An approach for simulating the air brake system of long freight trains based on fluid dynamics

Air brake systems are critical equipment for railway trains, which affects the running safety of the trains significantly. To study air braking characteristics of long freight trains, an approach for simulating air brake systems based on fuid dynamics theory was proposed. The structures and working mechanisms of locomotive and wagon air brakes are introduced, and mathematical models of the pipes, brake valves, reservoirs or chambers, cylinders, etc., are presented.Besides, the dynamic motions of parts in the main valve are considered. The simulation model of the whole air brake system is then formulated, and the solving method based on the finite-difference method is used. New efficient pipe boundary conditions without iterations are developed for brake pipes and branch pipes, which can achieve higher computational efficiency. The proposed approach for simulating the air brake system is validated by comparing with published measured data. Simulation results of different train formations indicate that models that consider the dynamic behavior of brake pipes are recommended for predicting the characteristics of long trains under service braking conditions.

Simulating the strong ground motion of the 2022 MS6.8 Luding,Sichuan,China Earthquake

Stochastic finite-fault simulations are effective for simulating ground motions and are widely used in engineering to determine the impacts of ground motion and develop relevant predictive equations.In this study,the source,path,and site amplification coefficient of western Sichuan Province,China,and stochastic finite-fault simulations were used to simulate the acceleration time series,Fourier amplitude spectra,and 5%damped response spectra of 28 strong-motion stations with rupture distances within 300 km of the 2022 MS6.8 Luding earthquake.The simulation results of 14 stations at rupture distances of 45-185 km match the observation.However,the simulation results of 3 near-and 6 far-field stations at rupture distances of 12-36 km and 222-286 km,respectively,were obviously deviated from the observations.Simulation results of the near-field stations are larger than the observations at high frequencies(>6 Hz).The discrepancy likely comes from the nonlinear site effect of near-field stations,which reduced the site amplification at high frequencies.Simulation result of the far-field stations is smaller than the observation at frequencies above 1 Hz.As these stations are located close to the Longmenshan Fault Zone(LFZ),thus,we obtained a new quality factor(Q)from data of historical events and stations located around LFZ.Using the new Q value,the discrepancies of the high-frequency simulation results of the far-field stations were corrected.This result indicated that the laterally varying Q values can be used to address the impact of strong crustal lateral heterogeneity on simulation.

Ballistic response of skin simulant against fragment simulating projectiles

The response of biological phantoms against high velocity impact is actively sought for applications in defense,space,soft robotics and sensing.Towards this end,we study the ballistic response of silicone based skin simulant against fragment impact.Using a pneumatic gas gun setup,six chisel-nosed and three regular shaped(sphere,cylinder,and cube)fragments were impacted on the skin simulant.The resulting skin simulant response was studied in terms of ballistic limit velocities,energy densities,failure pattern,and the mechanics of interaction.The results indicate that the shape of the fragment affects the ballistic limit velocities.The ballistic limit velocities,energy densities of the chisel-nosed fragment simulating projectiles were relatively insensitive to the size(mass),except for the smallest(0.16 g)and largest(2.79 g)chisel-nosed fragment.For the same size(1 g),ballistic limit velocities and failure are dependent on the shape of the fragment.The skin simulant failed by combined plugging and elastic hole enlargement.Failure in the spherical fragment was dominated by the elastic hole enlargement,whereas plugging failure was dominant in all other fragments.The spherical,cylindrical,and chisel-nosed fragments created circular cavities,and the cubical fragment created a square cavity.In the case of the spherical fragment,slipping of the fragment within the skin simulant was seen.Cubical fragments created lateral cracks emanating from the corners of the square cavity.Interestingly,for all the fragments,the maximum deformation corresponding to the perforation was lower than the non-perforation indicating rate dependent,stress driven failure.The maximum deformation was also dependent on the shape of the fragment.Overall,these results provide unique insights into the mechanical response of a soft simulant against ballistic impact.Results have utility in the calibration and validation of computational models,design of personal protective equipment,and antipersonnel systems.

Evaluation of Performance of Polar WRF Model in Simulating Precipitation over Qinghai-Tibet Plateau

Considering the complex topographic forcing and large cryosphere concentration,the present study utilized the polar-optimized WRF model(Polar WRF)to conduct downscaling simulations over the Qinghai-Tibet Plateau(TP)and its surrounding regions.Multi-group experiments with the 10 km horizontal resolution are used to evaluate the modeling of precipitation.Firstly,on the basis of the model ground surface properties upgrade and the optimized Noah-MP,the“better-performing”configuration suite for modeling precipitation is comprehensively examined.Various model parameters such as nudging options,five cumulus parameterization schemes,two planetary boundary layer schemes,and six microphysics schemes are investigated to further refine the Polar WRF configuration.Moreover,the precipitation simulation for a full calendar year is compared with multiple reanalyses and observations.The simulations demonstrate that the Polar WRF model successfully captures the general features of precipitation over this region and is sensitive to model parameters.Based on the results,it is recommended to use grid nudging with q intensity coefficient of 0.0002,the multi-scale kain-fritsch cumulus parameterization,the Yonsei University boundary layer scheme,and the Morrison 2-mom microphysics with reduced default droplet concentration value of 100 cm-3.Overall,the model performance is better than the ERA-interim and TRMM 3b42.It is comparable to,and in some cases slightly better than,the CRA-Land,especially in the prediction for the western part of the plateau where in situ observations are limited,and the cryosphere-atmosphere interaction is more pronounced.

Method of simulating hybrid STT-MTJ/CMOS circuits based on MATLAB/Simulink

The spin-transfer-torque(STT)magnetic tunneling junction(MTJ)device is one of the prominent candidates for spintronic logic circuit and neuromorphic computing.Therefore,building a simulation framework of hybrid STT-MTJ/CMOS(complementary metal-oxide-semiconductor)circuits is of great value for designing a new kind of computing paradigm based on the spintronic devices.In this work,we develop a simulation framework of hybrid STT-MTJ/CMOS circuits based on MATLAB/Simulink,which is mainly composed of a physics-based STT-MTJ model,a controlled resistor,and a current sensor.In the proposed framework,the STT-MTJ model,based on the Landau-Lifshitz-Gilbert-Slonczewsk(LLGS)equation,is implemented using the MATLAB script.The proposed simulation framework is modularized design,with the advantage of simple-to-use and easy-to-expand.To prove the effectiveness of the proposed framework,the STT-MTJ model is benchmarked with experimental results.Furthermore,the pre-charge sense amplifier(PCSA)circuit consisting of two STT-MTJ devices is validated and the electrical coupling of two spin-torque oscillators is simulated.The results demonstrate the effectiveness of our simulation framework.

The Assessment of the Application of the CFD Package OpenFOAM to Simulating Flow around the Propeller

During the design process of the ship,a lot of attention is given to tune-up parameters of the propeller,which is one of the most important part of the propulsion system.Designing new generation,more effective and efficient propellers require knowledge of hydrodynamic phenomena occurring in the propeller area.For this reason,a lot of time and funds is spent on the propeller research and development.Usually these are experimental tests in cavitation tunnels and towing tanks.However,more and more research is carried out by CFD simulation.OpenFOAM software is open source CFD package,which becomes popular alternative to commercial codes.This paper attempts to answer the question:if OpenFOAM is suitable for such specific applications like accurate simulation of flow around the propeller?The paper presents the results of a CFD simulation of marine propeller created with OpenFOAM software.The obtained results were compared with the of the commercial CFD codes simulations and the experimental research.

仿真技术在船舶舱室单元生产线设计中的应用

采用流水线模式生产船舶预制舱室单元正越来越受到关注,但目前针对其生产线设计方法的研究较少,为了改进流水生产线设计方案,提高生产力,本文开展仿真技术在舱室单元流水生产线设计不同阶段中的应用研究。首先在工序规划阶段运用遗传算法模块优化生产工序,其次在布局设计阶段基于仿真试验模块求解最佳库容,最后在方案比选阶段通过模拟复杂生产系统运行输出关键指标。研究结果表明,仿真技术在能为流水线工艺和布局设计提供有力支撑,对工程设计具有应用价值。

耦合超声场的气液流动特性

功率超声作为一种新兴的绿色技术,越来越受到石油行业的重视。结合稠油超声降黏机制,从气泡瞬态演化规律和溃灭特性出发,对超声作用下空化气泡和空化流场进行数值模拟和实验验证。模拟结果表明,增加超声频率和减小气泡之间的距离会导致单个空化气泡最大半径的减小,气泡个数的增加会使气泡生长至破裂过程的速度减小,延长超声作用时间和增大超声频率可增加超声场中最大空化压力。实验表明,空化气泡不断在超声场中振荡并互相聚并,且随着超声作用时间的延长,该过程更加剧烈。研究内容为稠油超声降黏在石油化工行业的应用提供了重要的理论指导。

静态混合器结构优化设计与流场特性分析

为油田高能效驱油以提高原油产量,针对SK型和SX型静态混合器混合单元结构,通过创新设计和三维建模开发多重螺旋混合单元静态混合器,基于静态混合原理,利用FLUENT数值模拟软件,采用有限体积法,对所开发混合器内流体的流场进行仿真分析,研究该结构静态混合器的流动特性,结果表明,该种静态混合器使流体产生剪切和正反向涡旋作用,流体被充分扰动,混合均匀,满足油田注聚驱油要求,可为油田开发新型高效静态混合器提供一定技术支持。

汽车涂层样本单颗粒冲击破坏仿真分析

研究汽车涂层在冲击载荷下的破坏现象,对于预测涂层抗石击性能以及指导涂层结构设计和优化具有重要意义。建立了汽车涂层样本单颗粒冲击破坏有限元模型,使用自主开发的显式有限元求解器模拟汽车涂层冲击破坏过程。涂层层内破坏、基底与涂层界面分离破坏模式的仿真结果与试验结果的良好一致性,验证了仿真分析方法的有效性,揭示了涂层在冲击载荷下的层内破坏与界面分离破坏的失效机理。

元宇宙技术发展综述及其在建筑领域的应用展望

新冠疫情的暴发使得人们的活动越来越多地向线上转移,元宇宙概念热潮的出现使得基于虚拟数字世界的生产生活模式越来越多地受到人们关注。目前,元宇宙概念已经在教育、商业、工业等领域有所应用。随着建筑信息化、数字化技术的广泛应用,建筑行业智能化水平不断提高,虚拟数字技术在建筑行业发展中扮演着越来越重要的角色。对元宇宙概念的最新发展和应用进行介绍,重点阐述元宇宙与建筑信息化技术的关系以及元宇宙在建筑领域的潜在应用。分析结果表明,元宇宙的发展依赖于拓展现实、数字孪生、区块链等既有数字化技术的集成,作为一种新技术,元宇宙将为建筑领域的生产方式带来新的改变,也可能催生新的产业模式。

基于驾驶模拟的超车仿真教学实验设计

道路交通运输专业具有多学科融合、紧密结合实践的特点,但许多交通专业课程的实践教学环节往往会受到场地大小、条件不可控、重复性差和实际道路危险性等不利因素的限制而无法顺利开展。为提升学生的实践能力与课程参与度,基于驾驶模拟技术,探讨可用于交通仿真、道路交通安全及交通行为分析等课程教学的超车仿真教学实验项目,教学实验以锻炼学生分析解决问题能力和实践操作能力为目标,详细地设计实验流程与实践教学内容,并将该实验项目在道路交通安全、交通仿真等课程的实践环节进行应用,为驾驶模拟系统在教学实验中的应用提供参考。

基于虚实结合的雷达操作训练方法研究

针对雷达训练中缺环境、缺装备的现状,提出了基于虚实结合的雷达操作训练方法。首先,分析了虚实结合概念的内涵;其次,研究了实体雷达与虚拟环境和虚拟雷达与实体环境两种虚实结合的交互方法;最后,结合具体训练需求,在同一场景中分析了实-实、实-虚、虚-实、虚-虚四种雷达与环境交互方法在雷达训练中的应用。

雷达制导半实物仿真目标速度控制算法优化

针对末制导雷达半实物仿真试验中回波模拟质量问题,分析了时统不一致对回波模拟信噪比的影响,通过改进的中值滤波算法,优化了射频仿真系统中目标速度控制算法,有效消除了重帧、丢帧对回波信号的影响,大大提升了回波信噪比,保证了射频半实物仿真系统仿真结果的可信度。

虚实结合的驾驶人风险感知能力评测教学实验设计与实践

驾驶人风险感知能力评测教学实验立足于我国高质量人才培养课程这一核心要素,充分考虑不同道路交通因素对驾驶人安全驾驶的影响,致力于打造虚实结合的线上线下混合式一流教学实验课程。该教学实验基于交通仿真技术,通过线上实验与线下仿真模拟实验相结合的方式,在任课教师的指导下,由学生自主完成课程学习、场景设计、线上或线下实验和实验报告等实验流程。培养学生在课程学习与实验中的创新性与主观能动性,提升学生综合素质与团队协作能力,综合考量学生对道路交通多项学科专业课的掌握情况,并基于现阶段的教学情况对未来提出展望。

MVSim:面向VLIW多核向量处理器的快速、可扩展和精确的体系结构模拟器

设计了一个面向VLIW多核向量处理器的快速、可扩展、精确的体系结构模拟器MVSim。设计了可扩展的VLIW多核向量处理器模型、多级存储体系结构模型和多核性能模型;实现了指令集架构的节拍精准模拟,Cache、DMA和多核同步部件的高效功能模拟,采用多线程技术实现了多核处理器的高效和可扩展模拟。实验结果表明,MVSim能够准确模拟多核处理器的目标程序执行,模拟结果完全正确,具有良好的可扩展性。MVSim的平均模拟速度分别是RTL模拟和CCS的227倍和5倍,平均性能误差约为2.9%。

SiGe BiCMOS低噪声放大器激光单粒子效应研究

随着CMOS工艺的日益成熟和SiGe外延技术水平的不断提高,SiGe BiCMOS低噪声放大器(LNA)广泛应用于空间射频收发系统的第一级模块.SiGe HBT作为SiGe BiCMOS LNA的核心器件,天然具有优异的低温特性、抗总剂量效应和抗位移损伤效应的能力,然而,其瞬态电荷收集引起的空间单粒子效应是制约其空间应用的瓶颈问题.本文基于SiGe BiCMOS工艺低噪声放大器开展了单粒子效应激光微束实验,并定位了激光单粒子效应敏感区域.实验结果表明,SiGe HBT瞬态电荷收集是引起SiGe BiCMOS LNA单粒子效应的主要原因.TCAD模拟表明,离子在CMOS区域入射时,电离径迹会越过深沟槽隔离结构,进入SiGe HBT区域产生电子空穴对并引起瞬态电荷收集.ADS电路模拟分析表明,单粒子脉冲瞬态电压在越过第1级与第2级之间的电容时,瞬态电压峰值骤降,这表明电容在传递单粒子效应产生的瞬态脉冲过程中起着重要作用.本文实验和模拟工作为SiGe BiCMOS LNA单粒子效应抗辐射设计加固提供了技术支持.

苏北盆地建湖隆起沉积盆地型干热岩资源潜力评价

对苏北盆地建湖隆起的干热岩资源潜力进行评价,展示华东地区沉积盆地型干热岩资源的勘探前景。基于野外勘察、室内实验和数值模拟等多手段地质分析方法分析研究区干热岩地热地质条件,以4个区域地震地质剖面为基础,建立二维热传导数值模型,模拟分析深部地温分布,确定评价深度。应用基于体积法的蒙特卡罗模拟给出合理的资源量评价分析。该方法可充分考虑参数估计的不确定性。结果表明,建湖隆起3~10 km深度内干热岩资源的可采热资源量约为44.6亿t标煤,发电潜力为692 769.9 MWe,约为江苏省2022年全年用电量的49倍。

基于Plant Simulation的化纤自动落丝系统仿真实验分析

基于Plant Simulation软件,构建一种化纤自动落丝系统的3D数字化模型,对系统效率关键输入因子进行参数化设置,将系统各工位三维数字模型导入软件中建立层次化运动机构图形结构,并运用Simltalk语言实现三维动作仿真,通过基础物理参数设置,保证了仿真数字化模型与现实系统更具一致性。通过多级实验设计分析了系统影响因子对于系统效率的影响特性曲线,并进一步通过动态参数化实验方法,计算出双输入因子对系统效能影响的敏感度。该实验结果可为化纤自动落丝系统的建设成本控制与可行性分析提供指导,具有较好的工程应用价值。

MW级大储能量飞轮轴系结构力学及动力学研究

当前,对于高功率大储能量飞轮储能系统的仿真和实验研究还不够充分,本工作主要针对MW/100 MJ级飞轮储能样机展开。比较分析了内置式和表贴式两种结构飞轮电机转子的结构力学,比较了不同动平衡块材质对应力及形变的影响,并开展了轴系的动力学特性分析。对飞轮样机开展了实验测试,验证了系统的稳定性。数值计算结果表明,表贴式结构形式可以使电机硅钢片应力显著降低,但是通常这种结构需要在硅钢片外缠绕碳纤维加强层,以确保运行时磁钢不会因为离心力与硅钢片发生分离。动平衡块材质为不锈钢时的应力值相较于动平衡块为铝合金时提高了45%以上。对轴系进行了动力学特性分析,在工作转速下存在着1300 r/min和4200 r/min两个刚性振型,分别为平动和锥动。测试运行中,飞轮轴系在1300 r/min出现振动峰值,证明了数值仿真计算的准确性。但是数值仿真中的4200 r/min临界转速(锥动)在实际运行中并未出现明显峰值,在本工作的轴系结构中,相较于锥动,平动振型更容易被激发。