冲击波作用下气泡动态响应数值研究

采用边界元法模拟冲击波作用下气泡动态响应,应用Mixed-Eulerian-Lagrangian(MEL)法模拟气泡的演化。分别模拟规则冲击波和爆破冲击波与气泡的相互作用,三维数值模型计算结果与已有实验数据进行对比,结果表明,计算值与实验数据吻合良好,验证了计算模型的有效性。改变冲击波参数和气泡初始状态及特征参数,研究不同参数下气泡的动力学特性,得出规律性曲线。     

近壁面气泡的动态特性研究

基于势流假设，建立气泡与壁面耦合数值模型，运用边界积分法求解，开发了三维计算程序，计算值与实验值吻合良好。从气泡与壁面相互作用的基本现象入手，基于开发的程序系统地研究了刚性壁面附近气泡的动力学特性，其中包括水平壁面及倾斜壁面。研究壁面的Bjerknes效应与各特征参数之间的关系，并将各种工况的计算结果与基于Kelvin—impulse理论的Blake准则进行对比分析及讨论，得出偏射流方向及壁面压力与气泡的特征参数的密切关系，同时给出了Blake准则的适用范围。旨在为相关的近壁面气泡动态特性研究提供参考。     

深水爆炸水动压力场对潜体结构的动态影响

拓广ＤＡＡ法用于预报水中一次冲击波对悬浮体的动响应；引和当量能量与当量深度概念，计算了有自由水面的水下爆炸迁移气泡多次脉冲动力学特性，数值计算值与实测值作了对比，并给给出了水中存在圆柱壳时气泡脉动压力的经验公式。     

气泡动力学数值模型的稳定性研究

基于势流假设,建立气泡动力学数值模型,并开发计算程序.系统地分析了不同模型、不同单元类型的计算精度,以及网格划分、时间步等因素对计算结果的影响,验证了本文数值模型的收敛性,并在计算过程中分析了动能、势能及总能量随时间的变化.为考核文中建立的气泡动力学计算模型的有效性,分别将轴对称模型及三维模型与Rayleigh-Plesset气泡模型的精确解及实验数据、实验照片进行了对比分析,分析表明,计算结果与Rayleigh-Plesset模型及实验数据吻合很好,表明文中建立的计算模型是可行的、有效的.并分析了气泡在重力场中的运动特性.     

圆柱壳附近水下爆炸气泡动态特性研究

基于不可压缩势流理论,运用边界元方法,建立圆柱壳附近水下爆炸气泡三维数值模型。然后采用该模型模拟深水中圆柱壳附近近场水下爆炸气泡运动,并对气泡动态特性以及攻角大小对其影响规律进行了研究。计算结果表明,膨胀阶段气泡受浮力作用以及壁面的排斥作用影响较小;收缩阶段气泡受浮力作用以及气泡受壁面的吸引作用影响较大,随攻角的减小,气泡射流作用和气泡脉动压力均逐渐增强,即爆点位于圆柱壳结构正下方时所造成的结构损伤最为严重。研究结论有益于潜艇结构抗爆防护设计,也为水下爆炸气泡载荷作用下潜艇结构毁伤机理研究提供了参考依据。     

螺旋桨梢涡空泡初生及尺度效应研究

应用气泡动力学方程和气泡运动微分方程研究了螺旋桨梢涡空泡的初生问题,并根据简化Reyleigh-Plesset方程推导了不同尺度模型空化初生空泡数换算公式,建立了空化初生尺度换算模型,研究了螺旋桨梢涡空泡初生尺度效应问题。螺旋桨梢涡流场应用RANS方法求解,湍流模型为经过旋转和曲率修正的代数雷诺应力模型(EARSM-CC)。计算结果表明,文中建立的数值方法能够准确预报出螺旋桨梢涡流场分布;螺旋桨梢涡空泡初生空泡数计算结果高于试验观察值;应用文中建立的空化初生尺度换算模型得到的结果与数值模拟结果基本吻合,而且其结果偏于安全。     

两个气泡相互作用的某些动力特性研究

文章采用边界积分方法模拟三维水下气泡的动力特性,详细阐述气泡计算的数学模型和数值实施过程,探究了三种不同浮力参数情况下(无重力、弱浮力、强浮力)气泡的演变情况。计算结果表明,在不同的浮力参数下,气泡形状和射流特点有着显著的区别,射流形成和发展与重力有着密切的联系。文中计算了两气泡在不同距离和不同强度参数下的相互作用的特点,为气泡动力特性的研究提供了参考。     

水下爆炸气泡及其对结构毁伤研究综述

水下爆炸,特别是近场水下爆炸,会对舰船结构造成严重的毁伤,研究表明,水下爆炸气泡将与含初始毁伤的结构产生强烈的耦合效应,造成二次毁伤。水下爆炸气泡与自由面、壁面、弹性结构等不同边界的相互作用是流体力学和流固耦合领域的研究热点,有很多机理性问题亟待解决。围绕水下爆炸气泡对结构的毁伤,从实验研究、理论研究、数值研究等方面阐述该领域国内外的研究现状。在现有的研究动态中,仍存在着不足,一些问题仍需深入研究,例如,要研究水下爆炸冲击波对水中结构造成破口后,气泡与具有初始破口的不完整边界的耦合动力学特性,并计入结构的弹塑性、自由液面效应、气泡周围流场的可压缩性、气泡的初始形状以及气泡内部的温度变化,探索气泡的"腔吸现象"、射流特性及其载荷规律。     

威海船厂港域波高数值计算*

应用能量平衡方程研究近岸随机波的传播变形是一种简单而实用的方法,其在海洋学以及海岸动力学中得到了广泛的应用。采用考虑绕射作用的能量平衡方程作为计算随机波浪传播变形的控制方程,以此建立的数学模型考虑了波浪的浅化、折射、绕射、反射和破碎。利用该模型对威海船厂港内随机波传播变形进行数值模拟,通过数值计算值与试验值的比较,发现在相同的考虑因素下两者是相当吻合的,说明模型在计算近岸随机波的传播变形时是实用而可靠的。     

水下爆炸气泡对水面舰船载荷的数值研究

文章基于势流理论采用边界积分法求解拉普拉斯方程,阐述水面舰船附近三维爆炸气泡脉动过程的计算模型.通过数值计算获得气泡运动规律的同时,着重研究爆炸气泡对船体的载荷.计算结果揭示出爆炸气泡对水面舰船的整体破坏作用.     

超声降解废水机理及空化气泡运动过程数值模拟

阐述了超声降解废水的机理,并根据以体积作为动力学参数的气泡动力学模型进行数值模拟,结果表明,低频下的空化强度更大,更有利于降解过程,而驱动声压和初始气泡大小则存在一个最佳值,同时与传统的R-P方程作了比较,两个模型模拟结果基本一致,表明本文所用模型也适用于对气泡运动过程的模拟.     

Prediction of tip vortex cavitation inception using coupled spherical and nonspherical bubble models and Navier–Stokes computations

A spherical and a nonspherical bubble dynamics models were developed to study cavitation inception, scaling, and dynamics in a vortex flow. The spherical model is a modified Rayleigh–Plesset model to account for bubble slip velocity and for nonuniform pressures around the bubble. The nonspherical model is embedded in an unsteady Reynolds-averaged Navier–Stokes code with appropriate free-surface boundary conditions and a moving chimera grid scheme around the bubble. The effect of nonspherical deformation and bubble/flow interaction on bubble dynamics is illustrated by comparing spherical and nonspherical models. It is shown that nonspherical deformations and bubble/flow interactions are important for an accurate prediction of cavitation inception. The surface-averaged pressure-modified Rayleigh–Plesset scheme is a significant improvement over the conventional spherical model, and is able to capture the volume changes of a bubble during its capture. It is also a fast scheme for studying scaling. In a preliminary study, the scaling effects on cavitation inception were examined using two different Reynolds numbers owing to two different chord lengths. The nuclei-size effect on the prediction of cavitation inception was also studied, and its important effects are highlighted.     

Interaction of two three-dimensional explosion bubbles

The interaction of two underwater explosion bubbles was mathematically analyzed in this paper. Based on the assumption of potential flow, high-order curved elements were used to discretize the boundary integral equation and solve it. Assuming that gas inside the bubble follows the isentropic rule, the Euler-Lagrange method was used to trace the evolution of the bubble, and when calculating the singular integral, the singularity of the double-layer singular integral was eliminated by reconstructing a principal-value integral of double-layer potential so that a more precise result could be obtained. Elastic mesh technique (EMT) was also used when tracing the evolution of the bubble interface, and numerical smoothing wasn't needed. A comparison of calculations using this three-dimensional model with results of the Reyleigh-Plesset bubble model shows that the three-dimensional model and calculation method in this paper is practical. This three-dimensional model was applied to simulate the interaction of two bubbles under the action of gravity, and the dynamic characteristics of two bubbles near the surface was also analyzed. Bubbles influenced by surface effects and gravity present severe non-linearity. This paper provides a reference for research into the dynamics of multi-bubbles.     

快艇气泡减阻的原理研究与相似比分析

分析了高速气泡船气液两相流动的特征,进而将气泡船复杂的三维流动简化为两维人工气泡绕流的两相流物理模型,并提出了两维人工气泡绕流的相似律.采用有限体积法和VOF方法,建立了两维人工气泡绕流的数学模型.应用该数学模型,研究了气泡船在无气泡、气泡封闭、气泡半开三种典型绕流时的气液流场特性,得到了气泡长度、气泡形状随来流速度、气泡腔压力、气体流量的变化规律,分析得出了在高速气泡船底部形成稳定气泡的力学条件.相关研究结果对高速气泡船底部气泡腔的设计具有指导意义.     

空泡尾部流场特性数值模拟研究

使用商用软件FLUENT6.0,对不同的空泡形态下空泡尾部的阻力特性进行了数值模拟研究.研究表明,随着通气率的增大和空泡形态的增长,运动体尾部阻力系数逐渐减小,并且在减小至谷底后又开始回升.尾部压差阻力系数大于粘滞阻力系数,二者均随着通气率的增加而减小.并且压差阻力系数在达到最小值后开始逐渐增大,因而使得总尾部阻力系数在减小至谷底后开始回升.运动体尾部沾湿长度随着通气率的增大而减小,尾部阻力系数则随着尾部沾湿长度的增大而增大.     

基于Star-CCM+的摆式波浪能装置水动力性能研究（英文）

A two-dimensional numerical Computational Fluid Dynamics(CFD) model is established on the basis of viscous CFD theory to investigate the motion response and power absorption performance of a bottom-hinged flap-type wave energy converter(WEC)under regular wave conditions. The convergence study of mesh size and time step is performed to ensure that wave height and motion response are sufficiently accurate. Wave height results reveal that the attenuation of wave height along the wave tank is less than 5% only if the suitable mesh size and time step are selected. The model proposed in this work is verified against published experimental and numerical models. The effects of mechanical damping, wave height, wave frequency, and water depth on the motion response, power generation, and energy conversion efficiency of the flap-type WEC are investigated. The selection of the appropriate mechanical damping of the WEC is crucial for the optimal extraction of wave power. The optimal mechanical damping can be readily predicted by using potential flow theory. It can then be verified by applying CFD numerical results. In addition, the motion response and the energy conversion efficiency of the WEC decrease as the incident wave height increases because the strengthened nonlinear effect of waves intensifies energy loss. Moreover, the energy conversion efficiency of the WEC decreases with increasing water depth and remains constant as the water depth reaches a critical value. Therefore, the selection of the optimal parameters during the design process is necessary to ensure that the WEC exhibits the maximum energy conversion efficiency.     

Characteristics of a bubble jet near a vertical wall

A numerical model of a coupled bubble jet and wall was built on the assumption of potential flow and calculated by the boundary integral method. A three-dimensional computing program was then developed. Starting with the basic phenomenon of the interaction between a bubble and a wall, the dynamics of bubbles near rigid walls were studied systematically with the program. Calculated results agreed well with experimental results. The relationship between the Bjerknes effect of a wall and characteristic parameters was then studied and the calculated results of various cases were compared and discussed with the Blake criterion based on the Kelvin-impulse theory. Our analyses show that the angle of the jet＇s direction and the pressure on the rigid wall have a close relationship with collapse force and the bubble＇s characteristic parameters. From this, the application range of Blake criterion can be determined. This paper aims to provide a basis for future research on the dynamics of bubbles near a wall.     

不同布置方向对可倾瓦轴承性能的影响

研究了3种不同布置方向对可倾瓦轴承油膜温度、承载力、功耗及动态系数等性能的影响.计算联立求解雷诺方程、能量方程及温粘方程,应用数值解法求出轴承压力和温度分布,进而求出轴承静态性能、轴承刚度和阻尼.理论计算结果表明:载荷在瓦块上时,承载能力最大,功耗最小,但需要的供油量最大;对主刚度Kxx影响较大;载荷作用在瓦块前部时,交叉刚度也不再为0.在轴承试验台上,对可倾瓦轴承不同布置方向对油膜温度的影响进行试验验证,理论和试验趋势一致,油膜最高温度差最大达到8.8℃.