136 research outputs found
The effect of different combinations of boundary conditions on the average radiation efficiency of rectangular plates
The boundary conditions of a vibrating plate are known to have an influence on its sound radiation for frequencies below the critical frequency. To investigate this effect in a systematic way, the average radiation efficiency and radiated power are calculated for a rectangular plate set in an infinite baffle using a modal summation approach. Whereas analytical expressions exist for simply supported boundary conditions, a numerical approach is required for other cases. Nine combinations of boundary conditions are considered, consisting of simply supported, clamped and free edges on different plate edges. The structural vibration is approximated by using independent beam functions in orthogonal directions allowing simple approximate formulae for mode shapes and natural frequencies. This assumption is checked against a finite element model and shown to give reliable results. It is shown that a free plate has the lowest radiation efficiency and a clamped plate the highest for most frequencies between the fundamental panel natural frequency and the critical frequency. Other combinations of boundary condition give intermediate results according to the level of constraint introduced. The differences depend on frequency: excluding the extreme case of a fully free plate all the other boundary conditions give results within a range of 8 dB in the middle part of the short-circuiting region, decreasing towards the critical frequency. At low frequency the differences can be even greater, in some cases up to 20 dB. These conclusions are shown to hold for a range of plate thicknesses and dimensions
Rail roughness and rolling noise in tramways
Companies which manage railway networks have to cope continually with the problem of operating safety and maintenance intervention issues related to rail surface
irregularities. A lot of experience has been gained in recent years in railway applications but the case of tramways is quite different; in this field there are no specific criteria to define any intervention on rail surface restoration. This paper shows measurements carried out on some stretches of a tram network with the CAT equipment (Corrugation Analysis Trolley) for the principal purpose of detecting different states of degradation of the rails and identifying a level of deterioration to be associated with the need for maintenance through rail grinding. The measured roughness is used as an input parameter into prediction models for both rolling noise and ground vibration to show the potential effect that high levels of roughness can have in urban environment. Rolling noise predictions are also compared with noise measurements to illustrate the applicability of the modelling approach. Particular attention is given to the way the contact filter needs to be modelled in the specific case of trams that generally operate at low speed. Finally an empirical approach to assess vibration levels in buildings is presented
Wind loads analysis at the anchorages of the Talavera de la Reina cable stayed bridge
This paper describes wind tunnel tests performed on wind tunnel models of the Talavera de la Reina cable stayed bridge. The work describes the aeroelastic model construction and it is focused on the evaluation and analysis of the mean and peak wind loads at the tower foundation and the cable anchorages since these data can be very useful by the bridge manufacturer as a support for the bridge design. The work is part of a complete wind tunnel study carried out to analyze the aeroelastic stability of the bridge
The STARDAMP software: an assessment tool for wheel and rail damper efficiency
STARDAMP (Standardization of damping technologies for the reduction of railway noise) is a Franco-German research project within the DEUFRAKO framework that unites end users, manufacturers and research institutes. The target of STARDAMP is to support the transfer from R&D of wheel and rail dampers to their regular application. A software tool has been developed within STARDAMP that is dedicated to the prediction of the efficiency of wheel and rail dampers. The necessary input can be produced using relatively simple laboratory measurements. The rail response is assessed by combining track decay rates measured on a real track with decay rates measured in laboratory on a free rail that is equipped with dampers. The wheel response is calculated by using a finite element model of the wheel together with measured damping data. The tool is designed not only for the use by experts within the development of wheel and rail dampers. Indeed, a main goal of STARDAMP was to provide an easy-to-use tool to infrastructure managers and public authorities in order to help the decision making process regarding railway noise mitigation measures
A holistic approach for the design and assessment of railway tracks
In spite of the global financial crisis, considerable investments are being made in railway infrastructure in the UK and many countries around the world. Improvements in the quality and capacity of current services and the development of new railway infrastructure are needed to meet the increasing demand for transferring more people and goods in a more sustainable way. In particular, the performance of the track system is crucial to the successful and cost-effective operation of the railway. This has motivated much scientific research with the aim of better understanding the performance of the railway system, including both existing railway tracks and improved tracks for the future. Much current research on railway track focuses on individual aspects of the design and performance, e.g. track settlement, rail fatigue, ballast degradation, ride quality, maintenance, and noise and vibration. However to achieve substantial advances in railway track design, it is important to consider all these aspects in an integrated way. Changes that can benefit one aspect should not be allowed to have a negative impact on others. To facilitate this, a single tool should be developed or the computational tools that consider individual aspects of the design need to be integrated. The resulting tool can therefore be used to assess the behaviour of railway tracks in a holistic manner. A preliminary version of such a holistic tool is presented here. In this version, fast running models and empirical relationships are put together in order to calculate the performance of a railway track with regard to ride quality, ground-borne noise and vibration and rolling noise. Results for practical case studies are presented and discussed. The paper also highlights the limitations of the preliminary version and the future plans to achieve a reliable and comprehensive tool
An imaged 15Mjup companion within a hierarchical quadruple system
Since 2019, the direct imaging B-star Exoplanet Abundance Study (BEAST) at
SPHERE@VLT has been scanning the surroundings of young B-type stars in order to
ascertain the ultimate frontiers of giant planet formation. Recently, the
Myr HIP 81208 was found to host a close-in (~50 au) brown dwarf
and a wider (~230 au) late M star around the central 2.6Msun primary. Alongside
the continuation of the survey, we are undertaking a complete reanalysis of
archival data aimed at improving detection performances so as to uncover
additional low-mass companions. We present here a new reduction of the
observations of HIP 81208 using PACO ASDI, a recent and powerful algorithm
dedicated to processing high-contrast imaging datasets, as well as more
classical algorithms and a dedicated PSF-subtraction approach. The combination
of different techniques allowed for a reliable extraction of astrometric and
photometric parameters. A previously undetected source was recovered at a short
separation from the C component of the system. Proper motion analysis provided
robust evidence for the gravitational bond of the object to HIP 81208 C.
Orbiting C at a distance of ~20 au, this 15Mjup brown dwarf becomes the fourth
object of the hierarchical HIP 81208 system. Among the several BEAST stars
which are being found to host substellar companions, HIP 81208 stands out as a
particularly striking system. As the first stellar binary system with
substellar companions around each component ever found by direct imaging, it
yields exquisite opportunities for thorough formation and dynamical follow-up
studies.Comment: 12 pages, 9 figures, 5 tables. Accepted for publication as a Letter
in Astronomy and Astrophysics, section 1. Letters to the Edito
TOI-179: a young system with a transiting compact Neptune-mass planet and a low-mass companion in outer orbit
Transiting planets around young stars are key benchmarks for our
understanding of planetary systems. One of such candidates was identified
around the K dwarf HD 18599 by TESS, labeled as TOI-179. We present the
confirmation of the transiting planet and the characterization of the host star
and of the TOI-179 system over a broad range of angular separations. To this
aim, we exploited the TESS photometric time series, intensive radial velocity
monitoring performed with HARPS, and deep high-contrast imaging observations
obtained with SPHERE and NACO at VLT. The inclusion of Gaussian processes
regression analysis is effective to properly model the magnetic activity of the
star and identify the Keplerian signature of the transiting planet. The star,
with an age of 400+-100 Myr, is orbited by a transiting planet with period
4.137436 days, mass 24+-7 Mearth, radius 2.62 (+0.15-0.12) Rearth, and
significant eccentricity (0.34 (+0.07-0.09)). Adaptive optics observations
identified a low-mass companion at the boundary between brown dwarfs and very
low mass stars (mass derived from luminosity 83 (+4-6) Mjup) at a very small
projected separation (84.5 mas, 3.3 au at the distance of the star). Coupling
the imaging detection with the long-term radial velocity trend and the
astrometric signature, we constrained the orbit of the low mass companion,
identifying two families of possible orbital solutions. The TOI-179 system
represents a high-merit laboratory for our understanding of the physical
evolution of planets and other low-mass objects and of how the planet
properties are influenced by dynamical effects and interactions with the parent
star.Comment: 25 pages, 24 figures, A&A, in pres
The high-albedo, low polarization disk around HD 114082 harbouring a Jupiter-sized transiting planet
We present new optical and near-IR images of debris disk around the F-type
star HD 114082. We obtained direct imaging observations and analysed the TESS
photometric time series data of this target with a goal to search for planetary
companions and to characterise the morphology of the debris disk and the
scattering properties of dust particles. HD 114082 was observed with the
VLT/SPHERE instrument: the IRDIS camera in the K band together with the IFS in
the Y, J and H band using the ADI technique as well as IRDIS in the H band and
ZIMPOL in the I_PRIME band using the PDI technique. The scattered light images
were fitted with a 3D model for single scattering in an optically thin dust
disk. We performed aperture photometry in order to derive the scattering and
polarized phase functions, polarization fraction and spectral scattering albedo
for the dust particles in the disk. This method was also used to obtain the
reflectance spectrum of the disk to retrieve the disk color and study the dust
reflectivity in comparison to the debris disk HD 117214. We also performed the
modeling of the HD 114082 light curve measured by TESS using the models for
planet transit and stellar activity to put constraints on radius of the
detected planet and its orbit. The debris disk appears as an axisymmetric
debris belt with a radius of ~0.37 (35 au), inclination of ~83 and a
wide inner cavity. Dust particles in HD 114082 have a maximum polarization
fraction of ~17% and a high reflectivity which results in a spectral scattering
albedo of 0.65. The analysis of TESS photometric data reveals a transiting
planetary companion to HD 114082 with a radius of 1~ on an
orbit with a semi-major axis of au. Combining different data, we
reach deep sensitivity limits in terms of companion masses down to ~5 at 50 au, and ~10 at 30 au from the central star.Comment: 27 page
A scaled-up planetary system around a supernova progenitor
Stars and planetary system
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