基于改进型消灭曲线法的横摇阻尼估算

自由衰减试验仍是目前最为有效且常用的估算横摇阻尼系数的方法.横摇阻尼系数的估算精度对于船舶横摇运动的预报起着至关重要的作用.通常采用所谓的消灭曲线法来分析自由横摇衰减数据.该方法的一个不足之处在于其推导是基于忽略了非线性恢复力项的自由横摇运动方程.另一方面,考虑更多非线性成分的能量法能够纳入该因素影响但在实施过程中较为复杂.文中提出了一种改进型的消灭曲线法,能够纳入船体非线性恢复力项的影响.所提出的方法形式简单且相比能量法更易于实施.数值试验证明了改进型消灭曲线法的正确性,并展现了其相对传统消灭曲线法所具有的优势.     

Centrifuge modelling of pipe-soil interaction in clay with crust layer

Seabed in regions, such as the Gulf of Guinea and North West Shelf of Australia, may exhibit a crust layer where the undrained shear strength can be an order of magnitude higher than that of the immediately underlying sediment. This can complicate design of steel catenary risers, where fatigue depends on the cyclic vertical stiffness of the pipe-soil interaction. Potential punch-through of the riser into the underlying soft soil may invalidate design assumptions based on the pipe-soil stiffness within the crust layer. The long-term evolution of pipe-soil stiffness within the crust layer, which exhibits similar properties to an over-consolidated soil, is also poorly understood. This paper describes centrifuge model tests undertaken in a clay sample with a crust layer, simulating the punch-through process of a pipe under load control and investigating the pipe-soil stiffness during long-term cyclic loading tests under displacement control. Results confirm that the potential for punching-through the crust layer depends strongly on the relative ratio of pipe diameter to crust layer thickness. The long-term evolution of pipe-soil stiffness showed a steady increase after an initial remoulding stage in contractile soils (normally consolidated and lightly over-consolidated), but a steady reduction in the heavily over-consolidated, more dilatant, crust. The magnitude of pipe-soil stiffness changes (during both remoulding and reconsolidation) is governed by the over-consolidation ratio of the soil and the amplitude of the cyclic displacements. This study provides insights on the relevant cyclic stiffness to consider when assessing SCR fatigue life in over-consolidated soils and soils exhibiting a superficial crust layer.     

悬索桥并列双吊索整体风振特性与气动阻尼研究

通过并列耦合双吊索节段模型的整体测振与测力风洞试验,研究不同间距下双吊索的整体振动行为与气动阻尼特性。引入驰振气动阻尼非线性项的动力方程模型,得到非线性振动的近似解析方法。基于弹性悬挂节段模型动力响应识别出驰振非线性气动参数,并与经典单自由度驰振理论结果进行对比分析。研究结果表明:并列耦合双吊索在一定工况下会发生剧烈的整体尾流致振现象,结构阻尼比对其起振风速影响明显;经典驰振理论求得的气动负阻尼绝对值要小于识别得到的气动负阻尼绝对值,横、顺风向两自由度耦合失稳较单自由度驰振更易发生。     

Assessment of fatigue strength of steel butt-welded joints in as-welded condition – Alternative approaches for curve fitting and mean stress effect analysis

Experimental fatigue data for butt-welded joints in as-welded condition and under constant amplitude tensile loading (secondary bending included) were analyzed using the nominal stress system and the notch stress system. Two approaches were used; a standard fitting procedure and minimization of the sum of squared perpendicular distances from a line with a fixed and free slope. In all cases, the latter method gave better agreement between the experimental and predicted fatigue life and fatigue strength. The analyses showed both with all broken specimen data included and with reduced data that the FAT225 curve, as recommended by IIW, might be too optimistic for the notch stress approach in the case of butt-welded joints in as-welded condition. It was also found that use of the local stress ratio instead of the applied stress ratio might explain many issues concerning current observations and apparent inconsistencies in reported literature.     

混凝土在路桥桩基施工中的作用及技术

路桥桩基混凝土施工中，为了保障灌注桩混凝土的质量，必须加强对准备工作及施工工艺的重视。通过对混凝土及其施工质量要求进行分析，探讨了混凝土在路桥桩基施工中的配合比、泵送等，并阐述了路桥桩基施工技术。     

小型直喷式柴油机燃用生物质能燃料的性能研究

文章主要研究了生物质能混合燃料在柴油机上的应用,通过在一台小型直喷式柴油机上进行不同组分柴油-生物柴油-乙醇混合燃料的燃烧、油耗和排放性能对比试验,分析了乙醇含量的改变对混合燃料的发动机燃烧压力、滞燃期、放热规律、比油耗和排放的影响．     

铁路车辆编组连挂中车钩缓冲装置冲击特性分析

为了提高车辆编组连挂时的平稳性,保证所运货物的完整无损,通过对铁路车辆编组连挂时车钩缓冲装置的冲击特性进行分析,建立编组连挂时的缓冲装置的力学模型,对模型分析解微分方程得出位移时间曲线、加速度时间曲线以及加速度峰值,从而得出编组连挂的最大加速度与车钩系统的阻尼有关。     

自行车流视频识别判断方法研究

考虑算法的实时性,交通流个体识别往往采用轮廓特征来描述。由于自行车与行人的很多轮廓特征值相近,在复杂城市交通环境中,从慢行交通流中准确地识别出自行车是目前采用视频检测交通流的难点之一。通过现场视频检测获取足够的样本外轮廓数据,分析检测目标轮廓的高、宽、高宽比、面积等典型轮廓特征,发现目标轮廓高宽比特征能较好地识别出行人、自行车等慢行交通,并给出合适的取值范围。研究表明自行车高宽比能够较好地成为视频识别的依据,为自行车视频识别提供数据。     

自密实混凝土扩展度影响因素分析与评价

扩展度是表征自密实混凝土填充性的一项重要指标,同时也是混凝土工作性能的重要指标。从砂率、粉煤灰用量、微硅粉掺量三方面探讨自密实混凝土扩展度大小的影响因素。试验结果表明:砂率的大小对自密实混凝土的影响主要体现在对粗骨料的润滑,本试验条件下的合理砂率约为46%;当粉煤灰含量约占胶凝材料的30%时,粉煤灰能够与水泥充分反应,自密实混凝土的扩展度达到最大;因微硅粉对混凝土拌合物起到了保水作用,减少了拌合物发生离析、泌水的几率,使得拌合物具有较好的工作性和稳定性。因此,本试验条件下微硅粉的复拌含量为粉煤灰总量的5%较为适宜。     

纤维用量对沥青混合料高温性能影响分析

纤维材料作为混凝土的一种外加剂,可以提高混合料生产的稳定性和施工的和易性,同时可以增加成型路面的强度,特别是在SMA沥青路面中大量使用。而文中选择了高性能沥青路面superpave-13作为研究对象,通过添加不同掺量的木质纤维,在马歇尔试验方法基础上确定各自的最佳油石比。并进一步分析纤维掺量对各自最佳油石比中体积参数的影响,旨在为高性能沥青路面级配设计提供参考。