Numerical investigation of ocean waves generated by three typhoons in offshore China

The influences of the three types of reanalysis wind fields on the simulation of three typhoon waves occurred in2015 in offshore China were numerically investigated.The typhoon wave model was based on the simulating waves nearshore model(SWAN),in which the wind fields for driving waves were derived from the European Centre for Medium-Range Weather Forecasts(ECMWF)Re-Analysis-Interim(ERA-interim),the National Centers for Environmental Prediction climate forecast system version 2(CFSv2)and cross-calibrated multi-platform(CCMP)datasets.Firstly,the typhoon waves generated during the occurrence of typhoons Chan-hom(1509),Linfa(1510)and Nangka(1511)in 2015 were simulated by using the wave model driven by ERA-interim,CFSv2 and CCMP datasets.The numerical results were validated using buoy data and satellite observation data,and the simulation results under the three types of wind fields were in good agreement with the observed data.The numerical results showed that the CCMP wind data was the best in simulating waves overall,and the wind speeds pertaining to ERA-Interim and CCMP were notably smaller than those observed near the typhoon centre.To correct the accuracy of the wind fields,the Holland theoretical wind model was used to revise and optimize the wind speed pertaining to the CCMP near the typhoon centre.The results indicated that the CCMP wind-driven SWAN model could appropriately simulate the typhoon waves generated by three typhoons in offshore China,and the use of the CCMP/Holland blended wind field could effectively improve the accuracy of typhoon wave simulations.

Numerical investigation of solitary wave run-up attenuation by patchy vegetation

Coastal vegetation is capable of decreasing wave run-up.However,because of regrowth,decay or man-made damage,coastal vegetation is always distributed in patches,and its internal distribution is often non-uniform.This study investigates the effects of patchy vegetation on solitary wave run-up by using a numerical simulation.A numerical model based on fully nonlinear Boussinesq equations is established to simulate the wave propagation on a slope with patchy vegetation.By using the model,the process of solitary wave run-up attenuation due to patchy vegetation is numerically analysed.The numerical results reveal that patchy vegetation can considerably attenuate the wave run-up in an effective manner.In addition,high-density patched vegetation can attenuate the solitary wave run-up more effectively than low-density patched vegetation can.For the same density,patchy vegetation with a uniform distribution has a better attenuation effect on wave run-up compared to that of patchy vegetation with a non-uniform distribution.

Effects of sea level rise on storm surge and waves within the Yangtze River Estuary

Sea level rise (SLR) can cause water depth increase (WDI) and coastal inundation (CI).By applying the coupled FVCOM + SWAN model,this study investigates the potential impacts of WDI and CI,induced by a 1.0 m SLR,on storm surge and waves within the Yangtze River Estuary.A 1.0 m WDI decreases the maximum storm surge by 0.15 m and increases the maximum significant wave height by 0.35 m.The CI effect size is smaller when compared with WDI.CI decreases the maximum storm surge and significant wave height by 0.04 and 0.07 m,respectively.In the near-shore area,WDI significantly alters the local hydrodynamic environment,thereby stimulating changes in maximum storm surges and wave heights.Low-lying regions are negatively impacted by CI.Conversely,in deep-water areas,the relative change in water depth is minimal and the effect of CI is gradually enhanced.The combined effect of WDI and CI decreases the maximum surge by 0.31 m and increases the maximum significant wave height by 0.21 m.As a result,CI may be neglected when designing deep-water infrastructures.Nonetheless,the complex interactions between adoption and neglect of CI should be simulated to achieve the best seawall flood control standards and design parameters.

Computational investigation on hydrodynamic and sediment transport responses influenced by reclamation projects in the Meizhou Bay,China

Reclamation projects are the main method of coastal exploitation,and the hydrodynamic environmental effect,together with the sediment transport response of the reclamation project,is important to the project’s site selection and environmental protection.Herein,a 3D numerical model based on the finite volume community ocean model(FVCOM)is applied to simulate the changes in the Meizhou Bay’s hydrodynamic environment and sediment transport after a reclamation project.The reclamation project greatly alters the shape of the shoreline and narrows the bay,leading to a significant change in its hydrodynamic environment and sediment transport.After the project,the clockwise coastal residual current in the corner above the Meizhou Island gradually disappears.An obvious counter-clockwise coastal residual current emerges around the rectangular corner.The tidal prism decreases by 0.65×10^9 and 0.44×10^9 m^3 in the spring and neap tides,respectively.The residence time presents a major increase.These changes lead to the weakening of the water exchange capacity and the reduction of the self-purification capacity of the bay.Currents in the tidal channel weaken,whilst currents in the horizontal channel strengthen.The strength and scope of particle trajectories around the horizontal channel and the Meizhou Island enhance.The suspended sediment concentration(SSC)increases in the majority of the Meizhou Bay but decreases in the lateral bay.The eastern corner of Z2 shows a tendency to erode.The western region of the Meizhou Island,the upper portion of the rectangular corner and the western corner of Z4 show a tendency to deposit.The reclamation project increases the maximum storm surges by 0.06 m and decreases the maximum significant wave heights by 0.09 m.

Coupling hydrodynamic models with GIS for storm surge simulation： application to the Yangtze Estuary and the Hangzhou Bay, China

Storm surge is one of the most serious oceanic disasters. Accurate and timely numerical prediction is one of the primary measures for disaster control. Traditional storm surge models lack of accuracy and time effects. To overcome the disadvantages, in this paper, an analytical cyclone model was first added into the Finite-Volume Coastal Ocean Model （FVCOM） consisting of high resolution, flooding and drying capabilities for 3D storm surge modeling. Then, we integrated MarineTools Pro into a geographic information system （GIS） to supplement the storm surge model. This provided end users with a friendly modeling platform and easy access to geographically referenced data that was required for the model input and output. A temporal GIS tracking analysis module was developed to create a visual path from storm surge numerical results. It was able to track the movement of a storm in space and time. MarineTools Pro＇ capabilities could assist the comprehensive understanding of complex storm events in data visualization, spatial query, and analysis of simulative results in an objective and accurate manner. The tools developed in this study further supported the idea that the coupled system could enhance productivity by providing an efficient operating environ- ment for accurate inversion or storm surge prediction. Finally, this coupled system was used to reconstruct the storm surge generated by Typhoon Agnes （No. 8114） and simulated typhoon induced-wind field and water elevations of Yangtze Estuary and Hangzhou Bay. The simulated results show good correlation with actual surveyed data. The simple operating interface of the coupled system is very convenient for users, who want to learn the usage of the storm surge model, especially for first-time users, which can save their modeling time greatly.

APPLICATION OF CDF(2,2) TO ANALYSIS OF SUSPENDED SEDIMENT IMAGE

The characteristics of suspended sediment image can be reflected by the coefficients of biorthogonal wavelet transform of CDF（2,2）. Based on the power distribution in different scales, an adaptive algorithm is proposed in this paper, whereby the coefficients are adjusted non-linearly. The particle information can be well retained while the useless background is removed. In this way, satisfactory binary image can be obtained for further analysis of the sediment particle.