初始扰动下水下超高速运动体弹道数值模拟

本文建立了铅垂平面内水下超高速运动体动力学方程,采用Logvinovich的空泡截面独立扩张原理,给出空泡截面表达式.对运动体的受力特性进行了分析,引进了较精确的滑行升力计算方法.建立了发动机推力偏心以及装配工艺误差对运动体弹道扰动的数学模型.编制了有初始扰动的弹道仿真程序,对一个模型弹进行了各种初始扰动下的仿真计算.得出了初始扰动对运动体弹道特性的影响曲线.     

基于改进扰动功率和能量法的暂态扰动定位

功率和能量法是一种定位电能质量扰动问题的常用方法，但它在定位向系统注入能量的扰动类型时，会发生原理性错误。文中对此进行了改进，提出一种基于改进功率和能量法的暂态扰动定位方法。改进法结合了扰动初始能量的极值和扰动初始电压的极值，使其可以同时处理向系统注入能量的扰动和系统释放能量的扰动。改进方法不需要在定位前对暂态扰动进行分类，就可以对2类暂态扰动进行准确的定位。对比仿真分析表明，改进方法达到了准确定位2类暂态扰动的目的。     

三层流体系统中初始扰动和密度比对孤立波生成的影响

本文讨论了初始扰动和密度比对三层流体系统中孤立波生成的影响出发点是所导得的ＫｄＶ方程和散射反演理论的结果。分析结果表明，增加初始扰动的高度和宽度会生成更多的孤立波，这与Ｍａｘｗｏｒｔｈ＾［３］的实验结果一致；此外，在较弱分层情形，密度比对孤波生成的影响极小，而在较强的分层情形，其影响较大。     

干湿循环作用下膨胀岩崩解的粒度熵特征

膨胀岩遇水崩解是引发工程灾害的重要原因,其在干湿循环作用下的崩解情况将更加明显。采用湖南株洲的膨胀岩样进行室内崩解试验,并基于粒度熵概念,对其在不同干燥温度、外界扰动、不同初始单块质量情况下的标准基础熵进行研究。结果表明:静态崩解方式下,相对于105、30℃而言,60℃干燥温度下的标准基础熵最小;而扰动崩解方式下,膨胀岩崩解的标准基础熵几乎不受干燥温度的影响。在干燥温度、初始单块质量等因素不变的情况下,外界扰动对膨胀岩崩解的标准基础熵存在显著影响。初始单块质量对膨胀岩崩解的标准基础熵存在一定的影响,初始单块质量越大,标准基础熵越小。试验研究表明,标准基础熵是评价岩石崩解性的一种重要指标。     

基于Ｈｏｅｋ－Ｂｒｏｗｎ准则的隧道围岩塑性变形研究

基于Ｈｏｅｋ－Ｂｒｏｗｎ准则,推导了考虑应力重分布（不考虑地下水作用）的深埋圆形隧洞弹塑性区应力位移计算公式。并对不同地质强度指标ＧＳＩ、围岩类别、支护力和初始应力对围岩塑性区半径和位移的影响进行了分析。在ＧＳＩ取相同值时,不论岩石的种类,初始地应力对围岩塑性区的应力和位移都有较大的影响,尤其是在初始地应力大于15ＭＰａ时影响效果明显增大。将现场观测的围岩累计沉降值和塑性区范围与理论值计算值对比分析发现,围岩累计沉降按斜率可划分为严重扰动区、中度扰动区和微扰动区,且塑性区范围与实际观测结果较为接近,围岩剧烈变形区域集中在距围岩表面0．8ｍ范围内,其变形量占理论计算值的90％左右,可以为以后类似工程提供参考。     

基于孔穴扩张理论的黏性土不排水剪强度计算

确定黏性土不排水抗剪强度(c_u)的常规测试方法存在着取样扰动或测试深度不足等缺陷,提出了基于孔穴扩张理论的黏性土不排水抗剪强度的测试方法,并应用于花岗岩残积黏性土、辉绿岩残积黏性土和花岗岩残积砂质黏性土的旁压试验和静力触探试验成果解释中,将两种试验得到的c_u值进行对比。结果表明:旁压理论的假设条件导致旁压试验得到的c_u值较静力触探试验得到的c_u值大,其中等容剪切法计算过程对初始扰动和应变数据的选择非常敏感,导致计算结果差异较大;直接传统法能够克服初始扰动,c_u值受临塑压力的影响较小,计算结果与土体性质以及试验点深度较吻合,其c_u值约为静力触探试验的1.2倍,是一种简单、有效的确定黏性土不排水抗剪强度的方法。     

抓斗下降时流场和最优下降方式的数值计算

疏浚作业时如何能有效减少水体浑浊,减轻污染一直是人们关注的问题。利用可以分析流体和固体间运动相互作用的数学模型,模拟了环保型抓斗下降过程中的流场情况,并讨论了不同下降方式对流场的影响,提出了能适度控制流场扰动的操作方法。结果表明:抓斗在下降过程中减速能有效减少底面流速,达到抑制底面浑浊的效果,其中抓斗在距离底面3m处减速为初始速度的1/3能最有效减少水体扰动从而抑制底面浑浊。研究结果可为环保型疏浚施工提供参考。     

基于贝叶斯网络的扰动后预想事故分析方法

针对连锁故障影响因素复杂、演变过程随机及故障组合多样的分析难点，在分析和总结连锁故障发生、发展过程及其特点的基础之上，抽取初始扰动后的潮流转移过程作为研究重点，建立了能在不确定性环境下进行概率推理并具有良好可扩展性的贝叶斯网络相继开断模型，同时考虑继电保护隐藏故障的线性概率模型，提出了基于贝叶斯网络的扰动后预想事故分析方法，以量化分析线路过载和保护装置的动作行为对连锁故障发展过程的影响。该方法抓住了连锁故障防控的有效阶段及本质特征并简化了分析的复杂度，为特定扰动下的具体故障发展模式研究提供了快速分析手段。算例结果表明模型合理、方法有效，具有在线应用的前景。     

双球体颗粒沉降过程实验研究

颗粒沉降是泥沙运动力学的基本课题之一,同时也是环境泥沙学的基础。对球体双颗粒并排释放时的沉降过程在雷诺数过渡区进行实验研究,发明颗粒电磁释放装置,研究颗粒初始间距对沉降过程的影响。结果表明:电磁释放装置可以实现颗粒同步释放,消除释放装置对液体的扰动,保证颗粒沉降实验初始条件严格可控;并排释放的双颗粒沉降过程中产生排斥作用,颗粒沉降过程经历3个阶段;颗粒初始间距对沉降过程影响显著,初始间距越小,排斥作用越强烈,在初始间距超过5倍粒径后,颗粒间几乎不存在相互作用。     

考虑岩体强度演化的全强风化岩质边坡主动加固设计方法

全强风化岩质边坡由于岩体破碎,易受工程扰动和降雨影响而导致强度发生弱化,因此在公路路基开挖过程中极易失稳。以某公路全强风化岩质边坡为例,通过对处于不同阶段的边坡稳定性进行反分析,分别得到岩体初始强度和弱化后强度,获取了岩体强度的演化过程。通过主动加固和被动加固工程措施的对比分析,表明主动加固设计能够有效利用岩体原始强度,大大降低加固工程量。对于受工程扰动和降雨影响较大的全强风化岩质边坡,采用主动加固设计十分必要且有效,可为全强风化岩质边坡设计提供参考。     

Enhancement of Model Reliability by Integrating Prediction Interval Optimization into Hydrogeological Modeling

This paper presents a single-objective optimization-based perturbation analysis to quantify model prediction uncertainty. A new index named coverage width index (CWI), which combines two commonly used uncertainty indices, the percentage of coverage (POC) and the average width (AW), was proposed to facilitate the optimization. Considering the outperformance of the wavelet neural network (WNN) among various data-driven modeling approaches in hydrogeological modeling, the proposed approach was integrated into WNN (called OPWNN). A case study was conducted to demonstrate the application of OPWNN in groundwater level forecasting at two wells in the Amaravathi River Basin, India. The sensitivity analysis of the effect of initial perturbation range on CWI suggested that uncertainty is sensitive to the selected perturbation range and a small perturbation does not guarantee an acceptable prediction interval (PI). The modeling results demonstrated that the OPWNN can optimize the PI effectively with minimized AW corresponding to an expected high POC. Therefore, this approach can yield more reliable predictions/forecasts for water resources management.

     

水平流作用下的混合流体行进波对流

利用高阶紧致有限差分格式,数值模拟研究了物性参数对具有Soret效应的混合流体的Poiseuille-Rayleigh-Bénard流动系统的影响。在正的小分离比下,附加一个微小的温度扰动作为扰动源,流动系统时空结构的发展在经历了初始状态、线性波指数型成长和非线性发展三个阶段之后,最终演变成为稳定的周期性行进波状态。还进一步探讨了水平流强度和Rayleigh数对流场结构的影响。     

Numerical investigation of a swirling flow under the optimal perturbation

The nonlinear evolution of 3-D instability of a viscous swirling flow, namely, the Oseen vortex, is addressed by direct numerical simulation with a Reynolds number equal to 5000. The global optimal perturbation is considered as the initial perturbation. In axisymmetric cases, three flow regimes are found: (1) the linear growth; (2) the decay of perturbation energy; (3) secondary energy growth. The linear energy growth, which is characterized by the amplification of radial perturbations, is arrested by the interaction between the vortex ring and the Oseen vortex core. The development of the vortex structure is also investigated for non-symmetric flows.

     

An Assimilation Simulation Approach for the Suspended Sediment Concentration in Inland Lakes Using a Hybrid Perturbation Generation Method

Suspended sediments, one of the most important factors affecting the water environments of inland lakes, are closely related to the migration and interaction of various pollutants. Existing studies show that the suspended sediment concentration can be accurately predicted based on assimilation methods coupled with hydrodynamic models. However, in the hydrological assimilation simulation process, the existing perturbation generation methods consider the perturbation error to follow a random Gaussian distribution, which does not consider the spatial variation characteristics of errors. Thus, in this paper, we proposed a new method that generates a hybrid perturbation field for the assimilation simulation instead of using random error. The proposed approach was validated through assimilation simulations of the suspended sediment concentration of Taihu Lake, China, and five assimilation experiments were conducted. The proposed method was compared with the existing methods for generating the perturbation field. After three days and 72 time steps of assimilation simulation based on the hybrid perturbation field, the proposed assimilation method provided results that were more consistent with the buoy-measured data. These findings demonstrate that the proposed method for generating a hybrid perturbation field has a higher simulation accuracy than other methods and is therefore effective and provides a new idea for the assimilation simulation of suspended sediment concentrations in inland lakes.

     

Experiments on the short-term development of sine-generated meandering rivers

This paper presents recent works on the simulation of short-term development of sine-generated meandering river in laboratory conditions. The influences of initial system parameters on the evolution process of rivers are investigated, including control over channel sinuousness, channel width and dominant discharge, eventually leading to different results of planforms. Measurements on the bank-line, flow field, bed topography and sediment transport rate were carried out. Braided rivers are easy to produce using non-cohesive sediments in floodplains, whereas environmental temperatures and humidities could influence the fluvial process by their effects on material cohesion. Channelized rivers were obtained in the “High Flow” conditions and the river corridor width was proven to be mainly connected with initial channel sinuousness and water discharge. Sickle-shaped and bamboo leaves-shaped sandbars were formed in the channels during the transformation process of meandering to braiding, the stability degree of sandbars reflects the adaption of channel morphology to hydrodynamic condition. Quantitative analysis confirms the formation of free steady bars, which manifests the free response as a downstream oscillation of the perturbation. Damping length is mainly affected by dominant discharge, channel width is the secondary factor, and channel sinuousness is the weakest factor. The wavelength of steady bars approximately equals to half of the initial streamwise wavelength. Sediment transport rate tends to increase with the increasing of channel sinuousness but stops growing due to the excessive increase of flow route and flow friction. The experiment results could be useful for verifying river pattern discriminant functions and offer a basis for further study on the morphological evolution of large-scale natural rivers, such as Yangtze River.     

PRESSURE TRANSIENT ANALYSIS OF HETEROGENOUS RESERVOIRS WITH IMPERMEABILITY BARRIER USING PERTURBATION BOUNDARY ELEMENT METHOD

The transient flow mathematical model of arbitrary shaped heterogeneous reservoirs with impermeability barrier is proposed in this paper. In order to establish this model, the perturbation method is employed and the solution of model is expanded into a series in powers of perturbation parameter. By using the Boundary Element Method (BEM) and Duhamel principle, wellbore pressure with effects of skins and wellbore storage is obtained. The type curves are plotted and analyzed considering effects of heterogeneity, arbitrary shape and impermeable barriers. Finally, the results obtained by perturbation boundary element method is compared with the analytical solution and is available for the transient pressure analysis of arbitrary shaped reservoirs.     

基于随机化方法的叶绿素a含量神经网络预测模型输入因子敏感性分析

为了区分神经网络预测模型输入因子敏感性强弱,以探寻水体叶绿素a含量变化的主要影响因素,引入随机化方法,分别采用偏导、连接权值、改进连接权值、百分比扰动及改进扰动方法对叶绿素a含量神经网络预测模型输入因子进行1 000次敏感性分析,以计算结果均值对输入因子敏感性进行评价。结果表明:引入随机化方法后,敏感性分析结果稳定,研究区域pH相对敏感度最高,光照、降雨量、极大风速相对敏感度最小。受输入因子波动范围过大影响,百分比扰动方法与其他敏感性分析方法得到的结论不一致;对扰动方法进行改进,基于输入因子标准差扰动进行敏感性分析,光照、降雨量、极大风速相对敏感度分别为0.032、0.030、0.029,pH相对敏感度为0.148,因子敏感性强弱与其他方法一致;改进的扰动方法物理概念清晰,耗机时少,易实现。研究结果可为基于神经网络分析水体水华主要影响因素提供方法,为水体治理措施有效开展提供研究基础。     

SOLUTION OF THE ENSO DELAYED OSCILLATOR WITH HOMOTOPY ANALYSIS METHOD

An ENSO delayed oscillator is considered.The El Nino atmospheric physics oscillation is an abnormal phenomenon involved in the tropical Pacific ocean-atmosphere interactions.The conceptual oscillator model should consider the variations of both the eastern and western Pacific anomaly patterns.Using the homotopy analysis method,the approximate expansions of the solution of corresponding problem are constructed.The method is based on a continuous variation from an initial trial to the exact solution.A Maclaurin series expansion provides a successive approximation of the solution through repeated application of a differential operator with the initial trial as the first term.This approach does not require the use of perturbation parameters and the solution series converges rapidly with the number of terms.Comparing the approximate analytical solution by homotopy analysis method with the exact solution,we can find that the homotopy analysis method is valid for solving the strong nonlinear ENSO delayed oscillator model.     

THE PRESSURE TRANSIENT ANALYSIS OF DEFORMATION OF FRACTAL MEDIUM

The assumption of constant rock properties in pressure-transient analysis of stress-sensitive reservoirs can cause significant errors in the estimation of temporal and spatial variation of pressure. In this article, the pressure transient response of the fractal medium in stress-sensitive reservoirs was studied by using the self-similarity solution method and the regular perturbation method. The dependence of permeability on pore pressure makes the flow equation strongly nonlinear. The nonlinearities associated with the governing equation become weaker by using the logarithm transformation. The perturbation solutions for a constant pressure production and a constant rate production of a linear-source well were obtained by using the self-similarity solution method and the regular perturbation method in an infinitely large system, and inquire into the changing rule of pressure when the fractal and deformation parameters change. The plots of typical pressure curves were given in a few cases, and the results can be applied to well test analysis.     

A NEW METHOD IN GROUNDWATER FLOW MODELING

One of the challenges in groundwater modeling is the prediction of hydraulic head related to local stress fluctuations with a regional scale model. Typical applications of numerical models require extensive field information for input data and for calibration. If we can model the change directly, we may not have to know all the modeling parameters because sometimes the changes only depend on fewer parameters. In this article, we present an improved methodology for groundwater modeling related to local stress fluctuations using a perturbation approach. Our results demonstrate that this approach is capable of matching an exact solution for drawdown in both confined and unconfined aquifers. The results suggest that this perturbation method can provide an accurate representation of head in a large-scale hydrogeological system.