34 research outputs found
Ostracoda and Mollusca biodiversity and hydrochemical features in Late Miocene brackish basins of Italy
Arctic quaternary ostracods and their use in paleoreconstructions
The paper deals with original and published data on fossil ostracodal assemblages from the Eurasian Arctic Kara, Laptev and Chuckchi seas. As a whole, six ecologically different assemblages were distinguished (freshwater, brackish water, marine of the inner, middle and outer shelves and upper continental slope), they replace each other upcore reflecting a gradual increase in water depth and distance from the coast. These assemblages are stable in the entire Arctic region and can be used for interpretation of environments in different Arctic areas
Experimental and Numerical Analysis of the Shear Ring.
The shear ring is dependent on a weak link that is activated in case of emergency situations. The failure of the weak link needs to be propagated in a controlled way and it is the only component in the tool that is allowed to brake. In an emergency attempt performed offshore, the current design of the shear ring did not shear at the required load. The testing of the ring was unsuccessful and the attempt caused failure instead on the surrounding parts of the main tool. The reasons behind this unsuccessful event were due to both the material and the geometry of the ring. A new design of the shear ring was proposed. The purpose of this master thesis was to evaluate the failure of both the old and new design. The theoretical analyses on the current design of the shear ring were performed with two methods; implicit and explicit. The results were compared to a physical test in order to evaluate the accuracy of the computational methods. The implicit method and the physical test provided similar results. The explicit gave slightly higher forces but it followed the same behavior as the physical test. Both experimental and theoretical analyses show that the current design of the shear ring gets stuck to the component below the ring. The value of the explicit method is the modeling of the damage and failure in a material. This cannot be performed by the implicit method. The theoretical analysis of the proposed design of the shear ring was performed with the explicit method using the shear failure model to simulate the failure of the ring. The shear failure criterion is robust and simple but this method requires a full stress train curve until failure. The proposed design of the shear ring broke in a predictable way.SĂ€kerhetsringen Ă€r en komponent som skall gĂ„ sönder vid olyckshĂ€ndelser eller oförberedda situationer för att skydda utrustning och miljö ute i havs. DĂ€rför Ă€r det viktigt att sĂ€kerhetsringen, vid rĂ€tt kraft, gĂ„r sönder pĂ„ ett förutbestĂ€mt sĂ€tt. Eftersom sĂ€kerhetsringen Ă€r den enda komponenten i verktyget som fĂ„r gĂ„ sönder Ă€r det vĂ€ldigt viktigt att denna process Ă€r kontrollerad. Vid ett test som utfördes ute till havs sĂ„ gick inte den nuvarande konstruktionen pĂ„ sĂ€kerhetsringen sönder pĂ„ ett förutbestĂ€mt sĂ€tt. Testet av ringen var ej lyckosamt vilket orsakade skada pĂ„ de omkringliggande delarna pĂ„ huvudverktyget. Anledningarna bakom det misslyckade testet berodde pĂ„ bĂ„de materialval och geometrin pĂ„ sĂ€kerhetsringen. En ny konstruktion pĂ„ ringen togs fram. Den hĂ€r uppsatsen har till uppgift att utvĂ€rdera brottet av den gamla och nya konstruktionen. De teoretiska analyserna pĂ„ den nuvarande konstruktionen pĂ„ sĂ€kerhetsringen genomfördes med tvĂ„ olika metoder, implicita och explicita metoden. Resultaten jĂ€mfördes med ett fysiskt test för att sĂ€kerstĂ€lla trĂ€ffsĂ€kerheten av de bĂ„da berĂ€kningsmetoderna. Implicita metoden och det fysiska testet pĂ„visade liknande resultat. Den explicita metoden gav en aning högre krafter men det följde samma beteendemönster som det fysiska testet. BĂ„da det fysiska testet och de teoretiska berĂ€kningarna visade att ringen fastnade pĂ„ komponenten direkt under den. VĂ€rdet av den explicita metoden Ă€r modelleringen av brott i ett material. Detta kan inte genomföras med den implicita metoden. De teoretiska berĂ€kningarna pĂ„ den föreslagna konstruktionen pĂ„ sĂ€kerhetsringen genomfördes med den explicita metoden och ââShear failureââ kriteriet för att simulera hur ringen gĂ„r sönder. Detta kriterium Ă€r robust och simpelt men det krĂ€ver en dragprovkurva tills brott av det material som anvĂ€nds. Den föreslagna konstruktionen pĂ„ sĂ€kerhetsringen gĂ„r sönder pĂ„ utrĂ€knat sĂ€tt
THE SPECIES OF CYPRIDEIS PONTICA KRSTIC ' , 1968 (OSTRACODA, CRUSTACEA) â THE INDICATOR OF THE BOUNDARY OF THE PLIOCENE AND QUATERNARY SEDIMENTS (THE NW BLACK SEA)
Late Miocene ostracod assemblages from eastern Mediterranean coral reef complexes (central Crete, Greece)
Ostracods from ten Late Miocene coral reef complexes built by Siderastrea, Tarbellastrea and Porites, cropping out in the Messara Plain (southern
Iraklion basin, central Crete), have been investigated and five assemblages have been recognised, which point to different marine environments: (1)
assemblage from the basal sandy silts, dominated by very shallow inner-infralittoral species, such as Cyamocytheridea meniscus, Cyamocytheridea
obstipa, Cyamocytheridea dertonensis, Cytheretta semiornata and Nonurocythereis seminulum; (2) assemblage from the coral reef complexes within
which Grinioneis haidingeri, Aurila cicatricosa, Cimbaurila diecii, Tenedocythere cruciata, Pokornyella italica and Callistocythere quadrangula
are dominant and point to a stable inner-infralittoral environment characterised by warm, quiet and well-oxygenated waters; (3) assemblage from
the silts intercalated among the coral reef complexes, mainly characterised by Neomonoceratina laskarevi, Cytheridea acuminata, Phlyctenophora
farkasi and Aurila albicans together with Callistocythere spp., Xestoleberis communis and Xestoleberis dispar, which points to a very shallow
marine environment rich in aquatic vegetation; (4) assemblage from the upper silts, which records the absolute dominance of Xestoleberis species,
reflecting a very shallow and highly-vegetated environment and (5) assemblage from the uppermost silty clays, dominated by Hemicytherura
defiorei, Xestoleberis spp. and Palmoconcha dertobrevis, accompanied by Acanthocythereis hystrix, Cytherella scutulum, Bairdoppilata conformis,
Semicytherura spp., Krithe sp., Cytheropteron alatum, Bythocypris sp. and Pseudocythere caudata, which suggest deeper marine environments
probably located in the outer infralittoral/inner-circalittoral zones. The studied section has been dated by means of calcareous nannoplankton to be
not younger than Zone MNN9 (Early Tortonian), which is the biostratigraphical datum recorded in the fine-grained deposits that overlie the coral
reef complexes. An age not older than Tortonian can be inferred by the stratigraphical distribution of the recognized ostracods. Thus, the coral reef
complexes have been tentatively referred to the Early Tortonian