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121.
The shelf-slope front (SSF) is a continuous shelf-break front running from the Tail of the Grand Banks to Cape Hatteras, North Carolina, separating colder and less-saline continental shelf waters from warmer and more saline slope waters. Time series containing mean monthly SSF positions were produced along each of 26 longitude lines between 75° and 50°W by workers located at Bedford Institute of Oceanography by digitizing individual frontal charts and computing mean monthly latitudinal positions over a 29-year (1973–2001) period. After removing seasonal variability at each longitude, interannual variability (IAV) of the SSF position at each longitude was computed as the annual mean of all monthly SSF position anomalies for each year over the 29-year period. Despite some missing data, a longitude-time plot reveals alternating bands of offshore (late-1970s, late-1980s, late-1990s) and onshore (early-1980s, early-1990s, early-2000s) annual mean SSF anomaly values, exhibiting a period of approximately 10 years. Annual mean SSF anomaly amplitudes are largest in the east, with maxima of O (± 100 km) located east of 60° W for years when data are available. Empirical orthogonal function (EOF) modes 1–4 (accounting for > 90% of the variance) form a set of basis functions that describe the SSF anomaly data and allow reconstruction of the entire data set since missing data are relatively few (14%). A complex empirical orthogonal function (CEOF) analysis using the “reconstructed” data reveals a wavelength scale of approximately 20° of longitude, a distance nearly equal to the entire study domain, along with steady, westward phase propagation of SSF anomalies over approximately the same distance. Speed calculations for the westward-propagating features yield a value of approximately 1.2 to 2.4 cm s− 1 (1 to 2 km d− 1), with annual mean SSF anomalies thus requiring about 4 years to propagate from the Tail of the Grand Banks in the east to Cape Hatteras, North Carolina, in the west. This propagation speed and the timing of the SSF positional anomalies at the Tail of the Grand Banks for the 29-year study period are in agreement with speeds computed for the propagation of quasi-decadal salinity anomalies through the Labrador Sea and the time of their arrival at the Tail of the Grand Banks. The small westward SSF anomaly propagation speed is an order of magnitude smaller than the associated currents, in agreement with a highly damped flow-through system originating from both Davis Strait and the West Greenland Current as discussed by other workers. Observations from both southern and northern portions of the study domain, within both continental shelf and slope waters, show that interannual changes in the volume of shelf water along with shelf water bulk properties exhibit a strong relationship with IAV of the SSF position over long time periods. 相似文献
122.
Recent observations of hydrography, currents and volume transports in the straits of the East/Japan Sea are reviewed. It is newly found that bottom cold water in the Korea/Tsushima Strait originating from the northern region of the East/Japan Sea appears not only in summer and autumn but also in winter. Intensive observations in the Korea/Tsushima Strait revealed two distinct cores of northeastward currents in the upper layer of the western and eastern channels. Mean volume transport through the Korea/Tsushima Strait is calculated as 2.5 ± 0.5 Sv from four-year direct and indirect measurements. As continuous monitoring has started in the Tsugaru and Soya Straits, understanding of temporal variability of currents and volume transports through the straits is in progress. For the first time, simultaneous time series of volume transports are available in the Korea/Tsushima and Tsugaru Straits during the winter of 1999–2000. Ouflow through the Tsugaru Strait accounts for about 70% of inflow through the Korea/Tsushima Strait for this period. 相似文献
123.
In 1994, Townend proposed a method to calculate the relative changes in various wave characteristics and structure-related parameters due to sea level rise for regular waves. The method was extended to irregular waves by Cheon and Suh in 2016. In this study, this method is further extended to include the effect of future change in offshore wave height and the sea level rise. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height in nearshore area are presented as functions of the relative changes in water depth and offshore wave height. The calculated relative changes in wave characteristics are then used to estimate the effect of sea level rise and offshore wave height change on coastal structures by calculating the relative changes in wave run-up height, overtopping discharge, crest freeboard, and armor weight of the structures. The relative changes in wave characteristics and structure-related parameters are all expressed as a function of the relative water depth for various combinations of the relative changes in water depth and offshore wave height. 相似文献
124.
This article examines noncavitating and cavitating flow fields around a semi-spade rudder in the ship wake and propeller slipstream
based on a computational method. The article seeks to explain the erosion that can occur around the gap due to cavitation;
such erosion has been reported to occur while a ship is at sea. Another area of research is the effect of the gap size and
shape. The effects of erosion-evading devices such as elongated gap edges, an increased edge radius, flow control projections,
and vertical and horizontal guide plates were also studied. 相似文献
125.
This paper explores the temporal stability of activity type-choice models and models of travelers' home-stay duration. To empirically evaluate this stability, a nested logit model of activity-type choice and a proportional hazards model of home-stay duration are estimated using data from two-day travel diaries collected in the fall of 1989 and again, from the same individuals, in the fall of 1990. The results show that the models are not temporally stable over the one year time period separating the two travel-diary samples. A number of possible reasons for this instability are discussed. 相似文献
126.
Enhancing the competitiveness of Korea’s container shipping industry through structural improvements
Byoung-Wook Ko Juhyeoun Kim Young-Jae Choi Kwang-Soo Kil 《Maritime Policy and Management》2020,47(1):57-72
ABSTRACTAfter the collapse of Hanjin Shipping in 2016, Korea faced the task of reconstructing its container shipping industry by enhancing the competitiveness of its shipping companies in a rapidly evolving market environment. Responding to this need for policy design, this study first attempts to understand the industry based on the shipping ecosystem, which comprises the following four areas: shipping finance, collection of cargo, acquisition of ships, and partnership among carriers. Second, it lists the structural problems, along with the remedial policy alternatives, that were identified after conducting in-depth interviews with industry experts, which included mid-level managers. Third, it conducts an importance-performance analysis to classify problems according to their importance and performance, followed by an analytic hierarchy process analysis to define the priorities of policy alternatives. Finally, drawing on the empirical results, the paper concludes with suggestions on an integrated policy package for the container shipping industry. 相似文献
127.
Xiaohui Cui Hoe Kyoung Kim Cheng Liu Shih-Chieh Kao Budhendra L. Bhaduri 《Transportation Research Part D: Transport and Environment》2012,17(7):548-554
This paper presents a multi agent-based simulation framework for modeling spatial distribution of plug-in hybrid electric vehicle ownership at local residential level, discovering “plug-in hybrid electric vehicle hot zones” where ownership may quickly increase in the near future, and estimating the impacts of the increasing plug-in hybrid electric vehicle ownership on the local electric distribution network with different charging strategies. We use Knox County, Tennessee as a case study to highlight the simulation results of the agent-based simulation framework. 相似文献
128.
The objective of this study is to investigate the dynamic deformation characteristics of an automotive A/C hose assembly using
the finite element method and experimentation. The finite element analysis consisted of two analyses, specifically, a modal
and a transient analysis. The dynamic modal analysis was conducted to assess the dynamic characteristics of the A/C hose structure,
and the dynamic transient analysis was performed to investigate the dynamic stresses of an automotive A/C hose by dynamic
loading with particular emphasis on the reinforced braid. Furthermore, the analyses results are expected to provide useful
reference data in the design optimization of the hose layout related to the constrained design space. Modal testing was undertaken
to verify the FE model. The FE result was in good agreement with the experimental results. The modal analysis result showed
that the bending and swing modes of the hose occurred in the first six natural frequencies. The dynamic transient result showed
that the maximum stress in the hose components occurred in the reinforced braid layers, which are particularly damage-prone. 相似文献
129.
The motions of an infinitely long, two-dimensional runway subjected to the dynamic moving load imposed by an airplane taking
off are investigated. The runway is assumed to be floating in an inviscid fluid and is initially at equilibrium before the
plane takes off. The deformation of the runway resulting from the take-off is wave-like and moves in the same direction as
the plane. The maximum drag occurs when the plane catches up with the first wave. Three different runway configurations were
considered: a baseline and ones which were ten and one hundred times more flexible than the baseline. For these runways, the
added drag to the aircraft was very small, ranging from 1% for the stiffest to 10% for the most flexible runway. 相似文献
130.
Bu-Geun Paik Jin Kim Young-Ha Park Ki-Sup Kim 《Journal of Marine Science and Technology》2007,12(2):72-82
The vortex structure of the wake behind a marine propeller was investigated in terms of loading variation by using particle
image velocimetry. One hundred and fifty instantaneous velocity fields were ensemble averaged to study the spatial evolution
of the wake and the behavior of the tip vortices in the region ranging from the trailing edge to one propeller diameter downstream.
The trailing vorticity was found to be related to the radial velocity jump, and the viscous wake was affected by the boundary
layers developed on the blade surfaces. A vortex identification method using the swirling strength was employed to extract
the location of the tip vortex. The loading on the blade made a clear difference to the contraction angles. Slipstream contraction
occurred in the very near wake region, and unstable oscillation occurred because of reduced interaction between the tip vortex
and the wake sheet behind the maximum contraction point for each loading condition. The maximum tangential velocity around
the tip vortex center revealed the average radius of its core, which was used for calculating the vortex strength. Additionally,
variation of the average radius of tip vortices with the change of blade loading was related to vortex tube stretching in
the wake region. The nearly constant vortex strength continued up to one diameter downstream for light loading and design
loading conditions. 相似文献