Numerical Modeling and Experimental Comparison of the Response of Elastically Connected Barges

2018 ◽  
Author(s):  
Daniele Dessi ◽  
Edoardo Faiella
Keyword(s):  
Numerical Model ◽  
Model Development ◽  
Numerical Code ◽  
Experimental Comparison ◽  
Mooring Line ◽  
Linear Potential ◽  
Offshore Platforms ◽  
Floating System ◽  
The Time Domain ◽  
Linear Potential Theory

This paper presents a numerical model for the investigation of some hydroelastic issues related to floating systems used for the transportation and installation of components of offshore platforms, e.g., topsides. The system consists of two symmetric barges, linked together by the carried structure to form a catamaran-like layout. The flexibility of the transported structure may allow for proper excitation of the float-over system under oblique wave conditions at certain wave lengths, both during transportation and installation phases. The developed numerical code, based on multi-body dynamics and linear potential theory regarding the calculation of hydrodynamic loads, allows for a robust and fast description of the flexible floating system dynamics, including also the effect of mooring-line dynamics in the time-domain. Comparison with experimental data from a previous experimental campaign [1] shows that, notwithstanding the simplifying assumptions in the numerical model development, the amplitude of the relative pitch rotation between the barges due to the system flexibility can be properly described with the present approach.

Multi Vessel Interaction in Shallow Water

2009 ◽  
Author(s):  
Hans Fabricius Hansen ◽  
Stefan Carstensen ◽  
Erik Damgaard Christensen ◽  
Jens Kirkegaard
Keyword(s):  
Shallow Water ◽  
Wave Model ◽  
Irregular Waves ◽  
Numerical Code ◽  
Scale Model ◽  
Hydrodynamic Characteristics ◽  
Mooring Line ◽  
Industry Standard ◽  
Physical Scale ◽  
The Time Domain

A numerical package for simulating vessel motions in the time domain, WAMSIM, is extended to handle multiple moving bodies interconnected through a nonlinear mooring system. WAMSIM relies on the industry standard program WAMIT to calculate the hydrodynamic characteristics and interaction of multiple bodies in the frequency domain. The numerical code is used to simulate the motions and mooring line and fender forces of two LNG tankers moored side-by-side in shallow water. One of the gas tankers is moored to the sea floor through a turret with chain catenaries. Realistic short-crested irregular waves obtained from a Boussinesq wave model are used to force the model. Motion spectra of the simulated motions are compared to measured motions from physical scale model tests. The model shows good agreement with measured motions and mooring line forces.

scholarly journals Hydro-Elastic Modelling of an Electro-Active Wave Energy Converter

2013 ◽  
Author(s):  
Aurélien Babarit ◽  
Benjamin Gendron ◽  
Jitendra Singh ◽  
Cécile Mélis ◽  
Philippe Jean
Keyword(s):  
Numerical Model ◽  
Wave Energy ◽  
Ocean Basin ◽  
Wave Energy Converter ◽  
Scale Model ◽  
Linear Potential ◽  
Energy Converter ◽  
Outer Flow ◽  
Modal Expansion ◽  
Linear Potential Theory

Since 2009, SBM Offshore has been developing the S3 Wave Energy Converter (S3 WEC). It consists in a long flexible tube made of an Electro-Active Polymer (EAP). Thus, the structural material is also the Power Take Off (PTO). In order to optimize the S3 WEC, a hydro-elastic numerical model able to predict the device dynamic response has been developed. The inner flow, elastic wall deformations and outer flow are taken into account in the model under the following assumptions: Euler equation is used for the inner flow. The flow is also assumed to be uniform. Elastic deformation of the wall tube is linearized. The outer flow is modeled using linear potential theory. These equations have been combined in order to build the numerical model. First, they are solved in the absence of the outer fluid in order to obtain the modes of response of the device. Secondly, the outer fluid is taken into account and the equation of motion is solved by making use of modal expansion. Meanwhile, experimental validation tests were conducted in the ocean basin at Ecole Centrale De Nantes. The scale model is 10m long tube made of EAP. The tube deformations were measured using the electro-active polymer. The model was also equipped with sensors in order to measure the inner pressure. Comparisons of the deformation rate between the numerical model and experimental results show good agreement, provided that the wall damping is calibrated. Eventually, results of a technico-economical parametric study of the dimensions of the device are presented.

Study of Motion Performance of a Floating System With Four Moonpools and a VAWT

2021 ◽  
Author(s):  
Lei Tan ◽  
Satsuya Moritsu ◽  
Tomoki Ikoma ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Potential Theory ◽  
Theoretical Calculations ◽  
Model Tests ◽  
Hydrodynamic Performance ◽  
Linear Potential ◽  
Gyroscopic Effect ◽  
Floating Foundation ◽  
Motion Responses ◽  
Floating System ◽  
Linear Potential Theory

Abstract In this paper the hydrodynamic performance of a barge-type floating foundation installed with four moonpools and a VAWT was investigated through model tests and theoretical calculations. The characteristics of wave-induced motion responses and tether tensions and the effects of turbine rotations were examined. Physical model tests were conducted in a wave tank using regular waves with the wave period ranging from 0.6 to 1.6 seconds and 0.01 or 0.02 meters in amplitude. A 2-MW-class VAWT was modelled with a scale ratio of 1/100 in the experiments. By varying the mass and the rotational speed of the turbine, gyroscopic moment effects were studied. In addition, numerical calculations based on the linear potential theory and Green function method were carried out to estimate motion responses and tether tensions. The present results indicate that the gyroscopic effect due to turbine rotations can be profound. It was found that the first-order motions of the floating system were substantially reduced by the gyroscopic effect, while the second-order motions and tether tensions may be significantly increased. Moreover, the viscous damping of water motions in moonpools was found not negligible. As a result, theoretical models based on linear potential theory should be used with care in hydrodynamic analysis with regard to the floating systems with VAWT rotations. In addition, the present in-house program code was validated against WAMIT through comparing hydrodynamic predictions of a floating foundation with four moonpools, with reasonable agreement.

Response Characteristics of a Floating Structure With Moon Pools Installed With Vertical Axis Wind Turbines

2019 ◽  
Author(s):  
Mitsuru Nakamura ◽  
Tomoki Ikoma ◽  
Hiroaki Eto ◽  
Yasuhiro Aida ◽  
Koichi Masuda
Keyword(s):  
Wind Turbines ◽  
Vertical Axis ◽  
Linear Potential ◽  
Floating Structure ◽  
Response Characteristics ◽  
Gyroscopic Moment ◽  
Vertical Axis Wind Turbines ◽  
Motion Responses ◽  
Floating System ◽  
Linear Potential Theory

Abstract This paper describes characteristics of motion responses and tether tensions of a floating structure with four moon pools, on which one or two vertical axis wind turbines are installed. In this study, the authors proposed a twin-VAWT installed floating system, which was a pontoon based structure. However four moon pools were set on. The study conducted model experiments in a wave tank using regular waves with 0.6 to 2.0 seconds in wave periods and 0.02 and 0.04 m in wave height. The model had four moon pools and was installed with one or two vertical axis turbine models. From it, gyroscopic moment effects were investigated. Besides, the study performed numerical calculations with the linear potential theory based method which were a Green function method. As a results, responses of the twin-turbine model are not affected by gyroscopic moment. The study discusses motion responses and tether tensions with nonlinear behaviours from mainly the experimental results.

Effects of Four Moon Pools on a Floating System Installed With Twin-VAWTs

2019 ◽  
Author(s):  
Tomoki Ikoma ◽  
Mitsuru Nakamura ◽  
Satsuya Moritsu ◽  
Yasuhiro Aida ◽  
Koichi Masuda ◽  
...  
Keyword(s):  
Vertical Axis ◽  
Linear Potential ◽  
The Moon ◽  
Vertical Axis Wind Turbine ◽  
Floating Structure ◽  
Gyroscopic Moment ◽  
Motion Responses ◽  
Floating System ◽  
Heave Motion ◽  
Linear Potential Theory

Abstract This paper describes characteristics of motion responses and tether tensions of a floating structure with four moon pools, on which one or two vertical axis wind turbine models are installed. Effects of several moon pools founded in a floating structure on motion characteristics have been unclear. In this study, the authors proposed a twin-VAWT installed floating system, which was a pontoon based structure. However four moon pools were set on. The study conducted model experiments in a wave tank using regular waves with 0.6 to 2.0 seconds in wave periods and 0.02 and 0.04 m in wave height. The model had four moon pools and was installed with one or two vertical axis turbine models. From it, gyroscopic moment effects were investigated. Besides, the study performed numerical calculations with the linear potential theory based method which were a Green function method. As a results, responses of the twin-turbine model are not affected by gyroscopic moment. The study discusses motion responses and tether tensions with nonlinear behaviours from mainly the experimental results. Also the effect of moon pools were investigated from the calculations. From comparisons of motion results on calculation models with same displacement but different draft, the results suggested that not only heave motion but also roll motion could be reduced because of the moon pools if the size of the moon pools were optimized.

scholarly journals Numerical Parametric Study on the Effectiveness of the Contact-Point Response of a Stationary Vehicle for Bridge Health Monitoring

2021 ◽  
Vol 11 (15) ◽  
pp. 7028
Author(s):  
Ibrahim Hashlamon ◽  
Ehsan Nikbakht ◽  
Ameen Topa ◽  
Ahmed Elhattab
Keyword(s):  
Numerical Model ◽  
Health Monitoring ◽  
Contact Point ◽  
Response Spectra ◽  
Roughness Effects ◽  
Moving Vehicle ◽  
Bridge Health Monitoring ◽  
Vehicle Response ◽  
Instrumented Vehicle ◽  
The Time Domain

Indirect bridge health monitoring is conducted by running an instrumented vehicle over a bridge, where the vehicle serves as a source of excitation and as a signal receiver; however, it is also important to investigate the response of the instrumented vehicle while it is in a stationary position while the bridge is excited by other source of excitation. In this paper, a numerical model of a stationary vehicle parked on a bridge excited by another moving vehicle is developed. Both stationary and moving vehicles are modeled as spring–mass single-degree-of-freedom systems. The bridges are simply supported and are modeled as 1D beam elements. It is known that the stationary vehicle response is different from the true bridge response at the same location. This paper investigates the effectiveness of contact-point response in reflecting the true response of the bridge. The stationary vehicle response is obtained from the numerical model, and its contact-point response is calculated by MATLAB. The contact-point response of the stationary vehicle is investigated under various conditions. These conditions include different vehicle frequencies, damped and undamped conditions, different locations of the stationary vehicle, road roughness effects, different moving vehicle speeds and masses, and a longer span for the bridge. In the time domain, the discrepancy of the stationary vehicle response with the true bridge response is clear, while the contact-point response agrees well with the true bridge response. The contact-point response could detect the first, second, and third modes of frequency clearly, unlike the stationary vehicle response spectra.

Optimized Mooring Line Simulation Using a Hybrid Method Time Domain Scheme

2014 ◽  
Author(s):  
Niels Hørbye Christiansen ◽  
Per Erlend Torbergsen Voie ◽  
Jan Høgsberg ◽  
Nils Sødahl
Keyword(s):  
Hybrid Method ◽  
Time Domain ◽  
Computation Time ◽  
Mooring Line ◽  
Mooring Lines ◽  
Fem Model ◽  
Input Variables ◽  
The Time Domain ◽  
The Cost ◽  
Short Time

Dynamic analyses of slender marine structures are computationally expensive. Recently it has been shown how a hybrid method which combines FEM models and artificial neural networks (ANN) can be used to reduce the computation time spend on the time domain simulations associated with fatigue analysis of mooring lines by two orders of magnitude. The present study shows how an ANN trained to perform nonlinear dynamic response simulation can be optimized using a method known as optimal brain damage (OBD) and thereby be used to rank the importance of all analysis input. Both the training and the optimization of the ANN are based on one short time domain simulation sequence generated by a FEM model of the structure. This means that it is possible to evaluate the importance of input parameters based on this single simulation only. The method is tested on a numerical model of mooring lines on a floating off-shore installation. It is shown that it is possible to estimate the cost of ignoring one or more input variables in an analysis.

Less=Moor: A Time-Efficient Computational Tool to Assess the Behavior of Moored Ships in Waves

2017 ◽  
Author(s):  
Yijun Wang ◽  
Alex van Deyzen ◽  
Benno Beimers
Keyword(s):  
Dynamic Response ◽  
Research Effort ◽  
Equations Of Motion ◽  
Line Tension ◽  
Mooring Line ◽  
Induced Response ◽  
Wave Forces ◽  
Computational Tool ◽  
The Time Domain ◽  
Nonlinear Equations Of Motion

In the field of port design there is a need for a reliable but time-efficient method to assess the behavior of moored ships in order to determine if further detailed analysis of the behavior is required. The response of moored ships induced by gusting wind and/or waves is dynamic. Excessive motion response may cause interruption of the (un)loading operation. High line tension may cause lines to snap, introducing dangerous situations. A (detailed) Dynamic Mooring Analysis (DMA), however, is often a time-consuming and expensive exercise, especially when responses in many different environmental conditions need to be assessed. Royal HaskoningDHV has developed a time-efficient computational tool in-house to assess the wave (sea or swell) induced dynamic response of ships moored to exposed berths. The mooring line characteristics are linearized and the equations of motion are solved in the frequency domain with both the 1st and 2nd wave forces taken into account. This tool has been termed Less=Moor. The accuracy and reliability of the computational tool has been illustrated by comparing motions and mooring line forces to results obtained with software that solves the nonlinear equations of motion in the time domain (aNySIM). The calculated response of a Floating Storage and Regasification Unit (FSRU) moored to dolphins located offshore has been presented. The results show a good comparison. The computational tool can therefore be used to indicate whether the wave induced response of ships moored at exposed berths proves to be critical. The next step is to make this tool suitable to assess the dynamic response of moored ships with large wind areas, e.g. container ships, cruise vessels, RoRo or car carriers, to gusting wind. In addition, assessment of ship responses in a complicated wave field (e.g. with reflected infra-gravity waves) also requires more research effort.

The Anchor-Last Deployment Problem for Inextensible Mooring Lines

1975 ◽  
Vol 97 (3) ◽  
pp. 1046-1052 ◽  
Author(s):  
Robert C. Rupe ◽  
Robert W. Thresher
Keyword(s):  
Numerical Model ◽  
Equations Of Motion ◽  
Simultaneous Equations ◽  
Mooring Line ◽  
Integration Scheme ◽  
Lumped Mass ◽  
Mooring Lines ◽  
Concentrated Masses ◽  
Predictor Corrector ◽  
Lagrange’S Method

A lumped mass numerical model was developed which predicts the dynamic response of an inextensible mooring line during anchor-last deployment. The mooring line was modeled as a series of concentrated masses connected by massless inextensible links. A set of angles was used for displacement coordinates, and Lagrange’s Method was used to derive the equations of motion. The resulting formulation exhibited inertia coupling, which, for the predictor-corrector integration scheme used, required the solution of a set of linear simultaneous equations to determine the acceleration of each lumped mass. For the selected cases studied the results show that the maximum tension in the cable during deployment will not exceed twice the weight of the cable and anchor in water.

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