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Ormberg H.,Norwegian Marine Technology Research Institute | Bachynski E.E.,Japan Agency for Marine - Earth Science and Technology
Proceedings of the International Offshore and Polar Engineering Conference

This paper describes the extension of a well-proven state-of-the-Art simulation tool for global analysis of floating structures to also include offshore wind turbine applications, floating as well as bottom-fixed. All structural components of the wind turbine system are included in the finite element model of the complete system. The aerodynamic formulation is based on the blade element/momentum theory, including empirical tip loss and dynamic stall corrections and upwind tower shadow effects. Various wind field descriptions are included, covering simple steady uniform wind to fluctuating turbulent wind, with or without shear profile. A simple PI-control algorithm is used for regulation of the blade pitch angle, and the electrical torque is determined by a lookup table based on generator speed. The system response is calculated by nonlinear time domain analysis. This approach ensures dynamic equilibrium every time step and gives a proper time domain interaction between the blade dynamics, the mooring dynamics and the tower motions. The developed computer code provides a tool for efficient analysis of motions, support forces and power generation potential, as influenced by waves, wind, and current. Results from the developed code are presented and compared with results obtained from other simulation codes. This study also includes the sensitivity of results with regard to various modelling aspects. The last part of the paper presents a benchmark study against the codes of the Offshore Code Comparison Collaboration project. The floater motions, tower forces, and power generation, are presented and discussed. Copyright © 2012 by the International Society of Offshore and Polar Engineers (ISOPE). Source

Myrhaug D.,Norwegian University of Science and Technology | Fouques S.,Norwegian Marine Technology Research Institute
Coastal Engineering

The paper provides a joint distribution of significant wave height and characteristic surf parameter. The characteristic surf parameter is given by the ratio between the slope of a beach or a structure and the square root of the characteristic wave steepness in deep water defined in terms of the significant wave height and the spectral peak period. The characteristic surf parameter is used to characterize surf zone processes and is relevant for e.g. wave run-up on beaches and coastal structures. The paper presents statistical properties of the wave parameters as well as an example of results corresponding to typical field conditions. © 2010 Elsevier B.V. Source

Wu M.,Norwegian Marine Technology Research Institute
Ocean Engineering

Offshore renewable wind energy market is expected to expand dramatically in the next 5-10 years. Reduction of downtime is crucial to the competitiveness of this new sector. One important part of the research efforts is the evaluation of operational limits (weather limits) of different vessel/access concepts for transportation of maintenance personnel, equipment, and spare parts to the offshore wind turbines. This paper gives a brief description of possible types of service vessel and access system. It presents methodologies for numerical analysis of docking operation by an active motion compensated access device and a simple fender. The proposed frequency-domain approach to the analysis of docking operation with fender is new and highly efficient compared to time-domain simulation. The methods have been applied to two vessel/access concepts in this paper and they can be used in docking operability assessments for a variety of vessels that employ an active motion compensated device or a fender as access system to offshore wind turbines. © 2014 Elsevier Ltd. All rights reserved. Source

Lindstad H.,Norwegian University of Science and Technology | Lindstad H.,Norwegian Marine Technology Research Institute | Asbjornslett B.E.,Norwegian University of Science and Technology | Stromman A.H.,Norwegian University of Science and Technology
Energy Policy

CO2 emissions from maritime transport represent a significant part of total global greenhouse gas (GHG) emissions. According to the International Maritime Organization (Second IMO GHG study, 2009), maritime transport emitted 1046 million tons (all tons are metric) of CO2 in 2007, representing 3.3% of the world's total CO2 emissions. The International Maritime Organization (IMO) is currently debating both technical and market-based measures for reducing greenhouse gas emissions from shipping. This paper presents investigations on the effects of speed reductions on the direct emissions and costs of maritime transport, for which the selection of ship classes was made to facilitate an aggregated representation of the world fleet. The results show that there is a substantial potential for reducing CO2 emissions in shipping. Emissions can be reduced by 19% with a negative abatement cost (cost minimization) and by 28% at a zero abatement cost. Since these emission reductions are based purely on lower speeds, they can in part be performed now. © 2011 Elsevier Ltd. Source

Kristiansen T.,Norwegian University of Science and Technology | Kristiansen T.,Norwegian Marine Technology Research Institute | Faltinsen O.M.,Norwegian University of Science and Technology
Applied Ocean Research

In this study we present a numerical wavetank with a floating body based on a new domain-decomposition method. The method couples a Naviér-Stokes solver (CFD) with potential theory. The main feature is that the CFD domain is fully submerged in the fluid such that the free surface is computed in the potential domain. The thought is that potential theory is best at propagating waves, while the CFD incorporates flow separation e.g. at bilge keels. The presently implemented code is two-dimensional, but the method is directly applicable for three dimensions. The goal is to provide a methodology capable of being the basis for an engineering type of tool for analyzing gap resonance problems, such as moonpools and ship-by-ship operations. Focus is therefore put on computational speed. © 2011 Elsevier Ltd. Source

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