A Two-Dimensional Experimental and Numerical Study of Moonpools With Recess

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Senthuran Ravinthrakumar ◽  
Trygve Kristiansen ◽  
Babak Ommani
Keyword(s):  
Potential Flow ◽  
Numerical Study ◽  
Domain Boundary ◽  
Flow Theory ◽  
Mode Shapes ◽  
Linear Potential ◽  
Two Dimensional ◽  
Potential Flow Theory ◽  
Mode Behavior ◽  
Piston Mode

Abstract Moonpool resonance is investigated in a two-dimensional setting in terms of regular, forced heave motions of a model with moonpool with different rectangular-shaped recess configurations. A recess is a reduced draft zone in the moonpool. Dedicated experiments were carried out. The model consisted of two boxes of 40 cm width each, with a distance of 20 cm between them. Recess configurations varying between 5 cm and 10 cm in length and 5 cm in height were tested. Different drafts were also tested. A large number of forcing periods and five forcing amplitudes were tested. A time-domain boundary element method (BEM) code based on the linear potential flow theory was implemented to investigate the resonance periods, mode shapes, as well as the moonpool response as predicted by the (linear) potential flow theory. Dominant physical effects were discussed, in particular damping due to flow separation from the sharp corners of the moonpool inlet and recess. The effect of the recess on the piston-mode behavior is discussed. The nondimensional moonpool response suggests strong viscous damping at the piston-mode resonance. The viscous BEM (VBEM) simulations demonstrate improvement over inviscid BEM, although further improvement of the method is needed. The VBEM simulations are, in general, in good agreement with the experiments. For the largest recess case, some discrepancies are observed in the amplitude-dependent response amplitude operators (RAOs). The piston-mode shapes are clearly different from the near flat free-surface elevation for a moonpool without recess, consistent with the recently published theory.

scholarly journals A 2D Experimental and Numerical Study of Moonpools With Recess

2018 ◽  
Author(s):  
Senthuran Ravinthrakumar ◽  
Trygve Kristiansen ◽  
Babak Ommani
Keyword(s):  
Free Surface ◽  
Flow Separation ◽  
Potential Flow ◽  
Flow Theory ◽  
Surface Elevation ◽  
Mode Shapes ◽  
Linear Potential ◽  
Free Surface Elevation ◽  
Potential Flow Theory ◽  
Piston Mode

Moonpool resonance is investigated in a two-dimensional setting in terms of regular, forced heave motions of a model with moonpool with different rectangular-shaped recess configurations. A recess is a reduced draft zone in the moonpool. Dedicated experiments were carried out. The model consisted of two boxes of 40 cm width each, with a distance of 20 cm between them. Recess configurations varying between 5 cm to 10 cm in length and 5 cm in height were tested. Different drafts were also tested. The free-surface elevation inside the moonpool was measured at eight locations. A large number of forcing periods, and five forcing amplitudes were tested. A time-domain Boundary Element Method (BEM) code based on linear potential flow theory was implemented to investigate the resonance periods, mode shapes as well as the moonpool response as predicted by (linear) potential flow theory. Dominant physical effects were discussed, in particular damping due to flow separation from the sharp corners of the moonpool inlet and recess. The effect of the recess on the piston-mode behavior is discussed. BEM simulations where the effect of flow separation is empirically modelled were also conducted. The non-dimensional moonpool response suggests strong viscous damping at piston-mode resonance. The viscous BEM simulations demonstrate improvement over inviscid BEM, although further improvement of the method is needed. The piston mode shapes are clearly different from the near flat free-surface elevation for a moonpool without recess, consistent with recently published theory.

Nonlinear corrections of linear potential-flow theory of ship waves

2018 ◽  
Vol 67 ◽  
pp. 1-14 ◽  
Author(s):  
Chao Ma ◽  
Yi Zhu ◽  
Jiayi He ◽  
Chenliang Zhang ◽  
Decheng Wan ◽  
...  
Keyword(s):  
Potential Flow ◽  
Flow Theory ◽  
Linear Potential ◽  
Ship Waves ◽  
Potential Flow Theory

Implementation of Linear Potential-Flow Theory in the 6DOF Coupled Simulation of Ship Collision and Grounding Accidents

2016 ◽  
Vol 60 (03) ◽  
pp. 119-114
Author(s):  
Zhaolong Yu ◽  
Yugao Shen ◽  
Jørgen Amdahl ◽  
Marilena Greco
Keyword(s):  
Potential Flow ◽  
Structural Damage ◽  
Flow Theory ◽  
Ship Motions ◽  
Linear Potential ◽  
Hydrodynamic Loads ◽  
Potential Flow Theory ◽  
Highly Nonlinear ◽  
Ship Collision ◽  
Fully Coupled

Ship collisions and groundings are highly nonlinear and transient, coupled dynamic processes involving large structural deformations and fluid structure interactions. It has long been difficult to include all effects in one simulation. By taking advantage of the user-defined load subroutine and the user common variable, this article implements a model of hydrodynamic loads based on linear potential-flow theory into the nonlinear finite element code LS-DYNA, facilitating a fully coupled six degrees of freedom (6DOF) dynamic simulation of ship collision and grounding accidents. Potential-flow theory both with and without considering the forward speed effect is implemented for studying the speed influence. With the proposed model, transient effects of the fluid, global ship motions, impact forces, and structural damage can all be predicted with high accuracy. To the authors' knowledge, this is the first time the fully coupled 6DOF collision and grounding simulations are carried out with linear hydrodynamic loads for transient conditions but without simplification of collision forces. The proposed method is applied to calculations of an offshore supply vessel colliding with a rigid plate and with a submersible platform. The results are compared with a decoupled method and discussed with emphasis on the influence of different initial velocities. The proposed method is capable of predicting both the 6DOF ship motions and structural damage simultaneously with good efficiency and accuracy; hence, it will be a very promising tool in the application to ship collision and grounding analysis.

scholarly journals Numerical simulation of hydrodynamic oscillation of side-by-side double-floating-system with a narrow gap in waves

Open Physics ◽  
2021 ◽  
Vol 19 (1) ◽  
pp. 188-207
Author(s):  
Zhiyang Zhang ◽  
Weixing Liu ◽  
Xiongbo Zheng ◽  
Hengxu Liu ◽  
Ningyu Li
Keyword(s):  
Potential Flow ◽  
Oil And Gas ◽  
Flow Theory ◽  
Future Research ◽  
Linear Potential ◽  
Narrow Gap ◽  
Floating Structures ◽  
Potential Flow Theory ◽  
Wave Basin ◽  
Floating System

Abstract In offshore oil and gas exploration and transportation, it is often encountered that the multi-floating structures work side by side. In some sea conditions, there is a strong coupling between the multi-floating structures that seriously affects the safety of offshore operations. Therefore, the prediction of the relative motion and force between the multi-floating structures and the wave elevation around the multi-floating-system has become a hot issue. At present, the problem of double-floating-system is mostly based on linear potential flow theory. However, when the gap width between two floating bodies is small, the viscous and nonlinear effects are not negligible, so the potential flow theory has great limitations. Based on the viscous flow theory, using the finite difference solution program of FLOW3D and using volume of fluid technology to capture the free surface, a three-dimensional numerical wave basin is established, and the numerical results of the wave are compared with the theoretical solution. On this basis, the hydrodynamic model of side-by-side double-floating-system with a narrow gap is established, and the flow field in the narrow gap of the fixed double-floating-system under the regular wave is analyzed in detail. The law of the gap-resonance is studied, which provides valuable reference for the future research on the multi-floating-system.

On the Application of Linearized Theory to Multi-Element Aerofoils Part I: Tandem Flat Plate Aerofoils

1983 ◽  
Vol 34 (1) ◽  
pp. 46-60 ◽  
Author(s):  
G.D. Watt ◽  
G.V. Parkinson
Keyword(s):  
Flat Plate ◽  
Potential Flow ◽  
Flow Theory ◽  
Two Dimensional ◽  
Potential Flow Theory ◽  
Linearized Theory ◽  
Good Agreement ◽  
Hand Calculator

SummaryA linearized two-dimensional incompressible potential flow theory for two-element uncambered tandem aerofoil sections is developed. It leads to formulas for lift and moment which can be calculated rapidly on a programmable hand calculator, and which reduce, when the two aerofoil elements come together, to the familiar thin-aerofoil formulas for an aerofoil with a simple flap. The theory is shown to give lift and moment predictions which are in good agreement with predictions of numerical potential flow theory.

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