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  • 1
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    Modeling and stabilization of large flexible space stations (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A preliminary formulation of a large space structure is presented. The system consists of a (rigid) massive body, which may play the role of experimental modules located at the center of the space station and a flexible configuration, consisting of several beams, which is rigidly attached to the main body. The equations that govern the motion of the complete system consist of several partial differential equations with boundary conditions describing the vibration of flexible components coupled with six ordinary differential equations that describe the rotational and translational motion of the central body. The problem of (feedback) stabilization of the system is discussed. This study is expected to provide an insight into the complexity of design and stabilization of actual space stations.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center, Proceedings of the Workshop on Computational Aspects in the Control of Flexible Systems, Part 2; p 943-956
    Format: application/pdf
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  • 2
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    Efficient sensitivity analysis and optimization of a helicopter rotor (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Aeroelastic optimization of a system essentially consists of the determination of the optimum values of design variables which minimize the objective function and satisfy certain aeroelastic and geometric constraints. The process of aeroelastic optimization analysis is illustrated. To carry out aeroelastic optimization effectively, one needs a reliable analysis procedure to determine steady response and stability of a rotor system in forward flight. The rotor dynamic analysis used in the present study developed inhouse at the University of Maryland is based on finite elements in space and time. The analysis consists of two major phases: vehicle trim and rotor steady response (coupled trim analysis), and aeroelastic stability of the blade. For a reduction of helicopter vibration, the optimization process requires the sensitivity derivatives of the objective function and aeroelastic stability constraints. For this, the derivatives of steady response, hub loads and blade stability roots are calculated using a direct analytical approach. An automated optimization procedure is developed by coupling the rotor dynamic analysis, design sensitivity analysis and constrained optimization code CONMIN.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA. Langley Research Center, Recent Advances in Multidisciplinary Analysis and Optimization, Part 1; p 195-208
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  • 3
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    A-2000: Close air support aircraft design team (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The US Air Force is currently faced with the problem of providing adequate close air support for ground forces. Air response to troops engaged in combat must be rapid and devastating due to the highly fluid battle lines of the future. The A-2000 is the result of a study to design an aircraft to deliver massive fire power accurately. The low cost A-2000 incorporates: large weapons payload; excellent maneuverability; all weather and terrain following capacity; redundant systems; and high survivability.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-CR-190022 , NAS 1.26:190022
    Format: application/pdf
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  • 4
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    Design sensitivity analysis for an aeroelastic optimization of a helicopter blade (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The sensitivity of vibratory hub loads of a four-bladed hingeless rotor with respect to blade design parameters is investigated using a finite element formulation in space and time. Design parameters include nonstructural mass distribution (spanwise and chordwise), chordwise offset of center of gravity from aerodynamic center, blade bending stiffnesses (flap, lag and torsion). Hub loads selected are 4/rev vertical hub shear and 3/rev hub moment in the rotating reference frame. The sensitivity derivatives of vertical hub loads with respect to blade design parameters are compared using two approaches, finite difference scheme and analytical approach using chain rule differentiation. The analytical derivative approach developed as an integral part of response solution (finite element in time) is a powerful method for an aeroelastic optimization of a helicopter rotor.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 87-0923
    Format: text
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  • 5
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    Stability sensitivity analysis for the aeroelastic optimization of a helicopter rotor (1988)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A sensitivity study of blade stability in forward flight for a hingeless rotor with respect to structural design variables is carried out using a direct analytical method. Structural design variables include nonstructural mass distribution (spanwise and chordwise), chordwise offset of center of gravity, and blade bending stiffnesses (flap, lag and torsion). The formulation for blade steady response is based on a finite element method in space and time. The vehicle trim and blade steady response are calculated iteratively as one coupled solution using a modified Newton method. Eigenvalues corresponding to different blade modes are calculated using Floquet transition matrix theory. The formulation for derivatives of the eigenvalues with respect to design variables is implemented using a direct analytical approach (chain rule differentiation), and constitutes an integral part of the regular stability analysis. The stability sensitivity derivatives were obtained at a fraction of computation time compared to the frequently adopted finite difference method. A parametric study showed that nonstructural mass and chordwise cg offset of outboarad elements, and lag bending stiffness of inboard elements, have powerful influence on blade stability.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 88-2310 , Structures, Structural Dynamics and Materials Conference; Apr 18, 1988 - Apr 20, 1988; Williamsburg, VA; United States
    Format: text
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  • 6
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    Aeroelastic optimization of a helicopter rotor using an efficient sensitivity analysis (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 29-37
    Format: text
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  • 7
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    Stability sensitivity analysis of a helicopter rotor (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA Journal (ISSN 0001-1452); 28; 1089-109
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  • 8
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    Response and hub loads sensitivity analysis of a helicopter rotor (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA Journal (ISSN 0001-1452); 28; 75-82
    Format: text
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  • 9
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    Aeroelastic optimization of a helicopter rotor using an efficient sensitivity analysis (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: To reduce oscillatory hub loads in forward flight, a structural optimization analysis of a hingeless helicopter rotor has been developed and applied. The aeroelastic analysis of the rotor is based on a finite element method in space and time, and linked with automated optimization algorithms. For the optimization analysis two types of structural representation are used: a generic stiffness-distribution and a single-cell thin-walled beam. For the first type, the design variables are nonstructural mass and its placement, chordwise center of gravity offset from the elastic axis, and stiffness. For the second type, width, height and thickness of spar are used as design variables. For the behavior constraints, frequency placement, autorotational inertia and aeroelastic stability of the blade are included. The required sensitivity derivatives are obtained using a direct analytical approach. An optimum oscillatory hub load shows a 25-77 percent reduction for the generic blade, and 30-50 percent reduction for the box-beam.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 90-0951 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference; Apr 02, 1990 - Apr 04, 1990; Long Beach, CA; United States
    Format: text
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  • 10
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    Aeroelastic optimization of a helicopter rotor (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Structural optimization of a hingeless rotor is investigated to reduce oscillatory hub loads while maintaining aeroelastic stability in forward flight. Design variables include spanwise distribution of nonstructural mass, chordwise location of blade center of gravity and blade bending stiffnesses (flap, lag and torsion). A comprehensive aeroelastic analysis of rotors, based on a finite element method in space and time, is linked with optimization algorithms to perform optimization of rotor blades. Sensitivity derivatives of blade response, hub loads, and eigenvalues with respect to the design variables are derived using a direct analytical approach, and constitute an integral part of the basic blade response and stability analyses. This approach reduces the computation time substantially; an 80 percent reduction of CPU time to achieve an optimum solution, as compared to the widely adopted finite difference approach. Through stiffness and nonstructural mass distributions, a 60-90 percent reduction in all six 4/rev hub loads is achieved for a four-bladed soft-inplane rotor.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Annual Forum of the AHS; Jun 16, 1988 - Jun 18, 1988; Washington, DC; United States
    Format: text
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