基于自适应非结构化网格的VOF方法

本文提出了一种基于自适应非结构化网格的VOF算法,根据相界面网格的相函数值对相界面网格进行自适应细化与合并,通过基于非结构化网格的界面构造方法构造相界面,在适量增加网格单元数量的情况下提高了计算的精度。该方法随着时间及相界面的变化无需重新整体生成网格,算法效率较高。经典算例的验证结果表明,本文自适应网格方法计算得到的结...     

离心叶轮及无叶扩器内湍流的非结构化网格数值解法

利用非结构化网格上的有限体积法对三维湍流进行了数值研究,提出了不用求解单元顶点处变量值的二阶混合差分格式,既避免了复杂耗时的单元顶点处变量值的计算,又避免了普通差分格式在非结构化网格上易于引起网格界面方向相关性问题。最后利用非结构化网格计算程序,数值求解了一台离心风机内叶轮及无叶扩压器通道内三维相对定常湍流,计算结果与实验值的比较表明速度的计算值与实验值吻合较好。     

SPH核函数光滑长度最优选取和自适应准则研究

基于小波分析理论和RKPM再生核函数研究无网格方法 SPH中多尺度诊断工具,多尺度再生核函数使得数值计算在不同尺度上的响应分离,并通过动态伸缩窗函数给出计算域不同位置的时频特性,实现在无网格体系下构造网格计算方法的"自适应网格",从而达到对不同流场位置多分辨率分析的目的.利用多尺度诊断工具中的小波分解算法给出SPH核函数在频域内能量残差估计,发展一种核函数光滑长度最优选取准则.最后,基于可压缩流场激波稀疏波共存的现象,针对传统的光滑长度自适应的缺陷,构造一种避免数值计算"拖尾"现象的自适应准则.     

径向基函数及其耦合方法在电磁场数值计算中的应用

针对带电导体附近急剧变化的位函数和场函数这一难于处理的边界条件,将小波函数的紧支撑特性和全域径向基函数(RBF)的高精度逼近能力相结合,提出电磁场边值问题求解的耦合方法并应用于接地金属槽/箱的数值计算中;将径向基函数无网格方法引入波导本征值的计算中,给出其求解本征问题的思路,建立相应的离散方程,分析矩形、圆形和脊形波导的本征值并与有限元方法进行比较.数值仿真实验表明,径向基函数及其耦合方法在分析电磁场边值和本征值问题时是有效的且具有实现简单、节点少和精度高的优势.     

V型火焰稳定器上、下游可压缩湍流场的理论与实验研究

本文从V型火焰稳定器上游截面开始给定边界条件,用涡量-流函数方法对包括无分离区和完整迥流区的整个可压缩湍流场统一求解,得到突扩分离迥流区的数值预示,并用实验验证了计算结果。计算中采用了重迭坐标网格;对突扩分离点涡量采用了间断值的处理方法。计算所得迥流区长度L/D与实验结果仅相差6.1％,表明本文数值方法是可行的。     

分段拉伸网格在分段点附近的平滑处理

在拉伸网格上进行高精度有限差分计算时,网格拉伸变换引入的几何参数常采用差分来近似。分段网格拉伸函数能够灵活地满足网格拉伸的需要,但是在分段点附近不光滑,几何参数的计算误差大,导致数值解的整体精度降低。为改善分段网格拉伸函数,本文针对喷流上下唇线的加密网格,构造了连续的网格拉伸函数以避免分段点,而对一般的分段网格,设计了基于拉格朗日插值的分段点平滑过渡算法。采用一维的一阶、二阶波动方程为考核算例,通过误差的网格收敛性来评估数值解的整体精度,并分析网格平滑处理对计算精度的影响。结果表明连续和平滑处理后的网格拉伸函数都能使数值解保持原有离散格式的理论精度。所得的网格平滑处理算法可以为提高使用分段网格的流场模拟精度提供参考。     

Zeta电位计算过程中Henry函数的优化表达式

利用电泳光散射法可以确定带电颗粒的电泳迁移率,由电泳迁移率计算颗粒的Zeta电位需要准确确定Henry函数的数值。为此,利用最小二乘算法对精确Henry函数值进行拟合,获得优化Henry函数表达式;基于Gouy-Chapman-Stern双电层模型理论,求解不同浓度、不同类型电解质溶液中颗粒的双电层厚度,从而获得准确的颗粒半径a与双电层厚度k-1的比值ka;最后利用优化的函数表达式获得准确的Henry函数值。使用该方法分别计算4种不同浓度电解质下颗粒的Zeta电位,实验结果表明,利用优化的Henry函数可以有效提高颗粒Zeta电位的计算精度,计算结果的相对误差小于1.0%。     

非线性热传导方程MLPG/RBF-FD无网格数值模拟

结合无网格局部彼得洛夫-伽辽金(MLPG)方法和径向基函数有限差分(RBF-FD)无网格方法求解非线性热传导问题。MLPG方法属于弱式无网格方法,具有处理边界条件方便的优点,然而因其要做大量的插值、积分运算而计算效率偏低;RBF-FD无网格方法属于强式无网格方法,直接对微分算子进行数值离散,计算效率高,然而其边界条件的处理较复杂。将二者相结合,在求解域边界附近采用MLPG方法,其它区域采用RBF-FD无网格方法,则能扬长避短。介绍了MLPG方法和RBF-FD无网格方法的基本原理,将该混合方法用来求解非线性热传导方程,数值算例显示了方法的正确性和高效性。     

修正内嵌边界法对颗粒运动的直接模拟

本文提出了一种基于内嵌边界法(IBM)的思想,在描述颗粒只有较少网格时能较为准确地计算气固多相流的模型.模型依据边界层理论,通过定义颗粒表面的速度分布函数来修正由于计算网格尺度大于边界层厚度所带来的误差.本文通过计算单颗粒绕流和单颗粒沉降的最终沉降速度并与实验进行比较验证了本文模型的准确性.     

考虑壁面接触效应的微流动数值模拟

使用level set和volume of fluid(VOF)方法对考虑壁面接触效应的不可压缩两相微流动进行数值模拟.对于level set方法,计算基于MAC网格,使用二阶投影算法求解二维Navier-Stokes(N-S)方程和level set函数方程;对于VOF方法,通过引入计算网格内的体积分数,将流场的参数转化为体积平均值,界面的形状由体积分数连续方程的解决定.给出一些计算实例,并和现有的实验结果进行比较.     

小尺度封闭空间声场的无网格数值算法

无网格法是一种新兴的数值计算方法,具有不需要网格支持的特点。本文将该方法引入室内声学建模,推导了无网格声场数值计算模型,并将其应用于典型小尺度封闭空间内部声场的数值分析。针对声传递函数,将本方法与理论解和SYSNOISE计算结果进行了比较,并将计算的混响时间与实验测量结果作了对比,表明本方法具有良好的精度。     

基于声粒子分布积分的无网格声场计算方法

小尺度封闭空间内部声场的数值计算是声学设计、噪声控制等领域的关键技术。由于波动声学及几何声学方法计算频率上的限制,中频段声场计算问题一直是个难点。本文以声学无网格法为基础,提出了一种基于声粒子分布积分的无网格声场数值计算方法。文中利用声线跟踪理论计算声场中的声粒子分布,并以某个时间点上的声粒子作为蒙特卡罗法中的积分点,将其应用于无网格法中,从而获得声场中的节点声压。利用该方法对一个矩形封闭空间的中低频声场进行了计算,并与模态叠加法、商用声场计算软件、经典无网格法的结果进行了对比,证明基于声粒子分布积分的无网格声场数值计算方法在中低频段相较于传统基于网格的方法具有更高的精度。     

Sound field prediction in long enclosures with branches: A combined method

The propagation of sound in long enclosures with branches has been studied theoretically and experimentally, and an efficient combined method is proposed to predict the sound field in long enclosures with branches. Based on the wave-acoustics theory, the theoretical analysis of the sound field of the long enclosures with branches is performed. This paper also investigated the sound field prediction of long enclosures with branches, by using the acoustic modeling program, ODEON. The results obtained by the theoretical analysis and the numerical simulation ODEON are compared with the experimental measurements, and the characteristics of the two methods for predicting the sound field of long enclosures with branches are analyzed. Compared with the experimental results, it is found that: (1) the results predicted by the theoretical analysis fluctuate relatively large with respect to the source-receiver distance, and the sound pressure level (SPL) attenuation obtained is smaller than that measured; and (2) the results predicted by the numerical simulation is smoother, and the calculated SPL attenuation is larger than that measured. To effectively predict the sound field of long enclosures with branches, a combined numerical method is thus proposed. The effectiveness of the proposed combined method is demonstrated by the scale-model experiments.     

Ensemble statistics of active and reactive sound intensity in reverberation rooms

This paper examines fundamental statistical properties of the active and reactive sound intensity in reverberant enclosures driven with pure tones. The existing theory for sound intensity in a diffuse sound field, which is based on Waterhouse's random wave model and therefore limited to the region of high modal overlap, is extended to the region of low modal overlap by taking account of the random fluctuations of the sound power emitted by the source that generates the sound field. The validity of the extended model is confirmed by experimental and numerical results.     

A hybrid modal analysis for enclosed sound fields

A hybrid modal expansion that combines the free field Green's function and a modal expansion will be presented in this paper based on a review and an extension of the existing modal analysis theories for the sound field in enclosures. The enclosed sound field will be separated into the direct field and reverberant field, which have been treated together in the traditional modal analysis. Studies on a point source in rectangular enclosures show that the hybrid modal expansion converges notably faster than the traditional modal expansions, especially in the region near the source, and introduces much smaller errors with a limited number of modes. The hybrid modal expansion can be easily applied to complex sound sources if the free field responses of the sources are known. Damped boundaries are also considered in this paper, and a set of modified modal functions is introduced, which is shown to be suitable for many damped boundary conditions.     

基于局部基本解法的静电场仿真分析

将局部基本解方法应用于静电场问题的模拟与分析。局部基本解方法是利用控制方程的基本解,基于局部理论和移动最小二乘原理提出的一种无网格算法。相比于有限元和有限差分等传统网格类方法,该方法仅需离散节点,避免了复杂的网格剖分难题。作为一种半解析数值技术,物理问题的基本解被作为插值基函数建立数值离散模型,从而保证了算法的较高精度。此外,与具有全局离散格式的无网格方法相比,局部基本解法更适用于高维复杂几何和大尺度模拟。二维和三维数值试验表明,该方法具有实施方便灵活,计算精度高和计算速度快等优势。为静电场仿真研究开辟新的途径,拓展了局部基本解方法的应用领域。     

The effect of multiple branches on sound propagation in long enclosures

Since the classical room acoustics can not be used for long enclosures due to the inhomogeneous sound field, much work has been carried out recently to investigate the sound propagation in long enclosures, which are helpful to the acoustic design of practical long enclosures, such as the high-speed railway tunnels. However, most of these works focuses on the straight long enclosures without branches or with one branch. In this paper, the effects of the multiple branches on sound propagation of long enclosures are studied. The sound pressure level (SPL) attenuation, early decay time (EDT), and reverberation time (T30) of long enclosures with multiple branches have been investigated by physical scale models based acoustic experiments. Several interesting results have been obtained concerning the sound propagation of long enclosures with multiple branches. It shows that the sound field of long enclosures with multiple branches is more complex and inhomogeneous than that of the long enclosures without branches or with one branch.     

A study of barriers in enclosures by a ray-tracing computer model

The theoretical study of the behaviour of barriers in enclosures is much more complicated than that of barriers in the free field. As a matter of fact, in the latter case one has to take into account the sound energy reflected at the boundary surface of the enclosure. The barrier-absorption joint effect has to be considered in defining the barrier sound attenuation. From this point of view, the barrier attenuation also depends on the enclosure shape and proportions. In this paper we suggest a numerical method, based on a ray-tracing technique, in which the concepts inherent in Keller's theory of diffraction are included. The results of some simulation examples are reported, together with some qualitative considerations which allow emphasis of the problems connected with the optimization of barrier design in enclosures.     

室内粗糙表面声散射体掠入射角度散射估计

针对经典边界元方法对掠入射角度下的散射估计精度较低的问题,发展了一种边界无网格模型.此模型将散射体视为具有无限延伸的形式,避免了经典边界元法中薄板形式所导致的声压差问题,而且更加符合实际房间中散射体的存在形式;模型利用无网格算法实现数值仿真,可对任意表面形状特别是曲面散射体具有更高的仿真精度。利用边界无网格模型计算了不同形状散射体的散射系数及散射声场,并将结果与解析方法、测量实验进行了对比.对比结果表明,边界无网格模型可以准确预测散射体的散射性质,特别是对掠入射角度的估计要优于经典边界元法.研究结论可应用于室内声学散射体特征预测及优化设计,对提高声场扩散及室内音质水平具有重要意义.