导航卫星观测量精度评定法研究

给出了一种导航卫星观测量精度的评定方法,并结合具体算例对该方法进行了实验验证。结果表明,文中给出的方法切实可行,能够对导航卫星的观测量精度进行较为合理的评定,相关研究成果对我国北斗卫星导航系统的测试评估具有一定的参考意义。     

Estimation of Land Subsidence Based on Groundwater Flow Model

This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. The proposed method is employed to analyze the consolidation of a soft layer due to withdrawal of groundwater from an aquifer under it. Moreover, this method is also applied to a field case of land subsidence due to groundwater pumping in a gas production field in Japan. The analytical results are compared with the field observed data. The results show that this approach simulates the field case well.     

Estimation of Land Subsidence Based on Groundwater Flow Model

This article presents an approach for estimating land subsidence due to withdrawal of groundwater. The proposed method calculates the groundwater seepage in 3-D-condition and calculates the land subsidence one-dimensionally. The governing equation on groundwater seepage is based on the three-dimensional mass conservation law and the principle of effective stress. The land subsidence calculation method is derived based on the following assumptions: (1) displacements occur only in the vertical direction, and (2) in vertical direction the total stresses do not change. The governing equation is solved by numerical method, i.e., finite element method (FEM) in spatial discretization and finite difference method (FDM) in time series discretization. In FEM Galerkin method is adopted and in FDM, lumped matrix method is employed. The proposed method is calibrated via analyzing 1-D consolidation problem and the results are compared with those from Terzaghi's one-dimensional consolidation theory and oedometer test. The proposed method is employed to analyze the consolidation of a soft layer due to withdrawal of groundwater from an aquifer under it. Moreover, this method is also applied to a field case of land subsidence due to groundwater pumping in a gas production field in Japan. The analytical results are compared with the field observed data. The results show that this approach simulates the field case well.     

A Finite Volume Method with Unstructured Triangular Grids for Numerical Modeling of Tidal Current

The finite volume method （FVM） has many advantages in 2-D shallow water numerical simulation. In this study, the finite volume method is used with unstructured triangular grids to simulate the tidal currents. The Roe scheme is applied in the calculation of the intercell numerical flux, and the MUSCL method is introduced to improve its accuracy. The time integral is a two-step scheme of forecast and revision. For the verification of the present method, the Stoker＇s problem is calculated and the result is compared with the mathematically analytic solutions. The comparison indicates that the method is feasible. A sea area of a port is used as an example to test the method established here. The result shows that the present computational method is satisfactory, and it could be applied to the engineering fields.     

基于粒度插值计算的底质划界与表示方法研究

针对传统海洋底质几何划界方法精度不足和表示方法单一的问题,提出一种基于站点粒度数据进行Delaunay三角网插值计算的底质划界方法,利用底质分类阈值进行区域定性,实现底质的空间定量划界;针对底质划界结果,提出一种应用于不同比例尺下的底质符号(线状和面状)表示方法,并且设计与比例尺相衔接的显示机制.实验表明,该划界方法可...     

水面之上法测量水体光谱的关键技术

对水体光谱特征的研究是海洋水色遥感的基础工作之一。水体的光谱特征包括:表观光学特性和固有光学特性。在水体的表观光学特性研究方面,目前国际水色界推行的有:剖面法和水面之上法(也称表面法)。由于我国近岸水体混浊度较高,浅水区域较多,研究这类水体的表观光学特性应以水面之上法为主、剖面法为辅。介绍了水面之上法水体光谱的测量技术,就其中关键技术问题进行了讨论。     

Approximation of wave forces on cylinder arrays

An approximate method for the estimation of wave forces on groups of fixed vertical cylinders is presented. The method is based upon a large spacing approximation and involves replacing scattered diverging waves by plane waves. The method is shown to give good results when compared with an exact method, even when the spacing is small. Some new results for a group of five cylinders are presented.     

A new method of combination of electroosmosis,vacuum and surcharge preloading for soft ground improvement

As a rapid and effective ground improvement method is urgently required for the booming land reclamation in China＇s coastal area, this study proposes a new combined method of electroosmosis, vacuum preloading and surcharge preloading. A new type of electrical prefabricated vertical drain （ePVD） and a new electroosmotic drainage system are suggested to allow the application of the new method. This combined method is then field-tested and compared with the conventional vacuum combined with surcharge preloading method. The monitoring and foundation test results show that the new method induces a settlement 20% larger than that of the conventional vacuum combined with surcharge preloading method in the same treatment period, and saves approximately half of the treatment time compared with the vacuum combined with surcharge preloading method according to the finite element prediction of the settlement. The proposed method also increases the vane shear strength of the soil significantly. The bearing capacity of the ground improved by use of the new proposed method raises 118%. In comparison, there is only a 75% rise when using the vacuum combined with surcharge preloading method during the same reinforcement period. All results indicate that the proposed combined method is effective and suitable for reinforcing the soft clay ground. Besides, the voltage applied between the anode and cathode increases exponentially versus treatment time when the output current of power supplies is kept constant. Most of the voltage potential in electroosmosis is lost at electrodes, leaving smaller than 50% of the voltage to be effectively transmitted into the soil.     

Duffing振子系统周期解的唯一性与精确周期信号的获取方法

研究Duffing振子系统的周期解的唯一性与精确周期信号的获取方法. 应用定性分析方法,获得了一类Duffing振子系统具有唯一周期解的必要条件,同时也得到了一类更广泛的非线性周期系统的周期解的唯一性.在一定条件下,给出了Duffing振子系统精确周期信号的获取方法.     

利用EMD方法和小波变换进行信号奇异性检测

本文采用经验模式分解 (EMD)与小波变换相结合的方法分析非平稳机械故障信号的奇异性 ,进行机械故障诊断。与直接对原信号进行小波分析相比较 ,该方法提取的奇异性特征明显。数值模拟和对故障轴承的振动信号分析表明了该方法的有效性。     

A dynamic two-dimensional calculation of underwater lines

On the basis of a lumped mass method in two-dimension, we derive a dynamic calculation method for a system including both extensible and inextensible underwater lines. The Newmark beta method is used in numerical integration with respect to time. The Newton Raphson method is applied so that the numbers of iterations are reduced. A transient response of a line during deployment is calculated.     

Efficient computation of cross-spectral densities in the stochastic modelling of waves and wave loads

A new method is presented for efficient calculation of auto- and cross-spectral densities in the stochastic modelling of ocean waves and wave loads. As part of the short-term response analyses, the method may contribute to more efficient long-term response prediction. Specifically the cross-spectral densities of the first order wave excitation forces are considered, but the method is straightforwardly generalized to other cross-spectral densities, e.g. for wave elevation, wave kinematics or second order loads. The method can be used with any choice of directional spreading function, but special attention is given to the commonly used cos-2s type directional distribution. In addition to the development of the new method, the traditional method using the trapezoidal rule for numerical quadrature is improved by developing an adaptive way of choosing the number of integration points. The accuracy of the adaptive method and the new method is investigated, revealing rapid convergence for both methods. However, the new method appears more robust as it avoids so-called spurious hat errors. When applied to two different pontoon type floating bridges the adaptive method and the new method both achieve a great improvement in computational effort compared to the traditional trapezoidal rule method. When the dimensions of the floating bridge increase, i.e. the number of pontoons and their relative distances increase, the new method is superior with respect to computation time.     

Rain-Flow and Reverse Rain-Flow Counting Method for the Compilation of Fatigue Load Spectrum

The rain-flow counting method is widely used to compile the fatigue load spectrum. The second stage counting of the rain-flow method is a troublesome process. In order to overcome this drawback, the rain-flow and reverse rain-flow counting method is proposed in this paper. In this counting method, the rule for counting of the rain-flow method is modified, so that the sequence of load-time need not be adjusted. This is a valid and useful method to count cycles and compile the load spectrum and it can be widely used in ocean engineering.     

Plane wave fitting of the internal tidal sea-surface height signatures extracted from the TOPEX/Poseidon altimeter data along satellite tracks

The sea-surface height (SSH) signatures of internal tides extracted from the TOPEX/Poseidon (T/P) altimeter data along satellite tracks are fitted with superposition of several plane waves which have different wavenumber vectors. The key problem of plane wave fitting with iterative method is how to determine the initial value of wavenumber of each plane wave. The previous solving method is to analyze the internal tidal SSH signatures along each track with wavenumber spectrum. But it is found that the problem cannot be solved completely with the wavenumber spectrum analysis method only. The method based on the combination of wavenumber spectrum analysis method and the exhaustive method is proposed to determine the initial values of wavenumbers for iteration. Numerical results indicate that the proposed method is not only reasonable and feasible but also better than the previous method. The proposed method is an improvement of the previous one, which is beneficial to improving the precision of plane wave fitting of the T/P internal tidal SSH signatures and deepening the understanding of the internal tides in ocean.     

Downward continuation of aeromagnetic data to the marine surface

The existing methods of downward continuation of potential field cannot be used to continue the aeromagnetic data to the marine surface because of the limited continuation distance. An iteration method for the downward continuation of potential field with a much larger continuation distance has been developed, which can continue the aeromagnetic data to the marine surface and get the marine - magnetic chart with the same scale as the aeromagnetic data. This downward continuation method will greatly raise the ef- ficiency of marine - magnetic investigation. The principle of the iteration method is presented. The method is demonstrated on synthetic models and real aeromagnetic data. Also, the error brought by continuation is discussed. The efficiency of the iteration method for the downward continuation of potential field is compared with the fast fourier transform （FFT） method, the former is much better than the latter.     

气泡声学特性探潜方法研究

文中提出了一种探测潜艇的新方法,通过分析由潜艇螺旋桨产生的气泡特有的声学特征来探测潜艇。潜艇螺旋桨产生的气泡在水中会滞留比较长的时间,分布也很广泛,这给利用尾流气泡探测潜艇提供了可行性。利用此方法探测安静型潜艇具有理论和技术上的可行性。     

状态空间模型在海洋波能转换系统中的应用 Ⅰ.数值模拟方法改进

状态空间模型是研究海洋波能转换系统相互作用的一种有效数学模型.应用该模型的关键之一是如何根据实验或计算的脉冲响应函数来高效地确定状态空间模型中的矩阵参数.结合最优化理论中的单纯形法、最小二乘法以及矩阵指数的简化算法,提出了一种确定状态空间模型矩阵参数的有效数值方法.数值试验表明,由于该方法克服了高斯-牛顿方法的局部收敛性及其需求解矩阵指数关于参数的导数的缺点,因此大大扩展了初值的可选范围,有效地提高了数值模拟效率,并且使数值模拟结果具有较高精度.     

大弹涂鱼基因组DNA两种提取法的比较

采用传统的饱和酚提取法和上海生物工程公司的UN IQ-10柱式基因组DNA抽提试剂盒法对大弹涂鱼的总DNA进行了提取。琼脂糖凝胶电泳结果表明,得到的DNA片段分子量在21 kb以上;通过PCR扩增实验,证明了用两种方法提取的DNA均可直接用于随机扩增的DNA多态性(RAPD)遗传标记;试剂盒法具有简单、快速、高效的优点,是一种值得推荐的DNA提取方法。     

海底管道拖管法分析和研究

海底管道铺设是海洋油气工程建设的一项重要内容.海底管道铺设的方法有铺管船法和拖管法.铺管船法受铺管船舶资源的限制,而拖管法铺管不依赖铺管船,在一定的条件下,可以节约费用,因此研究拖管法铺管就非常有意义.文中首先介绍各种管道铺设施工方法,并对各种方法的优缺点进行比较.然后分别分析研究了浮拖法、底拖法和离底拖法三种拖管方法的施工工艺及管道应力变形,并结合实例对三种拖管方法的拖管过程进行了分析.     

Optimization of buoyancy of an articulated stinger on submerged pipelines laid with a barge

An analytical method is presented for finding the elastic deflection of submerged pipelines laid with an articulated stinger in which the buoyancy of each element is adjustable. The computer time required for the method is much less than that for the finite element method, so that optimization of the laying parameters can be performed in a large region using mathematical programming. A practical example shows the efficiency of the proposed method.