Numerical Investigation of Hydrodynamic Performance of a Light Buoy with Different Mooring Configurations in Regular Waves

2021 ◽  
pp. 1-26
Author(s):  
Xin Li ◽  
Yimei Chen ◽  
Lilei Mao ◽  
Huiyu Xia
Keyword(s):  
Experimental Data ◽  
Yangtze River ◽  
Coupled Model ◽  
Coupling Model ◽  
Numerical Approach ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Regular Waves ◽  
Induced Motion ◽  
Wave Induced

Abstract The single-moored light buoys employed in the lower reaches of the Yangtze River play an important role in indicating ship navigation and ensuring safety. To clarify the interaction between waves and floating buoys moored to the riverbed, this paper develops a numerical approach to investigate the wave-induced motion performance of a light buoy and reveal the effects of different mooring configurations to extend its service life. A new open-source SPH based numerical model named DualSPHysics coupled with MoorDyn is implemented. This coupled model is validated by simulating the motion of a moored rectangle buoy in regular waves, and compared with experimental data and the numerical results of REEF3D code, a new mesh-based CFD model. The validation results show that the coupled model reproduces experimental data well and has a smaller deviation in comparison with REEF3D. Then the coupling model is applied to simulate the hydrodynamic performance of the real-size light buoy employed in Yangtze River and investigate effects of encounter angle between wave propagation direction and mooring chain. The results demonstrate the capability of this coupled mooring model to simulate the motion of a moored buoy in regular waves, and this numerical approach will be extended to simulate the light buoy in more complex environments such as irregular waves, flow or extreme weather in further work.

An Experimental Investigation of Cylindrical Floater VIM in Current and Waves

2014 ◽  
Author(s):  
Masakatsu Saito ◽  
Toshifumi Fujiwara ◽  
Katsuya Maeda
Keyword(s):  
Wave Height ◽  
Safety Evaluation ◽  
Offshore Structures ◽  
Irregular Waves ◽  
Regular Waves ◽  
Cross Sectional ◽  
Strong Current ◽  
Induced Motion ◽  
Different Characteristics ◽  
Motion Amplitude

VIM (Vortex Induced Motion) is one of the important issues in the safety evaluation for cylindrical floating offshore structures. The VIM is basically placed as a phenomenon to occur in strong current, but that also appears in current and waves in the sea where offshore structures are installed. The authors have recognized the phenomenon that the motion amplitude of a cylindrical floater in current and irregular waves together is larger than the sum of the motion amplitude in current and in irregular waves respectively in a VIM experiment. This VIM amplification phenomenon in the current and waves is remarkable when wave height is relatively low that has high occurrence frequency in the sea. It is, therefore, expected that the amplification phenomenon has large influence on the accumulative fatigue damages of the offshore structure’s mooring system. In order to make clear this VIM amplification phenomenon, the authors have conducted detailed VIM experiment in waves using a circular cross sectional mono-column floater model. The results of the VIM experiment in current and waves are described in detail in this paper. The results of the experiment in irregular waves show different characteristics for VIM amplitude in current. The results in regular waves show the effect of wave height and wave period on VIM amplitude in waves. Using those results, the mechanisms of the VIM amplification in waves are investigated.

Experimental Study on Hydrodynamics of Hybrid Deep-V Monohull With Different Built-Up Appendages

2018 ◽  
Author(s):  
Shuzheng Sun ◽  
Hui Li ◽  
Muk Chen Ong
Keyword(s):  
Model Test ◽  
Performance Model ◽  
Hydrodynamic Performance ◽  
Irregular Waves ◽  
Hydrodynamic Characteristics ◽  
Vertical Acceleration ◽  
Test Results ◽  
Regular Waves ◽  
Sea State ◽  
Seakeeping Performance

The hydrodynamic characteristics of a hybrid deep-V monohull with different built-up appendages are investigated experimentally in order to improve the resistance and seakeeping performance. Model tests have been carried out to study the hydrodynamic performance between a bare deep-V vessel and a deep-V monohull with different built-up appendage configurations (i.e. a hybrid deep-V monohull). From the model test results, it is found that the existence of the appendages will reduce the amplitude of pitching angle and bow vertical acceleration compared to that of the bare deep-V vessel in heading regular waves. However, the resistances for the hybrid deep-V monohull with built-up appendages are increased 15.6% for Fn = 0.264, and 0.1% for Fn = 0.441 compared to the resistance of the bare deep-V vessel. The model test results of seakeeping performance in irregular waves show that the hybrid deep-V monohull gives a better seakeeping performance than the deep-V vessel. The pitching angle and bow vertical acceleration of the hybrid deep-V monohull containing a built-up appendage are reduced 15.3% and 20.6% compared to the deep-V monohull in irregular waves at Fn = 0.441 in 6th class sea state (H1/3 = 6m).

scholarly journals Irregular Wave Validation of a Coupling Methodology for Numerical Modelling of Near and Far Field Effects of Wave Energy Converter Arrays

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 538 ◽  
Author(s):  
Gael Fernández ◽  
Vasiliki Stratigaki ◽  
Peter Troch
Keyword(s):  
Experimental Data ◽  
Wave Field ◽  
Wave Energy ◽  
Near Field ◽  
Coupled Model ◽  
Propagation Model ◽  
Irregular Waves ◽  
Far Field ◽  
Engineering Research ◽  
Field Effects

Between the Wave Energy Converters (WECs) of a farm, hydrodynamic interactions occur and have an impact on the surrounding wave field, both close to the WECs (“near field” effects) and at large distances from their location (“far field” effects). To simulate this “far field” impact in a fast and accurate way, a generic coupling methodology between hydrodynamic models has been developed by the Coastal Engineering Research Group of Ghent University in Belgium. This coupling methodology has been widely used for regular waves. However, it has not been developed yet for realistic irregular sea states. The objective of this paper is to present a validation of the novel coupling methodology for the test case of irregular waves, which is demonstrated here for coupling between the mild slope wave propagation model, MILDwave, and the ‘Boundary Element Method’-based wave–structure interaction solver, NEMOH. MILDwave is used to model WEC farm “far field” effects, while NEMOH is used to model “near field” effects. The results of the MILDwave-NEMOH coupled model are validated against numerical results from NEMOH, and against the WECwakes experimental data for a single WEC, and for WEC arrays of five and nine WECs. Root Mean Square Error (RMSE) between disturbance coefficient (Kd) values in the entire numerical domain ( R M S E K d , D ) are used for evaluating the performed validation. The R M S E K d , D between results from the MILDwave-NEMOH coupled model and NEMOH is lower than 2.0% for the performed test cases, and between the MILDwave-NEMOH coupled model and the WECwakes experimental data R M S E K d , D remains below 10%. Consequently, the efficiency is demonstrated of the coupling methodology validated here which is used to simulate WEC farm impact on the wave field under the action of irregular waves.

CFD Analysis of Deck Impact in Irregular Waves: Wave Representation by Transient Wave Groups

2011 ◽  
Author(s):  
O̸ystein Lande ◽  
Thomas B. Johannessen
Keyword(s):  
Wave Field ◽  
Irregular Waves ◽  
Computational Domain ◽  
Cfd Analysis ◽  
Wave Group ◽  
Regular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Wave Induced ◽  
Random Background

Analysis of wave structure interaction problems are increasingly handled by employing CFD methods such as the well known Volume-of-Fluid (VoF) method. In particular for the problem of deck impact on fixed structures with slender substructures, CFD methods have been used extensively in the last few years. For this case, the initial conditions have usually been treated as regular waves in an undisturbed wave field which may be given accurately as input. As CFD analyses become more widely available and are used for more complex problems it is also necessary to consider the problem of irregular waves in a CFD context. Irregular waves provide a closer description of the sea surface than regular waves and are also the chief source of statistical variability in the wave induced loading level. In general, it is not feasible to run a long simulation of an irregular seastate in a CFD analysis today since this would require very long simulation times and also a very large computational domain and sophisticated absorbing boundary conditions to avoid build-up of reflections in the domain. The present paper is concerned with the use of a single transient wave group to represent a large event in an irregular wave group. It is well known that the autocovariance function of the wave spectrum is proportional to the mean shape of a large wave in a Gaussian wave field. The transient nature of such a wave ensures that a relatively small wave is generated at the upwave boundary and dissipated at the downwave boundary compared with the wave in the centre of the domain. Furthermore, a transient wave may be embedded in a random background if it is believed that the random background is important for the load level. The present paper describes the method of generating transient wave groups in a CFD analysis of wave in deck impact. The evolution of transient wave groups is first studied and compared with experimental measurements in order to verify that nonlinear transient waves can be calculated accurately using the present CFD code. Vertical wave induced loads on a large deck is then investigated for different undisturbed wave velocities and deck inundations.

Computing Acceleration Loads on Free-Fall Lifeboat Occupants: Consequences of Including Nonlinearities in Water Waves and Mother Vessel Motions

2010 ◽  
Author(s):  
Neil Luxcey ◽  
Se´bastien Fouques ◽  
Thomas Sauder
Keyword(s):  
Water Waves ◽  
Three Dimensional ◽  
Free Fall ◽  
Momentum Conservation ◽  
Irregular Waves ◽  
Stokes Waves ◽  
Induced Motion ◽  
Wave Models ◽  
Wave Induced ◽  
The Impact

The safety of occupants in free-fall lifeboats (FFL) launched from a skid is addressed, and the focus is on numerical evaluation of acceleration loads during water impact. This paper investigates the required level of detail when modeling the physics of a lifeboat launch in waves. The first part emphasizes the importance of the non-linearity of the wave surface. Severity of impacts in linear (Airy) waves is compared to impacts in regular Stokes waves of the 5th order. Correspondingly, severity of impacts in irregular waves of the 2nd order is statistically compared to impacts in linear irregular waves. Theory of the two wave models are also briefly presented. The second part discusses the importance of a more detailed modeling of the launching system. This concerns especially cases for which damage to the mother vessel induces major lifeboat heel angles. A three-dimensional skid model is presented, along with validation against experimental measurements. In addition, the wave induced motion of the mother vessel is included. Consequences on the severity of the impact of the lifeboat in regular waves are discussed. This study is based on MARINTEK’s impact simulator for free-fall lifeboats, in which slamming loads are evaluated based on momentum conservation, a long wave approximation, and a von Karman type of approach. It is coupled here to the SIMO software, also developed at MARINTEK. Performance of this coupling is discussed.

Hybrid Method for Predicting Ship Manoeuvrability in Regular Waves

2019 ◽  
Author(s):  
Tianlong Mei ◽  
Yi Liu ◽  
Manasés Tello Ruiz ◽  
Marc Vantorre ◽  
Evert Lataire ◽  
...  
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Potential Flow ◽  
Flow Theory ◽  
Regular Waves ◽  
Potential Flow Theory ◽  
Hydrodynamic Derivatives ◽  
Mmg Model ◽  
Calm Water ◽  
Wave Induced

Abstract The ship’s manoeuvring behaviour in waves is significantly different from that in calm water. In this context, the present work uses a hybrid method combining potential flow theory and Computational Fluid Dynamics (CFD) techniques for the prediction of ship manoeuvrability in regular waves. The mean wave-induced drift forces are calculated by adopting a time domain 3D higher-order Rankine panel method, which includes the effect of the lateral speed and forward speed. The hull-related hydrodynamic derivatives are determined based on a RANS solver using the double body flow model. The two-time scale method is applied to integrate the improved seakeeping model in a 3-DOF modular type Manoeuvring Modelling Group (MMG model) to investigate the ship’s manoeuvrability in regular waves. Numerical simulations are carried out to predict the turning circle in regular waves for the S175 container carrier. The turning circle’s main characteristics as well as the wave-induced motions are evaluated. A good agreement is obtained by comparing the numerical results with experimental data obtained from existing literature. This demonstrates that combining potential flow theory with CFD techniques can be used efficiently for predicting the manoeuvring behaviour in waves. This is even more true when the manoeuvring derivatives cannot be obtained from model tests when there is lack of such experimental data.

Effects of Marine Growth on Hydrodynamic Coefficients of Rigid Tubular Cylinders

2014 ◽  
Vol 567 ◽  
pp. 247-252 ◽  
Author(s):  
A. M. Al-Yacouby ◽  
V. John Kurian ◽  
A.A. Sebastian ◽  
M.S. Liew ◽  
V.G. Idichandy
Keyword(s):  
Experimental Data ◽  
Water Depth ◽  
Hydrodynamic Forces ◽  
Experimental Results ◽  
Hydrodynamic Coefficients ◽  
Regular Waves ◽  
Tank Model ◽  
Rigid Cylinder ◽  
Wave Heights ◽  
Wave Induced

In this paper the wave induced hydrodynamic forces and the corresponding hydrodynamic coefficients for a 42 mm diameter model pipe subjected to regular waves was investigated experimentally and the results were compared with the responses of a similar rigid cylinder fitted with marine growth. The main objective of this study was to quantify the effects of marine growth on the hydrodynamic forces experimentally and determine the associated hydrodynamic coefficients. The experimental data were generated from a set of wave tank model tests and the results were scaled up using a scale factor of 1:55. The thickness of marine growth applied on the model pipe was varied with respect to the water depth in the ratio of 3:2:1. Regular waves were generated with wave heights ranging from 0.02 m to 0. 2 m for modal period varying from 0.6 s to 3.25 s. The tests were conducted for Keulegan-Carpenter number ranging from 3.9 to 23.3. The findings of the experimental results revealed that increasing the thickness of the full scale prototype cylinder by 110 mm due to marine growth fittings, has increased the overall wave hydrodynamic forces by 16 to 90% depending on the wave heights and the wave frequencies at which the model was tested, proving that the drag coefficients have considerably increased.

Wave Effects on Vortex-Induced Motion (VIM) of a Large-Volume Semi-Submersible Platform

2012 ◽  
Author(s):  
Rodolfo T. Gonçalves ◽  
Guilherme F. Rosetti ◽  
André L. C. Fujarra ◽  
Kazuo Nishimoto ◽  
Allan C. Oliveira
Keyword(s):  
Experimental Study ◽  
Free Surface ◽  
Large Volume ◽  
Periodic Motion ◽  
Transverse Direction ◽  
Irregular Waves ◽  
Regular Waves ◽  
Sea State ◽  
Wave Effects ◽  
Induced Motion

Aiming to complete the results presented before by Gonçalves et al. (2011) – Experimental Study on Vortex-Induced Motions (VIM) of a Large-Volume Semi-Submersible Platform, OMAE2011, the present work brings new experimental results on VIM of a large-volume semi-submersible platform, particularly concerning its coexistence with waves in the free surface. The VIM tests were performed in the presence of three regular waves and also three different conditions of sea state. According to the results, considerable differences between the presence of regular or irregular waves were observed. The motion amplitudes in the transverse direction decreased harshly when the regular waves were performed and no VIM was observed. In the case of sea state condition tests, the amplitudes decreased slightly but a periodic motion characterized by the VIM was observed. The results herein presented concern transverse and yaw motion amplitudes, as well as spectral analyses.

scholarly journals On movement control of deformable hull for displacement ship in waves

2020 ◽  
Vol S-I (2) ◽  
pp. 237-241
Author(s):  
R. Mudrik ◽  
◽  
P. Mudrik ◽  
Keyword(s):  
Target Function ◽  
Bending Moment ◽  
Movement Control ◽  
Irregular Waves ◽  
Regular Waves ◽  
Propulsion Performance ◽  
Design Variables ◽  
Internal Forces ◽  
Wave Induced

This paper discusses the optimization of ship heading in given regular waves taking into account the limitations for wave-induced midship bending moment and roll amplitude. External and internal forces in irregular waves are determined as per finite-element method used for motion calculations. This study presents the obtained surfaces of responses for the variables of state depending on wave parameters and design variables. The optimization problem discussed in this study was solved taking the non-linearity of target function and limitation functions into account. the study also formulated and solved an inverse problem, i.e. determination of controlling parameters (heading and speed) so as to obtain optimal propulsion performance in given wave conditions without prejudice to reliability and seakeeping.

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