【作者】 刘艳；

【导师】 刘贵杰；

【作者基本信息】 中国海洋大学 ， 机械电子工程， 2011， 硕士

【摘要】 海洋蕴含着极为丰富的资源,海洋平台作为海洋资源开发的基础性设施,是海上生产作业和活动的基地,因此海洋平台健康状况检测是海洋平台安全与防护的重要一环,及时发现海洋平台结构中的裂纹对预防事故的发生具有重要意义。声发射技术作为一种新型动态的检测技术已被广泛应用于许多领域,研究海洋平台结构的声发射检测技术,有利于实现对海洋平台健康状况的实时掌握。本文针对海洋平台结构声发射检测中的传感器布置及声源定位进行了研究,目的在于利用相对较少的传感器实现海洋平台结构的全局检测,为海洋平台结构的安全评估和健康诊断提供依据。本文以导管架平台结构模型为研究对象,在理论分析导管架平台结构模型中裂纹形成和扩展所产生声发射波的传播特性的基础上,进行了能量衰减特性的试验研究,并基于能量衰减进行了声发射传感器布置的研究,通过声发射检测试验进行了声发射源定位的研究。在预制的导管架海洋平台结构模型上,进行断铅模拟声发射源实验,测量计算出平均实际波速约为3487m/s,信号幅值在距声源的距离增大到一定值时呈现明显的衰减规律,为确定最大传感器间距并进行传感器布置提供了依据。在导管架平台结构模型的一个管节点处,进行了能量衰减特性的试验研究,推导出能量衰减系数α的取值范围为0.30～1.70,在不同支撑上距声源位置相同距离处,衰减系数不尽相同。这是因为实际结构介质并非完全弹性介质,波在传播时不仅由于几何因素(即随着波阵面的扩大,弹性波的能量将分布在更大的体积内,从而使得单位体积内的能量减小)而按照一定的比例衰减,它还受到结构的形状和尺寸等多种因素的影响,所以在实际传播过程中的衰减要更复杂,通过试验研究也证明了这一点。根据管节点处能量衰减特性试验研究的结论,首次提出基于能量衰减的传感器布置方法,初步推导出试验模型的原型结构全局检测共需布置22个传感器,并得出了传感器的布置结构。声发射传感器布置的研究是海洋平台结构声发射研究中的关键一环。但是,声发射传感器的布置跟平台结构材料、尺寸等因素息息相关,有关的理论研究少之又少,现阶段均需要通过试验获取有用数据。最后根据声发射源定位的原理,采用时差线定位法对导管架平台结构模型的一条主腿进行了声发射源模拟试验。从试验结果来看,实际声源位置与试验所得位置间的误差在7mm以内,测定出的声源位置比较合理。从而验证了应用时差线定位法对导管架平台结构的某一支撑进行单一损伤位置确定(即声源定位)的可行性。综合试验结果及分析可知,声源定位精度的关键影响因素是声发射波的衰减及叠加,同时,定位方法也对准确判定声发射源的位置有很大影响。要想提高声发射检测过程中声发射源定位的精度和可靠性,必须合理布置声发射传感器,使得声发射传感器接收到真实有效的波形,并且在对定位方法原理透彻理解的基础上,不断积累声发射检测的实践经验,还有就是对影响声发射源定位的主要因素有多方面的详尽了解,以采取相应的有效措施。更多还原

【Abstract】 Offshore platform as the basic facilities for exploiting marine resources is a base for production and activities. It is important to detect cracks in offshore platform timely to prevent the accidents. Acoustic emission technology as a new type of dynamic detecting technology has been widely used in many fields. The study of acoustic emission testing technology of offshore platform is helpful to master offshore platform health in real time. In this paper, the sensors’arrangement and auditory localization for acoustic emission testing of offshore platforms have been studied, and the purpose is to use few sensors to achieve the global testing and to provide the basis for safety evaluation and health diagnosis of offshore platform.In this paper, jacket platform model is taken as research object. On the basis of the propagation properties of acoustic emission wave produced by crack formation and extension in jacket platform model, experiments on energy attenuation and acoustic emission testing are carried out, and the research on sensors’arrangement and auditory localization are conducted, too.The experiment that simulation acoustic emission source using broken lead on jacket platform model is carried out, the average real wave velocity is calculated, and the relationship between distance and signal amplitude is obtained. They provide the basis for determining the maximum distance between two sensors.Based on acoustic emission experimental study of one joint of jacket platform model, energy attenuation coefficient range from 0.30 to 1.70 is deduced. The attenuation coefficient is varying at the same distance from the sound source on different supports. This is because the actual structure medium is not entirely the elastic medium, and in the process of acoustic emission wave propagation, energy attenuation is affected by not only geometric attenuation, but also many other factors such as the shape and size of the structure. Experimental research also proves this point. According to the experimental conclusion, the sensors’arrangement method based on energy attenuation is put forward, the global testing of prototype structure which needs 22 sensors and the sensor arranging scheme are preliminary deduced. The study of acoustic emission sensors’arrangement is the key to conduct research on acoustic emission testing of offshore platform. In fact, we need to obtain useful data through the test, because the theoretical study of acoustic emission sensor arrangement which is closely related to such factors as the material and the size of the offshore platform are rare.Finally, according to the principle of acoustic emission source localization, the time difference line positioning method is used in the acoustic emission source simulation test which is experimented on a main leg of the offshore platform. Judging from the experimental results, the test error is within 7mm and the source position obtained with this method is quite reasonable. Therefore, the use of time difference line positioning method to determine the position of the single damage in one support of the offshore platform is feasible.Overall, the test results and analysis shows that the key factors influencing the precision of the auditory localization are acoustic emission wave attenuation and superposition. The localization method also has an important effect on determining the accurate acoustic emission source position. To improve the accuracy and reliability of auditory localization in the acoustic emission testing, acoustic emission sensors must be arranged reasonably to receive the real and effective waveform, acoustic emission testing experience based on understanding of the principle of localization method thoroughly should be accumulated, and corresponding effective measures which reduce the influence of main factors must be adopted.更多还原