Predicting the stability of armor blocks placed on breakwaters is one of the main challenges in coastal and ocean engineering. However, the armor layer’s damage mechanism is very complicated so that ...there are many uncertainties in the estimation of different parameters in armor design. The inherent uncertainties in these parameters necessitate reliability analysis to ensure the stability of the breakwaters. This study proposed a reliability-based framework for estimating the rock armors weight based on the probabilistic analysis. The effect of different sources of uncertainties in determining effective parameters such as wave height, wave period, water-level changes and armor density was introduced and applied in calculating rock armors weight. Moreover, the correlations between breakwater life span, its probability of failure and stable armor weight were also considered in the analysis. Based on this method, armor weight could be computed according to any desired reliability level and breakwater life span. Results of sensitivity analysis showed that the most critical parameters affecting the reliability of armor weight are wave height and dimensionless damage level. Finally, the presented case study in this article addressed the use of this method in the design of armor weight for a breakwater constructed in the southern part of the Caspian Sea. Results showed that the stable armor weight to maintain a probability of failure equal to 0.005 placed on a breakwater with 50-year life span under a 100-year design storm condition in the Caspian Sea is about 24.28 ton. Moreover, by increasing the breakwater life span from 50 to 100 years, the armor weight increases only by about 10%.
Slope stability formulae for rubble mound structures are usually developed for head-on conditions. Often, the effects of oblique waves are neglected, mainly because it is assumed that for oblique ...wave attack, the reduction in damage compared to perpendicular wave attack is insignificant. When the incident waves are oblique, the required armour size can be reduced compared to the perpendicular wave attack case. Therefore, it is important to consider the wave obliquity influence on slope stability formulae as a reduction factor. One of the most recent formulae for estimating the stability of rock-armoured slopes, referred to as Etemad-Shahidi et al. (2020), was proposed for perpendicular wave attack. The aim of this study is to develop a suitable wave obliquity reduction factor for the above-mentioned stability formula. To achieve this, first, laboratory experiment datasets from existing reliable studies were selected and analysed. Then, previously suggested reduction factors were evaluated and a suitable reduction factor for the mentioned stability formula were suggested. The suggested reduction factor includes the effect of wave obliquity and directional spreading explicitly. It is shown that the stability prediction is improved by using the wave obliquity reduction factor.
The present study was carried out in order to study the effective parameters on the secondary circulation and maximum values of the transverse velocity in river bends using a 3D numerical model. To ...this end, a total of 569 numerical tests were then performed to investigate the effect of different parameters, namely bed friction, bend angle and channel geometry including relative width (channel width/bend radius,
B
/
R
) and relative depth (water depth/bend radius,
H
/
R
) on Secondary circulation over a wide range of flow conditions. The results obtained from the numerical model were validated using the collected data sets from three distinct experiments according to which two equations for prediction of the maximum values of transverse velocity at the water surface and near the channel bed of the river bends were proposed. According to the obtained results, the increment of the
B
/
R
ratio results in higher transverse velocity both at the water surface (
v
ns(max)
) and near the channel bed (
v
nb(max)
). The
v
ns(max)
near the surface varying with the
H
/
R
ratio follows an incremental trend up to a critical relative depth (
H
/
R
)
scr
, after which the transverse velocity is decreased. Similarly, a critical relative depth (
H
/
R
)
bcr
exists near the channel bed. However, the
v
nb(max)
remains almost constant after (
H
/
R
)
bcr
. According to the obtained results, the greater the relative width, bed friction and bend angle, the higher the critical relative depth in the surface and the bed of the channel.
Predicting the lateral confinement coefficient in reinforced concrete columns is a very important issue in structural engineering. Therefore, several experimental formulas have developed to predict ...it. Recently, soft computing tools such as artificial neural networks have been used to predict the confinement coefficient. However, these tools are not as transparent as empirical formulas. In this study, another soft computing approach, i.e. model trees have been used for predicting the confinement coefficient. The main advantage of model trees is that, unlike the other data learning tools, they are easier to use and more importantly they represent understandable mathematical rules. In this paper, a new formula that includes some structural parameter is derived using dimensionless parameter for estimating the confinement coefficient. A comparison is made between the estimated confinement coefficient by this new formula and formula given by others researches shows the accuracy of prediction.
The prediction of rubble mound breakwaters' stability is one of the most important issues in coastal and maritime engineering. The stability of breakwaters strongly depends on the wave height. ...Therefore, selection of an appropriate wave height parameter is very vital in the prediction of stability number. In this study,
H
50, the average of the 50 highest waves that reach the breakwater in its useful life, was used to predict the stability of the armor layer. First,
H
50 was used instead of the significant wave height in the most recent stability formulas. It was found that this modification yields more accurate results. Then, for further improvement of the results, two formulas were developed using model tree.
To develop the new formulas, two experimental data sets of irregular waves were used. Results indicated that the proposed formulas are more accurate than the previous ones for the prediction of the stability parameter. Finally, the proposed formulas were applied to regular waves and a wide range of damage levels and it was seen that the developed formulas are applicable in these cases as well.
Offshore platforms have become lucrative in the oil and gas industries due to their capabilities, which are exposed to harsh environmental hazards that affect the Structural Integrity.
The scope of ...this study represents a risk assessment strategy for evaluating the structural integrity and proposed a framework for the Risk-Based Underwater Inspection to implement Structural Integrity Management for a fixed offshore jacket platform.
The jacket platform is adopted for the Non-linear Quasi-Static Analysis (Push-over) using relevant code criteria. Regarding the required site-specific meteorological and oceanographic parameters, wave is simulated using WAVEWATCH III, third-generation version 4.18, considered input data and uncertain parameters.
The Long-Term Load Distribution parameters are localized to determine the Probability of Failure due to the extreme wave loading action, and the platform structural damage rate is obtained by referring to the latest available underwater inspection carried out in the understudied oilfield. Moreover, the platform's structural failure may lead to safety, environmental, and economic impacts, which are the essential factors for evaluating the Consequence of Failure.
Finally, the risk level is estimated by ranking the Probability and Consequences of Failure in the risk matrix, and resulting from the risk analysis, the framework for the Risk-Based Underwater Inspection is carried out.
•Wave is Simulated using WAVEWATCH III to acquire the Metocean Data.•Platform is exposed to Extreme Environmental Loads to estimate Failure Probability.•The Long-Term Load Distribution parameter is localized for the studied region.•Members' Damage Probability is derived from Underwater Inspection in the Oilfield.•Consequence of Failure considers Safety, Environmental, and Economic impacts.
Estimation of the required armor size is a major task in the design of coastal structures under wave loading such as breakwaters and revetments. Several semi-empirical formulas have been developed ...for this purpose. However, these formulas are often either limited to certain water depth conditions or do not incorporate the permeability of the structure in an appropriate way. The main objectives of this study are to (a) develop a unified physically sound formula for the estimation of the required rock size in all relevant water depth conditions and (b) to relate the effects of the permeability of the structure directly to physical parameters. To achieve these, first a comprehensive data base of deep and shallow water experiments within the design conditions was built. Then physical reasoning along with a robust data mining approach, i.e. M5 model tree, were used to develop formulas for armor stability. In the stability formula, wave characteristics such as the significant wave height and spectral energy mean period (Tm-1,0) are invoked while the permeability is incorporated using the ratio between the size of the core material and the armor stones. Accuracy metrics such as discrepancy ratio and scatter index indicated high performance of the model in different conditions. Finally, a probabilistic formula and some guidelines are provided for practicing engineers.
•A compact formula was derived for the stability of rock armored structures in both deep and depth-limited conditions.•The effect of permeability is quantified by using the relative size of the core material.•The stability formula includes effects of the foreshore slope in depth-limited conditions.•The stability formula was validated with both small and large scale tests in a wide range of damage levels (0 < Sd ≤ 62).•Coefficients of variation were given to consider the uncertainty in the estimation of stability number.
The prediction of rubble mound breakwaters' stability is one of the most important issues in coastal and maritime engineering. The stability of breakwaters strongly depends on the wave height. ...Therefore, selection of an appropriate wave height parameter is very vital in the prediction of stability number. In this study, H50, the average of the 50 highest waves that reach the breakwater in its useful life, was used to predict the stability of the armor layer. First, H
On the toe stability of rubble mound structures Etemad-Shahidi, Amir; Bali, Meysam; van Gent, Marcel R.A.
Coastal engineering (Amsterdam),
March 2021, 2021-03-00, Letnik:
164
Journal Article
Recenzirano
Odprti dostop
Toe design is an important task for coastal engineers as it ensures the stability of the main armor layer and prevents scour in front of the armor slope. Several laboratory experiments have been ...conducted to investigate the toe stability using different testing approaches, i.e. damage due to a single test condition and cumulative damage due to a number of conditions. In addition, the methods of measuring and reporting damage to the toe are not the same as some researchers have counted only stones that were washed away from the toe; while others counted all the stones that have been displaced. Several formulas with different levels of success have been developed based on these studies. However, the scatter in the results is large and effects of some parameters are disregarded. The aims of this study are (a) to briefly review the abovementioned differences and exiting formulas, and (b) to develop a and physically sound formula for common design conditions, which considers the effect of all governing parameters. To achieve this, first a comprehensive data base from existing reliable studies was collected. Then nondimensional parameters which capture effects of governing parameters such as wave height, wave period, water depth, toe depth, toe width and foreshore slopes were deployed to develop a stability formula using physical reasoning and regression analysis. The new formula outperforms existing formulae for toe stability. The coefficient of variation of the formula was also determined to be used for probabilistic design applications. Finally, some design hints are provided for practitioners.
•A robust formula was derived for the stability of toe structures under design condition.•The formula has a compact form and includes effects of governing parameters such as toe depth, wave steepness, toe width and foreshore slope.•The stability formula was also tested for a wider range of damage levels (0 < Nod <10).•Standard deviations of the results were given to include the uncertainty of the toe stability.
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