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991.
992.
Dynamics of inorganic nutrient species in the Bohai seawaters 总被引:3,自引:0,他引:3
J. Zhang Z. G. Yu T. Raabe S. M. Liu A. Starke L. Zou H. W. Gao U. Brockmann 《Journal of Marine Systems》2004,44(3-4):189
Within the frame of a Sino-German Joint Research Program, two cruises of “R/V Dong Fang Hong 2” were carried out in September–October 1998 and April–May 1999, respectively, to understand the dynamics of nutrients in the Bohai. Nutrient species (NO3−, NO2−, NH4+, PO43− and SiO32−) are determined colorimetrically on board for five anchor and 30 grid stations. In situ incubation experiments are performed to determine planktonic nutrient uptake and benthic exchange flux. Nutrient concentrations display short-term variability and seasonal change in the Bohai, with higher levels in shallow coastal waters than in the Central Bohai. The influence of riverine discharge on nutrient levels can be seen from salinity isopleths, nutrient distribution and species ratios. Near-bottom (nb) waters have similar nutrient concentrations as to the surface waters in the Central Bohai, whereas stratification takes place in the Bohai Strait and North Yellow Sea. In situ incubation experiments provide evidence that the uptake ratio (i.e. N, P) by phytoplankton is proportional to the ratios among nutrient species in ambient waters. Based on the data of this study and previously publications, a preliminary estimate of nutrient budgets via riverine input and atmospheric deposition is established. The results indicate that atmospheric deposition gains importance over rivers in delivering nutrients into the Bohai and sustain the new production, following recent decrease in riverine inflow caused by drought periods in North China and damming practices. A historical review of nutrient data indicates that concentrations of nitrogen increase and phosphorus and silica decrease in the Central Bohai over last 40 years. This potentially has an important influence on the health of ecosystem in Bohai (e.g. food web and community structure), though further study is needed to examine the scenario in more detail. 相似文献
993.
Dagmar Hainbucher Wei Hao Thomas Pohlmann Jürgen Sündermann Shizuo Feng 《Journal of Marine Systems》2004,44(3-4):153
The circulation and the hydrography of the Bohai Sea are simulated with the Hamburg Shelf Ocean Model (HAMSOM). The model is three-dimensional, prognostic baroclinic and has a resolution of 5 min in latitude and longitude and 10 layers in the vertical. It is initialised and forced with the five main tidal constituents, temperature and salinity distributions taken from the Levitus database, monthly mean river run-off values and European Centre for Medium Range Weather Forecast (ECMWF) re-analysed data of air pressure, wind stress and of those parameters relevant for the calculation of heat fluxes. The simulation period covers 14 years from 1980 to 1993 due to the availability of the time-dependent ECMWF forcing.The results are analysed by means of time series and EOFs focussing on the interpretation of fluctuations with periods above the tidal cycle. Furthermore, tracer simulations are carried out and turnover times are calculated in order to evaluate the importance of these fluctuations on the renewal and transport of water masses in the Bohai Sea.One of the major outcomes of the investigation is the overall dominance of the annual cycle in all hydrographic parameters and the importance of stochastic weather fluctuations on the transport of water masses in the Bohai Sea. 相似文献
994.
995.
近年来随着大量非线性负载的投入使用,船舶电网谐波问题日益严重,直接影响到船舶电气设备的正常工作和使用寿命。论文结合船舶电力系统动态负荷多等特点采用节点电势法进行基波潮流计算,忽略传输线路压降,对非线性负荷进行迭代求解,因而收敛速度快,精度高。在迭代求解过程中,采用改进的自适应遗传算法。根据适应度值的集中程度自适应地变化整个种群的交叉概率和变异概率,增加了种群多样性,扩大了搜索空间。应用改进的自适应遗传算法对一个12节点船舶电力系统进行滤波器优化配置,优化结果表明了算法的有效性。 相似文献
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997.
998.
舰用齿轮箱抗冲击能力时域计算 总被引:3,自引:0,他引:3
为找出舰船设备的潜在问题或薄弱环节,从而保证舰船的战斗力;以及为避免由于对设备的抗冲击性能不了解即进行冲击试验可能对设备造成的损坏,抗冲击数值模拟分析对于舰用设备是必要的。对舰用齿轮箱抗冲击能力进行时域数值模拟,使用MDT软件建立齿轮箱三维几何模型,利用HyperMesh软件进行前处理以及有限元网格划分,并将有限元模型导入ABAQUS软件,对齿轮箱抗冲击能力进行时域计算。分析数值模拟结果得到了齿轮箱典型部位处冲击响应,总结了齿轮箱抗冲击的一些规律,并找出了齿轮箱结构抗冲击的薄弱环节,为齿轮箱结构优化设计提供了参考。 相似文献
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1000.