Vortex shedding modes around oscillating non-uniform double heave plates

2020 ◽  
pp. 147509022096691
Author(s):  
Abuzar Abazari ◽  
Mehdi Alvandi ◽  
Mehdi Behzad ◽  
Krish P Thiagarajan
Keyword(s):  
Vortex Shedding ◽  
Harmonic Oscillation ◽  
Added Mass ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Offshore Platforms ◽  
Vortex Interaction ◽  
Cfd Method ◽  
Vortex Shedding Modes ◽  
Strong Vortex

Multiple co-axial heave plates of uniform geometry are attached to offshore platforms for inducing damping and added mass. These effects generally decrease the magnitude of the dynamic response of the platform under applied environmental excitation forces. When spacing between heave plates is decreased the damping and added mass performance are altered due to their strong vortex interaction. A new non-uniform plate configuration is proposed that may create different hydrodynamic characteristics. The modes of vortex shedding around plate edges in a non-uniform arrangement under forced harmonic oscillation are investigated via the CFD method. Furthermore, a new simplified formula for the total theoretical added mass of a general non-uniform double disk is proposed when it is in the zone which vortex interaction take places. The results show that a non-uniform double disk has better hydrodynamic performance as compared to the uniform double configuration for a given spacing. It is also observed that the mode and direction of the vortex shedding are different for uniform and non-uniform arrangements in a given spacing and KC value.

Numerical Experimental Research on the Hydrodynamic Performance of Flow around a Three Dimensional Circular Cylinder

2011 ◽  
Vol 90-93 ◽  
pp. 2778-2781 ◽  
Author(s):  
Yuan Yuan Fang ◽  
Zhao Lin Han
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Vortex Shedding ◽  
High Reynolds Number ◽  
Three Dimensional ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Large Eddy ◽  
Drag And Lift ◽  
High Reynolds

Using the CFX software and the Large Eddy Simulaion (LES) method, this paper numerically simulates the hydrodynamic characteristics of the flow around a 3d circular cylinder at high Reynolds number (Re=5.6×103, 2.8×104, 1.1×105). The numerical simulation focuses on investigating the vortex shedding angle, the characteristics of the vortex shedding and the vortex tube, the base pressure, the static and the fluctuating drag and lift. The result of calculation shows that the forces of every section along the span of cylinder are symmetrical with respect to the middle section. Moreover the flow around the cylinder obviously appears three dimensional characteristics at high Reynolds number.

Two-Dimensional Numerical Simulation of Vortex Shedding of Multiple Stranded Ropes

2019 ◽  
Author(s):  
Xinxin Wang ◽  
Liuyi Huang ◽  
Yanli Tang ◽  
Fenfang Zhao ◽  
Peng Sun
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Flow Distribution ◽  
Hydrodynamic Performance ◽  
Navier Stokes ◽  
Hydrodynamic Characteristics ◽  
Two Dimensional ◽  
Navier Stokes Equation

Abstract The stranded rope is one of the important components of the fishery aquaculture equipment. We investigate the fluid flow through two-dimensional stranded rope by direct simulation of the Navier-Stokes equations. We show that for different kinds of stranded rope structures, there are significant differences in hydrodynamic performance. This paper established a numerical model of unsteady flow past the stranded rope based on the Navier-Stokes equation and Morison formulas to study the hydrodynamic characteristics of three-stranded rope, four-stranded rope, and seven-stranded rope, respectively. The turbulence flow was simulated using Standard k-ε model and Shear-Stress Transport k-ω (SST) model. The flow distribution strongly depends on the Reynolds number, a range of 3,900 and 30,000. With increasing Reynolds number, the alternate eddy formation and shedding were repeated behind the stranded ropes. Such parameters of hydrodynamic characteristics of multiple stranded ropes were calculated as the lift and drag coefficients, and vortex shedding frequencies. The numerical simulation results presented flow performances of different cross sections (a, b, c, d) at different Reynolds numbers. However, Reynolds number has no significant impact on the Strouhal number for the same attack angle of the stranded rope.

Evolution of unstable system.

2015 ◽  
Vol 9 (3) ◽  
pp. 2487-2502 ◽  
Author(s):  
Igor V. Lebed
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Stokes Flow ◽  
Stable Solution ◽  
The State ◽  
Unstable System ◽  
Unstable Flow ◽  
Unstable Solutions ◽  
Vortex Shedding Modes ◽  
Hydrodynamics Equations

Scenario of appearance and development of instability in problem of a flow around a solid sphere at rest is discussed. The scenario was created by solutions to the multimoment hydrodynamics equations, which were applied to investigate the unstable phenomena. These solutions allow interpreting Stokes flow, periodic pulsations of the recirculating zone in the wake behind the sphere, the phenomenon of vortex shedding observed experimentally. In accordance with the scenario, system loses its stability when entropy outflow through surface confining the system cannot be compensated by entropy produced within the system. The system does not find a new stable position after losing its stability, that is, the system remains further unstable. As Reynolds number grows, one unstable flow regime is replaced by another. The replacement is governed tendency of the system to discover fastest path to depart from the state of statistical equilibrium. This striving, however, does not lead the system to disintegration. Periodically, reverse solutions to the multimoment hydrodynamics equations change the nature of evolution and guide the unstable system in a highly unlikely direction. In case of unstable system, unlikely path meets the direction of approaching the state of statistical equilibrium. Such behavior of the system contradicts the scenario created by solutions to the classic hydrodynamics equations. Unstable solutions to the classic hydrodynamics equations are not fairly prolonged along time to interpret experiment. Stable solutions satisfactorily reproduce all observed stable medium states. As Reynolds number grows one stable solution is replaced by another. They are, however, incapable of reproducing any of unstable regimes recorded experimentally. In particular, stable solutions to the classic hydrodynamics equations cannot put anything in correspondence to any of observed vortex shedding modes. In accordance with our interpretation, the reason for this isthe classic hydrodynamics equations themselves.

scholarly journals Numerical Investigation on Hydrodynamic Performance of a Portable AUV

2021 ◽  
Vol 9 (8) ◽  
pp. 812
Author(s):  
Lin Hong ◽  
Renjie Fang ◽  
Xiaotian Cai ◽  
Xin Wang
Keyword(s):  
Numerical Investigation ◽  
Dynamic Model ◽  
Autonomous Underwater Vehicle ◽  
Dynamic Performance ◽  
Plane Motion ◽  
Hydrodynamic Performance ◽  
Wave Forces ◽  
Modeling And Control ◽  
Experiment Platform ◽  
Cfd Method

This paper conducts a numerical investigation on the hydrodynamic performance of a portable autonomous underwater vehicle (AUV). The portable AUV is designed to cruise and perform some tasks autonomously in the underwater world. However, its dynamic performance is strongly affected by hydrodynamic effects. Therefore, it is crucial to investigate the hydrodynamic performance of the portable AUV for its accurate dynamic modeling and control. In this work, based on the designed portable AUV, a comprehensive hydrodynamic performance investigation was conducted by adopting the computational fluid dynamics (CFD) method. Firstly, the mechanical structure of the portable AUV was briefly introduced, and the dynamic model of the AUV, including the hydrodynamic term, was established. Then, the unknown hydrodynamic coefficients in the dynamic model were estimated through the towing experiment and the plane-motion-mechanism (PMM) experiment simulation. In addition, considering that the portable AUV was affected by wave forces when cruising near the water surface, the influence of surface waves on the hydrodynamic performance of the AUV under different wave conditions and submerged depths was analyzed. Finally, the effectiveness of our method was verified by experiments on the standard models, and a physical experiment platform was built in this work to facilitate hydrodynamic performance investigations of some portable small-size AUVs.

Hydrodynamic characteristics of vertical and quadrant face pile supported breakwater under oblique waves

2021 ◽  
pp. 147509022110313
Author(s):  
T J Jemi Jeya ◽  
V Sriram ◽  
V Sundar
Keyword(s):  
Experimental Study ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Scattering Parameter ◽  
Oblique Waves ◽  
Test Conditions ◽  
Relative Water ◽  
Identical Test ◽  
Run Up ◽  
Water Depths

This paper presents the results from a comprehensive experimental study on the Quadrant Face Pile Supported Breakwater (QPSB) in two different water depths exposed to three different oblique wave attacks. The results are compared with that for a Vertical face Pile Supported Breakwater (VPSB) for identical test conditions. The paper compares the reflection coefficient, transmission coefficient, energy loss coefficient, non-dimensional pressure, and non-dimensional run-up as a function of the relative water depth and scattering parameter. The results obtained for QPSB are validated with existing results. The salient observations show that QPSB experiences better hydrodynamic performance characteristics than the VPSB under oblique waves.

Numerical Predictions and Verifications for Hydrodynamic Performance of Bidirectional Tidal Stream Turbine

2012 ◽  
Vol 229-231 ◽  
pp. 2478-2480
Author(s):  
Bin Guo ◽  
Da Zheng Wang ◽  
Jun Wei Zhou
Keyword(s):  
Hydrodynamic Performance ◽  
Power Coefficient ◽  
Speed Ratio ◽  
Numerical Predictions ◽  
Ansys Cfx ◽  
Tidal Stream ◽  
Cfd Method ◽  
Tidal Stream Turbine ◽  
Bem Theory ◽  
Blade Element

In this paper, the tidal stream turbine blade is designed by using blade element momentum (BEM) theory. The bidirectional airfoil is created derived from NACA airfoil. Ansys-CFX is used to predict the hydrodynamic performance of this bidirectional airfoil, and it turns out that the bidirectional airfoil works well at both of the tidal current directions. A test turbine named rotor 2 is used, and a comparison is made between experimental results of the test turbine and numerical prediction results to prove the correctness of the numerical method. The power coefficient of bidirectional tidal stream turbine obtained by CFD method is 39.36% at the design tip speed ratio.

Vortex-induced vibrations of a long flexible circular cylinder

1993 ◽  
Vol 250 ◽  
pp. 481-508 ◽  
Author(s):  
D. Brika ◽  
A. Laneville
Keyword(s):  
Circular Cylinder ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Abrupt Change ◽  
Velocity Range ◽  
End Effects ◽  
Synchronization Region ◽  
Vortex Induced Vibrations ◽  
Set Up ◽  
Vortex Shedding Modes

In an experimental study of the vortex-induced oscillations of a long flexible circular cylinder, the observed stationary amplitudes describe an hysteresis loop partially different from earlier studies. Each branch of the loop is associated with a vortex shedding mode and, as a jump from one branch to the other occurs, the phase difference between the cylinder displacement and the vortex shedding undergoes an abrupt change. The critical flow velocities at which the jump occurs concur with the flow visualization observations of Williamson & Roshko (1988) on the vortex shedding modes near the fundamental synchronization region. Impulsive regimes, obtained at a given flow velocity with the cylinder initially at rest or pre-excited, and progressive regimes resulting from a variation of the flow velocity, are examined. The occurrence of bifurcations is detected for a flow velocity range in the case of the impulsive regimes. The coordinates of the bifurcations define a boundary between two vortex shedding modes, a boundary that verifies the critical curve obtained by Williamson & Roshko (1988). The experimental set-up of this study simulates half the wavelength of a vibrating cable, eliminates the end effects present in oscillating rigid cylinder set-up and has one of the lowest damping ratios reported for the study of this phenomenon.

scholarly journals Numerical Analysis on the Effect of Artificial Ventilated Pipe Diameter on Hydrodynamic Performance of a Surface-Piercing Propeller

2019 ◽  
Vol 7 (8) ◽  
pp. 240
Author(s):  
Gao ◽  
Yang ◽  
Li ◽  
Dong
Keyword(s):  
High Speed ◽  
Water Immersion ◽  
Active Role ◽  
Numerical Results ◽  
Hydrodynamic Performance ◽  
Pipe Diameter ◽  
Pressure Area ◽  
Cfd Method ◽  
Thrust And Torque ◽  
Surface Piercing Propeller

Under the condition of large water immersion, surface-piercing propellers are inclined to be heavy loaded. In order to improve the hydrodynamic performance of the surface-piercing propeller, the installation of a vent pipe in front of a propeller disc is more widely used in the propulsion device of high speed planning crafts. Based on computational fluid dynamics (CFD) method, this paper studied the influence of diverse vent pipe diameters on hydrodynamic performance of the surface-piercing propeller under full water immersion conditions. The numerical results show that, with the increase of vent pipe diameters, the thrust and torque of the surface-piercing propeller decrease after ventilation, and the efficiency of the propeller increases rapidly; the low pressure area near the back root of the blade becomes smaller and smaller gradually; and the peak of periodic vibration of thrust and torque can be effectively reduced. The numerical results demonstrate that the installation of artificial vent pipe effectively improves the hydrodynamic performance of surface piercing propeller in the field of high speed crafts, and the increase of artificial vent pipe diameter plays an active role in the propulsion efficiency of the surface-piercing propeller.

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