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As the most vulnerable part of the aircraft,the fuel tank is damaged by hydrodynamics ram effect when attacked by high-speed projectiles,which will directly threaten the safety of the aircraft.The numerical research on the hydrodynamics ram effect is of great significance.In this paper,CEL(coupled Eulerian Lagrangian)method is used to simulate the hydrodynamics ram effect.Firstly,the accuracy of the numerical model is verified by comparing with the existing experimental results;Then,the effects of impact velocity and liquid filling rate on the hydrodynamics ram effect are analyzed.Finally,in order to reduce the damage power of hydrodynamics ram effect,the design of protective structure is numerically analyzed.The results show that the damage power of hydrodynamics ram effect comes from shock wave.The greater the kinetic energy of projectile and the higher the liquid filling rate,the greater the damage of oil tank.The protective baffle can reduce the damage caused by shock wave to the oil tank structure to a certain extent,and the air-interlayer protective structure is the best for the protective effect.

The number of the collision accidents between Unmanned Aerial Vehicle (UAV) and people on the ground increase in recent years. It is necessary to clarify human injury characteristics brought by the impact of UAV and promote its management. This study focuses on head and neck injury risk resulted from the impact of the UAV with a relatively large mass, and the difference brought by the UAV with a small mass. First, the model of the Y3-dummy (Hybrid III 50th) is developed. Second, simulations are conducted to analyse head and neck injury characteristics from Y3's impact under different velocities, angles, and locations. With increasing the impact velocity, HIC and Nij increase with an exponential function and a power function, respectively. When the vertical impact velocity exceeds 5 m/s, both head and neck have a high probability of injury, while for the horizontal impact, the corresponding velocity is 9 m/s. As the impact angle increases, the changes of HIC satisfy the form of the sum of two exponential functions, and Nij changes in the form of the sum of a power function and a quadratic polynomial function. When the impact angle is close to 0°, the head injury risk is relatively high, while for 58°, the neck is more likely to be injury. The injuries induced by the top of mainframe and the front of the long arm are more serious. Finally, the differences in head and neck injury characteristics under different velocities and locations for UAVs with different masses are compared. [ABSTRACT FROM AUTHOR]

In order to study the uniaxial compression properties of closed-cell metal foam, three different modeling methods were used in this paper to establish 2D random cell, 3D Kelvin and 3D voronoi metal foam model. Based on the LS-DYNA software, the differences of the compressive mechanical properties of the closed-cell metal foam under three different models were analyzed. The deformation mode and the stress strain response of the metal foam under three models were studied. The results show that 2D random cell model is more suitable for the study of the compression regularity of metal foam, and the 3D model is more suitable for the prediction and optimization of the compression response of metal foam. The 2D random cell model is restricted by its plane geometry, it can only simulate the closed-cell metal foam with low porosity in most cases. The Kelvin model and Voronoi model can simulate the closed- cell metal foam with high porosity. Compared with the Kelvin model and 2D random cell model, the voronoi model is more realistic and reasonable, and it is able to better characterize the compressive mechanical properties of closed-cell metal foam.

A shock absorber based on the progressive failure of a composite tube was developed. The composite tube is subjected to axial compression from the pressing cap at one end and folds inward at the other end under the effect of the crush cap without debris overflow. The crushed composite is compacted into a hollow tube and increases the resisting force once it reaches the pressing cap. For larger strokes without a load increase, a hole is made in the pressing cap for the crushed composite. Three crush caps with different curvatures of the inward-folding surface and two composite tubes were evaluated through static and dynamic tests. The crush cap lowered the initial peak load and varied the specific energy absorption (SEA). We also investigated the effects of connection rivets. Aluminum rivets were severed and had little effect on the load curve while steel rivets did not shear but cut the composite tube into strips, resulting in a lower sustained load because failure was induced. A set of shock absorbers with larger strokes was tested for use in the legged landing gear of a drone assumed to crash with a speed of 10 m/s, energy of 5000 J, and overload of less than 25 g. The maximum SEA of the absorbers, including the two caps, was 20 kJ/kg. [ABSTRACT FROM AUTHOR]

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