1,721,069 research outputs found
Nonlinear Aeroelastic Formulation and Postflutter Analysis of Flexible High-Aspect-Ratio Wings
No full textThe nonlinear aeroelastic modeling and the post-flutter behavior of high-altitude long-endurance wings are discussed. A parametric structural model of wings based on an exact kinematic approach is formulated and coupled with an incompressible unsteady aerodynamic model that is obtained via an indicial formulation accounting for viscous effects, including dynamic stall and flow separation. To this end, a modified Beddoes-Leishman model is employed, and the equations of motion, together with the equations governing the aerodynamic states, are obtained via a total Lagrangian formulation. The critical and post-critical dynamic aeroelastic response is evaluated, and the limit cycles occurring in the post-flutter condition past the Hopf bifurcation are studied. Together, with comparisons from the available data of an experimental wing model with tip store, the effects of the unsteady loads and dynamic stall are evaluated and compared with predictions obtained from a model using a classical quasi-steady aerodynamic formulation. Aeroelastic simulations are concurrently performed within a finite element solution platform. Space and time integrations are conducted using a numerical scheme that directly discretizes the partial differential equations, which are associated with the equations of motion of the flexible wing, and the ordinary differential equations, which are associated with the added lag-state formulation pertinent to the unsteady aerodynamic loads, in a hybrid solution form. The aim is the study of the aeroelastic behavior of these highly nonlinear wings for an improved understanding of the nonlinear phenomena occurring particularly in the neighborhood of the flutter boundary and in the post-critical regime when the unsteady aerodynamic effects and dynamic stall contribute more significantly to the wing dynamic behavior
On-condition evaluation of how inertial and aerodynamic characteristics affect the dynamics of a small wind turbine system
No full textWith the goal of developing system performance integrity monitoring tools for wind turbines the dynamic analysis of a small horizontal-axis wind turbine subjected to changes in the inertial and aerodynamic properties are investigated. The identification of the three- blade turbine modal properties, i.e. natural frequencies, damping ratios, and mode shapes, is provided for a rotor subjected to simulated operating conditions during wind tunnel tests. Several wind speeds and different angular speeds are considered by controlling the inflow to the rotor and its generated power. An identification procedure to infer about how dynamic properties are changing from the data recorded during the simulated operating conditions is developed. The operational deflection shape identification procedure proposed accounts for the presence of harmonic loading and uses dynamic strain measured from Fiber Bragg Grating (FBG) transducers bonded on the surface, suction side, of the three-blades wind turbine. © 2012 AIAA
Aeroelastic System Control by a Multiple Spoiler Actuation and MRAC Scheme
Full text linkA novel wing configuration to control flutter and post-flutter limit cycle oscillations is proposed. The new wing consists of a multiple spoiler control surface, with a predefined and coordinated actuation strategy.The proposed architecture, optimized through CFD analysis, is fabricated and tested in the wind tunnel to validate the aerodynamic properties of the wing section. The experimentally obtained nonlinear aerodynamic database is implemented in a simulation environment, which is used to investigate the dynamic response of the proposed wing configuration aeroelastic model. The coupled, two degree of freedom, structural model has nonlinear plunging/pitching characteristics, which allow the system to exhibit LCOs above flutter speed. The open and closed loop responses of the system are investigated and compared to a trailing-edge flap solution of the same wing section. The regulation problem is obtained for a normalized MRAC scheme, modified for performance improvement. The same algorithm is applied to both plants and results validate the robustness and the adaptation capabilities of the implemented control scheme. Further sensitivity analyses to external disturbances, which are different gust distributions, demonstrate the efficacy and solidity of the overall configuration investigate
Considerations on beam-wise structural models used for aeroelastic analysis of slender wings
No full textUncertainty Quantification of High-Velocity Impact Fracture in Fiber-Reinforced Composites Using a Robust Stochastic Sampling Approach
Full text linkComposite materials are known for their excellent mechanical and light weight properties. However, their vulnerability to interlaminar damages poses a significant challenge for the design of safe and lightweight aerospace structures. Advanced Finite Element Analysis tools based on Cohesive Zone Method and Continuum Damage Mechanics offer a new prospective to investigate impact and damage scenarios to aid the design of structures while paying attention to damage initiation and propagation. A physical-based stacked shell-cohesive modeling technique was implemented in this study to conduct a stochastic analysis of a standardized ASTM composite panel subjected to a blunt high-velocity impact. A comprehensive structured Monte Carlo Latin Hypercube method was applied to quantify uncertainties in interlaminar fracture toughness distribution and to investigate their impact on delamination size and projectile’s residual velocity. The results indicate that while resultant global delamination size and shape is less sensitive to material uncertainties, residual projectile’s velocity is significantly affected, emphasizing the importance of structured stochastic methods in analysing uncertainty propagation in macro-scale physical-based numerical models subjected to impact or fracture phenomena
Validation of an UAV F.E. Model Using Operational Data
No full textIn this paper an approach that uses the modal signature of an Unmanned Aerial Vehicle (UAV) extracted directly from the operative conditions for the validation of a finite element model is proposed. Different operational conditions of the Clarkson University Golden Eagle UAV are considered, ranging from laboratory components and UAV assembly to on-ground taxiing performed on asphalt and grass. To properly model the UAV individual subcomponents (wing, fuselage, horizontal tail, vertical tails and tail booms) have been tested. Only selected components testing are presented in this paper, to illustrate the methodology proposed for testing and FE modeling. These initial investigations are instrumental toward developing a correlated nite element model representing the global dynamic behavior of the UAV structure
Development of a FBG based distributed strain sensor system for wind turbine structural health monitoring
No full textThe development of a fiber Bragg grating (FBG) based distributed strain sensor system for real time structural health monitoring of a wind turbine rotor and its validation under a laboratory scale test setup is discussed in this paper. A 1 kW, 1.6 m diameter rotor, horizontal axis wind turbine with three instrumented blades is used in this study. The sensor system consists of strain sensors, surface mounted at various locations on the blade. At first the sensors are calibrated under static loading conditions to validate the FBG mounting and the proposed data collection techniques. Then, the capability of the sensor system coupled with the operational modal analysis (OMA) methods to capture natural frequencies and corresponding mode shapes in terms of distributed strains are validated under various non-rotating dynamic loading conditions. Finally, the sensor system is tested under rotating conditions using the wind flow from an open-jet wind tunnel, for both a baseline wind turbine and a wind turbine with a structurally modified blade. The blade was modified by attaching a lumped mass at the blade tip simulating structural damage or ice accretion. The dynamic characteristics of the baseline (healthy) blade and modified (altered) blade are compared to validate the sensor system's ability for real time structural health monitoring of the rotor
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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