Fengyan Shi - Academia.edu (original) (raw)

Papers by Fengyan Shi

Estuaries and Coasts, 2007

The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were in... more The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were investigated using a modified Nearshore Community Model (NearCoM). The model was enhanced to account for cohesive sediment erosion and deposition, sediment transport, combined wave and current shear stresses, and seagrass effects on drag. Expressions for seagrass drag as a function of seagrass shoot density and canopy height were derived from published flume studies of model vegetation. The predicted reduction of volume flux for steady flow through a bed agreed reasonably well with a separate flume study. Predicted wave attenuation qualitatively captured seasonal patterns observed in the field: wave attenuation peaked during the flowering season and decreased as shoot density and canopy height decreased. Model scenarios with idealized bathymetries demonstrated that, when wave orbital velocities and the seagrass canopy interact, increasing seagrass bed width in the direction of wave propagation results in higher wave attenuation, and increasing incoming wave height results in higher relative wave attenuation. The model also predicted lower skin friction, reduced erosion rates, and higher bottom sediment accumulation within and behind the bed. Reduced erosion rates within seagrass beds have been reported, but reductions in stress behind the bed require further studies for verification. Model results suggest that the mechanism of sediment trapping by seagrass beds is more complex than reduced erosion rates alone; it also requires suspended sediment sources outside of the bed and horizontal transport into the bed.

We provide preliminary calculations of wave generation, propagation and inundation for the Decemb... more We provide preliminary calculations of wave generation, propagation and inundation for the December 26, 2004 Indian Ocean tsunami. Calculations are based on Boussinesq model FUNWAVE and are carried out on a Cartesian grid with spatial resolution comparable to 2 minutes in latitude and longitude. Initial conditions are provided by the TOPICS model and are based on estimates of ground motion

an2 We formulate a general multiphase model representing water-bubble mixture fluid and multi-com... more an2 We formulate a general multiphase model representing water-bubble mixture fluid and multi-component bubble populations. An enhanced 2-DV VOF model with ak turbulence closure is used to model the mixture fluid phase. The bubble phase is governed by the advection-diffusion equations of the gas molar concentration and bubble intensity for groups of bubbles with different sizes. The initial bubble entrainment

From a true color image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbvie... more From a true color image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbview-2 satellite, we observed two packets of orderly wave clouds on two sides of Hainan Island in the South China Sea. A packet of 23 wave clouds stretches southward from the island.

Based on differences in seafloor morphology and informatio n about the earthquake, we develop fou... more Based on differences in seafloor morphology and informatio n about the earthquake, we develop four separate sources for the December 26, 2004 tsunami, along a 1200 km long rupture zone. We trigger these sources in a time sequence spanning 331 s, to perform a numerical simulation of the tsunami, with a higher-order Boussinesq model. We find reasonable agreeme nt of

Coastal Engineering, 2014

The newly developed nearshore circulation model, SHORECIRC, using a hybrid finite-difference fini... more The newly developed nearshore circulation model, SHORECIRC, using a hybrid finite-difference finite-volume TVD-type scheme, is coupled with the wave model SWAN in the Nearshore Community Model (NearCoM) system. The new modeling system is named NearCoM-TVD and the purpose of this study is to report the capability and limitation of NearCoM-TVD for several coastal applications. For tidal inlet applications, the model is verified with the semi-analytical solution of for an idealized inlet-bay system. To further evaluate the model performance in predicting nearshore circulation under intense wave-current interaction over complex bathymetry, modeled circulation patterns are validated with measured data during RCEX field experiment . For sediment transport applications, two sediment transport models are applied to predict three sandbar migration events at Duck, NC, during August to October 1994. The model of incorporates wave-induced onshore sediment transport rate as a function of the standard deviation of wave-induced horizontal velocities. The modeled beach profile evolution for two offshore events and one onshore event agrees well with the measured data. The second model investigated here combines two published sediment transport models, namely, the total load model driven by currents under the effect of wave stirring (Soulsby, 1997) and the wave-driven sediment transport model due to wave asymmetry/skewness . The model study with limited field data suggests that the parameterization of wave stirring is appropriate during energetic wave conditions. However, during low energy wave conditions, the effect of wave stirring needs to be re-calibrated.

Coastal Engineering 2002 - Solving Coastal Conundrums - Proceedings of the 28th International Conference, 2003

Coastal Engineering Proceedings, 2011

This paper demonstrates that numerical modeling tools such as a RANS-VOF model can be applied con... more This paper demonstrates that numerical modeling tools such as a RANS-VOF model can be applied confidently to reduce the level of uncertainty from empirical guidance and provide for a deterministic quantification of the hydraulic response associated with any arbitrary Caisson breakwater superstructure geometry. The RANS-VOF model used for this paper is first satisfactorily validated against laboratory measurements (surface elevation, overtopping and pressure) of a caisson breakwater on a rubble-mound foundation and then applied to several prototype caisson breakwater superstructure geometries. Numerical simulations presented in this paper for prototype geometries demonstrate that curved/inclined parapets, when compared with vertical face caisson breakwaters with the same crest elevation, can lead to large increases in overtopping as well as downward forces. Expectedly, the landward forces are reduced by the implementation of a curved or recessed and inclined parapet when compared to a caisson with a completely vertical face. During large overtopping events, the model results show that much larger short-duration seaward loads can be generated for curved and inclined superstructures when compared to vertical face geometries. This is in general agreement with previous laboratory experiments as well as field observations of seaward caisson sliding and failure resulting from large overtopping events. Further, numerical experiments indicate that the overtopping response of a superstructure can vary noticeably due to small changes in the recessed length of an inclined or curved parapet. The numerical model also easily provides for the quantification of the variation of instantaneous and peak overtopping discharges along the crest of the caisson superstructure, and which can provide for useful guidance in the design of various crest infrastructure components, such as drainage systems, flow deflectors, wave power devices etc.

Ocean Wave Measurement and Analysis (2001), 2002

Based on the fully nonlinear Boussinesq equations in Cartesian coordinates, the equations in gene... more Based on the fully nonlinear Boussinesq equations in Cartesian coordinates, the equations in generalized coordinates are derived to adapt computations to irregularly shaped shorelines, such as harbors, bays and tidal inlets, and to make computations more efficient in large near-shore regions. Contravariant components of velocity vectors are employed in the derivation instead of the normal components in curvilinear coordinates or original components in Cartesian coordinates, which greatly simplifies the equations in generalized curvilinear coordinates. A high-order finite difference scheme with staggered grids in the image domain is adopted in the numerical model. The model is applied to five examples involving curvilinear coordinate systems. The results of these cases are in good agreement with analytical results, experimental data, and the results from the uniform grid model, which shows that the model has good accuracy and efficiency in dealing with the computations of nonlinear surface gravity waves in domains with complicated geometries. q

Journal of Waterway, Port, Coastal, and Ocean Engineering, 2015

Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a s... more Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours.

From a true colour image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbvi... more From a true colour image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbview-2 satellite, we observed two packets of orderly wave clouds on two sides of Hainan Island in the South China Sea. A packet of 23 wave clouds stretches southward from the island. A second packet of more than 20 wave clouds stretches north-eastward off the north-east

Journal of Geophysical Research, 2003

1] A time domain Boussinesq model for nearshore hydrodynamics is improved to obtain the conservat... more 1] A time domain Boussinesq model for nearshore hydrodynamics is improved to obtain the conservation of vertical vorticity correct to second order and extended for use on an open coast using longshore periodic boundary conditions. The model is utilized to simulate surface waves and longshore currents under laboratory and field conditions. Satisfactory agreement is found between numerical results and measurements, including root mean square wave height, mean water level, and longshore current. One striking result of the simulations is the prediction of the strong longshore current in the trough shoreward of the bar as observed during the Duck Experiment on Low-frequency and Incident-band Longshore and Across-shore Hydrodynamics field campaign. The model results give insight into the spatial and temporal variability of wave-driven longshore currents and the associated vertical vorticity field under the phase-resolving, random wave forcing with wave/current interaction. Numerical experiments are carried out to examine the response of the modeled longshore currents to the randomness of surface waves and the cross-shore distributions of bed shear stress coefficient. We find that both regular and irregular waves lead to very similar mean longshore currents, while the input of monochromatic, unidirectional waves results in much more energetic shear waves than does the input of random waves. The model results favor Whitford and finding that the bed shear stress coefficient for the area offshore the bar is larger than that in the trough, as better agreement with the field data for both regular and irregular waves is found if such coefficients are used in the Boussinesq model.

The Proceedings of the Coastal Sediments 2011, 2011

ABSTRACT Episodic river flooding triggered by large rainfall may contribute a significant amount ... more ABSTRACT Episodic river flooding triggered by large rainfall may contribute a significant amount of terrestrial sediment deposits in the estuary/river mouth. Understanding the influence of these sediment deposits in the estuaries and continental shelves is important in predicting the changing coastal morphology and assessing future reclamation activities. In this study a two-dimensional-vertical (2DV) non-hydrostatic model solving Reynolds-Averaged Navier-Stokes (RANS) equations for salt-stratified fine sediment-laden flow is demonstrated to be capable of computing unsteady and inhomogeneous frontal processes. The numerical model predicts the main features of turbidity current with reversing buoyancy similar to that observed by Hurzeler et al. (1996) in a small laboratory flume. To study large-scale hyperpycnal flow events for a realistic setting, a 3D open-source hydrostatic coastal modeling system, FVCOM (The Unstructured Grid Finite Volume Coastal Ocean Model) is utilized to study hypopycnal and hyperpycnal plumes. Preliminary results of FVCOM for simulating Gaoping River plume (Taiwan) due to a moderate discharge event are shown. Future work will be focus on inter-comparisons between these two models to evaluate the importance of hydrostatic assumptions in determining the resulting plume dynamics and deposits.

Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007

The paper analyzes the mixing features in numerically generated shear waves by simulating the cir... more The paper analyzes the mixing features in numerically generated shear waves by simulating the circulation during SANDYDUCK experiments. Different wave resolving Boussinesq type models and a wave averaged model have been compared. They produce different velocity/vorticity fields and in turn different mixing properties. Lagrangian statistics have been used to study this aspect. Differences in absolute and relative dispersion and diffusion

Quaternary Science Reviews, 2009

We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska usin... more We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska using results from numerical simulation of hypothetical but plausible mass-flow sources such as submarine landslides and volcanic debris avalanches. The Aleutian arc consists of a chain of volcanic mountains, volcanic islands, and submarine canyons, surrounded by a low-relief continental shelf above about 1000-2000 m water depth. Parts of the arc are fragmented into a series of fault-bounded blocks, tens to hundreds of kilometers in length, and separated from one another by distinctive fault-controlled canyons that are roughly normal to the arc axis. The canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes. The volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large-scale sector collapse into the sea. Large scale mass-flow deposits have not been mapped on the seafloor south of the Aleutian Islands, in part because most of the area has never been examined at the resolution required to identify such features, and in part because of the complex nature of erosional and depositional processes. Extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the Aleutian Islands. Because the Aleutian arc is surrounded by deep, open ocean, mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources. To test this hypothesis we present a series of numerical simulations of submarine mass-flow initiated tsunamis from eight different source areas. We consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope. The flows have lengths that range from 40 to 80 km, maximum thicknesses of 400-800 m, and maximum widths of 10-40 km. We also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse, at four locations (Makushin, Cleveland, Seguam and Yunaska SW volcanoes), which represent large to moderate sized events in this region. We calculate tsunami sources using the numerical model TOPICS and simulate wave propagation across the Pacific using a spherical Boussinesq model, which is a modified version of the public domain code FUNWAVE. Our numerical simulations indicate that geologically plausible mass flows originating in the North Pacific near the Aleutian Islands can indeed generate large local tsunamis as well as large transoceanic tsunamis. These waves may be several meters in elevation at distal locations, such as Japan, Hawaii, and along the North and South American coastlines where they would constitute significant hazards.

Estuaries and Coasts, 2007

The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were in... more The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were investigated using a modified Nearshore Community Model (NearCoM). The model was enhanced to account for cohesive sediment erosion and deposition, sediment transport, combined wave and current shear stresses, and seagrass effects on drag. Expressions for seagrass drag as a function of seagrass shoot density and canopy height were derived from published flume studies of model vegetation. The predicted reduction of volume flux for steady flow through a bed agreed reasonably well with a separate flume study. Predicted wave attenuation qualitatively captured seasonal patterns observed in the field: wave attenuation peaked during the flowering season and decreased as shoot density and canopy height decreased. Model scenarios with idealized bathymetries demonstrated that, when wave orbital velocities and the seagrass canopy interact, increasing seagrass bed width in the direction of wave propagation results in higher wave attenuation, and increasing incoming wave height results in higher relative wave attenuation. The model also predicted lower skin friction, reduced erosion rates, and higher bottom sediment accumulation within and behind the bed. Reduced erosion rates within seagrass beds have been reported, but reductions in stress behind the bed require further studies for verification. Model results suggest that the mechanism of sediment trapping by seagrass beds is more complex than reduced erosion rates alone; it also requires suspended sediment sources outside of the bed and horizontal transport into the bed.

Journal of Geophysical Research: Oceans, 2015

We formulate a CL-vortex form of surface wave force for a quasi-3D nearshore circulation model. T... more We formulate a CL-vortex form of surface wave force for a quasi-3D nearshore circulation model. The CL-vortex force formulation is obtained by applying surface wave equations to depth-integra ted and wave-averaged momentum equations. A new splitting algorithm of current velocity is used to facilitate the application of wave equations to the wave-averaged equations. The derivation shows that the CL-vortex term

Coastal Engineering 2000, 2001

A single solitary wave interacting at normal incidence with a semi-infinite vertical breakwater r... more A single solitary wave interacting at normal incidence with a semi-infinite vertical breakwater results in the formation of a single vortex which is subsequently shed from the structure. In this paper, we describe experiments which were conducted using a solitary wave propagating along a uniform depth wave flume past a vertical wall. Both surface elevations and strength of the vortex were measured in the experiments. A fully nonlinear Boussinesq model with Smagorinsky subgrid mixing is then employed to simulate the experiments. Comparisons are made between the numerical results and experimental data. It is shown that the present numerical model is capable of simulating wave-induced vortices. It is also shown that the model predicts wave height better than the potential flow models do.

Estuaries and Coasts, 2007

The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were in... more The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were investigated using a modified Nearshore Community Model (NearCoM). The model was enhanced to account for cohesive sediment erosion and deposition, sediment transport, combined wave and current shear stresses, and seagrass effects on drag. Expressions for seagrass drag as a function of seagrass shoot density and canopy height were derived from published flume studies of model vegetation. The predicted reduction of volume flux for steady flow through a bed agreed reasonably well with a separate flume study. Predicted wave attenuation qualitatively captured seasonal patterns observed in the field: wave attenuation peaked during the flowering season and decreased as shoot density and canopy height decreased. Model scenarios with idealized bathymetries demonstrated that, when wave orbital velocities and the seagrass canopy interact, increasing seagrass bed width in the direction of wave propagation results in higher wave attenuation, and increasing incoming wave height results in higher relative wave attenuation. The model also predicted lower skin friction, reduced erosion rates, and higher bottom sediment accumulation within and behind the bed. Reduced erosion rates within seagrass beds have been reported, but reductions in stress behind the bed require further studies for verification. Model results suggest that the mechanism of sediment trapping by seagrass beds is more complex than reduced erosion rates alone; it also requires suspended sediment sources outside of the bed and horizontal transport into the bed.

We provide preliminary calculations of wave generation, propagation and inundation for the Decemb... more We provide preliminary calculations of wave generation, propagation and inundation for the December 26, 2004 Indian Ocean tsunami. Calculations are based on Boussinesq model FUNWAVE and are carried out on a Cartesian grid with spatial resolution comparable to 2 minutes in latitude and longitude. Initial conditions are provided by the TOPICS model and are based on estimates of ground motion

an2 We formulate a general multiphase model representing water-bubble mixture fluid and multi-com... more an2 We formulate a general multiphase model representing water-bubble mixture fluid and multi-component bubble populations. An enhanced 2-DV VOF model with ak turbulence closure is used to model the mixture fluid phase. The bubble phase is governed by the advection-diffusion equations of the gas molar concentration and bubble intensity for groups of bubbles with different sizes. The initial bubble entrainment

From a true color image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbvie... more From a true color image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbview-2 satellite, we observed two packets of orderly wave clouds on two sides of Hainan Island in the South China Sea. A packet of 23 wave clouds stretches southward from the island.

Based on differences in seafloor morphology and informatio n about the earthquake, we develop fou... more Based on differences in seafloor morphology and informatio n about the earthquake, we develop four separate sources for the December 26, 2004 tsunami, along a 1200 km long rupture zone. We trigger these sources in a time sequence spanning 331 s, to perform a numerical simulation of the tsunami, with a higher-order Boussinesq model. We find reasonable agreeme nt of

Coastal Engineering, 2014

The newly developed nearshore circulation model, SHORECIRC, using a hybrid finite-difference fini... more The newly developed nearshore circulation model, SHORECIRC, using a hybrid finite-difference finite-volume TVD-type scheme, is coupled with the wave model SWAN in the Nearshore Community Model (NearCoM) system. The new modeling system is named NearCoM-TVD and the purpose of this study is to report the capability and limitation of NearCoM-TVD for several coastal applications. For tidal inlet applications, the model is verified with the semi-analytical solution of for an idealized inlet-bay system. To further evaluate the model performance in predicting nearshore circulation under intense wave-current interaction over complex bathymetry, modeled circulation patterns are validated with measured data during RCEX field experiment . For sediment transport applications, two sediment transport models are applied to predict three sandbar migration events at Duck, NC, during August to October 1994. The model of incorporates wave-induced onshore sediment transport rate as a function of the standard deviation of wave-induced horizontal velocities. The modeled beach profile evolution for two offshore events and one onshore event agrees well with the measured data. The second model investigated here combines two published sediment transport models, namely, the total load model driven by currents under the effect of wave stirring (Soulsby, 1997) and the wave-driven sediment transport model due to wave asymmetry/skewness . The model study with limited field data suggests that the parameterization of wave stirring is appropriate during energetic wave conditions. However, during low energy wave conditions, the effect of wave stirring needs to be re-calibrated.

Coastal Engineering 2002 - Solving Coastal Conundrums - Proceedings of the 28th International Conference, 2003

Coastal Engineering Proceedings, 2011

This paper demonstrates that numerical modeling tools such as a RANS-VOF model can be applied con... more This paper demonstrates that numerical modeling tools such as a RANS-VOF model can be applied confidently to reduce the level of uncertainty from empirical guidance and provide for a deterministic quantification of the hydraulic response associated with any arbitrary Caisson breakwater superstructure geometry. The RANS-VOF model used for this paper is first satisfactorily validated against laboratory measurements (surface elevation, overtopping and pressure) of a caisson breakwater on a rubble-mound foundation and then applied to several prototype caisson breakwater superstructure geometries. Numerical simulations presented in this paper for prototype geometries demonstrate that curved/inclined parapets, when compared with vertical face caisson breakwaters with the same crest elevation, can lead to large increases in overtopping as well as downward forces. Expectedly, the landward forces are reduced by the implementation of a curved or recessed and inclined parapet when compared to a caisson with a completely vertical face. During large overtopping events, the model results show that much larger short-duration seaward loads can be generated for curved and inclined superstructures when compared to vertical face geometries. This is in general agreement with previous laboratory experiments as well as field observations of seaward caisson sliding and failure resulting from large overtopping events. Further, numerical experiments indicate that the overtopping response of a superstructure can vary noticeably due to small changes in the recessed length of an inclined or curved parapet. The numerical model also easily provides for the quantification of the variation of instantaneous and peak overtopping discharges along the crest of the caisson superstructure, and which can provide for useful guidance in the design of various crest infrastructure components, such as drainage systems, flow deflectors, wave power devices etc.

Ocean Wave Measurement and Analysis (2001), 2002

Based on the fully nonlinear Boussinesq equations in Cartesian coordinates, the equations in gene... more Based on the fully nonlinear Boussinesq equations in Cartesian coordinates, the equations in generalized coordinates are derived to adapt computations to irregularly shaped shorelines, such as harbors, bays and tidal inlets, and to make computations more efficient in large near-shore regions. Contravariant components of velocity vectors are employed in the derivation instead of the normal components in curvilinear coordinates or original components in Cartesian coordinates, which greatly simplifies the equations in generalized curvilinear coordinates. A high-order finite difference scheme with staggered grids in the image domain is adopted in the numerical model. The model is applied to five examples involving curvilinear coordinate systems. The results of these cases are in good agreement with analytical results, experimental data, and the results from the uniform grid model, which shows that the model has good accuracy and efficiency in dealing with the computations of nonlinear surface gravity waves in domains with complicated geometries. q

Journal of Waterway, Port, Coastal, and Ocean Engineering, 2015

Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a s... more Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours.

From a true colour image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbvi... more From a true colour image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbview-2 satellite, we observed two packets of orderly wave clouds on two sides of Hainan Island in the South China Sea. A packet of 23 wave clouds stretches southward from the island. A second packet of more than 20 wave clouds stretches north-eastward off the north-east

Journal of Geophysical Research, 2003

1] A time domain Boussinesq model for nearshore hydrodynamics is improved to obtain the conservat... more 1] A time domain Boussinesq model for nearshore hydrodynamics is improved to obtain the conservation of vertical vorticity correct to second order and extended for use on an open coast using longshore periodic boundary conditions. The model is utilized to simulate surface waves and longshore currents under laboratory and field conditions. Satisfactory agreement is found between numerical results and measurements, including root mean square wave height, mean water level, and longshore current. One striking result of the simulations is the prediction of the strong longshore current in the trough shoreward of the bar as observed during the Duck Experiment on Low-frequency and Incident-band Longshore and Across-shore Hydrodynamics field campaign. The model results give insight into the spatial and temporal variability of wave-driven longshore currents and the associated vertical vorticity field under the phase-resolving, random wave forcing with wave/current interaction. Numerical experiments are carried out to examine the response of the modeled longshore currents to the randomness of surface waves and the cross-shore distributions of bed shear stress coefficient. We find that both regular and irregular waves lead to very similar mean longshore currents, while the input of monochromatic, unidirectional waves results in much more energetic shear waves than does the input of random waves. The model results favor Whitford and finding that the bed shear stress coefficient for the area offshore the bar is larger than that in the trough, as better agreement with the field data for both regular and irregular waves is found if such coefficients are used in the Boussinesq model.

The Proceedings of the Coastal Sediments 2011, 2011

ABSTRACT Episodic river flooding triggered by large rainfall may contribute a significant amount ... more ABSTRACT Episodic river flooding triggered by large rainfall may contribute a significant amount of terrestrial sediment deposits in the estuary/river mouth. Understanding the influence of these sediment deposits in the estuaries and continental shelves is important in predicting the changing coastal morphology and assessing future reclamation activities. In this study a two-dimensional-vertical (2DV) non-hydrostatic model solving Reynolds-Averaged Navier-Stokes (RANS) equations for salt-stratified fine sediment-laden flow is demonstrated to be capable of computing unsteady and inhomogeneous frontal processes. The numerical model predicts the main features of turbidity current with reversing buoyancy similar to that observed by Hurzeler et al. (1996) in a small laboratory flume. To study large-scale hyperpycnal flow events for a realistic setting, a 3D open-source hydrostatic coastal modeling system, FVCOM (The Unstructured Grid Finite Volume Coastal Ocean Model) is utilized to study hypopycnal and hyperpycnal plumes. Preliminary results of FVCOM for simulating Gaoping River plume (Taiwan) due to a moderate discharge event are shown. Future work will be focus on inter-comparisons between these two models to evaluate the importance of hydrostatic assumptions in determining the resulting plume dynamics and deposits.

Coastal Engineering 2006 - Proceedings of the 30th International Conference, 2007

The paper analyzes the mixing features in numerically generated shear waves by simulating the cir... more The paper analyzes the mixing features in numerically generated shear waves by simulating the circulation during SANDYDUCK experiments. Different wave resolving Boussinesq type models and a wave averaged model have been compared. They produce different velocity/vorticity fields and in turn different mixing properties. Lagrangian statistics have been used to study this aspect. Differences in absolute and relative dispersion and diffusion

Quaternary Science Reviews, 2009

We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska usin... more We analyze mass-flow tsunami generation for selected areas within the Aleutian arc of Alaska using results from numerical simulation of hypothetical but plausible mass-flow sources such as submarine landslides and volcanic debris avalanches. The Aleutian arc consists of a chain of volcanic mountains, volcanic islands, and submarine canyons, surrounded by a low-relief continental shelf above about 1000-2000 m water depth. Parts of the arc are fragmented into a series of fault-bounded blocks, tens to hundreds of kilometers in length, and separated from one another by distinctive fault-controlled canyons that are roughly normal to the arc axis. The canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes. The volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large-scale sector collapse into the sea. Large scale mass-flow deposits have not been mapped on the seafloor south of the Aleutian Islands, in part because most of the area has never been examined at the resolution required to identify such features, and in part because of the complex nature of erosional and depositional processes. Extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the Aleutian Islands. Because the Aleutian arc is surrounded by deep, open ocean, mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources. To test this hypothesis we present a series of numerical simulations of submarine mass-flow initiated tsunamis from eight different source areas. We consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope. The flows have lengths that range from 40 to 80 km, maximum thicknesses of 400-800 m, and maximum widths of 10-40 km. We also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse, at four locations (Makushin, Cleveland, Seguam and Yunaska SW volcanoes), which represent large to moderate sized events in this region. We calculate tsunami sources using the numerical model TOPICS and simulate wave propagation across the Pacific using a spherical Boussinesq model, which is a modified version of the public domain code FUNWAVE. Our numerical simulations indicate that geologically plausible mass flows originating in the North Pacific near the Aleutian Islands can indeed generate large local tsunamis as well as large transoceanic tsunamis. These waves may be several meters in elevation at distal locations, such as Japan, Hawaii, and along the North and South American coastlines where they would constitute significant hazards.

Estuaries and Coasts, 2007

The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were in... more The effects of seagrass bed geometry on wave attenuation and suspended sediment transport were investigated using a modified Nearshore Community Model (NearCoM). The model was enhanced to account for cohesive sediment erosion and deposition, sediment transport, combined wave and current shear stresses, and seagrass effects on drag. Expressions for seagrass drag as a function of seagrass shoot density and canopy height were derived from published flume studies of model vegetation. The predicted reduction of volume flux for steady flow through a bed agreed reasonably well with a separate flume study. Predicted wave attenuation qualitatively captured seasonal patterns observed in the field: wave attenuation peaked during the flowering season and decreased as shoot density and canopy height decreased. Model scenarios with idealized bathymetries demonstrated that, when wave orbital velocities and the seagrass canopy interact, increasing seagrass bed width in the direction of wave propagation results in higher wave attenuation, and increasing incoming wave height results in higher relative wave attenuation. The model also predicted lower skin friction, reduced erosion rates, and higher bottom sediment accumulation within and behind the bed. Reduced erosion rates within seagrass beds have been reported, but reductions in stress behind the bed require further studies for verification. Model results suggest that the mechanism of sediment trapping by seagrass beds is more complex than reduced erosion rates alone; it also requires suspended sediment sources outside of the bed and horizontal transport into the bed.

Journal of Geophysical Research: Oceans, 2015

We formulate a CL-vortex form of surface wave force for a quasi-3D nearshore circulation model. T... more We formulate a CL-vortex form of surface wave force for a quasi-3D nearshore circulation model. The CL-vortex force formulation is obtained by applying surface wave equations to depth-integra ted and wave-averaged momentum equations. A new splitting algorithm of current velocity is used to facilitate the application of wave equations to the wave-averaged equations. The derivation shows that the CL-vortex term

Coastal Engineering 2000, 2001

A single solitary wave interacting at normal incidence with a semi-infinite vertical breakwater r... more A single solitary wave interacting at normal incidence with a semi-infinite vertical breakwater results in the formation of a single vortex which is subsequently shed from the structure. In this paper, we describe experiments which were conducted using a solitary wave propagating along a uniform depth wave flume past a vertical wall. Both surface elevations and strength of the vortex were measured in the experiments. A fully nonlinear Boussinesq model with Smagorinsky subgrid mixing is then employed to simulate the experiments. Comparisons are made between the numerical results and experimental data. It is shown that the present numerical model is capable of simulating wave-induced vortices. It is also shown that the model predicts wave height better than the potential flow models do.