典型水文条件对气泡运动的影响规律研究

本文以认知海洋中普遍存在的气泡上浮过程为目的,通过建立气泡运动、半径、传质传热等微分方程,综合构建了气泡运动的耦合模型,据此结合典型海洋水文条件与海水物性参数的关系,数值模拟获得水文条件对气泡运动的影响规律:(1)盐度、水温、波长、波高是影响气泡的水平偏移和上升时间的主要参数;(2)水温和波高的变化将导致气泡偏离海面预定释放位置;(3)低温气泡上浮时间少于高温气泡。本文有效模拟了水中气泡的上浮过程,为人类认知海水气泡现象,进而为海洋工程、航运安全、海气相互作用等工程实践与理论提供了技术支撑。     

浅层气逸出到海水中的气泡声学探测方法

针对南黄海西部等地区在海洋调查仪器上发现的海水中浅层气逸出气泡产生的声学羽流等气泡记录,首先根据水体中气泡共振发生非线性振动形成的强烈散射现象,计算了我国浅层气分布海区的常见浅层气逸出气泡共振频率范围、不同调查仪器在水深变化时的探测气泡大小,据此分析了不同调查仪器探测浅层气逸出气泡的范围。其次,根据气泡在水中的变化、运动规律,提出了浅层气逸出气泡应当具备的声学特点,排除了南黄海西部地区形成水体中特征反射的其他可能因素,并探讨了云状扰动的可能形成原因。     

气泵法生成气泡帷幕的特性研究

气泡帷幕在水下噪声抑制方面有非常广泛的应用。为了更好地利用气泡帷幕的衰减特性,在实验室水槽设备中采用气泵法产生气泡帷幕,通过对不同深度、气流量接收信号的时频分析,利用共振谱法对气泡分布进行反演。研究表明:(1)气泡的分布可以利用高斯分布近似描述。(2)随着深度增加,气泡含量也有略微增加。(3)气泵法产生的气泡帷幕的气流量大小对衰减的峰值所在的频段基本没有影响,但气流量的改变会影响声波衰减的强弱,气流量大的情况下,气泡帷幕对声波衰减效果更强。通过掌握气泵法生成气泡帷幕中气泡的分布规律,可以有效指导气泡帷幕的设计。     

人工回灌过程中含水介质物理堵塞的试验研究

采用土柱渗流试验,模拟人工回灌过程中含水层的物理堵塞过程。通过测定回灌过程中含水介质渗透系数的时-空变化,系统分析和评价回灌液悬浮物浓度和水动力条件对堵塞的影响,并探讨含水介质的物理堵塞机理。研究表明,随着回灌液中悬浮物浓度的增大,悬浮物首先在含水介质的表层沉积,当悬浮物浓度为50、100、200mg/L时,回灌结束后砂柱表层介质的渗透系数分别降至初始的21%、13%和4%,表明表层发生了不同程度的堵塞现象;悬浮物浓度的大小对深部介质的渗透性影响较弱。另外,当进-出水面的水头差△H较小(即水力坡度较小)时,物理堵塞主要发生在砂柱表层,当△H为19.25cm时,回灌结束后表层渗透系数降为初始的7%;随着△H的增大,物理堵塞深度和程度越大,当△H为48.64cm时,19~34cm深度砂层渗透系数变成初始的60%。     

风生海中气泡对海洋光学反射比的影响

风浪破碎是海中气泡的主要成因.先前的研究基于理论计算和数值模拟,揭示了海中气泡对光散射和海水反射比有不可忽略的影响.利用海洋光学和海面风速现场观测数据,结合Mie散射理论计算和海中光辐射传递数值模拟,研究风浪破碎产生的海中气泡对海水反射比的影响.现场观测和数值模拟结果表明,在光学性质稳定的I类海水中,不同风速下海洋光学反射比的不同主要源于海中气泡的贡献.     

船舶含气泡尾迹的光学特性研究

基于充分挖掘卫星遥感应用于海洋监测能力的需求,通过海上试验测量船舶含气泡尾迹海水的物理、光学特征,研究气泡群对不同水体光学特征的影响,例如离水辐亮度、遥感反射率.这些工作可为通过星载光学传感器遥感获取船舶尾迹信息提供理论依据.试验证明在可见光和近红外波段船舶含气泡尾迹相对于背景海水的离水辐亮度、遥感反射率都不同程度地得到了增强,并且在一类水体中含气泡尾迹的光谱后向散射无论是相对增幅还是绝对增幅都要远大于二类水体中的.     

气泡帷幕拦浑效率试验研究

为评估气幕帘拦浑效果,开展气泡羽流、浑水异重流以及与气幕拦污室内试验。试验水深一定时,测量并分析气幕羽流产生的流场;研究气幕对浑水输运方式的影响;分析不同供气量对浑水拦截效率的影响。通过控制变量法研究,结果表明:气泡羽流速度与供气量有关,供气量小于60 L/min时,气幕所形成环流水平范围约为6倍水深;气幕会使泥沙细颗粒在向上羽流作用下来到表层,并在下游侧环流的作用下,沿水深均匀分布。气幕的拦浑效果不仅与供气量有关,也与泥沙颗粒有关,当气泡羽流速度与泥沙颗粒沉速之比足够大,气幕便具备良好拦截效果;若供气量增加至一定量,更多泥沙颗粒会通过紊动扩散的方式穿过气幕。本文对气幕拦污进行的实验研究与分析弥补了该项研究在实验方面的不足,可为气幕拦污工程应用提供支持与指导。     

壳体厚度对战斗部爆炸气泡特性影响的数值模拟研究

采用LS-DYNA软件,对装药半径为0.15m、0.42m、0.55m的战斗部有、无壳体的爆炸特性进行数值模拟研究,分析了炸药在有无壳体的水下爆炸时的冲击波压力、气泡脉动压力等特性参数,对比总结了不同当量、不同装药半径及有无壳体的数值计算结果。结果表明:壳体对水下爆炸气泡脉动的影响是较为显著的。壳体厚度对气泡形成时间没有太多影响,但对气泡压力峰值影响较大。因此,研究战斗部水下爆炸威力时必须考虑壳体因素,不能简化。     

近场水下爆炸对背空圆板冲击作用仿真研究

在一定的假设条件下,圆板在空气中接触爆炸具有理论解;而在水介质中,近场条件下很难推导理论解。 通过 LS-Dyna 近场条件下全过程模拟计算技术研究水下爆炸载荷对水面圆板冲击作用,得到自由场压力、气泡脉动周期及最大半径、水射流速度等典型特征参数的变化规律,与理论分析结果一致。 揭示了气泡第一周期内脉动形态发展变化过程,获取了结构应力响应、圆板结构变形。 该技术可进一步应用于近场水下爆炸对水面舰船的毁伤评估工作。     

基于连续帧间差分的抛弃式探头三维下沉运动处理方法研究

抛弃式探头由无人机装载,能够在较远目标区域和危险海域开展海洋水文环境剖面参数的测量。通过安装不同传感器,可以实现对温度、盐度的剖面测量,其深度的测量采用数学方法计算得到。针对双摄像机水箱实验获得的5个不同攻角实验结果,分析了常用的运动目标的检测方法,最终选择基于连续帧间差分法,确定探头的三维坐标位置,进而得到探头下沉运动的三维运动轨迹和速度曲线等信息。探头从水面释放后攻角在下沉过程中不断调整,改变运动姿态,同时伴随自身的旋转,抵消水平方向阻力作用,初始攻角产生的深度测量误差主要体现在加速过程,探头达到匀速运动后测量误差不变,在不考虑横流的情况下,探头最后以匀速垂直下落运动。     

冷泉系统甲烷气体渗漏的声学特征及潜在环境效应

The amount of methane leaked from deep sea cold seeps is enormous and potentially affects the global warming,ocean acidification and global carbon cycle. It is of great significance to study the methane bubble movement and dissolution process in the water column and its output to the atmosphere. Methane bubbles produce strong acoustic impedance in water bodies, and bubble strings released from deep sea cold seeps are called "gas flares"which expressed as flame-like strong backscatter in the water column. We characterized the morphology and movement of methane bubbles released into the water using multibeam water column data at two cold seeps. The result shows that methane at site I reached 920 m water depth without passing through the top of the gas hydrate stability zone(GHSZ, 850 m), while methane bubbles at site II passed through the top of the GHSZ(597 m) and entered the non-GHSZ(above 550 m). By applying two methods on the multibeam data, the bubble rising velocity in the water column at sites I and II were estimated to be 9.6 cm/s and 24 cm/s, respectively. Bubble velocity is positively associated with water depth which is inferred to be resulted from decrease of bubble size during methane ascending in the water. Combined with numerical simulation, we concluded that formation of gas hydrate shells plays an important role in helping methane bubbles entering the upper water bodies, while other factors, including water depth, bubble velocity, initial kinetic energy and bubble size, also influence the bubble residence time in the water and the possibility of methane entering the atmosphere. We estimate that methane gas flux at these two sites is 0.4×10~6–87.6×10~6 mol/a which is extremely small compared to the total amount of methane in the ocean body, however, methane leakage might exert significant impact on the ocean acidification considering the widespread distributed cold seeps. In addition, although methane entering the atmosphere is not observed, further research is still needed to understand its potential impact on increasing methane concentration in the surface seawater and gas-water interface methane exchange rate, which consequently increase the greenhouse effect.     

Far-Field Noise Induced by Bubble near Free Surface

The motion of a bubble near the free surface is solved by the boundary element method based on the linear wave equation, and the influence of fluid compressibility on bubble dynamics is analyzed. Based on the solution of the bubble motion, the far-field radiation noise induced by the bubble is calculated using Kirchhoff moving boundary integral equation, and the influence of free surface on far-field noise is researched. As the results, the oscillation amplitude of the bubble is weakened in compressible fluid compared with that in incompressible fluid, and the free surface amplifies the effect of fluid compressibility. When the distance between the bubble and an observer is much larger than that between the bubble and free surface, the sharp wave trough of the sound pressure at the observer occurs. With the increment of the distance between the bubble and free surface, the time of the wave trough appearing is delayed and the value of the wave trough increase. When the distance between the observer and the bubble is reduced, the sharp wave trough at the observer disappears.     

表面波破碎泡径谱的理论研究

采用新的无量纲变量组合推导出波浪破碎形成的气泡总数与气体体积卷入率、湍流能谱密度以及表面张力之间的关系;利用观测结果提出两点假设,并据此将泡径谱N(a)推广为随泡径和深度的分布函数N(a,z)。     

Vertical spatial coherence of backscatter from bubbles

A basic formalism is developed to treat the vertical spatial coherence of backscatter from wind-generated microbubbles beneath the ocean surface. This formalism treats signals multiply scattered by the sea surface and the subsurface scatterers, as well as absorption in the bubble layer. Approximate solutions are obtained for the case of narrow beamwidth sources and are applied to study the influence of measurement system and environmental parameters on coherence. Using bubble densities derived from acoustic backscatter data, the coherence is found to depend strongly on source frequency and beam pattern. The primary environmental effect is due to the increase in both bubble density and penetration depth below the surface that occurs with increasing windspeed. At high wind speeds, the vertical coherence is sufficiently dependent on the scatterer depth distribution to provide a viable means of studying this phenomenon.     

影响海洋光学遥感的海面白泡云研究回顾及进展

回顾了国内外影响海洋光学遥感的白泡云的反射率和覆盖率的研究进展情况。根据海洋水色高光谱遥感发展的需要，指出应当开展海洋白泡云中信号白浪和白沫光学反射特征的测量和研究，以便评价和排除白泡云的反射分量在光学遥感中的干扰。     

一种海面微波散射模式的迭代解

采用随机粗糙面上部分覆盖球形气泡的海面微波散射模式,将非均质大气中的光散射的辐射传输理论推广到此模式中去,得到了辐射强度满足的积分方程关系式。     

Experimental study on bubble pulse features under the combined action of horizontal and vertical walls

The pulse features of a bubble have a close connection with the boundary condition. When a bubble moves near a rigid wall, it will be attracted by the Bjerknes force of the wall, and a jet pointing at the wall will be generated. In real application, the bubble may move under the combined action of walls in different directions when it forms at the corner of a pipe or at the bottom of a dam. The motion of the bubble shows complex and nonlinear characteristics under these conditions. In order to investigate the bubble pulse features near complex walls, a horizontal wall and a vertical wall are put into the experimental water tank synchronously, and an electric circuit with 200 voltages is designed to generate discharge bubbles, and then experimental study on the bubble pulse features under the combined action of horizontal and vertical walls is carried out. The influences of the combined action of two walls on the bubble shape, pulse period, moving trace and inside jet are obtained by changing the distances from bubble center to the two walls. It aims at providing references for the relevant theoretical and numerical research.     

Assessment of acoustic iterative inverse method for bubble sizing to experimental data

Comparative study was carried out for an acoustic iterative inverse method to estimate bubble size distributions in water. Conventional bubble sizing methods consider only sound attenuation for sizing. Choi and Yoon [IEEE, 26(1), 125–130 (2001)] reported an acoustic iterative inverse method, which extracts the sound speed component from the measured sound attenuation. It can more accurately estimate the bubble size distributions in water than do the conventional methods. The estimation results of acoustic iterative inverse method were compared with other experimental data. The experimental data show good agreement with the estimation from the acoustic iterative inverse method. This iterative technique can be utilized for bubble sizing in the ocean.     

热带大西洋年际和年代际变率的时空结构模拟

使用美国夏威夷大学发展的中等复杂程度海洋模式(IOM)在给定表面强迫条件下模拟了热带大西洋上层海洋年际和年代际变率的时空结构.利用NCEP的41a(1958～1998年)逐月平均表面资料作为强迫场,积分海洋模式41a作为控制试验,并利用模式分别做动量(风应力)通量和热量通量无异常变化的平行试验,与控制试验作比较.对3组试验模拟上层海洋变率状况的比较,并按年际和年代际时间尺度分别分析,揭示表面风应力和热通量异常对海表面温度和温跃层深度变化的影响,并比较了其影响的相对重要性.结果表明模式成功地模拟出了热带大西洋上层海洋的变率.模式模拟的海表面温度年际变化主要表现为弱ENSO型,年代际变化表现为南、北大西洋变化相反的偶极子型.在年际时间尺度上,热力强迫和动力强迫对海表温度变化都有贡献,其中赤道外海表面温度异常(SSTA)变化主要由热通量异常引起,而近赤道SSTA的变化主要由动量异常强迫引起.在年代际时间尺度上,热通量强迫的作用远比动量强迫重要.模式不仅能够模拟SST在年际和年代际时间尺度上的变率,还能够模拟温跃层深度在年际和年代际时间尺度上的变率.年际和年代际时间尺度上,温跃层深度的变率主要由动量异常决定,热通量异常强迫的贡献很小.     

A determination of the seismic velocity structure of sediments using both sources and receiver near the ocean floor

A trial experiment proves the power and practicality of using both sources and receivers near the ocean floor to make precise measurements of deep (∼6000 m) ocean sediment velocity structure. A digitally recording ocean bottom hydrophone receiver operating at a sampling rate of 1800 Hz recorded clear arrivals with bubble pulse frequencies of ∼500 Hz from 41b. explosive charges detonated at depths of 5500m along a 4 km long wide angle reflection profile. It is shown that corrections for changes in source depth may be computed without approximation and without prior knowledge of the velocity structure. The experiment was located at longitude 56° W in the trough of the Kane Fracture Zone. The velocity structure of the 1 km thick sedimentary section reveals a 310 m thickness of 3 km s⁻¹ material overlying igneous basement.