Finite element based meta-modeling of ship-ice interaction at shoulder and midship areas for ship performance simulation

The climate change has made the transit through Arctic area more feasible, which demands reliable methods to evaluate ship performance. Ship performance in ice is a cross-scale problem, where the desired output such as ship speed lies in larger scale while the actual ship-ice interaction happens in smaller scale. Due to insufficient knowledge in ice mechanics and the demand for computational efficiency, existing approaches for modelling ship-ice interaction from ship performance perspective are mostly either (semi-) empirical, or simplified analytical, with reduced dimensions and extensively simplified mechanics. This paper presents a novel approach to model ship-ice interaction, which maintains the accuracy of the modelling with Finite Element Method (FEM) in ship-ice interaction scale, while being computationally very cheap, therefore is capable to be applied in ship scale simulations. The ice failure is firstly qualitatively investigated through full-scale and model-scale observations, as well as a numerical simulation with Extended Finite Element Method (XFEM). The model is then simplified and executed by Abaqus to automatically run a large database. A neural network is used to fit the results to get a simulation-free tool for ship-ice interaction calculation. Finally, the uncertainty in the results due to an important assumption is quantified. The results show that the obtained neural network fits the database with excellent performance. Therefore, it can be applied in ship scale simulations with improved accuracy compared to empirical or analytical approaches.     

车路协同系统信息交互仿真方法

为提高车路协同系统信息交互网络通信质量, 在规定延时范围内实现数据的准确交互, 构建了基于OPNET的车路协同系统信息交互平台。研究了多种车辆自组织网络路由协议, 应用最小距离路由竞争机制设计了基于车辆位置的分簇路由协议优化方法。基于OPNET对基于车辆位置的分簇优化路由协议和传统的路由协议进行仿真对比, 分析了不同路由协议对车路协同系统通信性能的影响。对DCF和PCF两种不同的信道接入协议进行仿真比较。仿真结果表明: 基于车辆位置的分簇路由协议中簇头变化率为1.47次·s^-1; 在信息延时方面, 较AODV、DSR分别减少18.92%、26.90%, 较基于最高节点度和基于ID的分簇路由协议分别减少14.20%、21.54%;在网络负载方面, 较AODV、DSR分别减少20.83%、22.92%;PCF较DCF信道接入协议延时效果优越, 延时减少了约29.60%。     

关于公路桥梁冲击系数的探讨

参照简化的车辆模型和桥梁模型建立车-桥相互作用的数学模型,给出在移动车辆荷栽作用下连续梁桥各截面动力响应的时程曲线和连续梁桥前几阶模态的振型曲线,研究表明,连续粱桥各控制截面起主要作用的模态并不都一样;另外,数值分析表明,对于连续梁桥,冲击系数公式仅考虑桥梁第一阶频率是不合理的。     

城市交通与土地利用互动机理研究

城市交通与土地利用之间存在着复杂的互动关系,研究二者的互动机理,对从根本上解决城市交通问题以及实现城市可持续发展具有重要的理论与现实意义。首先分析城市交通与土地利用的关系,指出二者之间存在相互依存、相互促进的互动关系;然后建立数学模型描述二者互动的方向及程度,从模型稳定性分析可以看出,当满足一定条件时,二者能够达到一种“互补共生”的稳定平衡状态;在此基础上,结合实例对模型进行仿真,验证了模型的稳定性条件;最后,基于二者的互动机理提出一些城市规划对策。     

均值-极差法分析评价人-零件间的交互作用

给出了用均值—极差法评价人和零件间的交互作用的公式，用实例进行了分析，并与方差分析方法作了比较，结果显示两者差异不大。     

剧烈动态轮轨相互作用的自动检测

轨道几何形状检查记录车是检测轨道表面问题的主要方法。在重载运输中 ,重复运输可能产生一系列特殊轮轨不平顺 ,当车辆以临界速度运行时 ,即使这些不平顺是均匀分布的 ,它们仍然能激起剧烈的轮轨相互作用。本文阐述了一种安装在正常运营中的运煤车上的轮轨相互作用的监控和记录系统     

Stochastic modelling of quadratic wave components

This paper deals with stochastic wave models and their influence on wave load modelling of marine structures. The need for more refined theories is underlined for some applications and an entirely new quadratic model for the wave elevation is outlined. Finally, a number of physical phenomena relevant to waves are illustrated which are likely to be important for marine structures and could, in the near future, require ad hoc modelling.     

Seasonal variability in sea surface oceanographic conditions in the Aegean Sea (Eastern Mediterranean): an overview

Seasonal variability and the spatial distribution of sea surface temperatures (SST) and salinities (SSS) are reviewed, in relation to the prevailing climatological conditions, heat fluxes, water budget and general water circulation patterns. Within this context, consideration is given to: sea surface temperatures; air temperatures; precipitation; evaporation; wind speeds and directions; freshwater (mainly riverine) discharges throughout the Aegean; and the exchange of water masses with the Black Sea and eastern Mediterranean Sea. The investigation of satellite images, covering a 6-yr period (1988–1994), has enabled a synthesis of the monthly sea surface thermal distribution to be established.The climate of the Aegean Sea is characterised by annual air temperatures of 16–19.5°C, precipitation of about 500 mm yr⁻¹ and evaporation of some 4 mm d⁻¹. The Aegean has a negative heat budget (approximately −25 W m⁻²) and positive water balance (+ 1.0 m yr⁻¹), when inflow from the Black Sea is considered. During the summer, the (northerly) Etesians are the dominant winds over the Sea.Mean monthly sea surface temperatures (SST) vary from 8°C in the north during winter, up to 26°C in the south during summer. SST depends mainly upon air temperature; there is a month's delay between the former and latter maxima. The sea surface salinity (SSS) varies also spatially and seasonally, ranging from less than 31 psu, in the north, to more than 39 psu, in the southeast; lower values (< 25 psu) occur adjacent to the river mouths. SSSs present their maximum differences during summer, whilst during winter and autumn the distribution of SSS is more uniform. The overall spatial SST and SSS distribution pattern is controlled by: distribution of the (colder) Black Sea Waters; advection of the (warmer) Levantine Waters, from the southeastern part of the Aegean; upwelling and downwelling; and, to a lesser extent, but locally important, freshwater riverine inflows.     

冠状动脉结扎前后容量负荷对狗两心室功能的影响

本实验研究了狗左冠状动脉前降支(LAD)结扎前后,以动脉放血和静脉输液改变容量负荷(VL),对左、右心室功能的影响。结果表明,LAD 结扎前后,两心室舒缩性能和泵功能对 VL 改变的反应均有明显差别。提示,心肌梗塞后,降低 VL可改善左心室功能,应防止 VL 过重对心功能的不利影响。