In this paper, a general three-dimensional finite element model composed of eight-node three-dimension cohesive elements and eight-node solid elements with reduced integration for low-velocity impact analysis of composite materials is established. Firstly, the continuum damage mechanics is applied to simulate the initiation and evolution of the intra-laminar damage. Based on cohesive zone model, the cohesive elements are inserted between layers to predict the inter-laminar damage. Three failure criteria, including 2D Hashin, 3D Hashin and Chang-Chang criteria, are coded in VUMAT and are implemented in ABAQUS/Explicit. The numerical results of energy time curves, force time curves, force displacement curves and damage distribution under three impact energies (7.35 J, 11.03 J and 14.7 J) are in good agreement with previously published data in literature, which indicates that the finite element model is suitable for studying the mechanical response and damage distribution of composites laminates subjected to low-velocity impact. Moreover, the influence of stacking sequence and friction coefficient on mechanical response and damage distribution is analyzed. It is concluded that the composite laminate with a stacking sequence of [45°/0°/−45°/90°]S can reduce the area of damage region compared to [0°/90°]2S because the ±45° layer can improve the shear resistance of composite laminate. Also, the computation accuracy will be the best when the friction coefficient is adopted between 0.5 and 0.7.

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It is difficult to propose boundary conditions for the PDEs with higher order space derivatives like Euler-Bernoulli beam. In this paper we use a absorbing boundary condition method to solve the Cauchy problem for one-dimensional Euler-Bernoulli beam with fast convolution boundary condition which is derived through the Padé approximation for the square root function. We also introduce a constant damping term to control the error between the resulting approximation Euler-Bernoulli system and the original one. Numerical examples verify the theoretical results and demonstrate the performance for the fast numerical method.

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Purpose This study aims to improve the survivability and maneuverability of the fighter,and study the stealth performance of fighter in the jet noise of aeroengine, it is of great significance to study the jet noise characteristics of double S-bend nozzles. Design/methodology/approach The multiparameter coupling and super-ellipse design methods are used to design the cross section of double S-bend nozzle. Taking unsteady flow information as the equivalent sound source, the noise signal at the far-field monitoring points were calculated with Ffowcs Williams–Hawkings (FW–H) method, and then, the sound source characteristics of the double S-bend nozzle are analyzed. Findings The results show that the internal flow of the S-bend nozzle with rectangular section is smoothed and the aerodynamic performance is better than super-ellipse section, the shear layer length of rectangular section is longer, the thickness is smaller and the mixing ability is stronger. The sound pressure level of the two S-bend nozzles decreases with the increase of the monitoring angle, and the sound pressure on the horizontal plane is greater than the vertical plane. In the direction of 40°–120°, the jet noise of rectangular nozzle is smaller, and the multiparameter coupled rectangular cross section structure is more applicable. Practical implications It is beneficial to reduce the jet noise of the engine tail nozzle and improve the stealth performance of the aircraft. Originality/value There is very little research on the jet noise characteristics of the double S-bend nozzle. The multiparameter coupling and the super-ellipse method are used to design the nozzle flow section to study the aerodynamic performance and jet noise characteristics of the double S-bend nozzle and to improve the acoustic stealth characteristics of the aircraft.