Study of electromagnetic characteristics of stress distribution and sudden changes in the mining of gob-surrounded coal face

The incidence of dynamic coal or rock disasters is closely related to the distribution of stress in the surrounding rock. Our experiments show that electromagnetic radiation （EMR） signals are related to the state of stress of a coal body. The higher the stress, the more intense the deformation and fractures of a coal body and the stronger the EMR signals. EMR signals reflect the degrees of concentrated stress of a coal body and danger of a rock burst. We selected EMR intensity as the test index of the No.237 gob-surrounded coal face in the Nanshan coal mine. We tested the EMR characteristics of the stress distribution on the strike, on the incline and in the interior of the coal body. The EMR rule of rock bursts, caused by sudden changes in stress, is analyzed. Our research shows that EMR technology can be not only used to test qualitatively the stress distribution of the surrounding rock, but also to predict a possible occurrence of rock burst. Based on this, effective distress measures are used to eliminate or at least weaken the incidence of rock bursts. We hooe that safetv in coalmines will be enhanced.

Research on the sudden changes and the controlling factors of deep coal mining conditions

It was illustrated that the mining conditions inducing disasters changed with depth both in regularity of gradual and sudden change.The sudden change depth for different disaster conditions are different and controlled by different factors.The high temperature and its change with depth are mainly controlled by strata structures and rock heat conductiv- ity property,the high rock stress and dynamical engineering disasters and their change with depth are mainly controlled by tectonic conditions,roof strata rock property and deep rock mechanical property,coal mine water disasters and their change with depth are mainly con- trolled by rock mechanical property of coal seam floor and regional groundwater circulation conditions,gas disaster conditions and their change with depth are mainly controlled by buried conditions of coal seam and opening conditions of geological structures.It is men- tioned that the key point for the control of deep coal mining disaster is to clearly understand the sudden change depth of different factors causing disasters.

Effects of sudden change in wind loads on running performance of trains on a highway-railway one-story bridge in crosswinds

To investigate the effects of sudden change in wind loads on the running performance of trains on the bridge in crosswinds,a highway-railway one-story bridge was taken as the research object.Aerodynamic coefficients of the train and the bridge were measured in a series of train-bridge system segment models through wind tunnel tests when two trains passed each other on the bridge and when a train entered and left the wind barrier section of the bridge.Based on the improved SIMPACK and ANSYS rigid-flexible coupling simulation method,a wind-double train-track-bridge system coupled vibration model was established.The dynamic responses of the train were analyzed under the effects of sudden change in wind loads caused by two trains passing each other and a train entering and leaving the wind barrier section of the bridge.The results show that the effects of sudden wind load change caused by the trains passing each other had less effects on the running safety of the leeward-side train than the wind shielding effect caused by the windward-side train in the wind speed range of 10−25 m/s.With the decrease in the porosity of wind barriers,the effects of the sudden wind load change played an increasingly important role in the running safety and comfort of the train.With the increase in wind speed,the lateral response of the train increased obviously because of the effects of sudden wind load change,which affects both the lateral running stability and the comfort of the train.

机床加工的精密气动卡盘研发

数控机床精加工工序中,自动卡盘夹紧力突变可引起机床精加工的形状误差、位置误差和环形工件的圆度误差。通过对数控机床加工的精密气动卡盘的研发与设计,可有效解决气动卡盘夹紧力突变的问题,推动我国数控机床的科技进步,为同类其他产品的设计提供分析基础和理论参考。

基于磁流体轴承的大载荷磁流体二维导轨平台研究

在现有的精密机床中,空气静压导轨平台存在阻尼突变、载荷不高的问题,基于磁流体轴承,提出了一种大载荷磁流体二维导轨平台。首先,对基于磁流体的导轨平台关键问题进行了研究,包括空气损耗问题和磁流体尾迹问题;然后,采用磁流体压力轴承设计了一个双U形导轨平台结构,并将顶部、底部和侧部轴承垫紧密地放置在一起,从而在动子上形成了一个储液层;采用上下磁化配置的导轨平台具有6个轴承垫,每个轴承垫由多个小型磁体组成;其次,对载荷能力、刚度和涡流阻尼进行了数值模拟;最后,选用了煤油基磁液、铝材和铁素体不锈钢制备了一台平台样机,进行了平台的性能测试,对该导轨平台的有效性进行了验证。研究结果表明:该平台的平面度为±7μm,具有较高的可重复性,明显优于现有基于磁流体轴承的精密运动系统;在相同行程和尺寸条件下,与气动平台相比,该平台的最大有效载荷为140 N,提高了40%;阻尼在2 N·s/m至4 N·s/m之间相对恒定,且可预测,解决了气动平台的阻尼突变问题,有利于实现导轨平台高精度定位的目的。

季风涡旋对台风“烟花”路径突变的影响

台风“烟花”于2021年7月22日00时(世界时,下同)在台湾岛东侧突然向北转向,但美国、日本和中国的业务预报均没有正确预报出该过程。基于NCEP/NCAR提供的全球再分析资料(Final Operational Global Analysis,FNL),采用Lanczos滤波方法分析发现,台风“烟花”转向前的西行减速主要受到与季风涡旋有关的季节内尺度环境引导气流分量的影响,向北转向及转向后的向北加速则主要受到季风涡旋和台风相互作用导致的天气尺度环境引导气流分量的引导,主要和beta涡旋对旋转、与季风涡旋的合并、以及加强的Rossby波能量频散这3个重要过程有关。台风“烟花”在纬向尺度约3 000 km的季节内尺度季风涡旋北部的偏东气流西移过程中,与季风涡旋相互作用导致beta涡旋对气旋性旋转,通风流经历东南风—东北风—西南风的转变,使得“烟花”向西减速并逐渐向季风涡旋中心移动,并于7月22日00时与季风涡旋合并,加强了Rossby波能量频散,使得“烟花”东南边缘的天气尺度西南风加强,为缓慢移动的“烟花”提供了向北的引导,“烟花”突然向北转向。

基于正序突变量相轨迹辨识的可再生能源配电网电流保护

【目的】随着可再生能源的大量接入,中性点经小电阻接地的配电网潮流不确定性使得传统三段式电流保护的整定变得日趋复杂,其灵敏性和可靠性都有所降低。为了解决上述问题,提出了一种基于正序突变量电流相轨迹辨识的新型电流保护方法予以应对。【方法】首先,分析了故障点上游、下游的正序突变量电流大小及其分布特征;其次,利用亲和力聚类算法,根据聚类结果识别定义的主故障路径;最后,提出一种搜索方法,将搜索得到的正序突变量产生源头,即位于主故障路径上的最后一级馈线视为故障馈线。【结果】基于PSCAD的仿真研究表明,所提出的保护方法能够适应各种故障工况,不受分布式电源加入的影响,具有较高的灵敏度和可靠性。【结论】研究结果有助于提升中性点经小电阻接地的配电网运行安全性,同时提升故障排查效率。

全移相双有源全桥直流变换器的瞬态电流偏置抑制策略

针对双有源全桥(DAB)直流变换器在功率突变时产生的电流偏置问题,该文提出一种新的瞬态直流偏置抑制策略。首先,以基于全移相调制的双有源全桥直流变换器为研究对象,分析DAB变换器产生直流偏置的原因及危害。然后,在全局电感电流应力最优结果的基础上,对功率在四个工作区域突变时产生的瞬态直流偏置问题进行详细分析,推导各种电流突变情况下的直流偏置表达式,并据此提出一种新的过渡态引入方法,对于不同的功率突变状态可以得到统一的过渡移相角表达式,简化了控制过程。接着,根据所得过渡态结果,提出统一的载波调制方法,并对调制策略的适用性进行分析。最后,通过实验平台验证了所提方法可以有效消除功率突变时产生的电流偏置。

不同含水率对磷块岩热红外辐射特征的影响研究

为探究不同含水率磷块岩的热红外辐射特征,分别对烘干磷块岩、天然含水磷块岩和饱水磷块岩进行单轴加载试验,分析不同含水率磷块岩的受力特性、破坏特征和红外辐射特征。结果表明:磷块岩含水率越高,在失稳前红外辐射的升温幅度越大,含水率越低,升温幅度越小;磷块岩红外前兆异常显示,临近破裂前会出现短暂降温现象,含水率越高,降温幅度越小,含水率越低,降温幅度越大;磷块岩在最终破裂瞬间会发生红外辐射温度突升,含水率越低,突变值越大,含水率越高,突变值越小。

厚度突变煤层采动围岩应力显现及岩移规律研究

为研究煤岩层厚度突变条件下采动围岩应力显现及岩层移动规律,采用FLAC3D数值模拟软件对平煤十矿己15.16-24110工作面煤厚和倾角突变影响区域进行建模,模拟赋存条件突变煤体在采动影响下围岩位移和应力显现规律,进而分析顶底板失稳产生的原因及规律。结果表明,随着开采深入,卸压区和应力集中范围变大;在煤层突变的位置,煤层工作面煤壁及围岩出现卸压区影响范围突然扩大,顶板卸压范围变大,形成“双驼峰”状,煤壁的应力集中系数增加明显;煤厚突变区域上覆及下伏岩层应力显现和岩移量均明显高于其他区域,说明该区域易蓄积能量,成为动力灾害及岩层失稳频发区域。

离子推进器屏栅电源稳压控制方法研究

为了解决离子推进器屏栅电源在负载突变过程中产生的过压、过流等问题,对LLC谐振变换器采用移相-变频控制(PS-PFM)稳定输出电压,当采样电压低于设定值下限时,进入变频控制模式,当采样电压高于设定值上限时,进入移相控制模式。实验证明,相比于常用的调频控制,移相控制的加入能够解决轻载或空载模式下的电压飘高问题,通过PID参数的调整,可以实现负载跳变时的稳定快速调节,使输出电压保持在设定值;通过PCB布局与磁性元件优化设计,所研制的原理样机在额定情况下效率高达98.9%,功率密度可达6.47×10^(6)W/m^(3),在同等级的电源产品中具有优势。

1961—2012年河南省生长季时空演变特征分析

根据河南省111个气象站1961—2012年共52年的气象数据,基于0、3、5、10、15、20℃6个温度临界值,对生长季(生长季初日、生长季终日和生长季长度)的演变特征进行了分析研究。结果表明,52年中,河南省除豫中外的豫北、豫东、豫西、豫南、豫西南5个地区生长季初日表现出了明显提前的趋势。生长季初日整体由东向西逐渐推迟,终日整体由东向西逐渐提前,生长季长度也由东向西逐渐提前。突变检验表明,生长季长度在6个临界温度值下均有较明显的延长趋势。

柴油发电机组的瞬态特性和选型分析

本文结合柴油发电机组在可变负载下的瞬态特性,对柴油发电机组性能等级的定义和重要性进行深入分析,给出柴油发电机组性能等级的标定和验证方法,进而根据柴油发电机组的瞬态特性及负载对电能质量的实际要求,为柴油发电机组的合理选型及柴油发电机组和实际负载的匹配提出一些建议。

采煤机重载工况下转矩自动化补偿控制方法的研究

采煤机是进行煤矿开采的重要设备,具有破煤能力强的特点。在破煤过程中,由于煤岩分布的复杂多变,使得滚筒受到随机性多载荷的冲击作用,容易造成滚筒的磨损,特别是硬质颗粒引起的重载冲击作用。针对采煤机重载工况下的“截割-牵引”系统的调节控制进行分析,以直接转矩控制及自动化转矩补偿控制两种方式进行对比分析,建立“截割-牵引”系统的耦合模型,对重载突变工况下的转矩控制效果进行仿真分析,从而提高采煤机的调节控制效果,保证重载工况下使用的稳定可靠性。

基于零序电流突变量的配电线路带电回路识别

配电线路带电回路识别过程中,未对线路异常情况进行检查,导致识别效果存在误差,对此,研究基于零序电流突变量的配电线路带电回路识别。首先,分析配电网的等效电路结构,计算零序电流的数值和分布情况。然后,通过零序电流突变量计算,检测三相电流是否平衡,识别存在电流异常的线路和节点。最后,采用深度优先遍历算法进行带电回路的识别,并结合粒子群优化算法提升识别效率。实验结果表明:采用所提方法后,配电线路带电回路识别精度均高于90%;配电线路带电回路识别时间始终低于15s,说明所提方法能够更准确地识别出带电回路,提高计算效率。

Changing Characteristics of Temperature in Longnan City in Recent 54 Years

Based on the observation data of temperature in Chengxian meteorological station（ the climate representative station of Longnan City,Gansu Province） during 1961-2014,the annual,seasonal and monthly changes of temperature were analyzed,and the abrupt changes in relevant variables were tested using the cumulative anomaly method. The results showed that annual average temperature in Chengxian County increased by 0. 138 ℃/10 a in the past 54 years. There was an obvious sudden change in annual average temperature around 1996. The annual average temperature showed a downward trend before 1996 and an upward trend after 1996. Average temperature in spring,summer,autumn and winter increased by 0. 113,0. 028,0. 157 and 0. 259 ℃/10 a respectively. The fluctuation of average temperature in spring and winter was the largest,followed by summer,while the fluctuation was the smallest in autumn. There were certain differences between various seasons in terms of the years with sudden changes in average temperature,which was not consistent with the years with the sudden changes in annual average temperature. The changing rate of monthly average temperature was the largest in February（ up to 0. 412 ℃/10 a）,followed by March,April and November,but it was the smallest in May（ only 0. 005 ℃/10 a）. The maximum of monthly average temperature appeared mostly in the 21 stcentury,while the minimum appeared in the 20 thcentury.

含混合储能的风光储荷微电网运行特性分析

气象因素变化以及负荷突变等情况都会影响微电网的稳定运行,本文提出基于超级电容器和全钒液流电池的两层混合储能控制策略。以某园区实际需求为依据,在MATLAB/Simulink仿真环境下建立风光储荷微电网运行系统仿真模型。将典型日的实测风速和光照数据导入模型,分析负荷突变工况下微电网系统并网、离网模式运行状态。仿真结果表明:混合储能可以有效地维持微电网稳定运行,在系统受到干扰后,能快速找到平稳点,从而实现功率平稳输出。

1969-2019年四川省极端气温事件时空分布特征

【目的】全球气候变暖背景下极端气候事件频发,为诊断气候变化环境下四川省极端气温事件的动态演变特征,【方法】基于1969—2019年四川省33个国家地面气象观测站逐日最高和最低气温资料,利用线性倾向估计法、反距离加权法和Mann-Kendall突变检验法分析了四川省近50 a极端气温事件的时空变化特征,并探讨了海拔高度等因子对各极端气温指数的影响。【结果】结果显示:四川省极端气温事件存在明显的年际变化和空间分布特征,海拔高度为影响四川省极端气温指数的最主要影响因子。【结论】结果表明:(1)四川省极端暖事件显著增加,极端冷事件显著减少;极端气温指数中霜冻日数、冷日指数和冷夜指数均未检测到突变点,其余指数存在明显突变。(2)受复杂地形影响,四川省极端气温存在明显空间差异,位于低海拔地区的叙永为年内日最高气温值最大、高温日数出现最多的地区;高海拔地区的红原为年内日最低气温值最低的地区,色达为霜冻日数出现最多的地区,巴塘为暖日和暖夜日数最少的地区,若尔盖为冷日和冷夜日数最多的地区。(3)经度、海拔高度和平均气温均会影响极端气温指数,而海拔高度为极端气温指数的最主要影响因子,极端暖指数由低海拔区向高海拔区递减,而极端冷指数由高海拔区向低海拔区递减。上述结果为制定合理的灾害减缓措施提供了科学依据。

离子推进器屏栅电源负载突变分析

离子推进器在工作过程中需要进行打火操作,突变负载会对电源处理单元(PPU)造成过压过流等影响。为满足离子推进器PPU负载突变的需求,选择PPU中的屏栅电源作为研究对象,结合全桥LLC谐振变换器拓扑,采用平均大信号建模法,建立了全桥LLC非线性状态空间方程,并通过方程中快慢变量的近似处理,推导出平均大信号模型,通过仿真验证了平均大信号模型与状态空间方程基本一致。据此大信号模型设计了控制器,通过Matlab/Simulink仿真和实验验证了控制的有效性。所研制的原理样机可以实现软开关和负载突变下的快速调节,最低效率为97.1%,输出稳定性较高,可以提升推进器电源模块的可靠性。