Irregular Wave Forces on Monopile Foundations: Effect of Full Nonlinearity and Bed Slope

2011 ◽  
Author(s):  
Signe Schlo̸er ◽  
Henrik Bredmose ◽  
Harry B. Bingham
Keyword(s):  
Stream Function ◽  
Function Theory ◽  
Wave Train ◽  
Wave Theory ◽  
Irregular Waves ◽  
Wave Forces ◽  
Linear Wave ◽  
Irregular Wave ◽  
Bed Slope ◽  
Force Profiles

Forces on a monopile from a nonlinear irregular unidirectional wave model are investigated. Two seabed profiles of different slopes are considered. Morison’s equation is used to investigate the forcing from fully nonlinear irregular waves and to compare the results with those obtained from linear wave theory and with stream function wave theory. The latter of these theories is only valid on a flat bed. The three predictions of wave forces are compared and the influence of the bed slope is investigated. Force-profiles of two selected waves from the irregular wave train are further compared with the corresponding force-profiles from stream function theory. The results suggest that the nonlinear irregular waves give rise to larger extreme wave forces than those predicted by linear theory and that a steeper bed slope increases the wave forces both for linear and nonlinear waves. It is further found that stream function theory in some cases underestimate the wave forces acting on the monopile.

Numerical Non-Reflecting Irregular Wave Flume Based on VOF Method

2009 ◽  
Author(s):  
Bing Ren ◽  
Xuelin Li ◽  
Peng Han ◽  
Yongxue Wang
Keyword(s):  
Wave Theory ◽  
Vof Method ◽  
Numerical Results ◽  
Irregular Waves ◽  
Open Boundary ◽  
Linear Wave ◽  
Reflected Waves ◽  
Irregular Wave ◽  
Wave Flume ◽  
Sponge Layer

A numerical irregular wave flume is developed using VOF method in conjunction with Reynolds equations. An active absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume to absorb the re-reflected waves. A sponge layer is set on the open boundary to absorb the outgoing waves. The numerical results of regular and irregular waves using the active absorbing-generating boundary are compared to the numerical results using the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The linear damping coefficient is used in the sponge layer. The damping characteristics of the sponger layer implemented in the wave flume are discussed. The computed wave spectra are compared with the target spectra.

scholarly journals THE MEASURED PROPERTIES OF IRREGULAR WAVE BREAKING AND WAVE HEIGHT CHANGE AFTER BREAKING ON THE SLOPE

1988 ◽  
Vol 1 (21) ◽  
pp. 29 ◽  
Author(s):  
Akira Seyama ◽  
Akira Kimura
Keyword(s):  
Wave Height ◽  
Water Depth ◽  
Wave Theory ◽  
Irregular Waves ◽  
Linear Wave ◽  
Periodic Waves ◽  
Zero Crossing ◽  
Irregular Wave ◽  
Height Change ◽  
Cross Waves

Wave height change of the zero-down-cross waves on uniform slopes were examined experimentally. The properties of shoaling, breaking and decay after breaking for a total of about 4,000 irregular waves of the Pierson-Moskowitz type on 4 different slopes (1/10, 1/20, 1/30 and 1/50) were investigated. The shoaling property of the zero-down-cross waves can be approximated by the linear wave theory. However, the properties of breaking and decay after breaking differ considerably from those for periodic waves. The wave height water depth ratio (H/d) at the breaking point for the zero-down-cross waves is about 30% smaller than that for periodic waves on average despite the slopes. Wave height decay after breaking also differs from that for periodic waves and can be classified into three regions, i.e. shoaling, plunging and bore regions. Experimental equations for the breaking condition and wave height change after breaking are proposed in the study. A new definition of water depth for the zero-crossing wave analysis which can reduce the fluctuation in the plotted data is also proposed.

Investigation of Shallow Water Kinematics and Local Loading Effects on Reliability of Minimum Structures

2001 ◽  
Vol 124 (1) ◽  
pp. 41-47
Author(s):  
Suhartodjo Tuty ◽  
Mark J. Cassidy ◽  
Beverley F. Ronalds
Keyword(s):  
Shallow Water ◽  
Stream Function ◽  
Function Theory ◽  
Strong Relationship ◽  
Wave Theory ◽  
Wave Crest ◽  
Linear Wave ◽  
North West ◽  
Wave Kinematics ◽  
The North

In shallow water, and specifically for minimum structures, the critical wave height exponent α has been shown to vary significantly with structural configuration. Because of the strong relationship to the wave kinematics, α is also sensitive to the wave theory chosen. The North West Shelf offshore Australia has numerous minimum structures located in relatively shallow water, which requires non-linear wave theory. In the near-breaking condition, estimation of the wave crest kinematics is difficult, with Stream Function theory being the most widely used. However, various other wave theories and nonlinear numerical techniques have been developed to predict wave kinematics for shallow water conditions. The following wave theories are compared: regular Stream Function theory, Cnoidal wave theory, Stokes’ theory, NewWave theory, and a second-order correction to NewWave theory. Kinematics, loads and α results are presented for a cylinder in three different water depths.

Prediction of Surface Wave Elevation Based on Pressure Measurements

1999 ◽  
Vol 121 (4) ◽  
pp. 242-250 ◽  
Author(s):  
E. Meza ◽  
J. Zhang ◽  
R. J. Seymour
Keyword(s):  
Wave Train ◽  
Wave Model ◽  
Wave Theory ◽  
Linear Wave ◽  
Pressure Measurements ◽  
Transient Wave ◽  
Irregular Wave ◽  
Wave Elevation ◽  
Modulation Methods ◽  
Elevation Measurement

A deterministic method for predicting wave elevation based on pressure measurements is developed. The method is based on the hybrid wave model (HWM), which employs both conventional and phase modulation methods for modeling wave-wave interactions in an irregular wave train. The predicted wave elevation using the HWM based on the pressure measurement of a steep transient wave train is in excellent agreement with the corresponding elevation measurement, while that using linear wave theory (LWT) has relatively large discrepancies.

Alternative Methodologies for Subsea Flexible Strength Analysis

2018 ◽  
Author(s):  
Anskey A. Miranda ◽  
Fred P. Turner ◽  
Nigel Barltrop
Keyword(s):  
Real World ◽  
Wave Train ◽  
Irregular Waves ◽  
Wave Crest ◽  
Strength Analysis ◽  
New Wave ◽  
Regular Wave ◽  
Wave Analysis ◽  
Sea State ◽  
Irregular Wave

This paper presents a study of the analysis methodologies used to predict the most likely response of flexibles in a subsea environment, with the aim of determining an efficient and reliable prediction methodology. The most accurate method involves simulating multiple wave realisations of a real world sea state, i.e. irregular waves, and post-processing the results to determine the most probable maximum (MPM). Due to the computationally intensive nature of this approach, however, regular wave analysis is typically used to determine flexible response. This approach considers the maximum wave within a design storm at a desired period; the choice of periods may leave room for uncertainty in the conservatism of the approach. With proper screening, regular wave analysis can be a valid yet overly conservative approach resulting in over design and additional cost. However, if screened incorrectly, there is a possibility that the choice of periods could give results that are under conservative. In addition to regular wave analysis, the paper presents two alternative methodologies to determine the most likely response, with the focus on reducing the computational resources required. The first alternative is an ‘Irregular Wave Screen’ approach in which the wave train is screened at areas of interest for waves within a user defined threshold of the maximum wave height, in addition to other user defined parameters. Only waves within these parameters are simulated to determine responses. The second alternative is the ‘New Wave’ approach, which models the most probable wave elevation around the maximum wave crest. The calculated new wave is then placed at the desired location to determine responses. The responses of the Regular, Irregular Wave Screen and New Wave methodologies are compared with the Irregular MPM approach to determine their feasibility to predict the response of flexibles in a real world irregular sea state with lower computational requirements.

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.

scholarly journals LABORATORY STUDY ON TWO-DIMENSIONAL BEACH TRANSFORMATION DUE TO IRREGULAR WAVES

1986 ◽  
Vol 1 (20) ◽  
pp. 102 ◽  
Author(s):  
Nubuo Mimura ◽  
Yukinori Otsuka ◽  
Akira Watanabe
Keyword(s):  
Wave Train ◽  
Irregular Waves ◽  
Two Dimensional ◽  
Beach Profile ◽  
Irregular Wave ◽  
Sand Ripple ◽  
Ripple Formation ◽  
Sand Movement ◽  
Incident Waves ◽  
Profile Change

In the present study, effects of irregular waves on two-dimensional beach transformation and related phenomena were investigated through a series of laboratory experiments. Attempts were made to determine a representative wave of irregular wave trains which controlled individual phenomenon related to the two-dimensional beach profile change. It was found that the representative wave is different for each phenomenon. For the macroscopic beach profile change, it is the mean wave which represents whole incident waves. On the other hand, some of microscopic phenomena, such as initiation of sand movement and sand ripple formation, are controlled by larger waves in the wave train selectively, of which representative wave is the significant wave.

A Study for Statistical Characteristics of Riser Response in Global Dynamic Analysis With Irregular Wave

2014 ◽  
Author(s):  
Yanqiu Zhang ◽  
Zhimin Tan ◽  
Yucheng Hou ◽  
Jiabei Yuan
Keyword(s):  
Dynamic Simulation ◽  
Wave Train ◽  
Time History ◽  
Irregular Waves ◽  
Statistical Characteristics ◽  
Normal Process ◽  
Autocorrelation Functions ◽  
Irregular Wave ◽  
Global Dynamic ◽  
Time Histories

A study was conducted to have a deeper understanding to the statistical characteristics of response of flexible riser in global dynamic simulation with irregular wave. If consider the numerical simulation model as a system and the input wave train as an excitation to it, the time histories of riser load should be the response of the system to the excitation. In order to look the effect of riser configuration and water depth, the study was conducted with three kinds of configuration: Free-Hanging, Lazy-S and Tethered-Wave, which were in different water depths. In order to examine the stationarity and ergodicity of riser response, 100 simulations were performed. Each simulation was performed with a 3-hours-long storm. Except the seeds used to generate the random phases to the wave components, the 100 irregular wave processes for each riser are completely the same. When the number of wave components is enough large, the input irregular wave train should be a stationary normal process. Since the software used for the dynamic simulation is high nonlinear, however, the time history of riser response may not be perfectly stationary normal process. Then different probability distribution theories were applied to fit these time histories and the most fitting one was found out for different riser responses and for different riser configurations. The ensemble autocorrelation functions and the time autocorrelation functions were also examined for both irregular waves and the riser responses. Then the study indicated that both irregular waves and riser responses as random processes should be ergodic stationary. Finally the cross correlations between the irregular waves and riser responses were also examined and it was found that the irregular wave for each riser should be jointly stationary with each response of the riser.

Numerical Simulation of Flows Past Partially-Submerged Horizontal Circular Cylinders in Free Surface Waves

2013 ◽  
Author(s):  
Hans Bihs ◽  
Muk Chen Ong
Keyword(s):  
Free Surface ◽  
Surface Waves ◽  
Wave Theory ◽  
Circular Cylinders ◽  
Navier Stokes ◽  
Wave Forces ◽  
Linear Wave ◽  
Numerical Wave Tank ◽  
Linear Wave Theory ◽  
Free Surface Waves

Two-dimensional (2D) numerical simulations are performed to investigate the flows past partially-submerged circular cylinders in free surface waves. The 2D simulations are carried out by solving the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with the k-ω turbulence model. The level set method is employed to model the free-surface waves. Validation studies of a numerical wave tank have been performed by comparing the numerical results with the analytical results obtained from the linear-wave theory. Wave forces on the partially-submerged cylinders have been calculated numerically and compared with the published theoretical and experimental data under regular-wave conditions. The free-surface elevations around the cylinders have been investigated and discussed.

Calculation of Wave Forces Acting on a Cylinder With a Porous Plate Fixed Inside

2009 ◽  
Author(s):  
Weiguang Bao ◽  
Fenfang Zhao ◽  
Takeshi Kinoshita
Keyword(s):  
Body Surface ◽  
Porous Body ◽  
Porous Plate ◽  
Wave Theory ◽  
Wave Forces ◽  
Linear Wave ◽  
Normal Velocity ◽  
Wave Loads ◽  
Eigen Values ◽  
Eigen Function

To evaluate wave forces and to estimate the motion of breakwater, a circular cylinder is investigated based on the linear wave theory in the present work. The cylinder possesses a porous sidewall, an impermeable bottom and a horizontal porous plate inside that is fixed in the cylinder to work as obstruct and make wave dissipation more effectively. To simplify the problem, the Darcy’s fine-pore model is applied to the boundary condition on the porous body surface. The boundary value problem is solved by means of the eigen-function expansion approach. The fluid domain is divided into three regions and different eigen-function series are used. The so-called dispersion relation for the region inside the cylinder is quite different from a conventional one due to the existence of the porous plate. It leads to eigen values of complex number. To obtain solutions for the radiation problems, particular solution should be constructed to take account of the normal velocity appearing on the porous boundary. The wave loads are evaluated by integrating the pressure difference on two sides of the wetted body surface. The theoretical works are in good consistence with the experimental results. The Haskind relations are examined for the porous body. It is found that the damping coefficient consists of two parts. In addition to the component of conventional wave-radiating damping, exists a second component caused by the porous effects.

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