Tag Archives: Offshore Wind

Computationally efficient modelling of dynamic soil-structure interaction of offshore wind turbines on gravity footings


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M. Damgaard, L.V. Andersen, and L.B. Ibsen – Renewable Energy, August 2014

Abstract

The formulation and quality of a computationally efficient model of offshore wind turbine surface foundations are examined. The aim is to establish a model, workable in the frequency and time domain, that can be applied in aeroelastic codes for fast and reliable evaluation of the dynamic structural response of wind turbines, in which the geometrical dissipation related to wave propagation into the subsoil is included. Based on the optimal order of a consistent lumped-parameter model obtained by the domain-transformation method and a weighted least-squares technique, the dynamic vibration response of a 5.0 MW offshore wind turbine is evaluated for different stratifications, environmental conditions and foundation geometries by the aeroelastic nonlinear multi-body code HAWC2. Analyses show that a consistent lumped-parameter model with three to five internal degrees of freedom per displacement or rotation of the foundation is necessary in order to obtain an accurate prediction of the foundation response in the frequency and time domain. In addition, the required static bearing capacity of surface foundations leads to fore–aft vibrations during normal operation of a wind turbine that are insensitive to wave propagating in the subsoil—even for soil stratifications with low cut-in frequencies. In this regard, utilising discrete second-order models for the physical interpretation of a rational filter puts special demands on the Newmark β-scheme, where the time integration in most cases only provides a causal response for constant acceleration within each time step.

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Filed under Modeling, Wind

Offshore wind structure weight algorithms


Mark J. Kaiser and Brian F. Snyder – Ships and Offshore Structures, February 2014

Abstract

Decommissioning requirements for offshore renewable energy facilities in US federal waters requires that all facilities be removed and the seafloor be cleared of all obstructions at the end of the life of the lease. Before construction activities are permitted, developers are required to post a bond based on the estimated cost of decommissioning to ensure that the federal government is protected in case of company default. The purpose of this note is to provide weight algorithms of offshore wind farm components to estimate the lift requirements in decommissioning, the scrap value of material, and disposal cost. Weight algorithms are calibrated and compared with North Sea project data and examples illustrate the procedures. The component weights at the Cape Wind farm offshore Massachusetts are estimated.

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Filed under Analytics, Economics, Installation

HVDC Transmission for Offshore Wind Farms


Raymundo Enrique Torres Olguin, Alejandro Garces, Gilbert Bergna – Large Scale Renewable Power Generation, 2014

Abstract

Large-scale wind energy expansion is limited by factors such as the land use and the visual impact of facilities on land. Offshore wind energy can overcome the above-mentioned limitations. In addition, wind velocity is higher and more constant offshore than onshore. This chapter will present an overview of different topologies for grid integration of offshore wind farms. Special emphasis is made on the offshore grid topologies and types of power electronic converters.

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Filed under Grid, Sector Overview

Uncertainties in the design of support structures and foundations for offshore wind turbines


Vicente Negro, José-Santos López-Gutiérrez, M. Dolores Esteban, and Clara Matutano – Renewable Energy, March 2014

Abstract

Offshore wind industry has exponentially grown in the last years. Despite this growth, there are still many uncertainties in this field. This paper analyzes some current uncertainties in the offshore wind market, with the aim of going one step further in the development of this sector. To do this, some already identified uncertainties compromising offshore wind farm structural design have been identified and described in the paper. Examples of these identified uncertainties are the design of the transition piece and the difficulties for the soil properties characterization. Continue reading

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Filed under Component Development, Sector Overview, Standards and Protocols

Off-shore wind farm development: Present status and challenges


Rehana Perveen, Nand Kishor, and Soumya R. Mohanty – Renewable and Sustainable Energy Reviews, January 2014

Abstract

Offshore wind farm (OWF) is an emerging technology in the wind energy conversion system. These wind resources are abundant, stronger, and are more consistent in terms of their availability than land-based wind resources. As a matter of fact significantly higher energy production is achieved due to larger wind turbine ratings and stronger wind profiles. Continue reading

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Filed under Review, Sector Overview

Analysis of grouted connections for offshore wind turbines


Thomas Löhning, Marc Voßbeck, and Martin Kelm – Proceedings of the ICE – Energy, November 2013

Abstract

In offshore wind turbines grouted connections are generally used to install a transition piece between the steel tower and the monopile foundation. The transition piece is plugged on to the monopile, aligned vertically and the annulus in between is filled with high-strength grout. During service operations unexpected settlement of the transition piece has been observed at several wind turbines. The serious findings have called for additional, extensive numerical analyses for the detailed design of the London Array offshore wind farm. The advanced non-linear finite-element analyses provide a more detailed insight into the structural behaviour of grouted connections. Important effects and a possible mechanism for the settlement at existing wind turbines are detected. The previous practice of designing separately for bending moment and transverse force on the one hand and axial force and torsion on the other hand leads, among other things, to the overestimation of capacity. The interaction has to be taken into account.

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Filed under Modeling, Operation and Maintenance

Capacitive sensors for offshore scour monitoring


Panagiotis Michalis, Mohamed Saafi, and Martin Judd – Proceedings of the ICE – Energy, November 2013

Abstract

One of the main challenges in the design and operation of offshore wind turbines arises from the uncertainty about maximum scour depth around their foundations. Scour action can lead to excessive excavation of the surrounding seabed and is being considered as a major risk for offshore wind farm developments. An ability to gather information concerning the evolution of scouring will enable the validation of models derived from laboratory-based studies, the assessment of different engineering designs and the development of improved scour countermeasure techniques. However, real-time scour data are not being collected due to a lack of available instrumentation techniques. This paper proposes a new scour monitoring technology for offshore wind turbine installations. The monitoring system consists of arrays of small capacitive scour probes installed around the foundation structure and linked to a wireless network to enable remote data acquisition. Based on this research, it is concluded that the sensor is capable of exhibiting high sensitivity to scour and sediment deposition processes for common sea floor mediums under different temperature conditions in saline water. The proposed monitoring system has considerable potential for field applications that will contribute to improving the resilience and sustainability of offshore structures.

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Filed under Instrumentation, Operation and Maintenance

Offshore Wind-turbine Structures: A Review


Muhammad Arshad and Brendan C. O’Kelly – Proceedings of the ICE – Energy, November 2013

Abstract

This paper reviews various issues related to wind-power generation, one of the more popular forms of renewable energy, including attractions and challenges of electric power generation through onshore and offshore resources. Significant increases in wind-turbine dimensions, rated power-generation capacity and size of wind farm developments over the past two decades are projected to continue. Offshore wind-power generation presents many engineering challenges including: limited guidelines available for analysis and design of foundation/support structures; inadequate logistics for construction/fabrication; and comparatively expensive operation and maintenance costs, which combined result in current levelised cost of energy approximately double that for onshore wind-power generation. Different offshore foundation options are discussed in terms of general layout, loading characteristics and related fundamental natural frequency. Outlooks for some new approaches/developments and areas for further research are identified that may go towards reducing the levelised cost of energy for wind-power generation more in line with that from other energy resources, thereby enhancing the attractiveness of this industry for potential investors.

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A New Way for Access and Maintenance of Offshore Wind Farms: The Use of Cableway to Reduce Cost and Improve Accessibility


Massimo Grecchi, Luigi Meroni, and Piergiorgio Betteto – Wind Engineering, June 2013

Abstract

This work proposes a new method in order to deploy an affordable and reliable way for maintenance when it is necessary to access to offshore wind farms. The new system, based on cableway infrastructure is aimed to allow a lower cost of maintenance compared to other system for the same kind of operation but also to improve the reactivity and accessibility compared to them. Maintenance activities are taken into consideration in term of cost, period, nature, accessibility of wind farm, kind of maintenance we want/need to use in order to ameliorate the availability/reliability of the wind farm. Five different configurations with related cableway system are analyzed in order to demonstrate that facing a reasonable increasing of Capital Cost, sizable saving and extra revenue can be obtained if projected on the expected life of wind farms.

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The current status of wind and tidal in-stream electric energy resources


H.H.H. Aly and M.E. El-Hawary – American Journal of Electrical Power and Energy Systems, March, 2013

Abstract

Renewable energy is an effective and clean source of supplying electrical loads especially in remote and rural areas. In this paper we discuss offshore wind and tidal in-stream energy as they rely on similar technologies for generating electricity at offshore sites. In particular, we survey the impacts of offshore wind and tidal current integration into the grid, various types of generators and their dynamic modeling, fault ride-through techniques used to improve generator and grid integration performance, the aggregated wind turbines modeling and finally put the light on the stability and control problems.

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Filed under Grid