期刊文献+
共找到37,525篇文章
< 1 2 250 >
每页显示 20 50 100
Influence of Different Velocities on Muzzle Flow Field 预览
1
作者 LI Zijie WANG Hao 《南京航空航天大学学报:英文版》 EI CSCD 2019年第1期88-97,共10页
A two-dimensional axisymmetric numerical simulation was successfully carried out on the muzzle flow field of a 300 mm-caliber counter-mass propelling gun. Based on the FLUENT software,using the finite volume method (F... A two-dimensional axisymmetric numerical simulation was successfully carried out on the muzzle flow field of a 300 mm-caliber counter-mass propelling gun. Based on the FLUENT software,using the finite volume method (FVM)and the realizable k-ε turbulence model,we adopted the holistic movement of a partitioned mesh processing method coupled with the intermediate ballistic model and the six degree-of-freedom model(6-DOF). We compared the flow field characteristics at the velocity of 1 730.4,978.3,and 323.4 m/s. The results indicate that the pressure of the hypersonic initial flow field is much higher than that of the subsonic and supersonic initial flow fields. In the case of the subsonic(323.4 m / s)flow field,the tiny disturbance spreads throughout the whole domain. But in the cases of the supersonic (978.3 m / s) and the hypersonic (1 730.4 m / s) flow fields,it cannot spread to the upstream disturbance source,and the disturbance domain of the supersonic flow field is wider than that of the hypersonic. It is noted that the subsonic flow field has a rounded shock wave before the projectile. However,in the supersonic and hypersonic flow fields,a shear layer is formed which begins from the head of the projectile and extends outward from the side of the projectile. Then a multi-layer shock wave is formed composed of coronal shock waves,bottom shock waves,reflected shock waves,and Mach disk. 展开更多
关键词 MUZZLE flow field DIFFERENT VELOCITIES dynamic MESH TWO-DIMENSIONAL AXISYMMETRIC
在线阅读 下载PDF
Astrophysical constraints on the proton-to-electron mass ratio with FAST
2
作者 Xi Chen Simon P.Ellingsen Ying Mei 《天文和天体物理学研究:英文版》 SCIE CAS CSCD 2019年第2期15-24,共10页
That the laws of physics are the same at all times and places throughout the Universe is one of the basic assumptions of physics. Astronomical observations provide the only means to test this basic assumption on cosmo... That the laws of physics are the same at all times and places throughout the Universe is one of the basic assumptions of physics. Astronomical observations provide the only means to test this basic assumption on cosmological time and distance scales. The possibility of variations in the dimensionless physical constant μ-the proton-to-electron mass ratio, can be tested by comparing astronomical measurements of the rest frequency of certain spectral lines at radio wavelengths with laboratory determinations. Different types of molecular transitions have different dependencies on μ and so observations of two or more spectral lines towards the same astronomical source can be used to test whether there is any evidence for either temporal or spatial changes in the physical fundamental constants. μ will change if the relative strength of the strong nuclear force compared to the electromagnetic force varies. Theoretical studies have shown that the rotational transitions of some molecules which have transitions in the frequency range that will be covered by FAST(e.g., CH3 OH, OH and CH) are sensitive to changes in μ. A number of studies looking for possible variations in μ have been undertaken with existing telescopes, however, the greater sensitivity of FAST means it will open new opportunities to significantly improve upon measurements made to date.In this paper, we discuss which molecular transitions and sources(both in the Galaxy and external galaxies)are likely targets for providing improved constraints on μ with FAST. 展开更多
关键词 ISM:molecules radio lines:ISM techniques:radial VELOCITIES ELEMENTARY particles
Global kinematics of tectonic plates and subduction zones since the late Paleozoic Era 预览
3
作者 Alexander Young Nicolas Flament +4 位作者 Kayla Maloney Simon Williams Kara Matthews Sabin Zahirovic R. Dietmar Müller 《地学前缘:英文版》 CAS CSCD 2019年第3期989-1013,共25页
Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth’s surface. A new generation of nume... Detailed global plate motion models that provide a continuous description of plate boundaries through time are an effective tool for exploring processes both at and below the Earth’s surface. A new generation of numerical models of mantle dynamics pre-and post-Pangea timeframes requires global kinematic descriptions with full plate reconstructions extending into the Paleozoic(410 Ma). Current plate models that cover Paleozoic times are characterised by large plate speeds and trench migration rates because they assume that lowermost mantle structures are rigid and fixed through time. When used as a surface boundary constraint in geodynamic models, these plate reconstructions do not accurately reproduce the present-day structure of the lowermost mantle. Building upon previous work, we present a global plate motion model with continuously closing plate boundaries ranging from the early Devonian at 410 Ma to present day.We analyse the model in terms of surface kinematics and predicted lower mantle structure. The magnitude of global plate speeds has been greatly reduced in our reconstruction by modifying the evolution of the synthetic Panthalassa oceanic plates, implementing a Paleozoic reference frame independent of any geodynamic assumptions, and implementing revised models for the Paleozoic evolution of North and South China and the closure of the Rheic Ocean. Paleozoic(410-250 Ma) RMS plate speeds are on average ~8 cm/yr, which is comparable to Mesozoic-Cenozoic rates of ~6 cm/yr on average.Paleozoic global median values of trench migration trend from higher speeds(~2.5 cm/yr) in the late Devonian to rates closer to 0 cm/yr at the end of the Permian(~250 Ma), and during the Mesozoic-Cenozoic(250-0 Ma) generally cluster tightly around ~1.1 cm/yr. Plate motions are best constrained over the past 130 Myr and calculations of global trench convergence rates over this period indicate median rates range between 3.2 cm/yr and 12.4 cm/yr with a present day median rate estimated at~5 cm/yr. For Paleozoic times(410-251 Ma) 展开更多
关键词 TECTONIC reconstruction PALEOZOIC Plate VELOCITIES SUBDUCTION zone KINEMATICS Lower MANTLE structure South China
在线阅读 下载PDF
斜角碰撞时轿车后排青少年乘员的损伤研究
4
作者 张道文 张光辉 +1 位作者 黎华惠 彭一峻 《安全与环境学报》 CSCD 北大核心 2018年第6期2086-2090,共5页
为研究轿车左侧30°斜角碰撞刚性壁障时后排左侧和右侧青少年乘员的损伤特点,利用Presys建立有限元轿车、刚性障碍壁和假人整体模型,经Ls-Dyna求解计算后用Presys有限元软件分析了3种车速下的后排左右侧青少年乘员的损伤情况。结果... 为研究轿车左侧30°斜角碰撞刚性壁障时后排左侧和右侧青少年乘员的损伤特点,利用Presys建立有限元轿车、刚性障碍壁和假人整体模型,经Ls-Dyna求解计算后用Presys有限元软件分析了3种车速下的后排左右侧青少年乘员的损伤情况。结果表明,随碰撞车速增加,后排左右侧假人的头部加速度均增大。当碰撞车速为50km/h时,后排右侧假人头部加速度最大;不同碰撞车速下,后排右侧假人颈部受力均大于后排左侧假人颈部受力;不同碰撞车速下,后排左侧假人胸部加速度均大于右侧假人胸部加速度;随碰撞车速增加,后排左侧假人和右侧假人的左腿胫骨和右腿胫骨受力峰值接近。 展开更多
关键词 安全人体学 斜角碰撞 后排乘员损伤 车速 青少年 Presys软件
Effects of rotation and tidal distortions on the shapes of radial velocity curves of polytropic models of pulsating variable stars
5
作者 Tarun Kumar Arvind Kumar Lal Ankush Pathania 《天文和天体物理学研究:英文版》 CSCD 2018年第6期17-26,共10页
Anharmonic oscillations of rotating stars have been studied by various authors in literature toexplain the observed features of certain variable stars. However, there is no study available in literaturethat has discus... Anharmonic oscillations of rotating stars have been studied by various authors in literature toexplain the observed features of certain variable stars. However, there is no study available in literaturethat has discussed the combined effect of rotation and tidal distortions on the anharmonic oscillationsof stars. In this paper, we have created a model to determine the effect of rotation and tidal distortionson the anharmonic radial oscillations associated with various polytropic models of pulsating variablestars. For this study we have used the theory of Rosseland to obtain the anharmonic pulsation equationfor rotationally and tidally distorted polytropic models of pulsating variable stars. The main objective ofthis study is to investigate the effect of rotation and tidal distortions on the shapes of the radial velocitycurves for rotationally and tidally distorted polytropic models of pulsating variable stars. The results ofthe present study show that the rotational effects cause more deviations in the shapes of radial velocitycurves of pulsating variable stars as compared to tidal effects. 展开更多
关键词 stars: ROTATION -- stars: OSCILLATIONS -- stars: BINARIES -- technique: radial VELOCITIES
岩石物理综合实验——压力、温度和流体对岩石速度的影响 预览
6
作者 张佳佳 张广智 +2 位作者 吴国忱 曹丹平 宗兆云 《实验室研究与探索》 北大核心 2018年第2期72-75,共4页
结合勘查技术与工程专业人才培养目标及学生自身特点,设计了一个地震岩石物理综合实验——压力、温度和流体对岩石速度的影响。将岩石放置在反应釜中,加载轴压和围压,并对岩石加热,测量岩石在高温高压状态下的纵波速度和横波速度。获得... 结合勘查技术与工程专业人才培养目标及学生自身特点,设计了一个地震岩石物理综合实验——压力、温度和流体对岩石速度的影响。将岩石放置在反应釜中,加载轴压和围压,并对岩石加热,测量岩石在高温高压状态下的纵波速度和横波速度。获得了岩石纵波速度和横波速度均随压力增加而增加,以及随温度增加而减小的变化规律,以及含水岩石纵波速度高于含气岩石,而横波速度低于含气岩石的特征。 展开更多
关键词 岩石物理 综合实验 岩石 流体 速度
在线阅读 下载PDF
A numerical modelling approach to assess the behaviour of underground cavern subjected to blast loads 预览
7
作者 Saikat Kuili Vedala Rama Sastry 《矿业科学技术学报:英文版》 CSCD 2018年第6期975-983,共9页
The paper gives an insight into the behaviour of large underground caverns which are subjected to blast loads.Caverns are generally constructed in hard rock formation which compels us to use blasting methods for the e... The paper gives an insight into the behaviour of large underground caverns which are subjected to blast loads.Caverns are generally constructed in hard rock formation which compels us to use blasting methods for the excavation works.Comparative study was done between models with intact rock mass and discontinuities to assess the stability of cavern as a result of blast loads.Numerical modelling was performed with 3 dimensional distinct element code(3DEC)to analyse the performance of cavern walls in terms of displacement and to compute peak particle velocities(PPV)both around the cavern periphery and at surface of models.Results showed that the velocity wave with higher frequency exhibited large displacements around the periphery of cavern.Computation of PPV showed that model with horizontal joint sets showed lower PPV in comparison to model with intact rock mass.PPV values were also analysed on the surface for model consisting vertical joints spaced at 4 m intervals.Comparative study of PPV on surface vertically above the blast location between models with horizontal joints spaced at 4 m and vertical joints at 4 m intervals were conducted.Results depicted higher magnitudes of PPV for model with vertical joints in comparison to model with horizontal joints. 展开更多
关键词 Large UNDERGROUND caverns HARD rock formation NUMERICAL modelling 3 dimenssional DISTINCT element code PEAK particle VELOCITIES
在线阅读 下载PDF
Influence of loading and heating processes on elastic and geomechanical properties of eclogites and granulites 预览
8
作者 Hem Bahadur Motra Sascha Zertani 《岩石力学与岩土工程学报:英文版》 CSCD 2018年第1期127-137,共11页
Increased knowledge of the elastic and geomechnical properties of rocks is important for numerous engineering and geoscience applications(e.g.petroleum geoscience,underground waste repositories,geothermal energy,earth... Increased knowledge of the elastic and geomechnical properties of rocks is important for numerous engineering and geoscience applications(e.g.petroleum geoscience,underground waste repositories,geothermal energy,earthquake studies,and hydrocarbon exploration).To assess the effect of pressure and temperature on seismic velocities and their anisotropy,laboratory experiments were conducted on metamorphic rocks.P-(Vp)and S-wave(Vs)velocities were determined on cubic samples of granulites and eclogites with an edge length of 43 mm in a triaxial multianvil apparatus using the ultrasonic pulse emission technique in dependence of changes in pressure and temperature.At successive isotropic pressure states up to 600 MPa and temperatures up to 600 C,measurements were performed related to the sample coordinates given by the three principal fabric directions(x,y,z)representing the foliation(xy-plane),the normal to the foliation(z-direction),and the lineation direction(x-direction).Progressive volumetric strain was logged by the discrete piston displacements.Cumulative errors in Vp and Vs are estimated to be<1%.Microcrack closure significantly contributes to the increase in seismic velocities and decrease in anisotropies for pressures up to 200e250 MPa.Characteristic P-wave anisotropies of about 10%are obtained for eclogite and 3e4%in a strongly retrogressed eclogite as well as granulites.The wave velocities were used to calculate the geomechanical properties(e.g.density,Poisson’s ratio,volumetric strain,and elastic moduli)at different pressure and temperature conditions.These results contribute to the reliable estimate of geomechanical properties of rocks. 展开更多
关键词 Anisotropy ELASTIC wave VELOCITIES Dynamic ELASTIC MODULI Geomechanical rock properties MICROCRACK
在线阅读 下载PDF
Effect of interaction of the various modes on the radial velocity curves of the polytropic models of rotationally and tidally distorted pulsating variable stars
9
作者 Tarun Kumar Ankush Pathania Arvind Kumar Lal 《天文和天体物理学研究:英文版》 SCIE CAS CSCD 2018年第12期53-66,共14页
In our previous work,we developed a model to study the effects of rotation and/or tidal distortions on anharmonic radial oscillations and hence on the radial velocity curves of the polytropic models of pulsating varia... In our previous work,we developed a model to study the effects of rotation and/or tidal distortions on anharmonic radial oscillations and hence on the radial velocity curves of the polytropic models of pulsating variable stars.We considered the first three modes (fundamental and the next two higher modes)for the polytropic models of index 1.5 and 3.0in that work.In the present paper,we are further extending our previous work to study the effect of the interaction of various modes on anharmonic radial oscillations and hence on radial velocity curves of the rotationally and/or tidally distorted polytropic models of pulsating variable stars.For this purpose,we have considered the following cases:(i)fundamental mode (ii)fundamental and the first mode,(iii)fundamental and the next two modes and finally (iv)fundamental and the next three higher modes of pulsation in our study.The objective of this paper is also to investigate whether the interaction of various modes affects the results of our previous study or not.The results of this study show that the interaction of the fundamental mode with higher modes appreciably changes the shape of the radial velocity curve of rotationally distorted and rotationally and tidally distorted polytropic models of pulsating variable stars. 展开更多
关键词 STARS rotation-stars oscillations-stars binaries-technique radial VELOCITIES
Spacecraft Doppler tracking with possible violations of LLI andLPI: a theoretical modeling
10
作者 Xue-Mei Deng 《天文和天体物理学研究:英文版》 SCIE CAS CSCD 2014年第3期319-328,共10页
Currently two-way and three-way spacecraft Doppler tracking techniquesare widely used and play important roles in control and navigation of deep space mis-sions. Starting from a one-way Doppler model, we extend the th... Currently two-way and three-way spacecraft Doppler tracking techniquesare widely used and play important roles in control and navigation of deep space mis-sions. Starting from a one-way Doppler model, we extend the theory to two-way andthree-way Doppler models by making them include possible violations of the localLorentz invariance (LLI) and the local position invariance (LPI) in order to test theEinstein equivalence principle, which is the cornerstone of general relativity and allother metric theories of gravity. After taking the finite speed of light into account,which is the so-called light time solution (LTS), we make these models depend on thetime of reception of the signal only for practical convenience. We find that possibleviolations of LLI and LPI cannot affect two-way Doppler tracking under a linear ap-proximation of LTS, although this approximation is sufficiently good for most cases inthe solar system. We also show that, in three-way Doppler tracking, possible violationsof LLI and LPI are only associated with two stations, which suggests that it is betterto set the stations at places with significant differences in velocities and gravitationalpotentials to obtain a high level of sensitivity for the tests. 展开更多
关键词 space vehicles -- techniques RADIAL VELOCITIES -- GRAVITATION
二维斑点追踪技术评价房间隔缺损封堵术前后右室应变及应变率的变化 被引量:4
11
作者 雍永宏 庄燕 +5 位作者 姚静 杨荣 盛燕辉 周蕾 许迪 曹克将 《南京医科大学学报:自然科学版》 CAS CSCD 北大核心 2009年第8期1128-1132,共5页
目的:运用二维超声斑点追踪技术评价经皮房间隔封堵术前后患者右心室运动速度、应变及应变率的急性期变化。方法:检测25例房间隔缺损患者封堵术前、术后第3天的常规心脏二维多普勒超声参数,并运用二维斑点追踪技术对患者的右心室运动... 目的:运用二维超声斑点追踪技术评价经皮房间隔封堵术前后患者右心室运动速度、应变及应变率的急性期变化。方法:检测25例房间隔缺损患者封堵术前、术后第3天的常规心脏二维多普勒超声参数,并运用二维斑点追踪技术对患者的右心室运动速度、应变及应变率进行分析,以探讨房间隔缺损封堵术对右心室运动的影响。25例年龄性别匹配的正常人作为对照。结果:房间隔缺损患者术前的右心室游离壁的运动速度较正常对照显著加快(P〈0.05),而封堵术后出现了明显的下降并且接近正常对照的运动速度(P〉0.05)。在房间隔缺损封堵术前,右心室游离壁的应变较正常对照升高(P〈0.05),右心室游离壁的应变率较正常对照升高但是差异无统计学意义(P〉0.05)。封堵术后,右心室游离壁的峰值应变及应变率出现下降趋势,但是较术前而言差异不显著(P〉0.05)。较正常对照而言,房间隔缺损患者术前室间隔的运动速度及峰值应变显著升高(P〈0.05),并且在术后出现显著的降低(P〈0.05)。而室间隔部位的应变率则未发现类似变化,无论和正常对照比较还是和术前比较,均未发现明显变化(P〉0.05)。结论:经皮室间隔缺损封堵术通过迅速减轻右心室的容量负荷而影响右心室的运动速度、应变及应变率。其中右心室的形变参数对右心室容量负荷的急性变化不敏感,而右心室的运动速度受负荷改变的影响明显。 展开更多
关键词 房间隔缺损 经皮封堵术 超声心动图 速度 应变 应变率 斑点追踪显像
液-固(气)旋流器分离性能分析及环保工程应用 预览 被引量:1
12
作者 张作萍 陈海 +4 位作者 郭金基 张开成 姚云 李航飞 贺炜 《中山大学学报:自然科学版》 CAS CSCD 北大核心 2008年第3期 41-46,共6页
阐述环保工程和化学工业中的广泛使用的液-固(气)旋流分离器结构特性,并分析液-固(气)旋流分离器的流场结构,观察旋流器的流线和流动现象。根据实验数据,采用圆柱室内二维轴对称涡流模型,计算涡室内准自由涡区压力分布,得准自... 阐述环保工程和化学工业中的广泛使用的液-固(气)旋流分离器结构特性,并分析液-固(气)旋流分离器的流场结构,观察旋流器的流线和流动现象。根据实验数据,采用圆柱室内二维轴对称涡流模型,计算涡室内准自由涡区压力分布,得准自由涡区的速度函数;按旋流器液-固(气)流体运动规律,计算分离的颗粒直径和分离效率。通过实验方法揭示液-固(气)旋流器流体运动的规律,最后给出废气治理工程的实例,并讨论其在环境保护领域中的应用前景。 展开更多
关键词 液-固(气)旋流 分离器 速度 流线 压力 分离粒径
在线阅读 下载PDF
Melting Behaviour of Mo by Shock Wave Experiment
13
作者 张修路 蔡灵仓 +2 位作者 陈军 徐济安 经福谦 《中国物理快报:英文版》 SCIE CAS CSCD 2008年第8期2969-2972,共4页
以便在融化在钻石铁砧之间的瞬间的温度 T-m 的决心澄清明显的差异从 0 的房间(数模转换器)大小到大约 100 GPa 和冲击波( SW )在仅仅由有视觉推测的比较的大约 390 GPa 的一个压力的测量,我们执行 SW 实验填满更多的 T-m 数据故意... 以便在融化在钻石铁砧之间的瞬间的温度 T-m 的决心澄清明显的差异从 0 的房间(数模转换器)大小到大约 100 GPa 和冲击波( SW )在仅仅由有视觉推测的比较的大约 390 GPa 的一个压力的测量,我们执行 SW 实验填满更多的 T-m 数据故意也更直接并且讲道理地做这比较。采用的技术为稳固、多孔的瞬间为多孔的瞬间和导致吃惊的版本 T-m 大小由 Hugoniot 健全速度测量组成。完全,五个 SW T-m 数据,它从以前的大约 390 GPa 扩大测量压力范围在下面到接近最高的压力(大约 100 GPa ) 的大约 136 GPa 由以前的数模转换器实验到达了,因此被获得。这些测量了 T-m 数据,除以外是提及在上面外推,与压力展出连续变化的一种方式并且能与融化描述的 Lindemann 被适合很好。更显著地,在最低压力的测量 T-m 数据仍然比数模转换器和数据对的这些 Tm 的全面趋势的高得多到二片断的融化曲线模型与在在大约 210 GPa 的 dT (m) /d (P)的一个突然的变化,以前由 Errandonea 求婚了[ Physica B 357 ( 2005 ) 356 ]。不过,在 T-m 数据的大差异的问题在数模转换器之间测量了, SW 完全没被解释,自从规划下一澄清具有值,我们这件事上的知识获得不容置疑的进步。为进一步澄清在数模转换器和 SW 大小之间的大差异的问题的一些建议也被建议。 展开更多
关键词 振动波 熔化条件 物理研究
黏度和矿化度对岩石速度各向异性影响的实验研究 预览 被引量:1
14
作者 李金臣 史(讠哥) 陈思远 《北京大学学报:自然科学版》 EI CAS CSCD 北大核心 2005年第6期851-858,共8页
利用不同黏度(煤油和真空泵油)、不同矿化度(蒸馏水、50mg/L和150mg/L的NaCl溶液)的流体对页岩和具有明显层理的砂岩进行饱和,在实验室超声频率下研究样品不同方向纵、横波速度以及各向异性参数ε、γ随压力的变化规律.结果表明:(1) 随... 利用不同黏度(煤油和真空泵油)、不同矿化度(蒸馏水、50mg/L和150mg/L的NaCl溶液)的流体对页岩和具有明显层理的砂岩进行饱和,在实验室超声频率下研究样品不同方向纵、横波速度以及各向异性参数ε、γ随压力的变化规律.结果表明:(1) 随着黏度的增加,岩石纵、横波速度增大,各向异性参数ε、γ减小;(2) 随着矿化度的增加,岩石纵、横波速度增大,各向异性参数ε、γ的变化在实验误差范围内可以忽略不计. 展开更多
关键词 黏度 矿化度 页岩 砂岩 速度 各向异性
在线阅读 免费下载
高速公路上不同车型源强噪声及速度的统计分析 被引量:1
15
作者 马春燕 王钧利 《公路》 北大核心 2005年第7期199-202,共4页
选取了西安地区平坦且周围环境开阔的几条高速公路,通过对行驶在高速公路上不同车辆(大卡车和大客车、中卡车和中客车、小型车)的源强噪声、速度进行测试,运用统计学原理分析.结果表明:高速公路上不同车型源强噪声及速度遵循正态分布.... 选取了西安地区平坦且周围环境开阔的几条高速公路,通过对行驶在高速公路上不同车辆(大卡车和大客车、中卡车和中客车、小型车)的源强噪声、速度进行测试,运用统计学原理分析.结果表明:高速公路上不同车型源强噪声及速度遵循正态分布.得出其所产生的源强噪声、速度的最大值、最小值、平均值、分布区间;与经验方法所得数值比较,实际上大型车和中型车速度普遍提高而源强噪声下降,但小型车速度提高,源强噪声增大.说明路况等级提高,新车增多、车辆性能改善,高速公路上车辆的源强噪声、速度也在发生变化.将以上研究结果应用于交通噪声预测及其研究中,能更切合实际,更科学地进行环境评估和治理. 展开更多
关键词 交通噪声 源强噪声 行驶速度 统计分析
单向复合纤维材料弹性系数的超声测量 预览 被引量:12
16
作者 许明翔 王耀俊 《应用声学》 CSCD 1996年第1期 1-4,共4页
本文将单向复合纤维材料视作六角对称晶体,认为其弹性特征由五个独立的弹性系数来描述,利用Christoffel方程,我们得到这一各向异性介质中不同方向的声波速度与弹性系数的关系。我们还建立了一套计算机控制的实验测量系统... 本文将单向复合纤维材料视作六角对称晶体,认为其弹性特征由五个独立的弹性系数来描述,利用Christoffel方程,我们得到这一各向异性介质中不同方向的声波速度与弹性系数的关系。我们还建立了一套计算机控制的实验测量系统,通过它对纤维板样品的声速进行测量,反演得到了五个独立的弹性系数C11,C33,C13,C44和C12。理论计算得到的声速和实验测量值吻合较好,表明我们的方法是有实用意义的。 展开更多
关键词 弹性系数 声速 反演 复合纤维材料 超声测量
在线阅读 下载PDF
弹性磨具磨抛SKD-11钢工艺参数优化研究 预览
17
作者 吴晓君 李彦磊 +1 位作者 贾慧波 杨洋 《组合机床与自动化加工技术》 北大核心 2019年第8期136-138,156共4页
在超精磨抛加工中,主要通过材料的微量去除来达到表面光洁的目的。为提高弹性磨抛SKD-11的表面加工效率和磨抛效果,获得弹性磨具磨抛SKD-11钢工件曲面最佳工艺参数组合,首先采用尺寸为?18×55mm的钢试样进行柔性磨抛单因素优选法与... 在超精磨抛加工中,主要通过材料的微量去除来达到表面光洁的目的。为提高弹性磨抛SKD-11的表面加工效率和磨抛效果,获得弹性磨具磨抛SKD-11钢工件曲面最佳工艺参数组合,首先采用尺寸为?18×55mm的钢试样进行柔性磨抛单因素优选法与正交实验深入分析磨具直径、磨抛深度等磨抛过程参量对表面质量的影响,并利用Fluent模拟切削区流场,通过使用高速射流进一步提高表面质量。实验结果表明:当球头磨具直径为D=50mm,磨抛深度t=0.3mm,进给速度V=10mm/min,射流速度v=19m/s时,试样表面粗糙度Ra为0.056μm,有效的提高了SKD-11钢材表面质量,为SKD-11钢零件的光整加工提供了重要的理论依据。 展开更多
关键词 球头弹性磨具 超精磨抛 高速射流 表面质量优化
在线阅读 下载PDF
弯管体系内浆液流动分析 预览
18
作者 孙贤 刘德俊 +1 位作者 王文武 荣峰 《化学工程》 CAS CSCD 北大核心 2019年第6期58-63,共6页
针对弯管系统中易在弯头处出现水合物堵塞的现象,以弯管系统中水合物浆液输送过程为研究对象,通过数值模拟对影响弯管系统中水合物颗粒最大体积分数的2个因素(颗粒直径、管径)进行了分析。结果表明:当水合物浆流速较小时,弯管系统中水... 针对弯管系统中易在弯头处出现水合物堵塞的现象,以弯管系统中水合物浆液输送过程为研究对象,通过数值模拟对影响弯管系统中水合物颗粒最大体积分数的2个因素(颗粒直径、管径)进行了分析。结果表明:当水合物浆流速较小时,弯管系统中水合物最大体积分数受粒径的影响较大,即随着粒径的增大,水合物的最大体积分数趋近迅速增大的状态,而当浆液流速较快时,水合物最大体积分数受流速影响较大;管径的增大可以减小水合物颗粒直径对弯管系统中水合物最大体积分数的影响,到管道直径达到200mm时,水合物颗粒直径的变化几乎不会影响水合物最大体积分数。研究结果为水合物浆液混输领域的发展提供理论依据。 展开更多
关键词 弯管 水合物浆 数值模拟 体积分数 流速
在线阅读 下载PDF
航空沉头铆钉动态加载试验及失效模式研究 预览
19
作者 牟浩蕾 赵一帆 +2 位作者 刘义 解江 冯振宇 《航空科学技术》 2019年第4期69-78,共10页
为研究航空沉头铆钉在动态加载下的失效模式,以航空器结构中使用的100°沉头铆钉为研究对象,采用高速液压伺服材料试验机,进行不同加载速度下的纯拉伸、30°拉剪耦合、45°拉剪耦合、60°拉剪耦合和纯剪切动态试验,获... 为研究航空沉头铆钉在动态加载下的失效模式,以航空器结构中使用的100°沉头铆钉为研究对象,采用高速液压伺服材料试验机,进行不同加载速度下的纯拉伸、30°拉剪耦合、45°拉剪耦合、60°拉剪耦合和纯剪切动态试验,获得不同工况下铆钉动态力学失效试验数据,研究加载角度、加载速度对铆钉失效模式和失效载荷的影响规律,并拟合铆钉失效本构参数及失效判据。结果表明,此种铆钉主要有沉头拉脱和钉杆剪断失效模式,不同加载角度下铆钉失效模式差异较大,不同加载速度下铆钉失效模式差异较小;失效载荷随加载速度增大而增大。对纯拉伸和纯剪切试验,失效载荷与加载速度线性相关;建立不同加载速度下的铆钉失效判据,可应用于铆钉有限元建模及机身结构适坠性仿真分析。 展开更多
关键词 沉头铆钉 动态加载试验 加载角度 加载速度 失效模式 失效判据
在线阅读 下载PDF
利用GPS数据反演中国红河断裂带活动特性
20
作者 徐文 许才军 +1 位作者 肖卓辉 王帅 《武汉大学学报:信息科学版》 EI CSCD 北大核心 2019年第5期706-713,共8页
为了研究中国红河断裂带近年的活动特性,利用块体模型对红河断裂带周围块体内1999—2014年的GPS水平速度场进行建模,反演得到块体的刚体旋转、内部应变率以及断层的滑动速率与三维闭锁程度。结果表明,考虑内部应变的块体模型可以显著提... 为了研究中国红河断裂带近年的活动特性,利用块体模型对红河断裂带周围块体内1999—2014年的GPS水平速度场进行建模,反演得到块体的刚体旋转、内部应变率以及断层的滑动速率与三维闭锁程度。结果表明,考虑内部应变的块体模型可以显著提升速度场的拟合效果,反演得到的红河断裂带滑动速率与二维速度剖面的结果吻合较好。红河断裂带的闭锁程度大致呈现中段闭锁较强、南段与北段闭锁较弱的对称分布,南段、中段与北段在地表以下15 km深度范围内的断层闭锁程度分别约为0.34~0.52、0.67~0.75、0.26~0.53,右旋滑动亏损速率分别为1.7、3.0、1.4 mm/a。利用最小二乘配置方法计算了研究区域的应变场分布,发现红河断裂带从南至北由压缩转换为拉张,中段处于压缩与拉张的交界带,剪应变率低于南北两段,这可能是由于中段闭锁较强、断层错动量较小造成的。 展开更多
关键词 红河断裂带 GPS速度场 块体模型 闭锁程度 滑动亏损速率
上一页 1 2 250 下一页 到第
使用帮助 返回顶部 意见反馈