• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.6
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• pp.615-620
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• 2013

There is considerable interest in developing energy sources capable of larger power densities. In our previous works, we proved that by coupling an exothermic chemical reaction with 1D nanostructures, a self-propagating reactive wave can be driven along its length with a concomitant electrical pulse of high specific power, which we identified as a thermopower wave. Herein, we discuss details about many different aspects of a thermopower wave. Different alignment degree in vertically aligned CNT films is evaluated in the reactive wave speed and correlated with its thermal reaction that affects the change in the magnitude of energy generation. The effects of the temperature-dependent properties of chemical fuels and CNTs are evaluated. Furthermore, we explore the convection and radiation portions in this thermal wave as well as the synchronization between the thermal reaction transfer and the oscillation of the electrical signal.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.05a
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• pp.65-66
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• 2018

국내 항만의 건설 및 확장 보수를 위한 설계 단계에서의 평면배치 검토시 항내측으로 내습하는 파랑변형특성에 대한 정밀한 평가는 필수적이다. 이에 따라 많은 수학적 모델들이 연안역과 항만에서의 파랑전파와 변형에 대해 개발되어 왔다. 특히 항내정온도의 해석은 항만 사용성 측면에서 매우 중요하며 실제 해상의 파랑상태와 유사한 불규칙파로의 해석이 요구되어 지고 있다. 항내정온도 해석에 있어서 항내파랑장 형성에 크게 영향을 미치는 구조물의 반사율을 효과적으로 적용하는 것은 매우 중요하다. 하지만, 구조물의 반사율은 이론계산이 어렵고, 일반적으로는 모형실험 혹은 현지관측에 의해 추정된다. 따라서, 일반적인 경우 비용 및 시간상의 제약으로 인해 평면 파랑모형으로 정온도 해석시 반사율의 적용은 구조형식별로 연구자들에 의해 개략 제시된 반사율을 적용하고 있다. 특히, 다방향 불규칙파의 적용시에 경계조건으로는 다방향 불규칙파를 효과적으로 제어할 수 있는 부분반사 경계면과 계산영역 밖으로 나가는 파랑에 대해서 인공적인 흡수층 또는 감쇠층(artificial damping layer)을 설정하여 반사를 제어하는 기법을 많이 적용하고 있다. 이때 항만구조물의 부분반사는 파랑제원에 따른 damping layer의 parameter의 조정에 의해 구조물의 구조형식별 반사율을 적절히 재현할 필요성이 있다. 본 연구에서는 불규칙파를 대상으로 damping layer의 parameter(무차원 감쇠계수, 감쇠층의 두께)등의 변화에 따른 반사율의 변화특성을 고찰하고, 향후 부분반사 경계면으로 damping layer가 적용되는 평면 파랑모형의 정온도 해석시 부분반사의 적용에 대한 기초자료를 제공하고자 한다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2012.05a
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• pp.278-281
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• 2012

Numerical studies were performed to investigate the three-dimensional front structure and dynamics features of detonation wave propagating in a circular tube such as Pulse Detonation Engine (PDE). By carrying out a series of parametric study using one step irreversible Arrhenius kinetics model, mechanisms of the three-dimensional front structure were investigated for two-, three-, four and six-cell mode detonations. A comparison with two-dimensional results, the effects of slapping transverse waves in radial direction were confirmed. In the all muti-cell modes, the detonation front structures and smoked-records on the wall are formed by the propagation of transverse waves along the wall in clockwise and counter-clockwise while the slapping move in radial direction. And the strength of reflected waves on the curved wall is changed by the multi-dimensional confinement effect.

• Geophysics and Geophysical Exploration
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• v.14 no.1
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• pp.98-104
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• 2011

Numerical simulation in exploration geophysics provides important insights into subsurface wave propagation phenomena. Although elastic wave simulations take longer to compute than acoustic simulations, an elastic simulator can construct more realistic wavefields including shear components. Therefore, it is suitable for exploration of the responses of elastic bodies. To overcome the long duration of the calculations, we use a Graphic Processing Unit (GPU) to accelerate the elastic wave simulation. Because a GPU has many processors and a wide memory bandwidth, we can use it in a parallelised computing architecture. The GPU board used in this study is an NVIDIA Tesla C1060, which has 240 processors and a 102 GB/s memory bandwidth. Despite the availability of a parallel computing architecture (CUDA), developed by NVIDIA, we must optimise the usage of the different types of memory on the GPU device, and the sequence of calculations, to obtain a significant speedup of the computation. In this study, we simulate two- (2D) and threedimensional (3D) elastic wave propagation using the Finite-Difference Time-Domain (FDTD) method on GPUs. In the wave propagation simulation, we adopt the staggered-grid method, which is one of the conventional FD schemes, since this method can achieve sufficient accuracy for use in numerical modelling in geophysics. Our simulator optimises the usage of memory on the GPU device to reduce data access times, and uses faster memory as much as possible. This is a key factor in GPU computing. By using one GPU device and optimising its memory usage, we improved the computation time by more than 14 times in the 2D simulation, and over six times in the 3D simulation, compared with one CPU. Furthermore, by using three GPUs, we succeeded in accelerating the 3D simulation 10 times.

• Applied Chemistry for Engineering
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• v.5 no.2
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• pp.263-273
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• 1994

Titanium powder prepared by dehydrogenating the titanium hydride which is synthesized by reacting Ti-sponge (99.67%) with hydrogen using the self-propagating high-temperature synthesis method. In the synthesis of titanium hydride, the particle size of the product was found dependent on the amount of hydrogen incorporated into the titanium such that the particle size of titanium hydride decreased with increasing hydrogen pressure and after-burn time. In the dehydrogenation process, as the dehydrogenation time increase, the particle size of titanium powder increased due to partial melting and sintering of titanium particles.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.183-188
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• 2005

This study targets to investigate thermal wave transfer in a droplet strongly coupled with acoustic pressure and its effects on combustion response. The one-dimensional vaporization model uses SRK equation of state and flash calculation method to obtain more accurate thermophysical properties and compute vapor-liquid equilibrium. Calculations of an n-pentane droplet exposed into a perturbing nitrogen gas is carried out in terms of different ambient gas pressures and wave frequencies. The thermal wave is transferred more effectively at lower frequencies, which results in the decrease in the amplitude of the response.

• Applied Chemistry for Engineering
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• v.10 no.3
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• pp.432-437
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• 1999

Pyrolysis of polyethylene was carried out in the stainless steel reactor of internal volume of $10cm^3$. Pyrolysis reactions were performed at temperature $390{\sim}450^{\circ}C$ and the pyrolysis products were collected separately as reaction products and gas products. The molecular weight distributions(MWDs) of each product were determined by HPLC-GPC and GC analysis. Distribution balance equation for MWDs of random and specific products were proposed to account for initiation-termination and propagation-depropagation, such as hydrogen abstraction, chain cleavage, coupling of polymer and radical. A separate chain-end scission process produces low molecular weight noncondensable gases(C1 through C5) of average molecular weight 38. Activation energies of the random-chain scission and chain-end scission rate parameters, respectively, were determined to be 35, 17 kcal/mole.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.343-346
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• 2005

Three dimensional structures of detonation wave propagating through a square-shaped duct were investigated using computational method and parallel processing. Inviscid fluid dynamics equations coupled with $variable-{\gamma}$ formulation and simplified one-step Arrhenius chemical reaction model were analysed by MUSCL-type TVD scheme and four stage Runge-Kutta time integration. The unsteady computational results in three dimension show the detailed mechanism of transverse mode and diagonal mode of detonation wave instabilities resulting same cell length but different cell width in smoked-foil record.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.1-6
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• 1997

In home-style microwave oven, silica-Al powder mixture was ignited among pellets and combustion wave-front propagated to produce Si+AIN+Al2O3 as resultant phases under N2 atmosphere. Without cooling pro-cedure the resultant phases of Si+AIN+Al2O3 continously absorbed microwave and were heated to be syn-thesized into sialon phases. This synthesis rate of sialon phases from silica-Al powder mixture in home-style microwave oven was higher than that in conventional furnace, and total processing time was around 1 hour, which could save energy and cost.

• Korean Journal of Materials Research
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• v.7 no.6
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• pp.510-516
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• 1997

반응성RF 마그네트론 스퍼터링 법으로 상온에서 c-축으로 우선 배향된 AIN 박막을 여러 기판 위에 증착하였다. SiO$_{2}$/Si, Si$_{3}$N $_{4}$Si, Si(100), Si(111)그리고 $\alpha$-AI$_{2}$O$_{3}$(0001) 기판에서 AIN(0002)로킹커브 피크의 표준편차는 각각 2.6˚, 3.1˚2.6˚, 2.5˚ 그리고 2.1˚ 의 값을 나타내었다. $\alpha$-AI$_{2}$O$_{3}$(0001) 기판에 증착된 AIN박막은 epitaxial 성장을 나타내었다. Si기판에 증착된 AIN박막에서 측정된 비저항과 1MHz 주파수에서 측정된 유전상수의 값은 각각 $10^{11}$Ωcm와 9.5였다. IDT/AIN/$\alpha$-AI$_{2}$O$_{3}$(0001)구저를 갖는 지연선 소자의 표면 탄성과 특성을 측정하였다. 상 속도, 전기기계 결합계수 그리고 전파손실은 H/λ가 0.17-0.5 범위에서 각각 5448-5640m/s, 0.13-0.17% 그리고 0.41-0.64dB/λ의 값을 나타내었다.다.