Stern waves consisting of forward-oriented breaking waves and the remaining following waves

When a ship with a wide, immersed transom stern runs on a deep draft, forward-oriented wave breaking often occurs just behind the transom stern. In such conditions, stern waves can be considered to consist of two main components: the forward-oriented breaking wave and the remaining following waves. In our previous study, which was the first part of the present study, we developed a method to treat the forward-oriented breaking wave, and have clarified that it has a scale effect and its resistance coefficient decreases with an increase in the size of the model ship. On the other hand, the study also indicated that the height of the remaining following waves increases with an increase in the model ship size. The purpose of this paper is a more complete understanding of the two different component characteristics of the stern waves. We have developed a method to estimate the resistance due to the remaining following waves. Using this method, we have reached three main conclusions. The resistance increases considerably if the remaining following waves change to forward-oriented breaking waves. The resistance coefficient of the remaining following waves increases only slightly with an increase in model ship size. This stern wave resistance coefficient is strongly affected by the forward-oriented breaking waves, and therefore decreases with an increase in model ship size. Received: January 5, 2001 / Accepted: May 28, 2001     

铁道车辆用滚动轴承及其润滑技术——车轴用轴承(1)

在铁道车辆中,滚动轴承用作走行装置的车轴轴承及动力发生和传递的牵引电动机和驱动装置等的轴承,分别发挥着重要作用。这些轴承的故障对车辆的运行影响很大,因此,对滚动轴承的设计、生产和维护一向都特别重视。另外,各轴承在载荷、转速和润滑方法等方面不尽相同。本文在叙述各轴承特点的同时,就与高速化、轻量小型化、减少维护和提高耐久性等车辆新理念相适应的轴承和润滑技术进行了介绍。     

纳米氧化铁的制备及其形貌

利用乙酰丙酮铁在空气中的低温热分解反应，制备了Fe3O4，γ-Fe2O3纳米微粒．采用X射线衍射（XRD）、透射电子显微镜（TEM）、比表面积法（BET）对制得的产物进行粒径及形貌表征．结果表明：Fe3O4一次颗粒粒径为16nm左右；γ-Fe2O3一次颗粒粒径约为20nm，颗粒间排列紧密，二次颗粒呈链状，有形成一个封闭空间的趋势．