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Fatigue assessment for FPSO hawsers
Yakimov Vladimir,Gaidai Oleg,Wang Fang,Xu Xiaosen,Niu Yuhao,Kelin Wang 대한조선학회 2023 International Journal of Naval Architecture and Oc Vol.15 No.-
Floating Production Storage and Offloading Unit (FPSO) is designed to produce, store and transport hydrocarbon products. FPSO's hawsers may be exposed to both extreme and fatigue loads during operations. Hence prediction of their fatigue life is important for operational safety. During some unloading operations, consistent hawser tensions could develop as a result of internal friction in nylon ropes, casing wear and accumulated fatigue damage. Methodology, suggested in this study, may be effectively employed at the vessel design phase, when optimizing vessel parameters, reducing potential FPSO hawser tension fatigue damage. This study aims to contribute to development of novel fatigue assessment approaches, in order to use limited available datasets more effectively. Stresses occurring within FPSO hawsers have been modelled, using actual in situ environmental conditions. Simulated continuous stress time series were used as input for the rainflow counting analysis; the cumulative fatigue damage was then evaluated. Note on experimental validation has been provided.
A.I. Yakimov,V.V. Kirienko,A.A. Bloshkin,A.V. Dvurechenskii,D.E. Utkin 한국물리학회 2020 Current Applied Physics Vol.20 No.7
The paper is devoted to optical testing of mid-infrared Ge/Si photodetectors obtained by stacking of self-assembled Ge quantum dots in multilayer structures, which are near-field coupled to the adjacent nanoplasmonic arrays of subwavelength holes in metallic films. It is shown that photocurrent and near-field spectra consist of several sets of peaks, which are attributted to surface plasmon waves, localized surface plasmon modes or diffractive Rayleigh anomaly depending on the hole diameter and the angle of incidence θ. We find that for small holes the greatest contribution to the photocurrent enhancement is due to the excitation of the surface plasmonpolariton waves for all θ. As the hole diameter is increased and becomes comparable with the array periodicity, the normal-incident photoresponse improvement is provided by the Rayleigh anomaly. With the increase of incident angle, the photocurrent enhancement is supposed to arise from coupling of the localized shape resonance and propagating plasmon modes.
Quantum Barrier Growth Temperature Affects Deep Traps Spectra of InGaN Blue Light Emitting Diodes
Polyakov, A. Y.,Smirnov, N. B.,Shchemerov, I. V.,Yakimov, E. B.,Yakimov, E. E.,Kim, Kyu Cheol,Lee, In-Hwan The Electrochemical Society 2018 ECS journal of solid state science and technology Vol.7 No.5
<P>Electroluminescence (EL) efficiency, deep electron and hole traps spectra, microcathodoluminescence (MCL), electron beam induced current (EBIC) imaging, and MCL spectra were studied for blue GaN/InGaN multi-quantum-well (MQW) light emitting diodes differing by the temperature at which the GaN barriers of the MQW active region were grown. It was found that increasing the growth temperature from 850 to 920 degrees C very strongly suppressed the formation of deep electron traps with level at E-c-1 eV in the GaN barriers and of the hole traps with levels at E-v+0.7eV in InGaN QWs. The suppression of the formation of the E-c-1 eV electron trap, a known prominent nonradiative recombination center in n-GaN, improved the carrier injection efficiency into the InGaN QWs and increased the external quantum efficiency by about 9%. EBIC and MCL imaging showed that the density of threading dislocations and terminating them V-pits was relatively low and similar for both studied growth temperatures, close to 10(8) cm(-2) . The cross-sectional dimensions of the V-pits were measurably higher for increased growth temperature. However, the rather low dislocation density and rather high dimensions of the V-pits were believed to result in minor contribution of these defects to the observed EL efficiency changes. (C) 2018 The Electrochemical Society.</P>
Oleg Gaidai,Vladimir Yakimov,Fang Wang,Yu Cao 한국정밀공학회 2024 International Journal of Precision Engineering and Vol.25 No.5
Energy harvesting is a component of contemporary offshore and onshore green energy engineering. Rigorous experimental studies, as well as safety and reliability research, being essential for modern green energy design and engineering. In order to evaluate dynamic performance of galloping energy harvesters, this study utilized extensive wind-tunnel tests, performed under realistic in situ windspeed conditions. State of art Gaidai structural reliability approach has been presented, that is particularly well suitable for non-stationary imperfect or damaged multi-dimensional energy harvesting systems. This approach utilizes analog observations made during representative timelapse, producing quasi-ergodic system dynamic record. As shown in the current study, the recommended technique may be utilized to evaluate the risk of damage or failure in dynamic systems. Additionally, high-dimensionality, deterioration, and nonlinear cross-correlations between dynamic system's key components are challenging to handle for standard reliability approaches, dealing with nonstationary, multidimensional systems. The goal of this study was to benchmark novel Gaidai multivariate reliability approach that allows for effective processing of pertinent statistical data even from limited, multivariate non-stationary underlying dataset. Gaidai multivariate reliability approach attempts to assist designers in evaluating risks of failure and hazards for nonlinear multidimensional dynamic energy harvesting systems, when initial manufacturing imperfections being present.