A new numerical methodology to examine fluid-structure interaction of a wing/pylon/store system has been developed. The aeroelastic equation of motion of the complete system is solved iteratively in the time domain using a two-entity numerical code comprised of ABAQUS/Standard and the Unsteady-Vortex-Lattice Method. Both codes communicate through an iterative handshake procedure during which displacements and air loads are updated. For each increment in time the force/displacement equilibrium is found in this manner. The wing, pylon, and store data considered in this analysis are based on an F16 configuration that was identified to induce flutter in flight at subsonic speeds. The wing structure is modeled as an elastic plate and pylon and store are rigid bodies. The store body is connected to the pylon through an elastic joint exercising pitch and yaw degrees of freedom. Vortex-Lattice theory featuring closed ring-vortices and continuous vortex shedding to form the wakes is employed to model the aerodynamics of wing, store, and pylon. The methodology was validated against published data demonstrating excellent agreement with documented key phenomena of fluid-structure iteration. The model correctly predicts the effects of the pylon induced lateral flow disruption as well as wing-tip-vortex effects. It can identify the presence of aerodynamic interference between the store, pylon, and wing wakes and examine its significance with respect to the pressure and lift forces on the participating bodies. An elementary flutter study was undertaken to examine the dynamic characteristics of a stiff production pylon at near-critical airspeeds versus those of a soft-in-pitch pylon. The simulation reproduced the stabilizing effect of the stiffness reduction in the pitch motion. This idea is based on the concept of the decoupler pylon, introduced by Reed and Foughner in 1978 and flight tested in the early 1980's. NOTE: (3/07) An updated copy of this ETD was added after there were patron reports of problems with the file. / Ph. D.

The physics of flapping is very important in the design of MAVs. As MAVs cannot have an engine that produces the amount of thrust required for forward flight, and yet be light weight, harnessing thrust and lift from flapping is imperative for its design and development. In this thesis, aerodynamics of pitch and plunge are simulated using a 3-D, free wake, vortex lattice method (VLM), and structural characteristics of the wing are simulated as a membrane supported by a rigid frame. The aerodynamics is validated by comparing the results from the VLM model for constant angle of attack flight, pitching flight and plunging flight with analytical results, existing 2-D VLM and a doublet lattice method. The aeroelasticity is studied by varying parameters affecting the flow as well as parameters affecting the structure. The parametric studies are performed for cases of constant angle of attack, plunge and, pitch and plunge. The response of the aeroelastic model to the changes in the parameters are analyzed and documented. The results show that the aerodynamic loads increase for increased deformation, and vice-versa. For a wing with rigid boundaries supporting a membranous structure with a step change in angle of attack, the membrane oscillates about the steady state deformation and influence the loads. For prescribed oscillations in pitch and plunge, the membrane deformations and loads transition into a periodic steady state. / Master of Science

L’objectif de cette thèse est de contrôler passivement une instabilité dynamique appliquée au flottement d’un profil aéroélastique à l’aide de différents types d’Amortisseurs à Masse Accordés (AMA). Un profil 2D appelé Section Typique est utilisé tout au long de l’étude. En première partie, une étude comparative de trois modèles mathématiques d’interaction fluide/structure appliqués à la Section Typique (Theodorsen, LUVLM et UVLM) met en valeur les forces et faiblesses de chacun. Le banc d’essai aéroélastique en soufflerie, utilisé par la suite, est présenté puis identifié avec et sans vent (GVT). En deuxième partie, les calculs des vitesses critiques de Divergence, d’Inversion des Gouvernes et de Flottement sont automatisés avec le modèle Theodorsen afin de réaliser une étude paramétrique du banc d’essai et mettre en lumière les variables de conception les plus influentes. L’analyse modale présente différentes bifurcations liées au changement soudain du mode instable. Ensuite, le même algorithme est utilisé afin d’analyser la suppression du flottement à l’aide de trois géométries d’AMAs linéaires. La dernière partie présente l’étude expérimentale et numérique d’un AMA non linéaire de type Nonlinear Energy Sink (NES). La singularité de cette configuration est d’utiliser le volet en tant qu’amortisseur et ainsi, ne pas ajouter de masse (FSI-VA). En soufflerie, six comportements non linéaires sous-critiques (en deçà de la vitesse de flottement dans la configuration linéaire) sont observés, identifiés et analysés : cinq Cycles Limites d’Oscillations (LCO) et un battement non linéaire chaotique. / The aim of this thesis is to passively control a dynamic instability applied to an aeroelastic profile’s flutter using different types of Tuned Mass Dampers (TMD). A 2D profile called Typical Section is used throughout the study. In the first part, a comparative study of three mathematical models of fluid-structure interaction applied to the Typical Section (Theodorsen, LUVLM and UVLM) highlights the strengths and weaknesses of each code. The aeroelastic test bench, used subsequently, is presented and identified with and without wind (Ground Vibration Test, GVT). In the second part, critical velocities computations (Divergence, Control Surface Reversal and flutter) are automated while using the Theodorsen model in order to carry out the test bench parametrical study to highlight most influential variables. The modal analysis presents different bifurcations linked to the sudden change of the unstable mode. The last part presents the experimental and numerical studies of a nonlinear TMD called Nonlinear Energy Sink (NES). The uniqueness of this configuration consists in recycling flap’s vibrations as a flutter damper and thus, get a zero added mass. A nonlinear restoring force can be achieved by a highly nonlinear mechanism. The nonlinear structural behavior is derived analyticaly and is in good agreement with experimental torsion tests. In the wind tunnel, six subcritical nonlinear behaviors (below the flutter velocity in the linear configuration case) are observed, identified and then analyzed : five Limit Cycle Oscillations (LCO) and a chaotic nonlinear beating.

This dissertation considers an American put option written on a single underlying which does not pay dividends, for which no closed form solution exists. As a conse- quence, numerical techniques have been developed to estimate the value of the Amer- ican put option. These include analytical approximations, tree or lattice methods, ¯nite di®erence methods, Monte Carlo simulation and integral representations. We ¯rst present the mathematical descriptions underlying these numerical techniques. We then provide an examination of a selection of algorithms from each technique, including implementation details, possible enhancements and a description of the convergence behaviour. Finally, we compare the estimates and the execution times of each of the algorithms considered.

Um modelo numérico para simulação da resposta aeroelástica de asas fixas é proposto. A estratégia adotada no trabalho é a de tratar a aerodinâmica e a dinâmica estrutural separadamente e então acoplá-las na equação de movimento. A caracterização dinâmica de uma asa protótipo é feita pelo método dos elementos finitos e a equação de movimento é escrita em função das coordenadas modais. O carregamento aerodinâmico não-estacionário é determinado pelo método de malha de vórtices. A troca de informações entre as malhas estrutural e aerodinâmica é feita através do método de interpolação por splines de superfície e a equação de movimento é resolvida iterativamente no domínio do tempo, utilizando-se um método preditor-corretor. As teorias de aerodinâmica, dinâmica estrutural e do acoplamento entre elas são apresentadas separadamente, juntamente com os respectivos resultados obtidos. A resposta aeroelástica da asa protótipo é representada por curvas de deslocamentos modais em função do tempo para várias velocidades de vôo e a ocorrência de flutter é verificada quando estas curvas divergem (i.e. as amplitudes aumentam progressivamente). Transformadas de Fourier destas curvas mostram o acoplamento de freqüências característico do fenômeno de flutter. / A numerical model for the simulation of the aeroelastic response of fixed wings is proposed. The methodology used in the work is to treat the aerodynamic and the structural dynamics separately and then couple them in the equation of motion. The dynamic characterization of a prototype wing is done by the finite element method and the equation of motion is written in modal coordinates. The unsteady aerodynamic loads are predicted using the vortex lattice method. The exchange of information between the aerodynamic and structural meshes is done by the surface splines interpolation scheme, and the equation of motion is solved interactively in the time domain, employing a predictor-corrector method. The aerodynamic and structural dynamics theories, and the methodology to couple them, are described separately, together with the corresponding obtained results. The aeroelastic response of the prototype wing is represented by time histories of the modal coordinates for different airspeeds, and the flutter occurrence is verified when the time histories diverge (i.e. the amplitudes keep growing). Fast Fourier Transforms of these time histories show the coupling of frequencies, typical of the flutter phenomenon.

<p>Theoretical and experimental studies are conducted in the field of aeroelasticity. Specifically, two rectangular and one cropped delta wings with a hole are analyzed in this dissertation for their aeroelastic behavior.</p><p>The plate-like wings are modeled using the finite element method for the structural theory. Each wing is assumed to behave as a linearly elastic and isotropic, thin plate. These assumptions are those of small-deflection theory of bending which states that the plane sections initially normal to the midsurface remain plane and normal to that surface after bending. The wings are modeled in low speed flows according to potential flow theory. The potential flow is governed by the aerodynamic potential equation, a linear partial differential equation. The aerodynamic potential equation is solved using a distribution of doublets that relates pressure to downwash in the doublet lattice method. A hole in a wing-like structure is independently investigated theoretically and experimentally for its structural and aerodynamic behavior.</p><p>The aeroelastic model couples the structural and aerodynamic models using Lagrange's equations. The flutter boundary is predicted using the V-g method. Linear theoretical models are capable of predicting the critical flutter velocity and frequency as verified by wind tunnel tests. Along with flutter prediction, a brief survey on gust response and the addition of stores(missile or fuel tanks) are examined.</p> / Dissertation

<p>This thesis presents the work done to implement new computational tools and methods dedicated to aircraft conceptual design sizing and optimization. These tools have been exercised on different aircraft concepts in order to validate them and assess their relevance and applicability to practical cases.First, a geometry construction protocol has been developed. It is indeed essential to have a geometry description that supports the derivation of all discretizations and idealizations used by the different analysis modules (aerodynamics, weights and balance, stability and control, etc.) for which an aircraft concept is evaluated. The geometry should also be intuitive to the user, general enough to describe a wide array of morphologies and suitable for optimization. All these conditions are fulfilled by an appropriate parameterization of the geometry. In addition, a tool named CADac (Computer Aided Design aircraft) has been created in order to produce automatically a closed and consistent CAD solid model of the designs under study. The produced CAD model is easily meshable and therefore high-fidelity Computational Fluid Dynamics (CFD) computations can be performed effortlessly without need for tedious and time-consuming post-CAD geometry repair.Second, an unsteady vortex-lattice method based on TORNADO has been implemented in order to enlarge to scope of flight conditions that can be analyzed. It has been validated satisfactorily for the sudden acceleration of a flat plate as well as for the static and dynamic derivatives of the Saab 105/SK 60.Finally, a methodology has been developed to compute quickly in a semi-empirical way the buffet envelope of new aircraft geometries at the conceptual stage. The parameters that demonstrate functional sensitivity to buffet onset have been identified and their relative effect quantified. The method uses a combination of simple sweep theory and fractional change theory as well as the buffet onset of a seed aircraft or a provided generic buffet onset to estimate the buffet envelope of any target geometry. The method proves to be flexible and robust enough to predict within mainly 5% (and in any case 9%) the buffet onset for a wide variety of aircrafts, from regional turboprop to long-haul wide body or high-speed business jets.This work was done within the 6^th European framework project SimSAC (Simulating Stability And Control) whose task is to create a multidisciplinary simulation environment named CEASIOM (Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods), oriented toward stability and control and specially suited for aircraft conceptual design sizing and optimization.</p> / SimSAC

The performance of a horizontal axis marine current turbine is predicted by three numerical methods, vortex lattice method MPUF-3A, boundary element method PROPCAV and a commercial RANS solver FLUENT. The predictions are compared with the experimental measurements for the same turbine model. A fully unsteady wake alignment is utilized in order to model the realistic wake geometry of the turbine. A lifting line theory based method is developed to produce the optimum circulation distribution for turbines and propellers and a lifting line theory based database searching method is used to achieve the optimum circulation distribution for tidal turbines. A nonlinear optimization method (CAVOPT-3D) and another database-searching design method (CAVOPT-BASE) are utilized to design the blades of marine current turbines and marine propellers. A design procedure for the tidal turbine is proposed by using the developed methods successively. Finally, an interactive viscous/potential flow method is utilized to analyze the effect of nonuniform inflow on the performance of tidal turbines. / text

Um modelo numérico para simulação da resposta aeroelástica de asas fixas é proposto. A estratégia adotada no trabalho é a de tratar a aerodinâmica e a dinâmica estrutural separadamente e então acoplá-las na equação de movimento. A caracterização dinâmica de uma asa protótipo é feita pelo método dos elementos finitos e a equação de movimento é escrita em função das coordenadas modais. O carregamento aerodinâmico não-estacionário é determinado pelo método de malha de vórtices. A troca de informações entre as malhas estrutural e aerodinâmica é feita através do método de interpolação por splines de superfície e a equação de movimento é resolvida iterativamente no domínio do tempo, utilizando-se um método preditor-corretor. As teorias de aerodinâmica, dinâmica estrutural e do acoplamento entre elas são apresentadas separadamente, juntamente com os respectivos resultados obtidos. A resposta aeroelástica da asa protótipo é representada por curvas de deslocamentos modais em função do tempo para várias velocidades de vôo e a ocorrência de flutter é verificada quando estas curvas divergem (i.e. as amplitudes aumentam progressivamente). Transformadas de Fourier destas curvas mostram o acoplamento de freqüências característico do fenômeno de flutter. / A numerical model for the simulation of the aeroelastic response of fixed wings is proposed. The methodology used in the work is to treat the aerodynamic and the structural dynamics separately and then couple them in the equation of motion. The dynamic characterization of a prototype wing is done by the finite element method and the equation of motion is written in modal coordinates. The unsteady aerodynamic loads are predicted using the vortex lattice method. The exchange of information between the aerodynamic and structural meshes is done by the surface splines interpolation scheme, and the equation of motion is solved interactively in the time domain, employing a predictor-corrector method. The aerodynamic and structural dynamics theories, and the methodology to couple them, are described separately, together with the corresponding obtained results. The aeroelastic response of the prototype wing is represented by time histories of the modal coordinates for different airspeeds, and the flutter occurrence is verified when the time histories diverge (i.e. the amplitudes keep growing). Fast Fourier Transforms of these time histories show the coupling of frequencies, typical of the flutter phenomenon.

This thesis presents the work done to implement new computational tools and methods dedicated to aircraft conceptual design sizing and optimization. These tools have been exercised on different aircraft concepts in order to validate them and assess their relevance and applicability to practical cases. First, a geometry construction protocol has been developed. It is indeed essential to have a geometry description that supports the derivation of all discretizations and idealizations used by the different analysis modules (aerodynamics, weights and balance, stability and control, etc.) for which an aircraft concept is evaluated. The geometry should also be intuitive to the user, general enough to describe a wide array of morphologies and suitable for optimization. All these conditions are fulfilled by an appropriate parameterization of the geometry. In addition, a tool named CADac (Computer Aided Design aircraft) has been created in order to produce automatically a closed and consistent CAD solid model of the designs under study. The produced CAD model is easily meshable and therefore high-fidelity Computational Fluid Dynamics (CFD) computations can be performed effortlessly without need for tedious and time-consuming post-CAD geometry repair.Second, an unsteady vortex-lattice method based on TORNADO has been implemented in order to enlarge to scope of flight conditions that can be analyzed. It has been validated satisfactorily for the sudden acceleration of a flat plate as well as for the static and dynamic derivatives of the Saab 105/SK 60.Finally, a methodology has been developed to compute quickly in a semi-empirical way the buffet envelope of new aircraft geometries at the conceptual stage. The parameters that demonstrate functional sensitivity to buffet onset have been identified and their relative effect quantified. The method uses a combination of simple sweep theory and fractional change theory as well as the buffet onset of a seed aircraft or a provided generic buffet onset to estimate the buffet envelope of any target geometry. The method proves to be flexible and robust enough to predict within mainly 5% (and in any case 9%) the buffet onset for a wide variety of aircrafts, from regional turboprop to long-haul wide body or high-speed business jets.This work was done within the 6th European framework project SimSAC (Simulating Stability And Control) whose task is to create a multidisciplinary simulation environment named CEASIOM (Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods), oriented toward stability and control and specially suited for aircraft conceptual design sizing and optimization. / QC 20101104 / SimSAC