【作者】 陶春辉；

【导师】 金翔龙；

【作者基本信息】 浙江大学 ， 地质学， 2005， 博士

【摘要】 本文较系统地研究了海底沉积物的声学原位测试技术、原理与海洋沉积物声传播特性。研究内容包括声学原位测试系统的设计研制、海上资料采集、土工实验室测试、资料处理解释、中美不同性质沉积物的对比研究、Biot-Stoll模型与BISQ模型的海洋沉积物声学多参数反演,以及声场数值模拟。本文在国家863计划的支持下,首次设计研制出国内具有自主知识产权的实时监控多频多深度声学原位测试系统,该系统既具有美国声学长矛测量深度较深的能力,又具有美国原位沉积物声学测量系统多个频率发射接收可研究频散特性的优点,系统具有实时监控甲板供电、多点高精度测量等特点。系统在整体设计思路上具有一定的先进性和创新性。在浙江乍浦港首次取得了8、10、12和15kHz四个频率八个深度声学原位测试数据后,进行了土工力学和粒径分析。开发了利用对比法精确提取声速、声衰减技术。浙江乍浦港沉积物具有明显频散现象,即声速和声衰减随频率的增大而增大,声速随深度增加而增大(从1442到1462m/s)。得到了该海区2米深度内15kHz以下声速与深度及频率的一次正比关系。声衰减由于沉积物松软而较低。在沉积物中测到的声波主频比水中测得的主频低最高达300Hz。对夏威夷檀香山岛的二处钙质沉积物20-100kHz的测量数据进行了原位纵波声速和声衰减提取。二处均测得轻微的频散。随频率的增加有效衰减从15增加到75 dB/m。声衰减较大。利用Blot-Stoll模型进行夏威夷钙质沉积物多参数反演,发现Biot理论能很好地描述珊瑚质砂纵波速度频散。通过调整低频耗散系数(超过Stoll的假设范围)对声衰减也能较好地描述。得到海洋沉积物BISQ多参数反演方法。通过对浙江乍浦泥沙质沉积物的BISQ多参数反演,发现BISQ模型可用于描述海洋沉积物的声频散和声衰减特性。海洋沉积物声衰减总体上分段符合衰减系数lnα=αlnf~b的规律。按斜率可以分成三段:f为高频时,b≈1;中频时,0≤b≤0.5;低频时b≈2。高频与中频分界在40kHz之间,中频与低频分界在16-18kHz之间。系数α与沉积物特性密切相关。利用基于Biot理论模型的高阶交错网格有限差分算法,通过对比模拟和原位测试波形特征,表明该系统具有较好的首波避干扰和吸声设计,对下一步系统升级具有指导意义。更多还原

【Abstract】 The in situ acoustic experimental technology, principle and propagation features inmarine sediments are described in this dissertation. This research includes the designand developing of the new in situ acoustic instrument, the experiment, engineeringanalysis, data processing, comparison of the different acoustic properties of USA andChinese sediments, multi-parameters inversion of Biot-Stoll model and BISQ model,and the finite-difference modeling.Supported by 863 project, a real time control, multi-frequency and multi-depth in situacoustic system was developed with intellectual asset in the form of copyright. It hasreal time monitoring and on deck power supply, multi-point high resolutionmeasurement functions.With four frequencies, which are 8, 10, 12 and 15 kHz, in situ acoustic data have beenacquired in 8 different depths at Zhapu bay, Zhejiang, China. By using antitheses, newtechnology of getting velocity and attenuation was used. Velocity dispersion in Zhapusediments is observed. The velocity and attenuation increase as the frequencyincreases. A linear relation between frequency and velocity as well as attenuation isfound while water depth less than 2 meters and frequency below 15 kHz. Thesediment is so soft that the attenuation is low. The dominate frequency in sediment is300Hz lower than that in water because of attenuation.In situ compressional wave velocity and attenuation measurements were made at 2carbonate sediment sites over a frequency interval between 20 and 100 kHz. Velocitydispersion, while slight, appears in the data. Effective attenuation ranges from 15 to75 dB/m at H3 and from 22 to 62 dB/m at H4. Parameters determined by coreanalysis were fixed in Biot-Stoll models and inversion of velocity and attenuation datawas used to evaluate the 6 un-measurable parameters. An increase in the lowfrequency logarithmic decrement well above Stoll’s recommended values allowed fitsto both velocity and attenuation very well.The multi-parameter BISQ inversion method is achieved for Zhapu marine sediments.It is found that the BISQ model could be used to describe the marine sediment’scharacteristics of velocity dispersion and attenuation.The lnα=alnf~b relationship for attenuation and frequency is approved in marinesediments. The slope b divides into three segments: b≈1 for higher frequency (f > 40kHz); 0≦ b≦0.5 for intermediate frequency (16-18 kHz); b≈2 for lower frequency(<16 kHz). The constant a depends on the characteristics of the sediments.By comparing the high-order staggered finite-difference modeling based on the Biotmodel, with the in situ wave characteristics, it is indicated that the system is welldesigned in avoiding head wave inference and sound absorbing. This modeling hassignificance for upgrading the system.更多还原