45,624 research outputs found
Calculation of wind-driven surface currents in the North Atlantic Ocean
Calculations to simulate the wind driven near surface currents of the North Atlantic Ocean are described. The primitive equations were integrated on a finite difference grid with a horizontal resolution of 2.5 deg in longitude and latitude. The model ocean was homogeneous with a uniform depth of 100 m and with five levels in the vertical direction. A form of the rigid-lid approximation was applied. Generally, the computed surface current patterns agreed with observed currents. The development of a subsurface equatorial countercurrent was observed
Synthetic photometry for carbon-rich giants II. The effects of pulsation and circumstellar dust
By using self-consistent dynamic model atmospheres which simulate
pulsation-enhanced dust-driven winds of AGB stars we studied in detail the
influence of (i) pulsations of the stellar interiors, and (ii) the development
of dusty stellar winds on the spectral appearance of long period variables with
carbon-rich atmospheric chemistry. While the pulsations lead to large-amplitude
photometric variability, the dusty envelopes cause pronounced circumstellar
reddening. Based on one selected dynamical model which is representative of
C-type Mira variables with intermediate mass loss rates, we calculated
synthetic spectra and photometry for standard broad-band filters from the
visual to the near-infrared. Our modelling allows to investigate in detail the
substantial effect of circumstellar dust on the resultant photometry. The
pronounced absorption of amorphous carbon dust grains leads to colour indices
which are significantly redder than the corresponding ones based on hydrostatic
dust-free models. Only if we account for this circumstellar reddening we get
synthetic colours that are comparable to observations of evolved AGB stars. The
photometric variations of the dynamical model were compared to observed
lightcurves of the C-type Mira RU_Vir which appears to be quite similar to the
model. We found good agreement concerning the principal behaviour of the
BVRIJHKL lightcurves and also quantitatively fitting details. The analysed
model is able to reproduce the variations of RU_Vir and other Miras in (J-H)
vs. (H-K) diagrams throughout the light cycle. Contrasting the model photometry
with observational data for a variety of galactic C-rich giants in such
colour-colour diagrams proved that the chosen atmospheric model fits well into
a sequence of objects with increasing mass loss rates, i.e., redder colour
indices.Comment: Accepted for publication in A&
A framework for modelling linear surface waves on shear currents in slowly varying waters
We present a theoretical and numerical framework -- which we dub the Direct
Integration Method (DIM) -- for simple, efficient and accurate evaluation of
surface wave models allowing presence of a current of arbitrary depth
dependence, and where bathymetry and ambient currents may vary slowly in
horizontal directions. On horizontally constant water depth and shear current
the DIM numerically evaluates the dispersion relation of linear surface waves
to arbitrary accuracy, and we argue that for this purpose it is superior to two
existing numerical procedures: the piecewise-linear approximation and a method
due to \textit{Dong \& Kirby} [2012]. The DIM moreover yields the full
linearized flow field at little extra cost. We implement the DIM numerically
with iterations of standard numerical methods. The wide applicability of the
DIM in an oceanographic setting in four aspects is shown. Firstly, we show how
the DIM allows practical implementation of the wave action conservation
equation recently derived by \textit{Quinn et al.} [2017]. Secondly, we
demonstrate how the DIM handles with ease cases where existing methods
struggle, i.e.\ velocity profiles changing direction with
vertical coordinate , and strongly sheared profiles. Thirdly, we use the DIM
to calculate and analyse the full linear flow field beneath a 2D ring wave upon
a near--surface wind--driven exponential shear current, revealing striking
qualitative differences compared to no shear. Finally we demonstrate that the
DIM can be a real competitor to analytical dispersion relation approximations
such as that of \textit{Kirby \& Chen} [1989] even for wave/ocean modelling.Comment: 25 pages, 8 figures, 1 table, submitted to J. Geophys. Res.: Ocean
Simulations of galactic winds and starbursts in galaxy clusters
We present an investigation of the metal enrichment of the intra-cluster
medium (ICM) by galactic winds and merger-driven starbursts. We use combined
N-body/hydrodynamic simulations with a semi-numerical galaxy formation model.
The mass loss by galactic winds is obtained by calculating transonic solutions
of steady state outflows, driven by thermal, cosmic ray and MHD wave pressure.
The inhomogeneities in the metal distribution caused by these processes are an
ideal tool to reveal the dynamical state of a galaxy cluster. We present
surface brightness, X-ray emission weighted temperature and metal maps of our
model clusters as they would be observed by X-ray telescopes like XMM-Newton.
We show that X-ray weighted metal maps distinguish between pre- or post-merger
galaxy clusters by comparing the metallicity distribution with the
galaxy-density distribution: pre-mergers have a metallicity gap between the
subclusters, post-mergers a high metallicity between subclusters. We apply our
approach to two observed galaxy clusters, Abell 3528 and Abell 3921, to show
whether they are pre- or post-merging systems. The survival time of the
inhomogeneities in the metallicity distribution found in our simulations is up
to several Gyr. We show that galactic winds and merger-driven starbursts enrich
the ICM very efficiently after z=1 in the central (~ 3 Mpc radius) region of a
galaxy cluster.Comment: 18 pages, 25 figures, 2 tables, accepted for publication in A&A, more
technical details added - results are unaffected, high resolution PDF version
is available at http://astro.uibk.ac.at/Kapferer.pd
Numerical simulation of the airflow–rivulet interaction associated with the rain-wind induced vibration phenomenon
Rain-wind induced vibration is an aeroelastic phenomenon that occurs on the inclined cables of cable-stayed bridges. The vibrations are believed to be caused by a complicated nonlinear interaction between rivulets of rain water that run down the cables and the wind loading on the cables due to the unsteady aerodynamic flow field. Recent research at the University of Strathclyde has been to develop a numerical method to simulate the influence of the external air flow on the rivulet dynamics and vice versa, the results of which can be used to assess the importance of the water rivulets on the instability. The numerical approach for the first time couples a Discrete Vortex Method solver to determine the external flow field and unsteady aerodynamic loading, and a pseudo-spectral solver based on lubrication theory to model the evolution and growth of the water rivulets on the cable surface under external loading. The results of the coupled model are used to assess the effects of various loading combinations, and importantly are consistent with previous full scale and experimental observations of rain-wind induced vibration, providing new information about the underlying physical mechanisms of the instability
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