Jinhai Zheng

Numerical Simulation of Sloshing Phenomena in Cubic Tank with Multiple Baffles

A two-phase fluid flow model solving Navier-Stokes equations was employed in this paper to investigate liquid sloshing phenomena in cubic tank with horizontal baffle, perforated vertical baffle, and their combinatorial configurations under the harmonic motion excitation. Laboratory experiment of liquid sloshing in cubic tank with perforated vertical baffle was carried out to validate the present numerical model. Fairly good agreements were obtained from the comparisons between the present numerical results and the present experimental data, available numerical data. Liquid sloshing in cubic tank with multiple baffles was investigated numerically in detail under different external excitation frequencies. Power spectrum of the time series of free surface elevation was presented with the aid of fast Fourier transform technique. The dynamic impact pressures acting on the normal and parallel sidewalls were discussed in detail.

Numerical simulation and analysis of saltwater intrusion lengths in the Pearl River Delta, China

ABSTRACT Zhang, W.; Feng, H.C.; Zheng, J.H., Hoitink, A.J.F.; Van Der Vegt, M.; Zhu, Y., and Cai, H.J., 2013. Numerical simulation and analysis of saltwater intrusion lengths in the Pearl River delta, China. In recent years, large-scale saltwater intrusion has been threatening the freshwater supply in the metropolitan cities surrounding the Pearl River delta (PRD). Therefore, a better understanding of the saltwater intrusion process in this region is necessary for local water resource management. In this paper, a one-dimensional flow and salinity model of the Pearl River networks was established to improve our understanding of saltwater intrusion problems in deltas. The model has high spatial resolution, discretized into 328 reaches and 5108 cross-sections, and the time step is 300 seconds for the hydrodynamic model and 30 seconds for the salinity model on the basis of the Courant–Friedrichs–Lewy condition. The model is calibrated and validated against the field measurements of the water surface elevation, discharge, and salinity at around 40 gauges in 2005 and 2001, respectively. The estimated results are in reasonable agreement with the observational data, suggesting that the model is sufficiently robust to simulate the movement of flow and salinity in the Pearl River networks. The simulated 0.5 parts per thousand salinity isohaline in the Pearl River networks displays a shape similar to “S” and slanting to the right, indicating that the maximum saltwater intrusion length occurs at the Humen outlet. In 2005, the saltwater intrusion lengths intruded far upstream at an average length of 32.4 km from the eight outlets, which is nearly two times that in 2001. Four representative upstream flows were also simulated to acquire quantitative knowledge of the response of the saltwater intrusion to discharges. Finally, historical data were collected to compare the situations of saltwater intrusion in the river networks in the 1960s and 2005. The result implies that the abrupt change in topography due to intensive dredging campaigns in the river networks is probably the most crucial factor leading to the saltwater intrusion outbreaks in large areas of the PRD in recent years.

Three-dimensional numerical model for wave-induced seabed response around mono-pile

In this study, a new three-dimensional model was developed to provide a better understanding of the mechanism for wave-induced seabed response around the mono-pile. Based on the poro-elastic theory, the fully dynamic formulations were adopted in the present model to simulate the pore pressure, soil stresses and the displacements of both soil and mono-pile. Good agreement between the numerical simulation and experimental results was obtained. Based on the parametric study, the numerical results concluded that (1) the wave diffraction and reflection have significant effects on the pore pressure and soil displacements around the mono-pile; (2) the largest discrepancy of pore pressure due to the variation in seabed parameters appears in front of mono-pile, while the smallest discrepancy is at the position of angle 3π/4 with respect to the incident wave direction and (3) the increase in the mono-pile horizontal displacement corresponds to the increase in the wave height and the decrease in the seabed Youngs modulus.

A process-based model for sediment transport under various wave and current conditions

The purpose of this study is to investigate the capability of a newly developed process-based model for sediment transport under a wide variety of wave and current conditions. The model is based on the first-order boundary layer equation and the sediment advection-diffusion equation. In particular, a modified low Reynolds number k-ɛ model is coupled to provide the turbulence closure. Detailed model verifications have been performed by simulating a number of laboratory experiments, covering a considerable range of hydrodynamic conditions such as sinusoidal waves, asymmetric waves and wave-current interactions. The model provides satisfactory numerical results which agree well with the measured results, including the time-averaged/dependent sediment concentration profiles and sediment flux profiles, as well as the time series of concentration at given elevations. The observed influences of wave orbital velocity amplitude, wave period and sediment grain size are correctly reproduced, indicating that the fundamental physical mechanisms of those processes are properly represented in the model. It is revealed that the present model is capable of predicting sediment transport under a wide range of wave and current conditions, and can be used to further study the morphodynamic processes in real coastal regions.

Numerical study of sandbar migration under wave-undertow interaction

Reliable simulation of onshore-offshore sandbar migration under various wave and current conditions has remained a challenging task over the last three decades because wave-undertow interaction in the surf zone has been neglected in the existing numerical models. This paper presents the development of an improved sandbar migration model using a phase- and depth-resolving modeling approach. This new model includes interactions between waves and undertow and an empirical time-dependent turbulent eddy viscosity formulation that accounts for the phase dependency of turbulence on flowvelocity and acceleration.The authorsdemonstrate through extensive model-data comparisons thattheseenhancementsresultedinsignificantimprovementsinthepredictivecapabilityofthecross-shoresandbarmigrationbeneathmoderate and energetic waves. The comparison showed wave-undertow interaction playing a crucial role in cross-shore sediment transport. Waves increased the undertow-induced suspended-load flux during offshore sandbar migration, and a weak undertow suppressed the wave-induced onshore bed-load transport during onshore sandbar migration. The proposed empirical time-dependent turbulent eddy viscosity significantly improved the prediction of onshore-directed bed-load transport during onshore sandbar migration. DOI: 10.1061/(ASCE)WW.1943- 5460.0000231.

Numerical simulation of solitary-wave propagation over a steady current

AbstractA two-dimensional numerical model is developed to study the propagation of a solitary wave in the presence of a steady current flow. The numerical model is based on the Reynolds-averaged Navier-Stokes (RANS) equations with a k-e turbulence closure scheme and an internal wave-maker method. To capture the air-water interface, the volume of fluid (VOF) method is used in the numerical simulation. The current flow is initialized by imposing a steady inlet velocity on one computational domain end and a constant pressure outlet on the other end. The desired wave is generated by an internal wave maker. The propagation of a solitary wave traveling with a following/opposing current is simulated. The effects of the current velocity on the solitary-wave motion are investigated. The results show that the solitary wave has a smaller wave height, larger wave width, and higher traveling speed after interacting with a following current. Contrariwise, the solitary wave becomes higher with a smaller wave width and l...

Propagation of tidal waves up in Yangtze Estuary during the dry season

Tide is one of the most important hydrodynamic driving forces and has unique features in the Yangtze Estuary (YE) due to the complex geometry of third-order bifurcations and four outlets. This paper characterizes the tidal oscillations, tidal dampening, tidal asymmetry, and tidal wave propagation, which provides insights into the response of the estuary to tides during the dry season. The structural components of tidal oscillations are initially attained by tidal analysis. The increasingly richer spectrum inside the estuary shows an energy transfer corresponding to the generation and development of nonlinear overtides and compound tides. A 2-D numerical model is further set up to reproduce tidal dynamics in the estuary. The results show that the estuary is a strongly dissipative estuary with a strong nonlinear phenomenon. Three amplifications are presented in the evolution process of tidal ranges due to the channel convergence. Tidal asymmetry is spatiotemporally characterized by the M4/M2 amplitude ratio, the 2M2-M4 phase difference, and the flood-ebb duration-asymmetry parameter, and the estuary tends to be flood-dominant. There exists mimic standing waves with the phase difference of the horizontal and vertical tide close to 90° when tidal wave propagates into the estuary, especially during the neap tide. In addition, the differences in tidal distortion, tidal ranges, and tidal waves along the two routes in the South Branch (S-B) suggest the branched system behaves differently from a single system.

Comparison of Analytical Solutions for Salt Intrusion Applied to the Modaomen Estuary

ABSTRACT Xu, Y.; Zhang, W.; Chen, X.; Zheng, J.; Chen, X., and Wu, H., 2015. Comparison of analytical solutions for salt intrusion applied to the Modaomen Estuary. Salt intrusion in estuaries is an urgent environmental challenge across the world, because salinity influences water quality. The Modaomen Estuary is the main source of freshwater supply in the economically advanced Pearl River Delta, and it is experiencing a salt intrusion problem. Analytical models of salinity variation offer a simple and efficient approach to studying salt intrusion in estuaries. In this paper, two analytical models used worldwide to assess salinity variation in alluvial estuaries are applied to the Modaomen Estuary. The models are derived from salt convection-dispersion equations, with different assumptions for the dispersion coefficient. The performance of these two models was evaluated by comparing their results with field measurements; this revealed that both analytical models apply well to both the estimation of salinity distribution and the prediction of salt intrusion in the Modaomen Estuary. One model agrees more with the field measurements of salinity distribution along the estuary; the second better predicts salt intrusion length.

NUMERICAL WAVE FLUME WITH IMPROVED SMOOTHED PARTICLE HYDRODYNAMICS

This article presents an improved Nearest Neighboring Particle Searching (NNPS) technique for numerical modeling of water waves with the Smoothed Particle Hydrodynamics (SPH) method. The proposed technique differs from others by introducing the concept of Inner and Outer Particle Searching (IOPS) and shifting most of advanced CPU operations into simple addition operations. The IOPS method is shown to significantly improve the computational efficiency and reduce the CPU time especially for large number of particles, based on comparisons with other two NNPS methods. This method is implemented in a 2DV numerical wave flume conducted by the SPH method. Three test cases are examined, including generations and propagations of dam-breaking induced waves, solitary wave and irregular wave. Calculated results are in good agreements with experimental data and theoretical solutions with fairly satisfactory CPU time-consuming. The wave motions observed in physical facilities are successfully reproduced by the SPH numerical wave flume, revealing its robust capability of modeling realistic wave propagation and substantial potential for a wide variety of hydrodynamic problems.

Spatial and temporal variations of the seasonal sea level cycle in the northwest Pacific

The seasonal sea level variations observed from tide gauges over 1900–2013 and gridded satellite altimeter product AVISO over 1993–2013 in the northwest Pacific have been explored. The seasonal cycle is able to explain 60–90% of monthly sea level variance in the marginal seas, while it explains less than 20% of variance in the eddy-rich regions. The maximum annual and semiannual sea level cycles (30 and 6 cm) are observed in the north of the East China Sea and the west of the South China Sea, respectively. AVISO was found to underestimate the annual amplitude by 25% compared to tide gauge estimates along the coasts of China and Russia. The forcing for the seasonal sea level cycle was identified. The atmospheric pressure and the steric height produce 8–12 cm of the annual cycle in the middle continental shelf and in the Kuroshio Current regions separately. The removal of the two attributors from total sea level permits to identify the sea level residuals that still show significant seasonality in the marginal seas. Both nearby wind stress and surface currents can explain well the long-term variability of the seasonal sea level cycle in the marginal seas and the tropics because of their influence on the sea level residuals. Interestingly, the surface currents are a better descriptor in the areas where the ocean currents are known to be strong. Here, they explain 50–90% of interannual variability due to the strong links between the steric height and the large-scale ocean currents.