Performance of large-diameter pneumatic down-the-hole (DTH) hammers: A focus on influences of the hammer structure

Pneumatic down-the-hole (DTH) hammer has been extensively used in air drillings through hard and ultra-hard geological formations. Numerical modeling can offer close observation on the working behaviors by visualizing internal pressure status as well as provide reliable performance predictions for large-diameter DTH hammers to which conventional empirical and experimental approaches cannot be applied. In this study, CFD simulations coupled with dynamic meshing are utilized to simulate the air flow and piston movement inside the large-diameter DTH hammers. The numerical modeling scheme is verified against a theoretical model published in literature. Effects of structural parameters on hammer performance, including piston mass, piston upper-end diameter, piston groove diameter, and lengths of intake and exhaust stroke in both front and rear chambers, are analyzed in detail by virtue of sets of numerical simulations. The simulations suggest that changing the intake stroke of front chamber has a negligible influence on hammer performance while increasing the piston groove would lower all the four indicators of hammer performance, including impact energy, impact frequency, maximum stroke, and air consumption rate. Changing the other structural parameters demonstrates mixed effects on the performance indicators. Based on the numerical simulations, a large GQ-400 DTH hammer has been designed for reduced air consumption rate and tested in a field drilling practice. The air drilling test with the designed hammer provided a penetration rate 1.7 times faster than that of conventional mud drilling.

China Hammers Out Effective Steps to Protect Its Wetlands

The Chinese government will step up its efforts to stop the country’s wetlands from shrinking, said Ma Fu, Deputy Director of the State’s Forestry Administration, while announcing the newly drafted the Action Plan for National Wetlands Conservation on November 8th in Beijing.

Study on liquid-liquid bimetal composite casting hammers

Crusher hammers for the mineral processing industry must meet the demands of both high wear resistance at the hammer head and high impact toughness at the hammer handle. The crusher hammers made of Hadfield steel have typically low service life of less than 40 hours. To solve the problem, a kind of bimetal crusher hammers made of high chromium cast iron(HCCI) and low alloy steel(LAS) has been successfully developed by using liquid-liquid composite casting. The microstructure and composite interface bonding was analyzed using optical microscope, SEM, EDX and XRD. Micrographs indicate that the composite interface is metallurgically bonded with a zigzag shape across the boundary and without unbound region or void. After heat treatment, the composite hammers have shown excellent properties. The hardness of HCCI is at least 63 HRC and its αk is greater than 3.5 J·cm-2; the hardness of LAS is greater than 35 HRC and its αk is no less than 80 J·cm-2. Diffusion of elements takes place at the interface and forms a transition region. The micro hardness increases from LAS to the interface and then to HCCI. Wear comparison was made separately between the bimetal composite hammer and a Hadfield steel hammer in two quarries of Jilin province and Liaoning province. The results showed that the liquid-liquid bimetal composite hammers did not have the falling off of hammer head or impact fracture phenomenon, and their service life was 3.75 times as long as that of the Hadfield steel hammers.

Construction and Solution to a New Dynamic Model of Forging Hammers Damping System

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Aseismic performances of constrained damping lining structures made of rubber-sand-concrete

Flexible damping technology considering aseismic materials and aseismic structures seems be a good solution for engineering structures.In this study,a constrained damping structure for underground tunnel lining,using a rubber-sand-concrete(RSC)as the aseismic material,is proposed.The aseismic performances of constrained damping structure were investigated by a series of hammer impact tests.The damping layer thickness and shape effects on the aseismic performance such as effective duration and acceleration amplitude of time-domain analysis,composite loss factor and damping ratio of the transfer function analysis,and total vibration level of octave spectrum analysis were discussed.The hammer impact tests revealed that the relationship between the aseismic performance and damping layer thickness was not linear,and that the hollow damping layer had a better aseismic performance than the flat damping layer one.The aseismic performances of constrained damping structure under different seismicity magnitudes and geological conditions were investigated.The effects of the peak ground acceleration(PGA)and tunnel overburden depth on the aseismic performances such as the maximum principal stress and equivalent plastic strain(PEEQ)were discussed.The numerical results show the constrained damping structure proposed in this paper has a good aseismic performance,with PGA in the range(0.2-1.2)g and tunnel overburden depth in the range of 0-300 m.

Digital monitoring of rotary-percussive drilling with down-the-hole hammer for profiling weathered granitic ground

Rock and geotechnical engineering investigations involve drilling holes in ground with or without retrieving soil and rock samples to construct the subsurface ground profile.On the basis of an actual soil nailing drilling for a slope stability project in Hong Kong,this paper further develops the drilling process monitoring(DPM)method for digitally profiling the subsurface geomaterials of weathered granitic rocks using a compressed airflow driven percussive-rotary drilling machine with down-the-hole(DTH)hammer.Seven transducers are installed on the drilling machine and record the chuck displacement,DTH rotational speed,and five pressures from five compressed airflows in real-time series.The mechanism and operations of the drilling machine are elaborated in detail,which is essential for understanding and evaluating the drilling data.A MATLAB program is developed to automatically filter the recorded drilling data in time series and classify them into different drilling processes in sub-time series.These processes include penetration,push-in with or without rod,pull-back with or without rod,rod-tightening and rod-untightening.The drilling data are further reconstructed to plot the curve of drill-bit depth versus the net drilling time along each of the six drillholes.Each curve is found to contain multiple linear segments with a constant penetration rate,which implies a zone of homogenous geomaterial with different weathering grades.The effect from fluctuation of the applied pressures is evaluated quantitatively.Detailed analyses are presented for accurately assess and verify the underground profiling and strength in weathered granitic rock,which provided the basis of using DPM method to confidently assess drilling measurements to interpret the subsurface profile in real time.

基于Bently-Hammer软件的长距离输水管道水锤防护模拟

基于Bently-Hammer软件对某实际工程中长距离输水系统进行建模,通过实际运行中的不同工况,模拟突发事件在管道与水泵间产生的水锤影响,同时针对系统内突发事件增加液压气动罐、缓闭止回阀等水锤消除措施加以改进,为实际工程提供有效抑制水锤破坏的技术保障。

基于Bentley Hammer的长距离有压管道输水工程的水锤防护研究

【目的】在长距离有压管道输水工程中,因管道内部水流条件复杂而容易产生水锤现象,不仅会影响水流正常输送,还可能导致管道破裂。因此,有必要进行长距离有压管道输水工程的水锤防护研究。【方法】基于台前县城乡供水一体化南水北调配套工程,通过Bentley Hammer软件,在最不利工况下分别建立三种数值模拟模型:无防护措施、加装复合式高速进排气阀水锤防护、气囊式空气罐和复合式高速进排气阀,进行联合水锤防护,对以上三种情况进行水力过渡过程数值模拟分析,研究复合式高速进排气阀与气囊式空气罐联合防护时的水锤防护效果以及气囊式空气罐的防护能力与预设压力和罐体体积之间的关系。【结果】结果表明:复合式高速进排气阀和气囊式空气罐可以很好地消除管道内水锤带来的危害,气囊式空气罐防护能力随着罐体体积和预设压力的增大而增强,罐体体积对其防护能力影响更显著。【结论】选择合理的罐体体积和预设压力可以使水锺防护发挥最好的防护效果,最大化输水工程的经济性。

Bentley Hammer V8i软件在城乡一体化供水管道水锤计算中的应用

应用Bentley Hammer V8i软件模拟城乡统筹供水工程中输水和配水管道的稳态工况与事故断电工况的水锤安全性,可以清楚地展示管内水流压力的变化趋势。本文以新和县城乡一体化实际供水工程为研究对象,评估其供水管网水锤安全性。模拟结果显示,虽然该工程在稳态工况与事故断电情况下管道内压力会有剧烈波动,但仍在管道的承载能力之内,可以通过优化关阀时间及相关操作来确保供水的安全稳定。本应用可供类似城乡一体化供水工程管道设计参考。

Water hammer protection for diversion systems in front of pumps in long-distance water supply projects

For a water supply system with long-distance diversion pipelines, in addition to the water hammer problems that occur beyond pumps, the safety of the water diversion pipeline in front of pumps also deserves attention. In this study, a water hammer protection scheme combined with an overflow surge tank and a regulating valve was developed. A mathematical model of the overflow surge tank was developed, and an analytical formula for the height of the overflow surge tank was derived. Furthermore, a practical water supply project was used to evaluate the feasibility of the combined protection scheme and analyze the sensitivity of valve regulation rules. The results showed that the combined protection scheme effectively reduced the height of the surge tank, lessened the difficulties related to construction, and reduced the necessary financial investment for the project. The two-stage closing rule articulated as fast first and then slow could minimize the overflow volume of the surge tank when the power failure occurred, while the two-stage opening rule articulated as slow first and then fast could be more conducive to the safety of the water supply system when the pump started up.

城市深层隧洞输水系统水力过渡过程特性分析

【目的】研究城市深层隧洞输水系统的水力过渡过程特性。【方法】以西丽水库至南山水厂原水管工程实例为研究对象,利用Bentley hammer软件建立输水系统模型;分析启泵间隔时间对输水系统稳定性的影响,并进一步分析典型工况下管道糙率对输水系统稳定性的影响;探究增设3#竖井为调压井对输水系统稳定性的影响。【结果】当启泵间隔时间大于240 s时,2#竖井最低瞬态水位趋于稳定;管道糙率越大,启泵工况下最低瞬态水位越低,事故停泵工况下涌浪水位的超调量越大;增设3#竖井作为调压井对输水系统水锤压力极值影响不大。【结论】启泵间隔时间大于240 s时,启泵间隔时间对输水系统稳定性几乎没有影响;管道糙率越大,典型工况下系统稳定性越差;增设3#竖井作为调压井后需投入大量维护成本,且对输水系统水锤压力极值影响不大,故不建议设置为调压井。

Compressive Strength of Basic Magnesium Sulfate Cement Coral Aggregate Concrete(MCAC)on Non-Destructive Testing

Basic magnesium sulfate cement coral aggregate concrete(MCAC)is a new type of concrete consisting of basic magnesium sulfate cement,coarse coral aggregate,coral reef sand and seawater.The rebound hammer(RH),the ultrasonic pulse velocity(UPV)and the compressive strength(fcu)tests of 14 sets of cube specimens of the MCAC after 28 d of aging were conducted.The impact of the content and length of sisal fiber on the relationship between the fcu-RH and the fcu-UPV was determined.A mathematical model was established to predict the strength of the MCAC using the UPV,RH,and comprehensive UPV/RH methods and to obtain the curves of test strength.The applicability of the test strength curves of ordinary portland concrete(OPC),light-weight aggregate concrete(LAC),and coral aggregate concrete(CAC)to MCAC was assessed.The results showed that the test strength curves of OPC,LAC and CAC were inappropriate to determine the strength of MCAC using non-destructive method.The relative standard error of the curves of test strength of the RH method and the comprehensive method met the specifications,whereas that of the UPV method did not.

Research on Breeze Vibration Law and Modal Identification Method of Conductor Considering Anti-Vibration Hammer Damage

In the harsh environment,the structural health of the anti-vibration hammer,which suffers from the coupled effects of corrosion and fatigue damage,is significantly reduced.As part of the conductor structure,the anti-vibration hammer is rigidly attached to the conductor,effectively suppressing conductor vibration.The conductor’s breeze vibration law and natural modal frequency are altered damage to the anti-vibration hammer structure.Through built a vibration experiment platform to simulate multiple faults such as anti-vibration hammer head drop off and position slippage,which to obtained the vibration acceleration signal of the conductor.The acceleration vibration signal is processed and analyzed in the time and frequency domains.The results are used to derive the breeze vibration law of the conductor under multiple faults and propose an anti-vibration hammer damage online monitoring technology.The results show that the vibration acceleration value and vibration intensity of the conductor are significantly increased after the anti-vibration hammer damage.The natural frequency increases for each order,with an absolute change ranging from 0.15 to 6.49 Hz.The anti-vibration hammer slipped due to a loose connection,the 1st natural frequency increases from 8.18 to 16.62 Hz.Therefore,in engineering applications,there can be no contact to determine the anti-vibration hammer damage situation by monitoring the modal natural frequency of the conductor.This is even a tiny damage that cannot be seen.This method will prevent the further expansion of the damage that can cause accidents.

基于Bentley Hammer的泵站输水系统管道优化前后的水力过渡过程研究

为了研究泵站输水系统管道优化前后事故停泵的水力过渡过程的特性,基于实际工程,运用Bentley Hammer软件,建立泵站输水系统双泵并联机组数学模型,研究两阶段不同关阀方案下管道优化前后对水锤压力、机组转速等最不利水锤参数的影响。结果表明,管道优化后最大水锤压力降低了3.76%~8.85%,最小水锤压力提升了4.89%~8.85%,最大倒转速度提高了1.47%~81.35%;快关时间对最不利水锤参数有显著影响,管道优化后泵站输水系统最不利水锤参数均比优化前提前发生。表明管道优化有效改善了泵站输水系统的水锤特性,提高了泵站输水系统的安全性。

Reliability analysis of retractable drill bit with air reverse circulation used for drilling while casing

Casing-while-drilling(CWD)with down the hole(DTH)hammer drilling technology has been widely used in unconsolidated formations,due to its advantages in protecting the borehole wall,excellent rock cuttings capacity,and fast penetration rate in hard rock.As an important component of the CWD system,the structure of the retractable drill bit needs not only to ensure to form stronger reverse circulation,but also to be expandable or retractable as needed,otherwise the drill bit cannot be lift and put down smoothly in the casing,and may lead to drilling accidents.This paper developed a new type of reverse circulation DTH hammer drill bit used for CWD drilling technology.The retractable performance of this type of drill bit is studied using ADAMS software.The results show that it is smoothly expandable and retractable as designed under the conditions of the weight of the bit(WOB)of 0.5–2.0 t and the rotation speed of 30–60 r/min.To investigate the reverse circulation effect of the drill bit,Fluent software was used to simulate the flow characteristic inside it.The simulation results indicated that it can form strong reverse circulation,and the entrainment ratio h can reach 9.5%.

逆向工程中数据的处理

讨论了逆向工程中几种数据采集的方法以及经采集后的数据如何进行处理。测量中进行数据采集常用随机采集法、网格采集法、Hammersely点法和故障函数法等。数据处理的一个重要工作是对扫描点进行编辑,如补偿点产生、噪声点删除、数据点精化、数据点加密以及坐标转换等。还叙述了一般产品建模技术。

重力流输水管道关阀水锤模拟研究

确定重力流输水管道最合理的关阀时间需要考虑如下因素:一是管道的水锤压力不要过高,防止管道破裂;二是水锤压力不要过低,严禁管道沿线出现断流弥合水锤,防止出现负压压瘪管道;三是要有利于操作方便、保护设备。以北京市某南水北调配套工程为例,选择HAMMER软件模拟管道瞬变流,分析重力流输水管道关阀过程中的水锤现象。结果表明:关阀时间越长,管道最大压力越小,最小压力越大,水流条件越好。蝶阀关闭时间为50 s时管道最大压力达169.27 m,关闭时间为500 s时管道最大压力为65.18 m。在线性关阀时间不小于200 s时,管道沿线不产生负压,且最大压力小于管道的设计压力。综合考虑保护管道、操作方便、便于管理、保护设备等因素,确定蝶阀线性关闭时间为300 s。研究成果对重力流输水管道阀门管理和保护具有参考价值。

基于Hammer积分的三维地面磁共振高精度正演方法

为满足三维地面磁共振正演计算的精度要求,本文提出了基于非结构不均匀四面体网格的Hammer积分算法。首先利用有限元方法实现了对地下空间的三维磁场计算,完成了地面磁共振灵敏度核函数表达式的推导。针对现有地面磁共振正演方法中常规网格尺寸大、计算精度差、细化网格尺寸小、但是数量大的问题,应用Hammer积分在常规网格中完成核函数的高精度计算。三维核函数和3个含水模型的正演仿真实验表明:基于Hammer积分的地面磁共振正演方法具有网格少、计算节点少、积分精度高的特点,能够高效解决核函数的正演计算问题。

有限元方法的Gauss积分和Hammer积分方案

研究了一致网格剖分下矩形单元的Gauss数值积分和三角形单元的Hammer数值积分;再利用有限元方法求解偏微分方程,且通过非奇异问题和奇异问题的数值算例观察解的l2范数误差;进而研究单元数值积分对有限元解的精度的影响,并给出了有效且经济的数值积分方案。

长距离输水管道启泵水锤模拟及试验验证

水锤是流体的一种非稳定流动。在长距离输水工程中,水锤现象有可能会造成很大的危害。本文以南水北调来水调入密云水库调蓄工程为例,对长距离输水管道启泵过程中的水锤现象进行模拟,并通过试运行时的实测资料对模拟结果进行验证。结果表明,模拟结果与试验结果非常接近。通过本次模拟及试运行发现,在长距离输水管道启泵过程中,管道内会产生明显的升压,必须予以重视,否则存在管道破裂的风险。