基于小波分析的海洋平台实时结构健康监测

由于海洋平台结构长期处于恶劣的海洋环境中,并受到各种载荷的交互作用,结构容易产生各种形式的损伤。因此,对海洋平台进行实时监测有着十分重要的现实意义。以单筒简易导管架平台为例,主要在结构损伤的判定和定位两方面对海洋平台的实时结构健康监测进行研究,结果表明通过对结构响应信号进行小波分析,小波变换系数和小波包能量分布可以很好地定义损伤识别指标。     

基于小波变换的固定式海洋平台结构损伤识别方法研究

小波变换在分析非平稳信号方面较傅立叶变换更有效,为了检测出海洋平台结构中裂缝或因刚度降低引起的损伤,对海洋平台的响应信号进行离散小波变换,通过分析变换后的信号是否有突变现象判断结构是否出现损伤,并结合模态应变能法实现了对结构损伤的定位,探讨了传感器位置对识别效果的影响。     

基于小波变换的海洋平台损伤检测研究

当结构物产生损伤时,结构的动力特性会发生变化,从而引起结构振动响应产生相应的变化。小波变换是奇异性信号的良好检测工具,可以用于识别结构损伤的发生。建立了某海洋平台有限元模型,得到了随机海浪作用下不同损伤工况的结构振动响应。基于小波变换损伤检测,针对不同类型杆件损伤、不同位置杆件损伤、不同程度的噪声污染以及不同方向振动响应信号情况下,分别研究了海洋平台结构的损伤检测问题,得到了一些有用的结论。     

Multi-component seismic response analysis of offshore platform by wavelet energy principle

A wavelet energy method is presented to search the critical incidence of earthquake excitation in a multi-dimensional seismic response of offshore platforms. The total effective energy and the instantaneous effective energy input rate of an earthquake can be obtained by wavelet transformation to predict the critical incidence of the earthquake and then the maximum dynamic response of the platform can be calculated. The critical incidence is determined using this method for an actual platform and a group of single degree-of-freedom systems. Numerical results show that the application of wavelet transform in a multi-dimensional seismic response of structures is convenient and reliable.     

台湾龟山岛东南部海域白色热泉特征分析

海底热液活动及其周边环境的调查研究是海洋科学领域的热点之一。海底热液喷口环境的物理化学参数,尤其是浅水型热液,会受到潮汐变化的影响。台湾龟山岛靠近冲绳海槽南端分布有多处浅水型热液喷口(30m)。2010年5月,浙江大学、杭州电子科技大学和台湾中山大学对该海域实施了联合考察,利用电化学传感器获得了低温热液喷口(24.834 14°N,121.961 91°E)连续87h的温度和pH现场观测数据。基于Morlet复小波变换方法,分析了浅水型热液喷口的温度和pH现场观测时间序列的变化周期,并通过与当地潮汐记录数据作比较,获得了其与潮汐信号之间的潜在关系,证实了潮汐变化是海底白色热泉喷口物理化学参数现场观测最主要的影响因素。温度和pH现场观测数据经Morlet复小波变换后的小波系数分别存在规律的12.9h和12.5h变化周期,并且温度的小波系数在准半日周期尺度与潮汐高度呈负相关变化,相关系数为-0.89;pH的小波系数情况相反,相关系数为0.76。     

结构损伤初步定位的简便方法

提出将基于动态特性的检测方法与局部物理检测手段相结合的探伤思路。利用动力学方法进行实时监测及损伤区域的粗略定位,再由物理探测方法实现损伤程度和位置的精确判断,从而降低对动态检测方法的精度要求。此外,文中尝试直接由结构的动力响应信号构建能量指标识别结构损伤的方法,不需要进行模态参数识别,算法简单,有望应用于海洋平台、高层建筑等可简化为串联多自由度体系的结构的实时监测和损伤初步定位。     

深海悬链线立管涡激疲劳损伤研究

讨论海洋平台钢质悬链线式立管SCR(Steel Catenary Riser)的涡激疲劳损伤问题。对于悬链线立管外的流体,给出涡脱落频率和升力对立管作用的计算方法。悬链线立管采用索结构模型,进行动力学分析并利用模态叠加法对其进行动力响应分析。根据Palmgren-Miner线性累积损伤准则并结合S-N曲线,分析在不同流速下立管的涡激疲劳损伤。以工程中实际使用的1 500 m Spar海洋平台悬链线立管为例,对立管的涡激疲劳损伤进行了预报。并通过立管的参数研究,分别就立管外不同来流速度、立管壁厚、内部流体密度和柔性接头刚度对其疲劳损伤的影响进行了分析,得到了一些有意义的研究结果。     

利用连续小波提取近海大气湍流中的相干结构

利用Morlet子波对南海塔基风脉动资料进行连续小波分析,并根据能量极大值法则辨识相干结构的尺度,从而构建基于相干结构主要尺度的湍流模型。通过对小波系数进行谱分析,得到相干结构的生成周期,进而刻画相干结构的演变特征。结果表明:相干尺度提取的准周期结构在数值和波形上能够很好的反映原信号的主要结构。在分析频段内,大气湍流相干结构的生命尺度和生成周期相近,相干结构以连续出现为主,而小尺度涡旋结构的生成存在明显的不连续。最后,结合观测期间天气过程以及相应的湍流统计特征分析,给出了典型天气条件下相干结构涡动能量分布及其随时间的变化特征。     

Dynamic behaviour of axially pre-loaded tubular steel members of offshore structures subjected to impact damage

The behaviour of an axially pre-loaded cylindrical member of an offshore structure, hit by a supply ship, has been investigated. The effects of axial pre-loading on the dynamic properties of members, the extent of damage and propagation of dynamic instability in the tubular members have also been investigated. Numerical models have been validated using available experimental data from the literature although these are mostly static with no pre-loading. Axial pre-loading was found to change the dynamic characteristics of some cylindrical members quite dramatically while it had no significant effect on others. The study examined whether there was any change in the behaviour between local and global modes when the loading was dynamic rather than static. The effect of damping on the dynamic instability of axially pre-loaded tubes under lateral dynamic loads was also studied. It was observed that for some geometries the quasi-static response can be used to define the boundary between bounded and unbounded dynamic responses. The main contribution of this study, compared with previous investigations reported in the literature, is that both pre-loading and dynamic effects have been included.     

Application of Wavelet Algorithm to Spectral Analysis of Oceanic Waves and Offshore Structure Responses

Fourier transform (FT) is a commonly used method in spectral analysis of ocean wave and offshore structure responses,but it is not suitable for records of short length.In this paper another method,wavelet transform (WT),is applied to analyze the data of short length.The Morlet wavelet is employed to calculate the spectral density functions for wave records and simulated Floating Production Storage and Offloading (FPSO) vessels' responses.Computed wave data include simulated wave data based on JONSWAP spectr...     

一种基于状态空间模型的浮式海上升压站平台动力响应计算方法研究

浮式海上升压站的动力响应分析是其设计阶段的重要内容,对浮式升压站进行结构优化进而改进其水动力性能意义重大。提出一种基于状态空间模型的浮式海上升压站平台动力响应算法,该方法通过频域拟合的方法计算延迟函数频响函数有理分式的系数,得到延迟函数的极值和留数,进而构建延迟函数的状态空间模型,通过状态空间模型代替Cummins方程中的卷积项,从而计算浮式海上升压站的动力响应。采用日本福岛示范项目的浮式升压站模型对方法进行验证,结果表明计算得到的动力响应与商业软件SESAM计算结果吻合较好,说明方法的有效性。     

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。     

考虑桩土作用独桩海洋平台横向振动特性研究

采用动Winkler弹性地基梁模型模拟桩土问动力相互作用，并考虑了流体与桩问相互作用，通过组合成层土中、水中桩单元的刚度阵，推得了独桩海洋平台连续系统横向振动的动刚度阵及在波浪力作用下平台甲板处的频率响应函数，进而求得了在确定性波浪力及随机波浪力作用下桩身任意点的位移响应。最后，通过算例研究和分析了在随机波浪力作用下成层土参数、甲板上重量及冲刷淘深等因素对平台振动响应的影响。     

Identification of the excitation and reaction forces on offshore platforms using the random decrement technique

This paper describes a method to identify the parameters of the dynamic model of a fixed offshore platform subjected to wind-generated random waves using its stationary response. The structure is modeled as a single degree of freedom system. The parameters identified are the damping coefficient, the natural frequency, and the excitation. In addition, the moment and force acting on the foundation are also identified. The method uses the random decrement signature as a tool to identify the parameters in the equation of motion. Excellent agreements were obtained between the predicted and actual values of the parameters as well as for the reaction and moment at the platform's foundation. The method can be applied without any interruption to the operation of the offshore structure. The method is easy to apply, and uses inexpensive motion measurement instruments. The estimated force and moment can be used as a tool for an on-line foundation check.     

Wave parameters and functions in wavelet analysis

A preliminary study of wave parameters and functions in wavelet analysis is conducted in this paper. The Morlet wavelet transform is used to calculate the time–frequency wavelet energy density function, its volume (i.e. the total energy), its frequency-integral (i.e. the wavelet smoothed instantaneous wave energy history), its time-integral (i.e. the wavelet spectral density function), and two non-dimensional wave indices (NIF, NIT). The processing of the measured wave data obtained from the Chi-Gu coastal observation tower during the period August 2000 to July 2001 indicates that the inter-comparison of wavelet smoothed instantaneous wave energy history and smoothed instantaneous wave energy history (SIWEH) as defined by Funke and Mansard (Proc 17th Int Conf on Ocean Eng, 1980) can reveal the noise structure of the wave signal. The wave data with index NIF greater than 2 is always accompanied with noise, therefore NIF can be used as one of the data quality criteria. The index NIT is linearly correlated with the significant wave period and with the significant wave height, therefore NIT can be used to study the wave growth and decaying phenomena.     

冰激振动下简易平台的动态优化设计

简易平台是边际油田开发的主要结构形式,由于平台结构形式简单,受到动力荷载作用响应比较大。采用动态设计可以合理优化平台结构形式,达到降低平台动力响应的效果。文中以JZ20-2NW简易平台为原型,运用ANSYS有限元分析软件对其进行冰激振动下的动态优化设计。结果表明,动态设计减振效果明显,可供设计人员参考。     

小波变换在水下目标回波奇异性检测中的应用

小波变换突破了传统Fourier变换等信号处理方法均限制,具有表征信号局部特征的能力,信号的局部奇异性包含了信号的许多重要信息,论文研究了信号的奇异性检测问题。给出小波变换和信号奇异性的关系,实现小波分析对信号各类奇异间断点的有效检测,最后进行实例分析,说明此理论与方法适用于对边缘信号与突变信号的处理和提取,为海底底质识别提供理论依据。     

Wavelet and artificial neural network analyses of tide forecasting and supplement of tides around Taiwan and South China Sea

In multi-resolution analysis (MRA) by wavelet function Daubechies (db), we decompose the signal in two parts, the low and high-frequency contents. We remove the high-frequency content and reconstruct a new “de-noise” signal by using inverse wavelet transform. The calculation of tidal constituent phase-lags was made to determine the input and output data patterns used in building network structure of Artificial Neuron-Network (ANN) model. The “de-noise” signal was, then, used as the input data to improve the forecasting accuracy of the ANN model. The wavelet spectrum, conventional energy spectrum (fast Fourier transform, FFT), and harmonic analysis were used to analyze the characteristics of tidal data.Using only a very short-period data as a training data set in Artificial Neuron-Network Back-Propagate (ANN-BP) model, the developed ANN+Wavelet model can accurately predict or supply the missing tide data for a long period (1–5 years). The results also show that the concept of tidal constituent phase-lags can improve ANN model of tidal forecasting and data supplement. The addition of the wavelet analysis to ANN method can prominently improve the prediction quality.     

油气爆炸作用下海洋平台抗冲结构研究

海洋平台在服役期间,常会遭受到油气泄露而爆炸引起的冲击破坏.结合歧口QK18-2海洋平台结构,利用非线性瞬态动力学计算软件MSC.Dytran对气体爆炸造成海洋平台结构的损伤机理进行数值仿真研究.在此基础上,详细研究舱室在爆炸载荷下的动态响应,将舱室和爆炸区之间的围壁结构采用增加板厚和改变支撑结构形式、尺寸等四种不同的方式进行比较研究,得出支撑结构对于平台抗冲击的重要性,从而提出有效可行的抗冲结构形式.     

联合小波和NLM滤波的侧扫声纳回波信号降噪

为进一步降低侧扫声纳回波信号中非高斯分布的乘性噪声,获取更佳效果的侧扫声纳图像,提出了一种利用小波和NLM(nonlocal means)滤波的组合降噪方法。首先采用同态变换将侧扫声纳回波ping信号中的乘性噪声转换为加性噪声,然后利用小波阈值和NLM滤波对侧扫声纳每ping回波数据实施降噪处理,最后经过小波反变换和指数变换获取降噪后信号和图像。仿真实验和实测数据验证结果表明,该方法适用于侧扫声纳回波信号处理,可以获取较好的图像降噪效果。