Zebb Prime

Linear-Parameter-Varying Control of an Improved Three-Degree-of-Freedom Aeroelastic Model

Aeroelasticity is a broad term that describes the often complex interactions between aerodynamics and structural mechanics. The active control of aeroelastic phenomena is of particular research interest as it can lead to a reduction in weight and an increase in performance of an airframe. For more background on the analysis and control of aeroelastic systems, the reader is referred to the article by Mukhopadhyay [1]. A two degree-of-freedom wing section that is allowed to pitch and plunge due to supporting translational and torsional springs has often been used as a testbed for novel aeroelastic control methodologies. Two such apparatus are commonly used for the experimental validation of these methodologies; the Benchmark Active Control Technologies (BACT) wing [1, 2], and the Nonlinear Aeroelastic Test Apparatus (NATA) [3, 4]. This work focusses on the NATA platform, and presents an improved dynamic model along with a dynamic-less state-feedback Linear Parameter Vary-

On the dynamics of the furuta pendulum

The Furuta pendulum, or rotational inverted pendulum, is a system found in many control labs. It provides a compact yet impressive platform for control demonstrations and draws the attention of the control community as a platform for the development of nonlinear control laws. Despite the popularity of the platform, there are very few papers which employ the correct dynamics and only one that derives the full system dynamics. In this paper, the full dynamics of the Furuta pendulum are derived using two methods: a Lagrangian formulation and an iterative Newton-Euler formulation. Approximations are made to the full dynamics which converge to the more commonly presented expressions. The systemdynamics are then linearised using a Jacobian. To illustrate the influence the commonly neglected inertia terms have on the system dynamics, a brief example is offered.

A mixed H2/Hx scheduling control scheme for a two degree-of-freedom aeroelastic system under varying airspeed and gust conditions

This article investigates the control of a two degree-of-freedom aeroelastic system with a torsional stiness nonlinearity. The dynamics are transformed into a Linear Fractional Representation (LFR) such that the nonlinear eects of airspeed on the dynamics act as a gain feedback to the nominal system. A controller in LFR, which allows it to schedule with airspeed, is then synthesised using Linear Matrix Inequalities (LMIs). The performance objectives of the controller are the minimisation of the H2 norm from a gust input to the pitch and plunge outputs, and the minimisation of an H1 norm that corresponds to the systematic method of H1 loop-shaping. This method has a rigorous mathematical background that allows upper limits on these criteria to be established. The nonlinear system and controller are simulated under a variety of varying airspeed and gust conditions and is shown to exhibit both good robustness and rejection of gust disturbances.

An experimental application of aeroacoustic time-reversal to the Aeolian tone

This paper presents an experimental application of the aeroacoustic time-reversal (TR) source localization technique for studying flow-induced noise problems and compares the TR results with those obtained using conventional beamforming (CB). Experiments were conducted in an anechoic wind tunnel for the benchmark test-case of a full-span circular cylinder located in subsonic cross-flow wherein the far-field acoustic pressure was sampled using two line arrays (LAs) of microphones located above and below the cylinder. The source map obtained using the signals recorded at the two LAs without modeling the reflective surfaces of the contraction-outlet and cylinder during TR simulations revealed the lift-dipole nature of aeroacoustic source generated at the Aeolian tone; however, it indicates an error of 3/20 of Aeolian tone wavelength in the predicted location. Modeling the reflective contraction-outlet during TR was shown to improve the focal-resolution of the source and reduce side-lobe levels, especially in the low-frequency range. The experimental TR results were shown to be comparable to (a) the simulation results of an idealized dipole at the cylinder location in wind-tunnel flow and (b) that obtained by monopole and dipole CB, thereby demonstrating the suitability of TR method as a diagnostic tool to analyze flow-induced noise generation mechanism.

An Experimental Comparison of Beamforming, Time-reversal and Near-field Acoustic Holography for Aeroacoustic Source Localization

Aeroacoustic source localization is an important experimental tool that uses an array of microphones to locate and quantify aeroacoustic sources. Obtaining such information is the first step towards reducing noise emissions. One emerging method of aeroacoustic source localization is aeroacoustic time-reversal. With a unique blend of numerical simulation and experimental data, aeroacoustic time-reversal has the potential to provide superior source resolution and characterization performance over other microphone array processing techniques. This paper presents an experimental comparison of three different aeroacoustic source localization methods: aeroacoustic time-reversal, beamforming and near-field acoustic holography. The source resolution performance of all three source localization methods is investigated via a wind tunnel experimental study using two line arrays of microphones for the test case of a circular cylinder in low Mach number flow. The experimental results show that all three source localization methods are able to satisfactorily locate the cylinder noise source at the aeolian tone frequency to within �/6. In addition, information about the directivity characteristics of the noise source are obtained with aeroacoustic time-reversal and beamforming.

Experimental investigation of trailing edge noise from stationary and rotating airfoils

Trailing edge noise from stationary and rotating NACA 0012 airfoils is characterised and compared with a noise prediction based on the semi-empirical Brooks, Pope, and Marcolini (BPM) model. The NACA 0012 is symmetrical airfoil with no camber and 12% thickness to chord length ratio. Acoustic measurements were conducted in an anechoic wind tunnel using a stationary NACA 0012 airfoil at 0° pitch angle. Airfoil self-noise emissions from rotating NACA 0012 airfoils mounted at 0° and 10° pitch angles on a rotor-rig are studied in an anechoic room. The measurements were carried out using microphone arrays for noise localisation and magnitude estimation using beamforming post-processing. Results show good agreement between peak radiating trailing edge noise emissions of stationary and rotating NACA 0012 airfoils in terms of the Strouhal number. Furthermore, it is shown that noise predictions based on the BPM model considering only two dimensional flow effects, are in good agreement with measurements for rotating airfoils, at these particular conditions.

Flow modelling and noise generation of interacting prisms

ow velocity and turbulence intensity in various positions in the wake are compared with experimental hotwire data measured in the Anechoic Wind Tunnel (AWT) at The University of Adelaide, with good agreement. Finally, acoustic beamforming images of the noise generated by the interacting prisms measured in the AWT are presented. The acoustic results show that a blunt nose tends to increase noise at lower frequencies signicantly, while increasing prism separation tends to increase noise over most frequencies, but most signicantly at midfrequencies, and increasing yaw angle increases noise across all frequencies. Beamforming results show that at lower frequencies, this noise tends to be generated at the leading and trailing edges, while at higher frequencies the noise tends to be generated in the carriage gap.

An experimental study of the flow-induced noise created by a wall-mounted finite length airfoil

This paper presents the results of an experimental investigation of the sound produced by flow interaction with a wall-mounted finite length airfoil at low-to-moderate Reynolds number. Acoustic measurements have been taken in an anechoic wind tunnel at a range of Reynolds numbers, angles of attack and for a variety of airfoil aspect ratios (airfoil length to chord ratio) with a single microphone and two perpendicular planar microphone arrays. For comparison, measurements have also been taken with a semi-infinite or twodimensional airfoil and a half-span airfoil with tip flow but no boundary layer impingement. The experimental data is used to examine changes in wall-mounted finite airfoil noise production as a function of Reynolds number, angle of attack and airfoil aspect ratio. Additionally, the data gives insight into the airfoil noise generation mechanisms and the influence of flow at the airfoil tip and wall junction on noise production.

Longitudinal flight dynamics modelling and control of ScramSpace I

ScramSpace I is a free-flying hypersonic flight vehicle due to be launched in October 2012. The flight dynamics of ScramSpace I are calculated using Newtonian-flow aerody- namics and longitudinal point-mass equations of motion. These flight dynamics are then represented in Linear Parameter Varying (LPV) form using a curve-fit approximation to the true equations of motion. An LPV controller designed using an LQR-like H2 minimi- sation problem problem is designed to stabilise the vehicle during re-entry, and simulation results against the original equations of motion during re-entry are presented.

Characterisation and modelling of axial fan noise

This paper presents experimental data concerning the noise produced by an axial fan. Acoustic measurements have been taken with point microphones and a microphone array both with and without a grid at the entrance to the fan to examine the e↵ect of incoming turbulence levels on noise. The acoustic data are used to evaluate a strip-wise turbulent in-flow analytical broadband noise model. Two propagation models are employed in the analytical model to predict far-field noise. The first is based on the spherical spreading of acoustic waves and the second uses an experimentally measured transfer function. The best results are obtained with the experimental transfer function employed in the strip-wise noise model as it can recreate some of the finer spectral features of the recorded noise.