Availability simulation model of complex electromechanical systems with the consideration of testability parameters

This paper proposes a stochastic MFBD (maintenance function block diagram) to describe fault diagnosis dynamic behavior of availability fluctuation evaluation for complex electromechanical system, which considers comprehensive diagnostic parameters, maintenance process and resource. The availability evaluation of complex electromechanical systems is achieved by simulation method. Firstly, the faults are divided into several types according to the quantity relationship represented by testability parameters and the logic sequence of fault-related activities is modeled. Math models describing the uncertainty between activities are established, which are embedded within MFBD. The stochastic MFBD is transformed into a simulation model designed via PI (process interaction) algorithm. Finally, a discrete-event simulation example for availability analysis of complex electromechanical system is provided and the accuracy and applicability of the proposed method are verified

Synthesis and Photoluminescence Properties of Porous Silicon Nanowire Arrays

Herein, we prepare vertical and single crystalline porous silicon nanowires (SiNWs) via a two-step metal-assisted electroless etching method. The porosity of the nanowires is restricted by etchant concentration, etching time and doping lever of the silicon wafer. The diffusion of silver ions could lead to the nucleation of silver nanoparticles on the nanowires and open new etching ways. Like porous silicon (PS), these porous nanowires also show excellent photoluminescence (PL) properties. The PL intensity increases with porosity, with an enhancement of about 100 times observed in our condition experiments. A “red-shift” of the PL peak is also found. Further studies prove that the PL spectrum should be decomposed into two elementary PL bands. The peak at 850 nm is the emission of the localized excitation in the nanoporous structure, while the 750-nm peak should be attributed to the surface-oxidized nanostructure. It could be confirmed from the Fourier transform infrared spectroscopy analyses. These porous SiNW arrays may be useful as the nanoscale optoelectronic devices

Fault Sampling of Complex System Under Imperfect Maintenance

When conducting simulation for evaluating complex system reliability or availability, stochastic fault sample method is applied to simulate fault occasions of complex system. Current research of fault sample method generally assumes maintenance activity restores systems to â??good-as-newâ? and â??bad-as-oldâ?, however, system usually keeps its function through imperfect maintenance that restores system to â??partly goodâ? in reality. A stochastic fault sample method for availability evaluation for complex system under imperfect maintenance based on monte-carlo simulation principle is proposed. Firstly, single component fault occurrence process subjected to imperfect maintenance is analyzed and the formula for fault occurrence occasion is given. Secondly, fault sample becomes complicated when maintenance object converts to system with complex reliability structure. Not only fault occurrence occasions but also fault components in the system should be derived from the sample method. Fault sample for parallel system is especially difficult, so the Markov state transition process is embedded into the method to solve this problem .Finally, a numerical case using fault sampling method under imperfect maintenance is given and the number of faults and their occurrence time are obtained . Validity and feasibility of the proposed method is verified

Analysis on impact resistance of reed contact switch for naval ships

[Objectives] As an important component of the connecting circuit,the reed contact switch has been widely used in the electrical system of the naval ship. The switch is very sensitive to underwater non-contact explosion impact,and thus once damaged,it may lead to the failure of the electrical system. This paper studies the impact resistance of the reed contact switch in order to determine its critical working conditions.[Methods] To this end,this paper employs the finite element method to simulate the impact process,and analyzes the response characteristics of different frequency bands based on the critical acceleration amplitude of the corresponding band derived from the triangular wave impact load of certain band applied to the switch model.[Results] The results show that the switch contact will be separated once the shock spectrum of the excitation force at a fixed point exceeds the allowable value. Thus,the preload should be increased to improve the impact resistance of the switch.[Conclusions] This study provides the basis for the research on the damage modes and the protection of the electrical switches of naval ships

Analiza gotowości systemu wieloelementowego składającego się z różnych wygaszalnych podsystemów typu k-z-n:G stanowiących rezerwę ciepłą

Industrial equipment or systems are usually constructed as a multi-component series system with k-out-of-n:G subsystems to fulfill a specified function. As a common type of standby, warm standby is considered in the multi-component series system with k-outofn:G standby subsystems. When a subsystem fails, the non-failed subsystems are shut off and cannot fail, which is defined as suspended animation (SA). If the SA is ignored the non-failed subsystems are assumed to keep working in the SA time, which will cause inaccuracy in the availability analysis for the system. In this paper, we focus on the SA to construct an availability model for a multi-component series system with k-out-of-n:G warm standby subsystems. Multiple continuous time Markov chains are constructed to model the system availability. A Monte Carlo simulation has been carried out to verify our method. Several interesting findings are obtained. 1) The failure rates of subsystems with SA and their limits are derived. 2) The closed-form expressions for the stationary availability of the system and subsystems, mean time to failure, mean time to repair and stationary failure frequency are obtained considering SA. 3) The system stationary availability is a monotone function for its parameters. 4) The SA effect on the stationary availability should be emphasized in two cases, one is both the value of n/k and the failure rate of active components in a k-out-of-n subsystem are relatively large or small, the other is both the value of n/k and the repair rate are relatively small.Aby urządzenia i systemy przemysłowe mogły pełnić swoje określone funkcje, zwykle buduje się je w postaci wieloelementowych systemów szeregowych składających się z podsystemów typu k-z-n: G. W pracy rozważano zagadnienie rezerwy ciepłej w wieloelementowym systemie szeregowym składającym się z podsystemów rezerwowych typu k-z-n: G. W przypadku awarii jednego z takich podsystemów, pozostałe, działające podsystemy wyłącza się, dzięki czemu nie mogą one ulec uszkodzeniu. Procedurę taką określa się, przez analogię z organizmami żywymi mianem anabiozy (suspended animation) lub wygaszania. Pominięcie zjawiska wygaszania, prowadzi do założenia, że podsystemy, które nie uległy uszkodzeniu pracują w czasie wygaszenia, co skutkuje nieprawidłowościami w analizie gotowości systemu. W artykule koncepcję wygaszania podsystemów wykorzystano do budowy modelu gotowości wieloelementowego systemu szeregowego składającego się z podsystemów typu k-z-n: G stanowiących rezerwę ciepłą. W celu zamodelowania gotowości systemu, skonstruowano łańcuchy Markowa z czasem ciągłym. Przedstawioną metodę zweryfikowano za pomocą symulacji Monte Carlo. Uzyskano szereg interesujących wyników. 1) Obliczono intensywność uszkodzeń podsystemów wygaszonych i ich wartości graniczne. 2) Wyprowadzono, z uwzględnieniem procedury wygaszania, wyrażenia w postaci zamkniętej dla stacjonarnej gotowości rozważanego systemu i podsystemów oraz określono średni czas do uszkodzenia, średni czas do naprawy oraz stacjonarną częstotliwość uszkodzeń. 3) Gotowość stacjonarna systemu jest funkcją monotoniczną dla parametrów wejściowych systemu. 4) Należy podkreślić wpływ wygaszania na stacjonarną gotowość systemu w dwóch przypadkach: gdy stosunek n/k i intensywność uszkodzeń aktywnych elementów k-tego spośród n podsystemów są względnie niskie lub względnie wysokie, oraz gdy stosunek n/k i intensywność napraw są względnie niskie

A Method for Safety Evaluation of Train Braking System Considering Multiple Types of Preventive Maintenance Cycles

The train braking system with redundant components has an essential effect on driver safety. In this paper, we consider the failure of K-out-of-N brake motors during operation and the redundant recovery by preventive maintenance. Two Continuous Time Markov Chains (CTMC) are used to model the working process and the preventive maintenance process of the braking system corresponding to the real situation of the train. Considering the maintenance effect of intermittent daily and cyclical overhaul with nested relationships, a new operation risk assessment model of the K-out-of-N system is developed to evaluate the effectiveness of the preventive maintenance of the train. Some safety parameters are solved based on the two coupled preventive maintenance periods, which conveniently design the safety of the train braking system. Finally, a case study illustrates the effectiveness of the safety evaluation method. The results show that we can trade off the effects of the multiple PM intervals on train safety considering the redundancy structure of the braking system by the proposed model

A Method for Safety Evaluation of Train Braking System Considering Multiple Types of Preventive Maintenance Cycles

The train braking system with redundant components has an essential effect on driver safety. In this paper, we consider the failure of K-out-of-N brake motors during operation and the redundant recovery by preventive maintenance. Two Continuous Time Markov Chains (CTMC) are used to model the working process and the preventive maintenance process of the braking system corresponding to the real situation of the train. Considering the maintenance effect of intermittent daily and cyclical overhaul with nested relationships, a new operation risk assessment model of the K-out-of-N system is developed to evaluate the effectiveness of the preventive maintenance of the train. Some safety parameters are solved based on the two coupled preventive maintenance periods, which conveniently design the safety of the train braking system. Finally, a case study illustrates the effectiveness of the safety evaluation method. The results show that we can trade off the effects of the multiple PM intervals on train safety considering the redundancy structure of the braking system by the proposed model

Data Envelopment Analysis with Uncertain Inputs and Outputs

Data envelopment analysis (DEA), as a useful management and decision tool, has been widely used since it was first invented by Charnes et al. in 1978. On the one hand, the DEA models need accurate inputs and outputs data. On the other hand, in many situations, inputs and outputs are volatile and complex so that they are difficult to measure in an accurate way. The conflict leads to the researches of uncertain DEA models. This paper will consider DEA in uncertain environment, thus producing a new model based on uncertain measure. Due to the complexity of the new uncertain DEA model, an equivalent deterministic model is presented. Finally, a numerical example is presented to illustrate the effectiveness of the uncertain DEA model

The variability of NO2 concentrations over China based on satellite and influencing factors analysis during 2019–2021

The variation of tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) indirectly reflects the difference in pollution emissions from industrial production and transportation. Accurately analyzing its pollution sources and driving factors plays an important role in energy conservation, emission reduction, and air pollution reduction. NO2 concentration products of Sentinel-5P (Sentinel-5 Precursor) TROPOMI (TROPOspheric Monitoring Instrument) from 2019 to 2021 and Aura OMI (Ozone Monitoring Instrument) from 2009 to 2021, combined with China’s main energy consumption, the growth value of the industry, Gross Domestic Product (GDP), and other data were used to analyze the influencing factors of NO2 variations. Firstly, NO2 tropospheric vertical column densities (NO2 TVCDs) of China increased by 14.72% and 3.26% in 2021 and 2020 compared with the 2019. The secondary and tertiary industry and the national energy consumption increased synchronously, which was highly related to the increase in NO2 TVCDs. Secondly, the impact of COVID-19 (coronavirus disease 2019) on China’s industrial production and residents was mainly concentrated in the first quarter of 2020, which leading to a decline in the annual average NO2 concentration in densely populated areas in 2020 compared to the same period in 2019. The industrial production scale and production capacity has gradually recovered since April 2020, and the NO2 concentration has gradually reached or exceeded the level of the same period of 2019. Finally, atmospheric pollution prevention and control measures played a positive role in the decline of NO2 of China