Estimation of non-point source pollution loads with flux method in Danjiangkou Reservoir area,China

The estimation of non-point source pollution loads into the Danjiangkou Reservoir is highly significant to environmental protection in the watershed. In order to overcome the drawbacks of traditional watershed numerical models, a base flow separation method was established coupled with a digital filtering method and a flux method. The digital filtering method has been used to separate the base flows of the Hanjiang,Tianhe, Duhe, Danjiang, Laoguan, and Qihe rivers. Based on daily discharge, base flow, and pollutant concentration data, the flux method was used to calculate the point source pollution load and non-point source pollution load. The results show that:(1) In the year 2013, the total inflow of the six rivers mentioned above accounted for 95.9% of the total inflow to the Danjiangkou Reservoir. The total pollution loads of chemical oxygen demand(CODMn) and total phosphorus(TP) from the six rivers were 58.20 103 t and 1.863 10~3 t, respectively, and the non-point source pollution loads were 39.82 10~3 t and 1.544 10~3 t, respectively, indicating that the non-point source pollution is a major factor(with a contribution rate of 68.4% for CODMnand 82.9% for TP).(2) The Hanjiang River is the most significant contributor of pollution loads to the Danjiangkou Reservoir, and its CODMnand TP contribution rates reached 79.3% and 83.2%, respectively. The Duhe River took the second place.(3) Non-point source pollution mainly occurred in the wet season in 2013, accounting for 80.8% and 90.9% of the total pollution loads of CODMnand TP, respectively. It is concluded that the emphasis of pollution control should be placed on non-point source pollution.

Effects of slip condition on MHD stagnation-point flow over a power-law stretching sheet

The steady two-dimensional magnetohydrodynamic stagnation flow towards a nonlinear stretching surface is studied. The no-slip condition on the solid boundary is replaced with a partial slip condition. A scaling group transformation is used to get the invariants. Using the invariants, a third-order ordinary differential equation corresponding to the momentum is obtained. An analytical solution is obtained in a series form using a homotopy analysis method. Reliability and efficiency of series solutions are shown by the good agreement with numerical results presented in the literature. The effects of the slip parameter, the magnetic field parameter, the velocity ratio parameter, the suction velocity parameter, and the power law exponent on the flow are investigated. The results show that the velocity and shear stress profiles are greatly influenced by these parameters.

Wavelet analysis of stagnation point flow of non-Newtonian nanofluid

The wavelet approach is introduced to study the influence of the natural convection stagnation point flow of the Williamson fluid in the presence of thermophysical and Brownian motion effects. The thermal radiation effects are considered along a permeable stretching surface. The nonlinear problem is simulated numerically by using a novel algorithm based upon the Chebyshev wavelets. It is noticed that the velocity of the Williamson fluid increases for assisting flow cases while decreases for opposing flow cases when the unsteadiness and suction parameters increase, and the magnetic effect on the velocity increases for opposing flow cases while decreases for assisting flow cases. When the thermal radiation parameter, the Dufour number, and Williamson’s fluid parameter increase, the temperature increases for both assisting and opposing flow cases. Meanwhile, the temperature decreases when the Prandtl number increases. The concentration decreases when the Soret parameter increases, while increases when the Schmidt number increases. It is perceived that the assisting force decreases more than the opposing force. The findings endorse the credibility of the proposed algorithm, and could be extended to other nonlinear problems with complex nature.

Magneto Hydrodynamic Orthogonal Stagnation Point Flow of a Power-Law Fluid Toward a Stretching Surface

Steady two dimensional MHD stagnation point flow of a power law fluid over a stretching surface is investigated when the surface is stretched in its own plane with a velocity proportional to the distance from the stagnation point. The fluid impinges on the surface is considered orthogonally. Numerical and analytical solutions are obtained for different cases.

MHD stagnation point flow towards heated shrinking surface subjected to heat generation/absorption

The magnetohydrodynamic （MHD） stagnation point flow of micropolar flu- ids towards a heated shrinking surface is analyzed. The effects of viscous dissipation and internal heat generation/absorption are taken into account. Two explicit cases, i.e., the prescribed surface temperature （PST） and the prescribed heat flux （PHF）, are discussed. The boundary layer flow and energy equations are solved by employing the homotopy analysis method. The quantities of physical interest are examined through the presenta- tion of plots/tabulated values. It is noticed that the existence of the solutions for high shrinking parameters is associated closely with the applied magnetic field.

Numerical prediction of inner turbulent flow in conical diffuser by using a new five-point scheme and DLR k-ε turbulence model

The internal turbulent flow in conical diffuser is a very complicated adverse pressure gradient flow.DLR k-ε turbulence model was adopted to study it.The every terms of the Laplace operator in DLR k-ε turbulence model and pressure Poisson equation were discretized by upwind difference scheme.A new full implicit difference scheme of 5-point was constructed by using finite volume method and finite difference method.A large sparse matrix with five diagonals was formed and was stored by three arrays of one dimension in a compressed mode.General iterative methods do not work wel1 with large sparse matrix.With algebraic multigrid method(AMG),linear algebraic system of equations was solved and the precision was set at 10-6.The computation results were compared with the experimental results.The results show that the computation results have a good agreement with the experiment data.The precision of computational results and numerical simulation efficiency are greatly improved.

Development of point source method and its practical significance

The advantages of Reichardt＇s hypothesis in dealing with single and multiple circular jets in a stagnant environment are highlighted. The stages involved in the development of the point source method, an offshoot of the new hypothesis, are presented, Previous results of experiments on multiple circular jets in a stagnant environment justify the method of superposition. As a prelude to discussion of multiple jets in a co-flowing stream, results on the excess-velocity decay, the growth of the shear layer, and the dilutions for a single jet based on Reichardt＇s hypothesis are presented. The spreading hypothesis is generalized by introducing a link factor kl to account for the co-flowing stream. The distribution of excess-momentum flux uAu is shown to be Gaussian in nature. Based on the principle of superposition, the decay of the maximum excess velocity and the dilution are predicted for odd and even numbers of jets in an array. The predictions seem to be in good agreement with observed data.

一种基于物质点法的熔冰仿真方法

为了解决拉格朗日法模拟熔冰时产生的穿模现象,提出一种基于物质点法的熔冰仿真方法。首先,将欧拉空间中的每个拉格朗日粒子视为固-液双相耦合的集合体,实现固相到液相的平稳过渡;其次,在物质点法背景网格上计算热能,采用预处理共轭梯度法求解相变过程的温度线性系统;最后,对潜热现象进行处理,引入虚拟水模型,通过限制虚拟水的移动来实现对冰块外部水流现象的仿真。实验结果表明,该方法不仅能够利用物质点法处理自碰撞的优势解决穿模现象,而且能模拟出真实的潜热过程的水流现象。

线性化改进物质点法的颗粒流仿真

作为一种新近发展出的无网格法,物质点法综合了基于网格方法的准确性与计算效率,以及无网格法对多种极端情境的适应性,因此该方法对采取连续介质模型的颗粒流数值计算等大变形问题十分有效。为提高物质点法对于颗粒流的计算效率,本文对物质点法进行了线性化改进并基于改进算法给出了若干算例。以物质点法的背景网格的结构化特点以及Courant-Friedrichs-Lewy(CFL)条件为基础,改进了自然坐标系到整体坐标系的求解过程,并使用改进的物质点法对颗粒流的颗粒堆坍塌、筒仓排出以及曲面上颗粒流对半球体的碰撞等算例进行了计算。在计算精度损失较小的情况下,提高了物质点法求解颗粒流问题的效率,验证了此改进方法的有效性与稳定性。

基于物质点法的远程滑坡碎屑流运动过程模拟及特征分析

目的 研究远程滑坡碎屑流运动过程以及运动过程中速度、滑动距离、动能变化,为滑坡碎屑流灾害的预防和治理提供参考。方法 基于物质点法,以塔合曼和乱石包两个远程滑坡碎屑流工程实例为背景,对两个滑坡碎屑流的运动过程进行数值模拟;并对塔合曼滑坡碎屑流运动过程中水平、垂直方向运动速度分布,内摩擦角对运动过程的影响,以及乱石包滑坡碎屑流铲刮效应对堆积形态、动能变化的影响进行分析。结果 两个滑坡碎屑流最终堆积形态模拟结果与实测结果吻合良好,验证了数值模拟结果的有效性;塔合曼滑坡碎屑流随着内摩擦角从18°增加到33°,动能峰值降低71.4%,最终势能增加54.4%,滑坡碎屑流的能量耗散减小47.8%;在乱石包滑坡碎屑流实例的模拟中,速度云图呈现了滑体速度场的层状分布特征。结论 内摩擦角对滑坡碎屑流的动力过程影响十分显著;乱石包滑坡碎屑流的滑体在高速滑移阶段存在强烈的内部剪切作用,并且铲刮效应对滑坡碎屑流的运动起到了一定的阻碍作用。

外墙外保温工程施工技术要点及应用研究

外墙外保温工程是现代建筑工程中非常重要的子分部之一,它能够有效地提高建筑物的保温性能,降低能源消耗,延长建筑物的使用寿命。本文将从施工工艺流程、施工方法要点、作业安全等方面,对外墙外保温工程施工技术进行探讨。

培元调神针灸法联合子午流注穴位贴敷治疗卵巢早衰临床研究

目的:观察培元调神针灸法联合子午流注穴位贴敷治疗卵巢早衰的临床疗效及对患者卵巢体积、卵巢血流参数的影响。方法:采用随机数字表法将92例卵巢早衰患者分为对照组、治疗组各46例。对照组给予常规西药治疗,治疗组在对照组基础上给予培元调神针灸法联合子午流注穴位贴敷治疗。比较2组治疗前后中医证候积分、焦虑自评量表(SAS)评分、卵巢体积、卵泡数目、卵巢血流参数及血清性激素水平,评估2组临床疗效及不良反应发生情况。结果:治疗组总有效率91.30%,高于对照组73.91%(P<0.05)。治疗后,2组中医证候积分、SAS评分、阻力指数及血清促黄体生成激素(LH)、卵泡刺激素(FSH)水平均较治疗前降低(P<0.05),且治疗组中医证候积分、SAS评分、阻力指数及血清LH、FSH水平低于对照组(P<0.05)。治疗后,2组雌二醇(E2)水平、卵巢收缩期峰值流速、舒张末期流速较治疗前升高(P<0.05),左、右侧卵巢体积增大(P<0.05),卵泡数目增加(P<0.05),且治疗组上述指标高于对照组(P<0.05)。2组均未出现严重不良反应。结论:培元调神针灸法联合子午流注穴位贴敷治疗卵巢早衰疗效确切,能够调节患者性激素水平,改善患者卵巢血流参数,安全性较高。

特征点法与光流跟踪融合的视觉里程计算法

针对视觉里程计中特征点法因计算量大而导致实时效果不好的问题,提出了一种特征点法与光流跟踪融合的算法。首先,通过度量运动大小的视差阈值和地图点的跟踪衰减系数作为筛选策略选取关键帧;其次,仅对关键帧中的特征点计算描述符,而对于非关键帧中的特征点则是通过基于图像金字塔的稀疏光流法建立起关键点间的对应关系,从而降低计算量;最后,通过最小化重投影误差得到当前帧的位姿估计。通过实验测试证明,该算法的定位精度与ORBSLAM2相当,但运行速度可提高70%以上,实时性明显优于ORBSLAM2算法。

基于轻量化YOLOv8n的动态视觉SLAM算法

为了改善在动态场景下同步定位与地图绘制(Simultaneous Localization And Mapping,SLAM)算法定位精度低的问题,提出一种基于轻量化YOLOv(You Only Look Once version)8n的动态视觉SLAM算法。利用加权双向特征金字塔网络(Bidirectional Feature Pyramid Network,BiFPN)对YOLOv8n模型进行轻量化改进,减少其参数量。在SLAM算法中引入轻量化YOLOv8n模型,并结合稀疏光流法组成目标检测线程,以去除动态特征点,利用经过筛选的特征点进行特征匹配和位姿估计。实验结果表明:轻量化YOLOv8n模型参数量下降了36.7%,权重减少了33.3%,能够实现YOLOv8n模型的轻量化;与ORB-SLAM3算法相比,所提算法在动态场景下的定位精度提高83.38%,有效提高了动态场景下SLAM算法的精度。

土体颗粒物流动物质点法模拟的弹塑性和非牛顿流体本构模型比较研究

土体颗粒物流动是一种典型的大变形破坏,具有非牛顿流体的流动特征。准确模拟土体颗粒物的流动及冲击过程,对滑坡和泥石流等地质灾害的防治具有重要意义。物质点法是一种无网格粒子类方法,已在各类大变形问题中得到了广泛应用。以往土体颗粒物流动的模拟,通常采用弹塑性本构模型,但缺乏对非牛顿本构模型的模拟分析。本文引入非牛顿本构模型的模拟分析,旨在为土体颗粒物流动模拟提供一种新的方法与思路。非牛顿本构模型的模拟分析是将非牛顿广义Cross模型引入三维物质点法,通过人工阻尼力模拟颗粒间的摩擦力,对土体颗粒物的坍塌、沿斜面滑动以及冲击障碍物等问题进行了动态模拟,研究了其运动全过程,并与弹塑性本构模型的模拟结果进行了对比验证。结果表明,基于非牛顿流体本构模型的物质点法可以较好地模拟土体颗粒物加速、减速到再次稳定的流动全过程及其对障碍物的冲击效应。

插入式流量计两种测量方法的研究

本文介绍了插入式流量计的结构和原理,以及两种常用测量方法的理论依据,并在此基础上,设计了一种插入式流量计在水流量标准装置上的不同流速实验。通过对实验数据分析,为插入式流量计的校准和使用提供了更有效的方法。

基于有限差分-谱方法的分数阶Burgers流体的非稳态驻点流动

研究了分数阶Burgers流体通过拉伸平板的非稳态驻点流动问题。将分数阶导数引入Burgers流体模型可以更好地模拟流动过程,但也增加了模型的复杂性和求解难度。首次运用有限差分-谱方法求解分数阶Burgers流体模型,离散格式构造简单有效。采用谱方法对控制方程中的空间项进行离散,利用有限差分方法分别结合L-1和L-2算法离散控制方程中的时间项,给出了两种离散格式,并且通过构造数值算例证明了离散格式的收敛性。结果表明,在靠近平板处,速度随着分数阶导数的增加而减小,而无穷远处的流体速度呈现出相反的趋势,体现了分数阶导数的记忆特性。此外,雷诺数越小,流体的粘度越大,导致流体速度越大。由于松弛时间参数的松弛特性,靠近平板处松弛时间参数对速度分布有抑制作用,远离平板处松弛时间促进流体流动。

Security Constrained Distributed Optimal Power Flow of Interconnected Power Systems

The security constrained distributed optimal power flow (DOPF) of interconnected power systems is presented. The centralized OPF problem of the multi-area power systems is decom-posed into independent DOPF subproblems, one for each area. The dynamic security region (DSR) to guarantee the transient stability constraints and static voltage stability region (SVSR) constraints, and line current limits are included as constraints. The solutions to the DOPF subproblems of the different areas are coordinated through a pricing mechanism until they converge to the centralized OPF solution. The nonlinear DOPF subproblem is solved by predictor-corrector interior point method (PCIPM). The IEEE three-area RTS-96 system is worked out in order to demonstrate the effectiveness of the proposed method.

物质点法的物体断裂细节绘制算法优化

针对物体断裂仿真中因采样不均匀导致的断裂细节不真实问题,提出一种优化基于物质点法的断裂表面细节的方法.首先采用物质点法处理断裂过程中出现的大的拓扑变化,增强碰撞和断裂处理的效率,减少计算量;然后引入弹性与塑性之间的流动规则,解决物体断裂时屈服条件不稳定的问题,增强真实性;最后采用重采样方法处理产生的空洞区域,改进网格的划分方式,从而增加断裂面的细节,有效地体现断裂效果.实验结果表明,与现有的物质点法的物体断裂相比,所提方法在保证帧率、时间步长等相关参数稳定的前提下,填补了断裂空洞,能够在视觉上表现更加丰富的断裂面细节.

Determination of minimum flood flow for regeneration of floodplain forest from inundated forest width-stage curve

Floods are essential for the regeneration and growth of floodplain forests in arid and semiarid regions. However, river flows, and especially flood flows, have decreased greatly with the increase of water diversion from rivers and/or reservoir regulation, resulting in severe deterioration of floodplain ecosystems. Estimation of the flood stage that will inundate the floodplain forest is necessary for the forest＇s restoration or protection. To balance water use for economic purposes and floodplain forest protection, the inundated forest width method is proposed for estimating the minimum flood stage for floodplain forests from the inundated forest width-stage curve. The minimum flood stage is defined as the breakpoint of the inundated forest width-stage curve, and is determined directly or analytically from the curve. For the analytical approach, the problem under consideration is described by a multi-objective optimization model, which can be solved by the ideal point method. Then, the flood flow at the minimum flood stage （minimum flood flow）, which is useful for flow regulation, can be calculated from the stage-discharge curve. In order to protect the forest in a river floodplain in a semiarid area in Xinjiang subject to reservoir regulation upstream, the proposed method was used to determine the minimum flood stage and flow for the forest. Field survey of hydrology, topography, and forest distribution was carried out at typical cross sections in the floodplain. Based on the survey results, minimum flood flows for six typical cross sections were estimated to be between 306 m3/s and 393 m3/s. Their maximum, 393 m3/s, was considered the minimum flood flow for the study river reach. This provides an appropriate flood flow for the protection of floodplain forest and can be used in the regulation of the upstream reservoir.