Mesoscale and Microphysical Characteristics of a Double Rain Belt Event in South China on May 10–13,2022

A second rain belt sometimes occurs ahead of a frontal rain belt in the warm sector over coastal South China,leading to heavy precipitation.We examined the differences in the mesoscale characteristics and microphysics of the frontal and warm sector rain belts that occurred in South China on May 10–13,2022.The southern rain belt occurred in an environment with favorable mesoscale conditions but weak large-scale forcing.In contrast,the northern rain belt was related to low-level horizontal shear and the surface-level front.The interaction between the enhanced southeasterly winds and the rainfall-induced cold pool promoted the persistent growth of convection along the southern rain belt.The convective cell propagated east over the coastal area,where there was a large temperature gradient.The bow-shaped echo in this region may be closely related to the rear-inflow jet.By contrast,the initial convection of the northern rain belt was triggered along the front and the region of low-level horizontal shear,with mesoscale interactions between the enhanced warm-moist southeasterly airflow and the cold dome associated with the earlier rain.The terrain blocked the movement of the cold pool,resulting in the stagnation of the frontal convective cell at an early stage.Subsequently,a meso-γ-scale vortex formed during the rapid movement of the convective cell,corresponding to an enhancement of precipitation.The representative raindrop spectra for the southern rain belt were characterized by a greater number and higher density of raindrops than the northern rain belt,even though both resulted in comparable hourly rainfalls.These results help us better understand the characteristics of double rain belts over South China.

Lateral load-carrying capacity analyses of composite shear walls with double steel plates and filled concrete with binding bars

A method is developed to predict the lateral load-carrying capacity of composite shear walls with double steel plates and filled concrete with binding bars(SCBs). Nonlinear finite element models of SCBs were established by using the finite element tool, Abaqus. Tie constraints were used to connect the binding bars and the steel plates. Surface-to-surface contact provided by the Abaqus was used to simulate the interaction between the steel plate and the core concrete. The established models could predict the lateral load-carrying capacity of SCBs with a reasonable degree of accuracy. A calculation method was developed by superposition principle to predict the lateral load-carrying capacity of SCBs for the engineering application. The concrete confined by steel plates and binding bars is under multi-axial compression; therefore, its shear strength was calculated by using the Guo-Wang concrete failure criterion. The shear strength of the steel plates of SCBs was calculated by using the von Mises yielding criterion without considering buckling. Results of the developed method are in good agreement with the testing and finite element results.

Study on adhesively-bonded surface of tapered double cantilever specimen made of aluminum foam affected with shear force

Aluminum foam is widely used in diverse areas to minimize the weight and maximize the absorption of shock energy in lightweight structures and various bio-materials.It presents a number of advantages,such as low density,incombustibility,non-rigidity,excellent energy absorptivity,sound absorptivity and low heat conductivity.The aluminum foam with an air cell structure was placed under the TDCB Mode II tensile load by using Landmark equipment manufactured by MTS to examine the shear failure behavior.The angle of the tapered adhesively-bonded surfaces of specimens was designated as a variable,and three models were developed with the inclined angles differing from one another at 6°,8° and 10°.The specimens with the inclined angles of 6°,8° and 10° have the maximum reaction forces of 168 N,194 N when the forced displacements are 6,5 and 4.2 mm respectively.There are three specimens with the inclined angles of 10°,8° and 6° in the order of maximum reaction force.As the analysis result,the maximum equivalent stresses of 0.813 MPa and 0.895 MPa happened when the forced displacements of 6 mm and 5 mm proceeded at the models of 6° and 8°,respectively.A simulation was carried out on the basis of finite element method and the experimental design.The results of the experiment and the simulation analysis are shown not different from each other significantly.Thus,only a simulation could be confirmed to be performed in substitution of an experiment,which is costly and time-consuming in order to determine the shearing properties of materials made of aluminum foam with artificial data.

Double⁃Shear Experiments of Cold⁃Formed Steel Stud⁃to⁃Sheathing Connections at Elevated Temperatures

The behavior of cold⁃formed steel(CFS)stud⁃to⁃sheathing connections at elevated temperatures is an important parameter for the fire resistance design and modeling of mid⁃rise CFS structures.In this paper,three kinds of sheathings,namely,medium⁃and low⁃density calcium⁃silicate boards and oriented strand board,were selected for double⁃shear experiments on the mechanical properties of 253 screw connections at ambient and elevated temperatures.The effects of the shear direction,screw edge distance and the number of screws on the behavior of the connections were studied.The results showed that the shear direction and the screw edge distance more significantly influenced the peak deformation,while their impacts on the peak load varied with the type of sheathings.Compared with the single⁃screw connections,the peak loads of the specimens with double⁃screw connections obviously increased but did not double.Finally,a simplified load⁃displacement curve model of stud⁃to⁃sheathing connections at elevated temperature was generated first by establishing the prediction formula for characteristic parameters,such as the peak load,the peak deformation and the elastic stiffness,and then by considering whether the curves corresponded to stiffness increase phenomena.The present investigation provides basic data for future studies on the numerical modeling of CFS structures under fire conditions.

Study on the double-logarithmic profile of tidal flow velocity in the near-bed layers

Tidal current velocity profile in the near-bed layers has been widely studied. The results showed that velocity profile in the near-bed layer obviously departure from the traditional logarithmic profile, due to the acceleration or deceleration. Although the logarithmic linear profile can reduce the rate of deviation from this, only it is a lower-order approximate solution. In this paper, considering the unsteady and non-linear features of tidal motion, the double logarithmic profile near-bed layers in estuarine and coastal waters is established on the assumption that the turbulent shear stress along the water depth was parabolic distribution, and on the basis of Prandtl＇s mixing length theory and yon Karman＇s self-similar theory. Having been verified the data observed at the West Solent in the south of England, and comparison of the logarithmic linear profile, it found that the double logarithmic profile is more precious than the latter. At last, the discussed results showed that： （1） The parabolic distribution of the tidal shear stresses verified good by the field data and experimental data, can be better reflected the basic features of the tidal shear stress deviating from linear distribution that is downward when to accelerate, upward when to decelerate. （2） The traditional logarithmic velocity profile is the zero-order approximation solution of the double logarithmic profile, the logarithmic linear profile is the first order, and the logarithmic parabolic profile is the second order. （3） Ignoring the conditions of diffusion and convection in the tida movement, the double logarithmic profile can reflect the tidal properties of acceleration or deceleration, so that the calculation of the friction velocity and roughness length are more reasonable. When the acceleration or the deceleration is about zero, the double logarithmic profile becomes the logarithmic profile.

Fluid Vibration Induced in T-Junction with Double Side Branches

A T-junction is a fundamental fluid element prevalent in pipe networks of water supplies and power plants. In the present study, a double T-junction was investigated for flow instability and fluid vibration. Both axi-aligned and skewed double T-junctions are examined from viewpoint of flow instability. With single-phase flow in an open-ended double T-junction, fluid vibration is induced in both side branches because of a high shear rate with a point of inflection. The frequency of vibration in the downstream branch is higher than that in the upstream branch. Except for the upstream branch in the skewed double T-junction, the frequency is higher than that in a single T-junction. The fluid vibrations are closely associated with the fluid interference created by the presence of the two side branches.

Effects of m=0 Harmonics on Quasi-Linear Stage of m=1 Double Tearing Mode

Effects of tearing modes are inves shows that the effect of the m = 0 harmonics on the early quasi-linear stage of m = 1 double tigated. The numerical calculation with the harmonics m = 0 included the m = 0 harmonics on the mode is negligible in the linear stage. As the mode begins to grow nonlinearly, both the current and flow profiles are pinched due to the m = 0 harmonics. To make a comparison we also carry out the calculation with m = 0 harmonics turned off. The profiles of the total current, poloidal magnetic field, and poloidal shear velocity in the cases with or without the m = 0 harmonics are compared and discussed. In addition, the formation of a poloidal velocity shear is found and its mechanism is investigated.

Sawtooth-like oscillations and steady states caused by the m/n=2/1 double tearing mode

The sawtooth-like oscillations resulting from the m/n=2/1 double tearing mode(DTM)are numerically investigated through the three-dimensional,toroidal,nonlinear resistive-MHD code(CLT).We find that the nonlinear evolution of the m/n=2/1 DTM can lead to sawtooth-like oscillations,which are similar to those driven by the kink mode.The perpendicular thermal conductivity and the external heating rate can significantly alter the behaviors of the DTM driven sawtooth-like oscillations.With a high perpendicular thermal conductivity,the system quickly evolves into a steady state with m/n=2/1 magnetic islands and helical flow.However,with a low perpendicular thermal conductivity,the system tends to exhibit sawtooth-like oscillations.With a sufficiently high or low heating rate,the system exhibits sawtooth-like oscillations,while with an intermediate heating rate,the system quickly evolves into a steady state.At the steady state,there exist the non-axisymmetric magnetic field and strong radial flow,and both are with helicity of m/n=2/1.Like the steady state with m/n=1/1 radial flow,which is beneficial for preventing the helium ash accumulation in the core,the steady state with m/n=2/1 radial flow might also be a good candidate for the advanced steady state operations in future fusion reactors.We also find that the behaviors of the sawtooth-like oscillations are almost independent of tokamak geometry,which implies that the steady state with saturated m/n=2/1 islands might exist in different tokamaks.

ALTERNATIVE DESCRIPTION OF THE SHEAR PLANE OF THE R-PHASE

A high density of {110} shear planes has been observed in the R-phase (Al5CuLi3)following phase transformation from the AlCuLi icosahedral Phase. The Present paper shows that the atomic arrangement in the vicinity of the shear planes can be described as a two-dimensional periodic array of atom clusters with 5-fold symmetry. This result is obtained by projecting along the [1. 618...01] direction of the atomic positions from four adjacent lattice planes that cross the shear plane. The projection reveals that the shear plane consists of pentagonal arrangements of double triacontahedra,each pentagon incorporating 606 atoms. The calculated diffraction pattern from the pentagon has approximate 10-fold symmetry characteristic of a quasicrystal.

两种结构类型的走滑相关剪断裂带

里德尔剪切是走滑带的典型构造样式,但近年来发现的很多剪断裂带中的剪断裂组合样式与经典里德尔剪切不同。在这些剪断裂带中,剪断裂的排列方式与两盘位移方向性质相同,即左阶左行或右阶右行,被称为同阶行剪断裂,其叠合部位具有离散性质。基于库伦破裂准则,认为这些剪断裂带是在双剪切带夹持的断夹块上发育的。在双剪切作用下,最大主应力迹线方向上将产生2组共轭势剪破裂,在递进变形过程中,与最大剪应力(主走滑方向)成小锐夹角的剪破裂将优先得到发展,而与最大剪应力成大锐夹角的剪破裂将受到抑制而被限制在前者之间,形成一种不同于经典里德尔剪切组合样式的新型剪断裂带。这种类型的剪断裂带发育离散型叠合带,对成藏成矿具有重要意义。

Low Shear Strength and Shear-Induced Failure in Ti3SiC2

Shear strength and shear-induced Hertzian contact damage in Ti_3SiC_2 were investigated using double-notched-beam specimen and steel spherical indenter, respectively. The shear strength of 40 MPa that was only about 10% of bending strength was obtained for this novel ceramic. The SEM fractograph of specimens failed in shear test indicated a combination of intergranular and transgranular fracture. Under a contact load, plastic indent without cone crack could be formed on the surface of Ti3SiC2 sample. Optical observation on side view showed half-circle cracks around the damage zone below the indent, and the crack shape was consistent with the contrail of the principal shearing stress. The low shear strength and the shearing-activated intergranular sliding were confirmed being the key factors for failure in Ti3SiC2.

焊接多腔双钢板-混凝土组合剪力墙抗震性能分析

大多数双钢板-混凝土组合剪力墙采用螺栓连接或焊接肋的方式使钢板和混凝土协同工作。然而,这种连接方式可能导致整体性和塑性变形效率较低,且制作复杂,焊接多腔双钢板-混凝土组合剪力墙能够有效地避免这些问题。为了深入研究焊接多腔双钢板-混凝土组合剪力墙的抗震性能,基于约束混凝土真三轴塑性-损伤本构模型和钢材弹塑性混合强化-韧性损伤本构模型,建立了组合剪力墙的精细化三维实体-壳模型,将模拟所得的滞回曲线、骨架曲线、刚度退化曲线、弹性刚度、承载力、累积耗能、等效阻尼粘滞系数和延性系数与已有拟静力试验结果相比较,发现两者吻合较好。分析结果表明:轴压比对组合剪力墙模型算例刚度和承载力的影响较小,而随剪跨比增大,组合剪力墙模型算例的刚度和承载力呈线性降低;轴压比对组合剪力墙模型算例总塑性耗能的影响较小,而剪跨比的影响较大,剪力墙总塑性耗能随剪跨比增大而降低;轴压比和剪跨比都不会改变算例各部件的耗能分配机制,即组合剪力墙模型算例以外钢板和内隔板耗能为主。

双层滑带滑坡土环剪试验与稳定性分析

以云南省文山至麻栗坡高速公路K39段复合型双层滑带滑坡为例,采用室内环剪试验探明该滑坡深层、浅层滑带各自的残余强度,分析不同含水率、法向应力和剪切速率对滑带土残余强度的影响;采用FLAC3D软件进行数值模拟,基于滑坡应力-应变历史对滑坡稳定性进行评价。结果表明:滑带土在低含水率情况下力学强度较高,饱和状态抗剪强度参数表现出明显的衰减趋势;在地下水位保持高位时,深层滑带更易发生渐进式蠕动滑移。模拟结果显示:滑坡的深层滑带应力集中现象较为显著,浅层滑坡危险性较小,滑坡在暴雨工况下整体稳定性明显降低,存在一定风险,可通过设置排水洞等降水措施进行治理。

贯通型标准JRC双节理剪切力学及声发射特性研究

节理岩体的抗剪性能是影响工程岩体强度及稳定性的关键因素。基于3D打印技术制作标准JRC节理面模具和固定夹板,采取一体化浇筑方式制备不同节理面间距和不同粗糙度的双节理试样,结合声发射(acousticemission,AE)技术探究不同法向应力条件下粗糙双节理岩体剪切力学特性和破坏演化特征。结果表明:剪切应力-剪切位移曲线形态受节理粗糙度和法向应力共同影响。随JRC和法向应力的增加,剪切应力软化程度加重;法向应力较大时,峰后阶段剪切应力存在多次突降现象,突降值随法向应力的增加而增大。峰值剪切强度出现在双节理间岩石夹层断裂时刻,随JRC和法向应力的增加呈增大趋势,随节理面间距增加呈减小趋势。AE结果表明:岩石夹层断裂时刻AE能量大幅突增,AE能量峰值稍滞后于剪切应力峰值,随法向应力的增加,AE能量峰值和累积AE能量值增大;AE定位点空间上集中于岩石夹层部分,时间上频发于200~600 s内,随节理面间距的增加,AE定位点的集中范围扩大。

温度影响下不同轴压比双钢板混凝土组合剪力墙抗震性能

研究不同温度环境下不同轴压比双钢板混凝土组合剪力墙的抗震性能,以温度(40、20、-40℃)和轴压比(n=0.3、0.4、0.5、0.6)为控制参数,设计了12片剪力墙。利用ABAQUS对双钢板组合剪力墙试验进行对比验证,验证有限元结果的准确性。通过对12个剪力墙的承载能力、塑性变形能力、耗能能力、延性对比分析,探究其在代表性温度环境下轴压比对试件的抗震性能变化规律。结果表明,在相同的温度环境下,随着轴压比的增加,剪力墙的承载能力增加,延性降低。轴压比对于刚度退化的影响不明显。在20℃环境下,剪力墙的延性好于40和-40℃环境下延性。-40℃环境下,剪力墙的承载能力高于40和20℃环境。

新旧混凝土界面双面直剪性能尺寸效应试验研究

以界面处理方式、横向约束形式、混凝土强度、界面尺寸为变量,开展了8组50个新旧混凝土界面试件双面直剪试验研究,得到界面受剪破坏形态和抗剪强度-滑移曲线,分析界面抗剪强度的尺寸效应规律,拟合得到新旧混凝土双面直剪试件极限应力尺寸效应的换算系数,建立受剪承载力计算表达式。结果表明:在剪力作用方向上,新旧混凝土界面受剪极限应力存在明显的随界面高度增加而降低的尺寸效应现象;开裂应力、裂通应力以及滑移的尺寸效应不明显;施加横向约束可提升界面裂通应力和极限应力;施加预压应力可显著提升试件的裂通应力,并有效限制试件的极限滑移。无横向约束条件下,凿毛形式对极限应力影响显著,相比整浇混凝土试件,机械凿毛的同强度新旧混凝土双面直剪极限应力减少至整浇试件的0.22以下,而人工凿毛试件的折减系数在0.34~0.37之间。有横向约束条件下,同凿毛粗糙界面相比,规则齿槽试件的开裂应力、裂通应力以及滑移表现优势突出;约束下强度折减系数提高到无约束同等条件试件的2~2.5倍以上,最大可达到整浇试件强度的0.97倍。新旧混凝土强度提高可增加试件裂通应力和极限应力,但提升幅度有限。

低周反复荷载下T型双波纹钢板混凝土组合剪力墙受力性能试验研究

为研究低周反复荷载下T型双波纹钢板混凝土组合剪力墙的受力性能,对5个T型双波纹钢板混凝土组合剪力墙进行了低周反复加载试验。基于试验数据,分析了T型组合剪力墙的破坏模式、滞回曲线、变形能力及耗能能力,重点研究了边缘约束条件、波纹类型以及轴压比不同变化参数对T型组合剪力墙抗震性能指标的影响规律。研究结果表明:T型双波纹钢板混凝土组合剪力墙破坏模式主要有压屈破坏和压弯破坏两种;设置边缘约束构件是提高T型双波纹钢板混凝土组合剪力墙承载能力和变形能力的关键因素;纵向窄波纹钢板对内部混凝土的约束能力更强,在低周反复荷载下两者协同工作性更优,而横向窄波纹钢板试件强度退化最严重;采用全截面塑性设计方法进行T型双波纹钢板混凝土组合剪力墙正截面承载力计算,试验值与计算值吻合良好;T型双波纹钢板混凝土组合剪力墙具有较好的承载能力和变形能力,可适用于高层及超高层建筑结构中。

基于IDA方法的带可替换耗能梁段偏心支撑钢框架结构影响系数研究

为研究带可替换双槽钢型剪切耗能梁段偏心支撑钢框架中耗能梁段的截面尺寸、梁段长度、加劲肋个数以及结构层数对于结构影响系数R和位移放大系数C_(d)的影响,通过OpenSees有限元软件对18个不同参数的模型进行增量动力时程分析(IDA),得到各模型的结构影响系数和位移放大系数.结果表明:通过合理设计耗能梁段的构造参数,能够提高带可替换双槽钢型剪切耗能梁段防屈曲偏心支撑钢框架的抗震能力以及变形能力,给出R和C_(d)的建议值,为偏心支撑钢框架结构影响系数的研究提供参考.

考虑楼板作用的双面叠合剪力墙有限元分析

为了保证双面叠合剪力墙结构体系应用的安全性和可靠性,建立由上、下两层墙体和中间楼板组成的双面叠合剪力墙构件模型及现浇对比模型,并进行基于Abaqus软件的数值模拟分析。研究内容包括双面叠合剪力墙整体位移、混凝土及钢筋的应力分布、最大承载力、耗能能力。结果表明,在小震弹性阶段,带楼板的双面叠合墙板与现浇对比试件的刚度一致;在大震作用下,带楼板的双面叠合墙板的耗能能力低于现浇对比试件,但总体耗能能力都较好。因此,合理设计下的双面叠合剪力墙结构具有良好的抗震性能。

考虑双重剪切的开放系统梯形渠道Pasternak双参数冻土地基梁模型

Winkler冻土地基模型无法考虑土弹簧间相互作用,且需要预先假定切向冻结力分布。为克服这些不足之处,在现有模型基础上引入Pasternak剪切层反映冻土-衬砌间法向相互作用,引入切向弹簧组成的接触界面层反映冻土-衬砌间切向相互作用,构建考虑双重剪切的梯形渠道Pasternak双参数冻土地基模型。以塔里木灌区某渠道为例计算衬砌冻胀变形,并与材料力学法、Winkler模型计算值及观测值进行对比。结果表明:与材料力学法、Winkler模型相比,该文模型计算值更接近观测值。根据该模型估算的衬砌板易开裂范围也与灌区现场调查结果相符,表明模型适用性。通过参数研究分析了界面切向刚度kx对各处切向位移及切向冻结力分布的影响。结果表明:kx越小时,切向位移与切向冻结力趋于线性分布;kx较大时,两者均偏离线性分布且kx越大偏离越明显,线性分布假设不再适用。该模型可较充分地反映冻土与衬砌板间接触界面相互作用的基本特征,从而有效提高模型的计算精度。