Nonlinear Ship Motions

1998 ◽  
Vol 42 (02) ◽  
pp. 120-130 ◽  
Author(s):  
Yifeng Huang ◽  
Paul D. Sclavounos
Keyword(s):  
Free Surface ◽  
Numerical Method ◽  
Time Domain ◽  
Linear Time ◽  
Ship Motions ◽  
Experimental Measurements ◽  
Approximate Theory ◽  
Nonlinear Method ◽  
Motion Responses ◽  
Nonlinear Solutions

A nonlinear numerical method has been developed to compute motion responses for a ship traveling in steep ambient waves. The method is based on an approximate theory and is an extension to a well-established linear time-domain numerical method. The nonlinear solution is found to be greatly improved over the classical linear and quasi-nonlinear solutions, in comparison to experimental measurements for conventional commercial ships. Through this study, it is also demonstrated that the free surface hydrodynamic nonlinearities are at least as important as, if not more than, the hydrostatic and Froude-Krylov nonlinearities. Stability, consistency and convergence for the nonlinear method are also addressed.

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.

Nonlinear Local Analysis of Steady Flow About a Ship

1991 ◽  
Vol 35 (04) ◽  
pp. 288-294
Author(s):  
F. Noblesse ◽  
D. M. Hendrix ◽  
L. Kahn
Keyword(s):  
Free Surface ◽  
Fluid Velocity ◽  
Wave Profile ◽  
Local Analysis ◽  
Experimental Measurements ◽  
Surface Boundary ◽  
Nonlinear Method ◽  
Rapid Variation ◽  
Wigley Hull ◽  
Analytical Expressions

A nonlinear local analysis of the steady potential flow at a ship bow and stern, and more generally at any point along a ship waterline, is presented. The hull boundary condition and the nonlinear kinematic and dynamic free-surface boundary conditions are satisfied exactly, at the actual position of the free surface, in this analysis. The bow-flow analysis shows that the free surface at a ship bow is tangent to the stem. This theoretical result appears to agree with existing experimental measurements of steady bow waves of the Wigley hull. Simple analytical expressions defining the fluid velocity at the bow and the stern, and more generally at any point along the wave profile, in terms of the elevation of the free surface at the corresponding point are also given. These analytical expressions and the available experimental measurements of wave profiles along the Wigley hull show that the velocity of the flow disturbance due to this hull is fairly small compared to the hull speed everywhere along the wave profile except in very small regions around the bow and the stern, where the total fluid velocity is nearly equal to the hull speed in magnitude but directed vertically. Nonlinearities therefore appear to be quite important, although only in very small regions surrounding a ship bow and stern. A genuine nonlinear method of calculation must then be able to represent the very rapid variation in the direction of the fluid velocity occurring within small regions around a ship bow and stern. In particular, a sufficiently fine discretization is required in these regions.

Non-Linear Effects of Roll Damping Tanks on Ship Motions

2006 ◽  
Author(s):  
Carsten Schumann ◽  
Ricardo Pereira
Keyword(s):  
Free Surface ◽  
Numerical Methods ◽  
Linear Time ◽  
Ship Motions ◽  
Response Curves ◽  
Roll Damping ◽  
Time Simulation ◽  
Non Linear ◽  
Linear Effects

This article describes the application of two numerical methods of computing the flow in u-tube and free surface roll damping tanks. These methods account for the most important non-linear effects in tank flows. i) The programs based on these methods are integrated in a non-linear time simulation strip program. ii) Response curves of tanks are computed with the mentioned tank programs and the results are incorporated in a linear strip program. iii) With both strip programs (linear and non-linear), sea keeping computations are carried out and the results are compared.

Time Domain Assessment of Nonlinear Coupled Ship Motions and Sloshing in Free Surface Tanks

2015 ◽  
Author(s):  
Jose Luis Cercos-Pita ◽  
Gabriele Bulian ◽  
Antonio Souto-Iglesias
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Smoothed Particle Hydrodynamics ◽  
Internal Flow ◽  
Ship Motions ◽  
Simulation Approach ◽  
Safe Operation ◽  
External Fluid ◽  
Particle Hydrodynamics ◽  
Smoothed Particle

Ships at sea almost invariably carry liquids onboard, and liquids are contained in appropriate tanks. Being able to take into account the effects of liquids onboard when predicting ship motions is, therefore, of utmost importance for the safe operation of a vessel. In certain conditions, such predictions also require taking into account nonlinearities in both ship motions and in the internal flow, and linear approaches are not sufficient. Within this context, the present paper describes a simulation approach where a blended 6-DOF nonlinear ship motions prediction solver handling the external fluid-ship interaction, is coupled with a Smoothed-Particle-Hydrodynamics (SPH) solver for simulating the internal flow tank dynamics. The solvers are described and an example application is reported.

Investigation on Heave Motion and Load Response of a FPSO in Regular Waves by Fully Nonlinear Method

2020 ◽  
Author(s):  
Jia-Le Wang ◽  
Shi-Li Sun ◽  
Hui-Long Ren
Keyword(s):  
Free Surface ◽  
Dynamic Analysis ◽  
Time Domain ◽  
Mooring System ◽  
Analysis Method ◽  
Regular Waves ◽  
Nonlinear Method ◽  
Time Step ◽  
Load Response ◽  
Heave Motion

Abstract In this paper, the full nonlinear method based on the three-dimensional potential flow theory and the dynamic analysis method of flexible components are combined to simulate the motion and load response of a FPSO in waves. On the boundary of the hull body, the coupled motions are considered in the impenetrable condition. An improved Eulerian method is adopted to trace strongly nonlinear 3-D free surface deformation. In the far field, artificial damping zone is applied to eliminate reflected wave. Rankine source method is adopted to solve the velocity potential in time domain. Hydrodynamic mesh on hull body is generated by using accumulative chord length cubic parameter spline function. After solving Poisson equation, the initial mesh on free surface becomes orthogonal. In each time step, elastic-mesh-technique (EMT) is used to optimize the mesh on free surface. Several auxiliary functions are introduced to decouple the motions and load, and then the fourth-order Runge-Kutta method is adopted to update the numerical model in time domain. For the forces of the mooring system on the hull at each time step, the dynamic equation of the flexible member is established by the dynamic analysis method based on the elastic slender rod mechanical model, and then the equation is discretized into matrix form by the finite element discretization method and solved. The coupled motion of FPSO hull and mooring system in regular waves of various frequencies in various directions is simulated, and the time domain solutions are obtained. RAO of heave motion in each wave direction is given. The load response at the midship section is analyzed.

NON LINEAR ANALYSIS OF SHIP MOTIONS AND LOADS IN LARGE AMPLITUDE WAVES

2021 ◽  
Vol 153 (A2) ◽  
Author(s):  
G Mortola ◽  
A Incecik ◽  
O Turan ◽  
S.E. Hirdaris
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Large Amplitude ◽  
Linear Time ◽  
Ship Motions ◽  
Wave Loads ◽  
Time Step ◽  
Strip Theory ◽  
Non Linear ◽  
The Time Domain

A non linear time domain formulation for ship motions and wave loads is presented and applied to the S175 containership. The paper describes the mathematical formulations and assumptions, with particular attention to the calculation of the hydrodynamic force in the time domain. In this formulation all the forces involved are non linear and time dependent. Hydrodynamic forces are calculated in the frequency domain and related to the time domain solution for each time step. Restoring and exciting forces are evaluated directly in time domain in a way of the hull wetted surface. The results are compared with linear strip theory and linear three dimensional Green function frequency domain seakeeping methodologies with the intent of validation. The comparison shows a satisfactory agreement in the range of small amplitude motions. A first approach to large amplitude motion analysis displays the importance of incorporating the non linear behaviour of motions and loads in the solution of the seakeeping problem.

Motion Prediction of the Ship With Sloshing Tanks

2009 ◽  
Author(s):  
Kang Zou ◽  
Quan-ming Miao ◽  
Ren-qing Zhu
Keyword(s):  
Time Domain ◽  
Three Dimensional ◽  
Panel Method ◽  
Ship Motion ◽  
Motion Prediction ◽  
Ship Motions ◽  
Motion Responses ◽  
Motion Problem ◽  
Good Agreement

Sloshing flow in ship tanks is excited by ship motions, but it affects the ship motions in reverse. This paper focuses on the motion responses of the ship in waves with consideration of coupled effects with sloshing in tanks. A three-dimensional panel method in time-domain is applied to solve the ship motion problem, and the sloshing tanks are solved by commercial CFD software simultaneously. Experiments were carried out on a SL175 ship and good agreement is obtained.

Nonlinear Computation of Ship Motions in the Time-Domain Using 2D+t Theory

2015 ◽  
Author(s):  
Wei Meng ◽  
Wei Qiu
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Time Domain ◽  
High Speed ◽  
Field Method ◽  
Ship Motions ◽  
Strip Theory ◽  
Wigley Hull ◽  
Body Boundary ◽  
The Time Domain

Motions of high-speed displacement ships in waves have been predicted based on a body-exact strip-theory method in the time domain (2D+t). Nonlinear body boundary conditions were applied on instantaneous wetted surfaces. Linear boundary conditions were used on the free surface so that the 2D transient free surface Green function can be employed. Interactions among the strips of the ship hull were considered. A far field method was adopted to compute the hydrodynamic forces. Validation studies have been carried out for two Wigley hull ships in regular waves. Numerical results were compared with experimental data and those by other numerical methods.

Numerical Studies of the Effect of Sloshing on Ship Motions

2009 ◽  
Author(s):  
Seok Kyu Cho ◽  
Hang Shoon Choi ◽  
Hong Gun Sung ◽  
Sa Young Hong ◽  
Il Ryong Park
Keyword(s):  
Free Surface ◽  
Potential Theory ◽  
Time Domain ◽  
Ship Motion ◽  
Navier Stokes ◽  
Ship Motions ◽  
Linear Potential ◽  
Navier Stokes Equation ◽  
Numerical Studies ◽  
Linear Potential Theory

The effects of sloshing on ship motions are simulated in view of FSRU design and operation. The Navier-Stokes equation is solved for sloshing motion. For the analysis of free surface, Volume of Fluid (VOF) techniques is adopted. The ship motion is solved in time domain by taking account of memory effects, which are obtained from the linear potential theory. The ship motion and sloshing are linked by explicitly coupling the ship motion and sloshing force. The coupling method is used to simulate the interaction of side-by-side moored LNG FSRU and LNGC for beam sea condition. Also the effect of sloshing on the two body interaction is studied for the case including sloshing in LNGC.

Non-Linear Time Domain Simulation of Dynamic Instabilities in Longitudinal Waves

2008 ◽  
Author(s):  
S. Ribeiro e Silva ◽  
C. Guedes Soares
Keyword(s):  
Time Domain ◽  
Degrees Of Freedom ◽  
Linear Time ◽  
Simulation Method ◽  
Ship Motions ◽  
Computational Technique ◽  
Parametric Rolling ◽  
Longitudinal Waves ◽  
Six Degrees Of Freedom ◽  
Strip Theory

A time domain numerical simulation method is developed to determine ship motions in six degrees-of-freedom and to detect dynamic instabilities in both regular and irregular longitudinal waves. The basic approach of the simulation program involves computation of hydrodynamic coefficients of added mass and damping, restoring coefficients and diffraction and Froude-Krylov excitation forces at each step in time according to the instantaneous waterline and vessel position, using a strip theory method and a pressure integration technique along the segments. This paper briefly describes the computational technique utilized and makes comparisons between numerical and experimental roll damping data to infer about its influence on roll amplitude under parametric rolling conditions. An investigation into the dynamic stability in waves of a container vessel example.

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