Surf Similarity Parameter Research Articles

Experimental study on the bed shear stress under breaking waves

The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1:15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.

The effect of mesh-type bubble breaker on two-phase vertical co-flow

The influence of a mesh-type bubble breaker in a two-phase vertical co-flow is experimentally investigated using high-speed imaging. A range of liquid and gas flow rates were considered that correspond to the gas-to-liquid flow rates ratios (GLRs) from 0.05 to 39.6 covering bubbly, slug and churn flow regimes. The mesh-type bubble breaker was found to be effective in reducing the size of nozzle-generated bubbles in two-phase co-current vertical flow. The bubble size reduction by 50%-70% is observed in the presence of the mesh-type bubble breaker compared to that without a bubble breaker. The results also show that at a given GLR, the mesh-type bubble breaker delayed the flow regime transition compared to that without a bubble breaker. A Froude number correlation was proposed to predict the mean bubble size downstream of the bubble breaker for the bubbly flow regime, which accurately predicted the bubble size over a range of bubble breaker parameters. It is observed that the geometry of the bubble breaker influence the two-phase flow regime transition. At low liquid flow rates, small pore size of the breaker was found to be effective. This effect diminishes at higher liquid flow rate due to the elongation of the bubbles by the liquid inertia. The results also show that a longer bubble breaker located closer to the bubble generating nozzle is the most effective in producing bubbly flow over a longer range of gas-liquid flowrates ratios.

Sediment resuspension and the generation of intermediate nepheloid layers by shoaling internal bores

Abstract Numerical simulations of sediment resuspension due to shoaling internal bores are performed with a nonhydrostatic model, SUNTANS. Results show strong sediment resuspension induced by internal bores and a turbidity layer intruding offshore in the interior of the water column, known as an intermediate nepheloid layer (INL). Sediment resuspension processes and INLs reproduced in the model are in good agreement with observational data from Otuschi Bay, Japan. The formation of INLs by shoaling internal waves is explained as follows: (1) strong receding currents due to a previous run-up bore cause sediment resuspension along the slope, (2) the interaction of the receding currents and a subsequent run-up bore induce horizontal flow convergence and strong upward currents, (3) the upward currents lift the suspended sediments into the interior of the water column, (4) the run-up bore intrudes below the suspended sediments and forms an INL within the pycnocline. Sediment resuspension processes are also investigated for various internal Iribarren number conditions. The internal Iribarren number represents the ratio of the topographic slope to the internal wave steepness. In low internal Iribarren number conditions, strong currents near the bottom result in sediment resuspension and INL formation. In high internal Iribarren number conditions, sediment resuspension is weak, and INLs do not form.

Numerical Simulation of Shoaling Broad-Crested Internal Solitary Waves

The interaction between fully nonlinear Miyata-Choi-Camassa (MCC) internal solitary waves and topographic slopes are modeled by direct numerical simulation. The immersed boundary method is employed to describe the no-slip boundary of the slopes and a novel iterative Neumann boundary condition (INBC) enforcement strategy is proposed to ensure local mass conservation. The wave Reynolds numbers Rew used in the present work (∼104), although less than those of field scales (106−107), but are an order of magnitude greater than those in most laboratory scale experiments and previous numerical simulations (∼103). In the present study, three main internal wave breaking types (collapsing, plunging, and surging) together with two mixed mode breaking types (collapsing-plunging and plunging-surging) are observed for MCC wave shoaling process. The different breaking mechanisms are found to be related to the internal Iribarren number. New breaking regimes, breaking location criterion, and the maximum velocity prediction are also proposed.

Application of wave runup and wave rundown formulae based on long-term variation of wave conditions

The purpose of this note is to demonstrate that it is possible to use the proposed formulae in Blenkinsopp et al. [1] to estimate runup and rundown based on long-term variation of wave conditions by using the Myrhaug and Fouques [5] joint distribution of significant wave height and Iribarren number for a sea state. Examples of application are given for typical field conditions including a procedure of determining the 100-years return period values for the runup and rundown and the corresponding values of significant wave height and Iribarren number.

Estimation of the transmission coefficients of wave height and period after smooth submerged breakwater using a non-hydrostatic wave model

In the present study, new empirical formulas of wave transmission coefficients, including Kp for the mean wave period and Kt for the significant wave height, defined as the ratios between the transmitted and incident values of a smooth submerged breakwater, are proposed based on results simulated using the SWASH non-hydrostatic wave model. According to the analysis of the numerical results, both Kt and Kp are less than 1.0, and the transmitted peak period is close to the incident peak period in most cases. The reduction of wave height is mainly caused by energy loss due to wave breaking, and the reduction of the mean period is mainly caused by the generation of high-frequency harmonics after the submerged breakwater. Moreover, both Kt and Kp have good linear correlations with the relative submergences, and Kp has a good linear relationship with wave steepness. The relative crest width and slope have no significant effect on the transmission coefficient of the submerged breakwater compared with the effects of the relative submergences and wave steepness. Based on the factors mentioned above, new empirical formulas are formed. The coefficients of determination (RCor2) of Kt and Kp between measurements and values calculated using the new empirical formulas are 0.90 and 0.95, respectively, representing an improvement over the models of Van der Meer et al. (2003) and Carevic et al. (2013). The sensitivities of Kt and Kp to the variables in the empirical formulas are also investigated. According to the sensitivity analysis, a simplified formula of Kt is suggested based on the relative submergence and breaker parameter, and a simplified formula of Kp is proposed based on the relative submergence and wave steepness.

Parametric analysis of the hybrid HVDC circuit breaker

The hybrid circuit breaker design offers a fast low-loss operation that can be of paramount importance for the development of future meshed HVDC systems. This paper summarizes the main results obtained from a parametric analysis based on a simplified representation of both the circuit breaker and the test system. The main goals are to investigate the operation of the new device when running as a fault-current limiter and find out the influence that some breaker and system parameters (e.g. prospective short-circuit current in the test system, operation time of the mechanical switch, cable length, fault position, rated voltage of arrester) can have on the overcurrents and overvoltages that will occur during breaker operation. The results derived from this study can be useful for choosing some breaker parameters and to lesser extent for improving the breaker design.

Wave runup estimations on platform-beaches for coastal flood hazard assessment

Wave runup in a shore platform environment has been acquired by in situ measurements at high tide and along field debris following the December 6, 2010, flood near Rimouski (Quebec, Canada), south coast of the St. Lawrence estuary. Using offshore wave data and beach slopes, a linear empirical runup relationship has been adjusted to the study site and showed good predictive results. Two types of beach slopes, the upper foreshore and foreshore slopes, have been assessed in order to calculate the surf similarity parameter. It appears that the foreshore slope, located between the coastline and the end of the foreshore at the seaward edge of the platform, shows best results. This slope was thus used to calculate the wave runup on the shore platform. A static flood map, adding wave runup to observed peak tidal level including the storm surge during the December 6, 2010, flood, has been realized on a LiDAR base layer for a specific site in Sainte-Luce. A second flood map has been applied to validate the approach on an external site in Sainte-Flavie, outside the study area. In both cases, predicted flood extents highly correspond to observed flooded area. High underpredictions occur when using the observed storm tide level only (a 182-year event) without runup, where only 5 and 4 % of the studied area are considered as flooded, respectively. It appears that in a shore platform environment, a wider foreshore reduces wave runup and flood levels.

Strong turbulent mixing induced by internal bores interacting with internal tide‐driven vertically sheared flow

AbstractWe observed the formation of an internal bore interacting with the vertically sheared flow generated during the previous phase of the internal tide, which resulted in strong turbulent mixing. The rate of turbulent kinetic energy dissipation reached on the order of 10−5 W kg−1 during the event. Numerical simulations reproduced the observed interaction of internal bores with the sheared flow and verified the hypothesized breaking and mixing mechanism. The numerical results indicated that the Iribarren number, or the ratio of the topographic slope to the internal wave slope, plays a major role in the mixing intensity and types of internal bores. It was found that waves with low Iribarren numbers lead to bores that interact with vertically sheared flows induced by the previous phase of the internal tide and are more likely to produce strong wave breaking and mixing.

Empirical wave run-up formula for wave, storm surge and berm width

An empirical model to predict wave run-up on beaches considering storm wave and surge conditions and berm widths (dry beach) has been derived through a synthetic data set generated from a one-dimensional Boussinesq wave model. The new run-up equation is expressed as a function of a new Iribarren number composed of three regions: the foreshore, the berm or dry beach width, and the dune. The dissipative effect of the berm is included as a reduction factor expressed as a function of the berm width normalized by the offshore wavelength. The equation is relatively simple but is shown to be applicable for a fairly wide variety of berm widths and storm wave conditions associated with extreme events such as hurricanes, and it is shown to be an improvement over existing empirical run-up models that do not consider the berm width explicitly. In addition, the new parameterization of the Iribarren number considering the three regions and the berm width reduction factor are shown to improve other empirical models.

Wave runup prediction using M5′ model tree algorithm

In recent years, soft computing schemes have received increasing attention for solving coastal engineering problems and knowledge extraction from the existing data. In this paper, capabilities of M5′ Decision Tree algorithm are implemented for predicting the wave runup using existing laboratory data. The decision models were established using the surf similarity parameter (ξ), slope angle (cot α), beach permeability factor (Sp), relative wave height (H/h), wave spectrum (Ss) and wave momentum flux (m). 451 laboratory data of the wave runup were utilized for developing wave runup prediction models. The performance of developed models is evaluated with statistical measures. The results demonstrate the strength of M5′ model tree algorithm in predicting the wave runup with high precision. Good agreement exists between the proposed runup formulae and existing empirical relations.

Surfzone Wave Characteristics During Flood Tide on the Central West Coast of India

Surfzone wave characteristics, measured using a wave and tide gauge (WTG) during a flood tide, were studied at three different beaches having different nearshore slopes. The spectral wave characteristics viz., wave-height and mean wave period were estimated considering different sample sizes. Inter-comparisons of wave climate between each of three beaches for a similar tide level are presented. The wave-height and mean wave period values obtained from the wave analysis for each of the record using waves by wave method show that surfeone wave-height increased with time during a flood tide and the mean wave period decreased with time up to mid tide and then increased during the rest of the measurement period at Keri and Miramar beaches. At Candolim, the reversing trend of mean wave period increase is observed to occur much before reaching the mid tide level. The surfzone waves during a flood tide indicated that the wave-heights increased with time while the mean wave period showed a decreasing trend in general. The variation of breaker index showed a decreasing trend from low tide to high tide ranging between 0.45 and 0.23. The surf similarity parameter estimated corroborates with the visual observations.

TTP로 피복된 경사식구조물의 처오름높이 산정식: 사면경사 및 피복층 두께 효과

Wave runup is one of the most important factors affecting the design of coastal structure exposed to wave attack. In this study, two dimensional laboratory tests were conducted under the different random wave conditions and structure configurations to develop a formula to predict runup heights. Rubble-mound structure consisted of tetrapod armour blocks with 1:1.5 and 1:2 slopes. The relative water depths (the ratio of the significant wave height to water depth at the toe) ranged from 0.14 to 0.56. The formula proposed here is applicable to surf similarity parameter ranging from 2 to 6. Runup heights on 1:2 slope were higher than those on 1:1.5 slope. Runup heights were reduced by 5% when the armour layer thickness increased two times.

Estimation of regular wave run-up on slopes of perforated coastal structures constructed on sloping beaches

This study was carried out to investigate the regular wave run-up phenomenon on smooth slopes of perforated coastal structures constructed on sloping beaches and the various parameters that affect wave run-up. Experiments were conducted using various hydraulic and structural parameters. The relative coastal structure distance, relative depth, relative wave height, beach slope, coastal structure inclination, and surf similarity parameter were found to be positively correlated to the relative wave run-up. The wave steepness and coastal structure perforation percentage were found to be negatively correlated to the relative wave run-up. The results also show that the coastal structure perforation percentage plays a dominant role in the attenuation of short waves but a less significant role in the attenuation of long waves. The quantitative analyses were performed using multiple additive regression trees (MART) and multilayer perceptron neural networks (MLP) methods. The results indicate that the MART method׳s prediction accuracy and avoidance of over-fitting were superior to those of the MLP method. The percentage improvement in the root mean square error of the MART model over the MLP model in predicting relative wave run-up was 57.56%. The analysis results suggest that MART-based modeling is effective in predicting wave run-up.

TTP로 피복된 경사식구조물의 처오름높이 산정식: 사면경사 1:1.5 조건

The runup height is an important design parameter to determine the crest elevation of coastal structures and seawalls. In this study, two dimensional wave runup tests for rubble-mound structure covered by tetrapods were conducted. Incident waves at the toe include nonbreaking, breaking and broken random wave conditions. A empirical formula to predict runup elevation of rubble-mound structure with 1:1.5 front slope was proposed on the basis of physical model test results using a surf similarity parameter. The test results from this study were compared with those from van der Meer and Stam(1992).

Characteristic Time, Length and Velocity Scales of Transverse Flows in the Surf Zone

An ultrasonic velocity profiler (UVP) acquires instantaneous distributions of axial velocity along the ultrasonic beam emitted from the transducer. In this paper, organizations of the transverse flows over a span of a laboratory wave flume in the surf zone were identified experimentally on the basis of UVP measurements. Ensemble mean divergent and convergent flows were observed over the span of the flume in the surf zone regardless of breaker conditions. By analogy with the flow evolution in a previous computation, by Watanabe and Saeki [1999], we identified that the organization of the wave-breaking-induced counter-rotating vortices determined the spatial and temporal variations in the transverse flows at the early stages of the breaking process regardless of the widths of wave flumes and friction on the sidewalls and bottom. The observed transverse flows were driven by pairs of counter-rotating vortices produced under the breaking waves and the change in the orientation during the passage of breaking waves. The fundamental features of the transverse flows evolving in the breaking process, depending on the breaker type, are discussed statistically to parameterize velocity, time, and length scales of the variations of the transverse velocity. The dimensionless length and time scales had negative linear correlations with the Froude number (defined by relative transverse convection with respect to gravity) as well as a surf similarity parameter, which indicates that the gravity effect associated with the projections of the breaking wave crests defines the primary roller vorticity and shear intensity at the plunging location, resulting in destabilization of the flows in the transverse direction to form organized transverse flow structures.

The Breakwater, from Wave Breaker to Wave Catcher

The function of breakwater as a wave energy breaker needs to be changed into a coastal protection that can capture wave energy. Such Innovation is important for the maritime state that un-renewable energy was in critical deposit. This study examines the magnitude of the wave energy that can be captured through the slope breakwater over-topping. This research was conducted by physical model simulations at the Laboratory of Coastal Engineering, Department of Civil Engineering, Hasanuddin University.Physical model simulation 1:20 in geometric scale have been performed under regular wave conditionsto simulate six types of structure model where differ in slope and height of free-board.The results showed an over-topping discharge (q) is significantly influenced by the parameters of the breakwater free-board relative to the wave height (Rc/Hi), the slope of the structure (tan α) and wave steepness (Hi/Lo). The result of over-topping discharge (q) equation was found smaller thanthe Van Der Meer result in the breaker parameter (zp)less than 2, while in the zp higher than 2, the rate of qis much larger than the Van Der Meer rate. The power efficiency achievement is about 7.4% on averagefor zpsmaller than2, while the power efficiency for zphigher than 2 is about 34% in average.

An empirical solution for tsunami run-up on compound slopes

Deterministic numerical models for tsunami inundation provide the most accurate means for estimating tsunami run-up when the bathymetry/topography and water-level time history at the seaward boundary are well known. However, it is often the case that there is uncertainty in both the bathymetry/topography and water level at the seaward boundary. For these reasons, empirical solutions for tsunami run-up may be preferred because the run-up can be computed quickly allowing a probabilistic estimate the tsunami run-up risk. In this paper, an empirical solution for tsunami run-up is developed based on an analytic solution and calibrated using a Boussinesq wave model for plane-sloped and compound-sloped cases, including the effects of bottom friction, wave breaking, and the slope of the inundated land area. The new relation is a function of the tsunami wave amplitude at a specific water depth (100 m) to provide clear guidance for practical application, and of two values of the surf-similarity parameter to account for a compound slope. The model comprises three equations for three regions: breaking, transition, and non-breaking. The model predictions are compared with survey data from the 2011 Tohoku tsunami in Japan without recalibration. The new equation provides reasonable estimates of run-up height and is generally conservative.

Upwelling rebound, ephemeral secondary pycnoclines, and the creation of a near‐bottom wave guide over the Monterey Bay continental shelf

AbstractSeveral sequential upwelling events were observed in fall 2012, using measurements from the outer half of the continental shelf in Monterey Bay, during which the infiltration of dense water onto the shelf created a secondary, near‐bottom pycnocline. This deep pycnocline existed in concert with the near‐surface pycnocline and enabled the propagation of near‐bottom, cold, semidiurnal internal tidal bores, as well as energetic, high‐frequency, nonlinear internal waves of elevation (IWOE). The IWOE occurred within 20 m of the bottom, had amplitudes of 8–24 m, periods of 6–45 min, and depth‐integrated energy fluxes up to 200 W m−1. Iribarren numbers (<0.03) indicate that these IWOE were nonbreaking in this region of the shelf. These observations further demonstrate how regional upwelling dynamics and the resulting bulk, cross‐margin hydrography is a first‐order control on the ability of internal waves, at tidal and higher frequencies, to propagate through continental shelf waters.

The dynamics of breaking internal solitary waves on slopes

AbstractUsing direct numerical simulations (DNS), we investigate the structure and energetics of breaking internal waves on slopes. We employ a Navier–Stokes code in an idealized three-dimensional domain where an internal solitary wave of depression impinges upon a sloping bottom. Seven cases with varying initial wave amplitude and bathymetric slope, but constant wave Reynolds number $\mathit{Re}_{w}$ are considered. Volume-integrated values of dissipation and irreversible mixing are related to the density and velocity structure of the wave throughout the breaking process. The majority of dissipation (63 %) occurs along the no-slip bottom boundary. Most of the remaining dissipation (35 %) and nearly all irreversible mixing occurs in the interior after breaking, when density overturns are present at the interface. Breaking introduces three-dimensionality to the flow field that is driven by the lateral breakdown of density overturns and the lobe–cleft instability typical of gravity currents. The resulting longitudinal rolls (streamwise vorticity) increase dissipation by roughly 8 % and decrease irreversible mixing by roughly 20 % when compared with a similar two-dimensional simulation. The bulk mixing efficiency is shown to increase for larger and smaller values of the internal Iribarren number ${\it\xi}$, with a minimum for intermediate values of ${\it\xi}$ and a peak near ${\it\xi}=0.8$ for plunging breakers. This trend is explained by the degree of two-dimensionality in the flow, and agrees with previous results in the literature after accounting for Reynolds number effects. Local turbulence quantities are also calculated at ‘virtual moorings’, and a location upslope of the breakpoint but downslope of the intersection of the pycnocline and the bottom is shown to provide a signal that is most representative of the volume-integrated dissipation and mixing results.