基于颗粒流的高填黄土明洞加筋减载数值模拟分析

为研究高填黄土明洞加筋减载的荷载传递规律,采用颗粒流软件模拟高填黄土明洞加筋减载,通过分析洞顶竖向应力、颗粒竖向位移、颗粒间的接触力、格栅的竖向变形和孔隙率等细观参数的变化,从微观角度揭示土工格栅加筋减载明洞减载规律,并进一步研究土工格栅刚度和层数对洞顶减载效果的影响。结果表明： 1）土工格栅的竖向变形和颗粒竖向位移变化形式基本保持一致,格栅的变形依赖于洞顶内外土柱的沉降差; 2）在格栅所能承受的最大变形范围内,内外土柱负的沉降差越大,格栅的拉膜效应越显著,减载效果越好; 3）格栅的刚度和层数对其减载效果均有一定的影响,应根据实际填土高度和填土性质选择适宜刚度和层数的格栅进行减载。     

The impact of Low Emission Zones on particulate matter concentration and public health: A Comment

Malina and Scheffler estimated the impact of Low Emission Zones (LEZs). LEZ effects are small and bias control is of paramount importance. Based on our analyses we conclude that the point estimate of monetary health benefits calculated by Malina and Scheffler is probably too high and the uncertainty reported possibly too small.     

Fatigue analysis of water intake risers: Hydrodynamic damping effect and a hybrid frequency-time domain method

The fatigue performance is key to the design of water intake risers (WIRs), which is a novel concept used to convey cooling water for liquefaction of natural gas at sea. To estimate the fatigue life, it is crucial to accurately predict the response amplitude of the WIRs, which is dominated by hydrodynamic damping. In operational conditions, the motion amplitudes of WIRs are usually smaller than their diameter, and thus leading to a flow regime of KC < 5. It is found in this flow regime; the hydrodynamic damping largely depends on the motion magnitude of the risers. To consider this coupling effect, a hybrid frequency-time domain fatigue analysis method is proposed, where a nonlinear stress transfer function is adopted. The hybrid method accounts for the coupling effect between the hydrodynamic damping and the structural motion. Significantly reducing the computational cost, this method provides results as accurate as that from a time domain analysis based on the relative velocity model with a constant drag coefficient. Furthermore, recommendations for further simplification of the fatigue analysis recognizing the coupling effect are given.     

A reliability approach to fatigue crack propagation analysis of ship structures in polar regions

Fatigue is a common failure mode in ship structures. For structures with an initial crack, the fatigue crack propagation behavior needs to be considered. The purpose of this study is to establish a procedure for analysis of fatigue crack propagation of ship structures in combination with reliability methods. The stress intensity factor (SIF) and geometry correction factor are calculated by means of finite element analysis. Validation for the SIF calculation is achieved by comparing the computed results with those based on related solutions. Since fatigue damage usually occurs in weld areas, the effect of such components on the fatigue crack propagation behavior was also considered in this work. The Paris law in combination with the Monte Carlo technique are employed for the fatigue crack propagation analysis in this study. Reliability updating based on inspection for cracks is also carried out. A computer program was developed for the purpose of fatigue crack propagation analysis within the framework of reliability methods. An application example of fatigue crack propagation in relation to the hull of the icebreaker Xuelong 2 is presented. The sensitivity of the procedure to key analysis parameters (sample size, initial crack size) is also considered. Finally, the effect of low temperatures on the computed results is also analyzed.     

越野车复合型悬架平顺性的研究

为解决越野车在复杂路面行驶过程中平顺性较差的问题,本文中在某型越野车原悬架系统上加装空气弹簧,形成新型复合型悬架结构.首先为探究越野车悬架系统的振动机理,通过对越野车空气弹簧和原悬架系统进行理想化结构分析,构建出了空气弹簧与螺旋弹簧相并联的复合型悬架系统模型;然后针对越野车行驶要求,提出了一种新型工作模式切换控制策略,...     

深水TTR立管管中管结构非线性时域分析

在借鉴国外工程实践经验的基础上,采用多层管模型来模拟管中管结构,进行了顶张紧式立管管中管结构的非线性时域分析.多层管模型与传统的等效组合模型相比,其主要的优点在于:它可以模拟内外管之间的相互作用,而且可以通过改变扶正器的相关参数,对扶正器的大小和位置进行优化设计,以此保证内外管之间不会发生碰撞和摩擦;此外,文章还对张紧力在内外管之间的分配进行了研究,采用的管中管结构模拟技术对TTR立管在位强度分析技术PCYL单元犒管节点刚好发生的发展具有一定的指导意义.     

移相法在H半桥型励磁电流开关功放中的应用

本文提出采用两路占空比相同但具有一定相位差的PWM控制方法,可以在不影响响应速度的情况下减小电流纹波。分析了H半桥型励磁功放工作原理,给出了0~180°移相的电流纹波统一计算公式。以应用的开关功放为例,进行大量的仿真和实验,结果表明了上述理论分析和纹波计算公式的正确性。该方法简单有效,具有一定的应用价值。     

吉怀高速公路王坡大桥高压铁塔边坡加固设计与施工

结合吉怀高速公路王坡大桥高压铁塔边坡加固工程实例,介绍了高速公路建设过程中采用桩板式挡墙加固边坡技术,针对上述加固方法进行了岩土质边坡的稳定性分析计算及其加固工程设计,并对边坡加固工程施工程序与原则进行了探讨。工程成功实践表明,桩板式挡墙加固高压铁塔边坡在增加边坡安全系数的同时减少了对现有铁塔塔基的施工干扰,而与整体改移铁塔相比又大幅降低了工程投资。