【作者】 李少华；

【导师】 龙述尧； 丁桦；

【作者基本信息】 湖南大学 ， 固体力学， 2010， 博士

【摘要】 海洋平台是一类为开发和利用海洋资源提供海上作业与生活场所的海洋工程结构物。近年来,由于世界各国对海洋资源的日益重视,海洋开发事业迅速发展,海洋平台的需求量越来越大,海洋平台设计的安全可靠性的要求也越来越高。波浪荷载是海洋平台设计的重要环境荷载之一,工程设计中大多数海洋平台上的波浪载荷采用莫里森方程来计算,莫里森方程计算波浪力的关键在于水动力系数的选取,而规范中系数的选取多来自经验或实验,并不能准确反映出计算平台所处海况下的情况,因此反演出当前海况下的水动力系数对平台安全设计具有重要意义。本文主要面向工程实际问题,对海洋平台水动力系数的反演方法进行了研究,并利用实测数据对西江23-1导管架海洋平台所处海况下的水动力系数进行了反演,具有重要的工程应用价值。本论文研究的主要工作:1)当在频域内进行载荷反演时,针对在自振频率附近频响函数矩阵出现病态的情况,提出了基于频谱特征的载荷反演方法,该方法适合于载荷谱特征已知的情况。数值算例通过比较验证了该方法的优越性。2)在线性波情况下对圆柱形结构响应施加了白噪声之后频域内对水动力系数进行识别。根据谱分析的方法,考虑线性波前后桩腿相位差的影响,比较了单个频点反演与采样频率内利用对频率取矩法反演结果的准确度,结果表明在已知波浪谱的情况下利用矩来进行反演识别有明显的优越性。3)将模型简化的思想应用到海洋平台水动力系数反演中去。根据位移同步性假设将海洋平台结构划分为若干个同步性区域,然后用准刚体模态去等效每个区域的位移模式,得到简化模型,并对简化模型进行变形修正,得到更为精确的简化模型。通过这个简化方法对海洋平台结构进行自由度减缩,利用简化后的模型对水动力系数进行反演,并对载荷反演中的病态问题进行了探讨,同时给出了反演结果的评估方法和反演中测量数据的选取依据。4)根据海洋平台实测数据对实际流场中的水动力系数进行了反演。针对监测项目内容参与研发了相应的监测设备,利用测得的载荷和海况对水动力系数进行了反演。并用反演的结果和测得的海况来计算海洋平台的结构响应,与实测结构响应相比较来验证反演结果,结果证明用现场实测数据反演的水动力系数值是正确的。更多还原

【Abstract】 Offshore platform is a structure which provides the place for seafaring and offshore operation for the purpose of ocean exploitation and utilization of resources. Nowadays, ocean exploitation has been rapidly developed due to the more emphasis put by the countries of the world on sea resources. And the need of the offshore platform is increasingly demanded. The demand on the reliability of the design of the offshore platform is getting higher. Wave load is one of the important environmental loads in the design of the offshore platform. Most of the wave loads applied on the offshore platforms are computed through Morison equation in engineering design. The key of computing the wave force through Morison equation lies in the selection of the hydrodynamic coefficients which are basically acquired from the experience or experiments and can’t accurately reflect the actual sea condition acting on the offshore platforms. Thus, it is of great significance to identify the hydrodynamic coefficients in the current sea condition for the safety design of the offshore platform. Based on the engineering background, this dissertation is devoted to studying the identification method of the hydrodynamic coefficients of the offshore platform and identifying the coefficients in the sea condition acting on the Xijiang23-1 jacket offshore platform by using real-test data, which could be practically applied to the actual engineering problems.The main researches are as follows1) According to the ill-condition problem of the frequency response function appearing near the natural frequency during load identification in frequency domain, a new load identification method based on the characteristic of frequency spectrum is proposed. This method is applicable to the specific condition when the characteristic of load spectrum is given. And the advantage of this method is subsequently verified by comparison in the numerical example.2) The identification method of hydrodynamic coefficients in frequency domain is presented considering applying white noise to the cylindrical structural response under the circumstance of linear wave. Based on the spectrum analysis method, the effects of phase difference between the foremost and following legs of the linear wave are considered. Accuracy of the two identification methods is also compared between the single frequency and the quadrature about the frequencyωin the sampling frequency. The result shows that the identification method through the quadrature about the frequency has an obvious advantage over the condition that wave spectrum is given.3) The method of model reduction is applied into the identification of the hydrodynamic coefficients of offshore platform. Based on the synchronistic assumption, the structure of offshore platform can be divided into several displacement synchronous parts. Every synchronous part can be substituted by a quasi-rigid-body mode and the full-size models can be simplified. The more accurate reduction model can be acquired through deformation modification. The degrees of freedom of the offshore platform structure are reduced by the modification model. By using the simplified model, the hydrodynamic coefficients are subsequently identified. The ill-conditioned problem in force identification is discussed and both the assessment method of the identification result and the basis for acquiring the measurement data in the identification are given.4)On the basis of the real-test data from actual wave-current field, the hydrodynamic coefficients of offshore platform are identified. Corresponding monitoring equipments are developed for the need of monitoring program. By applying the measured load and data about wave field from Xijiang 23-1 offshore platform, the hydrodynamic coefficients are identified. The structural response of the offshore platform is computed by use of the identification results and data about wave field. The identification results are validated by comparison between the measured response and the computed response. The results prove the hydrodynamic coefficients identified by the real-test data are correct.更多还原