Sharif Digital Repository

Duo to the strictly pollution legislation in the last decade and increasing demand of lightweight internal combustion engines with rated power , turbocharging of the spark ignition engines become more interested. Therefore the turbocharging of M15GS engine was studied in both gasoline and natural gas fuels with purpose of enhancement of performance characteristic of engine. According to this approach 0-D turbocharger matching performed for gasoline and natural gas fueled M15GS engine. Also an innovative 1-D turbocharger matching performed for gasoline fueled engine. Then engine equipped with SJ50 turbocharger and dynamometer and combustion development tests performed on gasoline fueled... 

Chaos theory examines complex systems whose output results in large changes by applying small changes to the initial conditions. In other words, some seemingly accidental phenomena for which we have not yet found a reason can be justified with the help of chaos theory. The strong dependence of the response to the initial conditions is one of the most important features of turbulent systems, but their quasi-random behavior will be independent of these conditions after some time. Chaotic systems, as an important branch of nonlinear dynamic systems, behave close to stochastic systems. Perhaps the most important similarity between the two systems is the existence of invariant probability density... 

Sparse representation and compressed sensing have been widely used in various fields, one of the most popular of which is ISAR imaging. Inverse Synthetic Aperture Radar (ISAR) provides an electromagnetic image of the target, which is mainly used to identify and classify targets. In some applications, recognizing targets from a 2D image can be difficult and error-prone. One idea to deal with this problem is 3D ISAR imaging. The most widely used method of ISAR imaging is direct method based on Fourier transform. This method requires the measurement of radar data with high measurement density in 3 directions, which increases the data collection time and volume, which is the main problem of... 

The use of sandwich panels has become very common in recent engineering designs when the weight of the part or structure is important and we are looking to lose weight while maintaining strength. The mechanical properties of this type of structures, including yield stress, fatigue behavior and estimation of their life, failure modes, natural frequencies and resonance phenomena, etc. are affected by various factors, including geometric and environmental factors. Fatigue is one of the most common failures in these structures. Composite materials have complex structures. In these materials, due to the viscoelastic properties, the fatigue behavior changes with changing stress, stress frequency,... 

The vibration and flutter characteristics of sandwich shells and plates with constrained viscoelastic layer are presented. The mechanical properties of viscoelastic core is modeled using fractional order model and the thin shells theory has been used to obtain the structural equations of the outer layers. Linear piston theory has also been used for aerodynamic modeling. The equations governing the vibrations and flutter of shells and plates are obtained using Newton method and in some cases using the energy method. The Rayleigh-Ritz method is implemented to solve the discretized governing equations for linear examples and the method of multiple scales is used to solve the nonlinear ordinary... 

In recent decades, significant advances have been made in the manufacturing of micro/-nanofluidic equipment that can reduce the cost of conducting electrochemical experiments and increase the accuracy, speed, and control of these experiments. In this regard, by installing micro/nano-networks on laboratories on a chip, the above objectives have been made possible. Due to the increase in surface-to-volume with decreasing of size of devices, important surface phenomena such as electrokinetics may reach a special place to control the micro/nanoflow. On the other hand, since each of the materials used in the construction of the above equipment reveals a special property in contact with different... 

Flameless combustion is a regime of combustion that is caused by slowing down the chemical reactions of combustion, which is the result of reducing the local concentration of oxygen in the combustion chamber. This reduction in oxygen concentration is mainly due to the strong recirculation of hot gases from combustion and the high mixing of these gases with the reactants. In this type of combustion, due to the reduction of hot spots, the production of nitrogen oxide pollutant is significantly reduced compared to normal combustion. The aim of this research is to determine the performance limits of flameless combustion in order to seriously reduce NOx and other pollutants. For this purpose,... 

Inertial motion capture systems widely use low-cost IMUs to obtain the orientation of human body segments, but these sensors alone are unable to estimate link positions. Therefore, this research used a SLAM method in conjunction with inertial data fusion to estimate link positions. SLAM is a method that tracks a target in a reconstructed map of the environment using a camera. This paper proposes quaternion-based extended and square-root unscented Kalman filters (EKF & SRUKF) algorithms for pose estimation. The Kalman filters use measurements based on SLAM position data, multi-link biomechanical constraints, and vertical referencing to correct errors. In addition to the sensor biases, the... 

In this research, a multigeneration system was designed and evaluated, utilizing solar and geothermal energy to generate electricity, fresh water, hydrogen, and oxygen. The system's performance was assessed from energy, exergy, and economic perspectives. The setup involves a solar tower contributing energy to the gas cycle and a geothermal well supplying preheated water for the steam cycle. The system employs a molten salt cycle to capture heat from the solar receiver, transferring it to the air cycle. The remaining energy requirement is met by the Air Brayton cycle, which combines methane and hydrogen as fuels within the combustion chamber. Additionally, a steam cycle is integrated to... 

The need for cooling and creating thermal comfort conditions for human life is one of today's severe challenges. Therefore, development and innovation to enhance the efficiency of these systems are of great importance. Among the new ideas proposed in this domain, we can mention the M-cycle, which can greatly improve the energy consumption for cooling systems in this sector. In this cycle, the desired cooling is produced by utilizing the latent heat of water evaporation, which is considered a kind of renewable energy. The systems based on this cycle are still under development, and for this reason, there is a necessity to better investigate the heat and mass transfer in the aforementioned... 

We propose Hierarchical Web Services Composer (HWSC) as a technique for fully automatic Web services composition. It takes functional and nonfunctional requirements of a Web service and returns possible compositions that realize those requirements. In doing so, HWSC deploys the Hierarchical Services of Interacting Processes (HSIP), a formalism of concurrent systems, and integrates its capabilities with the existing methods and protocols for service oriented computing. The proposed framework technique is then analyzed and validated through a number of real-life examples  

Knowledge of Air-water two phase flows is significant to different engineering systems such as chemical reactors and power plant and petrochemical and petroleum industry. One of the most industrial cases of two phase flow is two phase flow in vertical large pipes. Because of gravity, two phase flow in Vertical pipes is different from horizontal pipes. Considering these flows can play a significant role in long-term reliability and safety of industrial systems. There are many parameters that effect on flow characteristics such as length and diameter of pipe and shape and condition of air inlet. Effect of air inlet is on the shape of bubbles and this can effects on flow pattern and another... 

Over the past few years there has been a rapidly growing interest in analysis, design and optimization of various types of collective behaviors in networked dynamic systems. Collective phenomena (such as flocking, schooling, rendezvous, synchronization, and agreement) have been studied in a diverse set of disciplines. In many applications involving multi-agent systems, groups of agents are required to agree on certain quantities of interest; in other words, it is important to develop information consensus protocols for networks of dynamic agents. There are many practical situations where it is desirable or even required to achieve stable convergence in finite-time domain. In this work, a... 

Pulse Tube Refrigerator (PTR) has an exceptional feature among all similar refrigerators, because of its unique characteristics such as long lifetime, compact size and no moving parts in low temperature. Despite of all these advantages because of its low efficiency, many researchers are trying to optimize performance of this refrigerator. Most of these efforts are based on one-dimensional simulation of the system. In this thesis, a two-dimensional analysis is performed to study the nature of flow field in an Inertance Tube Pulse Tube Refrigerator (ITPTR). This analysis is based on a numerical modeling of an entire ITPTR. To reach this purpose the two-dimensional form of mass, momentum and... 

In this thesis, we have derived the exact equations of motion for flexible beams. The derived equations are compared with similar equations reported in the literature, and they demonstrate significant power in prediction of the numerical results. The model for planar beams is verified by the performed experiments on carbon fiber rods. A new highly convergent, efficient technique which is quite fast is also developed for both approximating and controlling a system, entitled as fuzzy-Pade method. We then have studied effects of the wing flexibility on enhancing the lift and trust coefficients in the flapping flight. Aerodynamic force generation due to flapping is simulated for both the... 

Heat pipe is a device with several applications in various industries such as electronics cooling, nuclear and renewable technologies. This apparatus transfers heat from a hot source to a cold one. Thermosyphon is a special type of heat pipe that transmits heat using gravitational forces. Although scholars have performed many experiments on thermosyphon, mostly they were about the thermal characteristics of thermosyphon and rarely the hydraulic specifications of thermosyphon have been investigated. But it is clear that these two specifications (thermal, hydraulic) relate to each other closely and detailed study about their interaction may bring out better results. In this thesis, initially a...