حسین گل پرور

In this paper, theoretical and experimental simulations of the UAV hull’s structural strength in the landing phase on the water surface have been studied. In the seaplane design, calculating the strength of the hull structure against impact from the water surface is of special importance. Initially, the hull was numerically simulated using the finite element method, the interaction of the structure with the fluid (two-phase). Then, by performing an experimental study with variable speed, the results of numerical solution and experimental experiment are compared and evaluated. Comparing the results and graphs obtained from the numerical method with experimental experiments, it has been observed that throwing the seaplane free fall on the water surface can be a simulation of the most critical state for landing. The results show that increasing the descent height and velocity of the device when colliding with the water surface, causes the highest strain gradient along the axis perpendicular to the floor of the waterfowl and the least changes along the axis tangential to the water surface. According to the data obtained from the Tsai Hill and Tsai Wu rupture criteria for numerical solution and experimental testing, the values of stress and strength of the seaplane hull structure are within the allowable design range.

Hybrid joints (Metal–Composite) is being used more and more in aerospace industry due to their low weight and high strength. Dynamic study of this joint, owing to limitation of increase in screw’s preload in composite substructure, has certain importance. Effective factors on nonlinear behavior of the joint are low preload of the screw and high excitation force amplitude on the structure. Layer Element Model has been used to better the description of joint’s behavior in recent years. In this study effects of nonlinear behavior of joint on the structure has been investigated using 2D layer element theory in two divisions: increase of damping and decrease of stiffness which result in nonlinearity. Stiffness characteristics of the joint was modeled with normal stiffness and damping characteristics of the joint with structural damping in shear direction. Nonlinear frequency response function for two preload and two excitation force was extracted and nonlinear finite element model for stiffness and damping of the joint is suggested by High-order polynomial approximation in terms of response amplitude. Effects of increase of excitation force amplitude and decrease of screw’s preload on increase of nonlinearity was extracted by this finite element model. Results indicate that presented nonlinear finite element model corresponds closely to nonlinear vibration tests.

Today, the development of unmanned aircrafts with specific performance characteristics, Including UAVs which capable to fly at high altitude and long endurance is very regarded. In this paper, we have analyzed a nonlinear aeroelastic wing with a high aspect ratio as well as a store (tank) which attached to the wing. Also, the aerodynamic model and structural model have been coupled in steady states. The equations of motion have obtained from Hamilton's principle and the Lagrange equations have acquired from three modes of “bending outside the plate", "bending inside the plate" and” torsion". First of all, we have examined the aeroelastic stability analysis “k” approach. Then, by considering the non-linear terms in equations by using fourth order Rung -Kutta approach, we have studied the results of the simulation and noticed to some phenomena like limit cycle oscillations and bifurcation. The Nonlinear terms are structure and store types and aerodynamics flow have been studied in the linear modes. For solving the equations we have used Galerkin method. Also, the equations have governed in the domain time. By Comparing the results, acceptable accuracy of our modeling and undertaken analysis has observed.

In this paper flutter phenomena for a cropped wing with an external store using numerical and experimental methods in a subsonic and incompressible flight regime has been studied. Wing structure was modeled base on von Karman plate theory. A 3D time domain unsteady vortex lattice method was used for wing aerodynamic model and a slender body aerodynamic theory was used for store aerodynamic model. Finally, the aeroelastic governing equations with considering vibratory wing motion has been solved. The experimental tests were performed in an incompressible subsonic wind tunnel. Comparison of experimental results with theoretical analysis shows good agreement with each other especially in calculation of aeroelastic behavior of the wing. In continue, the effects of some parameters such as wing thickness, wing aspect ratio, store position, weight of the store, aerodynamic of the store, store vertical distance from under wing, and center of mass of the store on both flutter speed and instability boundary of the wing have been studied analytically and experimentally. The results show with both increasing aspect ratio and decreasing wing thickness, flutter speed will be decreased. Moreover, change in store position effects on flutter speed of the wing/store configuration. Aerodynamic of the store has no significant effect on flutter speed of the wing/store configuration and increasing store weight leads to increasing flutter speed. Change in center of mass of the store influences on flutter speed.

In this paper, linear and nonlinear analysis of an airfoil with two degrees of freedom in incompressible flow is accomplished for experimental test. Respective equations are extracted by Lagrange's method and used Wagner’s theory to solve this equation in time domain. Two-degree-of-freedom flutter is a combination of bending and torsion vibration modes. A flutter mount system with flexure supports has been developed for flutter tests with rigid wings in wind tunnels. This current study is an experimental investigation into the behaviour of a 2DOF wing section with a flexible structural linearity and nonlinearity support in pitch and plunge motion without free-play. This support system must be providing a well-defined 2DOF dynamical system on which rigid wings can encounter flutter. A classical 2DOF flutter can be described as combination of bending and torsion vibration modes. Evaluation of the results of wind tunnel experiments and effective parameters show that increasing frequency ratio cause the speed of flutter to decrease but it reducedes to minimum value at a frequency ratio and then it increase. Furthermore, it is observed that with increasing the distance center of elastic-axis from leading edge flutter speed decreases.

In this paper, firstly FEM model of the wing like plate is created by MSC NASTRAN software. This clamped plate is considered as swept and tapered. Moreover, the material is chosen as steel. Natural frequencies and their corresponding mode shapes are investigated via modal analysis by MSC NASTRAN. The results are compared with experimental modal analysis on a similar real model. Afterwards the aerodynamic FE model is created in MSC PATRAN, and then spliced to the structural model. The aeroelastic model is analysed by MSC NASTRAN in order to extract the flutter speed and corresponding frequency. Finally the real model installed in the wind tunnel and tested as a flutter experiment. The experimental result showed that the FEM flutter analysis results in MSC NASTRAN are close to experimental results.