There are many uncertainties associated with the estimation of extreme loads acting on a wave energy converter (WEC). In this study we perform a sensitivity analysis of extreme loads acting on the Uppsala University (UU) WEC concept. The UU WEC consists of a bottom-mounted linear generator that is connected to a surface buoy with a taut mooring line. The maximum stroke length of the linear generator is enforced by end-stop springs. Initially, a Variation Mode and Effect Analysis (VMEA) was carried out in order to identify the largest input uncertainties. The system was then modeled in the time-domain solver WEC-SIM coupled to the dynamic mooring solver Moody. A sensitivity analysis was made by generating a surrogate model based on polynomial chaos expansions, which rapidly evaluates the maximum loads on the mooring line and the end-stops. The sensitivities are ranked using the Sobol index method. We investigated two sea states using equivalent regular waves (ERW) and irregular wave (IRW) trains. We found that the ERW approach significantly underestimates the maximum loads. Interestingly, the ERW predicted wave height and period as the most important parameters for the maximum mooring tension, whereas the tension in IRW was most sensitive to the drag coefficient of the surface buoy. The end-stop loads were most sensitive to the PTO damping coefficient.
The shipping industry is paramount for global economic growth by enabling the trading of enormous volumes of goods across the world. However, maritime transport is a huge and growing source of greenhouse gas emissions. Consequently, the shipping industry is required to speed up its environmental transition towards a zero-carbon emissions fleet. Alternative marine fuels, in combination with ship optimization in realistic operating conditions, could be a solution to reduce the marine ship emissions drastically.
The emissions of harmful gases and particulates from the engine increase when the ship operates in waves. This phenomenon is particularity problematic for lean-burn natural gas engines because of the increased amount of unburnt methane emitted. The solution to this problem requires studying the interaction between the ship hydrodynamics and the engine dynamics. For this purpose, a coupled engine-shaft-propeller model capable of predicting its performance in waves needs to be developed. At the same time, evaluating the ship propulsion system performance in realistic operating conditions is essential to estimate the installed power of the main engine and to optimize the ship voyage.
The purpose of the present work is to investigate the interaction between propeller loads and engine response of a ship sailing in realistic operating conditions. First, an investigation was carried out to determine the propeller model necessary to estimate the propulsive forces in waves. Second, a coupled propeller-engine model was built to evaluate how the environmental effects influence the ship propulsion system performance in terms of propulsive forces and unburnt methane released in theatmosphere. Third, the effect of waves on the propulsive coefficients was studied by conducting numerical simulations and model experiments.
The traditional method applied to compute the propeller performance in waves, knownas the quasi-steady approach, was adequate to estimate the propulsive forces in realistic operating conditions. The simulations performed with the coupled engine-propeller model proved that neglecting time-varying wake field, ship motions,and propeller close-to-or-breaking water effects would lead to a poor prediction of the propulsive forces in waves. The coupled engine-propeller model allowed determining that the amount of unburnt methane released in the atmosphere considerably increases when the ship operates in waves. The investigation conducted on the propulsive coefficients showed that the effective wake fraction depends on both the propeller loading and the motions of the ship. An inverse non-linear correlation between the thrust deduction fraction and the propeller loading was observed. A small influence of the ship motions on the thrust deduction fraction was noticed. The propulsive efficiency was mainly affected by the variation of the open-water efficiency caused by the propeller loading. Therefore, using the propeller open-water curves or performing overload self-propulsion model-scale experiments in calm water would provide a sufficiently accurate estimation of the time-averaged propulsive efficiency in waves for the considered case studies.
The results of the PhD project are useful to investigate the performance of marine propulsion systems in realistic operating conditions. The techniques and tools employed in the current study can be directly applied in the ship propulsion optimization process to include the effect of waves. The work conducted in this research also constitutes a step towards the implementation of the liquefied-natural gas as a marine fuel.
There have been a number of recent papers in the literature that investigate the relationship between ship speed and required power, or between ship speed and fuel consumption. Using regression analyses for selected case studies these papers show that in many cases the traditional “cube law” is not valid, and exponents lower than 3 (and in some cases lower than 2 or even below 1) are more appropriate. Perhaps more important, they use these results to derive implications on the validity (or lack thereof) of policies to reduce greenhouse gas (GHG) emissions from ships through slow steaming. This paper reviews some of these papers and shows that their results are partially based on pitfalls in the analysis which are identified. Policy implications particularly on the quest to reduce GHG emissions from ships are also discussed.
Integrated community energy systems are an emerging concept for increasing the self-sufficiency and efficiency of local multi-energy systems. This idea can be conceptualized for the smart island energy systems due to their geographical and socioeconomic context, providing several benefits through this transformation. In this study, the energy system of the Ballen marina—located on the medium-sized Danish island of Samsø— is investigated. Particular consideration is given to the integration of PV, BESS, and—in the future—flexible loads. For this purpose, the BESS is modelled, incorporating the battery degradation process. The possibilities to improve energy utilization and maximize self-consumption from the marina's PV units are identified and evaluated, demonstrating a substantial enhancement of the local system operation.
A 3D fully nonlinear potential flow (FNPF) model based on an Eulerian formulation is presented. The model is discretized using high-order prismatic – possibly curvi-linear – elements using a spectral element method (SEM) that has support for adaptive unstructured meshes. The paper presents details of the FNPF-SEM development and the model is illustrated to exhibit exponential convergence. The model is then applied to the case of focused waves impacting on a surface-piecing fixed FPSO-like structure. Good agreement was found between numerical and experimental wave elevations and pressures.
This paper examines the stability of a weak island namely Sumbawa-Lombok of Indonesian grid, interconnected with two infeed HVDC links facilitating 2 x 120 MW power transfer from Sumba and Flores Island. Through power flow, short circuit, small signal stability, resonance stability, and transient stability analyses, it is demonstrated that the existing infrastructure fails to support such transfer due to voltage drops, overloading, and stability limitations. Upgrading to 150 kV and its subsequent component resolves the small-signal and transient stability constraint as its grid strength is increasing. The current findings underscore that the primary limitation lies in the grid's infrastructure, not in dynamic or control constraints. The current result establishes the need for strategic grid reinforcements to support HVDC integration in weak systems and sets the stage for future research on optimizing the extent of such reinforcements.
Increasing concerns related to fossil fuels have led to the introducing the concept of emission-free ships (EF-Ships) in marine industry. One of the well-known combinations of green energy resources in EF-Ships is the hybridization of fuel cells (FCs) with energy storage systems (ESSs) and cold-ironing (CI). Due to the high investment cost of FCs and ESSs, the aging factors of these resources should be considered in the energy management of EF-Ships. This article proposes a nonlinear model for optimal energy management of EF-Ships with hybrid FC/ESS/CI as energy resources considering the aging factors of the FCs and ESSs. Total operation costs and aging factors of FCs and ESSs are chosen as problem objectives. Moreover, a stochastic model predictive control method is adapted to the model to consider the uncertainties during the optimization horizon. The proposed model is applied to an actual case test system and the results are discussed.
Shore power is an important green technology used by ports to reduce carbon emissions. This paper investigates how to design subsidy strategy for promoting the installation and utilization of shore power. However, while installation subsidies may promote the installation of SPI in ports, resulting in a reduction in ship emissions, utilization subsidies may attract more ship visits, which may increase the total emissions of a port. Therefore, subsidies for shore power utilization and installation should be optimized to minimize the cost to government (comprising the environmental costs of ship emissions, the cost of utilization or installation subsidies, and carbon taxes) and maximize the profit for ports (including profit from original and new ships, utilization and installation subsidies, and carbon taxes). Using the Stackelberg game methodology, we discuss five cases to give a comprehensive analysis of the design of different subsidy policies, including no subsidy, SPI-utilization subsidy undertaken by port, SPI-utilization subsidy undertaken by port and government, carbon emission tax policy considering SPI-utilization subsidy, and SPI-utilization and SPI-installation subsidies undertaken by port and government. Managerial insights are generated according to the theoretical analysis and numerical experiments results, which can give references to the government and port operators.
This report includes a broad description of the findings from work package 2 in the EFFORT project and is made as the fulfillment of delivery L2.1 in the project. First an overall description of the Port of Hirtshals together with its infrastructure is given in chapter 1 together with some background aspect for the development of the Port of Hirtshals. In this chapter also the 5 companies who had shown their interest in participation in the project are described in more detail. Based on this as outcome of task 2.1 and described in chapter 2 an overall system architecture is set up for the existing industries at the Port of Hirtshals and next for the future expansion of the port. Based on the overall system architecture an adaptation of the system to the EU SGAM model is performed and explained. Then the overall set up of the data hub is briefly introduced, to see how it is related to the overall energy system set up. The final part documented for task 2.1 is two examples of sequence diagrams for first the processes in Forskerparken and next one which is valid for both the Fish Terminal, Lineage as well as Danish Salmon, since many of their electrical consuming processes here in an overall manner look the same.
In chapter 3 the base scenarios for the existing industries at Port of Hirtshals are set up. This is done based on information and wishes from the industries and the local Distribution System Operator (DSO), which is gained partly by bilateral discussions as well as on a workshop held with all the involved industries present at the same time. The scenarios will be described according to the IEC standard 62559-2, to ensure better utilization of the ideas in other projects, by applying a standard template known in this area.
Finally, in chapter 4 scenarios for the future expected extension of industries and activities at the Port of Hirtshals are set up. This is based on inputs from GPN, HH, NEN as well as Hjørring Municipality, Hirtshals Fjernvarme and from inputs from workshops with the existing industries at the port. Also here the IEC 62559-2 standard will be applied when describing the use cases.
The scenarios set up will later be used for the further development of the data hub, which is to be set up in the project, as well as for the model set up and control perspectives in the later WPs.
Denmark has set ambitious targets, to reduce emission with 70% by 2030 and become independent of fossil fuels by 2050. To achieve those targets, Denmark is planning to accelerate the de-carbonization of the power system, by replacing fossil fuel generation plants with renewable energy sources (RES). Offshore wind power will form the backbone of power generation in a decarbonized system. Already world leading in electric consumption share covered by wind power, Denmark plans to install an additional 6.8 GW of offshore wind by 2030, quadrupling the 1.7 GW already connected to the system.