Eidgenossisches Nuklearsicherheitsinspektorat ENSI

Lauffohr (Brugg), Switzerland

Eidgenossisches Nuklearsicherheitsinspektorat ENSI

Lauffohr (Brugg), Switzerland
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Zerres P.,TU Darmstadt | Doring R.,Eidgenossisches Nuklearsicherheitsinspektorat ENSI | Vormwald M.,TU Darmstadt
Materialwissenschaft und Werkstofftechnik | Year: 2011

In this paper a procedure to simulate the crack growth under consideration of elastic-plastic material behavior by means of the finite element method is described. Within this procedure, after each increment of crack advance, the structure is remeshed and the status variables, such as the components of the backstress-tensor and the plastic strains, are transferred from the old mesh to the new one. Due to mapping of the variables, improper conditions are possibly prevailing at the beginning of the new analysis, which has to be captured by the used material routine. The main focus of this paper is to describe these necessary numerical adjustments. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Benisch K.,University of Kiel | Graupner B.,Eidgenossisches Nuklearsicherheitsinspektorat ENSI | Bauer S.,University of Kiel
Energy Procedia | Year: 2013

This paper presents a code comparison of coupled multiphase flow and geomechanical processes resulting from CO2 injection into deep saline formations. The coupled simulator OpenGeoSys-Eclipse as well as Eclipse-Visage, GEM and OpenGeoSys are used for this purpose. Comparison of the results of the different simulators shows a strong dependence of the results on the grid discretization and the numerical methods applied. Further investigations of the one-way coupled geomechanical simulations shows that even if the multiphase flow results are nearly identical for the simulators used, the geomechanical response on the pressure build up can be different.

Li D.,University of Kiel | Bauer S.,University of Kiel | Benisch K.,University of Kiel | Graupner B.,Eidgenossisches Nuklearsicherheitsinspektorat ENSI | Beyer C.,University of Kiel
Acta Geotechnica | Year: 2014

Sequestration of CO2 into a deep geological reservoir causes a complex interaction of different processes such as multiphase flow, phase transition, multicomponent transport, and geochemical reactions between dissolved CO2 and the mineral matrix of the porous medium. A prognosis of the reservoir behaviour and the feedback from large-scale geochemical alterations require efficient process-based numerical models. For this purpose, the multiphase flow and multicomponent transport code OpenGeoSys-Eclipse have been coupled to the geochemical model ChemApp. The newly developed coupled simulator was successfully verified for correctness and accuracy of the implemented reaction module by benchmarking tests. The code was then applied to assess the impact of geochemical reactions during CO2 sequestration at a hypothetical but typical Bunter sandstone formation in the Northern German Basin. Injection and spreading of 1.48 × 107 t of CO2 in an anticline structure of the reservoir were simulated over a period of 20 years of injection plus 80 years of post-injection time. Equilibrium geochemical calculations performed by ChemApp show only a low reactivity to the geochemical system. The increased acidity of the aqueous solution results in dissolution of small amounts of calcite, anhydrite, and quartz. Geochemical alterations of the mineral phase composition result in slight increases in porosity and permeability, which locally may reach up to +0.02 and 0.1 %, respectively. © 2013 Springer-Verlag Berlin Heidelberg.

Szymczak S.,Friedrich - Alexander - University, Erlangen - Nuremberg | Joachimski M.M.,Friedrich - Alexander - University, Erlangen - Nuremberg | Brauning A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Hetzer T.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 2 more authors.
Climate of the Past | Year: 2012

The Mediterranean is considered as an area which will be affected strongly by current climate change. However, temperature records for the past centuries which can contribute to a better understanding of future climate changes are still sparse for this region. Carbon isotope chronologies from tree-rings often mirror temperature history but their application as climate proxies is difficult due to the influence of the anthropogenic change in atmospheric CO2 on the carbon isotope fractionation during photosynthetic CO2 uptake. We tested the influence of different correction models accounting for plant response to increased atmospheric CO2 on four annually resolved long-term carbon isotope records (between 400 and 800 yr) derived from Corsican pine trees (Pinus nigra ssp. laricio) growing at ecologically varying mountain sites on the island of Corsica. The different correction factors have only a minor influence on the main climate signals and resulting temperature reconstructions. Carbon isotope series show strong correlations with summer temperature and precipitation. A summer temperature reconstruction (1448-2007 AD) reveals that the Little Ice Age was characterised by low, but not extremely low temperatures on Corsica. Temperatures have been to modern temperatures at around 1500 AD. The reconstruction reveals warm summers during 1480-1520 and 1950-2007 AD and cool summers during 1580-1620 and 1820-1890 AD. © Author(s) 2012.

Szymczak S.,Friedrich - Alexander - University, Erlangen - Nuremberg | Joachimski M.M.,Friedrich - Alexander - University, Erlangen - Nuremberg | Brauning A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Hetzer T.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 2 more authors.
Chemical Geology | Year: 2012

Stable carbon and oxygen isotopes in tree rings are considered as reliable climate archives as they provide past environmental information with high resolution. However, recent studies have shown that isotope chronologies may reveal a long-term age trend and be influenced by non-climatic factors as other tree-ring parameters as well. These trends can only be identified in chronologies measured on individual trees but not on pooled sample chronologies consisting of several trees. In order to test whether pooled chronologies from pine trees from the Island of Corsica (Mediterranean/France) can be used for climatic reconstructions, we compared calculated mean values from 5 individual trees with pooled chronologies from the same 5 individuals. Carbon and oxygen isotope chronologies for a 50-year interval with annual resolution and 400. years with decadal resolution were analysed in order to document secular changes in inter-tree variability and to test for age related trends in the isotope ratios. Pooled carbon and oxygen isotope series correspond well to chronologies based on mean values calculated from analyses of individual trees. Inter-tree variability in oxygen isotope ratios is higher than in carbon isotope ratios but remains relatively constant over time. Similarities between the isotope series of individual trees are stronger over the 400-year time scale documenting a common long-term signal in the isotope values. No long-term age related trends are observed. Oxygen isotope values of the juvenile phase are characterised by a remarkable decrease over 40-50. years, interpreted to be related to the less developed root system of the young trees. This age effect can be avoided by not considering the first 50. years from the chronologies. Our results confirm that pooled carbon and oxygen isotope chronologies from Pinus nigra can be used for environmental reconstructions without statistical detrending. © 2012 Elsevier B.V..

Szymczak S.,Friedrich - Alexander - University, Erlangen - Nuremberg | Joachimski M.M.,Friedrich - Alexander - University, Erlangen - Nuremberg | Brauning A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Hetzer T.,Friedrich - Alexander - University, Erlangen - Nuremberg | Kuhlemann J.,Eidgenossisches Nuklearsicherheitsinspektorat ENSI
Dendrochronologia | Year: 2011

Stable isotopes in tree rings have widely been used for palaeoclimate reconstructions since tree rings record climatic information at annual resolution. However, various wood components or different parts of an annual tree-ring may differ in their isotopic compositions. Thus, sample preparation and subsequent laboratory analysis are crucial for the isotopic signal retained in the final tree-ring isotope series used for climate reconstruction and must therefore be considered for the interpretation of isotope-climate relationships. This study focuses on wood of Corsican Pine trees (Pinus nigra ssp. laricio) as this tree species allows to reconstruct the long-term climate evolution in the western Mediterranean. In a pilot study, we concentrated on methodological issues of sample preparation techniques in order to evaluate isotope records measured on pooled whole tree-ring cellulose and whole tree-ring bulk wood samples. We analysed 80-year long carbon and oxygen chronologies of Corsican Pine trees growing near the upper tree line on Corsica. Carbon and oxygen isotope records of whole tree-ring bulk wood and whole tree-ring cellulose from a pooled sample of 5 trees were correlated with the climate parameters monthly precipitation, temperature and the self-calibrating Palmer Drought Severity Index (sc-PDSI). Results show that the offsets in carbon and oxygen isotopes of bulk wood and cellulose are not constant over time. Both isotopes correlate with climate parameters from late winter and summer. The carbon and oxygen isotope ratios of cellulose are more sensitive to climatic variables than those of bulk wood. The results of this study imply that extraction of cellulose is a pre-requisite for the reconstruction of high-resolution climate records from stable isotope series of P. nigra ssp. laricio. © 2011 Istituto Italiano di Dendrocronologia.

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