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71.
Luciana V. R. de Messano Barbara L. Ignacio Maria H. C. B. Neves Ricardo Coutinho 《船舶与海洋工程学报》2014,13(3):346-353
In the presence of biofilms, stainless steels (SS) exhibits an increase in corrosion potential, called ennoblement. In the present study, the corrosion potential (Eco,) behavior of the duplex SS UNS S32760 was recorded simultaneously with the in situ marine biofilm formation in two areas at Arraial do Cabo, Southeastern Brazil. The biofilm at Forno Harbor (an anthropogenically disturbed area) was characterized by higher relative abundances of Bacteria at day 2, followed by diatoms (especially Navicula sp.) on day 10 and dinoflagellates on day 18, whereas no clear trend was recorded at Cabo Frio Island (an undisturbed area). The ennoblement of Ecor values was site-dependent. In a complementary laboratory assay, biofilms were removed and the Eco values registered in sterile conditions for the subsequent 10 days and corroborated in situ results. Understanding biofilms and SS interactions has important implications for materials science and engineering decisions as well as helping to fill in imnortant gaps in this knowledge. 相似文献
72.
汽车筒式液阻减振器技术的发展 总被引:29,自引:1,他引:29
分析了汽车乘坐舒适性/行驶平顺性和操作稳定性对筒式液阻减振器特性的要求,提出汽车在不同行驶工况减振器特性的要求是不的;分析了被动式减振器的发展历程及非充气和充气减振器的特点,阐述了机械控制式可调阻尼减振器,电子控制式减振器以及电流变和磁流变液体减器等的结构特点,工作原理及其动态特性;分析了筒式液阻减振器其于经验设计/实验修正开发方法的缺点,阐述了基于CAD/CAE技术的现代设计开发方法的过程及其关键问题,最后分析了我国筒式液阻减振器技术的发展状况及问题,展望了减振器技术的发展前景。 相似文献
73.
Nancy L. Nihan 《先进运输杂志》2000,34(2):269-296
This paper documents the development of a simple method for identifying and/or predicting freeway congestion using single loop detection systems. The proposed algorithm is simple and easy to incorporate into most freeway management systems. The Washington State Department of Transportation's Traffic Systems Management Center (TSMC) sponsored the original study. The investigation also led to a recommendation to replace the original TSMC definition of congestion or forced flow conditions with a more reliable indicator. Although, the TSMC has recently implemented a more advanced prediction system based on fuzzy set theory and neural networks to further identify patterns and rules for ramp metering strategies, the findings presented here continue to be constructive to freeway managers looking for quick and easy analyses that rely solely on single‐loop detection systems. The Seattle Area freeway study section used for the original study was the portion of mainline 1–5 northbound starting at the downtown Seattle Station 108 and ending at the Mountlake Terrace Station 193. Several days' worth of volume and lane‐occupancy data were collected for the afternoon time period from 2:30 p.m. to 6:30 p.m. Time intervals of 20 seconds were chosen for each data collection period. Important products of this research include the following:
- simple, and more reliable criterion for the definition of “bottleneck” or forced flow conditions than that originally used by the TSMC.
- simple, and reliable criterion for predicting impending “bottlenecks” or forced flow conditions.
- A proposed variable for improved selection of the appropriate metering rate. (Further analysis of the use of this variable for determining metering rates is recommended for future studies.
74.
Joel L. Horowitz 《Transportation Research Part B: Methodological》1984,18(1):13-28
Most research and applications of network equilibrium models are based on the assumption that traffic volumes on roadways are virtually certain to be at or near their equilibrium values if the equilibrium volumes exist and are unique. However, it has long been known that this assumption can be violated in deterministic models. This paper presents an investigation of the stability of stochastic equilibrium in a two-link network. The stability of deterministic equilibrium also is discussed briefly. Equilibrium is defined to be stable if it is unique and the link volumes converge over time to their equilibrium values regardless of the initial conditions. Three models of route choice decision-making over time are formulated, and the stability of equilibrium is investigated for each. It is shown that even when equilibrium is unique, link volumes may converge to their equilibrium values, oscillate about equilibrium perpetually, or converge to values that may be considerably different from the equilibrium ones, depending on the details of the route choice decision-making process. Moreover, even when convergence of link volumes to equilibrium is assured, the convergence may be too slow to justify the standard assumption that these volumes are usually at or near their equilibrium values. When link volumes converge to non-equilibrium values, the levels at which the volumes stabilize typically depend on the initial link volumes or perceptions of travel costs. Conditions sufficient to assure convergence to equilibrium in two of the three models of route choice decision-making are presented, and these conditions are interpreted in terms of the route choice decision-making process. 相似文献
75.
Patricia J. Moser 《Transportation》1972,1(1):55-67
This paper discusses the aesthetic and ecological effects of highways. Little is known about the subject at the present time, and thus this treatment cannot be considered in any sense definitive.Part I offers a definition of aesthetic quality and considers its relevance to highway planning. It is noted that, although the principles of rural freeway design (curvilinear alignments, variable medians, etc.) generally accord with the aesthetic character of rural areas, freeways are infinitely more difficult to integrate aesthetically into urban areas. Comparisons are made in this regard among basic types of freeways.Part II notes that the effect of man's presence on the earth's ecology has resulted in new systems and processes to which man is now subject. Highways, as works of man, affect him and his environment in ways which are known only imperfectly. Nevertheless, there are steps which can be taken to minimize the more obvious forms of damage to the environment which can result from highway building.Part III discusses procedures for incorporating aesthetic and ecological considerations into highway planning. No method yet proposed is in itself sufficient, and none leads to a decision on an objective basis. A generally acceptable method must await further research. In the meantime, every effort must be made to assure full and fair consideration of environmental effects on an ad hoc basis. 相似文献
76.
Yunyoung?Kim Koji?GotohEmail author Masahiro?Toyosada 《Journal of Marine Science and Technology》2004,9(2):70-79
This article considers microgenetic algorithms (GAs), which explore in a small population with a few genetic operators, for cutting-path optimization problems. The major difference between GAs and simple genetic algorithms (SGAs) is how to make a reproductive plan for an improved searching technique because of population choice. It is shown that GAs implementation reaches the near-optimal region much earlier than the SGAs approach, and the GAs give a better solution than simulated annealing (SA). The main objective was to determine what temperature distribution can be obtained from the solution of a travelling distributed heat source. The solution of the travelling heat source on nested raw plate provides information about the vertices of each nested part of the raw plate. From the fact that the initial temperature at a piercing point strongly depends on the heat flow which stems from the previous cutting contour, the temperature of all piercing points must be lower than the critical temperature after each cutting of the components of a part. The critical temperature is identified as the mechanical melting temperature of steels. A heuristic back-tracking method is introduced to find the near-optimum cutting path considering the minimum heat effect on deformation. The heuristic back-tracking method is incorporated with the GAs. 相似文献
77.
The transient elastic deformation of a pontoon-type very large floating structure (VLFS) caused by the landing and take-off of an airplane is computed by the time-domain mode-expansion method. The memory effects in hydrodynamic forces are taken into account, and great care is paid to numerical accuracy in evaluating all the coefficients appearing in the simultaneous differential equations for the elastic motion of a VLFS. The time-histories of the imparted force and the position and velocity of an airplane during landing and take-off are modeled with data from a Boeing 747-400 jumbo jet. Simulation results are shown of 3-D structural waves on a VLFS and the associated unsteady drag force on an airplane, which is of engineering importance, particularly during take-off. The results for landing show that the airplane moves faster than the structural waves generated in the early stage, and the waves overtake the airplane as its speed decreases to zero. The results for take-off are essentially the same as those for landing, except that the structural waves develop slowly in the early stage, and no obstacle exists on the runway after the take-off of airplane. The additional drag force on an airplane due to the elastic responses of the runway considered in this work was found to be small in magnitude. 相似文献
78.
Toshiyuki?Shigemi Tingyao?ZhuEmail author 《Journal of Marine Science and Technology》2004,9(3):95-108
ClassNK has undertaken wide-ranging basic research covering many aspects related to the safety of ship structures, including design loads, structural analysis, strength assessment of buckling, collapse, and fatigue, and rational corrosion margins to develop new design standards which have transparency and consistency. Among the wide-ranging basic research, this article summarizes the results of extensive work on the design loads used for strength assessments of tanker and bulk carrier structures. The main aim of the research was to develop practical estimation methods of design loads with rational technical backgrounds relating to the actual loads acting on the primary structural members of tankers and bulk carriers. During this study, we proposed the following methodology. Design sea states that closely resemble the actual sea states which are considered to be the most severe for hull structures. Find practical estimation methods for the design sea states by parametric studies using the results of series calculations on representative tankers and bulk carriers. Find practical estimation methods for design regular waves which will result in the same level of stresses as those induced in irregular waves under the design sea states. We also briefly introduced some practical estimation methods for the design loads, such as ship motions, accelerations, hull-girder bending moments, and hydrodynamic pressures that are induced under design regular waves. The findings in this study have been summarized and implemented in the new design standards for tanker and bulk carrier structures.Updated from the Japanese original which won the 2003 SNAJ prize (J Soc Nav Archit Jpn 2002; 191:195–207; 2002; 191:208–220; and 2002; 192:723–733) 相似文献
79.
Nobuyoshi?FukuchiEmail author Changhong?Hu 《Journal of Marine Science and Technology》2004,8(4):177-184
In order to prevent the spread of marine compartment fires, it is necessary to understand the governing factors or characteristics of fire-spread phenomena. We present a pseudofield model approach to this problem. We first described a field model of turbulent heat convection based on a standard k – turbulence model. Two-dimensional numerical simulations of a two-linked compartment fire were carried out in order to predict the turbulent convection flow induced by the heat released from the fire. Then a more complicated fire-spread problem of multilinked compartment fires was analyzed by means of a zone model, in which the amounts of oxygen consumption and gas generation were solved by a gas-balance equations system. The effect of threshold conditions on fire propagation and the effect of the thickness of the heat insulation were investigated with numerical simulations. 相似文献
80.
Shoichi?HaraEmail author Kenji?Yamakawa Kunihiro?Hoshino Kazuhiro?Yukawa 《Journal of Marine Science and Technology》2004,8(3):138-146
A huge floating offshore platform (359m long, 60m wide, and 3m deep) was towed into the Pacific Ocean for a validation experiment for a floating airport. Full-scale measurements of towline tension and the bending strain on the upper-deck were made during towing. The measured bending moment agreed well with numerical calculation without taking the draught and towing speed into consideration. 相似文献