Numerical evaluation of passive control of VIV by small control rods

Flow past a circular cylinder with multiple small control rods is studied by numerical simulation for Re_D ranging from 1161.3 to 6387.1. The Reynolds-Averaged-Navier–Stokes (RANS) equations and shear stress transport (SST) k − ω turbulence model are used to calculate the vortex field, while a fourth-order Runge–Kutta method is employed for evaluating the structure dynamics of the cylinder group. Comparisons with experimental results demonstrate the validation of this method. This study is concerned with the vortex induced vibration (VIV) suppression efficacy of small control rods placed around a main cylinder. The effects of control rod number, diameter ratio, spacing ratio and Reynolds number on the hydrodynamics and vibration responses of the main cylinder are investigated. The reduced percents of in-line and cross-flow amplitudes and the increased percents of the whole cross-sectional area of cylinders and the drag coefficient are used to give a comprehensive evaluation. Results of simulation indicate that placing small rods with appropriate number at appropriate locations can achieve good suppression effectiveness at a wide range of Reynolds number. The numerical result for the case with nine control rods, diameter ratio of 0.15 and spacing ratio of 0.6 shows the best suppression effect among the cases investigated in this study.     

全球50 km分辨率SNU-AGCM模式模拟热带气旋活动

为了验证50 km分辨率的SNU-AGCM模式(Seoul National University Atmospheric General Circulation Model)模拟TC活动的能力, 利用Hadley中心月平均海温资料驱动模式, 模拟了1980—2009年全球热带气旋的活动特征。与观测资料对比分析, 两组利用不同对流参数化方案的试验, 都能够模拟与观测类似的TC结构以及全球TC活动的主要特点, 包括全球生成总频数、各海区路径分布和TC活动的季节变化。但是各个海域TC生成的年平均频数与观测还存在明显差异。模式中西北太平洋和南太平洋两组试验平均的TC频数较观测分别偏多21.5%和31.3%;而北大西洋、南北印度洋分别偏少11.4%、41.1%和50%。模拟的东北太平洋TC比观测少了将近88%, 而观测中TC极少的南大西洋在两组试验中平均每年却有1.5个TC生成。模拟的TC频数较观测的差异主要与模拟的北印度洋季风、西北太平洋季风槽、垂直风切变、850 hPa相对涡度与观测的差异有关。     

Dependence on the observational time intervals and domain of convergence of orbital determination methods

In the framework of the orbital determination methods, we study some properties related to the algorithms developed by Gauss, Laplace and Mossotti. In particular, we investigate the dependence of such methods upon the size of the intervals between successive observations, encompassing also the case of two nearby observations performed within the same night. Moreover we study the convergence of Gauss algorithm by computing the maximal eigenvalue of the jacobian matrix associated to the Gauss map. Applications to asteroids and Kuiper belt objects are considered.     

Propagation of blind normal faults to the surface in basaltic sequences: Insights from 2D discrete element modelling

A discrete element model is used to investigate the progressive deformation of a thin basaltic cover overlying a pre-existing, blind, normal fault as it propagates to the surface. The cover materials representing basalt are homogeneous, strong and display elastic-brittle material behaviour. Cover deformation is seen to evolve through a series of distinct stages. Initial displacement on the underlying fault produces a very gentle, monoclinal, flexure. With continued displacement, open fractures develop at the monocline surface and propagate downwards, whilst the deeper fault propagates upwards. Simultaneously, a series of fractures, in the future hanging-wall of the main fault, develop in the upper part of the cover. The monoclinal flexure is then cut by these structures, producing a surficial fault- and fracture-bounded wedge. Finally, a prominent surface fracture and the upward-propagating fault link, cutting the entire cover sequence. This fault is dilatant in the upper c. 100 m of the cover, has a significant surface aperture and forms a prominent fault scarp. Many of the key model results are strikingly similar to those seen in natural settings, and emphasise that the occurrence of dilatant faults, open fractures and cavities/caves in extensional settings is not necessarily restricted to the very shallow section but can extend to several hundred metres depth. Therefore, the results have implications for permeability and fluid flow in such settings. Comparison is also made with a weak cover experiment, using granular materials with no cohesion or tensile strength, similar to the dry sand used in many analogue modelling studies.     

FRY应变测量法的计算机模拟制图程序及应用

本文设计了一个简便的Fry应变测量法的计算机制图求解程序,将实测的标志体中心点化为坐标值输入机内,便可得到一张完整的Fry图解。本文还就Fry图解的正确解释和应用问题进行了讨论。     

MHD simulations of rayleigh-taylor instability in young supernova remnants

Radio observations shows that young supernova remnants such as Tycho and Cas A generally exhibit a circular clumpy shell. This shell shows a radial magnetic field whose equipartition strength is 2 to 3 orders of magnitude higher than the interstellar field. A simple compression of the ambient field by the shock can explain neither of these observations. We show that the Rayleigh-Taylor instability which occurs at the ejecta/ISM interface can explain these observations. We have done MHD simulations of the instability in the shell of Type-I supernova remnants for the first time by utilizing moving grid technique. Our simulation shows that Rayleigh-Taylor and Kelvin-Helmholtz instabilities amplify ambient magnetic fields locally and produce the clumpy radio shell. Strong magnetic field lines draped around the Rayleigh-Taylor fingers produce the radial B-vector polarization, whereas thermal bremsstrahlung from the dense fingers themselves produce the clumpy X-ray emission.     

分形图象模拟及生成

本文对一门新兴的图象学分支－分形图象学的基本内容作简单介绍。对分形图象模拟及生成的一般技巧和方法作了阐述。依据这些方法，给出了在计算机上实现的六个典型分形图模拟及生成的结果。本文同时对分形图象模拟及生成在天文学中的可能应用作了讨论     

“数字城市”中网络模拟实验系统建设研究

 本文就推动“数字城市”的顺利发展,提出了一个建设网络模拟实验系统的新的组织结构方式。就此较为详细地阐述了该系统的意义与功用,并指出适用的建设原则和首要任务,同时予以示例说明     

鲁山县农村地籍调查控制测量中坐标系统的建立方法

以县行政辖区为例,较详细地论述了在控制测量中应考虑的变形因素,以及解决变形的办法,详细地叙述了建立独立坐标系的作用及建立独立坐标系的方法,并介绍了因提高归化高程面而产生新椭球后的一些椭球常数的计算方法和步骤。