电动汽车驱动控制的PWM新技术

文章介绍了电动汽车交流驱动中采用确定脉宽调制(DPWM)技术和随机脉宽调制(RPWM)技术的比较研究结果.RPWM方法替代DPWM方法,采用Avant!公司先进的仿真软件SABER,其重点是降低电磁干扰(EMI).为了评估PWM技术对驱动性能的影响,同时对驱动效率,转矩脉动和电流控制系统动态响应进行了研究.文中考虑了逆变器开关频率随机变化定义的2种RPWM技术:一种技术是调制器的取样频率与开关频率同步变化;另一种技术是取样频率固定且等于平均开关频率.研究表明:在驱动性能几乎不受影响的同时,RPWM技术降低EMI的良好潜力,可使EMI下降10dB或更多.     

Fuzzy expert system for controlling swamp terrain intelligent air-cushion tracked vehicle

A fuzzy expert system was used in this study to control an intelligent air-cushion tracked vehicle (IACTV) as it operated in a swamp peat terrain. The system was effective in controlling the intelligent air-cushion vehicle while measuring the vehicle traction (TE), motion resistance (MR), power consumption (PC), cushion clearance height (CCH) and cushion pressure (CP). An ultrasonic displacement sensor, pull-in solenoid electromagnetic switch, pressure-control sensor, microcontroller, and battery pH sensor were incorporated into the fuzzy expert system (FES) to experimentally determine the TE, MR, PC, CCH, and CP. In this study, we provide an illustration of how an FES might play an important role in the prediction of the power consumption of the vehicle’s intelligent air-cushion system. The mean relative error in the actual and predicted values from the FES model with respect to tractive effort, total motion resistance and total power consumption were found to be 5.58 %, 6.78 % and 10.63 %, respectively. For all parameters, the relative error in the predicted values was found to be less than the acceptable limit (10%), except for the total power consumption. Furthermore, the goodness of fit of the predicted values was found to be close to 1.0 as expected and, hence, indicates the good performance of the developed system.     

Power Spectral Density of Road Profiles

The road profile is usually considered to be a random process x ( d ), where x is the road height and d is the distance along the road. As the vehicle travels along the road with velocity v , the random process x ( d ) is converted to a random process x ( t ) which is input to the vehicle suspension via the tyre. The random process x ( d ) is usually described in terms of its power spectral density as a function of frequency in either radians or cycles per unit distance. However, there are several different ways of defining power spectral density, and this makes it difficult to compare published data without knowing how the power spectral density has been defined. The proper calculation of RMS values of vehicle response for an assumed road power spectral density is explained by an example.     

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.     

A review of the European Union shipping policy

It is the aim of the European Union to develop a transport policy that supports its economic and sustainable growth and where the concept of sustainable mobility is a driver in the development of such policy. To achieve this goal, the European Union (EU) is promoting the shift of goods to unused existing capacity in rail and sea modes. As such, it is the objective of this paper to carry out a review of the European shipping policy at a time when the EU Member-States are suffering from high levels of congestion, noise and pollution that not only affect the environment but also the quality of life of all citizens. This paper considers the development of EU shipping policy in three stages.     

Late-Quaternary changes in productivity of the Southern Ocean

Paleoceanographic records based on new proxies of export production have been constructed for the South Atlantic sector of the Southern Ocean. A radionuclide-ratio proxy of particle flux (¹⁰Be/²³⁰Th) and the accumulation rate of authigenic uranium, which responds to the flux of organic carbon to the sea bed, both indicate a dramatic increase, compared to the present, in the export production of the Subantarctic zone (approximately the region between the present-day positions of the Subtropical Convergence and the Antarctic Polar Front) during glacial periods. If the South Atlantic is representative of the entire Southern Ocean, then export production in the Southern Ocean during the Last Glacial Maximum was substantially greater than at present. Previous studies, focusing on the burial of biogenic opal, failed to recognize the glacial increase in export production of the Southern Ocean because of a strong non-linearity between accumulation rates of opal and of organic carbon.     

Siliceous plankton dominate primary and new productivity during the onset of El Niño conditions in the Santa Barbara Basin, California

The potential for carbon export and the role of siliceous plankton in the cycling of C and N was assessed in natural plankton assemblages in the Santa Barbara Basin, California, by examining uptake rates of inorganic carbon, nitrate and silicic acid. In April–August 1997, the concentrations of chlorophyll a, particulate organic carbon, particulate organic nitrogen and biogenic silica were measured twice monthly, and results revealed the occurrence of at least three blooms, the largest in June. Particulate elemental ratios of C, N and Si were similar to ratios of nutrient-replete diatoms, suggesting that they dominated this bloom. Mean integrated rates of carbon, nitrate and silicon uptake during the 4-month study period are similar to other productive coastal and upwelling regions (103, 8.3 and 13 mmol m⁻² day⁻¹, respectively). New production rates were twice as high as previously reported in this region and indicate that high rates of new production along eastern boundary currents are not confined to the major coastal upwelling regions. C/NO₃⁻, Si/NO₃⁻ and Si/C uptake ratios varied widely, and mean integrated ratios were 14±5.4, 1.6±1.0 and 0.12±0.07 (S.D.), respectively. That mean C/NO₃⁻ uptake ratio corresponds to an f-ratio of about 0.5 indicating a large potential for particulate export. Based on the average Si/NO₃⁻ and Si/C uptake ratios, diatoms could perform all of the primary production and nitrate uptake that occurred during the study; these rates also suggest that export is controlled by diatoms in this system. The mean Si/C biomass ratio was lower than the mean Si/C uptake ratio, consistent with the preferential export of Si relative to C observed in sediment traps in the basin. The study took place during a period of surface-water warming, with nitrate and silicic acid concentrations decreasing throughout the onset of the 1997–1998 El Niño conditions. Although diatoms contributed less to particulate biomass during the low nutrient conditions, high f-ratios (0.33–0.66) were maintained.     

关于提升上海港集装箱码头竞争能力的调研与建议

在上海腹地经济飞速发展的背景下,上海港要建成国际航运中心和腹地型集装箱枢纽港,将面临前所未有的大好机遇,也面临着国内港口以及东亚等港口之间的激烈竞争。本文就如何合理布局上海港集装箱运输结构;如何构建上海港各集装箱码头之间的沟通桥梁;如何整合上海港现有集装箱码头的综合竞争力,充分发挥上海港整体的优势等上述问题作初步探讨。     

The onset of biological winter in the eastern Weddell Gyre (Antarctica) planktonic community

Data on hydrography, phyto- and zooplankton, obtained on a transect along the 0° meridian during the Winter Weddell Gyre Study, June 1992, revealed peculiarities of the early winter situation in the eastern Weddell Gyre. The vertical distribution and developmental stage composition of Rhincalanus gigas, Calanoides acutus, Calanus propinquus and krill, Euphausia superba larvae, were a good index for a general assessment of the seasonal condition of the plankton communities. There were five zones differing in seasonal situation: (1) The Polar Front and the southern ACC (not studied in detail), (2) The Weddell Front, (3) The Weddell Gyre interior, (4) The Maud Rise area, and (5) The Coastal Current zone. In the Weddell Front, the planktonic community resembled an autumnal situation with moderate phytoplankton biomass; the overwintering stock of copepods was not completely formed and the occurrence of calyptopes larvae of E. superba indicated that krill continued to reproduce until May. In the Weddell Gyre interior, a typical winter plankton community was found even before sea ice had formed. The specific hydrographic regime of the Maud Rise (governed by the mesoscale circulation over the seamount) support the late autumn conditions similar to the Weddell Front (but without early krill larvae). The plankton of the Coastal Current was a winter community. We conclude that in the eastern part of the Weddell Front (compared to the western part) seasonal development of both phytoplankton and herbivorous zooplankton is delayed in spring but prolonged in late autumn. Furthermore, it appears that the Weddell Sea ecosystem exhibits a much higher degree of spatial and temporal variability than thought before. This may have an impact on seasonal pattern of organic carbon transport from the pelagic realm to deeper water layers and to the sediment.