scholarly journals COMPARISONS OF NUMERICAL RANDOM WAVE SIMULATORS

1988 ◽  
Vol 1 (21) ◽  
pp. 70 ◽  
Author(s):  
Josep R. Medina ◽  
Carlos R. Sanchez-Carratala
Keyword(s):  
Random Wave ◽  
Random Numbers ◽  
Random Waves ◽  
Spectral Parameters ◽  
Mean Values ◽  
Simulation Techniques ◽  
Target Spectrum ◽  
Wave Superposition ◽  
Wave Heights ◽  
Fft Algorithms

A review of unidimensional numerical random sea simulators is provided, centering the attention on the measurement of distortions introduced by the different simulation techniques. Simulators by wave superposition are analyzed, with the conclusion being that they generate significant distortions on the realizations when the number of simulated points are larger than two times the number of wave components. Composed simulators are proposed for the purpose of generating long non-periodic realizations using FFT algorithms. In order to qualify simulators, a justification, based on physical properties of random waves, is given to use mn> m1» Qp and mo as the best spectral parameters to characterize processes. Mean values and variabilities of wave heights and periods are controlled by these parameters. A new robust technique is developed to estimate the parameters of an AR(p) model corresponding to a given target spectrum, S 77 ( f ). MA(q) and ARMA(p,q) approximations are studied. The source of pseudo-random numbers to generate the input white noise has a critical impact on the statistical properties of the output.

scholarly journals WAVE TRANSMISSION THROUGH A DOUBLE-ROW PILE BREAKWATER

1988 ◽  
Vol 1 (21) ◽  
pp. 165 ◽  
Author(s):  
John B. Herbich ◽  
Barry Douglas
Keyword(s):  
Wave Transmission ◽  
Random Wave ◽  
Random Waves ◽  
Double Row ◽  
Single Row ◽  
Pile Diameter ◽  
Gap Ratio ◽  
Wave Heights ◽  
Pass Through ◽  
Gap Spacing

Several previous investigators have conducted experiments leading to expressions for predicting the transformation of waves passing through closely-spaced pile or large cylinder breakwaters. The present study extends the earlier experiments which used a single row of piles instead of a double row of piles forming a breakwater. The experiments using the double-pile breakwater were performed in the same facility as the experiments conducted on a single-pile breakwater and employed the same method of analysis for a more meaningful comparison. The experiments consisted of allowing waves to pass through a pile array and measuring the incident and transmitted wave heights. The variables were: depth, period, diameter, monochromatic and random waves. The experimental matrix was three water depths, four wave periods, two pile diameters, two gap dimensions between piles and four random wave spectra: Darbyshire, I.T.T.C., Pierson- Moskowitz and JONSWAP, two pile diameters and two gap dimensions between piles. The two-row breakwater had less wave transmission than the single-row breakwater, as expected. For a gap to a pile diameter ratio, or b/D = 0.2 (where b = gap spacing, D — pile diameter), the wave transmission was reduced by 15 percent, as compared with a single-row breakwater; for a gap ratio of b/D - 0.1, the wave transmission was reduced by 5 to 10 percent.

scholarly journals PREDICTION OF WAVE GROUP STATISTICS

1984 ◽  
Vol 1 (19) ◽  
pp. 52
Author(s):  
Steve Elgar ◽  
R.T. Guza ◽  
R.J. Seymour
Keyword(s):  
Wave Group ◽  
Random Waves ◽  
Run Length ◽  
Depth Data ◽  
Simulation Techniques ◽  
Linear Behavior ◽  
Random Seas ◽  
Wave Heights ◽  
Significant Wave Heights ◽  
The Mean

Two methods of numerically simulating random seas, given a target power spectrum, are discussed. Wave group statistics, such as the mean length of runs of high waves, produced by the different simulation schemes are compared. For a large number of spectral components, no significant differences are found in the wave group statistics produced by the two simulation techniques. Using the simulation techniques, it is shown that ocean gravity wave group statistics are not inconsistent with an underlying wave field composed of linearly superposed random waves. The majority of the field data examined were collected in 9-10 m depth, significant wave heights ranged from about 20 to 200 cm, and the spectral shapes ranged from fairly narrow to broad. For the 9-10 m depth data, observed mean run length, variance of run length, and the probabilities of runs of a given number of high waves were statistically consistent with the linear simulations. In contrast to the apparent linear behavior in 9-3 0 m depth, waves in 2-3 m depth showed substantial departures from the linear simulations.

scholarly journals DIFFRACTION DIAGRAMS FOR DIRECTIONAL RANDOM WAVES

1978 ◽  
Vol 1 (16) ◽  
pp. 35 ◽  
Author(s):  
Yoshimi Goda ◽  
Tomotsuka Takayama ◽  
Tasumasa Suzuki
Keyword(s):  
Wave Diffraction ◽  
Spectral Characteristics ◽  
Wave Spectrum ◽  
Standard Form ◽  
Random Wave ◽  
Random Waves ◽  
Directional Spectrum ◽  
Spreading Function ◽  
Wave Heights ◽  
Directional Wave

Conventional wave diffraction diagrams often yield erroneous estimation of wave heights behind breakwaters in the sea, because they are prepared for monochromatic waves while actual waves in the sea are random with directional spectral characteristics. A proposal is made for the standard form of directional wave spectrum on the basis of Mitsuyasu's formula for directional spreading function. A new set of diffraction diagrams have been constructed for random waves with the proposed directional spectrum. Problems of multi-diffraction and multi-reflection within a harbour can also be solved with serial applications of random wave diffraction.

scholarly journals RANDOM WAVE SIMULATION IN A LABORATORY WAVE TANK

1976 ◽  
Vol 1 (15) ◽  
pp. 20 ◽  
Author(s):  
Akira Kimura ◽  
Yuichi Iwagaki
Keyword(s):  
Simulation System ◽  
Random Wave ◽  
New Wave ◽  
Random Waves ◽  
Sea Waves ◽  
Coastal Structures ◽  
Wave Tank ◽  
Wave Simulation ◽  
Simulation Techniques ◽  
Engineering Problems

Most of coastal engineering problems have been studied with monocromatic waves. However, sea waves which arrive at the coast are random. It is very difficult to estimate exactly the influence of these random waves to coastal structures. Then the model tests in a laboratory wave tank using random wave simulation techniques seem to be most desirable way to estimate the influence of randomness of sea waves. For this purpose, the accomplishment of random wave simulation system, which make possible generating random waves having statistically same properties as those of sea waves, has long been desired. The authors achieved to establish such a new wave simulation system. In this paper, the characteristics of this system are demonstrated experimentally through several cases of random wave simulations.

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.

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.

scholarly journals Comparison of Extreme Surface Elevation for Linear and Nonlinear Random Wave Theory for Offshore Structures

2018 ◽  
Vol 203 ◽  
pp. 01021
Author(s):  
Nurul 'Azizah Mukhlas ◽  
Noor Irza Mohd Zaki ◽  
Mohd Khairi Abu Husain ◽  
Gholamhossein Najafian
Keyword(s):  
Probabilistic Approach ◽  
Wave Theory ◽  
Offshore Structures ◽  
Random Wave ◽  
Linear Wave ◽  
Random Waves ◽  
Sea State ◽  
Higher Order Terms ◽  
Structural Responses ◽  
Nonlinear Random Wave

For offshore structural design, the load due to wind-generated random waves is usually the most important source of loading. While these structures can be designed by exposing them to extreme regular waves (100-year design wave), it is much more satisfactory to use a probabilistic approach to account for the inherent randomness of the wave loading. This method allows the statistical properties of the loads and structural responses to be determined, which is essential for the risk-based assessment of these structures. It has been recognized that the simplest wave generation is by using linear random wave theory. However, there is some limitation on its application as some of the nonlinearities cannot be explained when higher order terms are excluded and lead to underestimating of 100-year wave height. In this paper, the contribution of nonlinearities based on the second order wave theory was considered and being tested at a variety of sea state condition from low, moderate to high. Hence, it was proven that the contribution of nonlinearities gives significant impact the prediction of 100-year wave's design as it provides a higher prediction compared to linear wave theory.

The Diffraction of Multidirectional Random Waves by Trapezoidal Submarine Pits

2003 ◽  
Author(s):  
Hong Sik Lee ◽  
A. Neil Williams ◽  
Sung Duk Kim
Keyword(s):  
Numerical Model ◽  
Wave Diffraction ◽  
Boundary Integral ◽  
Random Wave ◽  
Linear Wave ◽  
Wave System ◽  
Random Waves ◽  
Random Surface ◽  
Directional Spectrum ◽  
Integral Equation Approach

A numerical model is presented to predict the interaction of multidirectional random surface waves with one or more trapezoidal submarine pits. In the present formulation, each pit may have a different side slope, while the four side slopes at the interior edge of any given pit are assumed equal. The water depth in the fluid region exterior to the pits is taken to be uniform, and the solution method for a random wave system involves the superposition of linear-wave diffraction solutions based on a two-dimensional boundary integral equation approach. The incident wave conditions are specified using a discrete form of the Mitsuyasu directional spectrum. The results of the present numerical model have been compared with those of previous theoretical studies for regular and random wave diffraction by single or multiple rectangular pits. Reasonable agreement was obtained in all cases. Based on these comparisons it is concluded that the present numerical model is an accurate and efficient tool to predict the wave field around multiple submarine pits of trapezoidal section in many practical situations.

scholarly journals Random wave-driven drag forces on near-bed vegetation in shallow water based on deepwater wind conditions

2019 ◽  
Vol 233 (4) ◽  
pp. 1287-1290
Author(s):  
Dag Myrhaug
Keyword(s):  
Shallow Water ◽  
Drag Force ◽  
Wind Waves ◽  
Wave Spectrum ◽  
Random Wave ◽  
Random Waves ◽  
Coastal Zones ◽  
Drag Forces ◽  
Mean Wind Speed ◽  
Wave Induced

This article provides a simple analytical method for giving estimates of random wave-driven drag forces on near-bed vegetation in shallow water from deepwater wind conditions. Results are exemplified using a Pierson–Moskowitz model wave spectrum for wind waves with the mean wind speed at the 10 m elevation above the sea surface as the parameter. The significant value of the drag force within a sea state of random waves is given, and an example typical for field conditions is presented. This method should serve as a useful tool for assessing random wave-induced drag force on vegetation in coastal zones and estuaries based on input from deepwater wind conditions.

scholarly journals Stochastic Response of Tension Leg Platform to Wave and Current Forces

1989 ◽  
Vol 111 (4) ◽  
pp. 221-230 ◽  
Author(s):  
A. Ertas ◽  
J.-H. Lee
Keyword(s):  
Constant Current ◽  
Response Analysis ◽  
Stochastic Dynamic ◽  
Superposition Method ◽  
Random Waves ◽  
Stochastic Response ◽  
Tension Leg Platform ◽  
Single Degree Of Freedom ◽  
Simulation Techniques ◽  
Wave Induced

The linear analysis in the frequency domain is presented for the surge motion of a tension leg platform (TLP) in the case of random waves only and random waves with constant current. A single-degree-of-freedom model of a TLP is employed for response. The superposition method, one of the simulation techniques, is applied to random sea wave, and the response analysis of TLP in time is developed with wave velocity and wave acceleration simulations. Wave-induced forces are calculated using the modified Morison equation, which takes into account relative motion. Computational methods for both analyses are developed, and the results of stochastic, dynamic response of the TLP, with and without the presence of current, are presented and compared.

Sign in / Sign up

Export Citation Format

Share Document