声源对浅海地震波传播特性的影响研究

为提升水雷的探测能力,利用浅海地震波识别水下目标声源,研究声源高度和频率对浅海地震波的影响。采用交错网格有限差分方法对波动方程进行离散求解,实现不同高度和不同频率声源形成的浅海地震波在砂岩介质中传播过程的仿真模拟,并利用f-k频散能量提取方法,获得浅海地震波的频散能量图。结果表明：声源高度和频率均会影响浅海地震波的传播特性,但对其波速、频率集中范围和极化特性影响较小,Scholte波稳定的波速为1 088 m/s, Scholte波振幅的频率范围在5～30 Hz之间;随着声源高度和频率的增加,形成的Scholte波在水下界面信号减弱。研究结果可为水雷引信的研制提供理论依据。     

深海甚低频水声与地震波场的联合探测试验

为我国深海水中兵器甚低频声场与地震波场联合引信技术提供可行性依据,设计并研制了深海自容式三分量地震波传感系统,利用深海坐底潜标搭载在我国南海海域(布深1825 m)开展了实船目标特性感知试验.通过设置走航测线,获取了目标深海甚低频水声场与地震波场实测数据,对比分析结果表明了舰船甚低频水声场与地震波场对目标探测的贡献具有...     

影响地震波传播的矿岩地质要素分析

地震波的得受地球介质影响的，本文把不同的地质要素从物理及数学角度抽象成不同的方程与边界条件，从而解出地震波在不同地质要素的影响下的传播规律，进而提出了关于人工隔震的“波导层”及“波导管”等新见解。     

计入衰减的地震波传播特性研究

在对多层无衰减介质中地震波传播特性研究的基础上,通过选取典型衰减系数,研究了地震波在多层有衰减介质中的传播特性。通过计算地震波在各层有无衰减介质中的幅值和位移以及绘制相应的传播位移图,对比分析了衰减因素对不同地质分布中地震波传播特性的影响。研究结果表明在不考虑衰减情况下,地震波从震源经过多个不同地质分布层传播到地表面时,地震波的幅值均有不同程度的放大;而计入地质层的衰减因素后,地震波经过与上相同的多个不同地质分布层时,地震波幅值的放大程度将明显减小。特别的对于＂表层-砾石层-岩石层-黏土层-基岩层＂地质分布层,将最大程度地衰减地震波对地表层的影响。     

弹性动力时程分析中地震波的选取方法研究

对建筑结构进行弹性动力时程分析时,为了既能让设计人员易于操作,又能在地震波选取方面不失合理性,根据上海市某超限高层结构设计实例的弹性动力时程分析结果,探讨了具有实际工程意义的选波方法。研究表明,无论是基底剪力还是基底弯矩,地震波三向输入的结构响应均比单向输入的结构响应小。采用小样本容量的地震波输入时,人工波输入数量的增加对降低地震波的总体离散性有显著作用。     

提高黄土塬地区地震波激发质量的几点认识

黄土塬地区表层黄土厚度达0～400m,土质疏松,纵横向变化剧烈,地震波的吸收和衰减严重,干扰波发育,记录信噪比极低,给地震数据采集尤其是地震波激发环节造成了巨大的困难,被认为是世界级难题。通过在长武黄土塬区进行地震波激发技术攻关,取得了一些新的认识:巨厚黄土塬地区在含水黄土层中或在速度1500～1800m/s层中采取单深井激发,能够有效保证地震资料的信噪比,为黄土塬地区的激发开辟了新的研究方向,使用的60m"超深单井"在黄土塬地区开了个先河;"超大基距"组合井打破了"标准"爆炸半径理论的限制,丰富和发展了黄土塬地区勘探理论认识;黄土结核的突破使激发效果得到了明显的提升。     

气枪声源激发的浅海地震波频散特性研究

为了研究由浅海中声源激发的海底地震波主要波动成分的频散特性,首先基于波动方程对液-固界面处的声场进行了推导,证明纵波和横波不具有频散特性,而表面波具有正常频散特性。随后基于高阶交错网格有限差分法,对气枪声源激发的液-固界面处的声场进行了数值仿真,通过分析仿真数据观察到表面波的频散现象,验证了理论分析结果;最后基于τ-p变换对海试数据处理与分析,精细提取了海底表面波的频散曲线。     

水中爆炸形成水射流现象的实验研究

针对水中爆炸气泡脉动水射流现象,应用开尔文冲量原理,分析了水中爆炸产生的气泡与固壁相互作用形成水射流现象的主要影响因素,开展了气泡与竖直放置的钢板相互作用产生水射流现象的实验研究工作。通过改变炸药到钢板的距离,得到气泡和钢板相互作用形成水射流的动态过程图像和水射流形成后的气泡二次脉动压力。理论分析和实验结果均表明:随着爆距的减小,Bjerknes力迅速增加,气泡与钢板相互作用形成的水射流逐渐垂直于钢板壁面.水射流具有非常明显的方向性,对目标毁伤作用明显.     

Propagation law of shock waves and gas flow in cross roadway caused by coal and gas outburst

In order to study the propagation law of shock waves and gas flow during coal and gas outburst, we analyzed the formation process of outburst shock waves and gas flow and established the numerical simulation models of the roadways with 45° intersection and 135° intersection to simulate the propagation of outburst gas flow and the process of gas transport. Based on the analysis of the simulation results, we obtained the qualitative and quantitative conclusions on the characteristics and patterns of propagation and attenuation of outburst shock waves and gas flow. With the experimental models, we investigated the outburst shock waves and gas flow in the roadways with the similar structures to the simulated ones. According to the simulation results, when the angle between the driving roadway and the adjacent roadway increased, the sudden pressure variation range in adjacent roadway and the influencing scope of gas flow increased and the sudden pressure variation duration decreased. The intersection between the driving roadway and the adjacent roadway has no effect on airflow reversal induced by the shock waves and gas flow.     

水中声波之间非线性作用时能量变化的分析

为研究声波之间的变参数相互作用,以伯格斯方程为基础,用谱分解方法推导了泵波与弱信号波整倍频率相互作用后弱信号波的数学解析式,研究了弱信号波在受到泵波不同频率、幅度和初始相位干扰时的能量变化情况.研究表明:二者频率比为2时,信号能量变化最大,可达9.84 dB;随着幅度比增大,信号能量变化减小;频率比大于3时,可不考虑二者初始相位差对信号波能量变化的影响;间断距离内随着传播距离的增加,弱信号波能量变化增大.     

城市建设引发场地地震反应变异的时程分析

大规模的城市建设行为导致了众多包括地震在内的地质灾害问题.通过总结城市建设的主要荷载以及城市建设影响场地动力特性的方式,针对未有城市建设因素作用前的均匀土层场地、均布桩基的场地、均布地下空间基础的场地、复合地基改良的场地等共4个工况建立场地地震时程分析模型.结果表明,城市建设改变了场地条件,不同场地对地震波的放大作用各不相同,城市建设因素造成场地刚度提高,土体对波传递能力增强,消耗波动能量的粘、塑性减少,但相应场地上短周期的建筑物危险性增大,城市建设因素使得场地地震反应发生变异.     

高速弹体水平入水产生冲击波特性

高速弹体入水产生的冲击波对弹体的水下运行与毁伤性能有着至关重要的作用.为得到高速弹体入水产生的冲击波及其传播特性,利用一级轻气炮高速发射平头和球形两种不同弹体水平入水,通过以不同方式分布于水下的压力传感器测量因此而形成冲击波峰值压力衰减特性.实验结果表明:初始冲击波峰值压力随着距离和角度以不同的方式衰减;在波的传播方向上,其满足指数衰减的形式,压力介于距离的倒数与距离平方的倒数之间的曲线之间.在球形波阵面上则以正弦曲线的形式衰减,这种沿距离和角度衰减的冲击波峰值不受弹体的初始速度的影响.     

改进的MRF水下目标检测方法

为取得更好的水下目标检测结果,提出了一种改进的MRF水下目标检测方法.即在海底混响区服从Gamma分布的情况下,将建立的三类空间邻域MRF模型参数和层次间相互作用的模型参数应用于空间分层MRF三类分割中,得到最终精确的水下目标检测结果.在海底混响区服从威布尔分布模型的情况下,对原始声纳图像和人造模拟声纳图像检测结果的比较表明,提出的检测方法能得到更精确的检测结果,且运算速度较快.     

Energy flux characteristics of seismic waves at the interface between soil layers with different saturations

Based on the multiphase poroelasticity theory describing the propagation of waves in the unsaturated fluid-saturated porous medium, the reflection and transmission coefficients of the seismic waves at the interface between soil layers with different saturations are obtained. Our unsaturated model consists of a deformable skeleton in which two compressible and viscous fluids (i.e., water and gas) flow in the interstices. Three compressional waves (i.e., P1, P2, and P3 waves) and one shear (i.e., S wave) wave exist in the unsaturated soils. The expressions for the energy ratios of the various reflected and transmitted waves at the interface during the transmission and reflection processes are presented in explicit forms accordingly. At last, numerical computations are performed and the results obtained are respectively depicted graphically. The variation of the energy ratios with the incident angle, wave frequency and saturation degrees of the upper and lower soil layers is illustrated in detail. The calculation results show that the allocation of incident seismic waves at the interface is influenced not only by the angle and frequency of the incident seismic waves, but also by the saturations of the upper and lower soil layers. It is also verified that, at the interface, the sum of energy ratios of the reflected and transmitted waves is approximately equal to unity as was expected. This study is of importance to several fields such as geotechnical engineering, seismology, and geophysics.     

Incipient motion of sediment by waves

In this paper, the forces acting on sediment particles are analyzed in all the aspects. Considering the cohesive force between particles, the additional static water pressure induced by the solid-body characteristics of film water and the inertia force of waves, a unified formula of the incipient motion for both coarse and fine particles is defined. The formula can reflect the variation in the initial velocity of fine particles with the volume weight of sediment. The verification of the formula is carried out by use of both experimental data and field observation data accumulated by experts at home and abroad. The verification shows that the formula expresses the law governing the incipient motion of sediment of all particle sizes inclusive of natural sediment and light-weight materials, and thus a basic formula for the study and solution of sediment problems in estuarine and coastal regions is provided.