• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.440-444
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• 2017

Two-dimensional hydrodynamic analysis was performed to analyze the attenuating characteristics of shock waves generated by the detonation of the bulkhead initiator. Through the interlocking analysis between HNS and HMX stacking initiator and STS bulkhead, we have precisely simulated detonation growth and pressure wave attenuation phenomena. The free surface velocity at the surface of the bulkhead was measured for quantitative comparison with the test data by VISAR. As a result, it was confirmed that the pressure attenuating pattern of the shock wave exponentially decreased according to the bulkhead thickness. The observed inflection point at the particle velocity measured over time is due to the subsequent propagation of the shock wave due to the rapid spallation of the interface between the detonator and the bulkhead.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.138-142
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• 2018

This study used HILS to test an expansion joint, which is vulnerable to the water hammer effect. The operation data for the HIL simulator was the length rate of the expansion joint by the water hammer, which was used for life prediction based on the vibration durability. For the vibration durability test, the internal pressure of the expansion joint was assumed to be a factor of the durability life, and the lifetime prediction model equation was obtained by curve fitting the lifetime data at each pressure. During the test, the major failure modes of crack and water leakage occurred on the surface of the bellows part. The lifetime prediction model typically follows an inverse power law model. The pressure is a stress factor, and the model is effective in only a specific environment. Therefore, another stress factor such as temperature will be added and considered for a mixed lifetime prediction model in the future.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.164-167
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• 2003

Thermal shock is a physical phenomenon that occurs upon a rapid, large temperature and pressure change or in the quenching condition of materials. In this study, thermal shock fracture resistance and thermal shock fracture toughness were evaluated by using laser irradiation. The temperature distribution of a specimen was detected using type K and C thermocouples. The irradiated surfaces were observed by SEM. It is concluded that the critical laser power necessary to fracture can be the major factor of thermal shock resistance and thermal shock fracture toughness of materials.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.5
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• pp.19-30
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• 2016

We presented a hydrodynamic modeling necessary to accurately reproduce shock-induced detonation of pyrotechnic initiator. The methodology for such numerical prediction of shock propagation is quite straight forward if the models are properly implemented and solved in a well-formulated shock physics code. A series of SSGT(Small Scale Gap Test) and detailed hydrodynamic simulation are conducted to quantify the shock sensitivity of an acceptor that contains 97.5% RDX. A TBI(Through Bulkhead Initiator) system, consisting of a train configuration of Donor(HNS+HMX) - Bulkhead(STS) - Acceptor(RDX), were investigated to further validate the interaction between energetic and non-reactive materials for predicting the detonating response for successful operation of such small pyro device.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.17-22
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• 1997

ASME SA508 Class 3 원자로압력용기강을 대상으로, 용접열영향부(heat affected zone, HAZ)의 최고온도(peak temperature) 등온분포도(isothermal diagram)를 작성 및 해석하였고, 재현(simulated) 열영향부 시험편을 제작하여 미세조직검사 및 기계적특성 시험을 실시하였다. 그 결과, 최고온도 등온분포도를 이용하여, 미소열영향부(subzone of HAZ)의 미세조직(microstructure)에 미치는 예열(preheat)온도와 용접입열량(weld heat input)의 크기 효과를 예측할 수 있었다. 또한, 재현 HAZ 의 기계적특성 시험결과, 용접용융선(fusion line) + 1 mm 이내의 위치로 대표되는 열 cycle 조건에서는 모재보다 양호한 강도와 인성을 보였고, 용접용융선 + 2~3mm부근에서 가장 미세한 조직(fine tempered lower bainite)과 우수한 충격인성을 나타냈다. 한편, 용접용융선 + 약 5mm 위치에서의 열 cycle 을 재현한 시험편에서는 미세조직의 변화(spheroidization of carbides)와 함께 인성 및 기계적 특성이 저하하여 모재보다 낮은 값을 보이는 것을 발견할 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.8
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• pp.652-661
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• 2018

It is necessary to resolve the absolute velocity as well as Mach number to reflect the high temperature effect in high speed flow. So this region is classified as high enthalpy flows distinguished from high speed flows. Many facilities, such as arc-jet, shock tunnel, etc. has been used to obtain the high enthalpy flows at the ground level. However, it is difficult to define the exact test condition in this type of facilities, because some chemical reactions and energy transfer take place during the experiments. In the present study, a quasi 1D code considering the thermochemical non-equilibrium effect is developed to effectively estimate the test condition of a shock tunnel. Results show that the code gives reasonable solution compared with the results from the known experiments and 2D axisymmetric simulations.

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.2
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• pp.10-18
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• 2010

Scramjet engine is one of the core parts of hypersonic vehicle of next generation and being investigated by many countries. Korea Aerospace Research Institute performed a ground test of the model scramjet engine S1 in 2007. And, S2 model which is improved from S1 model in engine startability and thrust was tested with HIEST (High Enthalpy Shock Tunnel) at Kakuda Space Center of JAXA. Design condition of S2 model was Mach 6.7, however, it was tested at Mach 7.7 as an off-design condition test. As a test result, flow separation was found at the inside of the intake, but the engine showed stable combustion pressure distribution. Furthermore, compared to other test models, S2 model showed a good performance value in thrust and specific impulse.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.5
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• pp.521-530
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• 2011

Since aircraft fuel tanks have many interfaces connected to the airframe as well as the fuel system, they have been considered as one of the system-dependent critical components. Crashworthy fuel tanks have been widely implemented to rotorcraft and rendered a great contribution for improving the survivability of crews and passengers. Since the embryonic stage of military rotorcraft history began, the US army has developed and practised a detailed military specification documenting the unique crashworthiness requirements for rotorcraft fuel tanks to prevent most, hopefully all, fatality due to post-crash fire. The mandatory crash impact test required by the relevant specification, MIL-DTL-27422D, has been recognized as a non-trivial mission and caused inevitable delay of a number of noticeable rotorcraft development programs such as that of V-22. The crash impact test itself takes a long-term preparation efforts together with costly fuel tank specimens. Thus a series of numerical simulations of the crash impact test with digital mock-ups is necessary even at the early design stage to minimize the possibility of trial-and-error with full-scale fuel tanks. In the present study the crash impact simulation of a few fuel tank configurations is conducted with the commercial package, Autodyn, and the resulting equivalent stresses and internal pressures are evaluated in detail to suggest a design improvement for the fuel tank configuration.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.2
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• pp.31-38
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• 2000

Pressure vessels by composite materials were damaged sometimes during manufacturing or assembling. The state and the size of damage by low-velocity tests were investigated in this paper. Impactors of various masses and various tup shapes were dropped freely in the range of 120mm height to 700mm height. Compared with hemispherical tup of 12.7mm diameter, for hemispherical tup of 25.4mm diameter the size of surface dent was smaller but the size of delamination was bigger.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.1-8
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• 2014

Overexpanded flow of an axisymmetric thruster nozzle is numerically simulated to investigate effects of nozzle pressure ratio (NPR) on the shock structure and thrust performance. The Reynolds-averaged Navier-Stokes equations with k-${\omega}$ SST turbulence model are solved utilizing FLUENT solver. As the NPR is raised, thrust performance monotonically increases with the shock structure and flow-separation point being pushed toward the nozzle exit. It is also discussed that the flow structure at nozzle-exit plane which is immediately affected by a position of nozzle-interior shocks and expansion waves, has strong influence upon the thrust performance of thruster nozzle.