Browsing by Author "Brennan, Feargal Peter"

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    Experimental investigation of mechanical and fracture properties of offshore wind monopile weldments: SLIC interlaboratory test results
    (Wiley, 2018-05-31) Mahmanparast, Ali; Taylor, Jessica; Brennan, Feargal Peter; Tavares, I.
    S355 structural steel is commonly used in fabrication of offshore structures including offshore wind turbine monopiles. Knowledge of mechanical and fracture properties in S355 weldments and the level of scatter in these properties is extremely important for ensuring the integrity of such structures through engineering critical assessment. An interlaboratory test programme was created to characterise the mechanical and fracture properties of S355 weldments, including the base metal, heat‐affected zone, and the weld metal, extensively. Charpy impact tests, chemical composition analysis, hardness tests, tensile tests, and fracture toughness tests have been performed on specimens extracted from each of the 3 material microstructures. The experimental test results from this project are presented in this paper, and their importance in structural integrity assessment of offshore wind turbine monopiles has been discussed. The results have shown a decreasing trend in the Charpy impact energy and Jmax values with an increase in yield stress from base metal to heat‐affected zone to weld metal. Moreover, the JIC fracture toughness value in the heat‐affected zone and weld metal is on average around 60% above and 40% below the base metal value, respectively. In addition, the average Charpy impact energy value in the heat‐affected zone and weld metal is around 5% and 30% below the base metal value, respectively. The effects of mechanical and fracture properties on the critical crack size estimates have been investigated, and the results are discussed concerning the impact of material properties on structural design and integrity assessment of monopiles.
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    Linking long‑term soil phosphorus management to microbial communities involved in nitrogen reactions
    (Springer, 2022-02-24) O'neill, R. M.; Duff, A. M.; Brennan, Feargal Peter; Gebremichael, A. W.; Girkin, Nicholas T.; Lanigan, G. J.; Krol, D. J.; Wall, D. P.; Renou‑Wilson, F.; Müller, C.; Richards, K. G.; Deveautour, C.
    The influence of soil phosphorous (P) content on the N-cycling communities and subsequent effects on N2O emissions remains unclear. Two laboratory incubation experiments were conducted on soils collected from a long-term (est. 1995) P-addition field trial sampled in summer 2018 and winter 2019. Incubations were treated with a typical field amendment rate of N as well as a C-amendment to stimulate microbial activity. Throughout both incubations, soil subsamples were collected prior to fertiliser amendment and then throughout the incubations, to quantify the abundance of bacteria (16S rRNA), fungi (ITS) and Thaumarcheota (16S rRNA) as well as functional guilds of genes involved in nitrification (bacterial and archaeal amoA, and comammox) and denitrification (nirS, nirK, nosZ clade I and II) using quantitative PCR (qPCR). We also evaluated the correlations between each gene abundance and the associated N2O emissions depending on P-treatments. Our results show that long-term P-application influenced N-cycling genes abundance differently. Except for comammox, overall nitrifiers’ genes were most abundant in low P while the opposite trend was found for denitrifiers’ genes. C and N-amendments strongly influenced the abundance of most genes with changes observed as soon as 24 h after application. ITS was the only gene correlated to N2O emissions in the low P-soils while microbes were mostly correlated to emissions in high P, suggesting possible changes in the organisms involved in N2O production depending on soil P-content. This study highlights the importance of long-term P addition on shaping the microbial community function which in turn stimulates a direct impact on the subsequent N emissions.
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    Reanalysis of offshore T-joint fatigue life predictions based on a complete weld profile model
    (Elsevier, 2014-06-20) Lozano-Minguez, Estívaliz; Brennan, Feargal Peter; Kolios, Athanasios J.
    A comparison between the fatigue life predictions obtained by the stress concentration factors (SCFs) of 3D solid finite element (FE) models considering the weldment and the existing SCF parametric equations for tubular T-joints, is presented in this paper. From the study carried out, it was concluded that the existing parametric equations for predicting hot spot SCFs are very conservative and insufficient to be used for optimisation. SCFs should be carried out by modelling 3D solid joints which include the weldment and should be based on notch stresses measured on the external surface at the weld toe. The Offshore and Marine Renewable Energy industry could significantly reduce their investment costs using contemporary FE models, since slight overestimations of the SCF results in a corresponding large reduction in predicted service life.
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    Structural integrity assessment of floating offshore wind turbine support structures
    (Elsevier, 2020-05-15) Moghaddam, Behrooz Tafazzoli; Hamedany, Ali Mahboob; Taylor, Jessica; Mehmanparast, Ali; Brennan, Feargal Peter; Davies, Catrin Mair; Nikbin, Kamran
    Floating offshore wind turbines are becoming more attractive to the wind industry due to their capability to operate larger turbines in deeper waters. The floating support structures are anchored to the seabed via mooring chains to impede the structure's unwanted movements. The combination of cyclic stresses and the corrosive marine environment makes the floating support structures vulnerable to corrosion pitting and subsequently fatigue crack initiation and propagation. In this study a framework is proposed to simulate fatigue crack growth from multiple corrosion pits at critical spots of the Spar-type floating support structures to examine the status of the crack during several years of operation. The proposed advanced fracture mechanics based approach provides a methodology to assess the integrity of the structure and subsequently plan for preventive or curative maintenance. The crack growth rate is examined for both singular and multiple cracks at different R ratios and for different stress levels using ABAQUS XFEM. Following numerical simulations, a sensitivity analysis is carried out using Crackwise software for different values of plate thickness, R ratio and initial crack size. The numerical results are discussed in terms of the corrosion pitting effects on fatigue life assessment of floating offshore wind turbines