不同形态海湾的水底平衡剖面研究

研究海湾平衡剖面对理解海湾地貌演变具有重要意义。本文给出了收缩型、扩张型和矩形3种典型海湾平面形态对平衡剖面的影响。建立了海湾长度远小于潮汐波长的短尺度海湾的平衡剖面和对应的时均悬沙浓度的解析解。采用水深平均的水动力方程、泥沙输移方程和地形演变方程的耦合模型对以上3种类型海湾的平衡剖面进行了数值模拟,得到了这3种类型海湾的水面、流速、时均悬沙浓度和平衡剖面的计算结果,并利用水面数值结果确定了海湾水面解析解所含的一个待定常数。研究结果给出了3种不同海湾平面形态所对应的平衡剖面形态:矩形海湾对应斜坡型;收缩型海湾对应下凹型;扩张型海湾对应上凸型。所得海湾平衡剖面和时均悬沙浓度的解析解与数值解一致。     

基于椭球不确定性的平差模型与算法

测量平差模型中的参数通常存在一些不确定的附加信息或先验信息,充分利用它们可以对部分参数进行约束,从而保证参数解的唯一性和稳定性。本文利用椭球集合描述不确定性,建立了一个新的带有椭球不确定性的平差模型。以两个椭球交集的外接椭球的特征矩阵的迹最小平差准则,分析了不确定度的传播规律,给出了带有椭球不确定性的平差方法。最后,通过算例验证了算法的有效性,说明了平差解与带权混合估计的关系。     

考虑冲刷影响的筒型基础竖向极限承载力研究

大直径宽浅式筒型基础,阻水宽度大,在位工作期间受波浪海流作用,其周围土体易被冲刷。为研究单侧地基土体受冲刷后筒型基础的竖向极限承载力变化,通过引进冲刷率的概念,采用有限元方法研究了不同冲刷率下筒型基础的竖向极限承载力;并基于Meyerhof理论建立了计算不同冲刷率下筒型基础竖向极限承载力的极限平衡方法。研究结果表明,随着冲刷率增大,筒型基础的极限承载力出现不同程度的下降,当冲刷率为0.8时,即筒型基础单侧土体冲刷深度达6.4 m时,筒型基础的竖向极限承载力折减率为3.28%。建立的极限平衡算法可准确计算冲刷条件下筒型基础的竖向极限承载力。     

利用椭球变换建立独立坐标系的方法

详细阐述了8种利用椭球变换建立独立坐标系的方法,推导了独立坐标系高程面与椭球面之间的相互关系,进而建立了椭球变换模型,减少了高程归化变形;并通过计算实例对其投影变形值进行分析,以探究不同方法间的特点与差异,得出了一些有益的结论。     

岬间海湾岸线平衡形态神经网络模型

讨论了目前海湾岸线平衡形态经验模型存在的不足之处。从沿岸输沙公式入手,阐述了平衡岸线的机理模式,重新定义了平衡海湾的“下岬角”,给出了模型参数与主波向的具体计算方法,并以华南典型海湾为学习样本,建立了岸线平衡形态的神经网络模型。通过模拟海湾与实际稳定海湾——乌场湾间的对比分析,表明所建神经网络模型是较抛物模型更为理想的平衡岸线模型。     

The effect of a topographic high on the morphological stability of a two-inlet bay system

The cross-sectional stability of two tidal inlets connecting the same back-barrier lagoon to the ocean is investigated. The condition for equilibrium is the cross-sectional area tidal prism relationship. In an earlier study [Van de Kreeke, J., 1990. Can multiple inlets be stable? Estuarine, Coastal and Shelf Science 30: 261–273.], using the same equilibrium condition, it was concluded that where two inlets connect the same basin to the ocean ultimately one inlet will close. One of the major assumptions in that study was that the water level in the basin fluctuated uniformly. In hindsight this assumption might be too restrictive. For example, in the Wadden Sea the back barrier lagoon consists of a series of basins, rather than one single basin, separated by topographic highs. These topographic highs limit but do not exclude the exchange of water between the sub-basins. For this reason in the present study, a topographic high in the form of a weir was added, separating the back-barrier lagoon in two sub-basins. The water level in the sub-basins, rather than in the back-barrier as a whole, is assumed to fluctuate uniformly. For this schematization the hydrodynamic equations are solved using a finite difference method. The results, together with the equilibrium condition, yield the equilibrium flow curve for each of the inlets. The intersections of the two equilibrium flow curves represent combinations of cross-sectional areas for which both inlets are in equilibrium. The stability of the equilibriums was investigated using a non-linear stability analysis resulting in a flow diagram. Calculations were carried out for different inlet and weir characteristics. Sinussoidal tides were the same for both inlets. The results show that for relatively large wetted cross-sectional areas over the topographic high, approaching the situation of a single basin, there are no combinations of inlet cross-sectional areas for which both inlets are in a stable equilibrium. This supports the conclusion in the earlier study. For relatively small wetted cross-sectional areas over the topographic high there is one set of stable equilibriums. In that case the two-inlet bay system approaches that of two single-inlet bay systems.     

北京房山侵入岩体：微量元素、稀土元素及Sr同位素组成对其成因的制约

房山岩体是由 3次脉动式侵位形成的复式岩体 ,不同期次侵位的岩石及其中的包体来自相同的岩浆源区 ,为下地壳的中、基性火成岩。全岩 矿物Rb Sr等时线年龄为 12 6± 3Ma。第 1期至第 2期 ,主要是由以斜长石为主的矿物平衡结晶造成的 ;第 2期至第 3期 ,则可能是批式熔融的结果。包体的成因机制可能不止一种 :英安玢岩质包体和石英粗安玢岩质包体可能分别代表第 2期和第 3期脉动式侵入体的冷凝壳 ;石英正长岩包体则可能代表该侵入体演化到最后的产物 ;而石英闪长质和石英二长闪长质包体则可能为同源岩浆早期结晶的产物。     

相变前的热力学平衡态对铁电液晶排列的影响

本实验选用ZLI-3654型铁电液晶(FLC)以及SE-3140型取向剂制备FLC器件样品,通过改变FLC相变过程中的降温速率以及相变前的热力学平衡态来研究FLC相变前的热力学平衡态对FLC排列的影响,共进行了十组实验.实验后,将FLC器件静态对比度进行比较,得出手性向列相到近晶A相(N^*-SmA)相变前的热力学平衡态对FLC实现均匀排列起着极其重要的作用的结论.实验结果表明:器件的静态对比度可高达620 ∶1, N^*-SmA相变前的热力学平衡态有利于形成高对比     

Static bay beach concept for scientists and engineers: A review

Headland-bay beach (HBB) is one of the most prominent physiographic features on the oceanic margin of many countries in the world. Under the influence of a predominant swell, its curved periphery in natural environment may reach static equilibrium and remains stable without sediment supply from updrift and/or a riverain source within its own embayment. Coastal scientists and engineers have attempted to develop mathematical expressions to quantify this ideal bay shape since the 1940s. As the scenario with depleting sediment supply has become a common reality on many parts of the world coastline in more recent time, some coastal engineers have advocated a rational approach to mimicking the static bay shape found in nature in order to mitigate beach erosion as well as for coastal management. Nowadays, many useful applications have emerged since the publication of the parabolic bay shape equation (PBSE) developed for static equilibrium planform (SEP) in late 1980s. The advance in modern computer technologies and international collaboration has further facilitated the exchange of knowledge and applications of this static bay beach concept (SBBC).