Rankine source time domain method for nonlinear ship motions in steep oblique waves

2018 ◽  
Vol 14 (3) ◽  
pp. 295-308 ◽  
Author(s):  
Malte Riesner ◽  
Guillermo Chillcce ◽  
Ould el Moctar
Keyword(s):  
Time Domain ◽  
Time Domain Method ◽  
Ship Motions ◽  
Oblique Waves ◽  
Rankine Source ◽  
Domain Method

Modelling the Effect of Sloshing on Ship Motions

2010 ◽  
Author(s):  
Tim Bunnik ◽  
Arthur Veldman
Keyword(s):  
Time Domain ◽  
Diffraction Method ◽  
Time Domain Method ◽  
Ship Motions ◽  
Linear Potential ◽  
Beam Seas ◽  
Domain Method ◽  
Outer Domain ◽  
Sloshing Mode ◽  
Surface Correction

Ships with partially filled liquid tanks, such as LNG carriers or FPSOs, are sensitive to sloshing in case they are exposed to waves. The effect of sloshing can have a pronounced effect on the ship motions, in particular roll in oblique seas. In this paper several methods are described which can be used to quantify this effect. The first is a linear diffraction method in which the effect of the liquid in the tank is modeled as a solid inertia of the fluid mass, an added mass and damping of the sloshing fluid and a hydrostatic free-surface correction to the GM. The response is easily computed in the frequency domain. The second is a time domain method in which the sloshing liquid in the tank is modeled with the CFD code ComFLOW. The forces exerted by the liquid on the tank walls are included in a time-domain simulation of the ship motions, based on linear potential flow for the outer domain (ship hull and ocean). The computed ship motions are again input for the motions of the liquid tank, generating a 2-way coupling between the dynamics of the tank and the ship. Both methods are applied to sloshing model tests, published by Molin (2008). In these tests, the response of a barge was measured with a completely filled and partially filled tank in beam seas. The results of the linear diffraction method agree reasonably well, but some differences in the roll response near the first sloshing mode are observed. The coupled time-domain method gives very good results for both low and high sea states.

Prediction of Ship Motions Via a Three-Dimensional Time-Domain Method Following a Quad-Tree Adaptive Mesh Technique

2020 ◽  
Vol 27 (1) ◽  
pp. 29-38
Author(s):  
Teng Zhang ◽  
Junsheng Ren ◽  
Lu Liu
Keyword(s):  
Free Surface ◽  
Incident Wave ◽  
Time Domain ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Wave Profile ◽  
Time Domain Method ◽  
Ship Motions ◽  
Quad Tree ◽  
Mesh Technique

AbstractA three-dimensional (3D) time-domain method is developed to predict ship motions in waves. To evaluate the Froude-Krylov (F-K) forces and hydrostatic forces under the instantaneous incident wave profile, an adaptive mesh technique based on a quad-tree subdivision is adopted to generate instantaneous wet meshes for ship. For quadrilateral panels under both mean free surface and instantaneous incident wave profiles, Froude-Krylov forces and hydrostatic forces are computed by analytical exact pressure integration expressions, allowing for considerably coarse meshes without loss of accuracy. And for quadrilateral panels interacting with the wave profile, F-K and hydrostatic forces are evaluated following a quad-tree subdivision. The transient free surface Green function (TFSGF) is essential to evaluate radiation and diffraction forces based on linear theory. To reduce the numerical error due to unclear partition, a precise integration method is applied to solve the TFSGF in the partition computation time domain. Computations are carried out for a Wigley hull form and S175 container ship, and the results show good agreement with both experimental results and published results.

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