A Novel Application of System Survival Signature in Reliability Assessment of Offshore Structures

© 2019, Springer Nature Switzerland AG. Offshore platforms are large structures consisting of a large number of components of various types. Thus a variety of methods are usually necessary to assess the structural reliability of these structures, ranging from Finite-Elements-methods to Monte-Carlo-Simulations. However, often reliability information is only available for the members and not for the overall, complex, system. The recently introduced survival signature provides a way to separate the structural analysis from the behaviour of the individual members. Thus it is then possible to use structural reliability methods to obtain information about how the failure of several constituent members of the offshore platform leads to overall system failure. This way it is possible to separate the structural from time-dependent information, allowing flexible and computationally efficient computation of reliability predictions

Airborne non-contact and contact broadband ultrasounds for frequency attenuation profile estimation of cementitious materials

[EN] In this paper, the study of frequency-dependent ultrasonic attenuation in strongly heterogeneous cementitious materials is addressed. To accurately determine the attenuation over a wide frequency range, it is necessary to have suitable excitation techniques. We have analysed two kinds of ultrasound techniques: contact ultrasound and airborne non-contact ultrasound. The mathematical formulation for frequency-dependent attenuation has been established and it has been revealed that each technique may achieve similar results but requires specific different calibration processes. In particular, the airborne non-contact technique suffers high attenuation due to energy losses at the air-material interfaces. Thus, its bandwidth is limited to low frequencies but it does not require physical contact between transducer and specimen. In contrast, the classical contact technique can manage higher frequencies but the measurement depends on the pressure between the transducer and the specimen. Cement specimens have been tested with both techniques and frequency attenuation dependence has been estimated. Similar results were achieved at overlapping bandwidth and it has been demonstrated that the airborne non-contact ultrasound technique could be a viable alternative to the classical contact technique.The authors acknowledge the support from University College Cork (Ireland), Universidad Politecnica de Valencia and the Spanish Administration under grant BIA2014-55311-C2-2-P and Salvador Madariaga's Programme (PR2016-00344/PR2017-00658).Gosálbez Castillo, J.; Wright, W.; Jiang, W.; Carrión García, A.; Genovés, V.; Bosch Roig, I. (2018). Airborne non-contact and contact broadband ultrasounds for frequency attenuation profile estimation of cementitious materials. Ultrasonics. 88:148-156. https://doi.org/10.1016/j.ultras.2018.03.011S1481568

Fatigue Reliability Analysis of Submarine Pipelines Using the Bayesian Approach

A fracture mechanics-based fatigue reliability analysis of a submarine pipeline is investigated using the Bayesian approach. The proposed framework enables the estimation of the reliability level of submarine pipelines based on limited experimental data. Bayesian updating method and Markov Chain Monte Carlo simulation are used to estimate the posterior distribution of the parameters of a fracture mechanics-based fatigue model regarding different sources of uncertainties. Failure load cycle distribution and the reliability-based performance assessment of API 5L X56 submarine pipelines as a case study are estimated for three different cases. In addition, the impact of different parameters, including the stress ratio, maximum load, uncertainties of stress range and initial crack size, corrosion-enhanced factor, and also the correlation between material parameters on the reliability of the investigated submarine pipeline has been indicated through a sensitivity study. The applied approach in this study may be used for uncertainty modelling and fatigue reliability-based performance assessment of different types of submarine pipelines for maintenance and periodic inspection planning