基于海洋平台单点系泊原型测量的模态分析

发布时间：2018-09-19 06:56

【摘要】：海洋平台是海上油气开发的主要设施,其健康状况与石油开采和工作人员的安全生产作业密切相关。海洋平台是大型振动结构,通过水池模型试验来研究其结构会受到缩尺效应的影响,仿真的外部激励也不能完全模拟海洋环境荷载,这些为结构的设计和分析带来很大困难。因此,海洋平台原型测量对相关的研究具有重要意义。本文对浮式生产储油卸油装置(FPSO)单点系泊系统的原型测量进行了研究,获得了系泊系统的原型测量数据。为了保证FPSO的安全生产作业,需要通过单点系泊系统限制FPSO的运动范围,但是长期使用会给系泊造成一定劳损。因此,需要通过监测数据分析系泊的健康状况,其目标之一是对系泊进行损伤识别,而准确地识别出模态参数是结构损伤识别的关键。FPSO长期处在复杂的环境激励下,系泊运动具有明显的非平稳特征。响应中的非平稳成分使随机减量偏离指数衰减信号,且系泊响应的模态分布密集,用已有方法识别出的模态相互耦合。针对以上问题,提出一种基于平稳化滤波器—独立分量分析(filter-ICA)的模态识别方法。在ICA的预处理中引入滑动平均平稳化滤波器,消除了非平稳成分对模态参数识别的影响。在多自由度仿真系统的模态识别中,识别结果与理论值吻合。用该方法分析了FPSO单点系泊系统的原型测量数据,与已有方法的识别结果相比,模态分布明显,与模态振型对应的系泊运动轨迹表现出单一运动形式。在对结构的长期监测中,阻尼从能量损耗的角度反映了结构的特征,其变化可以在一定程度上反映结构的损伤情况。但是基于监测数据对结构的识别中,特别是对具有非平稳响应的动力系统来说,阻尼比的识别精度不高。因此,本文提出一种基于时频ICA的结构阻尼比识别方法,减小阻尼比对模态识别准确度的影响,在仿真实验中验证了该方法的有效性。通过原型测量数据的分析,识别了FPSO单点系泊系统的阻尼比。将相同频率段的阻尼比识别结果进行比较,验证了该方法的稳定性更好。以上研究从时不变系统角度对系泊进行了模态分析,但船体发生纵荡运动时,系泊系统的软刚臂伸展长度会变化,此时可将系泊看作时变系统。当结构发生损伤时,其模态参数会发生变化,而瞬时频率能够更直观地反映出这种变化。本文提出一种基于系泊响应的瞬时频率识别方法,通过仿真实验及六自由度模型试验验证了该方法的有效性。将该方法应用于原型测量数据的分析,识别结果的准确度好于希尔伯特—黄变换(HHT)方法。
[Abstract]:The offshore platform is the main facility for offshore oil and gas development, and its health is closely related to the oil exploitation and the safety work of the staff. The offshore platform is a large vibrating structure, which will be affected by scale effect through tank model test, and the external excitation of simulation can not completely simulate the marine environmental load, which brings great difficulties to the design and analysis of the structure. Therefore, prototype measurement of offshore platform is of great significance to related research. In this paper, the prototype measurement of (FPSO) single point mooring system of floating production oil storage and unloading device is studied, and the prototype measurement data of mooring system are obtained. In order to ensure the safe operation of FPSO, it is necessary to limit the movement range of FPSO through single point mooring system, but the long-term use will cause certain strain to mooring. Therefore, it is necessary to analyze the health status of mooring by monitoring data. One of its objectives is to identify the mooring damage, and the accurate identification of modal parameters is the key of structural damage identification. FPSO is under complex environment excitation for a long time. Mooring motion has obvious non-stationary characteristics. The nonstationary component of the response makes the random decrement deviate from the exponential attenuation signal and the mooring response is densely distributed. The modes identified by the existing methods are coupled with each other. Aiming at the above problems, a modal recognition method based on stationary filter and independent component analysis (filter-ICA) is proposed. A moving average stationary filter is introduced into the preprocessing of ICA to eliminate the influence of non-stationary components on modal parameter identification. In the modal identification of multi-degree-of-freedom simulation system, the recognition results are in agreement with the theoretical values. The prototype measurement data of FPSO single point mooring system are analyzed by using this method. Compared with the existing identification results, the modal distribution is obvious, and the mooring track corresponding to the modal mode shows a single motion form. In the long-term monitoring of the structure, damping reflects the characteristics of the structure from the point of view of energy loss, and its variation can reflect the damage of the structure to a certain extent. However, in the identification of structures based on monitoring data, especially for dynamic systems with non-stationary response, the identification accuracy of damping ratio is not high. Therefore, a structural damping ratio identification method based on time-frequency ICA is proposed in this paper to reduce the influence of damping ratio on the accuracy of modal identification. The effectiveness of this method is verified by simulation experiments. The damping ratio of FPSO single point mooring system is identified by analyzing the prototype measurement data. The results of damping ratio identification in the same frequency range are compared to verify the stability of the proposed method. The modal analysis of mooring is carried out from the point of view of time-invariant system, but the length of flexible rigid arm of mooring system will change when the ship is swinging, and the mooring can be regarded as time-varying system at this time. When the structure is damaged, the modal parameters will change, and the instantaneous frequency can reflect the change more intuitively. In this paper, a mooring response based instantaneous frequency identification method is proposed. The effectiveness of the method is verified by simulation and six degrees of freedom model tests. The method is applied to the analysis of prototype measurement data and the accuracy of the recognition results is better than that of Hilbert-Huang transform (HHT) method.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P752

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