Gangfeng Ma - Academia.edu (original) (raw)

Papers by Gangfeng Ma

Coastal Engineering, 2015

Turbulence and sediment transport models are incorporated into a three-dimensional hydrodynamics ... more Turbulence and sediment transport models are incorporated into a three-dimensional hydrodynamics model to investigate the mechanisms of morphologic evolution of scour holes within the Indian River Inlet, Delaware, USA. The inlet bed had eroded slightly since stabilizing the channel walls in late 1930s through 1976. The mean rate of bed erosion roughly doubled as a response to anthropogenic activities within the inlet such as the removal of~80 piles remaining from an old bridge. Severe erosion near the in-water bridge supports and cofferdams for the replacement bridge necessitated channel bed stabilization that along with the remained debris from the removal of old bridge piles enhanced the growth of two deep scour holes on the bayside and oceanside of the bridge cofferdams. Scour hole and channel bed evolution has decreased drastically since 1994. The present investigation suggests that, initially, flow concentration through the cofferdams of the replacement bridge was the main reason for scour hole development. Bed shear stress over the forward-facing slope of the scour hole entrains sediment from the bed and extends the scour hole along the inlet and in the vertical direction. Flow separation within the developed scour holes after channel bed stabilization enhances turbulence and appears to be the dominant mechanism for further scour hole development.

Ocean Dynamics, 2014

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Ber... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com". Abstract To understand how vegetation canopies affect sediment transport on tidal flats, a numerical study of tidal flow and sediment transport on an idealized tidal flat with a patch of vegetation is conducted. The numerical model is firstly validated by laboratory measurements of flow and sediment deposition in a partially vegetated open channel.

Coastal Engineering Proceedings, 2012

Coastal Engineering Proceedings, 2012

Coastal Engineering Proceedings, 2011

This paper provides a review of our recent developments in numerical models for predicting physic... more This paper provides a review of our recent developments in numerical models for predicting physical processes related to optical properties inside the surfzone. Model components in the developments include the bubble entrainment model, 2D and 3D multiphase two-fluid models for modeling quiescent phase of bubbles, turbulence models with influences of bubbles, bubble coalescence and breakup models used in the two-fluid models, and foam model for predicting foam patch generation and evolution inside the surfzone. The paper summarizes theories used in the model components and shows some numerical results from model tests.

This report documents a three-dimensional shock-capturing Non-Hydrostatic WAVE model NHWAVE of , ... more This report documents a three-dimensional shock-capturing Non-Hydrostatic WAVE model NHWAVE of , which solves the incompressible Navier-Stokes equations in terrain and surface-following sigma coordinates. The model predicts instantaneous surface elevation and 3D flow field, and is capable of resolving coastal wave processes (shoaling, refraction, diffraction, breaking etc.) as well as tsunami wave generation by landslide. The documentation provides a detailed description of governing equations, turbulence models and numerical schemes. A user's manual is provided and gives instructions on how to set up the simulations. Finally, several examples are documented.

The coastal zone is an area that has the most active land-ocean interaction. Its evolution takes ... more The coastal zone is an area that has the most active land-ocean interaction. Its evolution takes in high complexity, fuzziness and non-linearity under the influence of many factors such as the coming water and sediment, marine dynamics, sea-floor terrain, crust movement, climatic change and human activities etc. Considering the ability of the neural network on non-linear problems, a BP model to predict the sub-delta evolution is established. Meanwhile, the scheme and coefficients of the network are investigated in this paper. Taking Huanghe Sub-delta as an example, its area and shoreline change are studied. The results indicate that the computed and the measured are in a good agreement. It is also proved that the artificial neural network can be perfectly used to forecast the evolution of the delta.

ABSTRACT When a great earthquake generates a large magnitude tsunami, the focus is on the relatio... more ABSTRACT When a great earthquake generates a large magnitude tsunami, the focus is on the relationship between the two, usually addressed through analysis of earthquake, tide and geodetic data, often in various combinations. These methods, however, have limitations in resolving the up-dip extent of rupture; onshore geodetic inversions have limited sensitivity to slip offshore, seismic inversions have instabilities in moment estimation where subfault segments are shallow, and tsunami inversions average over the large areas of ocean bottom uplift. Seismic wave estimates depend on the velocity structure, which affects both seismic moment estimation and inferred slip. Validation of tsunami generating mechanism is mainly from tide gauges, although there are problems and assumptions made in their use. Models may be circular, with inversion of the data used to identify earthquake rupture that is then modeled as the tsunami source. Different slip distributions may be modelled and the results compared with recorded surface elevations offshore and inundation data, then adjusted to provide new scenarios in order to improve the agreement with tidal observations. Tide gauge data may be both from near and far fields; invalidating the identification of a contribution from local submarine mass failure (SMF). "Green's functions" used for assimilating tsunami observations in source models may be based on non-dispersive equations which may not capture the correct phase speed of shorter wave trains, e.g. such as generated by SMFs. A major problem with identifying the generating mechanism is when tsunami magnitude is large compared to the earthquake such as with 'tsunami' earthquakes and where the earthquake is not slow, as in Papua New Guinea in 1998, where a SMF was identified as the tsunami source. However, with most great earthquakes, e.g. the Indian Ocean, it is accepted from the outset that the only source is the earthquake. Another, more recent event is the Tohoku-oki earthquake and tsunami that devastated the northeast of Japan in March 2011; although with some unusual rupture characteristics it is not a tsunami earthquake. There are now a number of simulations published, that mostly assume an earthquake source but that fail the simple test of using an independently defined earthquake rupture mechanism that can be validated by onshore fieldwork, tide gauge and offshore buoy data. Here we briefly consider some of the existing source models and present new tsunami simulations based on a combination of a FEM coseismic source and a SMF. We show that the multi-source tsunami agrees well with the available tide gauge data and field observations onshore and the wave data from offshore buoys.

The devastating coastal impact of the 2011 Tohoku-oki tsunami cannot at present be fully explaine... more The devastating coastal impact of the 2011 Tohoku-oki tsunami cannot at present be fully explained from a co-seismic source alone, because resulting tsunami simulations do not reproduce the elevated tsunami runup heights of up to 40 m along the (Sanriku) coast of northern Honshu, nor the higher frequency wave periods (3-4 min.) recorded at offshore buoys (both GPS and DART). Here, we model the tsunami generated from the combination of: (i) a new co-seismic source based on a detailed three-dimensional (3D) Finite Element Modeling (FEM) of the heterogeneous subduction zone, with geodetic data assimilation (Grilli et al., 2012a,b; Hugue, 2008); and (ii) an additional tsunami source from a submarine mass failure (SMF) triggered north of the main rupture with a time delay. We show that the multisource tsunami agrees well with all the available field observations, both offshore and onshore.

Coastal Engineering, 2015

Turbulence and sediment transport models are incorporated into a three-dimensional hydrodynamics ... more Turbulence and sediment transport models are incorporated into a three-dimensional hydrodynamics model to investigate the mechanisms of morphologic evolution of scour holes within the Indian River Inlet, Delaware, USA. The inlet bed had eroded slightly since stabilizing the channel walls in late 1930s through 1976. The mean rate of bed erosion roughly doubled as a response to anthropogenic activities within the inlet such as the removal of~80 piles remaining from an old bridge. Severe erosion near the in-water bridge supports and cofferdams for the replacement bridge necessitated channel bed stabilization that along with the remained debris from the removal of old bridge piles enhanced the growth of two deep scour holes on the bayside and oceanside of the bridge cofferdams. Scour hole and channel bed evolution has decreased drastically since 1994. The present investigation suggests that, initially, flow concentration through the cofferdams of the replacement bridge was the main reason for scour hole development. Bed shear stress over the forward-facing slope of the scour hole entrains sediment from the bed and extends the scour hole along the inlet and in the vertical direction. Flow separation within the developed scour holes after channel bed stabilization enhances turbulence and appears to be the dominant mechanism for further scour hole development.

Ocean Dynamics, 2014

Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Ber... more Your article is protected by copyright and all rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint is for personal use only and shall not be selfarchived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com". Abstract To understand how vegetation canopies affect sediment transport on tidal flats, a numerical study of tidal flow and sediment transport on an idealized tidal flat with a patch of vegetation is conducted. The numerical model is firstly validated by laboratory measurements of flow and sediment deposition in a partially vegetated open channel.

Coastal Engineering Proceedings, 2012

Coastal Engineering Proceedings, 2012

Coastal Engineering Proceedings, 2011

This paper provides a review of our recent developments in numerical models for predicting physic... more This paper provides a review of our recent developments in numerical models for predicting physical processes related to optical properties inside the surfzone. Model components in the developments include the bubble entrainment model, 2D and 3D multiphase two-fluid models for modeling quiescent phase of bubbles, turbulence models with influences of bubbles, bubble coalescence and breakup models used in the two-fluid models, and foam model for predicting foam patch generation and evolution inside the surfzone. The paper summarizes theories used in the model components and shows some numerical results from model tests.

This report documents a three-dimensional shock-capturing Non-Hydrostatic WAVE model NHWAVE of , ... more This report documents a three-dimensional shock-capturing Non-Hydrostatic WAVE model NHWAVE of , which solves the incompressible Navier-Stokes equations in terrain and surface-following sigma coordinates. The model predicts instantaneous surface elevation and 3D flow field, and is capable of resolving coastal wave processes (shoaling, refraction, diffraction, breaking etc.) as well as tsunami wave generation by landslide. The documentation provides a detailed description of governing equations, turbulence models and numerical schemes. A user's manual is provided and gives instructions on how to set up the simulations. Finally, several examples are documented.

The coastal zone is an area that has the most active land-ocean interaction. Its evolution takes ... more The coastal zone is an area that has the most active land-ocean interaction. Its evolution takes in high complexity, fuzziness and non-linearity under the influence of many factors such as the coming water and sediment, marine dynamics, sea-floor terrain, crust movement, climatic change and human activities etc. Considering the ability of the neural network on non-linear problems, a BP model to predict the sub-delta evolution is established. Meanwhile, the scheme and coefficients of the network are investigated in this paper. Taking Huanghe Sub-delta as an example, its area and shoreline change are studied. The results indicate that the computed and the measured are in a good agreement. It is also proved that the artificial neural network can be perfectly used to forecast the evolution of the delta.

ABSTRACT When a great earthquake generates a large magnitude tsunami, the focus is on the relatio... more ABSTRACT When a great earthquake generates a large magnitude tsunami, the focus is on the relationship between the two, usually addressed through analysis of earthquake, tide and geodetic data, often in various combinations. These methods, however, have limitations in resolving the up-dip extent of rupture; onshore geodetic inversions have limited sensitivity to slip offshore, seismic inversions have instabilities in moment estimation where subfault segments are shallow, and tsunami inversions average over the large areas of ocean bottom uplift. Seismic wave estimates depend on the velocity structure, which affects both seismic moment estimation and inferred slip. Validation of tsunami generating mechanism is mainly from tide gauges, although there are problems and assumptions made in their use. Models may be circular, with inversion of the data used to identify earthquake rupture that is then modeled as the tsunami source. Different slip distributions may be modelled and the results compared with recorded surface elevations offshore and inundation data, then adjusted to provide new scenarios in order to improve the agreement with tidal observations. Tide gauge data may be both from near and far fields; invalidating the identification of a contribution from local submarine mass failure (SMF). "Green's functions" used for assimilating tsunami observations in source models may be based on non-dispersive equations which may not capture the correct phase speed of shorter wave trains, e.g. such as generated by SMFs. A major problem with identifying the generating mechanism is when tsunami magnitude is large compared to the earthquake such as with 'tsunami' earthquakes and where the earthquake is not slow, as in Papua New Guinea in 1998, where a SMF was identified as the tsunami source. However, with most great earthquakes, e.g. the Indian Ocean, it is accepted from the outset that the only source is the earthquake. Another, more recent event is the Tohoku-oki earthquake and tsunami that devastated the northeast of Japan in March 2011; although with some unusual rupture characteristics it is not a tsunami earthquake. There are now a number of simulations published, that mostly assume an earthquake source but that fail the simple test of using an independently defined earthquake rupture mechanism that can be validated by onshore fieldwork, tide gauge and offshore buoy data. Here we briefly consider some of the existing source models and present new tsunami simulations based on a combination of a FEM coseismic source and a SMF. We show that the multi-source tsunami agrees well with the available tide gauge data and field observations onshore and the wave data from offshore buoys.

The devastating coastal impact of the 2011 Tohoku-oki tsunami cannot at present be fully explaine... more The devastating coastal impact of the 2011 Tohoku-oki tsunami cannot at present be fully explained from a co-seismic source alone, because resulting tsunami simulations do not reproduce the elevated tsunami runup heights of up to 40 m along the (Sanriku) coast of northern Honshu, nor the higher frequency wave periods (3-4 min.) recorded at offshore buoys (both GPS and DART). Here, we model the tsunami generated from the combination of: (i) a new co-seismic source based on a detailed three-dimensional (3D) Finite Element Modeling (FEM) of the heterogeneous subduction zone, with geodetic data assimilation (Grilli et al., 2012a,b; Hugue, 2008); and (ii) an additional tsunami source from a submarine mass failure (SMF) triggered north of the main rupture with a time delay. We show that the multisource tsunami agrees well with all the available field observations, both offshore and onshore.