Iranian Aerospace SocietyJournal of Aerospace Science and Technology1735-213412120180101Experimental and numerical investigation of unsteady flow around cylinder with four plates perpendicular to it with the rotational degree of freedomبررسی تجربی و عددی جریان ناپایا حول حول یک سیلندر بهمراه چهار صفحه عمود بر آن با درجه آزادی چرخشی114106124ENHassanIsvandAerospace Faculty-Shahid Sattari Aeronautical University of TechnologyAhmadSharafiAerospace Faculty- Shahid Sattari Aeronautical University of Technology- Tehran-IranAliSalmaninejadDepartment of Postgraduate Studies. Shahid Sattari Aeronautical University of Science and TechnologyJournal Article20180304In this study, the behavior of a subject consisting of a cylinder with 4 plates perpendicular to it with a rotational degree of freedom under airflow both through the numerical approach, known as improved discrete vortex and experimental approach were investigated. The experimental and numerical results have shown that oscillating regime occurs in low velocity and length. This movement is vibrations with irregular range around an equilibrium angle of 45 degree. In oscillating motion regime, it is seen that after releasing the object in free flow, a high torque force, due to the flow’s acceleration from the model, is induced to the plates and makes a big angular change, but after a while, the range of oscillation around the equilibrium angle of 45 degree decreases. The probability of rotational motion regime in length ratio of one and velocity of 13 m/sec in initial angle of attack is low. However, the experimental and numerical results have indicated that still in high initial angle of attack around 45 degree, owing to the induced decreased torque to plates, there exists an oscillating movement. Rotational regime in length ratio of 3 and free flow velocity 13 m/sec in all initial angle of attack is observed. In addition, rotational regime appears in all initial angle of attack with the length ratio of 4 and different free flow velocities because of increase in the area of plates.در این تحقیق، رفتار جسمی متشکل از استوانه با چهار صفحه عمود بر آن با درجه آزادی چرخشی تحت جریان هوا هم با روش عددی موسوم به گردابه گسسته و هم با روش آزمایشگاهی مورد بررسی قرار گرفته است. نتایج عددی و تجربی نشان میدهد که رفتارهای حرکتی دورانی و نوسانی و ترکیبی از آنها رخ میدهد. این نوع رفتارها به مشخصات هندسی از جمله نسبت طول صفحات به شعاع استوانه، زاویه حمله اولیه جسم و سرعت جریان آزاد بستگی دارد. نتایج حاصل از روش تجربی و عددی نشان دهنده آن است که رژیم حرکتی نوسانی در نسبتهای طولی کم و سرعت جریان آزاد پایین اتفاق میافتد. و این نوع حرکت به شکل نوسانات با دامنه نامنظم حول زاویه تعادلی 45 درجه میباشد. در رژیم حرکتی نوسانی دیده شده که پس از رها شدن جسم در جریان آزاد، به سبب شتاب گرفتن جریان از روی مدل نیروی گشتاوری زیادی به صفحات وارد شده و تغییرات زاویهای مدل زیاد میباشد ولی پس از گذشت مدت زمانی دامنه نوسانات حول زاویه تعادلی 45 درجه، کاهش مییابد. وقوع رژیم حرکتی دورانی در نسبت طولی 1 و سرعت جریان آزاد (m/s)30 در زوایای حمله اولیه پایین میباشد ولی نتایج تجربی و عددی نشان میدهد، همچنان در زوایای حمله اولیه بالا نزدیک به °45 به سبب کاهش نیروی گشتاوری وارد شده به صفحات، نوع حرکت به صورت نوسانی است. در نسبت طولی 3 و سرعت جریان آزاد (m/s) 13 رژیم حرکتی دورانی در تمامی زوایای حمله اولیه دیده میشود. همچنین در نسبت طولی 4 در تمامی زوایای حمله اولیه و سرعتهای جریان آزاد مختلف رژیم حرکتی دورانی به سبب افزایش مساحت صفحات قرار گرفته در جریان آزاد بروز میکند.http://jast.ias.ir/article_106124_50f42d630be09623a429b385dacd3c85.pdfIranian Aerospace SocietyJournal of Aerospace Science and Technology1735-213412120180101Post-buckling response of thin composite plates under end-shortening strain using Chebyshev techniquesPost-buckling response of thin composite plates under end-shortening strain using Chebyshev techniques1526106248ENS. Amir M.GhannadpourShahid Beheshti UniversityM.BarekatiShahid Beheshti UniversityJournal Article20180206In this paper, a method based on Chebyshev polynomials is developed for examination of geometrically nonlinear behaviour of thin rectangular composite laminated plates under end-shortening strain. Different boundary conditions and lay-up configurations are investigated and classical laminated plate theory is used for developing the equilibrium equations. The equilibrium equations are solved directly by substituting the displacement fields with equivalent finite double Chebyshev polynomials. Using this method allows one to analyze the composite laminated plates with combination of different boundary conditions on all edges. The final nonlinear system of equations is obtained by discretizing both equilibrium equations and boundary conditions with finite Chebyshev polynomials. Nonlinear terms caused by the product of variables are linearized by using quadratic extrapolation technique to solve the system of equations. Since number of equations is always more than the number of unknown parameters, the least squares technique is used to solve the system of equations. Some results for angle-ply and cross-ply composite plates with different boundary conditions are computed and compared with those available in the literature, wherever possible.In this paper, a method based on Chebyshev polynomials is developed for examination of geometrically nonlinear behavior of thin rectangular composite laminated plates under end-shortening strain. Different boundary conditions and lay-up configurations are investigated and classical laminated plate theory is used for developing the equilibrium equations. The equilibrium equations are solved directly by substituting the displacement fields with equivalent finite double Chebyshev polynomials. Using this method allows one to analyze the composite laminated plates with a combination of different boundary conditions on all edges. The final nonlinear system of equations is obtained by discretizing both equilibrium equations and boundary conditions with finite Chebyshev polynomials. Nonlinear terms created as the product of variables are linearized by using quadratic extrapolation technique to solve the system of equations. Since the number of equations is always more than the number of unknown parameters, the least squares technique is used to solve the system of equations. Some results for angle-ply and cross-ply composite plates with different boundary conditions are computed and compared with those available in the literature, wherever possible.http://jast.ias.ir/article_106248_069f6ffa3813a6f6d5f9fda88a22bbc0.pdfIranian Aerospace SocietyJournal of Aerospace Science and Technology1735-213412120180101Multi-objective optimization of buckling load for a laminated composite plate by coupling genetic algorithm and FEMبهینه سازی چند هدفه بار کمانش صفحات کامپوزیتی با ترکیب الگوریتم ژنتیک و FEM2737102190ENMahdiFakoorUniversity of TehranSeyed Mohammad NavidGhoreishiFaculty of New Sciences and Technologies, University of Tehran, Tehran, IranMohamadAminjafariSatellite Research Institute, Iranian Space Research Center, Tehran, IranJournal Article20190918In this paper, a combination method has been developed by coupling Multi-Objective Genetic Algorithms (MOGA) and Finite Element Method (FEM). This method has been applied for determination of the optimal stacking sequence of laminated composite plate against buckling. The most important parameters in optimization of a laminated composite plate such as, angle, thickness, number, and material of each layer are considered in the proposed method. These optimization processes have done for 3 types of compressive loads and optimal stacking sequences and Pareto front for each kind of compressive loads are determined. Unlike estimation methods like response surface and simple analytic methods, in the proposed optimization algorithm, objective functions are calculated directly by FEM software which leads to precise results. The results of proposed algorithm are validated against existing data in literature. The effects of different boundary conditions and aspect ratio of plate on Pareto front in buckling of a laminated composite plate are also studied.http://jast.ias.ir/article_102190_00ac9dc1a39c85ad6f3882cd499a7af0.pdfIranian Aerospace SocietyJournal of Aerospace Science and Technology1735-213412120180101Examination of Quadrotor Inverse Simulation Problem Using Trust-Region Dogleg Solution Methodبررسی مساله شبیه سازی معکوس کوادروتورها با استفاده از روش حل داگ لگ3951106251ENHamidrezaJafariDepartment of Aerospace Engineering, Malek Ashtar University of TechnologyFaridShahmiriMalek Ashtar University of Tech.
Aerospace Engineering Department0000-0003-1743-2136Journal Article20190915In this paper, the particular solution technique for inverse simulation applied to the quadrotor maneuvering flight is investigated. The trust-region dogleg (DL) technique which is proposed alleviates the weakness of Newton’s method used for numerical differentiation of system states in the solution process. The proposed technique emphasizes global convergence solution to the inverse simulation problem. This algorithm is evaluated by calculating the control inputs necessary to enable the quadrotor to follow a specified trajectory including climb-hover and cruise-hover maneuvers. The trajectory is generated by the direct simulation using a linear optimal control developed for the quadrotor. The model of rotors for the quadrotor is a nonlinear model developed based on blade element theory (BET), linear aerodynamics, and non uniform inflow over the rotor disc. The results show that the control inputs obtained from the inverse simulation are in good agreement with control inputs estimated by direct simulation. The results also confirm that the maximum difference between the prescribed trajectory and the trajectory generated by the direct simulation is less than 0.02%, and thus the potential application of the inverse simulation with the trust-region dogleg optimization is evident.http://jast.ias.ir/article_106251_2317ebb4b8149f1db6051c87e4e0bb1a.pdfIranian Aerospace SocietyJournal of Aerospace Science and Technology1735-213412120180101Nonlinear Vibration Analysis of Piezoelectric Functionally Graded Porous Timoshenko Beamsآنالیزارتعاشات غیرخطی تیرهای تیموشنکومدرج تابعی متخلخل با لایه پیزوالکتریک5363106250ENEnayatollahHosseinianDepartment of Aerospace Engineering, Shahid Sattari Aeronautical University of Science and Technology, Tehran , IranAliNouriAerospace Faculty, Shahid Sattry Aeronautical University of Science and TechnologyMajidZiaDepartment of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, IranJournal Article20171203In this paper, nonlinear vibration analysis of functionally graded piezoelectric (FGP) beam with porosities material is investigated based on the Timoshenko beam theory. Material properties of FG porous beam are described according to the rule of mixture which modified to approximate material properties with porosity phases. The Ritz method is used to obtain the governing equation which is then solved by a direct iterative method to determine the nonlinear vibration frequencies of FGP porous beam subjected to different boundary conditions. The effects of external electric voltage, material distribution profile, porosity volume fraction, slenderness ratios and boundary conditions on the nonlinear vibration characteristics of the FGP porous beam are discussed in detail. The results indicate that piezoelectric layers have significant effect on the nonlinear frequencies. Also it is found that the porosity has a considerable influence on the nonlinear frequency and these effects increased especially when the electric voltage is applied.http://jast.ias.ir/article_106250_c8f86780cf1493df1d92fc99ec46a24f.pdfIranian Aerospace SocietyJournal of Aerospace Science and Technology1735-213412120180101A Numerical Study on the Aeroacoustic Radiation from a Finite Length Rotating Cylinderتحلیل عددی انتشار آکوستیکی یک سیلندر چرخان6574106252ENHamid RezaTalesh BahramiSchool of Mechanical Engineering, Iran University of Science and Technology, Tehran, IranSajadGhasemlooyMalek Ashtar University, Tehran, IranHamidParhizkarMalek Ashtar University, Tehran, IranJournal Article20190607Rotating cylinders have wide applications in different areas, especially the aerodynamic area. However, the acoustic behaviors of these components have not been widely studied. The generating noise from a spinning cylinder is mainly due to the detached vortices from the leeward of the body. In this study, the large eddy simulation technique is used to simulate the flow field over a three-dimensional cylinder. In the following, the Ffowcs Williams and Hawkings equation is used to estimate the noise at the specified locations using the oscillating pressure components on the cylinder wall. The acoustic behavior of both stationary and rotating cylinders are studied. Results show that the acoustic behaviors of cylinders rotating with smaller frequencies (up to f=16f0, where f0 is the dominant detaching frequency of vortices on a stationary cylinder) are nearly the same. However, at higher rotational frequencies (24f0) where vortices are omitted, OASPL of the generated noise is reduced considerably (about 20 dB at different angles with constant radial positions, r=26D, at mid-span plane). On the other hand, when the rotational frequency is increased over this limit, the pressure oscillation on the wall becomes significant and the OASPL approaches higher values.http://jast.ias.ir/article_106252_a0a87e8f91303e74d0a873da4650c8d5.pdf