Reliability Of Dynamically Sensitive Offshore Platforms Exposed To Extreme Waves
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Reliability of Dynamically Sensitive Offshore Platforms Exposed to Extreme Waves
The growing interest in the use of offshore platforms in deeper waters and harsher environments, as well as the desire to extend the operation of existing structures beyond their design lives, is increasing attention on the assessment of their dynamic response and their failure conditions under extreme storm loading. There are a large number of factors influencing the performance of dynamically sensitive platforms, but a major issue is how to include all of the irregularity, directionality and nonlinearity that ocean waves cause on their loading. Therefore, the role each plays in the assessment of dynamically sensitive structures under extreme loads is investigated systematically in this thesis. The aim is to develop practical methods to estimate extreme response and the probability of failure of dynamically sensitive offshore structures in a given sea-state. The directionality and nonlinearity of ocean waves has been captured in this thesis by extending the formulations of the NewWave and Constrained NewWave theories. NewWave is a deterministic method that accounts for the spectral composition of the sea-state, and can be used as an alternative to both regular wave and full random time domain simulations of lengthy time histories. Based on this theory a predetermined crest height and the surface elevation around the crest during an extreme event can be theoretically simulated. Constrained NewWave, which is generated by mathematically constraining a NewWave within a random time series, allows the irregularity of ocean waves to be considered. These wave theories have been extended in this thesis to include 2nd order and directionality effects, and their formulations have been written into a new Fortran code for calculation of the water surface and water particle kinematics. The effects of irregularity, directionality and nonlinearity of ocean waves on dynamically sensitive structures are then shown for an example mobile jack-up drilling platform. The sample jack-up platform is modelled in the USFOS software, and includes the effects of material and geometrical nonlinearities as well as spudcan-soil-structure nonlinear interactions. Finally, based on structured application of multiple Constrained NewWaves in combination with the Monte Carlo method, a framework is proposed to estimate the extreme response and the failure probability of dynamically sensitive offshore structures exposed to a given duration of the one extreme sea-state. The results demonstrate that in an extreme event the irregularity, directionality and nonlinearity of ocean waves have considerable effects on the overall performance of the sample jack-up platform. It is shown that the extreme response and the probability of failure of the sample jackup are not only governed by the maximum crest elevation but also depend on the random background of ocean waves. In addition, it is indicated that the inclusion of the directionality effects of ocean waves results in reductions in the extreme response and failure rate of the sample jack-up platform. On the other hand, the nonlinearity effects cause additional energy in low and high frequencies and raise the crest height, which increases the extreme response of the sample jack-up platform. The methods developed in this thesis have application to any dynamically sensitive structure and will help reduce the level of uncertainty in predicting their extreme response or failure probability. This may help in extending their operational conditions, say into deeper waters and harsher sea-states, or in extending their operational life.
Reliability Evaluation of Dynamic Systems Excited in Time Domain - Redset
RELIABILITY EVALUATION OF DYNAMIC SYSTEMS EXCITED IN TIME DOMAIN – REDSET Multi-disciplinary approach to structural reliability analysis for dynamic loadings offering a practical alternative to the random vibration theory and simulation Reliability Evaluation of Dynamic Systems Excited in Time Domain – REDSET is a multidisciplinary concept that enables readers to estimate the underlying risk that could not be solved in the past. The major hurdle was that the required limit state functions (LSFs) are implicit in nature and the lack of progress in the reliability evaluation methods for this class of problems. The most sophisticated deterministic analysis requires that the dynamic loadings must be applied in the time domain. To satisfy these requirements, REDSET is developed. Different types and forms of dynamic loadings including seismic, wind-induced wave, and thermomechanical loading in the form of heating and cooling of solder balls used in computer chips are considered to validate REDSET. Time domain representations and the uncertainty quantification procedures including the use of multiple time histories are proposed and demonstrated for all these dynamic loadings. Both onshore and offshore structures are used for validation. The potential of REDSET is demonstrated for implementing the Performance Based Seismic Design (PBSD) concept now under development in the United States. For wider multidisciplinary applications, structures are represented by finite elements to capture different types of nonlinearity more appropriately. Any computer program capable of conducting nonlinear time domain dynamic analysis can be used, and the underlying risk can be estimated with the help of several dozens or hundreds of deterministic finite element analyses, providing an alternative to the simulation approach. To aid comprehension of REDSET, numerous illustrative examples and solution strategies are presented in each chapter. Written by award-winning thought leaders from academia and professional practice, the following sample topics are included: Fundamentals of reliability assessment including set theory, modeling of uncertainty, the risk-based engineering design concept, and the evolution of reliability assessment methods Implicit performance or limit state functions are expressed explicitly by the extensively modified response surface method with several new experimental designs Uncertainty quantification procedures with multiple time histories for different dynamic loadings, illustrated with examples The underlying risk can be estimated using any computer program representing structures by finite elements with only few deterministic analyses REDSET is demonstrated to be an alternative to the classical random vibration concept and the basic simulation procedure for risk estimation purposes REDSET changes the current engineering design paradigm. Instead of conducting one deterministic analysis, a design can be made more dynamic load tolerant, resilient, and sustainable with the help of a few additional deterministic analyses This book describing REDSET is expected to complement two other books published by Wiley and authored by Haldar and Mahadevan: Probability, Reliability and Statistical Methods in Engineering Design and Reliability Assessment Using Stochastic Finite Element Analysis. The book is perfect to use as a supplementary resource for upper-level undergraduate and graduate level courses on reliability and risk-based design.
Nonlinear Stochastic Mechanics
Author: Nicola Bellomo
language: en
Publisher: Springer Science & Business Media
Release Date: 2012-12-06
The Symposium, held in Torino (lSI, Villa Gualino) July 1-5, 1991 is the sixth of a series of IUTAM-Symposia on the application of stochastic analysis to continuum and discrete mechanics. The previous one, held in Innsbruck (1987), was mainly concentrated on qual itative and quantitative analysis of stochastic dynamical systems as well as on bifurcation and transition to chaos of deterministic systems. This Symposium concentrated on fundamental aspects (stochastic analysis and mathe matical methods), on specific applications in various branches of mechanics, engineering and applied sciences as well as on related fields as analysis of large systems, system identifica tion, earthquake prediction. Numerical methods suitable to provide quantitative results, say stochastic finite elements, approximation of probability distribution and direct integration of differential equations have also been the object of interesting presentations. Specific topics of the sessions have been: Engineering Applications, Equivalent Lineariza tion of Discrete Stochastic Systems, Fatigue and Life Estimation, Fluid Dynamics, Numerical Methods, Random Vibration, Reliability Analysis, Stochastic Differential Equations, System Identification, Stochastic Control. We are indebted to the IUTAM Bureau for having promoted and sponsored this Sympo sium and the Scientific Committee for having collaborated to the selection of participants and lecturers as well as to a prompt reviewing of the papers submitted for publication into these proceedings. A special thank is due to Frank Kozin: the organization of this meeting was for him ';ery important; he missed the meeting but his organizer ability was present.