Behaviour of the Normal Contact Force Under Multiple Wheel/Rail Interaction

The wheel/rail contact forces are calculated in the frequency domain using a track model with multiple wheels on the rail. The effects of the wave reflections between the wheels on the contact force are studied. Different pad stiffnesses are used in the calculations to investigate the influence on the contact force. It is shown that the contact force can have up to four main peaks in the frequency region 550-1200?Hz due to the wave reflections between the wheels, so that the wavelengths of short pitch corrugation can be expected to be associated with multiple frequencies. As a conclusion, it is recommended that in a model for predicting short pitch corrugation the effects of multiple wheel/rail interactions need to be included.     

A summary of the formation and seasonal progression of the Northeast Water Polynya

A summary of the seasonal development of the Northeast Water Polynya ice cover characteristics is presented. This is based primarily on satellite remote sensing observations, with some in situ measurements, including both new and published data.     

低地板轻轨车的"积木"式模块设计

以低地板轻轨车ＣＯＭＢＩＮＯ车体承载结构为实例，阐明了采用“积木”式模块设计的优点。     

Importance of Addressing Human Systems Integration Issues Early in the Science and Technology Process

Historically, human systems integration (HSI) and other operational issues are not addressed during the science and technology (S&T) phase because the focus is on technology development. That view is to solve the "tough science" first, and the rest is simple application by a program office or operational forces. An imbalance between technology development efforts and total system performance considerations, e.g., total ownership cost, workload, manning, training, operational concept, skills, and human performance, leads to suboptimal solutions at best, and at worst prevents the technology's benefits from transitioning out of S&T at all. If HSI is not addressed during the S&T phase, the responsibility falls to the acquisition programs to ensure that operator, maintainer, and total system performance are optimized in the final design. By this point, cost and schedule constraints can make this prohibitive, limiting the options to either using a legacy system or accepting the technology with suboptimal performance and high life-cycle costs (because design problems lead to manpower, training, and human error problems). However, if the S&T community uses HSI in their technology readiness level evaluation criteria, the Department of Defense can reduce its out-year costs and recapitalize that funding to buy required weapons systems and platforms while still reaping the tactical benefits that a new technology offers.     

Improvement of Propeller Hydrodynamic Drag and Efficiency on USCG Cutters Operating in Trailshaft Mode

Large US Coast Guard cutters spend much of their underway time with only one of two propellers operating. The offline propeller is "trailed," often creating a significant amount of hydrodynamic drag. Operators from the fleet do not appear to have any specific guidance on how best to reduce this drag. Using the propeller analysis tools PSF-3 and PSF-10, propeller thrust coefficient values versus advance coefficient values were created for the propellers of the USCG 270' cutters. These values—and the associated drag—vary significantly in magnitude based on the trailed propeller pitch. Based upon sea trial measurements, expected magnitudes of this drag versus pitch setting were predicted. Minimum drag pitch settings were identified for an operational 270' cutter at 8 knots. RPM and pitch settings for maximum hydrodynamic efficiency for the online shaft are sometimes developed during ship acquisition. In the current work, a methodology for conducting such a study is discussed to demonstrate to ship operators the relative ease with which they could perform this analysis on board, if effective power and propeller thrust coefficient values are available. Consideration of prime mover specific fuel consumption rates together with propeller hydrodynamic efficiencies is discussed.     

OPA 90

The Donaldson Report has been published and we are entitled to ask 'where do we go from here?' The majority of the shipping world, recognizing the international nature of the business moves by consensus such that rules applicable in Europe are also applicable in, say, Asia or South America. By its very nature this method takes time to bring rules into effect. By contrast the United Stated of America takes the unilateral approach to transport regulations and because it is such an important trading nation, particularly with regard to shipping, those wishing to participate in the trade must comply with the U.S. rules. One such example is the Oil Pollution Act of 1990 (OPA 90) passed just four year ago. The shipping industry in general and the tanker industry in particular has had to adapt if it wishes to trade within the United States' navigable waters, adjoining shorelines, or the exclusive economic zone (200 miles). This paper looks at those sections of the Act that, from the standpoint of the tanker industry, have had the biggest impact when trading to the United States. We therefore look at how OPA 90 addresses the issues of prevention, clean up and who will pay?     

What determines transit energy use?

A comparison of the energy use per passenger-mile of eight modes of urban transportation is made in terms of eleven variables, resulting in conclusions about the direction transit system design should take to provide adequate transportation with minimum energy use. The method can easily be programmed on a personal computer to be used to study the effects of parameter variations on energy use.     

基于全矢量显式算法的双相流填充数值模拟

基于模拟填充过程显式算法,提出用于模拟双相流的全矢量化运算显式算法。在双相流混合理论的基础上,对各类双相流填充及组份分离现象进行模拟。为高效求解耦合的Navier Stokes方程,新算法中的矩阵操作仅在单元一级进行,避免全局求解,使全局操作完全矢量化。新算法的另一显著优势,是采用等阶插值的普通单元,使不可压缩条件通过反馈修正的方法得到满足,通过系统化的光顺处理来避免由于应用等阶插值而导致的自锁。由于全局操作完全矢量化,计算代价与节点的自由度近似成正比,可实现高效的双相流填充及组份分离现象的模拟,满足工业应用中模拟复杂实际问题的需要。