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Browsing by Issue Date, starting with "2019-04-01"

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  • Review of condition-based maintenance strategies for offshore wind energy
    Publication . Kang, Jichuan; Sobral, José; Guedes Soares, Carlos
    The existing maintenance strategies of offshore wind energy are reviewed including the specific aspects of condition-based maintenance, focusing on three primary phases, namely, condition monitoring, fault diagnosis and prognosis, and maintenance optimization. Relevant academic research and industrial applications are identified and summarized. The state of art, capabilities, and constraints of condition-based maintenance are analyzed. The presented research demonstrates that the intelligent-based approach has become a promising solution for condition recognition, and an integrated data platform for offshore wind farms is significant to optimize the maintenance activities.
    2019-04-01Journal article Restricted access Show more
  • Damage evaluation under complex fatigue loading conditions
    Publication . Reis, Luis; Caxias, J.; Soares, Henrique; Rodrigues da Costa, Pedro; Anes, Vitor; Freitas, M.
    Fatigue damage and life assessment of multiaxial loadings is still an issue yet to resolve. Many methods have been proposed with promising agreements with the experimental results. However, the performance of such methods is, more than often, purely based on fatigue tests with simple loading conditions. In this work the stress scale factor (SSF) criterion and the virtual cycle counting (vcc) method are used to estimate fatigue life and damage accumulation with two damage accumulation rules. Fatigue tests were carried out with three different variable amplitude random loadings, applied to several specimens made from a 42CrMo4 high-strength steel. Fatigue crack plane measurements were compared with predictions from several critical plane models. The applied methods provided very acceptable results making the SSF package (SSF equivalent stress and virtual cycle counting method) a good method to estimate fatigue life and assessment of the damage accumulation in random fatigue loadings.
    2019-04-01Journal article Open access Show more
  • C-scorpionate iron(II) complexes as highly selective catalysts for the hydrocarboxylation of cyclohexane
    Publication . Matias, Inês; Da Costa Ribeiro, Ana Paula; Alegria, Elisabete; Pombeiro, Armando; Martins, Luisa
    The C-scorpionate iron(II) complexes [FeCl2{kappa(3)-HC(pz)(3)}](1) (pz = pyrazol-1-yl), Li[FeCl2{kappa(3)-SO3C(pz)(3)}] (2) and the new [FeCl2{kappa(3)-HOCH2C(pz)(3)}] (3) act as catalysts for the hydrocarboxylation of cyclohexane (with CO and H2O) to cyclohexanecarboxylic acid in a remarkable yield (up to 60%) and under mild conditions. The catalysts selectivity for the acid can be tuned by CO pressure, catalyst amount and reaction temperature. Complex [FeCl2{kappa(3)-HC(pz)(3)}] (1) provides the most effective catalyst requiring low CO pressure. This work constitutes an unprecedented use of iron complexes as catalysts for the hydrocarboxylation of alkanes.
    2019-04-01Journal article Restricted access Show more