Active Steering of a Rail Vehicle with Two-Axle Bogies Based on Wheelset Motion

Summary This paper deals with a basic study on the actively steered rail vehicle with two-axle bogie trucks, which employs a control law based on the self-steering ability of wheelset. However, this control law not only helps the steering performance, but also tends to lower the running stability. Two methods are proposed to improve the stability. The first method is to add a feedback of wheelset lateral velocity, the second one is to give some time lag to the control force, and both are proved to be affective. Here, the latter is more practical method and the delay of control due to the time lag does not deteriorate the steering performance.     

Exact and simplified estimations for elastic buckling pressures of structural pipe-in-pipe cross sections under external hydrostatic pressure

Structural pipe-in-pipe cross sections have significant potential for application in offshore oil and gas production systems because they combine thermal insulation performance with structural strength and self weight in an integrated way. Such cross sections comprise inner and outer thin-walled pipes with the annulus between them fully filled by a selectable filler material to impart an appropriate combination of properties. Structural pipe-in-pipe cross sections can exhibit several different collapse mechanisms, and the basis of the preferential occurrence of one over the others is of interest. This article presents an exact analysis for predicting the elastic buckling behaviours of a structural pipe-in-pipe cross section when subjected to external hydrostatic pressure. Simplified approximations are also investigated for elastic buckling pressure and mode when the outer pipe and its contact with the filler material is considered as a pipe on an elastic foundation. Results are presented to show the variation of elastic buckling pressure with the relative elastic modulus of the filler and pipe materials, the filler thickness, and the thicknesses of the inner and outer pipes. Case studies based on realistic application scenarios are used to show that the simplified approximations are sufficiently accurate for practical structural design purposes.     

Estimating micro-scale intermittency of fluorescence fields from conventional CTD measurements

A free-fall microstructure profiler (TurboMAP) reveals highly intermittent features in the fluorescence field. Conventional CTDs that mount a fluorometer are usually deployed with a tethered cable, and the data are averaged or smoothed over a given time or water depth. Because of the nature of the operation and the data processing involved, intermittent features of fluorescence fields are masked. We have developed a statistical technique to extrapolate the intermittency using a lognormal mixture probability density function (mixture pdf). The statistics obtained from the mixture pdf are consistent with microstructure data, thus the conventional CTD can provide statistics appropriate to a micro-scale fluorescence field.     

CFD simulation of 3-dimensional motion of a ship in waves: application to an advancing ship in regular heading waves

A new computational fluid dynamics simulation method has been developed for the unsteady motion of a ship advancing in waves. The objective is to evaluate the added resistance and predict the performance of a ship in waves. In this study, a finite volume method, in the framework of a boundary-fitted grid system, is employed. The motion of the ship is solved with six degrees of freedom by using the hydrodynamic forces and moments obtained from the solution of the simulation method. The marker–density–function method is employed to calculate the nonlinear free surface. This method is applied to the coupled motion problem of heaving and pitching. Received for publication on Nov. 15, 1999; accepted on Nov. 18, 1999     

Collapse strength of hatch cover of bulk carrier subjected to lateral pressure load

A series of elastoplastic large deflection FEM analyses has been performed on hatch covers of bulk carriers subjected to lateral load. Two types of hatch covers are considered which are the folding type and the side-sliding type. For the folding-type cover, one size is considered which is for Handy size bulk carrier, whilst for the side-sliding-type cover, two sizes are considered which are for Panamax and Cape size bulk carriers. For each type, two hatch covers are selected which are designed in accordance with the old ICLL rule and new IACS rule, respectively. Calculated collapse strengths are compared with individual design loads, and a strength assessment is performed. On the basis of collapse behaviour observed in FEM analyses, a simple method is proposed to evaluate the collapse strength of a hatch cover subjected to lateral load. It is confirmed that the collapse strength is accurately predicted by the proposed method.     

Numerical prediction of the dilution process and its biological impacts in CO2 ocean sequestration

 In order to investigate the biological impacts of the ocean sequestration of CO₂ (carbon dioxide), the dilution processes of CO₂ were investigated near injection points in the deep ocean. From a combined fluid-dynamics, chemical, and biological approach, a two-phase computational fluid dynamics (CFD) method with mass transfer was developed to predict droplet plume flow, the dissolution of CO₂ from droplets into seawater, and the advection–diffusion of dissolved CO₂ (DCO₂) in the deep ocean. Changes in pH due to the concentration of DCO₂ were also calculated. In addition, the isomortality concept of Auerbach et al. was incorporated to predict the lethal damage to marine organisms caused by DCO₂. The simulation results suggested that the biological impacts of CO₂ sequestration were insignificant in terms of mortality in both small-scale field experiments and the real-life cases we propose. Received: October 3, 2001 / Accepted: December 14, 2001     

A study on bubble plume behavior in stratified water

Plumes of air and carbon-dioxide (CO₂) bubbles in stratified water were studied experimentally and numerically. It is important to understand the plume behavior of droplets or bubbles in the ocean in marine environmental engineering. In sequestration of CO₂ in the ocean, liquid CO₂ is injected in the form of droplets, and thermal stratification in enclosed seas is possibly destroyed by a bubble generator. This study focuses on the relationship between intrusion depth and stratification intensity, gas flow rate, and bubble size. A desktop-sized tank was used to achieve no-background-flow conditions for salt stratification. The results from the air-bubble experiments indicated that the larger the bubble size, the smaller the intrusion depth. We also observed the behavior of CO₂ bubbles. They are different from air in that they dissolve in water and are reduced in volume. Our numerical simulation method for two-phase flow was validated by comparisons with the experiments. Received: August 13, 2001 / Accepted: October 9, 2001     

Combustion characteristics of hydrotreated vegetable oil – diesel blend under EGR and supercharged conditions

This paper investigates the effects of Hydrotreated vegetable oil-diesel blend to combustion characteristics under various ambient oxygen concentrations and ambient pressure. Combustion characteristics were investigated using heat release rate analysis, two color method, soot concentration measurement and NOx concentration measurement. The experiments were carried out on a rapid compression expansion machine to simulate the ambient condition of a CI engine at TDC. Synthetic gas with oxygen concentrations of 21 %, 15 % and 10 % were used to simulate EGR conditions. A single hole injector was used with five different fuels: commercial diesel, HVO-commercial diesel blends and HVO. The results showed that increasing HVO blending percentages decreased ignition delay, flame temperature, soot concentration and NOx concentration. Heat release at oxygen concentration of 10 % dramatically dropped due to a shortened ignition delay, which resulted in less combustion. A decreased oxygen concentration from applied EGR conditions not only increased ignition delay, heat release, flame temperature and NO_x concentration, but also increased soot concentration. A combination of EGR and supercharged conditions by increasing ambient pressure and decreasing oxygen concentrations resulted in increased heat release, decreased flame temperature, ignition delay and soot concentration, compared to EGR conditions.     

欧洲高速列车的最新技术发展动向

法国、德国、意大利等国的高速铁路迅猛发展,成为引领世界高速铁路的主力,并且,欧洲高速铁路已进入商业运行速度(320 km/h)的新时代。文章介绍了法国、德国、意大利、西班牙等国家高速铁路列车所采用的新技术、新装备、新工艺及发展前景。     

Test of large-eddy simulation models for homogeneous-shear turbulence in stratification

Numerical tests of various subgrid-scale (SGS) models were conducted for turbulence in thermally stratified homogeneous-shear flow at a relatively low Reynolds number. Compared with a direct numerical simulation (DNS), we found that nondynamic isotropic SGS models are not able to represent the energy spectrum very well because the energy decays considerably during the transition between an initial random stage and a stage of coherent turbulent structures. Dynamic models performed well for simulating the energy spectrum and the change of GS properties with time; anisotropy is not a necessary feature under the present simulation conditions, although one of the special features of stratified turbulence is anisotropy. This may be because the present grids for large-eddy simulation were fine enough to resolve the patches of counter-gradient heat fluxes, which play an important role in the evolution of turbulent energy in stratified turbulence. With respect to the domain-averaged values of SGS stresses, only the dynamic two-parameter mixed (DTM) model produced results of the same order of magnitude as those of filtered DNS. This is because of the terms arising from re-decomposing of the SGS stresses in the DTM model. It was also found that this incompetence in simulating the SGS stress is not necessary to simulate GS energy evolution, as is known for wall turbulence. Updated from the Japanese original (J Soc Nav Archit Jpn 2001; 190:27–39)