53 research outputs found
Active Control of Fan Noise-Feasibility Study. Volume 2: Canceling Noise Source-Design of an Acoustic Plate Radiator Using Piezoceramic Actuators
The feasibility of using acoustic plate radiators powered by piezoceramic thin sheets as canceling sources for active control of aircraft engine fan noise is demonstrated. Analytical and numerical models of actuated beams and plates are developed and validated. An optimization study is performed to identify the optimum combination of design parameters that maximizes the plate volume velocity for a given resonance frequency. Fifteen plates with various plate and actuator sizes, thicknesses, and bonding layers were fabricated and tested using results from the optimization study. A maximum equivalent piston displacement of 0.39 mm was achieved with the optimized plate samples tested with only one actuator powered, corresponding to a plate deflection at the center of over 1 millimeter. This is very close to the deflection required for a full size engine application and represents a 160-fold improvement over previous work. Experimental results further show that performance is limited by the critical stress of the piezoceramic actuator and bonding layer rather than by the maximum moment available from the actuator. Design enhancements are described in detail that will lead to a flight-worthy acoustic plate radiator by minimizing actuator tensile stresses and reducing nonlinear effects. Finally, several adaptive tuning methods designed to increase the bandwidth of acoustic plate radiators are analyzed including passive, active, and semi-active approaches. The back chamber pressurization and volume variation methods are investigated experimentally and shown to be simple and effective ways to obtain substantial control over the resonance frequency of a plate radiator. This study shows that piezoceramic-based plate radiators can be a viable acoustic source for active control of aircraft engine fan noise
Vibration, Control and Stability of Dynamical Systems
From Preface: This is the fourteenth time when the conference âDynamical Systems: Theory and Applicationsâ gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled âDynamical Systemsâ with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled âDynamical Systems in Theoretical Perspectiveâ and âDynamical Systems in Applicationsâ
The Public Service Media and Public Service Internet Manifesto
This book presents the collectively authored Public Service Media and Public Service Internet Manifesto and accompanying materials.The Internet and the media landscape are broken. The dominant commercial Internet platforms endanger democracy. They have created a communications landscape overwhelmed by surveillance, advertising, fake news, hate speech, conspiracy theories, and algorithmic politics. Commercial Internet platforms have harmed citizens, users, everyday life, and society. Democracy and digital democracy require Public Service Media. A democracy-enhancing Internet requires Public Service Media becoming Public Service Internet platforms â an Internet of the public, by the public, and for the public; an Internet that advances instead of threatens democracy and the public sphere. The Public Service Internet is based on Internet platforms operated by a variety of Public Service Media, taking the public service remit into the digital age. The Public Service Internet provides opportunities for public debate, participation, and the advancement of social cohesion. Accompanying the Manifesto are materials that informed its creation: Christian Fuchsâ report of the results of the Public Service Media/Internet Survey, the written version of Graham Murdockâs online talk on public service media today, and a summary of an ecomitee.com discussion of the Manifestoâs foundations
Structural Health Monitoring Damage Detection Systems for Aerospace
This open access book presents established methods of structural health monitoring (SHM) and discusses their technological merit in the current aerospace environment. While the aerospace industry aims for weight reduction to improve fuel efficiency, reduce environmental impact, and to decrease maintenance time and operating costs, aircraft structures are often designed and built heavier than required in order to accommodate unpredictable failure. A way to overcome this approach is the use of SHM systems to detect the presence of defects. This book covers all major contemporary aerospace-relevant SHM methods, from the basics of each method to the various defect types that SHM is required to detect to discussion of signal processing developments alongside considerations of aerospace safety requirements. It will be of interest to professionals in industry and academic researchers alike, as well as engineering students. This article/publication is based upon work from COST Action CA18203 (ODIN - http://odin-cost.com/), supported by COST (European Cooperation in Science and Technology). COST (European Cooperation in Science and Technology) is a funding agency for research and innovation networks. Our Actions help connect research initiatives across Europe and enable scientists to grow their ideas by sharing them with their peers. This boosts their research, career and innovation
Electro-active polymer (EAP) dimple actuators for flow control
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Static, dynamic and levitation characteristics of squeeze film air journal bearing: Designing, modelling, simulation and fluid solid interaction
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Bearings today need to be able to run at very high speed, providing high positional accuracy for the structure that it supports, and requiring very little or no maintenance. For this to happen, bearings must have tight tolerances and very low or zero friction during operation. This pushes many traditional contact-type bearings to their limits as they often fail due to friction, generating heat and causing wear.
By comparison, existing non-contact bearings fare better because of their very low or zero friction. But some have their own problem too. For example, the fact that aerostatic bearings require an air supply means having to use a separate air compressor and connecting hoses. This makes the installation bulky. Aerodynamic and hydrodynamic bearings cannot support loads at zero speed. Both hydrodynamic and hydrostatic bearings may cause contamination to the work-pieces and the work environment because of the use of lubricating fluid.
A potential solution to the above-mentioned problems is the new squeeze film air bearing. It works on the rapid squeeze action of an air film to produce separation between two metal surfaces. This has the benefit of being compact with a very simple configuration because it does not require an external pressurized air supply, can support loads at zero speed and is free of contamination.
For this research, two squeeze film air journal bearings, made from material of Al 2024 â T3 and Cu - C101 with the same geometry, were designed. The bearing is in the shape of a round tube with three fins on the outer surface and the journal, a round rod. When excited at a certain normal mode, the bearing shell flexes with a desirable modal shape for the squeeze film action. The various modes of vibration of Al bearing were obtained from a finite-element model implemented in ANSYS. Two Modes, the 13th and 23rd, at the respective frequencies of 16.320 kHz and 25.322 kHz, were identified for further investigation by experiments with respect to the squeeze film thickness and its load-carrying capacity. For Cu bearing, the two Modes are also 13th and 23rd at the respective frequencies of 12.184 kHz and 18.459 kHz.
In order to produce dynamic deformation of the bearings at their modes, a single layer piezoelectric actuator was used as a driver. The maximum stroke length and the maximum blocking force of the single layer piezoelectric actuator were determined using manual calculation and ANSYS simulation.
In the coupled-field analysis, the single layer piezoelectric actuator was mounted on the outside surface of the bearing shell and loaded with an AC and a DC voltage in order to produce the static and dynamic deformation. For the static analysis, the maximum deformation of Al bearing shell is 0.124 ÎŒm when the actuators are driven at the DC of 75 V. For the dynamic analysis, the actuators are driven at three levels of AC, namely 55, 65 and 75V with a constant DC offset of 75V and the driving frequency coincided with the modal frequency of the bearing. The maximum dynamic deformation of Al bearing shell is 3.22ÎŒm at Mode 13 and 2.08ÎŒm at Mode 23 when the actuators were driven at the AC of 75 V and the DC of 75 V. Similarly, the FEA simulation was used for analyzing Cu bearing. Furthermore, the dynamic deformation of both Al and Cu bearing at Mode 13 and 23 are validated by experiments.
This research developed two theoretical models that explain the existence of a net pressure in a squeeze film for the levitation. The first model uses the ideal gas law as first approximation whilst the second uses the CFX simulation to provide a more exact explanation.
In terms of the load-carrying capacity, Mode 13 was identified to be better than Mode 23 for both bearings. However, at Mode 13, Al bearing has a higher load-carrying capacity than Cu bearing. This is due to Al bearing having a higher modal frequency and amplitude.
Finally, the coupled-field analysis for fluid solid interaction (FSI) was studied at both Mode 13 and 23 for Al bearing. The findings are that: a) the fluid force in the squeeze film can affect the dynamic deformation of the bearing shell, especially at high oscillation frequency, more at Mode 13 than at Mode 23 due to the relatively high pressure end-leakage in the latter; b) the dynamic deformation of the bearing shell increases with the gap clearance in a logarithmic manner at Mode 13; and c) the micron levels of gap clearance provide a damping effect on the dynamic deformation of the bearing shell at Mode 13 and at Mode 23, though much less dominant
14th Conference on Dynamical Systems Theory and Applications DSTA 2017 ABSTRACTS
From Preface:
This is the fourteen time when the conference âDynamical Systems â Theory and
Applicationsâ gathers a numerous group of outstanding scientists and engineers, who deal with
widely understood problems of theoretical and applied dynamics.
Organization of the conference would not have been possible without a great effort of the
staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over
the conference has been taken by the Committee of Mechanics of the Polish Academy of
Sciences and the Ministry of Science and Higher Education.
It is a great pleasure that our invitation has been accepted by so many people, including good
colleagues and friends as well as a large group of researchers and scientists, who decided to
participate in the conference for the first time. With proud and satisfaction we welcome nearly
250 persons from 38 countries all over the world. They decided to share the results of their
research and many years experiences in the discipline of dynamical systems by submitting many
very interesting papers.
This booklet contains a collection of 375 abstracts, which have gained the acceptance of
referees and have been qualified for publication in the conference proceedings [...]
Active fibre-reinforced composites with embedded shape memory alloys
This dissertation concerns active fibre-reinforced composites with embedded
shape memory alloy wires. The structural application of active materials allows to develop adaptive structures which actively respond to changes in the
environment, such as morphing structures, self-healing structures and power
harvesting devices. In particular, shape memory alloy actuators integrated
within a composite actively control the structural shape or stiffness, thus influencing the composite static and dynamic properties. Envisaged applications
include, among others, the prevention of thermal buckling of the outer skin of
air vehicles, shape changes in panels for improved aerodynamic characteristics
and the deployment of large space structures.
The study and design of active composites is a complex and multidisciplinary topic, requiring in-depth understanding of both the coupled behaviour of
active materials and the interaction between the different composite constituents. Both fibre-reinforced composites and shape memory alloys are extremely
active research topics, whose modelling and experimental characterisation still
present a number of open problems. Thus, while this dissertation focuses on
active composites, some of the research results presented here can be usefully
applied to traditional fibre-reinforced composites or other shape memory alloy
applications.
The dissertation is composed of four chapters.
In the first chapter, active fibre-reinforced composites are introduced by
giving an overview of the most common choices available for the reinforcement, matrix and production process, together with a brief introduction and
classification of active materials.
The second chapter presents a number of original contributions regarding
the modelling of fibre-reinforced composites. Different two-dimensional laminate theories are derived from a parent three-dimensional theory, introducing
a procedure for the a posteriori reconstruction of transverse stresses along the
laminate thickness. Accurate through the thickness stresses are crucial for the
composite modelling as they are responsible for some common failure mechanisms. A new finite element based on the First-order Shear Deformation Theory and a hybrid stress approach is proposed for the numerical solution of the
two-dimensional laminate problem. The element is simple and computationally
efficient. The transverse stresses through the laminate thickness are reconstructed starting from a general finite element solution. A two stages procedure is
devised, based on Recovery by Compatibility in Patches and three-dimensional
equilibrium. Finally, the determination of the elastic parameters of laminated
structures via numerical-experimental Bayesian techniques is investigated. Two
different estimators are analysed and compared, leading to the definition of an
alternative procedure to improve convergence of the estimation process.
The third chapter focuses on shape memory alloys, describing their properties and applications. A number of constitutive models proposed in the literature, both one-dimensional and three-dimensional, are critically discussed and
compared, underlining their potential and limitations, which are mainly related
to the definition of the phase diagram and the choice of internal variables. Some
new experimental results on shape memory alloy material characterisation are
also presented. These experimental observations display some features of the
shape memory alloy behaviour which are generally not included in the current
models, thus some ideas are proposed for the development of a new constitutive
model.
The fourth chapter, finally, focuses on active composite plates with embedded shape memory alloy wires. A number of diÂźerent approaches can be used
to predict the behaviour of such structures, each model presenting different advantages and drawbacks related to complexity and versatility. A simple model
able to describe both shape and stiffness control configurations within the same
context is proposed and implemented. The model is then validated considering
the shape control configuration, which is the most sensitive to model parameters. The experimental work is divided in two parts. In the first part, an active
composite is built by gluing prestrained shape memory alloy wires on a carbon
fibre laminate strip. This structure is relatively simple to build, however it
is useful in order to experimentally demonstrate the feasibility of the concept
proposed in the first part of the chapter. In the second part, the making of
a fibre-reinforced composite with embedded shape memory alloy wires is investigated, considering different possible choices of materials and manufacturing
processes. Although a number of technological issues still need to be faced, the
experimental results allow to demonstrate the mechanism of shape control via
embedded shape memory alloy wires, while showing a good agreement with the
proposed model predictions
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