Sharif Digital Repository

Recent studies in information computation technology (ICT) are focusing on Next-generation networks, SDN (Software-defined networking), 5G, and 6G. Optimal working mode for device-to-device (D2D) communication is aimed at improving the quality of service with the frequency spectrum structure is of research areas in 5G. D2D communication working modes are selected to meet both the predefined system conditions and provide maximum throughput for the network. Due to the complexity of the direct solutions, we formulated the problem as an optimization problem and found the optimal working modes under different parameters of the system through extensive simulations. After determining the links'... 

Regarding the geometric structural characteristics of innovative dual cooled annular fuel and the possibility of heat split and flow distribution among the internal and external channels, the development of new computational tools is essential for estimating safety margins and accurate assessment of its thermal-hydraulic performance. The SADAF code (Subchannel Analysis Dual cooled Annular Fuel) by COBRA-EN code is developed for this purpose. In the SADAF code, using COBRA-EN code for subchannel analysis in internal and external subchannels, a program has been developed to compute new variables that need to be considered in the thermal-hydraulic assessment. Also, fuel heat transfer... 

Freeze desalination (FD) works upon the separation of impurities from pure water during ice crystals formation. The required cold source could be supplied by the cold energy of liquefied natural gas (LNG). In the current study, freeze desalination of seawater is explored by directly exploiting the cold energy of LNG within an appropriate range of temperature after producing work in a power generation cycle. A detailed discussion has been given on the inlet temperature of LNG to the FD unit for the first time. The direct utilization has the privilege of eliminating the addition of a secondary refrigerant and its refrigeration cycle to the FD process. A multi-objective optimization is... 

Proppants transport is an advanced technique to improve the hydraulic fracture phenomenon, in order to promote the versatility of gas/oil reservoirs. A numerical simulation of proppants transport at both hydraulic fracture (HF) and natural fracture (NF) intersection is performed to provide a better understanding of key factors which cause, or contribute to proppants transport in HF–NF intersection. Computational fluid dynamics (CFD) in association with discrete element method (DEM) is used to model the complex interactions between proppant particles, host fluid medium and fractured walls. The effect of non-spherical geometry of particles is considered in this model, using the multi-sphere... 

The deformation and breakup dynamics of a compound ferrofluid droplet under shear flow and uniform magnetic field are numerically studied in this paper. Utilizing magnetic field provides the possibility to obtain better control over the compound droplet morphology and breakup in a simple shear flow. To solve the governing equations for interfaces motion and hydrodynamics, the conservative phase field lattice Boltzmann model is employed, and a finite difference approach is applied for calculating the magnetic field. To verify the accuracy of present simulations, the results are validated with those of four relevant benchmarks including liquid lens between two stratified fluids, three-phase... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

The present study employs Discrete Element Method (DEM) to establish a rheological model that relates the apparent viscosity of a granular material to shear rate, normal stress, and water saturation. In addition, a theoretical model was developed to determine water distribution and water-induced forces between particles for different saturations. The resulting forces were embedded in a 3D shear cell as a numerical rheometer, and a wet specimen was sheared between two walls. A power law rheological model was then obtained as a function of inertia number and saturation. It was found that up to a critical saturation, the apparent viscosity increased with saturation that was higher than that of... 

A finite difference-based numerical model simulating the cone penetration process in unsaturated sands is presented. Mohr–Coulomb model (MCM) with simple modifications and Sun model (SM) were implemented to capture the unsaturated sand behaviour. It was shown that the cone tip resistance values resulting from the two models were fairly comparable. Predicted cone tip resistance values in dry, saturated and unsaturated sands using MCM were validated by the results of field and calibration chamber tests. Sensitivity analyses were performed, and the influence of parameters including relative density, mean effective stress and apparent cohesion due to suction on the tip resistance was... 

We introduce two-dimensional space plus time (2D+1) structure and numerically investigate it using a developed multilayer simulation framework, for the first time. The new structure is consisting of crossed grating with time-varying permittivity which is inspired from1D+1. In this regard, we extend FourierModal Method (FMM) in a general approach for spacetime multilayer states. Our proposed framework is fast, robust, and powerful compared to various finite difference methods. We use the scattering matrix technique to develop the proposed spacetime simulation method for multilayer structures using a non-uniform stack of layers. The method is perfectly suitable to investigate the... 

Utilization of heat storage units in solar energy systems can resolve the challenge of fluctuation and uncertainty of the solar energy. Phase change materials (PCMs) are used as the storage media for solar energy storage systems. In this research, a system including of a solar collector and a PCM-based cascaded energy storage unit was numerically investigated. Air was used as the heat transfer fluid (HTF) and three paraffin-based materials (RT50, RT65, and RT80) were used as PCM for the energy storage unit. The investigated system mainly operates between 15 °C and 90 °C and considering different PCMs, the selected PCMs were appropriate. Paraffin-based PCMs also present acceptable thermal... 

A model of heat and mass transfer of two dimensional MHD micropolar fluid over a cone is constructed. Similarity transformation is adopted for the conversion of partial differential equations into ordinary differential equations have been linearized by employing the Newton's linearization technique and then new sets of equations are discretized using the finite difference method. The impact of non-dimensional parameters is further analyzed and the numerical results for profiles of velocity, temperature and concentration are expressed graphically and the results are discussed in detail. For the higher values of Dufour number, temperature field is enhanced graphically but show the opposite... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

A model of heat and mass transfer of two dimensional MHD micropolar fluid over a cone is constructed. Similarity transformation is adopted for the conversion of partial differential equations into ordinary differential equations have been linearized by employing the Newton's linearization technique and then new sets of equations are discretized using the finite difference method. The impact of non-dimensional parameters is further analyzed and the numerical results for profiles of velocity, temperature and concentration are expressed graphically and the results are discussed in detail. For the higher values of Dufour number, temperature field is enhanced graphically but show the opposite... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

In non-orthogonal multiple access (NOMA) systems, serving multiple users in shared resource blocks can allow untrusted users to overhear the messages of other users. In this context, we study a network consisting of a base station (BS), a near user and a far user, where the latter attempts to overhear the message of the former. The near user is a full-duplex (FD) node that can also act as a relay. Two operating scenarios are considered: 1) friendly jammer (FJ), where the FD node broadcasts noise for degrading the channel between the BS and the far user, while receiving data from the BS; and 2) friendly jammer relay (FJR), where, in addition to degrading the channel between the BS and the far... 

This paper aims to develop a boundary control solution for complicated gantry crane coupled motions. In addition to the large angle sway motion, the crane cable has a flexural transverse vibration. The Hamilton principle has been utilized to derive the governing partial differential equations of motion. The control objectives which are sought include: moving the payload to the desired position; reducing the payload swing with large sway angle; and finally suppressing the cable transverse vibrations in the presence of boundary disturbances simultaneously. These simultaneous boundary control objectives make the problem challenging. The proposed control approach is based on the original... 

In this study, a coupling of a hydrologic and hydraulic model was utilized to assess the impacts of river geometry data resolution on the flood inundation characteristics in a data-scarce environment. Hydrological modeling incorporates soil conservation service curve-number (SCS-CN) and the geomorphologic based instantaneous unit hydrograph model (GIUH) to compute the direct runoff hydrograph in Kashkan river basin located in western Iran. 1D HEC-Geo-RAS model was used and performed to simulate inundation extent of 100-yr floods (~1800 m3/s) along 40 km reach of Kashkan river with a ground survey of river cross-section (2000 cross-sections, each including 500 data-points). The effect of... 

The formation damage (FD) caused by the invasion of drilling fluid severely affects reservoir performance during production. Most of the published research studies which address this type of FD have been carried out at the core or field scale. Thus, the main aim of the paper is to investigate the pore-scale mechanisms of FD induced by drilling fluids and their control with silica nanoparticles (NPs) using a microfluidic approach. The proper identification of the mechanisms of FD can lead to the proper selection of NP type and concentration as well as a suitable method to remediate FD. The micromodel was designed in a way to closely simulate the cross-flow at the wellbore surface. A... 

We consider a cooperative wireless communication network comprising two full-duplex (FD) nodes transmitting to a common destination based on slotted Aloha protocol. Each node has exogenous arrivals and also may relay some of the unsuccessfully transmitted packets of the other node. In this article, we find the optimal static policies of nodes in order to minimize the sum of the average transmission delays, while the average transmission delay of each node is constrained. The static policy of each node specifies the probability of accepting an unsuccessfully transmitted packet of the other node and how the node prioritizes its transmissions. We show that in the optimal policies, just the node... 

Simulation of brittle regime machining of materials (such as ceramics) is often difficult because of the complex material removal mechanisms involved. In this study, the discrete element method is used to simulate the dynamic process for machining of slip-cast fused silica ceramics. Flat-joint contact model is exploited to model contacts between particles in synthetic discrete element method models. This contact model is suitable for modeling of brittle materials with high ratios (higher than 10) of unconfined compressive strength to tensile strength. The discrete element method has the ability to simulate initiation, propagation, and coalescence of cracks leading to chip formation in the...