铝合金板式节点初始刚度

铝合金板式节点变形分为节点板中心区域变形、节点板与杆件错动以及杆件自身变形三部分.对铝合金板式节点的受弯机理进行分析,得到节点初始弯曲刚度公式.在试验基础上,分析试件的抗弯性能,得到弯矩-转角曲线.采用ABAQUES软件对节点进行数值模拟,数值结果与试验结果吻合较好.通过参数分析得知节点板厚度、杆件截面高度、螺栓数量及节点板半径对节点初始弯曲刚度的影响.最后将理论结果分别与数值结果和试验结果进行比较,验证了公式的合理性.     

锚杆注浆联合支护大断面煤仓硐室围岩变形分析

以土朱矿井煤仓硐室为例,运用损伤力学分析了巷道开挖效应;利用FLAC4.0数值模拟软件计算分析了大断面硐室围岩的稳定性,并建立了无支护和锚杆注浆联合支护两种模拟方案,两种方案模拟结果的对比显示锚注联合支护形式能够有效地加固围岩和控制围岩变形;通过工程类比法和FLAC数值模拟相结合对大断面硐室锚杆注浆联合支护方案进行了设计,确定了锚注联合支护参数,通过后期的现场观测,说明了锚杆注浆联合支护在大断面煤仓硐室支护中效果良好,能够保证硐室围岩的长期安全稳定.     

高炉三维气固湍流和煤粉燃烧过程数值模拟

基于欧拉气相方程组、欧拉颗粒连续方程和动量方程以及拉氏颗粒能量和质量变化方程,建立并发展了高炉风口回旋区湍流气固两相流动和煤粉燃烧的三维数学模型.用所建模型分别对冷态模型内气固两相流动和某企业750 m3高炉风口回旋区内的气固两相三维流动与煤粉燃烧进行了数值模拟.采用三维激光相位多普勒分析仪(PDA)对冷态模型内气固两相流场进行了测量,实验结果与冷态两相流动的模拟结果基本一致.热态模拟结果给出了气相温度和组分浓度分布,模拟结果与实验测量结果较吻合,揭示了风口回旋区内气固两相流动和煤粉燃烧的基本性质和特点.     

刷式密封传热特性研究

采用求解Non-Darcian多孔介质模型的完全雷诺平均Navier-Stokes(RANS)方程和能量方程的方法,在考虑刷丝束内部空隙、安装角和转轴旋转效应下,数值研究了刷式密封的几何结构参数,即刷丝束厚度、干涉量,以及刷式密封的运行工况参数,即转速和压差等,对单级刷式密封传热特性的影响规律,刷丝束多孔介质的内部阻力系数是利用Eugrn方程推导并经过实验数据校准确定的.研究结果表明:刷丝束厚度内的温度沿轴向近似均匀分布,刷丝束围栏高度区域内的温度沿径向呈指数迅速下降;随着压差的增大,温度下降更加集中在刷丝束围栏高度区域内;随着热流量增加,最高温度呈指数迅速升高;随着刷丝束厚度增加,泄漏量减少,最高温度升高;随着转速提高和刷丝束与转轴间的干涉量增大,最高温度升高.     

多孔底面轴对称二相重力流的数值模拟

对于具有多孔介质底面的轴对称二相重力流,引进基于浅水近似的控制方程和相应的边界条件,采用贴体坐标变换使运动边界问题化为固定边界问题,提出了基于特征插值并结合使用梯形积分公式和Newton-Raphson迭代法在时间和空间都具有二阶精度的数值边界条件．为检验格式的性能和避免编写程序时可能出现的错误,对类似的方程构造了一类精确解．在空间上采用了二步Lax格式、二阶TVD格式、三阶ENO格式及五阶WENO格式,在时间上采用了二阶及三阶的TVD-Runge-Kutta方法对该问题进行数值模拟．数值结果表明,在解的光滑区域,这几种格式的精度都很高,但是在大梯度区,二步Lax格式将会产生强烈的数值振荡,且振荡不会随网格宽度的减小而减小,而其他3种格式将不会或仅会产生幅度要小得多的数值振荡,且振荡会随网格宽度的减小而趋向于零．对实际应用目的来说,结合使用二阶TVD-Runge-Kutta方法的二阶TVD格式是一个经济而又适当的选择．     

Thermal wave propagation in graphene studied by molecular dynamics simulations

The transient heat conduction in both armchair and zigzag-edged graphene ribbons pulsed by local heating with a duration of 1 ps was studied using nonequilibrium molecular dynamics simulations. The results show that the heat pulse excites two waves which indicates non-Fourier heat conduction. One of the two waves is a sound wave （first sound）, which has macroscopic momentum and propagates at the speed of sound. The other is a thermal wave （second sound）, whose propagation speed is 1/√3 of the sound velocity. The sound wave excited by the heat pulse is a longitudinal wave, whose energy is only transported in the longitudinal direction. The thermal wave excited by the heat pulse is generated by transverse lattice vibrations, with the energy only having the transverse component. The observed anisotropy of the transient heat conduction suggests that the system is in a non-equilibrium state during propagation of the heat pulse. Further statistical analyses show that the displacement of the heat pulse energy is related to the time as 〈σ2〉 ∝ t^1.80, which implies that heat transport is ballistic-diffusive transport in graphene. The higher proportion of the ballistic transport will lead to stronger heat waves. At the crest of the thermal wave, energy is transported ballistically, while in the diffusive region and during attenuation of the thermal wave, the energy is transported diffusively.     

用Monte Carlo方法计算非Gauss噪声的重整流和效率

为提高分子马达的流与效率,用Monte Carlo方法研究了非Gauss噪声驱动的布朗粒子在闪烁棘轮势场中的流和效率。在无势情况下,粒子向两边对称地自由扩散,其分布密度函数偏离Gauss分布,存在一个长拖尾或大随机力分布被截断;当势恢复后,不对称的棘轮势将无规扩散整流成定向输运流。结果表明:棘轮势整流非Gauss噪声驱动的布朗马达,能获得比Gauss噪声情况大很多的流和效率;而且随着噪声参数的变化,流能发生反向现象。     

NaF-NaCl和KF-KCl熔盐系统的分子动力学模拟

用分子动力学模拟方法研究了NaF-NaCl和KF－KCl熔盐系在氯化物一端1000℃的混杂过程。模拟表明该过程是一弱放热过程，与现有实验数据相符，同时利用偏径向分布函数的差别初步解释了模拟结果，分析偏径向分布函数图，观察到混合系统的Cl^-－Cl^-的第一峰分裂成双峰。     

具有线性趋势回归信度模型的随机效应及线性趋势的Score检验

讨论了具有线性趋势的回归信度模型的随机效应和线性趋势的Score检验问题.首先分别推导出模型中随机效应存在性和线性趋势显著性这2种检验的Score检验统计量,然后利用Monte-Carlo方法分别模拟了此2种检验统计量的功效.功效模拟结果显示,2种检验统计量都有很好的检验效果.最后利用所得到的检验方法对旅客意外身体伤害保险数据进行了实例分析,分析结果表明,该数据集的随机效应是存在的,线性趋势也是显著的.     

Enhanced nanocrystalline stability of BCC iron via copper segregation

Nanocrystalline alloys are known for their high density of grain boundaries (GBs), which results in low thermal stability and a tendency for coarsening. In this work, we investigated Fe–Cu alloys to explore the effects of Cu concentration on the thermal stability of nanocrystalline samples. Using hybrid molecular dynamics (MD) and Monte Carlo (MC) simulations, annealing treatments of nanocrystalline samples with varied Cu concentrations were conducted. The simulation results revealed that Cu atoms tended to accumulate at GBs. Subsequently, the model with Cu segregation was subjected to mechanical creep loading at various temperatures. Through the analysis of atomic structure evolution during creep deformation, it was found that Cu segregation efficiently stabilizes GBs and restricts their movement. The present findings highlight that the thermal stability of nanocrystalline Fe–Cu alloys can be effectively improved by introducing suitable Cu segregation at GBs.