Effects of cavity-induced mixing enhancement under oblique shock wave interference: Numerical study

In this research, the effects of oblique shock on the mixing characteristics in a supersonic combustor equipped with a cavity is numerically investigated. To reveal the flow structure of the supersonic flow field under oblique shock wave interference, three-dimensional steady RANS equations and SST k-ω turbulence model are adopted. The current work focuses on comparing the interaction effects between oblique shock wave and bow shock wave, which are formed by fuel jet on fuel mixing under different conditions. The numerical analysis demonstrates that an optimal angle exists for the mixing efficiency of the ramp. The optimal angle diminishes as the jet-to-crossflow pressure ratio increases. The oblique shock wave in a certain range is conducive to enhance the penetration depth of ethylene. The smaller angle of the ramp does not cause large stagnation pressure losses.     

Large piezoelectricity and potentially activated polarization reorientation around relaxor MPB in complex perovskite

Improving piezoelectric performance is always favorable to further enhance the sensitivity and accuracy of piezoelectric devices. Here, a complex piezoelectric system of Pb(Ni_1/3Nb_2/3)O₃-Pb(Yb_1/2Nb_1/2)O₃-Pb(Hf_0.1Ti_0.9)O₃ is designed and investigated in detail. Optimized piezoelectric response of ～ 880 pC/N is achieved at the composition of 0.51PNN-0.09PYN-0.40PHT. The characterization of TEM and In-situ high-energy synchrotron diffraction indicate that nanodomain growth and microdomain switching occurs in succession at around coercive electric field. Most interestingly, the coexisted tetragonal and rhombohedral-like phase transforms into multiple monoclinic-like phases with polarization vectors aligned as close to the electric field direction as possible under the strong electric field. The enhanced polarization instability in this complex morphotropic phase boundary sample should be ascribed to the strong local heterogeneity. The novel polarization rotation behavior found in this work would be important guidance for designing high-performance piezoceramics.     

四旋翼长续航飞行模式的设计与实现

更长的飞行时间是四旋翼无人机领域研究热点方向之一;在对实际飞行中瞬时消耗电流和电池电压数据的研究中发现,过大姿态角下电池电量消耗显著提升;为了延长飞行时间和提升电池电量使用效率,提出一种长续航飞行模式;在该模式下,基于现有的角速度串级PID姿态控制器,将飞行加速度的控制算法改为飞行速度控制,限制过大姿态角的操作;在无风、微风和强风环境下的飞行实验表明,长续航飞行模式比传统飞行方式飞行时间增加8%~20%;长续航飞行模式可广泛应用于多种无需快速变换飞行路径,但需要更长飞行时间的的应用场景中。     

刀具几何参数对圆柱类零件加工精度的影响

主要分析了数控车削加工中刀具刀尖圆弧、主偏角对各类零件表面加工精度的影响并提出了相应的措施。为在数控车削加工中正确地选择加工工艺、选择刀具参数和编制加工程序提供了依据,为在实际生产中提高零件加工精度提供了保证。     

缓推进大倾角综放工作面综合防灭火技术

为了控制缓推进大倾角综放工作面在回采及回撤期间煤炭自然发火,针对阳城煤矿3306工作面开采实际,综合利用多种防灭火技术有效避免了工作面自然发火事故的发生,确保了3306工作面安全回采。     

带式输送机物料断面系数的分析

对现行物料断面系数Ｋ的３种计算方法进行了分析与讨论，指出３种计算方法的Ｋ不同，主要是由物料在输送带上的有效宽度ｂ的取值不同造成的．找到了物料断面系数Ｋ合理的计算方法．     

基于MEMS 加速度计的倾斜姿态角传感器设计

针对应用领域中判断水平面及水平面夹角的问题,设计一种倾斜姿态角传感器。把MEMS加速度计SCA103T-D04与C8051F47单片机组合在一起,对MEMS加速度计输出信号进行调理和AD采集,单片机C8051F047完成数据分析和温度补偿,并通过CAN总线通讯接口和RS232通讯接口输出倾斜角度值,输出周期为200 ms。该倾斜姿态角传感器测量精度为0.03°,测量范围为–6°~6°,具有体积小、重量轻、精度高、温度适应范围宽的特性,可广泛应用于建筑、道路、桥梁及军用设备等领域。     

井下短路电流幅相保护及实现方式

建立了三相对称短路电流与相角的关系，给出了确定幅相保护特性的新方法，提出了相行的幅相保护的实现方式。     

大倾角薄煤层综采实践与探讨

薄煤层开采是许多矿井煤炭开采中不可避免的问题。目前,我国薄煤层开采大多仍采用炮采或普采,不仅劳动强度大、生产效率低,而且开采速度慢,影响近距离其它煤层的开采和高产高效矿井建设。论文针对开滦东欢坨矿大倾角薄煤层综合机械化开采所采取的技术措施及所取得的效果,对相关问题进行了分析探讨,提出了大倾角薄煤层机械化开采的有效方法。     

潜孔锤回转机构研究

将传统的潜孔锤与凿岩机相结合,研究了潜孔锤孔底回转机构,介绍了一种新型的潜孔锤。借鉴凿岩机的转钎机构,利用活塞的回程能量带动钻头旋转。经过研究表明,这种新型的潜孔锤,不用钻机,只用空压机带动潜孔锤,可以实现冲击与回转,为我国大口径帷幕工程、水利水电工程及非开挖工程等效率的提高提供了新的工艺方法。