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  • 1
    ISSN: 1573-2703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract The research reported herein involves the study of the steady state and transient motion of a system consisting of an incompressible, Newtonian fluid in an annulus between two concentric, rotating, rigid spheres. The primary purpose of the research is to study the use of an approximate analytical method for analyzing the transient motion of the fluid in the annulus and the spheres which are started suddenly due to the action of prescribed torques. The problems include cases where: (a) one (or both) spheres rotate with prescribed constant angular velocities and (b) one sphere rotates due to the action of an applied constant or impulsive torque. In this research, the coupled solid and fluid equations of motion are linearized by employing the perturbation technique. The meridional dependence in these equations is removed by expanding the dependent variables in a series of Gegenbauer functions with variable coefficients and employing the orthogonality property of these functions. The equations for the variable coefficients are solved by separation of variables and Laplace transform methods. Results for the stream function, circumferential function, angular velocity of the spheres and torque coefficient are presented as a function of time for various values of the dimensionless system parameters.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    International Journal for Numerical Methods in Fluids 19 (1994), S. 207-236 
    ISSN: 0271-2091
    Keywords: Finite element ; Fluid flow ; Rotating sphere ; Engineering ; Engineering General
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper presents results obtained by employing a modified Galerkin finite element method to analyse the steady state flow of a fluid contained between two concentric, rotating spheres. The spheres are assumed to be rigid and the cavity region between the spheres is filled with an incompressible, viscous, Newtonian fluid. The inner sphere is constrained to rotate about a vertical axis with a prescribed angular velocity, while the outer sphere is fixed. Results for the circumferential function Ω, streamfunction ψ, vorticity function ζ and inner boundary torque T1 are presented for Reynolds numbers Re ≤ 2000 and radius ratios 0.1 ≤ α ≤ 0.9. The method proved effective for obtaining results for a wide range of radius ratios (0.1 ≤ α ≤ 0.9) and Reynolds numbers (0 ≤ Re ≤ 2000). Previous investigators who employed the finite difference method experienced difficulties in obtaining results for cases with radius ratios α ≤ 0.2, except for small Reynolds numbers (Re ≤ 100). Results for Ω, Ψ, ζ and T1 obtained in this study for radius ratios 0.8 ≤ α ≤ 0.9 verified the development of Taylor vortices reported by other investigators. The research indicates that the method may be useful for analysing other non-linear fluid flow problems.
    Additional Material: 23 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2019-06-28
    Description: Balloon systems have proved to be a cost-effective means for conducting research experiments (e.g., infrared astronomy) in the earth's atmosphere. The purpose of this paper is to present a generalized mathematical model that can be used to simulate the motion of these systems once they have attained float altitude. The resulting form of the model is such that the pendulation and spin motions of the system are uncoupled and can be analyzed independently. The model is evaluated by comparing the simulation results with data obtained from an actual balloon system flown by NASA.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 697-704
    Format: text
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  • 4
    Publication Date: 2019-06-27
    Description: The attitude of the balloon system is determined as a function of time if: (a) a method for simulating the motion of the system is available, and (b) the initial state is known. The initial state is obtained by fitting the system motion (as measured by sensors) to the corresponding output predicted by the mathematical model. In the case of the LACATE experiment the sensors consisted of three orthogonally oriented rate gyros and a magnetometer all mounted on the research platform. The initial state was obtained by fitting the angular velocity components measured with the gyros to the corresponding values obtained from the solution of the math model. A block diagram illustrating the attitude determination process employed for the LACATE experiment is shown. The process consists of three essential parts; a process for simulating the balloon system, an instrumentation system for measuring the output, and a parameter estimation process for systematically and efficiently solving the initial state. Results are presented and discussed.
    Keywords: AERODYNAMICS
    Type: NASA-CR-145958
    Format: application/pdf
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  • 5
    Publication Date: 2019-06-28
    Description: The instantaneous orientation (i.e., the attitude) of the LACATE instrumentation platform with respect to a local vertical is discussed. An observer model for predicting the orientation of balloon-borne research platforms is described. Determination of the platform orientation as a function of time is addressed.
    Keywords: AERODYNAMICS
    Type: NASA-CR-168945 , NAS 1.26:168945
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  • 6
    Publication Date: 2019-06-28
    Description: The effect of wind gusts on the magnitude of the pendulation angles of a balloon-borne observation platform is determined. A system mathematical model is developed and the solution of this model is used to determine the magnitude of the observation platforms pendulation angles.
    Keywords: AERODYNAMICS
    Type: NASA-CR-168947 , NAS 1.26:168947
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  • 7
    Publication Date: 2019-06-27
    Description: A mathematical model for predicting the three dimensional motion of the balloon system is developed, which includes the effects of bounce, pendulation and spin of each subsystem. Boundary layer effects are also examined, along with the aerodynamic forces acting on the balloon. Various simplified forms of the system mathematical model were developed, based on an order of magnitude analysis.
    Keywords: AERODYNAMICS
    Type: NASA-CR-142193
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  • 8
    Publication Date: 2019-06-28
    Description: An observer model for predicting the orientation of balloon borne research platforms was developed. The model was employed in conjunction with data from the LACATE mission in order to determine the platform orientation as a function of time.
    Keywords: GEOPHYSICS
    Type: NASA-CR-169275 , NAS 1.26:169275
    Format: application/pdf
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