Coarsening of three-dimensional structured and unstructured grids for subsurface flow

We present a generic, semi-automated algorithm for generating non-uniform coarse grids for modeling subsurface flow. The method is applicable to arbitrary grids and does not impose smoothness constraints on the coarse grid. One therefore avoids conventional smoothing procedures that are commonly used to ensure that the grids obtained with standard coarsening procedures are not too rough. The coarsening algorithm is very simple and essentially involves only two parameters that specify the level of coarsening. Consequently the algorithm allows the user to specify the simulation grid dynamically to fit available computer resources, and, e.g., use the original geomodel as input for flow simulations. This is of great importance since coarse grid-generation is normally the most time-consuming part of an upscaling phase, and therefore the main obstacle that has prevented simulation workflows with user-defined resolution. We apply the coarsening algorithm to a series of two-phase flow problems on both structured (Cartesian) and unstructured grids. The numerical results demonstrate that one consistently obtains significantly more accurate results using the proposed non-uniform coarsening strategy than with corresponding uniform coarse grids with roughly the same number of cells.     

The solar abundance of thorium and lead

Two new Th ii lines have been identified in the spectrum of the solar photosphere. The abundance derived from these lines together with the previously known Th ii line at 4019 Å, is log _Th = 0.85 ± 0.20 in the log _H = 12.00 scale. Analysis of three Pb i lines in the photospheric spectrum resulted in an abundance of log _pb = 1.90 ± 0.10. The solar Th/Pb ratio is: _Th/ _Pb = 0.09 _-0.005 ^0.09 .     

Solar abundance of praseodymium

16 lines of Pr ii possibly present in the solar photospheric spectrum have been studied. When including hyperfine structure in synthetic calculations, investigations of 9 lines result in an abundance A _Pr = 0.71 ± 0.08 in the log A _H = 12.00 scale.     

Isotopes of rubidium in the Sun

Photoelectric measurements of photospheric velocity fields have been carried out with the Sacramento Peak Doppler Zeeman Analyzer. Emphasis was given to long periods and low spatial wavenumbers in deep photospheric layers, where the 5-min oscillations are less dominant.Multiple or double peaks cannot be detected in power spectra of the 5-min oscillations, provided that a sufficient number of physically independent points on the solar surface are observed.The most frequent wave-numbers in the spectra of 5-min oscillations (as well as of the low frequency field) agree with those derived from a model assuming statistically independent oscillators of 10 to 20 diameter. These two velocity fields are anti-correlated spatially.Kinetic power in the 20-to-50-min range of periods is closely linked to brightness changes in the same layer, an increase of brightness lagging about 250 sec behind rising motion. Granules can be excluded as a possible source for the appearance of low frequency flow patterns. Different explanations are suggested.On leave from Fraunhofer Institut, Freiburg, Germany.     

Isotopes of samarium in the sun

Terrestrial samarium consists of seven isotopes. Some spectral lines from Sm have isotope shifts and hyperfine structures that will modify the profile of the absorption lines in the Fraunhofer spectrum. The photospheric spectrum around the Sm ii lines at 4467 and 4519 Å has been studied. Although it is impossible to derive the solar abundance of each individual isotope, it is shown that a terrestrial isotopic composition can account for the anomal line width and asymmetry of the observed solar lines. The solar abundance found from the two lines is A(Sm) = 1.54 in the logarithmic A(H) = 12.00 scale.     

Prevention of oil spill from shipping by modelling of dynamic risk

This paper presents a new dynamic environmental risk model, with intended use within a new, dynamical approach for risk based ship traffic prioritisation. The philosophy behind this newly developed approach is that shipping risk can be reduced by directing efforts towards ships and areas that have been identified as high priority (high risk), prior to a potential accident. The risk model proposed in this paper separates itself from previous models by drawing on available information on dynamic factors and by focusing on the ship's surroundings. The model estimates the environmental risk of drift grounding accidents for oil tankers in real time and in forecast mode, combining the probability of grounding with oil spill impact on the coastline. Results show that the inherent dynamic risk introduced by an oil tanker sailing along the North Norwegian coast depends, not surprisingly, significantly upon wind and ocean currents, as well as tug position and cargo oil type. Results of this study indicate that the risk model is well suited for real time risk assessment, and effectively separates low risk and high risk situations. The model is well suited as a tool to prioritise oil tankers and coastal segments. This enables dynamic risk based positioning of tugs, using both real-time and projected risk, for effective support in case of a drifting ship situation.