On the application of the Haskind-Hanaoka relations to hydroelasticity problems

The Haskind-Hanaoka relations for obtaining the wave-exciting forces, given the incoming and radiation potentials in floating rigid-body dynamics, are extended to deformable-body dynamics in the presence of a free surface and within the assumption of linear potentials theory. These relations are applied to the mode-superposition and the direct methods of solution of hydroelasticity problems. In other words, it is shown that regardless of the structural analysis method used in a hydroelasticity problem, the Haskind-Hanaoka relations can be used to calculate the wave-exciting forces without solving for the diffraction potential explicitly. These relations can also be used in the composite singularity distribution method to increase further the computational efficiency.     

Extreme-response analysis of jack-up platforms

The extreme wave and current response of a typical North Sea jack-up drilling platform has been calculated using nonlinear, stochastic, time-domain analysis techniques. A statistical treatment of the response-time histories has been performed. Appropriate probability distributions have been fitted to simulated response amplitudes and extrapolated to determine extreme values in storms of 3 or 6 h duration. Nonlinear geometric effects and dynamic effects are also addressed.

The results of the nonlinear time-domain analyses are compared to the results of more simplified methods used in jack-up designs.     

Wave Propagation in a Finite Cascade of Masses and Springs Representing a Train

The response of a train, modelled with a cascade of bodies and springs, due to a step force at the locomotive is investigated. In this model the mass of the locomotive and the last wagon may differ from that of the other wagons. An analytic solution is given for a finite and for a semi-infinite cascade and a comparison to the solution of a continuous model is made.     

Microbial community structure in the marginal ice zone of the Bellingshausen Sea

Phytoplankton, bacteria and microzooplankton were investigated on a transect in the Bellingshausen Sea during the ice melt period in November–December 1992. The transect along the 85°W meridian comprised seven stations that progressed from solid pack-ice (70°S), through melting ice into open water (67°S). The abundance, biomass and taxonomic composition were determined for each component of the microbial community. The phytoplankton was mostly dominated by diatoms, particularly small (<20 μm) species. Diatom abundance ranged from 66 000 cells l⁻¹ under the ice to 410 000 cells l⁻¹ in open water. Phytoplankton biomass varied from <1 to 167 mg C m⁻³, with diatoms comprising 89–95% of the total biomass in open water and autotrophic nanoflagellates comprising 57% under the ice. The standing stocks of autotrophs in the mixed layer ranged from 95 mg C m⁻² under the pack-ice to 9478 mg C m⁻² in open waters. Bacterial abundance in ice-covered and open water stations varied from 1.1 to 5.5×10⁸ cells l⁻¹. Bacterial biomass ranged from 2.4 mg C m⁻³ under pack-ice to an average of 14 mg C m⁻³ in open water. The microzooplankton consisted mainly of aloricate oligotrich ciliates and heterotrophic dinoflagellates and these were most abundant in open waters. Their biomass varied between 0.2 and 54 mg C m⁻³ with a minimum at depth under the ice and maximum in open surface waters. Microheterotrophic standing stocks varied between 396 mg C m⁻² under pack-ice and 3677 mg C m⁻² in the open waters. The standing stocks of the total microbial community increased consistently from 491 mg C m⁻² at the ice station to 13 155 mg C m⁻² in open waters, reflecting the productive response of the community to ice-melt. The composition of the microbial community also shifted markedly from one dominated by heterotrophs (82% of microbial stocks) at the ice station to one dominated by autotrophs (73% of microbial stocks) in the open water. Our estimates suggest that the microbial community comprised >100% of the total particulate organic carbon (POC) under the ice and 62–66% of the measured POC in the open waters.     

欧洲最新城市快速铁路电动车组

对瑞士的Flirt、奥地利的Elektro-Talent和波兰的EN95 3种动车组的技术性能和价格进行了比较.     

Inter-firm relationships and shipping services: the case of car carriers and automobile importers to the United States

This paper is an initial exploration of inter-industry relationships and linkages in the context of automobile imports to the United States. It is our contention that the nature and structure of the engagement between automobile importers and shipping lines is central to understanding the evolution of the car carrier trade. Building on the literature on transactions costs, and supply and value chains, we show that the regimes currently governing car carriage services range from markets to vertical integration via network forms of engagement. We illustrate this through a detailed discussion of Japanese inter-firm networks and an examination of automobile import data to the US from 1980 to 2000. The findings raise important questions for future research on the impact of inter-industry relationships in various strategic decisions of steamship lines, shippers and port authorities including port entry, port choice and routeing, technological and investment choices, and trajectories of supply chain development.     

用特性模型分析IGBT功耗

文章介绍了IGBT特性模型的建模技术.通过特性模型简化了IGBT功耗的分析和计算,评估了正弦电路应用中IGBT的结温和损耗.仿真结果证实了特性模型的可行性.     

An Optimal Continuous Time Control Strategy for Active Suspensions with Preview

A continuous time control strategy for an active suspension with preview, based on optimal control theory, is presented. No approximation is needed to model the time delay between the excitation of the front and the rear wheels. The suspension is applied to a two DOF model of the rear side of the tractor of a tractor-semitrailer. The purpose of the suspension is to reduce either the required suspension working space or the maximum absolute acceleration of the sprung mass, without an increase of the dynamic tire force variation. For a step function as road input, reductions of 65% and 55%, respectively, are possible compared with a passive suspension.