Probabilistic Modelling of Extreme Offshore Structural Response due to Random Wave Loading

Wang, Y.; Mallahzadeh, H.; Husain, M. K. Abu; Zaki, N. I. Mohd; Najafian, G.

doi:10.1115/omae2013-10905

Cited by 7 publications

(6 citation statements)

References 8 publications

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“…Both effective water depth and node elevation are trailed to vary by 12% and 13%, respectively. A similar observation can be made when an analysis was made at lower significant wave heights; however, referring to Table 2, the difference is not as critical as at high significant wave heights [34]. In the analysis where a negative current loading was considered, the magnitude of -0.9m/s was incorporated.…”

Section: Effect Of Current Loading On 100-year Extreme Structural Resmentioning

confidence: 52%

“…Further observation of the results shows that although it has a lower magnitude of simulated extreme responses, the results lead to the highest percentage difference. This can be clearly seen as vertical stretching has significantly differed from Wheeler stretching in the range of 26% to 83% difference in magnitude of extreme responses, throughout 5m, 10m and 15m of significant wave heights [34]. Figure 9 represents the probability distribution of extreme base shear simulated at a critical wave height of 15 m. A similar observation can be made for this current condition as in the no current and positive current conditions, where vertical stretching has the highest distribution of extreme base shear and followed by the two effective methods.…”

Section: Effect Of Current Loading On 100-year Extreme Structural Resmentioning

confidence: 94%

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Various methods of simulating wave kinematics on the structural members of 100-year responses

Husain¹,

Zaki²,

Najafian³

2017

J. MECH. ENG. SCI.

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The main force acting on an offshore structure is usually due to wind-generated random waves. According to the Morison equation, the wave force on a cylindrical member of an offshore structure depends on wave kinematics at the centre of the element. It is therefore essential to accurately estimate the magnitude of wave-induced water particle kinematics at all points in a random wave field. Linear random wave theory (LRWT) is the mostfrequently used theory to simulate water particle kinematics at different nodes of an offshore structure. Several empirical techniques have been suggested to provide a more realistic representation of the near-surface wave kinematics. The empirical techniques popular in the offshore industry include Wheeler stretching and vertical stretching. Most recently, two new effective methods (effective node elevation and the effective water depth) have been recently introduced. The problem is that these modified methods differ from one another in their predictions. Hence, the aim of this study is to investigate the effects of predicting the 100-year responses from various methods of simulating wave kinematics accounting for the current effect. In this paper, four versions of the wave kinematics procedure have been tested by comparing the short-term probability distributions of extreme responses. For all current cases, the highest vertical ratios for zero, positive and negative current cases are 1.414, 1.175 and 1.831, respectively. It is observed that even for positive-current cases, the difference between Wheeler and vertical stretching predictions is quite high and cannot be neglected. Thus, further investigation is necessary to resolve this problem and the outcomes in providing useful design information for the oil and gas industry.

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Section: Effect Of Current Loading On 100-year Extreme Structural Resmentioning

confidence: 52%

Section: Effect Of Current Loading On 100-year Extreme Structural Resmentioning

confidence: 94%

Various methods of simulating wave kinematics on the structural members of 100-year responses

Husain¹,

Zaki²,

Najafian³

2017

J. MECH. ENG. SCI.

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“…As many as 100,000 simulated extremes of surface elevation has been simulated to verify the results from the short-term response analysis for 3 hours. Wang et al [24] used the Gumbel distributions for modelling of extreme responses by comparing them with empirical distributions derived from extensive Monte Carlo time simulations. In this study, the Gumbel distribution would be also considered to predict an accurate estimate for 100-year the extreme value of surface elevation.…”

Section: Methodsmentioning

confidence: 99%

Comparison of Various Spectral Models for the Prediction of the 100-Year Design Wave Height

et al. 2018

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Offshore structures are exposed to random wave loading in the ocean environment, and hence the probability distribution of the extreme values of their response to wave loading is required for their safe and economical design. In most cases, the dominant load on offshore structures is due to wind-generated random waves where the ocean surface elevation is defined using appropriate ocean wave energy spectra. Several spectral models have been proposed to describe a particular sea state that is used in the design of offshore structures. These models are derived from analysis of observed ocean waves and are thus empirical in nature. The spectral models popular in the offshore industry include Pierson-Moskowitz spectrum and JONSWAP spectrum. While the offshore industry recognizes that different methods of simulating ocean surface elevation lead to different estimation of design wave height, no systematic investigation has been conducted. Hence, the aim of this study is to investigate the effects of predicting the 100-year responses from various wave spectrum models. In this paper, the Monte Carlo time simulation (MCTS) procedure has been used to compare the magnitude of the 100-year extreme responses derived from different spectral models. Additionally, the linear random wave theory (LRWT) was implemented to simulate the offshore structural responses due to random wave loading. The models have been tested for three different environmental conditions represented by Hs = 15m, 10m and 5m respectively. The accuracy of the predictions of the 100-year responses from Pierson-Moskowitz and JONSWAP spectrums will then be investigated.

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“…A systematic technique to calculate all statistical data associated to uncertainties is a probabilistic analysis method [67][68][69][70]. Because of its capability on uncertainty, probabilistic analysis is suitable for simulating wave characteristics related to randomness mechanisms such as geometry, material properties, and measurement (i.e., wave load-induced responses) [71][72][73].…”

Section: Probabilistic Approaches For Fixed Offshore Structural Response Analysesmentioning

confidence: 99%

Offshore Structural Reliability Assessment by Probabilistic Procedures—A Review

Ahmad

Husain²,

Zaki³

et al. 2021

JMSE

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Offshore installations must be built to resist fatigue as well as extreme forces caused by severe environmental conditions. The structural reliability analysis is the popular practise to assess a variety of natural waves determined by the long-term probability distribution of wave heights and corresponding periods on the site. In truth, however, these structures are subjected to arbitrary wave-induced forces in the open ocean. Hence, it is much more reasonable to account for the changed loading characteristics by determining the probabilistic characteristics of the random loads and outcomes responses. The key challenges are uncertainties and the non-linearity of Morison’s drag element, which results in non-Gaussian loading and response distributions. This study would analyze advances achieved to date in a comprehensive probabilistic review of offshore fixed jacket-type platforms.

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Probabilistic Modelling of Extreme Offshore Structural Response due to Random Wave Loading

Cited by 7 publications

References 8 publications

Various methods of simulating wave kinematics on the structural members of 100-year responses

Various methods of simulating wave kinematics on the structural members of 100-year responses

Comparison of Various Spectral Models for the Prediction of the 100-Year Design Wave Height

Offshore Structural Reliability Assessment by Probabilistic Procedures—A Review

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