亚音速超空泡射弹尾拍动力学响应分析

超空泡射弹在运动过程中存在尾拍现象,在高速运动条件下,水的可压缩性是影响射弹尾拍运动的主要因素之一。文中考虑了流体与结构相互耦合的影响,建立了射弹尾拍运动的无约束动力学方程,使用有限元法求解得到了超空泡射弹在尾拍载荷作用下的动力学响应,并研究了马赫数对射弹动力学响应的影响。研究结果表明：亚音速条件下,流体的可压缩性使超空泡射弹刚体转动和弹性振动位移的周期和幅值增大;流体的可压缩性对结构弹性位移响应的影响随马赫数的增大而逐渐增大。     

超空泡流下壳结构模型动态特性实验研究

首次采用首部钢丝绳牵引方式进行了超空泡流下壳结构模型实验。实验模型壳体部分采用聚碳酸酯材料,锥部采用铝合金材料,首部空化器则采用不锈钢制作,最后各部分通过螺纹或者胶水粘结而成。三种不同速度下的超空泡实验结果表明：采用首部钢丝绳牵引方式进行超空泡实验是可行的。位于壳体上相对位置相同的部位其应变曲线趋势一致,超空泡形成后轴向的减阻效果是非常明显的,尾拍振动引起的应变则呈现出周期性的特征。在一定速度下,超空泡形成后轴向力引起的应变和尾拍振动引起的应变处于同一个水平上。随着速度的提高,超空泡减阻的效果更加明显,尾拍振动引起的应变幅值也相应增大。实验结果可为超空泡水下航行体的结构设计提供依据。     

自然超空泡形态特性的射弹试验研究

利用高速射弹试验对自然超空泡的形态特性和发展规律进行了深入研究。试验采用了不同尺寸的试验弹,射弹最大速度可达70m/s,最小空化数可达0.04。获得了水下航行体的自然超空泡形态参数随空化数变化的规律,并与相关文献中使用的经验公式进行了对比,在小空化数下一致性较好。研究结果表明,高速射弹试验是研究自然超空泡形态特性的一种有效手段,能够捕捉到大量超空泡水动力学现象,证实了自然超空泡的直径和长度都随空化数的增大而减小,且呈指数规律。     

空化器形状对超空泡射弹尾拍运动影响的数值研究

为研究空化器形状对超空泡射弹尾拍航行时运动特性的影响,基于有限体积法和Mixture多相流模型,结合动网格技术构建了三维自由尾拍运动仿真模型,在两种长径比下比较了平头弹、凹口弹、锥头弹的尾拍运动特性,并分析了其水动力影响因素。结果表明：较小长径比下,平头弹可以保持运动稳定,凹口弹和锥头弹易失稳,主要是由于空化器产生的空泡尺寸差异导致其临界失稳攻角依次降低。较大长径比下,临界失稳攻角消失,三种头型射弹均能保持尾拍稳定,锥头弹在速度较高时以“单侧尾拍”保持稳定,速度降低后以“双侧尾拍”保持稳定,而平头弹和凹口弹始终以“双侧尾拍”保持稳定;锥头弹由于“单侧尾拍”会产生与初始扰动方向相反的垂直位移,而平头弹和凹口弹由于弹头升力产生与初始扰动方向相同的垂直位移。     

水下射弹自然超空泡减阻特性的数值模拟

基于均质平衡多相流理论,采用Fluent6.3对水下射弹自然超空泡减阻特性进行了数值模拟。研究了空化数对水下射弹空泡闭合部位和阻力系数的影响,重点分析了水下射弹结构参数对自然超空泡减阻特性的影响,得到了空化器直径、模型长细比和不同尾部形状对水下射弹超空泡减阻特性影响的规律。数值模拟结果表明:随着空化器直径的增大,自然超空泡较易形成,但其减阻能力有所降低;随着长细比的增大,自然超空泡较难形成,但形成超空泡后,不同长细比模型的阻力系数基本一致;尾部形状只影响尾部空泡的发展过程,当尾部被空泡包裹后,模型的自然超空泡形态和阻力系数基本一致。     

悬索承重梁索耦合结构的垂向运动动力学模型及主共振分析

该文建立了描述结构大变形和主缆初始曲率产生的几何非线性对系统动力学影响的悬索承重梁索耦合结构垂向运动动力学偏微分方程组。通过Galerkin方法一次截断把偏微分方程组化为时域上的两自由度常微分方程组。使用多尺度法得到简谐激励下常微分方程组主共振时的一次近似解。结果显示,当外激励仅激发低频或高频主共振时,系统的振幅随激励的幅值或激励频率的变化出现突然的跳跃。当激励同时激发低频和高频主共振时则有两种情况：1) 若固定高频激励幅值和频率,则系统的低频和高频振动成分的振幅随低频激励参数变化同时增加或减小;2) 若固定低频激励的幅值和频率,则系统的低频和高频振动成分的振幅随高频激励参数变化以相反的趋势变化。即高频振动幅值增大时,低频振幅减小,反之亦然。     

电磁开关强非线性系统主共振分析

以电磁开关系统为研究对象,根据拉格朗日麦克斯韦方程建立三阶非线性动力学模型,应用MLP法得到电磁开关强非线性系统主共振的幅频响应方程及位移和电流分别随时间变化的振动规律,分析系统各参数对系统主共振幅频响应曲线的影响。结果表明,系统的幅频响应曲线存在跳跃现象;随着阻尼系数的增大,系统的振幅减小;随着激励电压幅值增大,系统的振幅和共振区域增大;随着电阻增大,系统的振幅和共振区域减小。     

强振动环境下缠绕式液压胶管流固耦合特性

针对TBM破岩过程产生基础振动对液压胶管内流体动态特性影响,根据层合板理论建立缠绕式液压胶管振动梁模型,并结合轴向流固耦合模型建立胶管轴向振动动力学模型。运用特征线法求解该数学模型,研究基础振动参数和胶管结构参数对流体响应特性影响,发现胶管出口压力波动幅值随基础振动振幅呈线性增加的趋势,随振动频率增加,在40 Hz左右达到最大,此时振动频率接近系统固有频率;胶管出口压力峰值随液压胶管长度增加而减小,胶管内径在8 mm到30 mm变化时,其先增大后减小,随泊松比增大而增大。研究结果表明振动沿胶管轴向分量加强了流体与胶管互动效应,可为TBM液压管系设计和抗振提供理论依据。     

基础振动下直动式减压阀动态特性分析

针对基础振动对TBM液压元件性能的影响,为TBM液压元件优化设计提供理论依据,选择直动式减压阀为研究对象,分析其工作原理,建立减压阀的动态响应数学模型,仿真研究基础振动幅值和频率对减压阀波动特性的影响规律,分析减压阀不同结构参数对压力波动的影响.结果表明：基础振动会引起减压阀出口压力波动,波动幅值随振动幅值增加而增大;当基础振动频率大于50 Hz时,压力波动幅值随频率的增加明显增大;减小背压腔初始容积和回流通道直径能提高减压阀的动态稳定性.     

同一轴线上双激振器驱动的振动体同步运动状态分析

以同一轴线上双激振器驱动的振动磨机为典型研究对象,通过对其实际模型的合理简化,得到运动系统的力学模型.利用Lagrange方程建立了运动系统的动力学方程,通过对动力学方程的求解分析,得到了振动体的运动轨迹随两个激振器转角差的变化规律,振动体在运动过程中,随着两个激振器转角差的增大,振动体质心的运动幅值减小,而沿质心轴线两端的运动幅值增大,当两个激振器转角差达到180度时,质心运动幅值为零,沿质心轴线两端的运动幅值达到极大,此时振动系统产生锥形运动,使得振动设备无法正常工作.研究结果可为研究更复杂振动系统的同步运动和利用同步运动减少参振体质量提供理论基础.     

水下超空泡航行体非线性动力学建模与仿真

超空泡技术可以大幅提高水下航行速度,根据空泡膨胀独立性原理,研究了空泡的记忆效应及其对空泡形态和航行体尾部滑行力等流体动力的影响,在计算超空泡航行体各部分所受的流体动力的过程中考虑了空化器的定向效应和空泡尾部的上漂变形,还研究了航行过程中尾翼浸水深度变化时尾翼效率的变化规律,从而建立了更加精确的超空泡航行体动力学模型。通过仿真分析了超空泡航行体运动的稳定性,最后设计了非线性控制策略来进行深度跟踪。     

超空泡水下航行器直航弹道三通道控制与动态特性仿真

水下航行器在超空泡状态直航时,其运动模式和常规全沾湿水下航行器完全不同,为保证该模式下直航弹道的稳定性,提出对超空泡航行器的纵平面、水平面和横滚三通道进行特殊控制。从超空泡航行器流体动力产生的机理出发,分析了其力学特性,建立了航行器三通道空间运动模型;采用空化器首舵和航行器尾舵对超空泡航行器直航弹道进行控制,利用极限操舵的控制模式降低了三通道之间的耦合。针对超空泡航行器直航三通道进行了动态特性仿真,仿真结果表明弹道航向稳定、深度偏差小、横滚振荡幅度可控     

Depth of penetration of high-speed penetrator with including the effect of mass abrasion

Mass abrasion is observed on the nose of projectile when a projectile strikes concrete target at high velocity. To evaluate the influence of the mass abrasion on the depth of penetration (DOP) limit, the relationship between the nose factor of the residual projectile after abrasion and the initial impact velocity is suggested according to the experimental data. Based on the dynamic cavity expansion theory, with considering the effects of varying nose factor and mass of projectile, a modified model is proposed to calculate the depth of penetration of kinetic energy penetrator. The model predicts that a theoretical maximum DOP exists due to the mass abrasion of the projectile. The model is checked by the different experimental data.     

侧滑角对超空泡航行体转弯运动沾湿区域的影响

为了提高通气超空泡航行体在转弯运动过程中空泡和航行体的运动一致性,基于有限体积法和VOF多相流模型,采用动态网格技术对航行体转弯运动的空泡形态特性进行了非定常数值模拟研究。通过对航行体沾湿区域的分析,揭示了沾湿区域形成的原因,利用空化器对空泡轴线的定向效应,提出了合理改变侧滑角减缓沾湿区域出现的具体方法。通过分析侧滑角和侧滑角速度对航行体沾湿区域的影响,提出了超空泡航行体转弯运动过程中,在给定偏航角条件下避免出现沾湿区域的侧滑角和侧滑角速度的适用范围,为进一步研究超空泡航行体机动运动问题提供参考。     

Optimum distribution of smart stiffeners in sandwich plates subjected to bending or forced vibrations

The problems of optimum distribution of active stiffeners manufactured from piezoelectric or shape memory alloy materials and bonded to or embedded within the facings of a sandwich plate are considered. The sandwich plate consists of thin composite or isotropic facings which are in the state of plane stress and a thick shear deformable core. The amplitude of forced vibrations of the plate is reduced using symmetric couples of piezoelectric stiffeners subjected to out-of-phase dynamic voltages. Shape memory alloy stiffeners are used to reduce bending deformations. In the latter case, a desirable effect is achieved by activating the stiffeners on one side of the middle surface. Optimum design is considered based on the requirement of minimal transverse static or dynamic deflections subject to a constraint on the volume of smart stiffeners. The variables employed in the process of optimization are the ratios of the cross-sectional areas of the stiffeners in each direction to their respective spacings. It is shown, that, dependent on the load, materials, and geometry, optimum design can significantly reduce deflections, i.e. enhance the strength, of sandwich plates.     

A Study of Cavitator Deformation and its Effect on Cavity Shape

The cavitator is the key component of a supercavitating vehicle. Based on the potential flow theory and ANSYS, we perform stress and deformation analysis of a cavitator and present a computational procedure of supercavitating shape when the vehicle was in high speed motion. Different shapes and materials models were examined to determine the deformation and the extent of influence on the cavity shape. Information obtained from these analyses reveals that the deformation of the cavitator can be one of the ca...     

Comparisons of buckling-to-weight behavior of cylindrical shells with composite and metallic stiffeners

The present research deals with the study of buckling pressure-to-weight ratio of cylindrical shells with laminated ring stiffeners. The research introduces a strain energy formulation for laminated rings, in which each ring stiffener may be treated individually and the geometrical dimensions and material properties of the stiffeners may be different from one another. In a parametric study, the impacts of various geometrical parameters of rings on the buckling pressure-to-weight ratio of shells for composite and metallic stiffeners are compared. The results show that the buckling-to-weight behavior of the shells with Steel stiffeners generally differs from the shells with stiffeners made of Aluminum, E-glass/epoxy, Graphite/epoxy, or Kevlar49/epoxy.     

Lift Force Acting on Body in Liquid in the Vicinity of Boundary Executing Tangential Oscillations

The average force acting on a cylindrical or spherical body placed near the boundary of cylindrical cavity filled with liquid and executing rotational vibrations is experimentally studied. The repulsive lift force acting on solid is found and measured using the method of body suspension in the gravity field. In horizontal cavity the repulsive force provides steady state of light cylinder near the upper boundary at a distance comparable with the thickness of the Stokes layer. The heavy sphere which hangs on thread repulses from the wall of vertical cylindrical cavity under torsional vibration. The dependence of the average lift force on the amplitude and frequency of vibrations and on distance between the body and the boundary has been investigated. Results are presented on the plane of dimensionless parameters. In the examined frequency range the lift force acting on cylinder decreases exponentially with distance from the boundary. Lift force acting on sphere decreases with distance and strongly depends on dimensionless frequency of vibration. Conclusion that lift force is generated by body oscillations excited by its viscous interaction with the oscillating boundary is done. The found phenomenon is important for control of inclusions under microgravity conditions.     

变速超空泡航行体壳结构的动力响应分析

通过对变速超空泡水下航行体壳结构受力模型的分析,建立了恒定推力下航行体的平面运动方程,确定了变速过程中的阻力和冲击力。利用有限元方法,进行了结构响应计算,分析了减速过程中节点时域上的最大应力值在轴向的分布情况及典型节点处的响应。结果表明：航行体所需推力和所受应力较大,对其结构强度要求较高;运动过程中,节点时域上的最大应力在空间域上的极大值主要分布在首尾端部和柱壳中部;存在一些振动频率对航行体结构响应影响显著。结果对超空泡航行体壳结构受力和强度分析以及优化设计有着重要的指导意义。&;#61472;