Crest Freeboard Research Articles

Physical modelling study on wave damping induced by an idealized floating kelp farm

A physical modelling study was carried out to investigate random wave damping promoted by an idealized floating kelp farm. The experimental conditions spanned intermediate water depths and both linear and nonlinear water waves. Unlike previous studies of wave damping promoted by vegetation, the floating kelp farm was placed close to the water surface with a ratio between vegetation height and water depth close to 0.25. The wave transmission coefficient induced by the floating kelp farm ranged between 0.56 and 0.96. This coefficient decreased for longer floating kelp farms and it was a function of the ratio between kelp farm length and incident wavelength and of the relative wave depth. Spectral analysis showed that wave damping was not frequency-dependent for wave frequencies close to the peak frequency. The wave transmission coefficients of a floating kelp farm with about 100 culture lines and with an extension of approximately 200 m were similar to those of submerged detached breakwaters with a relative crest freeboard smaller than -0.4. Furthermore, the bulk drag coefficient of near-surface idealized floating kelp farms can be modelled as a function of the Keulegan-Carpenter number. This study highlights the potential viability of nature-based solutions such as floating kelp farms for coastal protection.

Empirical Predictions on Wave Overtopping for Overtopping Wave Energy Converters: A Systematic Review

Over the past three decades, the development and testing of various overtopping wave energy converters (OWECs) have highlighted the importance of accurate wave run-up and overtopping predictions on those devices. This study systematically reviews the empirical formulas traditionally used for predicting overtopping across different types of breakwaters by assessing their strengths, limitations, and applicability to OWECs. This provides a foundation for future research and development in OWECs. Key findings reveal that empirical formulas for conventional breakwaters can be categorized as mild or steep slopes and vertical structures based on the angle of the slope. For the same relative crest freeboards, the dimensionless average overtopping discharge of mild slopes is larger than that of vertical structures. However, the formula features predictions within a similar range for small relative crest freeboards. The empirical formulas for predicting overtopping in fixed and floating OWECs are modified from the predictors developed for conventional breakwaters with smooth, impermeable and linear slopes. Different correction coefficients are introduced to account for the effects of limited draft, inclination angle, and low relative freeboard. The empirical models for floating OWECs, particularly the Wave Dragon model, have been refined through prototype testing to account for the unique 3D structural reflector’s influence and dynamic wave interactions.

Digital Profiler Based On A Low-Cost 3D-Scanner To Evaluate The Hydraulic Performance Of Homogeneous Low-Crested Structures

In order to evaluate the hydraulic performance of breakwaters, mechanical profilers were first used in wave flumes. Vertical bars and rolling wheels have been used to track the breakwater shape. Once surveyed, useful hydraulic parameters were able to be measured (e.g., envelope shape and eroded area). Nevertheless, the methodologies based on mechanical profilers have some limitations: they are intrusive, require specific equipment and are time-consuming. On the other hand, non-intrusive laser scanners can also be used; recent studies proved the feasibility of non-intrusive fast methods of surveying with 3D-scanning, (see Musumeci et al., 2018). These instruments are fast and reliable at capturing the shape of the breakwater in real-time. However, this method did not consider the distortion caused by light refraction. Laser scanners usually require to measure models in dry conditions, which is not efficient in time and resources. Regardless of the drawbacks when using non-intrusive laser scanners as digital profilers, the distortion can be corrected. The data suits for the usage of Neural Networks (NN) that can be trained to correct distortion. This study is focused on Homogeneous Low-Crested Structures (HLCS) which is a new typology of Low-Crested Structures (LCS), made out large quarry stones or concrete armor units that are suitable to reduce shoreline erosion on degraded coastlines and natural environments. HLCS can be classified as reef-type breakwaters and are considered an environmentally-friendly solution that fulfils two purposes: to protect beaches nearby and to enhance coral regeneration and marine colonization, (see Medina et at., 2020). For the correct design of HLCS or conventional LCS, it is required to evaluate both the hydraulic stability and wave transmission (see van der Meer and Daemen, 1994). HLCS are structures without core which may erode under intense wave attack. Breakwater damage and crest freeboard must be estimated depending on incident wave conditions. The breakwater envelope evolves and finds an equilibrium state related to the incident wave conditions in which the crest freeboard and the transmitted wave energy levels may change. The goal of this study is to provide a low-cost non-intrusive methodology based on 3D-scanning to study the hydraulic performance of mound breakwaters, specifically for Cubipod HLCS. This surveying procedure allows to obtain the real-magnitude shape of the envelope of the HLCS, even with a certain water level. The methodology mimics previous surveying techniques and provides relevant hydraulic and structural parameters (crest freeboard, damage, envelope shape, etc.) that can be then used to study the hydraulic performance of breakwaters.

Improved prediction of wave overtopping rates at vertical seawalls with recurve retrofitting

This study investigates the reduction in overtopping discharge along a vertical seawall through the implementation of a recurve retrofitting. A comprehensive set of physical modelling experiments were undertaken in a laboratory-scale wave flume at the University of Warwick, to investigate the wave overtopping processes under both swell and storm wave conditions. The tests measured overtopping discharges for impulsive and non-impulsive wave conditions. The effects of geometrical design of recurve retrofitting on overtopping reduction are examined by four configurations with varying overhang length and recurve hight. The study revealed that the reduction in overtopping is primarily determined by the length of the overhang in the recurve wall, while the influence of the recurve height is limited. A longer overhang length results in a more substantial decrease in overtopping discharges on the seawall crest. The results also highlight the role of incident wave steepness and the crest freeboard on the overtopping mitigation performance of the recurve walls. A new enhanced methodology is proposed to predict the wave overtopping from vertical seawalls with recurve retrofitting., considering the effects of freeboard and wave steepness. The findings of this study provide new important insight in the role of retrofitting as a robust intervention to improve the wave overtopping mitigation performance of seawalls. The predictive empirical formulae proposed by this study facilitate readily and accurate estimation of overtopping rates as a function of retrofitting geometrical design, allowing for wider application of retrofitting solutions.

OpenFOAM design sensitivity analysis on a homogeneous low-crested structure with concrete elements seaward of a vertical seawall to reduce overtopping

This study treats a detached homogenous low-crested structure (HLCS) made of Cubipod concrete elements placed seaward of a vertical wall (forming a basin in between) to reduce overtopping. Assessing the complex hydrodynamics and effects of changing the geometry of such a system in relation to overtopping reduction is challenging. The numerical model OpenFOAM was applied to this end. Forchheimer coefficients for wave transmission and the flow through the HLCS were calibrated and validated using existing physical modeling data (α = 500 and β = 1.0, with varying porosity based on the Cubipod shape), while the effect of the basin and vertical seawall was determined fully numerically. The crest freeboard (Rc), crest width (B), and basin length (LB) were the main geometrical parameters that influenced the performance of the HLCS in reducing overtopping. An exponential decay was observed in the overtopping discharge when the values of these geometrical parameters increased. As LB increased, this decay was primarily due to the dissipation of the broken-wave bores. The largest gradient in the predicted overtopping discharge was noted at Rc/Hs,i ≈ 0, B/Hs,i ≈ 4.5, and LB/Lp ≈ 1.2, where Hs,i is the incident significant wave height and Lp is the peak wavelength in the basin.

Wave overtopping layer thickness on the crest of rubble mound seawalls

During storms, ensuring the protection of people, vehicles and infrastructure on the crest of coastal structures from wave overtopping hazards is crucial. The thickness of the wave overtopping layer is a key variable used for assessing safety and maintaining a secure design. Traditionally, this parameter is associated with the height difference between the fictitious wave run-up level exceeded by 2% of waves and the crest freeboard of coastal structures. This study aims to investigate the wave overtopping layer thickness on the crest of rubble mound seawalls. To achieve this, a series of 125 small-scale 2D physical model tests were conducted on a two-layer rubble mound seawall with an impermeable core and slopes of 1:1.5 and 1:2. The obtained results indicated that the existing empirical formulas, originally developed for dikes, underestimate the overtopping layer thickness on the studied seawall. Therefore, modifications were made to the formulas found in the literature specifically tailored for rubble mound seawalls. The newly proposed formulas for estimating overtopping layer thickness at both the seaward edge and the middle of the crest showed improvements compared to the existing formulas.

Predictions of Wave Overtopping Using Deep Learning Neural Networks

Deep learning techniques have revolutionized the field of artificial intelligence by enabling accurate predictions of complex natural scenarios. This paper proposes a novel convolutional neural network (CNN) model that involves deep learning technologies, such as the bottleneck residual block, layer normalization, and dropout layer, to predict wave overtopping at coastal structures under a wide range of conditions. To optimize the performance of the CNN model, the hyperparameter tuning process via Bayesian optimization is used. The results of validation demonstrate that the proposed CNN model is highly accurate in estimating wave overtopping discharge from hydraulic and structural parameters. The testing accuracy of the overtopping predictions using a prototype dataset shows that the proposed CNN model outperforms those existing machine learning models. An example application of the CNN model is presented for predicting prototype overtopping considering various crest freeboards of coastal structures.

Physical Model Experiment for Estimating Wave Overtopping on a Vertical Seawall under Regular Wave Conditions for On-Site Measurements

Apart from implementing hardware solutions like raising the crest freeboard of coastal structures to efficiently counter wave-overtopping, there is a simultaneous requirement for software-driven disaster mitigation strategies. These tactics involve the swift and accurate dissemination of wave-overtopping information to the inland regions of coastal zones, enabling the regulation of evacuation procedures and movement. In this study, a method was proposed to estimate wave-overtopping by utilizing the temporal variation of wave heights exceeding the structure’s crown level, with the aim of developing an on-site wave measurement system for providing wave-overtopping information in the field. Laboratory model experiments were conducted on vertical seawall structures to measure wave-overtopping volumes and wave runup heights under different wave conditions and structural freeboard variations. By assuming that the velocity of water inundation on the top of the structure during wave-overtopping events is equivalent to the long-wave velocity, an overtopping discharge coefficient was introduced. This coefficient was utilized to estimate the rate of wave-overtopping based on the temporal changes in wave runup heights measured at the top of the structure. Upon reasonably calculating the overtopping discharge coefficient, it was verified that the estimation of wave-overtopping could be achieved solely based on the wave runup heights.

Experimental and numerical studies of solitary wave interaction with perforated caisson breakwaters

This study experimentally and numerically investigated interactions between solitary waves and the perforated caisson breakwaters. By caisson, we mean a sealed chamber filled with sand and rocks inside, and it is a common structure used for the construction of vertical breakwater. In the laboratory, the solitary waves with larger relative wave heights were well generated based on the “collapsing water column” technique and successfully acted on the perforated caisson models. Using the volume of fluid method and the k–ε model, combined with the ideal gas equation at a constant temperature, the wave transformation and vortex evolution in the vicinity of the perforated caisson breakwaters were simulated. A reasonable agreement was observed between the numerical and the experimental results. By comparing with the non-perforated caissons, the perforated caissons effectively reduced the reflected and transmitted wave heights, and the occurrence of the reflected waves was found to be delayed due to the existence of the wave chamber. Based on the numerical results, distributions of the fluid velocity and turbulence kinetic energy (TKE) near the perforated caissons were examined. The wave dissipation mechanism of perforated caisson under the solitary wave was different from that under the periodic wave. The results showed that vortices and TKE were mainly concentrated near the perforated front wall. The incident wave energy was dissipated in the generating vortices formed by fluids jetting through perforations. Additionally, variations of the wave reflection, transmission, dissipation coefficients, and wave overtopping volumes were investigated against different relative crest freeboards, relative wave chamber widths, caisson porosities, and relative wave heights under the solitary waves. Valuable results were presented for practical engineering applications.

Application of SWASH to Compute Wave Overtopping in Ericeira Harbour for Operational Purposes

This work aimed at testing the capability of the numerical model SWASH to be implemented in the prototype of the overtopping and flooding forecast system HIDRALERTA for Ericeira harbour. In contrast to the neural network NN_OVERTOPPING2, which is currently implemented in HIDRALERTA, SWASH is able to estimate the flood extension and wave propagation along the domain, which makes it a possible improvement to NN_OVERTOPPING2. The one-dimensional version of the SWASH model was implemented to simulate overtopping at two different profiles (antifer and tetrapods) and calibrated for three storms in 2019 by comparing the simulated overtopping discharge to NN_OVERTOPPING2 results. For the calibration, the Manning coefficient was used to represent the friction of the armour layer. Then, for operational purposes, four expressions to calculate the Manning coefficient were developed based on: the relative crest freeboard, the wave steepness, the incident wave angle and the type of armour layer. The expressions showed small errors between the calculated and calibrated Manning coefficients and highlighted the importance of the incident wave angle to obtain an accurate calibration. Despite an underestimation of the overtopping discharge in some cases, the SWASH model was found to provide overall good results when applied with calculated Manning coefficients and suitable to be implemented in HIDRALERTA.

The effect of variations in water level on wave overtopping discharge over a dike: An experimental model study

The water level during a storm event is never constant but variable in nature. A variable water level leads to varying crest freeboards at the coastal defense structure. A change in crest freeboards is directly linked to a changing average overtopping discharge q over the coastal defense structure. The existing prediction formulae for q are developed for constant water level ( C W L ) and do not take into account its variability ( V W L — variable water level) during a storm event. Hence, in this study the influence of the V W L on q was investigated experimentally. Model tests were conducted in the wave flume facility at Ghent University, where a range of V W L was modelled as representative for typical storm surges (total variation of the water level d h = 0.75–4.8 m) and a range of storm durations (time t = 2.7–22 h). During testing the q for these cases of V W L over a reference impermeable sloping (seaward slope of the structure cot( α ) = 2) dike structure was measured. Initial validation of model results for the C W L situation showed that the model setup was capable of reproducing the predicted q values from Eurotop (2018). For the V W L situation it was noted that the existing prediction formulae (Eurotop, 2018) are overestimating the measured q value, especially for smaller relative crest freeboards (relative freeboards R c / H m 0 < 1 . 5 ) when the smallest freeboard is considered. By using linear regression a new equivalent relative crest freeboard was derived to reduce the difference between q predicted by existing EurOtop (2018) and q measured during variable tests. The new equivalent freeboard is mainly dependant on the relative crest freeboard during the peak of the storm ( R c p e a k / H m 0 ), as well as the total storm surge variation ( d h). The existing formulation from EurOtop (2018) was kept by replacing R c by this new equivalent crest freeboard. The adapted formula for q is able to accurately predict the overtopping discharge for both, C W L and V W L situation. • 2D Physical model tests on wave overtopping performance of a smooth dike. • Influence of variable water level conditions on the average wave overtopping discharge. • New equivalent relative freeboard is determined to include this effect in the EurOtop formula for non-breaking waves. • Predictions are significantly improved with the new equivalent relative freeboard for the new data.

On the mean overtopping rate of rubble mound structures

Estimation of the mean overtopping discharge is a major task in the design and assessment of the crest level of rubble mound structures such as breakwaters and seawalls. The tolerable mean overtopping rates are given based on the associated risk and wave characteristics. Several empirical formulas have been developed for the prediction of mean overtopping discharge at coastal structures. These formulas can be applied to a wide variety of coastal structures, but have limited accuracy and/or do not reflect the physics of the phenomena. The main aim of this study is to overcome these issues for rubble mound structures by considering the physics of the process in the formula development. To achieve this, first, the references used in the extended CLASH database (also called the EurOtop-2018 database), were scrutinized, the reported wave characteristics were corrected (if required) and the rubble mound structure subset was extended using a recent study. Then noting that overtopping occurs when the wave runup exceeds the freeboard, the difference between the maximum wave runup and crest freeboard was considered as the governing parameter in the mean overtopping discharge formula. In the developed formula, a semi-empirical relationship between the mean overtopping and wave runup has been established. The performances of the developed formulas and existing ones were evaluated both qualitatively and quantitively. Accuracy metrics such as RMSE and BIAS indicated the superiority of the developed simple formula. Finally, a design formula to consider uncertainty and some guidelines are provided for practitioners. • A robust formula was derived for the mean overtopping of rubble mound structures. • The formula has a compact form and includes effects of governing parameters such as the wave runup and crest width. • The formula was evaluated for a wide range of cases such as oblique waves and wave walls as well as prototype data. • A probabilistic formula was also given to include the uncertainty and safety in the design.

Distribution of individual wave overtopping volumes at rubble mound seawalls

For a safe design of a rubble mound seawall, overtopping characteristics such as the mean overtopping discharge (q) and the maximum individual overtopping volume (Vmax) should be limited. Unlike q, the estimation of Vmax is more complex and requires a wave-by-wave analysis of overtopping as well as a statistical analysis. The present study contributes to the knowledge of the distribution of individual overtopping volumes and the estimation of Vmax at rubble mound seawalls. A total of 135, small-scale 2D physical model tests were conducted across a practical range of crest freeboards and considered the slopes of 1:1.5 and 1:2. The well-known 2-parameter Weibull and Exponential distributions were first fitted to the experimental data to estimate the Vmax. Different approaches to sample the observed distribution of wave-by-wave overtopping volumes were evaluated including a threshold method using the top 10%, 30%, and 50% of individual overtopping volumes, and a method that applies a greater weighting to the larger events. For both Weibull and Exponential distributions, the weighted method was found to be the best one providing a 23% and 17% decrease in scatter index (SI) values compared to the best of existing methods. To facilitate the estimation of Vmax for design purposes, a simple empirical formula was developed as a function of the dimensionless mean overtopping discharge (q*) and the number of overtopping waves (Now). This formula with SI = 37% outperformed the distribution-based methods as well as the best of existing formulae for Vmax. In the case of the normalised bias (NBIAS), the distribution methods underestimated Vmax by −21% (Weibull) and −31% (Exponential) whereas the new formula yielded NBIAS = −6%.

New insights in the probability distributions of wave-by-wave overtopping volumes at vertical breakwaters

Advances in the development of prediction tools for wave overtopping allow now for overtopping volumes to be estimated with good accuracy, with the combined use of mean overtopping rates and maximum wave by wave overtopping volumes in a sequence of wave overtopping events. While previous literature has tended to focus on mean overtopping rates at coastal structures, limited studies have investigated the wave by wave overtopping volumes at coastal sea defences; in particular, a paucity of studies have focussed on the prediction of the shape parameter in the Weibull distribution (i.e., Weibull b) of overtopping volumes. This study provides new insights on the probability distribution of individual wave overtopping volumes at plain vertical seawalls by analysing the measured Weibull b values derived from a series of laboratory experiments on seawalls performed on a wide range of wave conditions and crest freeboards. The influence of wave conditions (wave steepness, significant wave height), structural parameters (crest freeboard, toe water depth), impulsiveness, probability of overtopping waves, and overtopping discharge on Weibull b parameter were examined, and then compared with the well-established empirical formulae. For the conditions covered within this study, it was found that the probability distribution of wave-by-wave overtopping volumes follow a 2-parameter Weibull distribution. No apparent differences in Weibull b values were reported with the variation of incident wave steepness and impulsiveness parameter. Results of this study revealed that Weibull b values at vertical walls, subjected to non-impulsive wave conditions, can be predicted reasonably well using relative freeboard and relative overtopping rates. A new unified formula is proposed for the estimation of Weibull b values at vertical walls under impulsive and non-impulsive wave attack.

A comparative study between some different types of permeable breakwaters according to wave energy dissipation

This research investigates experimentally the effectiveness of different types of breakwaters as floating breakwaters (FB), low crested breakwaters (LCB), and piled breakwaters (PB). To examine the efficiency of the breakwaters, different models were tested under various wave and water depth conditions and by varying draught in floating models, crest freeboard in submerged models, spacing and arrangement in piled models. The results shows that the transmission coefficient decreases with increasing wave steepness and relative water depths for all breakwaters. For the FB, it decreases with increasing draught and the breakwaters’ width. But, for LCB, it decreases with increasing crest freeboard. And for PB, it decreases with increasing pile diameter, staggering of piles and adding strips suspended to the piles. Comparing the breakwaters states that FB with higher draught have likely the same efficiency as that of LCB. Suspended breakwaters have similar efficiency to that of FB with lower draught.

Experimental study of wave overtopping at rubble mound seawalls

Seawalls play a significant role in protecting coastal areas against wave attack and flooding. The accurate estimation of wave overtopping at seawalls is therefore crucial to adequately protect people and infrastructure in these regions. In this study, the mean wave overtopping rate at rubble mound seawalls was investigated through 140 small-scale physical model tests which adds to the limited existing data for this structure type in the extended CLASH database called EurOtop (2018). The combined dataset is used to evaluate the prediction skill of existing empirical formulae and to identify their limitations. The role of wave steepness on the mean overtopping rate is closely examined as it has not yet been considered properly in the EurOtop (2018) formulation. A new formula was derived using dimensional analysis and physical justifications of the overtopping phenomenon. The formula was found to provide a 40% decrease in RMSE in comparison to that of the EurOtop (2018). In addition, the new formula yields a BIAS ≈0, a significant improvement compared to −0.38 (non-dimensional discharge) of the EurOtop (2018) formula. The proposed formula has a simple form where non-dimensional overtopping discharge depends only on the relative crest freeboard and wave steepness, which were found to be the most important variables based on a sensitivity analysis.

Numerical Analysis of Sediment Transport Rates from Rip Currents at an Open Inlet between Low Crested Breakwaters (LCB): The Role of Infra-Gravity Waves

Lee, J.L. and Cho, Y.-J., 2021. Numerical analysis of sediment transport rates from rip currents at an open inlet between Low Crested Breakwaters (LCB): The role of infra-gravity waves. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 489–493. Coconut Creek (Florida), ISSN 0749-0208. Low Crested Breakwaters (LCB), the most preferred structural type in the coastal zone management project by the Korean Ministry of Ocean and Fisheries, has been designed to mitigate beach erosion by high waves occurring only a few times a year. Now that moderate sea conditions are dramatically different from those in rough seas, these poor design practices could interrupt the grand circulation process of natural beaches over the course of a year. As a result, the beach stabilizing effect of LCB often falls short of our expectations. In this study, in order to test this hypothesis, 3-D numerical simulation was carried out to analyze the rip currents and its associated sediment transport at the open inlet between LCB when LCB is subject to infra-gravity waves, which play an indispensable role in the beach restoring process in a mild sea with an annual prevalence rate of over 80%. Numerical results show that in the case of LCB with lower crest freeboard, rip currents gets increased by 2.6 times when compared to the one before the deployment of LCB since the water mass influx toward the down-wave side of LCB by overflowing LCB by the preceding waves is redirected toward the open inlet. The sediment transport rate was estimated using Bailard's model, the most referred cross-shore sediment model in the literature. It was shown that the primary sediment transport mode at the open inlet between LCB was bed load, and sand of 5.62 ×10–5 m3 / m was leaving the inner zone of LCB per unit wave period.

Mean Overtopping Discharges and Transmitted Wave Heights for Evaluation of Crest Freeboards of Breakwaters

ì „ë‹¬íŒŒê³ ì™€ 허용 월파량을 함께 ê³ ë ¤í•˜ì—¬ ë°©íŒŒì œì˜ 마루높이를 ê²°ì •í• ìˆ˜ 있는 방법을 ì œì‹œí•˜ì˜€ë‹¤. ë°©íŒŒì œë¥¼ 형식별로 구분하여 현재 가장 ì¼ë°˜ì ìœ¼ë¡œ 사용되는 경험식들을 활용하여 ìž ì‚¬íŒŒê³ ì™€ í‰ê· ì›”íŒŒëŸ‰ ê·¸ë¦¬ê³ ì „ë‹¬íŒŒì˜ 관계를 ì •ëŸ‰ì ìœ¼ë¡œ 해석하였다. 기존의 연구 결과와 비교하여 만족스럽게 검증되었으며, 임의의 ìž ì‚¬íŒŒëž‘ì— 대하여도 ì ìš©í• ìˆ˜ 있는 무차원 í‰ê· ì›”íŒŒëŸ‰ê³¼ ì „ë‹¬ê³„ìˆ˜ì˜ 관계도 ë°©íŒŒì œ 형식별로 ì œì‹œ, 비교하였다. 또한 주기 및 íŒŒê³ ë³€í™”ì— 따른 í‰ê· ì›”íŒŒëŸ‰ê³¼ ì „ë‹¬íŒŒê³ ì˜ 관계를 수립하여 허용 월파량을 ì‚°ì •í• ìˆ˜ 있었다. 마지막으로 허용 월파량에 따른 상대 마루높이 ê²°ì •ë°©ë²•ì„ ê²½ì‚¬ì œì™€ 무공 케이슨식 í˜¼ì„±ì œì— ì ìš©í•˜ì˜€ë‹¤. ê²½ì‚¬ì œì™€ í˜¼ì„±ì œ 모두에서 허용 월파량이 커지면 상대 마루높이는 급격하게 작아지는 경향을 보였다. 특히 ìƒëŒ€ì ìœ¼ë¡œ 작은 범위에서는 허용 월파량이 동일해도 í˜¼ì„±ì œì˜ 마루높이가 ê²½ì‚¬ì œì˜ 마루높이보다 커야 하지만, ì¼ì • 수준 이상의 큰 허용 월파량에 대해서는 ê·¸ 반대의 경향을 보였다. í˜¼ì„±ì œì˜ 경우는 월파량이 작아도 항내로 ì§ì ‘ 낙하하여 ìƒëŒ€ì ìœ¼ë¡œ 큰 항내 ì „ë‹¬íŒŒê³ ë¥¼ ìœ ë°œí•˜ì§€ë§Œ, 월파량이 ì¼ì • 수준을 넘어서면 ë°©íŒŒì œì˜ 형식에 따른 영향이 작아지면서 ì œì²´ë¥¼ 통한 투과파의 영향이 ê²½ì‚¬ì œì— ê³ ë ¤ë˜ê¸° 때문이다. 핵심용어: 허용월파량, ì „ë‹¬íŒŒê³ , ê²½ì‚¬ì œ, í˜¼ì„±ì œ, 마루높이

Estimation of layer coefficients of cubipod homogeneous low-crested structures using physical and numerical model placement tests

Homogeneous low-crested structures (HLCSs) on hard seabed are designed to protect beaches and regenerate coral reefs. The height of a HLCS depends on the placement grid which determines the crest freeboard, wave transmission and concrete consumption. In real seafloor conditions, it is not easy to define feasible placement grids for HLCSs on uneven sea bottoms. In this study, the parameters of the numerical model Bullet Physics Engine (BPE) are calibrated and validated using the results of small-scale physical model placement tests of five-layer Cubipod HLCSs on horizontal rigid bottom. The BPE model showed a low sensitivity to variations in the calibrated parameters; the numerical model estimated the layer coefficients with global mean relative errors of 1.04% and 1.39% in the triangular and rectangular placements grids, respectively. Once the numerical model was calibrated, new numerical and physical model tests on a 4% rigid bottom slope were compared for validation. A five-layer Cubipod HLCS on a 4% bottom slope was simulated using the BPE numerical model showing a global mean relative error of 2.75% compared to the small-scale physical model tests. A good agreement was found between numerical and physical model tests of five-layer Cubipod HLCSs on both horizontal as well as 4% rigid bottom slope. The BPE numerical model was found a suitable tool to estimate the structure height of HLCSs and to optimize placement grids of HLCSs on real cases with hard sea bottom.

HOMOGENEOUS LOW-CRESTED STRUCTURES FOR BEACH PROTECTION IN CORAL REEF AREAS

In many countries, the health of the marine ecosystems and the sun-sand-sea tourism depend on the coral reefs, which have been retreating around the world during the last decades. Homogeneous Low-Crested Structures (HLCS), made of large rocks or pre-cast concrete units, can be placed to mimic the functions of beach protection and eventually serve as a refuge for species. HLCS is a type of multi-purpose green infrastructure which is functionally similar to conventional low-crested structures but have higher porosity and are more easily dismantled for re-use. Contrary to conventional low-crested structures, the functionality of HLCS protecting beaches depends on the selected placement grid; this paper describes physical and numerical placement tests on horizontal bottom used to characterize the layers coefficients of Cubipod HLCS. The Bullet Physic Engine (BPE) numerical model used in the gaming industry, which is based on the rigid body method, is calibrated using the physical placement tests. The layer coefficients of Cubipod HLCS measured in the physical placement tests were similar to those obtained with the BPE numerical model, which could be used to optimize placement grids of HLCS on specific sea bottom conditions. Finally, the influence of the placement grid of Cubipod HLCS on the structure height, crest freeboard and wave transmission is analyzed.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5bi-jpuJYcQ