爆炸下球壳变形空间周期分布的理论计算方法

早期研究提出了对振动叠加应变增长现象的解剖式分析方法，进而发现爆炸加载下带扰动源球壳上的弯曲波和壳体变形呈空间周期分布的规律。参考Timoshenko梁的弯曲理论，基于平截面假定和壳体发生较小的弯曲变形的假设，推导出球壳上弯曲波波速和波长的关系，计算得到最短弯曲波和与膜振动频率相近的弯曲波的波速，还结合早期研究提出的壳体变形分布周期与弯曲波波速的关系，计算得到了壳体变形空间分布的周期。结果表明:（1）理论计算结果与数值仿真结果基本吻合，其中弯曲波波速的计算结果与数值仿真结果相差在15%以内，壳体变形空间分布周期的计算结果与数值仿真结果相差在12%以内；（2）弯曲波波长越短，波速越快，当波长无限短时，波速趋于极限值，约为声速的0.574倍。本计算方法为解剖式分析方法提供了一定的理论依据。     

基于LS-DYNA的液电效应冲击波数值模拟

液电效应机理复杂,鲜有成熟的商用数值模拟软件能够描述等离子体通道内部特性,为了将液电效应产生的冲击波运用于已有的数值模拟软件中,以满足工程需要,介绍了两种基于显式动力学软件LS-DYNA间接模拟液电效应产生冲击波的方法:水下爆炸等效（分为爆炸能量等效与冲击波能量等效）和理想气体等效,并进行了比较与改进,分析了不同沉积能量下采用不同等效方法得到的峰压计算结果的差异。结果显示,在沉积能量相同的条件下,基于爆炸能量等效方法得到的冲击波峰值压力最高,基于冲击波能量等效方法得到的冲击波峰值压力次之,基于理想气体等效方法得到的冲击波峰值压力最低,理想气体等效模拟的峰压相较于前两种等效方法小1～2个数量级;爆炸能量等效与冲击波能量等效的冲击波波速相等,且高于理想气体等效的冲击波波速;沉积能量减小会使得3种等效方法模拟的峰压均有不同程度的减小,但大小顺序不发生变化;改进后的等效爆炸方法能够适应沉积能量的变化,与Touya经验公式拟合较好;基于LS-DYNA对液电效应冲击波峰值压力进行准确模拟,除了选取适合的等效方法,还应结合具体的放电条件,建立适当的数值模型,在满足计算要求的条件下实现冲击波峰值压力的快速计算。     

一种计算交通波传播速度的方法

基于交通心理学和车辆跟驰的物理机制推导出一种交通波传播速度公式, 可以用于计算各种车流状态下的波速. 应用交通波传播速度公式计算了平面交叉口红灯变为绿灯时的起动波波速, 通过与实测数据比较, 证实了该计算方法的可行性.在此基础上推导了交通波速的特性, 以事故波波速特性为例进行了详细讨论, 所得结果符合交通实际.      

板中正交静应力与任意方向兰姆波波速的关系

运用部分波分析法(或子波分析)理论推导了在正交静应力下,板中任意方向的Lamb波的频散方程,给出了任意方向Lamb波波速、正交静应力和频率之间的关系. 进行了数值计算并讨论了对称方向的Lamb波波速对单向静应力的依赖关系,为将Lamb波用于应力测量提供了理论依据.      

虚拟质量力对酸性气体-钻井液两相流波速的影响

基于两流体模型、酸性气体和钻井液状态方程,考虑酸性气体与钻井液相间虚拟质量力、粘性剪切力、相间动量交换及狭义相间阻力等条件,建立酸性气体与钻井液两相中压力波传播速度的数学模型,依据小扰动原理,对波速模型求解,得到关于波数K的波速方程。结果表明,在一定范围内,随空隙率、频率的增大,虚拟质量力对波速的影响显著增强;在高空隙率下,压强增大,虚拟质量力对波速的影响减弱;增大流体的密度或不可压缩性,均可使两相压力波速增大;延长气液交换时间或减小波动频率使相间有足够时间进行动量交换,两相压力波波速随之减小。     

一种浆体管道中气体含量的测试方法

实际的浆体输送管道中通常都含有少量的气体并会使泵的性能明显下降,现有的常规方法很难测量该气体含量。本文给出了浆体管道中气液固三相伪均质流和非均质流压力波波速计算式,数值分析表明,波速随着浆体中气体含量增加而迅速降低,并应用实例探讨了利用声速来测量浆体管道中气体含量的可行性和具体的测试方法,结果表明,通过在线测量管路中声波的速度或频率可以较准确地获得浆体中微量气体体积含量。     

垂直向下管内两相流泡状-弹状流型转换研究

建立实验系统,在维持管道出口压力为0.2MPa的条件下,对内径分别为15mm、25mm、40mm、65mm的垂直向下管内空气-水气液两相流动进行了实验研究,获得了两相流泡状-弹状流型分布。实验研究发现:管径对于泡状流与弹状流流型特征有较大影响,并且进一步影响流型转换边界,随着管径增加,泡状流-弹状流的流型转换边界向折算气速减小的方向移动。基于理论推导及实验数据,建立了垂直向下管内气液两相流泡状流-弹状流流型转换预测模型,该模型对本文实验工况条件下的垂直向下管内空气-水气液两相流流型转换具有良好的预测效果,预测模型的计算结果与实验数据之间的误差小于10%。     

湍流模型对空泡形态影响的数值研究

为研究湍流模型对空泡尾部气体泄漏方式和空泡外形的影响,基于 FLUENT6.2的 VOF 多相流模型,对考虑重力作用下的三维通气空泡流进行了数值计算,比较了大涡模拟 LES 和 RNG k-ε两种湍流模型下的空泡形态和模型表面压力系数分布。结果显示,RNG k-ε模型计算的空泡内压力较大,空泡长度更长,而 LES 的瞬态计算结果更符合通气空泡的特性,相对而言更适用于通气空泡流的模拟。     

浆体管道输送水击压力波波速的探讨

 在考虑自由气体存在的影响下，推导出浆体水击压力波波速的 计算公式.分析表明很少量的气体存在会使波速明显降低. 气体体积 浓度较大时波速随浆体浓度的增大而减小，重质物料的减小趋势较 为明显；气体体积浓度较小时轻质物料波速随浓度的增加而增加. 相同条件下非均质流波速比伪均质流波速大，两者差异主要受浆体 中固体物料的密度和浆体体积浓度影响. 考虑气体影响作用的浆击 波速计算值与实测结果更吻合.     

小不耦合系数装药爆破孔壁压力峰值计算方法

基于轮廓爆破孔壁压力峰值计算方法的相关研究,充分考虑空气冲击波的传播与爆轰产物膨胀的过程,理论分析了小不耦合系数装药爆破过程中空气冲击波与炮孔壁的相互作用,建立了三维空气介质径向不耦合装药单孔爆破有限元模型,研究了工程爆破中常用的多种小不耦合系数装药组合工况下,炸药单点起爆后的炮孔壁压力峰值,并获得了相应工况下的孔壁压力峰值较爆生气体准静态等熵膨胀压力的压力增大倍数。结果表明:小不耦合系数装药爆破过程中,爆轰产物参数会对空气冲击波波后物质参数产生显著影响,揭示了小不耦合系数装药爆破与轮廓爆破在孔壁压力峰值计算方法上的本质差异;柱状装药结构爆轰波沿轴向传播使得空气冲击波撞击炮孔壁时存在叠加效应,孔壁压力峰值也相应增大,通过统计分析不同炸药类型、不同岩石类型工况下压力增大倍数与不耦合系数的关系,发现压力增大倍数随不耦合系数的增大近似呈线性增长;基于理论推导结果及常用爆破孔壁压力峰值计算形式,综合考虑炸药性能、孔壁岩石介质条件、不耦合装药系数对空气冲击波撞击炮孔壁后压力增大倍数的影响,提出了不耦合系数较小时爆破孔壁压力峰值计算方法。     

Wave propagation along a non-principal direction in a compressible pre-stressed elastic layer

The dispersive behavior of small amplitude waves propagating along a non-principal direction in a pre-stressed, compressible elastic layer is considered. One of the principal axes of stretch is normal to the elastic layer and the direction of propagation makes an angle θ with one of the in-plane principal axes. The dispersion relations which relate wave speed and wavenumber are obtained for both symmetric and anti-symmetric motions by formulating the incremental boundary value problem for a general strain energy function. The behavior of the dispersion curves for symmetric waves is for the most part similar to that of the anti-symmetric waves at the low and high wavenumber limits. At the low wavenumber limit, depending on the pre-stress and propagation angle, it may be possible for both the fundamental mode and the next lowest mode to have finite phase speeds, while other higher modes have an infinite phase speed. At the high wavenumber limit, the phase speeds of the fundamental mode and the higher modes tend to the Rayleigh surface wave speed and the limiting wave speeds of the layer, respectively. Numerical results are presented for a Blatz–Ko material and the effect of the propagation angle is clearly illustrated.     

Dispersion effects of extensional waves in pre-stressed imperfectly bonded incompressible elastic layered composites

The effect of an imperfect interface, on time-harmonic extensional wave propagation in a pre-stressed symmetric layered composite is considered. The bimaterial composite consists of incompressible isotropic elastic materials. The shear spring type resistance model employed to simulate the imperfect interface can accommodate the extreme cases of perfect bonding and a fully slipping interface. The dispersion relation obtained by formulating the incremental boundary-value problem and the use of the propagator matrix technique, is analyzed at the low and high wavenumber limits. For the perfectly bonded and imperfect interface cases in the low wavenumber region, only the fundamental mode has a finite phase speed, while other higher modes have an infinite phase speed when the dimensionless wavenumber approaches zero. However, for the fully slipping interface in the low wavenumber region, both the fundamental mode and the next lowest mode have finite phase speeds. In the high wavenumber region, when the dimensionless wavenumber tends to infinity, the phase speeds of the fundamental mode and the higher modes depend on the phase speeds of the surface and interfacial waves and on the limiting phase speed of the composite. An expression to determine the cut-off frequencies is obtained from the dispersion relation. Numerical examples of dispersion curves are presented, where when the material has to be prescribed either Mooney–Rivlin material or Varga material is assumed. The effect of the imperfect interface is clearly evident in the numerical results.     

Time-harmonic wave propagation in a pre-stressed compressible elastic bi-material laminate

The dispersive behaviour of time-harmonic waves propagating along a principal direction in a perfectly bonded pre-stressed compressible elastic bi-material laminate is considered. The dispersion relation which relates wave speed and wavenumber is obtained by formulating the incremental boundary value problem and the use of the propagator matrix technique. At the low wavenumber limit, depending on the pre-stress, both the fundamental mode and the next lowest mode may have finite phase speeds. For the higher modes which have infinite phase speeds in the low wavenumber region, an expression to determine the cut-off frequencies is obtained. At the high wavenumber limit, the phase speeds of the fundamental mode and higher modes tend to phase speeds of the surface wave, the interfacial wave or the limiting phase speed of the composite. For numerical examples, either a two-parameter compressible neo-Hookean material or a two-parameter compressible Varga material is assumed.     

An SPH multi‐fluid model based on quasi buoyancy for interface stabilization up to high density ratios and realistic wave speed ratios

We introduce a smoothed particle hydrodynamics (SPH) concept for the stabilization of the interface between 2 fluids. It is demonstrated that the change in the pressure gradient across the interface leads to a force imbalance. This force imbalance is attributed to the particle approximation implicit to SPH. To stabilize the interface, a pressure gradient correction is proposed. In this approach, the multi‐fluid pressure gradients are related to the (gravitational and fluid) accelerations. This leads to a quasi‐buoyancy correction for hydrostatic (stratified) flows, which is extended to nonhydrostatic flows. The result is a simple density correction that involves no parameters or coefficients. This correction is included as an extra term in the SPH momentum equation. The new concept for the stabilization of the interface is explored in 5 case studies and compared with other multi‐fluid models. The first case is the stagnant flow in a tank: The interface remains stable up to density ratios of 1:1000 (typical for water and air), in combination with artificial wave speed ratios up to 1:4. The second and third cases are the Rayleigh‐Taylor instability and the rising bubble, where a reasonable agreement between SPH and level‐set models is achieved. The fourth case is an air flow across a water surface up to density ratios of 1:100, artificial wave speed ratios of 1:4, and high air velocities. The fifth case is about the propagation of internal gravity waves up to density ratios of 1:100 and artificial wave speed ratios of 1:4. It is demonstrated that the quasi‐buoyancy model may be used to stabilize the interface between 2 fluids up to high density ratios, with real (low) viscosities and more realistic wave speed ratios than achieved by other weakly compressible SPH multi‐fluid models. Real wave speed ratios can be achieved as long as the fluid velocities are not very high. Although the wave speeds may be artificial in many cases, correct and realistic wave speed ratios are essential in the modelling of heat transfer between 2 fluids (eg, in engineering applications such as gas turbines).     

Anti-symmetric waves in pre-stressed imperfectly bonded incompressible elastic layered composites

The effect of an imperfect interface on the dispersive behavior of in-plane time-harmonic symmetric waves in a pre-stressed incompressible symmetric layered composite, was analyzed recently by Leungvichcharoen and Wijeyewickrema (2003). In the present paper the corresponding case for time harmonic anti-symmetric waves is considered. The bi-material composite consists of incompressible isotropic elastic materials. The imperfect interface is simulated by a shear-spring type resistance model, which can also accommodate the extreme cases of perfectly bonded and fully slipping interfaces. The dispersion relation is obtained by formulating the incremental boundary-value problem and using the propagator matrix technique. The dispersion relations for anti-symmetric and symmetric waves differ from each other only through the elements of the propagator matrix associated with the inner layer. The behavior of the dispersion curves for anti-symmetric waves is for the most part similar to that of symmetric waves at the low and high wavenumber limits. At the low wavenumber limit, depending on the pre-stress for perfectly bonded and imperfect interface cases, a finite phase speed may exist only for the fundamental mode while other higher modes have an infinite phase speed. However, for a fully slipping interface in the low wavenumber region it may be possible for both the fundamental mode and the next lowest mode to have finite phase speeds. For the higher modes which have infinite phase speeds in the low wavenumber region an expression to determine the cut-off frequencies is obtained. At the high wavenumber limit, the phase speeds of the fundamental mode and the higher modes tend to the phase speeds of the surface wave or the interfacial wave or the limiting phase speed of the composite. The bifurcation equation obtained from the dispersion relation yields neutral curves that separate the stable and unstable regions associated with the fundamental mode or the next lowest mode. Numerical examples of dispersion curves are presented, where when the material has to be prescribed either Mooney–Rivlin material or Varga material is assumed. The effect of imperfect interfaces on anti-symmetric waves is clearly evident in the numerical results.     

流动系统中爆轰波传播特性的数值模拟

基于带化学反应的二维Euler方程,采用氢气/空气的9组分19步基元反应简化模型,对充有当量 比的氢气/空气预混气体的矩形爆轰流场中爆轰波的传播过程进行了数值模拟,讨论了均匀来流对爆轰波传 播的影响。数值结果表明,在均匀来流的影响下,上游方向上的燃烧强度大于C-J爆速,下游方向上的燃烧强 度小于C-J爆速;上游方向传播的爆轰波的阵面压力大于下游方向传播的爆轰波的阵面压力。所以,经典的 C-J爆轰理论并不适用于流动系统中爆轰波传播特性的研究。     

蜿蜒边界下平面流的线性流动稳定性

为便于数值分析,蜿蜒河流水动力和演变模型中一般隐性假设二次时均流-二次涡的关系与明渠流时均流-明渠湍流的关系相同,但由于高雷诺数下的DNS算力限制和实验尺度限制,这种隐含假设是否成立目前尚无相关湍流研究来支撑.文章试图通过分析明渠湍流和二次湍流发展初期的研究,侧面揭示其湍流结构的异同.通过对曲线正交坐标系下的平面二维NS方程使用双参数摄动的方法,建立了一种求解蜿蜒边界弱非线性层流的摄动解法,并推导得出一个适用于蜿蜒边界的EOS方程以及其特征值问题的解法.蜿蜒边界下弱非线性层流解为一系列蜿蜒谐波分量的叠加,其中线性部分使得两壁产生流速差,非线性部分随着雷诺数增大呈指数增长.水流的扰动增长率特征谱的第一模态与直道流相似,由3条曲线、4个波段合成,但其长波段和短波段的扰动流场与直道流不同,所有短波段的扰动流速近似于KH涡.蜿蜒边界对内部水流扰动有一定的选择性.偏角幅值越大扰动增长越快;蜿蜒波数的影响则为先增后减,有一个使扰动增长最快的蜿蜒波数.扰动流场由一个典型的TS波和一对波包形式的二次涡叠加而成,波包只有纵向流速分量,包络线由蜿蜒波数控制,波包内是与直道扰动波参数相同的TS波.     

Magneto-thermo-elastic waves in an infinite perfectly conducting elastic solid with energy dissipation

The generalized thermo-elasticity theory, i.e., Green and Naghdi （G-N） Ⅲ theory, with energy dissipation （TEWED） is employed in the study of time-harmonic plane wave propagation in an unbounded, perfectly electrically conducting elastic medium subject to primary uniform magnetic field. A more general dispersion equation with com- plex coefficients is obtained for coupled magneto-thermo-elastic wave solved in complex domain by using the Leguerre＇s method. It reveals that the coupled magneto-thermoelastic wave corresponds to modified dilatational and thermal wave propagation with finite speeds modified by finite thermal wave speeds, thermo-elastic coupling, thermal diffusivity, and the external magnetic field. Numerical results for a copper-like material are presented.     

MODEL EXPERIMENT ABOUT RESPONSE OF FLOATING ICE SHEET SUBJECTED TO MOVING AIR CUSHION VEHICLE

基于弹性薄板振动微分方程和相似理论,建立了气垫船在浮冰上运动的原型系统与模型系统参数之间的相似对应关系. 导出了浮冰层自由振动波形传播的相速度和群速度计算公式,明确了相速度的极小值和浅水波传播速度即为气垫船的第一、第二临界速度. 根据研制的高精度非接触式激光位移测量系统,在变水深拖曳水槽中, 开展了不同速度移动气垫载荷激励薄膜变形响应的系列实验,证实了存在使薄膜变形达到最大的移动气垫载荷临界速度. 第一临界速度使气垫载荷之后的薄膜产生最大的下陷变形,第二临界速度使气垫载荷之前的薄膜产生最大的上凸变形. 通过实验结果进一步分析了气垫速度、高度、压力及水深等参数对薄膜变形和临界速度的影响,揭示了移动气垫载荷激励薄膜变形响应的聚能共振增幅机理,为利用气垫船实施有效破冰提供了依据.