atmospheric pass, highlighting the importance of various critical mission parameters such as the tether material. It is shown that the selection of the appropriate tether material while using simple controllers can reduce the effort needed for tethered deorbiting and can safely control the attitude of the debris/chaser connected with a tether, without the danger of a collision.
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    Autonomous inspection and repair of aircraft composite structures
    (Elsevier, 2018-11-23) Kostopoulos, Vassilis; Psarras, Spyridon; Loutas, Theodoros; Sotiriadis, George; Gray, Iain; Padiyar M, Janardhan; Petrunin, Ivan; Raposo Gaudencio Campos, Joao; Zanotti Fragonara, Luca; Tzitzilonis, Vasileios; Dassios, Konstantinos; Exarchos, Dimitrios; Andrikopoulos, George; Nikolakopoulos, George
    This paper deals with the development of an innovative approach for inspection and repair of damage in aeronautical composites that took place in the first two years of the H2020 CompInnova project which. The aim is a newly designed robotic platform for autonomous inspection using combined infrared thermography (IRT) and phased array (PA) non-destructive investigation for damage detection and characterization, while integrated with laser repair capabilities. This will affect the increasing societal need for safer aircraft in the lowest possible cost, while new and effective techniques of inspection are needed because of the rapidly expanding use of composites in the aerospace industry.
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    Diagnostics of gas turbine systems using gas path analysis and rotordynamic response approach
    (ISABE, 2017-09-08) Jombo, Gbanaibolou; Sampath, Suresh; Gray, Iain
    The modern gas turbine is plagued with issues centred on improving engine availability and limiting component degradation. The integrated use of different condition monitoring techniques presents a solution to addressing these challenges. This paper lays a foundation for the integration of gas path analysis and the rotordynamic response of the compressor to monitor the effect of fouling in the compressor. In investigating the resultant interaction between the aerodynamic and rotordynamic domain in a compressor caused by fouling, an approach involving the interaction of four different models is explored. The first model, a gas turbine engine performance model is used to simulate a fouled compressor and quantify the extent of performance deterioration with gas path analysis. The extent of performance deterioration from the engine performance model represented by scaling of the compressor maps becomes an input in the second model, a Moore-Greitzer compression system model, which evaluates the disturbed flow field parameters in the fouled compressor. The third model, a momentum-based aerodynamic force model, predicts the fouling induced aerodynamic force based on the disturbed flow field parameters. The aerodynamic force acting as a forcing function in the fourth model, a compressor rotordynamic model, produces the vibration response. From the investigation carried out in this work, it is observed, as the rate of fouling increases in the compressor, typified by a decrease in compressor massflow, pressure ratio and isentropic efficiency, there is a corresponding increase in the vibration amplitude at the first fundamental frequency of the compressor.
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    Fast, accurate, and reliable detection of damage in aircraft composites by advanced synergistic infrared thermography and phased array techniques
    (MDPI, 2021-03-19) Padiyar M, Janardhan; Fragonara, Luca Zanotti; Petrunin, Ivan; Raposo, João; Tsourdos, Antonios; Gray, Iain; Farmaki, Spyridoyla; Exarchos, Dimitrios; Matikas, Theodore E.; Dassios, Konstantinos G.
    This paper presents an advanced methodology for the detection of damage in aircraft composite materials based on the sensor fusion of two image-based non-destructive evaluation techniques. Both of the techniques, phased-array ultrasonics and infra-red thermography, are benchmarked on an aircraft-grade painted composite material skin panel with stringers. The sensors systems for carrying out the inspections have been developed and miniaturized for being integrated on a vortex-robotic platform inspector, in the framework of a larger research initiative, the Horizon-2020 ‘CompInnova’ project.
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    Improving depth resolution of ultrasonic phased array imaging to inspect aerospace composite structures
    (MDPI, 2020-02-20) Mohammadkhani, Reza; Fragonara, Luca Zanotti; Padiyar M, Janardhan; Petrunin, Ivan; Raposo, João; Tsourdos, Antonios; Gray, Iain
    In this paper, we present challenges and achievements in development and use of a compact ultrasonic Phased Array (PA) module with signal processing and imaging technology for autonomous non-destructive evaluation of composite aerospace structures. We analyse two different sets of ultrasonic scan data, acquired from 5 MHz and 10 MHz PA transducers. Although higher frequency transducers promise higher axial (depth) resolution in PA imaging, we face several signal processing challenges to detect defects in composite specimens at 10 MHz. One of the challenges is the presence of multiple echoes at the boundary of the composite layers called structural noise. Here, we propose a wavelet transform-based algorithm that is able to detect and characterize defects (depth, size, and shape in 3D plots). This algorithm uses a smart thresholding technique based on the extracted statistical mean and standard deviation of the structural noise. Finally, we use the proposed algorithm to detect and characterize defects in a standard calibration specimen and validate the results by comparing to the designed depth information.
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    Methodology for the assessment of distributed propulsion configurations with boundary layer ingestion using the discretized miller approach
    (Praise Worthy Prize, 2017-06-30) Valencia, Esteban; Liu, Chengyuan; Nalianda, Devaiah; Panagiotis, Laskaridis; Gray, Iain; Singh, Riti
    The growing global environmental awareness has motivated the search for more fuel-efficient aircraft propulsion systems. In this context, a configuration based on distributed propulsion with Boundary Layer Ingestion (BLI) has been found to present potential performance benefits. The concept has been documented and explored extensively during the last few years and various aerodynamic integration issues, such as: high levels of distortion and low intake pressure recovery; have been identified as factors that may be detrimental in realizing the technology full potential. Parametric and parallel compressor (PC) approaches have been used to assess the effect of these aerodynamic issues on propulsors fan performance. However, in the context of BLI, these tools are unable to assess the effects of combined radial and circumferential distortion that are present. In order to assess the combined distortion patterns and the effects of distortion at component and system levels, this study uses a novel method based on semi-empirical correlations denominated the Discretized Miller (DM) approach. This method was developed for BLI systems previously by the author, and it is now incorporated into the propulsor performance method to assess the effects of the combined radial and circumferential distortion patterns. The performance analysis, undertaken at a component and system level, aims to assess several propulsion architectures, using Thrust Specific Fuel Consumption (TSFC) as figure of merit. To define the suitability of the distributed propulsor array in this study, an airframe layout based on the N3-X aircraft concept and High Temperature Superconducting (HTS) electric motor capabilities were assumed. The key contribution of this study is to enable the introduction of the concept of thrust split between energy source and propulsion system in the system analysis, and thereby, allows the assessment of its effects on different propulsion system layouts, while considering the BLI induced distortion. The results obtained with this alternative performance method showed that BLI reduces the fan efficiency of a conventional fan by approximately 2%, whilst corroborating the TSFC trends observed in previous studies. The study also indicates that when sizing effects of propulsors and core-engines were neglected, a propulsion system configuration with 75% thrust split was found optimum.