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  • 1
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    Simulation of broadband ground motion including nonlinear soil effects for a magnitude 6.5 earthquake on the Seattle fault, Seattle, Washington (2002)
    In:  Bull. Seism. Soc. Am., Münster, 3, vol. 92, no. 2, pp. 831-853, pp. L23301, (ISBN: 0534351875, 2nd edition)
    Details
    Publication Date: 2002
    Keywords: Seismology ; Strong motions ; Broad-band ; Non-linear effects ; Site amplification ; Modelling ; USA ; Earthquake ; BSSA
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    BIBLIOGRAPHY SEISMOLOGY
  • 2
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    Nonlinear Stability and Response of Lifting Surfaces Via Volterra Series (2001)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: This investigation concerns the time and frequency formulations of non-linear two-dimensional lifting surfaces exposed to an incompressible flow field and subjected to an external pressure pulse. In order to address this problem, Volterra series approach in conjunction with the multidimensional Laplace transform is used. This methodology enabling one to solve the aeroelastic governing equations of lifting surfaces opens the way to connect this methodology with that based on neural networks and NARMAX/NARX networks models. Moreover, this extended way to address this problem constitutes a good basis for treatment of the theory of 3D lifting surfaces.
    Keywords: Aerodynamics
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Modeling transonic aerodynamic response using nonlinear systems theory for use with modern control theory (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The presentation begins with a brief description of the motivation and approach that has been taken for this research. This will be followed by a description of the Volterra Theory of Nonlinear Systems and the CAP-TSD code which is an aeroelastic, transonic CFD (Computational Fluid Dynamics) code. The application of the Volterra theory to a CFD model and, more specifically, to a CAP-TSD model of a rectangular wing with a NACA 0012 airfoil section will be presented.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA LaRC Workshop on Guidance, Navigation, Controls, and Dynamics for Atmospheric Flight, 1993; p 431-457
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Reduced Order Models Based on Linear and Nonlinear Aerodynamic Impulse Responses (1999)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: This paper discusses a method for the identification and application of reduced-order models based on linear and nonlinear aerodynamic impulse responses. The Volterra theory of nonlinear systems and an appropriate kernel identification technique are described. Insight into the nature of kernels is provided by applying the method to the nonlinear Riccati equation in a non-aerodynamic application. The method is then applied to a nonlinear aerodynamic model of an RAE 2822 supercritical airfoil undergoing plunge motions using the CFL3D Navier-Stokes flow solver with the Spalart-Allmaras turbulence model. Results demonstrate the computational efficiency of the technique.
    Keywords: Aerodynamics
    Type: CEAS/AIAA/ICASE/NASA Langley International Forum on Aeroelasticity and Structural Dynamics 1999; Pt. 1; 369-380; NASA/CP-1999-209136/PT1
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    NASA TECHNICAL REPORTS
  • 5
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    Aeroelastic deformation effects on the stopped-rotor dynamics of an X-wing aircraft (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Journal of Aircraft (ISSN 0021-8669); 26; 482-488
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    NASA TECHNICAL REPORTS
  • 6
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    Improving CAP-TSD steady pressure solutions through airfoil slope modification (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A modification of airfoil section geometry is examined for improvement of the leading edge pressures predicted by the Computational Aeroelasticity Program - Transonic Small Disturbance (CAP-TSD). Results are compared with Eppler solutions to assess improvement. Preliminary results indicate that a fading function modification of section slopes is capable of significant improvements in the pressures near the leading edge computed by CAP-TSD. Application of this modification to airfoil geometry before use in CAP-TSD is shown to reduce the nonphysical pressure peak predicted by the transonic small disturbance solver. A second advantage of the slope modification is the substantial reduction in sensitivity of CAP-TSD steady pressure solutions to the computational mesh.
    Keywords: Aerodynamics
    Type: NASA-TM-110214 , NAS 1.15:110214
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    AEROM: NASA's Unsteady Aerodynamic and Aeroelastic Reduced-Order Modeling Software (2018)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The origins, development, implementation, and application of AEROM, NASA's patented reduced-order modeling (ROM) software, are presented. Full computational fluid dynamic (CFD) aeroelastic solutions and ROM aeroelastic solutions, computed at several Mach numbers using the NASA FUN3D CFD code, are presented in the form of root locus plots in order to better reveal the aeroelastic root migrations with increasing dynamic pressure. The method and software have been applied successfully to several con figurations including the Lockheed-Martin N+2 supersonic configuration and the Royal Institute of Technology (KTH, Sweden) generic wind-tunnel model, among others. The software has been released to various organizations with applications that include CFD-based aeroelastic analyses and the rapid modeling of high- fidelity dynamic stability derivatives. Recent results obtained from the application of the method to the AGARD 445.6 wing will be presented that reveal several interesting insights.
    Keywords: Aerodynamics
    Type: NF1676L-29554 , Aerospace (e-ISSN 2226-4310); 5; 2
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    The effects of aeroelastic deformation on the unaugmented stopped-rotor dynamics of an X-Wing aircraft (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A new design concept in the development of vertical takeoff and landing aircraft with high forward flight speed capability is that of the X-Wing. The X-Wing is a stiff, bearingless helicopter rotor system which can be stopped in flight and the blades used as two forward-swept wings and two aft-swept wings. Because of the unusual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-Wing configuration aircraft was undertaken to determine if these problems could exist. This paper reports on the results of dynamic stability analyses in the lateral and longitudinal directions including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic 'washin' of the forward-swept blades and 'washout' of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to X-Wing aircraft.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 87-2563
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    NASA TECHNICAL REPORTS
  • 9
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    Development of Reduced-Order Models for Aeroelastic and Flutter Prediction Using the CFL3Dv6.0 Code (2002)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A reduced-order model (ROM) is developed for aeroelastic analysis using the CFL3D version 6.0 computational fluid dynamics (CFD) code, recently developed at the NASA Langley Research Center. This latest version of the flow solver includes a deforming mesh capability, a modal structural definition for nonlinear aeroelastic analyses, and a parallelization capability that provides a significant increase in computational efficiency. Flutter results for the AGARD 445.6 Wing computed using CFL3D v6.0 are presented, including discussion of associated computational costs. Modal impulse responses of the unsteady aerodynamic system are then computed using the CFL3Dv6 code and transformed into state-space form. Important numerical issues associated with the computation of the impulse responses are presented. The unsteady aerodynamic state-space ROM is then combined with a state-space model of the structure to create an aeroelastic simulation using the MATLAB/SIMULINK environment. The MATLAB/SIMULINK ROM is used to rapidly compute aeroelastic transients including flutter. The ROM shows excellent agreement with the aeroelastic analyses computed using the CFL3Dv6.0 code directly.
    Keywords: Aerodynamics
    Type: AIAA Paper 2002-1596 , 43rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 22, 2002 - Apr 25, 2002; Denver, CO; United States
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  • 10
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    Evaluation of Linear, Inviscid, Viscous, and Reduced-Order Modeling Aeroelastic Solutions of the AGARD 445.6 Wing Using Root Locus Analysis (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Reduced-order modeling (ROM) methods are applied to the CFD-based aeroelastic analysis of the AGARD 445.6 wing in order to gain insight regarding well-known discrepancies between the aeroelastic analyses and the experimental results. The results presented include aeroelastic solutions using the inviscid CAP-TSD code and the FUN3D code (Euler and Navier-Stokes). Full CFD aeroelastic solutions and ROM aeroelastic solutions, computed at several Mach numbers, are presented in the form of root locus plots in order to better reveal the aeroelastic root migrations with increasing dynamic pressure. Important conclusions are drawn from these results including the ability of the linear CAP-TSD code to accurately predict the entire experimental flutter boundary (repeat of analyses performed in the 1980's), that the Euler solutions at supersonic conditions indicate that the third mode is always unstable, and that the FUN3D Navier-Stokes solutions stabilize the unstable third mode seen in the Euler solutions.
    Keywords: Aerodynamics
    Type: AIAA Paper 2014-0496 , NF1676-16636 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; Jan 13, 2014 - Jan 17, 2014; National Harbor, MD; United States
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