An analytical expression of the normal force of hydrodynamic line contacts under transient conditions

Within this contribution an explicit analytical approximation of the normal force of hydrodynamic line contacts between non-conformal surfaces subjected to transient operating conditions is presented. The fluid is described by Reynolds's equation assuming rigid contacting bodies, constant viscosity and constant density.Existing formulas of the normal contact force are extended by regarding Reynolds boundary conditions which account for cavitation effects. The new approximation is shown to be outstandingly accurate.The presented model of the hydrodynamic normal force is implemented into a simple oscillatory system which exhibits highly non-linear behaviour due to the hydrodynamic contact. Furthermore, the new model is used as part of an approximation of elastohydrodynamic contacts.     

A simple finite element formulation of a higher-order theory for unsymmetrically laminated composite plates

A higher-order theory which satisfies zero transverse shear stress conditions on the bounding planes of a generally laminated fibre-reinforced composite plate subjected to transverse loads is developed. The displacement model accounts for non-linear distribution of inplane displacement components through the plate thickness and the theory requires no shear correction coefficients. A C∘ continuous displacement finite element formulation is presented and the coupled membrane-flexure behaviour of laminated plates is investigated. The nodal unknowns are the three displacements, two rotations and two higher-order functions as the generalized degrees of freedom. The simple isoparametric formulation developed here is capable of evaluating transverse shears and transverse normal stress accurately by using the equilibrium equations. The accuracy of the nine-noded Lagrangian quadrilateral element is then established by comparing the present results with the closed-form, three-dimensional elasticity and other finite element available solutions.     

边界元方法分析收发分置Benchmark潜艇低频目标强度

收发分置的潜艇目标强度对于双基地声呐和多基地声呐的探测性能具有重要的意义。采用快速多极边界元方法分析了收发分置情况下刚硬边界Benchmark潜艇低频目标强度。结果表明,潜艇的目标强度随频率、发射角和接收角的变化而变化。频率越高,潜艇的目标强度变化越复杂。此外,当入射方向和散射方向关于正横方向对称时,潜艇的目标强度取得极大值,并且在正向散射处亦出现极大值。进一步分析了潜艇收发分置目标强度对探测的影响。结果表明,目标潜艇在不同的情况下目标强度不同,在文中的计算频率处,分置角较大时目标强度更有可能取得较大值。     

基于波束计算的水下声学探测设备声兼容传播过程分析

对于搭载多种声学探测设备的水下平台,不同设备的信号可能会产生相互干扰。因此,根据探测设备的波束特性,针对水下平台对海底的探测情形,来分析探测设备声兼容传播过程的特性。结合射线声学和海底散射模型,建立了声兼容分析中声传播的计算方法,并且分析了传播过程中各种因素对声兼容设计的影响。结果表明,在算例的波束条件下,声速剖面对声兼容性的影响较小,而特定类型的海底底质的影响较大。此外,水下平台距海底越高,或者波束偏转越大,声学设备间的相互干扰就越大。为了尽可能减小干扰信号的影响,应尽量避免干扰信号的发射波束和接收波束交叠,此外还给出了波束覆盖角阈值和干扰信号衰减的关系。