高压IGBT和无变压器牵引应用中多电平变流器的功率损耗评估

轨道车辆目前所使用的低频线路变压器受低效和超重问题所困.未来的牵引传动系统可能直接与电网相连,无需该类变压器.典型的无变压器传动系统通常由多个使用HV-IGBT(高压绝缘栅双极型晶体管)的中等电压规格变流器串联而成.设计之初先对6.5 kVIGBT和目前已商业应用于牵引领域的3.3 kV、4.5 kV IGBT的开关特性和损耗进行比较,基于所考虑的HV-IGBT,对多电平变流器的特点及其在无变压器系统的应用进行了评估.本文侧重于变流器的损耗分析,同时简要地探讨了可靠性和谐波频谱问题.综合考虑上述各方面因素,三电平中点箝位变流器是一种较理想的方案,适用于无变压器牵引系统,可作为网侧变流器和电机侧变流器使用.     

Heterogeneous traffic flow modelling for an arterial using grid based approach

A grid based modelling approach akin to cellular automata (CA) is adopted for heterogeneous traffic flow simulation. The road space is divided into a grid of equally sized cells. Moreover, each vehicle type occupies one or more cell as per its size unlike CA traffic flow model where each vehicle is represented by a single cell. Model needs inputs such as vehicle size, its maximum speed, acceleration, deceleration, probability constants, and arrival pattern. The position and speed of the vehicles are assumed to be discrete. The speed of each vehicle changes according to its interactions with other vehicles, following some stochastic rules depending on the circumstances. The model is calibrated and validated using real data and VISSIM. The results indicate that grid based model can reasonably well simulate complex heterogeneous traffic as well as offers higher computational efficiency needed for real time application.     

Robust control of traffic networks under uncertain conditions

Uncertainty of traffic network operations has been a subject of lively debate in the last decade. However, little effort has been put in developing control frameworks that are not only aimed at improving the average performance of the system, but also at improving the system robustness and reliability. In fact, it can be argued that most of the current control approaches are only aimed at improving the efficiency, which can even be counterproductive from a robustness point of view. The main contributions of this article is the proposition of a new control framework based on the notion of controlled Markov processes, which explicitly takes into account the uncertainty in predicted traffic conditions and system performance. Furthermore, in contrast to traditional optimal control approaches, the objective function can include general statistic of the random system performance, such as the mean, standard deviation or 95‐percentile. The contribution aims to make clear how different performance function specifications yield different control strategies. This is shown for a relatively simple case study.     

Relationships between near-bottom dissolved oxygen and sediment profile camera measures

The United States Environmental Protection Agency (U.S. EPA) and other environmental authorities regulate concentrations of dissolved oxygen (DO) as a measure of nutrient-related eutrophication in estuarine and coastal waters. However, in situ DO concentrations are extremely variable, and their characterization requires an extensive sampling program to provide data over meaningful scales of time and space. In contrast, benthic faunal communities integrate the impacts of low DO over time, and can be rapidly assessed using benthic imaging. The goal of this study was to quantify the relationships between near-bottom dissolved oxygen and measures derived from benthic imaging with a sediment profile camera. We monitored three stations in Narragansett Bay (Rhode Island, USA) for DO and other water quality parameters 15–20 cm above the sediment surface on 15-minute intervals between July and November 2002, and regularly sampled these stations with a sediment profile camera throughout this time period. These soft-sediment stations encompassed several DO environments. We tested for relationships between near-bottom DO and several camera measures, including Nilsson and Rosenberg's Benthic Habitat Quality (BHQ) index, the apparent Redox Potential Discontinuity (aRPD) depth, and various faunal features that can be identified in sediment profile images. Camera measures were examined against a variety of methods of characterizing DO (including mean DO, and the percent of time under various DO thresholds), over a span of time scales from 1 day to 49 days. The best relationship (highest r²) between near-bottom DO and BHQ was found when DO was evaluated as the percent of time under a hypoxic threshold of 2.6 mg l^− 1 over a 28-day time scale (by examining DO records over the 28 days preceding each camera deployment). We found that, over several benthic settings, the BHQ index was successful at identifying environments that had experienced relatively high or low DO over the preceding four weeks. Our sediment profile data showed more variability with DO in the intermediate values of BHQ. We conclude that sediment profile camera measures correlate to DO in areas where low DO is the primary stressor, integrate DO over ecologically relevant time scales, and enable sampling over spatial scales that are meaningful for mapping by virtue of rapid deployment and analysis. We submit that sediment profile camera imagery is a useful assessment and mapping tool for environmental managers interested in benthic condition and in first-order quantitative estimates of near-bottom DO regimes in areas where low DO is the primary benthic stressor.     

Seabirds utilizing the Northeast Water polynya

A small seabird community depends on the resources of the Northeast Water (NEW) polynya. In spring, at least 1000 King Eiders and 2500 Common Eiders form pre-breeding congregations at Ob Bank before dispersing in mid June to breeding areas. The most abundant species is the Fulmar, which breeds in six colonies with a total of 2550 “apparently occupied sites”, corresponding to approx. 1475 active pairs in 1993. Kittiwakes occupied almost 900 sites at Mallemukfjeld, with an estimated 733 breeding pairs. The entire NEW area probably holds 400–500 pairs of Ivory Gulls, and about 500 individuals were associated with a colony on Henrik Krøyer Holme; this is one of the world's largest known colonies. Sabine's Gulls breed at the same islands and on Kilen (approx. 50 pairs in each place). Small colonies (total less than 1000 birds) of Arctic Terns are distributed along the edge of the polynya, with the largest colony of about 100 pairs on Henrik Krøyer Holme. The Black Guillemot is the only breeding auk species (< 20 pairs) in the area. Small numbers of Red Phalaropes were observed in the polynya in 1992 and 1993, and the species may have bred at Henrik Krøyer Holme in 1993; the polynya area may also serve as a staging area for transpolar migrants. In late summer a few hundreds of Ross's Gull—non-breeding adults and immatures—show up in and around the polynya, and in recent years a few cases of breeding have also been recorded. The relatively small seabird populations are evidence of a generally low carrying capacity of the polynya area.Apart from the benthic foraging eiders and the Black Guillemot, the seabird community of NEW consists of surface feeders—Fulmars and gulls—dependent on small fish and zooplankton. During their stay in the NEW area, the five most abundant surface feeders will annually consume approximately 243,000 kg (wet weight) of food, of which the Fulmars alone take 67%. Food demand in relation to area of open water in the polynya is highest in spring (approx. 0.2 kg/km²), which is     

Material transport from the nearshore to the basinal environment in the southern Baltic Sea: I. Processes and mass estimates

Processes involved in erosion, transport and deposition of cohesive materials are studied in a transect from shallow (16 m) to deep (47 m) water of the SW Baltic Sea. The wave- and current-induced energy input to the seabed in shallow water is high with strong variability and suspended matter concentrations may double within a few hours. Primary settling fluxes (from sedimentation traps) are less than 10 g m⁻² day⁻¹, whereas resuspension fluxes (evaluated from sedimentation flux gradients) are 15–20 times higher and the residence time for suspended matter in the water column is 1–2 days. Settling velocities of aggregates are on average six times higher than for individual particles resulting in an enhanced downward transport of organic matter. Wave-induced resuspension (four to six times per month) takes place with higher shear stresses on the bottom than current-induced resuspension (three to five times per month). The short residence time in the water column and the frequent resuspension events provide a fast operating benthic–pelagic coupling. Due to the high-energy input, the shallow water areas are nondepositional on time scales longer than 1–2 weeks. The sediment is sand partly covered by a thin fluff layer during low-energy periods. The presence of the fluff layer keeps the resuspension threshold very low (<0.023 N m⁻²) throughout the year. Evaluated from 3-D sediment transport modeling, transport from shallow to deep water is episodic. The net main directions are towards the Arkona Basin (5.5×10⁵ t per year) and the Bornholm Basin (3.7×10⁵ t per year). Energy input to the bottom in deep water is low and takes place much less frequently. Wave-induced resuspension occurs on average once per month. Residence time of particles (based on radioactive isotopes) in the water column is half a year and the sediment accumulation rate is 2.2 mm year⁻¹ in the Arkona Basin.     

Short‐term travel time forecasts for transport information system in hong kong

In this paper, a case study is carried out in Hong Kong for demonstration of the Transport Information System (TIS) prototype. A traffic flow simulator (TFS) is presented to forecast the short‐term travel times that can be served as a predicted travel time database for the TIS in Hong Kong. In the TFS, a stochastic deviation coefficient is incorporated to simulate the minute‐by‐minute fluctuation of traffic flows within the peak hour period. The purposes of the case study are: 1) to show the applicability of the TFS for larger‐scale road network; and 2) to illustrate the short‐term forecasting of path travel times in practice. The results of the case study show that the TFS can be applied to real network effectively. The predicted travel times are compared with the observed travel times on the selected paths for an OD pair. The results show that the observed path travel times fall in the 90% confidence interval of the predicted path travel times.     

Rail line length in a crosstown corridor with many-to-many demand

An analytical model that determines the optimal location and length of rail line along a crosstown transportation corridor with the objective of minimizing the total transportation cost is presented. A general, many-to-many passenger demand pattern is considered. The objective function, which includes the rail and bus riding costs, rail and bus operating costs, rail fleet costs and rail line costs, is minimized by using the classical optimization method with the aid of a computer program developed for the model. The model is applied to the Northwest-South transportation corridor in Calgary, Alberta, and the sensitivity of the optimal rail line location and length to the unit cost and demand parameters at their reasonable ranges is tested. It is found that although the total passenger demand, unit rail line cost, and unit bus operating cost have greater influence than the unit bus and rail riding costs, and unit rail fleet and operating costs, the optimal line length is generally insensitive to all these parameters. It is also found that the length of the existing LRT line in the corridor is comparable to the optimal line length obtained from the model, but the existing line should be extended further south in order to meet the heavier demand in that direction optimally.     

Measurement of roof deformation caused by vehicle rollover

A vehicle rollover is a critical accident that could have many causes. This paper describes a novel vision-based system for measuring vehicle roof deformation due to a rollover accident. A vision-based measurement system offers an overall view of structural deformation simply at low cost. Our measurement system was constructed using a Kinect camera from Microsoft, a battery, and a remote-controlled recording computer. Color images and distance maps can be obtained using two sensors embedded in the Kinect along with customized software, and the distance from the camera lens to a specific object can be calculated with a simple equation. To test our proposed approach, actual vehicle rollover experiments were conducted and the resulting roof deformations were compared to those indicated by our system. Moreover, cross-sectional image of Apillar was analyzed to calculate bending moment of inertia. From the research results, it was able to show that deformation errors were within 13 mm, and roof deformation was correlated with vehicle type, or vehicle curb weight.     

A Report on the State-of-Affairs on “Application of Multibody Computer Codes to Vehicle System Dynamics”

This report gives a preview to a state-of-the-art paper and a special session which are devoted to the problem of the applicability of multibody computer codes to vehicle system dynamics. These activities were initiated at the 11th IAVSD Symposium 1989 in Kingston, CAN, followed by a workshop in Herbertov, CSR, and to be reported at the 12th IAVSD Symposium in Lyon, 1991. The concluding documentation will be a special issue of the VSD journal. The status of this report is what has been achieved up to May 1991.