极大熵准则在降雨强度-历时-频率模型参数估计中的应用

根据频率与重现期的关系推导出三类常用降雨强度-历时-频率模型的无条件及条件概率分布(概率密度)函数及与模型相对应的约束。极大熵与极大似然准则产生一致估计,本文尝试基于极大熵准则建立降雨强度-历时-频率模型参数估计的优化模型,应用模拟退火算法求解该优化模型。根据比较发现,极大熵估计有时比常用的极大似然估计和最小二乘估计更精确。     

Prediction of the spatial distribution of the modified mercalli intensity using neural networks

This paper presents the development of an adaptive, non-parametric forecast model for the direct prediction of the spatial distribution of the Modified Mercalli Intensity (MMI) corresponding to an earthquake scenario. The model is based on recent advances in neural networks computation, and is constructed through supervised learning using historical earthquake and regional geological data as training sets. A MMI forecast model for moderate earthquakes with magnitudes between 6 and 7 was developed based on data from the Loma Prieta, Coalinga and Morgan Hill earthquakes. For these data sets, the neural networks forecast model is shown to have excellent data synthesis capability; multiple sets of data can be encapsulated by a relatively simple network architecture. Limited comparison of forecasts made by the neural networks model and conventional models demonstrates that improved accuracy can be achieved. Implementation and operational advantages of the neural networks approach such as general input features, minimum preconceived knowledge of the data sets, the ability to learn and to adapt incrementally and the autonomous and automatic synthesis of the structure underlying the data sets, have been illustrated.     

Peak and trough distributions of nonlinear waves

The exact and approximate probability density functions of wave peaks and troughs are derived for nonlinear, narrow-band waves. A comparison of these quantities with those of linear waves is given. It is shown that nonlinearity has significant effect on these quantities.     

Hydrodynamic forces on submerged vertical circular cylindrical tanks under ground excitation

This paper investigates hydrodynamic pressures and forces on submerged vertical cylindrical tanks under the action of harmonic ground excitations. Water is assumed to be imcompressible and inviscid, motion irrotational and waves are of small amplitude. Semi-analytical method is used for the solution, that is, the fluid domain is divided into inner and outer regions. The Laplace equations governing velocity potentials for the two regions are solved by separation of variables and expressed in terms of eigenfunctions of the resulting equations which satisfy appropriate boundary conditions. Continuity of pressure and velocity at the interface of the inner and outer regions provides the necessary equations from which the velocity potentials, pressures and forces are obtained. Numerical results are presented in graphical form for forces and pressures for a range of excitation frequencies for selected proportions of tank geometry and water depth.     

An integrated optimization algorithm for parameter structure identification in groundwater modeling

The inverse problem of parameter structure identification in a distributed parameter system remains challenging. Identifying a more complex parameter structure requires more data. There is also the problem of over-parameterization. In this study, we propose a modified Tabu search for parameter structure identification. We embed an adjoint state procedure in the search process to improve the efficiency of the Tabu search. We use Voronoi tessellation for automatic parameterization to reduce the dimension of the distributed parameter. Additionally, a coarse-fine grid technique is applied to further improve the effectiveness and efficiency of the proposed methodology. To avoid over-parameterization, at each level of parameter complexity we calculate the residual error for parameter fitting, the parameter uncertainty error and a modified Akaike Information Criterion. To demonstrate the proposed methodology, we conduct numerical experiments with synthetic data that simulate both discrete hydraulic conductivity zones and a continuous hydraulic conductivity distribution. Our results indicate that the Tabu search allied with the adjoint state method significantly improves computational efficiency and effectiveness in solving the inverse problem of parameter structure identification.     

Modelling climate‐change impacts on stream temperature of Formosan landlocked salmon habitat

A physics‐based model is provided for predicting the impact of climate change on stream temperature and, in turn, on Formosan landlocked salmon (Oncorhynchus masou formosanus) habitat. Because upstream watersheds on Taiwan Island are surrounded with high and steep mountains, the influence of mountain shading on solar radiation and longwave radiation is taken into account by using a digital elevation model. Projections using CGCM2 and HADCM3 models and CCCM and GISS models provided information on future climatic conditions. The results indicate that annual average stream temperatures may rise by 0·5 °C (HADCM3 short term) to 2·9 °C (CGCM2 long term) due to climate change. The simulation results also indicate that the average suitable habitat for the Formosan landlocked salmon may decline by 333 m (HADCM3 short term) to 1633 m (CGCM2 long term) and 166 m (HADCM3 short term) to 1833 m (CGCM2 long term) depending on which thermal criterion (17 °C and 18 °C respectively) is applied. The results of this study draw attention to the tasks of Formosan landlocked salmon conservation agencies, not only with regard to restoration plans of the local environment, but also to the mitigation strategies to global climate change that are necessary and require further research. Copyright © 2005 John Wiley & Sons, Ltd.     

Refining the origin of thermal water using stable isotope,hydrochemistry and GIS approaches in Jiaoxi,Taiwan

Comprehending the recharge of thermal springs is crucial for preserving the water quality of such springs. However, limited groundwater well data in mountainous areas presents a challenge to determining thermal-spring recharge areas. This study analyzes the isotopes (δ²H and δ¹⁸O) and major ions in rainwater, streamwater, mountain groundwater and thermal spring water in Jiaoxi, located near Taiwan's largest city, Taipei. The results of the isotope-elevation relationship and GIS recharge analysis indicate that the thermal spring water originated from a remote mountain at elevations of approximately 1170–1480 m, rather than the upstream watershed. The thermal spring water was divided into two groups based on the carbonate saturation index (SI) and isotope composition: the foothill group, which had a positive SI and lower δ value, and the downstream group, which had a negative SI and higher δ value. This study improved the conceptual model of the thermal flow path by demonstrating that the recharge of thermal water is a transboundary regional flow and that the foothill thermal water does not mix with the meteoric water. The revised model also highlights the role of structural lineament trends (faults, fractures and folds) in the movement of regional flow in fractured mountain blocks.     

Energy dissipation in rocking bridge piers under free vibration tests

This research aims to investigate the dynamic characteristic of rocking bridge columns subjected to quick release loads. Precast columns anchored by unbonded steel bars at the centre of each column can rock on the foundation surface without inducing any residual deformation after earthquakes. The restoring force of columns relies on gravity load from the superstructure and tensile strength in anchor bars. Radiation damping is evaluated through each impact of column rocking. To validate the theoretical damping proposed by previous researchers, four columns were constructed. Research parameters included steel or plastic materials used as rocking interfaces, area of anchor bars, aspect ratio and size effect of columns. Test results revealed that stocky columns slid apparently in the first impact then rocked, but taller columns rocked with minor slips in the entire motion. And freestanding columns slid significantly in the first impact that led to a higher damping. Radiation damping due to impact in the entire motion for all tests was within 5%. Copyright © 2006 John Wiley & Sons, Ltd.     

Incorporating daily rainfalls to derive rainfall DDF relationships at ungauged sites in Hong Kong and quantifying their uncertainty

Rainfall depth-duration-frequency (DDF) relationships are essential inputs for the design and management of various hydrosystem infrastructures (e.g., urban drainages, dams, dykes, etc.). In many cases, rainfall DDF relationships are required at a location where there is no gauge. However, due to the presence of intrinsic randomness of the precipitation process, limited rainfall record, and spatial interpolation, the derived DDF relationships at ungauged sites are subject to uncertainty. This is especially true in Hong Kong with regard to record length. To enhance the utilization of available rainfall data, a daily precipitation-based DDF generation framework for conventional rain gauges in Hong Kong has been developed by the authors utilizing a scaling model. In this article, the methodological framework is extended to derive rainfall DDF relationships at ungauged sites. Owing to the nonlinearity and complexity of the modeling process, exact statistical features of derived DDF relationships are difficult to obtain. In this study, Harr’s probabilistic point estimation method, known for its computational simplicity and accuracy, is applied to quantify the uncertainty features of rainfall DDF relationships derived for ungauged sites in Hong Kong. For illustration, four locations in different geographical locations in Hong Kong are considered. The results show that the uncertainty associated with the estimated statistical moments of annual maximum daily rainfall is significant in contributing to the overall uncertainty of derived rainfall DDF relationships.