基于有限元模型和模态参数的损伤识别

本文从特征值问题出发 ,结合结构系统的有限单元模型并引入单元损伤因子 ,导出了求解单元损伤因子的方程 ,从而可以确定结构的损伤位置和损伤程度。利用简支梁进行了数值模拟 ,建立了简支梁的有限单元模型 ,用不同单元弹性模量的降低来模拟各种不同的损伤工况 ,并对每种工况进行了损伤位置和损伤程度识别 ,数值模拟结果同实际情况吻合很好。     

Semi-Active Control of Wave-Induced Vibration for Offshore Platforms by Use of MR Damper

The objective of the present research is to examine the effectiveness of the lateral vibration control of wave-excited re-sponse of offshore platforms with magnelo-rheological (MR) damper, In this study, the offshore platform is simplified to be a single-degree-of-freedom (SDOF) system by extracting the first vibration mode of the struclure. The exlernal 'generalized' wave force is determined with a white noise via a designed filler. A semi-active control method based on optimal control the-ory is proposed considering that the yield stress of the MR damper can be varied continuously within a certain range. The dy-namics of SDOF structure coupled with the MR damper is investigated. Numerical simulation demonstrates that the MR damper with this control strategy can significantly reduce the maximum responses and the root-mean-square (RMS) values.     

Energy Anaiysis for TMD-Structure Systems Subjected to Impact Loading

This paper investigates the characteristics of reduction of the lateral vibration by use of a Tuned Mass Damper (TMD) for offshore jacket platforms under impact loading. Unlike traditional analysis, the present analysis focuses on the energy concept of TMD/structure systems. In this study, a time domain is taken. The platform is modeled as a simplified single-degree-of-freedom (SDOF) system by extraction of the first vibration mode of the structure and the excited force is assumed to be impact loading. The energy dissipation and energy transmission of the structure-TMD system are studied. Finally, an optimized TMD design for the modeled platform is demonstrated based on a new type of cost function - maxi-mum dissipated energy by TMD. Results indicate that TMD control is effective in reducing the Standard deviation of the deck motion but less effective in reducing the maximum response under impact loading.     

卤素和硼—金锑砷汞铊矿床指示元素

本文通过２０５个样品，８２０个Ｆ、Ｃｌ、Ｉ、Ｂ分析数据讨论它们在Ａｕ、Ｓｂ、Ａｓ、Ｈｇ、和Ｔｌ矿床中含量变化、富集程度及与矿的关系，特别是与Ａｕ、Ｔｌ成矿的密切关系，提出卤素和硼是低温矿床有重要意义的指示元素。它们在矿床岩矿石中含量，除个别样品外，一般富集系数均在０．ｎ￣ｎ范围变化。     

土地利用功能转型及其生态环境效应研究——以吐鲁番市高昌区为例

以吐鲁番市高昌区为例,利用1990、2000、2010年和2018年4期遥感影像解译获取研究区土地利用变化数据,基于格网尺度,综合运用土地利用转移矩阵、核密度估计、生态环境质量指数和生态贡献率等方法,定量分析研究期内高昌区城市化地区、农产品主产区、生态功能区三大主导功能区土地利用转型的时空格局特征及生态环境效应.结果表...     

Numerical study of three-dimensional wave-induced longshore current's effects on sediment spreading of the Huanghe River mouth

A three-dimensional wave radiation stress is introduced into the hydrodynamic sediment coupled model COHERENS-SED,which has been developed through introducing wave-enhanced bottom shear stress,wave dependent surface drag coefficient,wave-induced surface mixing,SWAN,damping function of sediment on turbulence,sediment model and depth-dependent wave radiation stress to COHERENS.The COHERENS-SED is adopted to study the effects induced by wave-induced three-dimensional longshore current on suspended sediment spreading of the Huanghe River (Yellow River) mouth.Several different cases divided by setting different wave parameters of inputting boundary waves are carried out.The modeling results agree with measurement data.In terms of simulation results,it is easy to know that three-dimensional wave radiation stress plays an obvious role when inputting boundary wave height is stronger than 3 m.Moreover,wave direction also affects the sediment spreading rules of the mouth strongly too.     

中国碳排放的空间格局及分布动态演进——基于县域碳排放数据的实证研究

基于中国1997—2017年2725个县域单元的碳排放数据,采用标准差椭圆、Theil指数三阶段嵌套分解和Kernel密度估计等方法,全面考察中国碳排放的空间格局及分布动态演进。研究发现：① 中国碳排放由1997年的30.97亿t增长到2012年的93.08亿t,年均增长达到7.86%,而后围绕93亿t上下波动,未出现下降的拐点。② 在空间分布上,中国碳排放呈现东高西低的分布格局,表现出东北-西南方向向心集聚、西北-东南方向空间发散的趋势。③ 在空间差异上,Theil指数三阶段嵌套分解结果表明,中国碳排放的总体差异呈下降趋势,地级行政单元内部差异的贡献率由1997年的43%增加到2017年49%,成为中国碳排放总体区域差异的主要来源。④ 在分布动态演进上,中国县域单元的碳排放存在空间收敛模式,具有显著的空间正相关性,地区间的相互作用影响中国碳排放的未来空间分布。     

Nitrogen deposition and its spatial pattern in main forest ecosystems along north-south transect of eastern China

A continuous three-year observation(from May 2008 to April 2011)was conducted to characterize the spatial variation of dissolved inorganic nitrogen(DIN)deposition at eight main forest ecosystems along the north-south transect of eastern China(NSTEC).The results show that both throughfall DIN deposition and bulk DIN deposition increase from north to south along the NSTEC.Throughfall DIN deposition varies greatly from 2.7 kg N/(ha·yr)to 33.0 kg N/(ha·yr),with an average of 10.6 kg N/(ha·yr),and bulk DIN deposition ranges from 4.1 kg N/(ha·yr)to 25.4 kg N/(ha·yr),with an average of 9.8 kg N/(ha·yr).NH4+-N is the dominant form of DIN deposition at most sampling sites.Additionally,the spatial variation of DIN deposition is controlled mainly by precipitation.Moreover,in the northern part of the NSTEC,bulk DIN deposition is 17%higher than throughfall DIN deposition,whereas the trend is opposite in the southern part of the NSTEC.The results demonstrate that DIN deposition would likely threaten the forest ecosystems along the NSTEC,compared with the critical loads(CL)of N deposition,and DIN deposition in this region is mostly controlled by agricultural activities rather than industrial activities or transportation.     

汶川地震前后都江堰山区滑坡滑动距离影响因素变化分析

滑坡滑动距离作为滑坡防灾减灾的主要评价指标之一,不仅受滑坡体积和落差的影响,还与滑坡运动的地质环境作用相关。本文在对都江堰地区51个地震滑坡、16个降雨滑坡详细调查编目的基础上,采用数理统计方法分析了斜坡原始坡度、滑坡前后缘高差、滑坡平面形态、体积、滑体平均厚度及坡面摩擦系数等6个因素与滑坡水平滑动距离的相关性,借此厘清了汶川Ms8.0级大地震前后不同因素对不同类型滑坡运动的贡献大小,进而构建了不同成因类型滑坡的滑动距离预测关系式,可为龙门山区的滑坡防灾减灾工作提供参考。研究表明:影响都江堰地区地震滑坡运动距离的主要因素有滑坡体积(lg V)、斜坡原始坡度(α)、滑坡平面形态(R)和滑坡前后缘高差(ΔH);而控制降雨滑坡运动距离的主要因素为滑坡前后缘高差(ΔH)、滑坡体积(lg V)、斜坡坡度(α)和斜坡表面摩擦系数(μ);汶川地震后,影响该地区降雨滑坡滑动能力的因素发生了变异,各因素与滑坡滑动距离的相关性较弱,显示出其贡献率在急剧减弱,仅滑坡体积(lg V)与滑动距离的相关性较强。     

Probabilistic analysis and fatigue damage assessment of offshore mooring system due to non-Gaussian bimodal tension processes

Both wave-frequency (WF) and low-frequency (LF) components of mooring tension are in principle non-Gaussian due to nonlinearities in the dynamic system. This paper conducts a comprehensive investigation of applicable probability density functions (PDFs) of mooring tension amplitudes used to assess mooring-line fatigue damage via the spectral method. Short-term statistical characteristics of mooring-line tension responses are firstly investigated, in which the discrepancy arising from Gaussian approximation is revealed by comparing kurtosis and skewness coefficients. Several distribution functions based on present analytical spectral methods are selected to express the statistical distribution of the mooring-line tension amplitudes. Results indicate that the Gamma-type distribution and a linear combination of Dirlik and Tovo-Benasciutti formulas are suitable for separate WF and LF mooring tension components. A novel parametric method based on nonlinear transformations and stochastic optimization is then proposed to increase the effectiveness of mooring-line fatigue assessment due to non-Gaussian bimodal tension responses. Using time domain simulation as a benchmark, its accuracy is further validated using a numerical case study of a moored semi-submersible platform.