On the Effects of Non-Gaussian Wave-Slope Distribution on the Failure Probability of an Armour block of Rubble Mound Breakwater

Cho, Yong Jun

doi:10.20481/kscdp.2021.8.3.165

Cited by 6 publications

(2 citation statements)

References 11 publications

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Section: Introductionmentioning

confidence: 99%

Reliability-Based Design Optimization for a Vertical-Type Breakwater with Multiple Limit State Equations under Korean Marine Environments varying from Sea to Sea

Cho

2024

Preprint

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In this study, as part of basic research aimed at enhancing the accuracy of load- and resistance coefficients to ensure their suitability for practical design and promoting the application of underutilized reliability-based design in Korea, the author conducts optimal design based on the reliability analysis of a vertical-type breakwater in the seas off Haeundae, Yeosu, Mokpo, Gunsan, and Incheon – representative ports in Korea. In doing so, the author utilized the double-loop approach that solves simultaneously a reliability problem nested in an optimization process. To alleviate the extremely large numerical efforts demanded in the double-loop approach, the Subset Simulation method was employed. In this process, the author deliberately refrained from using design waves of a specific return period and linear probabilistic models such as Gaussian distribution, especially concerning wave- and lift forces, often viewed as barriers to the widespread application of reliability-based design in Korea. Instead, the author focused on characterizing the uncertainties associated with wave force, lift force, and overturning moment —variables that significantly impact the integrity of vertical-type breakwaters- by developing probabilistic models for these random variables directly from long-term in-situ wave data, which captures the varied characteristics of the Korean marine environment from sea to sea. The limit state of the vertical-type breakwater was defined to encompass sliding, overturning, and collapse failures, and the strong interrelation between wave force, lift force, and overturning moment was described using the Nataf joint probability distribution. As anticipated, simulation results show that solely considering sliding failure, as in the current reliability-based design platform in Korea, leads to an underestimated failure probability. Furthermore, it becomes evident that ensuring a consistent failure probability for vertical-type breakwaters using design waves with a specific return period, as in past studies, is not feasible. In contrast, this study demonstrates that breakwaters optimally designed to meet the reliability index requirement of β-3.5 to 4 consistently maintain a target failure probability in all sea areas.

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Section: Introductionmentioning

confidence: 99%

Reliability-Based Design Optimization for a Vertical-Type Breakwater with Multiple Limit State Equations under Korean Marine Environments varying from Sea to Sea

Cho

2024

Preprint

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“…These variables, such as wave force, lift force, tidal level, friction coefficient, and overturning moment, significantly impact the structural integrity of vertical-type breakwaters (refer to Fig. 1 ) 9 – 13 . While of great importance, the current reliability-based design platform in Korea frequently relies on linear probabilistic models, such as the Gaussian distribution, particularly when dealing with wave and lift forces.…”

Section: Introductionmentioning

confidence: 99%

Reliability-based design optimization for a vertical-type breakwater with multiple limit-state equations under Korean marine environments varying from sea to sea

Cho

2024

Sci Rep

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In this study, as part of basic research aimed at enhancing the accuracy of load and resistance coefficients to ensure their suitability for practical design and promoting the application of underutilized reliability-based design in Korea, the author conducts optimal design based on the reliability analysis of a vertical-type breakwater in the seas off of Haeundae, Yeosu, Mokpo, Gunsan, and Incheon—representative ports in Korea. In doing so, the author utilized the double-loop approach, which simultaneously addresses a reliability problem nested within an optimization process, employing the Polak–He optimization algorithm. To mitigate the substantial numerical effort required by the double-loop approach based on the Polak–He optimization algorithm, which necessitates the gradients of both cost and constraint functions, the subset simulation method was employed. In this process, the author deliberately refrained from using design waves of a specific return period and linear probabilistic models such as the Gaussian distribution, especially concerning wave and lift forces, often viewed as barriers to the widespread application of reliability-based design in Korea. Instead, the author focused on characterizing the uncertainties associated with the wave force, lift force, and overturning moment—variables that significantly impact the integrity of vertical-type breakwaters—by developing probabilistic models for these random variables directly from long-term in situ wave data. These models capture the varied characteristics of the Korean marine environment from sea to sea. In this way, the need for additional assumptions concerning the interrelationship between significant wave and maximum wave heights, along with the wave period, can be eliminated. Following Occam's razor principle, which suggests that explanations constructed with the smallest possible set of assumptions are superior, the reliability-based design optimization of a vertical-type breakwater presented in this study demonstrates promise in terms of simplicity and practicality. The limit state of the vertical-type breakwater was defined to encompass sliding, overturning, and collapse failures, and the strong interrelations between the wave force, lift force, and overturning moment were described using the Nataf joint distribution. As anticipated, simulation results show that solely considering sliding failure, as in the current reliability-based design platform in Korea, leads to an underestimated failure probability. Furthermore, ensuring a consistent failure probability for vertical-type breakwaters using design waves with a specific return period, as in past studies, is not feasible. In contrast, this study demonstrated that breakwaters optimally designed to meet the reliability index requirement of β = 3.5–4 consistently maintain a target failure probability in all sea areas.

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Preliminary Study on an amendment to the Design Guideline of Outer Port Facilities Against Harsh Wave Conditions due to Climate Change based on Design Fidelity Index

Cho¹,

Cho²

2022

J Coast Disaster Prev

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This study aims to develop an amendment to the design guidelines for the outer port facilities based on quantitative indexes to address harsh wave conditions due to climate change. To this end, the author first looked into the in situ data of damage to outer port facilities collected in about a dozen major ports in Korea, where the outer port facility has failed in fulfilling its intended disaster prevention against typhoons over the last decade. In doing so, the design fidelity index, a quantitative index that can rationally determine the scope of reinforcement of outer port facilities, was developed based on the specified failure mechanism. The design fidelity index evaluates the degree of loss of armoring rocks, erosion of main body of breakwater, displacement of cap-concrete, lee side damage by overtopping, and scouring near the toe, which are the primary failure mode of the outer port facilities, and displays these damage extents of each of 5 primary failure mode in polar coordinates. Among the various failure modes mentioned above, scouring near the toe has been found in most outer port facilities, and as a result, the current design practice like whether to install scouring-prevention work is determined based on the limit depth for the incipient sediment motion needs to be revised. Numerical simulation shows that with sediment motion triggered by harsh water surface displacement in the standing waves formed in front of vertical type breakwater being accounted for, the robustness of scouring prevention works, which takes the maximum scour depth as the maximum wave height, could be secured. In addition, among the various quantitative indexes that can provide information concerned with how robust or vulnerable the outer port facilities would be by adjusting design waves return period, it turns out that the increasing rate of failure probability associated with the unit change in the nominal diameter of armoring rocks could provide most promising results.

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On the Effects of Non-Gaussian Wave-Slope Distribution on the Failure Probability of an Armour block of Rubble Mound Breakwater

Cited by 6 publications

References 11 publications

Reliability-Based Design Optimization for a Vertical-Type Breakwater with Multiple Limit State Equations under Korean Marine Environments varying from Sea to Sea

Reliability-Based Design Optimization for a Vertical-Type Breakwater with Multiple Limit State Equations under Korean Marine Environments varying from Sea to Sea

Reliability-based design optimization for a vertical-type breakwater with multiple limit-state equations under Korean marine environments varying from sea to sea

Preliminary Study on an amendment to the Design Guideline of Outer Port Facilities Against Harsh Wave Conditions due to Climate Change based on Design Fidelity Index

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