Sharif Digital Repository

This thesis deals with developing and applying reduced order modeling techniques for fluid and structure interaction problems. First, the basis and formulations of reduced order modeling technique in the function space are reviewed. Then the governing equations of structural dynamics as well as incompressible flow are reviewed and some simplifications are applied. Based on the modal analysis technique along with the finite element model of the structure and the boundary element model for flow field, some reduced order models are represented. The represented models are developed for liquid sloshing in moving and elastic tanks, fluid structure interaction in flexible shells conveying flow,... 

The aeroelastic behavior of wings made of functionally graded materials in supersonic flow is studied. For this purpose the flutter speed is calculated and in the next step the post flutter behavior is investigated. The structural model is based on the classical plate theory and material properties are assumed to be graded in the thickness direction according the power law distribution in terms of the volume fraction of material constituents. The linear piston theory which is modified to include thickness effects is used for supersonic aerodynamic modeling. The nonlinear structural model based on the Von-Karman strains is considered for prediction of the post-flutter behavior of the wing.... 

In this research, an anistropic thin-walled beam composite is used to consider the effects of fiber orientation and lay-up configuration on the aeroelastic stability and response of an aircraft wing. The circum ferentially asymmetric stiffness (CAS) model consists of a group of non-classical effects; such as transverse shear, material anisotropic, warping inhibition, etc. The aerodynamic load has been modeled based on the strip theory and compressible unsteady flow in the finite- state form. In addition, to form the mass, stiffness and damping matrices of non-conservative aeroelastic systems the extended Galerkin’s method (EGM) and the method of separation of variables has been used. After... 

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... 

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... 

One of the classic problems in the aeroelasticity field is panel Fluttr that occurs in supersonic flow. Panels as wing skins, fuselage missile, and so are prone to this phenomenon, which causes fatigue and structures, will be demolished.In many cases, the wall panels and a full tank of fuel, this in this case, the vibration of the fluid-filled panels will be affected. There is clearly fluid into a tank filled with considering the approximation of incompressible fluid dynamics and vibration modes of the panel will change. In this study, a three-dimensional rectangular tank is considered the high walls on the elastic and supersonic flow passes.Fuel density and structural dimensions of Full... 

The present thesis aims at investigating the dynamic interaction of slosh and aeroelasticity in the fuel contained aero vehicles. The main approach in this research is to develop reduced order models for description of the coupled system. In this regard, boundary element method is used to develop slosh dynamic model. Axisymmetric boundary element method with non-symmetric boundary conditions is used to develop slosh dynamic model for axisymmetric containers. Zoning method is used to develop slosh dynamic model for the multi-baffled tanks and based on it, slosh equivalent mechanical model is developed for multi-baffled tanks. Finite element method along with modal technique is used to develop... 

Propulsive efficiency of flapping wings is optimized via a combination of flapping and elastic wing behavior. In this thesis, a complex complete model of flapping air vehicles (FAV) is developed in order to simulate the wing aeroelastic behavior. The resulting model is in the form of a complex set of partial differential equations whose solution is only numerically possible. Using the resulting simulation model, the different flapping behavior of the right and left wings can also be evaluated along with the resulting forces and moments that make the FAV flight realizable. One of the key flight conditions considered in many simulations is that of cruise flight. In order to have a... 

In the present work the stability analysis for the coupled aeroelasticity and fuel sloshing in supersonic wings is represented. The wing and store structure is modeled using the finite element method. The supersonic wing aerodynamic is modeled by the linear piston theory and store aerodynamic is modeled by the semi-stable slender body piston theory. Fuel sloshing in the store with desired geometry is modeled by the boundary element method. The coupled structure, aerodynamic and sloshing governing equations are drawn by using the Galerkin method and reduce order modeling teqnique for them and an effective numerical model was developed that is capable to analyze the stability for... 

Aeroelasticity analysis and prediction of wind turbines sturcture deformations are fundamental parts in their design. Increasing the size of wind turbine blades and development of Mega-watt sized wind turbines have enhanced the importance of these studies. In this study, the aeroelasticity analysis of a wind turbine blade has been done based on flexible multibody dynamics method. For this purpose, the modal approach has been used for modeling blade structure which has been considered as a flexible beam with bending and torsion degrees of freedom. The unsteady vortex lattice method has been used to calculate aerodynamic loads in order to combine with wind turbine blade structure model. Using... 

One can use the vibrational energy available in environment to harvest energy via piezoelectric materials, for various applications and this research field has received growing attention by researchers over the last years. This research motivation is, harvesting electrical energy from a fluttering plate in 2D axial flow via piezoelectric materials. For this purpose, a nonlinear Euler-Bernoulli beam model is used to model structure, an incompressible 2D vortex lattice method is used to model the aerodynamics, and coupled linear piezoelectric electro-mechanical equations is used to model piezoelectric materials. The structure is considered into axial flow, and flow speed gradually increases,... 

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... 

This dissertation presents aeroelastic stability analysis (flutter) pertinent to the complete flexible aircraft based on analytical dynamics, structural dynamics and aerodynamics. The unified formulation is based on fundamental principles and incorporates in a natural manner both rigid body motions of the aircraft as a whole and elastic deformations of the flexible components (fuselage, wing and empennage), as well as the aerodynamic, propulsion and gravity forces. The aircraft motion is described in terms of three translations and three rotations of a reference frame attached to the undeformed fuselage, and acting as aircraft body axes, and elastic displacements of each of the flexible... 

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... 

Aiming to improve the extraction performance of wind energy has led to the noticeable increase of the structural dimensions in the modern wind turbines. The larger blade with more flexibility experiences large structural deformation even under nominal operational loading, so the nonlinear modeling and analysis of these structures have become as important subject of the recent wind turbine researches. In this dissertation, the geometrical exact model of the rotating wind turbine blade under the effects of the tower tip's motion, and also the operational loading comprising the aerodynamic and gravitational loadings is presented. In this way, the geometrical exact beam formulation is developed... 

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... 

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... 

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... 

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... 

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...