Reliability Analysis

This paper presents a process of systematization and analysis of the reliability parameters of a proportional hydraulic platform that aims to study position control using hydraulic systems. Currently the positioning systems using hydraulic circuits include mechanical and electronic components and software. These automatic systems involve diverse and complex technologies, for which reason the reliability analysis is difficult. Moreover, the failure modes which can occur in each item can produce distinct effects, increasing the complexity of this analysis. The control of all parameters involved becomes very difficult for the design agents, with consequences for the other phases of the life cycle. In this regard a methodology to systemize the information necessary to obtain a product with reliability is proposed. In this process, hierarchic FTA and FMEA diagrams are used as tools for the systematization of the reliability parameters, and Petri Nets are is used to represent the states a...

Risk is defined as the probability of a specific adverse event occurring within a specific period, while Quantitative risk assessment (QRA) is the development of a quantitative estimate of risk based on engineering evaluation and mathematical techniques by combining estimate of incident consequences and frequencies. In view of the increase in the use of railways as the mode of transportation for hazardous materials throughout the world, the associated risk analysis should be taken into concern. In this study, the failure frequency of the transportation of ammonia from the Petronas fertilizers Kedah (PFK) plant in Gurun (Northern part of Peninsular Malaysia), to the Chemical Company Malaysia (CCM) fertilizer's facilities in Port Klang (South-western part of Peninsular Malaysia) was evaluated by incorporating the human error assessment. The study highlighted the importance of human error contributions in the failure frequency analysis and its impact on the selected failure scenarios. Besides, it also shows that the application of the human error assessment and reduction technique (HEART), which is a useful human reliability analysis tool, should be used in parallel with the fuzzy arithmetic approach to reduce the uncertainties involved in the estimation of human error probabilities, and hence, to reduce the likelihood of incorrect risks estimates being assessed. The results suggested that the commonly applied approach in quantitative risk assessments, which only consider equipment failures in the failure frequency estimations, are clearly an underestimate of the potential causes of failures leading to hazardous material releases, and hence, the calculated risks based do not reflect the actual risks. © 2008 American Institute of Chemical Engineers Process Saf Prog, 2009

Geotechnical design has traditionally been done using working stress design (WSD). Working stress design identifies limit states for a structure, then protects against their occurrence using factors of safety. Load and resistance factor design (LRFD) uses load and resistance factors instead of factors of safety. LRFD also establishes the geotechnical resistance much more precisely than WSD. This research establishes load

Purpose – The purpose of this paper is to analyse and compare the downtime of four drilling machines used in two underground mines in Sweden. The downtime of these machines was compared to show what problems affect downtime and which strategies should be applied to reduce it. Design/methodology/approach – The study collects failure data from a two-year period for four drilling machines and performs reliability analysis. It also performs downtime analysis utilising a log-log diagram with a confidence interval. Findings – There are notable differences in the downtime of most of the studied components for all machines. The hoses and feeder have relatively high downtime. Depending on their downtime, the significant components can be ranked in three groups. The downtime of the studied components is due to reliability problems. The study suggests the need to improve the reliability of critical components to reduce the downtime of drilling machines. Originality/value – The method of analys...

Lifetime management of underground pipelines is mandatory for safe hydrocarbon transmission and distribution systems. The use of high-density polyethylene tubes subjected to internal pressure, external loading and environmental variations requires a reliability study in order to define the service limits and the optimal operating conditions. In service, the time-dependent phenomena, especially creep, take place during the pipe lifetime, leading to significant strength reduction. In this work, the reliability-based assessment of pipe lifetime models is carried out, in order to propose a probabilistic methodology for lifetime model selection and to determine the pipe safety levels as well as the most important parameters for pipeline reliability. This study is enhanced by parametric analysis on pipe configuration, gas pressure and operating temperature.

This paper proposes a methodology to apply Bayesian networks to structural system reliability reassessment, with the incorporation of two important features of large structures: (1) multiple failure sequences, and (2) correlations between component-level limit states. The proposed method is validated by analytical comparison with the traditional reliability analysis methods for series and parallel systems. The Bayesian network approach is combined with the branch-and-bound method to improve its efficiency and to facilitate its application to large structures. A framed structure with multiple potential locations of plastic hinges and multiple failure sequences is analyzed to illustrate the proposed method.

One of the most prominent statistical distributions is the Weibull distribution. The recent modifications in this distribution have enhanced its application but only in specific fields. To introduce a more generalized Weibull distribution, in this work beta exponentiated modified Weibull distribution is established. This distribution consolidate the exponential, skewed and symmetric shapes into one density. The proposed distribution also contains nineteen lifetime distributions as a special case, which shows the flexibility of the distribution. The statistical properties of the proposed model are derived and discussed, including reliability analysis and order statistics. The hazard function of the proposed distribution can have a unimodal, decreasing, bathtub, upside-down bathtub, and increasing shape that make it effective in reliability analysis. The parameters of the proposed model are evaluated by maximum likelihood and least squares estimation methods. The significance of the b...

Using the Stochastic Finite Element Method (SFEM) to perform reliability analysis of the free vibration of composite plates with material and fabrication uncertainties has received much attention lately. In this work the stochastic analysis is performed using the First-Order Reliability Method (FORM-method 2) and the Second-Order Reliability Method (SORM). The basic random variables include laminae stiffness properties and material density, as well as the randomness in ply orientation angles. Modeling of the composite behavior utilizes a nine-noded isoparametric Lagrangian element based on the third-order shear deformation theory. Calculating the eigenvectors at the mean values of the variables proves to be a reasonable simplification which significantly increases solution speed. The stochastic finite element code is validated using comparisons with results of Monte Carlo simulation technique with importance sampling. Results show that SORM is an excellent rapid tool in the stochastic analysis of free vibration of composite plates, when compared to the slower Monte Carlo simulation techniques.

The jurisprudence that has developed in the last twenty-five years under Batson v. Kentucky may be fairly described as indeterminate, unprincipled, and generally ineffective. Scholarly literature points to a variety of reasons for this state of affairs. This Article focuses on one source of the problem— the lack of clarity in the law concerning the evidentiary framework (methodology) needed for

In the Army mechanical fatigue subject to external and inertia transient loads in the service life of mechanical systems often leads to a structural failure due to accumulated damage. Structural durability analysis that predicts the fatigue life of mechanical components subject to dynamic stresses and strains is a compute intensive multidisciplinary simulation process, since it requires the integration of several

Six phoneticians rated the voices of 26 American and 22 German speakers on nine voice quality parameters which were discussed and illustrated by tape-recorded examples before the rating sessions. A reliability analysis showed highly significant interrater agreement on most parameters. Intercorrelations of the expert ratings and correlations with lay ratings of voice are reported and discussed. In concluding, empirical voice-personality

One of the most prominent statistical distributions is the Weibull distribution. The recent modifications in this distribution have enhanced its application but only in specific fields. To introduce a more generalized Weibull distribution, in this work beta exponentiated modified Weibull distribution is established. This distribution consolidate the exponential, skewed and symmetric shapes into one density. The proposed distribution also contains nineteen lifetime distributions as a special case, which shows the flexibility of the distribution. The statistical properties of the proposed model are derived and discussed, including reliability analysis and order statistics. The hazard function of the proposed distribution can have a unimodal, decreasing, bathtub, upside-down bathtub, and increasing shape that make it effective in reliability analysis. The parameters of the proposed model are evaluated by maximum likelihood and least squares estimation methods. The significance of the beta exponentiated modified Weibull distribution for modeling is illustrated by the study of real data. The numerical study indicates that the new proposed distribution gives better results than other comparable distributions.

This research study proposed a novel algorithm, called time-counter, to optimise inspection intervals of production systems. The developed algorithm was applied to two active draglines. The algorithm evaluated random uptime/downtime characteristics of the draglines and the planned dragline halts in the mine. Physical and random non-physical costs were included and annual maintenance cost minimisation was achieved. Dragline-1 and Dragline-2 inspection intervals were optimised as 232 and 184 h and their maintenance costs were reduced by 5.9 and 6.2% compared to the current interval, respectively. This study is the first initiative in cost-effective inspection interval optimisation of a mining machinery.

This paper explores the challenges, opportunities, benefits, and limitations of reliability assessment of major and critical components of infrastructure using structural health monitoring (SHM) data. The focus is on bridges but the discussion is intentionally kept at a general level so that it is applicable to a wide range of infrastructural systems. This paper argues that holistic and strategic approaches are required to pave the way to the realization of the latent befits of SHM and maximising the value of information derived from SHM data. Firstly, it discusses these benefits and situations were implementing SHM can be considered to be potentially most useful. It later discusses two frameworks for seeing the SHM technologies in a broader context of asset management decision making. The first framework is underpinned by prioritisation of structures for monitoring, moves to guidelines for instrumentation and SHM data analysis, and ends with the integration of SHM results into asset management and disaster emergency plans and decisions. The second framework understands SHM as a starting point in a value chain of enabling technologies delivering information to infrastructure stakeholders. A separate section is devoted to deliberations on the emerging and important way of thinking of SHM outputs as ‘big data’ and associated challenges. One of the opportunities brought about by abundant SHM big data is the prospect of creating better ‘digital twins’ – a high fidelity, multi-physics, multi-scale models of structural systems underpinned by and calibrated using SHM data to assess and forecast reliability. Finally, an example of a recently constructed 12-span, 690 m long post-tensioned concrete viaduct equipped with a continuously operating SHM system comprising around 90 channels of strain, temperature, displacement and environmental data, and also subjected to one-off ambient dynamic testing campaigns is presented. The proposed framework for structural reliability assessment of the bridge integrates information on the mechanical properties of construction materials obtained via laboratory and in situ tests, the heterogeneous SHM and dynamic testing data from the full scale structure, and predictions from numerical models of the bridge. Several aspects of this information fusion will be discussed. Dynamic tests and static responses, including time dependent creep and shrinkage behaviour, enable system identification of the structure and creation, via model updating, of numerical (finite element) structural models, or ‘digital twins’, of the physical structure. These models can in turn be used for assessing quantitatively the bridge time dependent condition, health, safety and performance via more realistic numerical reliability evaluations. The collected temperature and strain and displacement data form the basis for generating realistic spatial and temporal load fields for reliability assessment utilizing calibrated numerical models of the structure. The monitoring of responses to traffic loads enables formulation of the dynamic live load demands actually acting on the bridge and response to these.