The effect of hydrochemical factors on the dissolution rate of gypsiferous rocks in flowing water

In order to investigate the rate of dissolution of gypsiferous rocks under natural conditions in streams of the Ebro river basin, 55 dissolution trials were carried out with spheres of alabastrine gypsum placed in flowing water. Experimental conditions involved flow velocities between 0·3 and 1·2 m s^?1, electrical conductivities between 0·3 and 1·9 dS m^?1, and the saturation indices of gypsum between ?2·1 and ?0·33. Mean values of dissolution rate obtained vary from 104 to 226 gm^?2 h^?1. This loss of mass corresponded to a volume of gypsum of between 393 and 853mmm^?2 year^?1. The factors most affecting the dissolution of gypsum are in descending order of importance: flow velocity > electrical conductivity > gypsum saturation.     

The effects of drag reduction by ribbons attached to cylindrical pipes

This study proposes a drag reduction device that uses three ribbons attached 120 degree apart to vertical pipes. Experiments were conducted in a circulating water channel to investigate the effects of the ribbon length and the direction of the flow on various current velocities. Drag on a vertical cylinder was measured by a resistance dynamometer. Flow visualizations were conducted using laser sheet beams. Laser Doppler Velocimetry (LDV) was used to measure the velocity field in the wake. This experiment demonstrates that attached ribbons can be used to reduce the drag force on vertical pipes for various directions of incoming flows. The ribbon-type device is very simple and easy to fabricate for field applications. The results are promising for the application to offshore structures.     

Wake studies of a 1/30th scale horizontal axis marine current turbine

A 0.4 m diameter (1:30th scale) horizontal axis marine current turbine (MCT) was tested in a circulating water channel. The turbine performance and wake characteristics were determined over a range of flow speeds and rotor thrust coefficients. Measurements of the water surface elevation profiles indicated increasing variation and surface turbulence with increasing flow speeds. Blockage-type effects (where the measured point velocity was greater than the inflow velocity) occurred around the sides of the rotor for all flow speeds. Although the effects were exaggerated at model scale, it is expected that reasonable variations in water level and flow velocity could also occur over a full scale MCT array.     

Effects of solution mining on groundwater quality in the Kazan trona field,Ankara-Turkey: model predictions

Three aquifer systems as deep, middle, and shallow were identified in the Kazan trona ore deposit area. The flow conditions and the interaction between various layers were conceptualized into a site hydrogeological model. Each aquifer system was hydraulically and chemically characterized and represented in a numerical groundwater model. The resulting model has been calibrated under steady-state and transient conditions using available data. The flow model was used in conjunction with a three-dimensional solute transport model to assess the impacts of the pilot well solution mining of the trona deposit on groundwater resources during operation and post-operation periods. The results of operation period indicate that, even under the worse conditions (50 times increase in vertical hydraulic conductivity due to subsidence), ion contribution from the mine area with 118,000 mg/l maximum concentration would be about 58 mg/l into the deep aquifer system. This contribution is about 1.45% of the existing concentration (4,000 mg/l) in the deep aquifer. After 1,000 years of post-operation period, ion contribution from the mine area with maximum 119,000 mg/l concentration would be about 205 mg/l into the deep aquifer under extremely worse conditions. This contribution is about 5–20% of present concentrations in the deep aquifer. Retardation factors, which were not considered during model simulations would decrease the predicted concentrations. It is concluded that pilot well solution mining of the trona deposit would not have significant impact on the quality of groundwater resources in the overlying aquifers.     

不同权重的前期和始发日降雨量与泥石流产沙规模的分析——特大型泥石流灾害发生的思考

通过对特大型泥石流灾害发生的思考,详细分析了蒋家沟1995—1997年43场泥石流暴发的不同权重的前期和始发日降雨量与泥石流产沙规模的关系。分析结果表明：泥石流的产沙规模与不同权重降雨的入渗范围、深度的土体极限应力状态（C、Ф、P,）有关。根据不同权重的前期和始发日降雨量与泥石流产沙规模的关系,可以将泥石流分为：土力型（A）和迳流型（B）两大类型。土力型（A）泥石流有24场占总样本的55．81％,而其产沙量却占样本总产沙量的85％。迳流型（B）泥石流有19场占总样本的44．19％,但该类泥石流的产沙量只占样本总产沙量的15％。     

动态柔性地物三维模拟理论与方法新探

针对地学动态柔性物体建模,提出GIS流素与柔性体元(GIS Flow Element and Soft Voxel)的概念,作为动态柔性地物的基本模拟单元。当忽略体积时,称为GIS流素(FE);当强调体积时,则称为GIS柔性体元(SV)。GIS流素与柔性体元三维模拟基于计算机图形学中的粒子与元球技术,区别在于GIS流素与柔性体元具有明确的地学意义,并基于地学模型突出反映地学规律。现实世界中,水流、泥沙、雪花、云雾、泥石流、熔岩流、草原等均可用(7)IS流素进行模拟,而构造运动中岩层的挤压、扭曲变形、生物体、树木随风摆动等可用GIS柔性体元进行模拟。该文以水流与土壤模拟为例,论证该方法的应用前景。     

砂土力学性质的细观模拟

基于颗粒流理论,对砂土的室内双轴试验和砂土剪切带形成与发展进行了数值模拟,基本再现了砂土试样应力-应变关系。主要研究了颗粒粒径、颗粒摩擦系数等细观参数变化时试样宏观性质的变化情况。对比分析了室内试验和颗粒流数值模拟试验的砂土剪切带特征。同时对比研究了模型试样颗粒粒径、颗粒刚度和摩擦系数等细观参数的变化,对剪切带的形成与发展过程的影响。结果表明：通过颗粒流数值模型试验可以有效模拟砂土剪切带的形成与发展机理。     

Experimental study on the velocity-dependent dispersion of the solute transport in different porous media

The hydrodynamic dispersion is an important factor influencing the reactive solute transport in the porous media, and many previous studies assumed that it linearly varied with the average velocity of the groundwater flow. Actually, such linear relationship has been challenged by more and more experimental observations, even in homogeneous media. In this study, we aim to investigate the relationship between hydrodynamics dispersion and the flow velocity in different types of porous media through a laboratory-controlled experiment. The results indicate that(1) the dispersion coefficient should not be a linear function of the flow velocity when the relationship between the flow velocity and the hydraulic gradient can be described by Darcy's law satisfactorily;(2) Power function works well in describing the dispersion coefficient changing with the flow velocity for different types of porous media, and the power value is between 1.0-2.0 for different particle sizes.     

Engineered channel controls limiting spawning habitat rehabilitation success on regulated gravel-bed rivers

In efforts to rehabilitate regulated rivers for ecological benefits, the flow regime has been one of the primary focal points of management strategies. However, channel engineering can impact channel geometry such that hydraulic and geomorphic responses to flow reregulation do not yield the sought for benefits. To illustrate and assess the impacts of structural channel controls and flow reregulation on channel processes and fish habitat quality in multiple life stages, a highly detailed digital elevation model was collected and analyzed for a river reach right below a dam using a suite of hydrologic, hydraulic, geomorphic, and ecological methods. Results showed that, despite flow reregulation to produce a scaled-down natural hydrograph, anthropogenic boundary controls have severely altered geomorphic processes associated with geomorphic self-sustainability and instream habitat availability in the case study. Given the similarity of this stream to many others, we concluded that the potential utility of natural flow regime reinstatement in regulated gravel-bed rivers is conditional on concomitant channel rehabilitation.     

Modeling Monthly Mean Flow in a Poorly Gauged Basin by Fuzzy Logic

The estimation of the monthly mean flow is a critical issue in many water resource development projects. However, in practice the mean flow is not easily determined in ungauged and poorly gauged basins. Therefore, in the literature, various flow estimation methods have been developed recently for mountainous regions which are generally ungauged or poorly gauged basins. In this study a fuzzy logic model based on the Mamdani approach was developed to estimate the flow for poorly gauged mountainous basins. This model was applied to the Solakli Basin which is located in the Eastern Black Sea Region of Turkey. Limited rainfall and flow data are available for this basin. In addition to these variables, the stream and time coefficients were introduced and used as variables for modeling. The data was divided into training and testing phases. The model results were compared with the measured data. The comparison depends on seven statistical characteristics, four different error modes and the contour map method. It was observed that the fuzzy model developed in this study yielded reliable results.