scholarly journals A Semi-Analytical Method for Calculating the Hydrodynamic Force on Perforated Plates in Oscillating Flow

2019 ◽  
Author(s):  
Fredrik Mentzoni ◽  
Trygve Kristiansen
Keyword(s):  
Analytical Method ◽  
Hydrodynamic Force ◽  
Added Mass ◽  
Navier Stokes ◽  
Oscillating Flow ◽  
Force Model ◽  
Hydrodynamic Coefficients ◽  
Two Dimensional ◽  
Force Coefficient ◽  
Perforated Plates

Abstract A two-dimensional numerical analysis on the hydrodynamic force of perforated plates in oscillating flow is presented, and a new semi-analytical force model is proposed. Plates with ten different perforation ratios, τ, from 0.05 to 0.50 are simulated. The Keulegan–Carpenter numbers in the simulations cover a range from 0.002 to 2.2 when made nondimensional with the width of the plates. Resulting hydrodynamic added mass and damping coefficients are presented. All perforated plates with perforation ratios greater than or equal to 10% are found to be damping dominant. The numerical results are obtained using a two-dimensional Navier–Stokes solver (CFD), previously validated against dedicated 2D experiments on perforated plates. Furthermore, we present verification of the code against the analytical solid flat plate results by Graham. The presently obtained hydrodynamic coefficients are compared with the state-of-the-art semi-analytical method for force coefficient calculation of perforated plates by Molin, as well as the recommended practice for estimating hydrodynamic coefficients of perforated structures by DNV GL. Based on the CFD results, a new method for calculating the hydrodynamic force on perforated plates in oscillating flow is presented. The method is based on curve fitting the present CFD results for perforated plates, to the analytical expressions obtained for solid plates by Graham. In addition to its simplicity, a strength of the method is that coefficients for both the added mass and damping are obtained.

Added Mass and Damping of Rectangular Bodies Close to the Free Surface

1984 ◽  
Vol 28 (04) ◽  
pp. 219-225
Author(s):  
John Nicholas Newman ◽  
Bjørn Sortland ◽  
Tor Vinje
Keyword(s):  
Hydrodynamic Force ◽  
Standing Waves ◽  
Present Theory ◽  
Added Mass ◽  
The Body ◽  
Simple Explanation ◽  
Two Dimensional ◽  
Infinite Depth ◽  
Calm Water ◽  
Heave Motion

A submerged two-dimensional rectangle in calm water with infinite depth is studied. The rectangle is oscillating in a heave motion. Negative added mass and sharp peaks in the damping and added-mass coefficients have been found when the submergence is small and the width of the shallow region on top of the rectangle is large. Resonant standing waves will occur in this area. A linear theory is developed to provide a relatively simple explanation of the occurrence of negative added mass for submerged bodies. The vertical hydrodynamic force is associated only with the flow in the shallow region, and the resulting pressure which acts on the top face of the rectangle. The results from this theory are compared with numerical results from the Frank method. The importance of the interaction effect between the top and the bottom of the body, which is neglected in the present theory, is discussed.

Hydrodynamic Coefficients of a Flexible Pipe With Staggered Buoyancy Elements and Strakes Under VIV Conditions

2017 ◽  
Author(s):  
Shixiao Fu ◽  
Halvor Lie ◽  
Jie Wu ◽  
Rolf Baarholm
Keyword(s):  
Inverse Analysis ◽  
Natural Frequencies ◽  
Forced Oscillation ◽  
Hydrodynamic Force ◽  
Added Mass ◽  
Ocean Basin ◽  
Hydrodynamic Coefficients ◽  
Analysis Method ◽  
Flexible Pipe ◽  
Inverse Analysis Method

A 38m long flexible pipe with staggered buoyancy modules and strakes has been tested in the ocean basin of SINTEF Ocean (former Marintek) for VIV investigation of a lazy wave riser. In this paper the inverse analysis method was presented and applied into the investigation of the hydrodynamic force coefficients along this tested flexible pipe with the measured responses as inputs. The feasibility of the inverse analysis method is firstly validated by numerical simulations. The distributions of the added mass and excitation coefficients along the flexible pipe with staggered buoyancy modules and strakes are then investigated. The identified coefficients are validated by check of the natural frequencies and responses of the model, and are finally compared against those from the forced oscillation tests.

Numerical Simulation of Flows Driven by a Torsionally Oscillating Lid in a Square Cavity

1992 ◽  
Vol 114 (2) ◽  
pp. 143-151 ◽  
Author(s):  
Reima Iwatsu ◽  
Jae Min Hyun ◽  
Kunio Kuwahara
Keyword(s):  
Thin Layer ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Fluid Motion ◽  
Numerical Data ◽  
Navier Stokes ◽  
Physical Parameters ◽  
Phase Lag ◽  
Two Dimensional ◽  
Force Coefficient

Numerical studies were made of the flow of a viscous fluid in a two-dimensional square container. The flows are driven by the top sliding wall, which executes sinusoidal oscillations. Numerical solutions were acquired by solving the time-dependent, two-dimensional incompressible Navier-Stokes equations. Results are presented for wide ranges of two principal physical parameters, i.e., Re, the Reynolds number and ω′, the nondimensional frequency of the lid oscillation. Comprehensive details of the flow-structure are presented. When ω′ is small, the flow bears qualitative similarity to the well-documented steady driven-cavity flow. The flow in the bulk of cavity region is affected by the motion of the sliding upper lid. On the contrary, when ω′ is large, the fluid motion tends to be confined within a thin layer near the oscillating lid. In this case, the flow displays the characteristic features of a thin-layer flow. When ω′ is intermediate, ω′ ~ O(1), the effect of the side walls is pronounced; the flow pattern reveals significant changes between the low-Re and high-Re limits. Streamline plots are constructed for different parameter spaces. Physically informative interpretations are proposed which help gain physical insight into the dynamics. The behavior of the force coefficient Cf has been examined. The magnitude and phase lag of Cf are determined by elaborate post-processings of the numerical data. By utilizing the wealth of the computational results, characterizations of Cf as functions of Re and ω′ are attempted. These are in qualitative consistency with the theoretical predictions for the limiting parameter values.

Influence of Viscous Effects on the Hydrodynamics of Ship-Like Sections Undergoing Symmetric and Anti-Symmetric Motions, Using RANS

2008 ◽  
Author(s):  
A. Que´rard ◽  
P. Temarel ◽  
S. R. Turnock
Keyword(s):  
Free Surface ◽  
Potential Flow ◽  
Systematic Approach ◽  
Added Mass ◽  
Experimental Measurements ◽  
Hydrodynamic Coefficients ◽  
Two Dimensional ◽  
Viscous Effects ◽  
Numerical Predictions ◽  
Fluid Damping

The aim of this investigation is to assess the influence of viscous effects on the predicted hydrodynamic coefficients for a range of ship-like sections, such as rectangular, triangular, chine and bulbous. Hydrodynamic coefficients, of added mass or inertia and fluid damping, for two-dimensional sections harmonically heaving, swaying and rolling at the undisturbed free surface are obtained using the ANSYS-CFX11.0 RANS solver, for a range of frequencies of oscillation. All predictions are compared with available experimental measurements and other numerical predictions (potential flow and RANS). It is concluded from these comparisons that the proposed RANS approach can offer a better prediction for the hydrodynamic coefficients when viscous effects become significant, in particular for sway and roll motions. It is important that a reliable and systematic approach is adopted for the application of the unsteady free surface RANS methodology.

Hydrodynamic Coefficients for In-Line Vortex Induced Vibrations

2007 ◽  
Author(s):  
Kristoffer H. Aronsen ◽  
Carl Martin Larsen
Keyword(s):  
Driving Force ◽  
Added Mass ◽  
Large Set ◽  
Hydrodynamic Coefficients ◽  
Marine Structures ◽  
Force Coefficient ◽  
Vortex Induced Vibrations ◽  
Line Force ◽  
Set Up ◽  
Motion Amplitude

The paper presents results from an experimental investigation of hydrodynamic forces on a cylinder under forced in-line motions. Measured forces are decomposed into added mass, driving force and average drag components. From a large set of experiments it has been possible to draw a complete map for in-line force coefficients as function of arbitrary combinations of motion amplitude and frequency. The paper presents test set-up, data processing and how the coefficients can be used in an empirical force coefficient model for calculation of in-line vibrations of slender marine structures with arbitrary damping. Such analyses are in particular important for free spanning pipelines, where damping from pipe/seafloor interaction will reduce the response amplitudes and hence also stresses and fatigue damage.

Prediction of Hydrodynamic Coefficients of Coupled Heave and Pitch Motions of Heeled Planing Boats by Asymmetric 2D+T Theory

2018 ◽  
Author(s):  
Sasan Tavakoli ◽  
Abbas Dashtimanesh ◽  
Prasanta K. Sahoo
Keyword(s):  
Hydrodynamic Force ◽  
Vertical Plane ◽  
Current Method ◽  
Added Mass ◽  
Water Entry ◽  
Hydrodynamic Coefficients ◽  
Empirical Methods ◽  
Reasonable Accuracy ◽  
Stiffness Coefficients ◽  
Pitch Moment

This paper attempts to present a mathematical model to predict hydrodynamic coefficients of a heeled planing hull in vertical plane. This model has been developed by using 2D+T theory and theoretical solution of the water entry of wedge section bodies. Sectional hydrodynamic force acting on the vessel is determined and then extended over the entire length of the vessel. By simplifying final equations of heave force and pitch moment acting on a heeled planing hull, equations for prediction of hydrodynamic coefficients of the vessel are developed. Accuracy of the method is evaluated by comparing its results against previous empirical methods. It is seen that current method has reasonable accuracy in prediction of different hydrodynamic coefficients. Also, effects of heel angle on added mass, damping and stiffness coefficients are studied and discussed.

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