System Lifetime Research Articles

A new extended δ‐shock model with the consideration of shock magnitude

AbstractIn this article, a new ‐shock model that takes into account the magnitude of shocks is introduced and studied from reliability perspective. According to the new model, the system breaks down if either a shock after non‐critical shock occurs in a time length less than or a shock after a critical shock occurs in a time length less than where . The distribution of the system's lifetime is studied for both discrete and continuous intershock time distributions. It is shown that a new model is useful to describe a certain cold standby repairable system.

Techno-economic microgrid design optimization considering fuel procurement cost and battery energy storage system lifetime analysis

The importance of microgrids (MGs) lies in their capacity to enhance energy reliability, integrate renewable resources, and bolster resilience, yet their optimal design and sizing pose intricate challenges in balancing investment and operational cost while dispatching the MG equipment efficiently. This paper presents the optimal MG design problem formulated as an integer linear program (ILP) aimed at minimizing total investment and operational cost of MG as well as optimal hourly dispatch of MG asset over the project lifetime. Furthermore, a comprehensive analysis of the fuel procurement cost and the impact of ESS technical parameters, such as depth of discharge (Dod), ESS lifetime, and battery C-rate, on the optimal MG design, ESS lifetime and relevant costs is presented in this work for a MG operating in islanded and grid-connected modes. The simulation results demonstrate that the optimal design of a MG with the maximum load demand of 300 kW operating in the grid-connected mode can save about 28 k$ equivalent to 14% in total annual cost compared with the islanded mode operation thanks to the flexibility provided by the utility purchases and efficient MG equipment sizing. This study’s unique contributions provide significant insights into the practical implications of MG design optimization, potentially influencing regulatory policies and business strategies.

Lubrication failure mechanism of rolling‑sliding steel ball against oil-impregnated porous polyimide and bearing steel in double friction pair

Oil-impregnated Porous Polyimide (O-PPI) cages have been widely applied in aerospace bearings because of their exceptional performance and self-lubricating characteristics, where the surface blackening failure of the O-PPI cage during the operation process significantly shortens the service lifetime. However, the blackening failure mechanisms are still not fully understood due to the complex multiple contacts between steel balls, the cage, and the inner/outer rings in the bearing system. This study aims to deeply detect the surface blackening failure mechanism of PPI materials with a relevant improvement measuring method. A double-contact rolling-sliding ball holder was developed to simulate the contact and the motion in aerospace bearings with PPI cages, where the blackening phenomenon on the O-PPI surface was replicated as the bearing ball rubbed against the PPI and steel surfaces. Comparative experiments and subsequent characterization results revealed that the iron debris generated at the ball-steel sliding interface was infiltrated into the PPI surface pores along the rolling motion of the steel ball, and then the splitting reaction of PAO oil at the steel-PPI interface catalyzed by the iron (Fe) during friction resulted in the formation of blackening products and further lubrication failure. Based on these findings, effective countermeasures are proposed to prevent similar failures in the future. This analysis is expected to enhance the operational reliability and enlarge the service lifetime of the space-bearing systems.

FPSO/LNG hawser system lifetime assessment by Gaidai multivariate risk assessment method

Floating Production Storage and Offloading (FPSO) unit being an offshore vessel, storing and producing crude oil, prior to crude oil being transported by accompanying shuttle tanker. Critical mooring/hawser strains during offloading operation have to be accurately predicted, in order to maintain operational safety and reliability. During certain types of offloading, excessive hawser tensions may occur, causing operational risks. Current study examines FPSO vessel’s dynamic reactions to hydrodynamic wave-induced loads, given realistic in situ environmental conditions, utilizing the AQWA software package. Current study advocates novel multi-dimensional spatiotemporal risks assessment approach, that is particularly well suited for large dataset analysis, based on numerical simulations (or measurements). Advocated multivariate reliability methodology may be useful for a variety of marine and offshore systems that must endure severe environmental stressors during their intended operational lifespan. Methodology, presented in this study provides advanced capability to efficiently, yet accurately evaluate dynamic system failure, hazard and damage risks, given representative dynamic record of multidimensional system’s inter-correlated critical components. Gaidai risk assessment method being novel dynamic multidimensional system’s lifetime assessment methodology. In order to validate and benchmark Gaidai risk assessment method, in this study it was applied to FPSO and potentially LNG (i.e., Liquid Natural Gas) vessels dynamics. Major advantage of the advocated approach is that there are no existing alternative risk assessment methods, able to tackle unlimited number of system’s dimensions. Accurate multi-dimensional risk assessment had been carried out, based on numerically simulated data, partially verified by available laboratory experiments. Confidence intervals had been given for predicted dynamic high-dimensional system risk levels.

Correlation analysis of degrading systems based on bivariate Wiener processes under imperfect maintenance

AbstractThis article focuses on the correlation between the degradation levels of the two components that form a system. The degradation evolution of each component is modeled using Wiener processes. Both components are dependent and this dependence is described using the trivariate reduction method. To reduce the degradation and extend the system lifetime, preventive maintenance actions are periodically performed. These preventive maintenance actions are imperfect and they are modeled by using an arithmetic reduction of degradation of infinite order model with a determined maintenance efficiency parameter. The evolution of the maintained system is analysed by assessing the expectation and variance of both degradation processes at successive maintenance times. The novelty of this work is the analysis of the Pearson correlation coefficient between the degradation levels of the two components. Different properties of the monotonicity of the Pearson correlation coefficient between the two degradation paths are obtained by considering equal maintenance efficiency and equal general time scales functions for the two Wiener degradation processes associated to each degrading component.

Opportunistic and delayed maintenance as strategies for sustainable maintenance practices

PurposeOpportunistic and delayed maintenances are increasingly becoming important strategies for sustainable maintenance practices since they increase the lifetime of complex systems like aircrafts and heavy equipment. The objective of the current study is to quantify the optimal time window for adopting these strategies.Design/methodology/approachThe current study considers the trade-offs between different costs involved in the opportunistic and delayed maintenances (of equipment) like the fixed cost of scheduled maintenances, the opportunistic rewards that may be earned and the cost of premature parts replacement. The probability of the opportunistic maintenance has been quantified under two different scenarios – Mission Reliability and Renewal Process. In the case of delayed maintenance, the cost of the delayed maintenance is also considered. The study uses optimization techniques to find the optimal maintenance time windows and also derive useful insights.FindingsApart from finding the optimal time window for the maintenance activities the study also shows that opportunistic maintenance is beneficial provided the opportunistic reward is significantly large; the cost of conducting scheduled maintenance in the pre-determined slot is significantly large. Similarly, the opportunistic maintenance may not be beneficial if the pre-mature equipment parts replacement cost is significantly high. The optimal opportunistic maintenance time is increasing function of Weibull failure rate parameter “beta” and decreasing function of Weibull failure rate parameter “theta.” In the case of optimal delayed maintenance time, these relationships reverse.Originality/valueTo the best of our knowledge, very few studies exist that have used mission reliability to study opportunistic maintenance or considered the different cost trade-offs comprehensively.

Optimization of guide plates and orifice plates on thermal management of battery energy storage system

The performance, state of health and lifetime of the battery energy storage system (BESS) depend heavily on the temperature uniformity between batteries. The BESS is more prone to uneven temperature distribution due to the inclusion of more battery modules. Improving the air supply uniformity of each battery module is the key to ensure the temperature uniformity of the system. In order to solve the problem of uneven air supply in traditional duct, the present study proposes a composite duct structure with optimized L-type guide plates and orifice plates. Based on the orthogonal analysis method, the optimization of guide plate structures in the sub duct and the main duct is completed. Combined with power consumption analysis, the porosity of orifice plates in the ducts is determined. The results show that when guide plates and orifice plates are in the best design condition, compared with the initial scheme, the air supply uniformity coefficient of the BESS is reduced from 75.07 % to 6.29 %. The air supply uniformity of the system is increased by 91.62 %. The maximum temperature difference of the BESS is reduced from 17.36 K to 4.35 K. The temperature uniformity of the system is increased by 74.94 %. This study is helpful to the design and optimization of the duct for the thermal management system of BESS in the future.

A parametric study of the exergetic, exergoeconomic, and exergoenvironmental performances of chlorine family thermochemical cycles for sustainable hydrogen production

Hydrogen plays a crucial role in global net-zero policies due to its numerous advantages and is widely regarded as a key future fuel. Clean and sustainable hydrogen production technologies are currently a focal point of research, with thermochemical methods showing promise in achieving environmentally friendly hydrogen. This study builds upon previous research conducted by the authors on thermochemical hydrogen production through chlorine family cycles. It conducts a thorough sensitivity analysis of various system variables that significantly impact the overall performance of these processes. The investigation assesses the performance of chlorine family thermochemical cycles from exergetic, exergoeconomic, and exergoenvironmental perspectives. Exergetic performance parameters include net thermal exergies and exergy efficiencies, exergoeconomic parameters encompass hourly levelized and total cost rates, and exergoenvironmental parameters involve exergoenvironmental factors and component-associated environmental impact rates. The system variables under consideration include ambient temperature, system lifetime, annual operating hours, and operation and maintenance cost factor. The analysis reveals that the system's lifetime notably influences both the exergoenvironmental factors and component-associated environmental impact rates (by about 80%). Meanwhile, its impact on both the hourly levelized (around 11.5%) and total cost rates (approximately 1.2%) is comparatively less significant. Similarly, ambient temperature has a marginal effect on the net thermal exergies and exergy efficiencies of the considered cycles.

Expected lifetime prediction for time- and space-dependent structural systems based on active learning surrogate model

Predicting the expected lifetime of structural systems is fundamental for effective design and maintenance. However, existing methods based on physics overlook critical spatial considerations, particularly those related to random field inputs. In this study, we propose a new active learning surrogate-based method to predict the expected lifetime of structural systems affected by both time and space factors. The method starts by training an initial Kriging model with random samples and time-space coordinates. An extended expected feasibility function is proposed to select new training samples and their corresponding time-space coordinates, refining the Kriging model. A novel parallel learning strategy is proposed to expedite computations. By using the constructed Kriging model and the first failure time of random samples, we can predict the expected lifetime. The proposed method is adaptable to structural systems with multiple failure modes, implicit functions, and random field variations. The efficiency and accuracy of the proposed method are validated through four examples.

Longevity of different abutments placed on narrow diameter implants: Assessment of structural damage and loosening

ObjectivesTo evaluate structural damage and loosening of abutments placed on narrow diameter implants after cyclic fatigue. MethodsSixty Morse taper narrow diameter implants (Neodent, Brazil) received two types of abutments (1PA- one-piece abutment or 2PA- two-piece abutment), which were randomly divided into 3 fatigue experiments (n = 10). The implants were placed into a customized supporting holder and a software-assisted digital torque wrench secured the manufacturer recommended torque for each abutment. Cone beam computed tomography (CBCT) scans were acquired, before and after fatigue, and post-processed (software e-Vol DX) to assess damage and abutment displacement. The boundary fatigue method was adapted to use 2 × 106 cycles, 2 Hz of frequency and constant peak load of 80 N (first experiment) that varied according to the failure rate of previous specimens (second and third experiments). Failure was evaluated using CBCT scans and removal torque values. Data were used to estimate long-term torque degradation, probability of failure and Weibull modulus (software ALTA PRO9). ResultsAll 2PA specimens became loosen independently of the applied fatigue load, and structural bending was observed in 14 abutments. Eight 1PA got loosen during the fatigue experiment. The Weibull analysis showed a lower modulus (m = 1.0; 0.7, 1.4) for 1PA than for 2PA (m = 2.6; 2, 3.4) resulting in longer predicted lifetimes and slower torque degradation for 1PA than for 2PA specimens. Significance1PA showed greater long-term survival probability than 2PA. Predicting the lifetime and mechanical behavior of implant-abutment systems are useful information to clinicians during the decision-making process of oral rehabilitations.

Lead-acid battolysers for hydrogen cooking: A comparison with electric cooking for sub-Saharan Africa

A battolyser combines the function of battery and electrolyser in one device, i.e. it provides both electrical energy storage and a means to produce hydrogen. A battolyser with lead-acid chemistry has recently been proposed, and this has potential as a particularly low-cost solution. Here, the battolyser is considered for the production of hydrogen as a cooking fuel (“hCooking”) in sub-Saharan Africa, a region where cooking typically employs polluting fuels (firewood and charcoal). The more conventional approach for decarbonisation of cooking is the introduction of electric cookers (e.g. hotplate, induction hob, pressure cooker) which can be powered by PV and possibly battery storage; accordingly these electric cooking (“eCooking”) systems are considered as the competing decarbonised technology. Multi-objective optimisation is used to design both battolyser and eCooking systems for a notional off-grid community, with solar PV as the main energy source. Objectives are the minimisation of net present cost and lifetime greenhouse gas emissions, and Pareto frontiers are produced to show the play-off between these. Results show that a battolyser system could eliminate 95.6 % of CO2 emissions when compared with a baseline using charcoal, at an annualised cost of $507 per household, over a system lifetime of 20 years. However, eCooking systems appear superior to the battolyser, with the cleanest battery + eCook system achieving 95.8 % emissions reduction at annualised cost $422/household. More generally, hCooking systems are nearly always Pareto dominated by eCooking systems, even under a realistic range of sensitivity scenarios. This result is due to the inherently higher energy intensity of cooking over a flame compared to the eCooking options. Priorities to make the battolyser a more viable solution include extending its lifetime as far as possible, cheaper PV systems, and improved hydrogen burner efficiencies. We also show that eCooking together with some continued use of charcoal may be the cheapest possible cooking solution, whilst simultaneously curtailing 60 % of lifetime greenhouse gas emissions.

Reference dynamic power cable of floating offshore wind turbine for thermal and simple fatigue evaluation

With the increased interest in floating offshore wind turbines, there is an increased focus on evaluating the lifetime of the auxiliary systems, such as the mooring lines and the dynamic power cables, because these systems are in-mature compared to bottom-mounted offshore wind farms. This paper proposes a conceptual reference dynamic power cable suitable for the 15 MW NREL reference turbine mounted on the UMaine floater installed at 82 m water depth. This provides a basis for discussing the life evaluation of dynamic cables obtained from aeroelastic simulation of the floating offshore wind turbine platform exposed to the environmental conditions of the South Brittany site in France. An electromagnetic-thermal finite element simulation is used to determine the current capacity of the cable and aeroelastic simulations are used for a simple assessment of the main failure modes as maximum cable tension, minimum bending radius and fatigue damage accumulation.

Effect of nozzle contamination on microwave discharge cathode performance

An understanding of the degradation mechanism of a microwave discharge cathode is the key to extending the lifetime of microwave ion thruster systems. This study investigates the effect of nozzle contamination by sputtered Ag-polytetrafluoroethylene (PTFE) on microwave discharge cathode performance. The current–voltage characteristics were measured for nominal and contaminated (by PTFE spray with 0.2 µm thick or tape with 0.15 mm thick) cathodes. The contamination thickness and area on the nozzle were varied to investigate the characteristic differences. It was confirmed that the anode voltage increased by 20 V or more in the case of the contaminated cathode. The anode voltage was measured for the sputter-contaminated cathode to evaluate the effect of contamination under more realistic conditions. After 630 h of sputter-contamination operation, it is estimated that sputtered particles were deposited to a thickness of 77 µm at most, and the anode voltage increased by 8 V. The results show that the downstream surface of the nozzle is critical for maintaining cathode performance. The insulating coating formed by the sputtered PTFE may interfere with ion absorption and degrade electron emission capability. A theoretical model based on the extended Brophy model supports these results. This study provides important information for the use of PTFE-based materials around ion thrusters.

Effect of humidity and oxygen on friction, wear and durability of a polymer-bonded molybdenum disulfide (MoS2)-based dry film lubricant (DFL) coating system in large amplitude fretting

Investigations into effects of humidity and oxygen on a polymer-bonded MoS2-based dry film lubricant (DFL) coating, on grit-blasted Ti–6Al–4V using a cylinder-on-flat configuration, are reported. Sustained low friction and low wear occurred in both low-humidity air and low-humidity argon, producing significant extension of fretting wear lifetimes. A cracked-paved structure was observed in low-humidity air which was not observed in low-humidity argon. The Mo-DFL coatings were observed to be highly sensitive to humidity. As humidity increased, a notable rise of friction and wear ensued which reduced the system lifetime. Different friction evolution was observed in high-humidity air and high-humidity argon before failure, with a short-lived but established low friction phase in high-humidity air and a consistent high friction phase in high-humidity argon. Although oxidation of the MoS2 to MoO3 is a key process of degradation of DFLs of this type, this oxidation reaction does not operate in the absence of humidity.

On optimal allocation of redundancies in random weighted k$$ k $$‐out‐of‐n$$ n $$ systems

AbstractRandom weighted ‐out‐of‐ systems are very useful in modeling the lifetimes of systems, wherein the success or failure of a system depends not only on its current operational status, but also on the contributions made by its components. In this paper, we consider random weighted ‐out‐of‐ systems with redundant components drawn randomly from a mixed population consisting of different subpopulations/substocks. We study different optimal allocation policies of active redundancies and minimal repair components in a random weighted ‐out‐of‐ system. Moreover, we investigate how the heterogeneity of subpopulations of items impacts the lifetime of a random weighted ‐out‐of‐ system. We also present some simulational results and a real data analysis for illustrative purpose.

Gravitational disturbance on asteroidal ring systems by close encounter with a small object

To date, rings are found around a Centaur (10199) Chariklo, trans-neptunian objects (TNOs) (136108) Haumea, and (50000) Quaoar. These discoveries suggest that asteroidal ring systems may be common, particularly in the outer solar system. Since collisions are a ubiquitous and fundamental evolutionary process throughout the solar system, we conjecture that asteroidal ring systems must have experienced close encounters with small objects as part of their evolutionary process. Here, we investigate the response of ring systems when they experience gravitational disturbance by a close encounter with another small object, by calculating the change in eccentricity and the fraction of lost ring particles. We find that a perturber needs to be as massive as or more massive than the ringed object, and needs to pass in the immediate vicinity of the ring in order to cause significant disruption. The change in eccentricity expected for Chariklo's inner ring and Quaoar's outer ring agrees with the analytical expression derived from the impulse approximation, while that for Haumea's ring agrees with the analytical expression called “exponential regime”. If we define a lifetime of a ring as the mean time to experience disruptive close encounters that can raise the eccentricity of ring particles >0.1, the lifetime for ring systems around Chariklo, Haumea, and Quaoar are >104 Gyr. We conclude that ring systems around Chariklo, Haumea, and Quaoar are highly unlikely to suffer from close encounters with another small object even if those systems are as old as 4 Gyr. Close encounter with a small object may not be responsible for the finite eccentricity observed for Chariklo's ring system, although eccentricity of ring particles could be increased to ∼10−4 in 4 Gyr. We also find that the lifetime is shorter for smaller ringed objects, and it still exceeds 4 Gyr for km-sized ringed objects in the outer solar system. Therefore, regardless of the size of ringed objects, asteroidal ring systems in the outer solar system are unlikely to suffer severe damage by close encounter with a small object. On the other hand, the lifetime is estimated to be on the order of 100 Myr for km-sized asteroids and 10 Myr for 100 m-sized asteroids in the near-Earth region and the main belt. This finding offers a dynamical explanation why ring systems have not been found in the inner solar system.

Naphthyl substituted guest induce efficient room temperature phosphorescence by a triplet-triplet energy transfer mechanism

Room-temperature phosphorescent (RTP) materials have attracted more and more attention due to their long luminescence life and large Stokes displacement. Host-guest doping systems are highly regarded for their simplicity of preparation and the absence of complex synthesis processes. Strong RTP emission can be activated by the doping of a guest molecules, in particular by substituting the phenyl group in the host structure with a naphthalene group. In this study, derivatives of benzophenone were constructed as the host molecule, and used 2-Benzoylnaphthalene, a commercially available naphthyl-substituted analogue of benzophenone, as the guest molecule. The phosphorescent lifetime of the doped system can reach 335 ms and the phosphorescent quantum yield can reach 58 %, which is expected to be used in anti-counterfeiting encryption, biological imaging and other fields. This work provides a general and effective host-guest doping strategy for constructing various organic room temperature phosphorescent materials.

Lifetime prediction and replacement optimization for a standby system considering storage failures of spare parts

Spare parts redundancy is an effective way to improve system reliability and prolong system lifetime. Generally, preventive maintenance and inventory management of a standby system can significantly reduce operating and maintenance costs, particularly crucial in industrial systems. Additionally, during storage, spare parts may experience degradation failure due to internal mechanisms and sudden failure due to external shocks, complicating the health management of the standby system. Unfortunately, few existing studies consider the impact of spare parts’ competing failures in standby systems. To address this gap, this paper proposes a novel method for predicting the lifetime and optimizing the maintenance policy of nonlinear degradation standby systems, considering both degradation and sudden failures of spare parts. Firstly, we established the degradation model under the competing failure of spare parts and derived the analytical formula for life prediction of the standby system in the presence of competing failures, assuming that sudden failure follows the Weibull distribution. Furthermore, we developed a joint optimization model for replacement maintenance and inventory management based on predictive information, aiming to minimize the expected cost, in which the block replacement interval and the number of spare parts are treated as decision variables. Finally, the effectiveness and potential application value of the proposed method are verified through numerical simulation and a case study.

Estimating the parameter of a geometric distribution from series system data

In a traditional setup of estimation of an unknown parameter of component lifetime distribution, system’s continuous lifetime data is used. In this paper, we propose a simple and competitive estimator that is based on discrete lifetime data, i.e., the number of failed components at the time when the system fails. In particular, we consider the estimation of the parameter of a geometric distribution based on the system’s lifetime data, and the number of failed components upon the failure of the system when the system has a series structure. Two moment estimators that are based on the system lifetime data and the number of failed components at the moment of system failure are obtained and their performances are compared in terms of the mean square error. The associated Bayesian estimators with non-informative priors are also discussed.

Efficient multimode Wigner tomography.

Advancements in quantum system lifetimes and control have enabled the creation of increasingly complex quantum states, such as those on multiple bosonic cavity modes. When characterizing these states, traditional tomography scales exponentially with the number of modes in both computational and experimental measurement requirement, which becomes prohibitive as the system size increases. Here, we implement a state reconstruction method whose sampling requirement instead scales polynomially with system size, and thus mode number, for states that can be represented within such a polynomial subspace. We demonstrate this improved scaling with Wigner tomography of multimode entangled W states of up to 4 modes on a 3D circuit quantum electrodynamics (cQED) system. This approach performs similarly in efficiency to existing matrix inversion methods for 2 modes, and demonstrates a noticeable improvement for 3 and 4 modes, with even greater theoretical gains at higher mode numbers.