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40 st / July 2014 www.sea-technology.com Real data of meteorological conditions on December 16, 2011 were used for the OrcaFlex model, with some restrictions. A periodic sea wave, a constant wind and a time-constant profle of current were used. The day was chosen to represent typical wind conditions on the Vilanova coast instead of averaged values between time periods to offer more realistic ocean conditions for mod- eling. We fxed the real-world conditions at the time of 9 p.m. UTC, characterized by a maximum wind speed of 11.27 meters per second and 117° direction of ad- vance. The signifcant wave height was 3.05 meters, with a period of 7.52 seconds and 17° direction of advance. The current intensity profle was divided into three lay- ers: on the top, a linear boundary layer of 3 meters, with a maximum of 0.92 meters per second and 87° direction of advance; a middle layer of 10 meters depth, where current intensity was constant at about 0.55 meters per second; and a third layer of 7 meters above the seabed, with intensity decreasing linearly to zero. The current di- rection depended on depth. The OBSEA buoy simulation was moored with three chains on the seabed in a circle of 20 meters radius. The chains were equally spaced at 120°. The buoy consists of one cylinder 4 meters long and 0.8 meters in diameter, and another small cylinder on the bottom that is 0.9 meters long and 0.05 meters in diameter. It weighs 650 kilograms in air. At the bottom is a free link to three chain branches 0.65 meters long, 0.03 meters in diameter and 130° declination, equally distributed. The simulated power cable was 0.1 meters in diameter and 45 meters long, with a bending stiffness of 7 kilonew- tons per square meter moored at the steady state position. The cable was linked to the buoy with a vertical branch 0.65 meters long, 0.12 me- ters in diameter and 60 kilo- grams per meter. The unit segment length used to simulate chains was 0.25 meters. Dynamic simu- lations were done with fxed step size of an implicit inte- gration method. The step size was small enough to generate results that did not change when the step size was de- creased. A step size of 0.025 seconds was needed when the cable was added to the structure. Simulations were done from 20 to 600 seconds to study temporal behavior. Results and Conclusions The simulation results help us to predict the dynamics of a moored platform and its components under real-world conditions before deployment. When the power cable was added to the buoy in the simulation, the position of the buoy was modifed from its origin. However, the buoy's range of movement was similar in all cases. The modeling results with a power cable in all cases show oscillatory behavior. For instance, when the cable was The numerical simulations were done with the help of Or- caFlex software, a marine dy- namics program developed by Orcina (Ulverston, England) for static and dynamic analysis of a wide range of offshore systems. OrcaFlex provides fast and ac- curate analysis of umbilical ca- bles under wave and current loads and externally imposed motions. It is a 3D nonlinear time domain fnite element program capable of dealing with arbitrarily large defections from the initial confguration. Simulations of OBSEA's buoy show the dynamics of the buoy, power cable and chains under real-world conditions, i.e., the orbit of the buoy and cable and chain tension as a function of time or variations of curvature. The orbit of the buoy model with power cable shows an oscilla- tory pattern. (Top) 3D view at 10 minutes. (Middle) Horizontal projection view during one wave period (7.52 seconds). (Bottom) Temporal evolution of buoy coor- dinates. The amplitude spectrum of one relative horizontal position is a function of frequency without transient.