Dynamics and Stability of Boats With Aerodynamic Support

2013 ◽  
Vol 29 (01) ◽  
pp. 17-24
Author(s):  
Konstantin I. Matveev ◽  
Nikolai Kornev
Keyword(s):  
Ground Effect ◽  
Ground Vehicles ◽  
Marine Transportation ◽  
Technical Problems ◽  
Transient Regimes ◽  
High Speeds ◽  
Effect Theory ◽  
Stability Issues ◽  
Marine Vehicle ◽  
Very High

Aerodynamic support is beneficial for achieving very high speeds of marine transportation. Wing-in-ground vehicles, power-augmented ram platforms, and ultrafast planing multihulls are examples of marine craft with air assistance. The main technical problems in the development and application of these concepts for marine transportation are to ensure motion stability and to provide adequate seaworthiness. In this article, we illustrate applications of several mathematical models for various air supported marine vehicle concepts and discuss their specific stability issues. The aerodynamic submodels are based on nonlinear vortex-lattice methods and on the extreme ground effect theory, whereas unsteady hydrodynamics of planing surfaces are treated with added-mass strip theories. The static and dynamic stability in the vicinity of equilibrium states can be analyzed by linearized approaches. However, motions in transient regimes and unsteady environments require implementation of nonlinear and fully unsteady modeling methods.

scholarly journals Some Issues on the Foundations of Modern Cosmology, Gravitation and Quantum Physics

Universe ◽  
2020 ◽  
Vol 6 (11) ◽  
pp. 189
Author(s):  
Emilio Elizalde
Keyword(s):  
Quantum Physics ◽  
Pseudodifferential Operators ◽  
Casimir Effect ◽  
Technical Problems ◽  
High Speeds ◽  
Expansion Of The Universe ◽  
Historical Issues ◽  
The Universe ◽  
Physical Quantities ◽  
Very High

After the first clear evidence of the recession—at very high speeds—of the spiral nebulae was announced by V.M. Slipher in 1914, as a result of his work started in 1912, it still took several decades to properly understand the phenomenon in terms of an expansion of the Universe. Some historical issues around that crucial discovery and the contemporary attempts at determining the scale of the visible Universe will be discussed. Presently, very important questions to answer are: What is the precise value of the expansion rate? What drives the acceleration of the Universe’s expansion? The latter is called dark energy, but what is it actually? The possibility that this could be the result of a sort of Casimir effect at the cosmological level has not been discarded, yet. One of the main technical problems in tackling this issue is constituted by the regularization and corresponding renormalization procedures. Beautiful but rather non-trivial mathematics, involving the zeta function of pseudodifferential operators (associated with physical quantities), are key in this respect. A discussion of those items is provided here.

Gliding Flight of the Dog-Faced Bat Rousettus Aegyptiacus Observed in a Wind Tunnel

1971 ◽  
Vol 55 (3) ◽  
pp. 833-845 ◽  
Author(s):  
C. J. PENNYCUICK
Keyword(s):  
Wind Tunnel ◽  
Lift Coefficient ◽  
Trailing Edge ◽  
Number Range ◽  
High Speeds ◽  
Gliding Flight ◽  
Speed Range ◽  
Simple Regression Analysis ◽  
Drag Analysis ◽  
Very High

1. A bat was trained to fly in a tilting wind tunnel. Stereoscopic photographs were taken, both by reflected and by transmitted light, and measurements of best gliding angle were made. 2. Variation of wing span and area at different speeds was much less than in birds. This is attributed to the construction of the wing, which prevents the bat from folding back the manus in flight, because this would lead to collapse of the plagiopatagium. 3. The trailing edge of the wing is normally deflected upwards in flight, at least in the distal parts. This is interpreted as providing longitudinal stability. The plagiopatagialis proprii muscles appear to act as an elevator, by deflecting the trailing edge of the plagiopatagium upwards. 4. The speed range over which the bat could glide was 5·3-11·0 m/s. Its maximum lift coefficient was 1·5, and its best glide ratio 6·8:1. The Reynolds number range, based on mean chord, was 3·26 x 104 to 6·79 x 104. 5. A simple regression analysis of the glide polar indicated a very high span efficiency factor (k) and low wing profile drag coefficient (Cdp). On the other hand, a drag analysis on the assumption that k = 1 leads to an improbably large increase in the estimated Cdp at low speeds. It is suggested that the correct interpretation probably lies between these extremes, with k ≊ 1·5; Cdp would then be about 0·02 at high speeds, rising to somewhat over 0·1 at the minimum speed. 6. It would appear that the bat is not so good as a pigeon at fast gliding, but better at low-speed manoeuvring. On most points of performance, however, the two are remarkably similar.

Flow Field on Helodeck of a Frigate: A Review

2019 ◽  
Vol 161 (A4) ◽  
Keyword(s):  
Flow Field ◽  
Numerical Solutions ◽  
Offshore Structures ◽  
High Speeds ◽  
High Turbulence ◽  
The Subject ◽  
Offshore Industry ◽  
The Military ◽  
Very High ◽  
Made In

The various functions desired from a frontline warship such as a frigate, corvette or a destroyer, coupled with the requirement of very high speeds and economic viability restricting the size, necessitates a very dense arrangement of weapons and sensors on the top deck and superstructure. Accordingly, Navies across the world have faced several problems with respect to functions for which a good aerodynamic design for these structures is essential. Major issues include smoke nuisance created due to impinging of the ship's exhaust gases on to the top deck leading to possible suction by engine intakes and high turbulence in the ship's air-wake leading to ship aircraft interface concerns. The flow field on the helodeck is extremely complex due to its geometry and interaction with the wake of the ship’s superstructure. A knowledge of this complexity is essential for ensuring safe helo operations on the helodeck. The problem of ship helicopter interaction has hogged the lime light in recent times, due to rising demand for design of warships for increased stealth, especially in the past two decades. Consequently, several researchers in countries with advanced Navies have invested considerable resources towards evolving both experimental and numerical solutions for the problem. However, given the military nature of the operations, open literature on the subject containing details of such research, which can be used as reference material for present work, are limited. Considering the complexities involved in the problem, an attempt has been made in this paper to holistically review the widely scattered and limited literature in this field. A good amount of literature on marine helo applications emerge from the offshore industry. Keeping in mind that the fields of warship design and offshore structures are dissimilar and have their peculiar problems, informed conclusions have been made in drawing lessons from available literature.

Unsteady control surface loads of lifting re-entry vehicles at very high speeds

1967 ◽  
Author(s):  
R. GOLDMAN ◽  
M. MORKOVIN ◽  
R. SCHUMACHER
Keyword(s):  
Control Surface ◽  
High Speeds ◽  
Very High ◽  
Surface Loads

Modeling of Finite-span Ram Wings Moving Above Water at Finite Froude Numbers

2014 ◽  
Vol 58 (03) ◽  
pp. 146-156
Author(s):  
Konstantin I. Matveev
Keyword(s):  
Potential Flow ◽  
Ground Effect ◽  
Flow Theory ◽  
Solid Surfaces ◽  
Forward Motion ◽  
Variable Parameters ◽  
Finite Span ◽  
Effect Theory ◽  
Lifting Surfaces ◽  
Strong Ground

Power-augmented ram wings can be used for very fast transportation of heavy cargo over water and relatively flat solid surfaces. This article describes a coupled aerohydrodynamic model for a ram wing in steady forward motion. Effects of a finite wingspan and finite Froude numbers are accounted for by the extreme ground effect theory for airflow and a linearized potential flow theory for water. Representative results showing the influence of several variable parameters of the vehicle geometry and operational regimes are demonstrated for a selected ram-wing configuration. The developed method can be applied for modeling of airborne lifting surfaces operating in the strong ground effect on a variety of fast marine craft.

Vertical-Plane Dynamics of Power-Augmented-Ram Vehicle

2013 ◽  
Author(s):  
Konstantin I. Matveev
Keyword(s):  
Control Systems ◽  
High Speed ◽  
Dynamic Models ◽  
Vertical Plane ◽  
Ground Effect ◽  
Forward Speed ◽  
Unsteady Forces ◽  
Wind Gusts ◽  
Strip Theory ◽  
Effect Theory

Power-augmented-ram vehicles represent novel air-assisted marine craft that can be used for high-speed amphibious transportation of heavy cargo. These vehicles rely on combined hydrodynamic and aerodynamic support that is also augmented by front air-based propulsors. Dynamic models for these craft in the presence of wind gusts and surface waves are needed for confident design of these vehicles, including motion control systems. This study addresses 3-DOF vertical-plane dynamics. The models for unsteady forces are based on the aerodynamic extreme-ground-effect theory and hydrodynamic added-mass strip theory. Modeling of the vehicle motions are carried out for cases of head and following wind gusts and waves of low and high amplitudes. Simulation results can be used for determining amplitudes of the vehicle responses, peak accelerations, and forward speed degradation.

Modeling Machining at High Speeds as a Fluid Mechanics Problem

2008 ◽  
Author(s):  
Roman V. Kazban ◽  
James J. Mason
Keyword(s):  
Fluid Mechanics ◽  
Stagnation Point ◽  
Potential Flow ◽  
High Speed ◽  
Material Behavior ◽  
High Speed Machining ◽  
Flow Solution ◽  
High Speeds ◽  
Ultra High Speed ◽  
Very High

Even though many models for machining exist, most of them are for low-speed machining, where momentum is negligible and material behavior is well approximated by quasi-static plastic constitutive laws. In machining at high speeds, momentum can be important and the strain rate can be exceedingly high. For these reasons, a fluid mechanics approach to understanding high-speed, very high-speed, and ultra-high-speed machining is attempted here. Namely, a potential flow solution is used to model the behavior of the material around a sharp tool tip during machining at high speeds. It is carefully argued that the potential flow solution is relevant and can be used as a first approximation to model the behavior of a metal during high-speed, very high-speed, or ultra-high-speed machining events; and at a minimum, the potential flow solution is qualitatively useful in understanding mechanics of machining at high speeds and above. Interestingly, the flow solution predicts that there is a stagnation point on the rake face, not at the tool tip as is usually assumed. Because the stagnation point is not at the tool tip, the flow solution predicts a significant amount of deformation in the workpiece resulting in large residual strains that may lead to a temperature rise on the finished surface.

scholarly journals Foraging at the edge of the world: low-altitude, high-speed manoeuvering in barn swallows

2016 ◽  
Vol 371 (1704) ◽  
pp. 20150391 ◽  
Author(s):  
Douglas R. Warrick ◽  
Tyson L. Hedrick ◽  
Andrew A. Biewener ◽  
Kristen E. Crandell ◽  
Bret W. Tobalske
Keyword(s):  
Wind Speed ◽  
High Speed ◽  
Ground Effect ◽  
Natural State ◽  
Wingbeat Frequency ◽  
High Speeds ◽  
Aerial Insectivores ◽  
Video Systems ◽  
Shear Gradient ◽  
Barn Swallows

While prior studies of swallow manoeuvering have focused on slow-speed flight and obstacle avoidance in still air, swallows survive by foraging at high speeds in windy environments. Recent advances in field-portable, high-speed video systems, coupled with precise anemometry, permit measures of high-speed aerial performance of birds in a natural state. We undertook the present study to test: (i) the manner in which barn swallows ( Hirundo rustica ) may exploit wind dynamics and ground effect while foraging and (ii) the relative importance of flapping versus gliding for accomplishing high-speed manoeuvers. Using multi-camera videography synchronized with wind-velocity measurements, we tracked coursing manoeuvers in pursuit of prey. Wind speed averaged 1.3–2.0 m s −1 across the atmospheric boundary layer, exhibiting a shear gradient greater than expected, with instantaneous speeds of 0.02–6.1 m s −1 . While barn swallows tended to flap throughout turns, they exhibited reduced wingbeat frequency, relying on glides and partial bounds during maximal manoeuvers. Further, the birds capitalized on the near-earth wind speed gradient to gain kinetic and potential energy during both flapping and gliding turns; providing evidence that such behaviour is not limited to large, fixed-wing soaring seabirds and that exploitation of wind gradients by small aerial insectivores may be a significant aspect of their aeroecology. This article is part of the themed issue ‘Moving in a moving medium: new perspectives on flight'.

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