High-resolution Echo-sounding and Detection of Embedded Archaeological Objects with Nonlinear Sub-bottom Profilers

Sub-bottom profilers based on nonlinear acoustics offer many advantages especially for detecting and locating embedded objects in shallow waters. They have a narrow beam in spite of small transducers and virtually no side lobes. It is possible to realize mobile low-frequent sub-bottom profilers, which transmit very short sound pulses. Excellent vertical as well as horizontal resolutions at reasonable penetrations are proven benefits of using this technique. In this paper some technical aspects are discussed and a new experimental nonlinear scanning sub-bottom profiler system is described. Results from a field trial in archaeological prospection are shown to illustrate the successful application in practice.     

Calculation of Wave Reflection Coefficient for Perforated-Pipe Breakwater

The hollow-pipe perforated breakwater is of low reflection. In this paper the functions of reflection coefficients of both regular and random waves are theoretically derived, based on the concept of linear superimposition of reflected and incident waves and with the total flow rate continuity of integral form instead of the non-continuity of the boundary condition, and based on the concept of linear wave spectrum theory. Comparisons between theoretical results presented here and measurements of model tests show reasonable agreement.     

多向随机波浪反射的试验研究

试验研究了多向随机波浪在直立式防波堤和斜坡式防波堤前的反射情况。在试验中，改变波浪要素(波陡、周期)、波浪入射角度(正向、斜向)和方向分布以及防波堤的坡度，以充分研究这些因素对波浪反射的影响。遗传算法用来分析多向随机波从建筑物的反射。试验结果表明，直立堤的反射系数基本上不随入射波浪方向变化，斜坡堤的反射系数随波浪峰频的增大和堤坡的变缓而减小，且随波浪方向有一定变化。还探讨了多向随机波浪在斜坡式防波堤上的反射面位置问题。     

基于Chirp数据和Biot-Stoll模型反演南海北部陆坡海底表层沉积物物理性质

浅地层剖面是基于声学信号(频率在几百至几千赫兹)在沉积物中的传播得到可反映沉积地层结构的数据,海底反射系数与沉积物物理性质密切相关。Biot-Stoll声波传播理论模型可以预测海底沉积物的物理性质,构建反射系数等声学参数与物理参数之间的关系,但在不同的海域采用不同的参数所获得的效果不同。为此,本文基于南海北部陆坡海底表层沉积物的实测物理参数,利用BiotStoll模型建立研究区海底反射系数和沉积物物理性质之间的关系,结果表明模型计算值与样品实测值吻合度总体较好,偏差在0.1%～4.9%之间,并建立了频率3.5 kHz时海底反射系数与沉积物孔隙度、密度、平均粒径之间的关系方程,且方程拟合度较高,可决系数R2均大于0.99。在对典型Chirp剖面数据计算其海底反射系数的基础上,反演了海底表层沉积物的孔隙度、密度、颗粒平均粒径等物理性质,其中反演孔隙度、密度、平均粒径与实测孔隙度、密度、平均粒径相对误差均小于5%,结果与实测值基本相符,表明该反演方法在南海北部陆坡区的应用是可行的。     

Modelling of Random Waves over Submerged Breakwaters and Its Application to Reflection Estimation

1.IntroductionGreat efforts have been devoted to the protection of coastal areas over many years by erectingdikes,seawalls,groin systems,and detached breakwaters.The sea walls,jetties,detached breakwa-ters,etc.are traditionally adopted as absorbingfacilit…     

斜向波与带填料开孔板式防波堤相互作用的研究

基于线性势流理论,对斜向波与消浪室内带部分填料的开孔板式防波堤结构的相互作用进行了理论研究.利用匹配特征函数展开法给出了开孔防波堤结构反射系数和波浪力系数的理论计算方法,在极限情况下的计算结果与已有结果一致.利用数值算例分析了开孔结构反射系数和波浪力系数的主要影响因素.增加消浪室内填料厚度通常可以降低开孔墙结构的波浪力系数,加大结构的反射系数.随着波浪入射角度的增加,带填料防波堤结构的反射系数值先减小,达到最小值后又单调增加.     

海洋地震勘探中地震波、鬼波综合效应分析与应用

鬼波是影响海洋地震资料采集质量的重要因素之一,经过海水表面反射的鬼波与海底反射波相互叠加。“地震波、鬼波的综合效应”受很多因素的影响,文中从传播路径、传播时间等方面讨论了地震波与鬼波的综合效应。通过计算机模拟了二者的综合效应,与实测资料进行了对比,其幅频特性中陷波点、幅度等特性非常接近。结合水合物勘探的目的,文章探讨了基于识别BSR的勘探频率要求震源和电缆的最佳沉放深度,并通过实际应用验证了理论推算的正确性。