Sliding behaviors of the trapezoidal roof rock block under a lateral dynamic disturbance

The surrounding rock of underground space is always affected by external dynamic disturbance from the side position,such as blasting vibration from a stope at the same level or seismic waves from adjacent strata.A series of laboratory tests,numerical simulations and theoretical analyses were carried out in this study to disclose the sliding mechanism of roof rock blocks under lateral disturbance.Firstly,the experiments on trapezoidal key block under various clamping loads and disturbance were conducted,followed by numerical simulations using the fast Lagrangian analysis of continua(FLAC3D).Then,based on the conventional wave propagation model and the classical shear-slip constitutive model,a theoretical model was proposed to capture the relative displacement between blocks and the sliding displacement of the key block.The results indicate that the sliding displacement of the key block increased linearly with the disturbance energy and decreased exponentially with the clamping load when the key block was disturbed to slide(without instability).Meanwhile,when the key block was disturbed to fall,two types of instability process may appear as immediate type or delayed type.In addition,the propagation of stress waves in the block system exhibited obvious low-velocity and lowfrequency characteristics,resulting in the friction reduction effect appearing at the contact interface,which is the essential reason for the sliding of rock blocks.The results can be applied to practical underground engineering and provide valuable guidance for the early detection and prevention of rockfalling disasters.

Exploration of Operation and Maintenance Management Mode and Innovation Mechanism of Pilot Base of Chemical Park

Based on the current situation of the operation and maintenance management of the pilot base in many chemical parks in China,this paper conducts an in-depth exploration of the operation and maintenance management and innovation mode of the pilot base from the aspects of the evaluation of the pilot project entering the park,safety and environmental protection supervision,pilot mode,and industrialization mode of the pilot test results,so as to provide solutions for accelerating the process and industrialization of the pilot project and realizing the innovation value of the pilot base.

Dynamic flight stability of a hovering model insect:lateral motion

The lateral dynamic flight stability of a hovering model insect （dronefly） was studied using the method of computational fluid dynamics to compute the stability derivatives and the techniques of eigenvalue and eigenvector analysis for solving the equations of motion. The main results are as following. （i） Three natural modes of motion were identified： one unstable slow divergence mode （mode 1）, one stable slow oscillatory mode （mode 2）, and one stable fast subsidence mode （mode 3）. Modes 1 and 2 mainly consist of a rotation about the horizontal longitudinal axis （x-axis） and a side translation; mode 3 mainly consists of a rotation about the x-axis and a rotation about the vertical axis. （ii） Approximate analytical expressions of the eigenvalues are derived, which give physical insight into the genesis of the natural modes of motion. （iii） For the unstable divergence mode, td, the time for initial disturbances to double, is about 9 times the wingbeat period （the longitudinal motion of the model insect was shown to be also unstable and td of the longitudinal unstable mode is about 14 times the wingbeat period）. Thus, although the flight is not dynamically stable, the instability does not grow very fast and the insect has enough time to control its wing motion to suppress the disturbances.

ZERO MODE NATURAL FREQUENCY AND NONLINEAR VIBRATION OF COUPLED LATERAL AND TORSION OF A LARGE TURBINE GENERATOR

Zero mode natural frequency (ZMNF) is found during experiments. The ZMNF andvibrations resulted by it are studied. First, calculating method of the ZMNF excited byelectromagnetic in vibrational system of coupled mechanics and electrics are given from the view ofmagnetic energy. Laws that the ZMNF varies with active power and exciting current are obtained andare verified by experiments. Then, coupled lateral and torsional vibration of rotor shaft system isstudied by considering rest eccentricity, rotating eccentricity and swing eccentricity. UsingLargrange-Maxwell equation when three phases are asymmetric derives differential equation of thecoupled vibration. With energy method of nonlinear vibration, amplitude-frequency characteristics ofresonance are studied when rotating speed of rotor equals to ZMNF. The results show that ZMNF willoccur in turbine generators by the action of electromagnetic. Because ZMNF varies withelectromagnetic parameters, resonance can occur when exciting frequency of the rotor speed is fixedwhereas exciting current change. And also find that a generator is in the state of large amplitudein rated exciting current.

Optimization of High Power 1.55-μm Single Lateral Mode Fabry-Perot Ridge Waveguide Lasers

Optimization of the high power single-lateral-mode double-trench ridge waveguide semiconductor laser based on InGaAsP/InP quantum-well heterostructures with a separate confinement layer is reported. Two different waveguide structures of Fabry-Perot lasers emitting at a wavelength of 1.55 μm are fabricated. The influence of an effective lateral refractive index step on the maximum output power is investigated. A cw single mode output power of 165mW is obtained for a 1-mm-long uncoated laser.

Design of integral sliding mode guidance law based on disturbance observer

With the increasing precision of guidance,the impact of autopilot dynamic characteristics and target maneuvering abilities on precision guidance is becoming more and more significant.In order to reduce or even eliminate the autopilot dynamic operation and the target maneuvering influence,this paper suggests a guidance system model involving a novel integral sliding mode guidance law(ISMGL).The method utilizes the dynamic characteristics and the impact angle,combined with a sliding mode surface scheme that includes the desired line-ofsight angle,line-of-sight angular rate,and second-order differential of the angular line-of-sight.At the same time,the evaluation scenario considere the target maneuvering in the system as the external disturbance,and the non-homogeneous disturbance observer estimate the target maneuvering as a compensation of the guidance command.The proposed system’s stability is proven based on the Lyapunov stability criterion.The simulations reveale that ISMGL effectively intercepted large maneuvering targets and present a smaller miss-distance compared with traditional linear sliding mode guidance laws and trajectory shaping guidance laws.Furthermore,ISMGL has a more accurate impact angle and fast convergence speed.

Exploring mechanism of hidden,steep obliquely inclined bedding landslides using a 3DEC model:A case study of the Shanyang landslide in Shaanxi Province,China

Catastrophic geological disasters frequently occur on slopes with obliquely inclined bedding structures(also referred to as obliquely inclined bedding slopes),where the apparent dip sliding is not readily visible.This phenomenon has become a focal point in landslide research.Yet,there is a lack of studies on the failure modes and mechanisms of hidden,steep obliquely inclined bedding slopes.This study investigated the Shanyang landslide in Shaanxi Province,China.Using field investigations,laboratory tests of geotechnical parameters,and the 3DEC software,this study developed a numerical model of the landslide to analyze the failure process of such slopes.The findings indicate that the Shanyang landslide primarily crept along a weak interlayer under the action of gravity.The landslide,initially following a dip angle with the support of a stable inclined rock mass,shifted direction under the influence of argillization in the weak interlayer,moving towards the apparent dip angle.The slide resistance effect of the karstic dissolution zone was increasingly significant during this process,with lateral friction being the primary resistance force.A reduction in the lateral friction due to karstic dissolution made the apparent dip sliding characteristics of the Shanyang landslide more pronounced.Notably,deformations such as bending and uplift at the slope’s foot suggest that the main slide resistance shifts from lateral friction within the karstic dissolution zone to the slope foot’s resistance force,leading to the eventual buckling failure of the landslide.This study unveils a novel failure mode of apparent dip creep-buckling in the Shanyang landslide,highlighting the critical role of lateral friction from the karstic dissolution zone in its failure mechanism.These insights offer a valuable reference for mitigating risks and preventing disasters related to obliquely inclined bedding landslides.

Properties study of LiNbO_3 lateral field excited device working on thickness extension mode

This paper investigates the properties of thickness extension mode excited by lateral electric field on LiNbO3 by using the extended Christoffel-Bechmann method. It finds that the lateral field excitation coupling factor for amode （quasi-extensional mode） reaches its maximum value of 28% on Xmcut LiNbO3. The characteristics of a lateral field excitation device made of X-cut LiNbO3 have been investigated and the lateral field excitation device is used for the design of a high frequency ultrasonic transducer. The time and frequency domain pulse/echo response of the LiNbO3 lateral field excitation ultrasonic transducer is analysed with the modified Krimholtz-Leedom-Matthae model and tested using traditional pulse/echo method. A LiNbO3 lateral field excitation ultrasonic transducer with the centre frequency of 33.44 MHz and the -6 dB bandwidth of 33.8% is acquired, which is in good agreement with the results of the Krimholtz-Leedom-Matthae model. Further analysis suggests that the LiNbO3 lateral field excitation device has great potential in the design of broadband high frequency ultrasonic transducers.

Lateral buckling of non-trenched high temperature pipelines with pipelay imperfections

An analysis method for the buckling process of a pipe section with a random pipelay imperfection is proposed. Four basic lateral modes, acquired by finite-element （FE） eigenvalue buckling analysis, are combined to provide the needed grid configurations for describing a real pipelay imperfection and an arc-length algorithm is used to analyze the snap-through process of the shell-element-grid model under nonlinear frictional boundary conditions. This paper also presents evaluation methods for the lateral buckling of two types of pipe-in-pipe systems that are used in the offshore oil and gas industry. For evaluating the buckling and postbuckling of compliant pipe-in-pipe systems FE analyses were carried out to judge the occurrence of the system buckling and furthermore to check postbuckling stresses induced in the buckles. The calculated results of the modified Riks algorithm indicate that only when high temperature would not trigger an abrupt short-wavelength buckle and when no yielding has been induced in the unavoidable long-wavelength buckles, the thermal stability and safety of compliant pipe-in-pipe systems can be proved. In the non-compliant pipe-in-pipe systems, firstly small-amplitude buckles of the carrier pipe may occur in the annulus between carrier pipe and casing pipe and the contact forces between the spacers and the casing pipe may drive the buckle of the pipe-in-pipe systems on the seabed. Based on the classical analytical solution of pipe buckling, four potential buckling modes corresponding to finite- element models are developed to evaluate the stability and the postbuckling strength of such pipe-in-pipe systems.

Lateral resonances in initial stressed 1-3 piezocomposites

A theoretical analysis of the lateral resonances in 1-3 piezocomposites with poling initial stress is conducted using the Bloch wave theory. Based on the linear piezoelectricity theory, theoretical formulations that include initial stress for the propagation of acoustic plane waves are made. Numerical calculations are performed to study the effects of the initial stress on the lateral mode frequencies and the stop band. It is found that lateral mode frequencies increase with the piezoelectricity of the piezocomposites, but decrease with the poling initial stress. The influence of the initial shear stress on the lateral mode frequencies is minimal, and can thus be neglected.

High-Order Lateral Buckling Analysis of Submarine Pipeline Under Thermal Stress

It is of importance to study and predict the possible buckling of submarine pipeline under thermal stress in pipeline design.Since soil resistance is not strong enough to restrain the large deformation of pipeline,high-order buckling modes occur very easily.Analytical solutions to high-order buckling modes were obtained in this paper.The relationships between buckling temperature and the amplitude or the wavelength of buckling modes were established.Analytical solutions were obtained to predict the occurrence and consequence of in-service buckling of a heated pipeline in an oil field.The effects of temperature difference and properties of subsoil on buckling modes were investigated.The results show that buckling will occur once temperature difference exceeds safe temperature;high-order pipeline buckling occurs very easily;the larger the friction coefficients are,the safer the submarine pipeline will be.

Impact of Ground Effect on Airplane Lateral Directional Stability during Take-Off and Landing

Computational simulations of aerodynamic characteristics of the Common Research Model (CRM), representing a typical transport airliner are conducted using CFD methods in close proximity to the ground. The obtained dependencies on bank angle for aerodynamic forces and moments are further used in stability and controllability analysis of the lateral-directional aircraft motion. Essential changes in the lateral-directional modes in close proximity to the ground have been identified. For example, with approach to the ground, the roll subsidence and spiral eigenvalues are merging creating the oscillatory Roll-Spiral mode with quite significant frequency. This transformation of the lateral-directional dynamics in piloted simulation may affect the aircraft responses to external crosswind, modify handling quality characteristics and improve realism of crosswind landing. The material of this paper was presented at the Seventh European Conference for Aeronautics and Space Sciences EUCASS-2017. Further work is carried out for evaluation of the ground effect aerodynamics for a high-lift configuration based on a hybrid geometry of DLR F11 and NASA GTM models with fully deployed flaps and slats. Some aspects of grid generation for a high lift configuration using structured blocking approach are discussed.

A Computational Study on Lateral Flight Stability of the Cranefly in Hover

The dynamic flight stability of hovering insects includes the longitudinal and lateral motion.Research results have shown that for the majority of hovering insects the same longitudinal natural modes are identified and the hovering flight in longitudinal is unstable.However,in lateral,the modal structure for hovering insects could be different and the stability property of lateral disturbance motion is not as robust as that of longitudinal motion.The cranefly possesses larger aspect ratio and lower Reynolds number,and such differences in morphology and kinematics may make the lateral dynamic stability different.In this paper,the lateral flight stability of the cranefly in hover is investigated by numerical simulation.Firstly,the stability derivatives are acquired by solving the incompressible Navier–Stokes equations.Subsequently,the dynamic stability characteristics are checked by analyzing the eigenvalues and eigenvectors of the linearized system.Computational results indicate that the lateral dynamic modal structure of cranefly is different from most other insects,consisting of three natural modes,and the weakly oscillatory mode illustrates the hovering lateral flight is nearly neutral.This neutral stability is mainly caused by the negative derivative of roll-moment vs.sideslip-velocity,which can be attributed to the weaker‘changingLEV-axial-velocity’effect.These results suggest that insects in nature may exhibit different dynamic stabilities with different morphological and kinematic parameters,which should be considered in the designs of flapping wing air vehicles.

基于电流模分量特性的多端柔性直流配电网线路纵联保护

多端柔性直流配电网因在供电可靠性方面极具优势而受到广泛的关注,然而对于直流线路保护中故障的快速、可靠识别成为其急速发展所需解决的关键问题之一。因此,设计了一种利用电流模分量特性的直流线路纵联保护方法。该方法利用故障时正极电流线模分量方向来判别区内外故障,以不同故障条件下故障点正极电流零模分量平均值的差异来构造保护判据,从而判别故障类型,形成保护策略。最后,在PSCAD/EMTDC4.5上搭建了多端柔性直流配电网模型,对保护判据及关键影响要素进行了仿真分析。结果表明,该保护方法能够有选择性地快速、可靠识别区内外故障及故障类型,且具有较好的耐过渡电阻与抗噪声能力。

小组培养模式在耳鼻咽喉科临床医学博士试点班教学中的效果评估

目的 探讨小组培养模式在临床医学博士试点班(“4+4”医学博士项目)学生耳鼻咽喉科教学中的效果。方法 选取2022年5月至6月北京协和医院2019级临床医学博士改革试点班学生(本科非医学专业)共30名做为试点班组,临床实习采用小组培养模式,课前和课后发放调查问卷,收集问卷,统计分析数据。另2022年5月至6月北京协和医院2016级八年制学生89名,根据年龄、性别、基础医学成绩选取30名配对分组为八年制组,采用传统临床教学方法。教学后进行课后理论考试,按照满分100分的标准,统计分析两组学生理论成绩差异。结果试点班组30名学生课前问卷统计:前4年本科专业方向均来自于非医学专业,选择医学专业的原因是为了救死扶伤;51%的学生认为五官科在临床中占重要位置;课后问卷统计:90%的学生对床旁学习课程设计满意;40%的学生对耳鼻喉科新技术的应用比较感兴趣;28名针对教学中不足之处认为耳鼻喉科学知识深奥,29名认为应该增加多媒体教学方法。两组耳科理论成绩比较,差异无统计学意义(P>0.05),但试点班课时12学时较八年制20学时少。结论 改革试点班学生来自多个专业方向,为医学发展注入新的理念和思路;小组培养模式拉近学生与教师的距离,教学相长,提高学生学习效率,同时反馈改进教师教学方法。

适用于双馈风电场送出线的纵联方向保护研究

考虑风电场接入电网时,传统方向元件在短路故障发生时易受到风电场内部电力电子器件动态特性的干扰影响,导致频率特性偏移,系统参数不稳定和弱馈性等问题,使继电保护装置不能及时或正确判断故障发生区域。针对上述问题,首先对含有风电场的故障附加网络进行分析,寻找故障发生后纵联保护安装处各测量点电气量之间的关联性,确定其故障逻辑关系。其次通过对常用的相模变换解耦方式进行分析,选择一个合理的方法代入相关性表达式,根据相关系数值完成故障区域判定。最后利用PSCAD/EMTDC搭建双馈风电场并网模型,设置各种不同的故障类型和场景,并利用Matlab进行保护算法验证,检验故障区域判断结果,验证所提保护方法的正确性与合理性,并且仿真结果表明该方法具有较高的可靠性。

智能车横向跟踪控制模式切换策略及评价方法

针对智能车横向跟踪控制算法传统切换策略中模型匹配策略总是处于激活状态,占用计算资源和运动平顺性变差的问题,设计了一种基于最小二乘支持向量机(least squares support vector machine,LSSVM)的控制模式切换策略,在不同工况下根据误差判断策略切换控制模式.从安全性、舒适性和跟踪精度3个方面构建控制效果评估函数,并根据多目标优化数学模型实时执行系统最优控制量.仿真试验结果表明:该切换策略能够保证智能车在不同工况下具有优秀的横向跟踪性能,路径跟踪偏差范围为±0.1 m,横摆角速度波动范围为±2(°)/s,jerk值的范围为±10 m/s^(3),与传统的单一控制算法相比,具有更好的跟踪精度、稳定性和舒适性.

WOD模式优劣势分析及改进策略研究

为顺利推广应用水安全保障导向的开发(WOD)模式,有必要深入分析WOD模式的运行机制、优势和劣势,并加以完善与改进。采用对比分析法对WOD模式的优劣势进行了系统分析,优势包括不增加政府负债、支持项目总体进行打包开发、一体化实施、支持资金来源多元化等,劣势包括行业跨度大、见效周期长、土地开发风险大、不易实现自平衡等。针对存在的短板提出了改进措施,包括完善投融资体制机制、建立可持续发展模式、探索多元化融资模式、政府承担部分项目资本金、充分利用水土资源优势、推动公益类项目和可开发经营性用地打包开发试点、鼓励金融机构尽早介入等。采用WOD模式丰富了现有水安全保障项目投融资方法,具有推广应用价值,但应试点先行、依法合规,稳妥有序推行。

冲击荷载下内配圆形钢管混凝土的方形叠合柱剩余承载力研究

为研究内配圆形钢管混凝土方形叠合柱侧向冲击后剩余承载力性能,利用有限元软件ANSYS/LS-DYNA建立了叠合柱冲击后受压承载力数值模型。对经典侧向冲击试验进行了数值模拟,分析表明该数值模型能够较好地模拟结构柱的破坏形态、冲击力和挠度。基于该模型研究了不同参数下叠合柱侧向冲击后剩余承载力特性,对比了未遭受冲击叠合柱轴心受压承载力,分析两者轴压极限承载力差异,并提出损伤程度评价指标(D_(dag)),量化分析了剩余承载力。结果表明:侧向冲击后叠合柱进行轴压加载直至破坏时易发生弯剪破坏,所消耗的能量相比于未遭受冲击叠合柱降低较多;在相同冲击条件下,冲击速度、轴压比和长细比对叠合柱耐冲击性能和冲击后剩余承载力影响最为显著和全面,而边界条件和钢管壁厚影响较小,但也不可忽视;基于损伤程度评价指标(D_(dag))及对应的损伤描述,可以快速地判定叠合柱的损伤程度,为结构安全提供应对策略。

分布式驱动电动汽车横向稳定性抗饱和滑模控制

【目的】探讨轮毂电机输出转矩的幅值和响应速度饱和的问题。【方法】以分布式电动驱动汽车为研究对象,结合二阶嵌套饱和函数对滑模控制进行抗饱和设计,并基于轮毂电机的峰值转矩及其在台架试验中的实际响应设计抗饱和滑模控制器的上下限参数。【结果】抗饱和滑模控制器能严格限制直接横摆力矩的幅值和变化速率,能极大地提高极限工况下车辆的横向稳定性。【结论】本文提出的方法有效解决了极限工况下轮毂电机易陷入饱和的问题,避免了因车轮滑移导致车辆失稳。