低流速净蒸汽产生点模型预测过冷沸腾空泡率

空泡率是汽液两相流动的基本参数之一,而已有过冷沸腾空泡率计算方法研究以高质量流速为主,且大量文献报道现有空泡率模型难以适用于低流速过冷沸腾工况。本文基于低流速过冷沸腾净蒸汽产生点(NVG)理论模型,进一步建立了计算过冷沸腾空泡率的分布拟合模型。在较宽广的压力、质量流速、热流密度和流道尺寸范围内将模型计算结果与现有空泡率实验数据进行了比较,低流速工况下该模型与实验数据符合良好,表明该模型可适用于低流速过冷沸腾工况。     

负荷模型对电力系统失步振荡特性的影响

[目的]负荷作为最终消耗有功功率的部分,对系统的稳定起着十分重要的影响,为此,文章研究不同负荷模型对电力系统失步振荡特性的影响.[方法]以某大型电网区域间断面为研究对象,采用中国电力科学研究院的BPA程序,综合分析不同负荷模型对振荡中心及失步解列装置动作的影响.[结果]结果表明:采用ZIP静态负荷模型,线路Ucosφ曲...     

组合模型在能源需求预测中的应用

简述不同的能源需求预测方法的特点．结合某省区能源需求的历史数据,运用趋势外推法建立单项预测模型,并对趋势外推预测的优缺点进行分析;运用ARMA模型对趋势外推模型中的残差序列进行分析,得到趋势外推模型中非趋势分量的预测结果;测算出某省区“十一五”期间的能源需求总量,并得出这一组合模型的预测结果准确性高、稳定性好的结论。     

不同湍流模型在斜流泵性能预测中的应用

为研究不同湍流模型在斜流泵性能模拟上的差异,以比转速为425的斜流泵为研究对象,选取κ-ε、κ-ω、SST、RNGκ-ε四种湍流模型,对斜流泵设计工况下的内部流动进行数值计算,并分析各湍流模型在斜流泵内流计算中的适用性。结果表明,SST模型预测的扬程偏差较大,为7.69%,其余模型扬程预测偏差均小于5%,其中RNGκ-ε模型扬程预测偏差最小,为3.76%;SST模型预测的效率偏差最大,为3.70%,κ-ε模型和κ-ω模型的效率偏差最小,均为3.00%;4种模型在吸入段及导叶处的轴向速度分布基本一致,κ-ω模型对叶轮轴向速度预测的高速域范围略优于其余三种模型;κ-ε模型和RNGκ-ε模型对斜流泵涡量预测结果较为相似,而κ-ω模型和SST模型的预测结果比较接近。研究结果可为预测斜流泵性能和内部流动特性提供参考。     

ARIMA-RBFNN组合模型在白城市降水量预测中的应用

针对降水受大气环流、地形、气压等诸多环境因素影响致使准确预报降水量较为困难的问题,结合ARIMA模型和RBFNN模型各自优势,提出了ARIMA-RBFNN组合模型,对白城市2001~2010年降水量进行了预报,并与ARIMA模型和RBFNN模型预报结果进行了对比分析。结果表明,ARIMA-RBFNN组合模型在预测降水量时最大相对误差为27.33%,最小相对误差为0.70%,平均相对误差为8.54%,预测精度明显优于ARIMA模型和RBFNN模型,可见该组合模型发挥了ARIMA模型和RBFNN模型各自的优点,为精确预测降水量提供了一种有效方法。     

EEMD-NNBR模型在降水预测中的应用

为解决降水资源预测复杂的问题,建立了具有物理意义的新预测模型,即利用集合经验模态分解(EEMD)方法,分解降水资源并识别其演变模式,获得各本征模函数(IMF),然后结合最近邻抽样回归模型(NNBR)对数据进行预测分析,汇总相应的计算结果,从而构成了EEMD-NNBR降水预测模型。以无锡市惠山区的降水序列资料为例,采用EEMD-NNBR模型预测降水资源,并与单一的NNBR模型预测值进行对比分析。结果表明,所建模型稳定性较好,能合理预测水资源演变趋势,提高降水资源预测精度,具有一定的应用价值。     

IEA-PNN模型在水质预测中的应用

采用免疫进化算法(IEA)对概率神经网络(PNN)模型参数进行优化,并应用于水质预测中.以黄河小浪底至花园口段为例,使用该模型预测水体中的COD和NH3-N浓度.预测结果表明,IEA-PNN模型应用于水质预测切实可行,能同时实现分类预测和定量预测,且预测精度较高.     

改进灰色模型在电力负荷预测中的应用

灰色GM（1,1）模型是一种较有效的负荷预测模型,然而由于电力负荷具有多样性,导致对某些变化规律的负荷预测误差较大,精度不能满足要求,在实际应用中具有一定的局限陛。对灰色GM（1,1）模型进行必要的改进,利用等维新信息递推模型进行负荷预测,通过实例分析表明,可提高预测的精度。     

受热工况截面平均空泡率对漂移流模型分布参数C0的影响分析

空泡率是汽液两相流动的基本参数之一.在计算空泡率的众多模型中,Zuer-Findlay漂移流模型目前应用最为广泛.根据受热工况下局部界面参数径向分布特性实验研究结果,并通过对现有实验数据的处理,分析了受热工况下垂直上升两相流漂移流模型分布参数C0随截面平均空泡率的变化规律.证实了从过冷沸腾泡状流到饱和沸腾弹状流工况,随着空泡率的增加,分布参数C0从一个小于1的值增加到1.0～1.2.     

MCEEMD-HGWO-MGU混合模型在径流预测中的应用

为分析径流非线性特征对预测精度的影响,在改良的互补集成经验模态分解(MCEEMD)基础上,建立混合灰狼优化算法(HGWO)与最小门控单元(MGU)混合的径流预测模型,并利用该模型预测黄河下游三个水文站处的月径流.选取纳什效率系数和合格率评价模型性能,并选择多个误差指标与其他模型进行比较.结果表明,与其他模型相比,MCE...     

水力机械空化初生的分子动力学模拟

为研究水力机械空化初生瞬态特性,应用分子动力学的模拟方法,对存在空化核的水分子计算域进行了研究,得到空化核初始尺寸与系统亚稳态对空化初生的影响,并对空化核的演变过程、系统压力以及系统分子势能、分子径向分布函数等相关的热力学参数进行分析。研究表明:空化初生于液态水中的空化核,空化初生时空化核及其周围小范围内的液态水处于负压状态;一定体积的空化核系统存在临界亚稳态,未进入临界亚稳态的体系中空化核不能稳定存在,体系进入临界亚稳态后空化核体积增大,空化发生,空化核体积越大的系统越容易进入临界亚稳态,从而诱发空化;空化初生时体系压力迅速增加,分子势能减小,分子排布也发生改变。     

Thermal Bubble Dynamics Under the Effects of an Acoustic Field

In this research, dynamics of a micro thermal bubble existing in an acoustic field have been studied by a high-speed camera and a micro temperature sensor. The micro thermal bubble was generated by a micro heater, which was fabricated by the MEMS (micro-electro-mechanical system) technique and packed into a transparent mini chamber. The acoustic field inside the chamber was generated by a piezoelectric plate that was attached on the top side of the chamber's wall. Compared with micro thermal bubble dynamics in normal conditions, several different bubble dynamic phenomena in acoustic conditions have been found, such as bubble departure and attraction around the heater, bubble oscillating in the liquid volume, etc. By theoretical analysis, the main mechanism of bubble movements is attributed to the balance between Marangoni force and acoustic force. All these bubble dynamic phenomena improve the liquid convective flow and enhance the heat and mass transfer. Thus, this investigation about acoustic thermal bubble dynamics may find some potential applications in micro fluid devices for different functions, such as heat/mass transfer enhancement, micro electronic cooling, micro heater protection, etc. Temperature measurement in both normal conditions and acoustic conditions confirmed that the heat transfer was enhanced by the acoustic field.     

近壁面液膜层中微孔注气气泡动力学研究

为了降低近壁面沸腾过程中气泡动力学分析的不确定性,利用光谱共焦传感器构建了7 mm的液膜层,对近壁面液膜层中单孔注气气泡动力学进行了系统研究.实验测试段为270 mmx6 mm × 12 mm(长×宽×高)的矩形通道,注气小孔的直径为0.49 mm,气体流量为0.30～27.00 mL/min,液体流量为72.00～3...     

不同水文模型在老哈河流域的应用与比较

为研究不同水文模型在半湿润半干旱地区老哈河流域上的适用性,分别选取老哈河流域的西泉、初头朗两个子流域1970～2003年的实测资料,应用新安江模型和垂向混合产流模型进行模拟计算,并对比分析其模拟结果.结果表明,在西泉和初头朗流域,垂向混合产流模型的模拟精度总体上均高于新安江模型;垂向混合产流模型更适用于初头朗流域.     

An Improved Bubble Packing Method for Unstructured Grid Generation with Application to Computational Fluid Dynamics

An improved bubble packing method (BPM) is proposed to generate high-quality unstructured grids for prediction of the flow field in a domain with complex geometry. For a curved-boundary domain, bubble departure from the curved boundaries during the dynamic movement of bubbles can be avoided by using the mapping and the arc-length parameterization methods. Furthermore, the grid density of the whole region can be controlled effectively. Local mesh refinement is achieved by adding bubbles with different sizes to the real and artificial vertices of the domain, and vertex information is transferred to the inner nodes of the domain using the Shepard interpolation method. In order to validate the proposed BPM, a finite-volume solver on an unstructured collocated grid is developed to simulate both square and polar lid-driven cavity flows. The numerical simulation results agree well with the experimental data under different Reynolds numbers.     

不同湍流模型在旋风分离器三维数值模拟中的应用和比较

采用标准κ－ε模型，RNGκ－ε模型和RSM(SSG)模型，对气—固旋风分离器中的单相湍流流场进行数值模拟计算。旋风分离器网格划分采用分块划分技术，每一块采用贴体坐标划分网格，计算结果同试验比较，三种模型中以RSM模型的预报结果最为合理，对切向速度分布的涡结构给出了合理的预报结果，同时给出了雷诺应力的各向异性特性，但同实验值仍有一定的差别，分析认为同湍流模型本身的原因外，与入口边界条件的选取和网格划分的多少有一定的关系。     

分布活化能模型在垃圾热解/气化动力学研究中的应用

采用热重分析仪,对我国城市生活垃圾典型有机混合物(MMSW)的热解和气化特性进行了研究,并用分布活化能模型对TG-DTG曲线进行了动力学分析.试验表明:MMSW失重过程分为厨余中淀粉热解、厨余中脂肪分解、纸类纤维素热解和聚乙烯分解4个过程,并存在3种有机组分的相互作用;在相同失重率下,气化反应活化能值高于热解反应活化能值;整个反应过程中,热解反应活化能分布较窄,而气化反应活化能分布在相对较宽的范围内.     

动载荷作用下滑动轴承的气蚀问题:分析和预测

1引言 气蚀这种损坏机理实际特征在于：它不同于常见的磨料或粘着磨损的过程,其发生不需要两个固体表面之间相互接触.尽管如此,其材料的迁移亦可达到工程部件的功能严重损伤的程度,就像18世纪90年代第一批涡轮式轮船的推进器案例一样.历史上,正是这一大规模责任重大的事件,唤起了科学对该现象的普遍兴趣,但是在过去的5～10年（1978年前）里,滑动轴承存在气蚀损坏才被接受.     

Numerical Simulation of Orifice Cavitating Flows Using Two-Fluid and Three-Fluid Cavitation Models

A number of numerical simulations is carried out to study the turbulent cavitating flow through an orifice. We use two different two-fluid (consisting of two interpenetrating liquid and vapor phases) and three-fluid (consisting of three liquid, vapor, and non-condensable gas phases) cavitation models to extend our study. We use the finite-volume method to solve the multiphase flow governing equations, the SIMPLEC algorithm to link the pressure and velocity equations, and the standard k-? model to treat the turbulence closure problem. We fix the outlet pressure and change the inlet pressure suitably in our simulations. The discharge coefficient values obtained by the two chosen models are compared with each other and those of other reliable experimental and numerical works. The current study shows that there can be considerable differences between the results of two models in describing the inception of cavitations and their resulting vapor volume fraction and velocity distributions in the orifice. Generally, our results show that the three-fluid model provides better accuracy and physics. The current achievement resembles the importance of non-condensable gas consideration in improving the accuracy of numerical results for the orifice cavitating flow study.     

Numerical Simulation of Bubble Dynamics in a Uniform Electric Field by the Adaptive 3D-VOSET Method

This article presents a three-dimensional numerical simulation of the effect of a uniform electric field on the dynamics of bubbles in a viscous fluid. The two-phase interface is captured utilizing a coupled volume-of-fluid and level set (VOSET) method by solving the full Navier–Stokes equations coupled with electric field equations. To track the interface more accurately, the dynamically adaptive octree grids are used to refine the grids around the interface. The effects of different parameters such as the electric Bond number, the ratio of electrical permittivity, the gravitational Bond number, and the Reynolds number on the motion and deformation of the bubble are investigated. According to the computational results, it is found that the electric field has a significant influence on the bubble dynamic behavior. Increase of the electric Bond number or the ratio of electrical permittivity results in the larger deformation and rising velocity of the bubble. For a higher electric Bond number and the Reynolds number, separations of the tail of the bubble are observed. In this case, the jet above the bubble is strong enough to turn the spherical bubble to a toroidal shape.