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．     

液体超声驻波声场实验研究

研究了以蒸馏水为介质的驻波声场对微小颗粒群的作用,观察了颗粒群的运动规律,并应用声流和声辐射压力理论对其进行分析.运用谱分析方法,探讨了驻波声场中的空化现象.结果表明,大部分颗粒在声压波腹处聚集,而在声压波节处明显出现了高次谐波,说明空化效应发生在声压波节处.     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to