• Journal of The Korean Astronomical Society
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• v.44 no.2
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• pp.49-58
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• 2011

We calculate the energy spectra of cosmic ray (CR) protons and electrons at a plane shock with quasi-parallel magnetic fields, using time-dependent, diffusive shock acceleration (DSA) simulations, including energy losses via synchrotron emission and Inverse Compton (IC) scattering. A thermal leakage injection model and a Bohm type diffusion coefficient are adopted. The electron spectrum at the shock becomes steady after the DSA energy gains balance the synchrotron/IC losses, and it cuts off at the equilibrium momentum $p_{eq}$. In the postshock region the cutoff momentum of the electron spectrum decreases with the distance from the shock due to the energy losses and the thickness of the spatial distribution of electrons scales as $p^{-1}$. Thus the slope of the downstream integrated spectrum steepens by one power of p for $p_{br}$ < p < $p_{eq}$, where the break momentum decreases with the shock age as $p_{br}\;{\infty}\;t^{-1}$. In a CR modified shock, both the proton and electron spectrum exhibit a concave curvature and deviate from the canonical test-particle power-law, and the upstream integrated electron spectrum could dominate over the downstream integrated spectrum near the cutoff momentum. Thus the spectral shape near the cutoff of X-ray synchrotron emission could reveal a signature of nonlinear DSA.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.81-86
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• 2012

The shock absorber is very important in various mechanical field. Without the shock absorber, the structure might be broken. For lunar lander, honeycomb shock absorber to absorber the shock by using plastic deformation of honeycomb has been used. It is cheap and simple to use but impossible using again without changing the honeycomb. The oleo-pneumatic type shock absorber is not able to use in the cosmos because it is vacuum and its temperature. This study suggests the hybrid shock absorber combined spring-ratchet mechanical shock absorber and eddy current electromagnetic damper. The ratchet restricts rebound of lunar lander and the spring converts the impact energy to the potential energy of the spring. The eddy current damper dissipates the impact energy by eddy current force without contact between the parts. This hybrid shock absorber is reusable while the honeycomb shock absorber isn't. The impact absorbing test of the hybrid shock absorber was carried out. This paper shows that the compared results the hybrid shock absorber with ratchet and without ratchet and evaluates the possibility of using for lunar lander.

• Textile Coloration and Finishing
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• v.26 no.3
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• pp.173-180
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• 2014

Fall-arrest system have been widely applied to provide a safe stop during fall incidents for occupational activities. This research object to evaluate the energy capacity of fall arrest shock energy absorber lanyard in relation to the used super fiber. In this work, shock energy absorber lanyard was prepared using high tenacity PET, high tenacity PET/P-aramid and high tenacity PET/UHMWPE, respectively. Dynamic load and static load tests based on the Korea fall protection equipment standard(Korea Occupational Safety & Health Agency standard 2013-13) were conducted. Maximum arrest force by dynamic load test of shock energy absorber showed below 6,000N. Also, static strength by static load test of lanyard and rope remains 15,000N and 22,000N for 1 min.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.28-37
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• 2017

Recent modeling of thermal nonequilibrium processes in simple molecules like hydrogen and nitrogen has indicated that rotational nonequilibrium becomes as important as vibrational nonequilibrium at high temperatures. In the present work, in order to analyze rovibrational nonequilibrium, the rotational mode is separated from the translational-rotational mode that is usually considered as an equilibrium mode in two- and multi-temperature models. Then, the translational, rotational, and electron-electronic-vibrational modes are considered separately in describing the thermochemical nonequilibrium of nitrogen behind a strong normal shock wave. The energy transfer for each energy mode is described by recently evaluated relaxation time parameters including the rotational-to-vibrational energy transfer. One-dimensional post-normal shock flow equations are constructed with these thermochemical models, and post-normal shock flow calculations are performed for the conditions of existing shock-tube experiments. In comparisons with the experimental measurements, it is shown that the present thermochemical model is able to describe the rotational and electron-electronic-vibrational relaxation processes of nitrogen behind a strong shock wave.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.1
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• pp.147-153
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• 2011

A series of nonequilibrium molecular dynamics(NEMD) simulations are performed to investigate the kinetic energy and velocity distributions of molecules in shock waves. In the simulations, argon molecules are used as a medium gas through which shock waves are propagating. The kinetic energy distribution profiles reveals that as a strong shock wave whose Mach number is 27.1 is applied, 39.6% of argon molecules inside the shock wave have larger kinetic energy than molecular ionization energy. This indicates that an application of a strong shock wave to argon gas can give rise to an intense light. The velocity distribution profiles in z direction along which shock waves propagate clearly represent two Maxwell-Boltzmann distributions of molecular velocities in two equilibrium regions and one bimodal velocity distribution profile that is attributed to a nonequilibrium region. The peak appearing in the directional temperature in z direction is discussed on a basis of the bimodal velocity distribution in the nonequilibrium region.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.477-482
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• 2004

Shock waves form in the intergalactic space as an ubiquitous consequence of cosmic structure formation. Using N-body/hydrodynamic simulation data of a ACDM universe, we examined the properties of cosmological shock waves including their morphological distribution. Adopting a diffusive shock acceleration model, we then calculated the amount of cosmic ray energy as well as that of gas thermal energy dissipated at the shocks. Finally, the dynamical consequence of those cosmic rays on cluster properties is discussed.

• Journal of the Korean Society of Safety
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• v.15 no.4
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• pp.47-55
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• 2000

In this modern age which electric energy is the fundamental source of energy in the industry, electric shock disasters are unavoidable. Although numerous efforts, time, and money have been invested to prevent such electric shock disasters, the number of electric shock disasters are on the increase. In this study, models for equivalent electric circuit are developed for the different types of electric shock which are classified into three groups. The objective of these models is to calculate the electric current flowing through the body at the time of the shock. Based on the analysis, countermeasures to prevent the shock are suggested. The data used in this study are based on 28 actual incidents which occurred in the Daegu area during January of 1995 through June of 1999. The results of this study can be used as a technical manual for workers treating electrical facilities.

• Journal of the Optical Society of Korea
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• v.20 no.3
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• pp.407-412
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• 2016

We analyzed through numerical simulations the properties of a square beam homogenizer near the target for laser shock peening. The efficiency was calculated near the target by considering the plasma threshold of the metals. We defined the depth of focus of the square beam homogenizer with a given efficiency near the target. Then, we found the relationship between the depth of focus for the laser shock peening and four main parameters of the square beam homogenizer: the plasma threshold of the metal, the number of lenslets in the array-lens, the focal length of the condenser lens and the input beam size.

• Nuclear Engineering and Technology
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• v.32 no.2
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• pp.99-107
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• 2000

A probabilistic integrity analysis method is presented for a reactor vessel under pressurized thermal shock(PTS) based on Monte Carlo simulation. This method can be applied to the structural integrity assessment of a reactor vessel subjected to pressurized thermal shock where the coolant temperature transient cannot be expressed explicitly as a time function. An axially or circumferentially oriented infinite length surface crack is assumed to be in the beltline weld region of the rector vessel's inside surface. The random variables are the initial crack depth, neutron fluence on the vessel's inside surface, the copper and nickel content of the vessel materials, R $T_{NDT}$ , $K_{IC}$ , and K/aub la/. The reliability of a sample reactor vessel under PTS is assessed quantitatively and the influence of the amount of neutron fluence is also examined by applying the present method.sent method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.7
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• pp.612-618
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• 2007

The dynamic behaviors of a KT-1 family aircraft nose landing gear have been analyzed and the optimal design of an aircraft shock absorber has been conducted to improve efficiency of shock energy absorption. The nose landing gear is modeled as a 2 DOF system using ADAMS and various operational and environmental landing conditions were considered. The results of dynamic simulation for various landing conditions agree well with experiments. Also the effect of parameters of a shock strut on the dynamic behaviors and on shock energy absorption of the nose landing gear has been evaluated for optimal design to define design variables. It has been found that the parameters of a shock strut such as oil-density and orifice area have more effects on dynamic behaviors than those of operation conditions. Optimal design is performed to maximize the efficiency of shock energy absorption using Feasible Direction Method. As a result the design values of the shock strut for maximum efficiency of shock energy absorption are derived and it turns out that efficiency and dynamic behaviors of the nose landing gear were improved by the optimal design.