阀控非对称缸位置系统的非线性建模

针对伺服阀控非对称液压缸系统存在的非线性特性,根据液压系统工作原理,应用功率键合图建模理论,建立了阀控非对称缸位置系统的键合图模型.通过模型仿真及试验结果对比,验证了模型的准确性,为应用各种控制策略改善系统性能提供了理论基础.     

系杆拱受船舶撞击后的计算分析及加固措施

该文利用ANSYS对系杆拱桥墩受撞击后的受力性能进行了分析,探讨了单元类型的选取及材料的本构关系模型的建立等问题.分析时较为全面地考虑了桩一土之间的相互作用,并结合作者的经验提出了仿真分析时应该注意的问题.最后通过与实测数据的比较,验证了仿真结果的真实、可靠性,并根据分析的结果对大桥下部结构提出了相应的加固措施.     

船舶操舵仪仿真系统数学建模

考虑到船舶操舵仪是船舶操纵人员培训的重要工具,准确的数学模型是实现设计目标的关键,建立三自由度船舶运动模型和液压舵机模型,并进行仿真计算,验证模型的准确性,说明该模型可以提高培训效果.     

Modal-split effects of climate change: The effect of low water levels on the competitive position of inland waterway transport in the river Rhine area

Future climate change is expected to affect inland waterway transport in most main natural waterways in Europe. For the river Rhine it is expected that, in summer, more and longer periods with low water levels will occur. In periods of low water levels inland waterway vessels have to reduce their load factors and, as a result, transport prices per tonne will increase. One possible consequence of these higher transport prices is a deterioration of the competitive position of inland waterway transport compared with rail and road transport, and thus a change in modal split. We study this issue using a GIS-based software model called NODUS which provides a tool for the detailed analysis of freight transportation over extensive multimodal networks. We assess the effect of low water levels on the costs of transport operations for inland waterway transport in North West Europe under several climate scenarios. It turns out, that the effect on the modal split is limited. Under the most extreme climate scenario, inland waterway transport would lose about 5.4% of the quantity that is currently being transported annually in the part of the European inland waterway transport market considered. The very dry year of 2003 can be seen as an analogue for this scenario.     

The future tourism mobility of the world population: Emission growth versus climate policy

Much of global passenger transport is linked to tourism. The sector is therefore of interest in studying global mobility trends and transport-related emissions. In 2005, tourism was responsible for around 5% of all CO₂ emissions, of which 75% were caused by passenger transport. Given the rapid growth in tourism, with 1.6 billion international tourist arrivals predicted by 2020 (up from 903 million in 2007), it is clear that the sector will contribute to rapidly growing emission levels, and increasingly interfere with global climate policy. This is especially true under climate stabilisation and “avoiding dangerous climate change” objectives, implying global emission reductions in the order of −50% to −80% by 2050, compared to 2000. Based on three backcasting scenarios, and using techniques integrating quantitative and qualitative elements, this paper discusses the options for emission reductions in the tourism sector and the consequences of mitigation for global tourism-related mobility by 2050. It ends with a discussion of the policy implications of the results.     

Bacterial production and microbial food web structure in a large arctic river and the coastal Arctic Ocean

Globally significant quantities of organic carbon are stored in northern permafrost soils, but little is known about how this carbon is processed by microbial communities once it enters rivers and is transported to the coastal Arctic Ocean. As part of the Arctic River-Delta Experiment (ARDEX), we measured environmental and microbiological variables along a 300 km transect in the Mackenzie River and coastal Beaufort Sea, in July–August 2004. Surface bacterial concentrations averaged 6.7 × 10⁵ cells mL^− 1 with no significant differences between sampling zones. Picocyanobacteria were abundant in the river, and mostly observed as cell colonies. Their concentrations in the surface waters decreased across the salinity gradient, dropping from 51,000 (river) to 30 (sea) cells mL^− 1. There were accompanying shifts in protist community structure, from diatoms, cryptophytes, heterotrophic protists and chrysophytes in the river, to dinoflagellates, prymnesiophytes, chrysophytes, prasinophytes, diatoms and heterotrophic protists in the Beaufort Sea.Size-fractionated bacterial production, as measured by ³H–leucine uptake, varied from 76 to 416 ng C L^− 1 h^− 1. The contribution of particle-attached bacteria (> 3 µm fraction) to total bacterial production decreased from > 90% at the Mackenzie River stations to < 20% at an offshore marine site, and the relative importance of this particle-based fraction was inversely correlated with salinity and positively correlated with particulate organic carbon concentrations. Glucose enrichment experiments indicated that bacterial metabolism was carbon limited in the Mackenzie River but not in the coastal ocean. Prior exposure of water samples to full sunlight increased the biolability of dissolved organic carbon (DOC) in the Mackenzie River but decreased it in the Beaufort Sea.Estimated depth-integrated bacterial respiration rates in the Mackenzie River were higher than depth-integrated primary production rates, while at the marine stations bacterial respiration rates were near or below the integrated primary production rates. Consistent with these results, P_CO2 measurements showed surface water supersaturation in the river (mean of 146% of air equilibrium values) and subsaturation or near-saturation in the coastal sea. These results show a well-developed microbial food web in the Mackenzie River system that will likely convert tundra carbon to atmospheric CO₂ at increasing rates as the arctic climate continues to warm.     

舰艇发射装置抗冲击性能研究

为研究提高舰艇发射装置抗冲击性能,文章针对舰艇发射装置结构特点,分别采用静G法和时间历程法对其进行抗冲击计算分析。计算结果表明箱体与箱体及箱体与支架的连接处应力较为集中且发射装置对冲击载荷的响应与冲击加载方式和方向有很大关系。在同一冲击载荷下,结构响应特性以横向响应为主。所得分析结论可以对舰艇设备的抗冲击设计提供一定的参考。     

考虑波浪影响船舶进出港航道宽度分析

建立波浪对船舶航迹带宽度影响的模型,并结合模拟仿真试验得出船舶在风、流和船速等影响下的航迹带宽度,计算在风、流、波浪和船速等因素影响下的航迹带宽度。根据相应的规范公式计算对应的航迹带宽度和单、双向航道宽度,并进行比较分析。     

高层建筑外墙装饰格网架固定装置的受力分析

本文就高层建筑外墙装饰和遮阳用的轻型格网架固定装置的受力进行了分析,并进 行了模拟试验。提出了这种受力状态的理论计算公式。其计算结果与试验结果符合较 好,对轻型格网架的推广和使用有较大的参考价值.      

‘Each flight is different’: Carbon emissions of selected flights in three geographical markets

Air travel is considered the biggest individual climate sin. Avoiding flying, however, seems impossible. In this paper we argue that the flight a passenger chooses can be significant. For this purpose we compared the carbon emissions of selected flights in three geographical markets. We found tremendous differences in the environmental performance of individual flights. Furthermore, we also found that flying with the most modern aircraft or flying non-stop represents, in many cases, the least polluting option. Nevertheless, we were able to show that there are exceptions to this rule. Based on our results, we provide recommendations to the industry and for further research.