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981.
Abhra Roy Chowdhury Wang Xue Manasa Ranjan Behera S. K. Panda 《Journal of Marine Science and Technology》2016,21(1):102-114
This paper investigates the hydrodynamic characteristics of the rectilinear motion of a robotic fish underwater vehicle. This 2-joint, 3-link multibody vehicle model is biologically inspired by a body caudal fin carangiform fish propulsion mechanism. Navier–Stokes equations are used to compute the unsteady flow fields generated due to the interaction between the vehicle and the surrounding incompressible and Newtonian fluid (water) environment. The NACA 0014 airfoil aerodynamic profile has been designed to boost the swimming efficiency by reducing drag as the vehicle undergoes an undulatory/oscillatory motion. Using the Lighthill slender body model, a traveling wave mathematical function is defined to undulate the robotic fish posterior (caudal) region while the motion tracking is carried out by dynamic meshing technique. The results obtained show that though the net lift force approaches to zero, the net thrust or negative drag coefficient maintains a finite value dependent on kinematic parameters like tail beat frequency (TBF) and amplitude span (AS) at a given propulsive wavelength and the forward velocity of the vehicle. The results reveal the effects of TBF and AS on the coefficient of drag friction and the thrust force. Drag coefficients obtained from the simulations are compared and validated with the experimental results. The hydrodynamic results are found to be similar to the kinematic study results and suggest that TBF and AS play the most effective roles in the bioinspired propulsion technique. Relation of these parameters with propelling thrust force and forward velocity is also in conjunction over a given range of TBF and AS values. 相似文献
982.
This study examines the hydrodynamic performance of multiple-row vertical slotted breakwaters. We developed a mathematical model based on an eigenfunction expansion method and a least squares technique for Stokes second-order waves. The numerical results obtained for limiting cases of double-row and triple-row walls are in good agreement with results of previous studies and experimental results. Comparisons with experimental measurements of the reflection, transmission, and dissipation coefficients (C R , C T , and C E ) for double-row walls show that the proposed mathematical model adequately reproduces most of the important features. We found that for double-row walls, the C R increases with increasing wave number, kd, and with a decreasing permeable wall part, dm. The C T follows the opposite trend. The C E slowly increases with an increasing kd for lower kd values, reaches a maximum, and then decreases again. In addition, an increasing porosity of dm would significantly decrease the C R , while increasing the C T . At lower values of kd, a decreasing porosity increases the C E , but for high values of kd, a decreasing porosity reduces the C E . The numerical results indicate that, for triple-row walls, the effect of the arrangement of the chamber widths on hydrodynamic characteristics is not significant, except when kd<0.5. Double-row slotted breakwaters may exhibit a good wave-absorbing performance at kd>0.5, where by the horizontal wave force may be smaller than that of a single wall. On the other hand, the difference between double-row and triple-row vertical slotted breakwaters is marginal. 相似文献
983.
Although panels offer significant advantages over cross sectional data especially in terms of evaluating the effects of significant
policy changes, there are precious few examples of panels built around an important change to an urban transport system. For
this reason we took the opportunity of the introduction of Transantiago, a radically new public transport system for Santiago
de Chile in February 2007, to form a panel, the first wave of which was taken in December 2006. The final objective was to
use this Santiago Panel to estimate mode choice models considering both inertia and policy effects. This document describes both the design and construction
of the panel, and presents some results based on an analysis of its four waves; for example, we registered a high percentage
of mode change (55.1%) attributable to the introduction of the new system. The panel can claim the highest response rate (or
lowest attrition) reported in the literature (95% in the second wave, 92% in the third one, and 85% in the forth one). This
hints at the possibility of developing sophisticated models to evaluate the effects of a system shock in the presence of inertia
in decision making. 相似文献
984.
This work presents a methodology to evaluate the level of service (LOS) of an airport baggage claim. A psychometric scaling technique is employed to obtain quantitative data from qualitative data (user responses as a function of five rating categories). Regression analysis is applied to obtain a statistically valid relationship between user responses and observed operational indicators. The proposed model is developed from a case study of the West Jet baggage claim area at the Calgary International Airport – Canada, where 62 passengers have been observed and interviewed. The collected data allowed the proposal of standards, which indicate tolerable limits as a function of various LOS ranges (A–E). The results are useful for managers and designers on assessing the LOS offered in a terminal, but also during the planning and design stages of an airport. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
985.
S. R. Seyedalizadeh Ganji A. Babazadeh N. Arabshahi 《Journal of Marine Science and Technology》2010,15(4):408-416
The optimal usage of berths plays a key role in raising the efficiency of container terminals. The berth allocation problem
in a container terminal is defined as the feasible allocation of berths to incoming ships such that the total time that elapses
between the arrival of the ships to their exit from their berths is minimized. In the transportation literature, the latter
problem is usually formulated as a mixed integer programming model. Optimization methods, like the branch and bound algorithm,
are efficient ways to solve this model but become absolutely unusable when the size of the problem increases. An advanced
search method such as GA may be suited to such a situation. In this paper, a genetic-based algorithm is proposed for the problem.
Computational results for two test problems (a small and a large-sized problem) are also presented. The results from the small
test are also compared with the results obtained from the branch and bound algorithm. 相似文献
986.
The objective of this study was to estimate the strength and deformability of corroded steel plates under quasi-static uniaxial
tension. In order to accurately simulate this problem, we first estimated the true stress–strain relationship of a flat steel
plate by introducing a vision sensor system to the deformation measurements in tensile tests. The measured true stress–stain
relationship was then applied to a series of nonlinear implicit three-dimensional finite element analyses using commercial
code LS-DYNA. The strength and deformability of steel plates with various pit sizes, degrees of pitting intensity, and general
corrosion were estimated both experimentally and numerically. The failure strain in relation to the finite element mesh size
used in the analyses was clarified. Two different steels having yield ratios of 0.657 and 0.841 were prepared to examine the
material effects on corrosion damage. The strength and deformability did not show a clear dependence on the yield ratios of
the present two materials, whereas a clear dependence was shown with respect to the surface configuration such as the minimum
cross-sectional area of the specimens, the maximum depth of the pit cusp from the mean corrosion diminution level, and pitting
patterns. Empirical formulae for the reduction of deformability and the reduction of energy absorption of pitted plates were
proposed which may be useful in strength assessment when examining the structural integrity of aged corroded structures. 相似文献
987.
Introduction Automating medical image registration is be-coming an increasingly important goal. It formsthe basis of image processing techniques to com-bine information from the different modalities,which are now frequently acquired for many pa-tients. Such combined representations of patientimages have been shown to assistin the interpreta-tion of the complementary information provided bythe modalities[1,2 ] . A variety of imaging modalities gives insightto different parameters and in… 相似文献
988.
989.
在国家"公交优先"发展战略背景下,系统分析了中国大部分城市所采取的公交执行票价远低于成本票价的低票价政策,指出这种政策使得公交票价的制定与成本脱钩且长期不变,导致城市公交企业运营成本急剧攀升、企业经营难以为继、城市公共财政补贴不可持续、低票价对于客流吸引力逐渐减弱等一系列问题,进而引发公共交通服务质量难以有效提升。为构建可持续的城市公共交通运营财税机制,从城市公共交通三个利益主体即乘客、企业、政府对于公共交通的相关诉求出发,系统性研究了公共交通服务质量、成本、票价、财政补贴间的相互关系,在此基础上研究构建了以服务质量为导向的成本、补贴、票价联动的框架体系,以便为我国城市公共交通运营财税的可持续发展提供支持。 相似文献
990.
U. B. Azimov K. S. Kim D. S. Jeong Y. G. Lee 《International Journal of Automotive Technology》2011,12(2):159-171
An experimental study has been performed on spray combustion and two-dimensional soot concentration in diesel (ULSD), GTL
and GTL-biodiesel fuel jets under high-pressure, high-temperature quiescent conditions. Instantaneous images of the fuel jets
were obtained with a high-speed camera. It was confirmed that by blending GTL with 20% rapeseed biodiesel, certain fuel properties
such as kinematic viscosity, density, surface tension, volatility, lower heating value and others may be designed and improved
to be more like those of conventional diesel fuel but with considerable decrease in the amount of sulfur, PAH, cold filter
plugging point, etc. The results showed that the spray tip penetration increased and the spray cone angle decreased when 20%
biodiesel fuel was added to GTL fuel. Autoignition of the GTL-biodiesel blend occurred slightly earlier than that of diesel
fuel. Experiments under high-pressure, high-temperature conditions showed that higher injection pressure induced a lower soot
formation rate. The integrated flame luminosity, which serves as an indicator of soot concentration in the fuel jet, was slightly
higher for the GTL-biodiesel blend than for pure GTL fuel due to the slightly higher sulfur content of pure biodiesel fuel. 相似文献