Investigation on Dynamic Responses’ Characteristics and Fatigue Damage Assessment for Floating Offshore Wind Turbine Structures

Dynamic response analysis and fatigue damage assessment of floating offshore wind turbine (FOWT) structures are carried out in this paper with a focus on the statistical characteristics of the dynamic responses under wind–wave excitation. A proper spectral fatigue damage model is proposed to obtain better fatigue damage estimation. The OC3 floating spar (Hywind) with a 5 MW baseline wind turbine developed by the American National Renewable Energy Laboratory (NREL) is applied as the target model, and the fully coupled dynamic responses of the model are calculated in the time domain. The non-Gaussian nature is revealed based on the study of the statistical properties of the dynamic response of key components (the tower base and fairlead of the mooring line). Dirlik distribution is proved to be the best probability distribution function (PDF) that can fit the statistical distribution feature of the dynamic responses among several PDFs. The corresponding spectral fatigue damage models are applied to estimate fatigue damage of the tower base and mooring line following the proposed fatigue assessment procedure in the frequency domain, of which the results are compared with results from the time-domain analysis method. The results indicate that for non-Gaussian feature dynamic responses as FOWTs, the spectral fatigue damage model based on the Dirlik distribution can provide more accurate assessments of fatigue damage

Maternal urinary manganese and risk of low birth weight: a case–control study

Abstract Background Manganese (Mn) is an essential element for humans, but exposure to high levels has been associated with adverse developmental outcomes. Early epidemiological studies evaluating the effect of Mn on fetal growth are inconsistent. Methods We investigated the association between maternal urinary Mn during pregnancy and the risk of low birth weight (LBW). Mn concentrations in maternal urine samples collected before delivery were measured in 816 subjects (204 LBW cases and 612 matched controls) recruited between 2012 and 2014 in Hubei Province, China. Results The median Mn concentration in maternal urine was 0.69 μg/g creatinine. Compared to the medium tertile of Mn levels, an increased risk of LBW was observed for the lowest tertile (≤0.30 μg/g creatinine) [adjusted odds ratio (OR) = 1.28; 95 % confidence interval (CI) = 0.67, 2.45], and a significantly increased risk of LBW was observed for the highest tertile (≥1.16 μg/g creatinine) [adjusted OR = 2.04; 95 % CI = 1.12, 3.72]. A curvilinear relationship between maternal urinary Mn and risk of LBW was observed, showing that the concentration at 0.43 μg/g creatinine was the point of inflection. Similar associations were observed among the mothers with female infants and among the younger mothers < 28 years old. However, among the mothers with male infants or the older mothers ≥ 28 years old, only higher levels of Mn were positively associated with LBW. Conclusions Lower or higher levels of maternal urinary Mn are associated with LBW, though only the association of LBW risk and higher levels of Mn was statistically significant. The findings also show that the associations may vary by maternal age and infant sex, but require confirmation in other populations

Additional file 1: of Maternal urinary manganese and risk of low birth weight: a case–control study

Distribution of maternal urianry manganese and restricted spline curves association between urinary manganese concentration and risk of low birth weigh in the stratified analysis. (DOCX 104 kb