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O'Connor, William
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O'Connor, William
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O'Connor, William
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Now showing 1 - 10 of 21
- PublicationExperimental modal analysis of violin and similar thin plates by added point massesNovel methods are proposed to measure the modal properties of thin plates, such as free violin plates (prior to assembly), simply and inexpensively, by measuring certain changes when a small mass is added to the resonating plate. Iso-amplitude contours and mode shapes can easily be plotted. Modal mass, stiffness and damping can also be inferred. Underlying theory is developed, and experimental and numerical modelling methods of validation are briefly outlined.
687 - PublicationMultibody domain decomposition for parallel processing: a wave-based approach to handling interface dynamics(2012-05)
; For many good reasons there is growing interest in ways to allow parallel processing of multibody dynamics problems. Some recent approaches include “Domain Decomposition” and “Divide and Conquer”. This paper explores a new approach, reported as work in progress, with initial, promising results. The strategy is an extension of work done on wave analysis of lumped systems in another context. In the approach, a larger system is subdivided into smaller subsystems, which are solved in parallel. Interconnection points are boundaries for each. Dynamic coupling across boundaries is handled in terms of transmitted and reflected motion components (or "waves"), in both directions, across the boundaries.171 - PublicationAn alternative TLM method for steady-state convection-diffusionRecent papers have introduced a novel and efficient scheme, based on the transmission line modelling (TLM) method, for solving one-dimensional steady-state convection–diffusion problems. This paper introduces an alternative method. It presents results obtained using both techniques, which suggest that the new scheme outlined in this paper is the more accurate and efficient of the two. Copyright © 2009 John Wiley & Sons, Ltd.
290 - PublicationA new approach to modal analysis of uniform chain systemsA new method is presented to determine the mode shapes and frequencies of uniform systems consisting of chains of masses and springs of arbitrary number with arbitrary boundary conditions. Instead of the classical eigenproblem approach, the system is analysed in terms of circulating waves and associated phase lags. The phasor conditions for the establishment of standing waves determine the vibration modes. The conditions fully specify their shapes and frequencies, and lead to simple, explicit expressions for the components of the modal vectors and the associated natural frequencies. In addition, the form of the phasor diagrams of the modes gives insight into the modal behaviour. The orthogonality of mode shapes also readily emerges. Examples are presented for different boundary conditions. Although not presented, it is possible to extend the approach to non-uniform lumped systems and to forced frequency responses.
1083Scopus© Citations 7 - PublicationDevelopment and Validation of the Operations Procedures and Manual for a 2U CubeSat, EIRSAT-1, with Three Novel Payloads(2021-05-05)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The CubeSat standard, relatively short launch timescale, and orders of magnitude difference in cost in comparison to large scale missions, has allowed universities and smaller institutions to develop space missions. The Educational Irish Research Satellite (EIRSAT-1) is a 2U CubeSat being developed in University College Dublin (UCD) as part of the second round of the European Space Agency (ESA) Education Office’s Fly Your Satellite! (FYS) Programme. EIRSAT-1 is a student-led project to build, test, launch and operate Ireland’s first satellite. CubeSats typically use commercial off-the-shelf (COTS) components to facilitate new teams in developing a satellite on a rapid timescale. While some of the EIRSAT-1 subsystems are COTS procured from AAC Clyde Space, EIRSAT-1 has three novel experiments on-board which have been developed in UCD. The spacecraft’s Antenna Deployment Module has also been designed and built in-house. The on-board computer (OBC), procured from AAC Clyde Space, has been adapted to interface with these novel hardware components, accompanied by in-house developed software and firmware. All of these innovative subsystems complicate the CubeSat functionality making it essential to document and rigorously test the operations procedures for EIRSAT-1. In preparation for launch with these novel spacecraft subsystems, the EIRSAT-1 Operations Manual is being developed and incrementally verified. The Operations Manual contains the procedures to command and control the satellite, account for nominal and non-nominal scenarios and guide the operator in determining the cause of any anomalies observed during the mission and facilitate recovery. A series of operations development tests (ODTs) have been designed and conducted for a robust verification process. Each procedure is written up by a member of the EIRSAT-1 Operations Team in the EIRSAT-1 Operations Manual format. During an ODT, an in-flight scenario is considered in which the procedure under test is required. The procedure is then followed by a team member who has not been involved in the procedure development process. The feedback from these tests and from the operators is used to improve the procedures and continually update the Operations Manual. This paper will present the approach to operations development used by the EIRSAT-1 team and discuss the lessons learned for CubeSat operations development, testing and pre-flight verification.288 - PublicationWave-Echo Control of Lumped Flexible SystemsAn elegant, generic solution is presented to the problem of point-to-point control by a single actuator of a remote load through an intermediate flexible system, modelled by a system of lumped masses and springs. It is based on new ways of looking at the problem that respect and exploit the underlying dynamics. Under wide-ranging conditions the strategy allows rapid, almost-vibrationless, precise position control of the load, independently of the order of the system, without the need for a detailed system model or ideal actuator. During the start-up, the system itself reveals to the controller how to terminate the motion, so that the real system also acts as the model for the controller. The scheme is very robust to modelling, actuator and sensor errors. The strategy is presented, with some of the motivating ideas reviewed.
520Scopus© Citations 34 - PublicationBoundary-controlled travelling and standing waves in cascaded lumped systemsThis paper shows how pure travelling waves in cascaded, lumped, uniform, mass-spring systems can be defined, established, and maintained, by controlling two boundary actuators, one at each end. In most cases the control system for each actuator requires identifying and measuring the notional component waves propagating in opposite directions at the actuator-system interfaces. These measured component waves are then used to form the control inputs to the actuators. The paper also shows how the boundaries can be actively controlled to establish and maintain standing waves of arbitrary standing wave ratio, including those corresponding to the classical modes of vibration of such systems with textbook boundary conditions. These vibration modes are achieved and maintained by controlled reflection of the pure travelling wave components. The proposed control systems are also robust to system disturbances: they react to overcome external disturbances quickly and so to re-establish the desired steady motion.
518 - PublicationBoundary-controlled travelling and standing waves in cascaded lumped systemsThis paper describes how pure travelling waves in cascaded, lumped, uniform, mass-spring systems can be defined, established, and maintained, by controlling two boundary actuators, one at each end. In most cases the control system for each actuator requires identifying and measuring notional component waves, propagating in opposite directions, through the actuator-system interfaces. These measured component waves are then used to form the control inputs to the actuators. The paper also shows how the boundaries can be actively controlled to establish and maintain standing waves of arbitrary standing wave ratio, including those corresponding to classical modes of vibration with textbook boundary conditions. The proposed control systems are also robust to system disturbances: they react quickly to overcome external transient disturbances to re-establish the desired steady motion.
576Scopus© Citations 12 - PublicationTravelling waves in boundary-controlled, non-uniform, cascaded lumped systemsA companion paper in this conference considers travelling and standing waves in cascaded, lumped, mass-spring systems, controlled by two boundary actuators, one at each end, when the system is uniform. It first proposes definitions of waves in finite lumped systems. It then shows how to control the actuators to establish desired waves from rest, and maintain them despite disturbances. The present paper extends this work to the more general, non-uniform case, when mass and spring values are arbitrary. A special "bi-uniform" case is first studied, consisting of two different uniform cascaded systems in series, with an obvious, uncontrolled, impedance mismatch where they meet. The paper shows how boundary actuator control systems can be designed to establish, and robustly maintain, apparently pure travelling waves of constant amplitude in either the first or the second uniform section, in each case with an appropriate standing wave pattern in the other section. Then a more general non-uniform case is studied. A definition of a "pure travelling wave" in non-uniform systems is proposed. Curiously, it does not imply constant amplitude motion. It does however yield maximum power transfer between boundary actuators. The definition, and its implementation in a control system, involves extending the notions of "pure" travelling waves, standing waves, and input and output impedances of sources and loads, when applied to non-uniform lumped systems. Practical, robust control strategies are presented for all cases.
357Scopus© Citations 4 - PublicationWave-like modelling of cascaded, lumped, flexible systems with an arbitrarily moving boundaryThis paper considers cascaded, lumped, flexible systems, which may be short and non-uniform, which are driven by an arbitrarily moving boundary. Such systems exhibit vaguely wavelike behaviour yet defy classical wave analysis. The paper proposes novel ways to analyse and model such systems in terms of waves. It presents two new wave models for non-uniform systems, one series and one shunt, defining their component wave transfer functions, and thereby providing a way to define, identify and measure component waves. Features of the models are compared. The series and shunt configurations are mutually consistent and can be combined into a single composite wave model. The models are exact, but elements within them remain arbitrary to some degree, implying slight differences in the wave decomposition of the system. Some good model choices are proposed and explored. Wave speed and wave impedance are briefly considered, as are ways to measure component waves. Implications are discussed.
1917Scopus© Citations 14
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