Evaluation of stress intensity factors for multiple cracked circular disks under crack surface tractions with SBFEM     

刘钧玉  林皋  李晓川  徐凤琳 《中国海洋工程》2013,27(3):417-426

Stress intensity factors (SIFs) for the cracked circular disks under different distributing surface tractions are evaluated with the scaled boundary finite element method (SBFEM). In the SBFEM, the analytical advantage of the solution in the radial direction allows SIFs to be directly determined from its definition, therefore no special crack-tip treatment is necessary. Furthermore anisotropic material behavior can be treated easily. Different distributions of surface tractions are considered for the center and double-edge-cracked disks. The benchmark examples are modeled and an excellent agreement between the results in the present study and those in published literature is found. It shows that SBFEM is effective and possesses high accuracy. The SIFs of the cracked orthotropic material circular disks subjected to different surface tractions are also evaluated. The technique of substructure is applied to handle the multiple cracks problem.  相似文献   

基于ERSM涡轮盘径向变形的非线性动态概率分析          下载免费PDF全文

王桂华  费成巍  白广忱 《海洋科学进展》2013,(4):529-536

为了准确设计高压涡轮盘和叶尖间隙,从概率的角度进行了涡轮盘径向变形的分析。介绍了高精度高效率的非线性动态概率分析的极值响应面方法(Extremum Response Surface Method, ERSM),并建立了其数学模型。考虑材料属性和边界条件的非线性,以及热载荷和离心载荷的动态性,基于ERSM对涡轮盘径向变形进行了非线性动态概率分析,得到了输入输出参数的分布特征和影响涡轮盘径向动态变形的主要因素。最后,通过方法比较,验证了ERSM在保证计算精度的前提下能大大提高计算速度,节约计算时间,改善计算效率。为进行更有效的涡轮盘设计和优化,改善叶尖间隙设计和控制的合理性提供了有效依据。   相似文献   

Variation of the gas and radiation content in the sub-Keplerian accretion disk around black holes and its impact to the solutions     

Banibrata Mukhopadhyay  Parikshit Dutta 《New Astronomy》2012,17(2):51-60

We investigate the variation of the gas and the radiation pressure in accretion disks during the infall of matter to the black hole and its effect to the flow. While the flow far away from the black hole might be non-relativistic, in the vicinity of the black hole it is expected to be relativistic behaving more like radiation. Therefore, the ratio of gas pressure to total pressure (β) and the underlying polytropic index (γ) should not be constant throughout the flow. We obtain that accretion flows exhibit significant variation of β and then γ, which affects solutions described in the standard literature based on constant β. Certain solutions for a particular set of initial parameters with a constant β do not exist when the variation of β is incorporated appropriately. We model the viscous sub-Keplerian accretion disk with a nonzero component of advection and pressure gradient around black holes by preserving the conservations of mass, momentum, energy, supplemented by the evolution of β. By solving the set of five coupled differential equations, we obtain the thermo-hydrodynamical properties of the flow. We show that during infall, β of the flow could vary up to ∼300%, while γ up to ∼20%. This might have a significant impact to the disk solutions in explaining observed data, e.g. super-luminal jets from disks, luminosity, and then extracting fundamental properties from them. Hence any conclusion based on constant γ and β should be taken with caution and corrected.  相似文献   

径向粘滞力对薄盘稳定性的影响     

余文飞  杨兰田 《中国天文和天体物理学报》1995,(3)

在吸积盘内由于吸积物质的径向运动，盘内物质间沿径向的粘滞力将会对盘的性质产生一定影响．本文计算了等温吸积盘中（考虑径向粘滞力）的不稳定性问题，对所求得的色散方程的分析表明，径向粘滞力将使吸积盘趋向稳定。本文还对径向粘滞力对盘的稳定性的影响作了物理解释，并发现径向粘滞力的引入不会引入新的稳定或不稳定模式。  相似文献   

Analysis of magnetic field measurements for T Tau     

D. A. Smirnov  M. M. Romanova  S. A. Lamzin 《Astronomy Letters》2005,31(5):335-339

The presence of hot spots on the surface of T Tau attributable to mass accretion from the protoplanetary disk is shown to have virtually no effect on the accuracy of estimating the magnetic field strength for this star. By comparing the magnetic field strengths for T Tau at the photospheric level measured by various methods, we found that if the angle i at which we see T Tau does not exceed 10°, then the magnetic field of the star could be dipolar with the angle between the dipole axis and the rotation axis of the star ?85°. If, however, it later emerges that i > 10°, its magnetic field is essentially nondipolar and/or nonstationary.  相似文献   

星风吸积下的有盘X射线脉冲星     

李向东  汪珍如 《中国天文和天体物理学报》1995,(2)

近年来对吸积流的数值模拟工作证实了在星风吸积中吸积盘的存在。本文在此基础上，讨论具有早型伴星的Ｘ射线脉冲星吸积过程中吸积盘与球吸积流的相互作用。我们发现，盘吸积率和球吸积率的相对变化可以导致吸积盘和吸积矩的改变，从而解释了这类脉冲星脉冲周期的复杂变化，我们以典型星ＶｅｌａＸ－１和Ａ０５３５＋２６为例分别作了讨论。  相似文献   

矮新星AB Dra中的吸积盘模型   总被引：1，自引：0，他引：1  

李宗云  丁月蓉 《天文学报》1995,36(4):385-393

对矮新星ＡＢ Ｄｒａ的最小二乘拟合表明，黑体吸积盘模型预言的连续谱能粗略地拟合该星在爆发期间的ＩＵＥ观测，较小的偏差可以归因于光学薄气体的复合辐射或／和热斑的黑体辐射，拟合给出了一组吸积盘参量的合理值。  相似文献   

The scattered disk population as a source of Oort cloud comets: evaluation of its current and past role in populating the Oort cloud     

Julio A. Fernández  Tabaré Gallardo 《Icarus》2004,172(2):372-381

We have integrated the orbits of the 76 scattered disk objects (SDOs), discovered through the end of 2002, plus 399 clones for 5 Gyr to study their dynamical evolution and the probability of falling in one of the following end states: reaching Jupiter's influence zone, hyperbolic ejection, or transfer to the Oort cloud. We find that nearly 50% of the SDOs are transferred to the Oort cloud (i.e., they reach heliocentric distances greater than 20,000 AU in a barycentric elliptical orbit), from which about 60% have their perihelia beyond Neptune's orbit (31 AU<q<36 AU) at the moment of reaching the Oort cloud. This shows that Neptune acts as a dynamical barrier, scattering most of the bodies to near-parabolic orbits before they can approach or cross Neptune's orbit in non-resonant orbits (that may allow their transfer to the planetary region as Centaurs via close encounters with Neptune). Consequently, Neptune's dynamical barrier greatly favors insertion in the Oort cloud at the expense of the other end states mentioned above. We found that the current rate of SDOs with radii R>1 km incorporated into the Oort cloud is about 5 yr⁻¹, which might be a non-negligible fraction of comet losses from the Oort cloud (probably around or even above 10%). Therefore, we conclude that the Oort cloud may have experienced and may be even experiencing a significant renovation of its population, and that the trans-neptunian belt—via the scattered disk—may be the main feeding source.  相似文献   

密近双星中的驼峰现象     

张忠勇 《中国天文和天体物理学报》1993,(1)

本文首先介绍激变变星SU UMa型星的驼峰现象和最近发现的X射线新星中各类光变,再从理论上探讨这些光变与驼峰现象的关系,推测驼峰现象不仅出现于光学波段,而且可能出现于紫外和X射线波段.最后,建立一种由驼峰现象判断主星是否为黑洞的可能方法.  相似文献   

Formation of galactic subsystems in light of the magnesium abundance in field stars: The thick disk     

V. A. Marsakov  T. V. Borkova 《Astronomy Letters》2005,31(8):515-527

The space velocities and Galactic orbital elements of stars calculated from the currently available high-accuracy observations in our compiled catalog of spectroscopic magnesium abundances in dwarfs and subgiants in the solar neighborhood are used to identify thick-disk objects. We analyze the relations between chemical, spatial, and kinematic parameters of F–G stars in the identified subsystem. The relative magnesium abundances in thick-disk stars are shown to lie within the range 0.0 < [Mg/Fe] < 0.5 and to decrease with increasingmetallicity starting from [Fe/H] ≈ ?1.0. This is interpreted as evidence for a longer duration of the star formation process in the thick disk. We have found vertical gradients in metallicity (grad_Z[Fe/H] = ?0.13 ± 0.04 kpc^?1) and relative magnesium abundance (grad_Z[Mg/Fe] = 0.06 ± 0.02 kpc^?1), which can be present in the subsystem only in the case of its formation in a slowly collapsing protogalaxy. However, the gradients in the thick disk disappear if the stars whose orbits lie in the Galactic plane, but have high eccentricities and low azimuthal space velocities atypical of the thin-disk stars are excluded from the sample. The large spread in relative magnesium abundance (?0.3 < [Mg/Fe] < 0.5) in the stars of the metal-poor “tail” of the thick disk, which constitute ≈8% of the subsystem, can be explained in terms of their formation inside isolated interstellar clouds that interacted weakly with the matter of a single protogalactic cloud. We have found a statistically significant negative radial gradient in relative magnesium abundance in the thick disk (grad_R[Mg/Fe] = ?0.03 ± 0.01 kpc^{? 1}) instead of the expected positive gradient. The smaller perigalactic orbital radii and the higher eccentricities for magnesium-richer stars, which, among other stars, are currently located in a small volume of the Galactic space near the Sun, are assumed to be responsible for the gradient inversion. A similar, but statistically less significant inversion is also observed in the subsystem for the radial metallicity gradient.  相似文献