Sharif Digital Repository

Inlet performance has an important role in the operation of air-breathing propulsion systems. In this study, performance of a supersonic axisymmetric mixedcompression inlet in the supercritical operating condition is numerically studied. The effects of free-stream Mach number and engine-face pressure on performance parameters, including mass flow ratio, drag coefficient, total pressure recovery, and flow distortion, are investigated. For this sake, a multi-block density-based finite volume CFD code is developed, and Reynolds-averaged Navier-Stokes equations with Spalart-Allmaras oneequation turbulence model are employed. The code is validated by comparing numerical results against other... 

The performance of an HTPB/N2O hybrid motor was experimentally investigated. A hybrid motor was designed and manufactured in a laboratory with the purpose of studying the effects of various parameters on the motor's performance, including fuel regression rate and specific impulse. A series of tests were conducted to find a correlation between the fuel regression rate and the oxidizer's mass flux. The effects of chamber's pressure on the regression rate as well as other performance parameters were investigated. While the burning rate did not change dramatically, both the efficiency and ISP of the motor increased. The local fuel regression rate and the fuel port were also calculated. In... 

Numerous studies have investigated driving equations used to predict the slip factor in centrifugal compressors so far. Inevitably, through these studies, the ow field characteristics have been simplified and the effects of the related parameters have been neglected. The present study, experimentally and numerically, investigates the slip phenomenon in a specific centrifugal compressor with complex blade curves and splitter blades, considering the main effective parameters such as the number of blades, exit angle, etc. To this end, a three-dimensional simulation of the viscous flow field of the compressor via an appropriate turbulence method was performed. In addition, an experimental study... 

The aim of this study is to improve the performance of two-tier macro/femtocell networks using a power control approach. In wireless networks, power control plays an important role in improving a number of performance parameters such as co-channel interference and outage probability reduction, throughput increasing, and power saving. This study explores the evolution of centralised power control algorithm based on femtocell base station (FBS) clustering and predicted signal-to-interference-plus-noise ratio (SINR) of users. To reduce the computational complexity of centralised algorithm, dense deployed femtocells are considered in different clusters. In this case, femtocells inside one... 

Ground reaction force (GRF) characteristics of amputee walking are important for the analysis of clinical gait data, and also to update model reference adaptive impedance (MRAI) controllers. GRF estimation is a better alternative than direct GRF measurement because of the disadvantages of load cells, such as high cost, integration difficulties due to weight and physical dimensions, the possibility of overload, and measurement noise. This paper presents four robust MRAI observer/controller combinations for GRF estimation-based control of a prosthesis and a legged robot model in the presence of parametric uncertainties and unmodeled dynamics, in which the robot model is employed to mimic... 

Remote sensing satellites propulsion subsystem preliminary design based on performance sizing is discussed. The process is a fairly complicated one considering a variety of operational as well as performance requirements. This research aims to reduce the number of iterations required by the current practice to reach a compromise. It is based on a rapid-sizing method that helps lessen lengthy iteration cycles. The proposed technique, similar to such class of preliminary design processes, leads to an acceptable approximation that must be properly conveyed to other disciplines involved for further elaborations. With proper selection of design and performance parameters together with fundamental... 

Remote sensing satellites propulsion subsystem preliminary design based on performance sizing is discussed. The process is a fairly complicated one considering a variety of operational as well as performance requirements. This research aims to reduce the number of iterations required by the current practice to reach a compromise. It is based on a rapid-sizing method that helps lessen lengthy iteration cycles. The proposed technique, similar to such class of preliminary design processes, leads to an acceptable approximation that must be properly conveyed to other disciplines involved for further elaborations. With proper selection of design and performance parameters together with fundamental... 

The preliminary design of building structures is normally based on the equivalent lateral forces provided in seismic design guidelines. The height-wise distribution of these loads is predominantly based on elastic vibration modes. However, as structures exceed their elastic limits in severe earthquakes, these design load patterns may not necessarily lead to efficient distribution of strength within the structures. To address this issue, several alternative load patterns have been proposed for the seismic design of non-linear structures. However, due to the simplifications involved in the development of these design load patterns, their adequacy needs to be assessed for different structural... 

A new structure for the compression surfaces of a supersonic inlet is proposed which has improved the target performance parameter i.e. total pressure recovery ratio. This idea resulted in development of a new type of supersonic inlet, utilized four ramps and a cone simultaneously as the compression surfaces. A prototype of the proposed inlet has been designed for a free stream Mach number of 3 and its performance has been evaluated via numerical simulation for both design and off-design conditions. The performance of the newly designed inlet has been compared to the existing experimental data of two double-cone inlets. The acquired data are further compared with analytical calculations of... 

This paper focused on the conceptual design of a conventional gas turbine combustor via the multi-objective optimization approach. The suggested method integrated the design and estimation of the performance of the combustion chamber. The geometry and performance parameters could be found by applying the design tool. According to the level of available information in the primary phases of the design process, a chemical reactor network approach for modeling the combustion was chosen; thus, the droplet evaporation of the liquid fuel and unmixedness of the fuel-air mixture in the primary zone was modeled. The results obtained from the design tool for the two annular combustors were compared... 

This paper presents a kinetic data structure (KDS) for maintenance of the Euclidean minimum spanning tree (EMST) on a set of moving points in 2-dimensional space. For a set of n points moving in the plane we build a KDS of size O(n) in O(nlogn) preprocessing time by which the EMST is maintained efficiently during the motion. This is done by applying the required changes to the combinatorial structure of the EMST which is changed in discrete timestamps. We assume that the motion of the points, i.e. x and y coordinates of the points, are defined by algebraic functions of constant maximum degree. In terms of the KDS performance parameters, our KDS is responsive, local, and compact. The... 

In aerospace applications, the weight of structures is considered as a major performance parameter. One of the most effective ways for weight reduction is superplastic forming. By this technique, not only the weight, but also the stress concentration, the cost, and the time of manufacturing are noticeably reduced. Additionally, the components with complicated shapes could be formed in a single manufacturing step. Due to the wide demand for whiskers reinforced metal matrix composites (MMC's) in aerospace applications, many research works have been designed to extend the boarders of superplastic forming of metals to the area of MMC manufacturing. In the present study, the FEM modeling of... 

In this research, the centrifugal compressor of a turbocharger is investigated experimentally and numerically. Performance characteristics of the compressor were obtained experimentally by measurements of rotor speed and flow parameters at the inlet and outlet of the compressor. Three dimensional flow field in the impeller and diffuser was analyzed numerically using a full Navier-Stokes program with SST turbulence model. The performance characteristics of the compressor were obtained numerically, which were then compared with the experimental results. The comparison shows good agreement. Furthermore, the effect of area ratio and tip clearance on the performance parameters and flow field was... 

This paper introduces a new passive control device for protecting structures against earthquakes. The device consists of two welded pipes which have two smaller pipes inside them and the spaces between the pipes are filled with metals such as lead or zinc. The device is loaded in shear and takes advantage of plastification of the outer pipes, the inner pipes and the infilled metals, and the friction between metals as energy absorption mechanisms. Quasi-static cyclic tests are performed on six specimens all showing stable hystereses and high damping. A finite element model is developed and calibrated against test results. The model is used to find the optimum sizes of pipes needed for a... 

A new structure is suggested for simultaneous microwave chirped pulse generation and array antenna beam steering. It is based on using a multi-channel fiber Bragg grating in a photonic microwave delay-line filter. The paper presents a feasibility study of the idea, discussing the main performance parameters of both signal generation and beam steering functions. Specifically, it focuses on the effects of wavelength tuning, resolution and accuracy. The study shows that custom off-the-shelf components could be used to implement an all optical system capable of generating chirped pulses while steering the radiation pattern of a small sized antenna array. The advantages of the structure for...