A model of the galactic tidal interaction with the oort comet cloud     

John J. Matese  Patrick G. Whitman 《Celestial Mechanics and Dynamical Astronomy》1992,54(1-3):13-35

We consider a model of the in situ Oort cloud which is isotropic with a random distrihution of perihelia directions and angular momenta. The energy distribution adopted has a continuous range of values appropriate for long-period (>200 yr) comets. Only the tidal torque of the Galaxy is included as a perturbation of comet orbits and it is approximated to be that due to a quasi-steady state distribution of matter with disk-like symmetry. The time evolution of all orbital elements can be analytically obtained for this case. In particular, the change in the perihelion distance per orbit and its dependence on other orbital elements is readily found. We further make the assumption that a comet whose perihelion distance was beyond 15 AU during its last passage through the Solar System would have orbit parameters that are essentially unchanged by planetary perturbations. Conversely, if the prior passage was inside 15 AU we assume that planetary perturbations would have removed the comet from the in situ energy distribution accessible by the galactic tide. Comets which had their perihelia changed from beyond 15 AU to within 5 AU in a single orbit are taken to be observable. We are able to track the evolution of 10⁶ comets as they are made observable by the galactic tidal touque. Detailed results are obtained for the predicted distribution of new (0 < 1/ < 10^–4 AU^–1) comets. Further, correlations between orbital elements can be studied. We present predictions of observed distributions and compare them with the random in situ results as well as with the actual observed distributions of class I comets. The predictions are in reasonable agreement with actual observations and, in many cases, are significantly different from random when perihelia directions are separated into galactic northern and southern hemispheres. However the well-known asymmetry in the north-south populations of perihelia remains to be explained. Such an asymmetry is consistent with the dominance of tidal torques today if a major stochastic event produced it in the past since tidal torques are unable to cause the migration of perihelia across the latitude barriers ±26°.6 in the disk model.  相似文献   

Atmospheric Angular Momentum Transport and Balance in the AGCM-SAMIL     

LI Jun  WU Guoxiong 《大气科学进展》2010,27(5):1183-1192

NCEP/NCAR reanalysis data and the spectral atmospheric general circulation Model (AGCM) of IAP/LASG (SAMIL) are employed to investigate the transport and balance of atmospheric angular momentum (AAM). It is demonstrated that SAMIL depicts the general features of the AAM transport and balance reasonably well. The AAM sources are in the tropics and sinks are in the mid-latitudes. The strongest meridional transport occurs in the upper troposphere. The atmosphere gains westerly momentum and transports it upward in the areas of surface easterlies, and downward into the areas of surface westerlies. Consequently, AAM balance is maintained. Systematic biases of the model compared to the reanalysis and observations are revealed. Possible mechanisms for these biases are investigated. In SAMIL, the friction torque in the tropics is stronger compared to the observations, which is probably due to the excessive precipitation along the Inter-tropical convergence zone (ITCZ) in the model, since the simulated Hadley circulation is much stronger than observed. In the winter half of the year, the transport center is in the lower troposphere in the SAMIL model, but it is in the upper troposphere in the reanalysis and observations. These discrepancies also suggest that simulations of convection and tropical precipitation need to be improved and that higher resolution is necessary for a quantitative simulation of AAM transport and balance. Results also demonstrate that the analysis of the transport and balance of atmospheric angular momentum is a powerful tool in diagnosing climate models for potential improvement.  相似文献   

深井中钻铤螺纹联接的强度研究   总被引：6，自引：1，他引：5       下载免费PDF全文

张焱  陈平  施太和 《探矿工程》1998,(5):21-25

改进了文献（１）中的理论模型并利用一种修正的弹簧模型,通过对石油钻柱接头螺纹的受力分析,分别建立了上扣扭矩、轴向外载作用下螺纹载荷分布的计算模型详细分析了螺纹载荷分布规律,指出了螺纹锥度,不同润滑脂的润滑所产生的摩擦系数,螺纹牙的弹性系数对螺纹联接的载荷分布规律的影响关系,给出了改善接头受力状态,减小应力集中的主要措施。还通过一种简单的力学模型得到了螺纹联接的极限轴向外载。  相似文献   

水平分量磁变仪的定向与定向检查     

朱兆才 《东北地震研究》1996,12(4):50-55

水平分量磁变仪定向与定向检查是保证记录质量的一项重要工作。本文研究表明，失磁下影响的的一般条件下，定向与定向检查均可用”扭头带动镜面法进行，日常可根据定向记录位置ｎ。监 状态。已有精确定向结果的标度线圈用于定向检查与校正操作简便，如果度盘进一步改进，检查精度也可以达到较高水平。  相似文献   

牙轮钻头振动规律分析          下载免费PDF全文

张艺伟  杨海波  赵德云  杨跃波 《探矿工程》2002,(4):29-30

通过大量的实验数据，对三牙轮钻头在井底振动时干扰力的幅值和频率进行了全面而细致的分析，摸索出了其在井底的振动规律，提高了井下钻具动力学分析的准确度，可在一定程度上减少钻具失效、节约钻井成本。  相似文献   

Are hydrodynamic shape effects important when modelling the formation of depositional remanent magnetization?     

D. Heslop 《Geophysical Journal International》2007,171(3):1029-1035

Recent conceptual models have attributed the weak depositional remanent magnetizations observed in natural sediments to flocculation processes in the water column. Magnetic particles included into flocs have not only to rotate themselves into alignment with the geomagnetic field but also the larger particles to which they are attached, making remanence acquisition an inefficient process. Alignment is hindered further when the magnetization vectors of the particles in any given floc partially cancel, reducing the overall magnetic torque. Existing numerical simulations of flocculation effects on depositional remanence formation have been limited to spherical bodies with translational and rotational motion acting independently of each other. In the case of non-spherical flocs, the translational and rotational motion are coupled and such bodies will describe a complex trajectory through the water column. Calculations will be presented that show the torque exerted on a non-spherical floc by the surrounding water can be orders of magnitude greater than the magnetic torque. Non-spherical flocs will, therefore, align less efficiently with the geomagnetic field and hydrodynamic effects may play an important role in controlling the magnitude of sedimentary remanence.  相似文献   

液力衡扭旋冲提速工具及其在达深16井的应用          下载免费PDF全文

李秋杰  王春华  李玉海  万发明  李欢欢 《探矿工程》2015,42(1):31-33，37

大庆油田深部地层岩石坚硬、研磨性强,运用常规手段钻进,单只钻头进尺少、寿命短且机械钻速较低。应用液力衡扭矩提速工具,有效解决了这些问题,显著提高了机械钻速和单只钻头的进尺。通过达深16井的现场试验证明,该工具能够使钻头的破岩方式在剪切的基础上附加机械冲击和高压水力脉冲,有效提高PDC钻头剪切岩层的效率,为深井提速提供了一种有效的手段。  相似文献   

1998年5～6月区域大气角动量收支与东亚天气尺度系统变化   总被引：1，自引：0，他引：1       下载免费PDF全文

王亚非  魏东  李琰 《高原气象》2011,30(5):1189-1194

利用NCEP/NCAR再分析资料计算了1998年5～6月区域角动量收支的主要分量,对比分析了范围较大的欧亚区域角动量矩和限制在欧亚大陆范围内的喜马拉雅山角动量矩的差异,发现两者有很好的相关,限制较小范围的计算表明,喜马拉雅山山脉力矩的作用显著。角动量收支项占较大量级的山脉力矩和摩擦力矩,并与梅雨锋区域的700hPa高度...  相似文献   

Influence of Constant Torque on Equilibria of Satellite in Circular Orbit     

V. A. Sarychev  A. Guerman  P. Paglione 《Celestial Mechanics and Dynamical Astronomy》2003,87(3):219-239

We consider the equilibria of a satellite in a circular orbit under the action of gravitational and constant torques. The number of equilibria depending on the parameters of the problem is found by the analysis of an algebraic equation of order 6. The domains with different numbers of equilibria are specified, and the equations of boundary curves are determined in function of values of the components of constant torque. Classification of different distributions of number of equilibria is made for arbitrary values of the parameters.  相似文献   

盾构刀盘偏置中心刀对刀盘推力和扭矩的影响     

冷冬梅  蔡宗熙  王燕群  侯振德 《岩土力学》2015,36(6):1776-1783

盾构机是地下工程中的典型掘进装备,具有结构复杂、体积庞大、重型巨载等特点。刀盘载荷是装备的核心力学参量,实现刀盘载荷的合理计算是装备正向设计的理论基础,也是不同地质情况隧道施工中载荷控制的重要科学依据。盾构刀盘中心刀结构在掘进过程中承受很大比重的轴向载荷,为了进一步分析中心刀结构的改变对刀盘载荷的影响,采用数值仿真方法与模型试验方法对盾构刀盘与土体的相互作用进行了研究,得到了刀盘法向和切向切削载荷空间分布规律以及掘进过程中刀盘总推力和扭矩随掘进时间的变化规律,重点分析了偏置中心刀结构对刀盘推力和扭矩的影响。对比几种不同的中心刀结构,研究表明,偏置中心刀结构刀盘的总推力与总扭矩小于鱼尾中心刀结构刀盘的总推力与总扭矩。刀盘模型试验结果与数值仿真结果趋势一致。从载荷角度考虑,偏置中心刀刀盘优于鱼尾中心刀刀盘。该研究结果可为新型刀盘结构设计提供参考。  相似文献