An Improved Body-Exact Method to Predict Large Amplitude Ship Roll Responses

2018 ◽  
Author(s):  
Rahul Subramanian ◽  
Naga Venkata Rakesh ◽  
Robert F. Beck
Keyword(s):  
Incident Wave ◽  
Large Amplitude ◽  
Nonlinear Models ◽  
Body Position ◽  
Computational Cost ◽  
Offshore Structures ◽  
The Body ◽  
Surface Boundary ◽  
Strip Theory ◽  
New Formulation

Accurate prediction of the roll response is of significant practical relevance not only for ships but also ship type offshore structures such as FPSOs, FLNGs and FSRUs. This paper presents a new body-exact scheme that is introduced into a nonlinear direct time-domain based strip theory formulation to study the roll response of a vessel subjected to moderately large amplitude incident waves. The free surface boundary conditions are transferred onto a representative incident wave surface at each station. The body boundary condition is satisfied on the instantaneous wetted surface of the body below this surface. This new scheme allows capturing nonlinear higher order fluid loads arising from the radiated and wave diffraction components. The Froude-Krylov and hydrostatic loads are computed on the intersection surface of the exact body position and incident wave field. The key advantage of the methodology is that it improves prediction of nonlinear hydrodynamic loads while keeping the additional computational cost small. Physical model tests have been carried out to validate the computational model. Fairly good agreement is seen. Comparisons of the force components with fully linear and body-nonlinear models help in bringing out the improvements due to the new formulation.

Computing Large Amplitude Motions of a Floating Offshore Structure in the Time Domain

2008 ◽  
Author(s):  
Wei Qiu ◽  
Hongxuan Peng
Keyword(s):  
Time Domain ◽  
Large Amplitude ◽  
Offshore Structures ◽  
The Body ◽  
Surface Boundary ◽  
Offshore Structure ◽  
Floating Structure ◽  
Time Step ◽  
Large Amplitude Motions ◽  
The Time Domain

Based on the panel-free method, large-amplitude motions of floating offshore structures have been computed by solving the body-exact problem in the time domain using the exact geometry. The body boundary condition is imposed on the instantaneous wetted surface exactly at each time step. The free surface boundary is assumed linear so that the time-domain Green function can be applied. The instantaneous wetted surface is obtained by trimming the entire NURBS surfaces of a floating structure. At each time step, Gaussian points are automatically distributed on the instantaneous wetted surface. The velocity potentials and velocities are computed accurately on the body surface by solving the desingularized integral equations. Nonlinear Froude-Krylov forces are computed on the instantaneous wetted surface under the incident wave profile. Validation studies have been carried out for a Floating Production Storage and Offloading (FPSO) vessel. Computed results were compared with experimental results and solutions by the panel method.

An Improved Body-Exact Method to Predict the Maneuvering of Ships in a Seaway

2019 ◽  
Author(s):  
Rahul Subramanian ◽  
Robert F. Beck
Keyword(s):  
Incident Wave ◽  
Body Position ◽  
Surface Boundary ◽  
Wave Surface ◽  
Computationally Efficient ◽  
Regular Waves ◽  
Viscous Effects ◽  
Surface Boundary Conditions ◽  
Strip Theory ◽  
Calm Water

Abstract Over the last decade, the importance of considering the effects of waves on the maneuvering characteristics of ships has been widely recognized. This paper presents the application of a recently developed nonlinear body-exact scheme (Subramanian, Rakesh, and Beck (2018)) to directly simulate the maneuvering characteristics of a container ship in calm water and in regular waves. In the present body-exact scheme, the perturbation free surface boundary conditions are transferred to a representative incident wave surface at each station at each time. The hydrodynamic forces are computed on the exact instantaneous wetted surface formed by the intersection of the incident wave surface with the exact body position at each time. It is proposed that this model will not only improve first order sea loads but also the higher order drift force predictions which are critical for determining the trajectory of a maneuvering vessel in a seaway. The strip theory formulation has been found to be numerically stable, robust and computationally efficient, which are all critical aspects when performing long time maneuvering simulations. The hull maneuvering, rudder and propeller forces are adopted from standard systems-based approaches that are used to predict calm water maneuvers. Care is taken to ensure that ideal fluid effects are separated from viscous effects and not double counted. Results are presented for turning circle maneuvers in calm water and regular waves incident at various headings and wavelengths. The numerical results are compared with available experiments.

Time-Domain Simulations of Radiation and Diffraction Forces

2010 ◽  
Vol 54 (02) ◽  
pp. 79-94 ◽  
Author(s):  
Xinshu Zhang ◽  
Piotr Bandyk ◽  
Robert F. Beck
Keyword(s):  
Free Surface ◽  
Time Domain ◽  
Three Dimensional ◽  
The Body ◽  
Surface Boundary ◽  
Two Dimensional ◽  
Forward Speed ◽  
Time Step ◽  
Surface Boundary Conditions ◽  
Strip Theory

Large-amplitude, time-domain, wave-body interactions are studied in this paper for problems with forward speed. Both two-dimensional strip theory and three-dimensional computation methods are shown and compared by a number of numerical simulations. In the present approach, an exact body boundary condition and linearized free surface boundary conditions are used. By distributing desingularized sources above the calm water surface and using constant-strength flat panels on the exact body surface, the boundary integral equations are solved numerically at each time step. The strip theory method implements Radial Basis Functions to approximate the longitudinal derivatives of the velocity potential on the body. Once the fluid velocities on the free surface are computed, the free surface elevation and potential are updated by integrating the free surface boundary conditions. After each time step, the body surface and free surface are regrided due to the instantaneous changing wetted body geometry. Extensive results are presented to validate the efficiency of the present methods. These results include the added mass and damping computations for a Wigley III hull and an S-175 hull with forward speed using both two-dimensional and three-dimensional approaches. Exciting forces acting on a Wigley III hull due to regular head seas are obtained and compared using both the fully three-dimensional method and the two-dimensional strip theory. All the computational results are compared with experiments or other numerical solutions.

Time-Domain Second-Order Wave Radiation in Two Dimensions

1993 ◽  
Vol 37 (01) ◽  
pp. 25-33 ◽  
Author(s):  
Michael Isaacson ◽  
Joseph Y. T. Ng
Keyword(s):  
Circular Cylinder ◽  
Time Domain ◽  
Body Position ◽  
Two Dimensions ◽  
Boundary Integral ◽  
Second Order ◽  
The Body ◽  
Wave Radiation ◽  
Surface Boundary ◽  
Time Step

This paper presents a time-domain second-order method to study the nonlinear wave radiation problem in two dimensions. A time-stepping scheme is adopted to obtain the resulting flow development which satisfies the nonlinear free-surface boundary conditions and the radiation condition to second order, and the numerical procedure utilizes a boundary integral equation method based on Green's theorem to calculate the field solution at each time step. The body surface boundary condition is expanded about the mean body position to second order by a Taylor series. The method is applied to the cases of a semi-submerged circular cylinder and a rectangular cylinder undergoing sinusoidal sway, heave and roll motions. For the case of the circular cylinder, comparisons of the computed hydrodynamic forces at first and second order are made with previous theoretical and experimental results and a favorable agreement is indicated. The importance of second-order effects in the calculation of the hydrodynamic force is discussed.

A Forward-Speed Body-Exact Strip Theory

2015 ◽  
Author(s):  
Piotr J. Bandyk ◽  
George S. Hazen
Keyword(s):  
High Frequency ◽  
Numerical Data ◽  
The Body ◽  
Surface Boundary ◽  
Forward Speed ◽  
Rankine Source ◽  
High Frequency Oscillations ◽  
Surface Boundary Conditions ◽  
Strip Theory ◽  
Acceleration Potential

This paper develops an extension to the body-exact strip theory of Bandyk, Beck, and Zhang [1–8], focused on improved prediction of forward-speed effects. One of the known limitations of standard strip theory is the treatment of forward speed terms. The free surface boundary conditions completely neglect the forward speed, which is usually justified by the argument of high-frequency oscillations. The pressure equation on the body includes a speed-dependent term that must computed, most commonly using the Ogilvie-Tuck theorem or numerical approximations. The strip theory variation described here circumvents these deficiencies by applying the 2D+T approach. The model assumes that each two-dimensional frame, in which a boundary value problem (BVP) is solved, remains fixed relative to an earth-fixed frame. The numerical model is based on a time-domain Rankine source method, using the same body-exact approximation as described in earlier work [1]. A suitable acceleration potential BVP is derived. Added mass and damping coefficients are calculated for two Wigley hulls, using the the standard body-exact approach and forward-speed 2D + T variant, and compared to existing model test and numerical data.

Hydrodynamic Forces on a Submerged Sphere Undergoing Large Amplitude Motion

1994 ◽  
Vol 38 (04) ◽  
pp. 272-277
Author(s):  
G. X. Wu
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Large Amplitude ◽  
Multipole Expansion ◽  
The Body ◽  
Surface Boundary ◽  
Free Surface Boundary Condition ◽  
Submerged Sphere ◽  
Instantaneous Position ◽  
Surface Boundary Condition

The hydrodynamic problem of a sphere submerged below a free surface and undergoing large amplitude oscillation is investigated based on the velocity potential theory. The body surface boundary condition is satisfied on its instantaneous position while the free-surface boundary condition is linearized. The solution is obtained by writing the potential in terms of the multipole expansion.

Hydrodynamic forces on a submerged circular cylinder undergoing large-amplitude motion

1993 ◽  
Vol 254 ◽  
pp. 41-58 ◽  
Author(s):  
G. X. Wu
Keyword(s):  
Free Surface ◽  
Circular Cylinder ◽  
Large Amplitude ◽  
Surface Condition ◽  
Multipole Expansion ◽  
The Body ◽  
Surface Boundary ◽  
Instantaneous Position ◽  
Large Amplitude Oscillation ◽  
Surface Boundary Condition

The hydrodynamic problem of a circular cylinder submerged below a free surface and undergoing large-amplitude oscillation is investigated based on the velocity potential theory. The body-surface boundary condition is satisfied on its instantaneous position while the free-surface condition is linearized. The solution is obtained by writing the potential in terms of the multipole expansion. Various interesting results associated with the circular cylinder are obtained.

Nonlinear Ship Motions in the Time-Domain Using a Body-Exact Strip Theory

2008 ◽  
Author(s):  
Piotr J. Bandyk ◽  
Robert F. Beck
Keyword(s):  
Free Surface ◽  
Boundary Conditions ◽  
Time Domain ◽  
The Body ◽  
Ship Motions ◽  
Surface Boundary ◽  
Theory Approach ◽  
Offshore Structure ◽  
Time Step ◽  
Strip Theory

Modern offshore structure and ship design requires an understanding of responses in large seas. A nonlinear time-domain method may be used to perform computational analyses of these events. To be useful in preliminary design, the method must be computationally efficient and accurate. This paper presents a body-exact strip theory approach to compute wave-body interactions for large amplitude ship motions. The exact body boundary conditions and linearized free surface boundary conditions are used. At each time step, the body surface and free surface are regrided due to the changing wetted body geometry. Numerical and real hull forms are used in the computations. Validation and comparisons of hydrodynamic forces are presented. Selected results are shown illustrating the robustness and capabilities of the body-exact strip theory. Finally, an equation of motion solver is implemented to predict the motions of the vessel in a seaway.

Time-Domain Simulation of Motions of Large Structures in Nonlinear Waves

2002 ◽  
Author(s):  
Debabrata Sen
Keyword(s):  
Incident Wave ◽  
Time Domain ◽  
Nonlinear Waves ◽  
Large Amplitude ◽  
Time Integration ◽  
Offshore Structures ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Computational Scheme ◽  
Irregular Waves

In this paper, we discuss development of a time-domain motion simulation method for studying the interaction of nonlinear waves with large offshore structures. The computational algorithm follows a simplified numerical wave-tank approach based upon a boundary-integral method and time-integration of boundary conditions. The simplifying approximations include linearization of the interaction hydrodynamic effects (radiation and diffraction) while the incident wave effects are considered in full. The main aim is to develop a method that will consider all important nonlinear effects associated with a large-amplitude incident wave, and yet practical enough to be applied routinely by the industry. In the time-integration of motion equations, numerical instabilities usually arise if difference rules are applied for determining pressures, due to coupling between forces and motions. To avoid this, an algorithm has been developed for the pressure evaluation. The resulting computational scheme is numerically stable for all conditions. The method can incorporate effects of other forces such as Morison forces, forces from mooring lines etc. which can be nonlinear. After providing a description of computational scheme, force and motion results for the interaction of large amplitude regular waves as well as irregular waves with two practical semisubmersible configurations are presented.

Obesity impairs performing and learning a timing perception task regardless of the body position

2021 ◽  
Author(s):  
Fernanda Mottin Refinetti ◽  
Ricardo Drews ◽  
Umberto Cesar Corrêa ◽  
Flavio Henrique Bastos
Keyword(s):  
Body Position ◽  
The Body ◽  
Perception Task ◽  
Timing Perception
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