Abstract This paper presents laboratory testing results to explore the experimental and fundamental dynamic axial stiffness behaviour of polyester ropes for deepwater mooring systems. Effects of mean load, load range, load or stroke control, extensometer versus crosshead, peak trough versus linear regression, cyclic period and scale effect (60 to 600kN) have been studied. Understanding the axial stiffness behaviour is essential for calculating peak line tension and platform offset for riser excursion and fatigue life. Also, the effect of bedding-in of the rope structure, which increases stiffness, is required to establish the test matrix for certification. A thorough review of the methods of data collection, interpretation of data and calculation of stiffness has been conducted. For those methods reviewed, no significant differences in stiffness have been found except for crosshead, which tends to be higher than measured directly on the rope between splices. The effect of cyclic period and scale effect upon dynamic axial stiffness has shown to be insignificant and for dynamic mooring system response can be ignored, which reinforces previous work. For drift and longer term effects, the effect is very small and needs to be considered whether any allowance is needed. The effect of bedding-in on axial stiffness has shown that to reach peak axial stiffness, very large numbers of cycles are required. Typically, however, around 80-90% of the peak axial stiffness can be reached within several hundred cycles. For full-scale certification, the costs and time of large numbers cycles maybe prohibitive, so a technique has been suggested for conducting these tests on scale samples since there is no scale effect of stiffness. These results will add to the knowledge base for understanding axial stiffness behaviour from testing, data collection, stiffness calculation method and mooring/riser system design. It will also provide valuable data for the future rewrite of API 2SM, to ensure that certification test methods collect the appropriate axial stiffness data for polyester ropes. The information will also be of use to the regulatory bodies. Introduction The main purpose of the work presented in this paper was to investigate the experimental factors that can influence the measurement of dynamic axial stiffness of polyester rope when subjected to sinusoidal loading. The factors addressed in this paper are: - Testing medium (air or water). - Constants and variables, in the calculation of dynamic axial stiffness. - Linear regression stiffness versus peak trough stiffness. - Extensometer derived stiffness v crosshead based stiffness. - Machine load control versus stroke control. - Effect of cyclic period upon axial stiffness. - Load History. - 60 kN sub-rope to 600 kN rope stiffness scaling. A 60 kN sub-rope together with 600 and 2,500 kN ropes of parallel strand construction (PSC) were tested during this investigation.
479 An extra-corporeal perfusion model has been established in order to test the viability of hDAF transgenic pig livers when perfused with fresh, whole, human blood. Three groups have been studied: alloperfusions (pig blood), xenoperfusions of unmodified pig livers and xenoperfusions of hDAF transgenic pig livers. Liver function was measured using pH, base excess, potassium, bile production, oxygen consumption, ALT, bilirubin, urea synthesis, factor V synthesis and complement production. Hemolysis was assessed by serial hematocrit and free hemoglobin assessment. Histological appearances were assessed using light microscopy and immunohistochemistry staining for IgM, IgG, and complement deposition. In the alloperfusion control group function and structural integrity was demonstrated for at least 72 hours. Xenoperfusions were carried out for periods of up to 72 hours and, unlike alloperfusion, were limited by progressive hemolysis; histological appearances were of patchy necrosis with most lobules remaining normal. The cause of hemolysis has been investigated; porcine antibodies were demonstrated in the human blood perfusing both normal and transgenic pig livers. Peak antibody levels were reached within one minute of commencing perfusion and did not significantly change throughout the duration of perfusion. This implies elution of porcine antibodies rather than production of new antibodies by the porcine livers. We have further demonstrated by FACS analysis that a proportion of these antibodies are pig anti-human specific. In addition, porcine livers perfused with human blood have been shown to produce supraphysiologic levels of complement activity as assessed by CH50 analysis on sheep red blood cells (RBC). Interestingly, however, when serum from these xenoperfusions was incubated with fresh human RBC, it was not possible to demonstrate lysis. Thus, while there appear to be both pig anti-human antibodies and complement present, classical pathway complement hemolysis could not be demonstrated. Investigations of the hemolysis continues, in order to assess whether this would be a limitation in clinical studies. This research was funded by the Wellcome Trust and carried out in collaboration with Imutran (Novartis).
The results from an experimental study of a model FPSO in moderate to extreme regular waves are presented. Green sea events were recorded using measuring equipment that included wave probes in a grid at the bow and on the front deck, sensors recording the vessel motions, and load and pressure cells on the deck house and on the bow. High-resolution video recordings were also taken. The model, similar to one used in previous tests, was designed with a bluff cylindrically shaped bow to provide further information on the effects of bow geometry. The experiments were designed to support and provide validation for numerical work modelling green sea events. Aspects of the modelling related to the design of the experiments are discussed but details of the theory are not included. The experimental results are presented together with a limited set of preliminary theoretical results, which show good agreement for the ship motions and the flow of green water on deck.
ABSTRACT This paper demonstrates work being conducted which will result in advances in the technology of offshore tethering products; steel wire rope, synthetic fibre rope, chain and welded tubulars. The work will have major implications for the improvement of operational safety and discard criteria for mooring tethers. The objective of the paper has been achieved by discussing NEL's current involvement in several major studies and presenting an overview of the research conducted. This research has generated testing of the highest quality through the development of test assessment criteria and gained an insight into the fatigue behaviour of the tether products through the widespread use of condition monitoring techniques.
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