فهرست مطالب

  • Volume:18 Issue: 3, 2005
  • 104 صفحه،
  • تاریخ انتشار: 1384/10/05
  • تعداد عناوین: 9
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  • M. R. Tabeshpour, A. A. Golafshani Seif Pages 219-228
    The resulting motion in waves can be considered as a superposition of the motion of the body in still water and the forces on the restrained body. In this study the effect of added mass fluctuation on vertical vibration of TLP in the case of vibration in still water for both free and forced vibration subjected to axial load at the top of the leg is presented. This effect is more important when the amplitude of vibration is large. Also this is important in fatigue life study of tethers. The structural model used here is very simple. Perturbation method is used to formulate and solve the problem. First and second order perturbations are used to solve the free and forced vibration respectively.
  • M. Arabani Pages 229-238
    In recent years a great number of advanced theoretical - empirical methods has been developed for design & modeling concrete pavements distress. But there is no reliable theoretical method to be use in evaluation of conerete pavements distresses and making a decision about repairing them. Only empirical methods is used for this reason. One of the most usual methods in evaluating concrete pavements distresses is to determine the PCI of the Pavement Condition Index. As a result of large number of variables and complicated decision - making algorithm using the information obtained in this method, may have some difficulties. Presenting an analytic -theoretical method mixed with the PCI method may be the bases for the development of a theoretical empirical method in evaluation of concrete pavements distresses & can remove the diffculties.The present paper describes a method of applying the rough set theory for evaluation of reinforced concrete highway pavements distresses in PCI method to extract the minimal decisian algorithm and selecting the best suitable method of rehabilitation. The significance of the conditional attributes retained in the minimal decisian algorithmis evaluated, and a method of deriving rules from the algorithm for the constraction of expert system is described. The result of this procedure shows the high reliability of this method, using the minimum necessary informations.
  • S. Farahat, H. Ajam Pages 239-252
    In this research, the sensitivity analysis is applied to an electrohydraulic servovalve which is a nonlinear system. This system sensitivity study differs from previous studies by considering the dynamic behaviour and nonlinearity of the system performance. Different sensitivity analysis methods are compared to each other by studying the sensitivity of the actuator piston velocity of above servovalve with respect to eighteen parameters. By using the best method among the above mentioned methods, the sensitivity of the state variables of the sample system have been studied.
  • A. Raoufpanah, M. Rad, A. Nouri Borujerdi Pages 253-261

    In this paper a laminar flow of water on an ice layer subjected to a slip condition is considered numerically. The paper describes a parametric mathematical model to simulate the coupled heat and mass transfer events occurring in moving boundary problems associated with a quasi steady state steady flow process. The discretization technique of the elliptic governing differential equations of mass, momentum and energy is based on the control volume finite difference approach and enthalpy method. the results illustrate, the distribution of heat transfer coefficient, ice melting thickness, slip velocity at solid moving boundary and boundary layer thickness for some values of slip velocity coefficient, Cu.

  • M. Jain, G. C. Sharma Pages 263-271
    This investigation proposes Markov chain analysis of controllable multi-server queue with balking. We incorporate an additional server which is added and removed at pre-specified threshold levels of queue size to control the balking behaviour of the customers. The steady state equations are constructed by assuming interdependent arrival and service processes which are characterized by bivariate Poisson distribution. Recursive approach is employed to establish the queue size distribution, which is further used to determine various performance indices.
  • S. A. Torabi, S. M. T. Fatemi Ghomi, B. Karimi Pages 273-284
    This paper addresses the common cycle multi-product lot-scheduling problem in flexible flow lines (FFL) where the product demands are deterministic and constant over a finite planning horizon. Objective is minimizing the sum of setup costs, work-in-process and final products inventory holding costs per time unite while satisfying the demands without backlogging. This problem consists of a combinatorial part (machine assignment and sequencing sub-problems) and a continuous part (lot sizing and scheduling sub problems). To account for these two elements, a new mixed integer nonlinear program (MINLP) is developed which simultaneously determines machine allocation, sequencing, lot-sizing and scheduling decisions. In order to reduce computational complexity, instead of solving this MINLP directly, we propose an efficient enumeration method to determine optimal solution of the model. Moreover, the performance of the proposed method is evaluated by some numerical experiments. Two other applicable cases (zero setup costs and Lot streaming) are studied and required modifications in the model formulation and the solution method are described. Finally, a case example in a PCB assembly system is presented to illustrate applicability of the mathematical model and the proposed solution method.
  • H. Ateshy, R. Akhavan, M. Khoshnoodi Pages 285-293
    The effects of potassium promoter for production of heavy hydrocarbons from syngas with silica- supported cobalt catalysts has been studied. After preparing the catalysts in accordance with the sol-gel method, they were subjected to various tests by using a small steely micro-reactor and capable of operating in diversified situations, such as stable temperature range, flow rate, space velocity, etc. Thorough observations revealed that the conducive situations can be achieved by the ratio of H2/CO=2 with a temperature of 220 ºC, whereas the flow rate of CO and N2 components must be equal about 35 ml/min.
  • T. Ebadzadeh Pages 295-300
    A process is described which involves infiltration of aluminum nitrate into partially sintered (porous) zircon bodies. Infiltration kinetics were studied using infiltration curves with two distinct regions. The final infiltrated samples were sintered at 1600 °C for 2 h and yielded specimens containing the tetragonal zirconia.The experimental results show that in spite of the similar porosity of the infiltrated preform and of pure zircon sintered at 1600 °C, the former has a higher flexural strength and fracture toughness due to the incorporation of the ZrO2 particles and the elongated mullite grains resulting from the infiltration and subsequent heating of the preform.
  • M. Moghavvemi, S. Y. Tan, S. K. Wong Pages 301-318
    Automatic Meter Reading (AMR) is the remote collection of consumption data from customer’s utility meters over telecommunications, radio, power line and other links. AMR provides water, electric and gas utility−service companies the opportunities to streamline metering, billing and collection activities, increase operational efficiency and improve customer service. Utility company uses technologies that were developed several decades ago with the majority of the meters being read visually. With manual readings, considerable time is used to physically check out each unit. AMR becomes a viable option to overcome this problem of time wastage to obtain the meter readings. There are many different forms of communication links that can be utilized as the communication medium in an AMR system. One such link is the power line carrier or PLC. The advantages of using the PLC as the communication medium are readily apparent since the power line network is the property of the utility company and its infrastructure is already there. However, power lines are never meant for communication and creates much noise and therefore, various modifications has to be made to make the PLC suitable to be the AMR communication channel. The AMR system consists of three major components: the meter interface module, communications system, and data concentrator. This paper details a feasibility study on the creation of a robust bi-directional/two-way communication system between an electricity meter and a distant control unit (data concentrator) over the low voltage (LV) distribution grid. Basic functions of the AMR system include the provision for remote connection and disconnection of meter and fraud detection features at both the meter interface and the data concentrator. As a support system to the entire AMR, batteries are utilized. They are especially important in the cases of power failures. Lithium-ion batteries are the type of batteries that are used as these batteries tend to last longer than most other batteries. The main advantage of this system is that it is a low cost system that produces very encouraging results and it can be implemented upon existing electro-mechanical meters without the need of purchasing new meters. With many existing meters being the electromechanical meters, the need for a high-cost, large-scale implementation of new electronic device meters to enable implementation of the AMR system is unnecessary. The cost of implementation is low and the benefits, especially economically, that it brings to the utility company are immense.