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High-intensity acoustic waves existing commonly in aeronautical and aerospace vehicles manifest nonlinear propagation behaviors. Large-amplitude vibration and irregular shape of the aerospace vehicles further complicate the acoustic responses. This paper is concerned with numerical analysis of finite-amplitude acoustic responses of complex-shaped vibration objects. The time-dependent effect of the solid boundary position due to the large-amplitude vibration of the objects is considered. A set of first-order differential equations is derived to govern the finite-amplitude acoustic wave. A fourth-order dispersion-relation-preserving finite difference formulation is employed to solve the nonlinear acoustic equations on a fixed Cartesian grid. Acoustic responses of the fluid and the vibration of the complex-shaped object are coupled by considering the compatibility conditions on the fluid-solid interface. A ghost-cell sharp-interface immersed boundary method is utilized to relax the conformity requirement between the computational grid and solid boundary. Numerical filters are employed in the computational procedure to suppress numerical oscillations. The present method is validated through several numerical tests. Numerical analysis of finite-amplitude acoustic responses of a complex-shaped object is performed. The nonlinear effect of a finite-amplitude acoustic wave, the time-dependent effect of solid boundary position, and the coupling effect between them on the propagation behaviors of nonlinear acoustic waves are discussed. [ABSTRACT FROM AUTHOR]

We present a robust sharp-interface immersed boundary method for numerically studying high speed flows of compressible and viscous fluids interacting with arbitrarily shaped either stationary or moving rigid solids. The Navier–Stokes equations are discretized on a rectangular Cartesian grid based on a low-diffusion flux splitting method for inviscid fluxes and conservative high-order central-difference schemes for the viscous components. Discontinuities such as those introduced by shock waves and contact surfaces are captured by using a high-resolution weighted essentially non-oscillatory (WENO) scheme. Ghost cells in the vicinity of the fluid–solid interface are introduced to satisfy boundary conditions on the interface. Values of variables in the ghost cells are found by using a constrained moving least squares method (CMLS) that eliminates numerical instabilities encountered in the conventional MLS formulation. The solution of the fluid flow and the solid motion equations is advanced in time by using the third-order Runge–Kutta and the implicit Newmark integration schemes, respectively. The performance of the proposed method has been assessed by computing results for the following four problems: shock-boundary layer interaction, supersonic viscous flows past a rigid cylinder, moving piston in a shock tube and lifting off from a flat surface of circular, rectangular and elliptic cylinders triggered by shock waves, and comparing computed results with those available in the literature. [ABSTRACT FROM AUTHOR]

This paper presents an efficient method for predicting the free and transient vibrations of multilayered composite structures with parallelepiped shapes including beams, plates and solids. The exact three-dimensional elasticity theory combined with a multilevel partitioning hierarchy, viz., multilayered parallelepiped, individual layer and layer segment, is employed in the analysis. The continuity constraints on common interfaces of adjacent layer segments are imposed by a modified variational principle, and the displacement components of each layer segment are assumed in the form of orthogonal polynomials and/or trigonometric functions. Numerical studies are given for free vibrations of composite laminated and sandwich beams, plates, and solids. Some in-plane shear vibration modes missed in previous elasticity solutions for multilayered plates are examined. The natural frequencies derived from Reddy’s high-order shear deformation theory and layerwise theory for soft-core sandwich plates show significant deviation from elasticity solutions. Transient displacement and stress responses for angle-ply laminated and sandwich plates under four types of impulsive loads (including rectangular, triangular, half-sine and exponential pulses) are obtained by the Newmark integration procedure. The present solutions may serve as benchmark data for assessing the accuracy of advanced structural theories and new developments in numerical methods. [ABSTRACT FROM AUTHOR]

Abstract: A domain decomposition method is used to analyze the free and forced vibration characteristics of a spherical–cylindrical–spherical shell, based on Reissner–Naghdi''s thin shell theory. The joined shell is divided into some cylindrical and spherical shell segments along the meridional (longitudinal) direction. Double mixed series, i.e., Fourier series and Chebyshev polynomials, are employed as the admissible displacement functions to obtain the discretized equation of motion for the joined shell. Numerical comparisons with the results derived by FEM and those available in the previous literature are made to validate the present method. Moreover, the effects of length-to-radius and radius-to-thickness ratios on the natural frequencies are also investigated. [Copyright &y& Elsevier]

Abstract: This work presents a modified variational method for dynamic analysis of ring-stiffened conical–cylindrical shells subjected to different boundary conditions. The method involves partitioning of the stiffened shell into appropriate shell segments in order to accommodate the computing requirement of high-order vibration modes and responses. All essential continuity constraints on segment interfaces are imposed by means of a modified variational principle and least-squares weighted residual method. Reissner-Naghdi''s thin shell theory combined with the discrete element stiffener theory to consider the ring-stiffening effect is employed to formulate the theoretical model. Double mixed series, i.e., the Fourier series and Chebyshev orthogonal polynomials, are adopted as admissible displacement functions for each shell segment. To test the convergence, efficiency and accuracy of the present method, both free and forced vibrations of non-stiffened and stiffened shells are examined under different combinations of edge support conditions. Two types of external excitation forces are considered for the forced vibration analysis, i.e., the axisymmetric line force and concentrated point force. The numerical results obtained from the present method show good agreement with previously published results and those from the finite element program ANSYS. Effects of structural damping on the harmonic vibration responses of the stiffened conical–cylindrical–conical shell are also presented. [Copyright &y& Elsevier]

• Developing a vibro-acoustic coupling model for analyses of nonlinear acoustic wave behaviors of vibrational objects. • Numerical tests are carried out to confirm the validity of the developed coupling model. • Physical insights into the effects of high-order vibration responses on the nonlinear acoustic wave in the fluid are provided. • Effects of smooth and non-smooth nonlinearities on acoustic responses of vibrational objects are evaluated. This paper is concerned with numerical analyses of radiated sound behaviors of dynamic systems containing nonlinear vibrational objects immersed in a compressible and inviscid fluid of infinite extent. The vibrational solids are modelled by the Lagrangian description of motion, while the fluid surrounding the vibrational objects is formulated by the two-dimensional linearized Euler equations (LEEs). The nonlinear dynamic responses of the vibrational solids are computed by both the harmonic balance method (HBM) and direct time integration method. A fourth-order dispersion-relation-preserving (DRP) scheme is implemented on a fixed Cartesian grid to solve the governing equations of the fluid. A constrained moving least-squares sharp-interface immersed boundary method is adopted to impose the compatibility conditions on the common boundaries of the vibrational objects and the fluid. Selective filters are employed to suppress the spurious short waves appearing in numerical computations. Several numerical tests are carried out to confirm the validity of the developed vibro-acoustic coupling computational model by comparing the present solutions with the exact solutions. Nonlinear acoustic wave responses of vibrational objects with smooth and non-smooth nonlinearities are examined, including rigid cylinder-shaped oscillators resting on nonlinear mounts, ellipse-shaped objects suspended on nonlinear torsional springs, and rigid isolators with frictions and clearances. It is found that for vibrational objects containing nonlinearities, the amplitude-frequency responses of radiated sound pressure exhibit shifting resonance frequencies, secondary resonances and jump phenomenon. The intermittent collisions of the vibrational objects with clearances can result in abrupt fluctuations and distortions of the radiated acoustic waves in fluid. In addition, the radiation efficiency of high-order harmonics of nonlinear acoustic waves induced by stick/slip transitions of friction interfaces can reach to maximum with the friction coefficient. [ABSTRACT FROM AUTHOR]

• The hydroelastic response of propeller-shafting system in water was examined. • A coupled 3-D panel method/finite element method was proposed. • Propulsion system includes propeller, shaft, coupling, stern and thrust bearings. • The coupling of the fluid, propeller, and the shaft must be considered. The control of unsteady bearing forces generated by propellers is of great importance for the reduction of vibration and noise of underwater vehicles. This paper is concerned with the development of a numerical method for analyzing the hydroelastic behaviors of fully coupled marine propeller and shafting system immersed in water. A three-dimensional panel method for fluid modeling combined with a finite element method for modeling of the shafting system is developed. The two sets of equations of the structural system and the fluid are strongly coupled by considering the non-penetration boundary condition on the wet surface of the propeller. A modal reduction technique is employed to determine the hydroelastic responses of the coupled fluid-propeller-shafting system, which overcomes the low numerical efficiency of the method due to the asymmetric added matrices of the propeller. The validity of the proposed method is confirmed by comparing the present results with those solutions obtained from finite element analysis. It is found that for the case of the driving force frequency close to the umbrella mode frequencies of the propeller and longitudinal mode frequenices of the shaft, the coupling of the fluid, propeller, and the shaft must be taken into account for predicting the dynamic response of the system. A 3-D panel method coupled with a 3-D finite element method is developed for hydroelastic analysis of elastic propeller-shafting system in water. When the driving force frequency is close to the umbrella mode frequencies of the propeller and longitudinal mode frequencies of the shaft, the coupling of the fluid, propeller, and the shaft must be taken into account for predicting the dynamic response of the system. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper is concerned with the development of a numerical model for predicting the nonlinear structural and acoustic responses of a composite laminated plate induced by stick–slip motions. The structural model of the plate is formulated using a higher-order shear deformation zigzag theory for accommodating the analysis of both thin and relatively thick composite plates. A phenomenological macro-slip friction model is adopted to describe the stick and slip motions of the friction boundaries. The nonlinear dynamics model of the composite plate is established based on a finite element method, and the exterior acoustic fluid is modeled using a time-domain boundary element method. The nonlinear vibro-acoustic responses of the plate are calculated by considering the compatibility conditions on the common interface of the plate and the fluid. The role of the frictional forces in the vibration and sound radiation of the plate is explained. It is found that the periodical distortions of the sound pressure waves are mainly due to the stick-to-slip transitions of the friction boundary other than the slip-to-stick transitions. The effects of the preload, friction coefficient and stiffness of the boundary on the nonlinear structural and acoustic responses of composite plates are examined. [ABSTRACT FROM AUTHOR]

• The piezo-metastructure is shunted with a one-way electrical transmission line. • Local-resonance bandgaps are maintained in opposite directions. • Nonreciprocal wave attenuation behaviors exist in the bandgap. • The presented nonreciprocal system is linear, adaptive and easily implemented. • Theoretical and experimental results verify nonreciprocity of the system. In contrary to elastic media, it is easy to attain one-way coupling feature among electrical elements, which enables unidirectional transmission of electrical wave. In this paper, we explore and exploit the interaction of a piezoelectric beam with a one-way electrical transmission line to facilitate nonreciprocal transmission of elastic wave in the linear fashion. Theoretical dispersion analysis and numerical simulations are performed to reveal transmission behaviors of elastic wave in the presented piezoelectric metastructure. It is uncovered that, when the one-way electrical coupling feature is introduced, local-resonance bandgaps are maintained in opposite directions of the piezoelectric metastructure. However, the bandgap attenuation capability in one direction is increased compared to conventional local-resonance metastructures, in which no electrical coupling exists between cells, while that in the other direction is decreased. Therefore, nonreciprocal transmission of elastic wave emerges in this system due to the distinct bandgap attenuation capability in opposite directions. It is also revealed that this sort of nonreciprocal wave attenuation capability is adaptive with the one-way electrical coupling coefficient and the resistance of electrical cells. An experimental set-up of the piezoelectric metastructure is built and experimental results verify the nonreciprocity property and its adaptiveness. Overall, the presented piezoelectric metastructure provides a linear and concise approach to realize adaptive nonreciprocal transmission of elastic wave. [ABSTRACT FROM AUTHOR]

This paper focuses on the development of a numerical model for predicting the hydroelastic responses of marine propellers oscillating in the wake of a submarine. The added-mass and -damping matrices due to strongly coupled fluid-structure interaction were considered. Three-dimensional panel methods in time and frequency domains combined with the finite element method were employed to study the hydrodynamic performance of the propeller. The panel methods were used to evaluate the hydrodynamic forces generated by the wake, and the finite element method was applied to determine the hydroelastic response of the propeller due to the pressure fluctuation. For predicting the structural responses, a mode superposition method combined with Wilson-θ method was employed to overcome the low numerical efficiency caused by the asymmetric added mass and damping matrices. The proposed numerical model was validated by comparing with other numerical solutions. The performance of the propellers was examined by considering one-way and two-way fluid-structure interactions. [ABSTRACT FROM AUTHOR]