Experimental ivnestigation on flow fields of viscous fluid around two-dimensional wings and comparison with computational results

To examine the flow field of a viscous fluid around the trailing edge of a wing with respect to the Kutta condition or the Joukowski hypothesis, an experimental investigation into the velocity fields around two-dimensional (2D) wings NACA0012 and NACA4412 was carried out using an X-type hot-wire anemometer in a wind tunnel and the method of colored milk injection in a circulating water channel. The results of these investigations revealed that the flow of a viscous fluid at the trailing edge of a 2D wing is tangential to the face on the pressure side, and that the flow is very slow or reversed on the suction side due to separation when the angle of attack is greater than 7.5°. By flow visualization, a Kármán vortex street was found in the wake of both wings (NACA0012 and NACA4412) when the angle of attack was 5°. These results show that the ordinary Kutta condition with respect to the direction of outflow at the trailing edge is not necessarily satisfied in a viscous fluid, but the Kutta condition with respect to the pressure at the trailing edge is satisfied as usual. Numerical results, which have been obtained as the solution of Reynolds-averaged Navier-Stokes equations, show good agreement with above-mentioned experimental results. Therefore, CFD (Computational Fluid Dynamics) simulation has proved to be very effective for studying steady viscous flow around the trailing edge of a 2D wing.     

主动导向转向架的多体动力学仿真与试验研究

对主动导向转向架的半车模型进行了多体动力学计算,并进行了滚动台试验,计算结果和试验结果基本一致。将半车模型扩展为整车模型后,进行了计算分析,研究结果表明,主动导向转向架可以大大提高转向架的曲线通过性能。     

Passengers' perceptions and effects of bus‐holding strategy using automatic vehicle location technology

This study reports bus passengers' behavior and perceptions related to the use of potential features of an automatic vehicle location (AVL) system in bus transit through conducting an attitudinal on‐board survey in Bangkok. A passenger waiting‐time survey conducted as part of this study revealed that passengers perceive waiting‐time at bus stops to be greater than actually experienced. The other aim of this study is to examine the potential benefits of bus‐holding using an AVL technology, in terms of waiting‐time, through minimizing bus bunching under different congestion levels. The results are obtained using PARAMICS, and reveal a significant reduction in average waiting‐time.     

Use of cyanobacterial pigments to characterize the ocean surface mixed layer in the western Pacific warm pool

We collected biological and physical oceanographic data simultaneously from shipboard observations and mooring buoys in the Pacific equatorial warm pool during the 2002–2003 El Niño event and found that the vertical profiles of cyanobacterial pigments reflected the turbulent kinetic energy (TKE) better than did analyses of the mixed layer by temperature and salinity profiling. Zeaxanthin, an accessory pigment of cyanobacteria, was abundant and almost homogeneous in the warm pool within the surface mixed layer, although chlorophyll a concentrations were low. The intracellular content of chlorophyll a increases with increasing depth and decreasing light in a photoprotective response, but the zeaxanthin content does not change with depth. Hence, we hypothesized that the profile of the ratio of zeaxanthin to chlorophyll a would decrease with increasing depth if the water column were stable, without vertical mixing. On the contrary, vertically constant ratios would indicate vertical mixing. Our analysis using a numerical model showed a good agreement between profiles of these ratios and the profiles of TKE and supported the hypothesis. However, a comparative analysis of the zeaxanthin:chlorophyll a ratio profiles with mixed layer depth based on temperature and salinity data revealed two distinct patterns. In the first pattern, the ratio was uniform in the mixed layer when TKE was strong. In the second, the ratio decreased with increasing depth, even in the mixed layer, because of reduced TKE.     

Traffic conflict assessment for non-lane-based movements of motorcycles under congested conditions

Traffic conflict under congested conditions is one of the main safety issues of motorcycle traffic in developing countries. Unlike cars, motorcycles often display non-lane-based movements such as swerving or oblique following of a lead vehicle when traffic becomes congested. Very few studies have quantitatively evaluated the effects of such non-lane-based movements on traffic conflict. Therefore, in this study we aim to develop an integrated model to assess the traffic conflict of motorcycles under congested conditions. The proposed model includes a concept of safety space to describe the non-lane-based movements unique to motorcycles, new features developed for traffic conflict assessment such as parameters of acceleration and deceleration, and the conditions for choosing a lead vehicle. Calibration data were extracted from video clips taken at two road segments in Ho Chi Minh City. A simulation based on the model was developed to verify the dynamic non-lane-based movements of motorcycles. Subsequently, the assessment of traffic conflict was validated by calculating the probability of sudden braking at each time interval according to the change in the density of motorcycle flow. Our findings underscore the fact that higher flow density may lead to conflicts associated with a greater probability of sudden breaking. Three types of motorcycle traffic conflicts were confirmed, and the proportions of each type were calculated and discussed.     

A simulation model of train travel on a rail transit line

A simplified simulation model for the operational analysis of a rail rapid transit train is presented. The model simulates the movement of a train along a route, and develops the relationships of time—distance, time—speed and distance—speed. The inputs to the model are the profile of speed limits and the dynamic characteristics of the train. Without the information on the track geometry and tractive effort, the model determines the speed of the train at a location based on the previous and future speed limits relative to the location. It was found that the model can fairly accurately simulate the relationship between travel time and distance. A comparison of the train travel times between the actual and simulated runs is presented. Because of the simplicity of input and calculation method, the model can be a useful tool for the “desk-top” analysis of frequently occurring planning problems of a commuter rail or rail rapid transit line, such as the impacts of changes in speed limits, station locations, station stopping policy, addition/elimination of stations, and types of rail cars.     

Low-cost carriers in Asia: Deregulation, regional liberalization and secondary airports

While the demand for low-cost air transportation is potentially huge in Asia, development of low-cost carriers (LCCs) lags behind the region's overall aviation development, and certainly lags behind the LCC development in North America and Europe. It has been noted that market conditions and the regulatory environment of Asia are different from those of North America and Europe. What are the main differences here; and how do these differences impact market entry and success of Asian LCCs? This paper describes salient features of Asian LCCs and their developments. It examines the impact of Asia's domestic and international airline regulations and airport infrastructure on the performance of its LCCs. We find that the “Southwest effect” may also exist in Asia and that the development of low-cost terminals may compensate, at least partly, the scarcity of secondary airports in the region. The experiences of Thailand and China are investigated as case studies.     

Monorail development and application in Japan

The monorail has emerged recently as a serious mode for transit use in Japan. Three monorail lines are operational, and three more are being constructed. Approximately thirty other cities in Japan are considering the introduction of the monorail. This paper reviews the recent development of the monorail in Japan, examines its components, compares its performance with other transit modes, and assesses its potential in the context of the family of urban transit modes. This examination and comparison will be based on the features of the monorail designs recently adopted in Japan.     

试验台上的轮轨蠕滑力特性

阐述了在微缩试验台对轮轨蠕滑力进行的试验,重点介绍了试验设备、方法和试验结果。