Fatigue design approach for the spot-welded T-type member using a simulated single spot-welded joint

In order to develop a fatigue design method for actual railroad car and commercial vehicle body structures using the fatigue data of simulated single spot-welded lap joints, we first analyzed the stress distribution and evaluated fatigue strength of spot-welded T-type members that are the components of actual railroad car and commercial vehicle body structures. Next, fatigue design approach of these members using the fatigue data of single spot-welded lap joints was investigated. From our results, we found that, even though there was a quantitative difference of fatigue strength between the single spot-welded joint and the actual members over the same number of fatigue cycles, through the use of appropriate correction, the fatigue design criterion of actual spot-welded members, such as those used in railroad car and commercial vehicle body, can be predicted using the fatigue strength of single spot-welded joint.     

Ecology of bottom ice algae: II. Dynamics, distributions and productivity

Spring blooms of bottom ice algae are a common feature of landfast congelation ice in polar regions. Because ice algae are usually associated with a substrate, their population dynamics can be followed with considerable confidence. Although ice algal dynamics are closely related to irradiance, their dynamics and distributions are influenced by other abiotic and biotic factors. Ice algal abundance varies horizontally over all scales examined. Factors such as grazing and nutrient availability may contribute to local and geographic differences. Loss terms for most sea ice assemblages are largely unquantified. Ice algal biomass is most concentrated near the ice-water interface in spring.Environmental factors affecting ice algal abundance and productivity are considered here, emphasizing recent results from several well-studied sites. Biomass accumulation, growth rates and productivity have been documented for spring blooms of bottom interstitial and sub-ice assemblages. On an areal basis biomass accumulation in bottom ice assemblages can be comparable with planktonic systems. At low ambient temperatures and irradiances average specific growth rates (≤ 0.25 d⁻¹) and production rates (≤ 1.0 mg C mg Chl⁻¹ h⁻¹) for ice algae are low. Current methods of measuring productivity are compared. Results are consistently low but variable with little systematic difference among them. At present, apparent differences in productivity between bottom ice assemblages in the Arctic and Antarctic, or among different antarctic assemblages, are so confounded by methodological and other sources of variability that no firm differences can be detected.     

Active Contours and Mumford-Shah Segmentation Based on Level Sets

IntroductionThe basic idea in active contour models orsnakes is to evolve a curve,subject to constraintsfrom a given image,in order to detect objects inthat image.For instance,starting with a curvearound the object to be detected,the curve movestoward its interior normal and has to stop on theboundary of the object.LetΩ be a bounded open subset of R2 ,with Ω its boundary. Let u0 ∶Ω→ R be a given image,and C( s)∶ [0 ,1 ]→ R2 be a parameterized curve. Inthe classical snakes and active…     

Effects of mixture stratification on HCCI combustion of DME in a rapid compression and expansion machine

Compression ignition of homogeneous charges in internal combustion (IC) engines is expected to offer high efficiency of DI diesel engines without high levels of NOx and particulate emissions. This study is intended to find ways of extending the rich limit of HCCI operation, one of the problems yet to be overcome. Exhaust emissions characteristics are also explored through analyses of the combustion products. DME fuel, either mixed with air before induction or directly injected into the combustion chamber of a rapid compression and expansion machine, is compressed to ignite under various conditions of compression ratio, equivalence ratio, and injection timing. The characteristics of the resulting combustion and exhaust emissions are discussed in terms of the rate of heat release computed from the measured pressure, and the concentrations of THC, CO, and NOx are measured by FT-IR and CLD. The experimental data to date show that operation without knock is possible with mixtures of higher equivalence ratio when DME is directly injected rather than when it is inducted in the form of a perfectly homogeneous fuel-air mixture. Although fuel injected early in the compression stroke promotes homogeneity of the DME-air mixture in the cylinder, it causes the mixture to ignite too early to secure good thermal efficiency and knock-free operation at high loads. Low temperature reactions occur at about 660K regardless of the fueling methods, fuel injection timing and equivalence ratio. The main components of hydrocarbon emissions turned out to be unburned fuel (DME), formaldehyde and methane.     

Actively translating a rear diffuser device for the aerodynamic drag reduction of a passenger car

This research aims to develop an actively translating rear diffuser device to reduce the aerodynamic drag experienced by passenger cars. One of the features of the device is that it is ordinarily hidden under the rear bumper but slips out backward only under high-speed driving conditions. In this study, a movable arc-shaped semi-diffuser device, round in form, is designed to maintain the streamlined automobile??s rear underbody configuration. The device is installed in the rear bumper section of a passenger car. Seven types of rear diffuser devices whose positions and protrusive lengths and widths are different (with the basic shape being identical) were installed, and Computational Fluid Dynamics (CFD) analyses were performed under moving ground and rotating wheel conditions. The main purpose of this study is to explain the aerodynamic drag reduction mechanism of a passenger car cruising at high speed via an actively translating rear diffuser device. The base pressure of the passenger car is increased by deploying the rear diffuser device, which then prevents the low-pressure air coming through the underbody from directly soaring up to the rear surface of the trunk. At the same time, the device generates a diffusing process that lowers the velocity but raises the pressure of the underbody flow, bringing about aerodynamic drag reduction. Finally, the automobile??s aerodynamic drag is reduced by an average of more than 4%, which helps to improve the constant speed fuel efficiency by approximately 2% at a range of driving speeds exceeding 70 km/h.     

Hydrography, currents and distribution of suspended matter during a dumping experiment in the western Baltic Sea at a site near Warnemünde

During a dumping experiment on 20/21 June 2001, an extensive data record was collected to understand the dynamical processes in the water column of the investigation area and to validate model results. Weak westerly winds with strongly changing cloud coverage characterized the meteorological situation. During the second day the wind calmed down and moved shortly to easterly directions. The water column was characterized by a strong vertical stratification with discontinuity layers in temperature and salinity in 12 and 16 m. The current regime was dominated by outflow at the water surface and inflow along the German coast, with strong current shearing in the dumping area. The suspended matter clouds could be identified by optical methods and ADCP (Acoustic Doppler Current Profiler) scattering intensity. During the experiment the suspended matter plumes were only visible at the surface up to 1 h after the dumping. The aerial photographs document that the particle clouds at the surface drifted to the west and, after approximately 40 min, they were only weakly visible. The fine material was concentrated in the discontinuity layer leading to substantially higher values of optical parameters and suspended matter concentration than measured in the surface clouds. Due to the vertical current shears the material was transported in the water column in different directions. At the first day the maximum of the suspended matter in the discontinuity layer was in the north-western corner and in the bottom layer in the northeast corner of the dumping area. Strong wind conditions after the dumping led to periodical resuspension processes.     

Design analysis and comparison between standard and rotary porting systems for IC engine

Many porting systems for internal combustion engines have been tried and tested over the years, however the basic spring actuated poppet valve system has prevailed over the last century. In the goal to lower engine output parasitic losses, a simple rotary valve porting system design is proposed and analyzed. The proposed design concept takes into consideration and combines all the prominent advantages of many ealier mutlitiple design variations over the past century. The inherent primary advantage of such a rotary porting system is the elimination of reciprocating components, thus lowering vibration, and removal of highly stiff springs which contribute to considerable system power loss. Comparable sized 3-D representations of both systems are constructed in CAD (Computer Aided Design) software in order to run mechanical and fluid simulations to validate the efficiency advantage of a rotary valve porting system. Using Pro/Engineer Mechanism Dynamics module, the minimum torque required to actuate both systems at 2000 rpm and 3000 rpm is determined. Fluid simulations are performed using a commercial software CFDesign V10. Volumetric flow rates are compared during the intake stroke as well as turbulence intensity factors which characterizes a systems ability to properly mix the Air/Fuel mixture and the combustion efficiency. Some possible improvement on the rotary geometry is suggested.     

On the numerical accuracy of the wave load distribution on a ship advancing in short and steep waves

Defining numerical uncertainty is an important part of the practical application of a numerical method. In the case of a ship advancing in short and steep waves, little knowledge exists on the solution behaviour as a function of discretisation resolution. This paper studies an interface-capturing (VOF) solution for a passenger ship advancing in steep (kA = 0.24) and short waves (L _w /L _pp = 0.16). The focus is to estimate quantitative uncertainties for the longitudinal distributions of the first–third harmonic wave loads in the ship bow area. These estimates are derived from the results of three systematically refined discretisation resolutions. The obtained uncertainty distributions reveal that even the uncertainty of the first harmonic wave load varies significantly along the ship bow area. It is shown that the largest local uncertainties of the first harmonic wave load relate to the differences in the local details of the propagating and deforming encountered waves along the hull. This paper also discusses the challenges that were encountered in the quantification of the uncertainties for this complex flow case.     

轨道交通的产学研新模式——麻省理工学院/波多黎各地铁项目简介

波多黎各于20世纪90年代初才开始发展城市轨道交通,但因为善于利用后发优势,通过产学研的结合,充分考虑了地铁工程的多学科特性,走出一条有波多黎各特色的道路,成为美国和国际公共交通领域技术交流的典范.主要介绍了其产学研的项目,它由负责地铁项目的政府主管部门、波多黎各大学和美国麻省理工学院共同组织实施,历经地铁前期规划、修建、调试、运营和政策分析等全部过程,共13年的时间.这种方式提高了工程的质量和施工效率,推动当地轨道交通辅助产业的发展,加快了新技术的应用及研究,培养了一大批轨道交通的规划运营人才,为拉丁美洲城市轨道交通建设提供了一个新模式.波多黎各的经验对于我国当前的城市轨道交通建设同样具有借鉴意义.     

路段人行横道二次过街感应式信号控制算法设计

在现有感应控制二次过街系统中,道路两边以及安全岛按钮控制多为分开控制,没有相互协调,行人在安全岛等待时间过长易导致违章过街等问题。在一次过街感应控制算法基础上,结合二次过街相关理论、机动车与行人延误机理以及行人过街信号配时理论,提出"人行绿波"协调思路,对路段二次过街感应控制算法进行设计,并应用Vissim软件进行仿真验证,结果显示设计感应控制算法能有效地降低行人和机动车延误。