基于比例边界有限元法和有限元法的水下结构瞬态分析方法

针对冲击波作用下水下结构与无限声学水域的流固耦合问题,建立了基于比例边界有限元法和有限元法的瞬态分析方法。无限水域用比例边界有限元法离散,而水下结构等有限域用有限元法模拟。该方法利用声学近似法将无限水域施加给水下结构的载荷分解成冲击波载荷和散射波载荷。冲击波载荷由水下冲击波理论确定,而散射波载荷由比例边界有限元法估值。为改善比例边界有限元法动态质量矩阵的计算效率,发展了动态质量矩阵的时域递推公式。数值算例分析结果表明了所发展的瞬态分析方法和时域递推公式的正确性。     

水下近场爆炸冲击波与射流载荷联合作用分析方法

针对舰船水下近场爆炸,提出综合考虑冲击波载荷与射流载荷的分析方法。对水下近场爆炸气泡脉动过程进行数值模拟,建立射流冲击计算模型,进而简化射流载荷,在冲击波阶段流固耦合模拟结束后自动添加射流载荷,形成完整水下近场爆炸过程的计算流程。建立舷侧板架结构有限元模型,采用MSC.Dytran软件进行流固耦合数值模拟验证方法的可行性。该方法综合考虑冲击波与射流载荷对结构作用,能较真实模拟水下近场爆炸过程,具有一定工程意义及参考价值。     

远场水下爆炸结构动态响应的数值模拟方法研究

远场水下爆炸载荷作用下结构动态响应的数值模拟方法的研究一直是国内外专家关注的热点。针对远场爆炸中冲击波传播的消散过程,将爆炸冲击波载荷直接加载于结构附近的水域面,基于DAA和Taylor板理论,提出简化的改进数值计算方法。采用有限元软件模拟水下爆炸的冲击波传播,通过与经验公式对比,表明只有当水域网格较小时,才能比较真实的模拟冲击波传播过程。最后通过文献中的实验验证了改进方法的准确性,该方法可有效的分析远场水下爆炸下结构的非线性动力高频响应。     

静水压对加筋圆柱壳受水下爆炸冲击载荷作用的影响

应用有限元法，分析静水压对受水下爆炸载荷时的加筋圆柱壳体的变形及破坏模式的影响。通过对壳体结构及外部水域进行建模，并考虑流固耦合及空泡因素，模拟出结构受水下爆炸载荷及静水压力联合作用下的响应。通过比较有和没有外部压力时，不同冲击波下结构的破坏形式，得出外部水压对耐压结构受爆炸载荷时响应的影响。     

水下爆炸冲击波的数值模拟与试验研究

采用ANSYS/LS-DYNA有限元分析软件,对小当量TNT炸药在无限水域内爆炸进行数值模拟,并将数值计算结果与实验室内实测数据以及传统的经验公式计算结果进行对比。分析发现:用传统的经验公式计算小当量TNT炸药在水下爆炸时的爆炸冲击波压力峰值,与实测值相比存在较大误差;运用有限元显式动力分析方法计算得到的水下爆炸冲击波压力峰值与实测值相吻合,并且水下爆炸冲击波波形相近。对数值计算值进行拟合得到水下爆炸冲击波压力峰值的计算公式,可以对同等条件下的水下爆炸试验进行估算。     

基于AUTODYN的乳化炸药水下爆炸能量分布的数值研究

基于AUTODYN软件建立了水下爆炸一维楔形模型,对空气不耦合装药结构下爆炸能量的输出进行研究。首先获得炸药冲击波压力以及气泡脉动随时间的变化曲线,进一步获知径向不耦合状态下水下爆炸的冲击波峰值压力、气泡最大半径以及脉动周期等数据,并最终得到了不耦合系数下冲击波能以及气泡能的变化情况。将计算结果与已有的水下爆炸实验结果进行了比较分析。结果表明,该计算结果与实验数据吻合较好,证明了利用数值计算手段可以实现定量化表征炸药输出能量随不耦合装药结构的变化规律。     

基于AUTODYN的乳化炸药水下爆炸能量分布的数值研究

基于AUTODYN软件建立了水下爆炸一维楔形模型,对空气不耦合装药结构下爆炸能量的输出进行研究。首先获得炸药冲击波压力以及气泡脉动随时间的变化曲线,进一步获知径向不耦合状态下水下爆炸的冲击波峰值压力、气泡最大半径以及脉动周期等数据,并最终得到了不耦合系数下冲击波能以及气泡能的变化情况。将计算结果与已有的水下爆炸实验结果进行了比较分析。结果表明,该计算结果与实验数据吻合较好,证明了利用数值计算手段可以实现定量化表征炸药输出能量随不耦合装药结构的变化规律。     

不同类型炸药水下爆炸时冰层损伤特性研究EI北大核心CSCD

为了探究水下爆炸冲击波与气泡脉动载荷联合作用下冰层损伤特性以及不同类型含能炸药水下爆炸对冰层损伤特性。采用动力学分析软件LS-DYNA中的任意拉格朗日欧拉(ALE)法建立了计算水下爆炸气泡动力学模型及水下爆炸冰-水全耦合模型,考虑了冲击波载荷及复杂的气泡载荷耦合全过程;在此基础上,分析了烈性奥克托今炸药(HMX)及不同铝氧比黑索金炸药(RDX)对冰层损伤特性的影响。研究结果表明:计算模拟结果与试验结果吻合良好,验证了计算模型的有效性;揭示了水下爆炸冲击波和气泡载荷联合作用下的冰层损伤机理;HMX炸药对冰层的损伤威力更强,RDX(0.36)比RDX(0)、RDX(0.16)、RDX(0.63)对冰层产生的毁伤效应要强,其与TNT对冰层造成的毁伤效应强度接近。依据研究结果冲击波载荷是造成冰层损伤区域大小的主要毁伤元素,而气泡载荷主要影响冰层毁伤区域的破碎形态;根据不同毁伤目标应用特性,调节炸药配方比,改变冲击波能与气泡能的输出结构,可实现冰层的不同毁伤模式。     

基于总场公式的水下冲击结构响应分析方法

针对无限水域下的结构冲击响应问题,建立了基于PWA(平面波近似)总场公式和SBFEM(比例边界有限元)总场公式与FEM(有限元)耦合的结构响应分析方法。该方法分别采用PWA总场公式和SBFEM总场公式模拟无限域,FEM方程模拟水下结构。通过将其耦合,建立了PWA-FEM总场公式和SBFEM-FEM总场公式。通过数值算例,讨论了环向单元数量、无限域截断边界大小和形状对总场公式计算准确度的影响,比较了PWA-FEM总场公式和SBFEM-FEM总场公式的计算准确度。数值结果表明了总场公式用于模拟无限水域下结构冲击响应问题的可行性和准确性,且SBFEM-FEM总场公式模拟无限域时,可有效减小有限域离散范围,并对截断边界形状要求不高,适用范围更广,为水下冲击结构响应问题提供了一种有效可行的求解方法。     

船用柴油机油底壳声辐射计算及结构优化设计

以某船用高速柴油机油底壳为研究对象,通过测试获得油底壳激励载荷,分别利用声振耦合模式下有限元-边界元法及非耦合模式下有限元-边界元法计算油底壳辐射噪声。结果表明,不同模式下油底壳辐射声功率曲线基本吻合,油底壳与辐射介质间耦合作用可以忽略。分别利用非耦合模式下有限元-边界元法(FE-BEM)、有限元-匹配层技术(FE-AML)及有限元-无限元法(FE-IFEM)计算油底壳辐射噪声,探索了3种方法在建模规模、计算精度及计算耗时方面的差异性。研究发现,宜首选有限元-边界元法计算船用柴油机油底壳辐射噪声。为减小油底壳辐射噪声,对油底壳结构进行多目标形貌优化设计,结果表明,形貌优化可有效降低油底壳振动及辐射噪声,减少设计重复性并缩短设计周期。     

Finite Element Evaluation of Acoustic Energy Penetration of Partially Submerged Tube Bundles

In this paper, the finite element software ANSYS is used to model ultrasonic waves propagating through a liquid volume containing partially submerged tubes. An immersible transducer is used to generate the waves. The goal of the investigation is to find an appropriate excitation frequency in order to perform ultrasonic cleaning of the tubes. Modal analysis of the coupled tubes–liquid system is conducted to evaluate the dynamic behavior of the tube structures under ultrasonic wave excitations. The frequency at which the acoustic waves efficiently penetrate the tube array with least energy loss and least deformation to tube structures is obtained, and will be used to probe the capability and the potential of utilizing ultrasonic energy as a non-destructive technique for cleaning tube bundles.     

A new acoustic interface element for fluid-structure interaction problems

A new comprehensive acoustic 2-D interface element capable of coupling the boundary element (BE) and finite element (FE) discretizations has been formulated for fluid–structure interaction problems. The Helmholtz equation governing the acoustic pressure in a fluid is discretized using the BE method and coupled to the FE discretization of a vibrating structure that is in contact with the fluid. Since the BE method naturally maps the infinite fluid domain into finite node points on the fluid–structure interface, the formulation is especially useful for problems where the fluid domain extends to infinity. Details of the BE matrix computation process adapted to FE code architecture are included for easy incorporation of the interface element in FE codes. The interface element has been used to solve a few simple fluid–structure problems to demonstrate the validity of the formulation. Also, the vibration response of a submerged cylindrical shell has been computed and compared with the results from an entirely finite element formulation.     

Transient response of a submerged cylindrical foam core sandwich panel subjected to shock loading

Predicting the dynamic response of submerged vehicles subjected to hydrostatic pressure and underwater shock loading is of great interest to many structural designers and engineers for improving material and configuration design in recent years. In this paper, the finite element method is used to evaluate the dynamic response of a submerged cylindrical foam core sandwich panel subjected to shock loading. The sandwich panel consists of a foam core surrounded by fiber-reinforced laminates. The effect of fluid–structure coupling is included in the finite element analysis whereas the fluid is assumed to be compressible and inviscid. Time histories of circumferential stress for different composite plies are presented in graphical form and the effects of core type on circumferential stress and velocity of stand-off point are also investigated. Additionally, the distribution of pressure in fluid domain and the deformation of cylindrical foam core sandwich panel are estimated. To the best of the authors’ knowledge, the specialized literature addressing the dynamic response of submerged cylindrical foam core sandwich panel to underwater shock loading is rather scanty. This work is likely to fill a gap in the specialized literature on this topic.     

轴对称声振耦合的边界子波谱与有限元耦合方法及应用

在轴对称结构有限元和轴对称Helmholtz积分方程的基础上,建立了轴对称弹性结构构声振耦合的边界 子波谱有限元耦合方法,该方法能处理任意边界条件。采用提出的耦合方法研究了含有壳、肋、板复杂结构的水下航行 器的声辐射,给出了轴对称圆环肋的刚度矩阵和质量矩阵。进行了声振耦合的模态分析,研究了航行器的轴向激励、侧 向激励的声辐射;计算了0～2kHz的频率响应。结果对水下航行器的研究设计有一定的参考价值。     

预报振动噪声的径向基点插值无网格与无限元耦合方法

为克服传统的有限元耦合无限元方法中的单元匹配问题,研究了径向基点插值法和无限元法的耦合规律,提出了一种预报无限域结构振动噪声的径向基点插值无网格与可变阶无限声波包络单元耦合方法,推导了预报声压的计算公式。为提高声场预报精度和满足声波在无限域的自由衰减,结构外部无限声场分为使用无网格表示的近场和可变阶声波包络单元离散的远场。在该耦合方法中,通过在近场与远场之间的交界面上配置虚拟网格来构造具有连续性的声压形函数,确保了声压的连续与一致性。采用数值仿真和试验对该耦合方法进行了验证,结果表明该耦合方法拥有无网格法的高精度和可变阶声波包络单元法满足声波自由衰减的特点,具有良好的精度和收敛性,可用于实际噪声预报。     

水下压电/弹性材料复合层球壳声波反射的数值研究

采用有限单元计算软件ANSYS对无限水域中压电/弹性材料复合层球壳的声波反射进行了数值研究.研究表明,在压电层中加载适当的电压可以在一个圆锥形的流体区域内有效地减小壳体对于外来声波的反射,并且有可能完全消除任意选定空间点上的反射.     

A spectral‐element method for modelling cavitation in transient fluid–structure interaction

In an underwater‐shock environment, cavitation (boiling) occurs as a result of reflection of the shock wave from the free surface and/or wetted structure causing the pressure in the water to fall below its vapour pressure. If the explosion is sufficiently distant from the structure, the motion of the fluid surrounding the structure may be assumed small, which allows linearization of the governing fluid equations. In 1984, Felippa and DeRuntz developed the cavitating acoustic finite‐element (CAFE) method for modelling this phenomenon. While their approach is robust, it is too expensive for realistic 3D simulations. In the work reported here, the efficiency and flexibility of the CAFE approach has been substantially improved by: (i) separating the total field into equilibrium, incident, and scattered components, (ii) replacing the bilinear CAFE basis functions with high‐order Legendre‐polynomial basis functions, which produces a cavitating acoustic spectral element (CASE) formulation, (iii) employing a simple, non‐conformal coupling method for the structure and fluid finite‐element models, and (iv) introducing structure–fluid time‐step subcycling. Field separation provides flexibility, as it admits non‐acoustic incident fields that propagate without numerical dispersion. The use of CASE affords a significant reduction in the number of fluid degrees of freedom required to reach a given level of accuracy. The combined use of subcycling and non‐conformal coupling affords order‐of‐magnitude savings in computational effort. These benefits are illustrated with 1D and 3D canonical underwatershock problems. Copyright © 2004 John Wiley & Sons, Ltd.     

Finite element analysis of unbounded and incompressible fluid domains

A finite element technique of analysing the hydrodynamic pressure, resulting from the vibration of a structure submerged in an unbounded fluid domain, is presented. A suitable boundary condition is proposed for the surface where the unbounded fluid domain is truncated. Pressure is assumed to be the nodal unknown and the fluid is treated as being incompressible and inviscid. The proposed method is computationally very efficient and its implementation in a finite element program is quite straightforward. The efficiency of the method is demonstrated by analysing some two-dimensional problems.     

The method of fundamental solutions for acoustic wave scattering by a single and a periodic array of poroelastic scatterers

The method of fundamental solutions (MFS) is now a well-established technique that has proved to be reliable for a specific range of wave problems such as the scattering of acoustic and elastic waves by obstacles and inclusions of regular shapes. The goal of this study is to show that the technique can be extended to solve transmission problems whereby an incident acoustic pressure wave impinges on a poroelastic material of finite dimension. For homogeneous and isotropic materials, the wave equations for the fluid phase and solid phase displacements can be decoupled thanks to the Helmholtz decomposition. This allows for a simple and systematic way to construct fundamental solutions for describing the wave displacement field in the material. The efficiency of the technique relies on choosing an appropriate set of fundamental solutions as well as properly imposing the transmission conditions at the air–porous interface. In this paper, we address this issue showing results involving bidimensional scatterers of various shapes. In particular, it is shown that reliable error indicators can be used to assess the quality of the results. Comparisons with results computed using a mixed pressure–displacement finite element formulation illustrate the great advantages of the MFS both in terms of computational resources and mesh preparation. The extension of the method for dealing with the scattering by an infinite array of periodic scatterers is also presented.