Hydrodynamic Evaluation of a Generic Sail Used in an Innovative Prawn-Trawl Otter Board

In prawn-trawling operations, otter boards provide the horizontal force required to maintain net openings, and are typically low aspect ratio (∼0.5) flat plates operating on the seabed at high angles of attack (AOA; 35–40°). Such characteristics cause otter boards to account for up to 30% of the total trawling resistance, including that from the vessel. A recent innovation is the batwing otter board, which is designed to spread trawls with substantially less towing resistance and benthic impacts. A key design feature is the use of a sail, instead of a flat plate, as the hydrodynamic foil. The superior drag and benthic performance of the batwing is achieved by (i) successful operation at an AOA of ∼20° and (ii) having the heavy sea floor contact shoe in line with the direction of tow. This study investigated the hydrodynamic characteristics of a generic sail by varying its twist and camber, to identify optimal settings for maximum spreading efficiency and stability. Loads in six degrees of freedom were measured at AOAs between 0 and 40° in a flume tank at a constant flow velocity, and with five combinations of twist and camber. The results showed that for the studied sail, the design AOA (20°) provides a suitable compromise between greater efficiency (occurring at lower AOAs) and greater effectiveness (occurring at higher AOAs). At optimum settings (20°, medium camber and twist), a lift-to-drag ratio >3 was achieved, which is ∼3 times more than that of contemporary prawn-trawling otter boards. Such a result implies relative drag reductions of 10–20% for trawling systems, depending on the rig configuration.

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CFD Investigation on the Hydrodynamic Characteristics of Blended Wing Unmanned Underwater Gliders With Emphasis on the Control Surfaces

Volume 6B: Ocean Engineering ◽

10.1115/omae2020-19280 ◽

2020 ◽

Author(s):

Mukesh Guggilla ◽

Vijayakumar Rajagopalan

Keyword(s):

The Body ◽

Hydrodynamic Characteristics ◽

Longitudinal Motion ◽

Low Velocity ◽

Sweep Angle ◽

Underwater Gliders ◽

Naca0012 Airfoil ◽

Drag Ratio ◽

Control Surfaces ◽

Lift To Drag Ratio

Abstract Underwater Gliders are unique buoyancy propelled oceanographic profiling vehicles. Their speed and endurance in longitudinal motion are affected by the symmetry, sweep dihedral angle and span of the control surfaces. In the low-velocity regime, these parameters can be varied to examine the flow around the glider. They also affect the lift-to-drag ratio (L/D) essential for the manoeuvring path in longitudinal and transverse motions. In this paper, the sweep angle of the main wing of a blended wing autonomous underwater glider configuration is varied as 10°, 15°, 30°, 45° and 60° and the resulting hull forms are numerically simulated in the commercial software, STARCCM+. The main wing is a tapered NACA0018 section (taken as per the general arrangement requirement) with 1.5m chord at the root and 0. 1m at the tip. The numerical model is validated using the CFD results of NACA0012 airfoil from Sun.C et al, 2015 [1]. The hydrodynamic forces are obtained by varying the angle of attack (α) of the body from −15° to 15°, for flow velocity of 0.4m/s. The hydrodynamic coefficients (lift-to-drag ratios) and flow physics around the wing are analyzed to arrive at an optimum Lift-to-drag ratio for increased endurance.

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General Observations of the Time-Dependent Flow Field Around Flat Plates in Free Fall

Volume 1: Symposia ◽

10.1115/ajkfluids2015-12708 ◽

2015 ◽

Author(s):

Jakob Hærvig ◽

Anna Lyhne Jensen ◽

Marie Cecilie Pedersen ◽

Henrik Sørensen

Keyword(s):

Degrees Of Freedom ◽

Model Development ◽

Digital Camera ◽

Free Fall ◽

Flat Plates ◽

Time Step ◽

Future Studies ◽

Six Degrees Of Freedom ◽

Dependent Flow

The free fall trajectories of flat plates are investigated in order to improve understanding of the forces acting on falling blunt objects. The long term goal is to develop a general applicable model to predict free fall trajectories. Numerically the free fall of a flat plate is investigated using a six degrees of freedom (6DOF) solver and a dynamic mesh. To validate the simulation, the trajectories of aluminium plates falling in water are recorded by digital camera recordings and compared to the simulation. The simulation is able to calculate the motion of the plate within each time step with high accuracy, and thereby allowing the whole trajectory to be predicted with fair accuracy. With the numerical model able to predict the free fall and the complex plate fluid interactions, fluids forces can be extracted for model development in future studies.

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An Experiment for the Study of Free-Flying Supercavitating Projectiles

Journal of Fluids Engineering ◽

10.1115/1.4003560 ◽

2011 ◽

Vol 133 (2) ◽

Cited By ~ 12

Author(s):

Peter J. K. Cameron ◽

Peter H. Rogers ◽

John W. Doane ◽

David H. Gifford

Keyword(s):

High Speed ◽

Degrees Of Freedom ◽

Measurement Techniques ◽

Theoretical Models ◽

Dynamics Simulation ◽

Small Scale ◽

Successful Operation ◽

Six Degrees Of Freedom ◽

Impact Location ◽

Simulation Based

Applications and research utilizing supercavitation for high-speed underwater flight has motivated study of the phenomenon. In this work, a small scale laboratory experiment for studying supercavitating projectiles has been designed, built, and tested. Similar existing experimental work has been documented in literature but using large, elaborate facilities, or has been presented with ambiguous conclusions from test results. The projectiles were 63.5 mm in length and traveled at speeds on the order of 145 m/s. Measurement techniques are discussed and used to record projectile speed, supercavity dimensions, and target impact location. Experimental observations are compared with a six degrees-of-freedom dynamics simulation based on theoretical models presented in literature for predicting supercavity shape and hydrodynamic forces on the supercavitating projectile during flight. Experimental observations are discussed qualitatively, along with quantitative statistics of the measurements made. Successful operation of the experiment has been demonstrated and verified by agreement with theoretical models.

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Effects of Boundary Layer Control Method on Hydrodynamic Characteristics and Tip Vortex Creation of a Hydrofoil

Polish Maritime Research ◽

10.1515/pomr-2017-0047 ◽

2017 ◽

Vol 24 (2) ◽

pp. 27-39

Author(s):

Parviz Ghadimi ◽

Araz Tanha ◽

Navid Nemati Kourabbasloo ◽

Sasan Tavakoli

Keyword(s):

Boundary Layer ◽

Control Method ◽

Water Injection ◽

Tip Vortex ◽

Boundary Layer Control ◽

Hydrodynamic Characteristics ◽

Negative Case ◽

Drag Ratio ◽

Lift To Drag Ratio ◽

Layer Control

Abstract There is currently a significant focus on using boundary layer control (BLC) approach for controlling the flow around bodies, especially the foil sections. In marine engineering this is done with the hope of increasing the lift - to - drag ratio and efficiency of the hydrofoils. In this paper, effects of the method on hydrodynamic characteristics and tip vortex formation of a hydrofoil are studied. Steady water injection at the tip of the hydrofoil is simulated in different conditions by using ANSYS-CFX commercial software. Validity of the proposed simulations is verified by comparing the obtained results against available experimental data. Effects of the injection on the lift, drag, and lift - to - drag ratio are studied and the ranges within which the injection has the most positive or negative effects, are determined. Furthermore, flow pattern and pressure variation are studied upon the water injection to determine the most positive and negative case and to ascertain the main reasons triggering these phenomena.

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Research on Hydrodynamic Characteristics of Blended Wing Body Underwater Glider with Rudder

Xibei Gongye Daxue Xuebao/Journal of Northwestern Polytechnical University ◽

10.1051/jnwpu/20203810024 ◽

2020 ◽

Vol 38 (1) ◽

pp. 24-30

Author(s):

Yunlong Ma ◽

Guang Pan ◽

Qiaogao Huang ◽

Jinglu Li

Keyword(s):

The Body ◽

Hydrodynamic Characteristics ◽

Shape Design ◽

Underwater Glider ◽

Trailing Edge ◽

Blended Wing Body ◽

The Difference ◽

Drag Ratio ◽

Lift To Drag Ratio ◽

Rudder Angle

In order to improve the maneuverability and stability of the Blended Wing Body (BWB) underwater glider, the trailing edge rudder is integrated into its shape design in this paper. Through the numerical simulation of CFD, the variation laws of the hydraulic parameters such as lift, drag, lift-to-drag ratio with the angle of attack and rudder angle are given. Compared with the traditional underwater glider, the BWB underwater glider not only has high loading capacity, but also has a maximum lift-to-drag ratio three times that of the former, resulting in higher energy efficiency. At the same time, by adding trailing edge rudders, the maneuverability of the BWB underwater glider is improved, and the lift-to-drag ratio under the same large rudder angle is increased by more than 30% compared with the variable-wing underwater glider. Finally, through the analysis of the numerical results and the cloud image, the difference interaction extent between the rudder and the body of the BWB underwater glider and the traditional torpedo or AUV is illustrated.

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Design of a Simple Electronic Flutter Simulator

Journal of the Royal Aeronautical Society ◽

10.1017/s0368393100129840 ◽

1953 ◽

Vol 57 (505) ◽

pp. 29-38 ◽

Cited By ~ 1

Author(s):

F. Smith ◽

W. D. T. Hicks

Keyword(s):

Degrees Of Freedom ◽

Successful Operation ◽

Two Degrees Of Freedom ◽

Six Degrees Of Freedom ◽

Electronic Simulator

SummaryThis paper describes the construction of a simple electronic simulator for the solution of flutter problems in two degrees of freedom. It was intended as a prototype for a much larger machine to solve problems in six degrees of freedom.Details of the construction and circuits are given, together with some typical solutions obtained on the machine. As a result of the successful operation of this prototype a larger machine in six degrees of freedom has now been built.

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