The Numerical Modeling of Ship Motions and Capsizing in Severe Seas

1990 ◽  
Vol 34 (04) ◽  
pp. 289-301
Author(s):  
Jan O. de Kat
Keyword(s):  
Numerical Modeling ◽  
Free Surface ◽  
Numerical Model ◽  
Nonlinear Model ◽  
Time Domain ◽  
Ship Motions ◽  
First Order ◽  
Large Amplitude Motions ◽  
Flow Effects ◽  
The Time Domain

A numerical model has been developed to determine the large-amplitude motions of a steered vessel subjected to severe wave conditions, including those that may lead to capsizing. The model was used to identify different modes of capsizing, and to study relevant mechanisms and conditions. In this paper emphasis is placed on the theoretical aspects. The nonlinear model combines both potential and viscous flow effects, where integrations are carried out in the time domain over the instantaneous free surface; first-order memory effects are taken into account, and the free surface can be irregular, Some new results are presented concerning statistical properties relevant to the simulation of random following or quartering seas.

Time-Domain Analysis of Large-Amplitude Vertical Ship Motions and Wave Loads

1998 ◽  
Vol 42 (02) ◽  
pp. 139-153 ◽  
Author(s):  
N. Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Large Amplitude ◽  
Surface Condition ◽  
Memory Effects ◽  
Wave Loads ◽  
Strip Theory ◽  
Large Amplitude Motions ◽  
Free Surface Oscillations ◽  
The Time Domain

The vertical motions and wave induced loads on ships with forward speed are studied in the time domain, considering non-linear effects associated with large amplitude motions and hull flare shape. The method is based on a strip theory, using singularities distributed on the cross sections which satisfy the linear free surface condition. The solution is obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. In this way the linear radiation forces are represented in terms of impulse response functions, infinite frequency added masses and radiation restoring coefficients. The diffraction forces associated with incident wave scattering are linear. The hydrostatic and Froude-Krylov forces are evaluated over the instantaneous wetted surface of the hull to account for the large amplitude motions and hull flare. The radiation contribution for wave loads is also obtained in the time domain using convolution to account for the memory effects related to the free surface oscillations. Results of motions and wave loads for the S175 container ship are presented and analyzed. The results from the present method are compared with linear results.

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.

Modal Analysis of Transient Liquid Sloshing in Partially-Filled Tanks

2014 ◽  
Vol 526 ◽  
pp. 127-132 ◽  
Author(s):  
Xue Lian Zheng ◽  
Xian Sheng Li ◽  
Yuan Yuan Ren ◽  
Zhu Qing Cheng
Keyword(s):  
Fourier Transform ◽  
Free Surface ◽  
Time Domain ◽  
Periodic Oscillation ◽  
Liquid Sloshing ◽  
First Order ◽  
Liquid Free Surface ◽  
Fluent Simulation ◽  
Fill Level ◽  
The Time Domain

To investigate the dynamic characteristics of liquid sloshing in partially-filled tanks, FLUENT simulation for liquid sloshing in cylinder tanks with the 40% liquid fill level and subject to lateral accelerations of 0.1 g-0.4 g were carried out. By the observation of transient sloshing force and the liquid free surface, it was found that the liquid sloshing is a periodic oscillation. Fourier transform was utilized to transform the sloshing forces in the time domain to the signals in the frequency domain. By spectrum analysis, it was found that the first-order oscillation that has the biggest amplitude is the most important one for liquid sloshing. For further command on liquid sloshing, modal shapes for the first sixth modal were acquired by ANSYS. It is drawn that the odd modals have anti-symmetrical shapes and the first-order oscillation makes the biggest contribution on liquid sloshing, the even modals have symmetrical shapes and could not contribute to liquid sloshing.

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.

Generalized Modes in Time-Domain Seakeeping Calculations

2012 ◽  
Vol 56 (04) ◽  
pp. 215-233
Author(s):  
Johan T. Tuitman ◽  
Šime Malenica ◽  
Riaan van't Veer
Keyword(s):  
Rigid Body ◽  
Transient Response ◽  
Time Domain ◽  
Large Amplitude ◽  
Degrees Of Freedom ◽  
Mode Shapes ◽  
Nonlinear Load ◽  
Large Amplitude Motions ◽  
Rigid Body Modes ◽  
The Time Domain

The concept of "generalized modes" is to describe all degrees of freedom by mode shapes and not using any predefined shape, like rigid body modes. Generalized modes in seakeeping computations allow one to calculate the response of a single ship, springing, whipping, multibody interaction, etc., using a uniform approach. The generalized modes have already been used for frequency-domain seakeeping calculations by various authors. This article extents the generalized modes methodology to be used for time-domain seakeeping computations, which accounts for large-amplitude motions of the rigid-body modes. The time domain can be desirable for seakeeping computations because it is easy to include nonlinear load components and to compute transient response, like slamming and whipping. Results of multibody interaction, two barges connected by a hinge, whipping response of a ferry resulting from slamming loads, and the response of a flexible barge are presented to illustrate the theory.

scholarly journals Computation of Nonlinear Hydrodynamic Loads on Floating Wind Turbines Using Fluid-Impulse Theory

2015 ◽  
Author(s):  
Godine Kok Yan Chan ◽  
Paul D. Sclavounos ◽  
Jason Jonkman ◽  
Gregory Hayman
Keyword(s):  
Free Surface ◽  
Green Function ◽  
Wind Turbines ◽  
Time Domain ◽  
The Body ◽  
Nonlinear Loads ◽  
Frequency Wave ◽  
Linear And Nonlinear ◽  
The Time Domain ◽  
Nonlinear Free Surface

A hydrodynamics computer module was developed to evaluate the linear and nonlinear loads on floating wind turbines using a new fluid-impulse formulation for coupling with the FAST program. The new formulation allows linear and nonlinear loads on floating bodies to be computed in the time domain. It also avoids the computationally intensive evaluation of temporal and spatial gradients of the velocity potential in the Bernoulli equation and the discretization of the nonlinear free surface. The new hydrodynamics module computes linear and nonlinear loads — including hydrostatic, Froude-Krylov, radiation and diffraction, as well as nonlinear effects known to cause ringing, springing, and slow-drift loads — directly in the time domain. The time-domain Green function is used to solve the linear and nonlinear free-surface problems and efficient methods are derived for its computation. The body instantaneous wetted surface is approximated by a panel mesh and the discretization of the free surface is circumvented by using the Green function. The evaluation of the nonlinear loads is based on explicit expressions derived by the fluid-impulse theory, which can be computed efficiently. Computations are presented of the linear and nonlinear loads on the MIT/NREL tension-leg platform. Comparisons were carried out with frequency-domain linear and second-order methods. Emphasis was placed on modeling accuracy of the magnitude of nonlinear low- and high-frequency wave loads in a sea state. Although fluid-impulse theory is applied to floating wind turbines in this paper, the theory is applicable to other offshore platforms as well.

Whipping Response of Vessels With Large Amplitude Motions

2006 ◽  
Author(s):  
Nuno Fonseca ◽  
Eduardo Antunes ◽  
Carlos Guedes Soares
Keyword(s):  
Time Domain ◽  
Large Amplitude ◽  
Nonlinear Effects ◽  
Regular Waves ◽  
Structural Dynamic ◽  
Highly Nonlinear ◽  
Large Amplitude Motions ◽  
Structural Dynamic Characteristics ◽  
The Time Domain ◽  
Equations Of Motions

The paper presents a time domain method to calculate the ship responses in heavy weather, including the global structural loads due to whipping. Since large amplitude waves induce nonlinear ship responses, and in particular highly nonlinear vertical structural loads, the equations of motions and structural loads are solved in the time domain. The “partially nonlinear” time domain seakeeping program accounts for the most important nonlinear effects. Slamming forces are given by the contribution of two components: an initial impact due to bottom slamming and flare slamming due to the variation of momentum of the added mass. The hull vibratory response is calculated applying the modal analysis together with direct integration of the differential equations in the time domain. The structural dynamic characteristics of the hull are modeled by a finite element representation of a Timoshenko beam accounting for the shear deformation and rotary inertia. The calculation procedure is applied to a frigate advancing in regular waves. The contribution of whipping loads to the vertical bending moments on the ship structure is assessed by comparing this response with and without the hull vibration.

scholarly journals THE TIME DOMAIN ANALYSIS ON MOORED SHIP MOTIONS

1988 ◽  
Vol 1 (21) ◽  
pp. 219 ◽  
Author(s):  
Masayoshi Kubo ◽  
Naokatsu Shimoda ◽  
Shunsaku Okamoto
Keyword(s):  
Time Domain ◽  
Integral Method ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Ship Motions ◽  
Convolution Integral ◽  
Quay Wall ◽  
Calculation Results ◽  
The Time Domain

The ship refuge inside a harbor in storm requires the analysis of moored ship motions along a quay wall. In this case the time domain analysis with the convolution integral method becomes effective. But the calculation accuracy is not enough and must be improved to analyze actual moored ship motions. In this paper some methods of the improvement are proposed and their efficiency is verified by comparing the calculation results with the experimental ones.

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.

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