Mechanism of burst feeding in ZL205A casting under mechanical vibration and low pressure

The burst feeding behavior of ZL205 A casting under mechanical vibration and low pressure was investigated by casting experiment and physical model. Experimental results indicated that the burst feeding appeared repeatedly during solidification and left a shrinkage cavity with layered structure under mechanical vibration. The castings with less shrinkage and higher density could be achieved through the vibration. The calculation results of physical model showed that the burst feeding could perform spontaneously under vibration while difficultly without vibration in low-pressure die casting. The obstruction of a casting could be broken and the grains could be rearranged by the vibration. And the obstruction could be carried away due to the inner and outer pressure difference, causing a burst feeding.

Focal mechanism caused by fracture or burst of a coal pillar

As a regional, real-time and dynamic method, microseismic monitoring technology is quite an appropriate technology for forecasting geological hazards, such as rock bursts, mine tremors, coal and gas outbursts and can even be used to prevent or at least reduce these disasters. The study of the focal mechanisms of different seismic sources is the prerequisite and basis for forecasting rock burst by microseismic monitoring technology. Based on the analysis on the mechanism and fracture course of coal pillars where rock bursts occur mostly, the equivalent point source model of the seismicity caused by a coal pillar was created. Given the model, the seismic displacement equation of a coal pillar was analyzed and the seismic mechanism was pointed out by seismic wave theory. The course of the fracture of the coal pillar was simulated closely in the laboratory and the equivalent microseismic signals of the fractures of the coal pillar were acquired using a TDS-6 experimental system. The results show that, by the pressure and friction of a medium near the seismic source, both a compression wave and a shear wave will be emitted and shear fracture will be induced at the moment of breakage. The results can be used to provide an academic basis to forecast and prevent rock bursts or tremors in a coal pillar.

Formation mechanisms of water inrush and mud burst in a migmatite tunnel：a case study in China

This paper presents a case study of water inrush and mud burst occurring in a migmatite tunnel to study its formation mechanisms. The geological investigation and mineralogical analysis showed that water inrush and mud burst in the migmatite was closely related to the component of the host rock. High content of soluble minerals,e.g.,calcite and dolomite,would make the migmatite rock prone to be fragmentized,isintegrated and eventually form different sorts of connected or semi-connected veins. The field exploration revealed most cavities in the magmatite tunnel were eroded by groundwater and formed large interconnected networks. The two faults and the dike in the magmatite tunnel became the preferred paths and provided great convenience for plenty of precipitation and mud slurry. Due to high water pressure and blast disturbance,the cavities can soon connect each other as well as all sorts of veins,forming a complex ground channel for water inrush and mud burst. To estimate the potential occurrenceof water inrush and mud burst,the water bursting coefficient was employed. The results showed the water bursting coefficient of the magmatite tunnel was much bigger than the threshold values and it can be used to explain the accident of water inrush and mud burst occurring in the magmatite tunnel.

Bursting phenomena as well as the bifurcation mechanism in a coupled BVP oscillator with periodic excitation

We explore the complicated bursting oscillations as well as the mechanism in a high-dimensional dynamical system.By introducing a periodically changed electrical power source in a coupled BVP oscillator, a fifth-order vector field with two scales in frequency domain is established when an order gap exists between the natural frequency and the exciting frequency.Upon the analysis of the generalized autonomous system, bifurcation sets are derived, which divide the parameter space into several regions associated with different types of dynamical behaviors. Two typical cases are focused on as examples,in which different types of bursting oscillations such as sub Hopf/sub Hopf burster, sub Hopf/fold-cycle burster, and doublefold/fold burster can be observed. By employing the transformed phase portraits, the bifurcation mechanism of the bursting oscillations is presented, which reveals that different bifurcations occurring at the transition between the quiescent states（QSs） and the repetitive spiking states（SPs） may result in different forms of bursting oscillations. Furthermore, because of the inertia of the movement, delay may exist between the locations of the bifurcation points on the trajectory and the bifurcation points obtained theoretically.

Forced bursting and transition mechanism in CO oxidation with three time scales

The mathematical model of CO oxidation with three time scales on platinum group metals is investigated, in which order gaps between the time scales related to external perturbation and the rates associated with different chemical reaction steps exist. Forced bursters, such as point–point type forced bursting and point–cycle type forced bursting, are presented. The bifurcation mechanism of forced bursting is novel, and the phenomenon where two different kinds of spiking states coexist in point–cycle type forced bursting has not been reported in previous work. A double-parameter bifurcation set of the fast subsystem is explored to reveal the transition mechanisms of different forced bursters with parameter variation.

Transmission Mechanism Based on Burst Filling in Hybrid Optical Burst/Circuit Switching Networks

Hybrid optical switching networks make full use of the advantages of Optical Circuit Switching(OCS)and Optical Burst Switching(OBS).In parallel hybrid optical switching networks,edge nodes choose a switching mode for traffic and no longer change.The inflexible decision making of the traffic transfer mode leads to low resource utilization when the arrival rate of the OCS traffic is lower than the capacity of the light path.In this paper,a new transmission scheme is proposed to improve resource utilization for hybrid optical switching networks.When the traffic arrival rate of the light path is lower than the transmission rate of the light path,the OCS traffic flow is reshaped at the edge nodes to generate a series of voids.Then,several message packets are sent along the light path to inform the core nodes of the voids of the light paths that represent the unused bandwidth resources.To improve the resource utilization,the voids can be filled with data bursts by core nodes.The simulation results show that the new scheme can effectively reduce the burst loss rate and improve the link utilization of the hybrid optical switching network on the premise of a providing service quality guarantee for OCS traffic.

Research on Mechanism of Rock Burst Generation and Development for High Stress Rock Tunnels

Through the investigation and analysis of high stress distribution in surrounding rock during the excavation of rock tunnels,the key factors to cause rock burst and the mechanism of rock burst generation and development are researched. The result shows that the scale and range of rock burst are related with elastic deformation energy storied in rock mass and the characteristics of unloading stress waves. The measures of preventing from rock burst for high stress rock tunnels are put forward.

Anchoring effect and energy-absorbing support mechanism of large deformation bolt

To research the anchoring effect of large deformation bolt,tensile and drawing models are established.Then,the evolution laws of drawing force,bolt axial force and interfacial shear stress are analyzed.Additionally,the influence of structure element position on the anchoring effect of large deformation bolt is discussed.At last,the energy-absorbing support mechanism is discussed.Results show that during the drawing process of normal bolt,drawing force,bolt axial force and interfacial shear stress all gradually increase as increasing the drawing displacement,but when the large deformation bolt enters the structural deformation stage,these three values will keep stable;when the structure element of large deformation bolt approaches the drawing end,the fluctuation range of drawing force decreases,the distributions of bolt axial force and interfacial shear stress of anchorage section are steady and the increasing rate of interfacial shear stress decreases,which are advantageous for keeping the stress stability of the anchorage body.During the working process of large deformation bolt,the strain of bolt body is small,the working resistance is stable and the distributions of bolt axial force and interfacial shear stress are steady.When a rock burst event occurs,the bolt and bonding interface cannot easily break,which weakens the dynamic disaster degree.

Thermo-Mechanical Analysis of Water-Cooled Gun Barrel During Burst Firing

The thermo-mechanical stress and deformation of water-cooled gun barrel during burst firing are studied by finite element analysis (FEA). The problem is modeled in two steps: 1) A transient heat transfer analysis is first carried out in order to determine temperature evolution and to predict the residual temperatures during the burst firing event; 2) The thermo-mecha- nical stresses and deformation caused by both the residual temperature field and the gas pressure are then calculated. The results show that the residual temperature field tends to a steady state with the increasing of rounds. The residual temperature field has much effect on the gun barrel stress and deformation, especially on the assembly area between barrel and water jacket. The gage between the barrel and water jacket is the critical factor to the thermo- mechanical stress and deformation. The results of this analysis will be very useful to develop the new strength design theory of the liquid-cooled gun barrel.

Study on rock burst of fully mechanized sublevel caving mining in deep mine

The theoretical analysis, numerical simulation and field observation were used to study distribution characters of abutment pressure of fully mechanized sublevel caving face in deep mine, fully mechanized sublevel caving and pressure relief in entries along goaf to the influence of rock burst. The results show that： （1） With the increasing of mining depth, the abutment pressure zone is larger, its peak point is transferred to the front of face, the danger area occurring rock burst in the two fully mechanized sublevel caving entries is larger, and its position is far from the face; （2） There is larger failure area in the upper coal in front of the fully mechanized caving face, and strata possibly occurring rock burst transferred to the upwards or far from faces because of the main roof＇s buffer effect to the dynamic pressure burst, then possibility and strength reduced; （3） The position occurring rock burst is stress concentration zones （abutment pressure along the goaf and residual tectonic stress） and zones with geological structure; （4） Strenuous activities of roof is the inducing factor occurring rock burst.

电针通过调节膀胱及尿道平滑肌中的血清素受体表达改善骶上脊髓损伤大鼠的排尿功能

目的观察电针治疗后骶上脊髓损伤(suprasacral cord injury,SSCI)大鼠的膀胱最大容量(maximum cystometric capacity,MCC)、漏尿点压力(leakage point pressure,LPP),结合分析逼尿肌、内尿道括约肌(internal urethral sphincter,IUS)中血清素(5-hydroxytryptamine,5-HT)不同亚型受体的表达,探讨电针治疗通过突触后5-HT受体调节逼尿肌-尿道括约肌协同失调(detrusor sphincter dyssynergia,DSD)大鼠排尿功能的效应机制。方法36只SD雌性大鼠,随机抽取12只作为空白组,剩余24只采用改良Hassan Shaker脊髓横断法在T10脊髓节段全横断制作SSCI大鼠模型,成模后随机分为模型组和电针组,每组12只。电针组取次髎、中极、三阴交穴予持续电针刺激40 min,1次/d,连续治疗7 d;空白组与模型组只捆绑不治疗。采用膀胱造瘘法进行尿流动力学检测;处死大鼠后取逼尿肌和近端尿道组织,采用Western blot法检测5-HT受体含量。结果模型组大鼠MCC、LPP显著高于空白组(P<0.01);电针组MCC显著低于模型组且高于空白组(P<0.01),LPP显著低于模型组(P<0.01)。与空白组比较,5-HT1A受体在模型组大鼠逼尿肌中表达显著降低(P<0.01),IUS中显著增高(P<0.01);电针组大鼠逼尿肌中5-HT1A受体显著高于模型组(P<0.01),IUS中5-HT1A受体低于模型组(P<0.05),但仍显著高于空白组(P<0.01)。模型组大鼠逼尿肌中5-HT2B受体表达高于空白组(P<0.05);电针组大鼠逼尿肌中5-HT2B受体表达低于模型组和空白组(P<0.05)。与空白组比较,5-HT7受体在模型组大鼠逼尿肌中表达显著降低(P<0.01),IUS中表达显著增高(P<0.01);电针组大鼠逼尿肌和IUS中5-HT7受体的表达均低于模型组(P<0.05)。结论电针刺激SSCI后DSD大鼠次髎、三阴交、中极穴引起膀胱及尿道平滑肌中5-HT受体表达变化,5-HT1A和5-HT2B受体可能通过Ca^(2+)流入使平滑肌产生相性和/或强直性收缩,5-HT7受体可能通过环磷酸腺苷(cyclic adenosine monophosphate,cAMP)途径影响大电导Ca^(2+)激活K^(+)(big-conductance Ca^(2+)-activated K^(+),BK)通道活性介导平滑肌松弛,电针治疗由此抑制逼尿肌过度活动、增加其收缩能力并协调尿道阻力以改善SSCI后DSD大鼠下尿路功能。

煤炭开采等地下工程问题的数字岩石力学解决方案

煤炭开采等地下工程的可观测性极为有限,导致很多复杂的工程问题难以获得可靠的事前分析依据,尤其在面临深部作业和高强度开采所带来的全新工程环境时,现有理论体系和技术方案的适用性面临着严峻的挑战。基于数字化时代的技术发展特点,提出了融合数据规律、力学逻辑和工程经验的数字岩石力学解决方案;充分利用工程数据中包含着真实工程规律的客观特点,建立了理论成果、工程经验与数据规律挖掘进行底层融合的具体模式;借助煤岩物理力学参数无损推断场景,验证了上述技术路径的可行性,实现了兼具可靠性和可解释性的数据挖掘利用。进一步构建了以煤岩物性、矿井结构和空间应力为基本要素的数字岩石力学理论体系,提出了以“工程素描—物理嵌入—业务融合—决策生成”为步骤的数字岩石力学地下工程通用作业模式,并通过在复杂工程现场的应用检验了数字岩石力学解决方案的可靠性,为煤炭开采等地下工程的数字化转型、智能化升级提供了切实可行的实现路径。

冲击地压矿井充填工作面超前采动应力对充填体充实率的反馈机制

高应力是深部矿井冲击地压灾变频率走高的主要原因,充填开采则是控制岩层运动,缓解采动应力集中程度,降低围岩破坏和冲击风险的有效手段。为研究采空区充填体对超前采动应力的控制能力,以山东古城煤矿1123充填工作面为工程背景,采用理论分析、室内试验、现场实测手段探究充填开采工作面采动应力分布规律,揭示超前采动应力对充填体充实率的反馈机制,指导冲击地压矿井充实率确定。结果表明:工作面开采初期充填体充实率低于80%,坚硬顶板下沉量大,超前采动影响范围大于30 m,应力集中系数达到1.5,断层影响区采动应力影响范围和集中系数分别增至60 m和1.65,片帮冒顶等围岩失稳现象增多;实测了采空区充填体承载应力全程动态演化特征,承载应力分布曲线划分为“快速降低—短暂稳定—快速升高—缓慢降低—二次稳定”5个阶段,低充实率条件下采空区上、中、下3个区域承载应力稳定值分别为1.9、5.2、2.8 MPa;将采空区充填体划分为非充分压实区和充分压实区,构建了充填体支撑作用下坚硬顶板连续沉降模型,得到了坚硬顶板“ʅ”型沉降曲线,非充分压实区范围随充实率近似呈线性减小;试验得到充填体弹性模量和单轴抗压强度随凝固时间的演化曲线,结合顶板沉降曲线和推进速度得到工作面前后采动应力全区域分布曲线;建立了超前采动应力集中程度与充填体承载能力的负指数函数关系,揭示了超前采动应力对充填体充实率的负向反馈机制,实现充填开采降载防冲效果的定量评价;提出了充填体充实率“三位一体”协同提升措施,将1123工作面充实率升高至90%,增强了充填体承载能力,超前采动应力集中系数降至1.3,厚顶煤膨胀变形量减少至50 mm,坚硬顶板破断致冲风险显著降低。

大巷煤柱工作面过空巷矿压规律及控制技术

【目的】由于矿井工作面布置方式的调整,煤柱工作面经常会面临通过废弃巷道时覆岩顶板难以控制的情况。【方法】为解决这一问题,以河南赵固二矿二盘区外侧煤柱工作面过空巷为工程背景,采用理论分析、数值模拟和现场试验等方法,研究工作面与空巷覆岩破断组合结构,模拟不同支护强度下顶板应力-位移全周期演化规律,分析工作面矿压显现特征,提出相应的控制技术。【结果和结论】结果表明,基本顶不同破断形式对矿压显现特征影响显著,关键块断裂位置可分为煤柱上方、空巷上方和实体煤上方3种类型。通过建立工作面过空巷力学模型,研究基本顶超前破断力学机理,基本顶受到空巷-煤柱-工作面支护系统支撑作用,形成“砌体梁”稳定承载结构,判定基本顶滑落失稳时空巷支护强度的临界值为4.6MPa。数值模拟显示,工作面超前支承压力与空巷应力集中产生的叠加效应对煤柱影响显著,当工作面推进至距空巷5m时,煤柱失稳破坏,基本顶易发生超前破断。在工作面过空巷过程中,煤柱超前支承压力分布特征由“双峰型”转变为“孤峰型”。不同支护强度下的顶板应力分布特征存在明显差异,确定空巷支护强度为4.5MPa能够防止基本顶超前破断。最后,在研究区二盘区外侧煤柱工作面采用“锚网索”支护方式对空巷顶板进行补强支护,过空巷期间液压支架工作阻力在研究区域处于安全范围内,未发生顶板垮落和压架等事故,解决了二盘区外侧煤柱工作面过空巷技术难题,可为类似工作面提供参考依据。

物理指标与深度学习融合的冲击地压风险等级预测

为探究煤矿智能化开采背景下,冲击地压的预警问题。以数据分析为基础,以河南某矿21181工作面为背景,提出物理指标与深度学习融合的冲击地压预警方法。该方法通过分析大能量事件发生之前,各项物理指标在最大值、趋势性以及相对变化率绝对值3方面特性,得到与之对应的综合物理特征,并分析震源的空间分布特性,根据其特性提出坐标注意力机制,对震源坐标进行加权,得到震源特征。对综合物理特征以及震源特征,加入通道注意力机制对特征进行加权,并使用全连接层进行分类,达到风险等级预测的目的,最终将模型运用于实际工程。研究结果表明:物理指标与深度学习融合的冲击地压预警方法可以达到较高的准确率。研究结果可为实际工程提供一定借鉴。

深部构造区大倾角工作面回撤致冲机理及防治技术

深部构造区大倾角工作面回撤期间冲击风险较高,为研究回撤期间致冲机理及防治技术,以潘西煤矿6199工作面为背景,采用理论分析、数值模拟,结合现场数据开展研究。结果表明:工作面受多因素影响处于复杂高静载环境,上部基本顶尖角区剪应力集中明显,工作面液压支架撤离,上覆岩层压力向工作面前方转移,局部超过极限载荷可能发生高静载加载型冲击,基本顶破断及断层活化产生动载,可能诱发动静载叠加型冲击;根据回撤前矿压数据,前方岩层活动较为剧烈,工作面微震预警事件发生前后支架阻力升高,存在基本顶破断及断层活化可能,冲击风险较高。基于回撤致冲机理提出卸压-支护协同防冲技术,即通过弱化高静载影响,降低动载产生可能性,辅助提高顺槽支护强度、控制工作面顶板降低回撤期间冲击风险;工作面回撤期间矿压监测数据无明显升高,卸压-支护协同防冲技术效果较好。

核电厂重要设备爆破片服役寿命评价技术

针对爆破片现有的技术规范中鲜有服役寿命评价的技术说明,以某核电厂汽轮机低压缸爆破片为例,通过对寿命影响因素的梳理,进行了爆破片整体疲劳和爆破试验,并对金属部件的材质检验、缺陷检测,以及非金属部件进行加速老化试验和性能测试对比分析。研究结果表明,经过100次压力循环后,爆破片的性能保持在设计参数内,显示出良好的耐疲劳性能。金属部件的微观分析和非金属部件的加速老化测试均证明了材料的高稳定性和长寿命。在现有的服役条件和更换周期情况下,爆破片主要的寿命影响因素对其服役损伤影响有限,将更换周期延长一倍具有理论和试验数据支撑。该研究对破膜在工程中的应用、维护及更换策略具有一定的指导意义。

基于顶板结构特征的冲击危险性评价方法及应用

目前煤矿普遍采用的冲击危险性评价方法忽视了岩层层位、厚度等对冲击危险性评价结果的影响,致使现有冲击危险性评价体系对不同地层结构下顶板冲击危险性评价准确度不足。根据采空区覆岩破坏程度,建立了全悬顶结构、半悬顶结构及完全移动结构3类顶板结构力学模型,分析了各类顶板结构类型下的应力传递机制,提出了基于3类顶板结构与实测矿震数据相结合的动静载叠加应力计算方法及考虑顶板结构特征的冲击危险性评价指标及评价方法,并分析了岩层强度系数、关键层厚度以及岩层下沿距工作面距离对冲击特征参数p的影响规律;依托鄂尔多斯市某矿2201工作面、济宁市某矿63上06工作面及菏泽市某矿3301工作面地层结构条件,进行了顶板岩层结构下动静载叠加应力及冲击危险性评价参数的计算,并根据计算结果进行了冲击危险性评价验证分析。

弱胶结巨厚砂砾岩含水层离层突水机制研究

安新煤田主采煤层上覆巨厚弱胶结砂砾岩含水层,富水性弱,但多个工作面回采期间发生突水,查明突水机制是矿井水害防治的关键。通过水文地质特征分析,阐明了砂砾岩含水层厚度分布特征和富水性分区特征。采用岩石单轴抗压强度、三轴声发射、X衍射试验等方法,获得了顶板隔水层岩石物理力学性质。基于关键层理论分析、导水裂隙带与采动富水异常区层位关系及相似模拟试验成果,建立了4种条件下巨厚砂砾岩含水层突水的水文地质结构模型,揭示了砂砾岩含水层不同条件下的突水机制,并明确了研究区突水点的突水机制,提出了隔水保护层失稳导致突水的工程判据。研究结果表明:研究区东部局部区域含水层富水性中等,以往多次突水均发生在弱富水区;砂砾岩含水层下顶板泥岩中黏土矿物含量达到59.6%,亲水性强,具有良好的隔水作用;但在采动作用下顶板隔水层岩体卸压后强度降低,厚度较薄时,受上部岩层载荷和采动富水区静水压力作用易发生破坏,成为良好导水通道;砂砾岩含水层物理力学性质特殊,采动扰动后孔隙裂隙发育,形成了富水变化异常区;弱胶结砂砾岩突水的强度与下部基岩特征、导水裂隙带发育高度、隔水保护层厚度等因素相关;研究区弱胶结砂砾岩发生突水的工程判据为正常区隔水保护层厚度小于30 m,受背斜构造影响区隔水保护层厚度小于60 m。弱胶结巨厚砂砾岩含水层离层突水机制及工程判据对西部矿区水害防治提供了借鉴。

巨厚硬岩下综放工作面超前效应失效机制研究

以河南义马煤田上赋巨厚硬岩综放工作面为工程背景,采用现场实测、理论分析和数值模拟等方法,探索工作面开采中的超前效应失效机制,并提出了相应防控策略。研究表明,低位大厚度软岩的易垮性、高位巨厚硬岩的整体性和超前高强卸压是导致超前效应失效的根本原因,低位大厚度软岩随推采即时垮落,高位巨厚硬岩未达到极限跨距时以整体静载作用于下方煤体,煤体所承受的覆岩自重应力被均化,进而导致超前效应显现不明显;超前高强卸压不但阻断了传力路径,同时降低了应力集中程度。据此提出了设计合理推采长度、留设合理隔离煤柱以减少远场悬露岩层的生成,近场实施超前强卸压降力的防控策略,将大幅减少或消除巨厚硬岩下工作面超前效应的影响,对冲击地压防治具有重要意义。