Gaillimh, Ireland
Gaillimh, Ireland

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Dinh V.-N.,Galway Technology Park | Basu B.,Trinity College Dublin | Nagarajaiah S.,Rice University
Smart Structures and Systems | Year: 2016

A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses. Copyright © 2016 Techno-Press, Ltd.

Williams D.,Galway Technology Park
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2015

In many harsh environment or high current regions (e.g. West of Shetlands, East Africa and GoM) wellhead fatigue during drilling or workover activities can be a major concern. As a result extensive wellhead and conductor fatigue assessments are required in order to predict likely fatigue damage prior to landing the BOP on to the wellhead. These pre-drilling or predictive studies are based on a number of assumptions regarding actual environmental and soil conditions. In addition the uncertainty associated with the input data requires safety factors of 10 and 20 for wave and VIV effects respectively. As a result of these assumptions the predicted levels of fatigue damage to the wellhead may be highly conservative. In cases where wellhead and conductor fatigue life is a concern the operator may choose to deploy motion monitoring systems on the BOP stack so that actual fatigue loads recorded during drilling can be calculated. These systems can be configured to provide 'real-Time' updates on fatigue damage accumulation or can be used to record data for 'post- drilling' assessment. In each case the methodology applied to calculate stresses at fatigue hotspots is critical to the calculation of overall fatigue damage. The calculation of fatigue loads based on measured data is typically carried out by applying the measured BOP motions to a global finite element model of the drilling riser and wellhead system. However due to the large amounts of data involved this can be a very time consuming exercise and is not conducive to 'real-Time' presentation of results (e.g. for on-board systems). A proposed solution to this problem is to develop stress transfer functions (STFs) that relate BOP motion to stresses at critical fatigue hotspots. Thus 'real-Time' BOP motions and be instantly converted to 'real-Time' stresses. However, as is outlined in this paper, the frequency content of the system response can have a significant impact on the levels of stress calculated. If frequency dependent response is not accounted for a significant under-prediction in fatigue loads may occur. The objective of this paper is to outline a detailed methodology to derive STFs for critical fatigue hotspots in the wellhead and conductor. This methodology accounts for capturing the non-linear frequency dependence of the system and incorporating this into the STFs. In addition a methodology for rapidly calculating 'real-Time' fatigue damage accumulation in the wellhead and conductor system and presenting this data on-board is also outlined. © 2015 by ASME.

Quigley C.,Galway Technology Park | Williams D.,Galway Technology Park
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2015

As the industry continues to push the boundaries of offshore exploration into deeper water depths and harsher environments there is an increased need to ensure the integrity of both the drilling riser and wellhead in the event of loss of station-keeping in dynamically positioned (DP) rigs. In order to determine vessel limiting operating/alert offsets it is necessary to carry out a vessel drift-off analysis which predicts the vessel drift-off speed and direction in the event of a DP failure. This analysis is typically performed for a limited combination of environmental conditions (usually collinear wind, wave and current) and will generally assume a vessel position that is directly above the wellhead. Whilst the results of the standard drift-off analysis, and associated drift-off plots, are useful in determining expected drift-off speed and feasibility of the emergency disconnect sequence (EDS), the outputs are of little operational use to the rig personnel in determining allowable operational/alert offsets for day to day operations. As the vessel is rarely located directly above the wellhead and environmental conditions can vary significantly in both direction and magnitude over the drilling campaign a more comprehensive analysis methodology and set of load cases is required in order to develop useful inputs to the well specific operating guidelines (WSOG). The current standard industry approach is to generate drilling riser operability envelopes independently of drift-off curves and thus recommended operating offsets do not account for drift-off speed, reaction times or EDS times. This can lead to a potential lack of conservatism in WSOG. In order to avoid this lack of conservatism in calculation of operating offsets a coupled steady-state/transient response analysis approach is required to ensure that a DP failure event at limiting operational offset does not lead to damage to the wellhead or riser system. A new revised methodology for the calculation of allowable operating windows and associated alert offsets is presented in this paper. This new methodology couples both the steady state operating limits of the vessel and the transient system response during a drift-off, due to DP failure, in order to present a comprehensive go/no-go operability chart of allowable offsetvs. environment for use as input to the WSOG. © 2015 by ASME.

Kraan S.,Galway Technology Park
Journal of Applied Phycology | Year: 2016

The Asian invasive brown seaweed Undaria pinnatifida was found for the first time in the Republic of Ireland in Kilmore Quay in Co. Wexford in July 2016. As this brown kelp is of considerable economic importance and is cultivated in Asia as well as in Europe, it opens up the discussion if this invasive species is socially acceptable to be cultivated in the Republic of Ireland for food and other purposes. This paper briefly examines the global economic importance, cultivation aspects compared to the European native equivalents such as Alaria esculenta and Saccharina latissima, cultivation yield, economic considerations and the ecological impact of the spread of Undaria into non-native areas. Based on the information and facts presented, it is concluded that Undaria from a physical, social and economic point of view can be cultivated in Ireland. © 2016 The Author(s)

Williams D.,Galway Technology Park | Ashton P.,National University of Ireland
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

As has been noted in industry publications and conferences in the recent past the use of more modern deepwater capable 5th and 6th generation semisubmersible drilling rigs in relatively shallow water applications (when compared to design water depth) is likely to become more commonplace. Water depths of 500m or less will necessitate the use of mooring systems in order to maintain position close to the well centre whilst drilling. For fatigue assessments of moored MODUs, the current industry practice to estimate fatigue damage in the drilling riser and the wellhead, using global riser analysis techniques, is to consider both wave and VIV fatigue effects. Standard wave fatigue analysis considers two key response parameters, firstly the impact of the hydrodynamic loading on the riser joints due to drag forces, inertia and added mass effects, and secondly the effects of vessel motions on the riser system and wellhead loading. Standard practice for wave fatigue analysis is to consider only first order motion effects as described by the vessel RAO (response amplitude operator). However, for a moored MODU low frequency (100s-200s period) vessel response can have a significant impact on the overall vessel motions. The actual response and magnitude of MODU motion will be influenced by the size and displacement of the vessel in addition to the configuration of the mooring system. First order lateral motions for a semisubmersible tend to increase as wave period is increased and therefore at lower periods first order motions can be quite low. However, the opposite can be said of wave drift forces that contribute to second order response. Although the wave drift forces are largest for lower wave periods, these low period drift forces have a significant influence on the resulting long period second order response of a moored MODU. This has important implications for drilling riser and wellhead fatigue analysis as in many cases the critical seastates for fatigue damage are low period seastates with a large number of occurrences. Thus the current global analysis techniques for fatigue calculations may lead to an underestimation of fatigue damage contribution from low period seastates. The purpose of this paper is to present the key conclusions and findings of a study carried out in order to determine the effects of low frequency moored MODU motions on wellhead fatigue. These results are derived from a case study of a moored 6th generation semi-submersible drilling vessel in 500m water depth. Copyright © 2014 by ASME.

Holdt S.L.,Technical University of Denmark | Kraan S.,Galway Technology Park
Journal of Applied Phycology | Year: 2011

Seaweed is more than the wrap that keeps rice together in sushi. Seaweed biomass is already used for a wide range of other products in food, including stabilising agents. Biorefineries with seaweed as feedstock are attracting worldwide interest and include low-volume, high value-added products and vice versa. Scientific research on bioactive compounds in seaweed usually takes place on just a few species and compounds. This paper reviews worldwide research on bioactive compounds, mainly of nine genera or species of seaweed, which are also available in European temperate Atlantic waters, i. e. Laminaria sp., Fucus sp., Ascophyllum nodosum, Chondrus crispus, Porphyra sp., Ulva sp., Sargassum sp., Gracilaria sp. and Palmaria palmata. In addition, Undaria pinnatifida is included in this review as this is globally one of the most commonly produced, investigated and available species. Fewer examples of other species abundant worldwide have also been included. This review will supply fundamental information for biorefineries in Atlantic Europe using seaweed as feedstock. Preliminary selection of one or several candidate seaweed species will be possible based on the summary tables and previous research described in this review. This applies either to the choice of high value-added bioactive products to be exploited in an available species or to the choice of seaweed species when a bioactive compound is desired. Data are presented in tables with species, effect and test organism (if present) with examples of uses to enhance comparisons. In addition, scientific experiments performed on seaweed used as animal feed are presented, and EU, US and Japanese legislation on functional foods is reviewed. © 2011 Springer Science+Business Media B.V.

Calvey D.,Galway Technology Park | Mee L.,National University of Ireland
Journal of Renal Care | Year: 2011

The phenomenon of experiencing life dependent on haemodialysis is infinitely multi-faceted. It effects all aspects of people's lives, and not only their lives, but those of the people around them. Busy dialysis units often do not have time to explore these effects on the lives of their patients outside the clinical setting. Aims: The aim of this qualitative study was to step into the lives of seven patients once they were outside the dialysis unit. Method: Seven chronic haemodialysis patients were selected and interviewed using an in-depth semi-structured approach, following the philosophy of Heidegger. Data was analysed using Colaizzi's seven-stage process. Results: The strongest common theme emerged through descriptions of the patient's 'Sense of Self', within which emerged sub-themes; The Future Self, The Living Self, The Mortal/Fragile Self and The Growing/Learning Self. These were further explored and related back to importance of awareness of such findings within the renal haemodialysis practice setting. © 2011 European Dialysis and Transplant Nurses Association/European Renal Care Association.

Bohan P.,Galway Technology Park | Lang D.,Galway Technology Park
Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE | Year: 2014

Experience with modern ultra-deepwater capable drilling vessels and their associated marine riser tensioner systems has led to increased concerns over tensioner load variations in extreme environments. Modern drilling riser tensioners are complex hydro-pneumatic systems whereby the tension applied at the slip-ring can vary significantly with tensioner stroke in response to vessel heave. The aforementioned tensioner load variations that occur with modern tensioner systems can have a significant effect on the loads transferred to the wellhead and conductor/casing. This can lead to fatigue concerns at critical locations. The connectors along the conductor and surface casing can be highly susceptible to fatigue if they are located in regions of high bending loads below the mudline. This paper will give a detailed overview of recent technology advancements that have been incorporated into the latest version of an industry-standard tool for global analysis of drilling risers. Copyright © 2014 by ASME.

Kraan S.,Galway Technology Park
Mitigation and Adaptation Strategies for Global Change | Year: 2013

Global demand for bio-fuels continues unabated. Rising concerns over environmental pollution and global warming have encouraged the movement to alternate fuels, the world ethanol market is projected to reach 86 billion litres this year. Bioethanol is currently produced from land-based crops such as corn and sugar cane. A continued use of these crops drives the food versus fuel debate. An alternate feed-stock which is abundant and carbohydrate-rich is necessary. The production of such a crop should be sustainable, and, reduce competition with production of food, feed, and industrial crops, and not be dependent on agricultural inputs (pesticides, fertilizer, farmable land, water). Marine biomass could meet these challenges, being an abundant and carbon neutral renewable resource with potential to reduce green house gas (GHG) emissions and the man-made impact on climate change. Here we examine the current cultivation technologies for marine biomass and the environmental and economic aspects of using brown seaweeds for bio-ethanol production. © 2010 Springer Science+Business Media B.V.

O'Grady R.,Galway Technology Park | Harte A.,National University of Ireland
Ocean Engineering | Year: 2013

As offshore oil and gas developments move into ultra-deep water depths, the greater the impact onerous installation procedures will have on pipeline integrity. Current approaches for predicting this impact are mostly based on a global pipeline perspective, using installation analysis tools that model the entire length of suspended pipeline using a string of 'pipe' finite elements. While these analysis methods are proven to provide reasonable predictions for moderate installation loadings, they lack sufficient detail for considering the most extreme conditions and do not generally account for material plasticity, residual curvature and pipe twist. This lack of detail could represent a significant shortcoming in future developments where pipe joints will be subjected to more substantial loading during ultra-deep water installation. A detailed local finite element model of the pipe cross-section during installation has been developed that allows for greater insight into the actual as-laid condition of a given pipeline. Numerous installation scenarios are considered and comparisons are made with output from traditional global analysis methods. These comparisons demonstrate potential shortcomings of existing engineering design approaches for ultra-deep water. This ultimately leads to recommendations that will shape on-going developments in design methods. © 2013 Elsevier Ltd.

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