Time-Domain Simulation of a Multi-Body Floating System in Waves

2010 ◽  
Author(s):  
Xiaochuan Yu ◽  
Jeffrey M. Falzarano ◽  
Zhiyong Su
Keyword(s):  
Time Domain ◽  
Impulse Response Function ◽  
Hydrodynamic Interactions ◽  
Time Domain Simulation ◽  
Single Vessel ◽  
Close Proximity ◽  
Floating System ◽  
Response Amplitude Operators ◽  
Multi Body ◽  
Coefficient Method

It is important to study multi-body dynamics when analyzing the transfer of cargo between ships and platforms at sea. The hydrodynamic interactions should be considered in an accurate way to predict the relative motions between them. In this paper, the response amplitude operators (RAOs) of a single vessel will be compared with those of a multi-body system, considering different spacing between them. Further, the coupled hydrodynamic interactions among multiple vessels in close proximity are studied. Various levels of approximation, including the constant coefficient method (CCM) and the impulse response function (IRF) method, are employed to model the hydrodynamic interactions. Finally, the comparison between a single vessel and multi-body time domain simulation is also given.

scholarly journals Convolution-based time-domain simulation for fluidelastic instability in tube arrays

2021 ◽  
Author(s):  
Mingjie Zhang ◽  
Ole Øiseth
Keyword(s):  
Impulse Response ◽  
Response Function ◽  
Time Domain ◽  
Impulse Response Function ◽  
Time Domain Simulation ◽  
Unit Step ◽  
Tube Arrays ◽  
Unit Impulse ◽  
The Time Domain ◽  
Unit Impulse Response

AbstractA convolution-based numerical algorithm is presented for the time-domain analysis of fluidelastic instability in tube arrays, emphasizing in detail some key numerical issues involved in the time-domain simulation. The unit-step and unit-impulse response functions, as two elementary building blocks for the time-domain analysis, are interpreted systematically. An amplitude-dependent unit-step or unit-impulse response function is introduced to capture the main features of the nonlinear fluidelastic (FE) forces. Connections of these elementary functions with conventional frequency-domain unsteady FE force coefficients are discussed to facilitate the identification of model parameters. Due to the lack of a reliable method to directly identify the unit-step or unit-impulse response function, the response function is indirectly identified based on the unsteady FE force coefficients. However, the transient feature captured by the indirectly identified response function may not be consistent with the physical fluid-memory effects. A recursive function is derived for FE force simulation to reduce the computational cost of the convolution operation. Numerical examples of two tube arrays, containing both a single flexible tube and multiple flexible tubes, are provided to validate the fidelity of the time-domain simulation. It is proven that the present time-domain simulation can achieve the same level of accuracy as the frequency-domain simulation based on the unsteady FE force coefficients. The convolution-based time-domain simulation can be used to more accurately evaluate the integrity of tube arrays by considering various nonlinear effects and non-uniform flow conditions. However, the indirectly identified unit-step or unit-impulse response function may fail to capture the underlying discontinuity in the stability curve due to the prespecified expression for fluid-memory effects.

Application of Parametric Surfaces in Contact Assessment Between Two Floaters in Side by Side Operations

2012 ◽  
Author(s):  
Fabio Gouveia Telles de Menezes ◽  
Breno Pinheiro Jacob ◽  
Carl Horst Albrecht ◽  
Fabrício Nogueira Corrêa
Keyword(s):  
Natural Gas ◽  
Time Domain ◽  
Computational Cost ◽  
Time Domain Simulation ◽  
Parametric Surfaces ◽  
Time Step ◽  
Interference Analysis ◽  
Main Challenge ◽  
Close Proximity ◽  
Alternative Solutions

In front of the growing demand for natural gas, alternative solutions have been adopted to export the production to the several available markets. Conventional gas carriers have been converted to regasification units to operate close to the shore, treating the gas and delivering it to carriers which take the product to the shore. Side by side configurations for the gas transference by loading arms are common, and the reduce distance between the ships is the main challenge. For such application a time domain simulation is demanded. Due to the close proximity between the ships, at each time step, their distance has to be calculated in order to predict eventual ship to ship or ship to fenders collisions. When the ships are modeled by conventional meshes the interference analysis every time step is excessively time consuming, the use of parametric surfaces reduces the number of elements to be checked against each other and saves computational cost. The precision is also improved since the hull shapes are fully represented in comparison to the panel approximation provided by the meshing approach. The contact verification plays a fundamental role for that type of analysis and the gains obtained by the parametric surfaces appliance are significant.

Time-Domain Simulations of Multi-Body Systems in Deterministic Wave Trains

2006 ◽  
Author(s):  
Katja Jacobsen ◽  
Gu¨nther F. Clauss
Keyword(s):  
Frequency Domain ◽  
Impulse Response ◽  
Time Domain ◽  
Degrees Of Freedom ◽  
Wave Length ◽  
Impulse Response Function ◽  
Impulse Response Functions ◽  
Hydrodynamic Coupling ◽  
Lift Off ◽  
Multi Body

A growing amount of reports on heavy lift operations involving huge crane vessels prove that investigations on the motion behavior of multi-body systems are vital regarding the combined aspects of safety and economics. In this paper a method of transforming frequency-domain into time-domain results is presented. With the panel program WAMIT (WAMIT Inc.) the Response Amplitude Operators (RAO) of the motions in six degrees of freedom of the structures involved in a lift operation are calculated. The multi-bodies RAOs differ significantly from those of the single structures (without interaction effects). The consideration of hydrodynamic coupling is therefore essential for the prediction of accurate relative motions between the structures. Frequency-domain results are still important when determining operational limitations. But only with simulations in time-domain the relation between cause and reaction can be studied in detail. Results from simulations provide for example decision support for finding uncritical starting points of the lift off operation. By Fouriertransforming the RAOs the impulse-response functions are obtained. Having the impulse-response function the time-dependent system responses in arbitrary deterministic wave registrations are determined by convolution. This method allows fast and effective time-domain simulations of multi-body systems. Results are presented for a crane semisubmersible and a conventional transport barge. The influence, particularly the sensitivity of wave height and wave length on the response is shown in wave packets.

Simulation of Dynamic Tracking System for Rescue at Sea

2015 ◽  
Author(s):  
Qian Shi ◽  
Shixiao Fu ◽  
Ning Deng ◽  
Jinsong Xu
Keyword(s):  
Time Domain ◽  
Pid Control ◽  
Tracking System ◽  
Wave Loads ◽  
Time Domain Simulation ◽  
Empirical Formulas ◽  
Dynamic Tracking ◽  
Control Target ◽  
The Time Domain ◽  
Multi Body

In this paper, a time domain simulation is established to investigate the feasibility of a PID controller for rescue at sea. In the problem, the endangered ship loses its power and moves freely under environmental forces. The control target for Dynamic Tracking (DT) is to maintain a certain distance between the endangered and rescue ships. The time domain simulation includes multi-body hydrodynamics and Guidance Navigation Control (GNC) system. The multi-body hydrodynamics is modeled with the ship-ship interaction considered. The first and second order wave loads, added mass and damping in frequency domain is calculated using potential theory. Current and wind loads are estimated by empirical formulas summarized from experimental data. As for the design of the GNC system, PID control strategy is applied for the controller and the Kalman Filter for the observer. The time domain simulation in this research is performed in MATLAB.

Time Domain Turret Load and Motion Analyses for a FPSO

2020 ◽  
Author(s):  
Hyoungchul Kim ◽  
Bonjun Koo ◽  
Johyun Kyoung
Keyword(s):  
Time Domain ◽  
Interaction Model ◽  
Hydrodynamic Interactions ◽  
Test Results ◽  
Mechanical Coupling ◽  
Body Interaction ◽  
Nonlinear Springs ◽  
Frictional Damping ◽  
Multi Body ◽  
Fully Coupled

Abstract Fully coupled time domain turret/FPSO simulations are conducted using TechnipFMC proprietary software MLTSIM. To analyze hydrodynamic interactions and mechanical coupling effects between an FPSO and its turret, a multi-body interaction model is developed and analyzed. In the multi-body interaction model, full coupled hydrodynamic interactions are considered, and the bearing connections are modeled with nonlinear springs and frictional damping. The global performance analysis results are systematically compared with model test results (Kim et al. [1]), and hydrodynamic loads and mechanical coupling loads on the turret are presented in this paper.

Efficient Time-Domain Simulation of Side-By-Side Moored Vessels Advancing in Waves

2007 ◽  
Author(s):  
A. S. Murthy Chitrapu ◽  
Theodore G. Mordfin ◽  
Henry M. Chance
Keyword(s):  
Time Domain ◽  
Wind Waves ◽  
Hydrodynamic Performance ◽  
Forward Speed ◽  
Time Domain Simulation ◽  
Mooring Lines ◽  
Close Proximity ◽  
The Us ◽  
Naval Engineering ◽  
Skin To Skin

Evaluation of hydrodynamic performance of two vessels in close proximity that are either stationary or advancing in waves is of paramount importance for many offshore and naval engineering applications. Hydrodynamic interactions between the vessels combined with nonlinear mechanical interactions due to mooring and fendering systems make the problem more complicated. An efficient time-domain method is presented for evaluating the seakeeping and maneuvering performance of proximate vessels advancing with forward speed. The method computes the 6 degree-of-freedom motions of a pair of hydrodynamically interacting vessels subject to wind, waves, currents and maneuvering effects at zero and nonzero speeds in regular or random seaways. Model tests conducted to validate the method are described and results presented. The validation efforts conducted so far have yielded satisfactory comparisons, thereby reinforcing the confidence in the method and its applicability to such problems. The method has been used to predict safe operational limits of two vessels in skin-to-skin operations conducted by the US Navy. A similar analysis is presented herein for a different pair of vessels. Since it is based on time domain simulation, this method also allows the inclusion of non-linear effects due to mooring lines, fenders and effects of viscous roll damping, which is not possible with two-body hydrodynamic interaction solutions in frequency-domain. It is concluded that this method provides an efficient tool to predict the performance of hydrodynamically interacting vessels that are stationary or moving with forward speed. To date, it has proven very useful in the early stages of the design/concept development process in which many configurations are evaluated.

scholarly journals Effects of Gap Resonance on the Hydrodynamics and Dynamics of a Multi-Module Floating System with Narrow Gaps

2021 ◽  
Vol 9 (11) ◽  
pp. 1256
Author(s):  
Mingsheng Chen ◽  
Hongrui Guo ◽  
Rong Wang ◽  
Ran Tao ◽  
Ning Cheng
Keyword(s):  
Damping Ratio ◽  
Normal Wave ◽  
Hydrodynamic Interactions ◽  
Period Range ◽  
Artificial Damping ◽  
Potential Applications ◽  
Floating System ◽  
Parametric Studies ◽  
Multi Body ◽  
Narrow Gaps

Multi-module floating system has attracted much attention in recent years as ocean space utilization becomes more demanding. This type of structural system has potential applications in the design and construction of floating piers, floating airports and Mobile Offshore Bases (MOBs) generally consists of multiple modules with narrow gaps in which hydrodynamic interactions play a non-neglected role. This study considers a numerical model consisting of several rectangular modules to study the hydrodynamics and dynamics of the multi-module floating system subjected to the waves. Based on ANSYS-AQWA, both frequency-domain and time-domain simulations are performed to analyze the complex multi-body hydrodynamic interactions by introducing artificial damping on the gap surfaces. Parametric studies are carried out to investigate the effects of the gap width, shielding effects of the multi-body system, artificial damping ratio on the gap surface, and the dependency of the hydrodynamic interaction effect on wave headings is clarified. Based on the results, it is found that the numerical analysis based on the potential flow theory with artificial damping introduced can produce accurate results for the normal wave period range. In addition, the effects of artificial damping on the dynamics and connector loads are investigated by using a simplified RMFC model. For the case of adding an artificial damping ratio of 0.2, the relative heave and pitch motions are found to be reduced by 33% and 50%, respectively. In addition, the maximum cable and fender forces are found to be reduced by 50%, compared with the case without viscosity correction.

Hydrodynamics Interactions on Vortex-Induced Motions of a Multi-Body Floating System

2019 ◽  
Author(s):  
Yibo Liang ◽  
Longbin Tao
Keyword(s):  
Horizontal Plane ◽  
Numerical Data ◽  
Hydrodynamic Interactions ◽  
Gap Ratio ◽  
Floating System ◽  
Preliminary Study ◽  
Drag And Lift ◽  
Lock In ◽  
Multi Body ◽  
Floating Platforms

Abstract In this study, numerical analysis has been carried out to investigate the hydrodynamic interactions of two multi-columns platforms. The objective of the work is to preliminarily evaluate the feasibility of a tension-leg-platform (TLP) dry tree unit (DTU) with tender assisted drilling (TAD) from the aspect of vortex-induced motions, characterized by the current. Two multi-columns floating platforms with a small gap ratio (28% of the overall platform width) are numerically simulated with the scenario of 3 degree-of-freedom (DOF) on the horizontal plane (including transverse, in-line and yaw motions). A comprehensive numerical simulation was conducted to examine the hydrodynamics interactions due to the flow over two floating platforms. Horizontal plane motions including transverse, in-line and yaw motions as well as drag and lift forces on both structures are discussed. The numerical data on the multi-body VIM interactions within the “lock-in” region will serve as a preliminary study for future coupled motions analysis of the TLP-TAD system design.

scholarly journals Time-Domain Simulation of Multibody Floating Systems Based on State-Space Modeling Technology

2011 ◽  
Author(s):  
Xiaochuan Yu ◽  
Jeffrey M. Falzarano
Keyword(s):  
State Space ◽  
Time Domain ◽  
Numerical Study ◽  
Equations Of Motion ◽  
Impulse Response Function ◽  
Linear Quadratic Regulator ◽  
Linear Quadratic ◽  
Motion Responses ◽  
Space Modeling ◽  
Floating System

It is important to study MULTIBODY dynamics when analyzing the transfer of cargo between ships and platforms at sea. The hydrodynamic interactions between multiple bodies in close proximity are expected to be significant and complex. In this paper, two levels of approximation of hydrodynamic coefficients are considered, i.e., the constant coefficient method (CCM) and the impulse response function (IRF). The equations of motion are written in standard state-space format, in which the convolution terms are computed using the trapezoidal rule. Initially, this newly proposed numerical scheme is successfully applied to calculate motion responses of a two-body floating system. The time-domain responses of this multibody floating system in both regular waves and random sea are further verified numerically. In addition, an ideal case of the motion mitigation of this system using Dynamic Positioning (DP) system is also given and discussed. The mean drift force is considered using Newman’s approximation. Numerical study shows that the optimal Linear Quadratic Regulator (LQR) method can help to mitigate the motion responses of this two-body floating system at sea. Finally, this scheme is extended to a three-body floating system, with the relative motions in random seas determined.

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