Papers by Keyword: Lognormal Distribution

Abstract: Based on the constant amplitude CF test of oil well tube material TP140small specimen, the procedures of predicting the variable amplitude corrosion fatigue (VACF) life of given reliability of TP140 were developed. Through the multi-sample sinusoidal loading constant amplitude CF life texts, the reliability distribution of CF life was analyzed. The CF life prediction of the specified reliability was obtained under 4 different stress levels, and the corresponding P-S-N curve expressions were obtained. Using VACF loading block spectrum and P-S-N curve expressions, the VACF life was calculated without considering the loading sequence effect. Furthermore, 5 VACF life tests were carried out using the same loading block spectrum. The VACF life with reliability was predicted by the principle of reliability and statistics. VACF life was calculated and compared with the predicted life. Test results and analysis show that the predicted results agree well with the experimental results, and CF life of TP140 casing steel follows a lognormal distribution at the given equivalent stress level, which has been substantiated.

Abstract: The problems of theoretical grounds of machine tools specifications based on mathematic operational simulation are discussed in the paper. The proposed approach is based on the probability theory and mathematical statistics apparatus. It is universal and makes it possible to use automated design engineering systems at an initial development phase of the general concept of new equipment.

Abstract: New theoretical justification for the function of soil differential moisture capacity (dependence of the relative water volume content on the capillary pressure) and its antiderivative is presented. New method is based on the concept of capillarity and the lognormal distribution of the effective radii of pores. Relative hydraulic conductivity of soil is calculated with usage of these functions and Mualem's approach. Hydrophysical parameters have been interpreted and evaluated on the base of some physical and statistical soil characteristics. Also the approximation for functions of water-retention capacity and relative hydraulic conductivity of soil has been proposed.

Abstract: According to 62 field fault data from a certain type of 8 NC machine tools, maintainability distribution model is established based on the repair time. Hypothesis testing shows that the repair times of NC machine tools fit mathematical model of lognormal distribution. This provides the basis for maintainability assessment of NC machine tool as well as the development of maintenance strategy in the future.

Abstract: For the study of the applications of partial network coding based real-time multicast protocol (PNCRM) in Mobile Ad hoc networks, the researches should be developed in the probability distribution of delay. In this paper, NS2 is used to obtain the delay of data packets through simulations. Because the delay does not obey the strict normal distribution, the maximum likelihood estimate method based on the lognormal distribution is used to process the data. Using MATLAB to obtain the actual distribution of the natural logarithm of delay, then drawing the delay distribution with the maximum likelihood estimation method based on the lognormal distribution, the conclusion that the distributions obtained by the above mentioned methods are basically consistent can be obtained. So the delay distribution of PNCRM meets the lognormal distribution and the characteristic of delay probability distribution can be estimated.

Abstract: A method is introduced to analyze the reliability of wire cut electrical discharge machining by using the the failure data. It requires the least square method to estimate the parameters of the distribution model of the time between failures, utilizes the K-S test to test the hypothesis which distribution the reliability data obey, analyzes the common faults, and gives improvement approachs. Results show the fact that the time between failures obey thelognormal distribution, which provides the theoretical basis for improving the reliability of wire cut electrical discharge machining and have important application value.

Abstract: As one of the most important type of gold deposits, hydrothermal gold deposit has become the hot research area of mineral deposits at present and for a long time to come because of its great economic value and ore-prospecting potentials. Mathematical statistics on mineralization abundance, including grade and linear productivity, of a hydrothermal gold deposit in Jiaodong Peninsula, were done. The results show that mineralization abundance of the hydrothermal gold deposit follows lognormal distribution which is consistent with traditional research findings, which have academic significance for further studies on hydrothermal gold mineralization characteristics and deposition mechanism.

Abstract: Based on the pore size distribution simulation and the derivation of the effective diffusion coefficient, a mathematical model describing the mass transfer and chemical reaction in a cylindrical gas sensitive porous medium is formulated. The reaction features and the effective utilization of the gas sensitive porous medium are analyzed under different pore size distribution. The results indicate that, an increase in porosity or in the most probably pore diameter leads to a higher mass transfer rate of the target gas, while the surface chemical reaction ability decreases. Depending on the calculated value of the Thiele number, the variation of the gas sensitivity and the effective surface utilization can be analyzed. The gas sensitivity and the effective utilization coefficient of the gas sensitive porous medium can be controlled by adjusting pore structure parameters. This will be useful for the pore structure design of gas sensor and choosing the most reasonable operation conditions.

Abstract: Based on the property that micro-cells strength is consistent with lognormal distribution function, this paper presented a new statistical damage softening constitutive model simulating the full process of strain softening for rock. Through discussing the characteristics of random distributions for rock micro-cells strength, lognormal distribution assumption is tested by Kolmogorov-Smirnov test in statistics, and the reasonable method of geometry boundary condition is selected to determine model parameters that can be easily applied to the situations under different complex conditions. Gabbro experiment comparative analyses show that the new damage softening constitutive model is rational and convenient in engineering.

Abstract: Several life measures are defined in the literature. This paper deals with defining a service life measure for a component with lognormal life. It is proposed to set the service life at the inflection of the failure rate function. The service life defined in such a way is a function of the shape parameter. This implies that the shape parameter reflects the product quality. Based on the value of the shape parameter, the component quality can be classified and the component can have different quality improvement or maintenance strategy.