Sharif Digital Repository

Traditionally, solid-liquid mixing has always been regarded as an empirical technology with many aspects of mixing, dispersing and contacting where related to power draw. One important application of solid-liquid mixing is the preparation of brine from sodium formate. This material has been widely used as a drilling and completion fluid in challenging environments such as in the Barents Sea. In this paper large-eddy simulations, of a turbulent flow in a solid-liquid, baffled, cylindrical mixing vessel with a large number of solid particles, are performed to obtain insight into the fundamental aspects of a mixing tank. The impeller-induced flow at the blade tip radius is modeled by using the... 

In this note, we study on the existence and uniqueness of a positive solution to the following doubly singular fractional problem: {(-Δ)su=K(x)uq+f(x)uγ+μinΩ,u>0inΩ,u=0in(RN\u03a9).Here Ω ⊂ RN (N> 2 s) is an open bounded domain with smooth boundary, s∈ (0 , 1) , q> 0 , γ> 0 , and K(x) is a positive Hölder continuous function in which behaves as dist (x, ∂Ω) -β near the boundary with 0 ≤ β< 2 s. Also, 0 ≤ f, μ∈ L1(Ω) , or non-negative bounded Radon measures in Ω. Moreover, we assume that 0<βs+q<1, or βs+q>1 with 2 β+ q(2 s- 1) < (2 s+ 1). For s∈(0,12), we take advantage of the convexity of Ω. For any γ> 0 , we will prove the existence of a positive weak (distributional) solution to the above... 

To study the effect of the production method on physical and mechanical properties of Cu-rGO nanocomposites, nanocomposite powder samples with rGO content of 0.25–1 wt.% were prepared via combined routes of molecular-level mixing (MLM) and powder metallurgy (PM). Spark plasma sintering (SPS) was applied to consolidate nanocomposite powders with better control on the grain size. According to the specific electrical resistivity measurements, microhardness, and pin-on-disk wear tests, the sample with 0.5 wt.% rGO comprised the best overall properties. For assessment, samples containing 0.5 wt.% rGO were also produced via PM and MLM routes, separately. The physical and mechanical properties of... 

Interpreting the complex interaction of nanostructured fluid flow with a dipole in a duct, with peripherally uniform temperature distribution, is the main focus of the current work. This paper also sheds light on the changes in the Nusselt number, temperature profiles, and velocity distributions for the fully developed nanofluid flow in a vertical rectangular duct due to a dipole placed near a corner of the duct. A finite volume approach has been incorporated for the numerical study of the problem. It is interesting to note the unusually lower values of the Nusselt number for the higher values of the ratio Gr/Re. Due to the nanostructure in the fluid, an enhancement in the Nusselt number has... 

In Mixed-Criticality (MC) systems, multiple functions with different levels of criticality are integrated into a common platform in order to meet the intended space, cost, and timing requirements in all criticality levels. To guarantee the correct, and on-time execution of higher criticality tasks in emergency modes, various design-time scheduling policies have been recently presented. These techniques are mostly pessimistic, as the occurrence of worst-case scenario at run-time is a rare event. Nevertheless, they lead to an under-utilized system due to frequent drops of Low-Criticality (LC) tasks, and creation of unused slack times due to the quick execution of high-criticality tasks.... 

Improving the service quality of public transport is necessary to maintain the loyalty of current users and attract new travelers. Past studies show that users’ preferences for transit service quality are heterogeneous, but recognizing the factors describing this heterogeneity has not been investigated in depth. This paper aims to evaluate the sources of heterogeneity in passengers’ preferences for service attributes of bus transit regarding the regular bus system in the city of Tehran. Four attributes of bus travel, including in-vehicle travel time, fare, vehicle crowding, and headway, were considered. Stated preference (SP) data of 360 commuters with work purpose was collected through... 

Consideration is given to the buoyancy effects on the fully developed gaseous slip flow in a vertical rectangular microduct. Two different cases of the thermal boundary conditions are considered, namely uniform temperature at two facing duct walls with different temperatures and adiabatic other walls (case A) and uniform heat flux at two walls and uniform temperature at other walls (case B). The rarefaction effects are treated using the firstorder slip boundary conditions. By means of finite Fourier transform method, analytical solutions are obtained for the velocity and temperature distributions as well as the Poiseuille number. Furthermore, the threshold value of the mixed convection... 

An industrial-scale reactor for ethylene production was modeled using the oxidative dehydrogenation of ethane (ODHE) in a multi-tubular reactor system, examining a variety of parameters affecting reactor performance. The model showed that a double-bed multi-tubular reactor with intermediate air injection scheme was superior to a single-bed design, due to the increased ethylene selectivity while operating under lower oxygen partial pressures. The optimized reactor length for 100% oxygen conversion was theoretically determined for both reactor designs. The use of a distributed oxygen feed with a limited number of injection points indicated a significant improvement on the reactor performance... 

Aircraft landing problem is to assign an airport's runways to the arrival aircrafts as well as to schedule the landing time of these aircrafts. In this paper, first a mixed integer goal programming model is developed. Then, due to the complexity of the problem, which is NP-hard, we design a hybrid meta-heuristic applying simulated annealing framework. The computational results show that the proposed algorithm can obtain the optimal solution for instances up to 100 aircrafts, and also it is capable of finding very high quality and comparable solutions for the problems with up to 500 aircrafts and 5 runways in a short time  

In rail transportation, there have been several attempts to determine the best routes for shipments (a number of cars with the same origin-destination) through the network. Shipments enter into several intermediate yards on their routes to separate and regroup shipments into new trains. Most of time, every entering into a yard includes excessive delay for shipments; therefore it is an ideal plan that each shipment has been transported by an exclusive train service. Mainly because of restriction on a number of running trains, this plan cannot be adapted in most cases. Finding the optimal route over the rail network with above and other common constraints would be handled by railroad blocking... 

In this paper, the impact of demand response programs (DRPs) on reliability improvement of the restructured power systems is quantified. In this regard, the demand response (DR) model which treats consistently the main characteristics of the demand curve is developed for modeling. In proposed model, some penalties for customers in case of no responding to load reduction and incentives for customers who respond to reducing their loads are considered. In order to make analytical evaluation of the reliability, a mixed integer DCOPF is proposed by which load curtailments and generation re-dispatches for each contingency state are determined. Both transmission and generation failures are... 

In this paper a self-oscillating mixer is presented fundamental signal generated by the oscillator subcircuit in the mixing process. The oscillator core consumes 3mA of current from a 1.8 V DC supply and results in an output power of -0.867 dBm per oscillator, and a measured phase noise of -91, -102 and -108 dBc/Hz at 100 KHz, 600 KHz and 1 MHz from the carrier, respectively. In the mixing process the proposed mixer achieved IIP3 of 0 dBm with conversation gain of 1.93 dB. The circuit was designed and simulated in 0.18-μm CMOS technology by ADS2010  

Facility layout problem (FLP) is one of the classical and important problems in real-world problems in the field of industrial engineering where efficiency and effectiveness are very important factors. To have an effective and practical layout, the deterministic assumptions of data should be changed. In this study, it is assumed that we have dynamic and uncertain values for departments’ dimensions. Accordingly, each dimension changes in a predetermined interval. Due to this assumption, two new parameters are introduced which are called length and width deviation coefficients. According to these parameters, a definition for layout in uncertain environment is presented and a mixed integer... 

In this study a new version of adjacency, which provides a more flexible layout design, is proposed. In the proposed version, departments which are nonadjacent yet close to each other are considered to be adjacent with a smaller adjacency rating. It is shown that the proposed adjacency is a generalized version of the traditional adjacency. A mathematical programming model is developed for the proposed facility layout problem. To show the flexibility and efficacy of the proposed model, a computational study is conducted. The solution of an illustrative example as well as the solutions of several test problems, reveal flexibility and efficacy of the proposed model  

In this study, we consider a capacitated location–multi-allocation–routing problem with population-dependent random travel times. The objective is to find appropriate locations as server locations among the candidate locations, allocate the existing population in each demand node to server locations, and determine the movement path of each member to reach its corresponding server with respect to the simultaneous change of the random travel times so that the expected total transportation time is minimized. In our study, the concept of population-dependent random travel times incurs two issues: (1) consideration of some random factors in computing the travel times and (2) impact of the... 

This paper presents a formulation of fuzzy optimization for uncertainties in natural gas in fuel constraints for hourly individual unit and total unit fuel consumptions. Security Constrained Unit Commitment (SCUC) is usually a mixed integer programming and gas load flow has a non-linear equation a genetic algorithm is proposed to solve natural gas transmission network. A fuzzy mixed integer programming optimization is briefly discussed and adapted to deal with security constrained unit commitment schedule. Finally, two case studies are investigated (IEEE 6-bus system with 7-node natural gas transmission grid and the IEEE 118-bus power system linked with 14-node gas transmission test system)... 

Bi-objective optimization of a multi-product multi-period three-echelon supply chain network consisting of manufacturing plants, distribution centers (DCs) each with uncertain services, and customer nodes is aimed in this paper. The two objectives are minimization of the total cost while maximizing the average number of products dispatched to customers. The decision variables are: (1) the number and the locations of reliable DCs in the network, (2) the optimum number of items produced by plants, (3) the optimum quantity of transported products, (4) the optimum inventory of products at DCs and plants, and (5) the optimum shortage quantity of the customer nodes. The problem is first formulated...