Dynasim—A Time Domain Simulator of Anchored FPSO

Abstract

The prediction of the dynamic behavior of moored tankers like FPSO system is very important to the mooring systems design. There are several types of mooring systems, such as Turret, Spread Mooring System (SMS) and Single Point Mooring (SPM), for which the specification of number and dimensions of the lines depends on the dynamic of the entire system composed by tanker and mooring and riser lines. Although several moored systems were already installed as a positioning system of FPSO, there are still some unknowns that should be investigated to provide more safety and lower cost systems. The drag/damping terms on the ship hull and the mooring and riser lines damping are one of the most important terms in the dynamics of the moored tanker that should be investigated. The hydrodynamic model due to the interaction between hull and fluid has been very studied due to the complexity of the phenomenon. The authors have studied the models of several researchers and three of them were picked up and implemented in the DYNASIM, a moored ship dynamic simulator. These models will be discussed and compared. In deep water, the total length of the mooring lines and risers becomes large and consequently the forces acting on these elements become more important. However, in many cases these important forces acting on the lines have not been considered. There are some works that point out the magnitude of the damping forces of the lines. Recently, a full scale decay test using a 30kDWT moored tanker was realized in Brazil offshore. The results showed the significance of the line damping, in particular on surge motion. Another important phenomenon that has been discussed is the wave drift damping term. There are several research studies concern’s this force resulting in several estimation methodologies. However, only surge direction has been considered important and there is little research about the damping in others directions. The time simulation methodology will be used to analyze and compare the effects of each term in the dynamics of the system. Finally, the comparison between simulated results and model test data will be performed in order to validate the model proposed. In this study, the experimental data of DICAS system (Differentiated Compliant Anchoring System) will be used.

Reliability-based comparative study for mooring lines design criteria

“…In this work, the FPSO motion analyses have been performed with the computer program DYNASIM [28,29] using JONSWAP and Harris models [20] to represent the sea waves and wind spectra, respectively. After this, the surge, sway and heave motion time-series (including slow-drift and wave frequency components) at the top of the lines, obtained with DYNASIM, have been used as prescribed movements in the nonlinear time domain finite element-based program ANFLEX [30,31] in order to perform the mooring line dynamic analysis.…”

DOOLINES : an object-oriented framework for non-linear static and dynamic analyses of offshore lines

“…DOOLINES is currently employed by at least four systems, namely, DYNASIM [32], TPN [31], Prea3D [24], and VisGas [1]. These software platforms are long-term research and development projects, mainly funded by PETROBRAS.…”

“…An application of DOO-LINES in one of these systems, namely DYNASIM [31,32], is presented in Sect. 3.3.…”

Methodology for definition of new operating sectors fo DP assisted offloading operations in spread-moored platforms.

“…It is based on an adaptation of computer code simulation TPN/Dynasim (Nishimoto, Fucatu and Masetti, 2002), (Nishimoto et al, 2003). This program performs a static evaluation of the available thrust on the DP system, to verify if the shuttle is able to counter the resulting environmental forces and keep DP operating mode from -50° to +70°: Normal DP operating mode @75°: Bow Rotation DP operating mode @85°: Heading Restriction position for each environmental condition of the hindcast data.…”

“…The software is based on the TPN (Numerical Offshore Tank) numerical code (Nishimoto et al, 2002), which had several modifications, in order to perform realtime simulations. It helps in performing various maneuverings in extreme conditions, with different types of ship and in damaged conditions and/or command failures.…”