Overtopping flow velocity (OFV) and overtopping layer thickness (OTL) are essential parameters in breakwater design. Several empirical equations to predict these parameters are available in many works of literature, but most of the equations were derived based on impermeable structures such as sea dikes. In this study, we experimented with overtopping waves over a composite breakwater with tetrapod armor units. In the experiments, wave overtopping was generated from regular waves. We used a digital image-based velocimetry method, bubble image velocimetry (BIV), to measure the OFV and digitize the corresponding image to obtain the OLT. The patterns of OFV and OTL with respect to time steps, wave conditions, and corresponding events were provided and discussed. The application of the widely used empirical equations for sea dike to breakwater was also tested by calibrating the coefficients. New empirical coefficients and roughness factors were suggested to reduce the difference between predicted and measured OFV and OLT on breakwater through the bootstrap resampling technique. This study provides modified empirical equations on wave overtopping, which is further applicable to breakwater design.

Turbulence and pressure fluctuations are key elements in the bed protection design of hydraulic structures. However, their roles in a hydraulic jump are not yet fully understood, and the nature of their relationships are not conclusive. In order to better understand the relationships between pressure fluctuations and flow characteristics of a hydraulic jump downstream of a weir, detailed measurements of flow kinematics using the nonintrusive techniques of particle image velocimetry and bubble image velocimetry and pressure using voltage-type pressure gauges were carried out in this study. The physical modeling of the hydraulic jump was carried out using the simultaneous measurements of pressure and turbulent flow properties. The distributions of flow properties, such as water level and velocity, were assessed in each case. Based on the measurements, the correlations between the pressure fluctuations and the variables were investigated by coupling the statistical values of the variables at the same points. The analysis results show that the water level and turbulence intensity are the main factors influencing the pressure fluctuations in the hydraulic jump. Using these factors, an empirical formula and dimensionless numbers are proposed to show that the pressure fluctuations depend on the bubble flow behavior.

The safety of pedestrians on a breakwater structure or seawall is significantly influenced by two essential factors: the wave overtopping flow velocity (OFV) and the overtopping layer thickness (OLT). The main issue, however, is that most studies have predominantly focused on impermeable structures rather than composite breakwaters. This study conducted 55 physical experiments to investigate the OFV and OLT on a composite breakwater. The non-intrusive bubble image velocimetry (BIV) technique was employed to measure the OFV and OLT, as well as the plunging distance on the rear side of the structure. Empirical equations with two sets of dimensionless variables, the wave steepness and relative crest freeboard, were proposed as predictors. The results show that these two dimensionless variables perform well for both OFV and OLT estimation. The comparison between the proposed empirical equation and the available empirical equation in the literature is also presented. Finally, the proposed empirical equations were used to estimate the maximum instantaneous wave overtopping discharge and plunging distance. The findings of this research offer insights into the physical mechanisms of wave overtopping, providing an initial exploration into the design of composite breakwaters.

Adibhusana, M.N.; Lee, J.-I., and Ryu, Y., 2021. Wave overtopping plunging on the rear side of composite breakwater. 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. 574–578. Coconut Creek (Florida), ISSN 0749-0208. In this study the behavior of overtopping water falling on the rear side of composite breakwater were investigated through physical experiment. A series of regular wave with various wave period and wave height were used as wave parameters while velocity at the rear edge of breakwater, plunging location, and plunging velocity were used as the parameters of wave overtopping behavior on the rear side of composite breakwater. The geometry of the composite breakwater was kept constant through the experiment. The Bubble Image Velocimetry (BIV) and digital image analysis were applied to measure the velocity in the aerated region of overtopping water falling on the rear side of breakwater and the plunging location. The rear edge velocity was linearly increased as the wave parameter increased. The increment value of plunging location shows a logarithmic trend as wave period and wave height increased. The front velocity of overtopping flows right before plunging the rear water surface shows a linear trend with those wave parameters.

Adibhusana, M.N. and Ryu, Y., 2023. Image-based measurement method of overtopping flow velocity and layer thickness in irregular wave conditions. In: Lee, J.L.; Lee, H.; Min, B.I.; Chang, J.-I.; Cho, G.T.; Yoon, J.-S., and Lee, J. (eds.), Multidisciplinary Approaches to Coastal and Marine Management. Journal of Coastal Research, Special Issue No. 116, pp. 41-45. Charlotte (North Carolina), ISSN 0749-0208. Maximum overtopping flow velocity and layer thickness are the primary wave overtopping parameters when the safety of pedestrians, vehicles, or the stability of the lee side of the coastal defense structure is considered. These parameters require a study with respect to either individual waves or statistical estimations during the design process. Especially for irregular waves, many wave components make measurements difficult in addition to the nature of high turbulence and aeration of individual overtopping flows. This study applied the use of digital images to the measurements of wave overtopping flows from a set of irregular waves. Because a set of irregular waves require a long experimentation time and an image velocimetry like the Particle Image Velocimetry (PIV) needs image frame controls with very short time difference, the application of high-speed camera has not been well successful. In this study, a mosaic set of high-speed cameras to cover the overtopping flow field were installed and synchronized by being connected to an external trigger to control the measurement system and to secure the number of parameters per second enough for analysis. The experiments were carried out in a two-dimensional wave flume. A composite breakwater was used as the coastal structure model and irregular waves and following overtopping waves were generated. The captured images were processed to obtain the overtopping flow velocity and layer thickness. Unlike the point measurement method where the measurement data represent only a single location, using the image-based measurements gives the velocity and layer thickness in spatial and temporal variation in all individual wave overtopping. The velocity maps and layer thickness of the irregular waves by the image measurements were provided with more information rather than point measurements.

A numerical study was carried out in Bali Strait, Indonesia. Finite Volume Coastal Ocean Model (FVCOM) was used to simulate the seawater circulation in Bali Strait. The water circulations were forced by the four major tidal components (  ,   ,   , and  ). Comparisons of the seawater surface elevation obtained from both modeling and observations show a good result. The tide in Bali Strait is a mixed tide type with two different tidal ranges in one day. The seawater circulation moves from the Indian Ocean to the Bali Sea through narrow strait during the flood tide and then rush back during the ebb tide. In the spring tide, an eddy is also observed on the top of the narrow strait. The simulations show that the flows by tides along the sudden change of the cross-sectional width can be modeled by the finite volume method based model.