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Investigating the Feasibility of Self-Buoyant Concepts
The gravity concept, originally implemented in the Oil & Gas sector, is based on utilising the dead weight of the foundation material (typically concrete) to generate the restoring forces required to resist the high lateral loads and overturning moments resulting from the service loads. However, the significant dead weight of the foundation usually results in costly transportation and installation operations, given the high charter rates of the required vessels, lifting cranes and infrastructures. Achieving the EU targets for the levelised cost of energy (LCOE) of offshore wind encourages development of alternative approaches with cost reduction potentials. Several gravity concepts have been proposed in recent years, to attain a self-buoyant gravity base foundation, and thereby minimise the need for costly marine operations. This article reports a parametric study that investigates the feasibility and cost-benefit of such concepts, in terms of performance, intermediate stability and their impact on the overall cost of foundations.
By Dr Azadeh Attari and Dr Paul Doherty, GDG, Ireland
Often pitched as an unconventional substructure, gravity base foundations (GBFs) are in fact one of the most common foundation types employed in the offshore wind industry to date (Figure 1). At the end of 2013, 12% of the total number of fully installed substructures in European waters were gravity bases.
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Performance Stability of Continuous Wave Lidars in High Motion, Offshore Environments for Wind Resource Assessments
Remote sensing on floating offshore platforms such as buoys, barges and ships provides a cost-effective alternative to expensive foundation-mounted offshore wind monitoring towers for wind resource assessment [1][2]. In addition, it is unlikely that foundation-mounted offshore meteorological masts will ever be viable in water depths of over 30 metres, whereas floating platforms can be deployed in more or less any water depth. This will become particularly relevant as floating wind turbines in deep offshore waters start to come on-line.
By Mark Pitter, Scientist and Offshore Applications Leader, and Alex Woodward, Head of Product Development, ZephIR Lidar, UK
Remote sensors mounted on floating platforms are often subjected to motion. Buoys typically exhibit both translational and rotational motions and these motions have the potential to adversely affect the measurement of the wind vector. In this article the effect of motion on remote sensor performance and in particular the ZephIR 300 Continuous Wave (CW) wind lidar will be described. In addition it will be demonstrated by theory, experimental results and field trials that these motions can be tolerated, or the measurement methodology adapted such that their effect on the accuracy and precision of the wind measurement can be negligible, a unique property of the CW architecture found in all ZephIR lidars.
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Cold Climate Issues for Wind Turbine Machinery
Wind turbines are installed worldwide, and therefore these systems need to operate in different climates and environmental conditions, from arctic cold to blistering desert heat. And, they need to work in these extreme conditions for 15 to 20 years without having major breakdowns. Design engineers need to take such climates into account in order to have a reliable and efficient product in all conditions. Currently, wind turbines are more frequently installed in so-called ‘cold climate’ or ‘low temperature climate’ locations where temperatures below -20°C are not that uncommon. Standard turbines are designed to operate in -10°C temperatures, and survive in -20°C conditions. However, recent weather data from places such as Inner Mongolia and Canada indicates that even -45°C and -50°C can occur in some locations. This article discusses the problems such extreme temperatures can cause and how climatic chamber testing can help designers produce turbines suitable for the conditions.
By Pieter Jan Jordaens, Business Development & Innovation manager, OWI-Lab, Belgium
As the market for low temperature turbines expands the importance of having reliable and efficient turbines in such locations becomes of vital interest. Many of these cold climate locations have profitable average wind speeds and free installation space, and the higher air density in cold weather makes this market attractive to investors, if the turbine manufacturers can guarantee high availability, reliability and efficiency.
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The Need for and Advantages of Advanced Ground Testing
This article seeks to demonstrate the comprehensive capabilities and benefits of wind turbine generator (WTG) system test benches that are integrated into a multi-physical hardware in the loop (HIL) environment. In 2012 and 2013 the Center for Wind Power Drives successfully proved the use of HIL for advanced ground testing with a test campaign on a 1MW test bench demonstrator. In addition, a new 4MW WTG system test bench was brought into operation in late 2014. With regard to type certification tests, ground testing has the potential to be a substitute for field prototype testing as a faster, more cost efficient and flexible alternative. Beyond this, ground testing can be used for validating new WTG designs and improving reliability. The HIL operating mode makes it possible to simulate the working environment of a WTG and to consider the influence of the WTG controller strategy on the mechanical and electrical loads of the drive-train.
By Dipl.-Ing. Stefan Franzen, Dipl.-Ing. Dennis Bosse, Dipl.-Ing. Dominik Radner, Prof. Dr.-Ing. Georg Jacobs and Dr.-Ing. Ralf Schelenz, Center for Wind Power Drives, RWTH Aachen University, Germany
Following an introduction that outlines the need for a full-size ground-testing capability, the main part of the article introduces the design of the Center for Wind Power Drives’ 4MW WTG system test bench and the implementation of the HIL environment. The article concludes by outlining the benefits of and future prospects for the system test benches and the HIL integration.
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A Tool to Avoid Aerodynamic Imbalance
The accurate synchronisation of rotor blades is an important requirement for the optimal operation of wind turbines in relation to both generation and loads. Because of the lack of appropriate measurement devices that allow easy and timesaving inspection, the problem has long been underestimated and neglected at the same time. However, with the development of new, highly efficient wind turbines with extremely long rotor blades, misalignment has become a greater problem due to the substantial surplus loads caused by aerodynamical imbalance. The subject shifted into the focus of manufacturers and operators and caught growing interest as it applies to all wind energy converters.
By J. Dietrich Mayer, Managing Director, windcomp, Germany
Dynamic rotor geometry measurement (DRGM), developed by windcomp between 2008 and 2010, is a method for the verification of the aerodynamic condition and the aeroelastic behaviour of a wind turbine rotor and the turbine-tower system. DRGM is a laser‐based simultaneous distance measuring method at two profile‐sections of the blades. The system is weatherproof and can be operated in all seasons. Even so, weather conditions are a limiting factor, and heavy rain and fog in particular affect the measurement severely. The system allows the measurement of rotor blades during operation and thus downtime of the wind energy converter can be avoided. Collection and evaluation of data can be performed on site. This allows immediate action to adjust blade angles and optimise the turbine performance.
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Offshore Wind Turbines to Provide Combined Electricity and Deep-Sea Thermal Energy
Research at the University of Malta is evaluating the possibility of using offshore wind turbines in deep waters to exploit wind energy at the same time as making use of the enormous renewable thermal energy resources available in deep-sea cold water. The concept is based on the direct coupling of offshore wind turbines to positive displacement pumps, replacing the gearbox and electrical generator found in conventional systems. Rather than producing electricity directly, individual wind turbines would pump pressurised deep sea water to a centralised hydroelectric power station. After producing electricity, the sea water is pumped through a heat exchanger to provide district cooling. The idea of using cold water below the thermocline layer and offshore wind energy to extract it has evolved into the Offshore Wind and Thermocline Energy Production (OWTEP) system.
By Mr Daniel Buhagiar and Prof. Ing. Tonio Sant, Department of Mechanical Engineering, University of Malta
Despite the numerous advantages of offshore wind, it represents less than 2% of the world’s total installed wind power. This can be attributed to a number of technical issues that stem from the use of conventional onshore designs in the offshore environment. There is now a strong drive to develop offshore-specific turbine designs. The OWTEP system presents a radical approach to offshore wind turbine engineering; it is better suited for the offshore environment, without nacelle-based gearboxes or generators. The concept offers opportunities to improve the viability of the turbine by maximising the use of the infrastructure and concurrently harvesting the different resources available at deep water installation sites.
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Taking a Closer Look at Faulting and Seismic Hazards for Wind Farms
Across much of the world earthquake activity is a common occurrence. Although some places have more seismic activity than others, hazards from earthquakes may have a wider reaching long-term impact on wind farms than that expected by many in the design community. Even though a site may not have recent seismic activity, this does not preclude it from future seismic shaking or ground rupture. Within areas that have active seismic motion, seismic and fault hazard investigations are an important part of project development. For those not familiar with these types of investigations there are various review components which can be obscure without a guideline for interpretation. Even for technical specialists, variable code requirements and local geologic differences make individual project reviews difficult to achieve if someone is not familiar with a standard guidance document. The intent of this article is to discuss these considerations during wind farm seismic evaluations.
By Daniel E. Kramer, Petralogix Engineering, and Garret Hubbart, Neil O. Anderson & Associates, USA
