Sharif Digital Repository

Liquid marbles are droplets coated with hydrophobic particles that, due to their unique characteristics, have attracted considerable attention in recent studies in the field of fluid mechanics. These droplets can be used on both hydrophobic and even hydrophilic surfaces without breaking or undergoing significant deformation, thanks to their hydrophobic coating. This research is the first to comprehensively investigate the dynamics of liquid marbles’ impact and bouncing behavior on a surface. Additionally, it examines the effects of parameters such as impact velocity, marble diameter, core viscosity, and magnetic field on the parameters describing the dynamics of the marble during the... 

Power-to-X technologies play a key role in the future energy landscape, as they convert electricity from renewable sources into valuable fuels and chemicals. This study proposes an innovative solar-based system for methanol production, designed as a case study to decarbonize an existing power plant. The carbon dioxide used in the methanol synthesis unit is supplied from an existing power plant in Iran, which has been retrofitted with various oxy-fuel combustion configurations. In addition, the impact of co-firing with alternative fuels, including hydrogen and methanol, on the combustion process has been investigated. In this system, the copper–chlorine (Cu–Cl) thermochemical cycle is... 

Liquid marbles are droplets enwrapped by a layer of micro/nanoparticles. Due to the insulation of inner fluid from the environment, the lower evaporation rate of the fluid, and the capability of motion even on hydrophilic surfaces, these liquid marbles, as an alternative to conventional droplets, have attracted the attention of researchers in digital microfluidics. Utilizing ferrofluid as the liquid core of the liquid marbles enables remote control over the liquid marbles by an external magnetic field. In this research, the dynamic behavior of ferrofluid liquid marbles under the magnetic field generated by an electromagnet is investigated. In this research, governing physics on the motion of... 

This research introduces an accelerated training approach for Vanilla Physics-Informed Neural Networks (PINNs) that addresses three factors affecting the loss function: the initial weight state of the neural network, the ratio of domain to boundary points, and the loss weighting factor. The proposed method involves two phases. In the initial phase, a unique loss function is created using a subset of boundary conditions and partial differential equation terms. Furthermore, we introduce preprocessing procedures that aim to decrease the variance during initialization and choose domain points according to the initial weight state of various neural networks. The second phase resembles... 

Gorgan Bay and Miankaleh Wetland have been exposed to various environmental risks in the past years due to the decrease in the Caspian water level and the subsequent decrease in the water level of these water bodies. 2 channels, Chapgoli and Ashuradeh, are the only ways connecting the Gulf with the Caspian Sea. If the water level of the Caspian Sea and the Gulf continue to decrease, these 2 channels will be completely blocked and the connection between the Gulf and the sea will be completely closed. Due to the low depth of the bay and high evaporation on this water body, the blockage of these 2 channels will eventually lead to drying up of the bay or changing the flora and fauna of the area.... 

Hydrogen can serve as a green alternative to fossil fuels and contribute to improving environmental conditions. In this context, reducing the cost of hydrogen production is of fundamental importance. It is necessary to examine the impact of influential environmental parameters on hydrogen production cost reduction. In this study, a relationship for optimizing hydrogen production in two scenarios, with constant anode pressure and variable cathode pressure, as well as both variable anode and cathode pressures, has been presented. Furthermore, the effect of various parameters, including temperature, pressure, proton exchange membrane thickness, and solar cell efficiency, on hydrogen production... 

Wireless LANs are becoming widespread in enterprises due to extensive usage of mobile devices and appearance of bring-your-own-device policies. However, mechanisms common in home WLANs are not sufficient for managing lots of access point and clients in an enterprise WLAN and WLAN controllers which are used in enterprises nowadays are limited to a fixed set of commands operated from a CLI and the source code is not changeable. Also, their effectiveness can be harvested alongside access points from the same vendor. Thus, dynamic high level programming for whole network configuration is an absolute need in this changing business environment and Software-defined Networking (SDN) will empower us... 

This thesis experimentally investigates the enhancement of heat transfer in pool boiling using a passive vibration mechanism based on a mass–spring system, combined with the use of nanofluid. Pool boiling is one of the most effective heat transfer methods and is widely used in industries such as power generation, electronic cooling, nuclear reactors, and refrigeration systems. Despite its high ability to transfer large heat fluxes with small temperature differences, limitations such as critical heat flux and relatively low heat transfer coefficient under certain conditions highlight the need for performance improvement methods. Previous studies have mainly focused on active methods such as... 

As cost associated with obtaining energy has escalated on a global level, proper utilization and energy loss prevention has become more important and worthy of consideration. Methods of enhancing forced convection heat transfer through pipes prominently consist of geometry modifications, implementation of more efficient mechanisms and substituting 5 outdated hardware with more effective equipment. In the following paper, a novel technique employing rotation of bipolar magnetic spheres on inner surface of the tube using a rotating magnetic field has been explored for the first time and the outcomes have been promising. The rotating magnetic field is generated by a function generator and a... 

Diesel engines have widely used in past hundred years. During this time costly and extensive researches have been done to improve engine performance, which is going on. Important issues of these engines are higher specific power and efficiency and lower specific fuel consumption and pollutions formation. One of the best methods for engine performance improvement is matching a convenient turbocharger on engine. A turbocharger increases the engine air mass flow rate by increasing the inlet pressure and density. Due to increase of fresh air mass flow rate, fuel mass flow rate and power would increase. The aim of this research is to choose the convenient turbocharger for the OM355 naturally... 

Digital microfluidics has emerged as a promising tool in engineering and biomedicine over the past decade, with applications in drug delivery, biochemistry, sample manipulation in lab-on-chip systems, and tissue engineering. These systems enable the precise control of droplets and microfluids independently, which can be utilized as contamination-free chambers for conducting chemical reactions in medical applications. The precise control of the position of a ferrofluidic marble is also crucial in the field of digital microfluidics. Given the importance of this issue, this dissertation investigates, for the first time, the closed-loop control of a ferrofluidic marble’s position using a... 

Fog computing environment consists of several devices which distribute across an arbitrary topology. Each of these devices is capable of carrying out a designated computation simultaneously with other devices. One of the common ways of describing a computation is through the usage of workflows. Workflow is a flexible and formal way of modeling tasks and their requirements for execution. A workflow is essentially a DAG. Therefore, it can model the data dependency between tasks quite accurately. The complex structure of a workflow in conjunction with the homogenous nature of devices in a fog environment makes it difficult to find a resource management algorithm to minimize execution time, used... 

Nowadays, the shortage of freshwater resources and their widespread pollution have become one of the most critical global challenges. Considering the limitations of natural water resources and the large share of saline water on Earth, seawater desalination has emerged as an effective solution. In this study, solar radiation is employed as a clean and sustainable source for evaporating saline water in an evacuated tube solar collector. To enhance the evaporation rate of the system, a vacuum is created based on Bernoulli’s principle through the passage of a water cycle in an ejector and the suction of vapor, thereby improving the system’s performance. To evaluate the performance, four... 

This project focuses on the design of fuel drop tanks for airplanes that add minimal drag and positive lift to the flying object. This will obviously effect the stability and dynamic performance of the airplane. To reduce adverse dynamic effects the tank was divided to several segment with a special emptying sequence. The add-on tank has to have no interference with the object existing systems and require minimum structural changes in the object. Several designs were proposed and the one gaining highest marks was selected. The flow field and the dynamic behavior of combined vehicle and drop tanks were studied using FE simulations. The result shows that adding a drop tank with optimized... 

In recent years, due to environmental concerns together with rising costs of the fossil fuels, the wind energy usage in electricity generation of various countries has experienced a growing trend. Owing to inherent characteristics of wind turbines power generation, i.e. uncertainty in their output level as well as being undispatchable, the rapid growth of installed wind farms, however, has caused some new challenges in operation and planning studies of power systems. Among the major challenges in operation of high wind penetrated power systems, wind power curtailment has been emerged as a new problem in wind development. System operator may curtail wind farms output in order to meet system... 

Cancer can be defined as a stochastic phenomenon. Thus, the tumor growth can be defined as a stochastic process. A Cancer tumor can be analyzed by its geometric shape. Furthermore, computing fractal dimension of shapes is a useful technique to analyze chaosity and complexity of shapes. This approach can be used to compare results from laboratory with simulated results of a mathematical model. A stochastic model of tumor growth will be presented. And some geometrical properties will be analyzed through computer simulation of the model  

Solid oxide fuel cell (SOFC) is one of the promising candidates for clean energy production. Due to the high operating temperature of SOFC, a protective coating is commonly applied on the surface of interconnects to prevent oxidation. In this study, electrophoretic deposition was employed to prepare a manganese-cobalt spinel coating on the surface of ferritic stainless steel (AISISAE430) substrates. MnCo2O4 powder with an average particle size of 60 nm was utilized and the sintering behavior of the coatings at different temperatures was studied. Non-isothermal and isothermal sintering behavior of the powder compacts were examined by employing a sensitive dilatometer. Master sintering curve... 

Offshore platforms are one of the most important structures in oil-rich countries, so that their economic benefit makes it very expensive to stop their usage. Therefore, it is essential that their performance is not disrupted by earthquake or the tidal waves made by severe storms. In the conventional bracing systems, it is assumed that the braces buckle under compressive forces; but Buckling Restrained Brace (BRB) does not buckle under pressure. In this study performance of BRB in jacket platform, with a case study of Resalat platform, has been investigated under earthquake load and powerful wave. The modeling of jacket equipped with this brace has been done in Abaqus software, and results...