Browsing by Author "Brennan, Feargal P."
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Item Open Access A cluster analysis of investment strategies in the offshore wind energy market(Institute of Electrical and Electronics Engineers, 2017-08-18) Ioannou, Anastasia; Vaienti, Claudio; Angus, Andrew; Brennan, Feargal P.This paper maps different investor strategies in the offshore wind energy market based on data from existing wind farms in the UK. This is realized through the employment of cluster analysis, which classifies offshore wind energy investors - who have purchased equity stakes-in terms of the entry timing, exit timing, purchase timing and stake purchased. We, then, perform a SWOT analysis to identify the major strengths, weaknesses, opportunities and threats encountered by each cluster of stakeholders. Cluster analysis revealed the existence of three distinct investment strategy profiles: i) Late entry investors, ii) Pre-commissioning investors, and iii) Own-build-transfer investors. Corporate and institutional investors tend to be late entry investors, whose strategy is based on buying assets while they are fully operational avoiding construction risks, retaining a risk aversion profile. The exit timing of OEMs and EPCI contractors usually takes place before or right after the commissioning of the wind farm. Finally, major Utilities tend to keep the operating assets on their balance sheet and divest only part of them (mostly minority stakes) during the operating stage; Independent energy companies are found in both 2nd and 3rd cluster; however, exceptions may be observed.Item Open Access Corrosion fatigue crack growth mechanisms in offshore monopile steel weldments(Wiley, 2017-04-20) Adedipe, Oyewole; Brennan, Feargal P.; Mehmanparast, Ali; Kolios, Athanasios; Tavares, IsaacOffshore structures are generally fabricated of welded joints, which are considered as potential spots for crack initiation owing to the degree of stress concentrations imposed by the weld geometry and the effects of residual stresses introduced by welding processes. There are significant numbers of the current and anticipated offshore installations coupled with the use of newer materials and fabrication techniques. It is therefore important to understand the crack growth mechanisms in these structures accompanied with the effects of mean or residual stresses for a safe estimation of their service lives. In this paper, crack growth results of HAZ and weld materials similar to those used for offshore installations are presented. Tests were conducted in air and in simulated free-corrosion conditions at loading frequencies of 0.3 Hz in seawater, 5 Hz in air and at loading ratios of 0.1, 0.5 and 0.7. Results showed that crack growth rates were influenced by mean stresses, materials microstructure accompanied by welding procedure and environment. Crack growth results showed good agreement when compared with those obtained from other steels used for offshore structures.Item Open Access Design implications towards inspection reduction of large scale structures(Elsevier, 2017-05-09) Ioannou, Anastasia; Wang, Lin; Brennan, Feargal P.Operational management is a key contributor in life cycle costs, especially for large scale assets which are in most times complex in structural hierarchy and with a large nominal service life. Decisions on the operational management may concern the number of inspections or maintenance strategies which may allow full utilization of structural capacity or sacrifice residual life in order to avoid an unscheduled intervention. Design of such assets is often governed by design standards which offer the designer the flexibility to take certain decisions that may affect the CAPEX to OPEX ratio such as that of building a more robust structure which may eliminate the need for costly inspection operations. This paper is investigating this approach, taking the example of offshore wind turbine support structures as the reference case, and examines the relevant provisions of the DNV-Os-J101 Standard with respect to the design implications that such a decision may have to the overall life-cycle cost of the structure. Assessment of the structural properties under different design conditions is evaluated through a combination of detailed cost model and an iterative optimization algorithm. The approach which is followed and documented, can be applicable to other complex structural systems for decision making through evaluation of service life costs. Paper presented at: Complex Systems Engineering and Development Proceedings of the 27th CIRP Design Conference Cranfield University, UK 10th – 12th May 2017.Item Open Access Development of a defined compost system for the study of plant-microbe interactions(Nature Publishing Group, 2020-05-05) Masters-Clark, Emily; Shone, E.; Paradelo, M.; Hirsch, Penny R.; Clark, Ian M.; Otten, Wilfred; Brennan, Feargal P.; Mauchline, T. H.Plant growth promoting rhizobacteria can improve plant health by providing enhanced nutrition, disease suppression and abiotic stress resistance, and have potential to contribute to sustainable agriculture. We have developed a sphagnum peat-based compost platform for investigating plant-microbe interactions. The chemical, physical and biological status of the system can be manipulated to understand the relative importance of these factors for plant health, demonstrated using three case studies: 1. Nutrient depleted compost retained its structure, but plants grown in this medium were severely stunted in growth due to removal of essential soluble nutrients - particularly, nitrogen, phosphorus and potassium. Compost nutrient status was replenished with the addition of selected soluble nutrients, validated by plant biomass; 2. When comparing milled and unmilled compost, we found nutrient status to be more important than matrix structure for plant growth; 3. In compost deficient in soluble P, supplemented with an insoluble inorganic form of P (Ca3(PO4)2), application of a phosphate solubilising Pseudomonas strain to plant roots provides a significant growth boost when compared with a Pseudomonas strain incapable of solubilising Ca3(PO4)2. Our findings show that the compost system can be manipulated to impose biotic and abiotic stresses for testing how microbial inoculants influence plant growth.Item Open Access Dynamic modelling of microalgae cultivation process in high rate algal wastewater pond(Elsevier, 2016-11-04) Bello, Muhammadu; Ranganathan, Panneerselvam; Brennan, Feargal P.In this work, a comprehensive dynamic mathematical modelling to simulate the production of microalgae in a high rate algal pond (HRAP) is attempted. A synergetic algal–bacterial system comprising various interrelated biological and chemical system processes is presented. The dynamic behaviour of HRAP system is studied by solving mass balance equations of different components which account light intensity and gas–liquid mass transfer. The model predictions are compared with the previously reported studies in the literature. The influence of kinetic and operating parameters, including the supply of CO2, the maximum growth rate, pond depth and dilution rates, on the pond performance are evaluated. The sensitivity analysis of important process parameters is also discussed in this study. The developed model, as a tool, can be used to assess the factors that affect the pond performance criteria, including algal productivity and the dynamics of nutrient requirements.Item Open Access The effect of residual stresses arising from laser shock peening on fatigue crack growth(Elsevier, 2010-07) Chahardehi, Amir Ebrahim; Brennan, Feargal P.; Steuwer, AxelResidual stresses have in the past been introduced to manipulate growth rates and shapes of cracks under cyclic loads. Previously, the effectiveness of shot peening in retarding the rate of fatigue crack growth was experimentally studied. It was shown that the compressive residual stresses arising from the shot peening process can affect the rate of crack growth. Laser shock peening can produce a deeper compressive stress field near the surface than shot peening. This advantage makes this technique desirable for the manipulation of crack growth rates. This paper describes an experimental program that was carried out to establish this effect in which steel specimens were partially laser peened and subsequently subjected to cyclic loading to grow fatigue cracks. The residual stress fields generated by the laser shock peening process were measured using the neutron diffraction technique. A state of compressive stress was found near the surface and tensile stresses were measured in the mid-thickness of the specimens. Growth rates of the cracks were observed to be more affected by the tensile core than by the compressive surface stresses.Item Open Access Fatigue Crack Control in Structural Details using surface peening(Society of Naval Architects and Marine Engineers (SNAME), 2008-08) Brennan, Feargal P.; Shi Song, NgiamThis paper presents an analytical and experimental study of crack shape evolution in steel plate specimens under cyclic loading. It is widely known that the introduction of compressive residual stresses by cold working the surface can be highly beneficial in improving the fatigue performance of structural components. Although it is recognised that relaxation of surface compressive residual stress can reduce the potential benefits, the effects of residual stress on crack shape evolution are often overlooked. Previous studies have shown that the intensity of the surface compressive residual stress has a pronounced effect on fatigue crack initiation. A recently developed technique termed controlled stitch cold working, which applies differing intensities of compressive residual stress at specific regions in a structure, is shown in the paper to influence fatigue crack propagation life considerably. The approach can be used to prevent crack growth in particular directions for example encouraging a controlled or fail-safe scenario. The paper describes fatigue crack growth tests on shot peened specimens tested under uniaxial tension. The specimens were peened to varying intensities and of differing coverage areas. Cracks were initiated from starter notches after peening meaning the approach can be used for fatigue performance enhancement at the construction stage or later as part of a maintenance and repair strategy. Crack growth retardation is apparent in all tests and this is attributed to the constrained crack shape. Further work will consider the use of laser and ultrasonic peening to contain cracks from rapidly propagating from stress concentrations. This approach used with careful design of stiffness can significantly extend the fatigue crackItem Open Access Fatigue crack growth rates for offshore wind monopile weldments in air and seawater: SLIC inter-laboratory test results(Elsevier, 2016-11-02) Mehmanparast, Ali; Brennan, Feargal P.; Tavares, IsaacThe majority of fatigue crack growth (FCG) data sets available on steels in air and seawater environments are several decades old and may not be appropriate for structural integrity assessment of offshore wind turbine foundations, which are fabricated using contemporary materials and welding technologies. Therefore, the SLIC joint industry project was formed to investigate the fatigue crack initiation and growth behaviour in offshore wind welded steel foundations. The FCG test data from the SLIC inter-laboratory (round robin) test programme have been analysed using a new proposed shape function solution and the results are presented and discussed. The obtained FCG trends in air and seawater environments have been compared with the recommended trends available in standards. The Paris-law constants and ΔKth values obtained from this programme can be used for defect assessment and remaining life prediction of offshore monopile weldments in air and seawater environments. The results from the SLIC project show that for a given value of ΔK the fatigue crack growth rate, da/dN, is on average around 2 times higher in seawater compared to air for the base metal and weldments. This factor of 2 in the seawater environment is almost half of the crack acceleration factor recommended by standards.Item Open Access Influence of statistical uncertainty of component reliability estimations on offshore wind farm availability(Elsevier, 2017-05-05) Scheu, Matti Niclas; Kolios, Athanasios; Fischer, Tim; Brennan, Feargal P.Offshore wind turbine reliability, one of the industry's biggest sources of uncertainty, is the focus of the present paper. Specifically the impact of uncertain component failure distributions at constant failure rates has been investigated with respect to its implications for wind farm availability. A fully probabilistic offshore wind simulation model has been applied to quantify results; effects shown in this paper underline the significant impact that failure probability distributions have on asset performance evaluation. It was found that wind farm availability numbers may vary in the range up to 20 % just by changing the distributions of failure to a different pattern; in particular those scenarios in which extensive failure accumulation occurred led to significant losses in production. Results are interpreted and discussed mainly from the viewpoint of an offshore wind farm developer, owner and operator, with implications underlined for application in state-of-the-art offshore wind O&M (Operations and Maintenance) models and simulation tools.Item Open Access Life cycle optimization for sustainable algal biofuel production using integrated nutrient recycling technology(American Chemical Society, 2017-09-18) Bello, Muhammadu; Ranganathan, Panneerselvam; Brennan, Feargal P.In this study, a multi-objective optimization of sustainable integration of algal biofuel production using nutrient recycling technology, such as anaerobic digestion and hydrothermal liquefaction, is considered. Gross annual profitability and global warming potential (GWP) are the criteria chosen for the design of the algal biofuel production system. Three scenarios, such as full-scale (baseline), pilot-scale (conservative), and lab-scale (nominal), are chosen based on the expected maturity levels and nutrient demand. The results of the optimization produce Pareto sets of optimal solutions for acknowledging the trade-off between the economic and the environmental criteria of the integrated system. It is found that the anaerobic digestion (AD) technology shows better performance in terms of an environmental perspective, displacing the excessive fertilizer requirements due to its maturity in comparison with the hydrothermal liquefaction (HTL) process. However, HTL is a new, evolving, promising nutrient recycling technology which demonstrates economic preferences compared to the AD process due to its low cost of production.Item Open Access A novel weight function for RMS stress intensity factor determination in surface cracks(Elsevier, 2010-01) Chahardehi, Amir Ebrahim; Brennan, Feargal P.This paper discusses the problem of stress intensity factor determination in surface cracks. In particular, the concept of root mean square stress intensity factors (RMS SIF) is discussed for the general class of semi-elliptical surface cracks. The weight function SIF derivation method is considered problems with the existing techniques are highlighted, and a novel technique for the derivation of the RMS SIF weight functions for surface cracks is presented and results are compared with numerical solutions for a variety of loadings and geometries.Item Open Access A parametric whole life cost model for offshore wind farms(Springer, 2016-03-14) Shafiee, Mahmood; Brennan, Feargal P.; Armada Espinosa, InesPurpose Life cycle cost (LCC) considerations are of increasing importance to offshore wind farm operators and their insurers to undertake long-term profitable investments and to make electricity generation more price-competitive. This paper presents a cost breakdown structure (CBS) and develops a whole life cost (WLC) analysis framework for offshore wind farms throughout their life span (∼25 years). Methods A combined multivariate regression/neural network approach is developed to identify key cost drivers and evaluate all the costs associated with five phases of offshore wind projects, namely pre-development and consenting (P&C), production and acquisition (P&A), installation and commissioning (I&C), operation and maintenance (O&M) and decommissioning and disposal (D&D). Several critical factors such as geographical location and meteorological conditions, rated power and capacity factor of wind turbines, reliability of sub-systems and availability and accessibility of transportation means are taken into account in cost calculations. The O&M costs (including the cost of renewal and replacement, cost of lost production, cost of skilled maintenance labour and logistics cost) are assessed using the data available in failure databases (e.g. fault logs and O&M reports) and the data supplied by inspection agencies. A net present value (NPV) approach is used to quantify the current value of future cash flows, and then, a bottom-up estimate of the overall cost is obtained. Results and discussion The proposed model is tested on an offshore 500-MW baseline wind farm project, and the results are compared to experimental ones reported in the literature. Our results indicate that the capital cost of wind turbines and their installation costs account for the largest proportion of WLC, followed by the O&M costs. A sensitivity analysis is also conducted to identify those factors having the greatest impact on levelized cost of energy (LCOE). Conclusions The installed capacity of a wind farm, distance from shore and fault detection capability of the condition monitoring system are identified as parameters with significant influence on LCOE. Since the service lifetime of a wind farm is relatively long, a small change in interest rate leads to a large variation in the project’s total cost. The presented models not only assist stakeholders in evaluating the performance of ongoing projects but also help the wind farm developers reduce their costs in the medium–long term.Item Open Access Reliability of floating foundation concepts for vertical axis wind turbines(2010-12-31T00:00:00Z) Kolios, Athanasios J.; Collu, Maurizio; Brennan, Feargal P.; Sphaler, S. H.; Estefen, S. F.; Pasqualino, I. P.Offshore wind turbines are developing at a rapid pace. By far the most common turbine configuration is the HAWT (Horizontal Axis Wind Turbine) and development of these machines is largely centered about drive train and blade issues with some work concerning foundations/ supporting structures. Several teams around the world are developing floating supporting structures for HAWT, mainly for deep water deployment. This paper describes the development of a floating support structure for Vertical Axis Wind Turbines (VAWT) with particular focus on structural/survival risk and reliability. Unlike Oil & Gas floating support structures, wind turbine floaters need to resist significant dynamic wind and machine loading in addition to wave excitation. Coupling of dynamic response modes can be difficult and consideration of these within a reliability framework presents several challenges. The paper describes a simplified procedure for risk assessment so that potential areas of concern can be quickly identified and uses a VAWT to illustrate the methods and reasoning employed.Item Open Access Report of Committee III.2: fatigue and fracture(Elsevier, 2003-12-31) Brennan, Feargal P.COMMITTEE MANDATE Concern for crack initiation and growth under cyclic loading as well as unstable crack propagation and tearing in ship and offshore structures. Due attention shall be paid to practical application and statistical description of fracture control methods in design, fabrication and service. Consideration is to be given to the suitability and uncertainty of physical models. The work shall be coordinated with that of Committee V.2.Item Open Access Risk-based methods for sustainable energy system planning: a review(Elsevier, 2017-03-02) Ioannou, Anastasia; Angus, Andrew; Brennan, Feargal P.The value of investments in renewable energy (RE) technologies has increased rapidly over the last decade as a result of political pressures to reduce carbon dioxide emissions and the policy incentives to increase the share of RE in the energy mix. As the number of RE investments increases, so does the need to measure the associated risks throughout planning, constructing and operating these technologies. This paper provides a state-of-the-art literature review of the quantitative and semi-quantitative methods that have been used to model risks and uncertainties in sustainable energy system planning and feasibility studies, including the derivation of optimal energy technology portfolios. The review finds that in quantitative methods, risks are mainly measured by means of the variance or probability density distributions of technical and economical parameters; while semi-quantitative methods such as scenario analysis and multi-criteria decision analysis (MCDA) can also address non-statistical parameters such as socio-economic factors (e.g. macro-economic trends, lack of public acceptance). Finally, untapped issues recognised in recent research approaches are discussed along with suggestions for future research.Item Open Access Stochastic prediction of offshore wind farm LCOE through an integrated cost model(Elsevier, 2017-03-09) Ioannou, Anastasia; Angus, Andrew; Brennan, Feargal P.Common deterministic cost of energy models applied in offshore wind energy installations usually disregard the effect of uncertainty of key input variables – associated with OPEX, CAPEX, energy generation and other financial variables – on the calculation of levelized cost of electricity (LCOE). The present study aims at expanding a deterministic cost of energy model to systematically account for stochastic inputs. To this end, Monte Carlo simulations are performed to derive the joint probability distributions of LCOE, allowing for the estimation of probabilities of exceeding set thresholds of LCOE, determining certain confidence intervals. The results of this study stress the importance of appropriate statistical modelling of stochastic variables in order to reduce modelling uncertainties and contribute to a better informed decision making in renewable energy investments.Item Open Access Stress Monitoring of Civil and Mechanical Engineering Infrastructure(British Institute of Non-Destructive Testing, 2007-06) Brennan, Feargal P.Structural Integrity Monitoring is a rapidly growing science and practice which promises in the future to measure and record every shudder and twitch within the lifetime of future structural components. Indeed, structures will undoubtedly possess nervous systems which will sense and instantly communicate loading and damage information; however, it is timely to stand back and consider what is required from such systems before we drown in yotta-bytes of monitored data. The electronics industry is rapidly developing clever wireless data transmission and more efficient storage methods, with increased sampling frequencies and multiplexing technologies which can distract even the most focused Civil or Mechanical Engineer. Stress measurement and monitoring is more complex than traditional NDT which considers defect and crack detection, but if understood properly can in some ways be much simpler and promises safer and better optimised structures. The paper reports several case studies of stress monitoring in Rail applications and of Steel Structures using Stress Memory Technology and will discuss how stress monitoring systems might be evaluated in terms of reliability and value.Item Open Access Weld toe stress concentrations in multi-planar stiffened tubular KK joints(Elsevier Science B.V., Amsterdam., 2009-01-31T00:00:00Z) Woghiren, C. O.; Brennan, Feargal P.This paper reports a parametric stress analysis of various configurations of rack plate stiffened multi-planar welded KK joints using the finite element method. The KK joint finds application in the leg structure of offshore oil and gas jack-up platforms. The rack plate works as a stiffener which reduces the stress concentration at the brace/chord intersection. This could be an immense contribution to the increase in fatigue life of the joint, but other hot spot sites are introduced into the joint. The rack is also used for raising and lowering of the jack-up hull which gives the jack-up platform its jacking capability. Over 120 models using a combination of shell and solid elements have been built and analysed with ABAQUS. Non-dimensional joint geometric parameters (beta, gamma and Omega) are employed in the study, with the new parameter Omega being defined as the ratio of rack thickness to chord diameter. Stress concentration factors (SCFs) are calculated under applied axial and OPB (out-of- plane bending) loading. Three critical SCF locations are identified for each load case, with each location becoming the most critical based on the combination of the non-dimensional parameters selected for the joint. This is important as careful design can shift the critical SCIF from an area inaccessible to NDT to one that can be easily inspected. The SCF values extracted from the models are used to derive six parametric equations through multiple regression analysis performed using MINITAB. The equations describe the SCF at the different locations as a function of the non-dimensional ratios. The equations not only allow the rapid optimisation of multi-planar joints but also can be used to quickly identify the location of maximum stress concentration and hence the likely position of fatigue cracks. This in itself is an invaluable tool for planning NDT procedures and schedules. 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