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基于传质原理的二维随机水质模型研究与应用 【作者】许劲 【导师】龙腾锐

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基于传质原理的二维随机水质模型研究与应用

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【作者基本信息】重庆大学,市政工程,2007年,博士

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]~NtTsK Fq&s {0【中文摘要】 随机微分方程是解决复杂非线性和不确定性问题的有效工具,其在水污染控制规划领域的应用研究在国内外尚处于起步阶段。在较全面分析评述了河流水质模型的研究现状、传质原理、随机过程与扩散理论的基础上,本文提出并建立了基于传质原理的二维随机水质模型,主要用于河流污染带的模拟预测以及突发性水污染事故的实时预警,对水质模型的建模方法、建模原理以及河流排污口近区污染物初始浓度的模拟计算等进行了一些探索性的工作,为水质模拟提供了新途径,同时提高了国内现有水质预警模型的精度。论文假设河流中污染物浓度ct按几何Brown运动变化,由此引入一个非平稳随机过程,其中污染物初始浓度c0和污染物综合衰减系数α视为两个待定常数。在详细分析了河流中污染物的扩散过程、假设污染物在没有达到全水深混合之前只是在部分水深达到均匀混合之后,提出了c0的理论计算公式,其中部分均匀混合水深h p是关键参数。另外,为充分利用河流中实测污染物浓度数据序列,基于对灰数据处理及其建模思路的分析,通过积分构造一次生成序列,建立了非等间距序列一阶模型,给出了ct的时间响应函数表达式。实际算例表明,该模型对河流中实测污染物浓度的模拟误差一般小于15...更多%,可同时得到c0和α的具体数值,表明建模方法合理有效。由于用传质系数可以对扩散现象进行更为简便的近似描述,论文在传质学基础上,将传质学中反映物质通过传质界面速度的传质系数及其理论研究方法引入到水污染控制规划领域,认为河流中的传质界面就是污染带等浓度线,详细分析了河流中污染带等浓度线的形成与发展过程,构建了污染物传质速度的随机函数,表明污染物传质速度是一个非平稳随机过程,其大小取决于传质界面两侧浓度的差异。论文还对传质系数和传质界面进行了详细分析和比较,指出了本文所使用的传质系数与传质学中经典的传质系数由于传质界面的不同而出现数量级的差别,经比较决定采用瞬时传质系数,并假设其为常数,把由于传质系数的波动而导致的误差归入到随机扰动项中。此外,详细分析了河流中污染物综合衰减系数,并通过数据说明,在天然情况下,水流对污染物的稀释扩散作用远大于污染物自身的生物降解作用。本文将河流中污染带的形成与发展过程分为初始动量传递与污染物扩散传质两个阶段,同时假设河流流速为一平稳随机过程以反映水流湍流特征,这样河流中污染物扩散传质的绝对速度等于污染物随河流水体的移动速度与污染物传质速度的叠加,并利用传质椭圆及其在移动过程中所形成的包络线来描述污染带的发展过程,把污染带划分为包络线部分和传质椭圆部分,其中传质椭圆的长短半轴集中反映了污染物由于传质作用沿河流纵向和横向所移动的距离。这样,通过综合运用系统分析方法、传质原理和扩散过程理论,建立了不同排污条件下河流污染带长度、宽度、面积的随机泛函,并推导出相应的期望函数和方差函数表达式。论文利用1989年嘉陵江重庆段罗丹明河流中心连续稳定排放试验的实测数据和1997年长江重庆段黄沙溪岸边排污口同步实测资料对模型进行了参数率定,得到了传质系数的具体数值:纵向传质系数k x= ( 0.51) m /s,横向传质系数k y= ( 0.050.5 )m /s,且传质系数k正比于河流的平均流速u ;另外,对河流中心排污, h p= ( 0.5 0.75)h,对河流岸边排污, h p= 0.5h,污染云团的初始形状为全对称的正方形或圆形。模型验证的结果为:污染带包络线长度x? ( t )和宽度y? ( t )的模拟误差分别小于9%和16%,传质结束时传质椭圆长短半轴的模拟误差均小于21%,表明本模型可较准确模拟计算河流中心污染带以及岸边污染带。论文还对建库前后枯水期长江重庆段桃花溪和李家沱两个城市排污口岸边污染带进行了预测分析,得出了这两个污染混合区的范围。结果表明,在来流及排污条件不变的情况下,三峡水库蓄水后,随着库区流速的减小,岸边污染混合区的范围远大于建库前,其增值随排污口位置具体水流情况的不同而不同。排污口的位置对污染混合区的大小有重要影响,应尽量避免将排污口选在流动不畅的河段,特别是回水区或浅滩。本模型给出了污染带范围的随机泛函表达式,其期望函数为解析方程,可方便、快速地预测污染混合区的大小,特别适用于水质的实时预警。如果可获得河流流速和污染物浓度随机扰动强度的具体数值,便可以得出污染带长度、宽度以及面积的预测区间,便于进行水质风险评价与预警。  还原

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bzlKBm0【英文摘要】 Stochastic differential equation is an effective tool to solve complex problems about nonlinearity and uncertainty, and its research and application to water pollution control planning are still at the initial stage at home and abroad. After analyzing and reviewing the present research condition, mass-transfer theory, stochastic processes and diffusion theory of water quality model, a kind of two-dimensional stochastic water quality model based on mass-transfer theory is presented and established in this paper. It is mainly used in the simulation and predication of river pollution mixing zone (PMZ) and the real-time warning of emergency water pollution accidents. In this paper, the method and theory of modeling on water quality, as well as simulation and calculation of initial pollutant concentration ( c0 ) in the near field of the river’s outlet, are researched of exploratory. All these not only provide a new approach to the simulation of water quality, but also help to improve the ac...更多curacy of present pre-warning water quality models in our country.Supposing that the pollutant concentration ( ct ) in the river vary as the geometric Brownian motion, a non-stationary stochastic process can be introduced. In this process, c0 and the synthetic attenuation coefficient (α) of the pollutant are taken as two indefinite constants. Analyzing the pollutant’s diffusion process in the river in detail and supposing that the pollutant is only part depth homogeneous mixing before reaching whole depth homogeneous mixing, a theoretical formula to calculate c0 is proposed, and the part homogeneous mixing depth h p is a key parameter in this formula. In addition, in order to fully use the measure data of ct in the river, the first order model for unequal interval sequence is established and the time response function-expression for ct is proposed in this paper, basing on analysis of grey data treatment as well as its modeling way and the establishment, and a kind of the first accumulative generated sequence is constructed according to the geometrical meaning of integral in this model. Experimental computations show that this model’s error on simulating the river’s experimental pollutant concentration is generally less than 15%, and the concrete value of both c0 andαcan be obtained, which indicate that the modeling method is practical and effective.Since using transfer coefficient to approximately describe the diffusion process will be simpler, the transfer coefficient, which describe substances’speed at the transfer interface, and its theoretical research methods are introduced into the field of water pollution control planning in this paper, and the pollutant isoconcentration line in the river is taken as the transfer interface. The formation and development of the pollutant isoconcentration line in the river is analyzed in detail, the stochastic function which describes the pollutant’s transfer speed is established, which shows that the pollutant’s transfer speed is a non-stationary stochastic processes, and its value depends on the concentration difference between the two sides of interface. Also, in this paper, transfer coefficient and transfer interface are analyzed and compared in detail. And it is proposed that the transfer coefficient used in this paper is different from that classical one of mass-transfer science in the magnitude order because they are of different transfer interfaces. After comparison, the instantaneous transfer coefficient is used and taken as a constant in this paper, and the error which due to the fluctuation of the transfer coefficient is contained in the stochastic disturbance item. In addition, the synthetic attenuation coefficient of the pollutant in the river is analyzed in detail, and data series show that the dilution and diffusion actions of the water flow to the pollutant are more important than the biodegradation action of the pollutant itself.The formation and development process of the pollutant mixing zone (PMZ) in the river is divided into two stages, which are the stage of initial momentum transfer and the stage of pollutant’s diffusion process, while the velocity of flow is supposed to be a stationary stochastic process to reflect the turbulence characteristic of rivers. So it is supposed that the absolute speed of the pollutant’s diffusion equaled to the pollutant’s diffusion and transfer speed superposed to the moving speed of the pollutant according to the water flow, and the development process of the PMZ is described by transfer ellipse and envelope line generated during moving. The PMZ is divided into two parts, which are the envelope line part and the transfer ellipse part. The long and short half axle of the transfer ellipse respectively show the pollutant’s horizontal and vertical moving distances along the river because of the transfer process. So, comprehensively applying the method of system analysis and the theory of mass-transfer principle, stochastic functions which respectively describe the length, width and area of the pollutant zone in the river are established, correspondingly, their expected value and variance function-expression are deduced.In this paper, the measure data of the Rhodamine-B tracer in which pollutants are discharged continuously and stably in the center of the Jialing River during Chongqing (1989) , as well as the measure data in which pollutants are discharged in the riverside of Huangshaxi in the Yangtze River during Chongqing (1997), are used to determinate the parameters of the 2-D stochastic water quality model, and the concrete value of the transfer coefficient is that the horizontal one k x was( 0.51) m /s and the vertical one k y was ( 0.050.5 )m /s , and they are both proportional to u , the average velocity of the river flow. In addition, it is got that h p is ( 0.5 0.75 )h when the pollutants are discharged in the river center and respectively ( 0.5 0.75 )h in the riverside, the initial shape of the pollution cloud is a holosymmetric square or circle. The result of the model validation shows that the simulation error of the length x? ( t ) and the width y? ( t ) of the PMZ’s isoconcentration line are less than 9% and 16% respectively, and the simulation error of the transfer ellipse’s long and short half axle are both less than 21% at the end of the transfer process. This result indicates that the model can be used to simulate and calculate the river center PMZ and the riverside PMZ accurately.In this paper, the PMZs near the pollution discharge orifice at Taohuaxi and Lijiatuo in the Yangtze River during Chongqing, in low flow years before and after the impoundment of Three Gorges Reservoir, are respectively predicted and analyzed, and the areas of the two PMZs are calculated. The result indicates that, after the impoundment of Three Gorges Reservoir, the water flow’s velocity in the reservoir region will decrease when the incoming flow and pollutant discharge conditions are constant, and the range of the riverside PMZs will be much larger than before, the added value depends on the concrete water flow condition of the outlet. Since the location of the outlet has important influence on the range of the PMZs, it should be avoided to locate the outlet in non-fluent regions in the river, especially back water regions and shallows.This model gives the stochastic function-expression to the range of PMZ, its expected value function is an analytical equation, it can predict the limits of PMZ conveniently and quickly, and it is especially adequate to the real-time warning of water quality. If the concrete value of the river’s velocity and the pollutant concentration’s stochastic disturbance strength can be got, the predication interval of the pollutant zone’s length, width and area can be got as well, this will make the risk assessment and pre-warning of water quality more convenient.  还原

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【中文关键词】 传质原理; 二维随机水质模型; 实时预警; 污染带水利论文e B+L,r,C,jn
【英文关键词】 Mass-transfer theory; Two-dimensional stochastic water quality model; Real-time warning; Pollutant mixing zone水利论文0?zjz!X9x

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