System reliability analysis of structures subjected to fatigue induced sequential failures using evolutionary algorithms

In the past, many catastrophic failures have occurred due to lack of redundancy and managerial oversight. For example, it was found that local failures due to improper welds that connected the suspended truss to the anchor trusses caused the collapse of the Grand Sung-Soo Bridge in Seoul, South Korea on October 21, 1994. Due to a lack of structural redundancy, the initial bridge rib failure was followed by other bridge failures leading to system collapse. With proper system reliability analysis, such cascading failures could be foreseen by stakeholders. To help make better risk-informed decisions, system reliability methods have been developed to analyze general structures subjected to the risk of cascading system-level failures caused by local fatigue-induced failures. For efficient reliability analysis of such complex system problems, many research efforts have been made to identify critical failure sequences with significant likelihoods by an event-tree search coupled with system reliability analyses: however, this approach is time-consuming or intractable due to repeated calculations of the probabilities of innumerable failure modes, which often necessitates using heuristic assumptions or simplifications. Recently, a decoupled approach was proposed: critical failure modes are first identified in the space of random variables without system reliability analyses or an event-tree search, then an efficient system reliability analysis was performed to compute the system failure probability based on the identified modes. In order to identify critical failure modes in the decreasing order of their relative contributions to the system failure probability, a simulation-based selective searching technique was developed by use of a genetic algorithm. The system failure probability was then computed by a multi-scale system reliability method that can account for the statistical dependence among the component events as well as among the identified failure modes. Part of this work presents this decoupled approach in detail and demonstrates its applicability to complex bridge structural systems that are subjected to the risk of cascading failures induced by fatigue. Using a recursive formulation for describing limit-states of local fatigue cracking, the system failure event is described as a disjoint cut-set event. Critical cut-sets, i.e. failure sequences with significant likelihood are identified by the selective searching technique using a genetic algorithm. Then, the probabilities of the cut-sets are computed by use of crude Monte Carlo simulations. Owing to the mutual exclusiveness of the cut-sets, the lower-bound on the system cascading failure probability is obtained by a simple addition of the cut-set probabilities. A numerical example of a bridge structure demonstrates that the proposed search method skillfully identifies the dominant failure modes contributing most to the system failure probability, and the system reliability analysis method accurately evaluates the system failure probability with statistical dependence fully considered. An example bridge with approximately 100 truss elements is considered to investigate the applicability of the method to realistic large-size structures. The efficiency and accuracy of the method are demonstrated through comparison with Monte Carlo simulations. The aforementioned system reliability analysis is based off of an a priori inspection cycle time and computes the probability that the time until the system failure is smaller than the given inspection cycle. Since most field practitioners do not know this value beforehand, a new method has been developed to perform simplified reliability analysis for many performance levels simultaneously. The First-Order Reliability Method (FORM) is often used for structural reliability analysis. The proposed method uses a multi-objective genetic algorithm, called Non-dominated based Sorting Genetic Algorithm II (NSGA II) to perform many FORM analyses simultaneously to generate a Pareto Surface of design points. From this Pareto surface, data on cases of ???critical but unlikely failures??? for short inspection cycle times and cases of ???less-critical but highly likely failures??? for long inspection cycle times can be found at once. From the nature of this method, this approach is termed as ???Multi-Objective??? FORM. Part of this work presents this Multi-objective FORM in detail. The applicability of this approach is shown through two numerical examples. The first example is a general situation with few random variables. The second example analyzes a statically indeterminate truss subjected to cyclic loading. Both numerical examples are validated with crude-MCS results and show that the method can find a full Pareto Surface, which provides reliability analysis results at a range of performance levels along with the probability distribution of the performance quantity

System Reliability of an Existing Jacket Platform (Failure Paths and System Reliability Index)

The objective of the project is to determine the reliability of an existing jacket platform in Malaysia. This can be achieved by determining the system probability of failures as well as the accompanied system reliability index. Those two parameters are important indicators for assessing the integrity and reliability of the platform, and will point out whether the platform is strong enough for continued and prolonged operation. A lot of studies in the past have been focusing on component reliability which does not necessarily indicate the robustness of the platform as a whole. Thus, this project assess the whole system reliability by determining possible failure paths of the structure, the system probability of failures and its related system reliability index. In order to do that, first, the probability of failure of each component needs to be determined. From that, the probability of failure of each failure path and the probability of failure of the system can be calculated using the bounding formulae (Simple Bound). For component reliability, response surface method will be used to determine the global response as well as the local response of the structure. Those surfaces will be the input for the limit state functions. The probability of failure of each component can then be determined from the function using FORM method. Pushover analysis and the bounding formulae will used to determine most probable failure paths, the system probability of failures and corresponding reliability index. From the study, three probable failure paths have been determined, and it is found that the system reliability index of the structure is with corresponding failure probability, =1.36E-20 . With this, it can be assumed that the platform is robust and the probability of the collapse is very small

System Reliability of an Existing Jacket Platform (Failure Paths and System Reliability Index)

The objective of the project is to determine the reliability of an existing jacket platform in Malaysia. This can be achieved by determining the system probability of failures as well as the accompanied system reliability index. Those two parameters are important indicators for assessing the integrity and reliability of the platform, and will point out whether the platform is strong enough for continued and prolonged operation. A lot of studies in the past have been focusing on component reliability which does not necessarily indicate the robustness of the platform as a whole. Thus, this project assess the whole system reliability by determining possible failure paths of the structure, the system probability of failures and its related system reliability index. In order to do that, first, the probability of failure of each component needs to be determined. From that, the probability of failure of each failure path and the probability of failure of the system can be calculated using the bounding formulae (Simple Bound). For component reliability, response surface method will be used to determine the global response as well as the local response of the structure. Those surfaces will be the input for the limit state functions. The probability of failure of each component can then be determined from the function using FORM method. Pushover analysis and the bounding formulae will used to determine most probable failure paths, the system probability of failures and corresponding reliability index. From the study, three probable failure paths have been determined, and it is found that the system reliability index of the structure is with corresponding failure probability, =1.36E-20 . With this, it can be assumed that the platform is robust and the probability of the collapse is very small

System reliability evaluation of in-service cable-stayed bridges subjected to cable degradation

© 2018 Informa UK Limited, trading as Taylor & Francis Group The cables in a cable-stayed bridge are critical components supporting the long-span girders and ensuring their functionality. However, cables are prone to fatigue damage and atmospheric corrosion, which directly affect the bridge safety. This study presents a framework for system reliability evaluation of in-service cable-stayed bridges subjected to cable degradation. The effect of cable strength degradation on the system reliability is demonstrated through simulation on a parallel-series system representation. Learning machines are utilised to approximate the non-linear and dynamic response functions of critical components due to cable rupture, and the system reliability is finally evaluated from the event tree established by the β-unzipping method. Both short-span and long-span cable-stayed bridges are selected as prototypes to investigate the influence of cable degradation on the system reliability. On this basis it is revealed that cable degradation can significantly influence the collapse mechanism of a cable-stayed bridge and thereby lead to a significant reduction in the system reliability. This phenomenon is associated with cable spacing, where a spare cable system seems more sensitive to cable gradation. It is demonstrated that the consideration of cable corrosion and correlation is essential for lifetime safety evaluation of in-service cable-stayed bridges

Deep Space Network information system architecture study

The purpose of this article is to describe an architecture for the Deep Space Network (DSN) information system in the years 2000-2010 and to provide guidelines for its evolution during the 1990s. The study scope is defined to be from the front-end areas at the antennas to the end users (spacecraft teams, principal investigators, archival storage systems, and non-NASA partners). The architectural vision provides guidance for major DSN implementation efforts during the next decade. A strong motivation for the study is an expected dramatic improvement in information-systems technologies, such as the following: computer processing, automation technology (including knowledge-based systems), networking and data transport, software and hardware engineering, and human-interface technology. The proposed Ground Information System has the following major features: unified architecture from the front-end area to the end user; open-systems standards to achieve interoperability; DSN production of level 0 data; delivery of level 0 data from the Deep Space Communications Complex, if desired; dedicated telemetry processors for each receiver; security against unauthorized access and errors; and highly automated monitor and control

Optimisation methods in structural systems reliability

Imperial Users onl

Estimating Pump Reliability using Recurrent Data Analysis for Failure Modes

Major equipment such as centrifugal pumps play an important role in oil and gas business. The main concern which is highlighted is the pumps’ performance at site whether it is reliable or instead. In this study, the analysis is done in order to estimate pump reliability using recurrent data analysis (RDA) for failure modes. Thus four centrifugal pumps in Onshore Slugcatcher (OSC) terminal are used as the case study to verify the analysis done on repairable system. The reliability and availability of the centrifugal pumps could be determined using parametric recurrent data analysis approach. Thus the data regarding the centrifugal pumps operated in Onshore Slugcatcher terminal is collected from PETRONAS Carigali Sdn. Bhd before they will be further analysed using reliability software such as Weibull++ and BlockSim from ReliaSoft Corporation. Based on the explanatory results, the failure modes of respective centrifugal pumps are identified and categorized based on ISO 14224 standard. Next, Weibull++ software is used to determine the failure and repair distributions, while the reliability block diagram of the pump by failure modes is generated using BlockSim. The reliability and availability by failure modes and pump units are determined. The further analysis is hoped will benefit the maintenance team to come up with better maintenance strategy to improve the pumps’ performance. Keywords: Recurrent Data Analysis (RDA), Repairable System, Reliability Block Diagram, Centrifugal pump

Embracing open innovation to acquire external ideas and technologies and to transfer internal ideas and technologies outside

The objective of this dissertation is to increase understanding of how organizations can embrace open innovation in order to acquire external ideas and technologies from outside the organization, and to transfer internal ideas and technologies to outside the organization. The objective encompasses six sub-objectives, each addressed in one or more substudies. Altogether, the dissertation consists of nine substudies and a compendium summarizing the substudies. An extensive literature review was conducted on open innovation and crowdsourcing literature (substudies 1–4). In the subsequent empirical substudies, both qualitative research methods (substudies 5–7) and quantitative research methods (substudies 8–9) were applied. The four literature review substudies provided insights on the body of knowledge on open innovation and crowdsourcing. These substudies unveiled most of the influential articles, authors, and journals of open innovation and crowdsourcing disciplines. Moreover, they identified research gaps in the current literature. The empirical substudies offer several insightful findings. Substudy 5 shows how non-core ideas and technologies of a large firm can become valuable, especially for small firms. Intermediary platforms can find solutions to many pressing problems of large organizations by engaging renowned scientists from all over world (substudy 6). Intermediary platforms can also bring breakthrough innovations with novel mechanisms (substudy 7). Large firms are not only able to garner ideas by engaging their customers through crowdsourcing but they can also build long-lasting relations with their customers (substudies 8 and 9). Embracing open innovation brings challenges for firms too. Firms need to change their organizational structures in order to be able to fully benefit from open innovation. When crowdsourcing is successful, it produces a very large number of new ideas. This has the consequence that firms need to allocate a significant amount of resources in order to identify the most promising ideas. In an idea contest, customarily, only one or a few best ideas are rewarded (substudy 7). Sometimes, no reward is provided for the selected idea (substudies 8 and 9). Most of the ideas that are received are not implemented in practice

A new system formulation for the tolerance analysis of overconstrained mechanisms

The goal of tolerance analysis is to verify whether design tolerances enable a mechanism to be functional. The current method consists in computing a probability of failure using Monte Carlo simulation combined with an optimization scheme called at each iteration. This time consuming technique is not appropriate for complex overconstrained systems. This paper proposes a transformation of the current tolerance analysis problem formulation into a parallel system probability assessment problem using the Lagrange dual form of the optimization problem. The number of events being very large, a preliminary selective search algorithm is used to identify the most contributing events to the probability of failure value. The First Order Reliability Method (FORM) for systems is eventually applied to compute the probability of failure at low cost. The proposed method is tested on an overconstrained mechanism modeled in three dimensions. Results are consistent with those obtained with the Monte Carlo simulation and the computing time is significantly reduced