Efficient Design of Controlled Offshore Systems

A Holistic Approach

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Abstract

Designing a controlled offshore system is a challenging process, the system dynamics are often nonlinear and subjected to loads that are random in nature. Furthermore, the proper description of the system’s dynamical behaviour involves knowledge pertaining to several fields. Unfortunately, at the design level, the process is often segregated between the different fields which are using highly advanced technology from their own discipline on overly simplified models relating to the other disciplines. This thesis focuses on creating a generic framework enabling appropriate modelling and analysis methods for controlled offshore systems considered as a whole. To create a virtual prototype of the system in a generic and modular way, the modelling is based on the formalism of multibody dynamics coupled to hydrodynamics. Generic methods for the linearisation of the system equations are introduced and implemented to enable analysis in both the time and frequency domains. The short term statistics are also provided in both domains, using spectral analysis in the frequency domain and time traces in the time domain. These different modules can be used to build the complete model, including control and study the system using classical techniques. Lastly, an approach to efficiently compute the workability plots is proposed as they are an important performance indicator of offshore systems. The considerable increase in computational speed gained through this approach opens the door for new types of insights such as parameter optimisation and sensitivity analysis. This holistic view of the system should allow engineers to take the right decision during the early phase of the design process by allowing them to explore different integrated design solutions and understand the influence of design parameters on the system’s workability. The example of a motion compensated gangway is used throughout the thesis to illustrate how the developed framework and methods can be used in practice.