Analysis of the Draft Influence on the Numerical Resonant Effects in Side-by-Side Offloading Operation

2015 ◽  
Author(s):  
Pasquale Dinoi ◽  
Rafael A. Watai ◽  
Felipe Ruggeri ◽  
Jesus Gómez-Goñi ◽  
Alexandre N. Simos
Keyword(s):  
Time Domain ◽  
Wave Amplitude ◽  
Vertical Plane ◽  
Numerical Results ◽  
Floating Body ◽  
Damping Factor ◽  
Gap Flow ◽  
Resonant Behavior ◽  
Response Amplitude Operators ◽  
The Time Domain

In the last years hydrodynamic interaction between two vessels in side-by-side configuration is one of the hot issues in offshore floating body dynamics. The paper investigates the hydrodynamical aspects of a floating two body system. The topic is geared towards analysing the influence of the vessel’s draft in side-by-side configuration and in head sea condition. The need to solve this problem arises when one wants to study the hydrodynamic variation for the various stages of a offloading process with a defined operational gap. The system is composed of a barge and a prismatic geosim with a fixed gap value and with two barge’s draft values. Regular wave tests have been performed in the model basin of CEHINAV-Technical University of Madrid (UPM). The motion for the geosim was restricted to the surge, heave and pitch motions (just motions on the vertical plane), whereas the barge was kept fixed. The costant gap value is guaranteed during the tests. A numerical model has been created with WAMIT and with an in-house time-domain Rankine Panel Method (TDRPM). In each case the numerical and experimental response amplitude operators (RAOs) are obtained and compared, researching the limitation of the numerical codes for the gap flow modeling. In the past the gap effects on the numerical results have been studied varying the gap value finding resonant behavior in terms of motion and wave amplitude RAOs. Now the draft value contribution on the hydrodynamic effects is investigated. Also in this case the numerical results indicate a resonant behavior in determined frequencies in motion as well as in wave in the gap, that is not found in the tests. In order to overcome this problem, a procedure for introducing an external damping factor that attenuates the wave amplitude along the gap in the time-domain RPM is evaluated based on the experimental data.

Analysis of Hydrodynamic Resonant Effects in Side-by-Side Configuration

2014 ◽  
Author(s):  
Pasquale Dinoi ◽  
Rafael A. Watai ◽  
Hugo Ramos-Castro ◽  
Jesus Gómez-Goñi ◽  
Felipe Ruggeri ◽  
...  
Keyword(s):  
Time Domain ◽  
Wave Amplitude ◽  
Numerical Models ◽  
Vertical Plane ◽  
Damping Factor ◽  
Regular Waves ◽  
Resonant Behavior ◽  
Response Amplitude Operators ◽  
The Time Domain ◽  
The Waves

Seakeeping behavior of a multibody system in side-by-side configuration in head sea condition is discussed in this paper. The system, which can be assimilated to a FLNG and LNG carrier during an offloading operation is composed of a barge and a prismatic geosim with two gap values. Seakeeping tests in regular waves have been performed in the model basin of CEHINAV-Technical University of Madrid (UPM). The movements for the geosim were restricted to the surge, heave and pitch motions (on the vertical plane), whereas the barge was kept fixed. In this way the gap remained constant during the tests. Numerical modeling has been undertaken using WAMIT and an in-house time-domain Rankine Panel Method (TDRPM). Response amplitude operators in terms of movements and wave amplitude in the gap obtained from seakeeping test and numerical models are documented in the paper, illustrating the limitation of the numerical codes regarding the modeling of this hydrodynamic problem. Numerical results indicate a resonant behavior of the waves in the gap for a range of frequencies, with amplitudes much higher than those observed during the tests. Due to the small distances considered in the experiments, these resonant waves are related to longitudinal wave modes in the gap. In order to overcome this problem, a procedure for introducing an external damping factor that attenuates the wave amplitude along the gap in the time-domain RPM is evaluated based on the experimental data.

scholarly journals Generalized eigenfunction method for floating bodies

2011 ◽  
Vol 667 ◽  
pp. 544-554 ◽  
Author(s):  
COLM J. FITZGERALD ◽  
MICHAEL H. MEYLAN
Keyword(s):  
Time Domain ◽  
Water Waves ◽  
Equations Of Motion ◽  
Linear Equations ◽  
Two Dimensions ◽  
Floating Body ◽  
Floating Bodies ◽  
Abstract Wave Equation ◽  
Generalized Eigenfunction ◽  
The Time Domain

We consider the time domain problem of a floating body in two dimensions, constrained to move in heave and pitch only, subject to the linear equations of water waves. We show that using the acceleration potential, we can write the equations of motion as an abstract wave equation. From this we derive a generalized eigenfunction solution in which the time domain problem is solved using the frequency-domain solutions. We present numerical results for two simple cases and compare our results with an alternative time domain method.

scholarly journals Optimized Operator-Splitting Methods in Numerical Integration of Maxwell's Equations

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Z. X. Huang ◽  
X. L. Wu ◽  
W. E. I. Sha ◽  
B. Wu
Keyword(s):  
Numerical Integration ◽  
Time Domain ◽  
Maxwell’S Equations ◽  
Maxwell's Equations ◽  
Operator Splitting ◽  
Splitting Methods ◽  
High Order ◽  
Numerical Results ◽  
Operator Splitting Methods ◽  
The Time Domain

Optimized operator splitting methods for numerical integration of the time domain Maxwell's equations in computational electromagnetics (CEM) are proposed for the first time. The methods are based on splitting the time domain evolution operator of Maxwell's equations into suboperators, and corresponding time coefficients are obtained by reducing the norm of truncation terms to a minimum. The general high-order staggered finite difference is introduced for discretizing the three-dimensional curl operator in the spatial domain. The detail of the schemes and explicit iterated formulas are also included. Furthermore, new high-order Padé approximations are adopted to improve the efficiency of the proposed methods. Theoretical proof of the stability is also included. Numerical results are presented to demonstrate the effectiveness and efficiency of the schemes. It is found that the optimized schemes with coarse discretized grid and large Courant-Friedrichs-Lewy (CFL) number can obtain satisfactory numerical results, which in turn proves to be a promising method, with advantages of high accuracy, low computational resources and facility of large domain and long-time simulation. In addition, due to the generality, our optimized schemes can be extended to other science and engineering areas directly.

Numerical Solution of Wave Diffraction Problem in the Time Domain With the Panel-Free Method

2004 ◽  
Vol 126 (1) ◽  
pp. 1-8 ◽  
Author(s):  
W. Qiu ◽  
J. M. Chuang ◽  
C. C. Hsiung
Keyword(s):  
Body Surface ◽  
Time Domain ◽  
Diffraction Problem ◽  
The Body ◽  
Floating Body ◽  
B Splines ◽  
Rankine Source ◽  
Diffracted Waves ◽  
The Green Function ◽  
The Time Domain

A panel-free method (PFM) was developed earlier to solve the radiation problem of a floating body in the time domain. In the further development of this method, the diffraction problem has been solved. After removing the singularity in the Rankine source of the Green function and representing the body surface mathematically by Non-Uniform Rational B-Splines (NURBS) surfaces, integral equations were globally discretized over the body surface by Gaussian quadratures. Computed response functions and forces due to diffracted waves for a hemisphere at zero speed were compared with published results.

Study on a Time Domain Prediction Method for Wave Force: Application for a Point-Absorber WEC

2018 ◽  
Author(s):  
Qiao Li ◽  
Motohiko Murai
Keyword(s):  
Time Domain ◽  
Wave Spectrum ◽  
Time Domain Analysis ◽  
Wave Force ◽  
Domain Analysis ◽  
Irregular Waves ◽  
Floating Body ◽  
Control Force ◽  
Electric Generator ◽  
The Time Domain

There are a lot of numerical analysis for solving hydrodynamic responses of a floating body in the time domain. Most of them can give a theoretical solution in given irregular waves. It means, however, that the solution can be obtained only if the accurate irregular waves represented by the wave spectrum should be given. As we consider the actual operation, we know it is difficult to detect the accurate irregular waves instantaneously as needed accuracy in the most of the time domain analysis for feed backing the control force to the system. This paper proposes a new method to predict the practical wave force from the displacement of waves at a floating body in time domain analysis almost instantaneously. The method, that can apply to predict forces in wave energy converter with linear electric generator, helps us to choose the control force for convert more electric power in irregular waves. We confirm the algorithm and examine its effectiveness.

Numerical analysis of the effects on a floating structure induced by ship waves

2011 ◽  
Vol 55 (02) ◽  
pp. 124-134
Author(s):  
L. Sun ◽  
G.H Dong ◽  
Y. P. Zhao ◽  
C. F. Liu
Keyword(s):  
Time Domain ◽  
Equation Of Motion ◽  
Offshore Structures ◽  
Floating Body ◽  
Kutta Method ◽  
Floating Structure ◽  
Ship Waves ◽  
Runge Kutta Method ◽  
Frequency Domain Methods ◽  
The Time Domain

Ship-generated waves can make bad effects on offshore structures. A numerical model is presented for evaluating the forces exerted on a nearby floating structure by ship generated waves. The ship waves were modeled using Michell thin-ship theory (Wigley waves), the forces were computed using a boundary element method in the time domain, and the motions of the offshore structures were evaluated using the equation of motion of the floating body, and predicted using the fourth-order Runge-Kutta method. The numerical method was validated by comparing its results to those of frequency-domain methods reported in the literature. It was then applied to calculate the force of ship waves on a floating box. The ship's speed, dimensions, and distance were varied. The numerical results indicate some useful rules for varying these factors.

Nonlinear analysis of sloshing and floating body coupled motion in the time-domain

2018 ◽  
Vol 164 ◽  
pp. 350-366 ◽  
Author(s):  
Shuo Huang ◽  
Wenyang Duan ◽  
Xuliang Han ◽  
Ryan Nicoll ◽  
Yage You ◽  
...  
Keyword(s):  
Nonlinear Analysis ◽  
Time Domain ◽  
Floating Body ◽  
Coupled Motion ◽  
The Time Domain

Application of Linearized Morison Load in Pipe Lay Stinger Design

2008 ◽  
Author(s):  
Riaan van ‘t Veer
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Current Velocity ◽  
Extreme Values ◽  
Numerical Results ◽  
Analysis Time ◽  
Ship Motions ◽  
Hydrodynamic Analysis ◽  
Response Amplitude Operators ◽  
Nonlinear Time Domain

This paper presents numerical results of ship motions and global stinger loads through a combined hydrodynamic analysis of a pipe lay vessel with submerged stinger. The results of nonlinear time domain simulations are compared to those obtained through linearization of the Morison load on the slender stinger elements. Through linearization, an iterative frequency domain solution scheme is developed reducing analysis time significantly. Response amplitude operators in operating and limiting sea states are shown, including the influence of current velocity. Through nonlinear time domain simulations insight is obtained on the distribution and magnitude of the extreme values.

scholarly journals Initiating a Mathematical Model for Prediction of 6-DOF Motion of Planing Crafts in Regular Waves

2013 ◽  
Vol 2013 ◽  
pp. 1-15 ◽  
Author(s):  
Parviz Ghadimi ◽  
Abbas Dashtimanesh ◽  
Yaser Faghfoor Maghrebi
Keyword(s):  
Mathematical Model ◽  
Time Domain ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Vertical Plane ◽  
Time Domain Simulation ◽  
Regular Waves ◽  
Computer Simulation Program ◽  
The Time Domain ◽  
The Mathematical Model

Nowadays, most of the dynamic research on planing ships has been directed towards analyzing the ships motions in either 3-DOF (degrees of freedom) mode in the longitudinal vertical plane or in 3-DOF or 4-DOF mode in the lateral vertical plane. For this reason, the current authors have started a research program of describing the dynamic behavior of planing ships in a 6-DOF mathematical model. This program includes the developing of a 6-DOF computer simulation program in the time domain. This type of simulation can be used for predicting the response of these planing vessels to the environmental disturbances during high-speed sailing. In this paper, the development of the mathematical model will be presented. Furthermore, a discussion will be offered about the use of these static contributions in a time domain simulation for modeling the behavior of planing crafts in regular waves.

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