2001年1月滇黔准静止锋在演变过程中的结构及大气环流特征分析

利用地面常规观测资料和NCEP/NCAR再分析资料,分析2001年1月的滇黔准静止锋在演变过程中的温湿结构和大气环流特征。结果表明：滇黔准静止锋表现为湿度锋,其大气环流特征与高原关系密切。青藏高原的抬升作用与Hadley环流偏南导致Ferrel环流的生成、加强对云贵高原的天气有重大的影响。对于I、Ⅱ型静止锋,Hadley环流圈南北跨距小,环流圈下沉支偏南,易与高原南部的上升支一起形成反环流,该反环流可产生较强的雨雪、凝冻的灾害性天气;Ⅲ、IV型静止锋,Hadley环流圈北推,环流圈南北跨距大,此时在青藏高原的南部无反环流存在,云贵地区上升运动较弱,产生的降水与天气也较弱。由于受副高增强的间接影响,Hadley环流在Ⅱ、Ⅲ、IV型静止锋存在明显的双层结构。     

两层流体中振荡水平圆柱潜体水动力特性

研究了有限深两层流体中水平圆柱潜体的振荡辐射问题。在线性势流理论框架内,建立求解辐射势的多极展开理论,提出附加质量和阻尼系数的计算方法,进行了数值计算分析,并且与均匀流中的情况进行比较。结果表明,在圆柱潜体的某个振荡频率范围内,流体的分层效应对其附加质量和阻尼系数是有重要影响的。同时,对水平圆柱潜体振荡产生的自由面和内界面波动特性进行了数值分析。     

基于Winkler模型的有效桩长研究

有效桩长的定义有基于承载力角度和沉降角度两种方法,由于影响因素的多样性,有效桩长的研究比较复杂。运用桩顶刚度控制法确定有效桩长。基于Winkler地基模型,以荷载传递法为工具,推导出双层土的桩顶刚度计算公式,并对有效桩长影响因素进行了分析。结果表明,桩径的增大有效桩长增加;土层刚度比(第二层土刚度与第一层土刚度之比)增大有效桩长减小;桩端刚度的增大对有效桩长的影响都不明显,第一土层厚度的增加在一定范围内对提高有效桩长是有用的     

Interaction of Linear Waves with Infinitely Long Horizontal Cylinders Studied by Boundary Element Method

The two-dimensional problems concerning the interaction of linear water waves with cylinders of arbitrary shape in two-layer deep water are investigated by use of the Boundary Integral Equation Method (BIEM). Simpler new expressions for the Green functions are derived, and verified by comparison of results obtained by BIEM with those by an analytical method. Examined are the radiation and scattering of linear waves by two typical configurations of cylinders in two-layer deep water. Hydrodynamic behaviors including hydrodynamic coefficients, wave forces, reflection and transmission coefficients and energies are analyzed in detail, and some interesting physical phenomena are observed.     

Second-Order Solutions for Random Interfacial Waves Under Steady Uniform Currents

1.Introduction Owingtothesimilaritiesbetweenthesurfacewaveandtheinterfacialwave,itisnaturaltoapply themethodsdevelopedforsurfacewavestothestudyofinterfacialwavesasreviewedbyUmeyama (1998;2000).Recently,Song(2004)derivedsecond ordersolutionsforrandominterfacialwavesat aconstantdepthinatwo layerfluidsystemwitharigidlidusinganexpansiontechnique,analogousto thatusedbyLonguet Higgins(1963)andSharmaandDean(1979),tostudyrandomsurfacewaves. Inthispaper,Song’sresultsareextendedtoamoregeneralcaseoft…     

双层环境中圆桩柱对斜坡异重流动力特性影响的试验研究

利用开闸式异重流水槽试验,结合高速相机和粒子图像测速技术,量化不同强度双层环境中圆桩柱对斜坡异重流传播模式、速度与涡度场、波流作用等宏微观特性的影响。试验结果表明：在低理查森数Ri_ρ环境中,圆桩柱的存在抑制了异重流混合层厚度的增加,但延展了其在流向的长度;在高理查森数Ri_ρ环境中,圆桩柱打破了侵入流在密度跃层处对称的传播模式,并促进了异重流与环境流体的剪切过程。当内波弗劳德数Fr> 1时,产生锁定波,异重流头部出现强漩涡,在密度跃层产生有利压力梯度使内波尺寸增大;当内波弗劳德数Fr <1时,振荡产生发射波,波谷与异重流头部相互作用而使波形变平整;当内波弗劳德数Fr≈1时,锁定波和发射波并存。在低理查森数Ri_ρ环境中,圆桩柱的存在导致波流耦合作用减弱,而在高理查森数Ri_ρ环境,波流耦合作用反而增强。     

Higher-order Boussinesq-type equations for interfacial waves in a two-fluid system

Interfacial waves propagating along the interface between a three-dimensional two-fluid system with a rigid upper boundary and an uneven bottom are considered. There is a light fluid layer overlying a heavier one in the system, and a small density difference exists between the two layers. A set of higher-order Boussinesq-type equations in terms of the depth-averaged velocities accounting for stronger nonlinearity are derived. When the small parameter measuring frequency dispersion keeping up to lower-order and full nonlinearity are considered, the equations include the Choi and Camassa’s results (1999). The enhanced equations in terms of the depth-averaged velocities are obtained by applying the enhancement technique introduced by Madsen et al. (1991) and Schaffer and Madsen (1995a). It is noted that the equations derived from the present study include, as special cases, those obtained by Madsen and Schaffer (1998). By comparison with the dispersion relation of the linear Stokes waves, we found that the dispersion relation is more improved than Choi and Camassa’s (1999) results, and the applicable scope of water depth is deeper.     

浙江大桥坞铀矿床斑岩体的“双层结构”与铀矿化

大桥坞斑岩型铀矿床产于中生代蒙山破火山口中一石英斑岩体的内外接触带及其隐爆角砾岩筒中。铀成矿主要与斑岩体的“双层结构”有关,即”双层结构”成矿模式。浅部石英斑岩为含矿岩体,深部花岗斑岩为矿源岩体。矿化以裂隙型、角砾型为主,矿体的形态主要呈细脉状、浸染状,与围岩界线不清。成岩物质来源于壳幔混源的富铀钙碱性岩浆。成矿物质主要来源于该深部富铀花岗岩浆冷凝结晶分异产生的富铀岩浆期后热液。其成矿过程主要是富铀岩浆期后热液流体沿断裂构造系统上升、运移,在浅部石英斑岩体内外接触带发生隐爆,成岩成矿。早期铀-赤铁矿化阶段形成贫铀矿化,晚期铀-金属硫化物矿化阶段,形成富铀矿化,两期叠加作用致富。     

Statistical equilibrium distributions of baroclinic vortices in a rotating two-layer model at low Froude numbers

The point-vortex equilibrium statistical model of two-layer baroclinic quasigeostrophic vortices in an unbounded f-plane is examined. A key conserved quantity, angular momentum, serves to confine the vortices to a compact domain, thereby justifying the statistical mechanics model, and also eliminating the need for boundary conditions in a practical method for its resolution. The Metropolis method provides a fast and efficient algorithm for solving the mean field non-linear elliptic PDEs of the equilibrium statistical theory. A verification of the method is done by comparison with the exact Gaussian solution at the no interaction limit of zero inverse temperature. The numerical results include a geophysically and computationally relevant power law for the radii at which the most probable vortex distribution is non-vanishing: For fixed total circulation, and fixed average angular momentum, the radii of both layers are proportional to the square root of the inverse temperature β. By changing the chemical potentials μ of the runs, one is able to model the most probable vorticity distributions for a wide range of total circulation and energy. The most probable vorticity distribution obtained at low positive temperatures are consistently close to a radially symmetric flat-top profiles. At high temperatures, the radially symmetric vorticity profiles are close to the Gaussian distribution.