Examining the effect of adverse geological conditions on jamming of a single shielded TBM in Uluabat tunnel using numerical modeling

Severe shield jamming events have been reported during excavation of Uluabat tunnel through adverse geological conditions, which resulted in several stoppages at advancing a single shielded tunnel boring machine(TBM). To study the jamming mechanism, three-dimensional(3D) simulation of the machine and surrounding ground was implemented using the finite difference code FLAC3D. Numerical analyses were performed for three sections along the tunnel with a higher risk for entrapment due to the combination of overburden and geological conditions. The computational results including longitudinal displacement contours and ground pressure profiles around the shield allow a better understanding of ground behavior within the excavation. Furthermore, they allow realistically assessing the impact of adverse geological conditions on shield jamming. The calculated thrust forces, which are required to move the machine forward, are in good agreement with field observations and measurements. It also proves that the numerical analysis can effectively be used for evaluating the effect of adverse geological environment on TBM entrapments and can be applied to prediction of loads on the shield and preestimating of the required thrust force during excavation through adverse ground conditions.

Numerical Analyses of Ice Jamming in Jacket Platform Conductor Array in Bohai Sea

Serious ice accumulating,pile-up and ice jamming occur around the conductor array of offshore jacket platforms during the winter every year in Bohai Sea,which could cause grave threats to the stability of platform structure,the safety of people and equipment,and even severer calamity.Therefore,the process of ice accumulation and ice jamming in the jacket platform area needs more concern.This study focuses on ice accumulation and jamming behaviors in the jacket platform conductor area by using a coupled two-dimensional hydro-ice dynamics model.A series of cases are conducted with different flow conditions,such as flow velocity,drifting direction and oscillatory flow.Through the simulation,the ice pile-up process is described and changes in ice-jamming thickness,ice pile-up location and ice pile-up volume are investigated.The differences in ice pile-up in the steady flow and oscillatory flow are analyzed.This study proposes a new approach to simulate the ice jamming process in the jacket platform conductor area,providing a reference for ice management on the platform.

Markov Model Based Jamming and Anti-Jamming Performance Analysis for Cognitive Radio Networks

In this paper, we conduct a cross-layer analysis of both the jamming capability of the cognitiveradio-based jammers and the anti-jamming capability of the cognitive radio networks (CRN). We use a Markov chain to model the CRN operations in spectrum sensing, channel access and channel switching under jamming. With various jamming models, the jamming probabilities and the throughputs of the CRN are obtained in closed-form expressions. Furthermore, the models and expressions are simplified to determine the minimum and the maximum CRN throughput expressions under jamming, and to optimize important anti-jamming parameters. The results are helpful for the optimal anti-jamming CRN design. The model and the analysis results are verified by simulations.

TIME-VARYING AR MODELING AND ADAPTIVE IIR NOTCH FILTER FOR ANTI-JAMMING DSSS RECEIVER

Using Time-Varying AR (TVAR) model and adaptive notch filter is a new method for the non-stationary jammer suppression in Direct Sequence Spread Spectrum (DSSS). The performance of TVAR model for Instantaneous Frequency (IF) estimation will be affected by some factors such as basis functions. Focusing on this problem, the optimal basis function of TVAR model for the IF estimation of the LFM signal is obtained in this paper. Besides the depth and width of notching, the phase properties of notch filter affect the Signal-to-Interference plus-Noise Ratio (SINR) of correlation output to the narrowband jammer suppression in DSSS, in response to the problem the closed solution of correlation output SINR improvement has been derived when a single frequency jammer passes through direct IIR notch filter, and its performance has been compared with those of five coefficient FIR filters. Later, a novel method for LFM jammer suppression based on Fourier basis TVAR model and direct IIR notch filter is proposed. The simulation results show the effectiveness of the proposed method.

Feedback control scheme of traffic jams based on the coupled map car-following model

Based on the pioneering work of Konishi et al. [Phys. Rev. E （1999） 60 4000], a new feedback control scheme is presented to suppress traffic jams based on the coupled map car-following model under the open boundary condition. The effect of the safe headway on the traffic system is considered. According to the control theory, the condition under which traffic jams can be suppressed is analyzed. The results are compared with the previous results concerning congestion control. The simulations show that the suppression performance of our scheme on traffic jams is better than those of the previous schemes, although all the schemes can suppress traffic jams. The simulation results are consistent with theoretical analyses.

Research on the self-defence electronic jamming decision-making based on the discrete dynamic Bayesian network

The manner and conditions of running the decision-making system with self-defense electronic jamming are given. After proposing the scenario of applying discrete dynamic Bayesian network to the decision making with self-defense electronic jamming, a decision-making model with self-defense electronic jamming based on the discrete dynamic Bayesian network is established. Then jamming decision inferences by the aid of the algorithm of discrete dynamic Bayesian network are carried on. The simulating result shows that this method is able to synthesize different targets which are not predominant. In this way, various features at the same time, as well as the same feature appearing at different time complement mutually; in addition, the accuracy and reliability of electronic jamming decision making are enhanced significantly.

Asymptotic solution of a wide moving jam to a class of higher-order viscous traffic flow models

The boundary-layer method is used to study a wide moving jam to a class of higher-order viscous models. The equations for characteristic parameters are derived to determine the asymptotic solution. The sufficient and essential conditions for the wide moving jam formation are discussed in detail, respectively, and then used to prove or disprove the existence of the wide moving jam solutions to many well-known higher-order models. It is shown that the numerical results agree with the analytical results.

Evaluation for Success Probability of Chaff Centroid Jamming

As the chaff centroid jamming can introduce the guiding error of the anti-warship missile's seeker and decrease its hitting probability,a new quantitative analysis method and a mathematic model are proposed in this paper to evaluate the success jamming probability.By using this method,the optimal decision scheme of chaff centroid jamming in different threat situations can be found,and also the success probability of this scheme can be calculated quantitatively.Thus,the operation rules of the centroid jamming and the tactical approach for increasing the success probability can be determined.

Ice Jam Modelling of the Lower Red River

The lower reach of the Red River between Winnipeg and Lake Winnipeg is very prone to ice jam flooding. The one- dimensional ice jam model RIVICE was implemented for this reach to better understand the processes leading to such events and to provide a tool to evaluate strategies for ice jam mitigation. The most downstream portion of this river stretch flows through a delta and marsh system which poses challenges in modelling ice jams in such an area of low-lying topography and river banks. Solutions to overcome these challenges are discussed in this paper and results of one such solution using water abstractions from the main channel are also presented. Abstractions are inserted in the model to represent under-ice leakage from the main channel to side channel storage and diversions (up to 65% in the Red River delta) and spillage into the delta floodplain.

基于灰狼算法的箔条幕干扰构设方法研究

海战场环境中,箔条幕自卫干扰构设前由于未充分考虑风向、风速等因素,容易导致干扰失败,且无定量化的布放模型。针对此问题,提出一种新的箔条幕干扰构设方法。基于箔条幕干扰机理分析,构建干扰场景模型,具体包含导弹运动模型、舰船运动模型和箔条幕形态模型;综合考虑干扰有效性和资源损耗性,提出采用灰狼算法进行箔条幕干扰构设方案求取的思路,建立相应约束条件(遮蔽有效性约束条件、质心拖引有效性约束条件和干扰能力约束条件)、目标函数和补弹策略,且采用Logistic混沌映射和反向学习策略改进灰狼算法。最终通过仿真案例分析得出以下结论:所提出的箔条幕干扰构设方法寻优速率快,可保证整个对抗过程中舰艇始终能够进行有效自卫干扰。初始时刻构设的箔条幕轴线基本与弹目轴垂直,而箔条幕质心基本处于弹目轴线附近。风向与风速对自卫干扰效果影响较小,初始弹目距离主要影响箔条弹用量,初始反舰导弹攻击方向对自卫干扰效果影响较为明显。当从舰艇尾向进行攻击时,干扰效果最好;相反,从舰艇艏向进行攻击时,干扰效果最差。

限制环境下的GNSS精密授时方法研究综述

GNSS精密授时技术在国防军事领域得到了广泛的应用,但卫星导航信号具有先天的脆弱性,极易受到各种有意和无意干扰,为了提升GNSS精密授时的稳健性和安全性,亟需发展限制环境下的授时技术。介绍了GNSS授时应用存在的问题,分析了GNSS精密授时方法研究现状,给出了在无地面通信网络条件下利用北斗三号PPP-B2b信息进行实时PPP授时,在信号遮挡条件下利用惯性导航辅助PPP瞬时重新收敛和附加钟差模加快PPP重新收敛,以及在复杂电磁环境下利用多阵元抗干扰天线提高GNSS授时性能的发展对策建议,为拓展GNSS授时技术在时频领域的应用提供借鉴。

基于弹塑性模型的某舰炮抽壳力仿真计算

舰炮射击后药筒贴膛力对抽壳初速存在重要影响,贴膛过程药筒表现出弹塑性大变形特性,且沿口部至底部贴膛极不均匀,简化的二维模型及薄壁圆筒解析模型已经不能满足定量的分析需求。建立了基于弹塑性抽壳过程动力学仿真模型,采用Johnson-Cook本构模型描述药筒弹塑性大变形行为,通过仿真计算获取药筒及炮膛动态应力应变、接触力及摩擦力等参量,分析了药筒动态贴膛规律及受力特性。仿真结果表明,舰炮射击过程药筒经历贴闩、径向自由膨胀至贴膛、贴膛后与炮膛协同变形及回弹至平衡态四个阶段,平衡状态后抽壳阻力不再变化,保持在13320N左右,抽筒子作用于药筒后抽壳初速最高达到18.9m/s,该抽壳初速满足了舰炮高速连发的设计性能要求。

Lattice models of traffic flow considering drivers' delay in response

This paper proposes two lattice traffic models by taking into account the drivers＇ delay in response. The lattice versions of the hydrodynamic model are described by the differential-difference equation and difference-difference equation, respectively. The stability conditions for the two models are obtained by using the linear stability theory. The modified KdV equation near the critical point is derived to describe the traffic jam by using the reductive perturbation method, and the kink-antikink soliton solutions related to the traffic density waves are obtained. The results show that the drivers＇ delay in sensing headway plays an important role in jamming transition.

Travel time prediction with viscoelastic traffic model

Travel time through a ring road with a total length of 80 km has been predicted by a viscoelastic traffic model(VEM), which is developed in analogous to the non-Newtonian fluid flow. The VEM expresses a traffic pressure for the unfree flow case by space headway, ensuring that the pressure can be determined by the assumption that the relevant second critical sound speed is exactly equal to the disturbance propagation speed determined by the free flow speed and the braking distance measured by the average vehicular length. The VEM assumes that the sound speed for the free flow case depends on the traffic density in some specific aspects, which ensures that it is exactly identical to the free flow speed on an empty road. To make a comparison, the open Navier-Stokes type model developed by Zhang(ZHANG, H. M. Driver memory, traffic viscosity and a viscous vehicular traffic flow model. Transp. Res. Part B, 37, 27–41(2003)) is adopted to predict the travel time through the ring road for providing the counterpart results.When the traffic free flow speed is 80 km/h, the braking distance is supposed to be 45 m,with the jam density uniquely determined by the average length of vehicles l ≈ 5.8 m. To avoid possible singular points in travel time prediction, a distinguishing period for time averaging is pre-assigned to be 7.5 minutes. It is found that the travel time increases monotonically with the initial traffic density on the ring road. Without ramp effects, for the ring road with the initial density less than the second critical density, the travel time can be simply predicted by using the equilibrium speed. However, this simpler approach is unavailable for scenarios over the second critical.

Decisive Parameters for Backwater Effects Caused by Floating Debris Jams

The dimensional analysis of the backwater effect caused by debris jams results in the Froude number of the approach flow in the initial situation prior to debris jam formation and the debris density as decisive parameters. For the more precise detection of the influence of both parameters the results of different hydraulic model test series at the Laboratory of Hydraulic and Water Resources Engineering of the Technical University of Munich concerning debris jams at spillways as well as at racks for the retention of wooden debris were uniformly evaluated. On the one hand a significant increase of the backwater effect with a rising Froude number of the approach flow could be shown. This is in good correlation to recent test results for debris jams at retention racks at the Laboratory of Hydraulics, Hydrology and Glaciology of the Swiss Federal Institute of Technology Zurich. On the other hand a significant increase of the backwater effect could also be shown for a rising debris density. However, the test results also show that significantly different backwater effects can occur in different test runs with identical test conditions. These differences are a result of the randomness of debris jam development, and therefore, a more exact quantification of the dependence of the backwater effect on the Froude number of the approach flow and on the debris density is not considered useful for the present results.

Traffic Dynamics and Congested Phases Derived from an Extended Optimal-Velocity Model

Dynamics is studied for one-dimensional single-lane traffic flow by means of an extended optimal-velocity model with continuously varied bottleneck strength for nonlinear roads. Two phases exist in this model such as free flow and wide moving jam states in the systems having relatively small values of the bottleneck strength parameter. In addition to the two phases, locally congested phaseappears as the strength becomes prominent. Jam formation occurs with the similar mechanism to the boomerang effect as well as the pinch one in it. Wide scattering of the flow-density relation in fundamental diagram is found in the congested phase.

基于模型预测控制的可变目标距离自适应巡航控制研究

为解决在复杂交通环境中自适应巡航系统存在旁车切入本车前方工况时,目标期望距离计算模型得到的期望相对距离与实际相对距离发生阶跃以及堵车蠕行工况,车辆与前车距离较近,拥堵路况不断启停的目标车辆的速度、加速度和相对距离持续抖动,导致的纵向加速度幅值过大带来的驾驶平顺性、舒适性和安全性问题,提出可变目标距离的自适应巡航控制算法,基于模型预测控制理论,建立离散纵向运动学预测模型,综合考虑底盘加速度响应、极限安全纵向跟车距离、车辆自身物理限制、驾驶人乘坐舒适性等优化控制目标,引入松弛因子进行在线求得可行解.在旁车不同切入工况、综合工况行驶以及堵车蠕行工况对本算法进行仿真和实车测试并利用数据对IDM算法开环实验,研究成果对比表明,考虑旁车切入的可变目标距离的自适应巡航控制算法在旁车加速切入工况中,纵向控制产生的最大冲击度为-0.25 m/s^(3),相比于IDM模型降低50%,堵车蠕行工况中纵向控制产生最大减速度为-0.3 m/s^(2),相比于IDM模型降低30%,综合工况和定速巡航工况中,算法在保持安全距离情况下可以对车辆实现稳定纵向控制,加速度幅值不超过-0.36 m/s^(2),可有效提高驾驶人的舒适性、平顺性和安全性.

Torsional Models of Two-ply Yarn

In this paper,the vector equation of a generaliseddoubly wound helix was derived.Treloar’s pliedyarn geometry could be obtained as a special case ofthe generalised doubly wound helix.The shortest fi-bre length around the surface of a helical tube(formed by fibre helices)was determined by apply-ing variational principles.The fibre length as calcu-lated by using Treloar’s geometry was compared in-directly with the shortest possible fibre length at dif-ferent levels of yarn deformation when some of Tre-loar’s rigid geometrical constraints were relaxed.Anew idea based on non-concentric circles was intro-duced to approximate the fibre helix movement in atwo-ply yarn.A torsional model of two-ply yarnwas developed and the theoretical predictions werecompared with some preliminary experimental re-sults.

一种对卫星干扰源的高精度定位方法

随着空间卫星通信技术的发展,电磁环境日益复杂,信号在传输过程中更加容易受到干扰,从而导致出现了更多的安全问题,因此对卫星干扰源实现高精度定位具有十分重要的意义。为了解决干扰源定位问题,构建了合理的无源定位数学模型进行深入研究,设计了一种优化的单站定位方法,并且综合分析了卫星转发时延、卫星经纬度等误差因素以实现优化。最后通过仿真试验,验证了该方法的有效性和定位精度。

单根箔条平均雷达截面研究

箔条干扰是最为常用的无源干扰方式之一,主要依靠其电磁散射特性实现对雷达接收机的干扰。对箔条散射雷达截面进行研究,利用非相干模型推导了不同入射极化条件下单根箔条平均雷达截面,得到了箔条极化散射矩阵,并对单根箔条极化散射特性进行分析。提出了相干条件下的理想摆放模型,得到了更贴近实际使用的单根箔条平均雷达截面数值,为充分发挥箔条无源干扰效能打下基础。