Estimation of Added Mass and Radiation Damping of Large Ocean Observation Buoy Using Numerical Analysis

Diffraction/Radiation theory is used to calculate the wave kinematics and the motions of a floating body in area of varying bathymetry. The bathymetry is modeled as a second body, which, without special measures, leads to spurious reflection at the edge of the mesh. A modified formulation of the Boundary Element Method is introduced to model partially transparent panels. Those panels, when properly used to smoothly extend the actual (opaque) bathymetry, allow much more accurate computation. The efficiency of the method is tested with regards of several parameters concerning the bathymetry size and the way to smooth the truncation. Numerical results are satisfactorily compared with a 3D shallow water code based on Green-Naghdi theory. The sensitivity to the slope on the ship response is then investigated (motion, added mass, radiation damping and second order loads). The differences with the constant depth calculations are significant, due to the modified incident wave field, but also due to modified added mass and radiation damping terms. The method presented here could be useful in the context of LNG terminals where the depth is quite shallow and the bathymetric variations significant.

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Numerical analysis of added mass and damping of elastic hydrofoils

Journal of Hydrodynamics ◽

10.1007/s42241-020-0066-5 ◽

2020 ◽

Vol 32 (5) ◽

pp. 1009-1023

Author(s):

Jia-sheng Li ◽

Ye-gao Qu ◽

Hong-xing Hua

Keyword(s):

Numerical Analysis ◽

Added Mass

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J091021 Numerical Analysis for the Added Mass of Oscillating Body in Viscous Fluid

The Proceedings of Mechanical Engineering Congress Japan ◽

10.1299/jsmemecj.2011._j091021-1 ◽

2011 ◽

Vol 2011 (0) ◽

pp. _J091021-1-_J091021-5

Author(s):

Hideki SHINIOHARA ◽

Takashi TSUJI ◽

Katsuya HIRATA

Keyword(s):

Numerical Analysis ◽

Viscous Fluid ◽

Added Mass

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Parameter Identification of a Large Floating Body in Random Ocean Waves by Reverse MISO Method

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.1493201 ◽

2003 ◽

Vol 125 (2) ◽

pp. 81-86 ◽

Cited By ~ 5

Author(s):

S. K. Bhattacharyya ◽

R. Panneer Selvam

Keyword(s):

Nonlinear System Identification ◽

Ocean Waves ◽

Added Mass ◽

Radiation Damping ◽

Floating Body ◽

Mooring Line ◽

Nonlinear Stiffness ◽

Numerical Illustration ◽

Frequency Dependent ◽

Single Output

Dynamics of a large moored floating body in ocean waves involves frequency dependent added mass and radiation damping as well as the linear and nonlinear mooring line characteristics. Usually, the added mass and radiation damping matrices can be estimated either by potential theory-based calculations or by experiments. The nonlinear mooring line properties are usually quantified by experimental methods. In this paper, we attempt to use a nonlinear system identification approach, specifically the Reverse Multiple Inputs-Single Output (R-MISO) method, to a single-degree-of-freedom system with linear and cubic nonlinear stiffnesses. The system mass is split into a frequency independent and a frequency dependent component and its damping is frequency dependent. This can serve as a model of a moored floating system with a dominant motion associated with the nonlinear stiffness. The wave diffraction force, the excitation to the system, is assumed known. This can either be calculated or obtained from experiments. For numerical illustration, the case of floating semi-ellipsoid is adopted with dominant sway motion. The motion as well as the loading are simulated with and without noise assuming PM spectrum and these results have been analyzed by the R-MISO method, yielding the frequency dependent added mass and radiation damping, linear as well as the nonlinear stiffness coefficients quite satisfactorily.

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System Identification of a Coupled Two DOF Moored Floating Body in Random Ocean Waves

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.2199557 ◽

2005 ◽

Vol 128 (3) ◽

pp. 191-202 ◽

Cited By ~ 8

Author(s):

R. Panneer Selvam ◽

S. K. Bhattacharyya

Keyword(s):

System Identification ◽

Mass Matrix ◽

Ocean Waves ◽

Added Mass ◽

Radiation Damping ◽

Floating Body ◽

Mooring Line ◽

Frequency Dependent ◽

Linear And Nonlinear ◽

Random Ocean Waves

Dynamics of a large moored floating body in ocean waves involves frequency dependent added mass and radiation damping as well as the linear and nonlinear mooring line characteristics. Usually, the added mass and radiation damping matrices can be estimated either by potential theory-based calculations or by experiments. The nonlinear mooring line properties are usually quantified by experimental methods. In this paper, we attempt to use a nonlinear system identification approach, specifically the reverse multiple input-single output (R-MISO) method, to coupled surge-pitch response (two-degrees-of-freedom) of a large floating system in random ocean waves with linear and cubic nonlinear mooring line stiffnesses. The system mass matrix has both frequency independent and frequency dependent components whereas its damping matrix has only frequency dependent components. The excitation force and moment due to linear monochromatic waves which act on the system are assumed to be known that can either be calculated or obtained from experiments. For numerical illustration, a floating half-spheroid is adopted. The motion as well as the loading are simulated assuming Pierson-Moskowitz (PM) spectrum and these results have been analyzed by the R-MISO method yielding frequency dependent coupled added mass and radiation damping coefficients, as well as linear and nonlinear stiffness coefficients of mooring lines satisfactorily.

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Finite Element Analysis of Subsea Pipelines Subjected to Underwater Explosion

Volume 2A: Structures, Safety and Reliability ◽

10.1115/omae2013-10736 ◽

2013 ◽

Cited By ~ 1

Author(s):

F. Van den Abeele ◽

P. Verleysen

Keyword(s):

Shock Wave ◽

Finite Element ◽

Transient Response ◽

Acoustic Pressure ◽

Underwater Explosion ◽

Structural Response ◽

Added Mass ◽

Radiation Damping ◽

Time Response ◽

Subsea Pipelines

Underwater mines and explosives, left in ports and harbours after World War II, can still pose a threat to subsea pipelines. In case of an accidental explosion, or even during controlled detonation, such explosives can cause significant damage to subsea pipelines. To assess the safety of pipelines exposed to an underwater explosion, finite element analyses are performed to predict the transient response of the pipeline to an acoustic pressure shock wave. This type of problem is characterized by a strong coupling between the structural response of the pipe and the acoustic pressure on the wetted interface between the pipe surface and the surrounding seawater. The spherical pressure wave induced by an underwater explosion is characterized by a very steep wave front, where the maximum pressure is attained over an extremely short rise time. The pressure then drops off exponentially over a significantly longer period of time. As a result, the structural behaviour is a combination of a long time response, dominated by an added mass effect (low frequency), a short time response, governed by radiation damping (high frequency), and an intermediate time-frequency response, where both added mass and radiation damping effects are present. In this paper, a finite element model is presented to simulate the transient response of a subsea pipeline subjected to an underwater explosion. The close coupling between acoustic pressure and structural response gives rise to numerical challenges like the accurate formulation and representation of the shock wave, the mesh requirements for the acoustic domain, and the position of the surface based absorbing radiation boundaries. An explicit dynamic solver is used to tackle these challenges, and to predict the behaviour of subsea pipelines exposed to an underwater explosion. The numerical results are compared to published experimental data, and can be used to assess the safety of submerged pipelines in the vicinity of explosives.

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