半潜驳改造为坐底式风电安装船的设计及应用研究

为解决现有海上风电安装设备的不足,将原“三航工5”半潜驳改造为坐底式风电安装船,并研制了一套船体结构应力监测系统,对国内某海上风场砂性地质条件引起的冲刷和船底掏空进行监控,实际工程应用表明改造后的船舶在安全性和工效上满足坐底安装风机的要求。     

The regulatory cycle stalled? An assessment of current institutional obstacles to regulatory reform in the provision of road-based public transport in Cape Town, South Africa

Wide-ranging and ambitious proposals for the comprehensive transformation of public transport systems in major South African cities, including Cape Town, have now been in play for a decade or more since the country’s post-apartheid transition. To date, progress in implementing such proposals has been, at best, much delayed and, in Cape Town, appears to have stalled, and may now be significantly compromised. This paper draws on aspects of the concept of regulatory cycles in the bus transport sector to explore some of the key factors which have given rise to this situation, focusing primarily on obstacles embedded in the present institutional framework which governs the provision of road-based public transport in the city. It specifically identifies difficulties in establishing an appropriately mandated and resourced agency at the local level to drive forward the transformation project and the sustained opposition of existing, largely ‘self-regulated’ minibus-taxi operators as key factors which have obstructed the introduction of the proposed regime of ‘regulated competition’. A tentative conclusion is offered to the effect that perhaps a partial or ‘hybrid’ transformation of the public transport system may be the best - and, indeed, possibly the most appropriate - outcome of the transformation process that can be anticipated under the present and foreseeable future circumstances prevailing in the city.     

Cash flow sensitivities during normal and crisis times: Evidence from shipping

Using a system of equations model, we analyze how cash flow shocks influence the investment and financing decisions of shipping firms in different economic environments. Even financially healthy shipping firms felt strong negative effects on their financing activities during the recent crisis. These firms were nevertheless able to increase long-term debt. Banks internalized the impact of foreclosure decisions on vessel prices and avoided an industry-wide collateral channel effect. Even during benign economic conditions, financially weak shipping firms underinvest because of their inability to raise sufficient external capital. The substitution between long- and short-term debt during the pre-2008 crisis periods shows that the composition of financing sources is more indicative of whether firms face financial constraints than the pure size of the financing-cash flow sensitivities. An analysis of firms’ excess cash holdings confirms the importance of financial flexibility.     

How flexible is flexible? Accounting for the effect of rescheduling possibilities in choice of departure time for work trips

In departure time studies it is crucial to ascertain whether or not individuals are flexible in their choices. Previous studies have found that individuals with flexible work times have a lower value of time for late arrivals. Flexibility is usually measured in terms of flexible work start time or in terms of constraints in arrival time at work. Although used for the same purpose, these two questions can convey different types of information. Moreover, constraints in departure time are often related not only to the main work activity, but to all daily activities. The objective of this paper is to investigate the effect of constraints in work and in other daily trips/activities on the willingness to shift departure time and the willingness to pay for reducing travel time and travel delay. We set up a survey to collect detailed data on the full 24-hour out-of-home activities and on the constraints for each of these activities. We then built a stated preference experiment to infer preferences on departure time choice, and estimated a mixed logit model, based on the scheduling model, to account for the effects of daily activity schedules and their constraints. Our results show that measuring flexibility in terms of work start time or constraints at work does not provide exactly the same information. Since one-third of the workers with flexible working hours in the survey indicated that they have restrictions on late work-arrival times, their willingness to pay will be overestimated (almost doubled) if flexibility information is asked only in terms of fixed/flexible working hours. This clearly leads to different conclusion in terms of demand sensitivity to reschedule to a later departure time. We also found that having other activities and constraints during the day increases the individuals’ willingness to pay to avoid being late at work, where the presence of constraints on daily activities other than work is particularly relevant for individuals with no constraints at work. The important impact of these findings is that if we neglect the presence of constraints, as is common practise in transport models, it will generally lead to biased value-of-time estimates. Results clearly show that the shift in the departure time, especially towards a late departure time, is strongly overestimated (the predicted shift is more than double) when the effect of non-work activities and their constraints is not accounted for.     

Optimal road design through ecologically sensitive areas considering animal migration dynamics

With increasing land transportation requirements in both urban and rural areas, roads are encroaching ever more on animal habitats, where collisions with vehicles are a leading contributor to wildlife mortality. While road designers recognise the importance of accounting for such impacts at the design level, existing approaches simply either ignore viable habitat or avoid such regions entirely. Respectively, this can result in road alignments that are overly damaging to vulnerable species or prohibitively expensive to build and operate. The research presented in this paper investigates the effects of explicitly accounting for animal mortality on the design of a road through an ecologically sensitive area. The model presented achieves this by incorporating a spatially-explicit animal migration and road mortality model into an accepted optimal road alignment algorithm to propose low-cost roads that maintain the animal population above a minimum threshold by the end of a specified design horizon. The new method was applied to an example scenario to demonstrate the effect of setting a minimum required animal population on the road design. This model was able to consistently produce a road that met a minimum required species conservation benefit. This reflected a major improvement over the model that ignored animal habitats while only requiring a minor increase in construction and operating costs compared to the model that avoids habitat.     

变压器漏抗取代并联整流器平衡电抗器的分析

在分析了变压器漏抗对多脉波整流器影响的基础上，提出利用变压器漏抗取代平衡电抗器的设计思想，从而消除了平衡电抗器所带来的负面影响。这一思想在广州地铁2号线的二十四脉波整流器中的理论分析中得以实现。     

The Application of Ridge Regression in Dynamic Balancing of Flexible Rotors Based on Influence Coefficient Method

Introduction The influence coefficient method applied in thedynamic balancing of rotors is based on the experi-ence that the rotor's vibration amplitude is propor-tional to the unbalancing masses of the rotor with-in the range of practical interest under the assump-tion of linearity of both the machine and measuringsystem.According to the influence coefficient con-ception in mechanics,the influence coefficient ismeasured at a specific location,unite trial weightplaced in some known position in…     

塔梁间纵向弹性约束对斜拉桥抗震性能的影响

目前漂浮、半漂浮体系斜拉桥是广泛采用的的斜拉桥体系。在地震荷载作用下这两种体系的内力反应比较小,而位移反应比较大,常常不能满足要求。对塔梁间纵向弹性约束对斜拉桥抗震性能的影响进行了理论分析和实例计算。计算结果表明它能显著的减小漂浮、半漂浮体系斜拉桥在地震作用下的位移反应,又能使内力反应满足抗震要求,因此它不失为一种有效的改善漂浮、半漂浮体系斜拉桥抗震性能的手段。