Optimal Reliability Indices Research Articles

Analysis of Optimal HVDC Back-to-Back Placement Based on Composite System Reliability

HVDC is a promising interconnection solution for connecting asynchronous systems and ensuring power control. In Indonesia, a remote industrial system in Sumatra is experiencing load growth and has the option to draw power from the Sumatra system. However, due to frequency differences, the use of HVDC is crucial. The Generation Expansion Planning has proposed six converters but not their interconnection points. This study will determine the most reliable interconnection locations. The chosen converters are modular multilevel converters (MMCs) with high modularity. The converter reliability modeling considers voltage levels, the number of modules, and redundancy strategies. This modeling is then implemented at the power system level to obtain the best placement at the available high-voltage (HV) substation options. Determining the best placement is based on the optimal reliability index. The optimal placement also includes the option to convert from HV to medium-voltage (MV) interconnection. MV interconnection offers higher flexibility but tends to be more expensive. The availability for HV converters is 99.69%, while for MV converters, it is slightly higher, at 99.81%. Additionally, converting from HV to MV reduces the SAIFI (system average interruption frequency index) from 0.2668 to 0.2284 occurrences per year, lowering the interruption cost from 7.804 million USD to 5.737 million USD per year. The sensitivity of interruption, investment, and maintenance costs shows that converting at least one HV converter to MV remains economical. In this case study, the optimal converter placement includes Area VI–2, recommended for conversion from HV to a more distributed MV configuration, improving reliability and economic efficiency.

Attitudes scale toward cancer-related cognitive changes - an initial Colombian validation.

The aim of this study was to develop an initial valid tool to measure attitudes toward cancer-related cognitive changes. After revising the literature, three main dimensions were hypothesized. Eight judges were contacted to obtain content validity evidence. A robust Exploratory Factor Analysis (EFA) was performed via a parallel analysis with an Unweighted Least Squares (ULS) estimator and polychoric correlations. The results were crossed with sociodemographic variables to find possible statistical differences and estimate the size effect. Analysis was performed in the software Factor and the statistical package R. A sample of 374 participants was obtained, involving oncology patients, their caregivers, and people from the general community. A statistical fit was found in two dimensions: Awareness and Judgments [root mean squared error of approximation (RMSEA) = 0.042, standardized root mean square residual (SRMR) = 0.02, comparative fit index (CFI) = 0.99, Tucker-Lewis index (TLI) = 0.98] with a moderate correlation between them (r = 0.612). Optimal reliability indices were obtained for the total scale and its dimensions. No real statistical difference was found between sociodemographic variables; the interpretation norms were established via the quartiles. The first attempt to measure the construct of interest was developed with two primary validity evidence based on the content and its internal structure. This instrument could help strengthen the prevention of cancer-related cognitive changes. More research is needed to adhere more valid evidence to the scale.

Risk-Based Assessment of the Reliability Level for Extreme Limit States in IEC 61400-1

The annual target reliability level for structural components is given as β = 3.3 in the main design standard for wind turbines IEC 61400-1 ed. 4. However, since the same safety factors are used for a range of load cases and limit states, deviations in the obtained reliability level can be expected, and it should be considered how to handle this in relation to the development of the IEC TS 61400-9 on probabilistic design measures. In this paper, structural reliability analyses were performed for components designed using safety factors for a range of extreme load cases, and by using the correlation between limit states for different years, the development of the reliability level over time was calculated. A relative risk-based assessment was applied to assess the optimal target reliability level and safety factors. The risk-based assessment explicitly includes the uncertainties, benefits, and costs and can motivate differentiation of the annual reliability level between load cases. Annual reliability indices were found to be in the range of 2.9–3.4, and although this includes values below the target of 3.3, it was also found that the optimal reliability indices were in the same range. The variation in reliability level can be motivated since the optimal target reliability is found to be lower than the current target for load cases with high correlation, as this causes the lifetime reliability level to be comparable to that of other extreme load cases with less correlation.

Colombian Adaptation of the Self-Compassion Scale (SCS).

Self-Compassion is crucial for assessing how people relate to their suffering in moments of personal difficulty. The objective of this study was to check the psychometric properties of the Self-Compassion Scale (SCS) in a Colombian sample. The Spanish version of the SCS was adapted to the Colombian context via a content validity technique. This version was administered to 751 Colombians from the general community. Psychometric analysis was performed using R studio packages. 7 models were tested, the best fit was found for the bifactor ESEM model (χ2/df = 0.86, CFI = 1, TLI= 1, RMSEA= 0.00, SRMR= 0.01). This model produced optimal reliability indices (ωh = 0.83, FD= 0.93, H= 0.96). The study produced initial psychometric evidence of the structure of the SCS in Colombia, with evidence of a general factor in the bifactor ESEM model. More research is needed to justify the complete usage of the SCS in the country.

Relokasi Recloser Dengan Metode Section Technique Pada Jaringan Distribusi 20 kV

The distribution network is the part of the electric power system that is closest to the customer. The reliability of each component of the distribution system equipment can affect the continuity of power service. This study aims to evaluate the reliability of the distribution system at the Citarik Feeder and to improve the system reliability index. The method used is the section technique method and the reliability index values for the Citarik Feeder are obtained, namely SAIFI 1.08958323 faults per customer.year, SAIDI 12.9958323 hours per customer.year. Calculations using ETAP existing conditions, Citarik Feeder SAIFI 1.0679 faults per customer.year, SAIDI 12.9629 hours per customer.year. To increase reliability, a recloser was implemented on the feeder and the most optimal reliability index was obtained, namely, Citarik Feeder SAIFI 0.9885 faults per customer.year, SAIDI 12.8447 hours per customer.year

Determining Target Reliability Index of Structures Based on Cost Optimization and Acceptance Criteria for Fatality Risk

The target reliability index is pivotal to the design, assessment, inspection, and maintenance of structures. It is commonly determined by cost optimization. However, depending on the method of quantifying fatality cost, cost optimization may lead to inconsistent target reliability indices, causing inadequate or unnecessary investment for safety improvement. A new approach to determine the target reliability index is proposed by considering cost efficiency and human safety separately. In this approach, an optimal reliability index is determined through cost optimization, circumventing the quantification of fatality cost in failure consequences. The human safety requirement is fulfilled by adding a constraint to the cost optimization problem based on different acceptance criteria for fatality risk, including individual risk criteria, societal risk criteria, and marginal lifesaving cost principle. The reliability index associated with this constraint is termed herein as an acceptable reliability index. The target reliability index is determined as the maximum between the optimal and acceptable reliability indices. A parametric study is conducted to investigate the effects of various factors on the target reliability index, including the probability density distributions and uncertainties of structural demand as well as the number of potential fatalities.

An approach to the selection of target reliability index of Cable-stayed bridge's main girder based on optimal structural parameter ratio from cost-benefit analysis

A reasonable value of target reliability index is vital for long-span cable-stayed bridges. However, there are few methods to determine the reasonable target reliability index for long-span cable-stayed bridges. In this work, an original approach to solve this problem is developed. In this approach, a concept of optimal structural parameter ratio is presented from the perspective of cost-benefit. Determination of structural target reliability index should meet the requirements of safety and economy. This approach includes two parts. First, based on the statistical parameters of load and resistance of the cable-stayed bridge’s main girder and the most unfavourable bending moments obtained by finite element analysis, the structural reliability index was calculated by the JC method. Second, the reliability indexes with different structural parameter ratios were calculated, and the relational expression between the reliability index and structural parameter ratio was obtained by data fitting. Then the optimal structural parameter ratio was calculated from the perspective of cost-benefit. Finally, by substituting the optimal structural parameter ratio into the relational expression between the reliability index and structural parameter ratio, the optimal reliability index can be obtained. The optimal reliability index corresponding to the optimal structural parameter ratio can be regarded as the target reliability index.

First-order reliability method based on Harris Hawks Optimization for high-dimensional reliability analysis

The first-order reliability method (FORM) is a prevalent method in the structural reliability community. However, when solving the high-dimensional problem with a highly nonlinear limit state function, FORM usually encounters non-convergence or divergence. In this study, an improved FORM combining Harris Hawks Optimization (HHO-FORM) is presented for high-dimensional reliability analysis. HHO is a meta-heuristic algorithm mimicking the predatory behavior of Harris hawks, and efficient in finding the global optimum of high-dimensional problems. In HHO-FORM, the reliability index is firstly formulated as the solution of a constrained optimization problem according to the FORM theory. Then, the constraints are handled with the exterior penalty function method. In addition, the optimal reliability index is determined by the Harris Hawks Optimization that accelerates the convergence by the population-based mechanism and the strategy of Levy Flight. The HHO-FORM does not require the derivatives of the limit state functions that reduce the computational burden for high-dimensional problems. So the simplicity of HHO-FORM greatly improves the efficiency in solving high-dimensional reliability problems. The HHO-FORM is firstly tested on three challenging numerical high-dimensional problems and then applied to two high-dimensional engineering problems to verify its performance. Four gradient-based FORM algorithms and four heuristic-based FORM algorithms are also compared with the proposed method. The experimental results demonstrate that HHO-FORM provides good accuracy and efficiency for high-dimensional reliability problems.

Global optimal reliability index of implicit composite laminate structures by evolutionary algorithms

With uncertainty, reliability assessment is fundamental in structural optimization, because optimization itself is often against safety. To avoid Monte Carlo methods, the Reliability Index Approach (RIA) approximates the structural failure probability and is formulated as a minimization problem, usually solved with fast gradient-methods, at the expense of local convergence, or even divergence, particularly for highly dimensional problems and implicit physical models. In this paper, a new procedure for global convergence of the RIA, with practical efficiency, is presented. Two novel evolutionary operators and a mixed real-binary genotype, suitable to hybridize any Evolutionary Algorithm with elitist strategy, are developed. As an example, a shell laminate structure is presented and the results validated, showing good convergence and efficiency. The proposed method is expected to set the basis for further developments on the design optimization of more complex structures with multiple failure criteria.

RELIABILITY BASED DESIGN OF THE ROCK SIDE SLOPE FOR MIDDLE PLATEAU IN MOKATTAM AREA CONSIDERING OPTIMAL COST VALUE

Design solutions for the problems of the rock side slope stability, in general, are one of themost critical issues in geo-technical engineering profession, due to the fact that the values ofrock parameters are difficult to be considered reliable, because of the uncertainties existing ingeological system. This research aims to introduce reliability based design of the rock sideslope stability considering optimal cost value. The idea for obtaining the optimal cost valuedepends on two main critical parameters. These two main critical parameters are uni-axialcompressive strength (U.C.S) and geologic strength index (G.S.I). Both of them have beencalculated based on statistical calculations of mean and standard deviations. A strengthcriterion is needed to characterize the rockmass in geotechnical engineering. There are threecriteria are used to describe the strength of a material: bilinear Mohr-Coulomb criterion,nonlinear Hoek-Brown criterion and special spalling criterion must be used in special case ofmassive, brittle rocks. Nonlinear Hoek-Brown criterion has been used in this study; becauseof some limitations associated with the use of the Mohr-Coulomb criterion. RocData programhave been utilized for obtaining the Hoek-Brown parameters (m, s), Slide program has beenemployed for calculating the reliability index, factor of safety and probability of failure foreach case study for upper plateau in Mokattam area. The concept of design is based on thenecessity of using reinforcement. If the design of using rock parameters is safe and reliable,there is no need for reinforcement; otherwise design of rock bolts should be used as a supportsystem to improve reliability and factor of safety. The current simplified method has beenutilized to consider the cost of failure to find the optimal length of support and optimalreliability index. The study concluded that the suggested technique of nonlinear Hoek BrownCriterion is effective for helping the designer in finding the optimal length of support thatmeets the optimal reliability index and optimal cost value for two main critical parameters.

Impact analysis of observation coupling on reliability indices in a geodetic network

Abstract An optimally designed geodetic network is characterised by an appropriate level of precision and the lowest possible setup cost. Reliability, translating into the ability to detect blunders in the observations and higher certainty of the obtained point positions, is an important network characteristic. The principal way to provide appropriate network reliability is to acquire a suitably large number of redundant observations. This approach, however, faces limitations resulting from the extra cost. This paper analyses the possibility of providing appropriate reliability parameters for networks with moderate redundancy. A common problem in such cases are dependencies between observations preventing the acquisition of the required reliability index for each of the individual observation. The authors propose a methodology to analyse dependencies between observations aiming to determine the possibility of acquiring the optimal reliability indices for each individual observation or groups of observations. The suggested network structure analysis procedures were illustrated with numerical examples.

Reliability allocation method based on multidisciplinary design optimization for electromechanical equipment

Reliability design is one important link to assure the product’s quality. Reliability allocation is the main task of reliability design, which is influenced by cost, manufacturing consistency, and other factors. Reliability, cost, and manufacturing consistency are coupled and influenced by each other. To find the global optimal reliability indices, one modeling and solving method of reliability allocation based on multidisciplinary design optimization was proposed in the paper. The influence factors of reliability allocation were analyzed and calculated or fuzzy processed. The reliability allocation optimization models were created, and the models were decomposed by the calculation frame of collaborative optimization. The genetic algorithm of the system-level optimization and the sequential quadratic programming algorithm of the disciplinary-level optimization were adopted. As one typical electromechanical equipment, CNC cylindrical grinder was allocated of reliability by the method proposed in the paper. The results showed that the cost can be dropped 3.45%, 4.76%, 4.72%, and 8.45% compared by equal allocation method, fuzzy allocation method, AGREE allocation method, and actual cost, respectively. The reliability allocation method proposed in the article can be used in design of electromechanical equipment to reduce costs.

Optimal Network Topology and Reliability Indices to be used in the Design of Power Distribution Networks in Oil and Gas Plants

The cost of loss of production in oil and gas plants is on average 6.5 times higher than that of plants in any other industry. Thus the reliability performance and analysis of oil and gas plants are unique. There have been many studies that have produced reliability indices for equipment that is used in industrial distribution networks, but these are all industry generic and none are specific to the oil and gas industry. This paper presents a set of equipment reliability indices that has been established from data collected from oil and gas plants and is suitable for use in reliability evaluations of the distribution networks of oil and gas plants. In the design of distribution networks for new oil and gas plants, engineers either do not have enough operational data, enough time or do not know how to perform the analysis required for establishing what type of network topology to use. This paper recommends the optimal network topology to use in such cases and provides evidence to support this proposal.

Optimal reliability planning for a composite electric power system based on Monte Carlo simulation using particle swarm optimization

A methodology for planning the optimal reliability indices of system components for a composite electric power system based on state sampling non-sequential Monte Carlo simulation using particle swarm optimization (PSO) algorithm is presented. The indices designed are forced outage rate of system components and expected demand not served (EDNS) of the system. The optimal reliability planning problem has been formulated as an optimization problem of minimizing the system interruption cost and the component investment cost. The cost functions are modeled as a function of forced outage rate and EDNS. The EDNS of the system for a particular system reliability level is evaluated based on state sampling non-sequential–Monte Carlo simulation and the dc load flow based load curtailment model. PSO algorithm is employed to minimize the reliability planning model. The applications of the proposed methodology are illustrated through case studies carried out using Modified Stagg and El-Abiad 5-bus system and IEEE 14-bus system. The effectiveness of this approach is validated by comparing the results obtained with the solution of reliability planning model using genetic algorithm optimizer.

Risk assessment for structural design criteria of FPSO systems. Part II: Consequence models and applications to determination of target reliabilities

The paper presents applications of the framework for generic risk assessment for FPSO systems described in a companion paper [1]. Consequence models for structural risk assessment are developed for failure of hull girder sections, hull components and mooring lines using Bayesian Probabilistic Networks (BPN). The estimation of conditional probabilities required in the BPN models, such as the probability of a combined failure of several components and system failure conditional on components failure, are discussed. The risk assessment framework is applied for decision making on target reliabilities for ULS design of mooring lines. The target reliabilities are found by optimizing expected life-cycle costs and verifying compliance with risk acceptance criteria developed according to the Life Quality Index (LQI) principle. It is shown that the optimal reliability index, which minimizes total expected costs, may not always lead to an acceptable solution from the point-of-view of the LQI criterion.

생애주기비용을 이용한 잔교식 안벽의 신뢰도지수 최적화

Optimal reliability indices were found by optimizing life cycle cost(LCC) of pier type quay walls. Failure probability of pier and shore bridge were calculated by response surface method. Then, they were used to obtain recovery cost after damage. Costs for initial construction and maintenance were also considered in finding optimal reliability indices. Target reliability indices which may be used in reliability based design were suggested by numerical examples under seismic load and ship load.

A method for reliability-based economic design of building structures

In limit states design codes for building structures, the load and resistance factors are derived based on a ‘;target’ reliability index, which is determined based on a code calibration process. It is not clear whether the target reliability index selected through the code calibration is optimal with respect to the cost, because through calibration the structural safety is achieved quantitatively while the economic aspects are only considered qualitatively. The intention of the present paper is to formulate a basic approach to reliability-based economic design, based on structural reliability theory. The focus of the paper is to derive an analytical solution to optimized reliability index. A parametric study is conducted for sensitivity analysis of the optimal reliability index to different variables. Finally, the application of the solution to design codes, i.e. determining load and resistance factors in design formulae, is outlined. Dans les codes de conception d'états limite se rapportant à la construction des structures de bâtiments, la charge et les facteurs de résistance reposent au départ sur un index de fiabilitié ‘cible’, qui est basé sur un processus de calibrage de code. Il n'est pas possible de savoir si l'index de fiabilitié cible choisi par le calibrage de code est optimal en ce qui concerne le coût parce que lors du calibrage, la sécurité structurelle est évaluée de façon quantitative. L'objectif de cet article est de formuler une appréciation de référence sur la conception reposant sur la fiabilité économique, basée sur la théorie de fiabilité structurelle; le point fort de ce texte est de trouver une solution analytique afin d'optimiser l'index de fiabilité. Une étude paramétrique est conduite pour analyser la sensibilité de la fiabilitié optimale de l'index par rapport aux diffeérentes variables. Au total, est proposée une solution consistant à concevoir des codes, c'est-à-dire la détermination de la charge et des facteurs de résistance sous l'aspect de formules.

Evaluation of optimal-reliability indices for electrical distribution systems

A method to calculate the optimal values of reliability indices for a load point in an electrical distribution system is presented. The problem is formulated as an optimization problem and solved by the gradient projection method; the objective is to minimize interruption cost. The algorithm is very useful and powerful for extending the existing network and planning new networks. It has been tested on a practical system (the Port-Fouad power network), and the results are discussed. Once the optimal reliability indices are determined, modification of the system by equipment replacement and future system planning can be done in such a way that the interruption cost is minimized. >