Numerical simulations of stress wave propagation and attenuation at arc-shaped interface inlayered SiC/Al composite

The effects of interface shape on stress wave distribution and attenuation were investiga- ted using finite element method （ FEM ）. The simulation results indicate that when the stress wave propagates from SiC ceramic to A1 alloy, the tensile stress decreases and the attenuation coefficient of the stress wave increases with increasing central angle of the concave interface between SiC and A1. But for the convex interface, the tensile stress increases and attenuation coefficient decreases with increasing central angle. As the stress wave propagates from A1 alloy to SiC ceramic, the atten- uation coefficient of stress wave decreases with increasing the central angle of the concave interface. For the convex interface, the attenuation coefficient increases with increasing central angle.

Reduced-order proper orthogonal decomposition extrapolating finite volume element format for two-dimensional hyperbolic equations

This paper is concerned with establishing a reduced-order extrapolating fi- nite volume element （FVE） format based on proper orthogonal decomposition （POD） for two-dimensional （2D） hyperbolic equations. For this purpose, a semi discrete variational format relative time and a fully discrete FVE format for the 2D hyperbolic equations are built, and a set of snapshots from the very few FVE solutions are extracted on the first very short time interval. Then, the POD basis from the snapshots is formulated, and the reduced-order POD extrapolating FVE format containing very few degrees of freedom but holding sufficiently high accuracy is built. Next, the error estimates of the reduced-order solutions and the algorithm procedure for solving the reduced-order for- mat are furnished. Finally, a numerical example is shown to confirm the correctness of theoretical conclusions. This means that the format is efficient and feasible to solve the 2D hyperbolic equations.

隔水透气隔断层对寒旱区盐渍土水盐迁移及变形特性的影响

针对寒旱区盐渍土水盐迁移引起的盐冻胀变形病害问题,本研究提出了一种新型的隔水透气膜隔断层处理方法,并开展了相应的理论分析和室内试验研究。基于多孔介质理论和连续介质力学理论,通过考虑温度变化下孔隙水盐相变等因素,建立了非饱和盐渍土的水-热-盐-力多场多相耦合模型。在水盐补给条件下,采用数值模拟和室内模型试验研究了非饱和硫酸盐渍土的水盐迁移和盐冻胀变形特性,并验证了模型的有效性。重点分析了设置隔水透气膜对非饱和硫酸盐渍土热质迁移及变形行为的影响。研究结果表明:隔水透气层对液态水和溶解盐的迁移具有明显的阻滞作用。同时,由于隔断层的透气特性,可有效地解决传统土工膜隔断层下气体聚集现象。研究成果可为盐渍土路基处理提供技术与理论基础。

湍流风况下风电机组机舱近尾流的数值模拟研究

水平轴风电机组机舱风速是机组控制的主要信号参数。机舱风速受风电机组来流湍流与风电机组近尾流影响,变化复杂,对风电机组的优化控制有重要的影响。本文采用计算流体力学(CFD)方法,对端流风况下风电机组机舱近尾流进行了详细分析。对比研究了稳态均匀风况和瑞流风况下的近尾流的结构、机舱速度分布及其对风电机组总体性能的影响。研究发现,风电机组总体性能随流风况波动也呈现多尺度波动特征。流风况下,经过滤波后的机舱风速的时间序列和来流风速的时间序列体现出很强的相关性。对于湍流风况和稳态均匀风况,叶片/风轮旋转对风电机组机舱风速波动的影响最大。流风况会增加风电机组机舱风速的波动频率,增大波动的幅值,削弱风轮旋转对尾流和机舱风速的影响。流风况使得机舱周围的流动结构更复杂。稳态均匀风况与湍流风况下叶片吸力面叶根位置处都发生了分离流动,流强度增大了叶根位置处的流动分离。

全风化花岗岩滑坡稳定性与降雨关系分析

降雨是滑坡诱发的主要因素,当前我国防灾工作理念从注重灾后救助向注重灾前预防转变、从减少灾害损失向减轻灾害风险转变,因此明晰降雨诱发机理并建立合理的预警机制,对做好地质灾害防灾减灾工作至关重要。针对降雨型全风化花岗岩滑坡稳定性问题,以青岛崂山风景区全风化花岗岩返岭滑坡为实例,进行了不同含水率原状土剪切试验与大型物理相似模型试验。揭示了边坡的降雨响应规律,探究了全风化花岗岩滑坡稳定性与降雨关系,并拟合相关量化公式。同时采用ABAQUS建立边坡流固耦合三维数值模型,基于强度折减法验证了公式的合理性。研究结果表明:(1)降雨型全风化花岗岩滑坡的破坏模式分为浸润侵蚀→表层变形→破坏加深→整体失稳4个阶段,变形期间坡体存在“鼓状凸起”与“片状溜滑”现象,最终发生推移式破坏;(2)边坡对降雨入渗的响应规律在水平及竖向空间上存在差异,降雨强度越大,含水率与孔压增速越大;(3)基于试验结果推导了滑坡含水率、安全系数与降雨强度、降雨持时之间的影响关系公式,数值模拟验证误差率较小,能够较好的描述全风化花岗岩滑坡稳定性与降雨之间的定量关系。研究结果为类似强~全风化花岗岩地区滑坡的预警与防治提供参考。

地下连续墙受力变形光纤监测与数值模拟研究

地下连续墙是一种常见的深基坑支护方式,具有刚度大、防渗性能好、适应范围广等优点,但其受力变形规律较为复杂。基于超弱光纤光栅感测技术,对某地铁车站基坑地下连续墙水平位移进行实时监测。将监测数据与数值模拟结果进行对比,验证了数值分析模型选取的合理性,并基于该数值分析模型研究了不同厚度软土层中,地下连续墙水平位移的变化规律,通过墙体位移梯度(D_(w))和软土位移梯度(D_(r))进行临界厚度比计算。研究结果显示:水平位移随软土厚度的变化呈“凸肚”状,沿深度方向划分为相对稳定区、线性增长区、最大变形区和线性下降区。利用D_(w)和D_(r)标定出临界厚度比为0.24;土压力变化在基坑前四步开挖过程中较为稳定,而在第五步开挖与施工后40 d变化显著。上述研究结果为类似工程的设计、施工和监测方案的制定提供了重要参考。

铝合金薄板冲压成形过程中的侧壁起皱及有限元模拟

针对铝合金薄板的侧壁起皱问题,本文通过有限元软件分析工艺参数对成形质量的影响,提出了一种基于数值模拟与智能算法相结合的优化方法。首先,利用最优拉丁超立方抽样进行实验设计,并依据数值模拟获取实验值;其次,基于BP神经网络拟合工艺参数与成形质量之间的关系,预测结果的平均相对误差为2.69%,建立了准确的预测模型;最后,用遗传算法极值寻优获取了一组最优的工艺参数组合,起皱幅值的预测值和仿真值相对误差仅为4.03%,实验结果与仿真分析结果相近,验证了该优化方法的合理性和有效性。研究表明:以料厚、摩擦系数和压边力作为优化变量,以最大起皱幅值最小化为优化目标,建立几何模型,并利用有限元软件Autoform进行仿真分析;依据起皱轮廓线径向位移的实验和数值模拟对比,验证了有限元模型的正确性,表明利用神经网络和遗传算法极值寻优可以有效解决铝合金侧壁起皱缺陷。

扇形脉冲爆震燃烧室起爆过程数值模拟

为了探究不同障碍物结构对扇形脉冲爆震燃烧室起爆过程的影响,对采用3种典型孔板障碍物的扇形脉冲爆震燃烧室,截取其中间截面进行了起爆过程的数值模拟,研究了障碍物型式、障碍物堵塞比及障碍物间距对扇形脉冲爆震燃烧室爆燃转爆震(DDT)距离的影响规律。结果表明:障碍物堵塞比对扇形脉冲爆震燃烧室DDT距离的影响最大,且在堵塞比为0.35~0.70时,堵塞比越高DDT距离越短;在3种型式的障碍物中,在低堵塞比下,截面为前掠三角形的障碍物缩短DDT距离的效果最好,在高堵塞比下,截面为后掠三角形的障碍物缩短DDT距离的效果最好;在3种障碍物间距中,当间距分别等于1倍和1.2倍的爆震室当量直径时,扇形脉冲爆震燃烧室的DDT距离相差不大,且均短于障碍物间距等于0.8倍爆震室当量直径时的DDT距离。

影响岩溶热储采出温度的开采参数敏感性研究——以河南清丰地区为例

采出温度是影响地热能有效利用率的关键指标,采出温度越高,热储开发效果越好。岩溶热储作为一种重要的地热储层类型,其采出温度受到储层参数的影响。以河南清丰地热田奥陶系岩溶热储为例,通过建立热储地质模型并利用7口地热井资料,进行基于热流和井储耦合的数值模拟研究,探讨储层地质条件和回灌参数对采出温度的影响。研究结果发现,断层的存在加速了热储中低温区向生产井的扩散,导致热突破时间的提前。在开采后期,有断层情况下采出温度较高,且变化曲线斜率远高于无断层情况,表明断层有助于提高清丰地区热平衡时的采出温度,最终有利于增加采热量。目前,一般认为,注采井距越小采出温度越低。但是,当回灌速率高于50 kg/s时,随着开采时间的增加,采出温度呈现快速下降趋势,注采井距835 m下的采出温度甚至高于1000 m的情况。最后,确定清丰地区特定场景下的最优回灌参数组合为:回灌温度20℃、回灌速率50 kg/s、注采井距835 m。本研究结果将为清丰地区或其他类似岩溶热储开发方案的制定提供有益指导。

摩擦摆隔震地铁车站结构地震响应规律研究

基于ABAQUS软件建立土-隔震地铁车站结构静-动力耦合三维数值仿真模型,以典型两层两跨箱型结构为研究对象,将摩擦摆隔震支座应用于地铁车站结构,通过在中柱不同位置布置隔震支座,研究隔震地铁车站的地震响应规律和减隔震效果。结果表明:(1)摩擦摆隔震支座能够增大车站侧墙和板的相对水平位移以及中柱的绝对水平位移且能够有效减小中柱的相对水平位移;从控制结构中柱相对水平位移方面考虑,单支座隔震地铁车站结构应将隔震支座布置于车站底层中柱底部位置,而双支座隔震地铁车站结构应布置于车站顶层和底层中柱柱底位置;(2)摩擦摆隔震支座能够降低隔震层中柱的应力,隔震支座布置于顶层时,其对底层各构件的应力影响较小;隔震支座布置于底层时,最大应力出现在侧墙底部位置且能够有效减小隔震层中柱应力集中的现象;(3)摩擦摆隔震支座能够有效降低隔震层中柱的剪力和弯矩,而对于非隔震层中柱内力的降低则效果不佳;从控制结构中柱内力方面考虑,双隔震支座结构优于单隔震支座结构。

渤海海域印支期构造变形分带性及其特征的数值模拟研究

印支运动为现今渤海海域构造格局的形成奠定了基础,导致渤海海域内部发育3个主要逆冲带。渤海基底内部的先存断层与滑脱层在此过程中可能起到了极为重要的作用,但其如何影响渤海海域印支期的构造变形与分带特征的机制尚不清楚。为了解决上述问题,本文基于地震剖面数据,结合二维热力学数值模拟代码LaMEM对渤海海域印支期的构造变形展开了详细研究。模拟结果揭示,在先存断层存在的条件下,当基底内部无滑脱层或未呈阶梯式在渤海海域分布时,渤海海域内部不会形成相应的逆冲中心;而当基底内部的滑脱层呈阶梯状分布在渤海海域西南部、渤中坳陷以及辽东坳陷3个区域时,应力通过滑脱层在基底内部进行传导,使海域形成了3个逆冲中心,并导致渤海内部大规模的逆冲断层与褶皱变形的发育,与地震剖面具有较好的一致性。数值模拟实验结果证实,基底内部的先存断层与滑脱层是控制渤海海域构造分带性及构造变形特征的重要因素。同时,多逆冲中心演化模式也为解释现今龙门山和四川盆地的形成与演化过程提供了重要的借鉴。

大断面管幕箱涵隧道开挖面极限支护压力研究

【目的】箱涵隧道具有断面大、推进缓慢等特点,开挖面易失稳。【方法】依托合肥市庐州大道浅埋隧道下穿机场跑道实例工程,利用极限平衡理论、摩尔-库伦强度准则、全覆土重理论进行理论推导,并结合大型三维精细化数值模型,对开挖面极限支护压力进行研究。【结果】结果表明:提出了一种简便的管幕作用下大断面箱涵隧道开挖面极限支护压力计算方法。基于此,通过毕肖普条分法计算值与文章提出的极限支护压力计算值相比较,误差极小,证明了该方法的准确性。通过建立管幕箱涵施工三维数值模型,发现地表沉降量和开挖面纵轴线方向位移量随着支护压力的增大而减小,并趋于稳定状态。当支护压力超过静止土压力时,上部土体受强挤压作用,开挖面状态易呈倒S形。【结论】以上结果可为相类似工程提供参考。

矿山法地铁区间隧道切桩密接下穿既有地铁车站的施工沉降监测及控制措施

[目的]地铁区间隧道切桩密接下穿既有地铁车站时,对上部车站变形影响较大,为了确保施工的安全性,需要采取有效措施控制地铁车站沉降。[方法]依托某区间隧道下穿既有地铁车站工程,建立三维数值模型,分析不采取沉降控制措施直接切桩下穿时的车站沉降,研究了增设临时仰拱、错距开挖以及注浆加固等措施的沉降控制效果。提出了多措施组合控制方案,并采用实测的沉降监测数据验证了组合沉降控制方案的可行性。[结果及结论]研究结果表明,不采用控制措施直接下穿地铁车站时,车站最大沉降超过规定限值。注浆加固措施的沉降控制效果最优,沉降减小率为57.3%;增设临时仰拱次之,沉降减小率为40.4%;错距开挖效果最差,沉降减小率为20.8%。多措施组合施工方案,可以满足沉降限值。实测的沉降监测数据显示,多措施组合控制方案能有效控制施工沉降。

二硫化钼的原位力学和摩擦学研究

二硫化钼(MoS_(2))作为一种力学性能优异的典型二维半导体材料,成为制备柔性电子器件的最佳材料之一,同时其层间结合力相对较弱,也是润滑减摩的理想材料。二维材料的结构特性和受载下的力学行为对其服役寿命和摩擦学表现有直接影响。本文系统回顾了二维MoS_(2)原位力学性能和摩擦学性能的理论模拟和实验研究。首先关注了MoS_(2)在纳米压痕过程的弹塑性变形和断裂失效行为,以及缺陷对MoS_(2)机械可靠性的影响,梳理了基于原子力显微镜的原位测试方法的优势和局限。其次,探讨了温度、气氛、湿度和晶格取向等因素对MoS_(2)表面摩擦及层间剪切的影响,并对MoS_(2)作为润滑添加剂在工程应用领域实现宏观尺度减摩润滑的研究现状进行了总结与展望。

The Design and Control of Distillation Column with Side Reactors for Chlorobenzene Production

The distillation column with side reactors (SRC) can overcome the temperature/pressure mismatch in the traditional reactive distillation, the column operates at temperature/pressure favorable for vapor-liquid separation, while the reactors operate at temperatures/pressures favorable for reaction kinetics. According to the smooth operation and automatic control problem of the distillation column with side reactors (SRC), the design, simulation calculation and dynamic control of the SCR process for chlorobenzene production are discussed in the paper. Firstly, the mechanism models, the integrated structure optimal design and process simulation systems are established, respectively. And then multivariable control schemes are designed, the controllability of SRC process based on the optimal steady-state integrated structure is explored. The dynamic response performances of closed-loop system against several disturbances are discussed to verify the effectiveness of control schemes for the SRC process. The simulating results show that the control structure using conventional control strategies can effectively overcome feeding disturbances in a specific range.

Numerical simulations of buoyant reactive jets with sidewall effects

The near field dynamics of buoyant reactive jets with adjacent sidewalls is investigated by time-dependent three-dimensional direct simulations. The physical problem is a fuel jet issuing vertically into an oxidant ambient envi- ronment in a corner configuration with sidewall boundaries. Simulation results are presented for two cases with different jet nozzle geometries: a corner-round reactive jet and a cor- ner-square reactive jet with the same cross-sectional area on the nozzle plane. Buoyancy-induced large vortical structures evolve spatially in the flow field and transition to turbulence occurs downstream. Calculation of the mean flow properties shows that entrainment of the corner-round jet is stronger than that of the corner-square jet due to the stronger vortex deformation in the corner-round case.

Electromagnetic interaction between local surface plasmon polaritons and an atmospheric surface wave plasma jet

We analyze the electromagnetic interaction between local surface plasmon polaritons （SPPs） and an atmospheric surface wave plasma jet （ASWPJ） in combination with our designed discharge device. Before discharge, the excitation of the SPPs and the spatial distribution of the enhanced electric field are analyzed. During discharge, the critical breakdown electric field of the gases at atmospheric gas pressure and the surface wave of the SPPs converted into electron plasma waves at resonant points are studied. After discharge, the ionization development process of the ASWPJ is simulated using a two- dimensional fluid model. Our results suggest that the local enhanced electric field of SPPs is merely the precondition of gas breakdown, and the key mechanism in maintaining the discharge development of a low-power ASWPJ is the wave-mode conversion of the local enhanced electric field at the resonant point.

A study on the surface overpressure distribution and formation of a double curvature liner under a two-point initiation

The formation mechanism of an EFP(explosively formed projectile)using a double curvature liner under the overpressure effect generated by a regular oblique reflection was investigated in this paper.Based on the detonation wave propagation theory,the change of the incident angle of the detonation wave collision at different positions and the distribution area of the overpressure on the surface of the liner were calculated.Three dimensional numerical simulations of the formation process of the EFP with tail.as well as the ability to penetrate 45#steel were performed using LS-DYNA software,and the EFP ve locity,the penetration ability,and the forming were assessed via experiments and x_ray photographs.The experimental results coincides with those of the simulations.Results indicate that the collision of the detonation wave was controlled to be a regular oblique reflection acting on the liner by setting the di-mensions of the unit charge and maintai ning the pressure at the collision point region at more than 2.4 times the CJ detonation when the incident angle approached the cnitical angle.The distance from the liner midline to the boundary of the area within which the pressure ratio of the regular oblique reflection pressure to the qJ detonation pressure was greater than 2.5,2,and 15was approximately 0.66 mm,132 mm,and 3.3 mm,respectively.Itis noted that pressure gradient caused the liner to turn inside out in the middle to form the head of the EFP and close the two tails of the EFP at approximately 120μs.The penetration depth of the EFP into a 45#steel target exceeded 30 mm,and there was radial expansion between the head and tail of the EFP,increasing the penetration resistance of the EFP.Therefore,the structural size of the unit charge and the liner can be further optimized to reduce resist ance to increase the penetration ability of the EFP.

Numerical investigation of positive dihedral application conditions in compressor cascades

This study attempts to make a contribution to the understanding of dihedral application conditions and their aerodynamic mechanisms.The present efforts have finished contrastive investigations on several dihedral blades to their corresponding straight ones with different geometric or aerodynamic conditions including aspect ratio,solidity,aerofoil turning angle,inlet boundary layer configuration and inlet Mach number.A dihedral with the angle between the suction side and the endwall to be obtuse,i.e.,positive dihedral,is chosen.The result reveals the dihedral application conditions consist of aerofoil turning angle,inlet boundary layer,inlet Mach number and so on.The further analysis indicates:in a transonic cascade,two considerations are needed on the contrastive relationship between intensities of the two shocks,namely detached shock and passage shock,and the interaction of the shocks with the corner separation.

Calculation methods of lubricant film pressure distribution of radial grooved thrust bearings

In order to calculate the pressure distribution of radial grooved thrust bearing, analytical and numerical methods were applied respectively. Grooved region and land region were linked by u- sing the mass conservations principle at the groove/land boundary in each method. The block-weight approach was implemented to deal with the non-coincidence of mesh and radial groove pattern in nu- merical method. It was observed that the numerical solutions had higher precision as mesh number exceed 70 x 70, and the relaxation iteration of differential scheme presented the fastest convergence speed when relaxation factor was close to 1.94.