There are several developments concerned to simulate the behavior of floating bodies under waves in the restricted boundary conditions so called numerical wave tank. The main feature of these tanks is to calculate full Navier-Stokes equations taking account the viscosity and free surface conditions. However, the dynamic behavior of oil floating exploitation units in actual ocean environmental condition, in waves, wind and current, is more complex and very difficult to simulate using full non-linear Navier Stokes equations. In addition, in the ultra-deep water, it is the primer importance to consider the more precise mooring line and riser’s dynamics in the analysis. The present numerical simulator laboratory called Numerical Offshore Tank is a development that takes account almost all physical phenomena acting on the floating bodies and mooring and risers lines. Since full non-linear solution is not available, the several numerical, empirical and analytical models are being considered and integrated to numerical simulator. The time domain potential problem is solved to wave forces acting on the bodies and empirical models are used to simulate current and wind forces. To represent mooring & riser lines, the finite element model with more realistic hydrodynamic force models is used. Even the simulator is using the full hydrodynamic equation, the calculation time of the simulation for floating bodies with several risers & mooring lines is very high. Therefore, special cluster with 60 PC based computer was built running the code in the parallel processing. Since the preparation of all data set for numerical experiment is very tedious work, the special pre-processor PREA3D was developed for this purpose. This pre-processor allows the fast change of the environmental and system conditions to run several test conditions. Another important feature is the visualization of the results of the simulation tests. The entire 3D view of the system is presented in the Virtual Reality room with stereoscopic projection of the Numerical Tank Laboratory.
We present an object-oriented framework, named DOOLINES, for non-linear static and dynamic analyses of slender marine structures which often appear in offshore structures employed in the petroleum and gas industries as, among others, flexible risers, steel catenary risers, umbilicals, floating hoses, and mooring lines. DOOLINES allows the rapid development of tailored, modular, reusable and extensible large-size systems, being itself extensible. These properties, along with the ease of use of our framework, are assessed by means of case studies. Code examples are provided.
This work introduces a time-adaptive strategy that uses a refinement estimator on the basis of the first Frenet curvature. In dynamics, a time-adaptive strategy is a mechanism that interactively proposes changes to the time step used in iterative methods of solution. These changes aim to improve the relation between quality of response and computational cost. The method here proposed is suitable for a variety of numerical time integration problems, for example, in the study of bodies subjected to dynamical loads. The motion equation in its space-discrete form is used as reference to derive the formulation presented in this paper. Our method is contrasted with other ones based on local error estimator and apparent frequencies. We check the performance of our proposal when employed with the central difference, the explicit generalized-˛and the Chung-Lee integration methods. The proposed refinement estimator demands low computational resources, being easily applied to several direct integration methods.
This paper applies design of experiments (DOE) methodology to the design of Compliant Vertical Access Risers (CVAR). This relatively new riser configuration is characterized by its differentiated geometry, achieved by the use of syntactic buoyancy at the lower section of the riser and additional weight at its upper section. The characteristic compliance of the CVAR system is obtained by providing an excessive length of pipe and a horizontal offset between the riser top and end connections. Thus, this system provides vertical access to dispersed subsea wells and its compliance can also compensate for vessel motion. CVAR, being vertical access to the wells, brings the advantage of using dry trees, and also allows the completion and workover operations to be performed from the FPU, offering significantly economic and operational benefits to deepwater oil field development. To guarantee such benefits, some operational and structural constraints must be satisfied. The design of the CVAR system is dependent upon several parameters. This study can provide a better understanding about the behavior of the CVAR in terms of its design parameters by the use of the DOE methodology. DOE is a statistical technique that provides an objective measure of how design parameters are correlated and the effective contribution of each at the riser performance. Consideration of the main effects as well as interaction effects coupled with sensitivity analysis is essential for insightful interpretation of model results and effective decision-making. Thus, this study contributes with the design of Compliant Vertical Access Risers as well as with a methodology that can lead to efficient riser design, being a first step in the optimization design process.
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