Narrow Results

This paper investigates the impact of learning curve effect on setup cost for the continuous review inventory model involving controllable lead time with the mixture of backorder and partial lost sales. A learning curve is a well known tool which describes the relation between the performance of a task and the number of repetitions of that task. The objective of this study is to minimize the expected total annual cost by simultaneously optimizing order quantity, safety factor and lead time under different setup learning rates. There are two models considered in the paper, one with normal demand distribution and another with general demand distribution having both mean and variance known and finite. Numerical examples are presented to illustrate the procedures of the proposed solution algorithms, along with the savings on the total costs of the models with the inclusion of the learning effect on setup.

Both classical and Bayesian approaches are used in this article to estimate the median safety factor and the median coefficient of variation of the frequently used engineering stress-strength model, with lognormal distributions for both stress and strength. A numerical example on fire loads studies in civil engineering illustrates some of these results. A computer program, developed and tested by our group, is available upon request.

Risks associated with a vessel traffic system at sea are analyzed according to the elements in this system and a new method is developed to ensure safe ship operation. Based on Bayes' point estimation and probability influence diagram to estimate the traffic accidents related to vessel traffic, an analysis model is established for the quantitative risk assessment (QRA) of the vessel traffic system at sea. After the analysis on occurrence likelihood of the accidents related to ship traffic, a structure on the basis of Bayesian networks is developed to obtain the QRA of their relative risks. QRA is also put forward after analyzing the features and situations of the vessel traffic system and identifying the corresponding hazards including characteristics of those hazards. The risk distributions of ship traffic are described and results are presented on QRA in relation to various features by using this risk assessment model. This method, verified in the cases of QRA, turns out to be feasible by the use of identified posterior probability.

A butterfly valve of large diameter is commonly used as control equipments in applications where the inlet velocity is fast and the pressure is relatively high. Because the size of the valve is too large, it's too difficult to conduct testing experiment in a laboratory. In this paper, the numerical simulation using commercial package-CFX and ANSYS was conducted. In order to perform fluid analysis and structural analysis perfectly, large valve models are generated in three dimensions without much simplification. The result of fluid analysis is imported to structure analysis as a boundary condition. In addition, to describe the flow patterns and to measure the performance when valve are opened for various angles, the verification of the performance whether the valve could work safely at these different conditions or not was conducted. Fortunately, the result shows that the valve is safe in a given inlet velocity of 3 m/s, and it's not necessary to be strengthened anywhere. In the future, the shape of valve disc can be optimized to reduce the weight, and also to make the flow coefficient be closer to the suggested level.

The stability of tunnel surrounding rock is the mainly concerned content during tunnel design and construction procedure. It is one of the main tasks for researchers to accurately estimate the stability of tunnel surrounding rock. Generally, determined by its engineering geological features, surrounding rock of mountain tunnel is cut by joints into discontinuous blocks, which can be more accurately analyzed by discontinuum-base numerical methods, e.g., the discontinuous deformation analysis (DDA) method. In addition, progress of deformation and failure of tunnel surrounding rock is often a nonlinear catastrophe behavior, so that it is feasible to determine the tunnel stability by the catastrophe theory. The strength reduction method can be used to simulate failure progress development in its computation procedure by reducing the strength parameters. Based on the DDA method, the strength reduction method and the catastrophe theory are adopted to study the stability of tunnel surrounding rock. Firstly, the strength reduction method is used to obtain the function of displacement and the reduction factor varies, and then the catastrophe theory is used to judge the critical state of surrounding rock based on the function curve. The reduction factor at this critical point is defined as the stability safety factor of the tunnel. Thus the stability status of the surrounding rock can be determined. Jinjishan multiple-arch tunnel is a big span tunnel with eight traffic lanes, which is a very important project of the second phase project of Fuzhou city airport. This method is put into application of this project to guarantee safety of the tunnel.

In Korea, Tetrapods have been widely used to protect rubble mound breakwaters against erosion due to wave action. The deterministic design method has been used based on Hudson or van der Meer formula. In this study, we have performed reliability analyses for thus designed Tetrapod armors of 12 trade harbors and 8 coastal harbors in Korea. It is found that there is a linear relationship between the safety factor and the probability of failure; the larger the safety factor, the smaller the probability of failure. It is also found that the probability of failure during 50-year service lifetime is about 60% for the Tetrapod armors designed by the deterministic design method with the safety factor of 1.0. This finding seems to be natural since the encounter probability that a breakwater will experience storm waves greater than the design wave during its lifetime is 63% if the lifetime is set equal to the design return period. The results of this study could provide a guideline for determining the target probability of failure of Tetrapod armors in the future. A similar approach could be used for armor units other than Tetrapods.

Evaluating the seismic stability of a rock slope typically involves searching for the minimum value of calculated safety factors (SF) for each supposed sliding block. Because only the transient equilibrium is evaluated, the likelihood of any slope failure can be deemed negligible if all the calculated SFs are greater than unity. However, even if some of the calculated SF are less than unity, it cannot be assumed that the slope will collapse. Recently, in the wake of extremely large earthquakes in Japan, the design earthquake standards for nuclear power plants (NPP) have been extended. After the experience of the 2011 off the Pacific coast of Tohoku Earthquake, the designer is expected to consider beyond design basis earthquakes to determine whether more can reasonably be done to reduce the potential for damage, especially where major consequences may ensue [IAEA (2011). IAEA international fact finding expert mission of the Fukushima dai-ichi NPP accident following the Great East Japan Earthquake and Tsunami, Mission report, IAEA]. With this in mind, the method employed to evaluate the seismic performance of the slope surrounding an NPP needs to be capable of doing more than determining the likelihood of failure: it must also consider the process toward failure in the event of an earthquake beyond the design basis. In this paper, a new evaluation flow which considers the failure process is proposed to evaluate the seismic performance of slopes surrounding an NPP. This is followed by confirming the validity of the concepts in the proposed flow chart by re-evaluating centrifuge tests in past literature and the numerical simulations designed for those tests.

The arch dam design specification (SL282-2003) provides an allowable safety factor of 3.5 in abutment stability analysis, whether at the same level with value of 3.0 specified for gravity dams, or greater than it, which is preferred. Using the approach of ‘Ratio of Safety Margin’ proposed by the authors, this method can compare the safety factor with reliability index. Through computing the ratio safety margin can compare safety factor and reliability index whether at the same risk level, the researches confirm that allowable reliability index of 4.45 and the allowable safety factor of 3.5 at the same level of risk control.

In tunnel engineering, the forms of lining structure usually are similar. In order to conveniently and quickly evaluate and analyze the tunnel lining structure safety, based on the general finite element software ANSYS, a parameterized model for tunnel lining structure safety analysis with APDL and UIDL was researched in this paper. The results show as follows: The developed parameterized model using the numerical method of limit analysis of strata structure may not only conveniently and quickly evaluate and analyze the tunnel lining structure safety, but also analyze and calculate the safety factor of tunnel lining structure taking into account the effect of tunnel excavation process. The applicability and simplicity of the developed parameterized model in the paper also support its usefulness.

Stability of slopes is a significant geotechnical engineering topic and planar block slide is one of the most important rock slope failures. This paper tries to propose an interactive model for assessing the stability of planar sliding blocks in rock slopes using artificial neural network (ANN). This model analyzes a slice of unit thickness taken perpendicular to the strike of the slope face and allows users to estimate the safety factor (SF) to achieve and analyze rock slopes with an acceptable accuracy.