SARS疫情预测预报中的分段非线性回归方法

介绍了几种对累计SARS疫情预测预报中的非线性增长曲线模型，说明了Richards增长曲线在这次SARS疫情预测预报中合理性和可行性，由此建立了累计SARS疫情预测预报中的非线性回归点模型。并具体对北京SARS疫情进行了跟踪预测预报，包括整体和分时间段的预测预报，获得了北京SARS疫情随时间的预测预报结果，说明了北京4月底的一系列控制措施对北京SARS疫情所带来的影响，为进一步的后续研究打下了良好基础。     

An efficient iterative method for solving the governing equation of water infiltration problems in unsaturated soils

One of the significant problems in geo-environmental and geotechnical engineering is the unsaturated flow of soil in unsaturated soils. The model of this phenomenon in porous media is governed by the Richards equation. In this paper a new, efficient, iterative method is used to handle the Richards equation. This new technique is obtained from the variational iteration method by a simple reconstruction that is the Laplace iteration method (LIM). In order to evaluate the efficiency and accuracy of the solutions obtained by the proposed method, two representative examples were investigated. The obtained results show that the Laplace iteration method is a very effective method, simplifies the difficulty of classical techniques and is quite accurate for systems of partial differential equations.     

Drainage in heterogeneous sand columns with different geometric structures

This paper discusses multi-step drainage experiments in two heterogeneously packed sand columns (10 × 10 × 20 cm³). Different packing structures were generated using two different sand types. One purpose of the study was to test the influence of packing structures on the movement of water. The second purpose was to assess the quality of predictions for the outflow curves in both columns made with an upscaled model. The heterogeneous structures of the columns can be considered as two opposing extremes. The first column was packed with a random arrangement of two sand types that is not stochastically homogeneous and where a cluster running through the column exists for both materials. The second column was packed with a periodic pattern of coarse-sand inclusions in a fine-sand background and has a clearly defined unit cell. The depth-averaged (2D) spatial distribution of the water content in the columns was monitored during the whole multi-step outflow experiment using neutron radiography. The 3D water content was measured at the steady states by neutron tomography. The experimental results are compared with the model predictions of an upscaled model derived with the homogenization theory. The parameters for the upscaled model are calculated from the hydraulic parameters of the two sand types. These hydraulic parameters were first identified in independent measurements on samples of the two individual sand types, separately. Additionally, the hydraulic parameters of both sands were identified by fitting a numerical model to the measured outflow curves. The different column structures showed a significant effect on water retention and the effective retention function, as water was trapped in the coarse-sand inclusions of the periodic structure. We included this trapping effect in the effective retention function of the upscaled model with an apparent air entry pressure. Contrary to the retention, the different packing structures had no large effect on the dynamic behavior of the outflow. The effective conductivity of the columns is therefore not significantly influenced by the structure. The upscaled models predicted the movement of the averaged water content in the two columns well. This confirms the applicability of upscaled models even if the underlying requirements are not strictly met.     

Rainfall‐triggered shallow landslides: infiltration dynamics in a physical hillslope model

In this study, we investigate the triggering of shallow landslides through the analysis of physical experiments performed in an artificial hillslope. The physical model consists of a reinforced concrete box containing a soil prism with maximum height of 3.5 m, length of 6 m, and width of 2 m. In order to analyse and examine the factors leading to the failure and the triggering modes, the hillslope is equipped with sensors to monitor the pore water pressure and moisture content response to rainfall in a 60 cm thick sand layer overlying a sandy clay soil. Two experiments were performed with different degrees of the sand initial compaction, to investigate the role of porosity on the hydrologic response and the subsequent failure. The experimental results showed that, with initially loose sand, the failure occurred suddenly, without premonitory signs, the soil behaving like a viscous fluid. The collected data showed a rapid increase of the water pressure contextual to the failure of the sand layer. In the second experiment, with initially dense sand, three levels of instability were observed: (i) abundant runoff with limited erosion of the ground surface; (ii) local slip detachments involving a soil thickness of few centimetres; and (iii) a slow advancement of the entire sand layer volume. The hydrologic dynamics observed in the landslide experiments were simulated with numerical solutions of the Richards equation. The results of the simulations agree well with the experiments for the loose sand, while for the dense sand the comparison between experimental and numerical results shows some limitations related to the assumptions of single phase and rigid soil matrix implicit in the Richards equation. Copyright © 2016 John Wiley & Sons, Ltd.     

Advanced programming methods and data structures for computational modelling using edge‐based finite volume methods

The generation of a numerical model must consider the separate issues of the governing equations, the numerical representation of those equations, the data structure that describes the model, the choice of programming language and finally the implementation and code management issues. These issues are considered as a whole in this paper and as a consequence, 10 golden rules for numerical modelling are proposed. By way of application, a saturated–unsaturated flow problem is modelled using the Richards equation and an innovative edge‐based finite volume method. The implementation uses a novel data structure. This is shown to have over 91% code re‐use and hence code written in this way is highly flexible and applicable to many different problems. By way of example, a compacted core earth filled dam problem has been solved. Finally, we conclude that this advanced programming method can significantly reduce code development time. Copyright © 2004 John Wiley & Sons, Ltd.     

A new saturated/unsaturated model for stormwater infiltration systems

Infiltration systems are widely used as an effective urban stormwater control measure. Most design methods and models roughly approximate the complex physical flow processes in these systems using empirical equations and fixed infiltration rates to calculate emptying times from full. Sophisticated variably saturated flow models are available, but rarely applied owing to their complexity. This paper describes the development and testing of an integrated one‐dimensional model of flow through the porous storage of a typical infiltration system and surrounding soils. The model accounts for the depth in the storage, surrounding soil moisture conditions and the interaction between the storage and surrounding soil. It is a front‐tracking model that innovatively combines a soil‐moisture‐based solution of Richard's equation for unsaturated flow with piston flow through a saturated zone as well as a reservoir equation for flow through a porous storage. This allows the use of a simple non‐iterative numerical solution that can handle ponded infiltration into dry soils. The model is more rigorous than approximate stormwater infiltration system models and could therefore be valuable in everyday practice. A range of test cases commonly used to test soil water flow models for infiltration in unsaturated conditions, drainage from saturation and infiltration under ponded conditions were used to test the model along with an experiment with variable depth in a porous storage over saturated conditions. Results show that the model produces a good fit to the observed data, analytical solutions and Hydrus. Copyright © 2008 John Wiley & Sons, Ltd.     

Shoreline accretion and sand transport at groynes inside the Port of Richards Bay

The south-western shoreline along the entrance channel inside the Port of Richards Bay has experienced continued erosion. Four groynes were constructed to stabilise the shoreline. Monitoring of shoreline evolution provided valuable data on the accretion adjacent to two of the groynes and on the sediment transport rates at these groynes. Tides, beach slopes, winds, wave climate, current regime, and sand grain sizes were documented. The one site is “moderately protected” from wave action while the other is “protected” according to the Wiegel [Wiegel, R. L. (1964). Oceanographical engineering. Prentice Hall, Inc., Englewood Cliffs, NJ.] classification. The shoreline accreted progressively at the two groynes at 0.065 m/day and 0.021 m/day respectively. The shorelines accreted right up to the most seaward extremity of the groynes. Equilibrium shorelines were reached within about 3.5 years to 4 years, which compare well with other sites around the world. The mean wave incidence angle is large and was found to be about 22°. The median sand grain sizes were 0.33 mm and 0.37 mm. The groynes acted as total traps, the beach surveys were extended to an adequate depth, and cross-shore sediment transport did not cause appreciable net sand losses into the entrance channel. The net longshore transport rate along the study area, which is north-westbound, is only slightly lower than the gross longshore transport. The actual net longshore transport rates are 18 000 m³/year and 4 600 m³/year respectively at the two groynes. A rocky area limits the availability of sand at one groyne. There is fair agreement between the predicted and measured longshore transport rates at the other groyne.     

Analysis of runoff–storage relationships to evaluate the runoff-buffering potential of a sloping permeable domain

The runoff–storage relationship for a runoff system in a steady-state is analyzed as an indicator of the buffering potential of rainfall-runoff responses. In this relationship, a large storage increase in response to a given runoff increase indicates high buffering potential in the water balance equation. The evaluation method is applied to a sloping permeable domain. A two-dimensional form of the Richards equation is used to calculate runoff and storage. Macropore existence is represented by an enlargement effect of hydraulic conductivity near saturation. The runoff–storage relationship is controlled by the distribution of hydraulic quantities. The distribution of a pressure-head value is approximately classified into the following three zones: the I zone with vertical unsaturated flow, the U zone with unsaturated downslope flow, and the S zone with saturated downslope flow. The runoff-buffering potential is systematically evaluated by dependencies of the runoff–storage relationship on the classification of the pressure-head distribution. The potential is generally high for soil with a high permeability, but rather small in the range of low runoff rates where the S zone is not created. The macropore effect causes the range of high buffering potential to shift to high runoff rates through enlargement of the I zone. As a result, a moderate magnitude of the macropore effect gives the maximum increase in storage in response to a given increase in runoff.