Conceptual Design of a Closing Device for the Moonpool on Construction Support Vessels
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- Institutt for marin teknikk 
This thesis is based on an initial investigation of the problem concerning running a vessel with an open moonpool in transit, and how the added resistance can be reduced by installing a closing device in the moonpool opening. There are mainly two physical effects causing an increased resistance of an open moonpool, defined as piston mode excitations and vortex shedding at the leading edge of the moonpool (sloshing mode). Particularly if these two effects occur at the same time, the vessel can experience involuntary speed loss, increased resistance and also green water on deck if the vertical motions inside the moonpool are extreme. Through the use of a structured methodology for concept development, this thesis will try to develop a solution that will reduce the impact of these effects on the total resistance of the vessel. The methodology was developed through a combination of methods from mainly three sources of literature. The books studied were Product Design and Development (Ulrich & Eppinger 2012), Engineering Design (Pahl et al. 2007) and Systems Engineering (NASA 2007). The methodology and methods were tested on the moonpool closing device problem. One full iteration was conducted with input from the representatives at DOF Management and their collaborators. A mission statement connecting the project to the company strategy and business goals was established, and a stakeholder s analysis for the project was conducted. By using interviews and searching for information on similar concepts/solutions, the customer needs and a list of preliminary requirements for the product were investigated and developed. A functional hierarchy was developed, and four primary functions were identified as the most critical to solve; Opening and closing of the hatch, storage of the hatch in open position, locking the hatch in place, and managing water. A morphological matrix was used to generate concepts by combining solution principles for the identified sub-functions. The generated concepts were then screened. The process discarded alternatives that were not feasible or who did not fit the stated requirements. Three concepts were sent to DOF, together with a benchmark concept from TTS, for a concept scoring. The scoring process was completed using the Analytical Hierarchy Process. Using a structured methodology to develop a concept proved to be very useful. Product design and development is a complex undertaking, and a framework will aid the development and search for solutions. The methodology helps keeping track of information and ideas that come to life. By using a diverse and multidisciplinary team, the process could be further enhanced and the full potential of working with a systematic methodology be realized. The final concept showed good promise when it comes to economic feasibility and compliance with the stated needs, but it is advised to investigate further the potential benefits by establishing the exact resistance reduction component for the solution.