Estimation of Parameters of PTRC SRGM using Non-informative Priors

Reliability is an essentially important characteristic of software. The reliability of software has been assessed by considering Poisson Type occurrence of software failures and the failure intensity of one parameter say (η_1 ) Rayleigh class. Here, it is assumed that the software contains fixed number of inherent faults say (η_0 ). The scale parameter of Rayleigh density (η_1 ) and fixed number of inherent faults contained in software are the parameters of interest. The failure intensity and mean failure function of this Poisson Type Rayleigh Class (PTRC) Software Reliability Growth Model (SRGM) have been studied. The estimates of above parameters can be obtained by using maximum likelihood method. Bayesian technique has been used to about estimates of η_0 and η_1 if prior knowledge about these parameters is available. The prior knowledge about these parameters is considered in the form of non- informative priors for both the parameters. The proposed Bayes estimators are compared with their corresponding maximum likelihood estimators on the basis of risk efficiencies under squared error loss. The Monte Carlo simulation technique is used for calculating risk efficiencies. It is seen that both the proposed Bayes estimators can be preferred over corresponding MLEs for the proper choice of the values of execution time.

Effects of External Dynamic Disturbances And Structural Plane On Rock Fracturing Around Deep Underground Cavern

The occurrence of disasters in deep mining engineering has been confirmed to be closely related to the external dynamic disturbances and geological discontinuities. Thus, a combined finite-element approach was employed to simulate the failure process of an underground cavern, which provided insights into the failure mechanism of deep hard rock affected by factors such as the dynamic stress-wave amplitudes, disturbance direction, and dip angles of the structural plane. The crack-propagation process, stress-field distribution, displacement, velocity of failed rock, and failure zone around the circular cavern were analyzed to identify the dynamic response and failure properties of the underground structures. The simulation results indicated that the dynamic disturbance direction had less influence on the dynamic response for the constant in situ stress state, while the failure intensity and damage range around the cavern always exhibited a monotonically increasing trend with an increase in the dynamic load (stress-wave amplitudes). The crack distribution around the circular cavern exhibited an asymmetric pattern, possibly owing to the stress-wave reflection behavior and attenuation effect along the propagation route. Geological discontinuities significantly affected the stability of nearby caverns subjected to dynamic disturbances, during which the failure intensity exhibited the pattern of an initial increase followed by a decrease with an increase in the dip angle of the structural plane. Additionally, the dynamic disturbance direction led to variations in the crack distribution for specific structural planes and stress states. These results indicate that the failure behavior should be the integrated response of the excavation unloading effect, geological conditions, and external dynamic disturbances.

The Reliability Of Watertight Longitudinal Girders Of Fuel Tanks On Aging Bulk Carriers

During the exploitation of bulk carriers, the condition of structural elements and areas depends on the type of the cargo transported, operational conditions and maintenance systems. Corrosion significantly accelerates the aging of metal plates and girders thus causing the deterioration of steel surfaces, which consequently reduces the reliability of structural elements, areas and ships in general. The damage to metal structures can impair the stability of a ship, reduce longitudinal strength, cause the ingress of water into the hull as well as environmental pollution through fuel spills from the tanks. Therefore, the paper analyzes a part of a double bottom structure based on the available wear data on watertight longitudinal girders of fuel tanks. The research included 25 bulk carriers aged between 5 and 25 with the total of 110 fuel tanks. The reliability analysis of steel plates included the total of 1920 data measured. The allowable wear of structural plate thickness that equals 20% of the original thickness value was determined by the application of the acceptance criteria that were prescribed by classification societies. The calculations of the function of failure density, failure intensity and reliability determined the time when the condition of structural elements deteriorates due to corrosion up to the levels that require extensive maintenance services.

Group Maintenance Strategy of CNC Machine Tools Considering Three Kinds of Maintenance Dependence and Its Optimization

Unreasonable maintenance strategies will increase maintenance costs and reduce the efficiency of CNC (Computer Numerical Control) machine tools. Therefore, not only the degradation state of components but also their coupling effect should be considered to obtain a scientific and reasonable system-level maintenance strategy because of the dependence among different components of CNC machine tools. This study proposes a group maintenance strategy of CNC machine tools considering economic, structural, and stochastic dependence among critical components and optimizes the group maintenance strategy. The model of group maintenance of CNC machine tools is composed of four sub-models: sub-model of component degression, sub-model of group maintenance decisions, sub-model of imperfect maintenance, sub-model of maintenance cost. Utilizing the model of group maintenance of CNC machine tools, the time, objective, and measures of maintenance can be decided according to the degression state and failures. And then, the cost of each maintenance can be calculated. In the group maintenance model, economic dependence and structural dependence among components are quantified by cost, while stochastic dependence is quantified by failure intensity. On that basis, the Monte Carlo method is used to simulate the machine tool operation process and the long-term maintenance cost of CNC machine tools corresponding to a certain failure intensity threshold is calculated. Finally, Genetic Algorithm is used to optimize the failure intensity thresholds of preventive and group maintenance. A numerical example verifies the effectiveness of the proposed optimization method for group maintenance strategy.

Markov model of the operations & maintenance process of vehicles scheduled to be Operated

The article is dedicated to the modelling of operations & maintenance of vehicles scheduled to be operated. This specific feature is illustrative of the vehicle operation process in the military system. The presented model of the operation process of vehicles scheduled to be operated, using the Markov chain theory, contains indicators and measures essential for the vehicle operation, i.e. repair defectiveness, repair intensity, usage intensity and failure intensity. This model enables to quantify the impact of the introduced changes in operational practice or changes planned as a forecast, which is shown in the examples.

Research, processing and analysis of exploitation reliability results of high-speed radial diesel engine

This paper presents the research on reliability of high-speed radial marine diesel engine Zvijezda M 504 B2 based on experimental data of malfunctions on the engine and time required for repair. Exploitation reliability and failure intensity were calculated from operational data collected from the engine log book. Results were tested by computer program to determine the relevance of the obtained results. Mathematically calculated reliability model of high-speed radial marine diesel engine Zvijezda M 504 B2 showed continuous increasing function of the intensity of failure and the fact that the reliability of the engine can be reliably approximated by Weibull distribution. Based on the obtained results it has been shown that this distribution, regardless of its complexity, should be used in practice when calculating reliability of engines with similar constant and growing malfunction’s intensity. The conclusion is that proposed distribution enables a better depiction of the observed technical system and the impact of aging of components on the system reliability.

Optimal sequential preventive maintenance policy for a repairable system with maintenance windows

Optimization of sequential preventive maintenance has been widely studied. However, some issues need further discussion when considering certain real factors. Hence, an sequential preventive maintenance policy for a mono-unit repairable system with maintenance windows is proposed. The load strength and catastrophic failures of a system are considered in the reliability model, and an optimization of the SPM policy is rigorously proven by an analytical method. The existence and uniqueness of the optimal solution with a monotone increasing failure intensity function are presented in detail. The proof of theory indicates that the length of the maintenance window has an upper bound. Finally, a numerical example and some sensitivity analyses are given to illustrate the proposed sequential preventive maintenance policy. Results show that waste may occur when performing the general sequential preventive maintenance policy and may increase along with the length of the maintenance windows.