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.

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.

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.

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.

scholarly journals Time Scale for Scour Beneath Pipelines Due to Long-Crested and Short-Crested Nonlinear Random Waves Plus Current

2021 ◽  
Vol 9 (2) ◽  
pp. 114
Author(s):  
Dag Myrhaug ◽  
Muk Chen Ong
Keyword(s):  
Time Scale ◽  
Current Flow ◽  
Irregular Waves ◽  
Wave Crest ◽  
Random Wave ◽  
Random Waves ◽  
Flow Conditions ◽  
Regular Waves ◽  
Nonlinear Random Waves ◽  
2D And 3D

This article derives the time scale of pipeline scour caused by 2D (long-crested) and 3D (short-crested) nonlinear irregular waves and current for wave-dominant flow. The motivation is to provide a simple engineering tool suitable to use when assessing the time scale of equilibrium pipeline scour for these flow conditions. The method assumes the random wave process to be stationary and narrow banded adopting a distribution of the wave crest height representing 2D and 3D nonlinear irregular waves and a time scale formula for regular waves plus current. The presented results cover a range of random waves plus current flow conditions for which the method is valid. Results for typical field conditions are also presented. A possible application of the outcome of this study is that, e.g., consulting engineers can use it as part of assessing the on-bottom stability of seabed pipelines.

scholarly journals DESIGN OF MAIN BREAKWATER AT SINES HARBOUR

1976 ◽  
Vol 1 (15) ◽  
pp. 143 ◽  
Author(s):  
John Dorrington Mettam
Keyword(s):  
North Atlantic ◽  
Government Agency ◽  
Irregular Waves ◽  
Regular Waves ◽  
The West ◽  
The North ◽  
Flume Tests ◽  
Wide Range ◽  
The Subject ◽  
Engineering Conference

In March 1972 the author's firm in association with two Portuguese firms of consulting engineers, Consulmar and Lusotecna, were appointed by the Portuguese Government agency Gabinete da Area de Sines to prepare designs for the construction of a new harbour at Sines on the west coast of Portugal. The location is shown in Figure 1. The main breakwater, which is the subject of this paper, is probably the largest breakwater yet built, being 2 km long and in depths of water of up to 50 m. It is exposed to the North Atlantic and has been designed for a significant wave height of 11 m. Dolos units invented by Merrifield (ref. 1) form the main armour. The project programme required that studies be first made of a wide range of alternative layouts for the harbour. After the client had decided on the layout to be adopted, documents were to be prepared to enable tenders for construction to be invited in January 1973. This allowed little time for the design to be developed and only one series of flume tests, using regular waves, was completed during this period. Further tests in the regular flume were completed during the tender period and a thorough programme of testing with irregular waves was commenced later in the year, continuing until August 1974 when the root of the breakwater was complete and the construction of the main cross-section was about to start. The model tests, which were carried out at the Laboratorio Nacional de Engenharia Civil in Lisbon, were reported by Morals in a paper presented to the 14th International Coastal Engineering Conference in 1974. (ref. 2)

scholarly journals BREAKWATER ARMOR DISPLACEMENT THRESHOLDS: A POSSIBLE CORRELATION WITH CUMULATIVE WAVE ENERGY

1984 ◽  
Vol 1 (19) ◽  
pp. 186
Author(s):  
Daniel L. Behnke ◽  
Frederic Raichlen
Keyword(s):  
Wave Energy ◽  
Wave Train ◽  
Wave Length ◽  
Simple Wave ◽  
Wave Theory ◽  
Irregular Waves ◽  
Reconstruction Technique ◽  
Regular Wave ◽  
Regular Waves ◽  
Three Dimensional Model

An extensive program of stability experiments in a highly detailed three-dimensional model has recently been completed to define a reconstruction technique for a damaged breakwater (Lillevang, Raichlen, Cox, and Behnke, 1984). Tests were conducted with both regular waves and irregular waves from various directions incident upon the breakwater. In comparison of the results of the regular wave tests to those of the irregular wave tests, a relation appeared to exist between breakwater damage and the accumulated energy to which the structure had been exposed. The energy delivered per wave is defined, as an approximation, as relating to the product of H2 and L, where H is the significant height of a train of irregular waves and L is the wave length at a selected depth, calculated according to small amplitude wave theory using a wave period corresponding to the peak energy of the spectrum. As applied in regular wave testing, H is the uniform wave height and L is that associated with the period of the simple wave train. The damage in the model due to regular waves and that caused by irregular waves has been related through the use of the cumulative wave energy contained in those waves which have an energy greater than a threshold value for the breakwater.

The Transverse Plane Motions of Ships

1991 ◽  
Vol 28 (02) ◽  
pp. 55-72
Author(s):  
Bruce L. Hutchison
Keyword(s):  
Transverse Plane ◽  
Irregular Waves ◽  
Hydrodynamic Coefficients ◽  
Important Process ◽  
Regular Waves ◽  
Hull Form ◽  
Fishing Vessels ◽  
Transverse Stability ◽  
Roll Axis ◽  
The One

A detailed exposition of the kinematics of the transverse plane motions of ships is provided, with particular attention to the important process of total transverse acceleration in vessel coordinates. The loci of sway, sway velocity and sway acceleration are shown to follow hyperbolic distributions with respect to elevation in both regular and irregular waves. In regular waves the transverse acceleration in earth-fixed and vessel-fixed coordinates are shown to be congruent with a vertical shift in elevation of g/ω2 = λ/(2π). Expressions are given for the elevations minimizing transverse plane processes in regular and irregular waves. In long waves the elevation minimizing total transverse acceleration in vessel coordinates is shown to be g/ωn2 = g[Tn/ /(2π)]2 below the waterline. This is the roll center, which should be used in the traditional analysis of foundation loads. Its location, far below the keel for most vessels, is surprising. The elevation (OP) of the roll axis, which must be used when solving the one-degree-of-freedom equation for roll, is given and is shown to require hydrodynamic coefficients for sway as well as roll. In general, OP does not correspond to an elevation that minimizes any of the transverse plane processes. The effect of hull form, transverse stability and natural roll period on transverse plane motions are examined in an attempt to resolve the dichotomy of views between those who favor ships with low GMT and long natural roll periods and those who favor high GMT with short natural roll periods. It is demonstrated that large values of the beam-to-draft ratio (6/7) with low natural roll periods are advantageous at modest elevations above the waterline. This explains the favorable offshore experience in vessels meeting this description, such as tugs, supply vessels and fishing vessels. At higher elevations long natural periods are shown to present a clear advantage, which supports the preference for low GMT for large passenger vessels, containerships and ships with deck-loads of logs. The trends identified would seem to support the conjecture that, with regard to natural roll period, there is a "forbidden middle" that should be avoided in design.

Wave Attenuation Performance of Floating Breakwater Needs to be Evaluated by Using Irregular Waves

2021 ◽  
Author(s):  
Chien Ming Wang ◽  
Huu Phu Nguyen ◽  
Jeong Cheol Park ◽  
Mengmeng Han ◽  
Nagi abdussamie ◽  
...  
Keyword(s):  
Transmission Coefficient ◽  
Wave Height ◽  
Wave Attenuation ◽  
Wave Spectrum ◽  
Ocean Waves ◽  
Irregular Waves ◽  
Regular Waves ◽  
Transmission Coefficients ◽  
Floating Breakwater ◽  
Floating Breakwaters

<p>Floating breakwaters have been used to protect shorelines, marinas, very large floating structures, dockyards, fish farms, harbours and ports from harsh wave environments. A floating breakwater outperforms its bottom-founded counterpart with respect to its environmental friendliness, cost-effectiveness in relatively deep waters or soft seabed conditions, flexibility for expansion and downsizing and its mobility to be towed away. The effectiveness of a floating breakwater design is assessed by its wave attenuation performance that is measured by the wave transmission coefficient (i.e., the ratio of the transmitted wave height to the incident wave height or the ratio of the transmitted wave energy to the incident wave energy). In some current design guidelines for floating breakwaters, the transmission coefficient is estimated based on the assumption that the realistic ocean waves may be represented by regular waves that are characterized by the significant wave period and wave height of the wave spectrum. There is no doubt that the use of regular waves is simple for practicing engineers designing floating breakwaters. However, the validity and accuracy of using regular waves in the evaluation of wave attenuation performance of floating breakwaters have not been thoroughly discussed in the open literature. This study examines the wave transmission coefficients of floating breakwaters by performing hydrodynamic analysis of some large floating breakwaters in ocean waves modelled as regular waves as well as irregular waves described by a wave spectrum such as the Bretschneider spectrum. The formulation of the governing fluid motion and boundary conditions are based on classical linear hydrodynamic theory. The floating breakwater is assumed to take the shape of a long rectangular box modelled by the Mindlin thick plate theory. The finite element – boundary element method was employed to solve the fluid-structure interaction problem. By considering heave-only floating box-type breakwaters of 200m and 500m in length, it is found that the transmission coefficients obtained by using the regular wave model may be smaller (or larger) than that obtained by using the irregular wave model by up to 55% (or 40%). These significant differences in the transmission coefficient estimated by using regular and irregular waves indicate that simplifying assumption of realistic ocean waves as regular waves leads to significant over/underprediction of wave attenuation performance of floating breakwaters. Thus, when designing floating breakwaters, the ocean waves have to be treated as irregular waves modelled by a wave spectrum that best describes the wave condition at the site. This conclusion is expected to motivate a revision of design guidelines for floating breakwaters for better prediction of wave attenuation performance. Also, it is expected to affect how one carries out experiments on floating breakwaters in a wave basin to measure the wave transmission coefficients.</p>

scholarly journals VERIFICATION OF KIMURA's THEORY FOR WAVE GROUP STATISTICS

1984 ◽  
Vol 1 (19) ◽  
pp. 43 ◽  
Author(s):  
J.A. Battjes ◽  
G.Ph. Van Vledder
Keyword(s):  
Wave Motion ◽  
Random Phase ◽  
Wave Generation ◽  
Original Form ◽  
Wave Group ◽  
Sea Waves ◽  
Wave Groups ◽  
Wave Groupiness ◽  
Active Wave ◽  
Sea Wave

North Sea wave records, obtained in conditions of active wave generation, have been analyzed with respect to the distribution of the length of wave groups. The results are compared to a theory by Kimura, in its original form as well as with the addition of a new spectral wave groupiness parameter, based on the theory of Gaussian processes. The results lend support to the validity of Kimura's theory, this in turn implies further evidence that the phenomenon of wave groups in sea waves can by and large be explained, both qualitatively and quantitatively, in terms of the linear, random phase model for the wave motion, even in conditions of active wave generation.

Load Analysis from Wave Groups

1978 ◽  
Author(s):  
A.I. Kuznetsov ◽  
G.D. Khaskhatchikh
Keyword(s):  
Wave Groups ◽  
Load Analysis
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