Sharif Digital Repository

Due to several advantages, three-phase Dual Active Bridge (DAB) converter is widely used in numerous applications nowadays. On the other hand, this converter is very vulnerable to Transistor Open-Circuit Fault (TOCF). Therefore, a fault-tolerant (FT) scheme has been proposed in this paper to solve the problem. First, normal and faulty conditions are investigated, and according to the results, a fault-diagnosis (FD) approach is introduced. Using the outcomes of FD unit, a new post-fault strategy is proposed for the converter. The FD method is based on the DC component of transformer phase currents, and the basis of FT technique is shedding the faulty phase. Some benefits of the proposed... 

Winding turn-to-turn fault (TTF) is one of the most reported reasons for transformer unplanned outage. If its occurrence is not detected at an early stage, it can develop into a costly phase-to-ground fault. In this paper, a novel algorithm based on the fault-related incremental currents is proposed to detect a low-level transformer TTF. This paper shows that the performance of the proposed method is independent of the transformer operating condition. Therefore, it is reliable even under the presence of power system transients such as the external faults. In addition, the proposed algorithm can be configured uniquely and easily. This feature prevents the algorithm from unnecessary trips.... 

Joint multistage expansion planning of active distribution network (ADN) is well investigated in this paper. This expansion model considers the effects of optimal operating conditions in the planning studies. In the proposed model, for each planning time stage, several operating scenarios are defined based on operational status of the network. The utilization of distributed energy resources (DERs) around the network is determined for each operating scenario through active management of these resources. In the planning level, investment in distribution network assets including feeders, substations, and distributed generations (DGs) incorporating conventional gas turbines and renewable wind... 

Polyaniline nanofiltration membranes were synthesized to examine a potential candidate for application of solvent recovery from lube oil. An integrally skinned polyaniline membrane was cast on a woven polyester fabric and then was chemically crosslinked with glutaraldehyde in order to further increase the membranes resistant in a methyl ethyl ketone and toluene mixture. Subsequently, membrane performance was tested under different operational conditions. The operation pressure was fixed at 35 bar and was held constant for all of the tests. The membrane demonstrated a permeate flux of 10 l/(m 2  h) and oil rejection of 69%. Abbreviations: PANi: Polyaniline; PI: polyimide; MEK: methyl ethyl... 

Transformer turn-to-turn fault (TTF) is one of the most difficult failures to detect. The negative sequence percentage differential current (NSPD) and extended park vectors approach (EPVA) are the two most promising methods for detection of the TTF inception. In this paper, in order to evaluate the performance of these methods, various experimental tests are carried out to detect the TTF initiation on the winding of the transformer under different operating conditions such as: No-load operation, when an external fault or an open conductor fault is also occurred. The results show that the setting of the proper thresholds plays the main role in the reliable and secure performance of NSPD and... 

Operational modal analysis techniques classically have been developed based on the assumption that the input to the system is a stationary white noise. While, in many practical cases, the systems are excited by combination of white noise and colored noises (harmonic excitations). Consequently, in conditions where non-white noises are present, the existing OMA methods cannot completely distinguish between the system poles and the induced poles due to colored noises. In order to overcome this weakness of OMA methods, some researches have been conducted in the field. In this paper, a new method is proposed for identifying the modal parameters of the system under the unknown colored noises,... 

Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5 MW NREL... 

Gas turbine hot-section parts can be very expensive components with a finite lifetime. Their durability is strongly dependent on the operating service conditions which control the maintenance intervals and associated expenses. Blade damage is the most frequent reason for failures in gas turbine engines and also oxidation is one of the most critical degradation mechanisms when the power system operates in partially loading condition. This paper describes the methodology of oxidation life assessment for uncoated and coated blades with various metallic coatings in the first stage of a typical gas turbine engine. The resultant weight-change curves were validated by comparing them with the... 

The aim of this work is to investigate the effect of molybdenum disulfide on tribological properties of Ultra-high-molecular-weight polyethylene (UHMWPE). UHMWPE/MoS2 nano-composites were prepared using in-situ polymerization and Ziegler-Natta catalytic system. Studies showed that, in order to obtain the optimum tribological properties, interlayer distance between nanosheets should be as high as possible. Therefore, the nanosheets were subjected to oxidation using the required oxidants followed by thermal shock and ultrasound. Fourier-transform infrared spectroscopy (FTIR) analysis was used to determine the formation of functional groups which indicate the formation of S═O bond in the... 

This paper presents a mathematical formulation of lithium-ion batteries, including aging and temperature effects. The model is developed by integrating the simplified single particle model (SSPM) and reduced-order model (ROM) to predict solid electrolyte interphase growth (SEI). Results show agreement with the experimental data at 25 °C operating temperature and moderate cycling currents. A maximum error of 3.6% in finding the battery discharged Ah is observed in harsh operating conditions, including 60 °C and approaching the end of life of the battery. Due to the typical operating conditions of stand-alone renewable energy systems, more accurate estimations are expected. Finally, this... 

After proposing a semi-analytical solution for swirl laminar flow, macroscopic characteristics of open-end pressure-swirl injector including discharge coefficient and spray cone angle are calculated. In the presence of air core of the axial region inside the injector, the laminar rotational flow equations are simplified, and with the assumption of the quasi-developed axial flow along the nozzle, the equations are iteratively solved employing separation of variables method. The accuracy of the proposed semi-analytical solution is compared by some numerical and experimental results on an open-end injector. The validity of quasi-developed flow defined in the present work is confirmed based on... 

Concerns about climate change have persuaded the researchers to examine CO2 injection in the form of carbonated water (CW) into oil reservoir as a safe and effective CO2 storage and enhanced oil recovery process. Although interfacial tension (IFT) between crude oil and injected fluid has a vital role on the displacement of fluids in porous media, the effect of CO2 and crude oil type on the dynamic IFT of crude oil under different operational conditions is not well understood. Accordingly, this study was carried out to assess the effects of temperature, pressure, crude oil type and CO2 on the dynamic IFT of crude oil/CW. To achieve this goal, two types of crude oil were provided from southern... 

In this article, experimental and numerical investigations are performed to study a thermogravitational column (TGC) for the separation of toluene/n-heptane mixture. This research has tried to determine the main significant parameters and their effects on the performance of the process. In experimental examinations, the influence of the main parameters such as feed flow rate, cut and temperature gradient on the performance of the TGC efficiency is studied. In addition, computational fluid dynamics is used to simulate the separation process in this review. The response surface methodology (RSM) was also applied to minimize the number of runs and investigate the optimum operating conditions.... 

The increment of using fossil fuels has caused many perilous environmental problems such as acid precipitation, global climate change and air pollution. More than 50% of the energy that is used in the world is wasted as heat. Recovering the wasted heat could increase the system efficiency and lead to lower fuel consumption and CO2 production. Organic Rankine cycle (ORC) which is a reliable technology to efficiently convert low and medium temperature heat sources into electricity, has been known as a promising solution to recover the waste heat. There are numerous studies about ORC technology in a wide range of application and condition. The main objective of this paper is to presents a... 

Parabolic trough solar collector (PTC) is one of the most mature and widely used type of solar energy harnessing devices. Therefore, investigation of the effect of various operational conditions on the overall efficiency of these devices has been topic of substantial interest in the recent decade. Moreover, utilization of nanoparticles as a useful additive to the working fluid should be examined thoroughly to optimize the collector's outputs. To do so, in the present study, energy and exergy efficiencies of a typical PTC as a function of several involving parameters are numerically calculated. These parameters are nanoparticle volume fraction (from 0 to 5 percent), environment wind speed... 

Asphaltene which cover range of 1% to over 10% of oil by weight, is well-known as most problematic part of oil that can deposit during production in reservoir, well tubing, and surface production lines, and consequently impose a serious restriction on production which in turn increases total cost of entire operation. Through decades an extensive research has been performed in order to identify asphaltene molecular structure, its behavior at different condition, and its separation mechanism from oil. One of most critical parameter associated with asphaltene precipitation modeling is flocculated asphaltene weight percentage in oil at given operation condition. In this study, to eliminate cost... 

Polyaniline nanofiltration membranes were synthesized to examine a potential candidate for application of solvent recovery from lube oil. An integrally skinned polyaniline membrane was cast on a woven polyester fabric and then was chemically crosslinked with glutaraldehyde in order to further increase the membranes resistant in a methyl ethyl ketone and toluene mixture. Subsequently, membrane performance was tested under different operational conditions. The operation pressure was fixed at 35 bar and was held constant for all of the tests. The membrane demonstrated a permeate flux of 10 l/(m2 h) and oil rejection of 69%. Abbreviations: PANi: Polyaniline; PI: polyimide; MEK: methyl ethyl... 

AQM router aims primarily to control the network congestion through marking/dropping packets which are used as congestion feedback in traffic sources to balance their flow rate. However, stabilizing queuing delay and maximizing link utilization have been considered as the main control objectives, especially in media dominated networks. Usually, most of the AQM algorithms are designed for a nominal operating point. However, time-varying nature of network parameters frequently violates their robustness bounds. In this paper, a self-tuning compensated PID controller is proposed to address the time-varying nature of network conditions caused by parameter variations and unresponsive connections.... 

Due to the sensitivity of mammalian cell cultures, understanding the influence of operating conditions during a tissue generation procedure is crucial. In this regard, a detailed study of scaffold based cell culture under a perfusion flow is presented with the aid of mathematical modelling and computational fluid dynamics (CFD). With respect to the complexity of the case study, this work focuses solely on the effect of nutrient and metabolite concentrations, and the possible influence of fluid-induced shear stress on a targeted cell (cartilage) culture. The simulation set up gives the possibility of predicting the cell culture behavior under various operating conditions and scaffold designs.... 

Three-dimensional analysis of combustion chambers in industrial gas turbines suffers from lack of simple and accurate reduced mechanisms for oxidation of hydrocarbon fuels. Here, an integrated procedure is introduced based on a differential evolution optimization technique. The procedure is flexible and modular and allows optimization of many rate parameters of a multistep global mechanism based on many different combustion criteria and inlet or operational conditions. The procedure uses any selected chemical reactor model and any reference combustion mechanism provided. Sample design criteria used here are flame temperature, ignition delay time, and concentration of selected species,...