WAVE MODEL TESTS FOR A TLP MODIFIED WITH ICE-BREAKING COLLARS
A. Bolshev and S. Frolov, St. Petersburg State Technical University, Polytechnicheskaya Street 29, 195251 St. Petersburg, Russia
F. T. Christensen, Danish Hydraulic Institute, Agern Alle 5,2970 Horsholm, Denmark
T. Karna, Research Centre of Finland (VTT), Kemistintie 3,02150 Espoo, Finland
S. Rogachko, Moscow State University of Civil Engineering, Jaroslavskoye Shosse 26, 11726 Moscow, Russia
Abstract
In order to develop oil and gas fields in relatively deeper waters, floating platforms o r subsea completions currently have to be used, as fixed platform structures become economically unattractive. The Tension Leg Platform (TLP) is one example of a floating platform structure, which is in conventional operation today, e.g. off Norway. In order to utilize TLPs in ice infested seas, such as the Russian Barents Sea, some form of ice- breaking collars would have to be added on the legs. The presented study has investigated the modifications to open water performance of a TLP, when collars are attached to the legs. Ice related problems will hopefully be studied later.
BRITTLE COMPRESSIVE FAILURE OF MICROCRACKED ICE
Stephanie A. Wlmmer and Dale G. Karr, Department of Naval Architecture and Marine Engineering, University of Michigan, Ann Arbor, Michigan
ABSTRACT
Constitutive equations for brittle, polycrystalline ice are developed based on the damage mechanics of elastic materials containing microcracks. For homogeneous deformation modes, microcrack growth from defects causes changes in the average elastic compliance of the material. The microcrack growth equations are based on previously developed fracture mechanics models. The nonlinearity of the constitutive equations may result in singular conditions along the constitutive paths associated with homogeneous deformation of the evolving elastic medium. The system of constitutive equations are therefore examined as a nonlinear statical system under changing parameter values; the changing parameter being a particular combination of stress or strain ratios. Bifurcation approaches to nonlinear problems are used to determine the loss of uniqueness of particular equilibrium states.
Failure criteria in terms of bifurcations of the constitutive paths are established by examining the properties of the evolving tangent stiffness tensor. The influence of lateral stresses is studied for biaxial stress states. It is found that faulting may occur for moderate levels of lateral compressive stress and lateral tension. Higher lateral tension produces unstable crack growth and immediate splitting. Also, the analysis shows that n 0 purely elastic failure mechanisms occur for higher values of lateral compressive stress implying inelastic failure would limit strength for these circumstances.
