• 천문학회지
• /
• 제37권5호
• /
• pp.399-404
• /
• 2004

Cosmic rays are ubiquitous in space, and are apparently present wherever the matter density is small enough that they are not removed by collisions with ambient particles. The essential similarity of their energy spectra in many different regions places significant general constraints on the mechanisms for their acceleration and confinement. Diffusive shock acceleration is at present the most successful acceleration mechanism proposed, and, together with transport in Kolmogorov turbulence, can account for the universal specta. In comparison to shock acceleration, statistical acceleration, invoked in many situations, has significant disadvantages. The basic physics of acceleration and transport are discussed, and examples shown where it apparently works very well. However, there are now well-established situations where diffusive shock acceleration cannot be the accelerator. This problem will be discussed and possible acceleration mechanism evaluated. Statistical acceleration in these places is possible. In addition, a new mechanism, called diffusive compression acceleration, will be discussed and shown to be an attractive candidate. It has similarities with both statistical acceleration and shock acceleration.

• 한국전산유체공학회지
• /
• 제19권3호
• /
• pp.69-76
• /
• 2014

The shock buffet on a transonic transport aircraft are negative factors that reduce the aerodynamic performance of aircraft. The parametric studies were performed for position of nacelle/pylon to estimate the trend of flow mechanism under the wing that affects shock buffet. To generate external mesh of aircraft configuration that change the position of nacelle, snappyHexMesh provided in OpenFOAM was applied. Implicit density-based solver(ISAAC) was used for flow analysis. The change of nacelle position along horizontal direction dynamically affected the aerodynamic performance of transonic transport aircraft as comparing that of vertical direction. As a result of the parametric study of nacelle/pylon position, it was confirmed that the optimal position of nacelle can be obtained by aerodynamic design.

• 한국포장학회지
• /
• 제9권1호
• /
• pp.7-10
• /
• 2003

This study was carried out to investigate vibration shock of electric appliances during transport. Microwave oven, TV, washing machine and refrigerator were singled out as the study items. Transport courses were selected as follow ; an expressway between Kumi and Seoul for TV, an expressway between Kwangju and Seoul for microwave oven and washing machine, a national road between Inchon and Seoul for refrigerator. the values of vibration shock were measured to be ${\sim}3G$ on the national road and 1G on the expressway for up and down direction, ${\sim}0.5G$ on the national road and expressway for back and forth direction and ${\sim}0.8G$ on the national road and expressway for right and left direction. There was no damage during transport. These values were corresponding to grade II of KS A 1026 (General Rules of Performance Testing for Packaged Freights).

• Journal of Mechanical Science and Technology
• /
• 제16권10호
• /
• pp.1327-1335
• /
• 2002

The shock wave process represents an abrupt change in fluid properties, in which finite variations in pressure, temperature, and density occur over the shock thickness which is comparable to the mean free path of the gas molecules involved. This shock wave fluid phenomenon is simulated by using the finite difference lattice Boltzmann method (FDLBM). In this paper, a new model is proposed using the lattice BGK compressible fluid model in FDLBM for the purpose of speeding up the calculation as well as stabilizing the numerical scheme. The numerical results of the proposed model show good agreement with the theoretical predictions.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1995년도 가을 학술발표회 논문집
• /
• pp.76-83
• /
• 1995

Estimation of blasting behavior of explosives is prerequisite in the numerical analysis of blasting works. In this study, blasting pressure is estimated by the finite difference method using the Flux-Corrected Transport Algorithm. To formulate the behavior of blasting gas, the mass conservation equation, the moment conservation equation, the energy conservation equation and the ideal gas state equation are used. The simplified species conservation equation is included to simulate the behavior of reacting explosives. To verify the calculation, the Sod's shock tube problem, the strong shock problem and the reacting problem we used. Numerical results show that the shock wave can be captured by means of the FCT algorithm in the reacting and nonreacting states.

• Nuclear Engineering and Technology
• /
• 제56권2호
• /
• pp.375-388
• /
• 2024

In this study, to evaluate the shock and vibration load characteristics of used fuel, a sea transportation test was conducted using simulated fuel assemblies under normal transport conditions. An overall test data analysis was performed based on the measured strain and acceleration data obtained from cruise, rotation, acceleration, braking, depth of water, and rolling tests. In addition, shock response spectrum and power spectral densities were obtained for each test case. Amplification and attenuation characteristics were investigated based on the load path. The load was amplified as it passed from the overpack to the simulated used fuel-assembly. As a result of the RMS trend analysis, the fuel-loading position of the transportation package affected the measured strain in the fuel rod, and the maximum strains were obtained at the spans with large spacing. However, even these maximum strains were very small compared to the fatigue strength and the cladding yield strength. Moreover, the fuel rods located on the side exhibited a larger strain value than those at the center.

• Nuclear Engineering and Technology
• /
• 제54권11호
• /
• pp.4030-4048
• /
• 2022

In this study, road transportation tests were conducted with surrogate fuel assemblies under normal conditions of transport to evaluate the vibration and shock load characteristics of spent nuclear fuel (SNF). The overall test data analysis was conducted based on the measured acceleration and strain data obtained from the speed bump, lane-change, deceleration, obstacle avoidance, and circular tests. Furthermore, representative shock response spectrums and power spectral densities of each test mode were acquired. Amplification or attenuation characteristics were investigated according to the load transfer path. The load attenuated significantly as it transferred from the trailer to the cask. By contrast, the load amplified as it transferred from the cask to the surrogate SNF assembly. The fuel loading location on the cask disk assembly did not exhibit a significant influence on the strain measured from the fuel rods. The principal strain was in the vertical direction, and relatively large strain values were obtained in spans with large spacing between spacer grids. The influence of the lateral location of fuel rods was also investigated. The fuel rods located at the side exhibited relatively large strain values than those located at the center. Based on the strain data obtained from the test results, a hypothetical road transportation scenario was established. A fatigue evaluation of the SNF rod was performed based on this scenario. The evaluation results indicate that no fatigue damage occurred on the fuel rods.

• 한국포장학회지
• /
• 제8권1호
• /
• pp.23-26
• /
• 2002

This study was carried out to investigate vibration shock and dropping shock of refrigerator during physical distribution. The values of vibration shock were measured to be ${\sim}3G$ for up and down direction, ${\sim}0.8G$ for right and left direction and ${\sim}0.5G$ for back and forth direction on the national road. There was no damage during transport. From the results of dropping test by KS A 1026(General Rules of Performance Testing for Packaged Freights), relative equations were gained as follow : y = 0.12x + 7.63(where y is G-factor and x is Dropping height). The maximum values of dropping shock during materials handling were measured to be 11G. This shock value was corresponding to dropping shocks of dropping height 28.3cm by KS A 1026.

• 방사성폐기물학회지
• /
• 제17권2호
• /
• pp.167-181
• /
• 2019

최근 국내에서 육상 및 해상을 통한 소외 정상운반 시 진동 및 충격하중에 대한 사용후핵연료의 건전성 평가 기술 개발이 수행되고 있다. 이와 관련된 국내 연구사례는 전무하여 기존에 진행된 또는 현재 수행중인 해외연구사례를 조사하여 국내 연구에 참고하고자 한다. 2000년 이전 과거 미국의 사용후핵연료의 정상운반 시 진동 및 충격하중 측정 관련 연구현황을 조사하였고 2009년부터 미국국립연구소 주관으로 실시한 단축가진시험, 콘크리트블럭 트럭운반시험, 다축가진시험에 대해서 조사하였으며 2017년 미국 SNL, 스페인의 ENSA, 한국이 공동으로 수행한 복합운반시험을 상세히 조사하였다. 시험 준비과정, 절차, 가속도 및 변형률 측정결과, 유한요소 및 다물체동역학 해석과정 등이 조사되었다. 각 시험 별로 측정된 변형률 자료를 바탕으로 사용후핵연료 피로곡선과 비교한 결과 손상을 일으키기에는 매우 미미한 정도의 변형률이 발생한다는 초기 결론을 얻었음을 확인하였다. 하지만 현재 결론은 일부 결과만을 검토한 예비 결론으로 상세한 검토가 현재 미국에서 진행 중이다. 미국에서 지금까지 수행한 사용후핵연료의 정상운반조건에서의 진동 및 충격하중 측정과 관련하여 조사된 내용은, 국내 운반환경에서 사용후핵연료의 정상운반시험을 수행할 때 참고할만한 유용한 자료라 판단된다.

• 한국항공운항학회:학술대회논문집
• /
• 한국항공운항학회 2004년도 추계학술발표대회 논문집
• /
• pp.240-246
• /
• 2004

For the prediction on the onset of oblique shock wave-induced vortex breakdown, computational studies on the Oblique Shock wave/Vortex Interaction (OSVI) are conducted and compared with both experimental results and analytic model. A Shock-stable numerical scheme, the Roe scheme with Mach number-based function (RoeM), and a two-equation eddy viscosity-transport approach are used for three-dimensional turbulent flow computations. The computational configuration is identical to available experiment, and we attempt to ascertain the effect of parameters such as a vertex strength, streamwise velocity deficit, and shock strength at a freestream Mach number of 2.49. Numerical simulations using the ${\kappa}-{\omega}SST$ turbulence model and suitably modeled vortex profiles are able to accurately reproduce many fine features through a direct comparison with experimental observations. The present computational approach to determine the criterion on the onset of oblique shock wave-induced vortex breakdown is found to be in good agreement with both the experimental result and the analytic prediction.