Considering the coupling effects of the vessel and its riser and mooring system, hydrodynamic analyses of a geometric spar were performed both in frequency- and time-domains. Based on the boundary element method, the ...Considering the coupling effects of the vessel and its riser and mooring system, hydrodynamic analyses of a geometric spar were performed both in frequency- and time-domains. Based on the boundary element method, the 3-D panel model of the geometric spar and the related free water surface model were established, and the first-order and second-order difference-frequency wave loads and other hydrodynamic coefficients were calculated. Frequency domain analysis of the motion Response Amplitude Operators （RAO） and Quadratic Transfer Functions （QTF） and time domain analysis of the response series and spectra in an extreme wave condition were conducted for the coupled system with the mooring lines and risers involved. These analyses were further validated by the physical model test results.展开更多
为研究复杂开放环境下收获机械田间作业过程由质量时变影响的工作模态及振动行为,该文搭建了一套收获机械工作模态测试系统,以4YZP-4HA型122 k W玉米联合收获机械为研究对象,建立收获机械车架工作模态测点模型,测定工作模态试验下的土壤...为研究复杂开放环境下收获机械田间作业过程由质量时变影响的工作模态及振动行为,该文搭建了一套收获机械工作模态测试系统,以4YZP-4HA型122 k W玉米联合收获机械为研究对象,建立收获机械车架工作模态测点模型,测定工作模态试验下的土壤-机器-植物等边界条件,并进行田间收获作业和运输工况的振动响应数据采集和时频域分析,利用时域随机子空间SSI(stochastic subspace identification)和频域的增强型频域分解EFDD(enhanced frequency domain decomposition)算法,辨识了在质量时变(田间收获作业)和质量非时变(运输工况)影响下的模态参数(模态频率、阻尼比及模态振型),并比较分析了2种算法的工作模态辨识结果。利用时频域分析方法获取了不同测点振动加速度幅值统计特征及频率分布规律,研究结果表明:田间收获作业工况振动强度高于运输工况,振动频率集中分布在20~150 Hz范围内,测点频率之间存在差异主要由不同位置刚度变化所致;通过比较SSI和EFDD方法辨识的模态频率,发现SSI和EFDD方法在相同频率范围内相差较小,且均落入傅里叶变换方法的频率分布区间,表明SSI和EFDD方法计算结果可信,能够较为准确地确定模态频率;质量时变下的收获机械车架模态振型特征主要表现为扭转、弯曲、弯扭和局部模态振型,其中1阶扭转振型频率接近29 Hz(SSI:29.578 Hz;EFDD:29.300 Hz)。研究结果可为复杂农田作业环境下收获机械的工作模态分析与试验提供参考。展开更多
采用同电极体系,测量了电沉积镍、铜镀层以及铂片在HC l和N aC l溶液中的电化学噪声,研究发现:通过时域分析得到的噪声电阻是评价材料耐蚀性的重要指标,而点蚀指数反映了电极表面反应的均匀程度;通过频域分析可知,高频段斜率可以用于评...采用同电极体系,测量了电沉积镍、铜镀层以及铂片在HC l和N aC l溶液中的电化学噪声,研究发现:通过时域分析得到的噪声电阻是评价材料耐蚀性的重要指标,而点蚀指数反映了电极表面反应的均匀程度;通过频域分析可知,高频段斜率可以用于评价镀层发生腐蚀的类型,而白噪声水平可作为判断材料耐蚀性的指标之一。展开更多
The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formul...The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formula based on continuous wavelet transform. For an arbitrary given square-integrable function f(t),g(t) = f(t/λ) is derived by continuous wavelet transform and its inverse transform. The result shows that time-scale transformation may be obtained through the modification of the time-scale of wavelet function filter using equivalent substitution. The paper demonstrates the result by theoretic derivations and experimental simulation.展开更多
基金the National High Technology Research and Development Program of China (863 Program, Grant No. 2006AA09A107)the Key Fundamental Research Project of Science and Technology Commission of Shanghai Municipality (Grant No. 05DJ14001).
文摘Considering the coupling effects of the vessel and its riser and mooring system, hydrodynamic analyses of a geometric spar were performed both in frequency- and time-domains. Based on the boundary element method, the 3-D panel model of the geometric spar and the related free water surface model were established, and the first-order and second-order difference-frequency wave loads and other hydrodynamic coefficients were calculated. Frequency domain analysis of the motion Response Amplitude Operators （RAO） and Quadratic Transfer Functions （QTF） and time domain analysis of the response series and spectra in an extreme wave condition were conducted for the coupled system with the mooring lines and risers involved. These analyses were further validated by the physical model test results.
文摘采用同电极体系,测量了电沉积镍、铜镀层以及铂片在HC l和N aC l溶液中的电化学噪声,研究发现:通过时域分析得到的噪声电阻是评价材料耐蚀性的重要指标,而点蚀指数反映了电极表面反应的均匀程度;通过频域分析可知,高频段斜率可以用于评价镀层发生腐蚀的类型,而白噪声水平可作为判断材料耐蚀性的指标之一。
文摘The basic objective of time-scale transformation is to compress or expand the signal in time field while keeping the same spectral properties. This paper presents two methods to derive time-scale transformation formula based on continuous wavelet transform. For an arbitrary given square-integrable function f(t),g(t) = f(t/λ) is derived by continuous wavelet transform and its inverse transform. The result shows that time-scale transformation may be obtained through the modification of the time-scale of wavelet function filter using equivalent substitution. The paper demonstrates the result by theoretic derivations and experimental simulation.
