Characterizing parameter sensitivity and uncertainty for a snow model across hydroclimatic regimes

The National Weather Service (NWS) uses the SNOW17 model to forecast snow accumulation and ablation processes in snow-dominated watersheds nationwide. Successful application of the SNOW17 relies heavily on site-specific estimation of model parameters. The current study undertakes a comprehensive sensitivity and uncertainty analysis of SNOW17 model parameters using forcing and snow water equivalent (SWE) data from 12 sites with differing meteorological and geographic characteristics. The Generalized Sensitivity Analysis and the recently developed Differential Evolution Adaptive Metropolis (DREAM) algorithm are utilized to explore the parameter space and assess model parametric and predictive uncertainty. Results indicate that SNOW17 parameter sensitivity and uncertainty generally varies between sites. Of the six hydroclimatic characteristics studied, only air temperature shows strong correlation with the sensitivity and uncertainty ranges of two parameters, while precipitation is highly correlated with the uncertainty of one parameter. Posterior marginal distributions of two parameters are also shown to be site-dependent in terms of distribution type. The SNOW17 prediction ensembles generated by the DREAM-derived posterior parameter sets contain most of the observed SWE. The proposed uncertainty analysis provides posterior parameter information on parameter uncertainty and distribution types that can serve as a foundation for a data assimilation framework for hydrologic models.     

Analyzing urban water supply through an acceptability-index-based interval approach

Incorporation of uncertainties within an urban water supply management system has been a challenging topic for many years. In this study, an acceptability-index-based two-step interval programming (AITIP) model was developed for supporting urban water supply analysis under uncertainty. AITIP improved upon the traditional two-step interval programming (TIP) through incorporating the acceptability level of constraints violation into the optimization framework. A four-layer urban water supply system, including water sources, treatment facilities, reservoirs, and consuming zones, was used to demonstrate the applicability of proposed method. The results indicated that an AITIP model was valuable to help understand the effects of uncertainties related to cost, constraints and decision maker’s judgment in the water supply network, and capable of assisting urban water managers gain an in-depth insight into the tradeoffs between system cost and constraints-violation risk. Compared with TIP, the solutions from AITIP were of lower degree of uncertainty, making it more reliable to identify effective water supply patterns by adjusting decision variable values within their solution intervals. The study is useful in helping urban water managers to identify cost-effective management schemes in light of uncertainties in hydrology, environment, and decisions. The proposed optimization approach is expected to be applicable for a wide variety of water resources management problems.     

Prediction of probabilistic settlements via spectral stochastic meshless local Petrov–Galerkin method

This study introduces the prediction of probabilistic settlements with the uncertainty in the spatial variability of Young’s modulus to illustrate the preliminary development of a spectral stochastic meshless local Petrov–Galerkin (SSMLPG) method. Generalized polynomial chaos expansions of Young’s moduli and a two-dimensional meshfree weak–strong formulation in elasticity are combined to derive the SSMLPG formulation. Because of the local and truly meshless nature, the SSMLPG method is more computationally efficient than available stochastic numerical methods. Two examples further show that SSMLPG-based predictions remain sufficiently accurate even in case of scattered nodes. Therefore, the SSMLPG method can be a valuable alternative for solving stochastic boundary-value problems.     

原子荧光光度法测定地化样品砷不确定度评定

测定过程中的不确定度分量分析,并计算各分量标准不确定度及合成不确定度。通过合成标准不确定度,得出测量结果的扩展不确定度及最终结果表示:(14.8±0.50)μg/g。     

Use of formation pressure test results over a hydrate interval for long-term production forecasting at the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope: Implications of uncertainties

In the first part of this paper, the pressure and temperature measurements obtained using Schlumberger's Modular Formation Dynamics Tester (MDT) conducted on the C2 interval in the BPXA-DOE-USGS Mount Elbert Gas Hydrate Stratigraphic Test Well (Mount Elbert Well) are history matched, with the following three objectives: (i) to obtain a better understanding of hydrate decomposition and its reformation as conditions cross the p/T stability, (ii) to obtain formation properties (e.g., permeability) that are consistent with the measurements, and (iii) to explore the non-uniqueness in the history match; i.e., to explore the ranges of parameters that allow a reasonable match of the measured quantities. In the second part of this paper, long-term production performance is predicted, and the effect of the uncertain parameters on the predictions is demonstrated. The results are used to demonstrate the range of long-term production that may be expected, when a model is calibrated using the MDT data. Usefulness of short-term tests for long-term forecast prediction is then discussed.     

Numerical study on added resistance of ships by using a time-domain Rankine panel method

This paper considers the numerical computation of added resistance on ships. As a method of solution, a higher-order Rankine panel method is applied in time domain. Furthermore, two different formulations, Neumann-Kelvin and double-body linearizations, are applied to investigate the difference between computational results. The quantities of added resistance are obtained by integrating the second-order pressure on the body surface. Computational results are validated by comparing with experimental data and other computational results on several models, and fair agreements are found for all the models. The components of added resistance are observed with regard to integral terms, radiation and diffraction components. This study continues to the computation of added resistance in irregular waves. This kind of computational approach can provide some important information to understand the uncertainty level of towing-tank measurement of added resistance. In this study, a series of long numerical simulations are carried out, and their statistical variations are observed for different time windows. Based on this observation, an appropriate criterion and averaging method are proposed for the prediction of added resistance in irregular waves.     

A database for worldwide seismicity quantification

The first step in a seismicity analysis usually consists of defining the seismogenic units, seismic zones or individual faults. The worldwide delimitation of these zones involves an enormous effort and is often rather subjective. Also, a complete recording of faults will not be available for a long time yet. The seismicity model presented in this paper therefore is not based on individually defined seismic zones but rather on the assumption that each point in a global 1/2° grid of coordinates represents a potential earthquake source. The corresponding seismogenic parameters are allocated to each of these points. The earthquake occurrence frequency, one of the most important parameters, is determined purely statistically by appropriately spreading out the positions of past occurrences. All the other significant seismicity characteristics, such as magnitude-frequency relations, maximum possible magnitude and attenuation laws including the dependence on focal depth are determined in a global 1/2° grid of co-ordinates. This method of interpreting seismicity data allows us to establish a transparent, sufficiently precise representation of seismic hazard which is ideally suited for computer-aided risk analyses.     

地震活动性定量化研究的评述

简要回顾了地震活动性定量化研究的进程,概述了各综合定量指标参量的特点,介绍了地震活动度 S 及其在定量描述地震活动性中的某些应用成果,展望了 S 应用于地震监测预报中的可能性。     

断层活动性定量评定之现状与展望

随着活断层理论研究的深入和工程评价要求的提高，对断层活动性仅作定性评价，已不能满足重大工程选址和设计的要求，而必须走量化评定的道路。作者分析了断层活动性定量评定之现状，科学京、工程师们虽已做了一些有益的尝试和实践，但当前仍处在探索研究阶段，至今尚未找到一个能被普遍接受的断层活动性量化评定标准。作者对断层活动性量化评定之前景亦做了展望，并着重指出几个今后应特别予以注意的问题：１．明确断层活动性的概念含义；２．找到影响断层活动性大小的主要因素；３．加强断层活动年代测定研究；４．重视活断层的地震活动和地表破裂研究；５．用概率论方法定量评定断层活动性。     

Probabilistic modeling of aerated lagoons: A comparison of methodologies

Two stochastic models are developed to describe the BOD output (i.e. effluent) variation of facultative aerated lagoons in series. One of the models uses the uncertainty analysis (UA) technique and the other is based on the moment equation solution methodology of stochastic differential equations (SDE's). The former considers a second-order approximation of the expectation (SOAE) and a first-order approximation of the variance (FOAV). The SDE model considers that output variability is accounted for by random variations in the rate coefficient. Comparisons are provided. Calibration and verification of the two models are aciieved by using field observations from two different lagoon systems in series. The predictive performances of the two models are compared with each other and with another SDE model, presented in a previous paper, that considers input randomness. The three methods show similar predictive performances and provide good predictions of the mean and standard deviation of the lagoon effluent BOD concentrations and thus are considered as appropriate methodologies.