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Experimental Study on Aerodynamic Deformation of Flexible Wings of an Ornithopter
, M.Sc. Thesis Sharif University of Technology ; Mazaheri, Karim (Supervisor)
Abstract
Flapping motions of flexible wings generate dynamic forces. These forces include aerodynamic forces and inertial forces due to angular acceleration of wing mass, that cause aeroelastic deformation of wings. In this thesis a method is presented by use of a software and some experimental test conditions to study elastic behaviors and aerodynamic forces of flexible wings. A high speed camera records motion of wings in hovering condition and then these images is processed with software to recognize deformations (such as deflection, torsion, etc.) and aerodynamic forces due to them. Afterwards aerodynamic model and deformations is combined for better modeling. Finally we can compare results with...
Aerodynamic Investigation of an Aeroelastic Flapping Wing and Optimum Design Method
, Ph.D. Dissertation Sharif University of Technology ; Mazaheri, Karim (Supervisor)
Abstract
Flapping wing vehicles produce aerodynamic lift and thrust through the flapping motion of their wings. The dynamic performance of a flexible membrane flapping wing is experimentally investigated here. To investigate aeroelastic effects of flexible wings (specifically, wing’s twisting stiffness) on hovering and cruising aerodynamic performance, a flapping-wing system and an experimental setup were designed and built. This system measures the unsteady aerodynamic and inertial forces, power usage and angular speed of the flapping wing motion for different flapping frequencies, angles of attack, various wind tunnel velocities up to 12 m/s and for various wings with different chordwise...
Sharp edge gust effects on aeroelastic behavior of a flexible wing with high aspect ratio
, Article 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 10 January 2005 through 13 January 2005 ; 2005 , Pages 14279-14293 ; Shams, Sh ; Kheiri, M ; Sharif University of Technology
2005
Abstract
The subject of the present paper is the investigation of the sharp edged gust effects on the aeroelastic behavior of a flexible wing. It is important to determine the response of the wing to the atmospheric turbulences during normal flight. So, linear modal analysis technique and linear quasi-steady aerodynamic are used for structural modeling and aerodynamic loading, respectively. Also, Lagrange method is used to obtain the system of equations of motion. Using the normal modes of free vibration, structural and aerodynamic matrices can be constructed. Then the aeroelastic instability of the system is determined using p method. Kussner function is used to model the sharp gust effects on the...
6DOF Flight Dynamics Modeling of a Flexible Flapping wing using Unsteady Aerodynamics
, Ph.D. Dissertation Sharif University of Technology ; Pourtakdoust, Hossein (Supervisor)
Abstract
A complete 6DOF flight dynamic model of an elastic flapping wing (EFW), integrated with unsteady aerodynamic theory is developed. In this respect, initially efficient high fidelity modules for EFW structural dynamics (SD) as well as unsteady aerodynamics loadings (UAL) to be coupled with its flight dynamics are prepared. A modal approach is followed to model structural dynamics of plain and 3D EFWs. This is in contrast with the Euler-Bernoulli beam theory that is mostly utilized for SD in the existing literature. In addition, due to the possibility of large wing deformations as well as the existence of non-linear displacement regime for realistic EFW flights, non-linear modal approaches such...
Investigation and Optimization of Structural Parameters of an Elastic Flapping Wing
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Roohollah (Supervisor)
Abstract
In this thesis, effects of bending and torsional elasticity of a flapping wing on its average lift and input power are studied, using a semi-analytic method. Bending stiffness and torsional rigidity of wing spar, wing mass ratio and chordwise and spanwise center of gravity, also spar location are considered as variables for controlling elastic behavior of the wing.Governing integral equation is derived using Hamilton principle via modified quasi aerodynamic and linear Green-Lagrange strain tensor. Also an idealized flapping pattern is used to maximize average acceleration during each cycle. Next, integral equation is converted to a set of ordinary differential equations by means of Galerkin...
Experimental investigation on aerodynamic performance of a flapping wing vehicle in forward flight
, Article Journal of Fluids and Structures ; Volume 27, Issue 4 , 2011 , Pages 586-595 ; 08899746 (ISSN) ; Ebrahimi, A ; Sharif University of Technology
2011
Abstract
The aerodynamic performance of a flexible membrane flapping wing has been investigated here. For this purpose, a flapping-wing system and an experimental set-up were designed to measure the unsteady aerodynamic forces of the flapping wing motion. A one-component force balance was set up to record the temporal variations of aerodynamic forces. The flapping wing was studied in a large low-speed wind tunnel. The lift and thrust of this mechanism were measured for different flapping frequencies, angles of attack and for various wind tunnel velocities. Results indicate that the thrust increases with the flapping frequency. An increase in the wind tunnel speed and flow angle of attack leads to...
Experimental study on interaction of aerodynamics with flexible wings of flapping vehicles in hovering and cruise flight
, Article Archive of Applied Mechanics ; Volume 80, Issue 11 , 2010 , Pages 1255-1269 ; 09391533 (ISSN) ; Ebrahimi, A ; Sharif University of Technology
2010
Abstract
Flapping wings are promising lift and thrust generators, especially for very low Reynolds numbers. To investigate aeroelastic effects of flexible wings (specifically, wing's twisting stiffness) on hovering and cruising aerodynamic performance, a flapping-wing system and an experimental setup were designed and built. This system measures the unsteady aerodynamic and inertial forces, power usage, and angular speed of the flapping wing motion for different flapping frequencies and for various wings with different chordwise flexibility. Aerodynamic performance of the vehicle for both no wind (hovering) and cruise condition was investigated. Results show how elastic deformations caused by...
Dynamic Simulation of the Propulsion System of a Flapping Wing Vehicle
, M.Sc. Thesis Sharif University of Technology ; Meghdari, Ali (Supervisor)
Abstract
Flapping wing vehicles produce aerodynamic forces through the flapping motion of their wings. A sample flapping wing mechanism is studied in this project, which propulsion system consists of a battery, a DC motor, a gearbox, a flapping mechanism and a flexible membrane wing. The purpose of this study is simulation of the whole propulsion system through identification and simulation of each sub-system. In the current research, after an introduction to the flapping wing vehicles, literature of the flapping vehicles is reviewed. By studying relevant articles, lack of a comprehensive simulation of all sub-systems is observed. So the goal of this research is obtaining an appropriate tool for...
Developing a Method for the Dynamic Analysis of Flexible Flapping Wing
, M.Sc. Thesis Sharif University of Technology ; Meghdari, Ali (Supervisor)
Abstract
Flapping is one of the most usual solutions to produce aerodynamic lift and propulsive force in natural flights, in low Reynolds number. A sample flapping wing mechanism in which propulsion system consists of a battery, two very small DC electrical motors, two gearboxes, a flapping mechanism and flexible beams as wings is studied in this project.Different methods have been proposed to derive the governing equations of motion and simulate the flapping wing system. The main disadvantage of the previous proposed works is the lack of a comprehensive dynamical analysis of the complete system including its components.Therefore, the main objective of the present research is to propose an efficient...
Aeroelastic Modeling, Experimental Validation and Stability Analysis of a Flapping Wing Air Vehicle in Planar Flight
, Ph.D. Dissertation Sharif University of Technology ; Pourtakdoust, Hossein (Supervisor)
Abstract
In this research, aeroelastic model of an elastic flapping wing has been derived in order to be integrated with the flight dynamic model. The model developed in this research well describes the coupled and nonlinear behavior of the passive torsional deformations of the wing during flapping motion. Based on this obtained equations, a precise propulsion model proper for flapping wing vehicles has been introduced. The effect of geometric and mechanical properties of the wing is being accounted. In order to validation of the analytical model several FMAVs as well as an instrumented test stand for online measurements of forces, flapping angle and power consumption have been designed and built...
Development of the Hale Aircraft's Aeroelastic Model with Very Flexible Wings
, Ph.D. Dissertation Sharif University of Technology ; Dehghani Firouzabadi, Roohallah (Supervisor)
Abstract
In this study, a nonlinear aeroelastic model for an aircraft with fully flexible wings is obtained. This aeroelastic model is based on system identification and is created using the beam model for the structure and the three-dimensional panel method for aerodynamic analysis. The model intended for the structure is a nonlinear beam with exact geometry with initial deformation and rigid motion. The model intended for aerodynamics is an unsteady three-dimensional panel method for the airplane’s body, wings, and tail. The desired aeroelasticity model is a reduced-order model based on system identification using the time-domain/frequency-domain aerodynamic response under forced vibrations in the...
Multi-body simulation of a flapping-wing robot using an efficient dynamical model
, Article Journal of the Brazilian Society of Mechanical Sciences and Engineering ; Volume 38, Issue 1 , 2016 , Pages 133-149 ; 16785878 (ISSN) ; Selk Ghafari, A ; Ebrahimi, A ; Meghdari, A ; Sharif University of Technology
Springer Verlag
Abstract
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...
Optimization of Actuators Position of a Low Aspect Ratio Variable-camber Wing and Derivation of Its Aerodynamic
, M.Sc. Thesis Sharif University of Technology ; Dehghani Firouzabadi, Rouhollah (Supervisor) ; Haddadpour, Hassan (Supervisor)
Abstract
Morphing concepts can potentially improve the performance and fuel consumption of modern aircrafts. Smart materials can reduce the weight and complexity, and also are of the best choices to improve efficiency and reliability for realizing morphing wings. Developing of a simple model and optimization of smart piezocomposite actuators position of a thin wing with variable camber is considered. The goal is to gain desired properties in incompressible subsonic regime. Lifting surfaces of a composite wing are simplified using shell model. Keeping the problem simple, a piezocomposite patch is used to change the shell curvature. Basic modes are extracted from FEM software and behavior of bimorph...
Flutter of wings involving a locally distributed flexible control surface
, Article Journal of Sound and Vibration ; Volume 357 , November , 2015 , Pages 377-408 ; 0022460X (ISSN) ; Firouz Abadi, R. D ; Roshanian, J ; Sharif University of Technology
Academic Press
2015
Abstract
This paper undertakes to facilitate appraisal of aeroelastic interaction of a locally distributed, flap-type control surface with aircraft wings operating in a subsonic potential flow field. The extended Hamilton's principle serves as a framework to ascertain the Euler-Lagrange equations for coupled bending-torsional-flap vibration. An analytical solution to this boundary-value problem is then accomplished by assumed modes and the extended Galerkin's method. The developed aeroelastic model considers both the inherent flexibility of the control surface displaced on the wing and the inertial coupling between these two flexible bodies. The structural deformations also obey the Euler-Bernoulli...
Nonlinear analysis of 2D flexible flapping wings
, Article Nonlinear Dynamics ; Volume 81, Issue 1-2 , July , 2015 , Pages 299-310 ; 0924090X (ISSN) ; Zohoor, H ; Yoon, Yong Jin ; Sharif University of Technology
Kluwer Academic Publishers
2015
Abstract
Natural flyers have flexible wings, which deform significantly under the combined inertial and aerodynamic forces. In this study, we focus on the role of chord wise flexibility in 2D pitch and plunge motions. We derive the exact nonlinear 2D equations of motion for a flexible flapping wing with flying support. In achieving the closed-form equations, we use the exact strain field concerning considerable elastic deformations. After numerically solving the novel equations, we validate them in simulations with highly deformable wings. By coupling the derived equations of motion with fluid flow, we study the aerodynamic performance of the geometrically nonlinear flexible flapping wing. Through...
Experimental investigation of the effect of chordwise flexibility on the aerodynamics of flapping wings in hovering flight
, Article Journal of Fluids and Structures ; Volume 26, Issue 4 , May , 2010 , Pages 544-558 ; 08899746 (ISSN) ; Ebrahimi, A ; Sharif University of Technology
2010
Abstract
Ornithopters or mechanical birds produce aerodynamic lift and thrust through the flapping motion of their wings. Here, we use an experimental apparatus to investigate the effects of a wing's twisting stiffness on the generated thrust force and the power required at different flapping frequencies. A flapping wing system and an experimental set-up were designed to measure the unsteady aerodynamic and inertial forces, power usage and angular speed of the flapping wing motion. A data acquisition system was set-up to record important data with the appropriate sampling frequency. The aerodynamic performance of the vehicle under hovering (i.e., no wind) conditions was investigated. The lift and...
Application of the adjoint multi-point and the robust optimization of shock control bump for transonic aerofoils and wings
, Article Engineering Optimization ; Volume 48, Issue 11 , 2016 , Pages 1887-1909 ; 0305215X (ISSN) ; Nejati, A ; Chaharlang Kiani, K ; Sharif University of Technology
Taylor and Francis Ltd
Abstract
A shock control bump (SCB) is a flow control method which uses a local small deformation in a flexible wing surface to considerably reduce the strength of shock waves and the resulting wave drag in transonic flows. Most of the reported research is devoted to optimization in a single flow condition. Here, both equally and variably weighted multi-point optimization and a robust adjoint optimization scheme are used to optimize the SCB. The numerical simulation of the turbulent viscous flow and a gradient-based adjoint algorithm are used to find the optimum location and shape of the SCB for two benchmark aerofoils. A multi-point optimization method under a constant-lift-coefficient constraint is...
An efficient method for nonlinear aeroelasticy of slender wings
, Article Nonlinear Dynamics ; Volume 67, Issue 1 , 2012 , Pages 659-681 ; 0924090X (ISSN) ; Sadr, M. H ; Haddadpour, H ; Sharif University of Technology
2012
Abstract
This paper aims the nonlinear aeroelastic analysis of slender wings using a nonlinear structural model coupled with the linear unsteady aerodynamic model. High aspect ratio and flexibility are the specific characteristic of this type of wings. Wing flexibility, coupled with long wingspan can lead to large deflections during normal flight operation of an aircraft; therefore, a wing in vertical/forward-afterward/torsional motion using a third-order form of nonlinear general flexible Euler-Bernoulli beam equations is used for structural modeling. Unsteady linear aerodynamic strip theory based on the Wagner function is used for determination of aerodynamic loading on the wing. Combining these...
Nonlinear aeroelastic response of slender wings based on Wagner function
, Article Thin-Walled Structures ; Volume 46, Issue 11 , 2008 , Pages 1192-1203 ; 02638231 (ISSN) ; Sadr Lahidjani, M. H ; Haddadpour, H ; Sharif University of Technology
2008
Abstract
This paper presents a method for nonlinear aeroelastic analysis of Human Powered Aircraft (HPA) wings. In this type of aircraft there is a long, highly flexible wing. Wing flexibility, coupled with long wing span can lead to large deflections during normal flight operation; therefore, a wing in vertical and torsional motion using the second-order form of nonlinear general flexible Euler-Bernoulli beam equations is used for structural modeling. Unsteady linear aerodynamic theory based on Wagner function is used for determination of aerodynamic loading on the wing. Combining these two types of formulations yields the nonlinear integro-differentials aeroelastic equations. Using the Galerkin's...