Hydrodynamic Drag Forces on Groups of Flat Plates

Drag forces acting on Steller sea lions (Eumetopias jubatus) were investigated from ‘deceleration during glide’ measurements. A total of 66 glides from six juvenile sea lions yielded a mean drag coefficient (referenced to total wetted surface area) of 0.0056 at a mean Reynolds number of 5.5×10(6). The drag values indicate that the boundary layer is largely turbulent for Steller sea lions swimming at these Reynolds numbers, which are past the point of expected transition from laminar to turbulent flow. The position of maximum thickness (at 34 % of the body length measured from the tip of the nose) was more anterior than for a ‘laminar’ profile, supporting the idea that there is little laminar flow. The Steller sea lions in our study were characterized by a mean fineness ratio of 5.55. Their streamlined shape helps to delay flow separation, reducing total drag. In addition, turbulent boundary layers are more stable than laminar ones. Thus, separation should occur further back on the animal. Steller sea lions are the largest of the otariids and swam faster than the smaller California sea lions (Zalophus californianus). The mean glide velocity of the individual Steller sea lions ranged from 2.9 to 3.4 m s(−)(1) or 1.2-1.5 body lengths s(−)(1). These length-specific speeds are close to the optimum swim velocity of 1.4 body lengths s(−)(1) based on the minimum cost of transport for California sea lions.

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Rayleigh Damping Effects on Global Analysis of Umbilicals

Volume 4: Pipeline and Riser Technology ◽

10.1115/omae2011-49584 ◽

2011 ◽

Cited By ~ 1

Author(s):

Lauro Massao Yamada da Silveira ◽

Rafael Loureiro Tanaka ◽

Joa˜o Paulo Zi´lio Novaes

Keyword(s):

Global Analysis ◽

Time History ◽

Systems Design ◽

Hydrodynamic Drag ◽

Viscous Damping ◽

Structural Damping ◽

Peak Period ◽

Rayleigh Damping ◽

Drag Forces ◽

Offshore Industry

Despite global analysis of umbilicals is a well-known area in the offshore systems design, some topics are still opened for discussions. One of these topics refers to the structural damping. Obviously, the viscous damping caused by hydrodynamic drag forces is the major source of damping to the whole system. However, in some severe load cases, the host vessel dynamics may induce high snatch loads to the umbilical top end and these loads are more related to structural damping, specifically in tension–elongation hysteresis, than to viscous damping. The snatch loads must be taken into account in the whole design process, which leads to an umbilical designed to resist to higher tension loads and implies also, in most cases, in over-dimensioned accessories, such as the bending limiters. Actually, due to the high level of friction between layers, the umbilical presents some level of structural damping which is, in fact, related to hysteretic moment-curvature and tension-elongation relations. This intrinsic structural damping may in fact contribute to the reduction of the snatch loads and considering it may reduce the level of conservatism in the design. However, due to the complexity and diversity of umbilical designs, it is not straightforward to come up with general-use hysteretic curves. A simplification then is to apply classic Rayleigh damping. Typically, damping levels of 5% are accepted in the offshore industry when using stiffness-proportional Rayleigh damping (the 5% damping is a percentage of the critical damping and is accounted for at the regular wave period or irregular wave spectral peak period). The problem here is that stiffness-proportional Rayleigh damping increases linearly with the frequency and the damping level at 1Hz, for example, may get to 60%. This fact indicates that the high-frequency part of the response may be simply discarded from the results, which in turn may lead to an incorrect, over-damped analysis. The present work aims tackling the Rayleigh damping issue, evaluating its effects on tension levels and spectral density of the tension time history. A recommendation of how to apply Rayleigh damping is proposed.

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Neuro-Fuzzy Dynamic Position Prediction for Autonomous Work-Class ROV Docking

Sensors ◽

10.3390/s20030693 ◽

2020 ◽

Vol 20 (3) ◽

pp. 693

Author(s):

Petar Trslić ◽

Edin Omerdic ◽

Gerard Dooly ◽

Daniel Toal

Keyword(s):

Fuzzy Inference ◽

North Atlantic Ocean ◽

Prediction Method ◽

Hydrodynamic Drag ◽

Remotely Operated Vehicle ◽

Inference System ◽

Drag Forces ◽

Neuro Fuzzy ◽

Heave Motion ◽

Work Class

This paper presents a docking station heave motion prediction method for dynamic remotely operated vehicle (ROV) docking, based on the Adaptive Neuro-Fuzzy Inference System (ANFIS). Due to the limited power onboard the subsea vehicle, high hydrodynamic drag forces, and inertia, work-class ROVs are often unable to match the heave motion of a docking station suspended from a surface vessel. Therefore, the docking relies entirely on the experience of the ROV pilot to estimate heave motion, and on human-in-the-loop ROV control. However, such an approach is not available for autonomous docking. To address this problem, an ANFIS-based method for prediction of a docking station heave motion is proposed and presented. The performance of the network was evaluated on real-world reference trajectories recorded during offshore trials in the North Atlantic Ocean during January 2019. The hardware used during the trials included a work-class ROV with a cage type TMS, deployed using an A-frame launch and recovery system.

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Hydrodynamic drag of two frog species: Hymenochirus boettgeri and Rana pipiens

Canadian Journal of Zoology ◽

10.1139/z87-172 ◽

1987 ◽

Vol 65 (5) ◽

pp. 1085-1090 ◽

Cited By ~ 6

Author(s):

Julianna M. Gal ◽

R. W. Blake

Keyword(s):

Flow Visualization ◽

Rana Pipiens ◽

Swimming Performance ◽

The Body ◽

Hydrodynamic Drag ◽

Subtraction Method ◽

Flat Plates ◽

Hind Limbs ◽

Hymenochirus Boettgeri ◽

Visualization Experiments

Drag of the aquatic frog Hymenochirus boettgeri was investigated by a series of drop-tank and flow visualization experiments. The maximum drag coefficient (CD) of the body and hind limbs was 0.24–0.11, for a Reynolds number (Re) of 1500–8000. Results of the flow visualization experiment support the CD values obtained for the body and hind limbs of H. boettgeri. CD similarly measured for Rana pipiens was 0.060–0.050, for a Re range of 16 600 – 40 400. A comparison of CD under dynamically similar conditions suggests that jumping may not compromise swimming performance in these two species. CD for the foot of H. boettgeri was examined by three methods: drop-tank experiments with isolated frog's feet and with isolated acetate model feet, and a subtraction method. CD for the isolated foot was 2.5–1.6 for 100 < Re < 700. Results were similar to those obtained with isolated model feet, where 1.8 > CD > 1.2 for 300 < Re < 1300. The subtraction method gave similar results to those obtained from drop-tank experiments with isolated model and real feet, within the Re range of 300–3000. The results of all three methods and flow visualization experiments support the assumption that animal paddles can be treated as three-dimensional flat plates, oriented normal to the direction of flow.

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Impact—Response Behavior of Offshore Pipelines

Journal of Energy Resources Technology ◽

10.1115/1.3230423 ◽

1982 ◽

Vol 104 (4) ◽

pp. 325-329 ◽

Cited By ~ 3

Author(s):

P. G. Bergan ◽

E. Mollestad

Keyword(s):

Plastic Material ◽

Material Behavior ◽

Hydrodynamic Drag ◽

Offshore Pipelines ◽

Sea Floor ◽

Drag Forces ◽

Sea Bottom ◽

Nonlinear Dynamic Equations ◽

Numerical Formulation ◽

Inertia Forces

A method for analyzing the dynamic behavior of marine pipelines subjected to impact loads or sudden forced movements is outlined. Inertia forces (also from hydrodynamic mass), hydrodynamic drag forces as well as friction and lift effects for a pipe at the sea bottom are accounted for. An extensive nonlinear formulation is used for the pipe itself; it includes large displacements and elasto-plastic material behavior. Aspects of the numerical formulation of the problem and the solution of the nonlinear dynamic equations are discussed. The examples show computed dynamic response for pipelines lying on the sea floor and for a pipe section freely submerged in water when subjected to various force and displacement histories.

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Numerical Study of Hydrodynamic Forces for AFM Operations in Liquid

Scanning ◽

10.1155/2017/6286595 ◽

2017 ◽

Vol 2017 ◽

pp. 1-12 ◽

Cited By ~ 3

Author(s):

Tobias Berthold ◽

Guenther Benstetter ◽

Werner Frammelsberger ◽

Rosana Rodríguez ◽

Montserrat Nafría

Keyword(s):

Drag Force ◽

Numerical Study ◽

Viscous Friction ◽

Hydrodynamic Drag ◽

Water Mixture ◽

Ultrapure Water ◽

Liquid Environment ◽

Drag Forces ◽

Organic Sample ◽

Repulsive Forces

For advanced atomic force microscopy (AFM) investigation of chemical surface modifications or very soft organic sample surfaces, the AFM probe tip needs to be operated in a liquid environment because any attractive or repulsive forces influenced by the measurement environment could obscure molecular forces. Due to fluid properties, the mechanical behavior of the AFM cantilever is influenced by the hydrodynamic drag force due to viscous friction with the liquid. This study provides a numerical model based on computational fluid dynamics (CFD) and investigates the hydrodynamic drag forces for different cantilever geometries and varying fluid conditions for Peakforce Tapping (PFT) in liquids. The developed model was verified by comparing the predicted values with published results of other researchers and the findings confirmed that drag force dependence on tip speed is essentially linear in nature. We observed that triangular cantilever geometry provides significant lower drag forces than rectangular geometry and that short cantilever offers reduced flow resistance. The influence of different liquids such as ultrapure water or an ethanol-water mixture as well as a temperature induced variation of the drag force could be demonstrated. The acting forces are lowest in ultrapure water, whereas with increasing ethanol concentrations the drag forces increase.

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Vortex-Excited Response of Large-Scale Cylinders in Sheared Flow

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.3257061 ◽

1988 ◽

Vol 110 (3) ◽

pp. 272-277 ◽

Cited By ~ 10

Author(s):

J. A. Humphries ◽

D. H. Walker

Keyword(s):

Large Scale ◽

Shear Velocity ◽

Reynolds Numbers ◽

Hydrodynamic Drag ◽

Flow Induced Vibration ◽

Sheared Flow ◽

Drag Forces ◽

Linear Shear ◽

Series Of Experiments ◽

The Mean

A series of experiments were performed to measure the vortex-excited response of a 0.168-m-dia slender circular cylinder in a range of linear shear velocity profiles. Reynolds numbers of up to 2.5 × 105 were achieved. The results clearly showed that regular large-amplitude cylinder vibrations occurred well within the critical drag transition region. It was found that increasing the linear shear profile decreased the peak amplitude response but broadened the range of lock-on over which large oscillations occurred. The flow-induced vibration of the cylinder caused amplification of the mean hydrodynamic drag forces acting on the cylinder when compared with those expected for a similar rigid cylinder.

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Dragonfly flight. I. Gliding flight and steady-state aerodynamic forces.

Journal of Experimental Biology ◽

10.1242/jeb.200.3.543 ◽

1997 ◽

Vol 200 (3) ◽

pp. 543-556 ◽

Cited By ~ 7

Author(s):

JM Wakeling ◽

CP Ellington

Keyword(s):

Steady State ◽

Lift Coefficient ◽

Reynolds Numbers ◽

The Body ◽

Flat Plates ◽

Viscous Forces ◽

Drag Forces ◽

Aerodynamic Properties ◽

Gliding Flight ◽

Lift And Drag

The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles.

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A High Speed Boat for the Hydrodynamic Testing of Fouling Control Coatings

10.5957/attc-2017-0009 ◽

2017 ◽

Author(s):

J. Travis Hunsucker ◽

Harrison Gardner ◽

Geoffrey Swain

Keyword(s):

High Speed ◽

Video Camera ◽

Load Cell ◽

Structure Characterization ◽

Hydrodynamic Drag ◽

Experimental Uncertainty ◽

High Definition ◽

Fouling Control ◽

Drag Forces ◽

Fouling Control Coatings

An 8.2 m high speed boat was modified to measure the drag and to provide real time video of ship hull fouling control coatings under boundary layer conditions that developed at speeds up to 15 m/s. It consists of a through hull Hydrodynamic Drag Meter (HDM) placed in a wet-well built into the aft section of the boat. The HDM consists of a load cell attached to a floating element balance and a high definition video camera to observe fouling. Test panels are attached to the load cell such that they remain flush with the hull. Fouled test panels are placed in the facility to observe the velocities required for fouling removal and changes in drag forces associated with different fouling community structure. Characterization studies of the HDM were undertaken to understand the overall accuracy of the novel testing system. These experiments included 1) Smooth acrylic drag measurement with the HDM and a Preston tube and 2) Drag measurements with the HDM on panels with 60- grit and 220-grit sandpaper. Smooth panel wall shear stress values obtained using the HDM were within experimental uncertainties of results from Preston tube. Roughness function values for 60-grit and 220-grit sandpaper agree within the experimental uncertainty of the Nikuradse-type roughness function for uniform roughness. Skin friction coefficients of a smooth panel determined on the HDM had an experimental uncertainty of around 5% for Froude numbers greater than 1. Roughness function values for a 220-grit and 60-grit sandpaper surface had maximum uncertainties of 11% and 13% respectively.

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New Design Code for Interference Between Trawl Gear and Pipelines: DNV RP-F111

Volume 4: Terry Jones Pipeline Technology; Ocean Space Utilization; CFD and VIV Symposium ◽

10.1115/omae2006-92127 ◽

2006 ◽

Author(s):

Dag O̸. Askheim ◽

Olav Fyrileiv

Keyword(s):

Otter Trawl ◽

Hydrodynamic Drag ◽

Potential Hazard ◽

Test Results ◽

Design Code ◽

Acceptance Criteria ◽

Drag Forces ◽

Analysis Methodology ◽

Concrete Coating ◽

Pipeline Design

The offshore petroleum and the fishing industries are often operating in the same areas. Fishing, in particular bottom trawling, is of concern to pipeline integrity. Such trawling is mainly conducted with two types of trawl gear: otter or beam trawls. The otter trawl boards are steel, more or less rectangular boards which keep the trawl bag open by hydrodynamic drag forces. While the beam trawls use a 10–20 meters long beam to keep the trawl bag open. These trawl gears are dragged along the seabed and represent a potential hazard to pipelines. This paper gives a brief description of types and dimensions of trawl gear. Further it deals with methods for calculating the pipeline response when interacting with bottom trawl gear and finally adresses acceptance criteria for pipeline design and assessment during operation. The calculation methods and acceptance criteria given in this paper are based on test results and research done during the last decades including results from the Kristin, Sno̸hvit and Ormen Lange projects. The above mentioned trawl data, analysis methodology and acceptance criteria are taken from the new DNV Recommended Practice, DNV RP-F111 (2006). This Recommended Practice is an update of the former design code DNV GL 13 (1997). The update was performed mainly due to new types of trawl gear, updated trawl gear data, various experience from application of GL 13 in projects and a general harmonizing process with the pipeline code, DNV OS-F101, and the Hotpipe project, ref Collberg et al. (2005). Large sums are often spent in pipeline projects to protect against trawl gear interaction in terms of concrete coating, trenching or burial. On the other hand the costs of not providing a sufficient protection could be extremely high, with costs related to leakages, failures, stop in production and repair/replacement. This Recommended Practice provides a rational tool to optimize the costs related to trawl gear interference and still ensure that the integrity of the pipeline becomes acceptable.

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