A dynamic condition-based maintenance optimization model for mission-oriented system based on inverse Gaussian degradation process

An effective maintenance policy optimization model can reduce maintenance cost and system operation risk. For mission-oriented systems, the degradation process changes dynamically and is monotonous and irreversible. Meanwhile, the risk of early failure is high. Therefore, this paper proposes a dynamic condition-based maintenance(CBM) optimization model for mission-oriented system based on inverse Gaussian(IG) degradation process. Firstly, the IG process with random drift coefficient is used to describe the degradation process and the relevant probability distributions are obtained. Secondly, the dynamic preventive maintenance threshold(DPMT) function is used to control the early failure risk of the mission-oriented system, and the influence of imperfect preventive maintenance(PM)on the degradation amount and degradation rate is analysed comprehensively. Thirdly, according to the mission availability requirement, the probability formulas of different types of renewal policies are obtained, and the CBM optimization model is constructed. Finally, a numerical example is presented to verify the proposed model. The comparison with the fixed PM threshold model and the sensitivity analysis show the effectiveness and application value of the optimization model.

INVESTIGATION ON MICROELECTRODES Ⅻ THE DETERMINATION OF THE INVERSE CURRENT IN THE PROCESSES OF STEADY-STATE OR QUASI-STEADY-STATE

A simple method for determining the inverse current of cyclic voltammetry in the processes of steady-state or quasi-steady-state was presented. The experimental result verified the theoretical relation or inverse and forward current at microelectrode. Their ratio is proportional to the square root of scan rate.

Reliability modeling of the bivariate deteriorating product with both monotonic and non-monotonic degradation paths

Fiber optical gyroscope(FOG)is a highly reliable navigation element,and the degradation trajectories of its two accuracy indexes are monotonic and non-monotonic respectively.In this paper,a flexible accelerated degradation testing(ADT)model is used for analyzing the bivariate dependent degradation process of FOG.The time-varying copulas are employed to consider the dynamic dependency structure between two marginal degradation processes as the Wiener process and the inverse Gaussian process.The statistical inference is implemented by utilizing an inference function for the margins(IFM)approach.It is demonstrated that the proposed method is powerful in modeling the joint distribution with various margins.

Parallel Fuzzy P+Fuzzy I+Fuzzy D Controller:Design and Performance Evaluation

In this paper, a parallel fuzzy proportional plus fuzzy integral plus fuzzy derivative （FP＋FI＋FD） controller is proposed. It is derived from the conventional parallel proportional-integral-derivative （PID） controller. It preserves the linear structure of a conventional parallel PID controller, with analytical formulas. The final shape of the controller is a discrete-time fuzzy version of a conventional parallel PID controller. Computer simulations are performed to evaluate the performance of the FP＋FI＋FD controller for setpoint tracking and load-disturbance rejection for some complex processes, such as first- and second-order processes with delay, inverse response process with and without delay and higher order processes. Also, the performance of the proposed fuzzy controller is evaluated experimentally on highly nonlinear liquid-flow process with a hysteresis characteristic due to a pneumatic control valve. The simulation and real time control is done using National InstrumentTM hardware and software （LabVIEWTM）. The response of the FP＋FI＋FD controller is compared with the conventional parallel PID controller, tuned with the Ziegler-Nichols （Z-H） and /~strSm- H^gglund （A-H） tuning technique. It is observed that the FP＋FI＋FD controller performed much better than the conventional PI/PID controller. Simulation and experimental results demonstrate the effectiveness of the proposed parallel FP＋FI＋FD controller.

Reaction ergodography for the 1,2-H shift and inversion processes of amino-carbene

The ab initio calculations have been performed on the reaction paths of 1,2-H shift and inversion processes of amino-carbene molecule by the Intrinsic Reaction Coordinate(IRC)method. We have determined the equilibrium geometries and energies of the reactant,transition state and product,and obtained the activation energies,reaction heats,frequency factors and the activation entropies of these two reaction processes.The vibrational correlation from reactant to transition state indicated that the IRCs of 1,2-H shift and inversion processes were associated with the deformation modes of 1540 and 1208 cm^(-1),respectively.The vibrational coupling between normal coordinates in the inversion process would be helpful for selecting the inversion reaction channel.

Inverse Gaussian process-based corrosion growth modeling and its application in the reliability analysis for energy pipelines

This paper describes an inverse Gaussian process-based model to characterize the growth of metal-loss corrosion defects on energy pipelines.The model parameters are evaluated using the Bayesian methodology by combining the inspection data obtained from multiple inspections with the prior distributions.The Markov Chain Monte Carlo(MCMC)simulation techniques are employed to numerically evaluate the posterior marginal distribution of each individual parameter.The measurement errors associated with the ILI tools are considered in the Bayesian inference.The application of the growth model is illustrated using an example involving real inspection data collected from an in-service pipeline in Alberta,Canada.The results indicate that the model in general can predict the growth of corrosion defects reasonably well.Parametric analyses associated with the growth model as well as reliability assessment of the pipeline based on the growth model are also included in the example.The proposed model can be used to facilitate the development and application of reliability-based pipeline corrosion management.

Solving and analyzing PDOL inverse process

The importance of L inverse process is emphasized and an algorithm is given to realize PO0L inverse process. On the basis of algorithm analysis, this note discusses the possibility of apply-ing L inverse process to data compression and the difficulties in doing that.

Bivariate Constant-Stress Accelerated Degradation Model and Inference Based on the Inverse Gaussian Process

Modern highly reliable products may have two or more quality characteristics(QCs) because of their complex structures and abundant functions. Relations between the QCs should be considered when assessing the reliability of these products. This paper conducts a Bayesian analysis for a bivariate constant-stress accelerated degradation model based on the inverse Gaussian(IG) process. We assume that the product considered has two QCs and each of the QCs is governed by an IG process. The relationship between the QCs is described by a Frank copula function. We also assume that the stress on the products affects not only the parameters of the IG processes, but also the parameter of the Frank copula function. The Bayesian MCMC method is developed to calculate the maximum likelihood estimators(MLE) of the model parameters. The reliability function and the mean-time-to-failure(MTTF) are estimated through the calculation of the posterior samples. Finally, a simulation example is presented to illustrate the proposed bivariate constant-stress accelerated degradation model.

The absorption coefficient measurement of underwater materials in a water tube by using the wide-band pulse method

The existing absorption coefficient measurement in a water tube is limited in low frequency due to the limitation of the pulse tube length.A wide-band pulse tube method based on the post-processing inverse filter is proposed.After obtaining the response of the entire system,the transducer is excited with wide-band,short-duration signals.Then,the received signals are processed with inverse filters and the ＂blurred＂ reflective signals of standard reflector and test sample are recovered respectively,finally,the reflection coefficient and absorption coefficient are calculated.Simulation work is implemented to verify the advantage of postprocessing inverse filter over pre-processing inverse filter in terms of low frequency measurement.To verify the proposed method,two different wide-band pulses in the separate frequency ranges are adopted to measure the same rubber material.The experimental results indicate that the wide-band pulse method and CW（Continuous Wave） pulse method have good agreement in both low frequency range and high frequency range.Wide-band pulse method is of high efficiency,and the low frequency reaches 350 Hz,which is able to extend the low frequency range.