涡流发生器对3/4汽车模型风洞流场品质的影响

采用数值计算的方法对3/4开口回流式汽车风洞喷口处的涡流发生器进行了研究.对比研究了三种不同片数的涡流发生器对流场品质的影响.首先采用定常雷诺时均纳维斯托克斯方程求解了流场的定常特性,接着采用大涡模拟(LES)方法对流场的非定常特性进行了研究.并就两种计算方法给予了相应的试验验证.对比计算结果得到涡流发生器可以在一定程度上提高流场均与性,尤其是三片式涡流发生器的工况能较好地拓宽风洞测试区的高流速区域的范围,降低测试区的静压梯度,减小试验段内的湍流度和剪切层内的湍流度,延长测试段内低湍流区的长度,分散流场内的脉动能量,降低低频颤振敏感频率区的能量聚集.     

阻塞比对开口式风洞喷口风速测量方法的影响

以1∶15的3/4开口回流式模型风洞为研究对象,通过放置不同比例大小的Ahmed body模型,采用试验和数值计算相结合的方法,研究阻塞比对于喷口法和驻室法这两种喷口风速测量方法的影响.结果表明:不同的阻塞比工况下,虽然驻室法测量误差稍大于喷口法测量误差,但驻室法对于修正系数的敏感度明显低于喷口法,即驻室法可使用更少的修正系数修正更多的工况,更易进行修正.     

汽车风洞试验段非定常流场的试验

采用三维热线风速仪测量了不同工况下某全尺寸汽车风洞1∶15模型风洞试验段内的非定常流场.对测点自功率谱密度(PSD)分析表明,对于喷口风速小于37m.s-1的低速工况,湍流能量主要集中在20Hz附近,当喷口风速为25m.s-1时,该频率对应的PSD数值最大;喷口风速大于37m.s-1的高速工况,湍流能量主要集中在43Hz附近,当喷口风速为41m.s-1时,该频率对应的PSD数值最大.无论是高速工况还是低速工况,气流从喷口到收集口处脉动速度的振动幅值都逐渐增加,且在高速工况下的脉动速度幅值增量明显大于低速工况.通过试验还发现脉动速度在收集口角度为0°的工况下的振动能量远高于收集口角度为15°的工况.     

风洞结构对试验段静压系数和静压梯度的影响

静压系数和静压梯度是评估汽车风洞试验段流场品质的重要参数.以数值仿真为主,风洞试验为辅的方法研究了风洞结构对试验段静压系数和静压梯度的影响.通过研究发现,使用包含2个拐角的计算模型进行静压系数和静压梯度仿真,可以得到真实的结果.无论是大喷口还是小喷口,收集口高度为270mm时,对应试验段静压系数和静压梯度最平缓,试验段可用长度最长,对试验测量影响最小.对于大喷口,随着收集口高度降低,收集口处静压系数和静压梯度不断下降;当收集口高度为240mm时,靠近收集口处的静压系数和静压梯度变为负值.对于小喷口,收集口面积远大于喷口面积,气流到达收集口的速度有所减少,当地静压系数和静压梯度均为正值.     

固固界面剪切分层的超声波耦合共振机理

针对结构表面吸积层去除问题,提出了两种分层模型,研究了超声波激励下固固界面的剪切分层问题,揭示了固固界面剪切分层的超声波耦合共振机理。利用傅里叶积分变换方法,通过严格推导,获得了超声波激励下吸积层结构中的位移场与应力场,进一步获得了固固界面剪切应力场。通过数值积分方法,计算了铝与石膏界面的剪切应力幅值,研究了激励频率与吸积层厚度对界面剪切应力幅值的影响。在固固界面剪切分层条件的基础上,提出了超声波分层频率的选择方法。依据两种分层模型,分别建立了超声波分层实验系统,完成了铝和石膏的分层实验。通过理论分析可知,激励幅值与界面剪切应力幅值存在线性正相关性,界面剪切应力幅值存在共振特性。对于水平剪切(SH)波分层模型,界面剪切应力幅值在第2模态的截止频率处发生了耦合共振。3.5mm厚的石膏层粘附于3mm厚的铝板的耦合共振频率是86kHz。对于Love波分层模型,界面剪切应力幅值在第1模态群速度最小的频率处发生了耦合共振。3.5mm厚的石膏层粘附于半无限大铝基体的耦合共振频率是88kHz。吸积层厚度增大,界面剪切应力幅值的耦合共振频率向低频移动。相同激励下,在耦合共振厚度范围内,吸积层厚度越大,界面剪切应力幅值越大。在耦合共振频率附近产生超声波分层频带。通过改变超声波换能器的输出功率调节激励幅值,实验验证了越厚的石膏层分层所需的输出功率越小的结论。随着超声波换能器输出功率的增大,粘附于铝板上的4mm厚的石膏层首先掉落,接着2.5mm厚的石膏层掉落,但是1mm厚的石膏层未掉落;粘附于铝块上的4mm厚石膏层首先掉落,接着1.5mm厚的石膏层掉落。研究结果对超声波分层技术在航空航天、风电及空调等领域的推广具有重要价值。     

颤振系统中一个特殊的几何缩比效应

颤振是弹性结构在气流中发生的一种动力学不稳定现象,确定颤振系统的颤振临界速度和颤振频率是颤振分析的主要目的.数值分析和模型试验是确定系统颤振特性的两个主要手段.本文根据相似理论的第二定理,通过量纲分析证明,对于任何线性颤振系统,在结构材料保持不变的情况下,几何尺寸放大或者缩小n倍,颤振系统的固有振动频率和颤振频率相应的缩小或者放大n倍,而颤振临界速度保持不变.通过简支均匀梁和四边简支板的固有频率公式以及曲壁板颤振临界速度和颤振频率的数值算例,验证了该结论.颤振系统这种特殊的几何缩比效应揭示了在模型风洞颤振实验中,由于要对颤振临界速度进行缩比设计,因此必须使用与原型结构不同属性的材料.     

3/4开口式风洞喷口来流风速的修正

采用数值仿真方法对1∶15的3/4开口回流式汽车风洞进行模拟,并将喷口法和驻室法推导得到的风速与风洞喷口来流风速监测值进行对比,提出来流风速的修正方案.与风洞试验数据对比,验证了数值仿真方法的有效性.空风洞仿真结果表明:在不同来流风速下,两种方法计算结果皆与风洞喷口来流风速监测值接近.安装车辆模型的风洞计算结果表明:在不同雷诺数下,由于安装车辆导致的阻塞作用,喷口附近的压力受到影响,两种方法推导得到的风速皆需进一步修正.用于压差修正的系数,是依赖于风速的高阶多项式,可有效降低风速测量的误差.     

开口式风洞喷口来流风速的修正

采用数值仿真方法对1∶15的３／４开口回流式汽车风洞进行模拟,并将喷口法和驻室法推导得到的风速与风洞喷口来流风速监测值进行对比,提出来流风速的修正方案.与风洞试验数据对比,验证了数值仿真方法的有效性.空风洞仿真结果表明：在不同来流风速下,两种方法计算结果皆与风洞喷口来流风速监测值接近.安装车辆模型的风洞计算结果表明：在不同雷诺数下,由于安装车辆导致的阻塞作用,喷口附近的压力受到影响,两种方法推导得到的风速皆需进一步修正.用于压差修正的系数,是依赖于风速的高阶多项式,可有效降低风速测量的误差.     

生物液膜振荡器中的振动共振

通过数值模拟的方法研究了生物液膜振荡器在高、低两种不同频率信号作用下的振动共振现象。结果表明：体系线性响应随高频信号振幅的变化发生了多重振动共振,且低频信号的频率越低,系统的多重振动共振强度越大。体系线性响应随高频信号频率的变化可以发生高频频率依赖的多重振动共振,体系对大振幅低频信号的放大程度要比小振幅低频信号大;低频信号频率越低,系统的高频频率依赖的多重振动共振强度越大。通过负反馈机制可以有效调节体系多重振动共振峰的个数和高频频率依赖的多重振动共振的强度。当低频信号的频率等于高频信号的频率时,体系可以发生类频率共振强化的振动共振。     

不同扩散角下汽车风洞试验段轴向静压系数

轴向静压系数是衡量汽车风洞试验段流场品质的重要参数.收集口角度影响轴向静压系数,它的改变对不同风洞表现出不一致的变化规律.通过研究不同风洞在不同扩散角下试验段轴向静压系数的变化发现,当扩散角为1.70°时,试验段轴向静压系数不随收集口角度的变化而变化;当它小于1.70°时,收集口角度越大,试验段轴向静压系数越大;当它大于1.70°时,变化规律相反.扩散角所导致试验段轴向静压系数变化规律的深层次的原因是,射流剪切层存在固定的耗散角,当扩散角等于耗散角时,收集口角度变大导致的扩散效应与外界气流进入带来的效应相同;当扩散角小于耗散角,收集口角度变大导致扩散效应更强.这揭示了收集口角度导致静压系数变化的机理,为风洞建设确定收集口和试验段等关键尺寸提供理论和设计参考.     

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.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

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