水下爆炸对沉箱重力式码头毁伤效应

通过开展不同爆距下水下爆炸对沉箱重力式码头模型毁伤效应试验,对水下荷载进行了采集分析,对毁伤因素、毁伤模式和毁伤机理开展了研究,初步讨论了爆距的影响。结果表明:试验中未形成完整的气泡脉动过程,荷载超压主要出现在冲击波传播阶段,爆炸冲击波、水底反射波和侧壁反射波是主要的毁伤因素;水下爆炸对沉箱重力式码头造成的毁伤程度大、模式多、机理复杂,主要毁伤部位为迎爆面外墙、迎爆侧管沟、封仓板和面板;爆距越近码头毁伤越严重;当爆距过近时,爆炸能量被迎爆面结构变形大量吸收,迎爆面毁伤程度大幅增大,码头其他部位毁伤程度增幅放缓。     

舱段结构在气泡射流作用下的毁伤效果

为研究水下爆炸气泡载荷对船舶局部结构的毁伤效果,设计建造了实尺度舱段模型,并进行水下 爆炸实验,测量了水中压力、气泡脉动周期、舱段外板结构的动应变与塑性变形。分析了不同冲击因子作用下 舱段结构的动态响应,并结合水中压力测量结果,探讨了气泡射流的成因。在此基础之上,分析了气泡射流载 荷的影响范围以及外板在不同载荷作用下的毁伤模式。实验结果表明,相比冲击波载荷,在某些情况下射流 冲击载荷引起的结构响应更剧烈,毁伤效果更严重,因此在中近场水下爆炸作用下,气泡射流冲击载荷对船体 结构的影响不能忽视。     

爆炸气泡与自由水面相互作用动力学研究

为探究爆炸水幕形态与水下流场变化之间的联系,设计了小当量RDX装药水箱内爆炸实验系统.采用两台高速录像机同步拍摄了气泡和水幕形态的演变过程,获得了三种典型气泡形态和六种典型水幕形态.通过观察气泡-水面-空气之间的流场变化和理论分析,揭示了六种形态水幕的演变规律及其形成机理,并与电火花形成气泡实验结果进行了对比分析.通过对不同比例深度条件下的气泡横向半径、纵向半径、膨胀时间、脉动周期、气泡边界运动过程等的统计分析,揭示了近水面水下爆炸形成气泡的动力学过程.     

基于贻贝启发的水下仿生胶黏剂

海洋中的贻贝依靠丝足(Byssus)与足盘(Plaque)可以在潮湿及水下环境中快速而牢固地黏附于各种固体表面。贻贝强健的足部具有沟渠状的生理结构,通过类似于“注塑生产”的生理过程,它们可以生成丝足与足盘。贻贝将液态的蛋白质挤压到沟渠里,只需几秒钟时间,这些蛋白质就能形成一条条发丝一样纤细的丝足。每条丝足的末端都有一个黏性足盘,足盘可以牢牢地黏附在岩石及固体表面。丝足及足盘由多种黏附蛋白(Mfps)组成,且几乎每种黏附蛋白都含有L-3,4-二羟基苯丙氨酸(DOPA)成分。在过去的数十年间,科研人员基本揭示了贻贝黏附蛋白的结构及其黏附机理。DOPA的儿茶酚基团,通过氧化交联、金属螯合、氢键、静电作用、疏水作用、π-π作用、阳离子-π作用等各种共价和非共价相互作用,实现强大的界面黏接。基于贻贝黏附蛋白的结构及其黏附机理,通过使用DOPA及其类似物修饰的聚合物体系,人们得到了多种具有优秀机械性能和功能化的新型仿生多巴类水下胶黏剂。本综述首先介绍了贻贝黏附蛋白的组成特点及其黏附机理;随后分别介绍了凝聚层类胶黏剂、水凝胶类胶黏剂、智能型水下胶黏剂的结构特点及黏附机理;最后讨论了目前仿生水下胶黏剂存在的问题及未来发展前景。     

Numerical simulation of compressible multifluid flows using an adaptive positivity-preserving RKDG-GFM approach

The Runge-Kutta discontinuous Galerkin method together with a refined real-ghost fluid method is incorporated into an adaptive mesh refinement environment for solving compressible multifluid flows, where the level set method is used to capture the moving material interface. To ensure that the Riemann problem is exactly along the normal direction of the material interface, a simple and efficient modification is introduced into the original real-ghost fluid method for constructing the interfacial Riemann problem, and the initial conditions of the Riemann problem are obtained directly from the solution polynomials of the discontinuous Galerkin finite element space. In addition, a positivity-preserving limiter is introduced into the Runge-Kutta discontinuous Galerkin method to suppress the failure of preserving positivity of density or pressure for the problems involving strong shock wave or shock interaction with material interface. For interfacial cells in adaptive mesh refinement, the data transfer between different grid levels is achieved by using a L² projection approach along with the least squares fitting. Various numerical cases, including multifluid shock tubes, underwater explosions, and shock-induced collapse of a underwater air bubble, are computed to assess the capability of the present adaptive positivity-preserving RKDG-GFM approach, and the simulated results show that the present approach is quite robust and can provide relatively reasonable results across a wide variety of flow regimes, even for problems involving strong shock wave or shock wave impacting high acoustic impedance mismatch material interface.     

Aperture-averaged scintillation index and fade statistics in weak oceanic turbulence

With the rapid demand for underwater optical communication(UOC), studies of UOC degradation by oceanic turbulence have attached increasing attention worldwide and become a research hot-spot in recent years. Previous studies used a simplified and inaccurate oceanic turbulence spectrum, in which the eddy diffusivity ratio between temperature and salinity is assumed to be unity and the outer scale of turbulence is assumed to be infinite. However, both assumptions are not true in most of the actual marine environments. In this paper, based on the Rytov theory in weak turbulence, we derive analytical expressions of "the aperture-averaged scintillation index"(SI) for both plane and spherical waves, which can clearly demonstrate how SI is influenced by several key factors in UOC. Then, typical fade statistics of the UOC system in weak turbulence is discussed including the probability of fade, the expected number of fades per time, the mean fade time,signal-to-noise ratio and bit error rate. Our results show that spherical wave is preferable in the UOC system in weak turbulence compared to plane wave, and the aperture-averaged effect has a significant impact on UOC system's performance.Our results can be used to determine those key parameters for designing the UOC system over reasonable ranges.     

枪弹间隙对水下枪内弹道的影响

为了研究枪炮全水下发射过程中枪弹耦合间隙对内弹道特性的影响,运用AUTODYN有限元仿真软件,针对滑膛水下枪枪弹耦合设置0.1 mm间隙与不设置间隙两种情况的内弹道过程进行了数值模拟;采用21、25和30 g装药量对水下枪全水下带间隙发射内弹道过程进行了仿真分析,获得了膛压、射弹速度以及过间隙燃气射流在内弹道过程中组分、压力与速度的分布规律;并设计了实弹射击实验用于验证仿真结果。仿真和实验结果表明,合适的枪炮耦合间隙能够有效地提高水下枪发射性能。当枪弹耦合设置0.1 mm间隙时,采用3种装药量发射均能产生弹前气幕,内弹道过程膛压下降明显,弹丸炮口速度提升较为显著,有利于产生稳定的超空泡包裹弹体,使其在水下运动时所受阻力大大降低,从而增加射弹水下行程。     

水下训练服浮力配平的整数非线性规划方法

针对水下训练服随遇平衡和特定角度下稳定平衡的浮力配平需求,通过对配平过程进行数学描述,基于分支定界算法的整数非线性规划,提出了一种用于浮力配平方案优化计算的方法.对给定初始值的水下训练服,在随遇平衡和不同角度下的稳定平衡条件下,计算得到最优的浮力配平结果,表明了该方法计算配平方案的有效性.该方法对不同配平对象、配平目标的浮力配平过程都有很好的指导意义.     

基于光子图海水点扩展函数的估计

海水中粒子对光的散射是水下图像模糊的主要原因。点扩展函数能够反映海水中光的空间扩散程度,使用点扩展函数,水下图像能被恢复或增强。提出了一种基于光子图海水点扩展函数的估计方法,该方法通过用光子图求解辐射传输方程,对光场内任意点的辐射强度进行估计。通过与蒙特卡洛仿真点扩展函数的方法相比较,结果表明两者具有较好的一致性。     

水下近距爆炸作用下船体梁的动态响应特性

为研究舰船在水下近距爆炸作用下的结构响应及损伤模式,以相似准则为基础,设计了船体梁模型,选用4种不同能量结构的炸药,将其置于模型中部正下方爆炸,通过改变药量和爆距,实验研究了船体梁在近距爆炸作用下的动态响应特性。利用高速摄影技术观察了模型的整个运动过程,结合实验数据定量分析了结构的应变和加速度响应特性,比较了冲击波和气泡脉动对结构的损伤特点。研究发现:近距爆炸气泡脉动会使结构下方形成一个低压流体区,该低压区的存在会使模型受到中垂弯矩作用,并可能使其发生中垂弯曲破坏;随着爆距的增大,爆炸能量与损伤效果之间的相关性变得明显;近距条件下,为了发挥爆炸气泡的最大破坏作用,爆距应该接近于最大气泡半径。