斜压模、正压模和异常海温时间变化的位相关系

利用 1958- 1997共 4 0年 NECP/ NCAR再分析大气资料和 GISST海表温度资料集 ,研究了大气斜压模、正压模与海表温度变化这三者之间位相关系 ,并从大气动力学方程组解释了这些位相关系。指出 :大气斜压西风异常时间变化的位相落略微后于 SSTA的变化位相 ,而正压西风异常的变化位相则超前于SSTA变化位相。斜压纬向风异常的变化又超前于正压异常纬向风的变化。斜压纬向风异常与海表温度异常之间存在正相关关系 ,而异常正压纬向风与异常海表温度之间则存在负相关关系。斜压模的产生联系于热力强迫 ,而正压模的产生则归因于斜压扰动间的非线性相互作用。这些由动力和热力过程控制的位相关系包含着ENSO循环的可能机制。

正斜压模演变所揭示的武汉暴雨过程

对 1998年 7月 2 1— 2 2日发生在武汉附近的大暴雨过程的大气正、斜压分量演变过程进行了研究 ,结果表明 :大气流场正压分量的演变与此次大暴雨的酝酿、发展和消亡具有内在的联系 ;正压分量在暴雨区的演变在一定程度上反映高、低空急流耦合形势 ;正、斜压平均相对模的演变与暴雨生命史相吻合。

亚洲季风变动与大气正压/斜压运动动能变化的气候特征

使用 NCEP/NCAR 40年 ( 1 95 8～ 1 997年 )月平均再分析资料 ,通过动力学诊断研究了大气斜压 /正压运动动能的变化及其相互转换 ,分析了亚洲季风变动与这两种动能变化的联系。指出 :季风区大气运动动能的组成和变化具有独特的特征。冬季风时期 ,大气斜压运动动能与正压运动动能具有正相关线性关系 ,斜压运动动能向正压运动动能转换 ;春、秋季无论是东亚还是印度季风区斜压运动动能与正压运动动能之间的转换都处于极小值 ,只是印度季风区始终是斜压动能向正压动能转换 ,而东亚季风区则出现正压动能向斜压动能的转换。夏季风时期季风区以斜压运动动能为主 ,而中、高纬度地区一直以正压运动动能为主。由冬至夏季风区正压动能减少并在盛夏达到极小值。春夏转换时期季风区斜压运动动能和转换因子曲线的随时间的变化位相与夏季风建立的位相同步 。

自由表面海洋环流模式的正、斜压模分解算法

大气物理研究所海洋环流模式（IAPOGCM）特点之一是消除“刚盖”近似，引入海面起伏作为模式的预报变量。为此，是设计有效的时间积分方案，以克服模式中所保留的表面重力被对时间步长的苛刻限制．本文绘出了适应过程中流场正压和斜压模分解算法。研究表明，把海洋模式适应过程进一步分解为与海面起伏相联系的正压模和与密度不均匀分布相联系的斜压模，用不同的时间步长数值来解，计算效率可提高数倍以上．文中用四层IAPOGCM在北太平洋区域定量地比较了节省计算时间的有效性，并给出数值计算实例。

ENSO循环与低纬度大气的正压和斜压运动

:利用一个 2层海洋模式和 GISST资料、NCEP再分析资料 ,对大气正压 /斜压运动与 ESNO循环之间的联系进行了研究。结果表明 ,在赤道中、东太平洋地区 ,大气斜压模在 ENSO时间尺度上的变化位相略超前于正压模的变化 ,正压模的变化位相超前于 SSTA变化 ,SSTA变化位相超前斜压模的变化位相。斜压纬向风异常与SSTA具有正相关关系 (西太平洋西部相反 ) ;正压模则与 Nino3区海温异常有负相关关系 (西太平洋西部相反 )。斜压模与海表异常加热相互激励 ,促进异常海温增长 ,是增长模 ;而正压模则抑制斜压模的和海温异常的增长 ,是转换模。正压模的位相超前对预测 El Nino/ L a Nina的发生发展具有参考意义。

阻塞流场与瞬变涡动相互作用的动力学研究

借助于一个 β通道正压模型 ,模拟了瞬变天气尺度扰动与大尺度阻塞流场相互作用 ,以及所形成的“Ω”型阻塞对风暴轴地带瞬变扰动涡列移动路径的影响 ,并用描述局地能量变化率的方程分析了能量收支情况的细致结构。结果表明 ,瞬变扰动在其与背景流场的相互作用过程中 ,在阻塞发展阶段 ,阻塞受到瞬变扰动涡的涡度和能量强迫 ,背景流场增强发展成为阻塞系统。对两种不同的阻塞流场背景下瞬变扰动能量变化的分析表明 :在阻塞区扰动瞬变涡失去能量 ,在南北边缘瞬变扰动的能量变化趋势表现为沿着阻塞外围向下游传播的特征并从背景流场得到能量 ,从而瞬变涡动由源区的一列分裂为绕行于阻塞外围的两列。在两种不同背景阻塞流场结构下瞬变涡动的移动路径表现出不同的分布特征 :当偶极子型阻塞作为背景流场时 ,瞬变涡动的移动路径呈南北对称分布于阻塞区的外缘 ;当瞬变涡的背景流场为“Ω”型阻塞时 ,瞬变扰动带受到“Ω”型阻塞流场结构的影响 ,表现出北支强南支弱的特征。这些结果与实际观测一致。

亚洲夏季风环流结构与热带印度洋偶极型海温异常

使用T42L28大气环流模式就夏季风时期大气对印度洋海温偶极子型异常的响应进行了数值试验研究,结果表明,印度洋偶极子型海温异常可以引起感热和潜热加热异常并进而形成异常辐合辐散,导致热带印度洋及其邻近地区夏季降水异常。同时此热带扰动可激发或造成中纬度异常波列。通过改变季风区温度场分布,偶极子型海温强迫可以影响大气的正/斜压环流结构和斜压性强弱。强的纬向风垂直切变趋向于靠近海洋异常偏暖的地区。不论是正偶极子型强迫或负偶极子型强迫,西太平洋暖池和东亚地区的大气环流均出现异常并激发出中纬度的异常波列,但异常类型并未显著反相。

基本气流的垂直切变作用下的低纬低频波

在低纬地区 ,风速的垂直切变也是很明显的 ,作者解释了这些纬向气流的垂直切变对低纬长波性质以及对不同模态的相互作用的影响 。

大气中非线性Kelvin波的一个特殊形态

通过对非线性方程组的求解和讨论,指出:非线性Kelvin波与线性波相比,在扰动的水平结构和时间演变上都存在着显著的差异;在波动的传播方式上也较线性情形复杂。与层结大气中的正压模态有关的波动亦有与上述类似的特征。

Low-frequency data analysis and expansion

The use of low-frequency seismic data improves the seismic resolution, and the imaging and inversion quality. Furthermore, low-frequency data are applied in hydrocarbon exploration; thus, we need to better use low-frequency data. In seismic wavelets, the loss of low-frequency data decreases the main lobe amplitude and increases the first side lobe amplitude and results in the periodic shocking attenuation of the secondary side lobe. The loss of low frequencies likely produces pseudo-events and the false appearance of higher resolution. We use models to examine the removal of low-frequency data in seismic data processing. The results suggest that the removal of low frequencies create distortions, especially for steep structures and thin layers. We also perform low-frequency expansion using compressed sensing and sparse constraints and develop the corresponding module. Finally, we apply the proposed method to real common image point gathers with good results.

Study on fault induced rock bursts

In order to study the rules of rock bursts caused by faults by means of mechanical analysis of a roof rock-mass balanced structure and numerical simulation about fault slip destabilization, the effect of coal mining operation on fault plane stresses and slip displacement were studied. The results indicate that the slip displacement sharply increases due to the decrease of normal stress and the increase of shear stress at the fault plane when the working face advances from the footwall to the fault itself, which may induce a fault rock burst. However, this slip displacement will be very small due to the increase of normal stress and the decrease of shear stress when the working face advances from the hanging wall to the fault itself, which results in a very small risk of a fault rock burst.

Ensemble Simulations of a Nonlinear Barotropic Model for the North Atlantic Oscillation

A numerical ensemble-mean approach was employed to solve a nonlinear barotropic model with chastic basic flows to analyze the nonlinear effects in the formation of the North Atlantic Oscillation （NAO）. The nonlinear response to external forcing was more similar to the NAO mode than the linear response was, indicating the importance of nonlinearity. With increasing external forcing and enhanced low-frequency anomalies, the effect of nonlinearity increased. Therefore, for strong NAO events, nonlinearity should be considered.

Vertical Structure of the Tidal Currents on the Continental Shelf of the East China Sea

The available data on tidal currents spanning periods greater than six months for the continental shelf of the East China Sea (26°30.052′N, 122°35.998′E) were analyzed using several methods. Tidal Current Harmonic Analysis results demonstrated that semi-diurnal tides dominated the current movement. The tidal currents of the principal diurnal and semidiurnal rotated clockwise with depth, with the deflection of the major semi-axes to the right in the upper layer and to the left in the lower layer. The vertical structures of two principal semi-diurnal constituents-M2 and S2-were similar, which indicates that the tidal currents are mainly barotropic in this area. The main features of the variation of the four principal tidal constituents with depth demonstrate that the currents in this region are influenced by the upper and lower boundary layers. Therefore, the tidal constituents of the shallow water are similar. Different vertical modes were calculated based on the Empirical Orthogonal Function (EOF) analysis of the Eastern and Northern components of the tidal currents, with a variance contribution for the zero-order model of at least 90%. The variance contribution of the baroclinic model is minimal, which further reveals a strong barotropic character for the tidal currents of this region.

A smart calibration model on track's pressure-sinkage characteristic of a tracked vehicle moving on soft seabed sediments

The bentonite-water mixture was selected as the substitute of seabed sediments according to the in-situ measurement data of sediments 15-20 cm deep in China's ocean poly-metallic mining contract area and the soft seabed sediments could be simulated with certain proportion of the bentonite and water; besides, based on the theory on the interaction between the vehicle and ground and referenced to Bekker's apparatus and related experimental methods, a scenario on the experimental system of the pressure-sinkage characteristics of interaction between the track of tracked vehicle and soft seabed sediments was designed. The pressure-sinkage experiments were performed with different dimensions of penetration plates. The "pressure-sinkage" model based on Bekker's formula and correlation parameters were obtained to describe the corresponding characteristics of the seabed sediments and a smart calibration model on the pressure-sinkage characteristic of the track was established based on the function chain neural network, which could provide boundary loading conditions for simulation analysis of the tracked vehicle moving on the seabed.

Impact of nonlinear processes on formation of the Kuroshio large meander path in a barotropic inflow-outflow model

Based on a barotropic inflow-outflow model,we examine the formation of the Kuroshio large meander(LM) using conditional nonlinear optimal perturbation(CNOP) method.Both linear and nonlinear evolutions of such perturbations obtained by this method are investigated.The results show that the nonlinear evolution can result in the Kuroshio transition from a straight to LM path,whereas the linear evolution cannot.This implies that nonlinearity plays an important role in the formation of the Kuroshio LM path.The nonlinearity exists as advection in the evolution equations of the perturbation derived from the barotropic inflow-outflow model,namely the nonlinear advection of the perturbation by the perturbation(NAPP).By examining the role of this nonlinearity,we find that the NAPP tends to move the cyclonic eddy induced by the CNOP-type perturbation westward.Together with the beta effect,this offsets part of the eastward advection caused by the interaction between the perturbation and the background flow.Hence,the eastward movement of the cyclonic eddy is significantly weakened,effectively causing the eddy to develop.The sufficient evolution of this cyclonic eddy leads to the formation of the Kuroshio LM.

Single-jet Spray Mixing with a Confined Crossflow

In order to achieve uniform mixing between spray droplets and crossflow, cold-model experiment of a hollow-cone water spray in an air crossflow is investigated via a numerical simulation. The simulation cases are designed by using the orthogonal design method. The Eulerian-Lagrangian formulation is employed for modeling the droplets-crossflow two-phase flow while the realizable k-ε turbulence model is used to describe the turbulence. A new index, mixedness quality, is proposed to assess the overall mixing of the droplets in the crossflow. The simulation results demonstrate that the counter-rotating vortex pair (CVP) imposes a more significant impact on the spatial distribution than on the size distribution of the droplets. Pairs of CVP with smaller scales are preferable for achieving a better mixing. The influencing factors are listed in the following order in terms of the degree of their impact from the greatest to the least: the Sauter diameter of the initial droplets, the mixing tube diameter, the spray angle, the velocity of the inlet crossflow, and the vertical velocity of the initial droplets. A moderate droplet diameter, a smaller tube diameter, a moderate spray angle, a greater crossflow velocity and a moderate vertical velocity of the droplet are favorable for achieving a higher mixedness quality of the jet spray in a confined crossflow.

Forward hot extrusion forming process of 4-lobe aluminum alloy helical surface rotor

The 4-lobe aluminum alloy helical surface rotors are widely applied in industry,such as superchargers.Generally,the conventional manufacturing processes of aluminum alloy helical surface are time consuming and costly.To make the manufacturing processes more flexible and economical,the forward hot extrusion process is proposed to form the 4-lobe aluminum alloy helical surface rotors.In this work,we implement both simulations and experiments to the forming process of the helical surface,of which the material is 6063 aluminum alloy.The forward hot extrusion process is simulated with finite element method in DEFORM-3D.Based on the simulation method,the influences of different extrusion parameters,such as extrusion temperature,extrusion speed and extrusion ratio,on the extrusion process are studied.According to the numerical simulation results,the optimal case is chosen to carry out the experiment.Furthermore,the experimental results show that the surface is smooth;the toothed fill is full;the twist angle in the length direction is evenly distributed;the value of twist angle is roughly in line with the design angle,which is mainly due to the modified die structure,having a positive and significant effect on the increment of twist angle.Therefore,the twist angle has an increase of about 76%,which verifies the modified die structure.

3D numerical simulation of high pressure squeezing process with revised Drucker-Prager/Cap model

In order to investigate the sand mold strength after the aeration sand filling-high pressure squeeze moldingprocess,a tree-dimentional(3D)numerical simulation was introduced.The commercial finite element method(FEM)software ABAQUScombined with a revised Drucker-Prager/Cap model was used to simulate the squeeze compaction process.Additionally,the sand bulk density after the aeration sand filling process was tested by a specially designed experiment,which divided the whole sand bulk in the molding chamber into5x9regions and it was used as the input to simulate the squeeze process.During the simulation process,the uniform modeling simulation and the patition modeling simulation methods were used a d the3D numercal simulation results were compared with correlative benchmark testings.From the3D numerica simulation results,it can be concluded that the uniform sand bulk density distribution can obtain a high quality sandmold and the revised Drncker-Pager/Cap model is suitable for handling the situation with the complex paaern.The3D numerical simulation results can predict well the sand mold strength distribution and can be used as guidelines for the production practice.

Accurate Reactive Power Controller and Power Factor Correction Using Fuzzy Logic

This paper presents the use of fuzzy logic technique to control the reactive power of load and hence improve the source power factor. A shunt compensator is proposed, which consists of a voltage controlled reactor by full-wave thyristor bridge in parallel with a capacitor. The proposed voltage control technique composed of two independent fuzzy controllers, primary and secondary. The PFC （primary fuzzy controller） is designed based on linearization method to introduce to the network the nearest value of reactive power （VAR） required to correct the power factor. The SFC （secondary fuzzy controller） is designed to achieve accurate compensation for the required VAR to achieve the pre-set power factor value. Simulations for 15 different practical study cases are presented to evaluate the performance of the controller, and the results show how the designed controller is fast and accurate. Harmonics analyses are carried out up to the 13th harmonic to determine the requirement of harmonics filter.