1,517 research outputs found
Pre-posterior analysis of inspections incorporating degradation of concrete structures
The framework of pre-posterior decision analysis has a large potential as a decision support tool in structural
engineering. It seems ideally suited to tackle problems related to determining the value of Structural Health
Monitoring and is commonly applied in inspection and maintenance planning. However, the application of this
methodology for integrated life-cycle cost decision making related to monitoring of time-dependent and
spatial degradation phenomena in concrete structures, needs further investigation. In this work, the timedependent
and spatial degradation phenomena will be coupled to the pre-posterior decision making approach
and applied on concrete beams under bending, subjected to corrosion of the reinforcement. A framework is
set up to determine the value of information of inspections enabling adequate decision-making. The
methodology incorporates Bayesian updating based on the uncertain inspection outcomes. The framework
will be illustrated by application on a simply supported reinforced concrete beam
Wind-structure interaction simulations for the prediction of ovalling vibrations in silo groups
Wind-induced ovalling vibrations were observed during a storm in October 2002 on several empty silos of a closely spaced group consisting of 8 by 5 thin-walled silos in the port of Antwerp (Belgium). The purpose of the present research is to investigate if such ovalling vibrations can be predicted by means of numerical simulations. More specifically, the necessity of performing computationally demanding wind-structure interaction (WSI) simulations is assessed. For this purpose, both one-way and two-way coupled simulations are performed. Before considering the entire silo group, a single silo in crosswind is simulated. The simulation results are in reasonably good agreement with observations and WSI simulations seem to be required for a correct prediction of the observed ovalling vibrations
PACS and SPIRE range spectroscopy of cool, evolved stars
Context: At the end of their lives AGB stars are prolific producers of dust
and gas. The details of this mass-loss process are still not understood very
well. Herschel PACS and SPIRE spectra offer a unique way of investigating
properties of AGB stars in general and the mass-loss process in particular.
Methods: The HIPE software with the latest calibration is used to process the
available PACS and SPIRE spectra of 40 evolved stars. The spectra are convolved
with the response curves of the PACS and SPIRE bolometers and compared to the
fluxes measured in imaging data of these sources. Custom software is used to
identify lines in the spectra, and to determine the central wavelengths and
line intensities. Standard molecular line databases are used to associate the
observed lines. Because of the limited spectral resolution of the spectrometers
several known lines are typically potential counterparts to any observed line.
To help identifications the relative contributions in line intensity of the
potential counterpart lines are listed for three characteristic temperatures
based on LTE calculations and assuming optically thin emission. Result: The
following data products are released: the reduced spectra, the lines that are
measured in the spectra with wavelength, intensity, potential identifications,
and the continuum spectra, i.e. the full spectra with all identified lines
removed. As simple examples of how this data can be used in future studies we
have fitted the continuum spectra with three power laws and find that the few
OH/IR stars seem to have significantly steeper slopes than the other oxygen-
and carbon-rich objects in the sample. As another example we constructed
rotational diagrams for CO and fitted a two-component model to derive
rotational temperatures.Comment: A&A accepte
Simplified models of stellar wind anatomy for interpreting high-resolution data: Analytical approach to embedded spiral geometries
Recent high-resolution observations have shown stellar winds to harbour
complexities which strongly deviate from spherical symmetry, generally assumed
as standard wind model. One such morphology is the archimedean spiral,
generally believed to be formed by binary interactions, which has been directly
observed in multiple sources. We seek to investigate the manifestation in the
observables of spiral structures embedded in the spherical outflows of cool
stars. We aim to provide an intuitive bedrock with which upcoming ALMA data can
be compared and interpreted. By means of an extended parameter study, we model
rotational CO emission from the stellar outflow of asymptotic giant branch
stars. To this end, we develop a simplified analytical parametrised description
of a 3D spiral structure. This model is embedded into a spherical wind, and fed
into the 3D radiative transfer code LIME, which produces 3D intensity maps
throughout velocity space. Subsequently, we investigate the spectral signature
of rotational transitions of CO of the models, as well as the spatial aspect of
this emission by means of wide-slit PV diagrams. Additionally, the potential
for misinterpretation of the 3D data in a 1D context is quantified. Finally, we
simulate ALMA observations to explore the impact of interefrometric noise and
artifacts on the emission signatures. The spectral signatures of the CO
rotational transition v=0 J=3-2 are very efficient at concealing the dual
nature of the outflow. Only a select few parameter combinations allow for the
spectral lines to disclose the presence of the spiral structure. The inability
to disentangle the spiral from the spherical signal can result in an incorrect
interpretation in a 1D context. Consequently, erroneous mass loss rates would
be calculated..
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