非连续问题中单元分割的模板方法

扩展有限元法(extended finite element method, XFEM)因具有裂纹几何独立于模拟网格、裂纹扩展时无需网格重分重映、计算精度高等优点,成为裂纹分析的主流数值方法之一.但该方法在工程实践中存在单元被裂纹分割的几何困难——现有精确几何分割方法实现复杂、计算量大、鲁棒性差.为克服这一困难,本文提出一种基于单元水平集的模板分割方法,用于非连续单元子剖分和数值积分.首先,遍历单元水平集值所有形态并建立标准单元分割模板库;然后,根据单元水平集值,对非标准单元进行形态查询和模板插值;最后,套用标准单元分割模板实现单元高效分割和子剖分.将该方法与常规XFEM、改进型XFEM进行结合,从而应用于孔洞、夹杂、裂纹等非连续问题分析中.算例分析表明,本文提出的模板分割方法具有较高计算精度.由于不引入复杂几何操作,该模板分割方法同时具有较高计算效率和鲁棒性,故可为XFEM类方法在实际工程应用中提供有效支撑.

三维非匹配网格上的扩散方程数值求解

将子网格剖分的支撑算子方法,拓展应用于三维非匹配网格上的扩散方程求解.算例表明该方法在正交非匹配网格上能够精确获得线性解;在一般非匹配网格上可以达到二阶精度;在求解曲面网格和节点不共面网格时,精度比平面近似的方法要高,也可以达到2阶精度,同时也适合求解含有物质界面的混合介质网格.

Salt－Water Dynamics in Soils：IV．Changes of Ionic Composition in Soil Profiles During Water Evaporation and Infiltration

Through a simulation test carried out with soil columns (61.8 cm in diameter), the changes of ioniccomposition in soil profile during the processes of water evaporation and infiltration were studied. Underevaporation conditions, ions moving upward with fresh groundwater were mainly Cl￣-, SO, Ca￣(2+), andNa￣+. When the mineralized groundwater took part in the salt accumulation, the ionic composition in soilswas close to that in ground water supplemented. Under rainfall infiltration conditions, the salt-leaching roleoccurred mainly in the top soil. With the decrease of total salt content, NO and Cl￣- reduced rapidly, SOdecreased slowly, but HCO had a little change only. Among cations, Na￣+ and Ca￣(2+) contents lowered atthe same speed, and Mg￣(2+) decreased slowly.

Molecular Dissection of Bombyx mori Nucleopolyhedrovirus orf8 Gene

Viruses including baculoviruses are obligatory parasites, as their genomes do not encode all the proteins required for replication. Therefore, viruses have evolved to exploit the behavior and the physiology of their hosts and olden coevolved with their hosts over millions of years. Recent comparative analyses of complete genome sequences of baculoviruses revealed the patterns of gene acquisitions and losses that have occurred during baculovirus evolution. In addition, knowledge of virus genes has also provided understanding of the mechanism of baculovirus infection including replication, species-specific virulence and host range. The Bm8 gene of Bombyx mori nucleopolyhedrovirus （NPV） and its homologues are found only in group I NPV genomes. The Autographa californica NPV Ac 16 gene is a homologue of Bm8 and, encodes a viral structural protein. It has been shown that BmS/Ac 16 interacts with baculoviral and cellular proteins. BmS/Ac 16 interacts with baculoviral IE1 that is facilitated by coiled coil domains, and the interaction with IE1 is important for Bin8 function. Acl6 also forms a complex with viral FP25 and cellular actin and associates with membranes via palmitoylation. These data suggested that this gene family encodes a multifunctional protein that accomplishes specific needs of group I NPVs.

Global characteristics of the second-order ionospheric delay error using inversion of electron density profiles from COSMIC occultation data

It is a well known fact that ionospheric delay error is a predominant factor which influences the positioning accuarcy of GNSS.Although the main part of the first-order ionospheric delay error can be removed by the frequency-dependent behaviors of the ionosphere,the second-order ionospheric delay error must be eliminated to achieve millimetre-scale positioning accuracy.Due to COSMIC occultation providing electron density profiles on the global scale,the paper presents the first-order and the second-order ionospheric delay error analysis on the global scale using the inversion of electron density profiles from COSMIC occultation data during 2009–2011.Firstly,because of the special geographical location of three ISR(incoherent scatter radar),the first-order and the second-order ionospheric delay errors are calculated and discussed;the paper also shows and analyzes the diurnal,seasonal,semi-annual variation of ionospheric delay error with respect to signal direction.Results show that for the L1 signal path,the first-order ionospheric delay error is the largest near the equator,which is circa 7 m;the maximum second-order ionospheric delay error are circa 0.6 cm,0.8 cm and 0.6 cm respectively for L1 signals coming from the zenith,the north and the south at 10 degree elevation angles.The second-order ionospheric delay error on the L1 signal path from zenith are the symmetry between 15°and 15°with respect to magnetic equator,and are nearly zero at the magnetic equator.For the first time,the second-order ionospheric delay error on the global scale is presented,so this research will greatly contribute to analysing the higher-order ionospheric delay error characteristics on the global scale.

Experimental study of a supersonic turbulent boundary layer using PIV

Particle image velocimetry was applied to the study of the statistical properties and the coherent structures of a fiat plate turbulent boundary layer at Mach 3. The nanoparticles with a good flow-following capability in supersonic flows were adopted as the tracer particles in the present experiments. The results show that the Van Driest transformed mean velocity profile satisfies the incompressible scalings and reveals a log-law region that extends to yld=0.4, which is further away from the wall than that in incompressible boundary layers. The Reynolds stress profiles exhibit a plateau-like region in the log-law region. The hairpin vortices in the streamwise-wall-normal plane are identified using different velocity decompositions, which are similar to the results of the flow visualization via NPLS technique. And multiple hairpin vortices are found moving at nearly the same velocity in different regions of the boundary layer. In the streamwise-spanwise plane, elongated streaky structures are observed in the log-law region, and disappear in the outer region of the boundary layer, which is contrary to the flow visualization results.

Line-profile analysis of excitation spectroscopy in the even 4p^5(~2P_(1/2))nl′ [K′]_J(l′=1,3) autoionizing resonances of Kr

The even-parity autoionizing resonance series 4p^5np＇ [3/2] 1,2, [ 1/2] 1, and 4p^2nf＇ [5/213 of krytpon have been investigated by laser excitation from the two metastable states 4p55s [3/2]2 and 4p^55s＇ [1/2]0 in the photon energy region of 2900（P40000 cm^-1 at experimental bandwidth of -0.1 cm-1. The excitation spectra of the even-parity autoionizing resonance series, most of which are experimentally studied for the first time in this work, show typical asymmetric line shapes. Complementary information on level energies, quantum defects, line profile indices and resonance widths, resonance lifetimes and reduced widths of the auto- ionizing resonances are derived by Fano-type line-shape analyses of the experimental results. Results from this work indicate that the line profile index （q） and the resonance width （F） are approximately proportional to the effective principal quantum number （n＊）; the line separation of the 4p^5np＇ autoionizing resonances is also in good agreement with theoretical model