Irregular Wave Simulation and its Impact on Riser Extreme Response for a Production Semi

2020 ◽  
Author(s):  
Shaosong Zhang ◽  
Yongming Cheng ◽  
Yuanlang Cai ◽  
Ning He ◽  
Xiaolong Yang ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Wave Spectrum ◽  
Irregular Waves ◽  
Wave Crest ◽  
Multiple Time ◽  
Irregular Wave ◽  
Wave Simulation ◽  
Extreme Response ◽  
Individual Wave ◽  
Wave Properties

Abstract Steel Catenary Risers (SCRs) are widely used in deepwater and ultra-deepwater field developments. The dynamic strength of SCRs is a concern in terms of the global performance. The analysis results are quite scattered in many cases due to the nature of the irregular wave stochastic properties. The widely accepted approach to predict the riser dynamic response in the irregular seas is to run the multiple time domain simulations based on different random seeds. This paper will address the impacts on the predicted riser dynamic response due to the random seeds selection. The discussion is based on the independent engineering verification work for a production Semi project in South China Sea. The site specific irregular waves are usually defined by not only the wave spectrum, but also the properties of individual waves, such as maximum wave height and minimum wave trough, which have big impacts on the riser extreme response. The code recommended approach for irregular wave simulation is based on the linear wave theory, which can ensure the match of the target wave spectrum, for example, Hs, Tp (or Tz), wave peakness for JONSWAP spectrum. But the variation of simulated individual wave properties to the specified value can be significant or there is no specified value to match. The simulated irregular waves based on linear theory is also a distortion to the real wave elevation time trace, such as the asymmetry of the wave crest and trough, especially for the tropical cyclone sea states. Some riser response, such as the compression load at riser touch down zone, can be significantly impacted by the nonlinear nature of the waves and the variation to the target individual wave properties. This paper will discuss the random wave simulation and its impacts on riser dynamic response. A SCR strength design case is presented for illustration in this paper. Key parameters are identified to show the correlation with the SCR dynamic response. The conclusion is finally drawn from the work presented in this paper.

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 Monitoring Individual Wave Characteristics in the Inner Surf with a 2-Dimensional Laser Scanner (LiDAR)

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Kévin Martins ◽  
Chris E. Blenkinsopp ◽  
Jun Zang
Keyword(s):  
Wave Spectrum ◽  
Laser Scanner ◽  
Correlation Technique ◽  
Swash Zone ◽  
Threshold Method ◽  
Individual Wave ◽  
Nearshore Waves ◽  
The Individual ◽  
Cross Correlation Technique ◽  
Wave Properties

This paper presents an investigation into the use of a 2-dimensional laser scanner (LiDAR) to obtain measurements of wave processes in the inner surf and swash zones of a microtidal beach (Rousty, Camargue, France). The bed is extracted at the wave-by-wave timescale using a variance threshold method on the time series. Individual wave properties were then retrieved from a local extrema analysis. Finally, individual and averaged wave celerities are obtained using a crest-tracking method and cross-correlation technique, respectively, and compared with common wave celerity predictors. Very good agreement was found between the individual wave properties and the wave spectrum analysis, showing the great potential of the scanner to be used in the surf and swash zone for studies of nearshore waves at the wave-by-wave timescale.

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.

Numerical Modeling Using CFD and Potential Wave Theory for Three-Hour Nonlinear Irregular Wave Simulations

2017 ◽  
Author(s):  
Aldric Baquet ◽  
Jang Kim ◽  
Zhenjia (Jerry) Huang
Keyword(s):  
Numerical Modeling ◽  
Potential Theory ◽  
Wave Spectrum ◽  
Nonlinear Effects ◽  
Wave Theory ◽  
Breaking Waves ◽  
Wave Crest ◽  
Fully Nonlinear ◽  
Irregular Wave ◽  
Stokes Waves

In this paper, we focus on the modeling of a fully-nonlinear, steep, irregular wave field of three-hour duration without structures in it. The fully-nonlinear effects are considered in the wave simulations using computational fluid dynamics (CFD), as well as potential theory. The overall approach for the numerical modeling is described in the paper. The Euler Overlay Method (EOM) is used to incorporate incoming waves, nonlinear effects, and CFD simulations in the numerical modeling. For computational efficiency, we also use potential theory to model the fully-nonlinear waves. Numerical damping was applied locally around the breaking region to enable simulations for large breaking waves. To compensate for energy loss in the numerical simulations, energy compensation factors of wave spectral frequency components are applied to the input wave spectrum. Results of convergence study, validation against high-order Stokes waves and fully-nonlinear irregular wave with prescribed target spectrum, as well as comparison between numerical wave crest distributions and those from multiple realizations of wave calibration tests are presented.

High frequency resonant response of a monopile in irregular deep water waves

2018 ◽  
Vol 853 ◽  
pp. 564-586 ◽  
Author(s):  
Bjørn Hervold Riise ◽  
John Grue ◽  
Atle Jensen ◽  
Thomas B. Johannessen
Keyword(s):  
Resonance Frequency ◽  
Deep Water ◽  
Water Waves ◽  
Irregular Waves ◽  
Breaking Wave ◽  
Wave Load ◽  
Irregular Wave ◽  
The Third ◽  
Extreme Response ◽  
Wave Slope

Experiments with a weakly damped monopile, either fixed or free to oscillate, exposed to irregular waves in deep water, obtain the wave-exciting moment and motion response. The nonlinearity and peak wavenumber cover the ranges: $\unicode[STIX]{x1D716}_{P}\sim 0.10{-}0.14$ and $k_{P}r\sim 0.09{-}0.14$ where $\unicode[STIX]{x1D716}_{P}=0.5H_{S}k_{P}$ is an estimate of the spectral wave slope, $H_{S}$ the significant wave height, $k_{P}$ the peak wavenumber and $r$ the cylinder radius. The response and its statistics, expressed in terms of the exceedance probability, are discussed as a function of the resonance frequency, $\unicode[STIX]{x1D714}_{0}$ in the range $\unicode[STIX]{x1D714}_{0}\sim 3{-}5$ times the spectral peak frequency, $\unicode[STIX]{x1D714}_{P}$. For small wave slope, long waves and $\unicode[STIX]{x1D714}_{0}/\unicode[STIX]{x1D714}_{P}=3$, the nonlinear response deviates only very little from its linear counterpart. However, the nonlinearity becomes important for increasing wave slope, wavenumber and resonance frequency ratio. The extreme response events are found in a region where the Keulegan–Carpenter number exceeds $KC>5$, indicating the importance of possible flow separation effects. A similar region is also covered by a Froude number exceeding $Fr>0.4$, pointing to surface gravity wave effects at the scale of the cylinder diameter. Regarding contributions to the higher harmonic forces, different wave load mechanisms are identified, including: (i) wave-exciting inertia forces, a function of the fluid acceleration; (ii) wave slamming due to both non-breaking and breaking wave events; (iii) a secondary load cycle; and (iv) possible drag forces, a function of the fluid velocity. Also, history effects due to the inertia of the moving pile, contribute to the large response events. The ensemble means of the third, fourth and fifth harmonic wave-exciting force components extracted from the irregular wave results are compared to the third harmonic FNV (Faltinsen, Newman and Vinje) theory as well as other available experiments and calculations. The present irregular wave measurements generalize results obtained in deep water regular waves.

Response of guyed tower to irregular waves for linear and nonlinear behaviour of mooring cables

1985 ◽  
Vol 12 (1) ◽  
pp. 200-212 ◽  
Author(s):  
Momen A. Wishahy ◽  
M. Arockiasamy
Keyword(s):  
Finite Element ◽  
Dynamic Response ◽  
Time History ◽  
Element Model ◽  
Irregular Waves ◽  
Wave Forces ◽  
Beam Model ◽  
Nonlinear Behaviour ◽  
Irregular Wave ◽  
Linear And Nonlinear

The dynamic response of a guyed tower to irregular waves has been studied by the finite element method. Hydrodynamic interaction is taken into account by the added water mass concept, and the fundamental frequencies are determined using (i) a lumped-parameter two-dimensional beam model and (ii) a three-dimensional truss finite element model. The effect of the mooring guy lines is simulated using one-dimensional boundary elements. The example structure analyzed is the Exxon test guyed tower erected in water of 89.3 m depth in the Gulf of Mexico. The measured wave height – time history reported by Exxon is used to determine the wave forces. Irregular wave forces are computed using the linearized Morison's equation. The nonlinearity of the mooring system is computed using an iterative technique in which the cable configuration is corrected using successive solutions. The tower response in terms of offset-time history to wave forces is determined for both linear and nonlinear cable behaviour. The computed frequencies and the responses agree reasonably well with the available measured values. Key words: guyed tower, irregular wave forces, linear and nonlinear mooring cable stiffness, dynamic response.

scholarly journals DECOMPOSITION OF NONLINEARLY REFLECTED IRREGULAR WAVES BY THE WAVE BREAKING AND DEFORMATION

1986 ◽  
Vol 1 (20) ◽  
pp. 31
Author(s):  
A. Kimura
Keyword(s):  
Reflection Coefficient ◽  
Wave Spectrum ◽  
Standing Waves ◽  
Wide Band ◽  
Irregular Waves ◽  
Band Spectrum ◽  
Reflected Waves ◽  
Irregular Wave ◽  
Effective Wave ◽  
Incident Waves

This paper deals with a new method to decompose incident and reflected waves from the measured data of irregular standing waves. The theory by Goda et al. is extended to cope with the reflection from such a coastal structure that has a sloping surface and brings about different reflection coefficient for each incident waves. Irregular standing waves are decomposed into incident and reflected irregular waves by the shortterm wave spectrum analysis method. And the reflection coefficient of the approximated zero-up-cross waves are defined as the ratio between envelopes of these irregular wave profiles. The calculated reflection coefficients can be discussed in terms of the incident zero-up-cross wave parameters such as a wave steepness, Ursell parameter, etc. An effective wave gauge system to measure irregular standing waves which have a wide band spectrum is also discussed and a method to compose the system is proposed.

Irregular Wave Simulation and Its Impact on Riser Extreme Response for a Production Semi

2021 ◽  
Author(s):  
Shaosong Zhang ◽  
Yongming Cheng ◽  
Yuanlang Cai ◽  
Ning He ◽  
Zhi Cao ◽  
...  
Keyword(s):  
Irregular Wave ◽  
Wave Simulation ◽  
Extreme Response

Methodology for Disconnect Analysis of CWO Risers in Random Seas

2009 ◽  
Author(s):  
Guttorm Grytoyr ◽  
Anne Marthine Rustad ◽  
Nils Sodahl ◽  
Per Christian Bunaes
Keyword(s):  
Wave Height ◽  
Irregular Waves ◽  
Regular Wave ◽  
Irregular Wave ◽  
Wave Approach ◽  
Random Seas ◽  
Extreme Response ◽  
Industry Practice ◽  
Operating Window

The term ‘riser recoil’ refers to the situation when the lower end of a top tensioned riser is released, and the riser is lifted up by the riser tensioner and/or top motion compensator system on the supporting vessel. The elastic energy stored in the riser is then released, and the riser ‘recoils’. This paper focuses on the case of planned disconnect. Recoil of Marine Drilling Risers has been the subject of several research papers over the past two decades. Some examples are listed in references [2] through [7]. Completion and Work Over (CWO) risers are unique in the sense that they may be simultaneously connected to both the riser tensioner system and the top motion compensator system of a drilling vessel. A Marine Drilling riser, on the other hand, is only connected to the riser tensioner system. Typically the riser tensioner system has a stroke of ± 8–9 m, whereas the top motion compensator system has only ± 3.5–4 m. It is imperative that the connector is lifted clear of the subsea structure in order to avoid damage to the equipment after the riser has been disconnected. The operating window for planned disconnect of CWO risers is severely limited by the available stroke of the top motion compensator. One of the purposes of the disconnect analysis is to establish the maximum wave height at which there is still sufficient clearance between the connector and the subsea structure after disconnect. Previous experience has shown that this may be the governing limitation for workover operations. The current industry practice is to use a regular wave approach in the analysis. The wave frequency is varied in order to find the maximum response, and hence one is actually searching for the extreme response, without paying attention to the probability that this will occur. In this paper a new method is presented, where the analysis is based on an irregular wave approach and the Monte Carlo technique, using time-domain simulations. Acceptance criteria are established based on a stochastic analysis, and are based on target levels of probability of exceedance. The results are documented through a case study of a typical CWO riser system connected to a semi-submersible in typical North Sea environmental conditions. The semi-submersible and the CWO riser system are exposed to both regular and irregular waves. Comparison of the resulting allowable wave height indicates that using the approach presented here with irregular waves will give a considerable increase in the operating window, and the resulting operability, compared to a regular wave analysis.

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.

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