Influence of microbubble diameter and distribution on frictional resistance reduction

Investigations into frictional resistance reduction by microbubbles were carried out using a two-dimensional channel. The flow velocity and the amount of air injected were varied, and the frictional resistance reduction was measured. The frictional resistance reduction increased with increasing mean void ratio. When the bubble diameter was changed, the influence on frictional resistance reduction was negligible. The influence of bubble distribution near a wall was also investigated. Although it is thought that the influence of microbubbles near a wall is large, further investigations are required. Received: February 6, 2002 / Accepted: April 30, 2002 Acknowledgments. This research was supported by a special research program of Toyo University, SR239 Research Committee of the Shipbuilding Research Association of Japan, and the Research Project on Smart Control of Turbulence. The authors express their sincere gratitude for these supports. Address correspondence to: H. Kato (kato@eng.toyo.ac.jp)     

新型双体船和三体船阻力性能研究

针对小水线面双体船(SWATH)的不足,提出了新型双体、三体船型.通过模型试验方法,对上述船型的阻力性能进行了研究.结果表明,新型三体船由于舯前首中体的设置使得阻力在一定的航速范围内大幅降低;新型双体和三体船型在阻力性能上较SWATH船表现出了一定的优越性.     

道碴清筛机挖掘阻力的试验研究

针对清筛机挖掘阻力的形成，对挖掘阻力中运碴阻力形成原因进行了分析．利用设计的试验装置对不同道碴条件下的道碴阻力进行了测试，并在测试数据的基础上，给出了修正挖掘阻力的计算公式     

十字头轴承裂纹的产生及防护措施

针对船用低速柴油机十字头轴承常见的龟裂现象，从十字头轴承的机械结构及其循环工作过程的角度，从理论上分析十字头轴承的受力情况及龟裂现象产生的原因，提出延长十字头轴承使用寿命的具体措施。     

SS7C电力机车抱轴承箱结构的疲劳寿命分析

对SS7C电力机车抱轴承箱进行动应力实测 ,根据动应力实测编制了抱轴箱的二维应力谱 ,对抱轴箱的疲劳寿命进行了估算 ,同时也估算了抱轴箱体的裂纹扩展寿命和临界裂纹尺寸 ,为确定合理的检修周期提供依据。     

运用线性兴波理论进行船型设计与改进

通过导出简化的兴波阻力理论公式,提出一种运用线性兴波阻力理论进行船型设计与改进的方法。实际应用结果显示,该方法对船型改进很有效,可供船型设计部门及人员应用。     

用现有疲劳试验数据确定疲劳裂纹扩展率

疲劳寿命的预报在船舶与海洋工程领域中相当重要，但其关键问题是要找到一种较科学的疲劳寿命预报方法。最近，本文第二作者提出了一种海洋结构物疲劳寿命预报的统一方法。该方法是基于疲劳裂纹扩展理论而发展起来的，在其九个参数模型的假设之下，能够较好地解释一些其它方法所不能解释的现象。采用该方法的主要障碍在于需要确定疲劳裂纹扩展率。作者通过对不同的疲劳裂纹扩展率的比较研究，并推广McEvily模型后，提出了一个具有较宽适用范围的九个参数疲劳裂纹扩展率模型(从门槛域一直到不稳定断裂域)。本文的主要目的是解决如何根据一些现有的疲劳试验数据来确定这九个模型参数的问题。文中给出了通过实验数据确定裂纹扩展率模型中各个参数的方法，并进行了模型参数的灵敏度分析。通过对文献中一些试验数据的收集，给出了几种常用金属材料的裂纹扩展率模型参数。     

混凝土的施工温度与裂缝

通过查阅有关混凝土内部应力方面的专著,结合现场观察,对混凝土温度裂缝产生的原因、现场混凝土温度的控制和预防裂缝的措施等进行阐述。     

纤维沥青混合料在高速公路大修改造中的应用

实践证明，将纤维加入到沥青混合料中，可以明显改善沥青路面的综合路用性能，尤其是在防止反射裂缝能力、增强抗车辙能力等方面效果突出。     

A probabilistic damage tolerance concept for welded joints Part 2: a supplement to the rule based S–N approach

The first part of this paper presented the required statistics and stochastic models for reliability analysis of the fatigue fracture of welded plate joints. This present Part 2 suggests a probabilistic damage tolerance supplement to the design S–N curves for welded joints. The goal is to provide the practising engineer with simple tools that predict the reliability against fatigue fracture during service life. The impact of the chosen fatigue design factors (FDF) and the uncertainty in the applied stresses is revealed. The effect of an in-service inspection programme is also predicted. The results are presented as dimensionless matrices and suggested for use in support of decision-making at the design stage, without any advanced fracture mechanics modelling and stochastic simulation. One important advantage of this format is that the probability levels are presented regardless of actual weld class and target service life (TSL). This is obtained by introducing the FDF as a key parameter to the results. This parameter is defined as the ratio of predicted fatigue life over TSL. FDF is always calculated in the S–N approach which is mandatory in fatigue life prediction. Various welded details (classes) will have the same reliability level for the same FDF. This is true at the end of TSL and at earlier stages, i.e. fractions of TSL. The absolute value of TSL is immaterial for a given FDF. In the case of in-service inspection, the inspection interval is also given without dimensions as a fraction of TSL.

Only the influence of future scheduled inspections is treated. Updating based on actual inspection results is not included as the scope of work is inspection planning at the design stage. Results for some frequent cases occurring in practice are readily derived and presented.