计及移相角的多边形自耦变压器12脉波整流系统分析

多边形自耦变压器一定程度上减小了整流系统的体积,节约了变压器制造成本。为使多边形自耦变压器输出较大的二次侧电压值,优化多边形自耦变压器移相角,分析多边形自耦变压器移相角对12脉波整流系统输入侧电流谐波总畸变率,输出侧电压纹波系数,变压器、平衡电抗器、零序电流抑制器等效容量的影响;对比移相角在π/6、π/2时各个参数的值;提出适用于升压场合的多边形自耦变压器升压移相角;仿真实验验证了理论分析的正确性。同匝比时,多边形自耦变压器采用新移相角其输出电压幅值约为输入电压幅值1.4142倍,等效容量约为62.8%,较传统隔离式变压器等效容量小约37.2%。     

Numerical simulations of fatigue crack initiation and propagation based on re-tensile plastic zone generating load criterion for in-plane gusset welded joints

Many accidents are caused by fatigue in welded built-up steel structures, and so it is important to estimate the fatigue lives of such structures quantitatively for safety reasons. By assuming that fatigue cracks cannot grow without an accumulation of alternating tensile/compressional plastic strain, one of the authors identified an improved effective stress intensity factor range ΔK _RPG based on the re-tensile plastic zone generating (RPG) load, which represents the driving force for fatigue cracks, and suggested that ΔK _RPG should be used as the parameter to describe fatigue crack growth behavior. The “FLARP” numerical simulation code in which ΔK _RPG is implemented as the fatigue crack growth parameter, was developed in order to predict fatigue crack initiation and propagation behavior. In this paper, it is demonstrated that FLARP gives accurate estimates for fatigue life by comparing the estimated fatigue crack growth curves and S–N curves with the experimental results for in-plane gusset welded joints, which are used in many welded steel structures. Moreover, the effect of induced bending moment due to the linear misalignment in the out of plane direction on the fatigue strength of in-plane gusset welded joints is investigated through numerical simulations.     

Shared autonomous electric vehicle (SAEV) operations across the Austin,Texas network with charging infrastructure decisions

Shared autonomous vehicles, or SAVs, have attracted significant public and private interest because of their opportunity to simplify vehicle access, avoid parking costs, reduce fleet size, and, ultimately, save many travelers time and money. One way to extend these benefits is through an electric vehicle (EV) fleet. EVs are especially suited for this heavy usage due to their lower energy costs and reduced maintenance needs. As the price of EV batteries continues to fall, charging facilities become more convenient, and renewable energy sources grow in market share, EVs will become more economically and environmentally competitive with conventionally fueled vehicles. EVs are limited by their distance range and charge times, so these are important factors when considering operations of a large, electric SAV (SAEV) fleet.This study simulated performance characteristics of SAEV fleets serving travelers across the Austin, Texas 6-county region. The simulation works in sync with the agent-based simulator MATSim, with SAEV modeling as a new mode. Charging stations are placed, as needed, to serve all trips requested (under 75 km or 47 miles in length) over 30 days of initial model runs. Simulation of distinctive fleet sizes requiring different charge times and exhibiting different ranges, suggests that the number of station locations depends almost wholly on vehicle range. Reducing charge times does lower fleet response times (to trip requests), but increasing fleet size improves response times the most. Increasing range above 175 km (109 miles) does not appear to improve response times for this region and trips originating in the urban core are served the quickest. Unoccupied travel accounted for 19.6% of SAEV mileage on average, with driving to charging stations accounting for 31.5% of this empty-vehicle mileage. This study found that there appears to be a limit on how much response time can be improved through decreasing charge times or increasing vehicle range.     

Measuring risk aversion to guide transportation policy: Contexts,incentives, and respondents

Road pricing may provide a solution to increasing traffic congestion in metropolitan areas. Route, departure time and travel mode choices depend on risk attitudes as commuters perceive the options as having uncertain effects on travel times. We propose that Experimental Economics methods can deliver data that uses real consequences and where the context can be varied by the researcher. The approach relies on the controlled manipulation of contexts, similar to what is done in the Stated Choice approach, but builds in actual consequences, similar to the Revealed Preference approach. This paper investigates some of the trade-offs between the cost of conducting Experimental Economics studies and the behavioral responses elicited. In particular, we compare responses to traditional lottery choice tasks to the route choice tasks in simulated driving environments. We also compare students (a low cost convenient participant pool) to field participants recruited from the driving population. While we see initial differences across our treatment groups, we find that their risk taking behavior converge with minimal repetition.     

The visual effects of port redevelopment alternatives

Abstract

In the early 1970s, Seattle Piers 90/91 were declared surplus federal property by the GSA. These obsolescent half‐mile‐long piers and their adjacent uplands were purchased by the Port of Seattle for redevelopment. This urban waterfront site of almost 200 acres presents the Port of Seattle with a number of severe planning problems. While it is the last large deep‐water site on Elliott Bay, it is also in a very sensitive location, since it is overlooked on two sides by vocal residential communities with a history of active intervention in development projects on visual and other environmental grounds.

At Piers 90/91, public concerns over the visual effects of port redevelopment include:

1. nuisance effects of night‐operations lighting on adjacent hillside residences;

2. nighttime obstruction of distant views due to increased foreground illumination;

3. day and night view obstruction by tall structures such as container‐handling cranes;

4. alteration of the character of both day and nighttime views by new port facilities.

As part of a program to study the effects of alternative redevelopment strategies for Piers 90/91, the Port has undertaken a through examination of the visual effects of different uses, their visual appropriateness, and the ways by which adverse visual effects can be mitigated. The results were incorporated into an environmental impact statement which documented compliance with the Seattle Shoreline Master Program and with view protection and glare provisions of the City's S.E.P.A. guidelines.

A systematic Visual Resource Management (VRM) approach was successfully employed on this coastal zone project. Major elements included visibility mapping, key view selection, analysis of existing visual character, simulation of alternatives, assessment of relative visual compatibility, and determination of effective mitigation measures. Community involvement has also been a critical element in this approach to assessing and managing the visual effects of redevelopment in a major urban port.     

The effect of spring pads in the secondary suspension of railway vehicles on bogie yaw resistance

This paper deals with properties of bogie yaw resistance of an electric locomotive with secondary suspension consisting of flexi-coil springs supplemented with tilting spring pads. Transversal stiffness of a sample of a spring/pad assembly was measured on a dynamic test stand of the University of Pardubice (Czech Republic) and the results were applied into a multi-body model of the locomotive created in the simulation tool ‘SJKV’. On the basis of the simulation results, a detailed analysis of the bogie yaw resistance was performed in order to explain the effect in dynamic behaviour of the locomotive when the moment against bogie rotation (and therefore the distribution of guiding forces on individual wheels, as well) is influenced with the vehicle speed in a certain curve. Results of this analysis show that the application of suspension elements with strongly directionally dependent transversal stiffness into the secondary suspension can just lead to a dependency of the bogie yaw resistance on cant deficiency, i.e. on the vehicle speed in curve. This fact has wide consequences on the vehicle dynamics (especially on the guiding behaviour of the vehicle in curves) and it also points out that the current method of evaluation of the bogie yaw resistance according to relevant standards, which is related with assessment of the quasistatic safety of a railway vehicle against derailment, is not objective enough.     

Splash zone lowering analysis of a large subsea spool piece

Lifting operation though the wave splash zone is challenging. Careful numerical analysis in the design phase is needed to minimize associated risks. This study addresses numerical modeling and analysis of the splash zone lowering of a large subsea spool. A typical offshore construction vessel is used for the operation. The objective is to compare the effects from different numerical methods and parameters on the allowable sea states and the operability. These methods and parameters include wave short-crestedness, shielding effects from the vessel, wave direction and wave seed number. A coupled numerical model of the spool-vessel system is established in SIMO program, which is a simulation tool for marine operations. Slamming and submergence-dependent loads on the spool during the transient lowering process are calculated. A large number of time-domain simulations has been performed to derive the allowable sea states. The operational criteria for assessment of the sea states include slack sling, snap loads in wires and clearance between spool and the vessel. Operability analysis of the operation at one reference site in the Barent Sea is established using 50-year hindcast data. The influences from different methods on the allowable sea states and the operability are compared and discussed in detail.     

Improving crosswind stability of fast rail vehicles using active secondary suspension

Rail vehicles are today increasingly equipped with active suspension systems for ride comfort purposes. In this paper, it is studied whether these often powerful systems also can be used to improve crosswind stability. A fast rail vehicle equipped with active secondary suspension for ride comfort purposes is exposed to crosswind loads during curve negotiation. For high crosswind loads, the active secondary suspension is used to reduce the impact of crosswind on the vehicle. The control input is taken from the primary vertical suspension deflection. Three different control cases are studied and compared with the only comfort-oriented active secondary suspension and a passive secondary suspension. The application of active secondary suspension resulted in significantly improved crosswind stability.     

船舶电力推进系统仿真及特性实验

讨论船舶电力推进系统仿真的设计思路,并阐述仿真系统的硬件设计及方案的确定过程.搭建好硬件平台,在实验室对船舶电力推进系统中4个典型特性过程进行了仿真,对结果做出了相应的分析.