基于CLEAN算法的GPS监测数据处理方法

对建筑物进行高精度的变形监测是后期信息提取,预防安全隐患的基础。针对GPS变形监测中存在的多径误差问题,本文提出一种基于CLEAN算法的GPS多径提取方法,首先对多径信号理论模型进行分析,结果表明多径信号可以作为直达信号的谐波分量,在此基础上利用CLEAN算法在频域对多径信号进行提取,基于仿真和实测数据的实验结果表明,所提方法相对于小波方法和经验模态分解(Empirical Mode Decomposition,EMD)方法具有更高的提取精度和更好的多径抑制性能。     

农户对禁牧政策的行为响应及其影响因素研究——以新疆策勒县为例

以新疆策勒县为例,对当地农牧民在封育禁牧影响下的经济行为响应及其影响因素利用对数线性模型进行定量分析,以研究不同背景条件的农牧民在进行行为选择时的规律性因素。研究表明,农户所属区域及其拥有的资本水平是农户对禁牧行为响应的显著影响因素;农户所属区域及当地的技术服务培训等政策配套水平是农户对禁牧态度的显著影响因素;农牧民畜牧生产观念的转变和草场承包责任制的落实是实施禁牧政策的先决条件。建议政府针对区域及农户的资本差异进行分类补偿;当地政府可整合利用各相关部门的项目资源和资金进行禁牧的政策前期和推广工作。     

中国大陆结构地震反应观测系统布设研究

本文简要介绍了结构地震反应观测研究的意义。并以中国地震局防灾大楼和北京市人大办公大楼结构地震反应观测系统为布设实例,阐述了中国大陆地区结构地震反应观测系统的两种布设方式。对两种方式进行了分析,指出简化布设中存在的问题,并提出了布设原则,用于指导结构地震反应观测系统的布设。     

城市精明发展与生态效率的协同测度及交互响应——以中国276个地级以上城市为例

城市发展与生态环境存在复杂的动态交互耦合过程,厘清精明发展与生态效率的协同发展关系及交互响应机理,是区域可持续发展的关键环节。本文以2003—2015年中国276个地级以上城市为研究对象,采用多指标综合评价法、Super-SBM模型、灰色关联模型和面板VAR模型对中国城市精明发展与生态效率的协同发展和交互响应关系进行综合测度。研究表明：① 城市精明发展呈现从沿海向内陆阶梯递减的空间演变趋势,多个城市群具有较高的城市精明发展指数。② 生态效率与精明发展的空间变化具有一定的耦合特征,沿海地区南北方向呈现出较高水平的“生态弧线”城市带。③ 城市精明发展与生态效率具有显著的关联性特征,协同发展关系有下降趋势。④ 城市精明发展与生态效率存在双向交互的Granger因果关系,具有正向的交互响应关系,且存在一定的路径依赖特征和惯性发展趋势。⑤ 长期而言,城市精明发展对生态效率变动的影响更大。     

椭球谐和球谐系数之间一个简单的转换关系

本文推导的椭球谐系数和球谐系数相互之间转换关系的核心思想是在ε~2量级下利用Legendre函数的正交性,从球谐系数求解的积分表示出发,将积分中的椭球坐标变量与球坐标变量相互转换,从而得出椭球谐系数与球谐系数之间的转换关系。本文导出的转换关系有以下优点:①对于第二类Legendre函数的计算采用Laurent级数表示,使计算第二类Legendre函数更为简单;②保留了ε~2量级下,导出的转换关系相比文献[2]的形式更简单,满足物理大地测量边值问题线性化的要求;③顾及了余纬和归化余纬的区别。     

Examining the sensitivity of spatial scale in cellular automata Markov chain simulation of land use change

Understanding the spatial scale sensitivity of cellular automata is crucial for improving the accuracy of land use change simulation. We propose a framework based on a response surface method to comprehensively explore spatial scale sensitivity of the cellular automata Markov chain (CA-Markov) model, and present a hybrid evaluation model for expressing simulation accuracy that merges the strengths of the Kappa coefficient and of Contagion index. Three Landsat-Thematic Mapper remote sensing images of Wuhan in 1987, 1996, and 2005 were used to extract land use information. The results demonstrate that the spatial scale sensitivity of the CA-Markov model resulting from individual components and their combinations are both worthy of attention. The utility of our proposed hybrid evaluation model and response surface method to investigate the sensitivity has proven to be more accurate than the single Kappa coefficient method and more efficient than traditional methods. The findings also show that the CA-Markov model is more sensitive to neighborhood size than to cell size or neighborhood type considering individual component effects. Particularly, the bilateral and trilateral interactions between neighborhood and cell size result in a more remarkable scale effect than that of a single cell size.     

Hydrodynamic performance of a T-shaped floating breakwater

The comprehensive utilization of floating breakwaters, specially acting as a supporting structure for offshore marine renewable energy explorations, has received more and more attention recently. Based on linear water-wave theory, the hydrodynamic performance of a T-shaped floating breakwater is semi-analytically investigated through the matched eigenfunction expansion method (MEEM). Auxiliary functions, to speed up the convergence and improve the accuracy in the numerical computations, are introduced to represent the singular behavior of fluid field near the lower salient corners of the structure. The effects of the height and installation position of the vertical screen on the reflection and transmission coefficients, dynamic response and wave forces are examined. It is found that the presence of the screen shifts the resonance frequency of RAO for both surge and pitch modes to the low-frequency area, while has no effect on heave mode. The identical added masses, damping and transmission coefficients can be obtained in the cases where the screen holds the same distance away from the longitudinal central axis of the upper box-type structure. Moreover, a relatively small pitch response can be achieved in a wide wave–frequency range, when the breakwater is Γ-shaped.     

Dynamic modeling and vibration suppression for an offshore wind turbine with a tuned mass damper in floating platform

The worldwide demand for renewable energy is increasing rapidly. Wind energy appears as a good solution to copy with the energy shortage situation. In recent years, offshore wind energy has become an attractive option due to the increasing development of the multitudinous offshore wind turbines. Because of the unstable vibration for the barge-type offshore wind turbine in various maritime conditions, an ameliorative method incorporating a tuned mass damper (TMD) in offshore wind turbine platform is proposed to demonstrate the improvement of the structural dynamic performance in this investigation. The Lagrange's equations are applied to establish a limited degree-of-freedom (DOF) mathematical model for the barge-type offshore wind turbine. The objective function is defined as the suppression rate of the standard deviation for the tower top deflection due to the fact that the tower top deflection is essential to the tower bottom fatigue loads, then frequency tuning method and genetic algorithm (GA) are employed respectively to obtain the globally optimum TMD design parameters using this objective function. Numerical simulations based on FAST have been carried out in typical load cases in order to evaluate the effect of the passive control system. The need to prevent the platform mass increasing obviously has become apparent due to the installation of a heavy TMD in the barge-type platform. In this case, partial ballast is substituted for the equal mass of the tuned mass damper, and then the vibration mitigation is simulated in five typical load cases. The results show that the passive control can improve the dynamic responses of the barge-type wind turbine by placing a TMD in the floating platform. Through replacing partial ballast with a uniform mass of the tuned mass damper, a significant reduction of the dynamic response is also observed in simulation results for the barge-type floating structure.     

Effects of wave directionality on extreme response for a long end-anchored floating bridge

Reliable design codes are of great importance when constructing new civil engineering concepts such as floating bridges. Previously only a scarce number of floating bridges have been built in rough wave conditions and only limited knowledge of the extreme environmental conditions and the associated extreme response exists. To form a better design basis an increased understanding of the sensitivity in the structural response towards changes in short-crested sea parameters is needed. Furthermore, acquiring the necessary accuracy in simulated extreme response is often a computationally expensive endeavour and the number of simulations needed is often based on experience. The present study investigates the wave-induced short-term extreme response of a simplified end-anchored floating bridge concept for several wave environments with a return period of 100 years. The study includes convergence of the coefficient of variation for the extreme response for different realization lengths as well as number of realizations. The sensitivity in the structural response towards different main wave directions and spreading exponents is investigated and includes both transverse and vertical displacement response spectra and extreme Von Mises stress in the bridge girder cross-section. The extreme response is based on an accuracy of 2% in the coefficient of variation equivalent to 40 3-h realizations and a low sensitivity in the response is found for natural occurring spreading exponents and for main wave directions within 15° from beam sea.     

Numerical Study on Tidal Mixing in the Bohai Sea

The spatial and temporal variability of tidal mixing in Bohai Sea is studied using a numerical approach. In calculating tidal mixing, accurate barotropic tidal current is obtained via a harmonic analysis package utilizing the simulated current output from a high-resolution regional ocean model. And a “small-scale” roughness map is adopted to describe the detailed topographic features of Bohai Sea. It is shown that the tidal mixing estimated in Bohai Sea is much higher than the level of global background, and fluctuates considerably at some regions within a single day. In Liaodong Bay, Bohai Bay and Bohai Strait, the mixing varies greatly, with the peak value of O (10^?2) m² s^?1. The order of magnitude of mixing in Laizhou Bay is about O (10^?5～10^?3) m² s^?1. Mixing with background level of O (10^?5) m² s^?1 only appears in central area. Result also shows that rough topography plays relatively a more important role than tidal current in enhancing diapycnal mixing in Bohai Sea. The distributions of tidal mixing in selected sections reveal that the vertical stratification in Bohai Sea is not obvious, generally renders a barotropic structure.