scholarly journals VORTICAL VLF MOTIONS UNDER SHORE-NORMAL INCIDENT WAVES

2012 ◽  
Vol 1 (33) ◽  
pp. 58 ◽  
Author(s):  
Matthieu Andreas De Schipper ◽  
Ad Reniers ◽  
Jamie MacMahan ◽  
Roshanka Ranasinghe
Keyword(s):  
Numerical Model ◽  
Incident Wave ◽  
Large Scale ◽  
Wave Spectrum ◽  
Normal Wave ◽  
Low Frequency ◽  
Velocity Fluctuations ◽  
Model Simulations ◽  
Frequency Spread ◽  
Incident Waves

Field observations and numerical model simulations are examined to investigate the magnitude of vortical very low frequency (VLF) velocity fluctuations (i.e. large scale surfzone eddies) under different offshore wave forcing. Observations of vortical VLF motions under shore -normal wave incidence at Duck, NC, USA are re-analyzed and compared with the characteristics of the incident wave spectrum. Long wave periods and narrow frequency spread incident waves were found to coincide with stronger vortical VLF motions. Numerical model simulations investigating the effect of the incident wave parameters in a more isolated way confirm the observed effect of frequency spread and wave period on the magnitude of VLF motions. Variations in incident wave spectrum resulted in changes in the vortical VLF magnitude of the same order as the magnitude of the vortical VLF velocity fluctuations themselves. These results imply that under shore-normal incident waves strong vortical VLF velocity fluctuations in the surfzone are more likely under swell conditions and at swell dominated coasts.

scholarly journals FINAL DESIGN OF THE NAGS HEAD BEACH NOURISHMENT PROJECT USING A LONGSHORE NUMERICAL MODEL

2012 ◽  
Vol 1 (33) ◽  
pp. 64 ◽  
Author(s):  
Haiqing Liu Kaczkowski ◽  
Timothy W Kana
Keyword(s):  
Numerical Model ◽  
Large Scale ◽  
Numerical Models ◽  
Normal Wave ◽  
Beach Nourishment ◽  
Shoreline Evolution ◽  
Longshore Transport ◽  
Final Design ◽  
Model Setup ◽  
The Impact

Nags Head, located at the northeastern part of North Carolina in the U.S., has sustained chronic erosion over the past 50 years. In 2005, Coastal Science & Engineering (CSE) was retained by the town of Nags Head to develop an interim beach restoration plan. Profile volume change was used in the planning and preliminary design of the project, and longshore and cross-shore numerical models were used in the final design to refine the preliminary nourishment plan and increase potential longevity of the project. This paper focuses on the key factors of the longshore numerical model setup for the project. These include model selection, input data and parameters, model calibration, and applications under different design alternatives. The Generalized Model for Simulating Shoreline Changes (GENESIS) was used in this study to evaluate shoreline evolution under normal wave conditions during various stages of the design life following the beach nourishment project. The model was used to identify the potential occurrence of erosional hotspots and to optimize the nourishment design so that the effects of such hotspots could be avoided or minimized where possible. Model results were also used to evaluate the impact of borrow area dredging on longshore transport in the project area and the impact of nourishment on shoaling in the adjacent inlet. The project encompasses 10.11 miles (mi) (16.28 kilometers-km) of ocean shoreline, and the design nourishment volume is based on the total permitted volume of 4 million cubic yards (cy) (3 million cubic meters-m³). [Note: As-built length was 10.0 mi and volume was 4.615 million cubic yards.] The final design has fill densities varying from north to south in relation to historical erosion rates and model projections. The average fill density is 75 cubic yards per foot (cy/ft) (188 m³/m) and ranges from 38 cy/ft to 150 cy/ft (95 m³/m to 375 m³/m). In conclusion, it is shown that the numerical model selected in this study was capable of predicting the overall performance of the large scale beach nourishment project in Nags Head as well as the performance at a particular location within or adjacent to the project, and its design methods can offer guidance to future projects.

scholarly journals An oceanic pathway for Madden–Julian Oscillation influence on Maritime Continent Tropical Cyclones

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Karthik Balaguru ◽  
L. Ruby Leung ◽  
Samson M. Hagos ◽  
Sujith Krishnakumar
Keyword(s):  
Numerical Model ◽  
Tropical Cyclones ◽  
Large Scale ◽  
Sea Surface ◽  
Madden Julian Oscillation ◽  
Surface Cooling ◽  
Maritime Continent ◽  
Large Scale Circulation ◽  
Model Simulations ◽  
Sea Surface Cooling

AbstractWhile the Madden–Julian Oscillation (MJO) has been shown to affect tropical cyclones (TCs) worldwide through its modulation of large-scale circulation in the atmosphere, little or no role for the ocean has been identified to date in this influence of MJO on TCs. Using observations and numerical model simulations, we demonstrate that MJO events substantially impact TCs over the Maritime Continent (MC) region through an oceanic pathway. While propagating across the MC region, MJO events cause significant sea surface cooling with an area-averaged value of about 0.35 ± 0.12 °C. Hence, TCs over the MC region immediately following the passage of MJO events encounter considerably cooler sea surface temperatures. Consequently, the enthalpy fluxes under the storms are reduced and the intensification rates decrease by more than 50% on average. These results highlight an important role played by the ocean in facilitating MJO-induced sub-seasonal variability in TC activity over the MC region.

scholarly journals WAVE RUN-UP OBSERVATION AND 2DV NUMERICAL INVESTIGATION ON BEACHES PROTECTED BY STRUCTURES

2012 ◽  
Vol 1 (33) ◽  
pp. 20
Author(s):  
Renata Archetti ◽  
Maria Gabriella Gaeta
Keyword(s):  
Numerical Models ◽  
Wave Spectrum ◽  
Low Frequency ◽  
Swash Zone ◽  
Flow Motion ◽  
Transmission Area ◽  
Wave Conditions ◽  
Run Up ◽  
Incident Waves

The main parameter for the assessment of coastal vulnerability and sediment transport is the wave run-up on the beach, defining the limit of maximum flooding, but also hydrodynamic properties in the Swash Zone (SZ) are trivial for the comprehension of hydro-morphodynamic processes. Several studies have been carried out on the SZ but few literature is still available on the run-up and on SZ flows on beaches protected by Low Crested Structures (LCSs), where flow motion is driven by a combination of low frequency infra-gravity waves and incident waves. In presence of breakwaters, swash incident waves are transmitted through the structure. In the transmission area behind the structures, wave energy is shifted to higher frequencies with respect to the incident wave spectrum and in general its mean period considerably decreases with respect to the incident one. Collecting in situ run-up measurements during storms is essential to understand the SZ processes and properly calibrate their both empirical and numerical models but measuring extreme run-up is difficult, due to the severe sea conditions and due to unexpected nature of storms. The present paper present a numerical and experimental analysis of the wave run-up and of the flow properties on a beach: the study shows the different behavior of unprotected and protected beach, subjected to the same wave conditions. In particular the paper shows that submerged breakwaters reduce in general the run-up height, on the basis of the calibrated 2DV numerical simulations, under extreme wave conditions (TR >50 years), the effect of submerged breakwaters seems to be negligible on the run-up height. Moreover a preliminary empirical equation for run-up with protected beach is proposed

scholarly journals MODELLING WAVE DISSIPATION ON PILE BREAKWATER USING XBEACH

2019 ◽  
Vol 10 (1) ◽  
pp. 1-14
Author(s):  
Eduardo Meyrianso Simanjuntak ◽  
Leo Eliasta ◽  
Juventus Welly Ginting ◽  
Ida Ayu Irawati Diah Ratna Putra
Keyword(s):  
Numerical Model ◽  
Wave Height ◽  
Incident Wave ◽  
Coastal Erosion ◽  
Wave Spectrum ◽  
Technical Aspect ◽  
High Accuracy ◽  
Wave Dissipation ◽  
Improved Design ◽  
Simulated Scenario

Breakwater is a common coastal structure used to reducing wave energy in order to prevent coastal erosion. Considering the economic and technical aspect, pile breakwater is an alternative for the conventional rubble breakwater. An improved design for pile breakwater is proposed here. In this research, we adapt a numerical model developed for vegetation wave dissipation to simulate the interaction between the wave and the pile breakwater. This developed model is hoped to be an assesment tool in planning the implemention of pile breakwater. The wave spectrum show that the numerical model is able to simulate the wave as the physical model with some overestimation. It also point out that the simulation with wave periode (T) = 2.5 s has more significant noise than the simulation with wave periode (T) = 2 s. In general, the numerical model has high accuracy for predicting incident wave height (Hi), transmitted wave height (Ht) and tranmission coefficient (KT) with error below 1 % RMSE. The numerical model also has limitation for KT value greater than 0.9 for the simulated scenario.

scholarly journals GRAVEL BEACH PROFILE EVOLUTION IN WAVE AND TIDAL ENVIRONMENTS

2012 ◽  
Vol 1 (33) ◽  
pp. 15
Author(s):  
Mohamad Hidayat Jamal ◽  
David J. Simmonds ◽  
Vanesa Magar
Keyword(s):  
Numerical Model ◽  
Water Level ◽  
Large Scale ◽  
Water Levels ◽  
Coarse Grained ◽  
Beach Profile ◽  
Model Simulations ◽  
Parameter Values ◽  
Future Work ◽  
Gravel Beach

This paper reports progress made in modifying and applying the X-Beach code to predict and explain the observed behaviour of coarse grained beaches. In a previous study a comparison of beach profile evolution measured during large scale experiments under constant water level with numerical model simulations was made. This placed particular emphasis on the tendency for onshore transport and profile steepening during calm conditions (Jamal et al., 2010). The present paper extends that investigation to study the influence of the advection of surf processes induced by tidal water level variations effects, on gravel beach profile evolution. The parameter values and numerical model used in the simulation is similar to that presented previously. It is assumed that, to good approximation, the groundwater interface inside the beach follows the tidally modulated water level. The results obtained from the model shows that the model provides reasonable simulations of beach profile change in a tidal environment. In comparison with simulations under stationary water levels, a larger berm is produced in agreement with literature. Finally, good agreement is obtained between the model simulations and an example of field observations from a beach at Milford on Sea, UK. Further developments are outlined for future work.

Structural similarity in radial correlations and spectra of longitudinal velocity fluctuations in pipe flow

1978 ◽  
Vol 88 (3) ◽  
pp. 585-608 ◽  
Author(s):  
K. J. Bullock ◽  
R. E. Cooper ◽  
F. H. Abernathy
Keyword(s):  
Turbulent Flows ◽  
Pipe Flow ◽  
Large Scale ◽  
Longitudinal Velocity ◽  
Broad Band ◽  
Low Frequency ◽  
Structural Similarity ◽  
Turbulent Energy ◽  
Physical Significance ◽  
Velocity Fluctuations

The paper describes correlation measurements in both broad and narrow frequency bands of the longitudinal velocity fluctuations in fully developed pipe flow at four positions for a reference probe whilst a second probe was traversed radially from deep in the sublayer to a position near the axis with both longitudinal and transverse separations zero (Δx = Δz = 0). Such measurements require that both the Covariant (Co) and Quadrature (Quad) correlations be determined for each of the 15 frequencies used to constrain the wave component λx.The new data demonstrate that low frequency, large scale turbulence fluctuations extend over the majority of the radial region and that these components are highly correlated. By using a similarity variable kxy, along with a normalized wall distance y/y REF, both correlation functions, i.e. the Co and the Quad components, are shown to collapse. The physical significance of this is discussed.The broad-band data do not collapse because of the large range of wave sizes. However, the present experiment does show that strong radial correlations exist even when one probe is at y+ = 1. This conflicts with the earlier data of Favre, but agrees with the more recent work of Comte-Bellot. There is a significant amount of turbulent energy in frequencies less than 16 Hz (ω+ = 0·008) for turbulent flows of about 105 Reynolds number.The spectral function ωΦ(ω) is also presented for a range of y+ values. Using this form for the power spectral density, along with the stochastic wave modelling and similarity arguments of this paper, it is shown how a consistent explanation for the behaviour of these spectra is obtained. In addition some preliminary results from cross-spectral analyses are presented and suggestions made as to their physical significance.

scholarly journals IS SURF BEAT FORCED OR FREE?

1984 ◽  
Vol 1 (19) ◽  
pp. 59 ◽  
Author(s):  
David A. Huntley ◽  
Chang S. Kim
Keyword(s):  
Incident Wave ◽  
Wave Motion ◽  
Field Experiments ◽  
Beat Frequency ◽  
Low Frequency ◽  
Strongly Correlated ◽  
Edge Waves ◽  
Weakly Coupled ◽  
Dominant Feature ◽  
Incident Waves

Although many field experiments have shown that surf beat motion, with periods longer than incident wave periods, becomes the dominant feature of the nearshore velocity field as the shoreline is approached, the nature of this motion is still not fully understood. This paper describes a field experiment on a sheltered beach which was designed to distinguish between long wave motion directly forced by the incident wave envelope (as suggested by Longuet-Higgins and Stewart, 1962), and wave motion which is only weakly coupled to the local incident waves and therefore essentially free. The results for on/offshore flows show that low frequency surf beat (frequency less than 0.03 Hz) is strongly correlated with the wave envelope, suggesting the dominance of forced wave motion at these frequencies. In a higher frequency band, between 0.06 and 0.095 Hz, the correlation is generally much lower, suggesting that free wave motion, possibly subharmonic edge waves, is significant in this band. The longshore flows are much more weakly correlated to the envelope of either the longshore or on/offshore components of the orbital velocity. This is consistent with previous observations that edge wave motion dominates the longshore surf beat motion.

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