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结合目前国内外超空泡技术的发展,论述发展超空泡潜艇的必要性,介绍了超空泡技术基本原理。依据超空泡鱼雷的配置,提出“变形空化器”的概念;论证超空泡潜艇推进和控制系统的选择;分析导引设备和尾舵的作用以及可能出现的问题。结合4种超空泡航行体稳定模式,分析超空泡潜艇水下稳定性问题,提出超空泡潜艇发展设想。结合对潜艇操纵研究,分析超空泡潜艇的水动力特性问题。同时,对 Suboff潜艇模型进行了流场特性的仿真计算,结果表明:潜艇的头部、指挥室的迎风面、指挥室的两侧艇体和潜艇的尾翼均存在一定的沾湿区域。基于此结果,提出相应的改进方案。对超空泡潜艇未来主要工作进行展望。 相似文献
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TLP立管系统以丛式方阵排列,台风条件下立管在波浪、海流及平台的联合作用下可能发生碰撞,有必要深入研究TLP串行立管系统的碰撞情况。文章基于DNV-RP-F203规范和Huse半经验尾流模型,提出台风条件下串行立管下游立管来流速度计算方法和立管系统碰撞分析方法,建立串行立管—井口—导管系统耦合有限元模型,研究台风条件下串行生产立管系统碰撞时的力学特性,在整体碰撞分析的基础上进行立管局部碰撞精细化分析,对比分析立管局部碰撞理论解和仿真解的不同。结果表明:下游立管来流速度的计算至少采用文中建立的方法迭代3次。串行立管发生碰撞时的最大应力发生在泥面导管处,碰撞位置应力发生了突变;立管发生碰撞的位置在水深100-120 m范围内。立管局部碰撞分析的理论解和仿真解基本吻合。 相似文献
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攻角空化器的超空泡形态非对称特性研究 总被引:1,自引:0,他引:1
为了满足水下高速超空化航行体运动平衡性和稳定性要求,必须采用非对称超空泡流动模式,采用具有非零攻角的空化器是实现该要求的一种重要策略.基于冲量定理,理论分析了非零攻角空化器引起的超空泡轴向变形量随轴向长度的关系,获得了空化器攻角对超空泡非对称性及其影响因素之间的定性和定量关系,其一阶近似与同类文献的结论是一致的,数值模拟表明了所得结论的合理性和分析的正确性.研究表明,非零攻角空化器引起的超空泡轴线变形量与沿空泡长度的距离呈线性规律增加,并在空泡尾部达到最大,不可能单独利用空化器攻角沿空泡长度来中和重力影响. 相似文献
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Phytoplankton carbon fluxes were studied in the Northeast Water (NEW) Polynya, off the eastern coast of Greenland (79° to 81°N, 6° to 17°W), during summer 1993. The downward flux of organic particles was determined during 54 days using a sediment trap moored at a fixed location, below the pycnocline (130 m). The hypothesis of the present study is that wind events were ultimately responsible for the events of diatoms downward flux recorded in the trap.Wind conditions can influence the vertical transport of phytoplankton by affecting (1) the environmental conditions (e.g. hydrostatic pressure, nutrient concentrations, and irradiance) encountered by phytoplankton during their vertical excursion, and (2) the aggregation and disaggregation of phytoplankton flocs. The first mechanism affects the physiological regulation of buoyancy, whereas the second one affects the size and shape of settling particles.Using field data (wind velocity, density profiles and phytoplankton abundance), we assessed the potential aggregation and the vertical excursion of phytoplankton in surface waters. The results show that, upstream from the trap, wind and hydrodynamic conditions were sometimes favourable to the downward export of phytoplankton. Lag-correlation between time series of wind and phytoplankton downward flux shows that flux events lagged wind events by ca. 16 days. Given that the average current velocity in the top 100 m was ca. 10 cm s−1, a lag of 16 days corresponded to a lateral transport of ca. 130 km, upstream from the sediment trap, where phytoplankton production was lower than at the location of the trap. According to that scenario, 21% to 60% of primary production was exported to depth during wind events. If we had assumed instead a tight spatial coupling between the material collected in the trap and the relatively high phytoplankton production at the location of the trap, we would have concluded that <7% of primary production was exported to depth. The difference between the two scenarios has great implications for the fate of phytoplankton. Our results stress the importance of investigating the spatial coupling between surface and trap data before assessing the pathways of phytoplankton carbon cycling. 相似文献
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Use of SeaWiFS data for light availability and parameter estimation of a phytoplankton production model of the Bay of Biscay 总被引:2,自引:0,他引:2
Martin Huret Francis Gohin Daniel Delmas Michel Lunven Vronique Garon 《Journal of Marine Systems》2007,65(1-4):509
Processing SeaWiFS (Sea-viewing Wide Field-of-view Sensor) data provides useful information for the observation and modelling of the phytoplankton production of the Bay of Biscay. Empirical algorithms allow the retrieval of chlorophyll a and non-living Suspended Particulate Matter (SPM) concentrations. These data are used to constrain a coupled 3D physical–biogeochemical model of the Bay of Biscay continental shelf. Two issues are investigated, depending on the variable used, to constrain the winter to spring phytoplankton production for the year 2001. First, SPM data is used as forcing data to correct the corresponding state variable of our model. This allows the realistic simulation of the light limited bloom at the end of February 2001, as observed with SeaWiFS chlorophyll a images and from the NUTRIGAS field cruise. Second, chlorophyll a data is used for parameter estimation of the biogeochemical model. The ability of assimilating these data is tested to improve the simulation of strong blooms observed in late May 2001 in the Loire and Gironde plumes. A global optimization method (Evolutive Strategies) is adapted to the complete 3-D coupled model, in order to find the best set of parameters. The hydrological conditions during the bloom can be validated with data from the PEL01 field cruise. After selection of the most sensitive parameters, the method is tested with twin experiments. Then, the use of real SeaWiFS data reduces the model/data misfit by a factor of two, improving the simulation of bloom intensities and extensions. The sets of parameters retrieved in each plume are discussed. 相似文献
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Internal solitary waves with a huge amount of energy easily trigger the large dynamic responses of riser-wellhead system and threaten its structural safety. However, previous studies have only focused on the dynamic response of the riser under internal solitary waves. The riser may experience excessive traction from the platform, especially from the mooring platform, in response to the arrival of internal solitary waves. The bottom of the riser connects to the wellhead system, which in turn exerts a reaction force on the riser. To address this problem, a coupled dynamic model of deep-water drilling mooring platform-riser-wellhead system under internal solitary waves is developed in this paper. A dynamic response analysis method based on the fourth-order Runge-Kutta method and finite element method is also proposed for the mooring platform-riser-wellhead system. A dynamical solver for the coupled system is then developed using MATLAB. The dynamic response characteristics of the riser-wellhead system under internal solitary waves are calculated. Results show that the displacement and bending moment of the system initially increases and then decreases along with the propagation of internal solitary waves, and finally reach equilibrium position. The displacement and bending moment reach their peak before the trough of internal solitary waves passes through the riser-wellhead system. The dynamic responses of the riser-wellhead system under the influence of internal solitary wave loads are much larger than those without the effect of internal solitary wave loads. The riser system experiences shearing loads at the interface of internal solitary waves, which trigger a step-like bending moment variation. The bending moment of the conductor under the mudline is greatly increased by the internal solitary waves. 相似文献
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讨论了基于USB接口的同步多路数据采集系统的设计。采用单片机控制数据实时采样,在主机WDM驱动程序设计中利用链表技术增加IRP(I/0Request Packet)USB总线驱动程序提交URB(USB Request Block)的数量,改善了采样数据的完整性,使整个采集系统的实时性能有所提高。 相似文献
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Recent measurements of wave induced hull strain and flexure in RN warships are presented together with the derivation of the current design criteria for extreme hull girder bending loads. The history of the development of the shipboard instrumentation used is given and recent developments to improve the quality and ease of analysis of the data are described. An unexpectedly high transverse asymmetry in the longitudinal strains measured in destroyers is shown to be the result of a combination of vertical and lateral bending in oblique seas. Finally recent theoretical comparisons between the loading of Deep-Vee hulls and conventional UK rounded bilge hulls are presented which demonstrate the higher loading experienced by this type of hull form. 相似文献
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In late summer 2002 and 2003, exceptionally warm inflow events of saline water were observed in the Baltic. These warm saline waters were embedded in the halocline of the Bornholm Basin and caused a strong anomaly of the seasonal temperature cycle. The temperature in October 2002 was the highest ever observed in the halocline of the Bornholm Basin.Although the oxygen content of the inflowing water was only about 1.5 ml l− 1 at the Darss Sill, it caused a moderate ventilation of the halocline in the Bornholm Basin. On the way through the Arkona Basin, the entrainment of ambient water increased the oxygen content of the inflowing saline water masses.Warm summer inflows were rare events in the last 50 years, but their frequency has increased since 1990. This is likely caused by climate change. The analysis of a 50-year time series of hydrographic parameters reveals significant changes of the thermal regime around the year 1988. The winter surface and intermediate water temperatures of the Bornholm Basin increased by about 1 °C. Also, the duration of warm water in the surface layer was prolonged after 1988. A high correlation between the minimum intermediate winter water temperatures and the NAO winter index was found.Since temperature is a key parameter for many biological processes various responses of the ecosystem to the change in hydrographic conditions could be expected. Possible biological implications of the warm inflow events for the ecosystem are discussed. 相似文献
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本文目的是通过液舱导移的方式实现船体平衡被破坏后的再平衡.本文利用船体结构有限元分析中的自动调整方法建立船体平衡模型.在选定液舱导移方案后,根据舰船静力学相关知识进行船体平衡的理论分析和计算,推导出液舱导移过程中参数之间的关系,并根据这些参数关系以及单容水箱液位控制模型,以LabVIEW为平台进行液舱导移和整个船体平衡调节过程的仿真.通过计算机仿真和物理实验说明,在一定条件下,通过液舱导移的方式可实现船体平衡被破坏后的再平衡. 相似文献
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Burke Hales Robert D. Vaillancourt Laura Prieto John Marra Robert Houghton Dave Hebert 《Journal of Marine Systems》2009,78(3):426
We present the observations from a pair of field experiments at the New England shelfbreak front in June and August of 2002, each consisting of 14 cross-frontal surveys using the Lamont Pumping SeaSoar. Measurements of the front's physical, chemical, and bio-optical characteristics were made at high spatial and temporal resolution. The front, based on water-column hydrographic distributions, was found within a few km of the 200 m isobath during both cruises. We present here composite sections, based on averages of individual sections shifted in space to a common frontal location, of the cross-frontal distributions of these properties as a measure of the mean state of the front in both June and August. The observations show the familiar temperature, salinity, and density distributions of the summertime front, dominated by surface thermal heating. Nutrient and bio-optical distributions show the combined effects of water-mass exchange and biological processes. T, S, silicate, and phosphate distributions are suggestive of cross-frontal exchange of slope- and shelf waters, although transport mechanisms and pathways are not apparent. These properties, along with nitrate and optical measures of the suspended particle distributions, show vertical displacements of isopleths as the front is approached: property contours slope upwards toward the front from the shoreward side, and downwards toward the front from the seaward side. Again, actual water-movement pathways are not constrained by these suggestive patterns. Bio-optical distributions show elevated indicators of photosynthetic efficiency both seaward and shoreward of the front, but the front itself is a minimum in biomass. Accumulation of photosynthetic biomass appears to be controlled primarily by nitrate scarcity in waters within and above the pycnocline. At the base of the pycnocline, light limitation appears to be the controlling factor, although the base of the euphotic zone is deeper than the biomass maxima and the base of the pycnocline. Mechanisms explaining this phenomenon are unclear, but tenuous evidence suggests low stratification at the depth of the 1% light level may not allow phytoplankton to optimize for the low-light, high-nutrient conditions at depth. Cross-frontal differences in nutrient and bio-optical parameters, particularly in August, suggest distinct phytoplankton assemblages, and the presence of calcite-forming or nitrogen fixing groups to the community structure, especially in very shallow waters across the front and in pycnocline waters seaward of the front. 相似文献
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为解决潜艇在设计过程中两个不同锥角的圆锥壳相连接时结合处存在的应力集中问题,基于加肋锥-环-柱结合壳,提出了加肋锥-环-锥这一新型结构形式。为得到锥-环-锥结构强度、稳定性随锥角的变化规律以及该结构适用的锥角范围,本文运用有限元软件建立锥角不同的系列模型,得出锥-环-锥结构在保持一侧锥角大小、锥锥相交处的半径及环壳跨长不变时结构过渡段各典型应力、舱段整体弹性失稳压力与失稳模式随另一侧锥角的变化规律。结果表明,各典型应力与锥角之间近似呈线性关系,环壳跨中处各典型应力对锥角变化最为敏感,锥壳段的纵向应力与两侧锥角的差值有关;随锥角的增加肋骨刚度较临界刚度下降较快,锥角变化可能会引起结构失稳模式的改变;在10°的锥角变化范围内,锥-环-锥结构过渡区域的峰值应力和舱段整体弹性失稳压力和锥-环-柱结构相差不大,在整个锥角变化范围内采用锥-环-锥结构都是可行的。研究结果可为锥-环-锥结构设计提供参考。 相似文献
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This paper is based on an advanced ecosystem model of the Baltic Sea (ERGOM [J. Mar. Sys. 25 (3–4) (2005) 405]), but with an increased resolution of the zooplankton stage variable [J. Plankton Res. 23 (2001) 1217; ICES Marine Science 219 (2003) 208]. The model copepods are represented by five stages: eggs, an aggregated variable of nauplii, two aggregated groups of copepodites and adults. The transfer among the stages, i.e., hatching, molting and reproduction, is controlled by food availability and temperature.As usual, the model food web is truncated at the level of zooplankton. The study explores the effects of different parametrization of zooplankton mortality and looks in particular on light-dependent rates. The light climate may serve a proxy for the effects of visual feeding of fish larvae and fish. Different choices of the mortality parameters can result in remarkable differences in abundances and biomass of the model zooplankton and in the timing of its development.It is found that the different choices of mortality affect the development of populations in several ways: Relative small initial differences of abundances at the beginning of the spring bloom are important for the development of the model populations. Higher mortality rates are less important at food rich conditions than at scarce resources. At low phytoplankton levels, the individual development of the copepods through the stages can be faster for elevated mortality rates because then less animals have to share the available food. 相似文献