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.

Numerical Simulation of Breaking Waves in a Wave Group by SPH

2015 ◽  
Vol 776 ◽  
pp. 151-156
Author(s):  
Ni Nyoman Pujianiki
Keyword(s):  
Surf Zone ◽  
Breaking Waves ◽  
Return Flow ◽  
Wave Group ◽  
Regular Waves ◽  
Wave Groups ◽  
Smoothed Particle ◽  
Wave Heights ◽  
Smoothed Particle Hydrodynamic ◽  
Wave Break

Smoothed Particle Hydrodynamic (SPH) numerical model is used to investigate wave group effects at breaking and after breaking by comparing individual waves in a group with equivalent regular waves. Regular wave break almost at the same position and with the same wave height. Meanwhile in a wave group, the wave breaks in the variant positions and with variant wave heights. These phenomena cause the breaking point to be more scattered in a wave group rather than in regular waves. Return flow due to the breaking of wave groups appears more significant and is extended to the full depth in the surf zone rather than in regular waves. Swash oscillations of the wave group in the surf zone appear irregular. Meanwhile in regular waves, swash oscillations are almost constant.

Interaction of Waves With a Moored Semisubmersible

1984 ◽  
Vol 106 (4) ◽  
pp. 419-425 ◽  
Author(s):  
S. K. Chakrabarti ◽  
D. C. Cotter
Keyword(s):  
Diffraction Theory ◽  
Nonlinear Damping ◽  
Irregular Waves ◽  
Test Results ◽  
Regular Waves ◽  
Mooring Lines ◽  
Wave Groups ◽  
First Order ◽  
Oscillating Motion ◽  
Theoretical Results

A semisubmersible moored in waves experiences a steady offset and two types of motion—a first-order motion at frequencies corresponding to the incident wave frequencies and a slowly oscillating motion near the natural frequency of the semisubmersible/mooring system. An extensive wave tank testing of a semisubmersible model was undertaken in which the motions of the semisubmersible and the loads in the mooring lines were measured. The semisubmersible was tested in the tank in a head sea as well as a beam sea heading in a series of regular waves, regular wave groups and irregular waves. The test results of the steady offset and first-order and slowly oscillating motions are presented for each heading and for each of these wave series as functions of the wave period. The experimental results are correlated with theoretical results based on a 3-D diffraction theory which takes into account the appropriate first and second-order terms. It is found that the nonlinear damping terms are quite important in explaining the behavior of the moored semisubmersible in waves and that the steady drift loads in wave groups can be determined from results based on regular waves.

Application of Focusing Wave Groups in Model Testing Practice

2014 ◽  
Author(s):  
Christian Schmittner ◽  
Joris Brouwer ◽  
Janou Hennig
Keyword(s):  
Hydrodynamic Model ◽  
Transfer Functions ◽  
Theoretical Description ◽  
Model Testing ◽  
Historical Background ◽  
Irregular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Floating Structures

For hydrodynamic model testing different types of model waves are applied, where the most common ones are regular (monochromatic) and irregular (multichromatic) waves. In addition to these wave types the application of focusing wave groups, which are also often denoted as wave packages or transient wave packets, can give insight into aspects that cannot be assessed by the conventional model waves. This paper describes the different applications of focusing wave groups for hydrodynamic model testing. The paper starts with the historical background, followed by a theoretical description and the generation procedure. The main part of the paper is dedicated to the practical application of focusing wave groups in the basin. Items that will be described are a) the derivation of transfer functions for floating structures and for anti-roll tanks b) the determination of hydraulic and electrical transfer function of wave makers c) the verification of position and calibration of wave probes in the basin d) the generation of extreme wave events e) the assessment of reflection coefficient of beaches f) the investigation of non-linear aspects of transfer functions. Finally, characteristics of the analysis of focusing waves are introduced and compared to conventional methods based on regular and irregular waves.

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.

scholarly journals LOAD ANALYSIS FROM WAVE GROUPS

1978 ◽  
Vol 1 (16) ◽  
pp. 140
Author(s):  
A.I. Kuznetsov ◽  
G.D. Khaskhatchikh
Keyword(s):  
Random Process ◽  
Group Structure ◽  
Theoretical Models ◽  
Point Of View ◽  
Irregular Waves ◽  
Regular Waves ◽  
Shore Zone ◽  
Wave Groups ◽  
Load Analysis ◽  
Sea Wave

At the present time sea wave is described by means of two theoretical models, the first is based on regular waves, components of which do not change in time and space, and the second model is based on irregular waves, components of which are randomly changed. The latter coincides to the greater extent with the rolling sea, but even this model does not characterize it to the full» Taking sea wave for a random process, the model of irregular waves does not take into account the sequence of their alternation. Prom the point of view of probability, on which the model of irregular waves is based, the maximum wave may be followed by the minimum wave, and the greater period may be followed by the smallest one. The real sea wave, especially in shore zone, where the main engineering constructions are placed, is characterized by clearly expressed group structure, which includes alternation of a number of great and small waves and the maximum wave is always followed by the wave having almost the same parameters.

Kinematics of Experimentally Generated Severe Wave Conditions and Implications for Numerical Models

2011 ◽  
Author(s):  
Lisa Minnick ◽  
Christopher Kent ◽  
Christopher Bassler ◽  
Scott Percival ◽  
Lauren Hanyok
Keyword(s):  
Free Surface ◽  
Ship Motions ◽  
Wave Group ◽  
Regular Waves ◽  
Validation Data ◽  
Data Set ◽  
Wave Groups ◽  
Wave Kinematics ◽  
Seakeeping Performance ◽  
Numerical Wave

An experiment was performed to measure and characterize wave kinematics in a large-scale experimental basin. The primary objective was to measure and characterize the wave kinematics of both regular waves of varying steepness and scaled irregular seas with embedded large-amplitude wave groups. The secondary objective was to provide a validation data set for wave theory and numerical simulation tool development. Measurements included free surface elevations and velocity field measurements under the free surface using particle image velocimetry (PIV). A discussion of free surface elevation data, the effect of wave steepness on the velocity profile of regular waves and an introduction to the analysis of the wave kinematics of the embedded wave groups was presented in a previous paper by the authors (OMAE2010-20240). The current paper expands on the analysis presented in the previous paper, providing a discussion of the effect of wave group composition, wave group location within irregular seas, and seaway scaling on the kinematics. This experiment is part of an ongoing effort at the Naval Surface Warfare Center Carderock Division (NSWCCD) to improve predictions and measurement of ship motions in waves and assess the dynamic stability and seakeeping performance of naval ships. NSWCCD has developed a deterministic wave generation method to be used in its seakeeping basin facility. The exploration of the above factors provides a better understanding of the employed method and its effectiveness for creating wave groups. Specifically, to model realistic severe conditions that a ship may encounter. These findings, in turn, lead to the possibility of improvements to current model testing methods at NSWCCD. In addition to assessing the experimental methods employed, the experimental data set can also be used to validate and improve current numerical wave models for ship motions prediction. A comparison of the measured wave elevations and kinematics with a pseudo-spectral numerical wave model is also presented and discussed.

scholarly journals Note on the Application of Transient Wave Packets for Wave–Ice Interaction Experiments

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1699
Author(s):  
Marco Klein ◽  
Moritz Hartmann ◽  
Franz von Bock und von Bock und Polach
Keyword(s):  
Amplitude Spectrum ◽  
Wave Structure ◽  
Wave Dispersion ◽  
Wide Frequency Range ◽  
Single Test ◽  
Regular Waves ◽  
Transient Wave ◽  
Wave Groups ◽  
Efficient Alternative

This paper presents the transient wave packet (TWP) technique as an efficient method for wave–ice interaction experiments. TWPs are deterministic wave groups, where both the amplitude spectrum and the associated phases are tailor-made and manipulated, being well established for efficient wave–structure interaction experiments. One major benefit of TWPs is the possibility to determine the response amplitude operator (RAO) of a structure in a single test run compared to the classical approach by investigating regular waves of different wave lengths. Thus, applying TWPs for wave–ice interaction offers the determination of the RAO of the ice at specific locations. In this context, the determination of RAO means that the ice characteristics in terms of wave damping over a wide frequency range are obtained. Besides this, the wave dispersion of the underlying wave components of the TWP can be additionally investigated between the specific locations with the same single test run. For the purpose of this study, experiments in an ice tank, capable of generating tailored waves, were performed with a solid ice sheet. Besides the generation of one TWP, regular waves of different wave lengths were generated as a reference to validate the TWP results for specific wave periods. It is shown that the TWP technique is not only applicable for wave–ice interaction investigations, but is also an efficient alternative to investigations with regular waves.

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.

Large-Scale Wave Kinematics Measurements of Regular Waves and Large-Amplitude Wave Groups

2010 ◽  
Author(s):  
Lisa Minnick ◽  
Christopher Bassler ◽  
Scott Percival ◽  
Lauren Hanyok
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Near Field ◽  
Field Measurements ◽  
Primary Objective ◽  
Irregular Waves ◽  
Ship Motions ◽  
Regular Waves ◽  
Wave Groups ◽  
Wave Kinematics

An experiment was performed to measure and characterize wave kinematics in an experimental basin. The experiment is part of an ongoing effort to improve predictions and measurements of ship motions in waves, including more accurate characterization of the near-field wave environment and its influence on ship motions. The primary objective of this experiment was to measure and characterize the wave kinematics of regular waves of varying steepness and scaled irregular seaways, including irregular waves with embedded wave groups. Measurements, including free-surface elevations and velocity field measurements under the free surface, are presented and discussed.

Multi-Focused Wave Groups in Wave Flume

2019 ◽  
Author(s):  
Qinghe Fang ◽  
Cunbao Zhao ◽  
Anxin Guo
Keyword(s):  
Irregular Waves ◽  
Frequency Resolution ◽  
Random Wave ◽  
Wave Group ◽  
Wave Groups ◽  
Large Wave ◽  
Wave Flume ◽  
Space And Time ◽  
Focused Wave ◽  
Focused Wave Group

Abstract People can simulate extreme hydrodynamic conditions in a laboratory facility by interfering a numbers of regular waves at a certain point in space and time, which is focused wave. It is obviously higher and steeper than any other wave, e.g. regular or irregular waves, within the propagating wave group. The focused wave occurs at a designed point both in space and time. It represents an event with a large return period which would take a long time to reproduce within a random wave sequence. The focused wave, representing of a large wave occurring in a random sea, is quite frequently used to investigate wave loading on marine or coastal structures. However, most research only employ one single focused wave group. Taking the randomness of the wave-structure interaction, repeated tests would be suggested by some textbooks or codes to eliminate the odd results. However, it would take more time to conduct those tests no matter in the laboratory or in the numerical simulations. In our present work, we use a novel method to experimentally generate several focused wave group with different focus time but same focus point at the same time to obtain multi-focused wave groups. The wave elevation and water particle kinematics are measured. The influence of peak frequency, frequency resolution and period of focused wave group are checked and discussed. The results show that present method can generate stable and repeatable focused wave groups in the wave flume.

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