Sharif Digital Repository

Electron guns are used as the electron sources in high-power electron tubes. The generated electron beam in electric guns passes through an aperture at the center of the anode. Since the electron beam has considerable kinetic energy, any collision between the electron beam and the anode aperture edge damages the electron gun. Therefore, electron guns are designed to meet the compatibility between the diameters of the electron beam and the anode aperture. However, this compatibility is disrupted during the transient time interval of the gun's power supply. In this article, the cause of failure of the electron gun of high-power electron tubes is investigated for the transient interval of the... 

Change in customers' consumption patterns due to the introduction of new electricity consuming technologies into human consumption practices has impacted the existing optimal loading profile of the grid facilities. Although some MV/LV distribution transformers (DTs) are operating under a light load profile, this does not guarantee that they are in a healthy condition, since necessary maintenance procedures are required. On the other hand, many unplanned overloading conditions occur on the other DTs and causes accelerated failures which contributes to very high operational costs. This paper presents the outcome of a study on how the planned DTs relocation can save asset managers against their... 

This paper presents a multi-objective availability-redundancy allocation optimization model for a hyper-system. The hyper-system consists of B systems with shared resources. The structure of the systems is series-parallel subsystems consisting of multi-failure and multi-state components. The components may be purchased from different suppliers based on their price and discounts. It is assumed that technical and organizational activities continuously affect the components' failure rates and the subsystems' working conditions before starting the system's mission horizon. The model aims to find the optimal number and the type of the subsystems' components for all systems from each supplier and... 

This study investigates the durability of confined geopolymer concrete with fiber-reinforced polymer and compares the results with ordinary Portland cement concrete (OPCC). Two hundred and seventy geopolymer concrete (GPC) specimens with different mix designs (fly ash- and granulated blast furnace slag(GBFS)-based GPC) were prepared and then wrapped with two different fiber-reinforced polymers (carbon and glass FRPs). For 12,960 hrs (eighteen months), the specimens were exposed to four different pHs (2.5, 7 (water), 7.25 (saltwater), 12.5). The reliability analysis was performed after modeling the compressive strength over time. Based on the results, the ductility of all specimens decreased... 

Drilled shafts are one of the most important types of pile foundations. Several researchers have suggested different soil failure patterns for driven piles; however, for drilled shafts, this issue is inadequately addressed in the literature. In this paper, a numerical approach was pursued to obtain the location and dimensions of plastic zones around the tip of drilled shafts. The dependence of the suggested failure pattern size on the soil properties and drilled shaft dimensions was investigated. Based on several analyses, a soil jug-shaped failure pattern around the tip of drilled shafts was proposed, and its dimensions were determined using the regression-based and trial and error... 

In the last decade, the scale of heterogeneous computing (HC) systems such as heterogeneous cloud computing environments was growing like never before. So network failures are unavoidable in such systems, which affect system reliability. Since the task scheduling algorithm in HC is challenging, we investigate a new reliability-aware task scheduling algorithm (RATSA) in this paper. RATSA is designed to schedule tasks on directed acyclic graphs (DAGs) by using the shuffled frog-leaping algorithm (SFLA) and genetic algorithm (GA) as evolutionary algorithms. The population-based SFLA-GA is applied to optimize makespan in the RATSA as an NP-complete problem. Moreover, the proposed algorithm... 

In cloud computing services, high availability is one of the quality of service requirements which is necessary to maintain customer confidence. High availability systems can be built by applying redundant nodes and multiple clusters in order to cope with software and hardware failures. Due to cloud computing complexity, dependability analysis of the cloud may require combining state-based and nonstate-based modeling techniques. This article proposes a hierarchical model combining reliability block diagrams and continuous time Markov chains to evaluate the availability of OpenStack private clouds, by considering different scenarios. The steady-state availability, downtime, and cost are used... 

The reliability of machinery and automated guided vehicle has been one of the most important challenges to enhance production efficiency in several manufacturing systems. Reliability improvement would result in a simultaneous reduction of both production times and transportation costs of the materials, especially in automated guided vehicles. This article aims to conduct a practical multi-objective reliability optimization model for both automated guided vehicles and the machinery involved in a job-shop manufacturing system, where different machines and the storage area through some parallel automated guided vehicles handle materials, parts, and other production needs. While similar machines... 

Conic shell structures are widely used in aerospace industries. In the literature various models have been proposed to failure analysis of composite materials. Clearly, each model has a favorable range of applications. In this paper tensile, compressive, shear and thermal expansion properties of tape-wounded Carbon/Phenolic composites are firstly measured at various temperatures in range 23–200°C. The captured properties are then taken into account to progressive failure analysis of a conic Carbon/Phenolic structure under internal pressure and thermal loadings. For this end, a particular failure criterion is proposed to predict failure in the composite structures with a reasonable margin of... 

In this paper static eccentricity (SE) fault diagnosis in wound rotor (WR) resolver is considered and a new noninvasive index is proposed. Using the proposed index not only leads to SE detection but also, helps to precisely determine the eccentricity level. Furthermore, the location of the fault is determined using two search coils. In this regard, a mathematical model based on the winding function method is proposed. In the proposed model the influence of non-uniform air-gap length on calculating the inductances is considered. Then, time-stepping finite element method (TSFEM) is used for approving the success of the proposed index. Finally, experimental tests are done to validate the... 

Public transport is amongst critical infrastructures in modern cities, especially megacities, home to millions of people. The reliability of these systems is highly crucial for both citizens and service providers. If service providers overlook system reliability, a considerable amount of expenses will be wasted. Several factors such as vehicle failure, accident, lack of budget weather factors, and traffic congestion cause unreliability, among which vehicle failure plays a prominent role. The brake system is the most vulnerable and vital component of a public transportation bus. Brake reliability depends on driver's expertise, component quality, passenger loading, line situation, etc.... 

In this article, we present a cost-effective solution for switching short-circuit fault diagnosis in a three-phase quasi-Z-source inverter (qZSI). The fault is announced to the processor utilizing a peripheral circuit that covers the fault detection in all switches of the inverter. After the fault detection, a nonmaskable interrupt is activated, cutting the CPU routine, and a fault-diagnosis algorithm is initiated. The exact location of the failed switch is identified through the proposed algorithm. The entire process is accomplished in advance of the critical overcurrent condition, which typically arises after a short-circuit fault. Thanks to this overtake, the proposed technique prevents... 

Mooring lines may be damaged under severe conditions during the life of an offshore platform. In the event of a mooring failure, it is possible to break remaining mooring lines in a severe condition, which ultimately leads to the total structural failure; Therefore, the post-failure analysis is very important for the mooring system. In this study, the Amir-Kabir semi-submersible platform has been modeled which is installed in 700 m’ depth of the Caspian Sea, and random waves have been generated towards the structure in the form of the JONSWAP wave spectrum according to the conditions of the Caspian Sea. For analysis, four different mooring configurations have been considered. Then, in each... 

I/O caching techniques are widely employed in enterprise storage systems in order to enhance performance of I/O intensive applications in large-scale data centers. Due to higher performance compared to Hard Disk Drives (HDDs) and lower price and non-volatility compared to Dynamic Random-Access Memories (DRAM), Flash-based Solid-State Drives (SSDs) are used as a main media in the caching layer of storage systems. Although SSDs are known as non-volatile devices but recent studies have reported large number of data failures due to power outage in SSDs. To overcome the reliability implications of SSD-based I/O caching schemes, RAID-1 (mirrored) configuration is commonly used to avoid data loss... 

I/O caching techniques are widely employed in enterprise storage systems in order to enhance performance of I/O intensive applications in large-scale data centers. Due to higher performance compared to Hard Disk Drives (HDDs) and lower price and non-volatility compared to Dynamic Random-Access Memories (DRAM), Flash-based Solid-State Drives (SSDs) are used as a main media in the caching layer of storage systems. Although SSDs are known as non-volatile devices but recent studies have reported large number of data failures due to power outage in SSDs. To overcome the reliability implications of SSD-based I/O caching schemes, RAID-1 (mirrored) configuration is commonly used to avoid data loss... 

In the last decade, the scale of heterogeneous computing (HC) systems such as heterogeneous cloud computing environments was growing like never before. So network failures are unavoidable in such systems, which affect system reliability. Since the task scheduling algorithm in HC is challenging, we investigate a new reliability-aware task scheduling algorithm (RATSA) in this paper. RATSA is designed to schedule tasks on directed acyclic graphs (DAGs) by using the shuffled frog-leaping algorithm (SFLA) and genetic algorithm (GA) as evolutionary algorithms. The population-based SFLA-GA is applied to optimize makespan in the RATSA as an NP-complete problem. Moreover, the proposed algorithm... 

Offshore platforms have had diverse applications in the marine industry, for example, oil or gas platforms can provide facilities to store the oil and gas before transport those to refineries. Offshore wind turbines are another well-known use of the offshore platform for generating power. As platforms encounter various strong forces from water and wind currents, the materials used for these structures are mainly steel or concrete. These platforms are classified into different types, according to the depth of water and their applications. In addition, offshore platforms, as artificial reefs may be used for decades at different marine conditions. Consequently, their design and maintenance are... 

The energy efficiency of emerging nonvolatile processors equipped with FRAM-SRAM memory makes them a promising solution for energy harvesting systems. To enable correct functionality and forward progress with an unreliable power supply, the system must accumulate sufficient energy in the capacitor to execute tasks atomically, even in the worst case scenario. Due to the large gap between the average and worst case energy consumption of tasks, state-of-the-art approaches like eM-map require a large capacitor to execute tasks on the SRAM. However, the size, cost, and charging time of the capacitor are major concerns in the energy harvesting systems. In this article, we proposed CHANCE, a... 

Mechanical failure of materials adjacent to the production cavity and material disaggregation caused by fluid drag are considered as the most important parameters that affect sand production. In light of such factors, the coupling of two mechanisms-mechanical instability and hydrodynamic erosion-is indispensable in order to model this phenomenon successfully. This paper examines the applicability of a coupled hydro-mechanical erosion criterion for simulating sand production using the finite element method. The porous medium was considered fully saturated. The onset of sanding and production of sand were predicted by coupling mechanical failure and subsequent erosion of the grain particles... 

The energy efficiency of emerging nonvolatile processors equipped with FRAM-SRAM memory makes them a promising solution for energy harvesting systems. To enable correct functionality and forward progress with an unreliable power supply, the system must accumulate sufficient energy in the capacitor to execute tasks atomically, even in the worst case scenario. Due to the large gap between the average and worst case energy consumption of tasks, state of the art approaches like eM-map require a large capacitor to execute tasks on the SRAM. However, the size, cost, and charging time of the capacitor are major concerns in the energy harvesting systems. In this paper, we proposed CHANCE, a...