Abstract: The paper presents a fluid structure interaction based numerical study of impact loading for a hemispherical structure upon water and a space capsule water landing. The study has a strong relevance in the determination of the crashworthiness of aerospace structures upon water impact loading. Finite element based numerical techniques have been used for the analysis of the underlying transient dynamic and fluid-structure interaction. Smoothed Particle Hydrodynamics (SPH) and Arbitrary Lagrange-Eulerian (ALE) methods have been used to simulate the behaviour of the fluid (water) under impact conditions. The accelerations and velocities of the impacting objects have been validated with by experimental measurements and analytical results. Numerical analyses showed a strong potential for the use of developed computational fluid structure interaction models for analyses of water impact loading related problems.
Abstract: Back in 1990, D. S. Stewart and the first author contributed significantly to understanding the one-dimensional stability of detonation waves . For this purpose, the reactive Euler’s equation with the one-component reaction term was linearized around the steady state of the well-known ZND (Zeldovich-Doering-von Neumann) model. The key aspect of this paper was to derive the linearized radiation condition (named after A. Sommerfeld). They numerically found multiple eigenvalues for pairs of the temporal frequency and temporal attenuation rate (TAR). Of course, the propagating-wave mode having the least value of the TAR (in the sense of its absolute value) was selected. The successful numerical implementation of the far-field radiation condition is a must when it comes to incorporating a large surrounding space into a problem of finite extent. To one of the sure examples in this category belong the problems involving detonation waves, where high-energy-rate processes take place in spatially confined spaces while the surrounding space should be taken into account for reasons of energy loss (or leaky waves in the language of optics). In another fascinating area of science is nano-photonics, where energy transport should be handled in highly confined regions of space, yet being surrounded by unbounded (dielectric) media. The total energy release in nano-photonics is certainly much smaller than that involved in detonation. However, the energy per unit nanometer-scale volume is not negligibly small in nano-photonics. Over the years, the first author has been successful in implementing both theory and numerical methods to find a multitude of eigenvalues in optics . In this case, the governing Maxwell’s equations are already in a linearized form, being in a sense similar to the linearized Euler equations. In addition, the noble metals such as gold and silver are instrumental in enhancing local electric-field intensities, for which the science of plasmonics is being vigorously investigated in nano-photonics. Even the Bloch’s hydrodynamic equation describing the collective motion of the electrons is akin to the Navier-Stokes equations . Meanwhile, assuming a real-valued frequency has been an old tradition in optics, partly because the real-valued photon’s energy is proportional to frequency and normally the continuous-wave (cw) approximation holds true. In a radical departure from this optical scientists’ tradition, we have recently attempted to deal with complex-valued frequencies in examining the wave propagations around nanoparticles [4, 5]. In consequence, the stability of multiple propagating waves was successfully determined for selecting most realizable wave mode. Further interesting points of the interplay between the two seemingly disparate branches of science (fluid dynamics and photonics) will be expounded in this talk.
Abstract: A framework for quantifying the thermomechanical response of polymer bonded explosives (PBX) at the microstructural level is developed using a cohesive finite element method (CFEM). This framework allows the contributions of individual constituents, fracture and frictional contact along failed crack surfaces to heating to be analyzed and tracked. Digitized micrographs of actual PBX materials and idealized microstructures with various distributions of grain sizes are used in the analysis. The analysis concerns impact loading of HMX/Estane with strain rates on the order of 104 – 105 s-1. Issues studied include large deformation, thermomechanical coupling, failure in the forms of microcracks in both bulk constituents and along grain/matrix interfaces, and frictional heating. The Estane matrix is described by a thermo-elasto-viscoelastic constitutive formulation, accounting for temperature dependence, strain rate sensitivity and strain hardening. The HMX crystals are assumed to be elastic under the conditions analyzed. Energy localization leading to formation of local hot spots as potential ignition sites is primarily due to the viscoelastic dissipation in the matrix in early stages of deformation and frictional heating along crack surfaces in later stages of deformation. Microstructure-response relations that can be used in the design of soft energetic composites are established.
Abstract: The aim of the present study is to improve heat transfer performance and to attenuate pressure drop in plate heat exchanger with the different plate shapes. In this study, the single plate model of the plate heat exchanger is made and the thermal fluid flow characteristics in the narrows channel are examined for two different shaped plates, i.e., separate herringbone and plover patterns and the results are compared with that of flat or herringbone plate. In addition, the flow of the fluid with the surface of the rugged plate in the plate heat exchanger was visualized by tuft method. It is found that if the separate herringbone plate whose pith is 2 is employed, heat transfer performance is substantially enhanced for the high Reynolds number region, while pressure drop is suppressed.
Abstract: In this paper, we demonstrate that an engineering device can be carefully designed in such a way that an overdriven solid state detonation can be initiated and propagated supersonically in a highly porous mixture of aluminum and Teflon. The equation of state and kinetics for the porous mixture are phenomenological models that were developed in our previous work . This demonstration can be regarded as a good verification that the models which were used mainly in 1-D simulation are practically applicable and consistent to higher dimensional simulation of a shock dynamics in practical engineering devices.
Abstract: One of the most important tasks of thermochemical codes for the calculation of detonation properties is the accurate description of the state of gaseous products within a rather wide range of pressures and temperatures – from several hundreds of kbar and several thousands of K to atmospheric pressure and temperature. Due to its simplicity and convenience, the Becker-Kistiakowski-Wilson (BKW) equation of state is used in many practical applications in the explosives field, despite its lack of rigorous theoretical background. The BKW EOS gives good agreement between calculated and experimentally obtained detonation parameters for many standard high explosives having densities in the range 1.2 – 2 g/cm3. However, it fails to predict accurately detonation properties at lower densities. To overcome this problem, we introduced the concept of density dependent molecular covolumes in the BKW EOS instead of invariant. The applicability of the approach is verified by comparing experimental and calculated values of detonation parameters for a series of explosives having different formulations and densities. It was found that by applying this approach the accuracy of the calculations for lower densities can be significantly improved.
Abstract: The glass containers crushing process for recycling by using underwater shockwave was observed and the new cullet generation technique by explosive energy was proposed. In this study, the high-speed fracture behaviors of glass containers were visualized by using the high-speed photography and FEM simulation.
Abstract: A pulse-echo technique, based on ultrasonic "long-bar" mode (LBM) velocity measurements, working up to 1700°C is described. Magnetostrictive transducers and ultrasonic lines used in a 40-350 kHz frequency range are detailed. The conditions of choice of fundamental parameters (frequency, line geometry, sample size) are discussed in relation with the nature and the microstructure of the materials under test. This technique can be used to study the variations of elastic moduli of materials at high temperature.
Abstract: Flame propagation characteristics of hydrogen/carbon monoxide/methane (or propane)–air premixed mixtures were studied in a constant pressure combustion chamber with a schlieren system at room temperature and elevated pressures. Unstretched laminar burning velocities and Markstein lengths of various mixtures were obtained by analyzing high-speed schlieren images. Also, the experimentally measured unstretched laminar burning velocities were compared with numerical predictions using the PREMIX code with a H2/CO/C1–C4 mechanism, USC Mech II, developed by Wang et al. . The two data from experiments and predictions show good agreement. The results indicate a significant increase in the unstretched laminar burning velocities with hydrogen enrichment and a decrease with the addition of hydrocarbons, whereas the opposite effects for the Markstein lengths were observed.