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河流泥沙模拟技术进展与展望 总被引:4,自引:1,他引:4
本文系统总结了河流模拟技术的发展过程和研究成果。河流模拟技术包括河流实体模型和泥沙数学模型两部分。在实体模型方面,已建立了一整套河工模型的相似理论、设计方法和试验技术,在模型变态、模型沙选择、高含沙水流模拟、模型测验等方面取得了重要的研究成果,并解决了大量的工程泥沙问题。在数学模型方面,建立了一维、二维和三维泥沙数学模型,并随着泥沙基本理论研究的不断深入与广泛的工程应用,在计算模式、数值计算方法、计算结果的后处理、参数选择、高含沙水流问题处理等方面均取得了重要进展。本文还展望了河流模拟技术今后的发展方向。 相似文献
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反射MT方法是一种分析MT数据的新方法,该方法与反射地震相似.本文提出了与时间域地震波脉冲响应Z变换相类似的伪脉冲响应u变换,用来分析多层介质中伪脉冲响应.该方法为MT数据的处理和解释提供了新的途径. 文章讨论了电磁波在电介性介质和导电介质中的传播特征和伪脉冲响应.对二层和三层地电模型的理论分析和数值计算表明,伪脉冲响应的u变换理论的正确性. 相似文献
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仿用反射地震法处理MT资料反演的理论探讨 总被引:1,自引:0,他引:1
本文讨论了电法勘探中电磁波场在水平层状介质中的传播特征,重点讨论它与地震波在水平层状介质中的传播特征在数学形式上的相似性,同时利用反射地震学中的脉冲响应概念来构建电法勘探中的伪脉冲函数响应.所恢复的伪脉冲响应是由一些离散脉冲函数组成,脉冲幅度与分层介面的波场反射系数和透射系数有关.本文采用拟合最小二乘法同时进行代数联合迭代(SIRT)跟踪的方法解决了欠定方程在其范数约束条件下的求解问题.并把该方法应用于一维多层导电体模型中,证实了伪脉冲理论的可靠性与实用性. 相似文献
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本文介绍了美国三维有限差分数学模型MODFLOW的原理,特点及在天津市区模拟计算中的使用情况,以一维固结理论为基础开发了夹层排水程序包IDP,并与MODFLOW耦合使用,在模拟市区大厚度沉降度的缓慢排水方面有了突破性的进展-地面沉降的模拟和预测由科研转入实用阶段。 相似文献
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强夯置换的应用已逐渐广泛,但其设计是高度经验性的。强夯置换的理论研究较为肤浅,特别是置换深度的计算尚无较好的方法。为此,提出了模拟夯击过程的一维波动方程理论模型;初步建议了模型中有关参数的取值并用工程实例进行了验证;用所提出的模型探讨了置换体形成与扩展的基本规律;给出了应用的简化形式。结果表明,一维波动方程法及其简化形式与实际吻合较好,可应用于强夯置换的置换深度估算。 相似文献
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土体与时间相关的一维应力-应变性状、弹粘塑性模型和固结分析 总被引:4,自引:1,他引:4
论文根据室内实验结果首先提出一维变形状态下应变与时间相关的应力-应变性状。回顾了已有的与时间相关的土体应力-应变性状和固结分析中的一维本构模型和团结理论,并对这些模型和理论的局限性以及一些错误进行了讨论.然后引入了等效时间的概念和其它一些概念,并且详细介绍了怎样使用这些概念推导弹-粘-塑性(EVP)本构模型(殷和格雷厄姆(Graham),1989a,1992b;殷,1990)。采用加拿大NovaScotia的Halifax港有机质粉质粘土的多级蠕变试验资料检验该模型中的基本概念、假设和确定该模型的参数。该模型已被用于荷载等级变化条件下粘土层的一维固结分析,其分析结果与大沙基固结理论和假说A进行了比较。分析结果表明应用EVP模型的固结模式可模拟不变荷载下粘土的粘滞性引起的孔隙水压力上升现象。 相似文献
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为了描述软黏土一维应力-应变关系的时效特性,基于Bjerrum的等时间线体系,提出等黏塑性应变率线概念,推导了黏塑性应变率与黏塑性应变增量的关系,建立了软黏土的一维弹黏塑性模型;从理论上分析了新建模型与3种典型的一维弹黏塑性时效本构模型的内在联系,表明新建模型与其他3种模型在本质上是等效的,且形式更简洁,物理意义更明确;利用新建模型对软黏土的固结-蠕变耦合效应、应变率效应、应力松弛效应等时效特性进行了理论分析,并得到了相应的解析解;结合宁波软黏土的一维固结试验,阐述了模型参数的确定方法,并用新建模型对宁波软黏土的固结-蠕变试验、温州软黏土的一维多级等应变率试验、香港海相软黏土的一维应力松弛试验进行模拟,验证了新建模型的有效性。研究结果表明,新建模型能很好地模拟软黏土的一维时效特性。 相似文献
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S. G. Chen J. Zhao A. Makurat C. Madshus 《Fragblast: International Journal for Blasting and Fragmentation》2000,4(2):164-174
Mesh size influence on dynamic modelling in 1-D and 2-D models is investigated by using discrete element code UDEC. It is shown that the modelling with smaller mesh ratio obtains higher accuracy, which agrees well with the common acceptance. Furthermore, it is found that the error, induced by the mesh size, increases with increasing distance from the wave source and also with increasing wave frequency. Therefore, it is suggested that the mesh distortion may resulted by a combination effect of mesh size, wave frequency and distance from the wave source. Comparing the results between 1-D and 2-D models indicates that the 2-D modelling produces higher error than 1-D model, which is explained as due to the error superposition in x and y directions in the 2-D model. 相似文献
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有耗媒质中电磁波的传播特性 总被引:7,自引:0,他引:7
讨论和分析了水平电偶极子源的辐射及电磁波在有耗媒质中的传播特性,有耗媒质是一种异常色散媒质,电磁波在这种媒质中传播时,群速大于相速,从而使波形发生某些失真。 相似文献
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阵列式观测是探地雷达系统研制和新型探测方法的一个重要发展趋势,而同形多源并发地下目标响应特征分析成为系统研制和数据处理研究的基础和前提。阵列式天线的多源并发信号及目标反射信号存在复杂的极化特性,但同时也包含更多目标特征的响应信息。本文针对基于似平面波探地雷达系统,分析了目标体在极化平面波照射下的响应特征,从多极化信号角度分析典型地下目标体形态特征;并采用时域有限差分正演分析方法,通过对阵列天线接收到的数据沿时间轴进行积分来获得目标在地表投影的分布情况,分析了一维及二维分布的收发天线阵列对目标的检测。研究成果表明,多极化综合特征分析能够有效改善目标检测的稳定性,提高目标响应信号的信噪比,减弱天线方向图和目标散射截面闪烁对数据剖面的影响,降低数据处理和解释的难度。 相似文献
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This paper reports on the numerical modelling of flash flood propagation in urban areas after an excessive rainfall event or dam/dyke break wave. A two-dimensional (2-D) depth-averaged shallow-water model is used, with a refined grid of quadrilaterals and triangles for representing the urban area topography. The 2-D shallow-water equations are solved using the explicit second-order scheme that is adapted from MUSCL approach. Four applications are described to demonstrate the potential benefits and limits of 2-D modelling: (i) laboratory experimental dam-break wave in the presence of an isolated building; (ii) flash flood over a physical model of the urbanized Toce river valley in Italy; (iii) flash flood in October 1988 at the city of Nîmes (France) and (iv) dam-break flood in October 1982 at the town of Sumacárcel (Spain). Computed flow depths and velocities compare well with recorded data, although for the experimental study on dam-break wave some discrepancies are observed around buildings, where the flow is strongly 3-D in character. The numerical simulations show that the flow depths and flood wave celerity are significantly affected by the presence of buildings in comparison with the original floodplain. Further, this study confirms the importance of topography and roughness coefficient for flood propagation simulation. 相似文献
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M. D. Sharma 《Journal of Earth System Science》2008,117(6):951-958
Biot’s theory for wave propagation in saturated porous solid is modified to study the propagation of thermoelastic waves in
poroelastic medium. Propagation of plane harmonic waves is considered in isotropic poroelastic medium. Relations are derived
among the wave-induced temperature in the medium and the displacements of fluid and solid particles. Christoffel equations
obtained are modified with the thermal as well as thermoelastic coupling parameters. These equations explain the existence
and propagation of four waves in the medium. Three of the waves are attenuating longitudinal waves and one is a non-attenuating
transverse wave. Thermal properties of the medium have no effect on the transverse wave. The velocities and attenuation of
the longitudinal waves are computed for a numerical model of liquid-saturated sandstone. Their variations with thermal as
well as poroelastic parameters are exhibited through numerical examples. 相似文献
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探地雷达是利用超高频脉冲电磁波探测地下介质分布的一种浅层地球物理勘探方法,探地雷达超高频、宽频带脉冲电磁波在地下有耗介质中的衰减特性是一个十分复杂的过程。本文从电磁波传播的麦克斯韦方程出发,较为系统地研究和分析了雷达脉冲电磁波在有耗介质中传播的衰减特性,对研究雷达脉冲电磁波在地下有耗介质中的传播机制有指导意义。 相似文献
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This paper investigates the generation of hydrodynamic water waves due to rockslides plunging into a water reservoir. Quasi-3D DEM analyses in plane strain by a coupled DEM-CFD code are adopted to simulate the rockslide from its onset to the impact with the still water and the subsequent generation of the wave. The employed numerical tools and upscaling of hydraulic properties allow predicting a physical response in broad agreement with the observations notwithstanding the assumptions and characteristics of the adopted methods. The results obtained by the DEM-CFD coupled approach are compared to those published in the literature and those presented by Crosta et al. (Landslide spreading, impulse waves and modelling of the Vajont rockslide. Rock mechanics, 2014) in a companion paper obtained through an ALE-FEM method. Analyses performed along two cross sections are representative of the limit conditions of the eastern and western slope sectors. The max rockslide average velocity and the water wave velocity reach ca. 22 and 20 m/s, respectively. The maximum computed run up amounts to ca. 120 and 170 m for the eastern and western lobe cross sections, respectively. These values are reasonably similar to those recorded during the event (i.e. ca. 130 and 190 m, respectively). Therefore, the overall study lays out a possible DEM-CFD framework for the modelling of the generation of the hydrodynamic wave due to the impact of a rapid moving rockslide or rock–debris avalanche. 相似文献