Benchmark Tests of Two Body Interaction in Waves

2017 ◽  
Author(s):  
Wei Qiu ◽  
Jean-Marc Rousset ◽  
Heather Peng ◽  
Wei Meng ◽  
Boris Horel
Keyword(s):  
Numerical Solutions ◽  
Ocean Engineering ◽  
Regular Waves ◽  
Towing Tank ◽  
Benchmark Data ◽  
Benchmark Tests ◽  
Wave Basin ◽  
Close Proximity ◽  
Two Bodies ◽  
Drift Forces

As part of the test campaign led by the 27th ITTC Ocean Engineering Committee to produce reliable experimental benchmark data for multiple-body interactions in waves, model tests of two identical models in close proximity were carried out at the towing tank of Memorial University, Canada and at the wave basin of Ecole Centrale de Nantes, France. This paper presents the experimental results for the two bodies in regular waves with various gaps. The experimental data, including motions of two bodies, wave elevations in the gap and drift forces, were compared with numerical solutions based on the potential-flow solution.

On Three-Dimensional Solutions of Drift Forces and Moments Between Two Ships in Waves

2002 ◽  
Vol 46 (04) ◽  
pp. 280-288
Author(s):  
Ming-Chung Fang ◽  
Gung-Rong Chen
Keyword(s):  
Numerical Solutions ◽  
Three Dimensional ◽  
Source Distribution ◽  
Regular Waves ◽  
Lateral Drift ◽  
Expansion Technique ◽  
Present Technique ◽  
Principal Value ◽  
Incident Waves ◽  
Drift Forces

A far-held approach solving the lateral drift forces and moments between two ships in regular waves is adopted. The velocity potentials for diffraction and radiation based on a 3-D-source distribution technique are obtained. Using the Telste & Noblesse algorithm with a series expansion technique for the principal value integral solves the numerical solutions for corresponding Green functions and their derivatives. One pair of ship models is used for numerical calculations and a 2-D method based on the near-held approach is also included for comparisons. Generally the results obtained by the present technique indicate that the interaction effects between two ships have a profound influence on the drift forces and moments, and the direction of incident waves plays an important role. The results also show that the values predicted by the 2-D method are always very much overestimated because of the trapping energy between two ships. Therefore, the 3-D method prediction model developed here is regarded as more physically reasonable than the 2-D one.

Hydrodynamic Interaction and Drift Forces on a Rectangular Barge and Modified Wigley Hull Arranged Side-by-Side

2008 ◽  
Author(s):  
Joa˜o Pessoa ◽  
Nuno Fonseca ◽  
C. Guedes Soares
Keyword(s):  
Free Surface ◽  
Hydrodynamic Interaction ◽  
Boundary Integral ◽  
Boundary Integral Method ◽  
Floating Platform ◽  
Close Proximity ◽  
Wigley Hull ◽  
Exciting Forces ◽  
Two Bodies ◽  
Drift Forces

The paper studies the hydrodynamic interactions between two bodies in close proximity oscillating on the free surface due to incident harmonic waves, inspired in the problem of offloading from a LNG floating platform to a tanker. It deals with a modified Wigley hull and a rectangular barge arranged side by side. The numerical results include hydrodynamic coefficients, exciting forces, absolute motions, and drift forces, and they are compared with published experimental data followed by further analysis of the effects of free surface elevation between the two bodies. The calculations are carried out with the WAMIT® code, which is based on a panel method, or boundary integral method.

Effects of Wave Drift Forces on Maneuvering of Ship

2008 ◽  
Author(s):  
Takeshi Kinoshita ◽  
Weiguang Bao ◽  
Motoki Yoshida ◽  
Yasunori Nihei ◽  
Yongze Xu ◽  
...  
Keyword(s):  
Dynamic Positioning ◽  
Positioning System ◽  
Ocean Engineering ◽  
Sea State ◽  
Dynamic Positioning System ◽  
Wave Drift ◽  
Wave Basin ◽  
Wave Drift Damping ◽  
Wave Drift Forces ◽  
Drift Forces

The dynamic positioning system of floating ocean structures requires hydrodynamic force derivatives to construct an accurate maneuvering model. In a severe sea state, the effects of ambient wave field on the maneuvering properties are not negligible. To investigate wave drift forces affecting on maneuvering of a ship relating to dynamic positioning system, an innovative model test, i.e. the Planer Motion Mechanism (PMM) test in waves is discussed in the present paper. Meanwhile, a theory to evaluate wave drift force including wave drift damping and wave drift added mass is summarized. Some examples of experiments done in Ocean Engineering Wave Basin of Institute of Industrial Science, University of Tokyo are presented and compared with calculated results based on the above theory.

Study on vertical motion reduction of a trimaran based on collaborative controlled appendages

2020 ◽  
Vol 17 (6) ◽  
pp. 172988142097677
Author(s):  
Zhilin Liu ◽  
Linhe Zheng ◽  
Guosheng Li ◽  
Shouzheng Yuan ◽  
Songbai Yang
Keyword(s):  
Experimental Study ◽  
Vertical Motion ◽  
Model Tests ◽  
Wave Period ◽  
Regular Waves ◽  
Towing Tank ◽  
Vertical Stability ◽  
Stabilization Control ◽  
Stability Performance

In recent years, the trimaran as a novel ship has been greatly developed. The subsequent large vertical motion needs to be studied and resolved. In this article, an experimental study for a trimaran vertical stabilization control is carried out. Three modes including the bare trimaran (the trimaran without appendages, the trimaran with fixed appendages, and the trimaran with controlled appendages) are performed through model tests in a towing tank. The model tests are performed in regular waves. The range of wave period is 2.0–4.0 s, and the speed of the carriage is 2.93 and 6.51 m/s. The results of the three modes show the fixed appendages and the actively controlled appendages are all effective for the vertical motion reduction of the trimaran. Moreover, the controlled appendages are more effective for the vertical stability performance of the trimaran.

scholarly journals E–ε Model of Spray-Laden Near-Sea Atmospheric Layer in High Wind Conditions

2014 ◽  
Vol 44 (2) ◽  
pp. 742-763 ◽  
Author(s):  
Yevgenii Rastigejev ◽  
Sergey A. Suslov
Keyword(s):  
Turbulent Flow ◽  
Drag Coefficient ◽  
Turbulent Mixing ◽  
Numerical Solutions ◽  
Turbulent Energy ◽  
Wave Crest ◽  
Mixing Length ◽  
High Wind ◽  
Close Proximity ◽  
Ocean Spray

Abstract In-depth understanding and accurate modeling of the interaction between ocean spray and a turbulent flow under high wind conditions is essential for improving the intensity forecasts of hurricanes and severe storms. Here, the authors consider the E–ε closure for a turbulent flow model that accounts for the effects of the variation of turbulent energy and turbulent mixing length caused by spray stratification. The obtained analytical and numerical solutions show significant differences between the current E–ε model and the lower-order turbulent kinetic energy (TKE) model considered previously. It is shown that the reduction of turbulent energy and mixing length above the wave crest level, where the spray droplets are generated, that is not accounted for by the TKE model results in a significant suppression of turbulent mixing in this near-wave layer. In turn, suppression of turbulence causes an acceleration of flow and a reduction of the drag coefficient that is qualitatively consistent with field observations if spray is fine (even if its concentration is low) or if droplets are large but their concentration is sufficiently high. In the latter case, spray inertia may become important. This effect is subsequently examined. It is shown that spray inertia leads to the reduction of wind velocity in the close proximity of the wave surface relative to the reference logarithmic profile. However, at higher altitudes the suppression of flow turbulence by the spray still results in the wind acceleration and the reduction of the local drag coefficient.

Effective Power and Speed Loss of Underwater Vehicles in Close Proximity to Regular Waves

2017 ◽  
Author(s):  
Stefan Daum ◽  
Martin Greve ◽  
Renato Skejic
Keyword(s):  
Free Surface ◽  
Deep Water ◽  
Water Waves ◽  
Underwater Vehicles ◽  
Total Resistance ◽  
Wave Load ◽  
Regular Waves ◽  
Effective Power ◽  
Close Proximity ◽  
Deep Water Waves

The present study is focused on performance issues of underwater vehicles near the free surface and gives insight into the analysis of a speed loss in regular deep water waves. Predictions of the speed loss are based on the evaluation of the total resistance and effective power in calm water and preselected regular wave fields w.r.t. the non-dimensional wave to body length ratio. It has been assumed that the water is sufficiently deep and that the vehicle is operating in a range of small to moderate Froude numbers by moving forward on a straight-line course with a defined encounter angle of incident regular waves. A modified version of the Doctors & Days [1] method as presented in Skejic and Jullumstrø [2] is used for the determination of the total resistance and consequently the effective power. In particular, the wave-making resistance is estimated by using different approaches covering simplified methods, i.e. Michell’s thin ship theory with the inclusion of viscosity effects Tuck [3] and Lazauskas [4] as well as boundary element methods, i.e. 3D Rankine source calculations according to Hess and Smith [5]. These methods are based on the linear potential fluid flow and are compared to fully viscous finite volume methods for selected geometries. The wave resistance models are verified and validated by published data of a prolate spheroid and one appropriate axisymmetric submarine model. Added resistance in regular deep water waves is obtained through evaluation of the surge mean second-order wave load. For this purpose, two different theoretical models based on potential flow theory are used: Loukakis and Sclavounos [6] and Salvesen et. al. [7]. The considered theories cover the whole range of important wavelengths for an underwater vehicle advancing in close proximity to the free surface. Comparisons between the outlined wave load theories and available theoretical and experimental data were carried out for a submerged submarine and a horizontal cylinder. Finally, the effective power and speed loss are discussed from a submarine operational point of view where the mentioned parameters directly influence mission requirements in a seaway. All presented results are carried out from the perspective of accuracy and efficiency within common engineering practice. By concluding current investigations in regular waves an outlook will be drawn to the application of advancing underwater vehicles in more realistic sea conditions.

THE INFLUENCE OF CENTRE BOW LENGTH ON SLAMMING LOADS AND MOTIONS OF LARGE WAVE-PIERCING CATAMARANS

2021 ◽  
Vol 160 (A1) ◽  
Author(s):  
J R Shahraki ◽  
G A Thomas ◽  
M R Davis
Keyword(s):  
Wave Height ◽  
Full Scale ◽  
Bending Moments ◽  
Regular Waves ◽  
Large Wave ◽  
Towing Tank ◽  
Segmented Model ◽  
Model Experiments ◽  
Slamming Load ◽  
Wave Induced

The effect of various centre bow lengths on the motions and wave-induced slamming loads on wave-piercing catamarans is investigated. A 2.5 m hydroelastic segmented model was tested with three different centre bow lengths and towed in regular waves in a towing tank. Measurements were made of the model motions, slam loads and vertical bending moments in the model demi-hulls. The model experiments were carried out for a test condition equivalent to a wave height of 2.68 m and a speed of 20 knots at full scale. Bow accelerations and vertical bending moments due to slamming showed significant changes with the change in centre bow, the longest centre bow having the highest wave-induced loads and accelerations. The increased volume of displaced water which is constrained beneath the bow archways is identified as the reason for this increase in the slamming load. In contrast it was found that the length of centre bow has a relatively small effect on the heave and pitch motions in slamming conditions.

Global Hydroelastic Analysis of Pontoon-Type VLFS

2009 ◽  
Author(s):  
L. L. Jiao ◽  
M. Greco ◽  
O. M. Faltinsen
Keyword(s):  
Numerical Solutions ◽  
Parameter Analysis ◽  
Local Analysis ◽  
Two Dimensional ◽  
Numerical Wave Tank ◽  
Regular Waves ◽  
Hydroelastic Analysis ◽  
Air Cushion ◽  
Numerical Wave ◽  
Hydroelastic Response

A two-dimensional composite strategy given by Greco et al. [1] is applied to couple a linear global solution with a nonlinear local analysis. Globally a linear hydroelastic analysis is performed by an accurate Beam-On-Elastic-Foundation (BOEF) method. A parameter analysis of hydroelastic response of the structure is also carried out. Locally, a two-dimensional fully-nonlinear numerical wave tank (NWT) in combination with a Boundary Element Method (BEM) is developed to estimate the interaction between regular waves and the structure restrained from rigid and elastic motions. The effect of air cushion is considered. Present results are compared with experimental data and other numerical solutions.

Finite Element Analysis of 2-D Structures by New Strain Based Triangular Element

2018 ◽  
Vol 35 (3) ◽  
pp. 305-313 ◽  
Author(s):  
C. Rebiai
Keyword(s):  
Dynamic Analysis ◽  
Degrees Of Freedom ◽  
Numerical Solutions ◽  
Time Integration ◽  
Triangular Element ◽  
Membrane Element ◽  
Lumped Mass ◽  
Element Analysis ◽  
Benchmark Tests ◽  
Three Degrees Of Freedom

ABSTRACTIn this investigation, a new simple triangular strain based membrane element with drilling rotation for 2-D structures analysis is proposed. This new numerical model can be used for linear and dynamic analysis. The triangular element is named SBTE and it has three nodes with three degrees of freedom at each node. The displacements field of this element is based on the assumed functions for the various strains satisfying the compatibility equations. This developed element passed both patch and benchmark tests in the case of bending and shear problems. For the dynamic analysis, lumped mass with implicit/explicit time integration are employed. The obtained numerical results using the developed element converge toward the analytical and numerical solutions in both analyses.

Experimental Study of Slow-Drift Ship Motions in Shallow Water Random Waves

2011 ◽  
Author(s):  
Carl Trygve Stansberg ◽  
Trygve Kristiansen
Keyword(s):  
Spectral Analysis ◽  
Shallow Water ◽  
Transfer Functions ◽  
Second Order ◽  
Ship Motions ◽  
Random Wave ◽  
Random Waves ◽  
Low Frequencies ◽  
Wave Basin ◽  
Drift Forces

Slowly varying motions and drift forces of a large moored ship in random waves at 35m water depth are investigated by an experimental wave basin study in scale 1:50. A simple horizontal mooring set-up is used. A second-order wave correction is applied to minimize “parasitic” long waves. The effect on the ship motion from the correction is clearly seen, although less in random wave spectra than in pure bi-chromatic waves. Empirical quadratic transfer functions (QTFs) of the surge drift force are found by use of cross-bi-spectral analysis, in two different spectra have been obtained. The QTF levels increase significantly with lower wave frequencies (except at the diagonal), which is special for finite and shallow water. Furthermore, the QTF levels frequencies at low frequencies increase significantly out from the QTF diagonal. Thus Newman’s approximation should preferrably not be used in these cases. Using the LF waves as a direct excitation in a “linear” ship force analysis gives random records that compare reasonably well with those from the cross-bi-spectral analysis. This confirms the idea that the drift forces in shallow water are closely correlated to the second-order potential, and thereby by the second-order LF waves.

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