Conceptual design of low-emission ships

Abstract

Human-induced climate change is one of the significant challenges of our time. In order to help limiting global warming, the International Maritime Organization has set out stepwise greenhouse gas emission reduction ambitions for the maritime industry. Other stakeholders exercise pressure to increase the maritime ambition level. Therefore, shipowners and designers today expect emission reduction requirements to tighten over time, but the precise level is currently uncertain. Against this background, the objective of this thesis has been defined as to “enhance conceptual ship design methodology to cater for greenhouse gas emission reduction ambitions along a ship’s operational lifetime”. The research objective is divided into two research questions. First, how to effectively explore and synthesize low-emission conceptual ship designs? Second, what is an effective method for selecting among alternative ship fuels and power systems under lifetime uncertainty and considering flexibility? For each research question, a working hypothesis is formulated, tested and evaluated through a method called ’validation square’. The results of this research are disseminated in six main and four supporting papers. From these papers, three main contributions are identified: C1 The coupling of a set-based approach with modular system-based ship design, a systems architectural model and discrete-event simulation for a case-dependent evaluation of conceptual designs C2 A method for the selection of the optimal ship fuel and power systems considering flexibility throughout the lifetime C3 An extension of the deterministic selection method (C2) that concurrently considers uncertainty through multiple stochastic scenarios Contribution 1 describes a ship synthesis model, and addresses primarily structural and behavioral complexity aspects. By structural complexity it is meant the multitude of possible systems, such as different hull concepts or different energy storage options, that can be combined in different ways. The behavioral complexity is related to the non-trivial system behavior that emerges from the different combinations of subsystem options. The set-based approach denotes an exploration and evaluation of such different options before commitment to one concept. Contribution 2 addresses the selection of fuels and power systems under an assumed certain lifetime scenario. Within this lifetime scenario, fuel costs and carbon prices are changing over time and fuel switches and retrofits are considered as flexibility options. Contribution 3 builds upon the developed selection method under certainty, but additionally considers uncertainty with respect to fuel costs and carbon prices through the sampling of multiple scenarios. The bi-objective nature of the developed stochastic programming method shows the effect of different cost-versus-emission compromises on the selection of ship fuel and power system.