The Atmospheric Remote-Sensing Infrared Exoplanet Large-survey (ARIEL) is one of the three candidate missions selected by the European Space Agency (ESA) for its next medium-class science mission due for launch in 2026. The goal of the ARIEL mission is to investigate the atmospheres of several hundred planets orbiting distant stars in order to address the fundamental questions on how planetary systems form and evolve.
During its four (with a potential extension to six) years mission ARIEL will observe 500+ exoplanets in the visible and the infrared with its meter-class telescope in L2. ARIEL targets will include gaseous and rocky planets down to the Earth-size around different types of stars. The main focus of the mission will be on hot and warm planets orbiting close to their star, as they represent a natural laboratory in which to study the chemistry and formation of exoplanets.
The ARIEL mission concept has been developed by a consortium of more than 50 institutes from 12 countries, which include UK, France, Italy, Germany, the Netherlands, Poland, Spain, Belgium, Austria, Denmark, Ireland and Portugal. The analysis of the ARIEL spectra and photometric data in the 0.5-7.8 micron range will allow to extract the chemical fingerprints of gases and condensates in the planets’ atmospheres, including the elemental composition for the most favorable targets. It will also enable the study of thermal and scattering properties of the atmosphere as the planet orbit around the star.
ARIEL will have an open data policy, enabling rapid access by the general community to the high-quality exoplanet spectra that the core survey will deliver.
This paper investigates the use of electrostatic forces for vibration control of MEMS devices. A micro beam subject to electrostatic loading is considered. The electrostatic forces cause softening nonlinearity and their amplitudes are proportional to the square of applied DC voltages. An optimization problem is set up to minimize the vibration level of the micro-beam at given excitation frequencies. A new method based on incrementing nonlinear control parameters of the system and Harmonic Balance is used to obtain the required DC voltages that suppress unwanted vibration of the micro-beam. The results are illustrated using numerical simulations
For a nonlinear beam-mass system used to harvest vibratory energy, the two-mode approximation of the response is computed and compared to the single-mode approximation of the response. To this end, the discretized equations of generalized coordinates are developed and studied using a computational method. By obtaining phase-portraits and time-histories of the displacement and voltage, it is shown that the strong nonlinearity of the system affects the system dynamics considerably. By comparing the results of single- and two-mode approximations, it is shown that the number of mode shapes affects the dynamics of the response. Varying the tip-mass results in different structural configurations namely linear, pre-buckled nonlinear, and post-buckled nonlinear configurations. The nonlinear dynamics of the system response are investigated for vibrations about static equilibrium points arising from the buckling of the beam. Furthermore, it is demonstrated that the harvested power is affected by the system configuration.
Composites with multiple (bi-) interpenetrating phases are ideally placed to realise multi-functionality and certain multifunctional
and smart materials may be modeled as bi-continuous two-phase composites. This paper estimates the
mechanical properties of such materials using finite element analysis and homogenization. The effect of phase volume
fraction and contiguity on the properties is investigated for a range of microstructures with triply periodic minimal P
interfaces between the two phases. The results show that the properties of the composite depend on not only the overall
volume fraction but also the contiguity of the constituent phases.
This paper develops an equivalent linear model for piezomagnetoelastic energy harvesters under broadband
random ambient excitations. Piezomagnetoelastic harvesters are used for powering low power electronic sensor
systems. Nonlinear behaviour arising due to the vibration in a magnetic field makes piezomagnetoelastic energy
harvesters different from the more classical piezoelastic energy harvesters. First numerical simulation of the
nonlinear model is presented and then an equivalent linearization based analytical approach is developed for the
analysis of harvested power. A cosed-form approximate expression for the ensemble average of the harvested
power is derived. The equivalent model is seen to capture the details of the nonlinear model and also provides
more details to the behaviour of the harvester to random excitation. Our results show that it is possible to
optimally design the system such that the mean harvested power is maximized for a given strength of the input
broadband random ambient excitation.
The design of the skins has been identified as a major issue for morphing aircraft wings. Corrugated laminates
provide a good solution due to their extremely anisotropic behavior. However, the optimal design of a morphing
aircraft requires simple models of the skins that may be incorporated into multi-disciplinary system models. This
requires equivalent material models that retain the dependence on the geometric parameters of the corrugated
skins. An analytical homogenization model, which could be used for any corrugation shape, is suggested in this
paper. This method is based on a simplified geometry for a unit-cell and the stiffness properties of original sheet.
This paper investigates such a modeling strategy and demonstrates its performance and potential.
This paper presents a fully coupled multi-scale finite element model for the description of the dissipative mechanical
response of wood cell walls under large strains. Results show the ability of the present model to capture
the main phenomenological responses found typically in wood at the microscopic scale. In addition, the structural
and mechanical concepts involved in wood cells are exploited further in order to design new wood inspired
composites. Numerical tests are conducted in prototypes of bio-inspired composites and demonstrate substantial
gains in terms of resistance to failure and in the control of the overall flexibility/stiffness balance in the material.
Acoustic emission (AE) testing is a sensitive technique capable of detecting many types of defect with a sparse sensor
array making it an attractive structural health monitoring technology. The widespread application of the technology is
limited by a lack of predictive modelling and in part, the lack of quantitative source characteristics. The vast majority of
current laboratory AE testing is conducted on small coupons which cannot be used to generate quantitative source
characteristics since reflected wave energy from the specimen edges influences the received waveforms. An alternative
approach is to test on large specimens where the modal properties of propagating waves can be examined with no
influence from reflected wave energy. However, the design and testing of large specimens is not trivial.
The work in this paper discusses the design of large fibre reinforced composite (FRC) specimens which are suitable for
making quantitative source measurements. The design considerations include the minimum plate dimensions and
placement of sensors. A novel technique, referred to as the location-time plot technique, is described which links
propagation characteristics, specimen dimensions and sensor locations to map the dispersion of elastic waves in plates.
The technique is demonstrated in the design of a simple AE experiment on a highly anisotropic plate. The technique is
then used in the design of a practical AE testing arrangement for monitoring delamination from artificial defects in a
large FRC plate. Experimental waveforms, recorded using this AE testing arrangement, are presented and are shown to
be in agreement with the location-time plot technique.
One approach to morphing aircraft is to use bistable or multistable structures that have two or more stable equilibrium configurations to define a discrete set of shapes for the morphing structure. Moving between these stable states may be achieved using an actuation system or by aerodynamic loads. This paper considers three concepts for morphing aircraft based on multistable structures, namely a variable sweep wing, bistable blended winglets and a variable camber trailing edge. The philosophy behind these concepts is outlined, and simulated and experimental results are given.
KEYWORDS: Transducers, Wave propagation, Structural health monitoring, Waveguides, Data modeling, Aluminum, Acoustic emission, Signal detection, Reflection, Signal attenuation
Acoustic emission (AE) testing is potentially a highly suitable technique for structural health monitoring (SHM) applications due to its ability to achieve high sensitivity from a sparse array of sensors. For AE to be deployed as part of an SHM system it is essential that its capability is understood. This is the motivation for developing a forward model, referred to as QAE-Forward, of the complete AE process in real structures which is described in the first part of this paper. QAE-Forward is based around a modular and expandable architecture of frequency domain transfer functions to describe various aspects of the AE process, such as AE signal generation, wave propagation and signal detection. The intention is to build additional functionality into QAE-Forward as further data becomes available, whether this is through new analytic tools, numerical models or experimental measurements. QAE-Forward currently contains functions that implement (1) the excitation of multimodal guided waves by arbitrarily orientated point sources, (2) multi-modal wave propagation through generally anisotropic multi-layered media, and (3) the detection of waves by circular transducers of finite size. Results from the current implementation of QAE-Forward are compared to experimental data obtained from Hsu-Neilson tests on aluminum plate and good agreement is obtained. The paper then describes an experimental technique and a finite element modeling technique to obtain quantitative AE data from fatigue crack growth that will feed into QAE-Forward.
KEYWORDS: Finite element methods, Matrices, Distributed computing, Chemical elements, Systems modeling, Seaborgium, Aerospace engineering, Motion models, Mathematical modeling, Dynamical systems
This paper considers the analysis of structures with nonlocal damping, where the reaction force at any point is obtained as a weighted average of state variables over a spatial domain. The model yields an integro-differential equation, and obtaining closed form solutions is only possible for a limited range of boundary conditions by the transfer function method. Approximate solutions using the Galerkin method for beams are presented for typical spatial kernel functions, for a nonlocal viscoelastic foundation model. This requires the approximation of the displacement to be defined over the whole domain. To treat more complicated problems with variable damping parameters, non-uniform section properties, intermediate supports or arbitrary boundary conditions, a finite element method for beams is developed. However, in nonlocal damping models, nodes remote from the element do have an effect on the energy expressions, and hence the damping matrix is no longer block diagonal. The expressions for these direct and cross damping matrices are obtained for separable spatial kernel functions. The approach is demonstrated on a range of examples.
Modal actuators and sensors may be used to excite or measure either single modes or combinations of modes. In beam structures they may be implemented using either discrete transducers or continuous, distributed transducers. Continuous transducers require less processing and thus can employ simple controllers. For beam structures the width of the transducer may be approximated using the underlying finite element model shape functions. The transducers may then be designed using a discrete model, and the shape recovered by using the shape functions. The side constraint of minimizing the curvature of the transducer shape is introduced to ensure that the resulting shape is as simple as possible. Assuming that the thickness of the transducer may be varied (for example using printing techniques) then this procedure may be extended to plate structures. The alternative is to determine the shape of a constant thickness modal transducer. One approach outlined in this paper is to use a fine finite element mesh and determine which elements should be covered with a transducer. The possibility of using a continuous shape definition will also be explored. The approaches are tested on various beam and plate structures to demonstrate their effectiveness and also to demonstrate the errors introduced for non-proportionally damped structures.
Structures with a large number of embedded sensors are becoming more common, and this refined spatial information can be used to advantage in damage location and model validation. These sensors could be accelerometers, strain gauges, piezoceramic patches, PVDF film sensors, or optical fibre sensors. This approach requires that the sensors are function correctly, which on a smart structure operating in the field should be continuous and automatically monitored. This paper considers possible approaches to sensor validation, based on the assumption that a model of the structure is available. The aim is to make use of the natural data redundancy since there will more sensors than modes in the data. The validation approaches considered are based on hypothesis testing based on a number of techniques, such as modal filtering. The methods are demonstrated on simple examples that exercise their strengths and weaknesses.
KEYWORDS: Actuators, Sensors, Vibration control, Control systems, Matrices, Active vibration control, Control systems design, Amplifiers, Telecommunications, Condition numbers
Active vibration control is using increasingly large numbers of sensors and actuators to achieve ever-improving results in the control of distributed systems. As the number of actuators and sensor increases, computational effort for control purposes increases. As the number of actuators and sensors grows, so too does the frequency range over which it is sensible to attempt active control and the time available for control calculations is therefore shrinking. Notwithstanding the remarkable rate at which processor speeds continue to increase, it is evident that full multi- input multi-output control cannot continue to be applied for increasing numbers of sensors and actuators. The requirements for every actuator to have an amplifier and every sensor to have signal conditioning is also very demanding. This paper addresses the issue of how best to implement the controller and estimator in smaller sensor/actuator groups and to determine the optimum topology, or grouping, of the sensors and actuators. The demands of both the control and the parameter estimation are addressed, and the implementation of modal control and selective sensitivity estimation algorithms are described.
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