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761.
G. Ruf 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1978,7(1):1-23
When applying the known power spectra of the random road roughness to the suspension behaviour of a four-wheeled vehicle, each of the four vertical input signals together with their related interdependence are to be considered, if exact results are to be obtained. The correlations are determined by way of calculation. The resulting roughness spectra of bounce, pitch, roll and torsional excitations will be applied to various vehicles, characterized by different design parameters. By means of a three-dimensional simulation model the virtual values of the random vehicle vibrations are calculated, while determining at the same time the influence of vehicle speed, waviness exponent, track width, wheel base, and axle design feature as well as the relationship between the vertical vibrations and the reference point in the vehicle body. 相似文献
762.
A Lowry-type land use-transport model stratified both by socio-economic group and urban sub-region is described. The parameters of this model are calibrated from a 1969 urban travel survey conducted in Delhi. Parameter magnitudes are estimated for several versions of the model and the qualities of these calibrations are reported. Applications of the calibrated models to the analysis of alternative development concepts for the Delhi urban region are described. 相似文献
763.
Ernst G. Frankel 《Maritime Policy and Management》1980,7(1):21-36
The maritime policy of the US has evolved over more than 100 years from the support of US shipping through mail and fleet auxiliary contracts before the turn of the century, to the present array of direct and indirect Government aids and regulations based on the assumption that a strong maritime industry composed of both US-flag shipping and US-shipbuilding capacity is essential for the economic well-being and defence of the country. Notwithstanding massive direct and indirect aid to the US merchant marine, amounting to well over a billion dollars a year in recent years, US shipping and shipbuilding has declined dramatically and now comprises less than 3% of world shipping. Only 2.8% of US foreign trade by volume and 6% by value is today carried in US flag ships. Government aids constitute well over 33% of total revenues of US-flag shipping.
The traditional argument for US Government support has been the need for cost parity to permit US-flag shipping to compete effectively in international trade against foreign shipping serving the same routes with presumably lower operating costs. This argument is difficult to sustain today, as vessel costs of many other industrialized nations are now about equal to those of US-flag ships.
In 1970 the US enacted a new, vastly more liberal, maritime act for the support of the US maritime industry. Notwithstanding its even more liberal terms and elimination of the strict cost-parity interpretation, the US maritime industry continues its decline. The recent bankruptcy of two old, established subsidized shipping companies has caused tremors in the industry, yet no new ideas, policies, or plans seem to be forthcoming. It is the objective of this paper to study the development and effects of various historic US Government policies relating to the support of the US maritime industry, and evaluate the positions taken by proponents or opponents of the maritime policy leading to the policy development.
The decision processes are studied by evaluating literature on the evolution of Congressional, administration, industry, and labour interest and positions on the issue of Government aid to the maritime industry. The impact and effectiveness of various elements of past and present US maritime policy is evaluated in relation to the stated objectives. The alternatives to these policies are reviewed in the light of the changing US position in international trade, military strategy, and political objectives. In addition the effectiveness of the present and alternative policies is evaluated as it is and will be affected by changing technology in use, composition of ownership, and operations of US-flag shipping and shipbuilding. 相似文献
The traditional argument for US Government support has been the need for cost parity to permit US-flag shipping to compete effectively in international trade against foreign shipping serving the same routes with presumably lower operating costs. This argument is difficult to sustain today, as vessel costs of many other industrialized nations are now about equal to those of US-flag ships.
In 1970 the US enacted a new, vastly more liberal, maritime act for the support of the US maritime industry. Notwithstanding its even more liberal terms and elimination of the strict cost-parity interpretation, the US maritime industry continues its decline. The recent bankruptcy of two old, established subsidized shipping companies has caused tremors in the industry, yet no new ideas, policies, or plans seem to be forthcoming. It is the objective of this paper to study the development and effects of various historic US Government policies relating to the support of the US maritime industry, and evaluate the positions taken by proponents or opponents of the maritime policy leading to the policy development.
The decision processes are studied by evaluating literature on the evolution of Congressional, administration, industry, and labour interest and positions on the issue of Government aid to the maritime industry. The impact and effectiveness of various elements of past and present US maritime policy is evaluated in relation to the stated objectives. The alternatives to these policies are reviewed in the light of the changing US position in international trade, military strategy, and political objectives. In addition the effectiveness of the present and alternative policies is evaluated as it is and will be affected by changing technology in use, composition of ownership, and operations of US-flag shipping and shipbuilding. 相似文献
764.
The results on the distribution of phytoplankton biomass (expressed as Chla) and primary production (14C assimilation), during three oceanographic cruises carried out during Austral spring and at the end of the summer and the autumn in the Straits of Magellan, suggest a strong variability of trophic levels for this ecosystem.Seasonal evolution of the biomass concentration goes from the spring maximum of 2.33 μg/l through a sharp decrease, 0.49 μg/l, observed at the end of summer, until the minimum of 0.24 μg/l measured during the autumn.The trophic conditions are dependent on hydrographic, meteo-climatic and geo-morphological characteristics: at the Atlantic entrance and between the two Angosturas the strong mixing of water column limit the development of phytoplankton; at the Western opening and along the Pacific arm the complex exchange mechanisms with the ocean, the glacio-fluvial contribution and the presence of a thermohaline front near the Isla Carlos III influence both biomass and primary production distributions. The maximum values are reached in the Central Zone (Paso Ancho) characterized by high stability of the water column.Primary production ranged from a minimum of 12.3 to a maximum of 125.9 mgC m−2 h−1. The overall trend seems to be a progressive and simultaneous increase from the Pacific and Atlantic openings to the Central Zone of Paso Ancho where the maximum value was reached. In general, biomass and primary production distributions correspond quite well except for the area of Isla Carlos III where biological and chemico-physical causes tend to limit 14C assimilation.Contribution of pico-phytoplankton (< 2 μm) to total biomass appears to be time dependent: in the blooms observed during spring a very modest incidence (< 6%) was observed whereas became more (> 50%) during the summer-autumn seasons when total biomass was decreasing.Within the Straits, at the end of summer, the contribution of pico-phytoplankton primary production is 59%, whereas nano and microplankton contribute 39% and 2%, respectively. At the oceanic external stations the photosynthetic activity of the bigger size-fraction (> 2 μm) is predominant (> 50%).These findings support the hypothesis that the pico-phytoplankton ( < 2 μm) is substantially constant, whereas temporal variations are due to the larger (> 10 μm) cells only. 相似文献
765.
王渤洪 《变流技术与电力牵引》2005,(2):36-39
一方面由于近郊客运的资金减少,另一方面由于安全性要求的提高,新造动车越来越受到压低价格的困扰.同时运营者和旅客又希望新车有更好的舒适性(如低地板上下车区、空调设备),因此要求制造厂在考虑现代化动车的最佳性能参数时,能够既降低车辆成本又满足现代化的要求.Talent动车一族的模块化设计提供了高度舒适且市场价格低廉的最现代化技术.这种成功的设计和理念已在不同用户的350辆Talent车辆上得到了证实. 相似文献
766.
Daniel G. Williams 《Maritime Policy and Management》2006,33(3):257-280
This paper is a stochastic risk simulation of the impact of proposed federal tonnage limits on US Maritime Security Fleet (MSF) bagged food aid shipments. Only MSF (i.e. federally subsidized carriers/vessels for war, or emergencies) and non-MSF US carriers (therefore, at competitive disadvantage) can compete for such shipments—representing an indirect subsidy to both groups. To compensate, US Congress proposed a financial penalty (loss of voyage subsidy) on MSF carriers for food aid above a certain limit. Accordingly, certain carriers will be policy 'winners' (non-MSF—larger food aid shipments), and others 'losers' (MSF). By simulating loss-minimizing economic behaviour by MSF carriers—using five stochastic factors—I obtain losses substantially below those claimed by the MSF owners.
Simulated annual-average MSF profits reduction is $3.5 million—within a large confidence interval; if no carriers surrender their subsidies (as claimed by MSF owners), a reduction of $6.0 million. Only 16% of annual MSF voyages are affected by a 2,500-ton limit (3%; 5,000-ton limit). Minimizing losses, 25 (of 41 affected) annual MSF voyages replace 38,000 tons of food aid with 23,000 tons of other cargo—forgoing $2.1 million in yearly direct subsidies. Two assumptions explain most of this simulated loss reduction. 相似文献
Simulated annual-average MSF profits reduction is $3.5 million—within a large confidence interval; if no carriers surrender their subsidies (as claimed by MSF owners), a reduction of $6.0 million. Only 16% of annual MSF voyages are affected by a 2,500-ton limit (3%; 5,000-ton limit). Minimizing losses, 25 (of 41 affected) annual MSF voyages replace 38,000 tons of food aid with 23,000 tons of other cargo—forgoing $2.1 million in yearly direct subsidies. Two assumptions explain most of this simulated loss reduction. 相似文献
767.
The primary aim of the present study is to investigate the collision resistance and residual strength of single side skin (SSS) and double side skin (DSS) bulk carriers subject to collision damage. The impact dynamics analyses were conducted using ANSYS LS-DYNA for the evaluation resistance forces, energy absorption and penetration depth for various collision scenarios. The struck vessels of Capsize SSS and DSS designs were assumed to be entirely standstill and the striking vessels of an Aframax-type oil tanker with different bulbous bow shapes were modeled as rigid bodies. The findings were compared, where possible, with existing analytical tools. Residual strength calculations on SSS and DSS vessels were computed corresponding to all considered collision damage scenarios. Traditional Smith's method was applied with the average stress — average strain relationships of elements based on derived semi - analytically. The effect of corrosion was also evaluated by Joint Bulker Project (JBP) Rules on the influence of plate and stiffener thickness. The safety of the vessels was determined as a ratio of the ultimate hull girder strength to bending moment in damaged condition. Finally, results and insights derived from the present work are summarized. 相似文献
768.
G. Chen W. M. Zhai 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2004,41(4):301-322
Based on the theory of vehicle-track coupling dynamics, a new wheel/rail spatially dynamic coupling model is established in this paper. In consideration of rail lateral, vertical and torsion vibrations and track irregularities, the wheel/rail contact geometry, the wheel/rail normal contact force and the wheel/rail tangential creep force are solved in detail. In the new wheel/rail model, the assumption that wheel contacts rail rigidly and wheel always contacts rail is eliminated. Finally, by numeric simulation comparison with international well-known software NUCARS, comparison with vehicle-track vertical coupling model, and comparison with running test results by China Academy of Railway Sciences, the new wheel/rail spatially dynamic coupling model is shown to be correct and effective. 相似文献
769.
Deterministic approximations for elevator trip times are applied to a system of m elevators. Comparisons of in-system time of passengers are made for elevators which are (a) physically separated, (b) ideally controlled, (c) zoned, or (d) uncontrolled. A more detailed study is then made of in-system passenger time for a pair of elevators subject to a minimum headway control at the lobby. Comparisons are made between rather primitive analytic estimates and simulation results.The main conclusion is that control of headways so as to prevent pairing is of doubtful value. At low traffic it is usually better to use no control; for higher traffic it is better to zone the building and have each elevator serve separate floors. 相似文献
770.
G. Levikov 《Maritime Policy and Management》1990,17(1):31-40
This paper highlights some of the major activities in developing an appropriate framework and modalities of co-operation among CMEA member countries in maritime transport. These include the working out of various basic documents determining objectives, directions and methods of co-operation. Particular attention is devoted to the Comprehensive Programme for the Further Extension and Improvement of Co-operation and the Development of Socialist Economic Integration of the CMEA Member Countries and to the first inter-governmental Agreement on Co-operation in Merchant Shipping. Relevant activities of the CMEA are described, in particular, in the fields of joint planning and chartering, as well as its mechanisms for developing and promoting co-operation. 相似文献