Dr. Gareth A. Vio

Photo of Dr. Gareth Vio

BEng (Hons) PhD Manchester SMAIAA

Lecturer in Aerospace Engineering

Phone:    +61 (0)2 9351 2394
Fax:         +61 (0)2 9351 7060
E-mail:     gareth (dot) vio at sydney (dot) edu (dot) au
Address: Room N306, Aeronautical Engineering Building J11
                 School of Aerospace, Mechanical and Mechatronic Engineering
                 The University of Sydney
                 NSW 2006
                 Australia

Qualifications

  • PhD, Aerospace Engineering, The University of Manchester, 2005
  • BEng (Hons), Aerospace Engineering, The University of Manchester, 1999

Employment history

  • Research Assistant, The University of Manchester, UK, 2002-2005
  • Research Associate, The University of Manchester, UK, 2005-2007
  • Research Associate, The University of Liverpool, UK, 2007-2010
  • Lecturer in Aerospace Engineering, The University of Sydney, 2010-present

Current Undergraduate Teaching

Past Undergraduate Teaching

Research interests

  • Non-linear Aeroelasticity
  • Non-linear Vibration
  • Non-Linear System Identification
  • Gust Response
  • Aeroelastic Tailoring
  • Design of Composite Structures
  • Morphing Structures
  • Natural Selection Optimisation

Research Projects

  • AeroThermoElasticity
  • Aeroelastic Tailoring
  • Non-linear Energy Sinks
  • Non-linear Vibration and System Identification
  • Highly Flexible Structures
  • Non-Linear Aeroelastic Prediction
  • Passive Gust Alleviation

    There is much recent interest, particularly at AFRL Air Vehicle Directorate in the development of unmanned High Altitude Long Endurance (HALE) or Sensorcraft air vehicles that are able to provide a 360 degree sensor coverage whilst maintaining moderate stealth characteristics. The sensor requirement has naturally led to a re-visit of the pioneering work into joined-wing aircraft by Wolkovich. Typical joined-wing sensorcraft structural lay-outs differ considerably form onventional aicraft configurations, where the the aeroelastic behaviour is likely to be very different. Much of the work on sensorcraft has been focused upon the optimisation of the aircraft structure. The outer wing of the sensor craft design leads to the high aspect ratio, which is very favourable for reduction in fuel consumption and range extension. However, it produces high bending moments stemming from manoeuvres or gusts. Due to its significant flexibility there have been concerns about:

    • the ability to maintain a shape that does not affect the sensor performance
    • the loads that may result from gusts
    • the need to use non-linear static and dynamic aeroelastic analysis in order to account for the large geometric deflections.

    One of the critical design cases for joined-wing designs is the buckling of the rear wing structure. Previous work has shown that non-linear buckling analysis is required in order to estimate accurately the deflections and resulting loads that occur. Linear analysis for buckling under critical gusts loads significantly increased the wing optimized structural weight, almost doubling it, and when non-linear analysis is used, the wing tip deflection increases and the optimized wing weight increases significantly again. The use of some form of gust load alleviation system is therefore very desirable, as this should lead to a significant reduction in structure, and hence weight, that is required. One possible solution is the design of active load alleviation systems using all of the control surfaces; however, such an approach is complex, requiring the avionics for such a system to be carried on the sensorcraft, and a certain amount of system redundancy must be included to allow for system failures.

  • Morphing Structures

    There is a growing interest in the development of adaptive aeroelastic structures to allow aeroelastic deflections to be used in a beneficial manner. They are a subset of Morphing Structures, but rather than attempting to change the wing plan-form, the stiffness of the structure is adjusted to influence the aerodynamic performance. Such an approach will lead to more efficient aircraft designs. For example, the wing twist could be adjusted throughout the entire flight in order to maintain a shape giving optimal lift-drag ratio for maximum range, and also as a means of roll and loads control. Other concepts are being developed to change the wing leading and trailing edge shape in order to adjust the lift coefficient, and also to change the wing planform shape. In recent years, a number of research programmes, for example the Active Aeroelastic Wing and the Morphing Programme, have started to develop active aeroelastic concepts. active aeroelastic concepts on a number of large wind tunnel models. The research programme is devoted towards investigating the use of changes in the internal aerospace structure in order to control the static aeroelastic behaviour. Such an approach is desirable, and arguably advantageous compared to other possible concepts. For instance, the use of leading and trailing control surfaces to control wing twist can lead to increased drag and poor observability characteristics. The use of smart materials (e.g. piezo and shape memory alloys) has received considerable attention in recent years, but still suffers from limits in the amount of force that can be achieved currently in relation to that required to twist or bend a wing. The key idea exploited in the Adaptive Internal Structures approach is to make use of the aerodynamic forces acting upon the wing to provide the moment to twist the wing. By changing the position of the shear centre of the wing, the bending moment, and hence the amount of twist, will also change. A far smaller amount of energy is required to adjust the structure compared to that required to twist the wing and keep it in that shape. Such an approach is very attractive for active aeroelastic wing concepts and leads the way for the adaptive structural control of aerodynamic performance as well as roll and loads control.

  • Non-Linear Damping Identification

    The problem of modelling damping in structures is not well-understood because often in traditional structural design it is not actually important, mainly because there are no instabilities and there is no reason to accurately model it. In the aeroelastic problem, instead, the occurrence of instabilities may strongly depend on damping and catastrophic events can occur. Flutter is a characteristic form of self-excited oscillations that can arise through the interaction of an aerodynamic flow with the elastic modes of a mechanical structure, e.g. the bending and torsion modes of an aircraft wing. The occurrence of flutter compromises the operational safety, flight performance and energy efficiency of the aircraft. From the structural point of view, the main sources of damping in a wing are the friction in joints, viscous damping due to air flow and material damping. Modelling of damping is a very difficult issue because the level of damping in a structure can depend, for example, on the material, the methods used for manufacturing and the final finishing processes. The interfacial damping mechanism, instead, results from Coulomb friction between members and connections and can depend on clamp force of bolts or welded connections. For all these reasons, normally the identification is preferred to modelling because trying to extract damping parameters by experiments is simpler than collecting all the information to model damping accurately. Damping identification in aeroelastic structure is often performed during Ground Vibration Testing (GVT). Very little attention has been given at the damping identification process while an aircraft is in flight, as different non-linear regions, both structural or damping, can be entered, giving different energy dissipation. A number of experimental techniques are available for the identification of modal parameters using curvefitting methods or signal processing techniques.

  • Worst Gust Response

    Unsteady loads calculations play an important part across much of the design and development of an aircraft, and have an impact upon the concept and detailed structural design, aerodynamic characteristics, weight, flight control system design, control surface design and performance. They determine the most extreme stress levels and estimate fatigue damage and damage tolerance for a particular design. The certification of large commercial aircraft is covered by the EASA CS-25 (Certification Specifications) or FAR-25 documents. A range of load cases that has to be accounted for are described and are a primary prerequisite for assuring structural integrity over the operating environment of the aircraft. Loads requirements are defined in the context of the design envelope. Certification specifications require that enough points, on or within the boundary of the design envelope, are investigated to ensure that the most extreme loads for each part of the aircraft structure are identified. The flight conditions and manoeuvres, which provide the largest aircraft loads, are not known a-priori. Therefore the aerodynamic and inertial forces are calculated at a large number of conditions to give an estimate of the maximum loads, and hence stresses, that the structure of the detailed aircraft design will experience in service. A simplistic estimate of the number of analyses required would multiply the numbers of conditions to give 10,000,000. Even with simplistic models of the aircraft behaviour this is an unfeasible number of separate simulations. However, engineering experience is used to identify the most likely critical loads conditions, meaning that approximately 100,000 simulations are required for conventional aircraft configurations. Furthermore these analyses have to be repeated every time that there is an update in the aircraft structure. Within the modern civil airframe industry, each of these loads calculation cycles takes a considerable time. The number of different flight conditions that need to be considered to assess the maximum loads that will be encountered by a civil aircraft is large and must be reduced. At present engineering experience is used to achieve a significant reduction for conventional aircraft geometries whose response can be calculated using assumptions of linearity. With the advent of non-linear control systems and new manufacturing techniques, even conventional aircraft are becoming increasingly nonlinear and the linearity assumption is becoming unacceptable.

Research Groups

Selected publications

Dr Vio has published over 30 conference publications on a wide range of subjects. A representative sample of his publications is given below:

  • J.D. El Tom and G.A. Vio, "Novel Wing Box Design", Applied Mechanics and Materials, 2013
  • N.F. Giannelis, G.A. Vio, D. Verstraete and J. Steelant, "Temperature Effect on the Structural Design of a Mach 8 Vehicle", Applied Mechanics and Materials, 2013
  • B.J. Morrell, D.J. Munk, G.A. Vio and D. Verstraete, "Development of a Hypersonic Aircraft Design Optimization Tool", Applied Mechanics and Materials, 2013
  • H.H. Khodaparast, G. Georgiou, J.E. Cooper, L. Riccobene, S. Ricci, G.A. Vio and P. Denner, "Efficient Worst Case '1-cosine' gust loads prediction", Journal of Aeroelasticity and Structural Dynamics, 2(3), 33-54, 2012.
  • M.R. Amoozgar, S. Irani and G.A. Vio, "Aeroelastic instability of a composite wing with a powered engine", Journal of Fluids and Structures, 2012.
  • A. Manan, G.A. Vio, M.Y. Harmin and J.E. Cooper, “ Optimisation of aeroelastic composite structures using evolutionary algorithms ”, Engineering Optimization, Vol 42, No 2, 2010, pp 171-184.
  • G.A. Vio, M. Prandina and G. Dimitriadis, “ Damping identification in a nonlinear aeroelastic structure”, International conference on Noise and Vibration, ISMA2010, Leuven, Belgium, 2010.
  • G.A. Vio, S. Marques and J.E. Cooper and K.J. Badcock, “ Adaptive aeroelastic concept applied to a civil jet aircraft model”, 51st AIAA Structures, Structural Dynamics and Material Conference, SDM2010, Orlando, Florida, 2010.
  • G.A. Vio, G. Dimitriadis nad J.E. Cooper “ Data clustering for the identification of the bifurcation behaviour in non-linear aeroelastic systems using a coupled harmonic balance/genetic algorithm approach”, International conference on Noise and Vibration, ISMA2008, Leuven, Belgium, 2008.
  • M.J. de C. Henshaw, G.A. Vio et all, “Nonlinear aeroelastic prediction for aircraft applications”, Progress in Aerospace Sciences, Vol 43, No. 4, 2007, pp 65-137.
  • G.A. Vio. G. Dimitriadis and J.E. Cooper, “A comparison of bifurcation nad LCO amplitude prediction methods applied to the aeroelastic galloping problem”, Journal of Fluids and Structures, Vol 23, No 7, 2007, pp 983-1011.
  • G.A. Vio, J.E. Cooper, G. Dimitriadis, K. Badcock, M. Woodgate and A. Rampurawala, “Aeroelastic system identiifcation using transonic CFD data for a wing/store configuration”, Aerospace Science and Technology, Vol 11, No (2-3), 2007, pp 146-154.
  • G.A. Vio, G. Dimitriadis and D. Shi, “ System identification of theoretical and experimental data for mechanical systems”, 9th International Conference on Recent Advances in Structural Dynamics, Southampton, UK, 2006.