圆管内旋转点声源声学频域分析

在任意运动点声源声辐射频域解的基础上，利用无限长圆环管道的格林函数推导了旋转点声源在圆管内空间任一点处的声压计算公式，讨论了单板子点声源作旋转运动时的声场分布规律和声场方向性特征，研究了源频率、旋转频率和流动马赫数等对声场声学结构的影响．研究结果表明：声场分布具有很强的空间指向性；源频率和旋转频率的变化将伴随着多普勒效应出现；在点源的上、下游，各频率的声压幅值基本对称；来流马赫数的大小对声场有影响，会使某些频率的声辐射出现尖锐的峰值，因此要避免点声源在某些流动马赫数下旋转．     

旋转源近场声学特性进一步研究

旋转运动源近场声学频域解可以表示为在远场解基础上叠加近场修正项．在此解基础上，本文得到宽频源和简谐源的近场声压谱密度，指出此２种声源近声场各自的特点及源的旋转半径和轴向位置对声场结构的影响．     

管道内旋转声源频域声场的数值仿真

为准确计算管道内的旋转声源声场,研究基于改进的点源模型和边界元法的声场仿真方法。首先从时域上将旋转点声源离散为均匀分布在旋转轨迹上的有限的静止点声源,通过静止点声源的依次发声模拟旋转点声源的发声过程;将时域声源变换到频域,然后结合边界元方法即可计算得到管道内所有离散的静止点声源声场,该声场即为旋转点声源声场。验证基于改进点源模型计算旋转声源自由声场以及利用边界元方法计算管道内静止点声源声场的可信性,以泵喷推进器为对象,将泵喷叶片分块划分并等效为偶极源,计算分析导管内的叶轮声场。研究结果表明:以改进的点源模型和边界元法为基础的管道内旋转声源声场仿真方法是有效易行的;对导管内叶轮声场而言,入射声场与散射声场存在较大差异,导管对径向测点处叶轮声场影响较大,对轴向测点处叶轮声场的影响可以忽略。     

超声珩磨工具头横向辐射声场的建模与仿真

对受纵向激励振动的功率超声珩磨工具头的横向辐射声场进行研究,以流固耦合系统运动方程为基础,利用弹性力学对超声珩磨工具头三维横向辐射声场进行理论计算,并通过有限元仿真分析了工具头横向辐射声场的声压分布规律。结果表明,该声场中的声压大小及分布分别与流固界面处振动工具头表面的应力大小和分布相有关。改变激励频率的大小,可以间接地改变横向辐射声场的声压分布。     

粗糙海面对空气中声源激发水下声场的影响

提出一种计算粗糙海面条件下空气中声源激发水下声场的方法,并通过数值仿真研究粗糙海面对水下声场的影响.在波数积分模型的基础上,采用微扰法将声场分为平均声场和散射声场之和.其中,平均声场采用国际流行的波数积分模型OAST计算,散射声场采用自相容扰动法计算.对不同风速、不同声源频率条件下的声场进行仿真,结果表明风速越大、声源频率越高,总声压变化范围越大,同时,水下接收到的平均声压和均方声压受到的影响越大.     

复频声场的研究

讨论了存在着两种、三种频率的声波时,媒质中声场的均匀性,给出了可反应声场均匀性的平均声压及声压均方差表达式。可根据平均声压及声压均方差,选择合适的参数,使得声场的均匀性满足实际应用要求。     

旋转封闭薄壁球壳辐射噪声的多极展开方法

针对旋转机械噪声问题,在旋转单极子声源和偶极子声源辐射声场频域解的基础上,基于这两种简单旋转声源的研究思路和方法,利用声学互易定理推导出了简单封闭薄壁球壳作旋转运动时的空间辐射声场的计算方法,以一具体的封闭薄壁球壳为对象对旋转运动进行了实例计算。在此基础上,利用覆盖域的思想,给出了一种可以计算任意复杂形状封闭薄壳在旋转运动时空间辐射声场的方法。所提方法可为研究气动噪声产生机理及定量分析提供可借鉴的思路,为旋转机械噪声的控制及优化提供了一种方法。     

敷设吸声尖劈的声纳平台水下声学特性试验研究

基于模型试验开展了敷设吸声尖劈的声纳平台水下声学特性研究,讨论了尖劈不同敷设方式下声纳平台的声场分布,分析了声波入射角度对声纳平台声场的影响.分析了声纳平台0%,36%,60%和100%敷设吸声尖劈,声波在0°方向和90°方向入射声纳平台的情况,以及尖劈不同敷设方式、声波不同入射角度时声纳平台的声场分布.研究表明:声纳平台内部各点声压不尽相同;随尖劈敷设密度的增加,声纳平台自噪声在降低,各水听器声压的差异在逐渐加大;吸声尖劈可改变声纳平台的声场,降低声纳平台的自噪声,但存在"声泄漏"现象;声波入射方向对声纳平台声场也有一定影响,但位置不同、声波频率不同,其影响也各有差异.     

基于等效源法的单全息面声场分离机理及技术

声场分离是实现声场精确重建的一种前处理技术。为改进双全息面分离声场技术采用的测点数目多、分离精度受两全息面之间距离影响等问题。提出一种等效源法的单全息面声场分离方法。利用空间变换的声全息技术识别出声源的大致位置,结合等效源法中声压和法向振速之间的关系,建立起声压和法向振速的分离公式。仿真分析了脉动球作为干扰源的分离结果,结果表明,该方法具有较好的分离精度。可见该方法能在单测量面下实现多相干声源声场的有效分离。     

基于逆边界元法的内燃机噪声源识别方法

对内燃机复杂噪声源进行识别和排序是内燃机噪声控制的关键．基于逆边界元法（IBEM）的噪声源识别技术,利用边界元法建立了声场与结构表面振动速度之间的声学传递向量（ATV）．将常规的声压测量作为输入数据,在逆向数值计算方法的基础上能够精确地重构出结构表面法向振动速度,进而获得源面详细的振声特征信息．针对某轿车柴油机,测试了额定工况下近场144个场点声压,应用该方法在发火频率点处,重构出了柴油机表面法向振动速度分布．通过对比预测和实测声场点声压,验证了该方法的有效性．在噪声面板贡献量分析的基础上,对该柴油机各功能部件的噪声贡献量进行了排序,并得知额定工况下该柴油机的机体裙部是主要的噪声辐射部位．应用实例说明了该方法对复杂噪声源识别易于实施。具有更广的工程适应性．     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with