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Characterization of aluminized RDX for chemical propulsion
여재익,김유천,김보훈,김민성,이경철,박정수,양승호,박홍래 한국항공우주학회 2015 International Journal of Aeronautical and Space Sc Vol.16 No.3
The chemical response of energetic materials is analyzed in terms of 1) the thermal decomposition under the thermal stimulus and 2) the reactive flow upon the mechanical impact, both of which give rise to an exothermic thermal runaway or an explosion. The present study aims at building a set of chemical kinetics that can precisely model both thermal and impact initiation of a heavily aluminized cyclotrimethylene-trinitramine (RDX) which contains 35% of aluminum. For a thermal decomposition model, the differential scanning calorimetry (DSC) measurement is used together with the Friedman isoconversional method for defining the frequency factor and activation energy in the form of Arrhenius rate law that are extracted from the evolution of product mass fraction. As for modelling the impact response, a series of unconfined rate stick data are used to construct the size effect curve which represents the relationship between detonation velocity and inverse radius of the sample. For validation of the modeled results, a cook-off test and a pressure chamber test are used to compare the predicted chemical response of the aluminized RDX that is either thermally or mechanically loaded.
여재익,함휘찬,김용현,육승근 한국생산제조학회 2019 한국생산제조학회지 Vol.28 No.6
A microjet with a velocity of approximately 140 m/s and 150 μm diameter is injected into a narrow nozzle by a pressure wave delivered by laser-induced bubble expansion. The driving force of such an injector is a discontinuous pulse of a 10 Hz period. Every time a pulse ends, unnecessary air bubbles are introduced into the injector due to the decrease in its internal pressure. Such air bubbles interfere with the flow inside the injector, deteriorating its performance. Therefore, we developed a nozzle closure that reacts automatically to the driving force with a pulse shape. When the flow occurs, the nozzle is opened; when it does not, the nozzle is closed to prevent unnecessary air inflow. In this study, a microjet injector was applied to needle-free drug injection. We compared and analyzed the drug penetration performance of the injector with and without the nozzle closure attached to the injector.
여재익(Jai-ick Yoh) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
We present two-dimensional models for two HMX-based explosives. The models are constructed based on measurements of thermal and mechanical properties along with small scale thermal explosion measurements obtained at the Lawrence Livermore National Laboratory. Confined high explosives (HE's) are heated at a rate of 1 C per hour until an explosion is observed. The heating, ignition, and deflagration phases are modeled using an Arbitrarily Lagrangian-Eulerian code that can handle a wide range of time scales that vary from a structural to a dynamic hydro time scale. During the pre-ignition phase, quasi-static mechanics and diffusive thermal transfer from a heat source to the HE are coupled with the finite chemical reactions that include both endothermic and exothermic processes. Once the HE ignites, a hydro dynamic calculation is performed as a burn front propagates through the HE in a level-set framework. The simulated dynamic response of HMX-based explosives is compared to measurements in large scale thermal explosion tests.
여재익(Jai-ick Yoh),김기홍(Ki-Hong Kim),이경철(Kyung-Cheol Lee),이현희(Hyun-Hee Lee),박경진(Kyoung-Jin Park) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
??Recent advances in energetic materials modeling and high-resolution hydrocode simulation enable enhanced computational analysis of bio-medical treatments that utilize high-pressure shock waves. Of particular interest is in designing devices that use such technology in medical treatments. For example, the generated micro shock waves with peak pressure on orders of 10 ㎬ can be used for treatments such as kidney stone removal, trans-dermal micro-particle delivery, and cancer cell removal.<br/> ??In this work, we present a new computational methodology for applying the high explosive dynamics to bio-medical treatments by making use of high pressure shock physics and multi-material wave interactions. The preliminary calculations conducted by the in-house code, GIBBS2D, captures various features that are observed from the actual experiments under the similar test conditions. We expect to gain novel insights in applying explosive shock wave physics to the bio-medical science involving drug injection. Our forthcoming papers will illustrate the quantitative comparison of the modeled results against the experimental data.
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여재익(Jai-ick Yoh),한태희(Tae-hee Han),하정무(Jung-moo Hah) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
A laser based needle-free liquid drug injection device has been developed. A laser beam is focused inside the liquid contained in the rubber chamber of micro scale. The focused laser beam causes explosive bubble growth, and the sudden volume increase in a sealed chamber drives a microjet of liquid drug through the micronozzle, The exit diameter of a nozzle is less than 100 11m and we verify the injected microjet is fast enough to penetrate human soft tissue. In the experiment, the microjet penetrated 5% gelatin-water solution, which replicates human thrombus, and pork fat tissue.