Sharif Digital Repository

In the last decade, harvesting energy from renewable phenomena in nature has attracted the attention of many researchers and turned it into a hot research focus. Wind flow around the world is an endless, repeatable and available source of energy. Therefore, harvesting wind energy disrupts the damaging cycle of fossil fuels to nature and fades over time. Therefore, in order to convert the mechanical green energy in the wind into electricity, mechanisms based on aeroelastic instabilities have attracted the attention of researchers. In this research, it is intended to design and build a test platform that is a suitable platform for research and testing on the aeroelastic instability of... 

In this research, with the help of a comprehensive dynamic model, the stability, control, dynamics and twisting of airships with flexible bodies and beams have been investigated. For the first time, the influence of the twisting mode of the body on the dynamic behavior and control of the airship has been investigated by considering the pressure drop inside the body. By obtaining the terms of kinetic energy and the potential of the body and beams, the governing equations of the bird have been extracted and with the help of mass integrals, the velocity of the body and beams has been obtained. The answer to this non-linear dynamic couple problem, due to the existence of two types of dynamic... 

This study is a comprehensive analysis on the nonlinear vibration of a sandwich plate containing magnetorheological (MR) fluid as the core layer. The nonlinear aeroelastic analysis of the structure is also discussed to determine the flutter boundaries. In this study, the numerical Generalized Differential Quadrature (GDQ) method is applied to investigate the free vibration analysis of a sandwich plate with a MR fluid core. The classical thin plate theory (CPT) and the First-order Shear Deformation Theory (FSDT) are assumed for face layers and core layer, respectively. These theories along with Von-Karman kinematic formulations are incorporated to extract governing equations. The equations of... 

In this research, a Reusable Flexible Launch Vehicle (RFLV) design problem is presented by Multi-Disciplinary Design Optimization (MDO) approach in primary design phase. Trajectory, structure, aerodynamic, aeroelasticity and thermal protection system are considered as involved disciplines in design problem. The study purpose will be to obtain an optimal trajectory which meets all the control and structure limitation while the estimating body skin and thermal protection thicknesses base on structural evaluating in re-entry trajectory is in process. The flexible launch vehicle body is considered as a free-free Bernoulli-Euler beam and D’alembert’s principle addresses inertia force in static... 

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... 

In this research, the dynamics, aero-elasticity, and control of an airship with a flexible body hull and fins are investigated. The flexible airship is modeled as a combination of several beams with specific boundary conditions. So that the dynamics and vibration of its body hull and fins can be taken into account regarding the aerodynamic, gravity, aerostatic, and control input forces. The governing equations of motion of the system are derived by using the velocity of an arbitrary point on each component and integration over the component and substituting them into the Euler-Lagrange equations in a body frame. Afterward, the added mass acting on the hull is calculated. Then, a perturbation... 

This study investigates the aeroelastic instability of functionally graded sandwich plate with viscoelastic core in supersonic airflow. The classical plate theory, first order shear deformation theory, Hamilton's principle and linear first-order piston theory have been employed to extract the governing equations of motion of the structure. The Ritz method and State space notation is used to solve the derived equations and identify the instability boundary of the sandwich plate with simply-supported boundary conditions. The derived are solved using a computer program which is validated and verified by comparing the results with available literature. Our attention is focused on analyzing the... 

As the aeronautical design evolves, the optimal solutions tend to employ slenderer and aeroelastic wings. These slender wings could help to increase the flight endurance, by decreasing the fuel consumption. However, as a wing becomes slenderer its structural stiffness decreases. The decrease in the stiffness highlights the structural vibrations and aeroelastic behavior in these wings. Atmospheric turbulences induce vibrations that can cause fatigue and structural failures. A possible solution to decrease these oscillations is to use active vibration control and flutter suppression. Conventional control surfaces on a wing can be used to implement the active vibration control. However, given... 

In this research the attitude control of a flexible launch vehicle using fractional order proportional-integral-derivative controller in the presence of actuators failures is described. Other work done in this study is the investigation of on-line fault detection and diagnosis effects in the attitude control of flexible launch vehicle in the presence of actuator failures. Rigid-elastic equations of motion and assumed modes have been used to simulate dynamics of launch vehicle in the Simulink environment of MATLAB software using two elastic bending modes. The performance of fractional order controller has been compared with conventional proportional-integral-derivative and adaptive augmented... 

In static floating structures such as floating bridges and offshore runways that are in contact with the water surface from the floor and with the open air from the top, three types of interactions occur: the interaction of the structure with air, the interaction of the structure with water and Interaction of air with water. Due to the long length of such structures and approaching their natural frequencies to the standing wave frequencies (seiche frequencies), the analysis of the elastic behavior of the structure alone is not enough, but the structure-air-water interaction must be evaluated simultaneously in a system. Leading research addresses this issue and examines the behavior of an... 

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... 

Study of the structural flexibility of large-scale wind turbine components on aeroelastic performance is important under the existence of critical atmospheric conditions. Prediction and control the critical deformations, identifying maximum local deformation and modeling the forces involved, are required. Aeroelasticity analysis is a suitable method for studying the coupling effects of wind turbine aerodynamics, dynamics and structures. This research has been done by modeling wind turbine components including blades, hub, nacelle and tower, taking into account aerodynamic couplings, dynamics and structures. Considering the large scale of reference wind turbine, nonlinear equations have added... 

This dissertaion deals with the vibration and aeroelasticity analysis of a turbomachinery cascade with Magnetorheological Elastomer (MRE) based sandwich blades. At first, bending vibration of the rotary blades equipped with an MRE core based on the three-layered sandwich beam theory have been studied in the flexural and edgewise directions. Further, the torsional vibration is investigated and the effects of different parameters such as the intensity of the magnetic field, rotating speed and the MRE layer thickness on the natural frequencies and loss factors of the system are studied. On the basis of the modeling obtained for the structural dynamics and based on the Whitehead's unsteady... 

In this research, the effect of application of viscoelastic material with fractional derivatives pattern in aeroelastic stability analysis for a sandwich wing, has been examined. In order to study the wing’s aeroelastic behavior and the effect of inner layer on aeroelastic instability boundaries (fluttering), the wing is modeled as a cantilever sandwich beam with a fractional viscoelastic core. The Wagner approximation is used for applying the unstable aeroelastic loads. To obtain the characteristics and behaviors of the structure some assumptions including non-classical effects, are considered. These non-classical effects are the inner layer shear stress, the axial movements, the wing’s... 

The issue of solid and fluid interaction in horizontal axis wind turbines with diameter of more than 120 meters is one of the most important researching subjects of this type of turbines. This issues needs quick and exact solutions because of the high computational cost of fluid and structural domains.In this research a quick method with acceptable accuracy has been suggested which is based on computational fluid dynamic to examine the aeroelastic behavior of rotor and wind turbine tower. The actuator disc method in two domains of axisymmetric and three-dimensional has been used to compute aerodynamic forces. For this purpose a code has been written in C++ to set down virtual momentum on... 

In order to investigaton of dynamics behavior and determination of the aeroelastic stability of the turbomachine blade. the turbomachine blade is modeled by using the beam model, taking into account all degrees of freedom, the effect of warping, rotation and seting angle. For aerodynamic modeling, the Smith and Whitehead models are used which are valid in subsonic flow. The validity of the derived formulation is confirmed through comparison with those obtained from the finite element software and the available results in the literature. Then, by using the state feedback controller, the effect of sensor and piezoelectric actuator on the vibrations reduction of the structure and increasing the... 

This study considers the flutter analysis rotating blade of a turbo machinery made of magneto rheological elastomer core. The Smith theory is used for modeling the compressible subsonic flow. The classical Hamilton’s principle along with the assume mode method is used to set up the equations of motion. The validity of the derived formulation is confirmed through comparison with those obtained from the finite element software and the available results in the literature. Various parametric studies including the effects of applied magnetic field, core layer thicknesses, rotating speed, setting angle are examined for considered configuration of the rotating blade. The results show that the first... 

A series of algorithms developed for performing aeroelastic topology optimization applying stress constraint on a three dimentional structure of a supersonic wing. The structure modeled using finite element method by three dimentional solid hexahedron elements. Bi-directional evolutionary structural optimization method used for developing optimization algorithms. In order to apply supersonic aerodynamic loading and developing aeroelastic model algorithms, the piston aerodynamic theory utilized. In order to apply static pressure loading, the maximum angle of attack of the wing performance is proposed. Using developed MATLAB code by modeling and meshing wing structure in ABAQUS a software... 

Nowadays Aeroelasticity is one of most important branch of aerospace science. The Aeroelastic analysis and get on aeroelastic safety margin, is one of the major steps that must be taken in flying crafts design. Diverse software have been developed for this purpose. Due to the increasing the demands of use of composite materials in aircraft structures, need to examine the effect of various parameters such as angles and stacking sequence on the aeroelastic instability (flutter and divergence) composite aircraft structures is determined. The analysis of wind turbines as a means of extracting energy from the wind and having a large diameter blades, causing the interference effects of aerodynamic... 

The subject of systemic reliability assessment, allocation and optimization as well as structural reliability (SR) of a two stage solid fuel launch vehicle (LV) is investigated. In this regards, first the LV reliability block diagram is broken-down into appropriate subsystems. Subsequently the total LV system reliability is determined assuming the subsystems reliability. In addition, using a hybrid GA-PSO algorithm optimal subsystems redundancy levels, reliabilities as well their type are determined to simultaneously maximize the total reliability while minimizing the LV cost (weight) as a constraint. While the reliability and cost of subsystems are not precisely known, the total LV...