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Aero-Engine Workshop Maintenance Procedure Modeling Based On Petri Nets And Its Application

Posted on:2008-10-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:X M TangFull Text:PDF
GTID:1102360245497415Subject:Mechanical design and theory
Abstract/Summary:PDF Full Text Request
Different from discrete manufacturing system, aero-engine workshop maintenance procedure is nondeterministic, aero-engine configuration is dynamic, maintenance procedure data acquisition is difficult, maintenance equipments lack flexibility, maintenance time distribute randomly. To improve automatization of production and rationalization of decision for maintenance workshop, Petri nets is introduce to logic, temporal and statistical layers modeling respectively.As for logic layer modeling, the maintenance level decision knowledge base and disassembly and assembly sequence model is proposed. To deal with uncertainty of aero-engine maintenance level decision, a fault and performance evaluation knowledge representation model based on fuzzy Petri nets (FPN) is proposed. Qualitative and quantitative reasoning algorithm of knowledge base is researched. To make decision knowledge base more adaptive, learning algorithm for performance evaluation knowledge base based on metal fuzzy Petri nets (MFPN) model is presented. To eliminate maintenance errors during assembly and construct disassembly process automatically, assembly sub Petri Nets is used to modeling aero-engine parts assembly sequence (PAS) based on assembly precedence relationship. Discrete-time Pontryagin's minimum principle (DTPMP) is introduced to find OFS and DTPMP states that an OFS must minimize the Hamiltonian function which can be treated as the heuristic information to find the PAS. After complexity analysis, the OFS algorithm complexity proved to be polynomial.As for logic layer modeling, the maintenance workflow and resource scheduling modeling is proposed. To identify and forecast time consistency, the hierarchical refinement workflow net (HRWF-net) is introduced to"top-down"aero-engine maintenance break-down structure workflow modeling. An equivalent transformation principle which keeps the schedulability of HRWF-net unaltered is analyzed. To verify the executive time of maintenance workflow, a matrix verifying algorithm based on max-min algebra is proposed. Because of the resource contention among different processes, a theory that synthesized resource sharing Petri net is introduced. To optimize the schedule performance of the discrete Petri net model, discrete model is transformed into determinate time continuous Petri nets (DTCPN) and whose stationary and periodic behavior is analyzed. Particle swarm optimization is used to optimize routing strategy. Furthermore, Dynamic factors affect scheduling is considered and the event-driven rescheduling strategy is presented.As for statistical layer modeling, the aero-engine transferring model in workshop based on extended stochastic Petri Nets is built and mean value analysis technique for product form stochastic Petri Nets is introduced. To deal with normal distribution of maintenance time and diversity of maintenance level, the approximate mean value analysis(AMVA) applied to extend stochastic Petri Nets is introduced, which evaluate multi-level maintenance service performance indexes using single level performance indexes. In addition, the sojourn time is divided to three parts and squared coefficient of variation is used to correct service time with normal distribution. It's proved that AMVA is an efficient method evaluating air-engine fleet maintenance capacity for maintenance workshop.Based on modeling for aero-engine workshop, Computer aided maintenance system (CAMS) is developed which includes five modules: maintenance level reason and decision, assembly and disassembly sequence planning, maintenance workflow modeling and procedure supervising, maintenance history tracing and performance evaluating. Applied to Beijing Aircraft Maintenance Engineering Ltd. Co, it is proved that CAMS can aid maintenance workshop transferring information automatically, making decision more intelligentized, reducing maintenance errors, improving maintenance resource utilization and cutting down on maintenance cost.
Keywords/Search Tags:aero-engine maintenance, Petri nets modeling, maintenance level reason and decision, procedure management and supervising, workshop performance evaluating
PDF Full Text Request
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