二维谐振腔中声驻波的格子气仿真

引入带温度的9_Bit正方形格子气自动机模型,利用Monte Carlo方法模拟声源并激发平面波,在二维谐振腔中建立了声驻波场。该模型能够动态地反映声波的建立和演化过程,为进一步模拟分析热声效应等物理过程提供了可视化的有力工具     

声波作用下球形颗粒外声流分布的数值模拟

综合考虑声学边界层内的热损失和黏性损失,建立处于平面驻波声压波节位置二维球形颗粒外声流计算模型,利用分离时间尺度的数值方法对颗粒外声流流场特征进行模拟。将模拟结果与相应的解析解和实验结果对比,验证了数值模拟的可靠性。在此基础上,研究了雷诺数Re和斯特劳哈尔数Sr对球形颗粒声学边界层内二阶声流流场结构、涡流强度及范围的影响规律。结果表明,随Sr和Re增大,声学边界层内的涡流结构尺度呈指数形式减小,其涡流尺度与颗粒直径D和激励频率f成反比,与流体介质运动黏度v成正比;且满足低Sr和高Re的声振系统可形成范围较大、更强烈的声流运动。该数值方法可用于对任意物理模型外声流特性的评估。     

二维顶盖驱动半圆腔内流动MRT-LBM研究

本文采用多弛豫时间格子玻尔兹曼方法(multi relaxation time lattice Boltzmann method—MRT LBM)对二维顶盖驱动半圆腔内流动进行了数值模拟,得到了雷诺数为500～50000范围内半圆腔内流场分布情况。在二维顶盖驱动半圆腔流场中,随雷诺数的增大,流场内旋涡的数目逐渐增加,且流动依次呈现出稳定流、周期流、混沌流等状态。本文计算结果表明,MRT-LBM模型可显著提高计算的稳定性,适用于大范围的雷诺数流动情况。     

二维谐振腔内声流的气-动格式模拟

在利用气-动格式模拟谐振腔内非线性声振荡行为的基础上建立了声流分析的气-动格式模型,并模拟了声谐振腔内的二维瞬时流场及平均流场(声流)。重点研究了有限振幅非线性情况下,激波对轴向速度、径向速度及流场的影响,进而分析了速度反转、涡流、不规则Rayleigh流等非线性现象形成的原因。     

方形薄板二维驻波的研究

通过对多种振源情形下的方形薄板二维驻波图形(克拉尼图形)的观测与研究,得到不同频率下驻波图形的波节数n+1,m+1及波矢k,从而导出波速(相速)u.实验结果与理论解析解(严格解)相比较符合得很好.     

二维空腔黏性流的格子Boltzmann方法模拟

用13速六方格子BhatnagarGrossKrook(缩写为BGK)模型模拟二维空腔黏性流.给出了上边界流体作匀速运动时,具有不同雷诺数的空腔黏性流的流场速度分布情况,模拟了在雷诺数Re=3000时,流场中的涡旋形成过程及流场稳定后,腔内密度、压力和温度的分布情况 关键词：     

扇形薄板二维驻波的研究

用分离变量法对极坐标下垂直板面方向的金属薄板的小振动方程求解,解出扇形薄板在全部边界均自由的条件下的解析解的简正模式及通解,并计算了不同频率下对应的简正振动模式下薄板上的圆弧形驻波波节线的半径和方程的本征值所满足的规律及薄板的弹性模量,给出了驻波图,与实验上观察到的仅有辐射状波节线或辐射状波节线与圆弧形波节线同时存在这两种简正模式(即克拉尼图形)相比较,发现理论结果与实验符合得很好.     

驻波型热声发动机的数值模拟

通过对驻波发动机热声边界条件的分析 ,给出了一种用“打靶法”进行迭代运算的循环模式 ,从而避开繁重的矩阵运算 ,计算效率得到有效地提高。最后以一个实例证明本方法计算结果与实验吻合较好。     

三维曲面腔顶盖驱动流的MRT-LBM研究

采用多松弛时间格子玻尔兹曼方法(MRT-LBM)的D3Q15模型分别对长方体腔、圆柱腔、半圆柱腔、旋转双曲面腔、旋转椭球面腔、半球腔以及两种组合腔体的三维顶盖驱动腔流进行数值模拟, 比较分析各腔体内流线分布、流速等值线分布和涡心的发展, 对于典型腔体模拟不同雷诺数下的流动情况。结果表明: 在同一雷诺数下, 曲面边界不仅能消除从边界产生的次涡, 还会导致腔内主涡的分离, 增大中心纵剖面纵向回流速度; “上长方体+下半圆柱”腔内流函数分布与边界贴合度最高。当雷诺数不断增大时, 半圆柱腔内主涡逐渐分离成两个同向涡, “上圆柱+下半球”腔内始终保持着圆柱腔与半球腔内的基本流动特征; 而长方体腔内主涡涡心保持在同一高度, 次涡逐渐增强, “上长方体+下半圆柱”腔内流动愈加规则, 主涡逐渐下沉, 流速等值线分布逐渐趋于中心小、四周大。     

Description of Finite-amplitude Standing Acoustic Waves Using Convection-diffusion Equations

This paper deals with problems of finite-amplitude standing waves in acoustical resonators of variable cross-section. Set of two one-dimensional partial differential equations in the third approximation, formulated in conservative form, is derived from the fundamental equations of gas dynamics. The model equations which takes into account external driving force, gas dynamic nonlinearities and thermoviscous dissipation are solved numerically in time domain using a central scheme developed for convection-diffusion equations integration. In this paper numerical results for closed air-filled acoustic resonators are presented.     

Standing Waves in the Lorentz-Covariant World

When Einstein formulated his special relativity, he developed his dynamics for point particles. Of course, many valiant efforts have been made to extend his relativity to rigid bodies, but this subject is forgotten in history. This is largely because of the emergence of quantum mechanics with wave-particle duality. Instead of Lorentz-boosting rigid bodies, we now boost waves and have to deal with Lorentz transformations of waves. We now have some nderstanding of plane waves or running waves in the covariant picture, but we do not yet have a clear picture of standing waves. In this report, we show that there is one set of standing waves which can be Lorentz-transformed while being consistent with all physical principle of quantum mechanics and relativity. It is possible to construct a representation of the Poincaré group using harmonic oscillator wave functions satisfying space-time boundary conditions. This set of wave functions is capable of explaining the quantum bound state for both slow and fast hadrons. In particular it can explain the quark model for hadrons at rest, and Feynman’s parton model hadrons moving with a speed close to that of light.     

The Limits of Primary Radiation Forces in Bulk Acoustic Standing Waves for Concentrating Nanoparticles

Acoustic waves are increasingly used to concentrate, separate, and pattern nanoparticles in liquids, but the extent to which nanoparticles of different size and composition can be focused is not well‐defined. This article describes a simple analytical model for predicting the distribution of nanoparticles around the node of a 1D bulk acoustic standing wave over time as a function of pressure amplitude, acoustic contrast factor (i.e., nanoparticle and fluid composition), and size of the nanoparticles. Predictions from this model are systematically compared to results from experiments on gold nanoparticles of different sizes to determine the model's accuracy in estimating both the rate and the degree of nanoparticle focusing across a range of pressure amplitudes. The model is further used to predict the minimum particle size that can be focused for different nanoparticle and fluid compositions, and those predictions are tested with gold, silica, and polystyrene nanoparticles in water. A procedure combining UV‐light and photoacid is used to induce the aggregation of nanoparticles to illustrate the effect of nanoparticle aggregation on the observed degree of acoustic focusing. Overall, these findings clarify the extent to which acoustic resonating devices can be used to manipulate, pattern, and enrich nanoparticles suspended in liquids.     

驻波法测超声波衰减系数

用驻波法测量超声波在空气中衰减系数的实验方法。与前人的方法进行比较。新的测量结果更符合实际。只有当换能器反射系数r〈0.619时,用简单波拟合得到的衰减系数才比较可信。同时讨论了该方法的实用意义。     

有厚度平板尾缘可压缩剪切层中的涡结构数值模拟

采用一个新型Fu Ma高精度UCD5 SCD6紧致差分算法,通过直接求解二维Navier Stokes方程,成功实现了有厚度平板尾缘可压缩剪切层中涡结构的数值模拟,并考查了平板厚度对其的影响.计算对流马赫数M_c=0.3,平板厚度分别为1,2,3,4个参考长度.结果表明,增加平板厚度可促使平板尾缘可压缩剪切层中的涡提前卷起,有利于两股气流混合.     

炉内单排换热器管束周围声流特性的数值模拟

建立行波场诱导振荡流与单排换热器管束非线性相互作用产生的二阶声流数值计算模型,采用分离时间尺度的数值方法,对不同声频率f、声压级SPL、入射方向θ和纵向节距比L/d的单排换热器管束周围声流特性进行了数值计算.结果 表明,低频高强度声波可在换热器管束外形成强烈的声流运动,f=l0 Hz、SPL=139 dB的声波引起的最...     

Interface Sensitive Investigation of 57Fe/Cr Superstructure by Means of Nuclear Resonance Standing Waves in Time Scale

With synchrotron pulsed radiation we have measured the time spectra of reflectivity for several grazing angles in vicinity of the Bragg peak for a microcrystalline periodical (Fe/Cr)₂₆ multilayer. In such a way a “scan” of hyperfine field distribution over bilayer depth was performed (as follows from the concept of standing waves). Variations of the spectrum shape have revealed that the orientation of hyperfine field is different in the middle part of ⁵⁷Fe layers and in the interfaces. Besides we observed the differences of Fe/Cr and Cr/Fe interfaces. This revised version was published online in August 2006 with corrections to the Cover Date.     

Analytical Study of Nonlinear Dust Acoustic Waves in Two-Dimensional Dust Plasma with Dust Charge Variation

The nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation is analytically investigated by using the formally variable separation approach. New analytical solutions for the governing equation of this system have been obtained for dust acoustic waves in a dust plasma for the first time. We derive exact analytical expressions for the general case of the nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation.     

Analytical Study of Nonlinear Dust Acoustic Waves in Two-Dimensional Dust Plasma with Dust Charge Variation

The nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation is analytically investigated by using the formally variable separation approach. New analytical solutions for the governing equation of this system have been obtained for dust acoustic waves in a dust plasma for the first time. We derive exact analytical expressions for the general case of the nonlinear dust acoustic waves in two-dimensional dust plasma with dust charge variation.     

A New Approach to Energy Integral for Investigation of Dust-Ion Acoustic(DIA)Waves in Multi-Component Plasmas with Quantum Effects in Inertia Less Electrons

Dust-ion acoustic waves are investigated in this model of plasma consisting of negatively charged dusts,cold ions and inertia less quantum effected electrons with the help of a typical energy integral.In this case,a new technique is applied formulating a differential equation to establish the energy integral in case of multi-component plasmas which is not possible in general.Dust-ion acoustic(DIA) compressive and rarefactive,supersonic and subsonic solitons of various amplitudes are established.The consideration of smaller order nonlinearity in support of the newly established quantum plasma model is observed to generate small amplitude solitons at the decrease of Mach number.The growths of soliton amplitudes and potential depths are found more sensitive to the density of quantum electrons.The small density ratio r(=1-f) with a little quantized electrons supplemented by the dust charges Z_d and the in-deterministic new quantum parameter C_2 are found responsible to finally support the generation of small amplitude solitons admissible for the model.