Influence of wave spreading on offshore wind turbine design: IEA 15-MW scenario

Offshore ocean waves are directionally spread, whereby the propagation of energy travels in different directions. Despite this multi-directionality, the use of 3-dimensional wave models for loading on fixed offshore wind turbines has been limited. This is partially due to the common assumption that uni-directional sea-states are conservative within a design philosophy. This may not always be true given that in operating conditions the amount of aerodynamic damping in the side-side direction is much lower than the fore-aft direction. This paper aims to address this issue by providing the influence of wave spreading on various offshore wind turbine design scenarios: fatigue, ultimate and service limit state design. This study demonstrates that wave spreading indeed results in more fatigue damage for operating load cases. Despite this, the overall fatigue and ultimate limit state utilisation is still reduced when a wave spreading is adopted

Monopile foundation stiffness estimation of an instrumented offshore wind turbine through model updating

Rapid development of offshore wind foundation models has resulted in a large number of built structures with generally underestimated foundation stiffness properties and a need to update and validate both the individual structural models and the underlying foundation design frameworks. This paper outlines a structural health monitoring approach, based on the combination of output only structural health monitoring methods and model updating, to estimate foundation stiffness parameters using field monitored data. Field monitoring data from an offshore wind turbine under idling conditions, over a large monitoring period, are presented and operational modal analysis is applied to estimate the modal parameters. Those are compared to modal properties predicted by finite element models, employing either old (API/DNVGL) or new (PISA) foundation design properties, which are calibrated using geotechnical site investigation data. A new approach to interpret seabed level statically equivalent foundation stiffness, in terms of effective lateral and rotational stiffness against load eccentricity, is presented. Seabed level statically equivalent foundation properties are updated by comparison against the observed modal behaviour and the optimised foundation parameters are presented, demonstrating a close match to the predictions of the PISA method

Axial resistance of piles during driving in chalk

The driveability and axial capacity of driven piles depend critically on their geometry, end conditions and the degree of drainage they experience during driving. This paper summarises the installation characteristics of 41 impact-driven piles driven for the ALPACA joint industry project (JIP). The installed piles covered open- and closed-ended steel tubular, sheet and reinforced square concrete piles with a wide range of diameters (from 139 mm to 1.8 m), wall thickness ratios (14 to 72), and embedment length-to-diameter ratios (6 to 40). Analyses that applied parameters interpreted from parallel piezocone penetration and dissipation tests indicated that pore-pressures of several MPa developed beneath large open-ended piles during rapid driving and led to surprisingly low shaft resistances. However, the slower driving of the closed-ended concrete and sheet piles permitted far higher degrees of dissipation and led to far greater shaft resistances. Signal matching analyses demonstrate how the End of Driving (EoD) shaft resistances were affected strongly by de-structuration of the chalk and the relative depth of the pile tip. The EoD shaft resistances corresponded closely with predictions made applying the short-term Chalk ICP-18 Soil Resistance to Driving (SRD) formulae. An updated base resistance formula was proposed that correlates with pile wall thickness ratio

Enhanced Stress Wave Analysis of Scaled Monopiles in Glacial Till at Cowden

Conventional stress wave analysis for pile driving involves a subjective signal matching process using pile driving analyser (PDA) measurements. The PICASO (PIle Cyclic AnalySis: Oxford and Ørsted) research project provided an opportunity to collect high frequency strain measurements using optical fibre Bragg grating (FBG) sensors over the embedded length of the pile, in addition to conventional PDA data. This paper reports the application of a novel hybrid approach incorporating FBG data into the signal matching process, as developed by Buckley et al. (2020a), to an overconsolidated glacial till site in Cowden, Hull, UK. The additional information on stress wave propagation, obtained through FBG measurements, provides insights into the development of soil resistance to driving (SRD) in stiff clays. The results obtained using the new framework are compared to the resistance predicted using a widely-adopted empirical method

Augmentation of abscisic acid (ABA) levels by drought does not induce short-term stomatal sensitivity to CO2 in two divergent conifer species

The stomata of conifers display very little short-term response to changes in atmospheric CO2 concentration (Ca), whereas the stomatal responses of angiosperms to Ca increase in response to water stress. This behaviour of angiosperm stomata appears to be dependent on foliar levels of abscisic acid (ABAf). Here two alternative explanations for the stomatal insensitivity of conifers to Ca are tested: that conifers have either low ABAf or a higher or absent threshold for ABA-induced sensitivity. The responsiveness of stomatal conductance (gs) to a sequence of transitions in Ca (386, 100, and 600 μmol mol−1) was recorded over a range of ABAf in an angiosperm and two divergent conifer species. The different ABA levels were induced by a mild drought cycle. Although the angiosperm and conifer species showed similar proportional increases in ABAf following drought, conifer stomata remained insensitive to changes in Ca whereas angiosperm stomata showed enhanced sensitivity with increasing ABAf. The conifers, however, had much higher ABAf prior to drought than the angiosperm species, suggesting that non-sensitivity to Ca in these conifers was due to an absent or inactive response/signalling pathway rather than insufficient ABAf

Linking Auxin with Photosynthetic Rate via Leaf Venation

International audienceLand plants lose vast quantities of water to the atmosphere during photosynthetic gas exchange. In angiosperms, a complex network of veins irrigates the leaf, and it is widely held that the density and placement of these veins determines maximum leaf hydraulic capacity and thus maximum photosynthetic rate. This theory is largely based on interspecific comparisons and has never been tested using vein mutants to examine the specific impact of leaf vein morphology on plant water relations. Here we characterize mutants at the Crispoid (Crd) locus in pea (Pisum sativum), which have altered auxin homeostasis and activity in developing leaves, as well as reduced leaf vein density and aberrant placement of free-ending veinlets. This altered vein phenotype in crd mutant plants results in a significant reduction in leaf hydraulic conductance and leaf gas exchange. We find Crispoid to be a member of the YUCCA family of auxin biosynthetic genes. Our results link auxin biosynthesis with maximum photosynthetic rate through leaf venation and substantiate the theory that an increase in the density of leaf veins coupled with their efficient placement can drive increases in leaf photosynthetic capacity

Optimization of impact pile driving using optical fiber Bragg-grating measurements

This paper reports the use of optical fiber Bragg-grating (FBG) sensors to monitor the stress waves generated below ground during pile driving, combined with measurements using conventional pile driving analyzer (PDA) sensors mounted at the pile head. Fourteen tubular steel piles with a diameter of 508 mm and embedded length-to-diameter ratios of 6∶20 were impact driven at an established chalk test site in Kent, United Kingdom. The pile shafts were instrumented with multiple FBG strain gauges and pile head PDA sensors, which monitored the piles’ responses under each hammer blow. A high-frequency (5 kHz) fiber optic interrogator allowed a previously unseen resolution of the stress wave propagation along the pile. Estimates of the base soil resistances to driving and distributions of shaft shear resistances were found through signal matching that compared the time series of pile head PDA measurements and FBG strains measured below the ground surface. Numerical solutions of the one-dimensional wave equation were optimized by taking account of the data from multiple FBG gauges, leading to significant advantages that have potential for widespread application in cases where high-resolution strain measuremen

Serum Amyloid A, C-Reactive Protein, and Retinal Microvascular Changes in Hypertensive Diabetic and Nondiabetic Individuals: An Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) substudy

To study the association of the inflammatory markers serum amyloid A (SAA) and C-reactive protein (CRP) with retinal microvascular parameters in hypertensive individuals with and without type 2 diabetes

Trehalose 6-phosphate promotes seed filling by activating auxin biosynthesis

Plants undergo several developmental transitions during their life cycle. One of these, the differentiation of the young embryo from a meristem-like structure into a highly specialized storage organ, is believed to be controlled by local connections between sugars and hormonal response systems. However, we know little about the regulatory networks underpinning the sugar–hormone interactions in developing seeds. By modulating the trehalose 6-phosphate (T6P) content in growing embryos of garden pea (Pisum sativum), we investigate here the role of this signaling sugar during the seed-filling process. Seeds deficient in T6P are compromised in size and starch production, resembling the wrinkled seeds studied by Gregor Mendel. We show also that T6P exerts these effects by stimulating the biosynthesis of the pivotal plant hormone, auxin. We found that T6P promotes the expression of the auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE RELATED2 (TAR2), and the resulting effect on auxin concentrations is required to mediate the T6P-induced activation of storage processes. Our results suggest that auxin acts downstream of T6P to facilitate seed filling, thereby providing a salient example of how a metabolic signal governs the hormonal control of an integral phase transition in a crop plant

Molecular Longitudinal Tracking of Mycobacterium abscessus spp. during Chronic Infection of the Human Lung

<div><p>The <i>Mycobacterium abscessus</i> complex is an emerging cause of chronic pulmonary infection in patients with underlying lung disease. The <i>M. abscessus</i> complex is regarded as an environmental pathogen but its molecular adaptation to the human lung during long-term infection is poorly understood. Here we carried out a longitudinal molecular epidemiological analysis of 178 <i>M. abscessus</i> spp. isolates obtained from 10 cystic fibrosis (CF) and 2 non CF patients over a 13 year period. Multi-locus sequence and molecular typing analysis revealed that 11 of 12 patients were persistently colonized with the same genotype during the course of the infection while replacement of a <i>M. abscessus sensu stricto</i> strain with a <i>Mycobacterium massiliense</i> strain was observed for a single patient. Of note, several patients including a pair of siblings were colonized with closely-related strains consistent with intra-familial transmission or a common infection reservoir. In general, a switch from smooth to rough colony morphology was observed during the course of long-term infection, which in some cases correlated with an increasing severity of clinical symptoms. To examine evolution during long-term infection of the CF lung we compared the genome sequences of 6 sequential isolates of <i>Mycobacterium bolletii</i> obtained from a single patient over an 11 year period, revealing a heterogeneous clonal infecting population with mutations in regulators controlling the expression of virulence factors and complex lipids. Taken together, these data provide new insights into the epidemiology of <i>M. abscessus</i> spp. during long-term infection of the CF lung, and the molecular transition from saprophytic organism to human pathogen.</p></div