Simplified analysis for estimation of the behavior of a submerged floating tunnel in waves and experimental verification

To achieve rational design in waves for a submerged floating tunnel which has emerged as a new offshore transportation infrastructure, it's necessary to understand its hydrodynamic behavior. For simple but accurate estimation of hydrodynamic forces, a theoretical method is proposed and the tests with physical models in a wave flume were carried out for verification. Morison's equation was used to estimate wave loads composed of inertia force and drag force. Forces calculated by applying the linear wave theory to Morison's equation coincided well with those measured by the tests. The test results showed that mooring systems played a significant role in the movement of the submerged floating tunnel in waves. A pendulum model could be used to describe the motion of the submerged floating tunnel with a single vertical mooring. Based on the verified relations, a simple slack condition which causes the submerged floating tunnel to be unstable was also proposed. The simplified approach proposed by this study proved to be useful in designing the submerged floating tunnel in the initial stage.     

钛合金大型环件热辗扩成形中的力能参数研究

准确确定辗扩力和辗扩力矩(统称为力能参数)是大型环件热辗扩模具设计和设备选择的重要依据。采用热力耦合三维弹塑性显式有限元法,从变形区当量形状参数角度,研究并揭示了工艺参数对钛合金大型环件热辗扩成形中力能参数的影响效应。结果表明:增大驱动辊转速n_1或环件初始温度T_0均有利于力能参数的减小和环件咬入变形区。     

ANSYS三维模型中SOLID65单元的内力提取问题

ANSYS有限元程序中的SOLID65单元是一种适合描述钢筋混凝土结构的三维单元。由于加强材料在本构矩阵中的组结方式,使用该单元建立的钢筋混凝土模型在进行常规内力提取时会发生错误。在分析单元本构矩阵组结的基础上,正确的内力提取方式被提出。通过例题验证了该提取方法的正确性,并和常规方式进行了对比。     

切头飞剪起制动过程动力学参数分析

切头飞剪是用于切断金属材料的一种机械设备，采用飞剪来剪切轧件，使轧钢车间的生产连续化，生产率大大提高，对双滚筒切头飞剪在剪切过程中的动能及起动、制动过程中的惯性力进行了定性的分析，并绘出了力能参数脉动图。     

Levitation force analysis of medium and low speed maglev vehicles

The rule of levitation force variation with different structure and electromagnetic parameters provides a basis for electromagnet design of electromagnetic suspension (EMS) medium and low speed maglev ...     

桃树坪隧道穿越富水粉细砂地层塌方处治施工技术

兰渝铁路桃树坪隧道为Ⅰ级铁路双线隧道,穿越上第三系富水粉细砂地层,由于粉细砂层成岩作用差,遇水呈流塑状自稳性变差,隧道施工困难,极易发生塌方,塌方处治难度极大,安全风险极高。为解决富水粉细砂层隧道塌方后砂层松散、流动性强、无自稳、塌方处治困难等一系列问题,确保安全快速通过塌方段,以桃树坪隧道3#斜井正洞塌方处治为工程实例,就如何采用 “真空降水+双层大管棚+小管棚+双侧壁法”有效处治富水粉细砂层隧道塌方进行详细论述与总结,成功案例可为类似工程施工提供一定的技术参考和经验借鉴。     

明挖公路隧道基坑钢支撑轴力监测与数值模拟分析

为研究深基坑开挖过程中钢支撑轴力的变化情况,以沈阳市南北快速干线隧道深17.8 m基坑工程支护体系中横向钢支撑为研究对象,对基坑开挖过程中的轴力变化值进行现场实时监测,并采用有限元软件MIDAS/GTS对不同工况下的钢支撑轴力进行模拟研究,得出各道钢支撑的轴力云图及变化规律。结果表明： 1）随着基坑开挖深度的增加,坑壁主动土压力逐渐增大,使得每道钢支撑轴力在短期内均呈线性增长趋势; 2）同一断面钢支撑全部架设完成后轴力有所衰减,其原因之一是连续墙后的土体发生了流变现象,使得土体应力重新分配并达到新的平衡。     

隧道“关门”塌方原因的力学分析及预防对策

为向施工技术管理人员解释隧道初期支护随施工的应力变化规律,进而找出发生“关门”塌方的原因,首先说明“关门”塌方发生时的施工状况,一般采取钢架+锁脚锚杆+喷射混凝土的支护结构,塌方时松散荷载已形成; 然后按荷载-结构模型,在初期支护承担全部设计荷载的条件下,通过施工三台阶法对上、中、下3个断面采取结构力学力法分别进行内力计算及承载能力分析。结果表明: 在围岩完全松散的极限情况下,上台阶绝对安全,中台阶基本安全,下台阶开挖尤其是仰拱开挖时塌方的风险极高。针对上述问题提出预防“关门”塌方的相应对策。结论认为采取钢架+锁脚锚杆+喷射混凝土的支护形式,支护结构处于极限应力平衡状态,很容易破坏而造成隧道坍塌。     

承担全部设计荷载的隧道初期支护的设计计算方法

针对当前隧道初期支护设计存在不能承担全部设计荷载、以初期支护仰拱闭合的有利结构而不是以仰拱未闭合的最不利结构为最终设计目标而造成结构存在安全隐患以及给不出锚杆锚固力设计值和现场围岩变形很大使得采用岩体力学进行设计初期支护不具备条件的问题,提出按照“荷载-结构”的计算模型,采取结构力学力法对隧道初期支护承担全部设计荷载、对应施工“三台阶”法、对型钢钢架和喷射混凝土按变形协调条件确定各自承担荷载的比例系数、就钢架和喷射混凝土承载能力分别进行计算分析,明确在各部施工时对喷射混凝土强度以及锚杆的锚固力的要求。计算结果表明： 1）采取除中心夹角60°范围外其余均匀布置分布锚杆、采用“型钢钢架+分布锚杆+喷射混凝土”支护型式的隧道初期支护完全具有承担全部设计荷载的能力,且仰拱开挖不会威胁支护的稳定; 2）应将锚杆作为支护结构的链杆支座来确定锚杆锚固力; 3）锚杆和喷射混凝土3 h的强度对支护结构的承载能力影响很大。     

Locomotive dynamic performance under traction/braking conditions considering effect of gear transmissions

Traction or braking operations are usually applied to trains or locomotives for acceleration, speed adjustment, and stopping. During these operations, gear transmission equipment plays a very significant role in the delivery of traction or electrical braking power. Failures of the gear transmissions are likely to cause power loses and even threaten the operation safety of the train. Its dynamic performance is closely related to the normal operation and service safety of the entire train, especially under some emergency braking conditions. In this paper, a locomotive–track coupled vertical–longitudinal dynamics model is employed with considering the dynamic action from the gear transmissions. This dynamics model enables the detailed analysis and more practical simulation on the characteristics of power transmission path, namely motor–gear transmission–wheelset–longitudinal motion of locomotive, especially for traction or braking conditions. Multi-excitation sources, such as time-varying mesh stiffness and nonlinear wheel–rail contact excitations, are considered in this study. This dynamics model is then validated by comparing the simulated results with the experimental test results under braking conditions. The calculated results indicate that involvement of gear transmission could reveal the load reduction of the wheelset due to transmitted forces. Vibrations of the wheelset and the motor are dominated by variation of the gear dynamic mesh forces in the low speed range and by rail geometric irregularity in the higher speed range. Rail vertical geometric irregularity could also cause wheelset longitudinal vibrations, and do modulations to the gear dynamic mesh forces. Besides, the hauling weight has little effect on the locomotive vibrations and the dynamic mesh forces of the gear transmissions for both traction and braking conditions under the same running speed.