Papers by Keyword: Shock Waves

Abstract: The computational fluid dynamics solver Eilmer has proven useful to The University of Queensland’s Centre for Hypersonics for its ability to simulate high-speed compressible flows. In Eilmer, turbulence is modelled using Wilcox’s 2006 k-ω model. While the turbulence model implementation has been validated for two-dimensional and axisymmetric flows, validation is required for three-dimensional flows. The present paper describes the progress of the validation of the k-ω turbulence model for two three-dimensional test cases. A case featuring Mach 4.5 air flow over a flat plate produced results that correlated with previous numerical results within 4%. A second case featuring the injection of Mach 1 air into a Mach 4 air cross-flow produced results indicating that the code successfully captured the main flow features.

Abstract: We present non-equilibrium molecular dynamic simulations of
the shock compression of polyurethane and its graphene-based nanocomposite systems. Using the projectile/wall approach, planar shock waves with piston velocity range from 0.1 to 2.5 km/s is applied for both systems. In this study, direct molecular-level simulations of shock-wave generation and propagation are utilized in order to construct the appropriate shock-Hugoniot relations. Through this study, we determined that inclusion of graphene into the polyurethane system has a significant effect on the shock propagation behavior when incorporated in the polymer matrix

Abstract: Due to their complexity, certain engineering problems like finding shock strength, Mach number etc. and the interaction of shock wave with a structure in free and restricted metal forming techniques cannot be achieved in a single experimentation, these can be obtained only through a number of trials and that leads to increase in cost and time. In such cases both cost and time can be reduced by adopting numerical simulations. In this projectcommercial software ANSYS is used to simulate the propagation shock wave through a shock tube, free and shape forming of metallic plates subjected to this shock wave. Shock Mach numbers up to 2.12 have been generated by varying the driver to driven pressure ratios. Thin copper plates of diameter 60mm and thickness of 0.5mm and 0.3mm are subjected to shock wave loadingin order to form into dies.These dies,madeof structural steel are modelled with pre-defined shapes. The plate peakoverpressures ranging from 9 to 20bar have been generated.The midpoint deflection, Von Mises stress and strain are calculated for free forming copper plates. The simulated results are compared with the experimental values available in literature. The simulated results match well with the experimental values.

Abstract: For the model of the nonlinear elastic medium with inhomogeneous properties represented by a continuous change of the elastic moduli and density, the motion problems of a plane longitudinal or transverse shock waves are considered. The matched asymptotic expansions method allows to determine the evolution equations reflecting the nonlinearity of the wave processes and the inhomogeneity of the medium. The transition to the limiting inner problem of the small parameter method is dictated by the chain of inner problems, the solutions of which require a changes in all of the independent variables and their scales.

Abstract: In a series of dynamic issues of continuum, a special role play surfaces of discontinuity. These surfaces are divided two areas of the body that are characterized by significantly different solutions of dynamics equations. All disturbances propagate with finite speed in the continuum. The purpose of this paper is to discuss the propagation of surface discontinuities in isotropic material with the hyperelastic potential Blatz-Ko. These disorder, according to the assumptions is the shock wave, or a wave of strong discontinuities.

Abstract: In this paper, a new mechanism of plasma radiation optics-ammunition inspired by electrically exploding wires blasting in inert gases is studied. The simulation results indicate that, plasma radiation intensity increased by Mach-number of shock waves, and in all insert gases, argons Mach-number of shock waves is the highest. Silver is the best in common metal materials, and the exploding time and current peak is about linear with the number of wires. And the simulation results agree with the known experiment data and are important to the study of strong pulsed IR optics-ammunition.

Abstract: The influence of processing parameters on the morphology of periodical structures on surface of steel 15Kh13MF after the nanosecond laser irradiation are discussed and analyzed. Modification of microstructure, surface morphology, and hardness by laser treatment is discussed

Abstract: Modelling of shockwave propagation in orthotropic materials requires an appropriate description of material behaviour within elastic and plastic regimes. To deal with this issues, a finite strain constitutive model for orthotropic materials was developed within a consistent thermodynamic framework of irreversible process in this paper. The important features of this material model are the multiplicative decomposition of the deformation gradient and a Mandel stress tensor combined with the new stress tensor decomposition generalised for orthotropic materials. The elastic free energy function and the yield function are defined within an invariant theory by means of the introduction of the structural tensors. The plastic behaviour is characterised within the associative plasticity framework using the Hills yield criterion. The complexity was further extended by coupling the formulation with the equation of state (EOS) to control the response of the material to shock loading. This material model which was developed and integrated in the isoclinic configuration provides a unique treatment for elastic and plastic anisotropy. The effects of elastic anisotropy are taken into account through the stress tensor decomposition and plastic anisotropy through yield surface defined in the generalized deviatoric plane perpendicular to the generalised pressure. To test its ability to describe shockwave propagation, the new material model was implemented into the LLNL-DYNA3D code. The results generated by the proposed material model were compared against the experimental Plate Impact test data of Aluminium Alloy 7010. A good agreement between experimental and simulation was obtained for two principal directions of material orthotropy.

Abstract: The laser shock processing(LSP) is a new surface treatment technique that induce a significant compressive residual stress field on the metal and alloys. The developed compressive stress field is beneficial to improve surface properties such as fatigue, wear, and corrosion. To improve the understanding of the shock process, investigation into the physical processes and its variability involved is necessary. This work examines the effect of LSP at different input variability to induce its compressive stress. Various factors that affect the compressive stress of the LSP are tested with a serial experimental using 30CrMnSiNi2A as workpiece. It was found that the in-depth residual stress induced by LSP were a function of laser power density,laser beam spot size, laser pulse width and pulse repetition.

Abstract: The present paper is concerned with the study of compressible flow in a converging-diverging nozzle. From a theoretical and experimental investigation of the flow in an illustrative channel with convergent-divergent area variation, the behavior of the flow along the channel was found to be generally similar in trend to the flow in a stationary convergent-divergent nozzle. In compressible flows, the density and temperature variations are often significant. Therefore, the following study provides additional information on shock location, Mach number behavior and pressure distribution by varying nozzle length. The obtained curves show pressure distribution and Mach number along the two dimensioned nozzles which enable us to compare the experimental data with the theoretical calculations. Furthermore, interesting graphs are plotted which show the relationship between some nozzle parameters and flow characteristics.