Hydrodynamics of Towed Vertical Surface-Piercing Cylinders

2019 ◽  
Author(s):  
Douglas A. Potts ◽  
Jonathan R. Binns ◽  
Hayden Marcollo ◽  
Andrew E. Potts
Keyword(s):  
Laboratory Testing ◽  
Relative Length ◽  
Vertical Surface ◽  
Tip Vortex ◽  
Towing Tank ◽  
Hydrodynamic Loading ◽  
Test Conditions ◽  
End Conditions ◽  
Flow Speeds ◽  
Surface Wakes

Abstract This project investigates a cantilevered cylinder projecting down into the water column moving at high velocity through still water, as is applicable to submarine masts. Surface-piercing cylinders differ from fully submerged cylinders due to the generation of surface wakes and under increasing flow speeds the formation of a ventilated pocket in the lee of the cylinder, both of which grow with increasing velocity, with concomitant effects on the hydrodynamic loading. The relative length of submergence, or immersed aspect ratio (L/D) and end conditions of the cylinder with respect to tip vortex drag effects may also impact the hydrodynamic loads and wake formation. Laboratory testing of surface-piercing cylinders to date has predominantly been confined to characterising the wakes shed from a rigid cylinder cantilevered down into the water from a towing tank carriage, which under certain test conditions will also exhibit significant Vortex-Induced-Vibration (VIV), though not adequately identified and accounted for in its magnification of drag and wake.

STUDY ON PROPULSIVE PERFORMANCE OF TWO GEOMETRICALLY SIMILAR PODDED PROPULSORS

2021 ◽  
Vol 155 (A4) ◽  
Author(s):  
M Islam ◽  
A Akinturk ◽  
B Veitch ◽  
Pengfei Liu
Keyword(s):  
Open Water ◽  
Operating Conditions ◽  
Towing Tank ◽  
Propulsive Performance ◽  
Lower Reynolds Number ◽  
Custom Made ◽  
Flow Speeds ◽  
Four Quadrant ◽  
Thrust And Torque ◽  
Straight Ahead

This paper presents the outcome of a research to evaluate the effect of size on the propulsive performance of podded propulsors in cavitating and non-cavitating open water conditions. Two cases are examined, namely: propeller-only case and pod-unit case. In the propeller-only case, a commercial propeller dynamometer is used to measure the thrust and torque of two propellers of different size at the four quadrants of propellers with varied shaft and flow speeds. Also, both propellers are tested at different tunnel pressure to study and compare the behaviour under similar cavitation conditions. In the pod-unit case, two geometrically similar but different sized pod-units are tested using two separate custom-made pod dynamometer systems in two towing tank facilities in straight-ahead and static azimuthing conditions. The study showed that the performance characteristics stabilize at lower Reynolds Number for the smaller propeller than the larger propeller. The propulsive performance of the two propellers was comparable in the four-quadrant experiments. Also, the experiments at the cavitating conditions showed that the cavitation characteristics of the two propellers were consistent at corresponding operating conditions. The experiment results of the two pod-units were also comparable for forces and moments in the three coordinate directions in the straight-ahead and static azimuthing conditions. A brief discussion on the uncertainty assessments for each of the measurements is also presented.

The effect of tailwater depth on the dynamics of local scour

2000 ◽  
Vol 27 (1) ◽  
pp. 138-150 ◽  
Author(s):  
R Balachandar ◽  
J A Kells ◽  
R J Thiessen
Keyword(s):  
Laboratory Testing ◽  
Scaling Laws ◽  
Stable Equilibrium ◽  
Imaging Technique ◽  
Laser Doppler Anemometer ◽  
Local Scour ◽  
Stable Equilibrium State ◽  
Sluice Gate ◽  
Video Imaging ◽  
Test Conditions

The two-dimensional local scour occurring downstream from a submerged sluice gate for various tailwater depths was studied using a video imaging technique and a laser-Doppler anemometer. The flow field was found to be dynamic (i.e., varied with time). Previously reported equilibrium scour profiles for similar test conditions were not attained even after 96 h of laboratory testing. The scaling laws suggested in the literature were found to be unsuitable. New scaling laws are presented for the condition when a stable equilibrium state has not yet been attained. Velocity profiles are presented at various stations during digging and refilling conditions. Key words: local scour, time scale, video imaging, scour profile, velocity profile, sluice gate, cohesionless material, tailwater effect.

Observations on the Development of a Tip Vortex on a Rectangular Hydrofoil

1988 ◽  
Vol 110 (2) ◽  
pp. 208-215 ◽  
Author(s):  
T. B. Francis ◽  
J. Katz
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Incidence Angle ◽  
Laser Sheet ◽  
Tip Vortex ◽  
Primary Vortex ◽  
Towing Tank ◽  
Empirical Relations ◽  
Rotating Structure ◽  
Secondary Vortices

The present paper describes a flow visualization study that focuses the development of a tip vortex on a rectangular NACA-66 hydrofoil. The experiments have been performed in a towing tank. Illumination with a thin laser sheet together with distribution of dye have been utilized as a means of observation. The results demonstrate the growth of the vortex along the chord, the increase in its dimensions with increasing incidence angle and decreasing Reynolds number. They also show that the center of the vortex moves inward towards the root with increasing incidence angle, increasing chordwise location, and decreasing velocity. Empirical relations for these trends have been computed. The observations also demonstrate that the flow around the tip is dominated by muliple vortex structures that include the primary vortex, a counter rotating structure, shear layer eddies, and several other secondary vortices.

scholarly journals Effect of external hydraulic head on swelling of unsaturated clay

2020 ◽  
Vol 195 ◽  
pp. 03035
Author(s):  
Shay Nachum ◽  
Mark Talesnick ◽  
Sam Frydman
Keyword(s):  
Laboratory Testing ◽  
Standard Procedure ◽  
Hydraulic Head ◽  
Extreme Conditions ◽  
One Dimensional ◽  
Upper Limit ◽  
Test Conditions ◽  
Field Situation ◽  
Unsaturated Clay ◽  
The One

Laboratory testing of the one-dimensional swell of soil (usually unsaturated clay) is generally performed according to ASTM standard D4546. The standard procedure requires that “the specimen is inundated with test water and the one-dimensional wetting-induced swell or collapse strain is measured”. This procedure undoubtedly provides an upper limit to the swell which may be expected under field conditions, and may be relevant to cases in which low lying areas are expected to be inundated as a result of a wetting episode. However, in other cases, wetting of the soil may result from less extreme conditions - for example absorption of water from underlying, wetted layers, or soaking of the lower portion of a swelling layer and resultant upward wetting due to suction forces. The present paper describes a laboratory investigation of the effect of external hydraulic head on swell. The results demonstrate the importance of applying test conditions consistent with those expected in the field situation.

Study on Propulsive Performance of Two Geometrically Similar Podded Propulsors

2013 ◽  
Vol 155 (A4) ◽  
Keyword(s):  
Open Water ◽  
Operating Conditions ◽  
Towing Tank ◽  
Propulsive Performance ◽  
Lower Reynolds Number ◽  
Custom Made ◽  
Flow Speeds ◽  
Four Quadrant ◽  
Thrust And Torque ◽  
Straight Ahead

This paper presents the outcome of a research to evaluate the effect of size on the propulsive performance of podded propulsors in cavitating and non-cavitating open water conditions. Two cases are examined, namely: propeller-only case and pod-unit case. In the propeller-only case, a commercial propeller dynamometer is used to measure the thrust and torque of two propellers of different size at the four quadrants of propellers with varied shaft and flow speeds. Also, both propellers are tested at different tunnel pressure to study and compare the behaviour under similar cavitation conditions. In the pod-unit case, two geometrically similar but different sized pod-units are tested using two separate custom-made pod dynamometer systems in two towing tank facilities in straight-ahead and static azimuthing conditions. The study showed that the performance characteristics stabilize at lower Reynolds Number for the smaller propeller than the larger propeller. The propulsive performance of the two propellers was comparable in the four-quadrant experiments. Also, the experiments at the cavitating conditions showed that the cavitation characteristics of the two propellers were consistent at corresponding operating conditions. The experiment results of the two pod-units were also comparable for forces and moments in the three coordinate directions in the straight-ahead and static azimuthing conditions. A brief discussion on the uncertainty assessments for each of the measurements is also presented.

The method of replication affects metal film granularity and resolution

1989 ◽  
Vol 47 ◽  
pp. 708-709
Author(s):  
George C. Ruben
Keyword(s):  
Electron Beam ◽  
High Resolution ◽  
Film Thickness ◽  
Single Molecule ◽  
Metal Film ◽  
Vertical Surface ◽  
High Resolution Imaging ◽  
Controllable Factors ◽  
Resolution Imaging

Single molecule resolution in electron beam sensitive, uncoated, noncrystalline materials has been impossible except in thin Pt-C replicas ≤ 150Å) which are resistant to the electron beam destruction. Previously the granularity of metal film replicas limited their resolution to ≥ 20Å. This paper demonstrates that Pt-C film granularity and resolution are a function of the method of replication and other controllable factors. Low angle 20° rotary , 45° unidirectional and vertical 9.7±1 Å Pt-C films deposited on mica under the same conditions were compared in Fig. 1. Vertical replication had a 5A granularity (Fig. 1c), the highest resolution (table), and coated the whole surface. 45° replication had a 9Å granulartiy (Fig. 1b), a slightly poorer resolution (table) and did not coat the whole surface. 20° rotary replication was unsuitable for high resolution imaging with 20-25Å granularity (Fig. 1a) and resolution 2-3 times poorer (table). Resolution is defined here as the greatest distance for which the metal coat on two opposing faces just grow together, that is, two times the apparent film thickness on a single vertical surface.

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