Numerical Simulation of Microphysics in Meso-β-Scale Convective Cloud System Associated with a Mesoscale Convective Complex

Numerical simulation of meso-β-scale convective cloud systems associated with a PRE-STORM MCC case has been carried out using a 2-D version of the CSU Regional Atmospheric Modeling System (RAMS) nonhydrostatic model with parameterized microphysics. It is found that the predicted meso-r-scale convective phenomena arc basically unsteady under the situation of strong shear at low-levels, while the meso-β-scale convective system is maintained up to 3 hours or more. The meso -β- scale cloud system exhibits characteristics of a multi-celled convective storm in which the meso-r-scale convective cells have lifetime of about 30 min. Pressure perturbation depicts a meso-low after a half hour in the low levels. As the cloud system evolves, the meso-low intensifies and extends to the upshear side and covers the entire domain in the mid-lower levels with the peak values of 5-8 hPa. Temperature perturbation depicts a warm region in the middle levels through the entire simulation period. The meso-r-scale warm cores with peak values of 4-8 ℃ are associated with strong convective cells. The cloud top evaporation causes a stronger cold layer around the cloud top levels.Simulation of microphysics exhibits that graupel is primarily concentrated in the strong convective cells forming the main source of convective rainfall after one hour of simulation time. Aggregates are mainly located in the stratiform region and decaying convective cells which produce the stratiform rainfall. Riming of the ice crystals is the predominant precipitation formation mechanism in the convection region, whereas aggregation of ice crystals is the predominant one in the stratiform region, which is consistent with observations. Sensitivity experiments of ice-phase mierophysical processes show that the microphysical structures of the convective cloud system can be simulated better with the diagnosed aggregation collection efficiencies.

Observation and Numerical Simulation of Cloud Physical Processes Associated with Torrential Rain of the Meiyu Front

Cloud micro-physical structures in a precipitation system associated with the Meiyu front are observed using the balloon-borne Precipitation Particle Image Sensor at Baoshan observatory station, Shanghai during June and July 1999. The vertical distributions of various cloud particle size, number density, and mass density are retrieved from the observations. Analyses of observations show that ice-phase particles (ice crystals, graupel, snowflakes, and frozen drops) often exist in the cloud of torrential rain associated with the Meiyu front. Among the various particles, ice crystals and graupel are the most numerous, but graupel and snow have the highest mass density. Ice-phase particles coexist with liquid water droplets near the 0°C level. The graupel is similarly distributed with height as the ice crystals. Raindrops below the 0°C level are mainly from melted grauple, snowflakes and frozen drops. They may further grow larger by coalescence with smaller ones as they fall from the cloud base. Numerical simulations using the non-hydrostatic meso-scale model MM5 with the Reisner graupel explicit moisture scheme confirm the main observational results. Rain water at the lower level is mainly generated from the melting of snow and graupel falling from the upper level where snow and graupel are generated and grown from collection with cloud and rain water. Thus the mixed-phase cloud process, in which ice phase coexists and interacts with liquid phase (cloud and rain drops), plays the most important role in the formation and development of heavy convective rainfall in the Meiyu frontal system.

NUMERICAL SIMULATION OF EXTREMELY HEAVY RAIN AND MESO-β SCALE LOW VORTEX IN INVERTED TYPHOON TROUGH

Large-scale and mesoscale analyses are made for extremely heavy rain (EHR) and meso-β scale low vortex (MSLV) in Jiading District of Shanghai Municipality during 6-7 July 2001.It is shown that the EHR forms in the situation of northern westerly trough linking together with southern inverted typhoon trough at northwest side of the West Pacific Ocean subtropical high. Numerical simulation is made using a 21-layer improved REM (regional η coordinate model) for this course.The results show that the precipitation forms earlier than MSLV.and the strong convergence in wind velocity mate (WVM) triggers the strong precipitation.The formative reasons of WVM.especially the weak wind velocity center are discussed,and the formative mechanisms of the MSLV and EHR are discussed using high spatial and temporal resolution model- output physical fields.The results show that the heavy rain releases latent heat and warms the air column,and enhances the low level positive vorticity that existed before.Then it causes the formation of MSLV.There is a positive feedback mechanism between low vortex and precipitation,so CISK must be an important mechanism.

Numerical Simulation on Development Mechanism of Meso-β Scale Flow Field During a Heavy Rain Process in Henan Area

Numerical simulation of a heavy rainfall case in Henan area during 16-17 July 2004 is performed using the LASG （State Key Laboratory of Numerical Modelling for Atmospheric Sciences and Geophysical Fluid Dynamics） mesoscale model AREM （Advanced Regional Eta Model） developed by Yu （1989） and Yu et al. （1994）. The results are shown： the air in the middle part of troposphere within the horizontal range of meso-β scale convective system is heated by condensation latent heat. The isobaric surface in the middle and upper part of troposphere is rising, and thus meso-β scale high is formed; the isobaric surface in the lower part of troposphere is depressed, and thus meso-β high and low layer flow promotes the strong development scale low is formed. The interaction between the of the vertical motion. While the rising motion is developing strongly, obvious compensation sinking motion appears around it. In the south of rising motion region, the divergence current in the upper part of troposphere backflows towards south, which leads to the vertical circulation appearing in the upper part of troposphere. The sinking branch of the circulation integrates in the compensation sinking air current in the south of rising motion region and takes the horizontal momentum of upper air to the lower part of troposphere and forms a new meso-β scale jet. In the north of the rising motion region, a mesoscale vertical circulation develops in the low layer of troposphere. The divergence current of the sinking branch of the circulation, which flows southward, converges with warm and humid air current in the low layer of troposphere which flows from southwest, and forms a meso-β scale convergence line. Then it strengthens the convergence over the low level of heavy rain area. In the east of the rising motion region, a mesoscale vertical circulation also develops in low layer of troposphere. The divergence current of the sinking branch of the circulation, which flows westward, causes originally more consistent southwest air current in this region to the east deflection, and thus forms the cyclone curve in the southwest air current. The convergence is further strengthened in the meso-β scale convergence line. The strong development of ageostrophic vorticity in the lower part of troposphere is the important factor of the formation of the meso-β scale cyclone. At last the three-dimensional structure chart of development of heavy rain meso-β scale stream filed is given.

弯-剪-扭复合受力CFRP布加固RC梁抗扭性能细观数值分析

为了研究弯-剪-扭复合受力条件下碳纤维增强复合材料(carbon fiber reinforced polymer, CFRP)布加固钢筋混凝土(reinforced concrete, RC)梁的抗扭性能,建立体现混凝土材料非均质性、钢筋-混凝土黏结滑移关系和CFRP布-混凝土相互作用关系的细观数值分析模型。由于缺乏CFRP布加固RC梁在弯-剪-扭复合受力作用下失效破坏的典型物理试验,采用复合对比验证法对数值模型的合理性进行验证,即分别与单独受剪、单独受扭以及受弯-扭复合作用下RC梁和CFRP布加固RC梁的试验结果进行对比验证。进而,基于建立的细观数值分析模型探究了配纤率和扭弯比对CFRP布加固RC梁在弯-剪-扭复合受力作用下抗扭力学性能的影响。结果表明:1)采用CFRP布加固能够显著提高RC梁的峰值扭矩;2)随配纤率增加,RC梁损伤分布范围逐渐变大,CFRP布应变逐渐减小,梁整体峰值扭矩增大,但其增大幅度减小;3)随扭弯比增加,RC梁裂缝分布愈加集中,裂缝与水平方向夹角逐渐减小,梁整体峰值扭矩增大,CFRP布应变减小。建立的考虑弯-剪-扭复合受力作用的数值模拟方法可为后续研究复杂应力状态下CFRP布加固RC梁尺寸效应行为等奠定基础。

Analysis of a Group of Weak Small-Scale Vortexes in the Planetary Boundary Layer in the Mei-yu Front

A mei-yu front process in the lower reaches of the Yangtze River on 23 June 1999 was simulated by using the fifth-generation Pennsylvania State University-NCAR （PSU/NCAR） Mesoscale Model （MM5） with FDDA （Four Dimension Data Assimilation）. The analysis shows that seven weak small mesoscale vortexes of tens of kilometers, correspondent to surface low trough or mesoscale centers, in the planetary boundary layer （PBL） in the mei-yu front were heavily responsible for the heavy rainfall. Sometimes, several weak small-scale vortexes in the PBL could form a vortex group, some of which would weaken locally, and some would develop to be a meso-α-scale low vortex through combination. The initial dynamical triggering mechanism was related to two strong currents： one was the northeast flow in the PBL at the rear of the mei-yu front, the vortexes occurred exactly at the side of the northeast flow; and the other was the strong southwest low-level jet （LLJ） in front of the Mei-yu front, which moved to the upper of the vortexes. Consequently, there were notable horizontal and vertical wind shears to form positive vorticity in the center of the southwest LLJ. The development of mesoscale convergence in the PBL and divergence above, as well as the vertical positive vorticity column, were related to the small wind column above the nose-shaped velocity contours of the northeast flow embedding southwestward in the PBL, which intensified the horizontal wind shear and the positive vorticity column above the vortexes, baroclinicity and instability.

Numerical study on structure of meso-β scale rainstorm system during IOP523 of HUAMEX

One of the scientific goals of HUAMEX (Torrential Rainfall Experiment over Both Sides of the Taiwan Strait and Adjacent Area), a special project in the National '863' Scientific Project, is to reveal meso-β scale structure of heavy rainfall. However, limited by the observational instruments, the resolution of the data attained from the outfield scientific observation network cannot reveal the meso-β scale structure. A 36-h numerical simulation of heavy rainfall case from May 23 to May 24, 1998 during IOP523 of HUAMEX was performed by the mesoscale numerical model of PSU/NCAR MM5, and the meso-p scale structure of con-vective system was examined based on the model output in this note. The results point out that the meso-β scale features of the heavy rainfall are clear considerably at low, middle and upper levels, respectively. There is a strong ageostrophic feature between the geopotential height field and the wind field on the upper level. The vertical cross sections of 54 km coarse grid and 18 km

THREE-DIMENSIONAL ELASTIC ATMOSPHERIC NUMERICAL MODEL AND THE SIMULATION OF A SEVERE STORM CASE

A three-dimensional meso-γ,scale elastic atmospheric numerical model has been established and used to simulate a severe storm case.The important characteristics of the modeled storm are close to those of the observed case.

NUMERICAL STUDY OF A MESO-β SCALE RAINSTORM EVENT

Diagnosis is performed of a thunderstorm rainstorm event occurring in the summer of 1996 at Nanjing and numerical simulation undertaken in the context of hydrostatic equilibrium framework of MM5 as the fifth version of the PSU/NCAR mesoscale model.Analyses show that the rainstorm-associated thermal condition was the accumulation of unstable potential energy and the dynamic condition was vigorous convergence updrafts.And the simulation within the hydrostatic framework indicates the significant role of latent heat release in the rainstorm occurrence:that even for a 30 km grid spacing horizontally of great importance to the successful modeling of the meso-β event was a convection parameterization scheme that led to less rainfall in our run based only on its explicit version but to the prediction in closer agreement with the observed when its implicit version was used in combination:for the thunderstorm-accompanied torrential rain.the Grell scheme was superior to the version of Kuo and the improved Arakawa-Schubert parameterization scheme(Grell 1993:Anthese and Kuo 1987:Arakawa and Scherbt 1974:Grell et al,1991).Moreover,better results came from the simulation in the context of hydrostatic framework of the MM5 compared to those from the run within the nonhydrostatic equilibrium framework,a problem that awaits further efforts.

冬季青岛-石岛近海中尺度涡旋数值模拟

利用二维全流水动力方程组 ,在考虑了海面风应力、潮余流和开边界入流等条件下 ,首次模拟出了石岛附近的中尺度反气旋式涡旋海水运动 ,并对南黄海西部冬季环流的特征作了初步探讨。数值模拟结果和实测吻合良好 ,数值模拟表明 :冬季南黄海西部环流形式主要决定因子是海面风应力、潮余流及从开边界的流入 (出 )该海域的黄海暖流及黄海沿岸流。黄海暖流在偏北风作用下沿西北方向可直达山东半岛近岸 ,后分为两支 :一支向南汇入黄海沿岸流流出 ,另一支北上并与黄海沿岸流相配合 ,在石岛附近形成一个中尺度反气旋式涡旋。

基于改进MCFT的GFRP-RC梁抗剪承载力分析

通过三维细观数值模拟方法,建立了大尺寸GFRP筋混凝土(GFRP-RC)梁剪切破坏力学分析模型,研究了剪跨比、纵筋率和梁深对GFRP-RC梁裂缝倾角及荷载-位移曲线的影响规律。并以修正压力场理论(MCFT)为基础,根据剪切裂缝宽度沿梁深变化的特点,建立了考虑裂缝宽度沿梁深变化的平均裂缝宽度计算模型,提高了修正压力场简化公式的计算精度。鉴于此,提出能考虑剪跨比及大尺寸影响的无腹筋GFRPRC梁抗剪承载力计算方法,并通过213组试验和模拟数据验证其合理性及准确性。与规范计算结果相比较,结果表明,本文所建立的平均裂缝宽度计算模型合理有效,基于此得到的MCFT简化公式能较好的预测大尺寸无腹筋GFRP-RC梁的抗剪承载力,为GFRP-RC梁的抗剪设计提供了理论参考和方法。

CNTs-纤维增强树脂基复合材料纳米-介观尺度数值模拟研究进展

CNTs的高刚度、高强度使得其成为复合材料领域极有前景的纳米增强体之一。然而,单纯依靠实验获得CNTs对复合材料力学性能影响规律的方法是不可行的,需要辅之以合适有效的数值模拟方法去解理和分析CNTs各个因素对于复合材料力学性能的影响机制和规律。本文首先依据实验中真实存在的CNTs形态确定了模型为纳米-介观尺度模型,然后基于建模方式和研究对象的差异综述了三种常见的纳米-介观尺度模型数值模拟方法,最后根据目前的数值模拟结果,从CNTs本征性能,CNTs的含量和分布两大方面综述了CNTs对复合材料力学性能的影响机制,为数值模拟研究提供了可靠支撑,同时也为实验性研究提供了有力的理论依据。此外,由于数值模拟方法和CNTs变量的多样性,CNTs-纤维增强树脂基复合材料的数值模拟仍存在着巨大的研究潜力。

热-水-力作用下混凝土细观XFEM全耦合建模

由运动方程、连续性方程及热量平衡方程建立了混凝土作为饱和多孔介质材料的扩展有限元热-水-力全耦合迭代格式.针对含界面的扩展单元,采用材料子域积分法进行其单元刚度矩阵的数值计算.中心含单个夹杂的多孔介质平板算例结果表明,建立的扩展有限元热-水-力全耦合模型的结果与有限元计算结果十分吻合,验证了模型的可靠性和有效性.将建立的扩展有限元模型应用到混凝土细观数值模拟中,获得了混凝土在热-水-力耦合作用下的应力、温度和孔隙水压力的分布规律,并探究了混凝土级配对内部温度应力的影响规律,得出了相同骨料含量下,降温冷缩时多级配混凝土产生的主拉应力更大,造成不利影响的结论.

指数分布型根系根-土复合体强度特性研究

指数分布型是排土场护坡植物根系中十分常见的根型,为进一步揭示根-土复合体固土护坡的内在机理,针对现有数值模拟方法不易还原自然条件下根系真实形态的问题,结合土工试验,优化数值模拟方法,研究了细观尺度下指数分布型根系根-土复合体的力学强度特性,结果表明:根-土复合体试样表现出与素土不同的颗粒位移特征,根系的存在能够显著提高土体的整体性,根的张拉作用限制了土体的侧向变形;构建的根-土复合体离散元模型可以较好地反映含根系土壤的力学效应,根系内部应力主要集中于剪切平面附近的根系部,各垂直荷载下未发现根系整体贯通断裂,断裂整体上呈现出在剪切平面集中、土体内零星分布的特点;素土试样的剪应力-剪切位移曲线呈现出带有波峰的应变软化趋势,而根-土复合体试样呈现出无波峰的应变硬化趋势;草本植物根系主要增大了根-土复合体的黏聚力,对内摩擦角的影响不明显。研究成果对于深入了解根土相互作用加固土壤的机理和推进根-土复合体的数值模拟研究具有重要的参考意义。

利用DQCT实现2018年8月超历史极值暴雨的高质量模拟

构建较全面的双级质量控制技术(DQCT).利用中尺度天气预报模式(WRF)对2018年8月下旬华南地区一次超历史极值的暴雨过程进行高分辨率数值模拟,并用DQCT评判暴雨的模拟效果.结果表明,在暴雨形势背景场中用WRF成功模拟大尺度季风风场、西南暖湿气流与低压交汇过程,并准确复制了造成高潭镇极端降雨的中尺度对流系统.总降雨量中的中γ尺度极值暴雨中心模拟得较为准确.该模式在24 h降雨量模拟中成功复制了暴雨中心的演变过程;在6 h降雨量模拟中较好地再现了中γ尺度雨带的演变过程.在暴雨重灾区高潭镇1 h降雨量演变过程的模拟中,总体降雨趋势与实况吻合较好.定性分析结果同步得到定量指标的验证.

CFRP布加固RC柱细观力学分析模型及抗扭分析

为了探究配纤率、截面形状、截面尺寸、轴压比对碳纤维增强复合材料(carbon fiber reinforced polymer,CFRP)加固钢筋混凝土(reinforced concrete,RC)柱抗扭性能的影响,采用了可以同时考虑混凝土材料非均质性、钢筋与混凝土间黏结-滑移关系、CFRP布与混凝土间界面关系的细观力学分析方法。首先,建立了用于CFRP布加固RC柱抗扭性能分析的三维数值模型;进而,将基于该模型的数值模拟结果与试验结果对比,验证了模型中加载方式、外贴CFRP布方法的合理性及材料参数的准确性;最后,基于建立的细观力学分析模型,探讨了配纤率、截面形状、截面尺寸、轴压比对扭转作用下CFRP布加固RC柱破坏模式和力学性能的影响机制。分析结果表明:CFRP布加固RC柱抗扭承载力随配纤率增大而提高,但提高幅度随配纤率增大而降低;受到围压分布的影响,圆形截面的有效约束面积大于方形截面,使得CFRP布对圆柱的约束效果好于方柱;CFRP布加固RC柱的名义扭转强度存在尺寸效应;轴压比的增大使其抗扭承载力先增大后减小,在轴压比为0.4时达到最大值。进一步,采用叠加规范公式方法提出了FRP布加固RC构件抗扭承载力计算公式,与数值模拟结果对比发现,该公式可给出安全储备冗余度30.2%的设计值,可初步用于CFRP布加固RC柱抗扭承载力的安全设计。

基于Python算法的混凝土球形骨料三维细观数值模拟方法

介绍了一种混凝土构件三维细观数值模型及球形骨料参数随机投放算法。基于Python语言自身的优势以及与有限元软件的良好对接,使用Python语言编写程序实现了骨料生成、骨料几何参数有效性判断、混凝土构件几何模型建立及网格划分的过程,并借助钢筋混凝土拉拔试验数值模拟验证了其有效性。

复杂地形边界层结构的数值模拟

首先发展了一个三维非静力中－β尺度动力学模式，以模拟地形的动力、热力作用对边界层结构的影响。模式放弃了静力近似假设，垂直方向采用地形跟随坐标，用较细的网格以提高空间分辨率和精度。在参数化过程中，太阳辐射吸收考虑了地形的坡向作用，地表潜热和水汽通量考虑了植被作用，闭合方案采用Ｅ－ε能量闭合。然后利用该模式对陕西省关中地区作了实例模拟和数值试验。结果表明：起伏地形对垂直流场及低层风场影响较大。迎风坡空气抬升，背风坡空气下沉。层结稳定时易形成背风波，层结不稳定时，在地形抬升、水平温度梯度（地表形状不同）和背风坡的共同作用下，地形边界区易形成局地环流。除迎风坡空气抬升和背风坡引起上升运动外，还有地形加热引起的上升运动，这些对水汽。

长江中游一次β中尺度低涡的数值模拟

利用PSU/NCAR的中尺度数值模式MM5,对1999年6月29日的一次东移低涡过程进行了数值模拟,结果表明:在东移的a中尺度低涡的东南部边界层激发出一个β中尺度的涡旋,该β中尺度涡旋与一强暴雨区相伴移动,稠密的实况降水资料证实了这一暴雨雨团的存在和移动过程。模拟分析揭示β中尺度涡旋出现在停滞的α中尺度低涡南侧偏西气流与暖区偏南气流相遇处及中尺度山脉的背风坡;在中尺度山脉背风坡的地面和近地面层分别有中尺度低压和增强的东南气流存在,由此产生或加强了近地面的强涡度和强辐合,有利于对流系统的发生发展。

云南一次切变线上中尺度低涡扰动的结构分析

利用η中尺度数值模式模拟的时空高分辨输出、常规资料、GMS红外云图及TBB资料,对2002年6月25日切变线上中α尺度低涡扰动的结构、形成过程及冷空气来源进行研究,结果表明,低涡环流的尺度属于中α尺度,持续时间7小时左右,低涡成熟阶段,700hPa正涡度中心与低涡环流中心相重合,低空急流及强辐合中心位于低涡的东南象限;低涡环流由三股气流构成;低涡区上空存在超强散度柱、倾斜涡柱、深厚的上升运动区及特强垂直上升运动,超强散度柱与特强垂直上升运动互耦,强辐合、辐散中心发生在南、北风辐合、辐散且有强的v分量垂直梯度处,低层正涡度中心的上方,存在一负涡度中心;最大的水汽辐合位于700hPa及550hPa;低涡区冷空气来自500hPa的滇缅高压;大暴雨中心位于低涡中心的东侧。