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  • Other Sources  (14)
  • 1995-1999  (14)
  • 1996  (14)
  • 1
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    Two-Dimensional Dynamic Simulation of a Continuous Foil Bearing (1996)
    In:  CASI
    Details
    Publication Date: 2011-09-13
    Description: In this paper, the two dimensional(radial and circumferential) transient Navier-Stokes equations are used to solve the hydrodynamic problem in conjunction with the time dependent motion of the journal, and the deformable, spring supported foil. The elastic deformation of the foil and its supports are simulated by a finite element model. The time-dependent Navier-Stokes formulation is used to solve for the interaction between the fluid lubricant, the motion of the journal and the deformable foil boundary. The steady state, the quasi-transient and the full transient dynamic simulation of the foil-fluid journal interaction are examined on a comparative basis. For the steady state simulation, the fluid lubricant pressures are evaluated for a particular journal position, by means of an iterative scheme until convergence is achieved in both the fluid pressures and the corresponding foil deformation. For the quasi-transient case, the transient motion of the journal is calculated using a numerical integration scheme for the velocity and displacement of the journal. The deformation of the foil is evaluated through numerical iteration in feedback mode with the fluid film pressure generated by the journal motion until convergence at every time step is achieved. For the full transient simulation, a parallel real-time integration scheme is used to evaluate simultaneously the new journal position and the new deformed shape of the foil at each time step. The pressure of the fluid lubricant is iterated jointly with the corresponding journal position and the deformed foil geometry until convergence is achieved. A variable time-stepping Newmark-Beta integration procedure is used to evaluate the transient dynamics at each time step of the bearing.
    Keywords: Mechanical Engineering
    Type: Seals Code Development Workshop; 267-280; NASA-CP-10181
    Format: text
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  • 2
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    Three Dimensional Flow and Pressure Patterns in a Single Pocket of a Hydrostatic Journal Bearing (1996)
    In:  CASI
    Details
    Publication Date: 2011-09-13
    Description: The flow in a hydrostatic pocket is described by a mathematical model that uses the three dimensional Navier-Stokes equations written in terms of the primary variables, u, v, w, and p. Using a conservative formulation, a finite volume multi-block method is applied through a collocated, body fitted grid. The flow is simulated in a shallow pocket with a depth/length ratio of 0.02. The flow structures obtained and described by the authors in their previous two dimensional models are made visible in their three dimensional aspect for the Couette flow. It has been found that the flow regimes formed central and secondary vortical cells with three dimensional corkscrew-like structures that lead the fluid on an outward bound path in the axial direction of the pocket. The position of the central vortical cell center is at the exit region of the capillary restrictor feedline. It has also been determined that a fluid turn around zone occupies all the upstream space between the floor of the pocket and the runner, thus preventing any flow exit through the upstream port. The corresponding pressure distribution under the shaft presented as well. It was clearly established that for the Couette dominated case the pressure varies significantly in the pocket in the circumferential direction, while its variation is less pronounced axially.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: Seals Code Development Workshop; 285-298; NASA-CP-10181
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  • 3
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    Three Dimensional Flow and Pressure Patterns in a Hydrostatic Journal Bearing (1996)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The flow in a hydrostatic journal bearing (HJB) is described by a mathematical model that uses the three dimensional non-orthogonal form of the Navier-Stokes equations. Using the u, v, w, and p, as primary variables, a conservative formulation, finite volume multi-block method is applied through a collocated, body fitted grid. The HJB has four shallow pockets with a depth/length ratio of 0.067. This paper represents a natural extension to the two and three dimensional studies undertaken prior to this project.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: Seals Code Development Workshop; 281-284; NASA-CP-10181
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  • 4
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    Integrated Thermal Control for Mars Rover (1996)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: The Mars Rover has been built, environmentally tested and qualified for the 1996 launch of the Pathfinder mission to Mars. The basic structure for the thermal control for the Mars Rover is the Warm Electronics Box (WEB). This consists of a thermal isolating composite structure with co-cured thermal control surfaces and an ultralightweight hydrophobic solid silica aerogel which minimizes conduction and radiation.
    Keywords: Lunar and Planetary Science and Exploration
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  • 5
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    The Pathfinder Microrover (1996)
    In:  Other Sources
    Details
    Publication Date: 2018-06-08
    Description: An exciting scientific component of the Pathfinder mission is the rover, which will act as a mini-field geologist by providing us with access to samples for chemical analyses and close-up images of the Martian surface, performing active experiments to modify the surface and study the results, and exploring the landing site area.
    Format: text
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  • 6
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    Use of the Collaborative Optimization Architecture for Launch Vehicle Design (1996)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: Collaborative optimization is a new design architecture specifically created for large-scale distributed-analysis applications. In this approach, problem is decomposed into a user-defined number of subspace optimization problems that are driven towards interdisciplinary compatibility and the appropriate solution by a system-level coordination process. This decentralized design strategy allows domain-specific issues to be accommodated by disciplinary analysts, while requiring interdisciplinary decisions to be reached by consensus. The present investigation focuses on application of the collaborative optimization architecture to the multidisciplinary design of a single-stage-to-orbit launch vehicle. Vehicle design, trajectory, and cost issues are directly modeled. Posed to suit the collaborative architecture, the design problem is characterized by 5 design variables and 16 constraints. Numerous collaborative solutions are obtained. Comparison of these solutions demonstrates the influence which an priori ascent-abort criterion has on development cost. Similarly, objective-function selection is discussed, demonstrating the difference between minimum weight and minimum cost concepts. The operational advantages of the collaborative optimization
    Keywords: Computer Programming and Software
    Format: application/pdf
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  • 7
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    Implementation and Performance Issues in Collaborative Optimization (1996)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: Collaborative optimization is a multidisciplinary design architecture that is well-suited to large-scale multidisciplinary optimization problems. This paper compares this approach with other architectures, examines the details of the formulation, and some aspects of its performance. A particular version of the architecture is proposed to better accommodate the occurrence of multiple feasible regions. The use of system level inequality constraints is shown to increase the convergence rate. A series of simple test problems, demonstrated to challenge related optimization architectures, is successfully solved with collaborative optimization.
    Keywords: Systems Analysis and Operations Research
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  • 8
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    Large Eddy Simulation in a Channel with Exit Boundary Conditions (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The influence of the exit boundary conditions (vanishing first derivative of the velocity components and constant pressure) on the large eddy simulation of the fully developed turbulent channel flow has been investigated for equidistant and stretched grids at the channel exit. Results show that the chosen exit boundary conditions introduce some small disturbance which is mostly damped by the grid stretching. The difference between the fully developed turbulent channel flow obtained with LES with periodicity condition and the inlet and exit and the LES with fully developed flow at the inlet and the exit boundary condition is less than 10% for equidistant grids and less than 5% for the case grid stretching. The chosen boundary condition is of interest because it may be used in complex flows with backflow at exit.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA-CR-198304 , NAS 1.26:198304 , ICASE-96-18
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  • 9
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    Six Degree-of-Freedom Entry Dispersion Analysis for the METEOR Recovery Module (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The present study performs a six degree-of-freedom entry dispersion analysis for the Multiple Experiment Transporter to Earth Orbit and Return (METEOR) mission. METEOR offered the capability of flying a recoverable science package in a microgravity environment. However, since the Recovery Module has no active control system, an accurate determination of the splashdown position is difficult because no opportunity exists to remove any errors. Hence, uncertainties in the initial conditions prior to deorbit burn initiation, during deorbit burn and exo-atmospheric coast phases, and during atmospheric flight impact the splashdown location. This investigation was undertaken to quantify the impact of the various exo-atmospheric and atmospheric uncertainties. Additionally, a Monte-Carlo analysis was performed to statistically assess the splashdown dispersion footprint caused by the multiple mission uncertainties. The Monte-Carlo analysis showed that a 3-sigma splashdown dispersion footprint with axes of 43.3 nm (long), -33.5 nm (short), and 10.0 nm (crossrange) can be constructed. A 58% probability exists that the Recovery Module will overshoot the nominal splashdown site.
    Keywords: Spacecraft Design, Testing and Performance
    Type: NASA-TM-112913 , NAS 1.26:112913 , AIAA Paper 96-0903 , Aerospace Sciences; Jan 15, 1996 - Jan 18, 1996; Reno, NV; United States
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  • 10
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    Quantification of Gear Tooth Damage by Optimal Tracking of Vibration Signatures (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper presents a technique for quantifying the wear or damage of gear teeth in a transmission system. The procedure developed in this study can be applied as a part of either an onboard machine health-monitoring system or a health diagnostic system used during regular maintenance. As the developed methodology is based on analysis of gearbox vibration under normal operating conditions, no shutdown or special modification of operating parameters is required during the diagnostic process. The process of quantifying the wear or damage of gear teeth requires a set of measured vibration data and a model of the gear mesh dynamics. An optimization problem is formulated to determine the profile of a time-varying mesh stiffness parameter for which the model output approximates the measured data. The resulting stiffness profile is then related to the level of gear tooth wear or damage. The procedure was applied to a data set generated artificially and to another obtained experimentally from a spiral bevel gear test rig. The results demonstrate the utility of the procedure as part of an overall health-monitoring system.
    Keywords: Aircraft Propulsion and Power
    Type: NASA-TM-107100 , E-10029 , NAS 1.15:107100 , 6th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery; Feb 25, 1996 - Feb 29, 1996; Honolulu, HA; United States
    Format: application/pdf
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