scholarly journals The geometry and dynamics of Danish anchor seine ropes on the seabed

2020 ◽  
Author(s):  
F G O’Neill ◽  
T Noack
Keyword(s):  
Environmental Impact ◽  
Angle Of Attack ◽  
Two Dimensional ◽  
Capture Process ◽  
Gear Selectivity ◽  
Operational Data

Abstract We present a two-dimensional kinematic description of the geometry and dynamics of the ropes of demersal seines during deployment, towing, and hauling, using piriform curves. Piriforms (which means pear shaped) are relatively simple analytical curves, which we parameterize, using basic positional and operational data from typical Danish anchor seine hauls. We then demonstrate how we can estimate the area fished, and the speed, direction and angle of attack of any part of the seine net rope, at any time during the fishing process. This sort of information is fundamental to a better understanding of the capture process of demersal seines, their whole gear selectivity, and their environmental impact.

The Political Economy and Political Aesthetics of Military Maps

2019 ◽  
pp. 184-205
Author(s):  
Catherine Lutz
Keyword(s):  
Political Economy ◽  
Environmental Impact ◽  
The Political ◽  
Two Dimensional ◽  
Island Populations ◽  
Political Aesthetics ◽  
The Us ◽  
Representational Power ◽  
The Impact

This chapter explores the representational power of maps and the violence inherent in removing volume with two-dimensional ‘objectivity’. The focus is on maps, norms and militarist institutions in Guam, foregrounding underexplored aesthetic dimensions in reports on the environmental impact of the US presence. The impact of overseas US bases is striking, a global archipelago of military infrastructure that impacts on ‘strategic and disposable’ island populations. This chapter recognizes the layers of security available even in ‘transparent’ maps.

Two-Dimensional Experimental Investigation on the Effects of a Fowler Flap Gap and Overlap Size on the Wake Flow Field

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
David Demel ◽  
Mohsen Ferchichi ◽  
William D. E. Allan ◽  
Marouen Dghim
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Angle Of Attack ◽  
Wake Flow ◽  
Two Dimensional ◽  
Edge Region ◽  
Suction Surface ◽  
Trailing Edge ◽  
Piv Measurements ◽  
Image Velocimetry

This work details an experimental investigation on the effects of the variation of flap gap and overlap sizes on the flow field in the wake of a wing-section equipped with a trailing edge Fowler flap. The airfoil was based on the NACA 0014-1.10 40/1.051 profile, and the flap was deployed with 40 deg deflection angle. Two-dimensional (2D) particle image velocimetry (PIV) measurements of the flow field in the vicinity of the main wing trailing edge and the flap region were performed for the optimal flap gap and overlap, as well as for flap gap and overlap increases of 2% and 4% chord beyond optimal, at angles of attack of 0 deg, 10 deg, and 12 deg. For all the configurations investigated, the flow over the flap was found to be fully stalled. At zero angle of attack, increasing the flap gap size was found to have minor effects on the flow field but increased flap overlap resulted in misalignment between the main wing boundary layer (BL) flow and the slot flow that forced the flow in the trailing edge region of the main wing to separate. When the angle of attack was increased to near stall conditions (at angle of attack of 12 deg), increasing the flap gap was found to energize and improve the flow in the trailing edge region of the main wing, whereas increased flap overlap further promoted flow separation on the main wing suction surface possibly steering the wing into stall.

scholarly journals Laser Displacement Sensors for Wind Tunnel Model Position Measurements

Sensors ◽  
2018 ◽  
Vol 18 (12) ◽  
pp. 4085 ◽  
Author(s):  
Matthew Kuester ◽  
Nanyaporn Intaratep ◽  
Aurélien Borgoltz
Keyword(s):  
Wind Tunnel ◽  
Angle Of Attack ◽  
Pitching Moment ◽  
Two Dimensional ◽  
Temperature Drift ◽  
Wind Tunnel Model ◽  
Multiple Sensors ◽  
Displacement Sensors ◽  
Tunnel Model ◽  
Linear Encoder

Wind tunnel measurements of two-dimensional wing sections, or airfoils, are the building block of aerodynamic predictions for many aerodynamic applications. In these experiments, the forces and pitching moment on the airfoil are measured as a function of the orientation of the airfoil relative to the incoming airflow. Small changes in this angle (called the angle of attack, or α ) can create significant changes in the forces and moments, so accurately measuring the angle of attack is critical in these experiments. This work describes the implementation of laser displacement sensors in a wind tunnel; the sensors measured the distance between the wind tunnel walls and the airfoil, which was then used to calculate the model position. The uncertainty in the measured laser distances, based on the sensor resolution and temperature drift, is comparable to the uncertainty in traditional linear encoder measurements. Distances from multiple sensors showed small, but statistically significant, amounts of model deflection and rotation that would otherwise not have been detected, allowing for an improved angle of attack measurement.

Aerodynamic characteristics of a two-dimensional porous sail

1989 ◽  
Vol 206 ◽  
pp. 463-475 ◽  
Author(s):  
S. Murata ◽  
S. Tanaka
Keyword(s):  
Numerical Analysis ◽  
Pressure Distribution ◽  
Dynamic Stability ◽  
Jacobi Polynomials ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Two Dimensional ◽  
Centre Of Pressure ◽  
Edge Conditions

A method is presented for the numerical analysis of the aerodynamic characteristics of a two-dimensional single-surface porous sail. In this analysis the authors apply a series of Jacobi polynomials to express the pressure distribution and chordwise shape, considering carefully leading-edge conditions. It is found that the aero-dynamic stability of a sail increases with increasing porosity. The effects of porosity on the value of the life coefficient and the position of the centre of pressure are shown in diagrams as functions of angle of attack and of excess length of membrane over the chord length.

The Actuator Surface Model: A New Navier–Stokes Based Model for Rotor Computations

2009 ◽  
Vol 131 (1) ◽  
Author(s):  
Wen Zhong Shen ◽  
Jian Hui Zhang ◽  
Jens Nørkær Sørensen
Keyword(s):  
Wind Turbine ◽  
Numerical Technique ◽  
Angle Of Attack ◽  
Vertical Axis ◽  
Navier Stokes ◽  
Surface Model ◽  
Two Dimensional ◽  
Vertical Axis Wind Turbine ◽  
Flow Past ◽  
Surface Technique

This paper presents a new numerical technique for simulating two-dimensional wind turbine flow. The method, denoted as the 2D actuator surface technique, consists of a two-dimensional Navier–Stokes solver in which the pressure distribution is represented by body forces that are distributed along the chord of the airfoils. The distribution of body force is determined from a set of predefined functions that depend on angle of attack and airfoil shape. The predefined functions are curve fitted using pressure distributions obtained either from viscous-inviscid interactive codes or from full Navier–Stokes simulations. The actuator surface technique is evaluated by computing the two-dimensional flow past a NACA 0015 airfoil at a Reynolds number of 106 and an angle of attack of 10deg and by comparing the computed streamlines with the results from a traditional Reynolds-averaged Navier–Stokes computation. In the last part, the actuator surface technique is applied to compute the flow past a two-bladed vertical axis wind turbine equipped with NACA 0012 airfoils. Comparisons with experimental data show an encouraging performance of the method.

Density and velocity fields in collisionless flow past a diffusely reflecting cone

1970 ◽  
Vol 48 (13) ◽  
pp. 1628-1631
Author(s):  
James Parker Elliott
Keyword(s):  
Flow Field ◽  
Free Stream ◽  
Angle Of Attack ◽  
Velocity Fields ◽  
Circular Cone ◽  
Two Dimensional ◽  
Transition Flow ◽  
Flow Past ◽  
Monatomic Gas

Results of flow field calculations for the collisionless flow of a neutral, monatomic gas past a diffusely reflecting right circular cone at zero angle of attack with the free stream are presented. Singularities at the vertex and at the shoulder of the base are illustrated and discussed. Comparison is made with similar results for spheres and two-dimensional polygonal bodies and with results for transition flow past sharp cones. Methods for improving the analysis are suggested.

Two-dimensional potential flow solutions with separation

2010 ◽  
Vol 657 ◽  
pp. 238-264 ◽  
Author(s):  
A. VERHOFF
Keyword(s):  
Integral Formula ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Surface Flow ◽  
Recirculation Region ◽  
Two Dimensional ◽  
Variable Theory ◽  
Generalized Poisson ◽  
Contour Maps ◽  
Complex Variable Theory

A procedure for constructing two-dimensional incompressible potential flowfield solutions with separation and a recirculation region is presented. It naturally makes use of complex variable theory and other analysis techniques such as conformal mapping and the generalized Poisson integral formula. Flowfield determination is reduced to solution of a boundary value problem in various simple domains. The entire velocity field is described analytically; stream function and velocity potential contour maps are readily constructed. Example solutions are presented. Solutions for sharp leading edge airfoils at arbitrary angle of attack are completely determined, including the limiting angle of attack for upper-surface flow re-attachment. For other configurations (e.g. circular cylinder, backward-facing step) the analytical solution contains one or more free parameters, whose values may be inferred from boundary layer theory or experiment.

Transonic flow around the leading edge of a thin airfoil with a parabolic nose

1993 ◽  
Vol 248 ◽  
pp. 1-26 ◽  
Author(s):  
Z. Rusak
Keyword(s):  
Pressure Distribution ◽  
Stagnation Point ◽  
Asymptotic Expansions ◽  
Potential Flow ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Two Dimensional ◽  
Small Disturbance ◽  
Outer Expansion ◽  
Inner Region

Transonic potential flow around the leading edge of a thin two-dimensional general airfoil with a parabolic nose is analysed. Asymptotic expansions of the velocity potential function are constructed at a fixed transonic similarity parameter (K) in terms of the thickness ratio of the airfoil in an outer region around the airfoil and in an inner region near the nose. These expansions are matched asymptotically. The outer expansion consists of the transonic small-disturbance theory and it second-order problem, where the leading-edge singularity appears. The inner expansion accounts for the flow around the nose, where a stagnation point exists. Analytical expressions are given for the first terms of the inner and outer asymptotic expansions. A boundary value problem is formulated in the inner region for the solution of a uniform sonic flow about an infinite two-dimensional parabola at zero angle of attack, with a symmetric far-field approximation, and with no circulation around it. The numerical solution of the flow in the inner region results in the symmetric pressure distribution on the parabolic nose. Using the outer small-disturbance solution and the nose solution a uniformly valid pressure distribution on the entire airfoil surface can be derived. In the leading terms, the flow around the nose is symmetric and the stagnation point is located at the leading edge for every transonic Mach number of the oncoming flow and shape and small angle of attack of the airfoil. The pressure distribution on the upper and lower surfaces of the airfoil is symmetric near the edge point, and asymmetric deviations increase and become significant only when the distance from the leading edge of the airfoil increases beyond the inner region. Good agreement is found in the leading-edge region between the present solution and numerical solutions of the full potential-flow equations and the Euler equations.

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