理论力学教学现代化——“理论力学计算机模拟实验”课程的探索

介绍开设“理论力学计算机模拟实验”的目的、做法及实施情况 .

基于力学理论计算的转炉悬挂系统优化分析

对某种转炉悬挂系统进行了受力分析,给出了炉壳平面力系平衡方程,得到了转炉悬挂系统各连杆受力曲线。基于该种转炉悬挂系统力学理论计算,研究悬挂系统结构参数变化时,悬挂系统各连杆受力峰值的变化趋势,为悬挂系统优化设计提供理论依据。

热电池用贫锂相磷酸铁锂正极材料的理论计算研究

为了开发小型化、高比功率热电池,助力新一代导弹武器性能发展,需要发掘新型高电压正极材料。研究发现,贫锂相磷酸铁锂(Li x FePO 4)具有优异的热稳定性和高的电极电位,具备热电池正极材料的应用潜力。通过热力学理论计算,对于Li x FePO 4正极材料高温电化学性能进行分析研究,研究结果表明,高温500℃时,Li x FePO 4的嵌锂量需小于0.028,才能实现电池的放电容量达到602A·s·g^(-1)。

弯曲-外压下钢丝缠绕增强复合管的力学分析

钢丝缠绕增强复合管(PSP)是一种性能优良的金属增强复合管。它由高密度聚乙烯(HDPE)基体层和高强度钢丝螺旋增强层组成。理论分析中采用考虑剪切变形的非线性环理论和虚功原理,依据回型模型法不考虑钢丝增强作用得出弹性系数来简化增强层,将PSP的受力情况简化成二维平面模型,研究弯曲-外压组合荷载作用下PSP的弯矩、曲率、椭圆度等参数变化情况。采用ABAQUS有限元软件建立嵌入钢丝的PSP模型,在相同的弯曲-外压组合荷载作用下得到相关力学参数。比较了理论分析和有限元方法,发现两者所得到的力学参数相近,可以用来对PSP进行弯曲-外压组合荷载下的力学分析。

大功率X射线源测试箱散热方案的设计与分析

为解决测试箱在测试大功率X射线源时遇到的散热问题,根据X射线源及测试箱的结构特点、工况要求、损耗功率等,通过热力学理论计算,初步得出了设备的散热方案;又运用有限元仿真,通过Flotherm软件对设备进行热仿真计算再次得出了散热方案。经过对两种方法进行数据对比后发现,理论计算和有限元仿真所得出的散热方案是一致的,均要求测试箱采用强迫通风散热方案。经实际测试证明,该方案顺利解决了测试箱的散热问题。

深埋近距离煤层开采底板破坏深度确定方法研究与应用

针对鄂尔多斯盆地深埋条件下煤层采动底板扰动破坏深度难以确定的问题,分别采用“三下”规范经验公式、多元线性回归模型、塑性力学理论公式计算、数值模拟和钻孔窥视探测等方法,研究了煤层采动底板破坏深度。研究结果显示,数值模拟结果与实际探测窥视结果较为接近,但该方法流程复杂,应用难度较大;钻孔探测窥视结果为实测值,可信度最高,但施工及观测困难,不宜作为常用手段;而塑性力学理论公式计算结果与实际探测窥视结果基本一致,且计算方便,可适用于近距离深埋煤层底板破坏深度的计算,从而为采空区探放水设计及底板灾害防治工作提供理论依据。

一种吹吸式排风罩的流场测试及数值模拟

采用计算流体动力学理论建立吹吸式排风罩流场的数学模型 .通过数值解法 ,得出了流场内各点的流函数 ,从而绘制成等速度线图 ,实现这种吹吸式排风罩作用范围的预测 .阐述了测试该流场所用的热球风速传感器微机采样系统的主要组成部分、标定原理和结果 .利用该测试系统实测风速绘制的等速度线图与理论模拟所得等速度线图进行了验证和对照 ,它们的作用范围是相符的 。

Recent advances in micro-alloyed wrought magnesium alloys:Theory and design

Micro-alloying design of wrought magnesium(Mg) alloys is an important strategy to achieve high mechanical properties at a low cost. In the last two decades, significant progress has been made from both theory and experiment. In the present review, we try to summarize recent advances in micro-alloying design of wrought Mg alloys from both theoretical and pragmatic perspectives, and provide fundamental data required for establishing the relationship between chemical composition and mechanical properties of Mg alloys. We start with theoretical attempts for understanding the mechanical properties of Mg alloys at different scales, by involving first principle calculations,molecular dynamics, cellular automata, and crystal plasticity. Then, the role of alloying elements is discussed for a series of promising Mg alloys such as Mg-Al, Mg-Zn, Mg-RE(rare-earth element), Mg-Sn, and Mg-Ca families.Potential challenges in the micro-alloying design of Mg alloys are highlighted at the end. The review is expected to provide helpful guidance for the intelligent design of novel wrought Mg alloys and inspire more innovative ideas in this field.

Numerical analysis on coal-breaking process under high pressure water jet

Based on the theory of nonlinear dynamic finite element,the control equation ofcoal and water jet was acquired in the coal breaking process under a water jet.The calculationmodel of coal breaking under a water jet was established;the fluid-structure couplingof water jet and coal was implemented by penalty function and convection calculation.The dynamic process of coal breaking under a water jet was simulated and analyzed bycombining the united fracture criteria of the maximum tensile strain and the maximal shearstrain in the two cases of damage to coal and damage failure to coal.

垂直式HVPE生长GaN材料的数值模拟

建立了HVPE的GaN流体动力学模型。基于CFD理论在三维空间内模拟了垂直式HVPE反应室生长GaN材料的流场、生成物的分布及沉积速率等重要物理参数。通过变化衬底距离出气口的距离、NH3出气口尺寸、衬底旋转等模型,分别进行数值模拟,模拟结果显示,衬底距离出气口的距离及NH3出气口尺寸是影响GaCl与NH3在衬底上的均匀分布和沉寂速率均匀性的重要因素。衬底不同转速则对本反应室中的GaCl与NH3在衬底上的均匀分布、沉寂速率的均匀性影响不大。通过数值模拟发现反应室存在的缺陷,并利用模拟结果对反应室进行了优化。

波能装置与浮式防波堤集成系统的水动力性能

为了研究波能装置与防波堤集成系统的发电与防波性能,使用粘性计算流体动力学软件Star-CCM+建立了二维数值波浪水槽模型。对比方箱在水槽中垂荡运动的实验结果,验证了数值模型,使用该模型研究了动力输出装置的阻尼为最优的情况下,方箱形、Berkeley-Wedge形、三角形和三角加挡板形4种不同底部形状对浮子防波性能和发电性能的影响。结果表明:浮子形状不对称的集成装置的防波和发电性能都要优于浮子形状对称的集成装置;三角加挡板形浮子的性能优越,具有成为理想的海岸保护与波能转换装置的巨大潜力。

Monte Carlo Hamiltonian： Inverse Potential

The Monte Carlo Hamiltonian method developed recently allows to investigate the ground state and low-lying excited states of a quantum system,using Monte Carlo(MC)algorithm with importance sampling.However,conventional MC algorithm has some difficulties when applied to inverse potentials.We propose to use effective potential and extrapolation method to solve the problem.We present examples from the hydrogen system.

Catalytic roles of the acid sites in different pore channels of H‐ZSM‐5 zeolite for methanol‐to‐olefins conversion

H‐ZSM‐5 zeolite is a typical catalyst for methanol‐to‐olefins(MTO)conversion.Although the performance of zeolite catalysts for MTO conversion is related to the actual location of acid sites in the zeolite framework,the catalytic roles of the acid sites in different pore channels of the H‐ZSM‐5 zeolite are not well understood.In this study,the MTO reaction network,involving the aromatic cycle,alkene cycle,and aromatization process,and also the diffusion behavior of methanol feedstock and olefin and aromatic products at different acid sites in the straight channel,sinusoidal channel,and intersection cavity of H‐ZSM‐5 zeolite was comparatively investigated using density functional theory calculations and molecular dynamic simulations.The results indicated that the aromatic cycle and aromatization process occurred preferentially at the acid sites in the intersection cavities with a much lower energy barrier than that at the acid sites in the straight and sinusoidal channels.In contrast,the formation of polymethylbenzenes was significantly suppressed at the acid sites in the sinusoidal and straight channels,whereas the alkene cycle can occur at all three types of acid sites with similar energy barriers and probabilities.Consequently,the catalytic performance of H‐ZSM‐5 zeolite for MTO conversion,including activity and product selectivity,can be regulated properly through the purposive alteration of the acid site distribution,viz.,the location of Al in the zeolite framework.This study helps to elucidate the relation between the catalytic performance of different acid sites in the H‐ZSM‐5 zeolite framework for MTO conversion,which should greatly benefit the design of efficient catalyst for methanol conversion.

Study on How to Design Knitted Fabric Pattern with Mathematical Theory

To improve design capabilities for the knitted fabric pattern,a preliminary study is carried out for the design method.Based on mathematical theory,pattern could be created automatically by computer with inputting different parameters for mathematical functions.The knitted fabric simulation is realized by M1 CAD pattern preparation system of STOLL Company.In the pattern,different color unit is replaced by obverse stitch with different color,or by obverse stitch and reverse stitch with the same color separately,after that the effects of knitted fabrics could be simulated.Designing with this method,it would not only help to acquire a great of diversity patterns,but also improve design efficiency and save cost.

近海风电设备安装船的底部砰击载荷研究

为了分析具有特殊船型的近海风电设备安装船的底部砰击问题,论文提出了一种适用于风电设备安装船的底部砰击载荷计算流程。其中,基于波浪势流理论计算有航速船舶在波浪中的运动响应,利用多项式拟合典型剖面在入水前后时刻的垂向速度时间历程曲线,基于计算流体力学理论数值模拟二维船型剖面入水砰击载荷。然后,针对计算流程中的关键环节进行实验数据对比分析,验证了船舶运动响应和二维剖面入水算法的准确性。最后,根据论文计算方法对近海风电设备安装船的底部砰击特性进行研究。

Insights into Syngas to Methanol Conversion on Cr_(2)O_(3) Oxide from First-Principles-based Microkinetic Simulations

Cr_(2)O_(3) has been recognized as a key oxide component in bifunctional catalysts to produce bridging intermediate,e.g.,methanol,from syngas.By combining density functional theory calculations and microkinetic modeling,we computationally studied the surface structures and catalytic activities of bare Cr_(2)O_(3)(001)and(012)surfaces,and two reduced(012)surfaces covered with dissociative hydrogens or oxygen vacancies.The reduction of(001)surface is much more difficult than that of(012)surface.The stepwise or the concerted reaction pathways were explored for the syngas to methanol conversion,and the hydrogenation of CO or CHO is identified as rate-determining step.Microkinetic modeling reveals that(001)surface is inactive for the reaction,and the rates of both reduced(012)surfaces(25−28 s^(-1))are about five times higher than bare(012)surface(4.3 s^(-1))at 673 K.These theoretical results highlight the importance of surface reducibility on the reaction and may provide some implications on the design of individual component in bifunctional catalysis.

Design of CuCs-doped Ag-based Catalyst for Ethylene Epoxidation

Our recent theoretical studies have screened out CuCs-doped Ag-based promising catalysts for ethylene epoxidation[ACS Catal.11,3371(2021)].The theoretical results were based on surface modeling,while in the actual reaction process Ag catalysts are particle shaped.In this work,we combine density functional theory(DFT),Wulff construction theory,and micro kinetic analysis to study the catalytic performance of Ag catalysts at the particle model.It demonstrates that the CuCs-doped Ag catalysts are superior to pure Ag catalysts in terms of selectivity and activity,which is further proved by experimental validation.The characterization analysis finds that both Cu and Cs dopant promote particle growth as well as particle dispersion,resulting in a grain boundary-rich Ag particle.Besides,CuCs also facilitate electrophilic atomic oxygen formation on catalyst surface,which is benefitial for ethylene oxide formation and desorption.Our work provides a case study for catalyst design by combining theory and experiment.

Study of Thermodynamics of Liquid Noble-Metals Alloys Through a Pseudopotential Theory

The Gibbs-Bogoliubov （GB） inequality is applied to investigate the thermodynamic properties of some equiatomic noble metal alloys in liquid phase such as Au-Cu, Ag-Cu, and Ag-Au using well recognized pseudopotential formalism. For description of the structure, well known Percus-Yevick （PY） hard sphere model is used as a reference system. By applying a variation method the best hard core diameters have been found which correspond to minimum free energy. With this procedure the thermodynamic properties such as entropy and heat of mixing have been computed. The influence of local field correction function viz; Hartree （H）, Taylor （T）, lehimaru-Utsumi （IU）, Farid et al. （F）, and Sarkar et al. （S） is also investigated. The computed results of the excess entropy compares favourably in the case of liquid alloys while the agreement with experiment is poor in the case of heats of mixing. This may be due to the sensitivity of the heats of mixing with the potential parameters and the dielectric function.

Thermochemical properties and thermokinetic behavior of energetic triazole ionic salts

The properties of dissolution in different solvents,the specific heat capacity and thermal decomposition process under the non-isothermal conditions for energetic triazole ionic salts 1,2,4-triazolium nitrate(1a),1,2,3-triazolium nitrate(1b),3,4,5triamino-1,2,4-triazolium nitrate(2a),3,4,5-triamino-1,2,4-triazolium dinitramide(2b)were precisely measured using a Calvet Microcalorimeter.The thermochemical equation,differential enthalpies of dissolution(△difH m ),standard molar enthalpies of dissolution(△difH m ),apparent activation energy(E),pre-exponential constant(A),kinetic equation,linear relationship of specific heat capacity with temperature over the temperature range from 283 to 353 K,standard molar heat capacity(C p,m)and enthalpy,entropy and Gibbs free energy at 283–353 K,taking 298.15 K as the benchmark for 1a,1b,2a and 2b were obtained with treating experimental data and theoretical calculation method.The kinetic and thermodynamic parameters of thermal decomposition reaction,critical temperature of thermal explosion(Tb),self-accelerating decomposition temperature(TSADT)and adiabatic time-to-explosion(t)of 1a,1b,2a and 2b were calculated.Their heat-resistance abilities were evaluated.Information was obtained on the relation between molecular structures and properties of 1a,1b,2a and 2b.

Energetic electron flux distribution model in the inner and middle magnetosphere

Based on the magnetospheric kinetic theory, a model is developed to specify the flux of energetic electrons in the inner and middle magnetosphere. Under the assumption of adiabatic motion and isotropic particle distribution maintained by pitch-angle scattering, the model calculates the electron flux by following bounce-averaged electric field, gradient, and curvature drift in the time dependent electric and magnetic field, meanwhile it counts the electron loss caused by pitch angle scattering. Using the model, the clectron flux distribution during a magnetic storm was calculated and compared with the observation data from the geosynchronous orbit. It is shown that the model can successfully reproduce most of the major electron flux enhancements observed at the geosynchronous orbit and generally tracks the satellite data well. The rms errors of the modeled logarithm of flux are between 0.5-1.0.