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Using the elliptic mild-slope equation to resolve wave fields in large coastal areas requires enormous computer resources, thus imposing a great restriction on the applicability of this equation for practical engineering problems. An improved numerical model based on the mild slope RCPWAVE model has been developed for computing wave refraction and diffraction in a large coastal area with complex coastline near the Pearl River estuary, in China. An operator splitting method is employed to solve the wave action equation, in which the advection terms are resolved by the Eulerian-Lagrangian method to increase numerical stability and the other terms are discretized by the implicit finite-element method to fit complex coastline geometries. A stable and efficient nominal-time finite-node method is proposed to solve the nonlinear irrotational wave number equation for wave directions. Numerical tests on wave propagation proved that the present model has significant improvements in model stability and efficiency over the RCPWAVE model. Different swell transformation scenarios in the Pearl River estuary have been simulated by the model. For such a large and complex estuarine region, the model simulated the wave distributions reasonably well, with good efficiency, and it also produced results that closely matched the field measurements collected at two wave gauges. DOI: 10.1061/(ASCE)0733-950X(2003)129:6(260) CE Database subject headings: Wave refraction; Wave diffraction; Wave propagation; Finite element method; Lagrangian method; China; Numerical models.

The accuracy of three-dimensional (3D) mass transport modeling strongly relies on how well the vertical structures of the transport processes are resolved with the model resolution. The widely used vertical 'stair-stepped' and topography following sigma ([Sigma])-coordinate systems are fixed in time and space. Hence, these techniques often fail to resolve the details of the time varying, and highly nonlinear, activities in the water column. To better capture the geometrical details of these activities, a new vertical solution-adaptive grid method is introduced in this paper. The method takes into account the gradient variation of a selected variable in the mass transport field as an additional controlling factor in [Sigma]-coordinate transformation and so the new transformed grid is called a Gradient-Adaptive-Sigma (GAS) grid. The transformed grid spacing automatically adjusts in time and space according to the local solution gradient of the selected variable and converges in the high gradient regions for better resolution. The solution-adaptive method is implemented in a surface water numerical model to transform Cartesian coordinates into GAS coordinates. The model is established on the basis of an operator splitting scheme coupled with a Eulerian-Lagrangian method. Four numerical experiments describing the sediment transport activities of net entrainment and net deposition, and also pollutant dispersion, are performed with the transformed model. The computed results agree with the laboratory measurements. A comparison between the results computed by the GAS-gridded model and a [Sigma]-gridded model show that using the GAS-grid arrangement can improve the solution accuracy by as much as one-fold in regions of high solution gradients.

In this paper, the effects of trees on CO2 concentrations in a street canyon in Guangzhou, China are examined by Computational Fluid Dynamics (CFD) simulations of the concentration distribution, taking into account both the CO2 absorption/emission and aerodynamic effects of trees. Simulation results show that, under a 2 m/s southerly prevailing wind condition, CO2 absorption by trees will reduce the CO2 concentration by around 2.5% in the daytime and at the same time the trees'' resistance will increase the difference of CO2 concentrations in the street and at the inflow by 43%. As the traffic density increases to 50 vehicles/min, the effect of trees on the ambient CO2 concentration will change from positive to negative. At night, trees have a negative effect on the concentration in the street canyon mainly because of their resistance to airflow. When environmental wind changes, the effect of trees will be different. [Copyright &y& Elsevier]

Abstract: Plants can improve air quality by removing pollutants. The air purification capability of plants has been receiving increasing attention because of the rapid deterioration of the environment. However, research on evaluating quantitatively the effect of plants on the environmental pollutant concentrations is still scarce. This paper studies the effect of a green roof on the ambient CO2 concentration as an example to assess the benefit of urban greening. The study comprises three parts: (1) Field measurement of the difference of CO2 concentration at a location in the middle of the plants in a small plot of green roof and one in the surrounding area, (2) Experiments to measure the plant’s CO2 absorption velocity and emission rate using a sealed glass chamber; and (3) Computer simulation of the CO2 concentration distribution around a green roof using the measured CO2 absorption velocity and emission rate to quantify the effects of the green roof on the ambient CO2 concentration. [ABSTRACT FROM AUTHOR]

Studies the chemical partitioning of heavy metal contaminants in sediments of the Pearl River Estuary in China. Sequential extraction; Sedimentsl Heavy metals.