Experimental Study of Sub-critical Velocity in Longitudinally Ventilated Tunnels

Fire Technology - The critical velocity is the minimum velocity blowing towards the fire seat in tunnels to reduce the length of back-layering to zero, and it has been extensively adopted in the...     

微生物矿化动力学理论与模拟

微生物矿化技术作为一个新兴研究课题,近些年来得到了广泛关注,然而因其反应机制复杂,很难从时间和空间尺度对矿化反应过程进行定量表示。在微生物诱导碳酸盐沉淀原理的基础上,考虑细菌的吸附和筛滤效应,以及尿素水解动力学和沉淀动力学模型,对微生物矿化反应动力学理论进行了探究,并结合孔隙尺度下的微生物矿化反应试验,采用有限元软件进行多物理场耦合模拟。结果表明,细菌吸附和筛滤行为引起了细菌分布的差异性,而这种差异性进而影响了碳酸钙的沉积分布;溶液汇合初始段碳酸钙生成量横向分布不均匀,纵向分布呈增长趋势;经历40h的反应时间,渗透率可降低80%左右;当钙离子含量丰富时,碳酸钙沉淀速率受限于尿素水解速率;附着细菌量和沉淀速率的叠加效应表现为细菌被沉淀包裹的衰亡速率。本模型验证了微生物矿化沉积反应过程,丰富了微生物矿化反应理论,并有望为现场工程应用的效果预测提供参考。     

外墙涂料在旧墙面翻新施工中存在的问题及质量控制

建筑物的旧墙面,由于长时间日晒和风吹雨淋,基层和表面状况都要比新建筑墙面复杂,对于旧建筑物涂料装饰如何施工,应根据具体墙面情况来考虑。介绍旧墙面建筑外墙涂料的施工工艺、施工后可能存在的问题,并分析其原因,以尽量避免质量问题的产生。     

高压线上任一点的平面位置和高度测量方法

阐述了在实际工作中，使用一般测量仪器实地外业观测高压线的基本数据，根据测量数据和相应几何关系计算出高压线上任一点的平面位置和高度，该过程的每一环节都有检核，能确保观测计算成果的正确性。     

天然气行业的开放

天然气行业从垄断逐步走向开放,有多重因素的作用,文章首先分析了促使天然气行业开放的内外因素,接着论述了天然气行业开放的进程以及非公有资本参与的现状。文章最后简述了开放带来的变化以及开放后需要注意的方面,有助于开放促进我国天然气工业的健康发展。     

一种方位及俯仰可调控制平台的实现

微波接收机是射电望远镜中专门用于接收射电信号的设备,而强度校准的目的是将接收到的射电信号响应等效地转换为天文意义上的流量密度。由于毫米波校准还易受到大气吸收作用,因此对大气不透明度的测试尤为重要。文中通过搭建机械转动平台及其控制系统,可以精确实现7 mm 波段常温接收机在目标方位下进 行0°~ 90°俯仰扫描观测。通过控制软件并行记录在不同仰角下的接收机输出功率,结合大气辐射转移方程,采用非线性最小二乘拟合的方式,最终得到当前方位7 mm 波段实时的大气不透明度值,很好地实现了精确控制及自动测试功能。     

Research and experimental analysis of drill string dynamics characteristics and stick-slip reduction mechanism

Stick-slip of the drill string, as one of the critical factors affecting drilling efficiency, has always been a hot topic for experts and scholars in related fields. Serious stick-slip vibration affects the well construction efficiency, drilling cost and even lead to a downhole accident. Therefore, based on the current research, this paper takes a new type of composite vibration tool as the research object, studies the working mechanism of the tool and analyzes the effect of stick-slip reduction. After establishing the multi-degree-of-freedom torsional dynamics model, we obtained the results of torsional vibration dynamics by cases analysis based on working conditions and related mechanical parameters. In addition, the results of the examples, compared with the field experimental data, verify that the vibration shock generated by the new composite tool can effectively reduce the torque fluctuation range of the system, avoid the occurrence of stick-slip phenomenon, improve the ROP (rate of penetration), and make drilling process more stable. This paper can provide reference for the optimization and development of stick-slip technology in drilling engineering, and the theoretical methods can also be developed to study the dynamics of drill string.     

Experimental research on the MRR of ultrasonic vibration aided electric discharge milling of ceramic materials using deionized water as processing medium

Abstract

Electric Discharge Milling Machining (EDMM) simplifies the electrode manufacturing process and reduces the cost. However, the introducing of new parameters, such as the three-dimensional motion and the electrode rotation speed, results in a periodic change of control state that can reduce the control performance and processing efficiency. In this work, ultrasonic vibration of tool electrode was used to improve the processing efficiency of ceramic materials. The effect of ultrasonic vibration on the EDMM process was analyzed by comparing the experimental findings. The results have shown that the ultrasonic vibration can improve the material removal rate, and a treble processing efficiency was achieved. The effect of processing parameters on the material removal rate, such as the open voltage, the peak current, the pulse during time and the pulse off time, was analyzed. When aided with the ultrasonic vibration, the best processing efficiency was achieved at 220?V for the open voltage, 10?A for the peak current and 15?μs for both the pulse during time and pulse off time.     

刀刃角与岩石节理倾角对盘型滚刀破岩效率的影响

为了研究节理倾角与刀刃角对滚刀破岩效率的影响,运用ABAQUS有限元分析软件,采用Druker-Prager弹塑性本构模型模拟岩石材料,使用不同刀刃角的滚刀对不同节理倾角的岩石进行滚切加工,并结合破岩比能理论研究破岩效率,以破岩比能最小为依据确定不同节理倾角下的最优刀刃角。研究结果表明:不论倾角如何,节理层处的岩石破碎效果优于其他地方的破碎效果;在节理倾角为0°和30°时,滚刀的破岩比能呈波动的趋势,而且最优刀刃角为60°;在节理倾角为60°时,最优刀刃角为45°～50°;在节理倾角为90°时,最优刀刃角为40°～45°;随着节理倾角的增加,最优刀刃角呈不断减小趋势。该研究结果可为不同地质条件下盾构施工时的刀具选型提供一定的理论依据。     

前刀面槽型结构对D型刀片车削球墨铸铁性能的影响

通过切削力、磨损和冲击切削试验,研究了前刀面槽型结构对D型刀片车削球墨铸铁切削性能的影响。试验结果显示,刀具的第一前角对切削力的影响最大;在10°~15°范围内,刀具前角越大,切削力越低;棱带宽度大的刀片具有更加优异的耐磨损性能;具有正刃倾角的刀片显示出更优异的耐冲击性能。