Development of Fixed Hydrodynamic Lifting Surfaces to Stabilise Anchoring Structures in Energetic Tidal Flows

2012 ◽  
Author(s):  
Samuel F. Harding ◽  
Ian G. Bryden
Keyword(s):  
Vertical Velocity ◽  
Lift Force ◽  
Longitudinal Velocity ◽  
Combined Effect ◽  
Potential Contribution ◽  
Velocity Fluctuations ◽  
Unsteady Aerodynamic ◽  
Tidal Flows ◽  
Lifting Surfaces ◽  
Set Up

This paper presents the research currently being carried out on the potential contribution of hydrofoils to generate additional down-force on seabed fastenings in energetic tidal flows. Firstly, the dynamic lift of a hydrofoil subjected to vertical velocity perturbations was analyzed numerically, showing the reduced response to the fluctuation when unsteady aerodynamic theories are introduced. Secondly, an experimental set-up was developed for the deterministic generation of two-dimension velocity perturbations in a recirculating water flume. This will allow the combined effect of vertical and longitudinal velocity fluctuations on the lift force to be measured.

Spectral analysis and coherence of aerodynamic lift on rectangular cylinders in turbulent flow

2017 ◽  
Vol 830 ◽  
pp. 408-438 ◽  
Author(s):  
Shaopeng Li ◽  
Mingshui Li
Keyword(s):  
Turbulent Flow ◽  
Closed Form ◽  
Vertical Velocity ◽  
Lift Force ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Velocity Fluctuations ◽  
Dimensional Effects ◽  
Decay Parameters ◽  
Rectangular Cylinders

The goal of the present work is to derive the closed-form expressions of coherence and admittances to describe the spatial distribution of lift on rectangular cylinders in turbulent flow, which can be used to investigate the three-dimensional effects of turbulence. The coherence of the three-dimensional aerodynamic admittance (3D AAF), which takes into full account the spanwise variations in the vertical velocity fluctuations, is introduced to assess the validity of the strip assumption. A theoretical coherence model expressed in a double-exponential form is derived starting from the two-wavenumber spectral tensor of the lift on a thin aerofoil in Fourier space, providing us with explicit insight into the coherence of the lift force. Notably, it is an intrinsic property that the lift force on the structure is more strongly correlated than the oncoming flow and 3D AAF. This coherence model is extended to rectangular cylinders by the introduction of three floating parameters into the decay parameters of the 3D AAF. Based on theoretical and experimental investigations, it is shown that the three-dimensional effects of turbulence grow more prominent as the difference between the decay parameters of the 3D AAF and vertical velocity fluctuations decreases. A generalized approach for rapidly deriving the closed-form expressions of the admittances is proposed to study the unsteady behaviour of the lift force and the distortion of the free stream passing through the rectangular cylinders.

Complementing the ICC Efforts to Curb the Impunity of International Crimes in Africa

2017 ◽  
Author(s):  
Pacifique Manirakiza
Keyword(s):  
South African ◽  
International Criminal ◽  
Criminal Court ◽  
Potential Contribution ◽  
African Continent ◽  
Community Based ◽  
Academic Literature ◽  
International Crimes ◽  
Set Up ◽  
Thabo Mbeki

A matter raised consistently by eminent personalities asked to report on atrocities in Africa, such as former South African President Thabo Mbeki, is the utilization of traditional justice mechanisms known to Africans. Their use has been limited to Gacaca courts in Rwanda, set up in haste and subject to much criticism. However, there exist several types and models of traditional justice mechanisms at the African level. The contribution of these sui generis mechanisms towards accountability for heinous crimes is largely unaddressed in academic literature. This chapter intends to fill this gap by exploring their potential contribution towards accountability for heinous crimes, alongside the International Criminal Court (ICC). In short, the chapter explores how community-based judicial mechanisms and the ICC, two types of accountability mechanisms with different methodologies and approaches, can work side by side to eradicate impunity regarding, and also to prevent, mass atrocities on the African continent.

Flight

2018 ◽  
Author(s):  
Anders Hedenström
Keyword(s):  
Bird Species ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Leading Edge Vortex ◽  
Confined Spaces ◽  
Unsteady Aerodynamic ◽  
Maneuvering Flight ◽  
Edge Vortex ◽  
Lifting Surfaces ◽  
Animal Flight

Animal flight represents a great challenge and model for biomimetic design efforts. Powered flight at low speeds requires not only appropriate lifting surfaces (wings) and actuator (engine), but also an advanced sensory control system to allow maneuvering in confined spaces, and take-off and landing. Millions of years of evolutionary tinkering has resulted in modern birds and bats, which are achieve controlled maneuvering flight as well as hovering and cruising flight with trans-continental non-stop migratory flights enduring several days in some bird species. Unsteady aerodynamic mechanisms allows for hovering and slow flight in insects, birds and bats, such as for example the delayed stall with a leading edge vortex used to enhance lift at slows speeds. By studying animal flight with the aim of mimicking key adaptations allowing flight as found in animals, engineers will be able to design micro air vehicles of similar capacities.

Linear and non-linear potential-flow calculations of free-surface waves with lift and induced drag

2000 ◽  
Vol 214 (6) ◽  
pp. 801-812
Author(s):  
C-E Janson
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Lift Force ◽  
Radiation Condition ◽  
Linear Potential ◽  
Surface Boundary ◽  
Model Approximation ◽  
Non Linear ◽  
Lifting Surfaces ◽  
The Waves

A potential-flow panel method is used to compute the waves and the lift force from surface-piercing and submerged bodies. In particular the interaction between the waves and the lift produced close to the free surface is studied. Both linear and non-linear free-surface boundary conditions are considered. The potential-flow method is of Rankine-source type using raised source panels on the free surface and a four-point upwind operator to compute the velocity derivatives and to enforce the radiation condition. The lift force is introduced as a dipole distribution on the lifting surfaces and on the trailing wake, together with a flow tangency condition at the trailing edge of the lifting surface. Different approximations for the spanwise circulation distribution at the free surface were tested for a surface-piercing wing and it was concluded that a double-model approximation should be used for low speeds while a single-model, which allows for a vortex at the free surface, was preferred at higher speeds. The lift force and waves from three surface-piercing wings, a hydrofoil and a sailing yacht were computed and compared with measurements and good agreement was obtained.

Artificially Thickened Turbulent Boundary Layers for Studying Heat Transfer and Skin Friction on Rough Surfaces

1983 ◽  
Vol 105 (2) ◽  
pp. 146-153 ◽  
Author(s):  
P. M. Ligrani ◽  
R. J. Moffat ◽  
W. M. Kays
Keyword(s):  
Skin Friction ◽  
Boundary Layers ◽  
Structural Characteristics ◽  
Turbulent Transport ◽  
Longitudinal Velocity ◽  
Hydrodynamic Characteristics ◽  
Rough Boundary ◽  
Turbulent Prandtl Number ◽  
Velocity Fluctuations ◽  
Normal Behavior

Thermal and hydrodynamic characteristics of boundary layers developing over uniform spheres roughness with momentum thicknesses as large as 1.43 cm are presented. To obtain thick hydrodynamic boundary layers, an artificial thickening device is employed. The normalized velocity and turbulence profiles produced using this device are two-dimensional and self-preserving. The turbulent transport and structural characteristics are representative of normal behavior to the level of spectra of the longitudinal velocity fluctuations. In the artificially thickened layers, the effect of the unheated starting length (ξ > 0, Δ < δ) on thermal boundary layer properties is present. Turbulent Prandtl number profiles are generally unaffected by the magnitude of the unheated starting length, whereas measured Stanton numbers, show different behavior as the unheated starting length varies. In thermal boundary layers which would have the same thickness as the augmented hydrodynamic layers (Δ ≃ δ), Stanton numbers are shown to be the same as skin friction coefficients, and are then provided for boundary layers much thicker than those previously studied. As fully rough boundary layers develop downstream and δ/ks increases, Cf/2 is proportional to δ2−b where b = 0.175. In order for such U∞ = constant, thick, rough wall layers to develop far enough downstream to reach smooth behavior where b = 0.250, ks Uτ/ν must become small, and b must increase from 0.175 to become greater than 0.250 in the transitionally rough regime.

Design of a Foldable Flapping Mechanism

2013 ◽  
Vol 437 ◽  
pp. 366-372
Author(s):  
Xiao Zhou Fan ◽  
Zhi Lin Zhang ◽  
Liang Chen
Keyword(s):  
Lift Force ◽  
Virtual Prototype ◽  
Flapping Wing ◽  
Optimal Parameters ◽  
Cam Mechanism ◽  
Set Up ◽  
3D Software ◽  
Flapping Mechanism

Folding motion is important for a flight creature using flapping wing mode, but it seldom used for flapping-wing robot. In this paper, we propose a new foldable flapping wing mechanism, which consists of spatial crank-rocker mechanism, parallelogram mechanism, and cam mechanism. We establish the kinematical models, calculate the optimal parameters, and set up the virtual prototype using 3D software. The tracks of wingtip and the comparison between foldable and unfoldable flap wing show that folding motion can improve lift force obviously.

scholarly journals Physical controls on orographic cirrus inhomogeneity

2007 ◽  
Vol 7 (14) ◽  
pp. 3771-3781 ◽  
Author(s):  
J. E. Kay ◽  
M. Baker ◽  
D. Hegg
Keyword(s):  
Vertical Velocity ◽  
Cloud Cover ◽  
Particle Growth ◽  
Physical Processes ◽  
Velocity Fluctuations ◽  
Ice Nuclei ◽  
Weather Model ◽  
Model Cloud ◽  
Homogeneous Freezing ◽  
The Relationship

Abstract. Optical depth distributions (P(σ)) are a useful measure of radiatively important cirrus (Ci) inhomogeneity. Yet, the relationship between P(σ) and underlying cloud physical processes remains unclear. In this study, we investigate the influence of homogeneous and heterogeneous freezing processes, ice particle growth and fallout, and mesoscale vertical velocity fluctuations on P(σ) shape during an orographic Ci event. We evaluate Lagrangian Ci evolution along kinematic trajectories from a mesoscale weather model (MM5) using an adiabatic parcel model with binned ice microphysics. Although the presence of ice nuclei increased model cloud cover, our results highlight the importance of homogeneous freezing and mesoscale vertical velocity variability in controlling Ci P(σ) shape along realistic upper tropospheric trajectories.

Calibration and use of a sailplane variometer to measure vertical velocity fluctuations

1979 ◽  
Vol 16 (1) ◽  
pp. 99-105 ◽  
Author(s):  
S. Sethuraman ◽  
R. M. Brown ◽  
G. S. Raynor ◽  
W. A. Tuthill
Keyword(s):  
Vertical Velocity ◽  
Velocity Fluctuations
Sign in / Sign up

Export Citation Format

Share Document