Multiphysical Simulation of Ocean Engineering Systems — Modelica Ocean Engineering Library — Cosimulation for Drilling Riser Analysis

Abstract

The advancements in computing has made it possible to carry out integrated simulation of complex multiphysical systems, to better evaluate system performance and safety. The discipline of multiphysical simulation, though well established in many domains, is not used as extensively in the analysis of ocean engineering systems, which even in their simplest applications, is highly multiphysical and interdisciplinary.

One factor that limits the of use of multiphysical simulation techniques in the analysis of offshore systems is the lack of mutiphysics capabilities in hydrodynamics simulation software, and vice versa.

This thesis presents the efforts and results in the direction of implementing such a multiphysical approach in the ocean engineering domain, and thereby encompasses facets such as the development of Modelica component models to constitute an Ocean Engineering Library for OpenModelica, a popular open-source multiphysics software; and the formulation of a co-simulation interface between Simulation X, a commonly used commercial multiphysics software, and OrcaFlex, a popular commercial ocean engineering software.

Being an article-based thesis, the project scope is divided into parts, and each part is dealt with in an article along with the relevant theory.

In the first article, preliminary results from the multiphysical simulation of a representative ocean engineering system in OpenModelica is compared with those obtained using OrcaFlex, as an indicator of the possibilities of implementing such a multiphysical approach. A detailed description of the theory behind the development of component models to simulate regular and irregular waves, and depth-varying current is presented in the second article, while the response of non-diffracting floating objects, and mooring response based on the quasi-static approach, is presented in the third article. The third article also brings out the limitations of the quasi-static approach in the simulation of mooring forces.

The fourth article describes the lumped-mass approach to simulation of mooring line dynamics, while the fifth article deals with the development of Modelica component-models for subsea cable dynamics based on the lumped-mass approach.

The sixth article lays the foundation for the future development of Modelica component-models for simulating the hydrodynamics of larger objects, where wave diffraction and radiation effects are significant, by presenting a Python code for the evaluation of the frequency dependent hydrodynamic coefficients.

The seventh article is concerned with the development of a co-simulation methodology for riser analysis and presents a co-simulation interface between SimulationX and OrcaFlex.

The last and eighth article compares the results of a multiphysical simulation, based on the above co-simulation methodology, of a planned riser disconnect procedure with field measurements, and demonstrates the possibilities that open up.

The conclusion section sums up the contributions of the present work and suggests avenues for future research in the domain.