Three‐dimensional modeling of problems in poro‐elasticity via a mixed least‐squares method using linear tetrahedral elements

In a previous publication we developed a new mixed least‐squares method for poro‐elasticity. The approximate solution was obtained via a minimization of a least‐squares functional, based upon the equations of equilibrium, the equations of continuity and weak forms of the constitutive relationships for elasticity and Darcy flow. The formulation involved four independent types of variables: displacements, stresses, pore pressures and velocities. All of them were approximated by linear continuous triangles. Encouraged by the computational results, obtained from the two‐dimensional implementation of the method, we extended our formulation to three dimensions. In this paper we present numerical examples for the performance of continuous linear tetrahedra within the context of the mixed least‐squares method. The initial results suggest that the method works well in the nearly and entirely incompressible limits for elasticity. For poro‐elasticity, the obtained pore pressures are stable without exhibiting the oscillations, which are observed when the standard Galerkin formulation is used. Copyright © 2010 John Wiley & Sons, Ltd.     

Facies Modeling Using a Markov Mesh Model Specification

The spatial continuity of facies is one of the key factors controlling flow in reservoir models. Traditional pixel-based methods such as truncated Gaussian random fields and indicator simulation are based on only two-point statistics, which is insufficient to capture complex facies structures. Current methods for multi-point statistics either lack a consistent statistical model specification or are too computer intensive to be applicable. We propose a Markov mesh model based on generalized linear models for geological facies modeling. The approach defines a consistent statistical model that is facilitated by efficient estimation of model parameters and generation of realizations. Our presentation includes a formulation of the general framework, model specifications in two and three dimensions, and details on how the parameters can be estimated from a training image. We illustrate the method using multiple training images, including binary and trinary images and simulations in two and three dimensions. We also do a thorough comparison to the snesim approach. We find that the current model formulation is applicable for multiple training images and compares favorably to the snesim approach in our test examples. The method is highly memory efficient.     

Fast and Accurate Approximation to Kriging Using Common Data Neighborhoods

Unknown values of a random field can be predicted from observed data using kriging. As data sets grow in size, the computation times become large. To facilitate kriging with large data sets, an approximation where the kriging is performed in sub-segments with common data neighborhoods has been developed. It is shown how the accuracy of the approximation can be controlled by increasing the common data neighborhood. For four different variograms, it is shown how large the data neighborhoods must be to get an accuracy below a chosen threshold, and how much faster these calculations are compared to the kriging where all data are used. Provided that variogram ranges are small compared to the domain of interest, kriging with common data neighborhoods provides excellent speed-ups (2–40) while maintaining high numerical accuracy. Results are presented both for data neighborhoods where the neighborhoods are the same for all sub-segments, and data neighborhoods where the neighborhoods are adapted to fit the data densities around the sub-segments. Kriging in sub-segments with common data neighborhoods is well suited for parallelization and the speed-up is almost linear in the number of threads. A comparison is made to the widely used moving neighborhood approach. It is demonstrated that the accuracy of the moving neighborhood approach can be poor and that computational speed can be slow compared to kriging with common data neighborhoods.     

Temporary-creep and post-creep properties of aquaculture netting materials

Creep in materials and structures may lead to increasing strains, permanent deformations, change in mechanical properties and rupture at loads significantly smaller than the breaking strength. In this paper, we present data on temporary-creep properties, recovery of strain post creep and post-creep tensile properties of a selection of Raschel knitted netting materials. Creep strain in wet netting materials subjected to a creep target load of 10–90% of average force at break for 30 min varied from 1.6% to 3.5%. The rate of creep decreased with time and decreased target load. The recovery of strain post creep was relatively fast and approximately half of the creep strain was elastic. Post-creep tensile testing showed that the length and force at break were not significantly affected by the creep load history. However, due to permanent deformations of the specimens from the creep test, the nominal breaking strain decreased and the stiffness increased with increased creep target load.     

Modulation of the Pacific Decadal Oscillation on the summer precipitation over East China: a comparison of observations to 600-years control run of Bergen Climate Model

Observations show that the summer precipitation over East China often goes through decadal variations of opposite sign over North China and the Yangtze River valley (YRV), such as the “southern flood and northern drought” pattern that occurred during the late 1970s–1990s. In this study it is shown that a modulation of the Pacific Decadal Oscillation (PDO) on the summer precipitation pattern over East China during the last century is partly responsible for this characteristic precipitation pattern. During positive PDO phases, the warm winter sea surface temperatures (SSTs) in the eastern subtropical Pacific along the western coast of North American propagate to the tropics in the following summer due to weakened oceanic meridional circulation and the existence of a coupled wind–evaporation–SST feedback mechanism, resulting in a warming in the eastern tropical Pacific Ocean (5°N–20°N, 160°W–120°W) in summer. This in turn causes a zonal anomalous circulation over the subtropical–tropical Pacific Ocean that induces a strengthened western Pacific subtropical high (WPSH) and thus more moisture over the YRV region. The end result of these events is that the summer precipitation is increased over the YRV region while it is decreased over North China. The suggested mechanism is found both in the observations and in a 600-years fully coupled pre-industrial multi-century control simulations with Bergen Climate Model. The intensification of the WPSH due to the warming in the eastern tropical Pacific Ocean was also examined in idealized SSTA-forced AGCM experiments.     

Melt‐bearing impactites (suevite and impact melt rock) within the Gardnos structure,Norway

Abstract– Melt‐bearing impactites dominated by suevite, and with a minor content of clast‐rich impact melt rock, are found within the central part of the Gardnos structure. They are preserved as the eroded remnants in the relatively small complex impact structure with a present diameter of 5 km. These rocks have been mapped in the field and in the Branden drill core, and described according to mineralogy/petrology, including matrix, litho clast, and melt content, as well as geochemistry. Based on our extensive field mapping, a simple 3‐D model of the original crater was constructed to estimate tentative volumes for the melt‐bearing impactites. The variations in lithic and melt fragment content and chemistry of suevite matrix can mostly be explained by incorporation of mafic rocks into a dominant mixture of granitic, gneissic, and quartzitic target rocks, reflecting mixing of material from different parts of the crater. Melt fragments within suevite occur with a variety of shapes and textures, probably related to different original target rock composition, to the various temperatures the individual fragments were subjected to during the impact event and deposition processes. This study discusses the impact‐related deposits based on a sedimentological approach. Their overall composition and structures indicate dominating gravity flow processes in the final transportation and deposition of the suevite.     

Landslide databases in the Geological Surveys of Europe

Landslides are one of the most widespread geohazards in Europe, producing significant social and economic impacts. Rapid population growth in urban areas throughout many countries in Europe and extreme climatic scenarios can considerably increase landslide risk in the near future. Variability exists between European countries in both the statutory treatment of landslide risk and the use of official assessment guidelines. This suggests that a European Landslides Directive that provides a common legal framework for dealing with landslides is necessary. With this long-term goal in mind, this work analyzes the landslide databases from the Geological Surveys of Europe focusing on their interoperability and completeness. The same landslide classification could be used for the 849,543 landslide records from the Geological Surveys, from which 36% are slides, 10% are falls, 20% are flows, 11% are complex slides, and 24% either remain unclassified or correspond to another typology. Most of them are mapped with the same symbol at a scale of 1:25,000 or greater, providing the necessary information to elaborate European-scale susceptibility maps for each landslide type. A landslide density map was produced for the available records from the Geological Surveys (LANDEN map) showing, for the first time, 210,544 km² landslide-prone areas and 23,681 administrative areas where the Geological Surveys from Europe have recorded landslides. The comparison of this map with the European landslide susceptibility map (ELSUS 1000 v1) is successful for most of the territory (69.7%) showing certain variability between countries. This comparison also permitted the identification of 0.98 Mkm² (28.9%) of landslide-susceptible areas without records from the Geological Surveys, which have been used to evaluate the landslide database completeness. The estimated completeness of the landslide databases (LDBs) from the Geological Surveys is 17%, varying between 1 and 55%. This variability is due to the different landslide strategies adopted by each country. In some of them, landslide mapping is systematic; others only record damaging landslides, whereas in others, landslide maps are only available for certain regions or local areas. Moreover, in most of the countries, LDBs from the Geological Surveys co-exist with others owned by a variety of public institutions producing LDBs at variable scales and formats. Hence, a greater coordination effort should be made by all the institutions working in landslide mapping to increase data integration and harmonization.     

Procedure,selection and application of plasticity models for a soil

A five-step procedure involving mathematical formulation, identification and determination of parameters and verification is presented for development and selection of appropriate and reliable constitutive law(s) for geologic media. Comprehensive analyses are performed toward determination of an appropriate law for a (artificial) soil. The most suitable model is obtained by critical evaluation of four different plasticity models; here verification and comparisons of predictions with observations from laboratory tests, and with those from two boundary value problems are used as the basis of the selection. The model thus selected is found to be appropriate for applications to relevant practical problems.