Browsing by Author "Yang, SK"

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A Petri net approach to early failure detection and isolation for preventive maintenance
(1998-09-01)
Yang, SK
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
To improve preventive maintenance, this study uses a hybrid Petri net modelling method coupled with parameter trend and fault tree analysis to perform early failure detection and isolation. A Petri net arrangement is proposed that facilitates alarm, early failure detection, fault isolation, event count, system state description and automatic shutdown or regulation. These functions are very useful for health monitoring and preventive maintenance of a system. A fault diagnosis system for district heating and cooling facilities is employed as an example to demonstrate the proposed method. (C) 1998 John Wiley Br Sons, Ltd.
Failure analysis for an airbag inflator by Petri nets
(1997-05-01)
Yang, SK
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
Petri nets are useful for modelling a variety of asynchronous and concurrent systems, such as automated manufacturing, computer fault tolerant systems, and communication networks. This study employs an airbag inflater system as an example to demonstrate a Petri net approach to failure analysis. This paper uses Petri nets to study minimum cut sets finding, marking transfer, and dynamic behaviour of system failure. For Petri net models incorporating sensors, fault detection and higher-level fault avoidance is dealt with. Compared with fault trees that present only static logic relations between events, Petri nets indeed offer more capabilities in the scope of failure analysis. (C) 1997 by John Wiley & Sons, Ltd.
Implementation of Petri nets using a field-programmable gate array
(2000-03-01)
Yang, SK
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
Although Petri nets have various capabilities, the Petri net approach is done on paper. A field-programmable gate array (FPGA) is implemented in this study so as to realize basic Petri net symbols, logic structures in Petri nets, and specific functions for Petri nets by logic circuits. As an example, a Petri net for an early failure detection and isolation arrangement (EFDIA) is implemented as an application-specific integrated circuit (ASIC) on a Xilinx Demonstration Board. This ASIC is verified by three simulations dealing with three different failure scenarios of a system, and the ASIC functions identically to the EFDIA Petri net. Accordingly not only the EFDIA Petri net but also any specific function Petri nets can be implemented by FPGA circuits. Copyright (C) 2000 John Wiley & Sons, Ltd.
Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy
(2005-12-08)
Yang, SK
;
Liu, SY
;
Chen, HF
;
Lee, YP
;
應用化學系
Following the photodissociation of o-fluorotoluene [o-C6H4(CH3)F] at 193 nm, rotationally resolved emission spectra of HF(1 <= v <= 4) in the spectral region of 2800-4000 cm(-1) are detected with a step-scan Fourier transform spectrometer. HF(v <= 4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature similar to 1080 K; a short extrapolation from data in the period of 0.5-4.5 mu s leads to a nascent rotational temperature of 1130 +/- 100 K with an average rotational energy of 9 +/- 2 kJ mol(-1). The observed vibrational distribution of (v=1):(v=2):(v=3)=67.6: 23.2: 9.2 corresponds to a vibrational temperature of 5330 +/- 270 K. An average vibrational energy of 25 +/-(12)(3) kJ mol(-1) is derived based on the observed population of HF(1 <= v <= 3) and estimates of the population of HF (v=0 and 4) by extrapolation. Experiments performed on p-fluorotoluene [p-C6H4(CH3)F] yielded similar results with an average rotational energy of 9 +/- 2 kJ mol(-1) and vibrational energy of 26 +/-(12)(3) kJ mol(-1) for HF. The observed distributions of internal energy of HF in both cases are consistent with that expected for four-center elimination. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. An observed vibrational energy of HF produced from fluorotoluene slightly smaller than that from fluorobenzene might indicate the involvement of seven-membered-ring isomers upon photolysis. (c) American Institute of Physics.
Photodissociation dynamics of formyl fluoride (HFCO) at 193 nm: Branching ratios and distributions of kinetic energy
(2005-08-15)
Lee, SH
;
Wu, CY
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Yang, SK
;
Lee, YP
;
應用化學系
Following photodissociation of formyl fluoride (HFCO) at 193 nm, we detected products with fragmentation translational spectroscopy utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Among three primary dissociation channels observed in this work, the F-elimination channel HFCO -> HCO+F dominates, with a branching ratio similar to 0.66 and an average release of kinetic energy similar to 55 kJ mol(-1); about 17% of HCO further decomposes to H+CO. The H-elimination channel HFCO -> FCO+H has a branching ratio similar to 0.28 and an average release of kinetic energy similar to 99 kJ mol(-1); about 21% of FCO further decomposes to F+CO. The F-elimination channel likely proceeds via the S-1 surface whereas the H-elimination channel proceeds via the T-1 surface; both channels exhibit moderate barriers for dissociation. The molecular HF-elimination channel HFCO -> HF+CO, correlating with the ground electronic surface, has a branching ratio of only similar to 0.06; the average translational release of 93 kJ mol(-1), similar to 15% of available energy, implies that the fragments are highly internally excited. Detailed mechanisms of photodissociation are discussed. (c) 2005 American Institute of Physics.
State estimation for predictive maintenance using Kalman filter
(1999-10-01)
Yang, SK
;
Liu, TS
;
機械工程學系
;
Department of Mechanical Engineering
Failure can be prevented in time by preventive maintenance (PM) so as to promote reliability only if failures can be early predicted. This article presents a failure prediction method for PM by state estimation using the Kalman filter on a DC motor. An exponential attenuator is placed at the output end of the motor model to simulate aging failures by monitoring one of the state variables, i.e. rotating speed of the motor. Failure times are generated by Monte Carlo simulation and predicted by the Kalman filter. One-step-ahead and two-step-ahead predictions are conducted. Resultant prediction errors are sufficiently small in both predictions. (C) 1999 Elsevier Science Ltd. All rights reserved.