•An optimal DIC formulation is proposed for color images based on noise properties.•Correlations in the color space exist for RGB images which can be disen- tangled.•Measurement uncertainty with ...plain DIC can be made optimal through re-encoding.
Within the context of Digital Image Correlation (DIC), the optimal treatment of color images is considered. The mathematical bses of a weighted 3-field image correlation are first introduced, which are relevant for RGB encoded images. In this framework, noise characterization methods are developed as noise properties dictate the best suited metric to compare images. Consistent ways to process an image from elementary Bayer matrices are derived. Last, a case study on uncertainty quantification is performed.
Abstract Mooring system of floating wind turbine design, as conditioned by fatigue analysis, requires time-consuming simulations. But to provide relevant solutions for the multiple coming tenders, ...efficient methodologies need to be developed to design quickly optimal floating platform mooring for specific metocean data and project constraints. This paper presents a comparison between a mooring fatigue assessment calculated with two standard detailed modelling of a 15MW wind turbine and a simplified Drag and Lift Model (DLM) based on global coefficients at hub often used in floating offshore wind preliminary analysis to carry out extreme analysis. The present contribution is here focused on the proper assessment of a quantitative error introduced by the simplified turbine model in the mooring fatigue assessment, and the evaluation of the missing contributions such as 3P excitation or low frequency induced by turbine control. Two different control approaches are assessed here to capture a range of coupled behaviour which have been observed on project. It has been shown that the DLM approach is accurate to carry out analysis under extreme conditions, but also gives relevant fatigue results for the most fatiguing lines. In general, the order of magnitude is consistent even for low damage. All the calculations have been made using DeepLines Wind TM software.
Abstract
Asbtract. Despite the availability of massive operation datasets, numerous uncertain parameters linger in offshore wind modeling. We propose an identification procedure based on reliability ...of information coming from both modeling and measurements. The procedure is constructed from the modified Constitutive Relation Error concept, which considers measurement noise and model uncertainties. This concept is extended to a multi-physics context involving nonlinear fluid-structure interactions. Several constitutive laws are assumed unreliable and relaxed for comparison with data and safe identification.
The collapse of a wind turbine can be caused by the buckling of the tower when it is subjected to a critical load. This load is related, for instance, to a strong storm or a blade impact on the ...tower. Buckling occurs when the elastic limit is reached in part of the tower. Plasticity leads to bending with large rotations and large displacements. Structures are designed to avoid this phenomenon. However, a wind turbine is subjected during its entire service life to operation loads which cause fatigue of the structure. This results in the initiation of cracks and their propagation in the tower. These cracks can reduce the tower strength and it is, thus, interesting to study how the presence of such damage can affect the resistance of a wind turbine tower to the buckling. The influence of different parameters, such as position and length of the crack, is analyzed. Finally, the critical buckling load is related to wind site condition by considering an aero-elastic modeling of the wind turbine.
In this paper, the coupled dynamics of the floating platform and the wind turbine rotor are analyzed. In particular, the damping is explicitly derived from the coupled equations of the rotor and ...floating platform. The analysis of the damping leads to the study of instability phenomena, thus obtaining the explicit conditions that lead to the non-minimum phase zero (NMPZ). Two NMPZs are analyzed, one related to the rotor dynamics and the other one to the platform pitch dynamics. The latter introduces a novelty, and an explicit condition is provided in this work for its verification. In the second part of the paper, from the analysis of the damping of the floating platform, a new strategy for the control of floating offshore wind turbines (FOWTs) is proposed. This strategy allows one to impose on the controller an explicit level of damping in the platform pitch motion that adapts with wind speed and operating conditions without changing the period of platform pitching. Finally the new strategy is compared to one without compensation and one with a non-adapting compensation by performing aero-hydro-servo-elastic numerical simulations of a reference FOWT. Generated power, motions, blade pitch and tower base fatigue are compared, showing that the new control strategy can reduce fatigue in the structure without affecting the power production.
A new approximation technique, called Reference Point Method (RPM), is proposed in order to reduce the computational complexity of algebraic operations for constructing reduced-order models in the ...case of time dependent and/or parametrized nonlinear partial differential equations. Even though model reduction techniques enableone to decrease the dimension of the initial problem in the sense that far fewer degrees of freedom are needed to represent the solution, the complexity of evaluating the nonlinear terms and assembling the low dimensional operator associated with the reduced-order model still scales with the size of the original high-dimensional model. This point can be critical, especially when the reduced-order basis changes throughout the solution strategy as it is the case for model reduction techniques based on Proper Generalized Decomposition (PGD). Based on the concept of spatial, parameter/time reference points and influence patches, the RPM defines a compressed version of the data from which an approximate low-rank separated representation by patch of the operators can be constructed by explicit formulas at low-cost without resorting to SVD-based techniques. An application of the RPM to PGD-based model reduction for a nonlinear parametrized elliptic PDE previously studied by other authors with reduced-basis method and EIM is proposed. It is shown that computational complexity to construct the reduced-order model can be divided in practice by one order of magnitude compared with the classical PGD approach.
•The technique reduces computational complexity in nonlinear model reduction.•Application to PGD-based model reduction of a nonlinear parametrized elliptic PDE.•An approximate low-rank separated representation of operators without SVD.•Accuracy can be improved by additional PGD modes while ensuring convergence.•Computational complexity can be divided in practice by one order of magnitude.
Background:
The relationship between pregnancy and a change in melanocytic nevi is still controversial. Moreover, management of the rapid evolution of a nevus in an unauspicious melanocytic lesion ...can be a clinical challenge in pregnancy.
Methods:
This article examines a case of a fast-growing deep penetrating nevus in a pregnant woman and provides a literature review of articles relative to pregnancy and nevi change, the management of fast-growing pigmented lesions, and the role and usefulness of dermoscopy in these cases.
Results:
Recent studies have documented that pregnancy is not associated with any significant change in the size of melanocytic nevi. The management of fast-growing melanocytic lesions during this period compulsorily leans toward excision. Dermoscopy can be useful, providing clinicohistopathologic correlations and a better assignment of the lesion.
Conclusion:
This case report and review provide important management considerations for nevi during pregnancy. Early intervention with aggressive treatment measures is the best management for fast-growing lesions, and epiluminescence dermoscopy can assist the management, although still remaining a second-level examination, useful for documentation and for a better classification of the lesion.
Objectives To investigate the anthropometric and metabolic correlates of different patterns of left ventricular (LV) geometry in a cohort of outpatient children with high prevalence of obesity. Study ...design Anthropometric measures, lipid profile, blood pressure (BP), fasting plasma glucose (FPG), and echocardiographic variables were evaluated in 281 white children (6-16 years), of whom 105 were obese and 105 were morbidly obese. Patterns of LV geometry were defined as follows: normal geometry, eccentric LV hypertrophy (LVH), concentric LV remodeling, and concentric LVH. Results One hundred forty-eight children exhibited normal LV geometry, 53 eccentric LVH, 36 concentric LV remodeling, and 44 concentric LVH. The 4 groups differed in body mass index, waist circumference, waist-to-height ratio, triglycerides/high-density lipoprotein cholesterol ratio (Tg/HDL-C), and BP ( P < .05-.0001). A statistically significant impairment of diastolic function (expressed as greater E/E′, P < .002) was observed across patterns of LV geometry. Among anthropometric measures, waist-to-height ratio showed better performance in relation to LVH, with an optimal cut-point of 0.58, compared with body mass index and waist circumference. Children with concentric LVH exhibited the worst metabolic risk profile, with greater prevalence of visceral obesity, high Tg/HDL-C, high BP, and high-normal FPG, than children with normal LV geometry. Conclusions In children with high levels of obesity, an unfavorable “cardiometabolic phenotype” can be identified, which includes concentric LVH, visceral obesity, high BP, high Tg/HDL-C, and high-normal FPG.
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