Effect of seepage force on tunnel face stability reinforced with multi-step pipe grouting

Tunneling in difficult geological conditions is often inevitable especially in urban areas. Ground improvement and reinforcement techniques are required to guarantee safe tunnel excavations and/or to prevent damage to adjacent structures. The steel pipe-reinforced multi-step grouting method has been recently applied to tunnel sites as an auxiliary technique in Korea for impermeabilization in underwater tunnels as well as for reinforcement. However, this technique has been usually employed empirically without much understanding with regard to its effect on the tunnel safety. In this study, the face stability with steel pipe-reinforced multi-step grouting in underwater tunnels was evaluated by simultaneously considering two factors: one is the effective stress acting on the tunnel face calculated by limit theorem and limit equilibrium method; the other is the seepage force obtained by means of numerical analysis. This study revealed that the influence of the steel pipe-reinforced multi-step grouting on the support pressure required for the stability of the tunnel face in dry condition is not significant while there is relatively a significant reduction in seepage forces by adopting the technique in the underwater tunnel. The effect of permeability anisotropy on the seepage force acting on the tunnel face was also assessed by conducting a coupled analysis.     

Microstructure and mechanical properties of TiC nanoparticle-reinforced Mg−Zn−Ca matrix nanocomposites processed by combining multidirectional forging and extrusion

TiC nanoparticle-reinforced Mg−4Zn−0.5Ca matrix nanocomposites were processed by combining multidirectional forging (MDF) and extrusion (EX). The grain size of the nanocomposite after MDF+EX multi-step deformation was significantly decreased compared with that processed only by MDF. The average size of the recrystallized grains gradually increased after EX with increasing the number of MDF passes at 270 °C. However, the grain size significantly decreased by MDF processing at 310 °C. Both fine and coarse MgZn₂ phases appeared in the (MDF+EX)-processed nanocomposites, and their volume fractions gradually increased with increasing the number of MDF passes before EX. Ultrahigh tensile properties (yield strength of ~404 MPa, ultimate tensile strength of ~450.3 MPa and elongation of ~5.2 %) were obtained in the nanocomposite after three MDF passes at 310 °C followed by EX. This was attributed to the refinement of the recrystallized grains, together with the improved Orowan strengthening provided by the precipitated MgZn₂ particles that were generated by MDF+EX multi-step deformation.     

Online multi-step prediction for wind speeds and solar irradiation: Evaluation of prediction errors

We propose a general method for predicting multiple steps ahead of our target system and estimating simultaneously the prediction errors in a real time. The requirement of the proposed method is that we have a time series of the target system. We demonstrate the method by artificial data, real wind speed data, and real solar irradiation data.     

User Independent Paging Scheme for Mobile IP

Multi-step paging has been widely proposed in personal communications services (PCS) systems to reduce the signaling overheads. Similar ideas can be applied to Mobile IP to provide IP paging services. However, current proposed multi-step paging schemes are user dependent under which the partition of paging areas and the selection of paging sequence are different for each user. The performance of a user dependent paging scheme for individual users may be affected by many factors. It is often difficult to achieve perfect performance for each user. In addition, when multiple users are paged at the same time, user dependent paging schemes may consume significant system resources. This paper introduces a user independent paging scheme where the paging criterion is not based on individual user information. The goal of user independent paging is to provide satisfactory overall performance of the whole system, when personalized optimal performance for each user is hard to obtain. The user independent paging scheme is proposed for IP mobility for its easy implementation and convenient combination with paging request aggregation. The paging criterion adopted is the mobility rate of each subnet determined by the aggregated movements of all mobile users. In order to implement the proposed scheme, a concept of “semi-idle state” is introduced and the detailed solution for obtaining mobility rate is presented. Analytical results show that when paging one user at a time, the performance of the proposed user independent paging scheme is comparable to that of the paging schemes based on perfect knowledge of user movement statistics. When paging multiple users simultaneously and when the knowledge on individual user behavior is not perfectly accurate, the proposed scheme has remarkable advantages in terms of reducing the overall paging cost. Jiang Xie received her B.E. degree from Tsinghua University, Beijing, China, in 1997, M.Phil. degree from Hong Kong University of Science and Technology in 1999, and M.S. and Ph.D. degrees from Georgia Institute of Technology in 2002 and 2004, respectively, all in electrical engineering. She is currently an assistant professor with the Department of Electrical and Computer Engineering at the University of North Carolina-Charlotte. Her current research interests include resource and mobility management of wireless networks,QoS provisioning, and next-generation Internet. She is a member of IEEE and ACM.     

基于网络时滞补偿的模型预测控制

为了解决网络控制系统中不确定时滞、尤其是随机的长时延对控制性能造成的影响,提出了基于模型匹配和多步预测输出补偿的预测控制思想来改善控制性能。该算法通过采集到的传感器端至控制器端的时滞来估算控制器端至执行器端的时滞,并给出了传感器端和执行器端数据处理的算法,建立起与实际网络结构匹配的预测控制模型,采用多步预测输出来补偿控制量的传输滞后。该模型不依赖于网络参数和时滞分布特性,可根据不同对象选取合适的预测控制算法,适用于实时系统。通过基于倒立摆对象的仿真和控制实例验证了该算法能有效地改善控制性能。     

基于数据序列分辨率压缩尺度优化的月度电量预测方法

准确的月度电量预测是指导电力部门安排运行计划和保障售电公司盈利能力的关键基础。针对基于人工智能算法电量预测模型在训练过程中存在样本分辨率选择不当导致预测精度降低的问题,提出了一种历史数据序列分辨率压缩尺度优化方法。首先将数据分辨率压缩尺度选择建模成一个优化问题。然后通过数据驱动方式进行求解。最后再利用长短期记忆(Long Short-term Memory, LSTM)神经网络实现月度电量预测,从而较好地实现了数据分辨率和电量预测步长之间的合理平衡以提升电量预测精度。利用美国PJM电力市场的历史电量数据对所提方法进行验证。仿真结果表明,较不进行分辨率压缩尺度选择所提方法具有更高的预测精度,同时LSTM网络在结合该方法时表现出了最佳的预测性能。     

一种全新的基于小电流过趋热效应的峰值结温电学测试方法

It has been a scientific and technological problem in the field of microelectronics for several decades that the electrical method is used to measure the peak junction temperature of power transistors. Based on the excessive thermotaxis effect of low current, a novel electrical measurement method of the peak junction temperature is presented in this paper. The method is called the thermal spectrum analysis method of transistors, simply designated TSA （thermal spectrum analysis method）. Unlike the common method which uses a single measuring current, TSA uses multi-step currents to measure temperature-sensitive parameters. Based on the excessive thermotaxis effect of low current and the sub-transistor parallel model, the peak junction temperature and non-uniform property of junction temperature distribution are analyzed successfully.     

基于行程时间多步预测的实时路径导航算法

针对现有车辆导航算法仅考虑单一数据,使所得路径实际行程时间比预期更长的问题,首先建立了基于卡尔曼滤波理论的行程时间多步预测模型;其次,提出了综合利用实时数据、行程时间多步预测数据及历史数据的实时路径导航算法,并改进了其实现的核心算法Dijkstra_pred.实验结果表明,基于三类数据的实时路径导航算法所得路径的实际行程时间从整体上优于仅采用实时数据的导航算法,且路径变化较少.     

多步逆成形有限元法中间构型初始解预示算法

在逆成形有限元法中,为考虑加载路径的影响,针对不同成形类型阶段引入中间构型,整个过程被划分为多阶段成形过程,即多步逆成形有限元法,一个好的中间构型初始解的构造是其中的关键问题之一。针对中间构型初始解的构造,提出一种基于滑移约束曲面的节点反向映射法：利用板材的纯几何弯曲效应构造出弯曲构型,经过伪最小面积法优化后生成空间滑移约束曲面;投影展平的最终构型网格面到展平滑移约束曲面网格中,利用面积坐标计算出所有投影节点的坐标;投影节点反向映射回到空间滑移约束曲面上,构造出对应中间构型的初始解。另外,针对中间构型初始解构造中可能出现部分节点无投影区域的问题,给出一种扩展空间滑移约束曲面轮廓的解决方法。零件的数值算例验证相应算法的可行性与有效性。     

冲击波平面性、稳定性实验用双边多台阶Al靶制备

多台阶靶是冲击波稳定性、平面性实验的重要实验用靶。本工作采用单点金刚石切削技术,优化工艺过程设计,完成了铝双边多台阶靶的制备。应用Veeco NT1100白光干涉仪对表面轮廓及粗糙度进行了测量。通过SPDT技术制备的具有微细双边结构的多台阶靶可满足实验要求。各台阶表面几何厚度误差小于1%,均方根粗糙度Rq小于50 nm,轮廓最大高度Tir仅在底部台阶处最大,约200 nm,其余台阶处均小于100 nm,台阶垂直度在90°±1°内。