基于小波变换的长周期桥梁选波方法研究

时程分析输入地震波的选取对长周期大跨度桥梁影响显著。本文基于规范目标谱,以MATLAB为依托,通过选取最优小波基并利用小波系数迭代法实现频域调整,使地震波反应谱不断逼近给定目标谱,最后结合相对误差和长周期拟合参数两个指标进行综合评价,选取适用于长周期大跨度桥梁的时程分析地震波,提出长周期桥梁全过程批量选波方法。将该方法应用于奉节长江大桥,与基于时域调整方法的Seismo Match选波软件对比选波效果,并将选波结果应用于背景桥梁的时程分析。结果表明,利用本文选波方法所得结构关键截面响应与软件选波所得响应在横桥向和竖桥向存在一定差异。本文方法可为长周期大跨度桥梁时程分析选波提供参考。

振动分选流化床气泡动态演变与细粒煤分选特性

振动流化床能够有效强化细粒煤的分选提质过程,通过利用二维振动分选流化床,以煤粉和磁铁矿粉混合作为二元复合加重质,采用压力传感器测量床层中的压力信号,结合高速动态摄像机同步捕捉气泡在床层中的演变行为,研究二维振动分选流化床中气泡的动态演变规律,探索气泡行为对细粒煤分选效果的影响。此外,利用塌落试验,研究不同操作条件下床层膨胀高度和气泡体积占比,进而揭示振动气流协同对气泡动态演变行为的抑制作用。研究结果表明,振动能量的引入能够促进颗粒床层均匀流化,在v=16 cm/s,f=20 Hz和A=2 mm条件下,床层压降波动稳定,随振动频率的增大,床层完全流化膨胀高度H_(e)先增加后减小,气泡相体积分数Y先减小后增大。但随着振幅的增加,床层完全流化膨胀高度H_(e)先增加后减小,气泡相体积分数Y逐渐增大。振动与气流的协同作用对床层中的气泡行为具有明显的抑制作用,但随着床层高度的增加,气泡尺寸的瞬时值和平均值均逐渐增大,且在床层中上部,气泡尺寸分布范围较宽。在最佳操作条件下,气泡平均尺寸为1.12~2.45 cm,气固接触效率高,床层介质颗粒呈准散式流化,此时,气泡对细粒煤分选效果的扰动作用弱,细粒煤分选效果最好,选后精煤灰分和产率分别为8.2%和56.1%,矸石的灰分和产率分别为44.5%和43.9%。

振动重介质分选流化床流化质量改善机理与细粒煤高效分选

煤炭清洁高效利用是国家重大战略需求。随着我国煤炭工业重心战略西移和综采技术的普及,所开采的原煤尤其是动力煤日趋“贫、细、杂”化,迫切需要细粒煤高效干法分选技术。细粒煤具有迎风面积小、重力效应弱的特点,风力分选时介质密度与分选密度差异大,传统的干法重介质分选时气泡大、返混严重,均无法在有限时间和空间内实现细粒煤有效分离。将简谐振动与上升气流协同输入气固重介质流化床,通过振动能量强化气固接触、抑制气泡兼并、改善流化质量。着重研究了振动能量在床层中的传递过程与床层响应规律,发现床层密度的扰动程度主要取决于上升气流与振动能量的竞争协调结果,气泡引发床层密度的随机性波动,振动能量将颗粒由无规律的随机运动转变为周期性振荡,沿床层轴向挤压破碎气泡;基于经典两相理论,结合床层塌落过程中气泡相与乳化相的逸出规律,计算得到了振动激励下气体在气泡相与乳化相中的分布比例,表明振动能量可以有效驱使气体由气泡相迁移至乳化相,气泡体积减少19.23%,削弱了气泡引起的床层波动,改善了流化质量,形成了均匀稳定的流态化分选环境。建立了振动对流化质量改善效果的量化评价模型,明确了适合细粒煤高效分选的振幅、频率、气速3因素协同操作范围,将新疆黑山矿薄煤层6~1 mm精煤发热量相较于原煤提高了4 571 kJ/kg。

复杂混合粒群简谐振动离析动力学特性

混合粒群在振动作用下的离析分层为矿物颗粒的筛分分级提供了实现基础,颗粒形状特征及粒级结构是影响离析速率及结果的重要因素。基于离散元法数值模拟探究了单个(非)球形大颗粒在小颗粒群中离析动力学特性,研究了颗粒形状对其离析速率的影响规律,分析了二元均匀混合粒群中形状与粒度之间的交互作用,揭示了多元混合粒群中离析速率及转动取向分布规律。试验结果表明:较强振动作用下,球形大颗粒离析速率随粒度比的增加呈现先增加后降低的非单调变化趋势,而非球形大颗粒离析速率显著高于球形大颗粒,主要原因是其颗粒底端延伸至孔隙率波动较大的深床层。此外,非球形大颗粒与球形大颗粒的离析速率差值随着振幅的增加同样呈现先升高后降低的变化趋势;当二元混合颗粒群中存在对流时,其离析速率明显高于无对流颗粒群的离析速率;二元混合料群中非球形大颗粒的离析速率与转动取向呈现“类高斯”分布特征,且非球形颗粒的形状与粒度对最终离析结果的影响存在竞争关系,导致球形大颗粒-非球形小颗粒床在小粒度比、低球形度条件下出现异常的“反巴西果”现象;此外,颗粒形状对离析速率的影响显著性高于粒级结构,增加中间粒级颗粒会减缓粒群的离析过程,而拓宽粒度分布范围同样也会造成离析速率下降。

湿黏细粒煤干法筛分理论及交叉筛技术发展现状

湿黏细粒煤的干法深度筛分理论与技术是当前国际筛分领域的研究热点和难点。其中,筛面易堵孔和筛面寿命短是湿黏细粒煤干法筛分时的核心基础问题。为了掌握当前湿黏细粒煤干法筛分理论及技术的发展现状,分析了2种广泛应用的细粒煤筛分设备:基于等厚筛分理论的等厚筛和基于弛张筛分理论的弛张筛的应用及研究存在的问题,讨论了筛分过程基础理论中颗粒分离机理的研究现状,总结了基于离散元方法(DEM,Discrete Element Method)的筛分过程中有关筛面颗粒流动特性数值模拟研究存在的不足。结果表明:筛分过程基础理论是发展新筛分技术和提升筛分设备设计水平的关键,非球形湿黏颗粒系统的分离行为和筛面高湿黏颗粒流动特性及透筛机理是筛分过程基础理论的关键问题,利用基于DEM的数值方法可以实现从颗粒尺度深入研究筛分过程中非球形湿黏颗粒的有关运动行为。此外,阐述了交叉筛的结构特点及筛分过程机理,总结了国内外有关交叉筛技术的应用及研究现状,分析了交叉筛的筛分过程基础理论研究的不足,以及存在缺少交叉筛关键结构及工艺参数的优化设计理论和方法的主要问题,提出了基于筛面-颗粒耦合模拟的交叉筛分过程机理、交叉筛结构轻量化设计及节能优化控制等研究展望。

振动流化床流化特性与细粒煤干法分选

将振动能量引入气固分选流化床,形成振动分选流化床,将煤粉和磁铁矿粉混合作为二元复合加重质,利用微差压传感器在线采集床层压力信号,并采用信号时频分析方法将信号进行划尺度分解,从微观角度分析振动流化床分选过程中的流化行为特性,研究振动能量对分选流化床流化质量的作用,并利用床层压力信号能量量化研究压力波动与不同流化现象的响应;基于对6~1 mm细粒煤分选试验结果的研究,结合床层中气泡行为的演变规律,提出了细粒煤分选效果的颗粒混合熵评价方法,研究了6~1 mm细粒煤在振动流化床中的分选特性及气泡运动行为对细粒煤离析分层效果的影响。结果表明,气泡引起压降信号的能量随着气速的增加,呈先增加后降低的趋势,随着振幅和频率的增加,气泡引起的压降信号能量逐渐增大,但床层压降信号的总能量随着气速、振动频率和振幅的增大逐渐增加。此外,通过对精煤和矸石组分的颗粒混合熵判定2组分的离析程度发现,随气速的增大,颗粒混合熵的变化趋势先降低后升高,随着振动频率和振幅的增加,精煤和矸石的颗粒混合熵逐渐增大,且在振幅A=2 mm,频率f=20 Hz,流化气速v=12 cm/s条件下,床层压力波动的能量和颗粒混合熵最低,床层压降波动平稳,床层密度分布均匀,对6~1 mm细粒煤具有最佳分选效果,其分选精度E值为0.095 g/cm^(3),精煤灰分为9.59%。

依托实验教学示范中心培养矿物加工工程创新人才

依托煤炭洁净加工与高效转化国家级实验教学示范中心建设,搭建"双一流"学科矿物加工工程创新人才培养体系和平台;通过建设高水平的实验教学师资队伍,实施大学生科技训练计划和开展第二课堂活动,全面开放实验教学示范中心,加强中心信息化硬件基础建设等,开展实验教学改革,并取得显著成效。

黑山露天矿薄煤层煤炭干法分选

基于黑山露天煤矿气候环境采用干法分选工艺对该地区煤炭进行提质。为明晰原煤可选性,对黑山露天矿薄煤层进行了煤质资料分析,确定了煤种及原煤质量,分析了原煤浮沉特征。同时对80~0 mm原煤进行了分选试验,通过床层颗粒能量分布确定了分选过程中床层密度分布规律,采用响应面交互试验分析了各因素对灰分离析度的影响,确定了最佳分选条件,并用分选试验验证了该分选技术的可行性。结果表明,黑山露天矿薄煤层原煤属中等可选,随频率、振幅和气速的增加(均会引起能量增加),密度分布差异和灰分离析度呈先增加后减小的趋势,合适的床层能量输入有利于颗粒按密度离析分层。响应面分析表明灰分离析度对各因素变化敏感性较高,在频率32 Hz,振幅2.8 mm,气速0.6 m/s时,灰分离析度最大为0.98。在最佳分选条件下,80~0 mm原煤分选密度为1.97 g/cm^(3),可能偏差E为0.22 g/cm^(3),精煤产率为74.92%,精煤灰分为21.77%;对13~0 mm精煤再选后,灰分较主选精煤降低6.79%,80~0 mm精煤综合产率为66.99%,灰分为17.91%,干法分选工艺可有效提高黑山矿薄煤层的产品煤质量。

基于DEM的变振幅等厚筛分粒群运动学特性及参数作用机制

采用离散元法(DEM)对变振幅等厚筛分过程进行数值模拟研究,分析激振频率、振幅差、给料速率等工艺参数对变振幅等厚筛分效果的影响。结果表明:变振幅等厚筛分较等振幅筛分具有明显的优势;当激振频率为16 Hz、振幅差0. 2 mm、给料速率0. 5 kg/s时,变振幅等厚筛筛分效果最佳,筛分效率为83. 72%。

基于机器学习的气固流化床最小流化速度预测

气固流化床以其高效、可灵活操作等优点广泛应用于煤化工、煤燃烧和煤炭分选等领域。最小流化速度作为气固流化床最主要的操作参数之一,与流化床的操作设计紧密相关。现有的最小流化速度预测模型大多为经验或半经验公式,其准确性和便捷性还存在较大问题。为准确预测气固流化床最小流化速度,基于机器学习建立气固流化床最小流化速度预测模型,并探索模型的内部信息。从颗粒性质与设备条件等方面综合考虑,研究气固流化床的最小流化速度,以系统评估对最小流化速度的综合影响。采用随机森林模型验证了其预测最小流化速度的可行性,并考察了设备参数、颗粒密度和颗粒粒度3个影响因素在预测最小流化速度时的相对重要性。结果表明,最小流化速度与颗粒粒径、颗粒密度和床体直径均呈正相关,皮尔逊相关系数分别为0.79、0.31、0.14,颗粒粒径与最小流化速度相关性最强。随机森林能够根据颗粒性质(密度、粒度)与床体直径准确预测最小流化速度,模型的决定系数达到0.875。特征相关性分析揭示了各特征因素对目标变量的影响方式,颗粒粒度与最小流化速度相关性最强,为预测气固流化床最小流化速度提供借鉴。

介尺度视角下干法重介流态化分选过程强化

煤炭在保障我国能源安全中具有重要作用。干法重介流态化分选是煤炭分选加工领域的重要组成部分,有助于推动我国煤炭资源的高效洁净利用。流态化分选密度的稳定调控是实现高效分选的必要条件,调控的核心是如何削弱气泡扰动作用,关键是理解流态化分选过程中介尺度结构的演变及调控机制。从介尺度视角分析了气固流态化干法分选调控过程的关键科学问题,梳理了单元干法分选设备以及系统放大过程中介尺度结构的研究进展,分析了介尺度结构的演变规律,提出了介尺度结构的精准调控策略,对干法流态化的工业推广应用及煤炭的分选提质具有重要意义。

深型空气重介流化床密度均匀性研究

采用床层空间各处局部压降波动表征深床层密度在径向分布的非均匀性结构,并通过布风结构的设计探索了由布风室结构改变优化深床密度分布的可行性。在床体直径为600mm,初始床高为520~760mm流化床中进行实验。研究表明,预布风室结构的改变可以有效改善床层密度径向分布均匀性,在新型布风室作用下床层径向高密度区域由集中于床层中轴部变为分散于床层四周,且床层密度均匀分布的区域范围也明显增加。床层密度径向分布随着流化气速的增加高密度区域先减小再增加,当流化数为1.6时,密度分布标准差为最小值0.1035g/cm3;随着初始床高的增加,床层径向密度分布规律越来越不明显,且波动越来越剧烈;此外,处于最均匀状态下的深床层分选50~150mm大块煤时,可能性偏差达到0.042g/cm3。

感觉统合训练对自闭症儿童康复影响的元分析

目的:系统评价感觉统合训练对自闭症儿童感统、语言、社交、感知、行为能力的影响。方法:检索相关文献,对文献进行质量评价,之后进行元分析。结果:共纳入5篇随机对照研究(RTC),样本共计267人。元分析结果显示,感觉统合训练可以改善自闭症儿童感统(RR=8.47,95%CI:6.55~10.40,P<0.00001)、语言(RR=-1.87,95%CI:-3.22^-0.52,P=0.007)、社交(RR=-2.97,95%CI:-4.43^-1.51,P<0.0001)、感知(RR=-3.02,95%CI:-4.32^-1.71,P<0.00001)、行为(RR=-5.80,95%CI:-7.50^-4.10,P<0.00001)能力。结论:感觉统合训练能够有效提高自闭症儿童的感统、语言、社交、感知、行为能力。

Characteristics analysis of a novel centralized-driving flip-flow screen

During screening operation, blinding or clogging of screen perforations generally occurs to reduce the sieving capacity and efficiency. Recently, the flip-flow screening has been widely recognized as a feasible method to deal with the problem. In this paper, a novel centralized-driving flip-flow screen(CFS) was developed for the separation of fine and moist coal, and the key structures, namely, a centralized-driving mechanism and a quasi-circle beam mounted with the mat were designed for high reliability and stability. By means of a test on an experimental prototype, the effect of some factors, i.e., initial stretch and hardness of the polyurethane panel, respectively, and the rotation speed of the driving motor on the kinematic characteristic of the screen surface was investigated. Results show that without an initial stretch, the sieve mat generates the largest vibratory amplitude while the slacker the sieve mat initially is, the smaller amplitude it will accomplish. And an increase in the rotation speed could cause a rise in the vibratory amplitude. Unlike the two factors, the hardness does not have a definite effect on the kinematic performance, on which a further study is required. Finally, screening processing on a laboratory prototype was conducted to draw the conclusion that the developed CFS also has a high sieving efficiency for the fine and moist coal.

Simulation of the screening process on a circularly vibrating screen using 3D-DEM

A numerical study of the motion particulates follow along a circularly vibrating screen deck was done using the three dimensional Discrete Element Method (DEM). The motion of the particles was analyzed. The effects of vibration amplitude, throwing index, and screen deck inclination angle on the screening process are discussed. The results show that the average velocity of the particles increases along the lon- gitudinal direction of the deck. The screening efficiency is highest when the vibration amplitude, throw- ing index, and screen deck inclination angle are 3-3.5 mm, 2.7 and 15°, respectively. This work is helpful for developing a deep understanding of particle motion and for optimizing screen separator designs.

△P index with different gas compositions for instantaneous outburst prediction in coal mines

In this study we measured the △P(initial speed of gas emission) index with different gas concentrations of carbon dioxide(pure CO2,90% CO2+10% CH4,67% CO2+33% CH4,50% CO2+50% CH4,30% CO2+10% CH4 and pure CH4) of coal samples from the No.2 coal seam in the Yaojie Coal Mine,Gansu province,China.The effect of carbon dioxide concentration,gas composition,coal strength and particle size of coal samples on the △P index was investigated.The experimental results show that with gas of various compositions,the △P value of three samples were clearly different.The △P index of coal samples A,B and C(0.2～0.25 mm) were 4,6 and 7 with pure CH4 and 22,30 and 21 when pure CH4 was used.Carbon dioxide concentration affects the △P index markedly.The △P index increases with an increase in carbon dioxide concentration,especially for coal B.Hence,the △P index and K(another outburst index) values tested only with pure CH4 for prediction of the danger of outburst is not accurate.It is important to determine the initial speed of gas emission given the gas composition of the coal seam to be tested for exact outburst prediction.

Numerical simulation of the pulsing air separation field based on CFD

The flow field of pulsing air separation is normally in an unsteady turbulence state.With the application of the basic principles of multiphase turbulent flows,we established the dynamical computational model,which shows a remarkable variation of the unstable pulsing air flow field.CFD(computational fluid dynamics) was used to conduct the numerical simulation of the actual geometric model of the classifier.The inside velocity of the flowing fields was analyzed later.The simulation results indicate that the designed structure of the active pulsing air classifier provided a favorable environment for the separation of the particles with different physical characters by density.We shot the movement behaviors of the typical tracer grains in the active pulsing flow field using a high speed dynamic camera.The displacement and velocity curves of the particles in the continuous impulse periods were then analyzed.The experimental results indicate that the effective separation by density of the particles with the same settling velocity and different ranges of the density and particle size can be achieved in the active pulsing airflow field.The experimental results provide an agreement with the simulation results.

CFD-DEM simulation of fluid-solid flow of a tapered column separation bed

Research on recycling waste Printed Circuit Boards(PCB) is at the forefront of preventing environmental pollution and finding ways to recycle resources.The Tapered Column Separation Bed(TCSB) is invented aiming at disposing the problem that fine particles of waste printed circuit boards cannot be separated efficiently so as to obtain further insight about the underlying mechanisms and demonstrate the separation feasibility in the tapered column separation bed.In this work,a Computational Fluid Dynamics(CFD) coupled with Discrete Element Method(DEM) model for two-phase flow has been extended to simulate the fluid-solid flow in the tapered column separation bed.Its validity is demonstrated by its successful capturing the key features of particles' flow pattern,velocity,the pressure distribution,the axial position with time and axial force for particles with different densities.Simulation results show that the plastic particles and resin particles become overflow,while copper particles,iron particles and aluminum particles successively become underflow,with a discharge water flow rate of 1 m^3/h,an obliquity of 30°.The simulated results agree reasonably well with the experimental observation.Using this equipment to separate waste PCBs is feasible,theoretically.

Relationship between coal size reduction and energy input in Hardgrove mill

Hardgrove grindability index (HGI) is an important indicator of coal grindability, and is one of the most important parameters to determine the capacity of coal pulverizer in power station. However, HGI is an empirical grindability index without linkages to any known physical parameters. To investigate the effect of energy input on the grinding in Hardgrove mill, a T20WN torque meter was installed on the shaft of a modified Hardgrove mill to record the torque driving the mill. Samples from four kinds of coals with HGI ranging from 36 to 72 were prepared according to the procedure of standard HGI test and ground in a modified Hardgrove mill at different revolutions. The relation of sample size reduction degree to specific comminution energy (E cs ) was studied with Shi-Kojovic model. The results show that Shi-Kojovic model predicted well the coal size reduction degree with E cs in Hardgrove mill. The grindability index given by Shi-Kojovic model has a similar trend with HGI. The relation of sample size reduction degree to E cs reveals that HGI has a non-linear relationship with effective specific energy in Hardgrove mill, which explains the non-linear relation of HGI to industrial pulverizer capacity.

Effect of the secondary air distribution layer on separation density in a dense-phase gas–solid fluidized bed

Dry coal separation has been the most significant process in the field of coal beneficiation to date, because of its special advantage of operation with no water consumption. Mineral dry separation research has received wide attention, particularly in countries and regions experiencing drought and water shortages.During the process of dense coal gas–solid fluidized bed beneficiation, the material is stratified according to its density; the high density material layer remains at the bed bottom, and thus the high density coarse particle bed becomes an important influencing factor in fluidized bed stability. In the steady fluidization stage, a small number of large radius bubbles are the direct cause of unsteady fluidization in the traditional fluidized bed. The dispersion effect of the secondary air distribution bed for air flow is mainly apparent in the gas region; when the particle size exceeds 13 mm, the secondary air distribution bed has a synergistic effect on the density stability of the upper fluidized layer. When the particle size is small, especially when less than 6 mm, particles will constantly move, accounting for instability of the secondary air distribution bed and distorting the stability of the upper fluidized bed. Under optimum operation conditions, the probable deviation E of gas–solid separation fluidized with a high density coarse particle layer can be as low as 0.085 g/cm3.