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861.
S. R. Tolofari 《运输规划与技术》2013,36(3-4):239-254
The pull of economic gravity on traditional tanker operators towards open registries has been caused primarily by the need to be cost‐competitive in a market which itself is competitive. By using transcendental logarithmic cost functions to model the cost structures of open and traditional tanker operations, this study highlights the general structure of the production technology of tanker services, the cost differentials between the two flag groupings and provides insights into the comparative statics effects of their production functions in the form of elasticities of factor substitution and demand, and scale economies. 相似文献
862.
This paper presents the development and assessment of models to estimate pedestrian demand based on the level of pedestrian activity (high and low). As activity varies by the time of the day, temporal variations were evaluated by considering different time periods. Data collected at 128 low and 48 high pedestrian activity signalized intersections (a total of 176 signalized intersections) in the City of Charlotte, North Carolina were used to develop and assess the models using stepwise regression analysis through backward elimination of independent variables (includes demographic, land use, and network characteristics). The use of different buffer widths (proximal area) to extract these characteristics was also evaluated. Results, in general, show that pedestrian demand varied by the level of activity, explanatory variables extracted by buffer width, and time of the day. The estimates from the models could be used in transportation planning (identify required pedestrian facilities, resource allocation), safety, and operational analyses. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
863.
R. L. Mackett 《运输规划与技术》2013,36(4):233-247
In this paper, the application of a model representing the impact of interaction between transport costs and the location of housing, population, job employment, shopping and land is described. Two particular uses of the model are considered. Firstly, the effects of changing transport costs upon people of different social status in terms of money and time spent on travelling are examined and compared with results based upon the assumption that the location of population and employment are not responsive to changes in transport cost, as in the conventional transport demand model. Secondly, the effects of six land use‐transport policy sets are examined in terms of the impact upon urban morphology, and the opportunities and travel behaviour of the three social groups. The effects are also compared with the objectives of the strategies. 相似文献
864.
On the use of the autocorrelation function to identify the damage in the side shell of a ship's hull 总被引:6,自引:0,他引:6
When structural damage occurs, the dynamic characteristics of the structure changes correspondingly. This can be used to detect damage occurrence. In this paper, an autocorrelation function was utilized to identify damage in the side shell of ship structures using a combination of experimental and numerical studies. A stiffened plate was used to model the side shell of a ship structure. The damage was simulated by a cut in the longitudinal near the transverse member. The cut was made using a hacksaw. An experimental study using modal testing methods was carried out to measure the random response time history of the undamaged and damaged stiffened plate model. The random response time history was used to obtain its autocorrelation function and its random decrement signature. The autocorrelation function was then compared with the random decrement signature. Finite element models were developed for the stiffened plate, in the undamaged and damaged conditions. The random responses of the model were used to obtain the autocorrelation functions. The autocorrelation functions obtained numerically were compared to the ones obtained experimentally. The results indicate that the autocorrelation functions can be used to identify the occurrence of damage in the stiffened plate model. 相似文献
865.
[目的]针对计入螺旋桨水动力的舰船轴系校中计算,传统方法通常容易忽略船体伴流场的影响,使得螺旋桨水动力计算的结果与真实值之间存在较大偏差,从而导致轴系校中精度下降。[方法]以某舰船长轴系为对象,建立桨-轴-船一体化有限元模型及其伴流场流域模型,利用CFD数值仿真的叠模方法计算螺旋桨水动力;采用流固耦合法将流体计算结果作用于螺旋桨表面,进行轴系校中计算,并得到螺旋桨水动力对轴系整体挠曲线及各轴承状态参数的影响规律。在此基础上,引入多目标优化算法开展轴系多目标优化校中,来解决轴系末端四套轴承间载荷差值过大的问题。[结果]考虑螺旋桨水动力后,轴系尾部挠度变化减小,越靠近螺旋桨处的轴承其载荷所受影响越大,载荷值随进速系数的增大而减小;对比多目标优化前后的轴系校中状态,轴系各轴承之间的载荷差值明显减小,轴系运行状态得到改善。[结论]所提方法提高了计入螺旋桨水动力的轴系校中计算精度,可为轴系校中质量的提升提供参考。 相似文献
866.
[Objective]This paper aims to suppress the adverse effects of tip clearance flow on the hydrodynamic performance and unsteady excitation force of a pump-jet propulsor. [Method]As for the pre-swirl stator pump-jet propulsor, an annular flexible seal structure closely matched with a rotor tip ring is used to study the validity of suppressing the clearance flow on the rotor tip. The rotor thrust and torque of the propulsor are measured by keeping the shroud approximately rigidly fixed, enabling the rotor open water efficiency to be obtained. In addition, the point of cavitation inception at each design condition is observed and recorded carefully with the help of a high-power stroboscope, and the cavitation inception curves of the propulsor with/without tip clearance are obtained through calculation. Finally, tests of shaft vibration acceleration on the pump-jet propulsor with/without tip clearance are conducted under conditions of cavitation and non-cavitation in order to evaluate the effects of diminishing tip clearance. [Results]The results show that the thrust and torque of the rotor of the pump-jet propulsor with a flexible seal structure are significantly increased, which in turn renders open water efficiency significantly increased at low and medium advance coefficients, unchanged near the design point and slightly decreased at the high advance coefficient. Moreover, the cavitation performance of the pump-jet propulsor without clearance is better at a wide range of advance coefficient, 0.85 相似文献