Showing papers on "Vortex lattice method published in 2011"

Flexible flapping systems: computational investigations into fluid-structure interactions

Abstract: In the present work, the authors examine two computational approaches that can be used to study flexible flapping systems. For illustration, a fully coupled interaction of a fluid system with a flapping profile performing harmonic flapping kinematics is studied. In one approach, the fluid model is based on the Navier-Stokes equations for viscous incompressible flow, where all spatio-temporal scales are directly resolved by means of Direct Numerical Simulations (DNS). In the other approach, the fluid model is an inviscid, potential flow model, based on the unsteady vortex lattice method (UVLM). In the UVLM model, the focus is on vortex structures and the fluid dynamics is treated as a vortex kinematics problem, whereas with the DNS model, one is able to form a more detailed picture of the flapping physics. The UVLM based approach, although coarse from a modeling standpoint, is computationally inexpensive compared to the DNS based approach. This comparative study is motivated by the hypothesis that flapping related phenomena are primarily determined by vortex interactions and viscous effects play a secondary role, which could mean that a UVLM based approach could be suitable for design purposes and/or used as a predictive tool. In most of the cases studied, the UVLM based approach produces a good approximation. Apart from aerodynamic load comparisons, features of the system dynamics generated by using the two computational approaches are also compared. The authors also discuss limitations of both approaches.

Velocity interference in the rear rotor of a counter-rotating wind turbine

Abstract: A counter-rotating wind turbine having two rotors rotating in opposite directions on the same axis is proposed to improve the aerodynamic performance of a wind turbine. In order to predict the aerodynamic performance of the counter-rotating wind turbine, the inflow interference in its rear rotor by the wake of the front rotor needs to be considered because the rear rotor operates inside the wake of the front rotor. In the previous research, the rear rotor was assumed to operate inside the fully developed stream tube of the front rotor to define the inflow condition on the rear rotor. In this study, to consider simultaneously the aerodynamic interaction between the two rotors of the counter-rotating wind turbine without any assumption on the inflow velocity of the rear rotor, an aerodynamic analysis of the counter-rotating wind turbine was carried out by using a free-wake vortex lattice method. The power coefficient and the wake geometry of the counter-rotating wind turbine were compared with those of a single rotor wind turbine, and the induction factors on the rear rotor were compared with that from the BEMT, assuming that the rear rotor operated inside the fully developed stream tube of the front rotor.

Optimal Structural Topology of a Platelike Wing for Subsonic Aeroelastic Stability

Abstract: This work discusses the construction of a Pareto trade-off curve between the flight speed at which a plate-like wing encounters an aeroelastic stability, and the weight of that wing. The thickness of each finite element is utilized as a design variable in order to locate the optimal topological reinforcement as a function of the desired location along the Pareto front, as well as the planform of the wing. Three main challenges are addressed. First, the destabilizing flight speed must be located in an accurate and efficient manner. Secondly, the derivative of the flight speed with respect to a large number of thickness design variables must be computed analytically. Finally, the gradient-based optimization must contend with a discontinuous switch in the critical aeroelastic mode, slowing convergence.

Influence of blade-tower interaction in upwind-type horizontal axis wind turbines on aerodynamics

Abstract: The blade-tower interaction of upwind horizontal axis wind turbines has become important to aerodynamic loading as the systems become larger. However, there are not enough studies describing these phenomena. To investigate this interaction, we performed numerical simulations for uniform, yawed, wind shear flow conditions, and various tower cases using the nonlinear vortex correction method with time-marching free wake. At 5 m/s, the change in the normal force coefficient is approximately 10% of the average. The blade root region has a larger azimuth range of the interaction and a bigger change in aerodynamic loading. The blade-tower interaction decreases as the yaw error and wind shear exponent increases. The interaction due to tower radius variations is higher than that due to tower clearance variations. With regard to stochastic load, the blade-tower interaction may affect the total fatigue load at low wind speed and in a more unstable atmospheric condition.

Development of a Solar Electric Powered UAV for Long Endurance Flight

Abstract: The development of a solar electric powered UAV (Unmanned Aerial Vehicle) is systematically introduced in this paper. The purpose of the project is to prove the feasibility of some crucial engineering techniques for future full-scale high altitude solar powered UAVs. The solar electric powered UAV adopted a normal configuration of a sailplane with wing of high aspect ratio, slender fuselage, and a tail boom. Aerodynamic geometry and longitudinal trim and stability performances were designed via lifting line theory, and verified using AVL code based on vortex lattice method. Composite and balsa combined structure was designed for the purpose of light weight and rigidness. Carbon-balsa-carbon laminated structure was used for the D-box of the wing and fuselage, which gave adequate strength and rigidness to the wing to carry solar array. Fragile photovoltaic cells were bended and mounted onto the surface of the wing, and would be working cooperatively with lithium-polymer secondary battery to drive the propulsion system. A miniature onboard power management device was developed to adjust and monitor the output power of PV cells and secondary battery. A set of ground tests and flight tests were carried out, the aerodynamic performance, power supply ability of solar array, function and efficiency of the power management device were all demonstrated and validated. The test results showed that the efficiency of the power management device was greater than 85%, the input power requirement for straight and level flight was less than 80 W, and the minimum solar radiation sufficient to support straight and level flight solely was 650 W/m 2 . All of the design objectives had been achieved.

Vortex Lattice Method Coupled with Advanced One-Dimensional Structural Models

Abstract: This work couples a Vortex Lattice Method, VLM, to a refined one-dimensional struc- tural model based on Carrera Unified Formulation, CUF Airfoil in-plane deformation and warping are introduced by enriching the displacement field over the cross-section of the wing Linear to fourth-order expansions are adopted and classical beam theories (Euler-Bernoulli and Timoshenko) are obtained as particular cases The VLM aero- dynamic theory is coupled via an appropriate adaptation of the Infinite Plate Spline method to the structural finite element model A number of wing configurations (by varying aspect ratio, airfoil geometry, dihedral, and sweep angle) and load cases are analyzed to assess both the calculation of aerodynamic loadings and the influence of in-plane airfoil deformation to the static response of the wing Comparison with shell results of commercial software such as MSC Nastran, which is taken as reference so- lution, is carried out and discussed The importance of higher-order models for an accurate evaluation of local and global response of aircraft wings is shown

A method for optimum cavitating ship propellers

Abstract: A practical design method was applied to obtain optimum cavitating ship propellers by combining a vortex lattice lifting line method (propeller design program) and a lifting surface method (propeller analysis program). The optimum circulation distribution that gives the maximum lift-to-torque ratio was computed for given thrust and given chord lengths along the radius of the propeller by a vortex lattice solution to the lifting line problem. The section details of the blades, such as pitch-to-diameter ratio and camber ratio, were then found to obtain the desired (optimal) circulation distribution automatically by a lifting surface method. In order to get the optimum circulation distribution, the radius of the blades was divided into a number of panels extending from hub to tip. The radial distribution of bound circulation could be computed by a set of vortex elements that have constant strengths. A discrete trailing free vortex line was shed at each of the panel boundaries with strength equal to the difference in strengths of the adjacent bound vortices. The vortex system was built from a set of horseshoe vortex elements, each consisting of a bound vortex segment of constant strengths and 2 free vortex lines of constant strengths. An algebraic equation system could be formed by using these vortex systems. Once this equation system for unknown vortex strengths was solved with a specified thrust, the optimum circulation distribution and the forces could be computed by the Betz-Lerbs method. When the radial distribution of optimum circulation and chord length were reached, the lifting surface method could be applied to determine the blade pitch and camber in order to produce the desired circulation automatically. The lifting surface method also accounts for cavitation, which is an avoidable physical phenomenon on the blades. The cavity effects in the present method were represented by using cavity sources and cavitating velocities, which were evaluated on the blade surface beneath the cavity. The practical design technique was applied both to noncavitating and cavitating DTMB 4119 and DTMB 4381 propellers, for which the hydrodynamic characteristics are given in the literature, and the results were compared with those given in the literature. A very good level of satisfaction was obtained for practical applications.

A practical technique for improvement of open water propeller performance

Abstract: A practical technique for the improvement of open water propeller performance has been described by using a vortex lattice lifting line method together with a lifting surface method. First, the optimum circulation distribution, giving the maximum thrust–torque ratio, has been computed along the radius of the propeller for given thrust and chord lengths, by adopting a vortex lattice solution to the lifting line problem. Then, by using the lifting surface method, the blade sectional properties such as pitch-to-diameter ratio and camber ratio, have been calculated for obtaining the desired circulation distribution. The effects of skew and rake on propeller performance have been ignored. The blades have been discretized by a number of panels extending from hub to tip. The radial distribution of bound circulation can be computed by a set of vortex elements having constant strengths. Discrete trailing free vortex lines are shed at each panel boundary, and their strengths are equal to the differences in strength of the adjacent bound vortices. The vortex system has been built from a set of horseshoe vortex elements, and they consist of a bound vortex segment and two free vortex lines of constant strengths. Each set of horseshoe vortex elements induces an axial and tangential velocity at a specified control point on the blades. An algebraic equation system can be formed by using the influencial coefficients. Once this equation system has been solved for unknown vortex strengths and specified thrust, the optimum circulation distribution and the forces can be computed by using Betz–Lerbs method. When the radial distributions of optimum circulation (loading) and chord lengths have been reached, the lifting surface method can be applied to determine the blade pitch and camber distribution. DTMB 4119 and DTMB 4381 propellers have been adopted for calculations and their hydrodynamic characteristics have been found in their open literature. A very good comparison has been obtained between the results of this practical technique and the experimental measurements.

A Framework for Constrained Control Allocation Using CFD-based Tabular Data

Abstract: This paper describes a framework for control allocation problem using Computational Fluid Dynamics (CFD) aerodata, which is represented by a multidimensional array of dimensionless coefficients of aerodynamic forces and moments, stored as a function of the state vector and control-surface deflections. The challenges addressed are, first, the control surface treatment for the automated generation of aerodata using CFD and, second, sampling and data fusion to allow the timely calculation of large data tables. In this framework, the generation of aerodynamic tables is described based on an efficient sampling/data fusion approach. Also, the treatment of aerodynamics of control surfaces is being addressed for three flow solvers: TORNADO, a vortex-lattice method, and two CFD codes, EDGE from the Swedis Defence Agency and PMB from the University of Liverpool. In TORNADO, the vortex points located at the trailing edge of the flaps are rotated around the hinge line to simulate the deflected surfaces. The transpiration boundary conditions approach is used for modeling moving flaps in EDGE, whereas, the surface deflection is achieved using mode shapes in PMB. The test cases used to illustrate the approaches is the Ranger 2000 fighter trainer and a reduced geometry description of Boeing 747-100. Data tables are then generated for the state vector and multiple control surface deflections. The look-up table aerodata are then used to resolve the control allocation problem under the constraint that each surface has an upper and lower limit of deflection angle.

Propeller Optimisation Considering Sheet Cavitation and Hull Interaction

Abstract: This paper presents an optimisation of a propeller blade with the propeller operating in behind conditions and considering sheet cavitation A genetic optimisation algorithm is used with multiple objectives considered: the efficiency is maximized while the propeller induced pressure pulses are minimized The blade design is constrained surveying cavity occurrence predicted from a vortex lattice method In this investigation the effect of the propeller on the flow field around the stern of the ship is taken into account by an iterative update of the effective wake, computed using a zonal approach for the hull flow simulation The chosen optimal propeller display reduced pressure pulses and cavitation extent while maintaining the efficiency of the original design

Development of an aeroelastic analysis tool for structural sizing of high-lift devices during preliminary design

Abstract: The design of complex aircraft elements such as high-lift devices has large influence on the performance of modern transport airplanes. At the cost of increased wing weight, these devices are included in the wing to ensure safe takeoff and landing. In order to meet sustainability challenges on future air transportation systems, high-lift devices need to be designed as efficiently as possible. Therefore, multidisciplinary design considerations should already start in preliminary design phase. Up to now the focus of high-lift flow-physics research has been mainly on the creation of high-fidelity aerodynamic analysis methods which are not applicable to early aircraft design stages. The increase in computational power in the last decade allows both a shift of design methodologies from empirical to computational methods and a more extensive incorporation of disciplines other than aerodynamics. The goal of this thesis is to present an initial solution to the requirement for improved high-lift system representations on preliminary design level. Structural and aerodynamic disciplines are jointly considered in the developed high-lift system analysis tool. First, a literature research is conducted considering high-lift device characteristics, parametric modelling techniques and possible aerodynamic calculation methods. Herewith a theoretical basis for development of the analysis tool is obtained. Based on the outcomes of an existing structural model generator, a link is established to a low-fidelity aerodynamic vortex-lattice calculation method. Obtained wing loads are thereafter applied at the structural wing representation to acquire stress and displacement distributions. Knowing these, an aeroelastic coupling method is established and extended with a structural sizing routine. Aerodynamic results are validated using existing data of the Fokker-100 wing. Finally, an application of the routine is shown by performing initial structural sizing of a forward-swept wing including a trailing edge flap. The aeroelastic analysis tool developed during this thesis provides a solid basis for enhancement of the understanding of interconnections and sensitivities between the aerodynamic and structural disciplines involved in preliminary high-lift device design. Although the initial results of the analysis tool are quite promising, extension of the aerodynamic analysis method, as well as incorporation of additional modelling capabilities are required for the methodology to become generally applicable.

A comparison of computational models for fluid-structure interaction studies of flexible flapping wing systems

Abstract: In this article, the authors examine two computational approaches that can be used to study the motions of flexible flapping systems. For illustration, a fully coupled interaction of a fluid system with a flapping profile performing harmonic flapping kinematics is studied. In one approach, the fluid model is based on the Navier-Stokes equations for viscous incompressible flow, where all spatio-temporal scales are directly resolved by means of Direct Numerical Simulations (DNS). In the other approach, the fluid model is an inviscid, potential flow model, based on the unsteady vortex lattice method (UVLM). In the UVLM model, the focus is on vortex structures and the fluid dynamics is treated as a problem of vortex kinematics, whereas with the DNS model, the focus is on forming a detailed picture of the flapping physics. The UVLM based approach, although coarse from a modeling standpoint, is computationally inexpensive compared to the DNS based approach. This comparative study is motivated by the hypothesis that flapping related phenomena are primarily determined by vortex interactions and viscous eects play a secondary role, which could mean that a UVLM based approach could be suitable for design purposes and/or constructing a predictive tool. In most of the cases studied in this work, the UVLM based approach produces a good approximation for CL/CD. Apart from comparisons of the aerodynamic loads, comparisons are also made of the features of the system dynamics generated by using the two computational approaches. Limitations of both approaches are also discussed.

Unsteady Subsonic Aerodynamic Characteristics of Wing in Fold Motion

Abstract: Aerodynamic characteristics of a wing during fold motion were investigated in order to understand how variations or changes in such characteristics increase aircraft performance. Numerical simulations were conducted, and the results were obtained using the unsteady vortex lattice method to estimate the lift, drag and the moment coefficient in subsonic flow during fold motion. Parameters such as the fold angle and the fold angular velocity were summarized in detail. Generally, the lift and pitching moment coefficients decreased as the angle increased. In contrast, the coefficients increased as the angular velocity increased.

Numerical And Experimental Studies On Wing In Ground Effect

Abstract: Numerical and experimental studies were performed to investigate the aerodynamic performance of a thin wing in close vicinity to the ground. The vortex lattice method (VLM) was utilized to simulate the wing in ground (WIG) effect, which included freely deforming wake elements. The numerical results acquired through the VLM were compared to the experimental results. The experiment entailed varying the ground clearance using the DHMTU (Department of Hydromechanics of the Marine Technical University of Saint Petersburg) wing and the WIG craft model in the wind tunnel. The aero-dynamic influence of the design parameters, such as angles of attack, aspect ratios, taper ratios, and sweep angles were studied and compared between the numerical and experimental results associated with the WIG craft. Both numerical and experimental results suggested that the endplate augments the WIG effect for a small ground clearance. In addition, the vortex lattice method simulated the wake deformation following the wing in the influence of the ground effect.

Unsteady Aerodynamic Vortex Lattice of Moving Aircraft

Abstract: It is aim of this thesis to develop a potential ow solver for unsteady aerodynamics in MATLAB environment. In order to achieve this target a vortex lattice method based has been developed. The vali ...

Flexible Aircraft Modelling for Flight Loads Analysis of Wake Vortex Encounters

Abstract: This report describes the development of an integral simulation model for flexible aircraft and its application to the flight loads analysis of wake vortex encounters of a large transport aircraft. The aerodynamic model consists of a databank containing the steady aerodynamic loading oft the quasi-flexible aircraft combined with an unsteady vortex lattice method for lifting surfaces and bodies. To improve accuracy and computational performance, a correction method based on steady reference data and an order reduction method are introduced. Aeroelastic coupling of the aeroelastic model to the structural model is achieved by a method based on finite interpolation beam elements. A parameterized wake vortex encounter is used to determine the loads-critical encounter type and to illustrate the impact of aircraft modeling on the obtained loads.

A discrete-time state-space model with wake interference for stability analysis of flexible aircraft

Abstract: Keywords. exible aircraft, linear stability, state-space, ight dynamics Abstract. This paper investigates the coupled aeroelastic and ight dynamics stabil- ity of exible lightweight aircraft. The aerodynamics are modelled by the discrete-time unsteady vortex lattice method, which can capture the large deformations of the lifting surfaces, and includes 3-D eects and in-plane motions. A geometrically-exact compos- ite beam formulation is used to model the nonlinear exible-body dynamics, including rigid-body motions, and the equations are accommodated to discrete-time formulation. The governing equations are linearised around an equilibrium conguration, which can be highly deformed, performing a small perturbation analysis and assuming a frozen aero- dynamic geometry. The resulting framework is a monolithic discrete-time state-space formulation, which provides a powerful tool for the stability boundary prediction of a exible vehicle through a direct generalized eigenvalue analysis. It oers increased delity as compared to traditional tools, and at very low computational cost. As a suitable test case to illustrate the capabilities of this approach, the utter of a T-tail is examined. In addition, previous open-loop results are extended in order to asses wake interference eects on exible aircraft dynamics.

Aerodynamics Study of Fixed-Wing MAV: Wind Tunnel and Flight Test

Abstract: Obtaining accurate aerodynamic characteristics of in-flight Micro Air Vehicles (MAVs) was viewed as difficult, due to the nature of very low Reynolds number, 3D complex flow, and strong influence from propulsion slipstream. This paper presents the study of the tailless, fixed-wing MAV, KuMAV-001, performed at Kasetsart University. The team investigated different analysis and testing methods to determine the aerodynamics characteristics of this MAV. The Vortex Lattice Method was introduced in the conceptual design phase and helped with the evaluation of the 3D effects for winglet configurations. The wind tunnel tests with main wing and fully configured MAV were conducted for powered and unpowered models. The influence of propulsion-induced flows on CL, CD, and CM(cg) was investigated during the wind tunnel testing. Verification of the performance results are to be completed with flight test data in the future.

Numerical methods for the prediction of unsteady performance of marine propellers and current turbines

Abstract: In this paper, the unsteady hydrodynamic analysis of marine propellers and horizontal-axis tidal current turbines is performed by using a vortex lattice method (MPUF-3A) and a boundary element method (PROPCAV). A fully unsteady wake alignment algorithm is implemented into MPUF-3A to satisfy the force-free condition on the propeller and turbine wake surfaces. It was found that the position of the trailing wake is very important in predicting the performance of propellers or turbines in steady or unsteady flow. The effects of a nonlinear interaction between uniform inflow and propeller/turbine blades have been taken into account by using a hybrid viscous/potential flow method, which couples the potential flow solver (PROPCAV/MPUF3A) for the unsteady analysis of the propeller/turbine and a viscous flow solver for the prediction of the viscous flow field around them. The present method is then applied to predict unsteady hydrodynamic performance of a propeller and a horizontal-axis tidal current turbine. The predicted unsteady forces of a propeller subject to an inclined inflow are compared with those from experiment. The hydrodynamic performance of tidal turbine in yawed flow for various yaw angles is investigated. The numerical results are compared with existing experimental data.

Study on longitudinal maneuverability and stability of folding wing morphing aircraft

Abstract: A morphing aircraft could enhance its behavior and performance by varying its state. In this paper,a kind of tailless folding wing morphing aircraft research model was built. Based on this model, the change of folding wing longitudinal static stability in wing folding process was calculated by using the Vortex Lattice Method (VLM). Through aircraft longitudinal disturbulance equations, the states of wing folded and unfolded of short period mode and phugoid mode were obtained, and then their longitudinal dynamic stabilities were discussed. Integrating the estimations of the engineering and wind tunnel test method, the variation of moment coefficient, elevator control derivatives and the elevator trimangle in wing folding process of the whole aircraftwas calculated. The analysis results and the verification aircraft fly test showthat the longitudinal controllability has some problems when the wing is folded. Against these problems, improvement measures were proposed.

와류격자법에 의한 프로펠러 성능추정 향상을 위한 제안

Abstract: Current trends in propeller design have led to the need for extremely complex blade shapes, Which place great demands on the accuracy of design and analysis methods. This paper presents a new proposal for improving the prediction of propeller performance with a vortex lattice method using the lifting surface theory. The paper presents a review of the theory and a description of the numerical methods employed. For 8 different propellers, the open water characteristics are calculated and compared with experimental data. The results are in good agreement in the region of a high advanced velocity, but there are differences in the other case. We have corrected the parameters for the trailing wake modeling in this paper, and repeated the calculation. The new calculation results are more in agreement with the experimental data.

Aero-structural wing analysis using a vortex, lattice method coupled with an equivalent plate model

Abstract: The present work describes the integration of a non-linear Vortex Lattice Method (VLM) aerodynamic solver and an Equivalent Plate Model (EPM) structural solver, culminating in an Aero-Structural tool capable of analyzing wings. The aerodynamic and structural tools used in the Aero-Structural solver are described and validated, using experimental and numerical data. The aerodynamic model is expanded with the decambering approach, in order to allow for non-linear wing characteristics to be computed. This solver showed good agreement with experimental data both in linear and in non-linear regimes. The structural solver revealed good agreement with Finite-Element calculations, in both static load deformation and modal analysis. After describing and validating the two disciplines, the coupling between aerodynamic and structural solvers is described. A rectangular wing composed of skins, spars and ribs is analyzed using the present Aero-Structural solver. An experimental validation of the program developed is carried out. To accomplish this, a rectangular wing made with aluminum and PVC foam is built and tested in a wind tunnel. To measure wing deformations under aerodynamic loading, an in-house fully automated measurement system was developed using a laser measuring sensor and linear-guides actuated by stepper motors. The results showed a general good agreement between the deformation calculated with the numerical model and the data collected from wind tunnel testing. Some sources of experimental errors are identified and some enhancements are proposed.

Aerodynamic unstable critical wind velocity for three-dimensional open cable-membrane structures

Abstract: The aerodynamic unstable critical wind velocity for three-dimensional open cable-membrane structures is investigated. The geometric nonlinearity is introduced into the dynamic equilibrium equations of structures. The disturbances on the structural surface caused by the air flow are simulated by a vortex layer with infinite thickness in the structures. The unsteady Bernoulli equation and the circulation theorem are applied in order to express the aerodynamic pressure as the function of the vortex density. The vortex density is then obtained with the vortex lattice method considering the coupling boundary condition. From the analytical expressions of the unstable critical wind velocities, numerical results and some useful conclusions are obtained. It is found that the initial curvature of open cable-membrane structures has clear influence on the critical wind velocities of the structures.

Approximated models for aerodynamic coefficients estimation in a multidisciplinary design environment

Abstract: In this paper variable fidelity analyses are investigated. Moreover different kind of approximations to be used in a wide multidisciplinary design environment for aircraft design are built. In order to obtain the surrogate models used in the main design process, a proper framework is built by different design of experiments techniques for process and variables management. Approximated models for the estimation of aerodynamic coefficients are evaluated on design spaces of different dimensions and considering different set of variables (i.e. geometric parameters and flight conditions). They are mainly based on the hybrid combination of Vortex Lattice Method (VLM) models (representing the basic low fidelity analysis) and 3D finite volume Computational Fluid Dynamics models (representing the basic high fidelity analysis). Different strategies for the evaluation of the surrogate model are considered and an original methodology for the model construction is here presented.

Longitudinal stability and motion of trimaran wing in ground effect model during take-off

Abstract: Wing in Ground Effect is a relatively new concept in transportation technology. It is more efficient than conventional aircraft and quicker compared to conventional marine vehicles. However WIG is still not widely use as a public transportation. One of the criteria to be fulfilled is stability. Longitudinal stability of WIG craft is still of concern to the designer and the solutions are being investigated. Instability of a small WIG craft occurs when aerodynamic-hydrodynamic phase changes into pure aerodynamic phase during the take-off. In this research, investigations were conducted to determine the longitudinal static and dynamic stability effect of Trimaran WIG craft during takeoff and to verify the factors affecting its stability. Two parameters considered are aerodynamic and hydrodynamic characteristics. The investigation resorts to vortex lattice method and examines the effects of flat ground and end plate on the performance of aerodynamic characteristic of the WIG craft. Planing hull has been chosen for the hull shape of the WIG craft due to higher speed takeoff. The hydrodynamics of prismatic planing surfaces, presented by Savitsky, is used to calculate the hydrodynamic characteristic. Numerical result is compared to the experimental results and against published data. The Static Stability Margin (SSM) for longitudinal static stability of Trimaran WIG model has been investigated and using the classical aircraft motion modification and calculating the aerodynamic, hydrostatic and hydrodynamic forces, the complete equation of motion that uses a small perturbation assumption for WIG during takeoff has been derived and solved. Finally, dynamic stability for Trimaran WIG during take-off has been investigated and analyzed using Routh-Hurwitz Stability Criterion and Control Anticipation Parameter (CAP).

VLM Tool for IDS Integration

Abstract: This paper is dedicated to a very specific type of analysis tool (VLM Vortex Lattice Method) to be integrated in a IDS Integrated Design System, tailored for the usage of small aircraft industry. The major interest is to have the possibility to simulate at very low computational costs a preliminary set of aerodynamic characteristics for basic aerodynamic global characteristics (Lift, Drag, Pitching Moment) and aerodynamic derivatives for longitudinal and lateral-directional stability analysis. This work enables fast investigations of the influence of configuration changes in a very efficient computational environment. Using experimental data and/or CFD information for a specific calibration of VLM method, reliability of the analysis may me increased so that a first type (iteration zero) aerodynamic evaluation of the preliminary 3D configuration is possible. The output of this tool is basic state aerodynamic and associated stability and control derivatives, as well as a complete set of information on specific loads on major airframe components. The major interest in using and validating this type of methods is coming from the possibility to integrate it as a tool in an IDS system for conceptual design phase, as considered for development for CESAR project (IP, UE FP6).

A refined 1D FE model for the application to aeroelasticity of composite wings

Abstract: The extension of a hierarchical one-dimensional structural model to aeroelasticity is the subject of the present paper. The aerodynamic model is based on the Vortex Lattice Method, VLM, whereas the refined 1D model is based on the Carrera Unified Formulation, CUF. Airfoil in-plane deformation and warping are introduced by enriching the displacement field over the cross-section of the wing. Linear to fourth-order expansions are adopted and classical beam theories (Euler-Bernoulli and Timoshenko) are obtained as particular cases. The VLM aerodynamic theory is coupled with the structural finite element model via an appropriate adaptation of the Infinite Plate Spline method. The aeroelastic tailoring is investigated for several wing configurations (by varying aspect ratio, airfoil geometry and sweep angle) and an excellent agreement with MD NASTRAN solution is provided for structural and aeroelastic cases. The effectiveness of higher-order models for an accurate evaluation of aeroelastic response of isotropic and composite wings is shown.

Aeroservoelastic Behavior of a Wind Turbine Typical Section with an Active Smart Flexible Flap

Abstract: In the past years, the consumption of energy produced by wind turbines had an exponential growth. This requirement gave momentum to the development of larger turbines with the goal of producing more energy at the same site, reducing the initial investment, and the operation and maintenance costs. In order to achieve this objective, longer, lighter, maintenance-free blades are required so that smaller loads are transferred to the other, more expensive, wind turbine components. The resulting larger flexibility, imposes new challenges to the blade and controller designs; henceforth, new concepts are being developed to add more intelligence into these systems. During the last few years, the electronics industry had invested resources into the research and development of practical applications for piezoelectric ceramic materials. The result of this effort was the development of high precision piezoelectric actuators and sensors, which achieve forces and deformations that are compatible with the ones needed for the control of aerodynamic surfaces. In this work, the aeroservoelastic behavior of a wind turbine blade typical section equipped with an active smart flap is numerically simulated. The bending and torsion stiffness of the blade are modeled by means of two springs placed at the shear center of the blade's section. The displacements associated to these two deformation modes are described by means of two discrete generalized coordinates. Structurally, the flap is modeled as a continuous beam, with fixed-free boundary conditions, and an embedded piezoelectric actuator. The bending mode of the flap is actively excited through the use of a commercially available piezoelectric actuator. The model response was compared to the data published by the actuator manufacturer. Aerodynamically, the blade-flap system is modeled assuming the hypotheses of thin airfoil theory. The aerodynamic loads are determined by replacing the vortex sheet with a two dimensional (2D) version of the non-linear, unsteady, vortex lattice method. To capture the physical aspects from the control-fluid-structure interaction, the models are combined using a strong coupling technique. The equations of motion of the system are integrated numerically and interactively in the time domain. In addition, the stability and sensitivity of the system for input perturbations are analyzed. The results show the feasibility of using this type of system in large horizontal wind energy turbines.