Influence of Structural Redundancy on Fatigue Life of Offshore Wind Turbine Jacket Structures

The concept of structural redundancy is implemented in the fatigue analysis of an offshore wind turbine jacket structure. The analyzed jacket is a real life example. Time domain analyses are performed for the most representative design load case. The uni-directional and multidirectional simulations of the offshore wind turbine system are carried out using a coupling of the aero-elastic code and the finite element code. Fatigue analyses are performed using hot spot stress approach and Miner's rule. Comparative studies show that considering structural redundancy leads to expanded fatigue life of the offshore wind turbine jacket structures. © 2017 ISOPEEC/Horizon202

Modeling of offshore wind turbines with braced support structures

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Offshore Code Comparison Collaboration Continuation (OC4), Phase I – Results of Coupled Simulations of an Offshore Wind Turbine with Jacket Support Structure

Heike von Waaden (REpower Systems SE) To be presented at the 22 nd International Society of Offshore and Polar Engineers Conference Rhodes, Greec

Verification of a Numerical Model of the Offshore Wind Turbine From the Alpha Ventus Wind Farm Within OC5 Phase III

The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project, is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project analyzes the Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. This paper shows results of the verification of the OWT models (code-to-code comparison). A subsequent publication will focus on their validation (comparison of simulated results to measured physical system response data). Based on the available data, the participants of Phase III set up numerical models of the OWT in their simulation tools. It was necessary to verify and to tune these models. The verification and tuning were performed against an OWT model available at the University of Stuttgart - Stuttgart Wind Energy (SWE) and documentation provided by Senvion and OWEC Tower. A very good match was achieved between the results from the reference SWE model and models set up by OC5 Phase III participants

Histogram analysis of lipid-core plaques in coronary computed tomographic angiography: Ex vivo validation against histology

PURPOSE: In coronary computed tomographic angiography (CTA), low attenuation of coronary atherosclerotic plaque is associated with lipid-rich plaques. However, an overlap in Hounsfield units (HU) between fibrous and lipid-rich plaque as well as an influence of luminal enhancement on plaque attenuation was observed and may limit accurate detection of lipid-rich plaques by CTA. We sought to determine whether the quantitative histogram analysis improves accuracy of the detection of lipid-core plaque (LCP) in ex vivo hearts by validation against histological analysis. MATERIALS AND METHODS: Human donor hearts were imaged with a 64-slice computed tomographic scanner using a standard coronary CTA protocol, optical coherence tomography (OCT), a histological analysis. Lipid-core plaque was defined in the histological analysis as any fibroatheroma with a lipid/necrotic core diameter of greater than 200 μm and a circumference greater than 60 degrees as well as a cap thickness of less than 450 μm. In OCT, lipid-rich plaque was determined as a signal-poor region with diffuse borders in 2 quadrants or more. In CTA, the boundaries of the noncalcified plaque were manually traced. The absolute and relative areas of low attenuation plaque based on pixels with less than 30, less than 60, and less than 90 HU were calculated using quantitative histogram analysis. RESULTS: From 5 hearts, a total of 446 cross sections were coregistered between CTA and the histological analysis. Overall, 55 LCPs (12%) were identified by the histological analysis. In CTA, the absolute and relative areas of low attenuation plaque less than 30, less than 60, and less than 90 HU were 0.14 (0.31) mm (4.22% [9.02%]), 0.69 (0.95) mm (18.28% [21.22%]), and 1.35 (1.54) mm (35.65% [32.07%]), respectively. The low attenuation plaque area correlated significantly with histological lipid content (lipid/necrotic core size [in square millimeter] and a portion of lipid/necrotic core on the entire plaque) at all thresholds but was the strongest at less than 60 HU (r = 0.53 and r = 0.48 for the absolute and relative areas, respectively). Using a threshold of 1.0 mm or greater, the absolute plaque area of less than 60 HU in CTA yielded 69% sensitivity and 80% specificity to detect LCP, whereas sensitivity and specificity were 73% and 71% for using 25.0% or higher relative area less than 60 HU. The discriminatory ability of CTA for LCP was similar between the absolute and relative areas (the area under the curve, 0.744 versus 0.722; P = 0.37). Notably, the association of the low attenuation plaque area in CTA with LCP was not altered by the luminal enhancement for the relative (P = 0.48) but for the absolute measurement (P = 0.03). Similar results were achieved when validated against lipid-rich plaque by OCT in a subset of 285 cross sections. CONCLUSIONS: In ex vivo conditions, the relative area of coronary atherosclerotic plaque less than 60 HU in CTA as derived from quantitative histogram analysis has good accuracy to detect LCP as compared with a histological analysis independent of differences in luminal contrast enhancement

Differentiation of Early from Advanced Coronary Atherosclerotic Lesions: Systematic Comparison of CT, Intravascular US, and Optical Frequency Domain Imaging with Histopathologic Examination in ex Vivo Human Hearts

Purpose:To establish an ex vivo experimental setup for imaging coronary atherosclerosis with coronary computed tomographic (CT) angiography, intravascular ultrasonography (US), and optical frequency domain imaging (OFDI) and to investigate their ability to help differentiate early from advanced coronary plaques.Materials and Methods:All procedures were performed in accordance with local and federal regulations and the Declaration of Helsinki. Approval of the local Ethics Committee was obtained. Overall, 379 histologic cuts from nine coronary arteries from three donor hearts were acquired, coregistered among modalities, and assessed for the presence and composition of atherosclerotic plaque. To assess the discriminatory capacity of the different modalities in the detection of advanced lesions, c statistic analysis was used. Interobserver agreement was assessed with the Cohen κ statistic.Results:Cross sections without plaque at coronary CT angiography and with fibrous plaque at OFDI almost never showed advanced lesions at histopathologic examination (odds ratio [OR]: 0.02 and 0.06, respectively; both P < .0001), while mixed plaque at coronary CT angiography, calcified plaque at intravascular US, and lipid-rich plaque at OFDI were associated with advanced lesions (OR: 2.49, P = .0003; OR: 2.60, P = .002; and OR: 31.2, P < .0001, respectively). OFDI had higher accuracy for discriminating early from advanced lesions than intravascular US and coronary CT angiography (area under the receiver operating characteristic curve: 0.858 [95% confidence interval {CI}: 0.802, 0.913], 0.631 [95% CI: 0.554, 0.709], and 0.679 [95% CI: 0.618, 0.740]; respectively, P < .0001). Interobserver agreement was excellent for OFDI and coronary CT angiography (κ = 0.87 and 0.85, respectively) and was good for intravascular US (κ = 0.66).Conclusion:Systematic and standardized comparison between invasive and noninvasive modalities for coronary plaque characterization in ex vivo specimens demonstrated that coronary CT angiography and intravascular US are reasonably associated with plaque composition and lesion grading according to histopathologic findings, while OFDI was strongly associated. These data may help to develop initial concepts of sequential imaging strategies to identify patients with advanced coronary plaques.© RSNA, 2012Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12111891/-/DC1

Verification of Numerical Offshore Wind Turbine Models Based on Full Scale Alpha Ventus Data within OC5 Phase III

The main objective of the Offshore Code Comparison Collaboration Continuation, with Correlation (OC5) project, is validation of aero-hydro-servo-elastic simulation tools for offshore wind turbines (OWTs) through comparison of simulated results to the response data of physical systems. Phase III of the OC5 project analyzes the Senvion 5M wind turbine supported by the OWEC Quattropod from the alpha ventus offshore wind farm. This paper shows results of the verification of the OWT models (code-to-code comparison). A subsequent publication will focus on their validation (comparison of simulated results to measured physical system response data). Based on the available data, the participants of Phase III set up numerical models of the OWT in their simulation tools. It was necessary to verify and to tune these models. The verification and tuning were performed against an OWT model available at the University of Stuttgart – Stuttgart Wind Energy (SWE) and documentation provided by Senvion and OWEC Tower. A very good match was achieved between the results from the reference SWE model and models set up by OC5 Phase III participants

Offshore code comparison collaboration continuation (OC4), phase I - Results of coupled simulations of an offshore wind turbine with jacket support structure

In this paper, the exemplary results of the IEA Wind Task 30 "Offshore Code Comparison Collaboration Continuation" (OC4) Project - Phase I, focused on the coupled simulation of an offshore wind turbine (OWT) with a jacket support structure, are presented. The focus of this task has been the verification of OWT modeling codes through code-to-code comparisons. The discrepancies between the results are shown and the sources of the differences are discussed. The importance of the local dynamics of the structure is depicted in the simulation results. Furthermore, attention is given to aspects such as the buoyancy calculation and methods of accounting for additional masses (such as hydrodynamic added mass). Finally, recommendations concerning the modeling of the jacket are given

Offshore Code Comparison Collaboration Continuation (OC4), Phase I—Results of Coupled Simulations of an Offshore Wind Turbine with Jacket Support Structure

In this paper, the exemplary results of the IEA Wind Task 30 Offshore Code Comparison Collaboration Continuation (OC4) Project - Phase I, focused on the coupled simulation of an offshore wind turbine (OWT) with a jacket support structure, are presented. The focus of this task has been the verification of OWT modeling codes through code-to-code comparisons. The discrepancies between the results are shown and the sources of the differences are discussed. The importance of the local dynamics of the structure is depicted in the simulation results. Furthermore, attention is given to aspects such as the buoyancy calculation and methods of accounting for additional masses (i.e., hydrodynamic added mass). Finally, recommendations concerning the modeling of the jacket are given