Incorporating irregular nonlinear waves in simulation of dropped cylindrical objects

2019 ◽  
Vol 234 (1) ◽  
pp. 272-283
Author(s):  
Gong Xiang ◽  
C. Guedes Soares
Keyword(s):  
Nonlinear Wave ◽  
Mass Density ◽  
Wave Spectrum ◽  
Density Wave ◽  
Wave Model ◽  
Irregular Waves ◽  
Regular Waves ◽  
Initial Wave ◽  
Target Wave ◽  
Good Agreement

This study investigates the use of second-order irregular waves for estimating loads on dropped objects. The theory for the irregular nonlinear wave model is integrated into a motion prediction model to simulate the falling process of a dropped cylinder under irregular waves. Through frequency analysis, the simulated irregular waves are transformed into wave spectrum by fast Fourier transform and compared with the target wave spectrum. A good agreement between simulated wave spectrum and target wave spectrum indicates the validity of the irregular nonlinear wave model. The effects of cylinder mass density, wave amplitude and initial wave phase on the trajectory and terminal conditions of dropped cylindrical object are systematically investigated, and the simulated results are compared with those induced by regular waves.

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 Nonlinear run-ups of regular waves on sloping structures

2012 ◽  
Vol 12 (12) ◽  
pp. 3811-3820 ◽  
Author(s):  
T.-W. Hsu ◽  
S.-J. Liang ◽  
B.-D. Young ◽  
S.-H. Ou
Keyword(s):  
Boussinesq Equations ◽  
Irregular Waves ◽  
Coastal Structures ◽  
Regular Waves ◽  
Wave Flume ◽  
Coastal Risk ◽  
Run Up ◽  
Two Parameters ◽  
Prediction Capability ◽  
Good Agreement

Abstract. For coastal risk mapping, it is extremely important to accurately predict wave run-ups since they influence overtopping calculations; however, nonlinear run-ups of regular waves on sloping structures are still not accurately modeled. We report the development of a high-order numerical model for regular waves based on the second-order nonlinear Boussinesq equations (BEs) derived by Wei et al. (1995). We calculated 160 cases of wave run-ups of nonlinear regular waves over various slope structures. Laboratory experiments were conducted in a wave flume for regular waves propagating over three plane slopes: tan α =1/5, 1/4, and 1/3. The numerical results, laboratory observations, as well as previous datasets were in good agreement. We have also proposed an empirical formula of the relative run-up in terms of two parameters: the Iribarren number ξ and sloping structures tan α. The prediction capability of the proposed formula was tested using previous data covering the range ξ ≤ 3 and 1/5 ≤ tan α ≤ 1/2 and found to be acceptable. Our study serves as a stepping stone to investigate run-up predictions for irregular waves and more complex geometries of coastal structures.

scholarly journals NUMERICAL INVESTIGATION OF BREAKING IRREGULAR WAVES OVER A SUBMERGED BAR WITH CFD

2018 ◽  
pp. 43
Author(s):  
Ankit Aggarwal ◽  
Mayilvahanan Alagan Chella ◽  
Arun Kamath ◽  
Hans Bihs
Keyword(s):  
Spectral Characteristics ◽  
Wave Spectrum ◽  
Practical Interest ◽  
Irregular Waves ◽  
Regular Waves ◽  
Spectrum Change ◽  
Individual Wave ◽  
Great Practical Interest ◽  
Submerged Bar ◽  
The Individual

The study of breaking irregular waves is of great practical interest, because of the waves found in the nature. Regular waves are seldom found in the field. Irregular waves can be viewed as the superposition of a number of regular waves (wave components) with the different frequencies and the amplitudes. The breaking process for irregular waves is more complex as compared to breaking regular waves. The energy transfer between the individual wave components of different frequencies also takes place during the breaking process. Due to this, the spectral characteristics of the incident wave spectrum change during the breaking process. The main purpose of the study is to investigate the hydrodynamics during the interaction of breaking irregular waves with a submerged bar.

Using a Nonlinear Spectral Model for Preparing Three-Dimensional Wave Experiments

2004 ◽  
Author(s):  
Fe´licien Bonnefoy ◽  
David Le Touze´ ◽  
Pierre Ferrant
Keyword(s):  
Low Cost ◽  
Three Dimensional ◽  
Perturbation Series ◽  
Irregular Waves ◽  
Experimental Conditions ◽  
Initial Wave ◽  
Spectral Models ◽  
Wave Patterns ◽  
Wave Trains ◽  
Target Wave

We are interested in an original numerical model based on a spectral approach and able to simulate the focalisation of waves in a wavetank. Such a technique involves fast FFT resolution, permitting accurate simulations of the target wave fields at low cost. This model is specifically designed to fit with experimental conditions, accounting for the physical wavetank geometry including the absorbing beach, sidewalls, and the snake-type wavemaker. The nonlinear equations are developed in perturbation series up to second order in wave steepness. An additional potential is employed to model the generator of the wave tank. Simulations start from rest in the basin, requiring no initial wave patterns as in other spectral models. Firstly, we consider two dimensional spectra to check the ability of the model to reproduce irregular waves. Secondly, cases of wave trains geometrically focusing at a given location of the test area are simulated. Finally, directional sea spectra are generated with imposing a focalisation of the phases at a given time.

Comparison of Numerical Models and Verification Against Experimental Data, Using Pelastar TLP Concept

2015 ◽  
Author(s):  
Luca Vita ◽  
G. K. V. Ramachandran ◽  
Antonia Krieger ◽  
Marit I. Kvittem ◽  
Daniel Merino ◽  
...  
Keyword(s):  
Experimental Data ◽  
Numerical Solutions ◽  
Numerical Models ◽  
Complex Problem ◽  
Ocean Basin ◽  
Irregular Waves ◽  
Test Results ◽  
Regular Waves ◽  
Numerical Tools ◽  
Good Agreement

The analysis of a FWT is a complex problem, which requires advanced tools. Several numerical solutions have been used to couple hydrodynamics and aerodynamics and some of the available numerical tools have been compared in code-to-code comparisons. However the code validation for analysis of FWTs is limited by the number of available experimental data. In the present article, DNV GL and Glosten present a code comparison of four numerical tools against model test results. The design used for the analysis is the Pelastar Tension Leg Platform (TLP) by Glosten. A 1/50 downscaled model of the platform and NREL-5 MW wind turbine was tested in MARIN ocean basin. The results from the model tests are used to verify the results from the numerical codes. The FWT is modelled using four different codes: HAWC2 (by DTU and used by DNV GL), BLADED (by DNV GL and used by DNV GL), SIMA (by Marintek and used by DNV GL) and ORCAFLEX (by Orcina and used by Glosten). Although differences exist among these codes, comparable approaches have been used. Results from the numerical codes are compared against the experimental data, in terms of: - Natural periods - Response in regular waves - Response in irregular waves - Response in irregular waves with aerodynamic loads. In general, the results show a good agreement between the different numerical models and all the codes are capable to reproduce the main dynamics of the system. Some deviations were found and should be solved, in order to use these models for a detailed analysis. However these differences do not seem to be due to limitations of the codes and they might be solvable with a more accurate model of the system.

scholarly journals STABILITY OF DOLOS SLOPES

1974 ◽  
Vol 1 (14) ◽  
pp. 99
Author(s):  
Michael Brorsen ◽  
H.F. Burcharth ◽  
Torben Larsen
Keyword(s):  
Surface Roughness ◽  
Wave Model ◽  
Irregular Waves ◽  
Regular Waves ◽  
Model Studies ◽  
Natural Stones ◽  
The Stability

The stability of dolos armour blocks against wave attack has been investigated in wave model studies. Simple definitions to describe the block movements are introduced and the following results are discussed: 1. The stability of dolos slopes against regular waves and the influence of the slope. 2. The stability of dolos slopes against irregular waves that are not Rayleigh distributed. 3. Comparison between the stability of dolos, natural stones and cubes. 4. The influence of the surface roughness of the dolos model blocks. 5. The applicability of Hudson's formula.

Qualification Criteria and the Verification of Numerical Waves: Part 2: CFD-Based Numerical Wave Tank

2021 ◽  
Author(s):  
Benjamin Bouscasse ◽  
Andrea Califano ◽  
Young Myung Choi ◽  
Xu Haihua ◽  
Jang Whan Kim ◽  
...  
Keyword(s):  
Wave Spectrum ◽  
Vertical Direction ◽  
Offshore Structures ◽  
Irregular Waves ◽  
Numerical Wave Tank ◽  
Regular Waves ◽  
Wave Impact ◽  
Wave Tank ◽  
Modeling Practices ◽  
Numerical Wave

Abstract There is increasing interest in numerical wave simulations as a tool to design offshore structures, especially for the prediction of stochastic nonlinear wave loads like those related to air-gap and wave impact. Though the simulations cannot replace all experiments, they are now competitive on some topics such as the computations of wind and current coefficients. To proceed further it is necessary to improve the procedure to account for another complex environmental factor, wave motion. This paper addresses an industrial collaboration to develop modeling practices and qualification criteria of CFD-based numerical wave tank for offshore applications. As a part of the effort to develop reliable numerical wave modeling practices in the framework of the “Reproducible Offshore CFD JIP”, qualification criteria are formulated for the wave solutions generated from either potential-flow based codes in Part 1 of this work. Part 2 presents first a set of solutions for forcing the qualified waves obtained with the potential codes in the CFD domain. Those solutions follow a set of coupling protocols previously proposed in the JIP framework. Two potential codes and two CFD solvers are combined, so that four possible methods of generating waves and modalities are described. Two different potential models are considered, one using the higher order spectral method for numerical wave tank (HOS-NWT), and another using the finite-element method in the horizontal direction and a modal expansion after a sigma transform in the vertical direction (solver is called TPNWT). Both are equipped with a breaking model to generate extreme sea states. The two CFD solvers tested are Simcenter STAR-CCM+ and OpenFOAM. Simulation setups are proposed for both software. Simulation results from eight academic or industrial partners are presented for two sets of 2D test cases in deep water, one with regular waves and one with irregular waves, both with one very steep condition (ratio of wave height over wavelength of 10% for regular waves and 1000 year return period for Gulf of Mexico for irregular waves). The irregular waves are simulated for 10 sets of 3 hours to apply a stochastic approach to verify the quality of the waves generated in the numerical domain. Attention is given to the wave spectrum and the ensemble probability of the crest distribution, both obtained from the wave elevation at the center of the domain.

scholarly journals THE STABILITY OF RUBBLE MOUND BREAKWATERS AGAINST IRREGULAR WAVES

1966 ◽  
Vol 1 (10) ◽  
pp. 54 ◽  
Author(s):  
Torkild Carstens ◽  
Alf Torum ◽  
Anton Tratteberg
Keyword(s):  
Wave Spectrum ◽  
Model Tests ◽  
Irregular Waves ◽  
Regular Waves ◽  
Destructive Effect ◽  
Wave Channel ◽  
Stability Data ◽  
Rubble Mound ◽  
The Stability ◽  
Rubble Mound Breakwaters

Through extensive model tests with rubble mound breakwaters conducted in many laboratories in recent years design criteria and stability data have been collected. To our knowledge such data have been based on tests with regular waves only. It has been more or less accepted that the destructive effect of a train of regular waves corresponds to a confused sea with a significant wave height equal to the height of the regular waves. At the Rxver and Harbour Research Laboratory at the Technical University of Norway a new wave channel has been equipped with a programmed wave generator which can produce irregular waves wxth any wanted wave spectrum. This paper deals with model tests of the stability of rubble mound breakwaters against irregular waves as compared with regular waves.

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 Null modes effect in Rossby wave model

2004 ◽  
Vol 11 (3) ◽  
pp. 281-293
Author(s):  
V. Goncharov ◽  
V. Pavlov
Keyword(s):  
Nonlinear Wave ◽  
Rossby Wave ◽  
Wave Model ◽  
Wave Fields

Abstract. The problem of the null-modes existence and some particularities of their interaction with nonlinear vortex-wave-like structures is discussed. We show that the null-modes are fundamental elements of nonlinear wave fields. The conditions under which null-modes can manifest themselves are elucidated. The Rossby-Hasegawa-Mima (RHM) model is used for the illustration of features of null-modes-waves interactions.

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