三角形绕流问题的分析解

三角形截面导弹气动性能的研究主要依靠实验,理论研究尚显不足。该文构造了一种从圆柱绕流到三角形绕流的近似解析变换,给出了复势、复速度、压力系数的表达式与典型算例。这种变换可便捷地给出三角形绕流的流动图谱、流速分布以及压力系数分布。其结果对认识三角形绕流以及其他非圆截面气动性能的研究具有重要意义。     

某非圆截面导弹的动态特性分析

利用小扰动飞行动力学方程和参数敏感性分析方法,研究了某非圆截面导弹在典型气动条件下的开环飞行稳定特性.对该导弹在不同静、动导数条件下的飞行稳定性进行了研究,得到了影响系统稳定性的主要因素以及出现较优横侧向稳定性的参数取值区间,这些结论为同类型导弹气动布局和控制系统的设计提供可靠的借鉴.     

弹载滚转稳定平台运动稳定性分析及试验验证

适用于高过载、高旋转弹药的滚转稳定平台有效解决了该类弹药的导航参数测试问题。该平台基于复摆运动原理设计,通过分析内弹道环境下平台的抗过载能力,以及在外弹道飞行过程中平台受力状况,对其内筒运动稳定性的影响,设计了轴向负荷承载区的过载转移装置。建立了平台在弹载环境下内筒运动的微分方程。通过对弹药的气动力仿真,以及系统动力学模型的计算,得到平台内筒滚转角速率与角度变化曲线;并在冲击台与高速飞行仿真转台上进行相应验证试验。试验结果与计算结果对比,表明平台可抗过载10 000g,且弹载环境下内筒作小幅的往复摆动,符合复摆的运动规律,其运动状态稳定。     

三角形截面长杆弹垂直侵彻半无限靶的成坑分析

为研究三角形截面弹体在垂直侵彻半无限靶时的成坑特性，通过分析三角形截面弹体头部接触面上的横向力，得到弹体头部碎渣颗粒的运动状态。根据侵彻速度关系式推断弹体瞬时速度对弹坑截面形状及大小的影响规律。采用ANSYS-DYNA有限元软件对不同速度的三角形截面弹体垂直侵彻半无限靶全过程进行数值模拟，并进行实验验证。仿真结果与实验结果一致。结果显示，三角形截面弹体在撞击平面上的质点横向应力分布不均匀，3个角方向上的力最大，边长中点位置处最小，总体呈U形分布。弹体瞬时速度逐渐减小，弹坑形状由近似规则圆形逐渐变为近似三角形的3瓣圆弧，且其截面积不断减小。在1 400～1 800 m/s的速度范围内进行了长杆弹撞击实验。速度为1 790 m/s时，弹坑在靶板表面的直径和深度分别为40 mm和7 mm,弹坑形状近似圆形。速度为1 510 m/s时，弹坑在靶板表面的直径和深度分别为38 mm和5 mm,弹坑截面表现为圆弧三角形。     

两种典型尾翼形状对无伞末敏弹气动特性的影响

为研究尾翼形状对双翼无伞末敏弹减速导旋性能的影响,分别对平板尾翼和S-C形尾翼结构末敏弹的气动特性进行研究。基于计算流体力学方法,获得了末敏弹气动外形的流场特性、表面压力分布和阻力系数、升力系数和转动力矩系数随攻角变化的规律。通过自由飞行试验对平板尾翼和S-C尾翼末敏弹进行了动态气动特性研究。数值计算结果显示,平板尾翼和S-C尾翼模型阻力系数在6～9间,其增阻效果明显;两模型升力系数均呈负线性变化,尾翼形状对升力系数影响较小;尾翼形状对转动力矩系数影响明显,平板尾翼几无转动力矩产生,S-C尾翼转动力矩相对较大并随攻角增加而减小。自由飞行试验表明,S-C尾翼结构自由飞行状态下增阻效果好于平板尾翼,并可使弹体获得转动力矩而维持稳定转速,能够实现稳态扫描运动。平板尾翼末敏弹自由飞行稳定性差。     

积冰对飞机本体纵向非线性动力学稳定域的影响

积冰威胁飞行安全,研究积冰对飞机稳定性的影响对确保飞行安全具有重要意义。积冰导致飞机失速迎角降低,仅研究飞机在小迎角线性段的稳定性是不充分的,还需对其非线性动力学稳定域进行研究。首先,基于积冰条件下的飞机气动系数曲线,建立积冰飞机纵向运动的非线性模型;然后,根据非线性动力学理论构造出飞机纵向运动的稳定域边界,并利用时域仿真对稳定域边界进行验证;最后,通过对比无冰与积冰条件下稳定域的变化,分析积冰对飞机稳定域的影响,并将积冰对飞机稳定域的影响和其对气动系数的影响进行对比。积冰条件下飞机稳定域在俯仰角速度方向上收缩约20%,稳定域边界处的最大迎角减小约1°。研究结果表明,积冰条件下飞机稳定域的变化与气动系数的变化一致,积冰导致飞机的稳定域缩小,容易引起飞行事故。     

异型截面弹芯垂直侵彻半无限靶板

为研究非圆截面长杆弹的侵彻特性,对长径比为20的圆形、三角形、正方形截面的三种长杆弹对半无限靶的垂直侵彻进行数值模拟,通过已有的实验结果对仿真结果进行验证,并利用数值模拟拓展研究长径比为5、10、15的3种截面形状的长杆弹以及长径比为20的正五边形和正六边形对靶板的侵彻威力,结果表明:异型截面弹在大长径比、高着靶速度条件下具有更优的侵彻威力,其中正三角形截面弹在几种正多边形截面弹中侵彻威力更优;提出弹芯的截面形状因子H,并基于销蚀长杆侵彻模型Alekseevskii-Tate模型,建立了异型截面弹对半无限靶侵彻深度的计算公式.      

基于Matlab的尾翼弹尾翼张开的运动分析与仿真

针对高速滑膛远程榴弹,要保证其飞行稳定性,必须采用张开式超口径尾翼稳定装置。本文对尾翼弹的尾翼稳定装置中活塞、尾翼片进行运动分析,根据其运动过程建立相应的数学模型,然后利用计算机对数学模型进行求解,根据解出的数据来验证该改进方案的可行性。     

三角形截面碳纤维在复合材料中的分布规律

 三角形截面碳纤维在复合材料内部的排布结构像微波暗室一样,能够对入射的电磁波进行多次反射,从而衰减电磁波,使三角形截面碳纤维复合材料具有吸波性能,因此,研究三角形截面碳纤维在复合材料中的排布规律对研究其吸波机理非常重要.采用实验和模拟的方法对三角形截面碳纤维在复合材料中的排布规律进行了分析.首先,通过扫描电子显微镜(SEM)观察了多组三角形截面碳纤维复合材料试样的截面微观形貌,分析了三角形碳纤维在复合材料中的排布角度及均匀性;其次,为进一步研究三角形截面碳纤维复合材料的吸波机理,根据蒙特卡洛原理,通过Matlab软件对三角形截面碳纤维在复合材料中的排布情况进行了模拟.实验及数值模拟结果吻合较好,均表明三角形截面碳纤维在复合材料中的排布是以各种排布角度随机排布的,而三角形碳纤维分布是比较均匀的,没有明显的密布区域和稀疏区域,该模拟方法可以用于模拟不同含量的三角形截面碳纤维在复合材料中的排布规律.     

基于三维重建飞机气动特性的飞行包线

为了确定未知飞机的飞行边界,提出了一种通过逆向三维建模进行气动特性分析后建立基本飞行包线的方法,对气动参数未知飞机的飞行安全和空战仿真问题提供了技术支撑.首先,综合运用明暗恢复图像和工程图重建法对飞机的几何外形进行了三维重建;然后通过数值模拟计算的方法计算并分析了其纵向气动特性;最后,计算了飞机的基本飞行包线并进行了对比验证.研究结果表明,所做工作探索出了一条研究外军缺乏气动参数飞机飞行性能的完整技术途径,所计算的飞行包线具有较高的可靠性,能够体现飞机的飞行性能.     

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.     

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.     

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.     

A computer generator for randomly layered structures

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

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.     

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     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the