Hydrodynamics and drive-train dynamics of a direct-drive floating wind turbine

Floating wind turbines (FWTs) are considered a new lease of opportunity for sustaining growth from offshore wind energy. In recent years, several new concepts have emerged, with only a few making it to demonstration or pre-commercialisation stages. Amongst these, the spar-buoy based FWT has been extensively researched concept with efforts to optimise the dynamic response and reduce the costs at acceptable levels of performance. Yet, there exist notable lapses in understanding of these systems due to lack of established design standards, operational experience, inaccurate modelling and inconsistent reporting that hamper the design process. Previous studies on spar-buoy FWTs have shown inconsistencies in reporting hydrodynamic response and adopted simplified mooring line models that have failed to capture the coupled hydrodynamic behaviour accurately. At the same time, published information on drive-trains for FWTs is scarce and limited to geared systems that suffer from reliability issues. This research was aimed at filling the knowledge gaps with regard to hydrodynamic modelling and drive-train research for the spar-buoy FWT. The research proceeds in three parts, beginning with numerical modelling and experimental testing of a stepped spar-buoy FWT. A 1:100 scale model was constructed and tested in the University of Edinburgh’s curved wave tank for various regular and irregular sea states. The motion responses were recorded at its centre of mass and nacelle locations. The same motions were also simulated numerically using finite element method based software, OrcaFlex for identical wave conditions. The hydrodynamic responses were evaluated as Response Amplitude Operator (RAO) and compared with numerical simulations. The results showed very good agreement and the numerical model was found to better capture the non-linearities from mooring lines. A new design parameter, Nacelle Magnification Factor, was introduced to quantify coupled behaviour of the system. This could potentially encourage a new design approach to optimising floating wind turbine systems for a given hub height. The second part of the research was initiated by identification of special design considerations for drive-trains to be successfully integrated into FWTs. A comparative assessment of current state of the art showed good potential for directdrive permanent magnet synchronous generators (PMSG). A radial flux topology of the direct-drive PMSG was further examined to verify its suitability to FWT. The generator design was qualified based on its structural integrity and ability to ensure minimal overall impact. The results showed that limiting the generator weight without compromising air-gap tolerances or tower-foundation upgrades was the biggest challenge. Further research was required to verify the dynamic response and component loading to be at an acceptable level. The concluding part of research investigated the dynamic behaviour of the directdrive generator and the various processes that controlled its performance in a FWT. For this purpose, a fully coupled aero-hydro-servo-elastic model of direct-drive FWT was developed. This exercise yet again highlighted the weight challenge imposed by the direct-drive system entailing extra investment on structure. The drive-train dynamics were analysed using a linear combination of multi-body simulation tools namely HAWC2 and SIMPACK. Shaft misalignment, its effect on unbalanced magnetic pull and the main bearing loads were examined. The responses were found to be within acceptable limits and the FWT system does not appreciably alter the dynamics of a direct-drive generator. Any extra investment on the structure is expected to be outweighed by the superior performance and reliability with the direct-drive generator. In summary, this research proposes new solutions to increase the general understanding of hydrodynamics of FWTs and encourages the implementation of direct-drive generators for FWTs. It is believed that the solutions proposed through this research can potentially help address the design challenges of FWTs

Association of Kinesthetic and Read-Write Learner with Deep Approach Learning and Academic Achievement

Background: The main purpose of the present study was to further investigate study processes, learning styles, and academic achievement in medical students.Methods: A total of 214 (mean age 22.5 years) first and second year students - preclinical years - at the Asian Institute of Medical Science and Technology (AIMST) University School of Medicine, in Malaysia participated.  There were 119 women (55.6%) and 95 men (44.4%).   Biggs questionnaire for determining learning approaches and the VARK questionnaire for determining learning styles were used.  These were compared to the student’s performance in the assessment examinations.Results: The major findings were 1) the majority of students prefer to study alone, 2) most students employ a superficial study approach, and 3) students with high kinesthetic and read-write scores performed better on examinations and approached the subject by deep approach method compared to students with low scores.  Furthermore, there was a correlation between superficial approach scores and visual learner’s scores.Discussion: Read-write and kinesthetic learners who adopt a deep approach learning strategy perform better academically than do the auditory, visual learners that employ superficial study strategies.   Perhaps visual and auditory learners can be encouraged to adopt kinesthetic and read-write styles to enhance their performance in the exams

Microsoft Word - SEAJME2009[1]final.15.9.09_ver2003_gaew.doc

Abstract Introduction: An assortment of learning styles is adopted by medical students. Some like to learn by seeing, some by hearing and some by demonstration. Understanding their preferred learning styles as visual, auditory, read-write or kinesthetic learners will help improve the teaching methods adopted. Objective and Goal: role of the educator necessitates making the most of each teaching opportunity by understanding the characteristics of the learning audience and incorporating demonstrated principles of adult educational design, with a focus on collaborative learning and variety in presentation techniques. The goal is to provide student oriented education, producing efficient doctors. Design and participants: A cross-sectional study among 214 medical students of the AIMST University, conducted in 2008. Main outcome measures were: 1. Learning style {visual (V), auditory (A), readwrite(R), kinesthetic (K)} 2. Preferred study practice (alone, in pairs or in groups). Results and Discussion: Preference for different learning styles were, visual (V) 9%, auditory (A) 28%, reading/writing (R) 38% and kinesthetic (K) 35%. 51.4 % of the total 214 students preferred a single mode of information presentation (either V, A, R, or K). Of the 104 students (48.6 % of the total 214 ) who preferred multiple modes of information presentation, some preferred two modes (bimodal, 25%), some preferred three modes (tri-modal, 12%), and some preferred four modes (quadri-modal, 67%). Practical implications: With growing interest in learning styles, an awareness of students' preferences will be of particular value in designing course delivery strategies which combine an appropriate mix of lectures, Problem based learning (PBL) sessions and practical hours. Originality/value: Multiplicity exists in the learning styles of students and the accomplishment of teaching goals is based on the ability to understand the complexity and to use the knowledge of these differences to balance these disparities among the students in a class

A 5 MW direct-drive generator for floating spar-buoy wind turbine: Drive-train dynamics

This article proceeds with investigations on a 5 MW direct-drive floating wind turbine system (FWTDD) that was developed in a previous study. A fully integrated land-based direct-drive wind turbine system (WTDD) was created using SIMPACK, a multi-body simulation tool, to model the necessary response variables. The comparison of blade pitch control action and torque behaviour with a similar land-based direct-drive model in HAWC2 (an aero-elastic simulation tool) confirmed that the dynamic feedback effects can be ignored. The main shaft displacements, air-gap eccentricity, forces due to unbalanced magnetic pull (UMP) and the main bearing loads were identified as the main response variables. The investigations then proceed with a two-step de-coupled approach for the detailed drive-train analysis in WTDD and FWTDD systems. The global motion responses and drive-train loads were extracted from HAWC2 and fed to stand-alone direct-drive generator models in SIMPACK. The main response variables of WTDD and FWTDD system were compared. The FWTDD drive-train was observed to endure additional excitations at wave and platform pitch frequencies, thereby increasing the axial components of loads and displacements. If secondary deflections are not considered, the FWTDD system did not result in any exceptional increases to eccentricity and UMP with the generator design tolerances being fairly preserved. The bearing loading behaviour was comparable between both the systems, with the exception of axial loads and tilting moments attributed to additional excitations in the FWTDD system

Results of IEA Wind TCP Workshop on a Grand Vision for Wind Energy Technology

The wind industry has realized substantial growth reaching over 500 gigawatts (0.5 terawatts) of installed capacity in 2017 (Global Wind Energy Council 2018) and producing about 5% of global electricity demand in 2016 (Wiser and Bolinger 2018). The levelized cost of energy (LCOE) for wind energy projects both on land and offshore has fallen as a result of substantial innovation over the last several decades. More specifically, equipment, installation, and operation costs have decreased while energy production per turbine has increased (Wiser et al. 2016). At the same time as LCOE has been decreasing, integration challenges in the broader electric system have been successfully addressed in many markets, thereby enabling the level of wind energy generation to grow to more than 10% of electricity consumption in at least eight countries around the world and more than 30% in Portugal and Denmark (Wiser and Bolinger 2018)

An overview and prospective on Al and Al-ion battery technologies

Aluminum batteries are considered compelling electrochemical energy storage systems because of the natural abundance of aluminum, the high charge storage capacity of aluminum of 2980 mA h g−1/8046 mA h cm−3, and the sufficiently low redox potential of Al3+/Al. Several electrochemical storage technologies based on aluminum have been proposed so far. This review classifies the types of reported Al-batteries into two main groups: aqueous (Al-ion, and Al-air) and non-aqueous (aluminum graphite dual-ion, Al-organic dual-ion, Al-ion, and Al-sulfur). Specific focus is given to Al electrolyte chemistry based on chloroaluminate melts, deep eutectic solvents, polymers, and “chlorine-free” formulations.ISSN:0378-7753ISSN:1873-275