Ship structure design process begins with the evaluation of environmental conditions a ship is expected to withstand. This paper deals with wave data, and more specifically with global wave dataset that can be used to evaluate waves encountered by a ship along its lifetime track. Benchmark of existing global hindcast datasets is performed, having in mind its use to assess extreme ship response. The presented comparison is thus not limited to the mean and standard deviation but includes also extreme significant wave height. Wave period that can significantly modify ship behaviour is also investigated. Five different hindcast datasets are selected for the present analysis and compared with buoy and altimeter data. Area of interest is region far from the coast, and more specifically the North-Atlantic, which is currently considered the most severe for sailing ships. In such area, the global wave models are expected to provide decent results (as opposed to near shore area where a local mesh would be required). Two datasets are provided by ECMWF (ERA5 and ERA-Interim) that uses WAM model, two others are from NOaAA/NCEP and Ifremer and use WaveWatchIII, finally WAV-ERYS dataset is provided by the Copernicus program, and uses MFWAM. Some differences are observed in the wave parameters projected by different models, especially on extremes. Reasons for this scatter are briefly discussed, but more emphasis is put on the consequence for ship response. This work has been performed within IACS (International Association of Classification Societies) framework.
IMO introduced Energy Efficiency Design Index (EEDI) to regulate the greenhouse gas (GHG) emissions from ships. The cheapest and easiest way to fulfil the EEDI requirement is to reduce installed power for most ships. Therefore, it has raised serious concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements and not consider ship safety in a satisfactory way. This could induce ship manoeuvrability and safety problems in adverse seas, which needs urgent investigations on minimum power to maintain ship manoeuvrability in adverse sea. A time domain code ‘Waqum’ has been developed based on the force superposition of unified theory to study the minimum required power for maintaining ship manoeuvring ability in adverse sea states. The code combines sea-keeping and maneuvering equations, together with an engine model to predict ship responses in waves. The code can help us to study ship responses in transit situation and give us better insight into ship maneuvering ability in adverse sea states. In order to improve the simulation speed, the time domain code does not calculate all the hydrodynamic forces directly. Thus, some precalculations should be done for some force components before launching the simulation for a new ship. Therefore, the methodology and accuracy of each force component will influence the accuracy of the manoeuvring code. The methodology for determining each force component will be discussed, especially the identification of maneuvering derivatives based on CFD simulations. The code has been improved recently, and another rudder model has been implemented. Further, the the code with new rudder model is verified in calm water. The code’s ability to capture ship maneuvering in waves is also demonstrated.
Energy Efficiency Design Index (EEDI) introduced by the IMO Resolution MEPC.203 (62) has been the first initiative to regulate the greenhouse gas (GHG) emissions from ships. However, it has raised serious concerns that some ship designers might choose to lower the installed power to achieve EEDI requirements not accounting satisfactorily for ship safety. This has encouraged investigations addressing the ability of ship to maintain maneuverability in adverse sea states. The Interim Guidelines proposed in 2013, in IMO Res. MEPC.232 (65), recommend minimum propulsion power to maintain ship maneuvering ability in adverse weather conditions for bulk carriers and tankers. These guidelines are mainly based on statistical analysis and equilibrium analysis in a steady state. Today, most of the available tools and methods handle ship responses in waves by separating it into seakeeping and maneuvering. The present study investigates ship maneuverability by use of a recently developed time domain code which combines the sea-keeping and maneuvering equation to predict ship responses in waves. In this way, better insight into ship responses in adverse conditions is obtained. The numerical results presented in the study are validated by model tests. The limitations of the time-domain code are discussed and future research needs are pointed out.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.