风速变化对竹湖流场结构影响的数值试验

利用EcoTaihu生态模型中的压缩坐标系下三维水动力学子模型，对4种吞吐流量（换水周期分别为36d、7．2d、3．6d、35h），东、西、南、北风向，不同风速的风场作用下的浅水湖泊进行了数值模拟，分析比较了不同风速作用下湖泊分层流场及垂向平均流场结构的差异。结果表明，随着风速的增大，湖泊垂向平均流场逐渐由受吞吐流控制转变成受风生流场控制；在此转变过程中存在着临界风速值，当风速大小超过该值时，流场结构发生明显的改变；风向和吞吐流量是影响临界风速值大小的主要因素。风速变化对稳定状态的湖泊表层、次表层流场有较大影响，而对底层和次底层影响不大。在水深水平变化较大的区域，垂直平均流场结构对风速变化的响应较为敏感，易形成环流，浅水区垂向平均流向和风向一致，深水区则和风向相反；水深变化较小的水域，流场结构对风速变化的响应则较为迟钝。     

定常风场和吞吐流对乌梁素海流场的影响

风场和吞吐流是浅水湖泊运动的主要驱动力,影响着湖区污染物的迁移转化。基于二维非结构网格,构建了乌梁素海水动力模型。通过对比定常风作用下湖流的方向、环流的分布及形式与无风条件下的区别,模拟不同算例吞吐流作用下湖区流速及环流结构的差异,探究了定常风和吞吐流对乌梁素海流场的影响。结果表明:乌梁素海在无风条件下出现大面积的滞流区;风场会增加湖流的流速,影响区域主要在西大滩区、东大滩区及湖区南部明水区,产生明显环流,风场是乌梁素海主要的驱动力; SSW与ENE向风场作用下,典型区域产生的环流位置、形态结构相近,方向相反;吞吐流量的增加会增大湖区整体流速,对湖区流场形态、结构影响较小;定常风条件下,吞吐流量的增加(一定范围)会导致环流强度减弱。研究结果为乌梁素海营养盐、污染物质输移规律研究奠定基础。     

热带大西洋表层环流及其月变化特征的分析

应用1993年4月至2001年3月的TOPEX/Poseidon卫星高度计遥感资料,分析了8 a平均热带大西洋(15°S～25°N,5°～50°W)表层环流结构的月变化特征.研究结果表明:热带大西洋表层环流中高纬度海区流速较小,赤道附近流速较大,表层环流系统大部分流系月变化不明显,部分流系月际波动较显著.具体来说,西南向的北赤道流下半年的纬向流速分量比上半年大.非洲沿岸流在5～11月流向为东北向,在其他月份主要为东南向.北赤道逆流可以分成两部分:25°W以东海区,北赤道逆流常年流向向东,到9月份前后流速达到最大值(约0.25 cm/s);25°W以西海区,7月至翌年1月流向向东,2～6月北赤道逆流减小,并有西向流产生.2°S～2°N,15°W以东海区的南赤道流在1～3月、9～10月流向向东,其他月份流向向西.南赤道流可认为是由南、北两支西向的海流构成,这两支海流的流轴分别位于6°S和1°N,在6～7月北支流速达到最大值0.6 m/s.南美洲纳塔耳东部西北向的北巴西海流流速月际变化不大,在5～6月份流速达到最大值0.3～0.4 m/s.相应的卫星风场遥感资料的分析表明热带大西洋表层环流结构的月变化特征与风场的分布及变化有较好的对应关系.用World Ocean Atlas 2001的月平均温盐数据反演出来的表层地转流场以及卫星跟踪ARGOS漂流浮标观测进行的对比验证表明,上述遥感分析的地转流场结果与水文数据以及海上观测结果一致.     

广西近岸海域潮流数值模拟

采用有限元三角形网格的分步杂交方法,建立了广西近岸海域的二维潮流数值模型,计算值与实测资料符合较好。采用主要分潮组合输入,模拟了研究海域的平均潮潮流场。模拟结果表明:涨急时,潮流向为东北方向,最大涨潮流速为74cm/s左右;落急时,潮流向为西南方向,最大落潮流速约100cm/s,落潮流速大于涨潮流速。近岸区域潮流为往复流,离岸边越远潮流越接近旋转流。     

黄海夏季近岸海区环流的初步分析及其与风速的关系

2008年夏季,青岛近海海域浒苔大规模暴发,引起人们对黄海夏季近海环流的特别关注。该文通过分析江苏外海一个观测站点上的近26 d的夏季海流观测资料,发现这里存在一支流向比较稳定的北向流,垂向平均流速约3.4 cm/s,最大流速8 cm/s。研究表明,该北向流的变化主要受局地风场控制,南北向的流动与南北向风速的大小关系密切。     

正方体人工鱼礁流场效应试验研究

采用无干扰的粒子图像测速技术(PIV),针对中空型正方体人工鱼礁,选取3个不同的来流速度6.7 cm/s、11.0 cm/s和18.0 cm/s,研究了该模型单体(90°和45°)和组合(平行和垂直)工况时的流场效应。结果显示,单体90°迎流时上升流的规模和强度大于45°迎流,但产生的缓流区和背涡流的规模远小于45°工况。横向组合中单个鱼礁模型产生的流场效应较强于单体工况。纵向组合中,第一个迎流鱼礁在不同间距时内部流速分布和单体时较为相似,间距为1.0L时流速大小与单体最为接近。第二个迎流鱼礁内部基本上未出现回流区域,水平流速较单体时明显减小,但随着间距的增加流速值不断增大。     

浙江近海夏季流场特征分析

为了揭示浙江近岸流场特征及沿程变化规律,于2006年和2009年夏季在浙江岸外3个固定点利用ADCP潜标进行了多个潮周期分层海流流速、流向观测。研究结果表明:(1)浙江沿岸流在中北部海域(A和B站位)为旋转流,流向呈顺时针方向旋转,在南部(C站位)涨潮流方向基本为北向,落潮方向为东偏北向;各站位海流在垂向上流向较一致。(2)3个站位垂线平均流速相近(44.4~51.1 cm/s),但平均流速的垂向分布差异明显;各站的最大流速均大于110 cm/s,且均出现在大潮涨急时刻。(3)观测期间,A(北部)、B(中北部)和C(南部)站位平均余流的大小分别为21.9,12.3和22.3 cm/s;受长江冲淡水影响,A和B站位中上层余流为西南向,从中层向底层流向呈逆时针方向偏转,下层流向呈东南向,可能为台湾暖流牵引所致,C站位余流流向在垂向较为一致,均为东北向,主要受季风影响。(4)夏季浙江沿岸流在沿浙江沿岸北上的过程中,在浙江中部(B和C站位中间)逐渐向东偏转(可能受台湾暖流的牵引),流经海域水深变大。(5)在夏季长江径流量偏小时段,浙江中北部近岸海域也存在向南的沿岸流(同冬季),其范围从长江口以南一直至浙江中北部。浙江近岸海流受季风、长江冲淡水和台湾暖流共同制约,但各区域的主要受控因素不同。     

潮汐和风对马六甲海峡海流的影响

基于非结构有限体积法海洋模型FVCOM(Finite-Volume Community Ocean Model), 建立了马六甲海峡及其毗邻海域高分辨率水动力数值模型, 研究了风和潮流作用下的余环流结构以及水体输运特征。结果表明, 马六甲海峡航道中央潮流运动以往复流为主, 边缘存在旋转流; 主要研究区域内落潮流速略大于涨潮流速, 东南窄道处流速最大; 因峡道束窄变浅, 在涨落潮过程中潮流发生汇聚与分离; 主要研究区域东南段存在3个显著的潮致余环流; 东北季风驱动时模型响应为海峡海流整体向西北方向流动, 西南季风时反之; 季风期间潮致表层余环流结构被破坏, 但底层余流仍存在水平环流结构, 且随着风速增加, 底层余环流的数目、大小、形状、位置均会产生变化; 季风过渡期余环流结构也会发生部分改变, 尤其是小潮期间风场影响效果显著。     

茂名港附近区域潮流特征分析

基于茂名港实测的潮流和泥沙等资料,给出了现场观测点的垂线平均流速、流向及垂线平均含沙量等特征,同时计算了余流的大小和方向、流量与输沙量,进而绘制了流场分布图、余流矢量图、输沙方向图等,并对该区域的流场和输沙时空变化的基本特征等进行了初步分析,得出如下结论:(1)茂名港区的余流大致沿海岸由北向南流,余流流速值由北向南递减,且离岸较远处的余流要比近岸处的大;(2)进入博贺港区的泥沙量大于输出量,由此将导致博贺港港区的淤积,但3#测线附近有冲刷现象,1#测线附近输沙受到径流输沙的影响.     

洋浦港附近冬季潮、余流特征分析

洋浦是典型的日潮区,潮型判别系数是7.32;最大潮流流速都出现在涨潮的北向流中,最大潮流速度为70cm/s.余流的表、中、底30d平均流向依次为188(°)、153(°)和95(°).表、中、底30d平均余流流速值依次为8.7、8.5和4.1cm/s.冬季余流的形成,主要受北部湾风生环流控制.     

滦河三角洲海岸潮汐汊道——潮盆体系的演变

近二千年以来，滦河尾闾从西向东迁移，形成了由不同时期的亚三角洲互相叠复而成三角洲体系。丰富的入海泥沙和弱潮环境使该三角洲海岸发育了我国较为完整的潮汐汊道——潮盆体系群。尽管滦河三角洲与密西西比河三角洲有诸多相异之处，但动力泥沙条件的某些相似性使它们的汊道潮盆体系的演变可以进行类比。研究表明，决定潮汐汊道——潮盆体系发育阶段的是它所在的亚三角洲的废弃年龄。从狼窝口到湖林口的各亚三角洲均处于演变的第一阶段。即以受蚀陆岬及其沙咀状堡岛为特色的第一阶段。而大清河口附近则处于以堡岛弧为代表的第二阶段。目前，曹妃甸附近的亚三角洲正在向第三阶段，即堡岛演化为内陆架浅滩的阶段演化。从现代滦河口向曹妃甸，对应于废弃年龄的增加，潮汐汊道分别属于五种类型，即新生波浪型、新生过渡型、潮汐型、老年过渡型及老年波浪型     

Anthropogenic impacts on the water and salt budgets of St Lucia estuarine lake in South Africa

Lake St Lucia in South Africa is part of a UNESCO World Heritage site and a Ramsar wetland of international importance. Like many coastal wetlands worldwide, anthropogenic activities including catchment land-use changes, water diversions/abstractions, and manipulation of the mouth state have significantly affected its functioning over the past century. Questions concerning its sustainability have motivated a re-evaluation of management decisions made in the past and of options for the future. A model for the water and salt budgets has therefore been used to investigate “what if” scenarios in terms of past anthropogenic interventions. In particular, simulations allow us to evaluate the effects of diverting the Mfolozi river from St Lucia on the functioning of the system and on the occurrence of various water level/salinity states that drive the biological functioning of the ecosystem. In the past, when the St Lucia estuary and the Mfolozi river had a combined inlet, the mouth was predominantly open. The lake had relatively stable water levels but variable salinities that increased during dry conditions due to evaporative losses and saltwater inflows from the sea. If the mouth closed, the Mfolozi flow was diverted into the lake which reduced salinities and maintained or increased water levels. Simulations indicate that without a link to the Mfolozi the lake system would naturally have a mainly closed inlet with lower average salinities but more variable water levels. During dry conditions water levels would reduce and result in desiccation of large areas of the lake as has recently occurred. We conclude that the artificial separation of the St Lucia and Mfolozi inlets underpins the most significant impacts on the water & salt budget of the lake and that its reversal is key to the sustainability of the system.     

Variability of the constant flow in Ôsaka Bay

Some current measurements were carried out in Ôsaka Bay to understand the characteristics and causes of fluctuations of the constant flow in the bay. It is shown that the major part of fluctuation of the constant flow in Ôsaka Bay is the wind-driven current. The direction of the wind-driven current in the near surface water deflects clockwise through 10 to 30 degrees from the wind direction while in the lower layer the current deflects counter-clockwise to that in the near surface water in the eastern half of Ôsaka bay. The speed of the wind-driven current in the near surface water is 0.5 to 1.5% of the wind speed while that in the lower layer is smaller than that in the near surface water in this area.     

Process-based modeling of morphodynamics of a tidal inlet system

The morphodynamic evolution of an idealized inlet system is investigated using a 2-D depthaveraged process-based model,incorporating the hydrodynamic equations,Englund-Hansen’s sediment transport formula and the mass conservation equation.The model has a fixed geometry,impermeable boundaries and uniform sediment grain size,and driven by shore-parallel tidal elevations.The results show that the model reproduces major elements of the inlet system,i.e.,flood and ebb tidal deltas,inlet channel.Equilibrium is reached after several years when the residual transport gradually decreases and eventually diminishes.At equilibrium,the flow field characteristics and morphological patterns agree with the schematized models proposed by O’Brien (1969) and Hayes (1980).The modeled minimum cross-sectional entrance area of the tidal inlet system is comparable with that calculated with the statistical P-A relationship for tidal inlets along the East China Sea coast.The morphological evolution of the inlet system is controlled by a negative feedback between hydrodynamics,sediment transport and bathymetric changes.The evolution rates decrease exponentially with time,i.e.,the system develops rapidly at an early stage while it slows down at later stages.Temporal changes in hydrodynamics occur in the system;for example,the flood velocity decreases while its duration increases,which weakens the flood domination patterns.The formation of the multi-channel system in the tidal basin can be divided into two stages;at the first stage the flood delta is formed and the water depth is reduced,and at the second stage the flood is dissected by a number of tidal channels in which the water depth increases in response to tidal scour.     

Sea ice evolution and internal wave generation due to a tidal jet in a frozen sea

The purpose of this study is to investigate the influence of tidal currents on sea ice in Spitsbergen fjords which may cause rapid decrease of the ice thickness due to erosion and melting of the ice. The effect was studied in-situ near the narrow channel connecting the Van Mijen Fjord and Lake Vallunden. The strong jet-like tidal currents in the strait driven by semidiurnal tide continue into the lake preventing ice freezing along a narrow strip during high tide and relatively warm weather. Understanding the formation of open water regions or regions with thin ice is important for the safe transportation on ice. We estimate conditions and representative time over which strong tidal current influences ice thickness along a narrow strip in solid ice. Changes of tidal phase and decrease in air temperature influence freezing of the strip in one-two days. While the tidal flow leaves the strait it overflows a shallow bar and generates internal lee waves propagating downslope and mixing the water. Tidal forcing of internal waves was measured using pressure gauges and by scanning of the ice surface during flood and ebb phases. Internal waves were measured using three types of CTD instruments and an ADCP current meter. The generation of wave packets occurs every tidal cycle when the current flows into the lake, but no generation occurs during the ebb phase of the tide because the currents over the bar slope are low. Parameters of internal waves are estimated. Model simulations confirm generation of internal wave train by the tidal current descending downslope.     

博斯腾湖小湖区出水水质矿化度模型与预测

根据１９９０－１９９４年博斯腾湖小湖区出入湖水质矿化度监测和开都河西支入湖水量和出湖水量观测资料，采用水量平衡和盐量平衡关系推导出博斯腾湖小湖区出湖水质矿化度模型。     

Spatial and Temporal Entry Patterns of Fish Larvae into North Carolina Estuaries: Comparisons Among One Pelagic and Two Demersal Species

A sampling programme targeting larvae of winter spawning fishes immigrating from the oceanic domain into the Pamlico-Albemarle Sounds system (NC, U.S.A.) was performed at the four major inlets of the lagoon system. Sampling yielded abundant catches of three species, a Clupeid (Atlantic menhaden,Brevoortia tyrannus) and two Sciaenids (Atlantic croaker,Micropogonias undulatusand spot,Leiostomus xanthurus). In this article, the author documents the differences in the mechanisms developed for estuarine recruitment among the three species. Abundance at the tidal inlets was dependent upon numerous factors, such as sampling month, inlet, luminosity, tide flow direction and depth. The spatial and temporal positioning of the larvae differed among the species and affected their capabilities to be transported through the inlets. More specifically, spot and croaker migrated vertically within the water column in accordance with the direction of the water flow. Sciaenids minimized the outwelling effects of ebb tides by migrating into the slowest ebbing currents, near the bottom. Menhaden did not rely on vertical migrations for estuarine transport and retention. For this species, landward transport is provided either when dusk and flood onset are coincident or through non-tidal flows developing under meteorological forcing. The Sciaenids were less, or not, dependent upon these conditions. In one inlet, the retention was dependent upon the strength of the flooding and ebbing flows. In this case, the retention of the pelagic species was lower than the retention of demersal species.     

太湖夏季环流成因的数值研究

强潮河口盐水入侵对饮用水源地危害极大。基于平面二维水动力盐度模型, 对典型强潮河口—钱塘江的水动力及盐水入侵过程进行了数值模拟研究。结果表明枯水径流时盐度变化与潮位过程曲线类似, 潮差对盐度大小影响显著, 径流量的增加将逐渐减小其相似程度。当流量增加到一定程度后, 继续增加的一定径流量所产生的抑咸效果减弱, 水资源有效利用率降低, 此时允许水源地盐度超标并改从蓄淡避咸水库取水可有效节约水资源。盐度平面分布显示, 盐水入侵在强潮河口弯道处受涨潮流主流线影响明显, 靠近主流线一岸的盐度大于对岸, 单从盐水入侵角度考虑, 强潮河口弯道段的取水口应设置在远离涨潮流主流线一岸。钱塘江河口盐度数值模拟对于研究减轻盐水入侵对水源地危害的措施具有指导意义。     

太湖梅梁湾三维水动力学的研究──Ⅰ.模型的建立及结果分析

建立了一个太湖梅梁湾三线水动力学模型,模拟了框架湾的水平及垂直流场分布。结果表明：（1）表面流场与风向一致,而底层流场与表面流场的方向完全相反,表现为很明显的补偿流;（2）水平流速基本上自表层向下递减,过渡层的流速比表层和底层小;（3）在风场的作用下可产生垂直环流系统,其中在东南风的作用下产生逆时针的垂直环流（由南向北看）,而在西北风的作用下产生顺时针垂直环流;（4）垂直速度自岸边向湖中心递减,其量级远小于水平流速。