Sound transmission from stiffened double laminated composite plates

An analytical model is developed to investigate the sound transmission loss from orthogonally rib-stiffened double laminated composite plates structure under a plane sound wave excitation, in which first order shear deformation theory is presented for laminated composite plates. By using the space harmonic approach and virtual work principle, the sound transmission loss is described analytically. The validity and feasibility of the model are verified by comparing the present theoretical predictions with numerical results published previously. The influences of structure geometrical parameters on sound transmission loss are subsequently presented. Through numerical results, it can be concluded that the proposed analytical model is accurate and simple in solving the vibroacoustic behavior of an orthogonally rib-stiffened double laminated composite plates.     

A special solution of wave dissipation by finite porous plates

The reflection and transmission of water waves caused by a small amplitude incident wave through finite fine porous plates with equal spacing and permeability in an infinitely long open channel of constant water depth and zero slope are studied. A special solution is obtained when the distance between the two neighbouring plates is an integral multiple of the half-wavelength of the incident wave. It is found, that when the dimensionless porous-effect parameter G_0 is equal to half the total plate number, the wave dissipation reaches a maximum, and only 50% of the incident wave energy remains in the reflected and transmitted waves. Meanwhile, the reflected and transmitted waves have the same amplitude.     

一种可以计算声波的反射和透射的层合板模型

本文给出一种层合板的模型,可以用来同时计算声波在层合板上的反射与透射,并且是严格满足层间位移和横向剪应力连续条件,然后给出一系列数值例子,与相应的准确解比较。以及说明在不同情况下声反射和透射的一些特点。     

Hydroelastic impact of a horizontal floating plate with forward speed

The hydroelastic responses of a horizontal plate impacting with the water at both forward and downward speeds are investigated theoretically. The longitudinal bending behavior of a horizontal elastic plate is approximated by the behavior of longitudinal strips represented as an Euler-beam model. A simplified method of hydroelastic responses of the plate is extended to the cases with forward speed and compressive force, for which the hydrodynamic pressure is found by solving a two-dimensional boundary value problem based on the linearized wave theory. In order to validate the theoretical model, a fully-coupled algorithm in LS-DYNA and the available experimental measurements are used for the predictions of the hydrodynamic pressure and deformations of the horizontal plates impacting with water at vertical velocities. The effects of the forward speed and compressive force which can occur at the bottom of ship ships, are investigated theoretically for the plates with different edge boundary conditions. The critical values of the forward speed and longitudinal compression are discussed regarding the plates with various longitudinal lengths.     

Equilibrium of a Prestressed Strip Reinforced with Elastic Plates

The contact problem for a prestressed elastic strip reinforced with equally spaced elastic plates is considered. The Fourier integral transform is used to construct an influence function of a unit concentrated force acting on the infinite elastic strip with one edge constrained. The transmission of forces from the thin elastic plates to the prestressed strip is analyzed. On the assumption that the beam bending model and the uniaxial stress model are valid for an elastic plate subjected to both vertical and horizontal forces, the problem is mathematically formulated as a system of integro-differential equations for unknown contact stresses. This system is reduced to an infinite system of algebraic equations solved by the reduction method. The effect of the initial stresses on the distribution of contact forces in the strip under tension and compression is studied     

轴向运动二维传输结构动力学有限元建模与仿真

基于物理中面概念和经典薄板理论，应用有限元法研究了机械工程中的二维传输结构作轴向运动时的面外自由振动特性．根据实际工程结构特点及设计要点，考虑受双向预张应力作用的传输薄板结构模型，由哈密顿原理出发严格导出了结构的有限元动力学方程，得到了体现轴向传输结构特性的陀螺矩阵．该矩阵具有反对称结构，这与加权余量法所得的陀螺矩阵结构不同．采用3 节点三角形单元离散求解域，且单元不受轴向运动影响，给出了单元密度对计算结果精度的影响．分析了传输结构预张应力和轴向速度与自由振动固有频率的关系；考察了不同结构的陀螺矩阵对数值结果的影响．将部分结果与ANSYS 软件模拟对比，显示出良好的一致性，证明了本文方法的有效性．研究结果可为典型传输带等结构的振动控制提供参考，建模方法可为ANSYS等计算软件添加轴向运动结构新模块提供理论依据．     

Theoretical model for sound transmission through finite sandwich structures with corrugated core

Due to the promising applications of lightweight double-leaf structures in noise control engineering, numerous investigations have been performed to study the vibroacoustic properties of these structures. However, no attention has been focused on the vibroacoustic properties of finite double-leaf structures with corrugated core used extensively in constructing the hulls of bullet passenger trains. In the present paper, a theoretical model is developed to predict the sound transmission loss (STL) characteristics of simply supported double-leaf partitions with corrugated core. The boundary conditions are accounted for by writing the displacements of the face plates in a series form of modal functions. The model predictions are validated by comparing with existing experimental measurements. The vibroacoustic properties of the sandwich construction are examined and the physical mechanisms for sound transmission through the structure explored, including the phenomena of ‘coincidence resonance’ and ‘standing wave resonances’. The effects of structural links, structural dimensions, inclination angle of the corrugated core, as well as the thickness of face plates and core layer on the STL are systematically investigated.     

Optimum separation of asymmetrically heated sub-channels forming a bundle: influence of simultaneous flow and temperature

This paper focuses on laminar heat and fluid flow in an array of sub-channels placed in an uniform stream, which is characterized by a fixed pressure difference and a developing velocity and temperature. The dominant feature of the study deals with the optimal selection of the plate-to-plate separation between subchannels placed in a specified volume that renders maximum heat transmission from the heated plates to the moving fluid. Asymmetric heating from one plate in a typical sub-channel to either air or water is produced by uniform temperature in one case and uniform heat flux in the other case. Upon relaxing the vital condition of developing velocity, the numerical computations for the optimal separation and the maximum heat transmission incurred in little error for both cooling fluids.     

The response of circular composite plates to underwater blast: Experiments and modelling

We present a new experimental technique to allow laboratory-scale observation of underwater blast loading on circular plates, including dynamic deformation and failure of the plates as well as the sequence of cavitation events in water. The apparatus is used to measure and compare the responses of a quasi-isotropic glass/vinylester composite and of a woven carbon/epoxy plate. Dynamic explicit FE simulations are conducted and their predictions are found in good agreement with experiments. Measurements and FE predictions are used to validate a recently developed theoretical model for the response of elastic orthotropic plates to underwater blast.     

Linear water wave propagation through multiple floating elastic plates of variable properties

We investigate the problem of linear water wave propagation under a set of elastic plates of variable properties. The problem is two-dimensional, but we allow the waves to be incident from an angle. Since the properties of the elastic plates can be set arbitrarily, the solution method can also be applied to model regions of open water as well as elastic plates. We assume that the boundary conditions at the plate edges are the free boundary conditions, although the method could be extended straightforwardly to cover other possible boundary conditions. The solution method is based on an eigenfunction expansion under each elastic plate and on matching these expansions at each plate boundary. We choose the number of matching conditions so that we have fewer equations than unknowns. The extra equations are found by applying the free-edge boundary conditions. We show that our results agree with previous work and that they satisfy the energy balance condition. We also compare our results with a series of experiments using floating elastic plates, which were performed in a two-dimensional wave tank.     

带水墙靶板对高速破片侵彻能力影响规律

针对大当量成型弹药破片毁伤威力试验风险系数大、试验效能低的问题，提出采用带水墙靶板的方式对破片毁伤参数进行测定的新方法。应用动力学模拟软件AUTODYN，对破片侵彻带水墙靶板及无水墙靶板的过程进行了有限元数值模拟，分析了水墙厚度和破片入射角度对破片侵彻能力的影响规律，通过实弹试验的方式对带水墙靶板的实用效果进行了验证。计算结果表明，带水墙靶板相比无水墙靶板，能够大大降低破片的侵彻能力，同时与实弹试验效果也能较好吻合，说明在实际试验中使用带水墙靶板收集破片毁伤参数的方法是可行的。     

Force and shapes of liquid bridges between circular pads

An analytical model is presented relating the shape of an axisymmetric liquid bridge in terms of volume,v, height,h, bounding radius,r, and contact angle, , to the residual force,f, resulting from the surface tension at the liquid-vapor interface. The model is based on the assumption that gravity is negligible and the surface of the liquid bridge possesses constant mean curvature. Measurements are made of the height, bounding radius, contact angle and force for known volumes of individual, axisymmetric liquid bridges between parallel plates. Force and height comparisons are made for mercury on aluminum plates, mercury on polysiloxane-coated plates and water on polysiloxane-coated plates in air for dimensionless volumes (v/r ³) of 10 and 18. Comparisons with model predictions are also made for mercury bridges spanning a contact angle range between 138 deg and 150 deg. Finally, the shapes of liquid bridges are compared to analytical predictions. The results suggest that the constant mean curvature model, even when gravity is neglected, is an appropriate design tool that can be useful for specifying solder volumes and standoff heights for solder grid array packages.     

Gas dynamics of a selectively excited gas

In order to describe the motion of a selectively excited gas, model kinetic equations are proposed in the present study, and they are used to construct the equations of gas dynamics. There is consideration of the one-dimensional problem of heat transmission between plates across a selectively excited gas. Discontinuities are found in the temperature on the boundaries of the phases. It is shown that a selectively excited gas may be used to transmit heat from a cold body to a hot one. Moscow. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 151–158, September–October, 1988.     

Transverse Stiffness of a Sinusoidally Corrugated Plate∗

Abstract

An analytical model for the initial transverse stiffness of a sinusoidally corrugated plate is derived, incorporating deformations due to extension, shear, and bending. A nondimensional plot is developed for determining transverse stiffness based on thickness and corrugation for a range of plate geometries. This model shows that for most corrugated plates the transverse stiffness is dramatically decreased from that of an uncomigated plate of the same thickness. For thin plates, a simple approximate polynomial expression for initial transverse stiffness is obtained. For thick plates with a small degree of corrugation, transverse stiffness is not negligible relative to longitudinal stiffness. The exact model is verified using a linear-elastic two-dimensional finite element model.     

On the stability of thin periodic plates

In this paper a new modelling method of thin plates with a periodic structure along one direction and with a slowly-varying structure along the perpendicular direction in the planes parallel to the plate midplane is presented. The model is a certain generalisation of the length-scale model of periodic plates, which makes it possible to take into account the effect of periodicity cell size on the dynamics of plates with two-directional periodic structure (Jȩdrysiak and Woźniak, 1995; Jȩdrysiak, 1998). In order to describe this effect in stationary processes, e.g. a plate stability, for one-directional periodic plates the generalised model is applied in this paper. Applications to the stability problems and a comparison with effective stiffnesses models will be shown.     

Dynamic modelling of thin plate made of certain functionally graded materials

The aim of the contribution is to formulate a macroscopic mathematical model describing the dynamic behaviour of a certain composite thin plates. The plates are made of two-phase stratified composites with a smooth and a slow gradation of macroscopic properties along the stratification. The formulation of mathematical model of these plates is based on a tolerance averaging approach (Woźniak, Michalak, Jędrysiak in Thermomechanics of microheterogeneous solids and structures, 2008). The presented general results are illustrated by analysis of the natural frequencies for two cases of plates: a plate band and an annular plate. The spatial volume fractions of the two different isotropic homogeneous components are optimized so as to maximize or minimize the first natural frequency of the plate under consideration.     

Photoelasticity with additional physical fields and optically active models

The aim of the paper is to enlarge the class of three-dimensional stress distributions which can be investigated in a transmission polariscope. The experimental data are shown to contain more information about the stress distribution on the wave normal if the rotation of the principal axes or that of the plane of polarization is induced. This can be obtained by additional physical fields or by using optically active models. Three examples are described. First, an exact theory for investigating bending stresses in plates by the aid of prefrozen models has been developed and applied to evaluate the experimental data. Second, the application of the magnetophotoelastic method to determine stress-concentration factors by cylindrical bending of plates is considered. Third, a nonlinear stress distribution along the wave normal has been determined experimentally in an optically active model.