Ning Jian-guo

Fuzzy interface treatment in Eulerian method

In this paper, we incorporate fuzzy mathematics approach into the Eulerian method to simulate three dimensional multi-material interfaces. In particular, we propose a fuzzy interface treatment for describing interfaces, designing transport plans, and computing transport quantities. Using a set of three-dimensional inviscid isothermal elastic-plastic hydrodynamic equations, we simulate shaped charge jet in different filled dynamite structures. Strain and stress have been under consideration in simulations. Numerical results demonstrate that the fuzzy interface treatment is correct and efficient for three-dimensional multi-material problems.

Propagation Mechanism of Cylindrical Cellular Detonation

We investigate the evolution of cylindrical cellular detonation with different instabilities. The numerical results show that with decreasing initial temperature, detonation becomes more unstable and the cells of the cylindrical detonation tend to be irregular. For stable detonation, a divergence of cylindrical detonation cells is formed eventually due to detonation instability resulting from a curved detonation front. For mildly unstable detonation, local overdriven detonation occurs. The detonation cell diverges and its size decreases. For highly unstable detonation, locally driven detonation is more obvious and the front is highly wrinkled. As a result, the diverging cylindrical detonation cell becomes highly irregular.

A Pseudo Arc-Length Method for Numerical Simulation of Shock Waves

A pseudo arc-length method is proposed for the numerical simulation of shock wave propagations. This method passes the discontinuities and establishes adaptive moving meshes in the physical space by introducing the arc-length parameter and transforming the computational domain. Numerical experiments of the Sod problem, double Mach reflection problem and explosion problem demonstrate that this approach is more efficient than traditional numerical methods in capturing and tracking discontinuous solutions of singular or nearly singular problems.

Perforation of Plastic Spherical Shells Under Impact by Cylindrical Projectiles

The objective is to study the perforation of a plastic spherical shell impacted by a cylindrical projectile. First, the deformation modes of the shell were given by introducing an isometric transformation. Then, the perforation mechanism of the shell was analyzed and an analytical model was advanced. Based on Hamilton principle, the governing equation was obtained and solved using Runge-Kuta method. Finally, some important theoretical predictions were given to describe the perforation mechanism of the shell. The results will play an important role in understanding the perforation mechanism of spherical shells impacted by a projectile.

Numerical Investigation on the Propagation Mechanism of Steady Cellular Detonations in Curved Channels

The propagation mechanism of steady cellular detonations in curved channels is investigated numerically with a detailed chemical reaction mechanism. The numerical results demonstrate that as the radius of the curvature decreases, detonation fails near the inner wall due to the strong expansion effect. As the radius of the curvature increases, the detonation front near the inner wall can sustain an underdriven detonation. In the case where detonation fails, a transverse detonation downstream forms and re-initiates the quenched detonation as it propagates toward the inner wall. Two kinds of propagation modes exist as the detonation is propagating in the curved channel. One is that the detonation fails first, and then a following transverse detonation initiates the quenched detonation and this process repeats itself. The other one is that without detonation failure and re-initiation, a steady detonation exists which consists of an underdriven detonation front near the inner wall subject to the diffraction and an overdriven detonation near the outer wall subject to the compression.

A comparative investigation on motion model of spherical fragments penetration into gelatin

Gelatin is a popular tissue simulant in biomedical applications. The behavior of a spherical fragment and the effects of penetrating a simulant are similar in biological tissue. In order to accurately describe the interaction between a spherical fragment and muscle tissue, this paper discusses the wounding mechanism and the difference between the Sturdivan model, the Segletes model, the Liu model, and an improved motion model previously established considering the effect of strain rate by us based on the properties of gelatin. In addition, experiments conducted into spherical fragment penetration into gelatin, with fragment diameters 3, 4 and 4.8 mm, and acquisition of the corresponding motion law are discussed. Numerical calculations reveal that the motion model has a better fit with experimental values than the Sturdivan, Segletes and Liu models. Further, it more accurately describes the motion of a spherical fragment penetrating gelatin than other models and also has good generality. Thus, it can provide a theoretical reference for small arms ammunition design and wound treatment.

Constitutive model, failure mechanism andnumerical method for reinforced concrete under intensive impact loading

Reinforced concrete has been widely used in the field of civil engineering, and the dynamic mechanical behavior of reinforce concrete under intensive dynamic loading is also a very important requirement for national security. However, the characteristics of its heterogeneity, anisotropy and multicomponent bring many difficulties to the study of its dynamic characteristics. Research progress of mechanical behavior of the reinforced concretes under intensive impact loading were reviewed in this paper, including: 1) the dynamical properties and the macrosopic constitutive laws of the reinforced concretes; 2) mechanisms of the penetration of the reinforced concrete structures; 3) numerical simulation method and software of structural mechanical behavior under intensive impact loading. On this basis, the inadequacy of the research which including the dynamic characteristics, penetration mechanism and numerical methods of the reinforced concretes under intensive impact loading were analyzed, and the further in-depth research work need to do in the future was prospected.

Numerical and experimental study on projectiles’high-velocity penetration into concrete targets

A series of experiments about 100 mm diameter projectiles into concrete targets around 800 m/s were carried out, and the results of large-size high-velocity projectile penetrating disconnected 1m diameter concrete targets were obtained. With the help of simulation, the design of concrete targets in projectiles’ high-velocity penetration experiments was investigated, and a new target design was put forward. Simulation helps design the targets in large-size projectiles’ penetration experiments, and guides further experimental designs and simulations in the future.

The visualization experiment and theoretical analysis of the flow field of honeybee flapping-wing

The goal of this study is to show characteristics of flow field of honeybee wings flapping with performing multiple sets of flow visualization experiment in low-speed smoke tunnel. Periodic flow field structures of far and near field of the honeybee were imaged using high-speed camera,and leading edge vortex,trailing edge vortex and wing tip vortex were analized.At the trailing edge of the wing, the downstroke stopping vortex and upstroke starting vortex were generated at the end of the down stroke. Both the forewing and hindwing could flex and rotate at the stroke reversal, leading the circular rectors of the trailing edge vortex of the forewing and hindwing to be in the opposite direction. The size of the leading edge vortex was increasing from wing root to wing tip, and the spanwise flow structure was composed of leading edge vortex and trailing edge vortex. At the end of the down stroke, the scroll generated by the wing tip vortex was connected with the wing margin circular rector, respectively forming the independent vortex rings on right and left wings. Meanwhile downstroke lift was estimated utilizing the vortex ring theory.

NUMERICAL SIMULATION OF DYNAMIC FAILURE FOR ALUMINA CERAMIC

The plate impact experiments have been conducted to investigate the dynamic behavior of alumina. Based on the experimental observations, the three-dimensional finite element models of flyer and alumina target are established by adopting ANSYS/LS-DYNA, several cases were performed to investigate the fracture behavior of alumina target under impact loading. By analyzing the fracture mechanism and damage process of the alumina target, it is concluded that the nucleation and growth of great number of radial and axial cracks and circumferential cracks play a dominant role in the fracture behavior of alumina target. The stress histories of alumina target are simulated. By the comparison of experimental results with the numerical predictions, a good correlation is obtained.