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  • 1
    Electronic Resource
    Electronic Resource
    Effect of wall cooling on the stability of compressible subsonic flows over smooth humps and backward-facing steps (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 381-389 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of wall cooling on the two-dimensional linear stability of subsonic flows over two-dimensional surface imperfections is investigated. Results are presented for flows over smooth humps and backward-facing steps with Mach numbers up to 0.8. The results show that, whereas cooling reduces the viscous instability, it increases the shear-layer instability and hence it increases the growth rates in the separation region. The coexistence of more than one instability mechanism makes a certain degree of wall cooling most effective. For the Mach numbers 0.5 and 0.8, the optimum wall temperature is about 80% of the adiabatic wall temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857788
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of a bulge on the subharmonic instability of boundary layers (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 937-948 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of a two-dimensional hump on the three-dimensional (3-D) subharmonic secondary instability on a flat plate is investigated. The mean flow is calculated by using interacting boundary layers, thereby accounting for the viscid/inviscid interaction. The primary wave is taken in the form of a two-dimensional (2-D) Tollmien–Schlichting (T–S) wave. The secondary wave is taken in the form of a 3-D subharmonic wave. The results show that increasing the hump height results in an increase in the amplification factors of the primary and subharmonic waves. When the hump causes separation, the growth rates of both the primary and subharmonic waves are considerably larger than those obtained in the case of no separation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857654
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of streamwise vortices on Tollmien–Schlichting waves (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3543-3549 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis is presented of the influence of steady quasiperiodic streamwise vortices on Tollmien–Schlichting (TS) waves. The vortices act as parametric exciters for the TS waves. The present analysis is for the subharmonic resonance in which the spanwise wavenumber of the vortices is twice that of the TS wave. Floquet theory is used to derive an eigenvalue problem for the complex streamwise wavenumber, which is then solved using a shooting technique. The results show that there are two components of the solution, one is stabilized and the other is destabilized by the vortices. For the same flow characteristics, calculations were obtained from the theory which Nayfeh [J. Fluid Mech. 107, 441 (1981)] developed using the method of multiple scales. The results obtained from both approaches are in excellent agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866921
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  • 4
    Electronic Resource
    Electronic Resource
    Surface waves in closed basins under parametric and internal resonances (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 2976-2983 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The method of multiple scales is used to analyze the nonlinear response of the free surface of a liquid in a cylindrical container to a harmonic vertical oscillation in the presence of a two-to-one internal (autoparametric) resonance. Four first-order ordinary-differential equations are derived for the modulation of the amplitudes and phases of the two modes involved in the internal resonance with the lower mode is excited by a principal parametric resonance. In the presence of small damping, the long-time response may be any of (a) a trivial motion, (b) a limit cycle involving both modes, (c) an amplitude- and phase-modulated sinusoid (motion on a two torus), and (d) a chaotically modulated sinusoid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866075
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  • 5
    Electronic Resource
    Electronic Resource
    Nonparallel stability of heated two-dimensional boundary layers (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 1263-1272 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The method of multiple scales is used to determine three partial differential equations describing the modulation of the amplitude and complex wavenumbers of three-dimensonal (3-D) waves propagating in two-dimensional (2-D) heated liquid layers. These equations are solved numerically along the characteristics subject to the condition that the ratio of the complex group velocities in the streamwise and transverse directions be real. A new criterion for the most dangerous frequency is proposed. For an n factor of 9, F=25×10−6 is found to be the most dangerous frequency for the Blasius flow. Three-dimensional waves yield lower n factors than 2-D waves, irrespective of the heating distribution. For a power-law heating distribution of the form T=Te+AxN, one cannot make a general statement on the effect of N on the stability. Numerical results are presented that show the n factor to increase with an increase or a decrease in N.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865009
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  • 6
    Electronic Resource
    Electronic Resource
    Interaction of surface gravity waves on a nonuniformly periodic seabed (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 209-213 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The interaction of surface gravity waves on a nonuniformly periodic seabed is considered. The method of multiple scales is used to analyze the interaction leading to two coupled-mode equations. The power reflection coefficient is used as an indicator to evaluate the filter action of the bottom corrugation. The results show that the modes are strongly coupled when the Bragg resonant condition is satisfied. The characteristics of the filtration are found to be enhanced by imposing special types of amplitude and phase modulated periodic nonuniformities, including amplitude taper and chirped periodic variations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868067
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of bulges on the stability of boundary layers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 796-806 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The instability of flows around hump and dip imperfections is investigated. The mean flow is calculated using interacting boundary layers, thereby accounting for viscous/inviscid interaction and separation bubbles. Then, the two-dimensional linear stability of this flow is analyzed, and the amplification factors are computed. Results are obtained for several height/width ratios and locations. The theoretical results have been used to correlate the experimental results of Walker and Greening (British Aeronautical Research Council 5950, 1942). The observed transition locations are found to correspond to amplification factors varying between 7.4 and 10.0, consistent with previous results for flat plates. The method accounts for both viscous and shear-layer instabilities. Separation is found to increase significantly the amplification factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866815
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  • 8
    Electronic Resource
    Electronic Resource
    Stability of flow over axisymmetric bodies with porous suction strips (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 2990-2998 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical-perturbation scheme is used to determine the stability of incompressible flows past axisymmetric bodies with porous strips. Linear triple deck, closed-form solutions are developed for the basic-flow quantities, which account for upstream influence. These solutions are linear superpositions of the flow past the body without suction plus the perturbations caused by the suction strips. The flow past the suctionless body is calculated using the Transition Analysis Program System (TAPS). A perturbation scheme is used to determine the increment aij in the complex wavenumber at a given location sj because of the presence of a strip centered at si. The end result is a set of influence coefficients that can be used to determine the growth rates and amplification factors for any suction levels without repeating the calculations. The influence coefficients are used to develop a simple linear optimization scheme to determine the number, spacing, and mass flow rate through the strips on an axisymmetric body.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865138
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  • 9
    Electronic Resource
    Electronic Resource
    Editor's introduction (1990)
    Springer
    Nonlinear dynamics 1 (1990), S. v 
    Details
    ISSN: 1573-269X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01857581
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  • 10
    Electronic Resource
    Electronic Resource
    Three-dimensional nonlinear vibrations of composite beams — I. Equations of motion (1990)
    Springer
    Nonlinear dynamics 1 (1990), S. 477-502 
    Details
    ISSN: 1573-269X
    Keywords: Composite beams ; flexural-flexural-torsional-extensional vibrations ; nonlinear equations of motion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Newton's second law is used to develop the nonlinear equations describing the extensional-flexural-flexural-torsional vibrations of slewing or rotating metallic and composite beams. Three consecutive Euler angles are used to relate the deformed and undeformed states. Because the twisting-related Euler angle ϕ is not an independent Lagrangian coordinate, twisting curvature is used to define the twist angle, and the resulting equations of motion are symmetric and independent of the rotation sequence of the Euler angles. The equations of motion are valid for extensional, inextensional, uniform and nonuniform, metallic and composite beams. The equations contain structural coupling terms and quadratic and cubic nonlinearities due to curvature and inertia. Some comparisons with other derivations are made, and the characteristics of the modeling are addressed. The second part of the paper will present a nonlinear analysis of a symmetric angle-ply graphite-epoxy beam exhibiting bending-twisting coupling and a two-to-one internal resonance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01856950
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