氨和甲醇等燃料供给系统设计对比及仿真

为满足国际海事组织（International Maritime Organization, IMO）对船舶主机COx、SOx和NOx排放的要求,基于MAN主机燃料进机需求,对多种清洁低碳燃料系统的设计进行对比分析。分别针对氨、甲醇和液化石油气（Liquefied Petroleum Gas, LPG）等燃料开展关键问题解决方案对比,并运用计算流体动力学（Computation Fluid Dynamics, CFD）方法对燃料系统回液方式进行仿真。仿真结果显示：在LPG回液管路上设计可调减压元件,能在1.8~2.3 MPa压力区间内实现燃料再利用,有效形成闭式循环回路;当损耗系数K为500~6 500时,供给LPG主机的燃料压力满足5.1~5.5 MPa的要求。对比分析表明,在LPG燃料供给系统上调整供给泵参数和回液损耗系数K,即可使该系统应用于氨燃料供给系统设计中。     

大型巡航救助船快速性研究

结合大型巡航救助船的功能需求和主尺度特点,对其快速性能进行分析。运用计算流体力学(CFD)技术对原型方案的线型进行阻力性能计算,依据计算信息,分别对首轮廓线形状、球首、呆木以及支架进行优化,得到最终方案,阻力相比原型方案有了大幅降低。将最终方案进行模型试验,模型试验结果与CFD计算吻合良好,证明了本船所采用的优化方法是可靠可用的。     

Simulations of pollutant dispersion at toll plazas using three-dimensional CFD models

Toll plazas are particularly susceptible to build-ups of vehicle-emitted pollutants because vehicles pass through in low gear. To look at this, three-dimensional computational fluid dynamics simulations of pollutant dispersion are used on the standard k − ε turbulence model. The effects of wind speed, wind direction and topography on pollutant dispersion were discussed. The Wuzhuang toll plaza on the Hefei-Nanjing expressway is considered, and the effects of the retaining walls along both sides of the plaza on pollutant dispersion is analysed. There are greater pollutant concentrations near the tollbooths as the angle between the direction of the wind and traffic increases implying that retaining walls impede dispersion. The slope of the walls has little influence on the variations in pollutant concentration.     

数值模拟在船型方案优选中的应用

随着计算机和CFD技术水平的提高,数值模拟所需时间逐渐缩短、准确度逐步提高,利用数值模拟作为一种辅助手段进行方案择优已经逐渐流行。本文利用商用软件对广船国际提供的某油船三种线型进行了设计和结构吃水工况下的数值计算,包括阻力、自航计算,并且根据ITTC推荐规程做了实船尺度下的数据分析;以实船尺度下保持目标航速所需要的收到功率最小为评判标准,通过对该船三个方案线型不同吃水情况下计算结果的比较分析,评价了线型方案的优劣。通过数值模拟结果与物理试验结果的比较分析,验证了本文计算方法可靠性和准确性,也展示了数值模拟在船型方案择优过程中的作用,可以用于综合评价不同方案线型的船舶水动力性能。     

海上浮式结构物的水动力仿真研究

基于粘性计算流体力学的方法建立三维数值波浪水池,模拟有限振幅波的传播,并计算三维球体在规则波环境下所受的波浪力。采用两相不可压的RANS方程求解非定常不可压缩粘性流体,并采用流体体积函数(VOF)法对自由面进行动态模拟。通过编写用户自定义函数(UDF)设置边界入口速度和波高,实现在波浪水池尾部1~2倍波长区域消波,最终求出有限振幅波的模拟结果以及规则波中三维球体所受的波浪力,该结果与势流理论边界元法得到的结果在趋势上吻合良好。该研究方法为模拟分析其他海洋结构物在波浪中的水动力奠定基础,丰富与扩展了数值波浪水池的应用。     

Research on the Dust Removal Technology for Shield Tunnel Overhaul Construction北大核心CSCD

The shield tunnel is an ultra-long linear space. It will cause a lot of dust during the tunnel maintenance and overhaul operation, which is extremely unfavorable to the physical and mental health of the construction personnel and the environment outside the tunnel. It is difficult to guarantee the ventilation effect of the linear space using the conventional dust removal technology, which directly affects the construction safety and overhaul period. Therefore, based on the overhaul of a cross-river tunnel in Shanghai, combined with Computational Fluid Dynamics (CFD) simulation, device optimization and process combination, a three-stage dust reduction standardization process for tunnel overhaul construction is proposed, namely taking a water sprayer at the working point to control the dust at the source (primary protection); installing electrostatic dust removal and water filtration dust removal equipment in the tunnel(secondary protection); and installing two sets of water curtain spray device at the two tunnel exits to prevent dusts from diffusing into the atmosphere. It explores the actual dust-reducing effects of different dust-removing measures and layout combinations, laying a technical foundation for green and efficient dust reduction. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Finite element calculations of rail vibration countermeasures

Elastic waves may constitute a nuisance for people living close to high-speed lines. In order to decrease the spread of vibrations, it is common to reinforce the ground with lime cement columns. This article presents the results of simulations of three different ways to install the columns. The calculations have been done with an integrated rigid body—finite element model. Equations from various physical domains are merged into one big system. The results indicate that the straight configuration works best to protect the track. When attention is focused on preventing vibrations from the soil, the leaning column method is more effective. The chosen technique would depend on the aims of the countermeasure.     

基于改进MPS方法的三维时域水弹性计算模型

本文在作者已有的二维改进MPS(Moving Particle Semi-implicit)方法基础上进行了三维拓展(主要包括三维自由面粒子判断),并通过将计算得到的三维溃坝问题结果与文献中实验结果相对比,验证了所发展模型的准确性。在结构响应计算方面,将刚性和柔性模态耦合并计及相互影响。在此基础上,将流体和结构部分通过迭代方式耦合,从而实现强流固耦合计算。最后,应用上述模型对涉及大刚体位移叠加弹性变形的三维方梁的强非线性时域水弹性问题进行了计算,验证了模型对此类问题的有效性。     

船用中小缸径直喷式柴油机燃烧室中油线网分布的计算

直喷式柴油机燃油喷射所构成的油线在燃烧室中的落点分布，对燃烧系统性能影响极大。本文针对船用中小缸径直喷式柴油机的结构特点，介绍了燃烧室中油线网布置的一般原则和具体方法，建立了油线网的计算模型。由此，即可通过计算机对燃烧室与喷油系统匹配实现辅助设计。     

船舶机舱机械通风数值模拟分析和优化设计

某海监船在进行机舱机械通风效用试验时,发现存在舱内气流分布不均、风速梯度变化较大、部分船员操作和活动区域温度偏高等问题。为解决上述问题,利用CFD技术对该船机舱机械通风系统进行数值分析,并提出机舱气流改进方案。随后,选取优化前、后的典型截面进行分析,指出在保证舱内适当负压的情况下可将机械送风改为机械抽风,从而实现机舱进风量增加50%,并消除舱内气流大漩涡和改善气流组织。此外,还提出可在右舷开一个新增风口,以更有效消除气流漩涡,并降低局部温度。结果显示,该优化方案能够满足海船规范要求且施工方便,对于工程设计具有一定的参考价值。