Sharif Digital Repository

There are different well-established strategies for making a process plant inherently safer. The benefits of applying these strategies on reducing the overall risk inside a plant are obvious. However, some of these changes are rejected many times because they appear to be too costly. But if the effects of applying inherently safer design strategies are investigated not only on the processing costs of a plant but also on the potential accident costs, the decision would in fact be different. In this paper an optimization procedure is proposed which integrates both processing and accident costs for different design schemes. In this procedure, some of the design variables are chosen with regard... 

Nowadays the maintenance of the deteriorating structures is an important subject in industry and research. Due to the limitations of the budget and time, the optimization algorithms have been used widely to determine the best maintenance strategies to provide the more economical structures. On the other side, the Less life-cycle cost will result in less safe structures. As safety is a vital criterion for the users of a structural system, there is a severe need to make a suitable trade-off between cost and safety. So, the optimal maintenance strategies are those that fulfill both the safety and the economical requirements. In this paper, the reliability of the structural system is selected to... 

We develop a replacement-repair model to study a renewing free replacement warranty (RFRW) for a class of multi-state deteriorating repairable products. Each product may experience N different working states with different hazard functions, before the warranty contract expires. Once the item enters working state j(j = 1, 2, . . . , N), it can either fail or move t any of the subsequent states. In the former case, the best rectification action, replacement or minimal repair, regarding the failure status, should be done to put the item into operation. In each working state there is a determined probability for transition to each of the subsequent working states. After a replacement the product... 

In this research, new software package for neutronic calculations, especially kinetic parameters of PWR reactors, has been developed. The program used to link the WIMS-D5, BORGES and CITVAP nuclear codes has been written in Visual C# programming language. This software was used for calculation of kinetic parameters of WER-1000 and NOK Beznau reaction The ration (βeff)i/(βeff)corewhich are an important input data for the reactivity accident analysis, were also calculated. The results were compared with final safety analysis report (FSAR) and published documents. Copyright  

In this paper wefirst propose two new concepts concerning the notion of key escrow schemes: provable partiality and independence. Roughly speaking, a scheme has provable partiality if the existence of a polynomial time for recovering the secret from escrowed information implies there is a polynomial time algorithm for solving a well known intractable problem. A scheme is independent if the secret key and the escrowed information are independent. Finally, we propose a new verifiable partial key escrow scheme, based on McCurley's encryption scheme, satisfying both of the above criteria  

Fuel management in PWR nuclear reactors is comprised of a collection of principles and practices required for the planning, scheduling, refueling, and safe operation of nuclear power plants to minimize the total plant and system energy costs to the extent possible. Despite remarkable advancements in optimization procedures, inherent complexities in nuclear reactor structure and strong inter-dependency among the fundamental parameters of the core make it necessary to evaluate the most efficient arrangement of the core. Several patterns have been presented so far to determine the best configuration of fuels in the reactor core by emphasis on minimizing the local power peaking factor (Pq). In... 

Wireless infrared optical code-division multiple access (W-OCDMA) is a new developing technique with many useful applications. Noting the limitation on power consumption and eye-safety requirements, wireless optical systems are power limited. Therefore control and efficient use of optical power is a key issue in analysis and design of these systems. Also, multi-user interference is the major source of impairment in these systems and power control is required to control and reduce this interference. Power control and the inevitable errors in its algorithms play an important role in design and implementation of these systems. In this article the authors study the uplink performance of W-OCDMA... 

In modern safety-critical real-time embedded systems, performance and reliability are two most important parameters. The joint consideration of these two parameters is called performability. This paper evaluates and compares different schedulability conditions, which are used for scheduling tasks with fault-tolerant Rate-Monotonic (RM) algorithm, with respect to their performability. The task reexecution scheme is used to implement fault tolerance in the RM scheduling algorithm. To evaluate the schedulability conditions, a software tool is developed to simulate an embedded processor with m schedulable periodic tasks. The results show that among five different schedulability conditions used... 

FlexRay communication protocol is expected to become the de-facto standard for distributed safety-critical systems. This paper classifies the effects of transient single bit-flip fault injections into the FlexRay communication controller. In this protocol, when an injected fault is activated, this may result in one or more error types, i.e.: Boundary violation, Conflict, Content, Freeze, Synchronization, Syntax, and Invalid frame. To study the activated faults, a FlexRay bus network, composed of four nodes, was modeled by Verilog HDL; and a total of 135,600 transient faults was injected in only one node, called the target node. The results show that only 9,342 of the faults (about 6.9%) were... 

The Failure Modes and Effects Analysis (FMEA) method has been used to study the reliability of many different power generation systems. This paper now applies that method to a wind turbine (WT) system using a proprietary software reliability analysis tool. Comparison is made between the quantitative results of an FMEA and reliability field data from real wind turbine systems and their assemblies. These results are discussed to establish relationships which are useful for future wind turbine designs. The main system studied is an existing design 2 MW wind turbine with a Doubly Fed Induction Generator (DFIG), which is then compared with a hypothetical wind turbine system using the Brushless... 

The accuracy of static neutronic parameters in the nuclear reactors depends upon the determination of group constants of the diffusion equation in the desired geometry. Although several methods have been proposed for calculating these parameters, there is still the need for more reliable methods. In this paper a powerful and innovative method based on Spatial Homogenization and Temperature Variation (SHTV) of physical properties of a WWER-1000 nuclear reactor core for calculating the relative power distribution of Fuel Assemblies (FA) and the hot fuel rod, is presented. The method is based on replacing the heterogeneous lattices of materials with different properties by an equivalent... 

Power consumption, performance and reliability are the most important parameters in modern safety-critical distributed real-time embedded systems. This paper evaluates and compares different schedulability conditions in faulttolerant Rate-Monotonic (RM) and Earliest-Deadline-First (EDF) algorithms, with respect to their power efficiency. The primary-backup scheme is used to implement fault tolerance in the algorithms. To evaluate the algorithms, a software tool is developed that can simulate an embedded system consisting of n processors and m periodic tasks. The results show that depending on the different schedulability conditions, the EDF algorithm implemented with the Best-Fit policy is... 

In some industries such as the consumable product industry because of small differences between products made by various companies, customer loyalty is directly related to the availability of products required at that time. In other words, in such industries demand cannot be backlogged but can be totally or partly lost. So companies of this group use make-to-stock (MTS) production policy. Therefore, in these supply chains, final product warehouses play a very important role, which will be highlighted by considering the demand uncertainty as it happens in real world, especially in the consumable product industries in which demand easily varies according to the customer's taste variation,... 

In order to evaluate the seismic behavior of confined masonry buildings, based on Iranian seismic code design, a single storey full-scale unreinforced confined brick masonry building has been constructed on the shaking table facility at the Earthquake Engineering Research Center (EERC) of Sharif University of Technology. The 4 by 4 meter model consists of four brick masonry walls confined with reinforced mortar tie-columns and steel bond beams, with a traditional jack-arch roof system. Three of the wall panels contained openings of different sizes and geometries. The model was subjected to the scaled earthquake records of Bam, Tabas and El Centro, as well as a harmonic acceleration with... 

The Burr XII distribution can closely approximate many other well-known probability density functions such as the normal, gamma, lognormal, exponential distributions as well as Pearson type I, II, V, VII, IX, X, XII families of distributions. Considering a wide range of shape and scale parameters of the Burr XII distribution, it can have an important role in reliability modeling, risk analysis and process capability estimation. However, estimating parameters of the Burr XII distribution can be a complicated task and the use of conventional methods such as maximum likelihood estimation (MLE) and moment method (MM) is not straightforward. Some tables to estimate Burr XII parameters have been...