Sharif Digital Repository

An experimental investigation of the flow field of pressure swirl atomizers for different pressure drops is performed. Two experimental methods are employed. For low injection pressures, a visual study is conducted while for higher pressures the velocity components and size of the droplets are measured by using Phase Doppler Anemometer. The spray formation, spray cone angle, and breakup length are visually investigated. Velocity and size of the droplets are measured on a plane of measurement along the axis of the spray so that the properties are carried out in a radial direction as a function of both pressure drop and axial distance from the nozzle. Self-similar mean axial velocity profiles... 

Radial Basis Function, a neural network based interpolation method, is used to simulate swirling spray phenomenon. From this model, the profile of mean velocity components' distribution along the main axis of the injector at various pressure drops and spray measurements' plane are obtained and analyzed. Experimental data obtained through Phase Doppler Anemometer is used to train this model. The results are compared with experimental data as well as to those obtained through General Regression Neural Network method as another neural network based interpolation method investigated previously by the authors. © 2003 by M.R. Soltani  

Ship motions affect the propulsion system, which causes fluctuations in the power system. Mutually, the power system variations impact the ship velocity by generating speed changes in the propeller. Therefore, interconnecting the ship hydrodynamic and power system has paramount importance in designing and analysing an all-electric ship (AES). The lack of an integrated model that can be evaluated in various operating conditions, such as manoeuvring, is evident. This paper explores the required perceptions for the power system and hydrodynamic analysis of an AES. Then, an integrated theoretical model comprising both the ship motion and power system is proposed. In addition to providing an... 

Switched Reluctance Motors (SRMs), which are simple and reliable motors, have attracted interest for electric vehicle propulsion systems. It is shown that an SRM offers a good performance at high acceleration and low speed driving conditions. Efficiency map of an electric motor is a very important characteristic specially when the motor is to be used in a wide range of speed and load variations, which is the case in electric propulsion systems. In this research, the efficiency map of an SRM is derived using a combination of the Finite Element Method (FEM) and a mathematical model. This efficiency map has been used for different driving cycles to test the SRM performance as a vehicle... 

In this study, we numerically investigate the size effect of a bluff body, embedded inside a combustor, on the formation of carbonaceous nano-particulate matter (PM). The combustor is fed with a jet propulsion fuel. We first evaluate our extended numerical tool by simulating a turbulent kerosene/air nonpremixed flame in a combustor. The achieved results are then compared with those of experiment. The comparisons show that there are good agreements between them. Next, we embed an O-ring type flame holder inside the combustor to change its configuration, i.e., to extend it to a bluff-body burner. Assuming a constant air mass flow rate, we investigate the blockage ratio effects of the burner... 

A review of worldwide activities in liquid-fed pulsed plasma thruster (LPPT) is discussed. Pulsed plasma thruster are extensively recognized as one of the most promising electric space propulsion systems to perform propulsive tasks on micro- and nanosatellites, including cubesats, because they offer many advantages compared with other electric space propulsion systems. The low plasma exhaust velocity measured by a Langmuir probe showed that thrust is mainly produced by 0.3 μg mass ionized by the first trigger and a much greater quantity of propellant introduced by the main discharge remained neutral at low speed. Various propellant feeding and discharge initiation methods have been applied... 

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... 

One of the most important aspects of a successful space mission is the transition to the correct orbit and maintaining it. As a result, many modern orbit transfer techniques have been developed in space industry in order to accomplish this task in a more reliable and less expensive way. However, when it comes to the design of student satellites, usually there are serious limitations on the financial resources, technical database and satellite industry experts. These limitations may compromise the access to advanced methods and techniques. Therefore, reliability and expenses may no longer be the only criteria to be met in the process of design. As a result, at each step of the design, a... 

This paper presents a new mechanism with unique and prominent features for a helical swimmer robot. "Double Helices Propulsion Mechanism" consists of two parallel helices with a single axis rotating in the same direction. The outer helix acts as the main propulsion component, and the inner helix, which is made of a Shape Memory Alloy (SMA), controls the forward velocity during swimming. This mechanism, by varying the geometrical parameters of its helical tail, can change the forward velocity of the helical swimmer robot that is required by its predefined missions. In order to study the effects of geometric parameters on the forward velocity in the single helical swimmer, a hydrodynamic model... 

The current paper presents a simple mathematical model for replication of the transient acceleration motion of displacement hulls in calm water under the action of a propulsion system. Different empirical methods are coupled, and an operational speed problem is solved in the time domain. The resistance of the ship is calculated by using the Holtrop method. The values of thrust force, torque and propeller efficiency are computed by using B-Series empirical equations. The acceleration motion of the vessel, which is triggered as the engine starts to work, is simulated by solving a set of first-order differential equations, which are discretised in the time domain. It is shown that different... 

In this study, we apply a hybrid direct simulation Monte Carlo (DSMC)/Navier-Stokes (NS) frame to simulate the effects of catalyst or splitter plates in propulsive efficiency of micro/nanopropulsion systems. Our hybrid frame uses the local Knudsen number based on the gradient of the flow properties (KnGLL) to distinct the continuum and molecular regions. This frame also uses the state-based coupling (Dirichlet-Dirichlet boundary-condition coupling) to transfer the information between the two regions. We simulate typical micro/nanopropulsion systems consisting of channels, catalyst or splitter plates, and convergent-divergent nozzles. According to the Kn GLL, we apply the NS solver to the... 

Nature presents a variety of propulsion, maneuvering, and stabilization mechanisms which can be inspired to design and construction of manmade vehicles and the devices involved in them, such as stabilizers or control surfaces. This study aims to elucidate and compare the propulsive vortical signature and performance of a foil in two important natural mechanisms: flapping and undulation. Navier–Stokes equations are solved in an ALE framework domain containing a 2D NACA 0012 foil moving with prescribed kinematics. All simulations are carried out using a pressure-based finite volume method solver. The results of time-averaged inline force versus Strouhal number (St) show that in a given... 

The aim of this article is to present an efficient dynamical model for simulating flapping robot performance employing the bond graph approach. For this purpose, the complete constitutive elements of the system under investigation, including the main body and accessories, flapping mechanism, flexible wings and propulsion system consisting of a battery, DC motors and gear boxes, are considered. A complete model of the system was developed appending bond graph models of the subsystems together utilizing appropriate junctions. The wings were also modeled using ANSYS only for an initial evaluation. Moreover, a computer model was developed employing the block-oriented structure of Simulink in... 

Modular linear doubly salient permanent magnet motors are well adapted to linear propulsion systems because of their distinct characteristics, such as high efficiency and power density, reduced maintenance and initial cost, low noise and permanent magnet (PM) leakage flux, and fault tolerance capability. However, such motors suffer from high cogging thrust. In this study, various techniques based on previously proposed methods for PM machines are applied on the studied motor and evaluated by using non-linear three-dimensional time-stepping finite element analysis; three novel, optimised techniques are then presented. The techniques presented are based on the minimisation of the variation in...