Time-based Reliability Research Articles

Rainwater Catchment System Reliability Analysis for Al Abila Dam in Iraq’s Western Desert

Rainwater Catchment System Reliability (RCSR) is the chance that a system will deliver the required water for an interval of time. Rainwater Harvesting (RWH) is gaining popularity as a potential alternative water source for household or agricultural use. The reliability of the Al Abila dam in the western desert of Iraq was analyzed using a water budget simulation model and two explanations of reliability, time-based reliability, and volumetric reliability. To evaluate rainwater harvesting system performance, comprehensive software utilizing a method for everyday water balance using data from 20 years of daily rainfall. According to the findings, volumetric reliability, and for the three climate scenarios (wet, average, and dry year), increased as the storage volume increased until a threshold accrued on the storage capacity of 11.7 × 105 m3. While time-based reliability shows an increase up to a storage volume of 10.2 × 105 m3. Volumetric reliability of roughly 34–75% may be achieved, while only 14–28% time-based reliability may be achieved. Water saving efficiency decreases with increasing demand fraction, while the runoff coefficient has no significant influence on water effectiveness. While growing storage fraction value increases the effectiveness of water conservation and the value of the runoff coefficient influences the water saving efficiency. For both cases, water saving efficiency for the dam does not reach 50%. Using daily rainfall data, the technique given in this paper might be applied to predict water savings and the RWH systems’ reliability in different arid and semi-arid areas.

Assessment of reservoir performance under climate change: A case study in Shumbrite reservoir, South Gojjam sub-basin, Ethiopia

Climate change has the potential to reduce the water resource availability and hence the amount of storage in reservoirs. In this study, we assessed the impact of climate change on the performance of the Shumbrite reservoir using outputs from the CORDEX-Africa project, MPI Global Circulation Model (GCM) under three Representative Concentration Pathways (i.e., RCP2.6, RCP4.5 and RCP8.5). The trend analysis of future precipitation shows a decrease in the range of 0.57%–4.2%, with a maximum decrease under RCP2.6, and temperature (both maximum and minimum) shows an increasing trend as compared to the baseline period. The HBV model simulated future mean annual flow volume shows a decrease (ranges 0.06% to 1.64%) for RCP2.6 and RCP4.5 and a significant increase of 5.03% for RCP8.5 compared to the baseline period. Mean annual irrigation water demand from CROPWAT shows an increase (0.74% to 8.4%) for all RCPs compared to the baseline period. The time-based reliability for the Shumbrite reservoir has an average value above 80%. The resilience values are below 50% for all RCPs and hence the reservoir will take an extended period to recover from an inability to achieve the target demand volume. The dimensionless vulnerability shows a value below 50% which indicates that the reservoir has no insufficient flow to meet the demand. Generally, the reservoir can be used sustainably with operation rule curves. Generally, this study adds a contribution to the evaluation of small-scale reservoirs under a changing climate and the preparation of guide curves for the respective release.

Smart Rainwater Harvesting for Sustainable Potable Water Supply in Arid and Semi-Arid Areas

This paper presents a smart rainwater harvesting (RWH) system to address water scarcity in Palestine. This system aims to improve the water harvesting capacity by using a shared harvesting system at the neighborhood level and digital technology. The presentation of this system is organized as follows: (i) identification of the challenges of the rainwater harvesting at the neighborhood level, (ii) design of the smart RWH system architecture that addresses the challenges identified in the first phase, (iii) realization of a simulation-based reliability analysis for the smart system performance. This methodology was applied to a residential neighborhood in the city of Jenin, Palestine. The main challenges of smart water harvesting included optimizing the shared tank capacity, and the smart control of the water quality and leakage. The smart RWH system architecture design is proposed to imply the crowdsourcing-based and automated-based smart chlorination unit to control and monitor fecal coliform and residual chlorine: screens, filters, and the first flush diverter address RWH turbidity. Water level sensors/meters, water flow sensors/meters, and water leak sensors help detect a water leak and water allocation. The potential time-based reliability (Re) and volumetric reliability (Rv) for the smart RWH system can reach 38% and 41%, respectively. The implication of the smart RWH system with a dual water supply results in full reliability indices (100%). As a result, a zero potable water shortage could be reached for the dual water supply system, compared to 36% for the municipal water supply and 59% for the smart RWH system. Results show that the smart RWH system is efficient in addressing potable water security, especially when combined with a dual water supply system.

Assessing Reservoir Performance under Climate Change. When Is It Going to Be Too Late If Current Water Management Is Not Changed?

Climate change is modifying the way we design and operate water infrastructure, including reservoirs. A particular issue is that current infrastructure and reservoir management rules will likely operate under changing conditions different to those used in their design. Thus, there is a big need to identify the obsolescence of current operation rules under climate change, without compromising the proper treatment of uncertainty. Acknowledging that decision making benefits from the scientific knowledge, mainly when presented in a simple and easy-to-understand manner, such identification—and the corresponding uncertainty—must be clearly described and communicated. This paper presents a methodology to identify, in a simple and useful way, the time when current reservoir operation rules fail under changing climate by properly treating and presenting its aleatory and epistemic uncertainties and showing its deep uncertainty. For this purpose, we use a reliability–resilience–vulnerability framework with a General Circulation Models (GCM) ensemble under the four Representative Concentration Pathways (RCP) scenarios to compare the historical and future long-term reservoir system performances under its current operation rule in the Limarí basin, Chile, as a case study. The results include percentiles that define the uncertainty range, showing that during the 21st century there are significant changes at the time-based reliability by the 2030s, resilience between the 2030s and 2040s, volume-based reliability by the 2080s, and the maximum failure by the 2070s. Overall, this approach allows the identification of the timing of systematic failures in the performance of water systems given a certain performance threshold, which contributes to the planning, prioritization and implementation timing of adaptation alternatives.

Allocation of reservoir releases under drought conditions: a conflict-resolution approach

One challenge facing water managers is how to supply various downstream claims with conflicting priorities, especially during droughts. This study calculates the total volumes of water released from the Shahid reservoir in the Fars province, Iran, during a 5 year drought period using a standard operation policy (SOP) and genetic programming (GP). The calculated releases show the vulnerability index (VulMax) equals 87 and 82%, the timebased reliability index is 45 and 42%, and the resiliency index reaches 23 and 13% for the SOP and GP, respectively, whereas the volumetric reliability index equals 55% for both methods, demonstrating superior results for the GP method. The releases calculated with SOP and GP are allocated to meet downstream water demands according to their supply priorities. The proportional (Pro) method is used for this purpose considering the available reservoir water is less than the total demands. Compliance with the priority of supplying demands is approached with nonlinear programming in the Pro method. The VulMax of allocated releases obtained with GP for urban, environmental, industrial and agricultural demands equals 5, 50, 60 and 100%, respectively. The results confirmed the Pro method effective in allocating water resources to meet downstream demands that have conflicting water-supply priorities.

Multi-objective probabilistic optimum monitoring planning considering fatigue damage detection, maintenance, reliability, service life and cost

Effective and efficient service life management is essential for a deteriorating structure to ensure its structural safety and extend its service life. The difficulties encountered in the service life management are due to the uncertainties associated with detecting and identifying structural damages, and assessing and predicting the structural performance. To reduce these uncertainties, continuous long-term structural health monitoring (SHM) can be employed. However, a rational and practical SHM planning is required to simultaneously maximize the accuracy, efficiency, and cost-effectiveness in service life management. This paper proposes a probabilistic optimum SHM planning based on five objectives to be simultaneously optimized: minimizing the expected damage detection delay, minimizing the expected maintenance delay, maximizing the damage detection time-based reliability index, maximizing the expected service life extension, and minimizing the expected life-cycle cost. The formulations of the five objectives are based on the probabilistic fatigue damage assessment. The monitoring plannings associated with both a single- and a multi-objective probabilistic optimization process (MOPOP) are investigated. For efficient decision making in identifying the essential objectives and selecting a well-balanced solution among the Pareto optimal solutions, the degree of conflict among objectives and objective weights are estimated. The novel approach proposed in this paper accounts for the interdependencies among the five objectives considered and demonstrates the role of the optimum SHM planning in service life management of deteriorating structures. The proposed MOPOP SHM planning is applied to the hull structure of a ship subjected to fatigue.

Climate change outlook for water resources management in a semiarid river basin: the effect of the environmental water demand

Iran is a developing country with arid and semiarid regions. Poor management of water resources combined with the effects of climate change is leading to the drying of several rivers and wetlands. Several planned water development projects, primarily for agricultural expansion, will be implemented in the coming years which could worsen impacts on vulnerable aquatic ecosystems. Proper water resources management is essential to meet present and future residential, environmental, industrial, and agricultural demands in semiarid regions. This paper presents projections of how the availability of water resources will change in the Karkheh river basin of Iran for the period 2010–2059 employing sustainability criteria in the form of time-based reliability, volumetric reliability, resiliency, and vulnerability. This paper’s results show that consideration of environmental receptors as a stakeholder of water use places limitations on agricultural development within the Karkheh river basin.

Dynamic Reliability Assessment for Nonrepairable Multistate Systems by Aggregating Multilevel Imperfect Inspection Data

Traditional time-based reliability assessment methods compute reliability measures of a multistate system (MSS) purely based upon historical time-to-failure data collected from a large population of identical systems. Using these methods, one can only assess the reliability of a system from a population or statistical perspective. Moreover, these methods fail to characterize the stochastic behavior of a specific individual MSS over time. Accordingly, in this paper, a dynamic reliability assessment method that can aggregate inspection data across multiple levels (such as component level, subsystem level, and system level) of a nonrepairable MSS has been studied. In general, inspection data collected from multiple levels of a system can be imperfect, but they are stochastically correlated with the actual states of the inspected system and components. A set of two-stage recursive Bayesian formulations has been put forth to dynamically update the reliability function of a specific MSS over time by utilizing imperfect inspection data collected simultaneously or asynchronously from multiple levels of the system. The proposed method is exemplified via an illustrative example of an underground flow transmission system. The impact of the probability of detection on the accuracy of the remaining useful life prediction is also examined.

Dynamic Reliability Assessment for Multi-State Systems Utilizing System-Level Inspection Data

Traditional time-based reliability assessment methods evaluate the reliability of a multi-state system (MSS) from a population or a statistical perspective that the reliability of a system is computed purely based upon historical time-to-failure data collected from a large population of identical components or systems. These methods, however, fail to characterize the stochastic behaviors of a specific individual system. In this paper, by utilizing system-level observation history, a dynamic reliability assessment method for MSSs is put forth. The proposed recursive Bayesian formula is able to dynamically update the reliability function of a specific MSS over time by incorporating system-level inspection data. The dynamic reliability function, state probabilities, and remaining useful life distribution of an MSS in residual lifetime are derived for two common cases: the degradation of components follows a homogeneous continuous time Markov process, and a non-homogeneous continuous time Markov process. The effectiveness and accuracy of the proposed method are demonstrated via two numerical examples.

Multiple Regression Model Using Performance Indices for Storage Capacity of a Reservoir System in Johor Catchment

Storage–yield–reliability (S–Y–R) relationship is useful in many areas of hydrology and water resources. With the availability of such a relationship, reservoir planning analysis can be implemented much more rapidly and at a much shorter time needed for sequential analysis applying time series data. Existing relationships have been developed mostly for over-year capacity without considering both reliability and vulnerability performance indices. Hence, in this study, streamflow data from Johor river was used to develop a predictive relationship for total (i.e. within-year plus over-year) storage capacity involving both reliability and vulnerability performance indices as for use during reservoir planning. The reservoir was analyzed using 1000 sequences of synthetic data having the same length as historical data involving both time-based reliability and vulnerability performance indices by modified SPA. The model was then calibrated based on the mean of 1000 simulation results. Subsequently, the performance of the model was observed by comparing the model’s results with simulation outcomes for study systems. It was found that the performance of the model was very good in reproducing, the total storage capacity.

Genetic algorithms optimization of hedging rules for operation of the multi-purpose Ubonratana Reservoir in Thailand

Abstract. This study has developed optimal hedging policies for the multi-purpose Ubonratana Reservoir in northeastern Thailand based on its existing rule curves. The hedging policy was applied whenever the reservoir storage falls below a critical level for each month of the year. The decision variables, i.e. the set of monthly storages defining the critical rule curve that triggers rationing and the rationing ratio, were optimized by genetic algorithm (GA). Both single stage (i.e. with one critical rule curve and one rationing ratio) and two-stage (with two critical rule curves and ratios) of the hedging policy were considered in the optimization. To test the effect of the optimized hedging policies on reservoir performance, simulations were carried out, forced alternatively with the existing rule curves (i.e. without hedging) and the two optimized hedging policies. Performance was summarized in terms of reliability (time- and volume-based) and vulnerability. The results showed that the vulnerability was significantly reduced by using the optimized hedging rules. However, the number of water shortages increased with the optimized rules, causing the time-based reliability to worsen significantly. This should not be of concern since, although the number of shortages increased, the associated shortage quantities on most of these additional occasions were small, leaving the volumetric reliability largely unchanged.

Estimating bearing lower bound reliability without past failures

For operators and maintainers, extension of maintenance intervals is desired to alleviate costs. For aircraft and helicopter components, traditional failure time-based reliability assessment methods can seldom be applied as the reliability is often very high and failure data are often not available. In this article, different approaches using Nelson’s method, Weibull plot equation and probabilistic damage model to estimate a rolling element bearing’s reliability without failure data are reviewed. Two methods are then proposed to improve the reliability assessing the Weibull plot equation and the probabilistic damage model approaches by estimating their lower confidence bounds. In the first proposed method, Monte Carlo simulation is applied with the Weibull plot equation to obtain the variation in the Weilbull slope parameter and then estimate the lower confidence bound. In the second proposed method, probabilistic damage accumulation model is applied to assess the bearing reliability and bootstrap techniques are applied to obtain the lower confidence bound. Both methods are used to assess the reliability of extending the replacement interval of a helicopter gearbox bearing from 2000 to 3000 h and are shown to perform better with the use of Nelson’s method.

Stochastic Assessment of Reservoir Storage-Yield Relationships in Portugal

AbstractThis paper aims to establish design criteria that simultaneously meet (1) the stochastic nature of the streamflow regime in Portuguese rivers and (2) the relationship between such a regime and the mean annual flow depth. The data set consists of 54 streamflow samples from unregulated Portuguese rivers. A large number of synthetic streamflow series were generated by using a probabilistic model at the annual level and a disaggregation model, namely the method of fragments, at the monthly level. Based on an operation with fixed yield and time-based reliability, behavioral analysis was applied to the synthetic series to estimate the storage capacities of hypothetical reservoirs. The Gumbel distribution was fitted to the previous estimates to obtain design storage capacities with specified values of reliability. After showing that the former design capacities were significantly correlated with the mean annual flow depth of the sample series, curves that expressed that relationship were defined. The res...

Evaluation de la fiabilité de gestion d'un barrage réservoir pour des événements secs / Assessment of the reliability of reservoir dam operation for dry events

Assessment of the reliability of the operation policy of a single dam was investigated. The methodology was based on implicit stochastic dynamic programming (SDP) of dry events. Several performance indices were used and a supplementary indicator, the number of deficits observed, was also considered. This study was carried out on hydrological data of 1985–2005 and the chronology of the operation of Ghézala Dam in northern Tunisia. The daily rainfall records for the period 1968–2005 were used in the identification of the dry and rainfall events according to a predetermined threshold value. A threshold equal to the average daily evapotranspiration in the area was selected. It was calculated from the data during the same period. The events time series extracted was used to generate several synthetic events time series. The rainfall events sequences were coupled with a rainfall—runoff model (production function of the runoff) to obtain synthetic streamflow series. Each synthetic streamflow sequence, obtained from synthetic rainfall events sequences and that derived from the historic rainfall events time series, was optimized and an optimal decision was formulated. These optimal decisions were examined to derive the operating rules of a reservoir for dry events. The comparison among all performance indices (IP) reveals that the occurrence-based reliability, IP(3) seems to be a weak indicator because it informs badly about the situation of the reservoir operation. Moreover, this indices only describes how the deficit and the non-deficit periods are distributed within the entire simulation time period. Time-based reliability, IP(2), and average inter-arrival times (mean length of a failure event), IP(5), seem to be comparable. The probability of not having any deficits during a rainfall event is about 0.90, whereas during a dry event, it is 0.81. The results presented clearly demonstrate that performance indicators play an essential role in the complete assessment of reservoir management.

Analyzing family interaction: Taking time into account.

Recent advances in hardware and software have made the coding and analyzing of family interaction an easier task. The availability of relatively inexpensive devices that preserve time as part of the record makes the coding of onset and offset times of a variety of behavioral events feasible. Such data can be represented as timed-event sequences through Sequential Data Interchange Standard conventions and analyzed with a computer program designed for sequential analysis (the Generalized Sequential Querier). Coding units (entities coded, such as events) need not be the same as tallying units (entities counted, such as seconds) ; in fact, much can be gained by regarding them separately. Examples of both time-based reliability assessment and sequential analysis, and lagged event-based log-linear analysis, are presented.