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821.
平行钢丝拉索Daniel效应分析 总被引:1,自引:0,他引:1
为了研究平行钢丝拉索丹尼尔效应随钢丝数的变化规律,以85Φ5 mm钢丝拉索索力仿真计算为例,采用蒙特卡罗法分析了不同钢丝数目平行钢丝索的丹尼尔效应。应用Matlab软件生成钢丝抗拉强度随机样本,引入矩阵计算简化分析过程。通过回归分析得出拉索丹尼尔效应计算的计算式。研究结果表明,拉索钢丝抗拉强度的平均值、标准差及衰减因子随钢丝数增加而减小,其衰减规律服从多项式分布;当钢丝数在10~50之间时,拉索丹尼尔效应十分显著;当钢丝数在50~100之间时,丹尼尔效应逐渐减弱;当钢丝数大于100以后,随着拉索钢丝数的增加,钢丝的平均抗拉强度衰减缓慢,拉索丹尼尔效应趋于稳定。 相似文献
822.
2005年英国政府宣布建立“交通创新基金”,后来人们才意识到所谓“创新”意味着道路收费,而与改进公共交通系统没有任何关系。2年之后,英国政府面临对轨道交通系统进行巨额投资,而该系统被认为是在大都市地区实施一系列道路收费项目的前提。因此,当前有必要对世界范围内的道路收费政策加以研究,以找出有效的道路收费系统所具有的特征以及能够成功实施应具备的条件。 相似文献
823.
高塔型矮塔斜拉桥初探 总被引:4,自引:1,他引:3
高塔型矮塔斜拉桥不仅保留了矮塔斜拉桥斜拉索的高利用率,同时由于斜拉索水平倾角的增加,提高了斜拉索的竖向荷载分担率。通过模型对索塔高度、索塔刚度和主梁刚度等参数进行了分析,并对高塔型矮塔斜拉桥的界定进行了讨论,最后展望了其发展前景。 相似文献
824.
We estimate the elasticities of fuel and travel demand with respect to fuel prices and income in the case of Norway. Furthermore, we derive the direct rebound effects that explain the degree to which a fuel price increase is “offset” in the form of greater fuel use and/or travel due to improvements in vehicle fuel efficiency. For this purpose, we use and compare two alternative econometric approaches: the error correction model (ECM) and the dynamic model. Our initial assumption is that one should not be indifferent with respect to the approach used to derive elasticities. The data used are for the period 1980–2011. Our results indicate the following: (1) the dynamic model fits the data better than the ECM model does; (2) the estimated elasticities of fuel demand with respect to price and income are −0.26 and 0.06 in the short run and −0.36 and 0.09 in the long run. For travel demand, the respective elasticities are −0.11 and 0.06 in the short run and −0.24 and 0.13 in the long run, implying inelastic demands for fuel and travel demand; and (3) rebound effects indicate that 0.26% and 0.06% of fuel savings as a result of fuel price increase will be offset in the form of more fuel use in the short run and in the long run, respectively, if fuel efficiency increases by 1%. Our policy recommendations are that policies should not be indifferent to the methods used to derive elasticities. We contend that it is crucial to seriously consider rebound effects in policy making because basic elasticity estimates exaggerate the impact of fuel price increases. 相似文献
825.
Major technological and infrastructural changes over the next decades, such as the introduction of autonomous vehicles, implementation of mileage-based fees, carsharing and ridesharing are expected to have a profound impact on lifestyles and travel behavior. Current travel demand models are unable to predict long-range trends in travel behavior as they do not entail a mechanism that projects membership and market share of new modes of transport (Uber, Lyft, etc.). We propose integrating discrete choice and technology adoption models to address the aforementioned issue. In order to do so, we build on the formulation of discrete mixture models and specifically Latent Class Choice Models (LCCMs), which were integrated with a network effect model. The network effect model quantifies the impact of the spatial/network effect of the new technology on the utility of adoption. We adopted a confirmatory approach to estimating our dynamic LCCM based on findings from the technology diffusion literature that focus on defining two distinct types of adopters: innovator/early adopters and imitators. LCCMs allow for heterogeneity in the utility of adoption for the various market segments i.e. innovators/early adopters, imitators and non-adopters. We make use of revealed preference (RP) time series data from a one-way carsharing system in a major city in the United States to estimate model parameters. The data entails a complete set of member enrollment for the carsharing service for a time period of 2.5 years after being launched. Consistent with the technology diffusion literature, our model identifies three latent classes whose utility of adoption have a well-defined set of preferences that are significant and behaviorally consistent. The technology adoption model predicts the probability that a certain individual will adopt the service at a certain time period, and is explained by social influences, network effect, socio-demographics and level-of-service attributes. Finally, the model was calibrated and then used to forecast adoption of the carsharing system for potential investment strategy scenarios. A couple of takeaways from the adoption forecasts were: (1) placing a new station/pod for the carsharing system outside a major technology firm induces the highest expected increase in the monthly number of adopters; and (2) no significant difference in the expected number of monthly adopters for the downtown region will exist between having a station or on-street parking. 相似文献
826.
为了保证大型船舶安全、经济地靠离码头,驾引人员应当对所需拖船协助力心中有数。国内外研究人员已在理论和实验方面做了大量的工作,但实用的计算方法仍不多见,且存在着一些问题。提高大型船舶横向靠离码头所需拖船协助力估算精度的关键是横流阻力系数C(wy)的估算。该文根据12条船模试验数据用逐步回归分析法获得了可以表达C(wy)与船型及水深之间关系的近似公式;同时依据大型船舶横向离码头实际是加减速运动这一事实,考虑了加速运动对C(wy)系数的影响;此外还分析了岸壁对船舶横向运动的影响。该文所提供的计算方法是实用和可靠的,可供船舶驾引人员使用,亦可供船舶操纵运动数学模型研究人员参考。 相似文献
827.
胡汉南 《交通部上海船舶运输科学研究所学报》1995,18(1):1-8
探讨影响导航雷达方位分辨力的3个理论因素:Fresnel区波束展宽、端馈阵列天线瞬变效应和激励脉冲波形较差引起波束展宽。指出在下述3种情况下方位分辨力会显著恶化:稳态Fresnel区R〈0.5L^2/λ、瞬态Ta/Ts〉1.1以及激励脉冲波形较差而且Ta/Ts〉1.1。 相似文献
828.
829.
应用具有短暂快速降压作用的ATP及具有α-肾上腺素受体阻滞作用的氟哌啶来抑制气管插管所引起的心血管反应,并进行临床观察及对照研究。结果表明:ATP对气管插管所致的血压升高有很好的抑制作用。 相似文献
830.
The hydrodynamic forces acting on a circular cylinder and a rectangular cylinder undergoing slow drift oscillation in regular
waves were investigated experimentally and numerically. Forced oscillation tests with low frequency and large amplitude in
regular waves and forced two-harmonic oscillation with combined low and high frequencies were carried out in the experimental
study. In the numerical study a finite-difference method was used to simulate viscous flow around a two-dimensional oscillating
cylinder. The results of experiments showed that a horizontal rectangular cylinder oscillating slowly in waves has much higher
damping coefficients than one oscillating in two-harmonic mode, while the numerical study indicated that such differences
in the damping coefficient arise partly from the different effects of one-direction harmonic flow and rotating flow on the
vortex shedding caused by the slow drift oscillation. 相似文献