Hydrodynamic Forces on a Cylinder With a Flexible Splitter Plate Near the Free Surface

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
S. Satheesh ◽  
H. R. Díaz-Ojeda ◽  
L. M. González ◽  
F. J. Huera-Huarte
Keyword(s):  
Free Surface ◽  
Drag Reduction ◽  
Lift Force ◽  
Cross Flow ◽  
Hydrodynamic Forces ◽  
Splitter Plate ◽  
Rigid Cylinder ◽  
Splitter Plates ◽  
Cylinder Diameter

Abstract Experiments were conducted on two splitter plates of different structural rigidities, attached to a rigid cylinder and exposed to cross-flow at different submergence depths in order to study the influence of free surface. It was found that the presence of flexible splitter plate results in drag reduction at all submergence depths when compared with a plain cylinder, with the reduction being dependent on the rigidity of the splitter plate. The lift force was also found to increase abruptly at low depths for the cases involving splitter plates. The results from the analyses of tip kinematics on flexible splitter plate indicated that it performs vertical oscillations symmetrically about its mounting position at high submergence depths but is displaced in one direction up to an order of cylinder diameter and undergoes minimal oscillations when located near the free surface.

Passive drag reduction in cross-flow rigid plates near the free surface

2020 ◽  
Vol 101 ◽  
pp. 102253
Author(s):  
Sukruth Satheesh ◽  
Francisco J. Huera-Huarte
Keyword(s):  
Free Surface ◽  
Drag Reduction ◽  
Cross Flow

Influence of a Splitter Plate in the Near Wake of a Divergent Trailing Edge

2002 ◽  
Author(s):  
L. Neau ◽  
J. Pruvost ◽  
O. Rodriguez ◽  
Ta Phuoc Loc
Keyword(s):  
Particle Image Velocimetry ◽  
Drag Reduction ◽  
Particle Image ◽  
Splitter Plate ◽  
Experimental Results ◽  
Near Wake ◽  
Splitter Plates ◽  
Image Velocimetry ◽  
Lift And Drag ◽  
Base Drag

This paper discusses experimental results aimed at defining a base drag reduction device based on splitter plates. The unsteady 3D nature of the flow is studied by Schlieren photographies, particle image velocimetry and measurement of the total unsteady lift and drag loads.

scholarly journals Hydrodynamic Forces Exerting on an Oscillating Cylinder under Translational Motion in Water Covered by Compressed Ice

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 822
Author(s):  
Yury Stepanyants ◽  
Izolda Sturova
Keyword(s):  
Lift Force ◽  
Wave Motion ◽  
Translational Motion ◽  
Added Mass ◽  
Hydrodynamic Forces ◽  
Wave Resistance ◽  
Translational Velocity ◽  
Damping Coefficients ◽  
Incompressible Ideal Fluid ◽  
Theoretical Results

This paper presents the calculation of the hydrodynamic forces exerted on an oscillating circular cylinder when it moves perpendicular to its axis in infinitely deep water covered by compressed ice. The cylinder can oscillate both horizontally and vertically in the course of its translational motion. In the linear approximation, a solution is found for the steady wave motion generated by the cylinder within the hydrodynamic set of equations for the incompressible ideal fluid. It is shown that, depending on the rate of ice compression, both normal and anomalous dispersion can occur in the system. In the latter case, the group velocity can be opposite to the phase velocity in a certain range of wavenumbers. The dependences of the hydrodynamic loads exerted on the cylinder (the added mass, damping coefficients, wave resistance and lift force) on the translational velocity and frequency of oscillation were studied. It was shown that there is a possibility of the appearance of negative values for the damping coefficients at the relatively big cylinder velocity; then, the wave resistance decreases with the increase in cylinder velocity. The theoretical results were underpinned by the numerical calculations for the real parameters of ice and cylinder motion.

The Numerical Simulation of Two-Degrees-of-Freedom Vortex-Induced Vibrations of Circular Cylinder with High Mass-Ratio

2013 ◽  
Vol 284-287 ◽  
pp. 557-561
Author(s):  
Jie Li Fan ◽  
Wei Ping Huang
Keyword(s):  
Circular Cylinder ◽  
Drag Force ◽  
Frequency Ratio ◽  
Lift Force ◽  
Degrees Of Freedom ◽  
Cross Flow ◽  
High Mass ◽  
Mass Ratio ◽  
Main Frequency ◽  
Line Amplitude

The two-degrees-of-freedom VIV of the circular cylinder with high mass-ratio is numerically simulated with the software ANSYS/CFX. The VIV characteristic is analyzed in the different conditions (Ur=3, 5, 6, 8, 10). When Ur is 5, 6, 8 and 10, the conclusion which is different from the cylinder with low mass-ratio can be obtained. When Ur is 3, the frequency of in-line VIV is twice of that of cross-flow VIV which is equal to the frequency ratio between drag force and lift force, and the in-line amplitude is much smaller than the cross-flow amplitude. The motion trace is the crescent. When Ur is 5 and 6, the frequency ratio between the drag force and lift force is still 2, but the main frequency of in-line VIV is mainly the same as that of cross-flow VIV and the secondary frequency of in-line VIV is equal to the frequency of the drag force. The in-line amplitude is still very small compared with the cross-flow amplitude. When Ur is up to 8 and 10, the frequency of in-line VIV is the same as the main frequency of cross-flow VIV which is close to the inherent frequency of the cylinder and is different from the frequency of drag force or lift force. But the secondary frequency of cross-flow VIV is equal to the frequency of the lift force. The amplitude ratio of the VIV between in-line and cross-flow direction is about 0.5. When Ur is 5, 6, 8 and 10, the motion trace is mainly the oval.

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.

Improvement of Torque Performance of a Vertical Axis Type Marine Turbine for a Water Current Generation System

2010 ◽  
Author(s):  
Tomoki Ikoma ◽  
Shintaro Fujio ◽  
Koichi Masuda ◽  
Chang-Kyu Rheem ◽  
Hisaaki Maeda
Keyword(s):  
Turbine Blades ◽  
Angle Of Attack ◽  
Cross Flow ◽  
Vertical Axis ◽  
Hydrodynamic Forces ◽  
Water Current ◽  
Current Channel ◽  
Marine Current ◽  
Water Turbine ◽  
Type Water

This paper describes the possibility of an improvement of torque performance and hydrodynamic forces on a vertical axis type water turbine, used for marine current generating system. The water turbine analyzed here is based on a Darrieus turbine with vertical blades. We considered possibilities of controlling the angle of attack of blades in order to improve the starting performance and to reduce energy loss during the rotation of the turbine. We used blade-element/ momentum theory in order to investigate the variations appearing in torque performance when the angle of attack were controlled. We also proved the validity of our predictions of hydrodynamic forces on the blade and the turbine, made through CFD calculation, by comparing them with the results of corresponding model tests in a current channel. In the corresponding model test we investigated not only the hydrodynamic forces on the turbine with three fixed blades, but also the inline force and the cross-flow force on the rotating turbine with three blades. Regarding the cyclic pitching of turbine blades, results suggest that significant increase in average turbine torque is possible.

scholarly journals HYDRODYNAMIC FORCES ACTING ON A SUBMERGED OBSTRUCTION IN STEADY FREE SURFACE FLOWS

2004 ◽  
Vol 48 ◽  
pp. 877-882
Author(s):  
Mirei SHIGE-EDA ◽  
Juichiro AKIYAMA ◽  
Masayuki NONAKA ◽  
Takanori ASANO
Keyword(s):  
Free Surface ◽  
Free Surface Flows ◽  
Hydrodynamic Forces ◽  
Surface Flows

Estimation of Hydrodynamic Coefficients for VIV of Slender Beam at High Mode Orders

2010 ◽  
Author(s):  
Jie Wu ◽  
Carl M. Larsen ◽  
Halvor Lie
Keyword(s):  
Modal Analysis ◽  
Traveling Waves ◽  
Flow Direction ◽  
Research Effort ◽  
Cross Flow ◽  
Bending Moment ◽  
Hydrodynamic Forces ◽  
High Mode ◽  
Excitation Region ◽  
Inverse Force

The Hano̸ytangen test program was caried out by MARINTEK for Norsk Hydro in 1997. One purpose of this research effort was to investigate VIV response of deep sea risers subjected to sheared current. A densely instrumented 90 meter long riser model was tested in shear current, and bending strains along the riser was measured. Oscillatory part of both in-line (IL) and cross-flow (CF) displacements can be obtained by applying modal analysis on the bending moment measurements. The primary results from the analysis are that the riser is vibrating at high modes in cross-flow direction (10th–30th mode). The response is dominated standing waves for the lowest speed cases and gradually is influenced by traveling waves for increasing speed. For highest speed cases, it is dominated by traveling waves. The vibration amplitude is significantly smaller than for a rigid cylinder under equivalent conditions. Inverse force analysis estimates hydrodynamic forces from measured response of a slender beam. The method has previously been applied to rotating rig test data. The response was for these cases dominated by relatively low mode orders and standing wave responses. To understand the stochastic behaviour of high mode VIV response, the method is applied to Hano̸ytangen test in the present study to provide valuable insights by estimating CF hydrodynamic forces and coefficients from displacement time series found from modal analysis of measured strains. The results from this work are presented in terms of CF hydrodynamic force coefficients, excitation region and their variations in time and space. New excitation database is extracted based on the analysis results. They are used in VIVANA to predict the displacement and stress against experiment results.

Drag Reduction for Blunt Body With Cross Flow by Extremum-Seeking Control

2008 ◽  
Author(s):  
Nobuhiko Kamagata ◽  
Susumu Horio ◽  
Koichi Hishida
Keyword(s):  
Control System ◽  
Drag Reduction ◽  
Shear Layer ◽  
Flow Velocity ◽  
Drag Force ◽  
Lift Force ◽  
Flow Direction ◽  
Extremum Seeking ◽  
Extremum Seeking Control ◽  
Separated Shear Layer

The active flow control, which can adapt to variation of flow velocity and/or direction, is an effective technique to achieve drag reduction. The present study has investigated a separated shear layer and established two control systems; the system reduces drag force and lift force by controlling the separated shear layer to reattachment for variation of flow velocity and /or direction. The adaptive control system to the variation of flow velocity was constructed by using a hot wire anemometer as a sensor to detect flow separation. The system to flow direction was constructed by using pressure transducers as a sensor to estimate drag force and lift force. The extremum-seeking control was introduced as a controller of the both systems. It is indicated from the experimental results that adaptive drag/lift control system to various flow velocity ranging from 3 to 7 m/s and various flow direction ranging from 0 to 30 deg. was established.

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