فهرست مطالب سیدعلی هاشمیان

In motorcycle accidents, the acceleration caused by the collision has a huge risk to the health of the motorcyclists and passengers. In this study, the finite element method was used for dynamic analysis of impact mechanics to predict the effect of the shell material and thickness on the head injury criteria of the helmeted head (including head, shell, foam, comfortable foam and strap). The open-face helmet, including three current market materials, were selected. Head orientation, in the most accidents, at the collision moment is oblique. In the simulated impact model, head is also placed obliquely. The results of this study are validated by the experimental results and valid published data. The simulation results show that there is an optimum thickness for the helmet shell regardless of its material. In order to determine the optimum thickness, there must be compromises between the various parameters such as head injury criteria, shell failure, weight, and price. According to the results obtained for the shell thickness, if the thickness increases, the weight and range of acceleration increase while the probability of shell failure decreases. If the thickness decreases, despite of decreasing the acceleration in the head, the stress in the shell increases that leads to failure.

The purpose of the present study was to investigate the psychological and sociological factors affecting student-teacher differences in Isfahan University of Technology in the educational process in order to find out the factors and barriers to students' social participation.

The statistical population of the study was teachers of Isfahan Farhangian University (total of 1902 Sisters and Brothers centers) among which 331 persons who had passed at least one semester were selected by stratified random sampling. Selected items were assessed using a researcher-made questionnaire on the effectiveness of (and other variables including gender, field of study and socioeconomic status on) indifference among this social intellectual. Data analysis was performed using SPSS and Amos software.

The results of this study showed that in analyzing the structural equation tables and patterns for the relationship between students' sense of effectiveness and social apathy, the standardized impact factor is -0.738 and P value of 0.003 confirms this hypothesis with confidence. At 95%, the severity of the correlation between gender with social participation and communication performance is at a moderate level, and there is a significant positive direct relationship with the field of study.

Accordin The results showed that there is a significant relationship between students 'socioeconomic status (subjective to students' social indifference but not objective and material).

The conventional power grid has several drawbacks and a new powerful smart grid perspective has been recently introduced. The smart grid principle, allowing to efficiently manage an electrical grid network, needs to exploit a communication network for interconnecting the Smart Grid devices. An increasing interest is toward wireless communications due to their higher flexibility. Within this context cognitive radio (CR) techniques has been introduced aiming to exploit more efficiently the radio spectrum resources. In neighborhood area network (NAN), mesh grids can be considered as one of possible network topologies. In such networks no base station is required and data will be sent to gateway by means of nodes themselves. Hence, routing is one of the main issues in such networks. Routing in such networks should be done by a protocol which maximizes throughput against cognitive radio drawbacks and Packets delay in such protocol needs to be minimum and suitable for smart grids applications. CORPL has been introduced as a routing protocol to meet some of these goals. In this paper by CORPL functionality would be evaluated under burst and poisson traffic. It will be shown that by increasing active nodes, CORPL functionality would be decreased. Then average upper limit for delay would be mathematically modeled and to reduce that a multigate scheme would be introduced.

Tolerance analysis plays a crucial role in predicting the quality of products and reducing production costs. This procedure is generally complex and available methods for analyzing different types of assemblies are not always applicable. Accordingly, having a comprehensive approach to assess the effect of tolerances on the quality and cost of products is a fundamental requirement in the manufacturing industry. This paper proposes the improved second-order method for tolerance analysis of complex assemblies. The conventional second-order tolerance analysis (SOTA) is an accurate and applicable method for obtaining the statistical specifications of the assembly’s key characteristic. However, determining the assembly function in SOTA entails forming vector loops and therefore, this method is limited to simple assemblies. On the other hand, in mechanical assemblies that are usually complex, creating vector loop may encounter some difficulties in practice. In this study, the mentioned issues have been overcome by linking SolidWorks and MATLAB software to employ the proposed methodology for any mechanical assemblies without creating vector loops. For this purpose, MATLAB software makes necessary changes in the SolidWorks model and calculates the derivatives of the assembly function, which are required for the analysis. Then, the statistical moments are computed and the probability distribution of the key characteristic is obtained using the Pearson system. The sent study is appropriate for analyzing either linear or nonlinear assembly functions with any statistical distribution. Finally, the applicability of the proposed approach is investigated by some practical examples and the accuracy of results is confirmed by Monte Carlo simulation.

The appearance quality of automotive bodies is among the features which are, in recent years, significantly taken into consideration by designers throughout the world. Automotive bodies are, to a great extent, constructed from flexible sheet metal components and would deform and distorted easily by even a slight assembly force. Therefore, errors due to manufacture and assembly processes of automotive bodies lead to major deviation from the ideal product and finally affect the appearance quality and cosmetic features of the vehicle. The effect of these errors, which are commonly arisen by dimensional, geometric or assembly tolerance of the components, can be examined by tolerance analysis. As one of the key quality characteristics in vehicle design, this paper evaluates the appearance quality of automotive bodies as a function of assembly derived errors. In the proposed methodology, by means of the nonlinear finite element analysis and by presenting the surface interrogation techniques, a comprehensive approach of quality appearance evaluation of vehicles is developed. The approach is validated by a vehicle example and the results show a great consistence with practical data obtained from the production line.

In a mechanical assembly, errors arising from part manufacturing or assembly process may cause significant variation in final assembly with respect to the ideal model and affect the quality and performance of product. In sheet metal products due to high order of compliancy of components, errors generated during assembly process are as important as parts’ manufacturing tolerances. Therefore, it is crucial to have a comprehensive model in order to analyze the assembly process of these structures and represent the relationship between part tolerances and final assembly errors. However, it should be noted that assembly processes are often complex and nonlinear in nature. In sheet metal structures, the most important factor that makes the assembly process nonlinear is contact interaction between mating parts during assembly. If this factor is disregarded and the assembly process is only represented based on linear force-displacement relationship, the model will result in part penetration and a remarkable difference between theoretical and experimental results will occur. Another important feature in sheet metal tolerance analysis is the surface continuity of components which makes the deformation of the neighboring points of a plate correlated. This paper aims to present a new methodology for tolerance analysis of compliant sheet metal assemblies in which a nonlinear finite element analysis is integrated with improved sensitivity-free probability analysis in order to account for effects of contact interaction and surface continuity of components and calculate the assembly error.The accuracy of this approach is confirmed by anexperimental casestudy and Monte Carlo simulation