A coloured Petri net framework for modelling aircraft fleet maintenance

The aircraft fleet maintenance organisation is responsible for keeping aircraft in a safe, efficient operating condition. Through optimising the use of maintenance resources and the implementation of maintenance activities, fleet maintenance management aims to maximise fleet performance by, for example, ensuring there is minimal deviation from the planned operational schedule,that the number of unexpected failures is minimised or that maintenance cost is kept at a minimum. To obtain overall fleet performance, the performance of individual aircraft must first be known. The calculation of aircraft performance requires an accurate model of the fleet operation and maintenance processes. This paper aims to introduce a framework that can be used to build aircraft fleet maintenance models. A variety of CPN (coloured Petri nets) models are established to represent fleet maintenance activities and maintenance management, as well as the factors that have a significant impact on fleet maintenance including fleet operation, aircraft failure logic and component failure processes. Such CPN models provide an ideal structured framework for Monte Carlo simulation analysis, within which calculations can be performed in order to determine numerous fleet reliability and maintenance performance measures

A hierarchical coloured Petri net model of fleet maintenance with cannibalisation

Cannibalisation refers to a maintenance action where an unserviceable part in an inoperative platform is replaced by a serviceable part of the same type from another platform. It helps a fleet meet operational requirements when spares are in short supply but leads to more maintenance tasks to be carried out. In practice, cannibalisation may be performed in an unrestricted manner, or through the use of cannibalisation birds. A cannibalisation bird is a platform which is selected as the primary source of cannibalisation, while any inoperative platform can be a cannibalisation source under the unrestricted policy. In order to aid fleet managers in making cannibalisation-related decisions, this paper presents a hierarchical coloured Petri net (HCPN) model of a fleet operation and maintenance process which considers mission-oriented operation, multiple level maintenance, multiple cannibalisation policies (no cannibalisation, unrestricted cannibalisation and cannibalisation bird), maintenance scheduling and spare inventory management. The model is applied to an example fleet to compare the effects of different cannibalisation policies on fleet performance using a number of performance measures related to reliability and maintenance and to optimise the number of cannibalisation birds used and the length of time that a platform is taken as a cannibalisation bird for the fleet

Using a Novel Hierarchical Coloured Petri Net to Model and Optimise Fleet Spare Inventory, Cannibalisation and Preventive Maintenance

Spare part availability is crucial to restoring inoperative platforms to the working state. Platforms failing during operation undergo corrective maintenance to replace failed components with spares. To reduce the frequency of this unplanned, corrective maintenance, platforms are inspected periodically and degraded components preventively replaced. Maintenance delays occur when spares are unavailable but cannibalisation can reduce these delays by allowing working components to be removed from inoperative platforms and used to restore other inoperative platforms. Fleets can be deployed across multiple bases that are served by one or more depots. Failed components that cannot be repaired at a base are sent to a depot for repair, along with associated requests for spares, which are satisfied by depot inventories.The management of fleet corrective and preventive maintenance, cannibalisation, spare inventories, provision of spares to bases and depots, and response of the depot to spare requests is a complex problem for fleet maintenance managers and critical to ensuring acceptable fleet performance. This paper presents a novel hierarchical coloured Petri net (HCPN) model of a fleet spare inventory system, which accounts for these issues alongside fleet deployment and mission-oriented operation. The application of the model is demonstrated using case studies of two example fleets

Analysis of swirling flow effects on the characteristics of unsteady hot-streak migration

AbstractThe temperature of flow at the combustor exit is inherently non-uniform and the hot fluid is called hot-streak. An in-house CFD software, NUAA-Turbo, was used to carry out 3D unsteady simulations on the PW-E3 single-stage high-pressure turbine. The hot-streak effect based on real stator and combustor counts was approximately evaluated by the contraction/dilatation method on the interface. The unsteady attenuation and migration process of hot-streaks in the turbine passage were well captured. The general performance parameters for different circumferential positions of hot-streaks were relatively consistent. Then, the influences of hot-streaks on blade surface temperature were investigated by comparing results under hot-streak and uniform inflow conditions. Unsteady simulations with combined inlet hot-streak and swirling flow show that the core of a hot-streak migrates to the tip under the influence of a positive swirl, while the phenomenon is just opposite with a negative swirl. Therefore, the heat transfer environment of rotor blades shows great differences with different directions of inlet swirl

Preference-based spectrum pricing in dynamic spectrum access networks

With market-driven secondary spectrum trading, licensed users can receive benefits in terms of monetary rewards or various transmission services, thus setting a fair pricing structure by suitably defining spectrum quality characteristics and accurately addressing participant’s requirement is a key issue. In this paper, we investigate the pricing-based spectrum access by casting the problem of spectrum pricing into a Hotelling game model according to spectrum quality diversity. Particularly, we first build a pricing system model where unused spectrum from primary systems with different qualities forms a spectrum pool and can be divided into a number of uniform channels. A secondary user purchases a channel for usage according to its selection preference which is closely related to the channel quality and spectrum evaluation. The secondary user not only needs to consider the channel’s quality and price, but also the interference cost on primary system. Detailed analysis on the policy preference of both primary system and secondary buyer are provided. By forming a game problem of spectrum pricing between primary and secondary users, we apply the Hotelling game model to handle the interaction between the participants. Specifically, by fixing Nash equilibrium of the game, an iterative algorithm for spectrum pricing is proposed based on the distribution characteristics of secondary user’s preference. Essential analysis for the existence and uniqueness of the Nash equilibrium along with algorithm’s convergence conditions are provided. Numerical results are also supplemented to show the effectiveness of the proposed algorithm in ensuring spectrum owner’s profit

Using coloured Petri nets to investigate fleet cannibalisation

Cannibalisation is a maintenance activity that involves removing serviceable parts from inoperative platforms to replace unserviceable parts of the same type in other platforms. It can provide a significant benefit to fleet readiness, particularly if spare parts are in short supply. However, cannibalisation also has drawbacks: it brings an increased workload for maintenance crews and parts can be damaged during the cannibalisation process. For this reason, it is important to have a clear understanding of the effects that cannibalisation will have on fleet operation and maintenance. Accurate models are needed to predict the effects of cannibalisation on fleet performance and to provide fleet managers with trustworthy information on which to base maintenance decisions relating to cannibalisation and spare parts provision. This paper presents a coloured Petri net (CPN) model of fleet cannibalisation that takes account of fleet operation and a number of factors relating to maintenance. An example fleet is modelled and measures of average fleet readiness and maintenance cost are used to evaluate the effects of cannibalisation on fleet performance. The model is used to assess the impact of a number of maintenance factors and fleet size on the use of cannibalisation and fleet performance

Piezoelectric Wind Energy Harvesting from Self-Excited Vibration of Square Cylinder

Self-excited vibration of a square cylinder has been considered as an effective way in harvesting piezoelectric wind energy. In present work, both of the vortex-induced vibration and unstable galloping phenomenon process are investigated in a reduced velocity (Ur=U/ωn·D) range of 4≤Ur≤20 with load resistance ranging in 100 Ω≤R≤1 MΩ. The vortex-induced vibration covers presynchronization, synchronization, and postsynchronization branches. An aeroelectromechanical model is given to describe the coupling of the dynamic equation of the fluid-structure interaction and the equation of Gauss law. The effects of load resistance are investigated in both the open-circuit and close-circuit system by a linear analysis, which covers the parameters of the transverse displacement, aerodynamic force, output voltage, and harvested power utilized to measure the efficiency of the system. The highest level of the transverse displacement and the maximum value of harvested power of synchronization branch during the vortex-induced vibration and galloping are obtained. The results show that the large-amplitude galloping at high wind speeds can generate energy. Additionally, energy can be harvested by utilization of the lock-in phenomenon of vortex-induced vibration under low wind speed

Printable magnesium ion quasi-solid-state asymmetric supercapacitors for flexible solar-charging integrated units.

Wearable and portable self-powered units have stimulated considerable attention in both the scientific and technological realms. However, their innovative development is still limited by inefficient bulky connections between functional modules, incompatible energy storage systems with poor cycling stability, and real safety concerns. Herein, we demonstrate a flexible solar-charging integrated unit based on the design of printed magnesium ion aqueous asymmetric supercapacitors. This power unit exhibits excellent mechanical robustness, high photo-charging cycling stability (98.7% capacitance retention after 100 cycles), excellent overall energy conversion and storage efficiency (ηoverall = 17.57%), and outstanding input current tolerance. In addition, the Mg ion quasi-solid-state asymmetric supercapacitors show high energy density up to 13.1 mWh cm-3 via pseudocapacitive ion storage as investigated by an operando X-ray diffraction technique. The findings pave a practical route toward the design of future self-powered systems affording favorable safety, long life, and high energy