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  • Articles  (21)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Flow, turbulence and combustion 58 (1997), S. 191-206 
    ISSN: 1573-1987
    Keywords: bubbles ; drops ; spray ; ocean spray ; evaporation ; Tropical Cyclones
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Because of the potentially important influence of ‘spray cooling’ on the thermodynamics of Tropical Cyclones, there is a need for estimates of ocean spray distribution at extreme wind speeds, at least twice those for which detailed spray observations have been made. To assist in such extrapolation, a simplified probabilistic model is developed, with the three main effects (gusts, gravity, evaporation) that influence how spray droplets are distributed taken into account, but with as much simplicity as possible in other respects.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of engineering mathematics 30 (1996), S. 35-78 
    ISSN: 1573-2703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract Helical distributions of stokeslets can valuably model microbial locomotion through a fluid, and also the flow field generated, wherever a flagellum actively executes helical undulations (as in many single-celled algae and protozoa) or where (as in many bacteria) the action of rotary motors causes a passive structure of helical shape (which may be a flagellum or else the cell body itself) to rotate. Here, previous biomechanical studies of such modes of locomotion are extended to include analyses of three-dimensional flow fields. In some cases, a rotlet field (curl of a stokeslet) needs to be incorporated in the models. For example, spirochete swimming is modelled by combined helical distributions of stokeslets and rotlets; the computed flow field being confined to within distances of less than twice the radius of the cell body's helical shape from its axis, while including a powerful jet-like interior flow through the coils of the swimming spirochete.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of engineering mathematics 30 (1996), S. 25-34 
    ISSN: 1573-2703
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract Lorentz [1] pioneered the representation of flows at very low Reynolds number by a surface distribution of stokeslets — whose strengths, nowadays, are computed by surface-velocity collocations. That method is here compared with a representation widely used in flagellar hydrodynamics, by a curvilinear distribution of stokeslets and dipoles along the flagellar centreline; with the velocity of each cross-section expressed as a centreline value of the combined fields of singularities beyond a certain cutoff distance. The latter is also a good representation, and offers moreover some computational advantages. This paper establishes the equivalence of the two representations, and identifies those properties of Stokes flows which make both the dipoles and the cutoff essential to that equivalence.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of engineering mathematics 35 (1999), S. 11-42 
    ISSN: 1573-2703
    Keywords: hurricanes ; typhoons ; spray ; droplets ; evaporation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Technology
    Notes: Abstract Serious gaps in knowledge about ocean spray at wind speeds over 40m/s remain difficult to fill by observation or experiment; yet refined study of the thermodynamics of Tropical Cyclones (including typhoons and hurricanes) requires assessment of the hypothesis that 'spray cooling' at extreme wind speeds may act to reduce (i) the initial temperature of saturated air rising in the eyewall and so also (ii) the input of mechanical energy into the airflow as a whole. Such progressive reductions at higher speeds could, for example, make any possible influence of future global warming on Tropical Cyclone intensification largely self-limiting. In order to help in extrapolation of knowledge on ocean spray to extreme wind speeds, a probabilistic analysis is introduced which allows for the effects of gusts, gravity and evaporation on droplet distributions, yet in other respects is as simple as possible. Preliminary indications from this simplified analysis appear to confirm the potential importance of spray cooling.
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  • 5
    Publication Date: 1979-08-01
    Description: Hoverming motions, by which an animal (or a helicopter) in stationary fluid generates a downflow to support its weight, entail energy costs that include the induced power (power supplied to that downflow). The simplest classical model for induced power is the actuator-disk model. This paper shows how a relatively insignificant modification can be made to that model to make it aerodynamically self-consistent. The modified simple model of the downflow may be evaluated in fluid that either is unbounded or is bounded below by horizontal ground. Comparison of the calculated induced powers in the two cases (even though made in this paper not for the true axisymmetric flow patterns but for the corresponding two-dimensional flow patterns) appears to give a more satisfactory analysis than was previously available of the observed reduction of induced power associated with proximity to the ground. © 1979, Cambridge University Press
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 6
    Publication Date: 1990-04-01
    Description: Cross-sectional shapes of many fish bodies are well approximated by ellipses. The simple elongated-body theory of balistiform locomotion was developed by Lighthill & Blake (1990) only in the limiting case when the axis ratio of the cross-section tends to zero. In that case they established that the movements of dorsal and anal fins, if attached to a rigid fish body of far greater depth, create fluid motions with substantially enhanced momentum. In this paper, standard conformal mappings are used to establish that enhancement is substantial also with elliptic cross-sections of arbitrary axis ratio, not only in balistiform locomotion with synchronous movement of two median fins but also in gymnotiform locomotion with movement of just a single (ventral) fin. © 1990, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 7
    Publication Date: 1979-03-23
    Description: Submerged resonant ducts offer an approach to the design of wave-energy extraction devices consistent with the need for maximum seaworthiness. This paper gives a full account of one type of analysis of these systems, based upon two-dimensional wave hydrodynamics and linearized duct dynamics. The mathematical analyses are given in detail in § 2 while § 1 describes as concisely as possible (i) the assumptions underlying each analysis, (ii) its results and their implications for design, and (iii) any available experimental comparisons. One theoretical prediction, unexpected when it was first made but since confirmed by experiment (Knott & Flower 1979), is that the effective pressure fluctuations to which a resonant duct responds can be substantially greater than those that would be present at the level of the duct mouth if the duct were absent. Other important predictions are concerned with added mass, radiation damping and the conditions for optimum energy extraction, calculated below for a wide variety of mouth design configurations and internal duct geometries. Broad tentative conclusions from the analyses are given at the end of § 1. © 1979, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 8
    Publication Date: 1979-02-01
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 9
    Publication Date: 1981-05-01
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 10
    Publication Date: 1990-04-01
    Description: Elongated-body theory, used by Lighthill & Blake (1990) to investigate fish locomotion by undulatory movements of median fins, and to demonstrate momentum enhancement in the case when motile fins are attached to a rigid fish body of far greater depth, approximates local fluid motions by solutions of the two-dimensional Laplace equation. Here, a better local approximation (equation (2) below) to the three-dimensional Laplace equation for fluid motions of undulatory type is used to investigate the possibility of short-wavelength limitations on momentum enhancement. In an extreme case (fish bodies of very small width and very large depth) when on elongated-body theory the momentum enhancement factor β is predicted to become very large, short-wavelength considerations are shown to place a specific upper limit on β (see figure 2). In more general cases, this upper limit should perhaps be regarded as coexisting with other upper limits associated with either nonzero width or finite depth of fish body. Short-wavelength limitations on momentum enhancement are of some biological interest as implying the existence not only of advantages (including a reduction in body drag) but also of some competing disadvantages (limitations in propulsive force) arising from progressive reductions in the wavelength of fin undulations. © 1990, Cambridge University Press. All rights reserved.
    Print ISSN: 0022-1120
    Electronic ISSN: 1469-7645
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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