827 research outputs found
The dynamics of geometrically compliant mooring systems
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2000.Geometrically compliant mooring systems that change their shape to accommodate deformations
are common in oceanographic and offshore energy production applications. Because of the inherent
geometric nonlinearities, analyses of such systems typically require the use of a sophisticated
numerical model. This thesis describes one such model and uses that model along with experimental
results to develop simpler forms for understanding the dynamic response of geometrically
compliant moorings.
The numerical program combines the box method spatial discretization with the generalized-
a method for temporal integration. Compared to other schemes commonly employed for the
temporal integration of the cable dynamics equations, including box method, trapezoidal rule,
backward differences, and Newmark’s method, the generalized-a algorithm has the advantages of
second-order accuracy, controllable numerical dissipation, and improved stability when applied to
the nonlinear problem. The numerical program is validated using results from laboratory and field
experiments.
Field experiment and numerical results are used to develop a simple model for dynamic tension
response to vertical motion in geometrically compliant moorings. As part of that development, the
role of inertia, drag, and stiffness in the tension response are explored. For most moorings, the
response is dominated by inertial and drag effects. The simple model uses just two terms to
accurately capture these effects, including the coupling between inertia and drag. The separability
of the responses to vertical and horizontal motions is demonstrated and a preliminary model for
the response to horizontal motions is presented.
The interaction of the mooring line with the sea floor in catenary moorings is considered. Using
video and tension data from laboratory experiments, the tension shock condition at the touchdown
point and its implications are observed for the first time. The lateral motion of line along
the bottom associated with a shock during unloading may be a significant cause of chain wear
in the touchdown region. Results from the laboratory experiments are also used to demonstrate
the suitability of the elastic foundation approach to modeling sea floor interaction in numerical
programs.During my initial three years of study
I was supported by an Office of Naval Research Graduate Fellowship. More recently, including
the time spent on the research described in this thesis, I have been supported by the Office of
Naval Research under grant numbers N00014-92-J-1269 and N00014-97-1-0583
Revisiting the role of the Thermally-Pulsating Asymptotic Giant Branch phase in high-redshift galaxies
We study the debated contribution from thermally pulsing asymptotic giant
branch (TP-AGB) stars in evolutionary population synthesis models. We
investigate the Spectral Energy Distributions (SEDs) of a sample of 51
spectroscopically confirmed, high-z (), galaxies using
three evolutionary population synthesis models with strong, mild and light
TP-AGB. Our sample is the largest of spectroscopically confirmed galaxies on
which such models are tested so far. Galaxies were selected as passive, but we
model them using a variety of star formation histories in order not to be
dependent on this pre-selection.
We find that the observed SEDs are best fitted with a significant
contribution of TP-AGB stars or with substantial dust attenuation. Without
including reddening, TP-AGB-strong models perform better and deliver solutions
consistent within from the best-fit ones in the vast majority of
cases. Including reddening, all models perform similarly. Using independent
constraints from observations in the mid- and far-IR, we show that
low/negligible dust attenuation, i.e. , should be
preferred for the SEDs of passively-selected galaxies. Given that TP-AGB-light
models give systematically older ages for passive galaxies, we suggest number
counts of passive galaxies at higher redshifts as a further test to
discriminate among stellar population models.Comment: 48 pages, 17 figures, 10 Tables. Accepted for publication in MNRA
Saxifrage bouc et veaux: une histoire d'amour
Version vulgarisée avec compléments de l'article en anglais (Vittoz et al., 2006). Situation et répartition de l'espèce au niveau européen, sociologie de l'espèce dans les différents marais jurassiens, hydrologie et microtopographie, enracinement, sol, rôle du bétail dans la conservation de l'espèce, génétique et quelques pistes pour sa protection
On the Initial Mass Function and tilt of the Fundamental Plane of massive early-type galaxies
We investigate the most plausible stellar Initial Mass Function (IMF) and the
main origin of the tilt of the Fundamental Plane (FP) for old, massive
early-type galaxies. We consider a sample of 13 bright galaxies of the Coma
cluster and combine our results with those obtained from a sample of 57 lens
galaxies in the same luminous mass range. We estimate the luminous mass and
stellar mass-to-light ratio values of the sample galaxies by fitting their SDSS
multi-band photometry with composite stellar population models computed with
different dust-free, solar-metallicity templates and IMFs. We compare these
measurements and those derived from two-component orbit-based dynamical
modelling. The photometric and dynamical luminous mass estimates of the
galaxies in our sample are consistent, within the errors, if a Salpeter IMF is
adopted. On the contrary, with a Kroupa or Chabrier IMF the two luminous mass
diagnostics differ at a more than 4 \sigma level. For the massive Coma
galaxies, their stellar mass-to-light ratio scales with luminous mass as the
corresponding effective quantities are observed to scale on the FP. This
indicates that the tilt of the FP is primarily caused by stellar population
properties. We conclude that old, massive lens and non-lens early-type galaxies
obey the same luminous and dynamical scaling relations, favour a Salpeter IMF,
and suggest a stellar population origin for the tilt of the FP. The validity of
these results for samples of early-type galaxies with different age and mass
properties still remains to be tested.Comment: 5 pages, 2 figures, accepted by MNRA
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