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A probabilistic analysis of Miner’s law for different loading conditions
Sergio Blasón,José A.F.O. Correia,Abílio M.P. De Jesus,Rui A.B. Calçada,Alfonso Fernández-Canteli 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.1
In this paper, the normalized variable V=(log N-B)(log Δσ-C), as derived from the probabilistic S-N field of Castillo and Canteli, is taken as a reference for calculation of damage accumulation and probability of failure using the Miner number in scenarios of variable amplitude loading. Alternative damage measures, such as the classical Miner and logarithmic Miner, are also considered for comparison between theoretical lifetime prediction and experimental data. The suitability of this approach is confirmed for it provides safe lifetime prediction when applied to fatigue data obtained for riveted joints made of a puddle iron original from the Fão bridge, as well as for data from experimental programs published elsewhere carried out for different materials (aluminium and concrete specimens) under distinct variable loading histories.
Strain energy-based fatigue life prediction under variable amplitude loadings
Shun-Peng Zhu,Peng Yue,José Correia,Sergio Blasón,Abílio De Jesus,Qingyuan Wang 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.2
With the aim to evaluate the fatigue damage accumulation and predict the residual life of engineering components under variable amplitude loadings, this paper proposed a new strain energy-based damage accumulation model by considering both effects of mean stress and load interaction on fatigue life in a low cycle fatigue (LCF) regime. Moreover, an integrated procedure is elaborated for facilitating its application based on S-N curve and loading conditions. Eight experimental datasets of aluminum alloys and steels are utilized for model validation and comparison. Through comparing experimental results with model predictions by the proposed, Miner’s rule, damaged stress model (DSM) and damaged energy model (DEM), results show that the proposed one provides more accurate predictions than others, which can be extended for further application under multi-level stress loadings.
Discrete-time Analysis of a Robust Model Reference Adaptive Sliding Mode Control
Deise Maria Cirolini Milbradt,Guilherme Vieira Hollweg,Hilton Abílio Gründling,Paulo Jefferson Dias de Oliveira Evald 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.5
In real-world applications, plants with parametric variations and unmodelled dynamics are very common, and, in most cases, fixed-gain controllers can not ensure global stability and hardly have high performance for large system variations. To overcome this challenge, this paper presents a Robust Model Reference Adaptive Sliding Mode Control, whose structure combines a Robust Model Reference Adaptive controller (RMRAC) and an adaptive first-order Sliding Mode controller (SMC). Its discrete-time robustness analysis and stability proofs by means of Lyapunov theory are provided. The mathematical analyses show that this hybrid adaptive controller is robust to parametric variations and unmodelled plant dynamics. Besides, it ensures that tracking error tends to a residual set in steady state, maintaining global stability. Simulation results are presented to show the controller effectiveness applied in a non-minimum phase unstable plant with unmodelled dynamics. Furthermore, a comparison with a Proportional-Resonant controller is also provided.
Pedro Tiago,Pereira Pedro,Costa Ana Sofia,Almeida Fábio,Loureiro Maria Luísa,Alfaiate Teresa,Gonçalves Abílio 대한신경집중치료학회 2022 대한신경집중치료학회지 Vol.15 No.1
Background: Blood pressure variability (BPV) is a predictor of short- and long-term disability in patients with acute ischemic stroke (AIS). Its effect on more immediate functional outcomes has been seldom studied, and the results are inconsistent. We aimed to determine the role of BPV during the first 5 days of hospitalization in functional status at the time of discharge of patients with AIS.Methods: We enrolled 134 patients diagnosed with AIS and BPV using standard deviation and coefficient of variation (CV %). These were associated with the dichotomized modified Rankin Scale at discharge using logistic regression. Results: Patients with unfavorable outcomes were significantly older (P=0.014), had a lower body mass index (P=0.001), were less likely to present with dyslipidemia (P=0.001), had lower serum triglyceride levels (P=0.012), had a longer hospitalization period (P<0.001), and had a higher mean National Institutes of Health Stroke Scale score at admission (P<0.001). After adjusting for multiple confounders, the CV % of systolic blood pressure (SBP) in the first 120 hours after admission had a significant effect on functional disability at discharge. Conclusion: Variability in SBP in the first 5 days of hospitalization had a deleterious effect on the functional outcomes at discharge of patients with AIS. The role of diabolic blood pressure variability seems to be significant only in the first 24 hours of admission; however, further research is required.
A Modified Robust Adaptive Super-twisting Sliding Mode Controller for Grid-connected Converters
Guilherme Vieira Hollweg,Wencong Su,Paulo Jefferson Dias de Oliveira Evald,Rodrigo Varella Tambara,Hilton Abílio Gründling 제어·로봇·시스템학회 2023 International Journal of Control, Automation, and Vol.21 No.10
This work introduces the application of a new adaptive control structure, which is a modification of the robust model reference adaptive controller (RMRAC) and adaptive super-twisting sliding mode (ASTSM). This controller was previously proposed in the literature and applied to the current control of a grid-connected converter under uncertain grid environments. However, its STSM structure used the tracking error signal function as a sliding surface, which tends to impose considerable chattering in the system. The proposed controller maintains the characteristics of the known structure but replaces the signal function in the STSM equations with a sigmoid function, reducing the current tracking error and improving the system regulation since it is smoother. As the control structure lies in RMRAC theory and some core equations change, stability analysis of the adaptation algorithm is also carried out. Experimental results in a 7.5 kW converter are presented in which the known RMRAC-ASTSM controller presents 2.45% total harmonic distortion while the modified adaptive structure obtains 2.22% total harmonic distortion and better regulation performance.