Sharif Digital Repository

An experimental study of a lab scale rotating detonation combustor (RDC) has been conducted to identify and classify its modes of operation under different feeding conditions. The chamber uses air as oxidizer and hydrogen as fuel. The stability diagram of the RDC has been determined based on the detonation chamber Reynolds number and reactants mixture equivalence ratio values. The Reynolds number is based on the air volume flow rate, chamber annulus size, and the reactants mixture feeding slot area. Hence the effects of geometrical parameters and operational parameters on the detonation wave stability can be presented in a single stability map. This diagram identifies different zones in... 

An experimental study of a lab scale rotating detonation combustor (RDC) has been conducted to identify and classify its modes of operation under different feeding conditions. The chamber uses air as oxidizer and hydrogen as fuel. The stability diagram of the RDC has been determined based on the detonation chamber Reynolds number and reactants mixture equivalence ratio values. The Reynolds number is based on the air volume flow rate, chamber annulus size, and the reactants mixture feeding slot area. Hence the effects of geometrical parameters and operational parameters on the detonation wave stability can be presented in a single stability map. This diagram identifies different zones in... 

In this study, the main recovery mechanisms behind oil/water/gas interactions during the water-alternating-gas (WAG) injection process, in a network of matrix/fracture, were fundamentally investigated. A visual micromodel was utilized to provide insights into the potential applications of WAG process in fractured oil-wet media as well as the possibility of observing microscopic displacement behavior of fluids in the model. The model was made of an oil-wet facture/matrix network system, comprised of four matrix blocks surrounded with fractures. Different WAG injection scenarios, such as slug arrangements and the effects of fluid injection rates on oil recovery were studied. A new equation... 

This work aims to discuss the results of wide ranges of laboratory investigations to evaluate the performance of a newly-formulated surfactant for heavy oil reservoirs in order to improve the microscopic sweep efficiency after water flooding processes. In the first part, the specific behavior of the formulated surfactant including its salinity tolerance, interfacial tension, and optimum performance window was determined. Then, the application of surfactant solutions in real sandstone reservoir rocks was assessed for both oil-wet and water-wet cases. Besides, the effect of changing the capillary and viscous forces and interfacial tension on the residual phase saturations were characterized.... 

In this work, a newly formulated sulfonate-based surfactant and two other commercial sulfate-based surfactants with the capability of tolerating harsh underground reservoir conditions, such as high-saline formation water and high temperature, were prepared. Sodium metaborate as an effective alkali compound was also used to provide alkali-surfactant combination. Interfacial tension (IFT) measurements as well as wettability examinations for different salinities and mixture conditions were performed for an extended range of the chemical concentrations. The wettability tests including both contact angle measurements and Amott cell tests were performed on saturated Berea sandstone plug samples... 

A newly-designed surfactant was formulated to tolerate the harsh conditions of oil reservoirs, including high salinity of the formation brine and temperature. The specific emulsion and interfacial tension (IFT) behavior of this new surface active agent were investigated by performing emulsion stability tests, emulsion size analysis, and IFT behavior in the presence of four different types of alkalis. Image processing was utilized to analyze the droplet size distribution using microscopic images of the samples. The results show that depending on the composition of the mixtures, the optimum phase region and interfacial tension behavior change considerably. Solutions containing a higher... 

In this work, a newly formulated sulfonate-based surfactant and two other commercial sulfate-based surfactants with the capability of tolerating harsh underground reservoir conditions, such as high-saline formation water and high temperature, were prepared. Sodium metaborate as an effective alkali compound was also used to provide alkali-surfactant combination. Interfacial tension (IFT) measurements as well as wettability examinations for different salinities and mixture conditions were performed for an extended range of the chemical concentrations. The wettability tests including both contact angle measurements and Amott cell tests were performed on saturated Berea sandstone plug samples... 

This work aims to discuss the results of wide ranges of laboratory investigations to evaluate the performance of a newly-formulated surfactant for heavy oil reservoirs in order to improve the microscopic sweep efficiency after water flooding processes. In the first part, the specific behavior of the formulated surfactant including its salinity tolerance, interfacial tension, and optimum performance window was determined. Then, the application of surfactant solutions in real sandstone reservoir rocks was assessed for both oil-wet and water-wet cases. Besides, the effect of changing the capillary and viscous forces and interfacial tension on the residual phase saturations were characterized.... 

Although simple additive weighting method (SAW) is the most popular approach for classical multiple attribute decision making (MADM), it is not practical any more if information is fuzzy. The existing methods of Fuzzy Simple Additive Weighting method (FSAW) apply defuzzification which distorts fuzzy numbers. Furthermore, most of the methods usually require lengthy and laborious manipulations. In this paper, we develop a new a fuzzy simple additive weighting method for multiple attribute decision making problems. To avoid defuzzification round off errors caused by multiplication or other arithmetic manipulations, fuzzy numbers are ranked prior to any fuzzy arithmetic in this method. The... 

We propose a ranking method for fuzzy numbers. In this method a preference function is defined by which fuzzy numbers are measured point by point and at each point the most preferred number is identified. Then, these numbers are ranked on the basis of their preference ratio. Therefore, fuzzy numbers are compared relatively and not necessarily one is preferred absolutely over the others. This method is especially designed to evaluate alternatives in multi criteria or multi-attribute decision making. The method is intuitive and can be used to discriminate between numbers easily. The method is specially tailored for triangular fuzzy numbers (TFN) and an algorithm is presented to determine the... 

In this study, electrolytic plasma processing (EPP) was employed for surface nitrocarburizing of AISI 1020 steel in a urea electrolyte, where the substrate samples were connected cathodically to a high-voltage DC current power supply. The structural, mechanical, wear and corrosion properties of the samples treated for 3-5 min were investigated. The results show that the surface layers formed on the samples by this treatment at 220 V have a ferritic nitrocarburizing characteristic which consists of a compound layer and diffusion zone. The surface layers of the treated samples at 240 V consisted of a compound layer, martensitic layer and diffusion zone, respectively, which is a marker of... 

In an acceptance-sampling plan, where items of an incoming batch of products are inspected one by one, if the number of conforming items between successive non conforming items falls below a lower control threshold, the batch is rejected. If it falls above an upper control threshold, the batch is accepted, and if it lies within the thresholds then the process of inspecting the items continues. The purpose of this article is to develop an optimization model to determine the optimum values of the thresholds such that constraints on the probability of Type I and Type II errors are satisfied. This article starts by developing a Markovian model to derive the expected total cost of the inspection... 

A new approach is developed in this paper to detect general mean shifts of multivariate quality control systems and to determine the quality characteristic(s) responsible for the shift. This approach takes advantage of both a decomposition method and an EWMA-based control statistics that are employed for multivariate normal distributions. In order to evaluate the performance of the proposed methodology, simulation studies are provided to estimate the in- and out-of-control average run lengths under different mean and variance shift scenarios. Simulation experiments are also given to compare the performances of the proposed procedure with the ones of the well-known MEWMA and MCUSUM methods.... 

In this paper, a heuristic threshold policy is developed to detect and classify the states of a multivariate quality control system. In this approach, a probability measure called belief is first assigned to the quality characteristics and then the posterior belief of out-of-control characteristics is updated by taking new observations and using a Bayesian rule. If the posterior belief is more than a decision threshold, called minimum acceptable belief determined using a heuristic threshold policy, then the corresponding quality characteristic is classified out-of-control. Besides using a different approach, the main difference between the current research and previous works is that the... 

A proper vertex k-coloring of a graph G is called dynamic, if there is no vertex v∈V(G) with d(v)<2 and all of its neighbors have the same color. The smallest integer k such that G has a k-dynamic coloring is called the dynamic chromatic number of G and denoted by χ2(G). We say that v∈V(G) in a proper vertex coloring of G is a bad vertex if d(v)<2 and only one color appears in the neighbors of v. In this paper, we show that if G is a graph with the chromatic number at least 6, then there exists a proper vertex χ(G)-coloring of G such that the set of bad vertices of G is an independent set. Also, we provide some upper bounds for χ2(G)- χ(G) in terms of some parameters of the graph G  

The response of large-scale building structures can be actively reduced using an appropriate control algorithm and a number of actuators and sensors located within the building. This paper presents a decentralized control approach for controlling the response of tall buildings. The proposed method aims to divide the structural model into several substructures, each one performing on its own controller algorithm. This approach has already been used in controlling large-scale systems such as power transmission systems and space structures. An instantaneous optimal control scheme is used as the control algorithm with different control feedbacks such as velocity feedback alone and displacement... 

A new-designed surfactant was prepared with capability of tolerating high saline formation water and real oil reservoir conditions. The specific emulsion behavior of this new chemical was investigated by doing all sets of emulsion stability and emulsion behavior tests in presence of different alkalis. Four types of alkalis (Sodium Hydroxide, Sodium Carbonate, Sodium Metaborate, and Triethanolamine) were mixed with the surfactant and their combined effect on aqueous-oil emulsion behavior was inspected. The experimental results shoine formation water and real oil reservoir conditions. The specific emulsion behavior of this new chemical was investigated by doing all sets of emulsion stability... 

In this study, a mixture-based sulfonate-based surfactant with a novel formula capable of functioning in real oil reservoir conditions was prepared and some microscopic parameters, like its compatibility state, emulsion behavior, interfacial tension, and temperature dependency in the presence of a heavy oil sample, and two of the most popular alkalis were analyzed; then the results were compared with those of a commercial sulfate-based surfactant. The designed surfactant provided an optimum three-phase region in relatively high salinity media; however, its optimum value decreased when adding any alkaline materials; this trend was reversed for the solutions made with the sulfate-based... 

In this study, a mixture-based sulfonate-based surfactant with a novel formula capable of functioning in real oil reservoir conditions was prepared and some microscopic parameters, like its compatibility state, emulsion behavior, interfacial tension, and temperature dependency in the presence of a heavy oil sample, and two of the most popular alkalis were analyzed; then the results were compared with those of a commercial sulfate-based surfactant. The designed surfactant provided an optimum three-phase region in relatively high salinity media; however, its optimum value decreased when adding any alkaline materials; this trend was reversed for the solutions made with the sulfate-based... 

The strength of a newly formulated surfactant with an alkali and polymer (AS/ASP) to improve an acidic heavy oil recovery was laboratory evaluated by various flooding experiments. The comparative role of the parameters like chemical nature, surface wettability, salinity, temperature and injection scheme were explored at high temperature and pressure on Berea sandstone rocks. According to the results the anionic surfactant is capable of providing proper oil displacement under high salinity conditions around 15 wt%. Continuous monitoring of differential pressure response and effluents’ state clearly represented the formation of an emulsified oil in high saline solutions with both alkali and...