Sharif Digital Repository

The performance of nanoparticles for biomedical applications is often assessed by their narrow size distribution, suitable magnetic saturation and low toxicity effects. In this work, superparamagnetic iron oxide nanoparticles (SPIONs) with different size, shape and saturation magnetization levels were synthesized via a co-precipitation technique using ferrous salts with a Fe3+/Fe2+ mole ratio equal to 2. A parametric study is conducted, based on a uniform design-of-experiments methodology and a critical polymer/iron mass ratio (r-ratio) for obtaining SPION with narrow size distribution, suitable magnetic saturation, and optimum biocompatibility is identified. Polyvinyl alcohol (PVA) has been... 

This paper investigates, experimentally and analytically, the capacity of channel shear connectors embedded in normal and polypropylene (PP) concrete. Limited testing is used to assess the accuracy of a proposed nonlinear finite element model for typical push-out test specimens. Using this model, an extensive parametric study is performed to arrive at a prediction for shear capacity of channel connectors in PP concrete. An equation, for inclusion in design codes, is suggested for the shear capacity of these connectors when used in PP concrete. © 2009 Elsevier Ltd. All rights reserved  

In this study, a cryogenic distillation column has been designed and simulated via a computer code based on the theta method of convergence. The required thermodynamic properties are determined from the enhanced predictive Peng-Robinson (E-PPR 78) equation of state which has a good accuracy in predicting the corresponding thermodynamic properties of natural gas components. The combined code of distillation column/equation of state has been verified with that of another study. In the present study, the results are achieved by the constant molar over-flow and inclusion of energy equations assumptions. In order to have more accuracy in the results, the energy equations were considered in the... 

Multigeneration systems (MGSs) driven by renewable sources are proved as cutting-edge technologies for multiple productions purposes to curb greenhouse gas emissions. With this regard, a novel geothermal-based MGS is proposed to produce multiple commodities of cooling, heating, power, and hydrogen, simultaneously, using liquefied natural gas (LNG) as cold energy recovery. The system is composed of an organic Rankine cycle (ORC), an ejector refrigeration cycle (ERC), an LNG power generation system, and a proton exchange membrane (PEM) electrolyzer system. To demonstrate the feasibility of the proposed MGS, energy, exergy, and exergoeconomic analysis are employed as the most effective tools... 

This research investigates the flexural behavior of a polymer concrete beam/pile encased with carbon fiber sleeve. The mechanical properties of carbon fiber sleeves in tension and cement and polymer concrete in compression were determined. Polymer concrete beams were tested in flexure to determine the bending moment capacity. Then, the test results were compared to the theoretical model results. Finally, a parametric study was conducted to determine the influence of beam/pile parameters on the capacity of the element. Based on the investigation, carbon fiber sleeve filled with polymer concrete exhibits outstanding structural performance including ductility and bending capacity  

Deep excavation in urban areas can cause instability problems due to significant settlement at the ground surface and large movements at the excavation facing walls. One of the most popular methods used to stabilise these excavations is utilising soil-nailing method. This method has also been widely used to stabilise natural slopes and earth retaining structures. Because of the complexity involved in the mechanism of this stabilising system due to interacting effects of the soil, nails, grout and shotcrete, numerical modelling with high accuracy should be used to analyse the behaviour of the soil-nailed walls. Considering all aspects of soil-structure interaction in the present research, a... 

Due to its unique properties, helium has wide application in different industries and scientific fields, which has turned it into a strategic material. Helium liquefaction plants include wide temperature range from 300 k to 4.2 k, so these plants have high energy consumption. A lot of studies have done to optimize the operation of these cycles. In this research, an exergy analysis is performed for a liquid helium production plant. The optimal performance of 3 and 4 stage cycles is extracted using parametric study and the results are compared with those of Collins dual-expander cycle. The results show that by increasing the number of cooling stages, not only the compressor optimum discharge... 

Due to its unique properties, helium has wide application in different industries and scientific fields, which has turned it into a strategic material. Helium liquefaction plants include wide temperature range from 300 k to 4.2 k, so these plants have high energy consumption. A lot of studies have done to optimize the operation of these cycles. In this research, an exergy analysis is performed for a liquid helium production plant. The optimal performance of 3 and 4 stage cycles is extracted using parametric study and the results are compared with those of Collins dual-expander cycle. The results show that by increasing the number of cooling stages, not only the compressor optimum discharge... 

Deep excavation in urban areas can cause instability problems due to significant settlement at the ground surface and large movements at the excavation facing walls. One of the most popular methods used to stabilise these excavations is utilising soil-nailing method. This method has also been widely used to stabilise natural slopes and earth retaining structures. Because of the complexity involved in the mechanism of this stabilising system due to interacting effects of the soil, nails, grout and shotcrete, numerical modelling with high accuracy should be used to analyse the behaviour of the soil-nailed walls. Considering all aspects of soil-structure interaction in the present research, a... 

Natural convection heat transfer in a concentric horizontal annulus with annular fins is numerically studied. Due to the low thermal conductivity of water, CuO-water and Al2O3-water nanofluids were used as heat transfer fluids. The effect of three different parameters, including fin spacing, fin eccentricity, and fin thickness at different fin diameters and Rayleigh number range of 104 to 9 (Formula presented.) 105, were studied. The obtained results revealed that Al2O3-water nanofluid has the highest heat transfer rate. The calculated heat transfer rates for Al2O3-water nanofluid for Rayleigh numbers of 9 (Formula presented.) 105, 105, and 104 were respectively up to 12.1%, 26.2%, and 31.6%... 

The application of incinerators for the municipal solid waste (MSW) is growing due to the ability of such instruments to produce energy and, more specifically, reduce waste volume. In this paper, a numerical simulation of the combustion process with the help of the computational fluid dynamics (CFD) inside a portable (mobile) incinerator has been proposed. Such work is done to investigate the most critical parameters for a reliable design of a domestic portable incinerator, which is suitable for the Iranian food and waste culture. An old design of a simple incinerator has been used to apply the natural gas (NG), one of the available cheap fossil fuels in Iran. After that, the waste height,... 

We investigate the resistance of reinforced concrete panels (RCPs) due to explosive loading using nonlinear finite element analysis and surrogate models. Therefore, gene expression programming model (GEP), multiple linear regression (MLR), multiple Ln equation regression (MLnER), and their combination are used to predict the maximum deflection of RCPs. The maximum positive and negative errors, mean of absolute percentage error (MAPE), and statistical parameters such as the coefficient of determination, root mean square error (RMSE). Normalized square error (NMSE), and fractional bias are utilized to evaluate and compare the performance of the models. We also present a novel statistical table... 

Seismic response of a Single Degree of Freedom (SDOF) system containing a rigid circular cylindrical liquid tank under the earthquake excitations is considered in the presence of fluid/structure interaction. The governing differential equations of the system is derived considering the first three liquid sloshing modes (1, 1), (0, 1) and (2, 1) under different strong ground motions. The dynamic response of the system is investigated in the neighborhood of 1:1 and 1:2 internal resonances between the SDOF system and the liquid sloshing modes. These internal resonances take place by tuning the frequency of the first asymmetric sloshing mode of the liquid to the fundamental frequency of the SDOF... 

In this second part of the two companion papers an effective numerical model is proposed using finite element method to simulate the push-out test of channel shear connectors. The focus is on the shear capacity of channel shear connectors embedded in a solid reinforced concrete slab under monotonic loading. The model has been validated against test results presented in Part (I) and compared with data given in North American design codes. Parametric studies using this nonlinear model are performed to investigate the variations in concrete strength, channel dimensions and the orientation of the channel. The results show that the concrete strength, web and flange thicknesses of the channel and... 

This paper is concerned with the development of buckling-restrained knee bracing frames for seismic design and retrofit of steel frame structures. Analytical models based on the new nonlinear finite element modeling of the system for the moment and shear yielding mode were developed in a structure with buckling-restrained knee-braces. Parametric study was performed with new and practical parameters of the system describing the specification of the system in elastic and inelastic behavior; and the results are shown in form of the appropriate graphs and charts. This study makes an offer to a simple design technique for this type of structure with a bilinear approach, using a nonlinear finite... 

For the design of rubble mound breakwaters on soft soil, it is essential to predict the behavior of soft soil and large deformations phenomena occurring in the course of construction of the rubble mound breakwater. Large deformations in various problems can be well simulated using the coupled Eulerian–Lagrangian (CEL) method. In this study, the CEL method has been used to simulate the rubble mounds construction on soft soil and predict the resulting settlements. To validate the numerical model, the results of three experiments conducted in the physical modeling laboratory at Kharazmi University were used. Also, two case studies of real rubble mound breakwaters constructed on soft seabeds... 

This research explores the effectiveness of the use of stiff diaphragm walls next to a rocking foundation through numerical simulation. This improvement technique is used as a means to increase in subsoil peripheral confinement and reduce rocking-induced settlement. The numerical model was verified by the centrifuge test of rocking shallow foundations on clay under cyclic loading. A parametric study was conducted to explore the effect of three stiff wall shapes on the performance of a rocking system. The general conclusion of the parametric investigation is that the use of stiff diaphragm walls reduced the sinking-dominated settlement response of the rocking system. © 2019 Taylor & Francis... 

Natural convection heat transfer in a concentric horizontal annulus with annular fins is numerically studied. Due to the low thermal conductivity of water, CuO-water and Al2O3-water nanofluids were used as heat transfer fluids. The effect of three different parameters, including fin spacing, fin eccentricity, and fin thickness at different fin diameters and Rayleigh number range of 104 to 9 (Formula presented.) 105, were studied. The obtained results revealed that Al2O3-water nanofluid has the highest heat transfer rate. The calculated heat transfer rates for Al2O3-water nanofluid for Rayleigh numbers of 9 (Formula presented.) 105, 105, and 104 were respectively up to 12.1%, 26.2%, and 31.6%... 

The fatigue life for T and cruciform welded joints containing different extents of lack of root penetration was calculated for different combinations of geometrical parameters, including thicknesses up to 45 mm, by integration of the Paris law and use of stress intensity factor solutions calculated previously. The effect of attachment and main plate thickness, weld leg length and initial lack of penetration size on fatigue life was studied. For T welded joints, the effect of different support span has also been investigated. The results are reported as fatigue life curves for both types of joints. All the curves show higher fatigue life for T joints than for cruciform joints. These curves... 

Saddle connections are semi-rigid connections that are widely used in Iran. Many existing buildings contain this type of connection. The present study conducted full-scale experiments and used extensive numerical modeling to study the mechanical characteristics of saddle connections. The mechanical characteristics examined were the moment-transfer mechanism, initial stiffness, yield moment, maximum moment, and fracture rotation. The configuration and dimensions of the experimental and numerical specimens were chosen to be similar to those of saddle connections in existing buildings. A parametric study was conducted to determine the factors affecting the mechanical characteristics of these...