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  • AERODYNAMICS  (4)
  • STRUCTURAL MECHANICS
  • 2005-2009
  • 1990-1994  (2)
  • 1980-1984  (5)
  • 1990  (2)
  • 1984  (5)
  • 1
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    A parametric shell analysis of the shuttle 51-L SRB AFT field joint (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Following the Shuttle 51-L accident, an investigation was conducted to determine the cause of the failure. Investigators at the Langley Research Center focused attention on the structural behavior of the field joints with O-ring seals in the steel solid rocket booster (SRB) cases. The shell-of-revolution computer program BOSOR4 was used to model the aft field joint of the solid rocket booster case. The shell model consisted of the SRB wall and joint geometry present during the Shuttle 51-L flight. A parametric study of the joint was performed on the geometry, including joint clearances, contact between the joint components, and on the loads, induced and applied. In addition combinations of geometry and loads were evaluated. The analytical results from the parametric study showed that contact between the joint components was a primary contributor to allowing hot gases to blow by the O-rings. Based upon understanding the original joint behavior, various proposed joint modifications are shown and analyzed in order to provide additional insight and information. Finally, experimental results from a hydro-static pressurization of a test rocket booster case to study joint motion are presented and verified analytically.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102748 , NAS 1.15:102748
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    ALESEP: A computer program for the analysis of airfoil leading edge separation bubbles (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The ALESEP program for the analysis of the inviscid/viscous interaction which occurs due to the presence of a closed laminar transitional separation bubble on an airflow is presented. The ALESEP code provides a iterative solution of the boundary layer equations expressed in an inverse formulation coupled to a Cauchy integral representation of the inviscid flow. This interaction analysis is treated as a local perturbation to a known solution obtained from a global airfoil analysis. Part of the required input to the ALESEP code are the reference displacement thickness and tangential velocity distributions. Special windward differencing may be used in the reversed flow regions of the separation bubble to accurately account for the flow direction in the discretization of the streamwise convection of momentum. The ALESEP code contains a forced transition model based on a streamwise intermittency function and a natural transition model based on a solution of the integral form of the turbulent kinetic energy equation. Instructions for the input/output, and program usage are presented.
    Keywords: AERODYNAMICS
    Type: NASA-CR-172310 , NAS 1.26:172310
    Format: application/pdf
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  • 3
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    Structural efficiency studies of corrugated compression panels with curved caps and beaded webs (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Curved cross-sectional elements are employed in structural concepts for minimum-mass compression panels. Corrugated panel concepts with curved caps and beaded webs are optimized by using a nonlinear mathematical programming procedure and a rigorous buckling analysis. These panel geometries are shown to have superior structural efficiencies compared with known concepts published in the literature. Fabrication of these efficient corrugation concepts became possible by advances made in the art of superplastically forming of metals. Results of the mass optimization studies of the concepts are presented as structural efficiency charts for axial compression.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TP-2272 , L-15703 , NAS 1.60:2272
    Format: application/pdf
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  • 4
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    Refinement and evaluation of helicopter real-time self-adaptive active vibration controller algorithms (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A Real-Time Self-Adaptive (RTSA) active vibration controller was used as the framework in developing a computer program for a generic controller that can be used to alleviate helicopter vibration. Based upon on-line identification of system parameters, the generic controller minimizes vibration in the fuselage by closed-loop implementation of higher harmonic control in the main rotor system. The new generic controller incorporates a set of improved algorithms that gives the capability to readily define many different configurations by selecting one of three different controller types (deterministic, cautious, and dual), one of two linear system models (local and global), and one or more of several methods of applying limits on control inputs (external and/or internal limits on higher harmonic pitch amplitude and rate). A helicopter rotor simulation analysis was used to evaluate the algorithms associated with the alternative controller types as applied to the four-bladed H-34 rotor mounted on the NASA Ames Rotor Test Apparatus (RTA) which represents the fuselage. After proper tuning all three controllers provide more effective vibration reduction and converge more quickly and smoothly with smaller control inputs than the initial RTSA controller (deterministic with external pitch-rate limiting). It is demonstrated that internal limiting of the control inputs a significantly improves the overall performance of the deterministic controller.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3821 , NAS 1.26:3821 , R83-956149-16
    Format: application/pdf
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  • 5
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    Analysis of airfoil transitional separation bubbles (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A previously developed local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation), has been modified to utilize a more accurate windward finite difference procedure in the reversed flow region, and a natural transition turbulence model has been incorporated for the prediction of transition within the separation bubble. Numerous calculations and experimental comparisons are presented to demonstrate the effects of the windward differencing scheme and the natural transition turbulence model. Grid sensitivity and convergence capabilities of this inviscid-viscous interaction technique are briefly addressed. A major conclusion of this paper is that a second, counter-rotating eddy has been found to exist in the wall layer of the primary separation bubble with the use of windward differencing.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 84-1613
    Format: text
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  • 6
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    Analysis of airfoil transitional separation bubbles (1984)
    In:  CASI
    Details
    Publication Date: 2019-08-28
    Description: A previously developed local inviscid-viscous interaction technique for the analysis of airfoil transitional separation bubbles, ALESEP (Airfoil Leading Edge Separation) has been modified to utilize a more accurate windward finite difference procedure in the reversed flow region, and a natural transition/turbulence model has been incorporated for the prediction of transition within the separation bubble. Numerous calculations and experimental comparisons are presented to demonstrate the effects of the windward differencing scheme and the natural transition/turbulence model. Grid sensitivity and convergence capabilities of this inviscid-viscous interaction technique are briefly addressed. A major contribution of this report is that with the use of windward differencing, a second, counter-rotating eddy has been found to exist in the wall layer of the primary separation bubble.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3791 , NAS 1.26:3791
    Format: application/pdf
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  • 7
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    High-performance equation solvers and their impact on finite element analysis (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The role of equation solvers in modern structural analysis software is described. Direct and iterative equation solvers which exploit vectorization on modern high-performance computer systems are described and compared. The direct solvers are two Cholesky factorization methods. The first method utilizes a novel variable-band data storage format to achieve very high computation rates and the second method uses a sparse data storage format designed to reduce the number of operations. The iterative solvers are preconditioned conjugate gradient methods. Two different preconditioners are included; the first uses a diagonal matrix storage scheme to achieve high computation rates and the second requires a sparse data storage scheme and converges to the solution in fewer iterations that the first. The impact of using all of the equation solvers in a common structural analysis software system is demonstrated by solving several representative structural analysis problems.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-102735 , AVSCOM-TM-90-B-017 , NAS 1.15:102735 , World Conference on Finite Element Methods; Oct 01, 1990 - Oct 05, 1990; Banff, Alberta; Canada
    Format: application/pdf
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