浸没的圆柱壳在冲击波作用下动响应的Galerkin解法

研究了无粘、无旋和不可压缩流体中两端简支圆柱壳在给定冲击波作用下的动响应。圆柱壳的运动方程中考虑了流体动压力和冲击波压力的共同作用，通过将冲击波压力分布函数表示为Ｆｏｕｒｉｅｒ级数有限项形式，并利用Ｇａｌｅｒｋｉｎ方法对耦合方程进行数值求解，得到了圆柱壳在冲击波作用下的位移响应特性     

Deformation and tearing of circular plates with varying support conditions under uniform impulsive loads

Transient dynamic finite element analysis of circular plates with varying support configurations under uniform single square wave form impulsive load has been carried out in FEA package ANSYS. Experimental results of Teeling-Smith and Nurick [The deformation and tearing of thin circular plates subjected to impulsive loads. Int J Impact Eng 1991;11(1):77–91] and Nurick et al. [Tearing of blast loaded plates with clamped boundary conditions. Int J Impact Eng 1996;18(7–8):803–27] for the onset of thinning and tearing at the boundary of clamped circular plates subjected to uniformly loaded air blasts have been used to compare and validate the numerical simulation and procedure. The Mode II failure with respect to clamped circular plates has been simulated using a rupture strain criteria. Mode III failure or plastic shear sliding, has been considered using a shear strain failure criteria as proposed by Wen and Jones for plates. A stiffness reduction scheme has been proposed to decide on the initiation and progression of tearing in conjunction with suitable failure model under Modes II and III. The evolution of deflections, plastic zones, rupture zones and failure modes under the blast loading conditions are found to match well with the experimental results. The validated numerical model has further been used to study the effect of plate thickness on the deformation and tearing response of the circular plates subjected to impulsive loads. The deformation, tearing and shock absorption response of clamped circular plates under uniform impulsive loads with ring support of varying edge configurations at the boundary have also been numerically studied. Further, the response of circular plate–tube combination with varying boundary support configurations has been studied. The plate has been considered at the mid-span of the tube of length equal to the plate diameter with the ends of the tube modelled as clamped. The numerical model has been used to study the effect of tube thickness variations on the deformation and tearing response of the circular plate under shock loads. The response of tube–plate combinations under uniform impulsive loads with ring support at the plate–tube junction have also been numerically studied.     

Deformation and fracture behaviour of plate specimens subjected to underwater explosion—a review

Behaviour of plate specimens subjected to underwater explosion is of interest to metal forming community and ship designers. The break down of the original molecule of an explosive into product molecules associated with the evolution of large amount of heat generates a shock front in the water medium, followed by a gas bubble pulsation. The interaction of the shock wave with a plate imparts energy to it, which is dissipated in the form of deformation. The intensity of explosion determines whether a plate undergoes elastic deformation, yielding, plastic deformation or fracture. When the deformation is in the elastic range, the stress developed in the plate is given as a function of the material and shock wave parameters. As the intensity of explosion progressively increases, the elastic to plastic transition occurs over a specific shock factor. Plastic deformation is predicted as a function of geometric and material properties of the plate and shock pulse impulse. Deflection-time history reveals the reloading effects of the shock wave. As the deforming plate absorbs maximum energy, depending on its strength and ductility, it undergoes fracture. Terminal strain to fracture is considered as the criterion for explosive shock performance of ship materials.     

敷设不同覆盖层圆板结构水下抗爆响应特性

在舰船壳体湿表面敷设柔性覆盖层是一种能有效提高其抗冲击性能的方法。多孔蜂窝覆盖层受爆炸冲击波载荷作用后胞元孔壁易于压溃,有效地分散冲击波能量,大幅度减少响应前期阶段的入射冲量,屈曲变形会吸收大量能量。水下爆炸试对于揭示模型的抗冲击机理起着重要的作用。总结对敷设不同覆盖层-圆板结构的水下爆炸响应特性的试验研究。考察有无柔性覆盖层对结构响应的影响,同时解释水下冲击波、气泡对柔性覆盖层的作用过程及覆盖层的抗冲机理。     

Fractional-derivative viscoelastic model of the shock interaction of a rigid body with a plate

The impact of a rigid body upon an elastic isotropic plate is investigated for the case when the equations of motion take rotary inertia and shear deformation into account. The impactor is considered as a mass point, and the contact between it and the plate is established through a buffer involving a linear-spring–fractional-derivative dashpot combination, i.e., the viscoelastic features of the buffer are described by the fractional-derivative Maxwell model. It is assumed that a transient wave of transverse shear is generated in the plate, and that the reflected wave has insufficient time to return to the location of the spring’s contact with the plate before the impact process is completed. To determine the desired values behind the transverse-shear wave front, one-term ray expansions are used, as well as the equations of motion of the impactor and the contact region. As a result, we are led to a set of two linear differential equations for the displacements of the spring’s upper and lower points. The solution of these equations is found analytically by the Laplace-transform method, and the time-dependence of the contact force is obtained. Numerical analysis shows that the maximum of the contact force increases, tending to the maximal contact force when the fractional parameter is equal to unity.     

冲击波作用下舰船刚体运动响应

在非接触水下爆炸冲击波载荷作用下,较小的船体或者刚度较大的船体会产生很大的刚体运动响应。以Taylor平板公式为基础,考虑横剖面运动的附加质量,建立二维横剖面在非接触水下爆炸冲击波作用下的运动方程。在此基础上,计算某艇在水下爆炸冲击波作用下的刚体响应,与实验结果比较一致,表明该方法可用于预报水下爆炸冲击波作用下船体的刚体响应。     

基于量纲分析的爆炸冲击波效应靶模型分析与实验研究

针对传统的冲击波压力电测法易受爆炸场寄生效应干扰问题,提出基于效应靶塑性变形的爆炸冲击波压力评定方法。由于效应靶理论模型复杂、参数较多,利用量纲分析方法简化模型获得爆炸冲击波压力作用的效应靶最大挠度与炸药TNT当量、炸高及炸距之关系,并建立冲击波压力作用的效应靶最大挠度计算模型;设计100 kg、60 kg、20 kg 三种标准TNT爆炸的立靶、平靶实验,用回归分析法获得二者经验模型系数。结果表明,立靶与平靶两种结构效应靶最大挠度实验结果与经验模型计算结果误差分别优于3.59%及3.33%。该研究可指导战斗部冲击波压力评估,进而减少爆炸实验量。     

Blast response of a lined cavity in a porous saturated soil

The paper proposes a comprehensive approach to simulate the blast response of a lined cavity in a porous soil. To calculate the soil–structure contact pressure, the coupled Godunov-variational-difference approach was developed. The lining is modeled by a Timoshenko elastic–plastic shell with kinematic linear hardening. To solve the problem in the lining domain, the variational-difference method is applied. The soil is modeled by the Lyakhov three-phase model that takes into account both bulk and shear elastic–plastic behavior, including the effect of soil pressure on the yield strength for the stress tensor deviator. The problem of blast wave propagation within the soil medium is solved by the Godunov method. The coupled approach to calculate the soil–lining contact pressure is based on the relationships on the shock and rarefaction waves with finite-difference equations of the shell motion using a simple iteration method. It allows the reduction of the contact problem to the self-similar symmetric Riemann problem. Solution of the problem of an explosion in a porous medium, and analysis of the soil–obstacle interaction under the blast action using the proposed method show good correspondence with available experimental results. Also, the plane problem of blast response of the circular cavity lined by a thin steel lining was solved. The effect of the gas volumetric content in the soil on the incident shock wave pressure as well as on the contact pressure and lining meridian strain was studied.     

漂浮式风力机平台动态响应的优化方法探讨

为研究漂浮式风力机平台动态响应的优化措施,分别提出平台附加螺旋侧板和平板的方式。建立基于Spar平台的5MW风力机整机模型,利用有限元软件进行水动力计算,得到了结构运动和波浪力的幅频特性。并通过与附加螺旋侧板和平板情况下的频域和时域动态特性参数对比,探讨两种措施是否对结构的运动性能起到提升作用。结果表明：附加螺旋侧板后,结构在垂荡和纵摇上的运动幅值均得到了明显抑制;附加平板可以有效降低结构的垂荡频域响应峰值,但对纵荡和纵摇影响很小;在考虑实际风、浪、流载荷作用时,两种措施都能起到对结构运动性能的优化作用,附加螺旋侧板的优化作用更为优越。     

规则波作用下开孔圆盘阵列绕射效应研究

在势流理论和线性波理论的假设下,运用特征函数展开法和贝塞尔函数加法理论,研究了规则波作用下开孔圆盘阵列的绕射效应。阵列中每个圆盘都是刚性、开孔的,固定在静水面以下,其厚度相对于入射波波长可以忽略,且通过其表面的流体运动满足达西定律。根据推导出的速度势,进一步得到圆盘的垂荡力和流场的自由表面高程解析表达式。利用该解析解与已发表的孤立圆盘计算结果进行验证;分析了四盘阵列在各种波浪和结构参数下的绕射现象。研究表明：当圆盘开孔率、吃水深度及入射波波长在一定范围内时,圆盘阵列内部将发生显著的相互作用现象,主要表现为迎浪侧圆盘对背浪侧圆盘的遮蔽效应。在特定的入射波波数下,选择适当的四盘阵列圆盘间距,最大可将背浪侧圆盘垂荡力降低至迎浪侧圆盘的76%。同时还发现,四盘阵列中,迎浪侧圆盘上可能发生波能聚焦现象,引起自由表面高程的急剧增大,但这种波能聚焦现象会随着圆盘开孔率的增大而逐渐减弱。     

远场水下爆炸作用下舰船设备冲击响应一体化动力学模型

提出了一种远场水下爆炸作用下舰船设备冲击响应一体化动力学模型。该模型将动态设计分析方法(DDAM)与Taylor平板理论相结合,使得对舰船设备冲击响应分析更为高效。将船体外壳看做平板,将船体各层甲板和设备看做附加在平板上的多个质量,将水下爆炸冲击波看做指数衰减波,形成了一维分析模型。能够根据水下爆炸当量、爆距、舰艇吨位、总尺度、结构和设备质量与支撑刚度等参数预测舰船与设备的冲击响应。预测结果与舰船缩比模型水下爆炸试验结果进行了对比。从总体上看,船体冲击响应谱的趋势和量级一致。     

On the propagation of Lamb waves in viscothermoelastic plates under fluid loadings

In this paper the propagation of plane and circular crested viscothermoelastic waves in a homogeneous isotropic, Kelvin-Voigt type viscoelastic thermally conducting, plate sandwiched between inviscid liquid layers is investigated in the context of classical and non-classical theories of thermoelasticity. The secular equations for the symmetric and skew-symmetric modes of plane and circular crested waves are derived in closed form and isolated mathematical conditions. It is noticed that the motion for both the plane and cylindrical waves in plates is governed by Rayleigh-Lamb-type secular equations. The secular equations for thin plate and short wave length waves are also obtained and discussed. The results in the absence of fluid loading, coupled and uncoupled theories of thermoelasticity have been obtained as particular cases from the derived secular equations. The dispersion curves, attenuation profiles and specific loss in case of symmetric and skew-symmetric wave modes are also presented graphically for a polymethyl methacrylate material plate under fluid loadings. The effect of dissipation due to viscosity is noticed to be quite significant and clearly visible from various curves in the graphs.     

AN INVESTIGATION OF HIGH-SPEED FORMING OF CIRCULAR PLATES IN A LIQUID SHOCK TUBE

High-speed metal forming with liquid shock waves, generated non-explosively in a liquid shock tube, is a new field of study. The advantage of forming with liquid shock waves in a shock tube in comparison to explosive forming is better control and increased safety. This paper describes the experimental set-up of the liquid shock tube and presents the results of experiments performed with fully clamped circular copper disks subjected to the impulsive load of the liquid shock wave. The strain conditions of the deformed disks are determined and the deformation energy is calculated. A theoretical approach is also given to predict the midpoint deflection of the specimen. The experiments show a good repeatability and the calculated deformation energy and the predicted midpoint deflections reveal a good agreement with the experiments. The deformation process of the metal disks during the impact of the liquid shock wave is investigated with a high-speed video camera. From the experiments the local and the average deformation velocities and the strain rates are determined. The pictures of the deforming plate also reveal a plastic hinge, which was theoretically predicted in literature.     

特种结构物内爆炸动力响应分析

本文从分析炸冲击波在障碍物上的反射开始,详细分析了结构物内部冲击波荷载的作用规律,给出了作用在具有球形顶壳的圆柱形建筑物侧壁和球形顶壳上的冲击波压力表达式,并通过经典弹性理论,假设结构材料是各项异性弹性材料,推导出了建筑物侧壁的轴向径向振动的计算表达式,计算得到了侧墙位移和内力曲线。计算表明：侧墙轴向位移最大,侧墙中间的某一位置径向位移和环向力 取得最大值,而侧墙下部弯矩 剪力 和法向内力 达到最大值。     

Normal impact of blunt projectiles on moving targets: Analytical considerations

An analytical model for the normal impact of blunt, cylindrical and undeformable projectiles on thin metallic targets moving in a plane normal to the initial bullet trajectory has been developed. This analysis is intended to depict the principal phenomena that occur when such a projectile strikes the center of a circular plate mounted at the end of an arm rotating about the other end at constant angular velocity. The first step in the simulation constructions of the construction of a three-stage plugging process involving plastic wave propagation, joint projectile/target motion and tensile failure designed for impact on a stationary plate, using a membrane theory for the target response. This axisymmetric representation was then applied to moving targets by employment of impulse-momentum laws. Petaling failure was portrayed by an upper-bound plasticity approach, while projectile motion was described by rigid-body dynamics. The principal assumption inherent in this representation were guided by geometric considerations and observations from tests described in a companion paper.

Model evaluation was performed for several cases of projectile and target speed combinations. Relevant solutions were compared with results from corresponding experiments. In general, good correlation were obtained; discrepancies could be attributed to the effect of features that had not been incorporated in the model.     

箱包炸弹内爆作用下单层球面网壳结构的动力响应分析

运用ANSYS/LS-DYNA建立跨度40 m凯威特K8单层球面网壳,采用流固耦合算法,考虑箱包炸弹在网壳内部爆炸的最不利类型,获取其动力响应规律。研究结果表明:在不同炸点水平位置下,网壳内部流场分布特征、冲击波传播路径以及冲击波与网壳作用过程存在差异,各特征响应随炸点水平位置的改变变化较大,网壳杆件塑性应变百分率大致在网壳半跨的3/4处达到极值;环杆塑性应变百分率较斜杆以及肋杆高,环杆轴向应力呈现的高频率、高幅值的"环杆效应"特征与环杆所处的位置有关,且主要位于网壳的倒数1~3环区域;由于冲击波的局部增强效应,内爆荷载作用下网壳结构的易损薄弱部位主要有柱脚、支座附近杆件以及网壳环杆3部分。     

穿孔式双浮体装置水动力及波能转换特性研究

为进一步解决波能转换装置向深水环境推进过程中存在能量转换效率问题,在现有双浮体点吸式波能装置基础上考虑穿孔阻尼板,提出新的穿孔双浮体带支撑立柱的结构形式。基于线性微幅波假设,通过特征函数展开和边界匹配的势流半解析方法,并结合多自由度振动理论,探索穿孔阻尼板对获能系统水动力、运动响应及俘获宽度比的影响。计算结果表明,阻尼板开孔会降低浮子及阻尼板自身受到的波浪激励力,浮子、阻尼板以及它们之间的耦合辐射作用力会随着阻尼板开孔半径增大而减小;阻尼板的开孔半径增大能有助于浮子与阻尼板的相对响应振幅;阻尼板会使系统出现两个耦合共振频率,在较小共振频率处的最优俘获宽度比均随着阻尼板开孔半径的增加先增大后减小。研究结果可为深水波浪能利用的工程应用提供理论基础,为后续振荡浮子波浪能发电装置优化提供依据。     

The large deflection dynamic plastic response of rectangular plates

By assuming a kinematically admissible, time-dependent velocity field and considering the global equilibrium of all the forces acting on each rigid segment during large deflection of a plate, a complete theoretical investigation is undertaken herein to trace the large deflection dynamic plastic response (including the transient phase) of simply-supported or fully-clamped rectangular plates. This procedure deduces two modifying factors ƒ₁ and ƒ₂ which reflect the effect of the membrane forces and are employed to formulate the governing equations in the case of large deflections. The present prediction of the final plate deflection coincides excellently with the corresponding experimental results for deflections up to 5–10 times the plate thickness. This theory greatly improves the estimates based on the bending-only theory and provides a new way to trace the transient phase of dynamically loaded plates when the effect of membrane forces is significant.     

The effect of surface waves on the interaction of incident particles with a solid surface

The incidence of two particles onto a thin solid plate has been studied by means of computer simulation. The influence of the impact-excited waves on the particle-surface interaction is considered. The waves excited in the target plate produce a significant change in the surface response dynamics. The distribution of surface damage and plastic strain generated by the incident particles is analyzed, and it is established that this distribution is correlated with the surface wave structure.     

Forced surface waves in the presence of porous walls

Summary A linearised surface wave motion is considered for a fluid of infinite extent and of infinite or finite constant depth in the presence of an impermeable plate and a porous wall immersed in the fluid parallel to each other. The motion is generated once by the plate and next by the wall. Analytical solutions are obtained for the velocity potentials of the motions, the hydrodynamic pressure distribution on the porous wall and the profile of the surface and the effects of porosity on these quantities are discussed. A scattering problem is investigated in conclusion.With 5 Figures