Research

18 pages, 8056 KiB

Open AccessArticle

Numerical Investigation of Sediment Flushing and Morphological Changes in Tamsui River Estuary through Monsoons and Typhoons

by Tung-Chou Hsieh, Yan Ding, Keh-Chia Yeh and Ren-Kai Jhong

Water 2022, 14(11), 1802; https://0-doi-org.brum.beds.ac.uk/10.3390/w14111802 - 02 Jun 2022

Cited by 1 | Viewed by 1905

Abstract

The removal of reservoir silt and the restoration of existing reservoir capacities through land excavation and hydraulic sediment flushing have become necessary. Hydraulic sediment flushing discharge changes flow and sediment conditions of the downstream river channel. In the Tamsui River estuary in Taiwan, [...] Read more.

The removal of reservoir silt and the restoration of existing reservoir capacities through land excavation and hydraulic sediment flushing have become necessary. Hydraulic sediment flushing discharge changes flow and sediment conditions of the downstream river channel. In the Tamsui River estuary in Taiwan, sediment flushing from the Shihmen reservoir upstream has potential impacts on the morphology of the navigation channels and the adjacent coasts. This study employed a validated coastal and estuarine processes model to investigate: (1) the influence of sediment flushing and tidal levels on morphological changes during flood and flushing-discharge operations of the reservoir, and (2) the differences in morphological changes on the estuary between monsoon and typhoon seasons. The prediction of the morphological changes was carried out by simulating hydrodynamic and morphodynamic processes under multi-year synthetic conditions combined by northeast monsoon and three historical typhoon events. The simulation results reveal that during the operation of sediment flushing when the peak discharge of river flood flow reaches the estuary section at ebb tides, more sediment can be transported to the open sea than that at flood tides. Additionally, the nature reserve area on the left bank of the estuary is eroded during monsoon and silted in typhoon seasons. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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30 pages, 5661 KiB

Open AccessArticle

Parallel-Computing Two-Way Grid-Nested Storm Surge Model with a Moving Boundary Scheme and Case Study of the 2013 Super Typhoon Haiyan

by Yu-Lin Tsai, Tso-Ren Wu, Eric Yen, Chuan-Yao Lin and Simon C. Lin

Water 2022, 14(4), 547; https://0-doi-org.brum.beds.ac.uk/10.3390/w14040547 - 12 Feb 2022

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Abstract

This study presents a numerical tool for calculating storm surges from offshore, nearshore, and coastal regions using the finite-difference method, two-way grid-nesting function in time and space, and a moving boundary scheme without any numerical filter adopted. The validation of the solitary wave [...] Read more.

This study presents a numerical tool for calculating storm surges from offshore, nearshore, and coastal regions using the finite-difference method, two-way grid-nesting function in time and space, and a moving boundary scheme without any numerical filter adopted. The validation of the solitary wave runup on a circular island showed the perfect matches between the model results and measurements for the free surface elevations and runup heights. After the benchmark problem validation, the 2013 Super Typhoon Haiyan event was selected to showcase the storm surge calculations with coastal inundation and flood depths in Tacloban. The catastrophic storm surges of about 8 m and wider, storm-induced inundation due to the Super Typhoon Haiyan were found in the Tacloban Airport, corresponding to the findings from the field survey. In addition, the anti-clockwise, storm-induced currents were explored inside of Cancabato Bay. Moreover, the effect of the nonlinear advection terms with the fixed and moving shoreline and the parallel efficiency were investigated. By presenting a storm surge model for calculating storm surges, inundation areas, and flood depths with the model validation and case study, this study hopes to provide a convenient and efficient numerical tool for forecasting and disaster assessment under a potential severe tropical storm with climate change. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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18 pages, 12279 KiB

Open AccessFeature PaperArticle

Solution of Shallow-Water Equations by a Layer-Integrated Hydrostatic Least-Squares Finite-Element Method

by Shin-Jye Liang, Dong-Jiing Doong and Wei-Ting Chao

Water 2022, 14(4), 530; https://0-doi-org.brum.beds.ac.uk/10.3390/w14040530 - 10 Feb 2022

Cited by 1 | Viewed by 2041

Abstract

A multi-layer hydrostatic shallow-water model was developed in the present study. The layer-integrated hydrostatic nonlinear shallow-water was solved with

θ

time integration and the least-squares finite element method. Since the least-squares formulation was employed, the resulting system of equations was symmetric and positive–definite; [...] Read more.

A multi-layer hydrostatic shallow-water model was developed in the present study. The layer-integrated hydrostatic nonlinear shallow-water was solved with

θ

time integration and the least-squares finite element method. Since the least-squares formulation was employed, the resulting system of equations was symmetric and positive–definite; therefore, it could be solved efficiently by the preconditioned conjugate gradient method. The model was first applied to simulate the von Karman vortex shedding. A well-organized von Karman vortex street was reproduced. The model was then applied to simulate the Kuroshio current-induced Green Island vortex street. A swirling recirculation was formed and followed by several pairs of alternating counter-rotating vortices. The size of the recirculation, as well as the temporal and spatial scale of the vortex shedding, were found to be consistent with ADCP-CDT measurements, X-band radar measurements, and analysis of the satellite images. It was also revealed that Green Island vortices were affected by the upstream Orchid Island vortices. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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18 pages, 5322 KiB

Open AccessArticle

Interplay between Asian Monsoon and Tides Affects the Plume Dispersal of the New Hu-Wei River off the Coast of Midwest Taiwan

by Chia-Ying Ho, Tien-Hsi Fang, Cheng-Han Wu and Hung-Jen Lee

Water 2022, 14(2), 152; https://0-doi-org.brum.beds.ac.uk/10.3390/w14020152 - 07 Jan 2022

Cited by 1 | Viewed by 1268

Abstract

In the coupled estuary–shelf system, plumes originating from the New Hu-Wei and Choshui rivers, consisting of many terrestrial materials, could contaminate the water of the Mailiao industrial harbor. To determine the contribution of the two rivers to pollution, the interaction between river-forced, tide-generating, [...] Read more.

In the coupled estuary–shelf system, plumes originating from the New Hu-Wei and Choshui rivers, consisting of many terrestrial materials, could contaminate the water of the Mailiao industrial harbor. To determine the contribution of the two rivers to pollution, the interaction between river-forced, tide-generating, and monsoon-driven water motions in and around the Mailiao industrial zone harbor was examined by performing a series of numerical model experiments. We used a three-dimensional general circulation model to examine the interplay between Asian monsoon-driven, river-forced, and tide-induced water motions, one of which could primarily affect the plume. The model-derived results for different river discharges revealed that almost all of the ammonium entering the harbor had a slope-positive trend, with oscillations in response to flood–ebb tidal cycles. The ammonium increased with time and flux, except for the 10 m³/s flux. Although the river discharge flux exceeded 200 m³/s, the ammonium entering the harbor was the same as that of the 200 m³/s flux; the ammonium concentration did not increase significantly with time after the flux exceeded 200 m³/s. In addition, irrespective of flood or ebb tidal currents being suppressed by strong Asian monsoons, this mechanism avoided contaminating the water quality of the harbor while northeasterly winds prevailed. By contrast, the southwesterly monsoon drove the geostrophic current northward along the coast; concurrently, the coastal sea level increased to form the surface isobar slope up toward the coast, producing a secondary flow to accelerate geostrophic alongshore currents. The northward geostrophic currents compressed the plumes shoreward, forming a relatively narrow-band plume; the coupling model demonstrated that the southwesterly monsoon-driven current pushed plumes favorably along the west pier into the harbor. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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17 pages, 6682 KiB

Open AccessArticle

A Weighted-Least-Squares Meshless Model for Non-Hydrostatic Shallow Water Waves

by Nan-Jing Wu, Yin-Ming Su, Shih-Chun Hsiao, Shin-Jye Liang and Tai-Wen Hsu

Water 2021, 13(22), 3195; https://0-doi-org.brum.beds.ac.uk/10.3390/w13223195 - 11 Nov 2021

Cited by 1 | Viewed by 1582

Abstract

In this paper, an explicit time marching procedure for solving the non-hydrostatic shallow water equation (SWE) problems is developed. The procedure includes a process of prediction and several iterations of correction. In these processes, it is essential to accurately calculate the spatial derives [...] Read more.

In this paper, an explicit time marching procedure for solving the non-hydrostatic shallow water equation (SWE) problems is developed. The procedure includes a process of prediction and several iterations of correction. In these processes, it is essential to accurately calculate the spatial derives of the physical quantities such as the temporal water depth, the average velocities in the horizontal and vertical directions, and the dynamic pressure at the bottom. The weighted-least-squares (WLS) meshless method is employed to calculate these spatial derivatives. Though the non-hydrostatic shallow water equations are two dimensional, on the focus of presenting this new time marching approach, we just use one dimensional benchmark problems to validate and demonstrate the stability and accuracy of the present model. Good agreements are found in the comparing the present numerical results with analytic solutions, experiment data, or other numerical results. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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25 pages, 1794 KiB

Open AccessArticle

A Theoretical Study of the Hydrodynamic Performance of an Asymmetric Fixed-Detached OWC Device

by Ayrton Alfonso Medina Rodríguez, Rodolfo Silva Casarín and Jesús María Blanco Ilzarbe

Water 2021, 13(19), 2637; https://0-doi-org.brum.beds.ac.uk/10.3390/w13192637 - 25 Sep 2021

Cited by 1 | Viewed by 1391

Abstract

The chamber configuration of an asymmetric, fixed-detached Oscillating Water Column (OWC) device was investigated theoretically to analyze its effects on hydrodynamic performance. Two-dimensional linear wave theory was used, and the solutions for the associated radiation and scattering boundary value problems (BVPs) were derived [...] Read more.

The chamber configuration of an asymmetric, fixed-detached Oscillating Water Column (OWC) device was investigated theoretically to analyze its effects on hydrodynamic performance. Two-dimensional linear wave theory was used, and the solutions for the associated radiation and scattering boundary value problems (BVPs) were derived through the matched eigenfunction expansion method (EEM) and the boundary element method (BEM). The results for the hydrodynamic efficiency and other important hydrodynamic properties were computed and analyzed for various cases. Parameters, such as the length of the chamber and the thickness and submergence of the rear and front walls, were varied. The effects on device performance of adding a step under the OWC chamber and reflecting wall in the downstream region were also investigated. A good agreement between the analytical and numerical results was found. Thinner walls and low submergence of the chamber were seen to increase the efficiency bandwidth. The inclusion of a step slightly reduced the frequency at which resonance occurs, and when a downstream reflecting wall is included, the hydrodynamic efficiency is noticeably reduced at low frequencies due to the near trapped waves in the gap between the OWC device and the rigid vertical wall. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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14 pages, 2114 KiB

Open AccessArticle

Metocean Criteria for Internal Solitary Waves Obtained from Numerical Models

by Liaqat Ali, Nageena Makhdoom, Yifan Gao, Pan Fang, Sikandar Khan and Yong Bai

Water 2021, 13(11), 1554; https://0-doi-org.brum.beds.ac.uk/10.3390/w13111554 - 31 May 2021

Cited by 2 | Viewed by 2046

Abstract

A numerical model in slice configuration was applied to the Central Andaman Sea in order to derive metocean operational and design criteria associated to internal solitary waves which are large amplitude interfacial waves. For that purpose, a 10 year hindcast was generated. The [...] Read more.

A numerical model in slice configuration was applied to the Central Andaman Sea in order to derive metocean operational and design criteria associated to internal solitary waves which are large amplitude interfacial waves. For that purpose, a 10 year hindcast was generated. The model was driven by tides at the open boundary and included realistic stratification and topography. The results have been compared to data mostly taken from satellites and proved to be accurate in determining parameters such as phase speed and interpacket distance. The phase speeds range from 2.21 m/s in March to 2.5 m/s in November. Corresponding interpacket distances range from 99 km to 111 km in close agreement with available data. According to the model results internal solitary waves are more/less frequent in March/August. Model outputs were specifically analyzed at 2 arbitrary locations. Maximum current speeds obtained with the model at those locations occur in November reaching a value close to 1.5 m/s. The computed velocities associated to return periods of 1, 10, 50, 100 and 1000 years are, respectively, 1.67 m/s, 1.76 m/s, 1.8 m/s, 1.81 m/s and 1.84 m/s. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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18 pages, 4139 KiB

Open AccessFeature PaperArticle

Interactions of Solitary Wave with a Submerged Step: Experiments and Simulations

by Wei-Ting Chao, Shin-Jye Liang, Chih-Chieh Young and Chao-Lung Ting

Water 2021, 13(9), 1302; https://0-doi-org.brum.beds.ac.uk/10.3390/w13091302 - 06 May 2021

Cited by 1 | Viewed by 2157

Abstract

A series of experiments exploring the propagation of a solitary wave over a submerged step were performed using a flow-field visualization measurement system, an image-connection technique as well as model simulations. The experimental data were used to validate a one-layer finite-element non-hydrostatic model [...] Read more.

A series of experiments exploring the propagation of a solitary wave over a submerged step were performed using a flow-field visualization measurement system, an image-connection technique as well as model simulations. The experimental data were used to validate a one-layer finite-element non-hydrostatic model and a multi-layer finite-difference non-hydrostatic σ model for various submerged step configurations and wave conditions—combinations of step height ratios d/h, width ratios B/h and solitary wave height ratios H/h, where d denotes the step height, B the step width, H the solitary wave height, and h the still water depth. The main differences between the numerical results and the experimental data are highlighted. The effect of the height and width of the submerged step as well as the wave height of the solitary wave are quantified in terms of reflection (R), transmission (T), and energy dissipation (D). Through a series of numerical experiments, an optimal combination of the height ratio d/h, width ratio B/h, and solitary wave height ratio H/h for breakwater design for coastal protection is suggested. Full article

(This article belongs to the Special Issue Hydrodynamics in Ocean Environment: Experiment and Simulation)

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