Torque ripple minimization control of permanent magnet synchronous motors for EPS applications

This paper identifies a control method used to reduce torque ripple of a permanent magnet synchronous motor (PMSM) for an electric power steering (EPS) system. NVH (Noise Vibration Harshness) is important for safe and convenient driving. Vibration caused by motor torque is a problem in column type EPS systems. Maintaining a very low torque ripple is one solution that allows for smoother steering. Theoretically, it is possible to design and drive the motor without torque ripple. However, in reality, a PMSM system torque ripple is caused by the motor itself (saturation in the iron core and EMF distortion) and the imperfect driver. This paper analyzes torque ripple of a PMSM system, and an advanced PMSM control method for the column typed EPS system is presented. Results of the analysis indicate that the compensation current is needed in order to minimize torque ripple when a PMSM is driven.     

Comparative analysis on dynamic behavior of two HMA railway substructures

A numerical analysis using a finite element program was performed on three structures:hot mix asphalt(HMA) reinforced trackbed(RACS-1),HMA directly supported trackbed(RACS-2),and traditional Portland Cement Concrete(PCC) slab track(SlabTrack).Although the comprehensive dynamic responses of RACS-1 were similar with SlabTrack,HMA layer can positively affect the stress distributions.In particular,the horizontal stresses indicate that the resilience of RACS-1 was improved relative to SlabTrack.In addition,HMA r...     

Assessment of IACS-CSR implicit safety levels for buckling strength of stiffened panels for double hull tankers

The present study aims at applying structural reliability methods to assess the implicit safety levels of the buckling strength requirements for longitudinal stiffened panels implemented in the IACS Common Structural Rules (CSR) for double hull oil tankers. The buckling strength requirements considered are used in the initial stage of the hull girder scantlings’ design to control the buckling capacity of longitudinal stiffened panels subjected to the compressive loads induced by the hull girder vertical bending. The following buckling collapse failure modes are explicitly considered in the design formulation: uniaxial buckling of the plating between stiffeners, column buckling of stiffeners with attached plating and lateral-torsional buckling or tripping of stiffeners.The paper presents the procedure used to assess the implicit safety levels of the strength requirements for the three buckling collapse failure modes above mentioned, which includes the optimization of the scantlings of the plate panels and longitudinal stiffeners in order to reflect the minimum strength required by the formulation. A first order reliability formulation is adopted, and stochastic models proposed in the literature are used to quantify the uncertainty in the relevant design variables. A sample of five oil tankers representative of the range of application of the IACS-CSR design rules is considered. The effect of corrosion in the implicit safety levels is quantified based on the three corrosion levels of the Net Thickness Approach (NTA) adopted in the design rules. Sensitivity analyses are also performed to quantify the relative contribution or importance of each design random variable to the implicit safety levels.     

A time-use investigation of shopping participation in three Canadian cities: is there evidence of social exclusion?

Increasing awareness and concern about the status of mobility-disadvantaged groups in society has given rise to a wide body of research that focuses on the social exclusion dimension of transportation. To date, much of the empirical work on this topic is mainly spatial in nature despite recent developments that call for the inclusion of time use analyses in social exclusion research. In this paper we attempt to fill this gap by estimating activity and trip durations to determine whether poverty, old age, or being a single parent results in time use patterns indicative of exclusion. Given the importance of shopping and using services for social inclusion objectives, these activities are the focus of this investigation. In terms of methods, use of a multiple equation approach allows for the estimation of the daily duration of shopping activities and trips while simultaneously controlling for daily durations of four broad categories of activities as well as their associated travel times. The results indicate: that being a senior citizen increases travel durations while decreasing shopping activity durations; that coming from a low income household decreases shopping activity durations; and single-parent status does not impact shopping activity durations when holding income and other activity durations constant. These results highlight the feasibility and challenges of time-use and activity analysis in social exclusion research.     

Optimal allocation of turns to lanes at an isolated signal-controlled junction

Conventional design methods require the lane marking patterns, which are painted on ground showing road users the permissible turning directions on different approach lanes, as exogenous inputs to define the traffic stream grouping for analysis. This predefined grouping of traffic movements may restrict the design of signal timings in the optimisation procedures. More recently, a lane-based design method has been developed to relax the lane markings as binary-type control variables in a mathematical programming approach. The lane marking patterns and the signal timings can then be optimised simultaneously in a unified framework. This paper presents an extension work to further relax the numbers of approach lane in traffic arms as new integer variables which can then be optimised to give optimal lane arrangement in various arms of a junction to manage the given traffic demands more efficiently. All well-defined signal timings variables in the phase-based approach as well as the lane marking and lane flow variables in the lane-based approach together with their governing constraints are all preserved in the new formulation for the reserve capacity optimisation of isolated signal-controlled junctions.     

Wind-triggered events of phytoplankton downward flux in the Northeast Water Polynya

Phytoplankton carbon fluxes were studied in the Northeast Water (NEW) Polynya, off the eastern coast of Greenland (79° to 81°N, 6° to 17°W), during summer 1993. The downward flux of organic particles was determined during 54 days using a sediment trap moored at a fixed location, below the pycnocline (130 m). The hypothesis of the present study is that wind events were ultimately responsible for the events of diatoms downward flux recorded in the trap.Wind conditions can influence the vertical transport of phytoplankton by affecting (1) the environmental conditions (e.g. hydrostatic pressure, nutrient concentrations, and irradiance) encountered by phytoplankton during their vertical excursion, and (2) the aggregation and disaggregation of phytoplankton flocs. The first mechanism affects the physiological regulation of buoyancy, whereas the second one affects the size and shape of settling particles.Using field data (wind velocity, density profiles and phytoplankton abundance), we assessed the potential aggregation and the vertical excursion of phytoplankton in surface waters. The results show that, upstream from the trap, wind and hydrodynamic conditions were sometimes favourable to the downward export of phytoplankton. Lag-correlation between time series of wind and phytoplankton downward flux shows that flux events lagged wind events by ca. 16 days. Given that the average current velocity in the top 100 m was ca. 10 cm s⁻¹, a lag of 16 days corresponded to a lateral transport of ca. 130 km, upstream from the sediment trap, where phytoplankton production was lower than at the location of the trap. According to that scenario, 21% to 60% of primary production was exported to depth during wind events. If we had assumed instead a tight spatial coupling between the material collected in the trap and the relatively high phytoplankton production at the location of the trap, we would have concluded that <7% of primary production was exported to depth. The difference between the two scenarios has great implications for the fate of phytoplankton. Our results stress the importance of investigating the spatial coupling between surface and trap data before assessing the pathways of phytoplankton carbon cycling.     

Al2O3陶瓷／Cu界面晶体位向关系对断裂性能的影响

以单晶α－Ａｌ２Ｏ３陶瓷和单晶Ｃｕ为母材,采用真空扩散焊接获得具有两种不同的界面晶体位向关系的Ｃｕ／Ａｌ２Ｏ３扩散焊接头以及带Ｎｂ膜中间层的Ｃｕ／Ｎｂ／Ａｌ２Ｏ３扩散焊接头,研究了面晶体位向关系对接头断裂能量的影响。     

Potential last-mile impacts of crowdshipping services: a simulation-based evaluation

Transportation - Crowdsourced delivery services (crowdshipping) represent a shipping alternative to traditional delivery systems, particularly suitable for e-commerce. Although some benefits in...