Rainstorm statistics conditional on soil moisture index: Temporal and spatial characteristics

Soil moisture is the primary hydrological state variable that controls and it is controlled by land surface processes. Assessment of feedback mechanisms between land surface and the atmosphere must involve soil moisture. The Midwestern region of the United States is used as a case example in the preliminary investigations on the hypothesis that the structure and development of storm events are influenced by soil moisture conditions. In particular we deal with the antecedent soil moisture condition influence on storm precipitation amounts and interstorm durations. The analysis based on observations indicates that when the soil moisture is low, the ensuing interstorm duration and drying period is anomalously long. We also show that storm precipitation amounts are larger when the antecedent soil moisture is anomalously high. This finding supports the hypotheses that the Summer 1993 floods over Midwestern United States were partially forced by moist antecedent conditions.

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Sommario L'umidità del suolo è la variabile idrological di stato primaria che controlla ed è a sua volta controllata dai processi sulla superficie del terreno. La quantificazione dei meccanismi di retroazione fra superficie del terreno ed atmosfera deve comprendere l'umidità del suolo. La regione centro-occidentale degli Stati Uniti è usata come esempio in uno studio preliminare sull'ipotesi che la struttura e lo sviluppo di eventi di precipitazione siano influenzati dalle condizioni di umidità del suolo. In particolare, viene considerata l'influenza delle condizioni antecedenti di umidità del suolo sulle quantità di precipitazione e gli intervallamenti dei vari eventi. Le analisi basate sulle osservazioni indicano, che quando l'umidità del suolo è bassa, il periodo secco di attesa della pioggia successiva è più lungo del normale. Viene anche mostrato che le quantità di precipitazione sono maggiori quando l'umidità del suolo nel periodo antecedente è più alta del normale. Questo risultato supporta l'ipotesi secondo la quale le alluvioni dell' estate del 1993 negli Stati Uniti centro-occidentali furono parzialmente causate dalle condizioni antecedenti di umidità del suolo.

     

Computation of moisture and temperature profiles in soil—The coupled model

The coupled model has been developed in this study for moisture transport and beat exchange in soil. The model is driven by atmospheric conditions measured in a field. The concept that soil has a surface resistance to evaporation is introduced in order to relate the evaporation from surface with the vapour flux in air. With the use of this concept, the simulation results agree quite well with the measured data.     

A comparison of ground vehicle mobility analysis based on soil moisture time series datasets from WindSat,LIS, and in situ sensors

Soil moisture is a key terrain variable in ground vehicle off-road mobility. Historically, models of the land water balance have been used to estimate soil moisture. Recently, satellites have provided another source of soil moisture estimates that can be used to estimate soil-limited vehicle mobility. In this study, we compared the off-road vehicle mobility estimates based on three soil moisture sources: WindSat (a satellite source), LIS (a computer model source), and in situ ground sensors (to represent ground truth). Mobility of six vehicles, each with different ranges of sensitivity to soil moisture, was examined in three test sites. The results demonstrated that the effect of the soil moisture error on mobility predictions is complex and may produce very significant errors in off-road mobility analysis for certain combinations of vehicles, seasons, and climates. This is because soil moisture biases vary in both direction and magnitude with season and location. Furthermore, vehicles are sensitive to different ranges of soil moistures. Modeled vehicle speeds in the dry time periods were limited by the interaction between soil traction and the vehicles’ powertrain characteristics. In the wet season, differences in soil strength resulted in more significant differences in mobility predictions.     

An empirical model to predict soil bulk density profiles in field conditions using penetration resistance, moisture content and soil depth

Cylindrical soil probes measuring 300 mm in diameter by 300 mm in height were prepared in the laboratory using samples extracted from a well drained loamy soil (FAO classification: Vertic Luvisol). These probes were compacted at different moisture contents [3, 6, 9, 12, 15 and 18 (% w/w)] and using different compaction energies (9.81, 49.05, 98.1 and 981 J). The soil penetration resistance was determined by means of the ASAE 129 mm² base area cone and seven other different cones with base sizes of 175, 144, 124, 98, 74, 39 and 26 mm². The variability of the penetration resistance measurements increased as the size of the cone decreased. Nevertheless, the penetration resistance values proved to be independent of the cone used, as long as the size of the latter was equal to or greater than 98 mm². This confirms the possibility of using cones with areas smaller than the ASAE standard when measurements are to be carried out in dry soils with high levels of mechanical resistance. The experimental data were used to develop an empirical model, a linear additive model on a log–log plane, capable of estimating soil bulk density depending on soil penetration resistance, soil moisture content and depth. This model has provided good results under field conditions and has allowed soil bulk density profiles and accumulated water profiles to be accurately estimated.     

Experimental validation of distinct element simulation for dynamic wheel–soil interaction

The deformation behaviour of the soil during dynamic wheel–soil interaction was studied by using the discontinuum modelling technique, distinct or discrete element method (DEM). The simulation model was developed using DEM for two types of soil, soil-A (coarse sand) and soil-B (medium sand). A transparent sided soil bin was used to observe the soil deformation. Three CCD video camera photographic images of the validation experiments were analyzed and compared with the simulation program results.This paper presents the simulation and validation results for two types of soil at three different vertical loadings of 4.9, 9.8 and 14.7 N. Wheel sinkage, vertical and horizontal draft force acting on the rigid wheel and the soil deformation images from the validation experiments were some of the data used to compare the simulation program results with the validation experiments. The simulation program was helpful to understand the complex deformation behaviour of the soils. The simulated results for the deformation behaviour of soil-B showed better correlation with the validation experiments than soil-A. The results obtained have also been compared with the previous work on DEM to explain phenomena such as the high simulated sinkage of the rigid wheel.     

An assessment of the finite termination property of the defect correction method

This paper investigates the use of defect correction procedures for the solution of finite volume approximations to systems of conservation laws. Particular emphasis is laid on the order of accuracy obtained after a fixed finite number of iterations. It is shown that a high order of accuracy may be achieved after only one defect correction iteration, involving two inversions of a stable lower-order-accurate operator. However, this result is found to be critically dependent on the consistency of the lower-order operator, a property which does not always hold for conservative finite volume discretizations. Through numerical experiments, the lack of consistency of these schemes is found to inhibit severely the finite termination property of the defect correction process. Results are presented for linear advection, Poisson's equation, and the Euler equations.     

Acceleration of the pressure correction method for a rotating Navier-Stokes problem

The behaviour of the pressure correction method is studied for the solution of the incompressible steady-state Navier-Stokes and continuity equations in a rotating cylindrical-polar co-ordinate system, the specific problem being that of laminar source-sink flow between two corotating discs. Modifications to improve the linearization and the handling of the rotation terms are introduced, and we compare three extended pressure correction schemes and also the use of a multigrid algorithm in part of the calculation procedure as a linear solver.     

一个多孔有机织物热湿传递过程的数学模型

利用多孔介质中的Darcy定律建立了一个多孔有机织物中热湿传递过程的数学模型，并提出了一个描述多孔有机织物中液相水重力与表面张力的对比关系的数H=5gρldcLτlεl1/3/2σcosФε1/3采用Crank—Nicolson方法数值求解了该模型，得到了在相同初始和边界条件下，不同有机材料织物中的热湿传递过程，并给出了多孔有机织物中的水蒸汽的浓度场分布、温度场分布以及纤维中的含水量的分布。计算结果与实验结果是吻合的。     

冲击波反射压测量曲线的动态修正与补偿方法

为准确获取爆炸冲击波反射压测量曲线,分析了影响其峰值的三个因素：测压系统的带宽、压力测量方式和信号传输线长度;使用激波管对冲击波测压系统进行动态校准,获取其动态特性;采用改进的levy法对其动态特性进行参数化建模,设计巴特沃斯滤波器作为补偿后的系统,计算出动态补偿环节,拓宽了测压系统的工作频带,且降低了测压系统谐振频率处的幅值;对冲击波反射压测量曲线进行动态修正与补偿,发现该方法能够修正冲击波反射超压峰值,明显降低由于测压系统的动态特性不够带来的峰值误差。该研究成果能够显著提高冲击波反射压测量峰值的准确度,为武器毁伤威力评价提供技术支持。

     

一种着装人体动态热湿传递模拟方法

针对服装热湿功能设计问题,结合改进的人体热调节模型和微元织物热湿耦合模型,实现了着装人体动态热湿传递过程的模拟。水分的蒸发凝结、纤维对湿的吸附解吸、液态水的毛细传递、人体汗水在体表积聚等现象,及其对服装热性能的作用在模型中都给予了考虑。并给出了计算流程。算例表明了模拟方法的有效性。     

Describing the soil physical characteristics of soil samples with cubical splines

The Mualem-Van Genuchten equations have become very popular in recent decades. Problems were encountered fitting the equations’ parameters through sets of data measured in the laboratory: parameters were found which yielded results that were not monotonic increasing or decreasing. Due to the interaction between the soil moisture retention and the hydraulic conductivity relationship, some data sets yield a fit that seems not to be optimal. So the search for alternatives started. We ended with the cubical spline approximation of the soil physical characteristics. Software was developed to fit the spline-based curves to sets of measured data. Five different objective functions are tested and their results are compared for four different data sets. It is shown that the well-known least-square approximation does not always perform best. The distance between the measured points and the fitted curve, as can be evaluated numerically in a simple way, appears to yield good fits when applied as a criterion in the optimization procedure. Despite an increase in computational effort, this method is recommended over the least square method.     

气体泄爆压力分步计算模型及其湍流修正

通过将密闭空间内爆燃泄放过程进行微分,假设各微分时段内爆燃泄放过程均按照先燃烧、再泄放、最后压力平衡的过程独立分步进行,最终得到泄爆压力分步计算模型。同时,在尺寸为2 m×1.2 m×0.6 m的爆炸腔体一端安装击穿压力相同、泄放面积不同的泄爆构件进行泄爆实验,对分步压力计算模型进行验证。对比发现:大面积泄放条件下,2个传感器测得的压力曲线基本重合,均为单峰值曲线,此时模型计算值与实验结果吻合较好;小面积泄放条件下,腔体内压力曲线均为双峰值曲线,由于泄放截面改变加剧口部湍流扰动,使得腔体内部产生压力梯度,近泄爆口处传感器测得的第2个压力峰值要大于腔体内部传感器相应的测量值,经湍流速度修正后的压力计算模型可以较好地描述近泄爆口处的压力变化情况。     

Discrete element method study of parameter optimization and particle mixing behaviour in a soil mixer

Soil mixing is an emerging research in the field of construction resource recovery. In this study, the mixing behaviour of soil particles in a mixer is numerically simulated by the discrete element method (DEM). A four-factor, three-level orthogonal experiment is designed to optimize the mixer design by selecting the fly-cutter speed, spindle speed, number of blades and fly-cutter diameter, using Lacey mixing index and power consumption as evaluation indicators. Then, the impact of soil cohesion and type on the mixing behaviour is investigated. The results show that the optimal parameter combination of this experiment is 280 rpm fly-cutter speed, 40 rpm spindle speed, 4 blades and 250 mm fly-cutter diameter. This optimal combination reaches a comparatively uniform state mix in 5.9 s with an average power consumption of 704.11 W. In addition, the wear and tear of the mixer increases as soil cohesion increases, while the mixing quality of materials declines, resulting in a “shaft hugging” phenomenon. The mixing efficiency varies greatly among different soil types, but the radial and tangential velocities have a similar law. This work can provide some guidance for the optimization design of a mixer and study of soil mixing.     

Real-time Bayesian data assimilation with data selection,correction of model bias,and on-the-fly uncertainty propagation

The work introduces new advanced numerical tools for data assimilation in structural mechanics. Considering the general Bayesian inference context, the proposed approach performs real-time and robust sequential updating of selected parameters of a numerical model from noisy measurements, so that accurate predictions on outputs of interest can be made from the numerical simulator. The approach leans on the joint use of Transport Map sampling and PGD model reduction into the Bayesian framework. In addition, a procedure for the dynamical and data-based correction of model bias during the sequential Bayesian inference is set up, and a procedure based on sensitivity analysis is proposed for the selection of the most relevant data among a large set of data, as encountered for instance with full-field measurements coming from digital image/volume correlation (DIC/DVC) technologies. The performance of the overall numerical strategy is illustrated on a specific example addressing structural integrity on damageable concrete structures, and dealing with the prediction of crack propagation from a damage model and DIC experimental data.     

吸收湿气对微电子塑料封装影响的研究进展

微电子塑料封装中常用的聚合物材料因易于吸收周围环境中的湿气而对器件本身的可靠性带 来很大影响, 本文回顾了封装材料中湿气扩散、湿应力及蒸汽压力的产生这3个互相联系过 程的研究情况, 从理论分析、特征参数描述及其实验测定、有限元模拟分析的角度来分别予 以介绍.从已有的理论分析与实验结果中可以看出, 塑封材料吸收湿气会给器件的可靠性带 来诸多影响, 湿气的吸收、扩散、蒸发等过程, 实验测量, 以及由湿气带来的其它相关问题正 成为微电子封装可靠性研究领域中的新热点, 受到越来越多的关注与重视.     

Reducing adhesion of soil against loading shovel using bionic electro-osmosis method

Bionic electro-osmosis, a new method of reducing soil adhesion to soil-engaging components or parts of terrain machines, is presented. It is based on the anti-adhesion mechanism of the body surfaces of soil burrowing animals. The key feature of bionic electro-osmosis is to arrange a series of electric pole plates to create a non-smooth working surface. The static and dynamic effects of bionic electro-osmosis on the reduction of soil adhesion have been examined. The pole plates of the non-smooth surfaces with different dimensions used for bionic electro-osmosis have been designed and tested based on an experimental optimization method. The result showed that the adhesion of soil to a shovel was substantially reduced at a low electro-osmosis voltage. This technique shows promise for practical applications in reducing adhesion of soil against machine parts.     

Enhancing water level prediction through model residual correction based on Chaos theory and Kriging

Hydrodynamic models based on the physical processes are indispensable tools for predicting water levels in ocean environment. Nonetheless, their accuracies are limited by various factors such as simplifying assumptions, complex ocean bathymetry, and so on. Residual correction, as one of the data assimilation techniques, can extract information from observation and assimilate it into a numerical model to correct the model output directly. Such correction is often performed in two steps: prediction of the model residuals at measured stations followed by spatial distribution at non‐measured locations. For long‐term residual forecast, the accuracy of prediction usually deteriorates with the forecast horizon. In addition to the residual correction at measurement locations, in this paper, we address the critical question as to how to effectively update outputs for computational points without measurements. We develop a hybrid data assimilation procedure, which combines a modified local model (MLM) and an approximated ordinary kriging (AOK). This technique improves the forecasts over a long horizon over the entire computational domain. Using the proposed residual correction technique, the hybrid procedure is examined on a case study of Singapore Regional Model for correcting the water level outputs at locations with and without measurements. In order to provide a comparison, the analysis is carried out throughout prediction horizon of model residuals, tidal residuals, and sea level anomaly, respectively. The comparisons show that the proposed method can successfully assimilate and forecast all variables. Results indicate that resulting prediction accuracy can be significantly improved for all locations of interest independently of the forecast horizon. Copyright © 2014 John Wiley & Sons, Ltd.     

基于离散元法的刚性履带低含水软地面附着特性数值分析

针对低含水软地面低黏性、高摩擦的力学特性,以刚性履带在干燥壤土行驶这一典型工况为试验条件,基于离散单元法选取合理的颗粒细观参数,在三轴剪切试验的基础上建立并验证了土壤数值仿真模型。通过数值牵引试验,对刚性履带低含水软地面的附着特性进行了离散元细观分析。分析表明,土壤附着力随履刺的向后排列而递减;垂直于履带行驶方向的附着作用不可忽略;离散元法能更好地还原低含水软地面的力学特性,揭示了土壤颗粒在动态荷载下非连续的本质,适合于干燥、松散的低含水软地面数值研究。