CERES :: Browsing by Author "Brennan, Feargal P."

Browsing by Author "Brennan, Feargal P."

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Open Access
Carbon Brainprint Case Study: novel offshore vertical axis wind turbines
(2011-07-31T00:00:00Z) Parsons, David J.; Chatterton, Julia C.; Brennan, Feargal P.; Kolios, Athanasios J.
As part of the transition to a ‘low carbon economy', renewable technologies are expected toplay an increasing role in reducing dependence on fossil fuels for energy and electricity. Windpower in particular is likely to become a much larger contributor to the UK's energy mix. Thecurrent dominant design for large, grid-connected wind turbines is a three blade rotor with ahorizontal rotating axis. The concept of a vertical axis wind turbine (VAWT) is relatively new, buthas several advantages over horizontal axis alternatives. It is able to capture the wind from anydirection, and the vertical axis is such that the rotor equipment is located at base level, makingit is simpler and less costly to install and maintain. The Energy Technologies Institute (ETI) is a UK-based company formed from global industriesand the UK government. One of three projects looking at new turbine design and concepts foroffshore wind is the Novel Offshore Vertical Axis (NOVA) project, a UK-based consortiumlaunched in January 2009 to look at the feasibility of a NOVA turbine. achieved through the installation of NOVA wind turbines, in comparison to conventionalhorizontal axis wind turbines (HAWTs) for offshore power generation. The increased powerrating of the NOVA turbines compared to current HAWTs is expected to provide considerablereductions in lifetime greenhouse gas emissions. It compared the emissions from 1 GWinstallations over 20 years, based on a life cycle analysis of construction, operation anddisposal. The comparison used the popular Vestas V90 3 MW model and the proposed NOVA10 MW units. The estimated lifetime emissions were 521 kt CO2e for the conventional design and419 kt CO2e for NOVA. Using budget share to attribute the reductions to the project partners,Cranfield's brainprint was 34 kt CO2e. As there are no current NOVA units in operation, there were high uncertainties associated withthe estimates. A Monte-Carlo simulation resulted in a mean difference in emissions betweenthe two installations of 102 kt CO2e, with a standard deviation of 108.
Open Access
Carbon brainprint – An estimate of the intellectual contribution of research institutions to reducing greenhouse gas emissions
(Elsevier, 2015-05-07) Chatteron, Julia C.; Parsons, David J.; Nicholls, John R.; Longhurst, Philip J.; Bernon, Mike; Palmer, Andrew; Brennan, Feargal P.; Kolios, Athanasios; Wilson, Ian; Ishiyama, Edward; Clements-Croome, Derek; Elmualim, Abbas; Darby, Howard; Yearly, Tom; Davies, Gareth J.
Research and innovation have considerable, currently unquantified potential to reduce greenhouse gas emissions by, for example, increasing energy efficiency. Furthermore, the process of knowledge transfer in itself can have a significant impact on reducing emissions, by promoting awareness and behavioural change. The concept of the ‘carbon brainprint’ was proposed to convey the intellectual contribution of higher education institutions to the reduction of greenhouse gas emissions by other parties through research and teaching/training activities. This paper describes an investigation of the feasibility of quantifying the carbon brainprint, through six case studies. The potential brainprint of higher education institutes is shown to be significant: up to 500 kt CO2e/year for one project. The most difficult aspect is attributing the brainprint among multiple participants in joint projects.
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.
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, Isaac
Offshore 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.
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.
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.
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.
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, Axel
Residual 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.
Open Access
An Experimental and Analytical study of Fatigue Crack Shape Control by Cold Working
(Elsevier, 2008-02) Brennan, Feargal P.; Ngiam, S. S.; Lee, C. W.
This paper presents an experimental and analytical study of crack shape evolution in steel 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. 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 considerably influence fatigue crack propagation by containing crack propagation in one primary direction.
Open Access
Experimental determination of the overturning moment and net lateral force generated by a novel vertical axis wind turbine: experiment design under load uncertainty
(Blackwell Publishing Ltd, 2013-01-31T00:00:00Z) Kolios, Athanasios J.; Chahardehi, Amir Ebrahim; Brennan, Feargal P.
Recent developments in harnessing wind energy propose new, radically different designs to alleviate some of the difficulties associated with conventional wind turbines. New designs however require testing for a variety of reasons ranging from gaining confidence in the analytical models used in the design and development through to satisfaction of certification requirements. Medium-scale prototype testing of large-scale concepts, where parameters such as the response of the structure and the loading conditions are often highly uncertain demand special consideration. This article presents the design of a special test rig and calculation methodology for the experimental determination of the overturning moment and net force generated by the NOVA Vertical Axis Wind Turbine using a field experimental setup. The design of the experimental model involves dealing with modelling uncertainties as loads in operation and therefore the response of the structure are largely unknown before testing has been carried out. The variability in the wind speed and direction also need to be accommodated for.
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, Ngiam
This 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 crack
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, Isaac
The 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.
Open Access
The Influence of Longitudinal Stiffeners on Weld Toe Stress Concentrations in Multi Planar Tubular KK joints
(Trans Tech Publications, 2007-01-01T00:00:00Z) Woghiren, Charles 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 & Gas jack-up platforms. The rack plate is a dual purpose element of the joint because it firstly functions 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 to 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 were built and analysed within ABAQUS. Non-dimensional joint geometric parameters; β, γ and Ω were employed in the study with Ω being defined as the ratio of rack thickness to chord diameter. Stress Concentration Factors (SCFs) were calculated under applied axial and OPB (out-of-plane-bending) loading. Three critical SCF locations were 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 SCF from an area inaccessible to NDT to one that can be easily inspected. The SCF values extracted from the models were 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.
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.
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.
Open Access
The Modelling, Simulation and Control of a 50 kW Vertical Axis Wind Turbine
(2012-09-13T00:00:00Z) Bati, Akram F.; Brennan, Feargal P.
This paper presents the modelling, Simulation and control of the APP 50 kW vertical axis wind turbine generating unit which is designed and built by Cranfield University, Department of Offshore, Process & Energy Engineering. Because of the increasing interest of Power Distribution companies to connect medium sized wind turbines to reinforce the Low Carbon future 11 kV networks, unit exploration and investigation will add valuable insight into operation scenarios and their effects on the local network. The main objectives of this work are to model all elements, verify the design figures-, analyse the operational aspects of the drive-train and improve the quality of the generated power with respect to the converter, harmonic filter and controller.
Open Access
Multi-criteria assessment of offshore wind turbine support structures
(Elsevier Science B.V., Amsterdam., 2011-11-30T00:00:00Z) Lozano Minguez, Estivaliz; Kolios, Athanasios J.; Brennan, Feargal P.
Wind power, especially offshore, is considered one of the most promising sources of ‘clean’ energy towards meeting the EU and UK targets for 2020 and 2050. Deployment of wind turbines in constantly increasing water depths has raised the issue of the appropriate selection of the most suitable support structures’ options. Based on experience and technology from the offshore oil and gas industry, several different configurations have been proposed for different operational conditions. This paper presents a methodology for the systematic assessment of the selection of the most preferable, among the different configurations, support structures for offshore wind turbines, taking into consideration several attributes through the widely used multi-criteria decision making method TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) for the benchmarking of those candidate options. An application comparing a monopile, a tripod and a jacket, for a reference 5.5 MW wind turbine and a reference depth of 40 m, considering multiple engineering, economical and environmental attributes, will illustrate the effectiveness of the proposed method
Open Access
Non-stationary stochastic optimization of an oscillating water column
(World Academy of Science, Engineering and Technology, 2017-07-31) Jalon, Maria L.; Brennan, Feargal P.
A non-stationary stochastic optimization methodology is applied to an OWC (oscillating water column) to find the design that maximizes the wave energy extraction. Different temporal cycles are considered to represent the long-term variability of the wave climate at the site in the optimization problem. The results of the non-stationary stochastic optimization problem are compared against those obtained by a stationary stochastic optimization problem. The comparative analysis reveals that the proposed non-stationary optimization provides designs with a better fit to reality. However, the stationarity assumption can be adequate when looking at averaged system response.
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.
Open Access
A parametric whole life cost model for offshore wind farms
(Springer, 2016-03-14) Shafiee, Mahmood; Brennan, Feargal P.; Armada Espinosa, Ines
Purpose 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.