Ehsan Roohi
Abstract
In this paper simulation of cavitating flow over a disk cavitator is reported using computational fluid dynamics (CFD) technique. To apply the cavitation model, the flow has been considered as a single fluid, two-phase mixture. A transport equation model for the local volume fraction of vapor is solved ...
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In this paper simulation of cavitating flow over a disk cavitator is reported using computational fluid dynamics (CFD) technique. To apply the cavitation model, the flow has been considered as a single fluid, two-phase mixture. A transport equation model for the local volume fraction of vapor is solved and a finite rate mass transfer model is used for the vaporization and condensation processes based on the Kunz model. The volume of fluid (VOF) method is applied to track the interface of liquid and vapor phases. Our simulation is performed using a two phase solver available in the framework of the OpenFOAM package, namely “interPhaseChangeFoam”. The solver is based on finite volume method. Two different turbulence model, i.e., k-w SST and large eddy simulation (LES) are employed. Simulation is performed for the supercavitation regime. The results of our simulation are compared with the experimental data and analytical expressions and suitable accuracy has been investigated.
Shahrokh Shams; َA.R. Torabi; Mahdi Fathi Narab
Abstract
In this paper, damage in composite wings is introduced, firstly, then using Euler- Bernoulli equations with including flexural and torsional coupling, governing equations on cantilevered composite wing is derived. By applying separation method damaged beam is converted to two interconnected intact beams ...
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In this paper, damage in composite wings is introduced, firstly, then using Euler- Bernoulli equations with including flexural and torsional coupling, governing equations on cantilevered composite wing is derived. By applying separation method damaged beam is converted to two interconnected intact beams and using boundary conditions and continues conditions in damage location, the dynamic stiffness matrix is composed and modal analysis of damaged wing is done. Composite type is fiber-reinforced and damage type is edge crack with various locations and depths. Also effects crack depths and locations on modal properties in various fiber angle are examined. Results showed that existence a crack even with small depth in root of large span wing can reduce natural frequencies, seriously.
Amirreza Kosari; Javad Bahremandjouy
Abstract
In this paper, a Force Control Solution on Space Docking is proposed providing low impact and safe connection between space modules in different missions. In this solution, the force control concept has been employed along with traditional position control in space docking process because the interaction ...
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In this paper, a Force Control Solution on Space Docking is proposed providing low impact and safe connection between space modules in different missions. In this solution, the force control concept has been employed along with traditional position control in space docking process because the interaction forces between those parties involved (the chaser spacecraft and the target) in this phase are quite significant. Among the available methods in the force control field, Position Based Impedance Control strategy has been used as this strategy controls neither position nor force but the dynamic relationship between relative positions and interaction forces which is used widely in robotic science; however, other methods exhibit instability problems at the connection stage due to change between the position controller and the force controller. As we know, there are different kinds of space vehicles with particular connection scenarios and various connection latches; in order that, each vehicle demands specific interaction force in the connection phase; therefore, Position Based Impedance Control combined with Hill's Equations, which is used for space docking in circular orbit as relative position, is presented to be applied to different docking strategies and mechanisms. For the position controller that lies into Position Based Impedance Control structure, a nonlinear-PID Controller has been utilized possessing an anti-windup property and good capability to track the reference signal. The results show that we can ensure low impact connection by modifying target impedance coefficients in addition to precise position control.
Mehrdad Hoseiniasl; Javad Jafari Fesharaki
Abstract
Optimization the volume/weight of the gear train is more important for industries and researchers. In this paper using particle swarm optimization algorithm a general gear train is optimized. The main idea is to optimum the volume/weight of the gearbox in 3 directions. So, the optimization process based ...
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Optimization the volume/weight of the gear train is more important for industries and researchers. In this paper using particle swarm optimization algorithm a general gear train is optimized. The main idea is to optimum the volume/weight of the gearbox in 3 directions. So, the optimization process based on PSO algorithm occurs along height, length and width of the gearbox to achieve the smallest possible gearbox. The constraints divided into three types of constraints: geometrical, design and control constraints. The optimization process presented for two and three stage gear trains and by choosing different values for the gear ratio, input power and hardness of gears the practical graphs for value of the optimum weight/volume and all the necessary design parameters of gearbox such as number of stages, position and modulus of gears, face width of gears and diameter of shafts are presented. The results are validated by comparing to the results reported in the previous publication.
A. Abdoli; Seyed Hossein Taghavi
Abstract
It is always easier to measure the deviation of a product from its design commitments, in comparison to making it identical to plan obligations. In this paper, this simple fact is utilized to compensate the inherent error of fixture fabrication by a mathematical modeling of possible sources of ...
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It is always easier to measure the deviation of a product from its design commitments, in comparison to making it identical to plan obligations. In this paper, this simple fact is utilized to compensate the inherent error of fixture fabrication by a mathematical modeling of possible sources of error, in calibration of strapdown inertial navigation system (INS). Since an INS should be mounted on the fixture, all deviations are completely transferred to INS. Compensating the inherent errors of a fixture surely guarantees a more accurate calibration, but its effectiveness depends on specific factors. Proposed method can upgrade a fixture with any manufacturing quality to accuracy level of measurement tool. This technique is explained by two examples. Data of industrial-grade strapdown INS is used to proof of claims.
I. Khabbazi; Vahid Behnamgol
Abstract
This paper presents robust nonlinear control law for a quadrotor UAV using fast terminal sliding mode control. Fast terminal sliding mode idea is used for introducing a nonlinear sliding variable that guarantees the finite time convergence in sliding phase. Then in reaching phase for removing chattering ...
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This paper presents robust nonlinear control law for a quadrotor UAV using fast terminal sliding mode control. Fast terminal sliding mode idea is used for introducing a nonlinear sliding variable that guarantees the finite time convergence in sliding phase. Then in reaching phase for removing chattering and producing smooth control signal, continuous approximation idea is used. Simulation results show that the proposed algorithm is robust against parameter uncertainty and has better performance than conventional sliding mode for controlling a quadrotor UAV.