Probability Distribution of the Hull Motion and Mooring Line Tension of Two Floating Systems

The statistical and distribution characteristics of the responses of a floater and its mooring lines are essential in designing floating/mooring systems.In general,the dynamic responses of offshore structures obey a Gaussian distribution,assuming that the structural system,and sea loads are linear or weakly nonlinear.However,mooring systems and wave loads are considerably nonlinear,and the dynamic responses of hull/mooring systems are non-Gaussian.In this study,the dynamic responses of two types of floaters,semi-submersible and spar platforms,and their mooring lines are computed using coupled dynamic analysis in the time domain.Herein,the statistical characteristics and distributions of the hull motion and mooring line tension are discussed and compared.The statistical distributions of the dynamic responses have strong non-Gaussianity and are unreasonably fitted by a Gaussian distribution for the two floating and mooring systems.Then,the effects of water depth,wave parameters,and low-frequency and wave-frequency components on the non-Gaussianity of the hull motion,and mooring line tension are investigated and discussed.A comparison of the statistical distributions of the responses with various probability density functions,including the Gamma,Gaussian,General Extreme Value,Weibull,and Gaussian Mixture Model(GMM)distributions,shows that the GMM distribution is better than the others for characterizing the statistical distributions of the hull motion,and mooring line tension responses.Furthermore,the GMM distribution has the best accuracy of response prediction.     

基于全波形激光雷达数据分解方法的研究

波形分解是全波形激光雷达数据处理的关键技术之一,通过雅克比矩阵更新与否以及阻尼系数的调整,对优化LM(Levenberg-Marquard)算法进行了研究。实验表明,该方法可最优化求解足印内各波形分量的振幅、中心位置和半宽,而不必每次迭代时都需计算雅克比矩阵,简化了计算过程,提高了计算效率,最终得到的模拟波形能够非常好地拟合原始波形。     

基于高斯距离加权格网法研究华北地区地壳形变特征

分析了高斯距离加权格网法计算应变率的原理和特征,研制了相应的计算程序,并用于华北地区现今地壳应变特征研究。基于华北地区1999～2009年的GPS观测结果,研究了确定高斯平滑半径的原则和方法,并给出华北地区地壳形变多个应变率物理量的分布。结果表明,基于150 km高斯平滑半径计算水平速度梯度能够较好地分辨华北地区的应变率空间变化特征,首都圈地区地壳以张渤带上的左旋剪切为主,其中唐山-秦皇岛地区同时存在南北向的拉张变形;山西带整体表现为沿断裂的右旋剪切变形,同时兼具“南挤北张”特性;郯庐断裂带整体形变特征不显著,在南北两端局部区域存在较小的剪切形变;鄂尔多斯块体内部比较稳定,北缘以拉张和左旋剪切变形为主,西缘表现为左旋剪切以及EW向的挤压特征,南缘的秦岭块体南北两侧分别具有左旋剪切和右旋剪切的特性,东西两侧分别表现为正断拉张与逆断挤压特征。     

利用GRACE卫星数据提取苏门答腊地震同震和震后重力变化

基于GRACE重力卫星数据,采用P3M6去相关滤波技术、350 km半径的高斯平滑技术与差分方法,提取2004年苏门答腊Mw9.3地震的同震和震后重力场时空演化过程。该地震断层下盘同震重力变化达到4.6 μGal,上盘同震重力变化最大值为-8.3 μGal,该结果与球体位错理论计算结果在量级和分布形态上具有较好的一致性。震后7 a断层下盘重力变化累计达到5.6 μGal,超过同震变化信号|而断层上盘震后重力变化只有0.6 μGal,仅为同震变化信号的11%。该现象表明,断层下盘所在海洋地层的粘滞性较低,地层相对柔软,其地层在震后由于较大的粘滞性松弛效应而持续变形,并伴随较大的重力变化|而断层上盘所在的地层接近陆地地壳特性,地层相对脆硬,震后受地层的粘滞性响应而导致的重力变化相对较小。     

半参数模型在GPS季节性信号分离中的应用

根据噪声序列的Hurst指数特性,提出一种新的确定半参数模型平滑因子的方法--基于Hurst指数的二分搜索法,并将该方法应用于分离时变GPS季节性信号。通过对模拟数据及实测GPS坐标序列的分析,验证了该方法是一种有效的确定平滑因子的方法。将计算得到的平滑因子代入半参数模型,能够将GPS坐标序列中的季节性信号充分地分离出来。     

历史解译知识引导下组合遥感图谱特征的变化检测方法

高空间分辨率遥感影像为地表变化监测提供了大量细节信息,这使得基于高分辨率影像的变化检测技术成为当前遥感领域的研究热点之一。本文提出了一种历史解译知识引导下组合遥感图谱特征的变化检测方法。首先,通过分割前后时相的组合影像构建空间位置一致的对象,并在提取对象光谱和纹理特征后,引入前期土地覆盖专题图指导2类图谱特征相似度的DS证据融合;然后,利用其历史存档图斑所属区域的优势地类标签指示不同特征相似度的证据差异融合;最后,基于GMM（Gaussian Mixture Mode）模型的二值化方法提取最终的变化区域。实验结果表明,该方法能充分利用历史解译知识指导不同时相高分辨率影像对象特征相似度组合,一定程度上提高了变化检测正确率。     

指数平滑模型在日本珍珠产量预测中的应用

为了准确地研判日本珍珠产业发展势态,科学地确立中国珍珠产业发展目标,有效地制定中国珍珠产业发展政策,采用EVIEWS5.0软件构建了指数平滑模型,并对日本2008～2015年的珍珠产量进行了预测,预测结果显示日本的珍珠产量持续下降,到2015年日本的珍珠产量达到12.35 t.     

Dimension and entropy in the soil-covered landscape

Both the Hausdorff dimension and the K-entropy supply a measure of the irregularity of the landspace surface. The relationship between the two measures is investigated over a variety of terrains in Britain and a method of calculating the entropy is checked against an independent estimate of the dimension with reasonable agreement. The calculation of the K-entropy requires that the landscape surface be represented by an homogenous ergodic random field. This condition is satisfied by the tendency of soil-covered terrains to progressively approximate to a form well represented by a Gaussian field. Gaussian random fields can either be very smooth, possessing derivatives of all orders at every point or they are highly irregular and non-differentiable everywhere. Within the regular conceptualization the Rice-Kac theory is used to predict the numbers of crossing points and the extent of excursion sets. These predictions are tested against an example terrain from the High Weald of East Sussex with very good agreement, apart from predictions of local maxima. A worked example of the calculation of the K-entropy is given as an appendix. The potential role of information theory in geomorphology extends beyond the use made of entropy in this investigation. In particular ergodic theory has important practical and theoretical implications.     

Conference Reports

18th International Symposium of Cipa by D. M. Barber, p.505
48th Photogrammetric Week by A. T. Smart, p.506
5th Conference on Optical 3D Measurement Techniques by G. Hunter, p.509     

Conditional Simulation of Random Fields with Bivariate Gamma Isofactorial Distributions

This work focuses on a random function model with gamma marginal and bivariate isofactorial distributions, which has been applied in mining geostatistics for estimating recoverable reserves by disjunctive kriging. The objective is to widen its use to conditional simulation and further its application to the modeling of continuous attributes in geosciences. First, the main properties of the bivariate gamma isofactorial distributions are analyzed, with emphasis in the destructuring of the extreme values, the presence of a proportional effect (higher variability in high-valued areas), and the asymmetry in the spatial correlation of the indicator variables with respect to the median threshold. Then, we provide examples of stationary random functions with such bivariate distributions, for which the shape parameter of the marginal distribution is half an integer. These are defined as the sum of squared independent Gaussian random fields. An iterative algorithm based on the Gibbs sampler is proposed to perform the simulation conditional to a set of existing data. Such ‘multivariate chi-square’ model generalizes the well-known multigaussian model and is more flexible, since it allows defining a shape parameter which controls the asymmetry of the marginal and bivariate distributions.