顶板定向长钻孔“以孔代巷”抽采瓦斯技术研究

为探究行之有效的“以孔代巷”瓦斯抽采技术,解决端氏煤矿高抽巷工程量大、经济成本高等问题,提出顶板定向长钻孔替代高抽巷治理采空区瓦斯模式。采用FLAC^3D数值模拟确定3号煤层顶板以上15～45 m为最佳抽采层位,并基于定向钻进轨迹控制技术,在端氏煤矿3019工作面进行成孔试验。结果表明：钻进轨迹能够按照预设参数实施,成孔直径达153 mm,一次成孔深度420 m以上,钻孔进入稳定抽采阶段的平均抽采瓦斯浓度达18%、平均抽采瓦斯纯流量达8.7 m³/min,钻孔抽采条件下工作面瓦斯抽采率达36.7%,工作面上隅角瓦斯浓度控制在0.50%以下,解决了瓦斯超限问题。与高抽巷抽采技术相比,顶板定向长钻孔成本降低62.5%、施工工期缩短50%,验证了“以孔代巷”的合理性和可行性。     

钻孔煤体破坏渗流模型及在煤层卸压抽采中的应用研究

为对比分析顺层钻孔在护孔和未护孔条件下的抽采效果,考虑煤体扩容特性,采用煤体孔隙率和渗透率动态数学模型,结合D-P屈服准则,建立了钻孔煤体破坏—渗流的流固耦合模型。以超化煤矿2煤层相关物理参数为基础,开展了钻孔卸压破坏范围及抽采瓦斯数值模拟,结果表明：钻孔发生卸压破坏后,虽然未护孔钻孔卸压范围是护孔钻孔的1.3倍,其周围煤体渗透率和孔隙率均大于护孔钻孔,但钻孔更易塌孔堵孔,当抽采90 d时,护孔钻孔有效抽采半径为未护孔钻孔的1.3倍。现场瓦斯抽采测定数据表明,护孔钻孔平均抽采瓦斯浓度为未护孔的1.6倍,平均抽采瓦斯纯流量为未护孔的1.4倍,并有效缩短了钻孔抽采时间。     

水力压裂过程的扩展有限元数值模拟方法

建立了基于扩展有限元法的水力压裂数值模拟方法,使水力裂缝独立于网格存在,无需预设裂缝扩展方位。在扩展有限元计算框架下,将裂缝面处理为求解域内边界,将缝内水压力转化为相关单元等效节点力;运用考虑缝内水压力作用的相互积分法来数值求解缝尖应力强度因子;采用最大能量释放率准则确定裂缝是否继续扩展及扩展方位;最终编制了计算机程序。利用该方法数值模拟了单条水力裂缝在恒定水压力作用下作非平面扩展,所得结果分别与室内试验和解析模型相对比。结果表明,数值结果与室内试验和解析解吻合较好,缝尖应力强度因子最大相对误差不高于0.45%,验证了该方法的可行性和准确性。     

基于动力显式算法的热成形数值模拟预测

考虑金属热处理相变动力学模型,建立了适用于高强度钢板热成形的热、力、相变多场耦合本构方程。基于大变形动力显式有限元算法及上述多场耦合本构方程,建立了热成形动力显式有限元方程。并将板料相变潜热释放引入到热成形温度场分析过程中。在自主开发的商业化金属成形CAE软件KMAS(King Mesh Analysis System)基础上开发了热成形动力显式分析模块,可用于预测热成形过程中零件的厚度变化、温度变化、微观组织各相的体积分数以及硬度分布。随后采用该模块对一款汽车B柱的热成形过程及最终力学性能进行数值模拟预测,并与试验结果进行对比,对比的一致性证明了所建立的多场耦合本构方程及KMAS热成形动力显式分析模块的正确性。     

基于神经网络的白酒勾兑目标规划算法优化

针对白酒勾兑过程中,现有的白酒勾兑目标规划算法难以确定权系数(优先因子)的缺点,本文提出了利用人工神经网络对目标规划算法进行改进和优化,选择三层前向BP神经网络结构,并通过选取理化指标向量与\     

Advanced modeling and control of wind conversion systems based on hybrid generators using fractional order controllers

The focus of this study is on modeling and management of a Wind Energy Conversion System (WECS) based on a Hybrid Excitation Synchronous Generator (HESG). Using a wind simulator, two controllers, CRONE and H_∞, are evaluated for Maximum Power Point Tracking (MPPT) and optimal rotation speed. The results show the CRONE controller's higher tracking capability, and robustness tests investigate the influence of parametric uncertainty. Space harmonic effects, commutation effects, and turbine shaft flexibility are all addressed in the sophisticated models. The introduction of Fractional Order Proportional-Integral (FOPI) control for MPPT is a game changer. Although fractional calculus-based accuracy and robustness are uncommon in WECS, they show promise for emissions reduction and increased energy efficiency. This work validates a dependable control approach inside an isolated HESG-based WECS's power-maximizing range. Extensive investigation of the parameters impacting FOPI control efficiency yields useful insights for effective MPPT control. A variable-speed wind turbine (WT) is linked to a HESG through a multiplier, with a controller controlling generator coil excitation voltages and a rectifier connecting the WECS to a load. A thorough 3 kW HESG electrical model that includes generator space harmonics and converter commutation effects is among the contributions. For HESG-based WECS stability, frequency analysis finds important resonant and anti-resonant frequencies. These issues are addressed by a FOPI control technique, which ensures system stability and performance. The necessity of exact frequency analysis in HESG-based WECS is highlighted by a step-by-step controller parameter tuning approach.     

真空炉温度均匀性测量的数值模拟研究

采用BNi-2镍基钎料对热流道板进行真空钎焊,须根据钎焊件设定加热工艺曲线。加热工艺曲线的设定是钎焊过程最重要的环节之一,决定着钎焊的质量和效率。该文结合真空加热的特点及钎焊要求,运用Ansys有限元软件数值模拟的方法,对壁厚、体积较大的多层热流道板真空钎焊进行仿真分析,通过对比不同工艺方案及不同钎焊件的模拟结果,探究真空钎焊过程升温规律,从而调整各阶段的相关参数及制定合理的加热工艺曲线,避免了现场反复调试参数造成的资源浪费,节约了时间和成本,提高了效率。此外,通过在实际钎焊试验过程中布置热电偶对钎焊件测量温度,并与数值模拟结果对比,两者基本吻合,验证了有限元分析的准确性,能为之后其他零部件的真空钎焊提供参考。

     

“十”字地铁换乘站多点火灾工况下的通风排烟

以某典型“十”字交叉换乘地铁车站为研究对象, 通过数值模拟的方法对换乘车站两站台同时发生火灾的极端情况下不同排烟方案的排烟效果进行了研究, 方案1是站厅层送风, 地下二层和三层站台分别排烟;方案2是在方案1的基础上, 将地下三层的车站屏蔽门打开, 利用车站隧道风机进行辅助排烟.火源设计为峰值2 MW的时间平方快速火.研究结果表明:两种方案都能有效控制地下二层站台烟气蔓延, 方案2中打开地下三层车站屏蔽门, 利用车站隧道系统辅助排烟的措施可以有效增加楼梯处的向下风速, 同时降低楼梯处烟气温度, 延长火源附近楼梯作为人员疏散通道的时间, 实现良好的换乘站防烟效果.     

沥青路面铺筑温度场数值仿真模型

为确定一定环境下沥青混合料铺筑过程温度衰减规律, 对铺筑过程路面温度场的仿真模型进行了研究.采用非连续的随碾压次数而变的层厚、材料热物性和洒水散热条件, 连续的随温度而变的对流换热、辐射换热条件, 以及非均匀的底层初始温度场, 建立了一维仿真模型.通过变换几何模型及循环调用初始温度场的方法, 实现了非连续条件在连续场分析中的应用.由仿真模型验证, 本文模型可以在不同环境条件下实现铺筑过程温度场仿真.     

Temperature Rise Inside Shear Bands in a Simple Model Glass

One of the key factors, which hampers the application of metallic glasses as structural components, is the localization of deformation in narrow bands of a few tens up to one hundred nanometers thickness, the so-called shear bands. Processes, which occur inside shear bands are of central importance for the question whether a catastrophic failure of the material is unavoidable or can be circumvented or, at least, delayed. Via molecular dynamics simulations, this study addresses one of these processes, namely the local temperature rise due to viscous heat generation. The major contribution to energy dissipation is traced back to the plastic work performed by shear stress during steady deformation. Zones of largest strain contribute the most to this process and coincide with high-temperature domains (hottest spots) inside the sample. Magnitude of temperature rise can reach a few percent of the sample’s glass transition temperature. Consequences of these observations are discussed in the context of the current research in the field.