• 천문학회지
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• 제51권6호
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• pp.185-195
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• 2018

Galaxy clusters are known to host many active galaxies (AGNs) with radio jets, which could expand to form radio bubbles with relativistic electrons in the intracluster medium (ICM). It has been suggested that fossil relativistic electrons contained in remnant bubbles from extinct radio galaxies can be re-accelerated to radio-emitting energies by merger-driven shocks via diffusive shock acceleration (DSA), leading to the birth of radio relics detected in clusters. In this study we assume that such bubble consist primarily of thermal gas entrained from the surrounding medium and dynamically-insignificant amounts of relativistic electrons. We also consider several realistic models for magnetic fields in the cluster outskirts, including the ICM field that scales with the gas density as $B_{ICM}{\infty}n^{0.5}_{ICM}$. Then we perform time-dependent DSA simulations of a spherical shock that runs into a lower-density but higher-temperature bubble with the ratio $n_b/n_{ICM}{\approx}T_{ICM}/T_b{\approx}0.5$. We find that inside the bubble the shock speed increases by about 20 %, but the Mach number decreases by about 15% in the case under consideration. In this re-acceleration model, the observed properties of a radio relic such as radio flux, spectral index, and integrated spectrum would be governed mainly by the presence of seed relativistic electrons and the magnetic field profile as well as shock dynamics. Thus it is crucial to understand how fossil electrons are deposited by AGNs in the ICM and how the downstream magnetic field evolves behind the shock in detailed modeling of radio relics.

• 천문학회지
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• 제53권3호
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• pp.59-67
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• 2020

We propose semi-analytic models for the electron momentum distribution in weak shocks that accounts for both in situ acceleration and re-acceleration through diffusive shock acceleration (DSA). In the former case, a small fraction of incoming electrons is assumed to be reflected at the shock ramp and pre-accelerated to the so-called injection momentum, p_inj, above which particles can diffuse across the shock transition and participate in the DSA process. This leads to the DSA power-law distribution extending from the smallest momentum of reflected electrons, p_ref, all the way to the cutoff momentum, p_eq, constrained by radiative cooling. In the latter case, fossil electrons, specified by a power-law spectrum with a cutoff, are assumed to be re-accelerated from p_ref up to p_eq via DSA. We show that, in the in situ acceleration model, the amplitude of radio synchrotron emission depends strongly on the shock Mach number, whereas it varies rather weakly in the re-acceleration model. Considering the rather turbulent nature of shocks in the intracluster medium, such extreme dependence for the in situ acceleration might not be compatible with the relatively smooth surface brightness of observed radio relics.

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

• 한국소음진동공학회논문집
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• 제18권5호
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• pp.558-563
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• 2008

Vibration/shock affects biggest taking a train subtraction of vehicle and durability decline. Therefore, absorber is used for vibration/shock isolation and various qualities of the material and design are applied to isolation. This paper proposes vibration/shock absorber that applies 'Disc' spring. Through comparison with 'Disc' spring that has nonlinearity and coil spring that is having linearity, see effect that nonlinearity of isolation gets in vibration/shock Isolation. Coil spring and 'Disc' spring are non-linear numerical analysis and simulation through theory for this, get and investigate comparison result through an experiment finally. Expressed and formulated shock through 'Runge-Kutta' method/impact response to nonlinear-vibration-equation of 1 degree of freedom for numerical analysis. Double half sine pulse of excitation used and analyzed result through spectrum response analysis here. Response of disc spring is compared to response of coil spring by changing $h_o/t$ ratio with computer simulation and the usage of disc spring is increased through analysis of effect of design factors. The purpose of this paper is that the shock response of disc spring is calculated through numerical simulation and to design the optimal absorber under the limited condition. And then, the isolation effect was analyzed through the shock test.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.990-993
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• 2008

Vibration/shock affects biggest taking a train subtraction of vehicle and durability decline. Therefore, absorber is used for vibration/shock isolation and various qualities of the material and design are applied to isolation. This paper proposes vibration/shock absorber that applies 'Disc'spring. Through comparison with 'Disc' spring that has nonlinearity and coil spring that is having linearity, see effect that nonlinearity of isolation gets in vibration/shock isolation. Coil spring and 'Disc' spring are non-linear numerical analysis and simulation through theory for this, get and investigate comparison result through an experiment finally. Expressed and formulated shock through 'Runge-Kutta' method/impact response to nonlinear-vibration-equation of 1 degree of freedom for numerical analysis. Double half sine pulse of excitation used and analyzed result through spectrum response analysis here. Response of disc spring is compared to response of coil spring by changing ho/t ratio with computer simulation and the usage of disc spring is increased through analysis of effect of design factors. The purpose of this paper is that the shock response of disc spring is calculated through numerical simulation and to design the optimal absorber under the limited condition. And then, the isolation effect was analyzed through the shock test.

• 한국농공학회지
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• 제17권4호
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• pp.3962-3969
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• 1975

1. When the frame of the experimental apparatus was directly fixed on the platform, result from the spectrum density analysis showed that the generated vibration frequecy of the system was nearly-same as the system's own characteristic vibration frequency, 80Hz, in the case of the forcing vibration frequency was 7.5 to 22.5Hz. The reduction ratio of acceleration by balanced type model compare to non-balanced type one was 26.66 percent. 2. When the frame of experimental apparatus was fixed on the platform with putting a shock absorbing rubber between the frame and the platform, the generated vibration frequency of the system was same as forcing vibration frequency. When either frequency or the amplitude of the forcing vibration was increased, the acceleration ratio was increased too. The average reduction ratio was resulted 44.77 per cent. It was concluded that this method of acceleration measurement(the method using a shock absorbing rubber) was a reaonable method, because actual machine will work under such condition. As the vibration frequency and aptitude were increased, the absolute magnitude of acceleration was increased. 3. unbalanced rotating parts, and unbalanced moment of inertia of links were supposed to be causing factors of residual vibration in spite of using the balanced type oscillating mole drainer. This fact suggested that the attachment of the counter weight on the rotating parts which satisfy the condition mw$.$rw=m0e, was necessary. And also, it was expected that the shock absorbing effect could be improved by putting the shock absorbing materials between the moving parts and their supports.

• International Journal of Aeronautical and Space Sciences
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• 제11권1호
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• pp.49-57
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• 2010

Several pyrotechnic devices are employed over the course of satellite's missions, generally for the separation of structural subsystems and deployment of appendages. Firing of pyrotechnic devices results in impulsive loads characterized by high peak acceleration and high frequency content which can cause failures of various flight hardware elements and small components. Thus, accurate prediction of acceleration level in various components of spacecraft due to pyrotechnic devices is important. In this paper, two methods for pyroshock prediction, an empirical model and statistical energy analysis in conjunction with virtual mode synthesis, are applied to predict shock response of a low altitude earth observation satellite during launch vehicle separation. The predicted results are then evaluated through comparison with the shock test results.

• 천문학회지
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• 제47권4호
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• pp.147-152
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• 2014

We present measurements of the Fe $K{\alpha}$ emission line of the intermediate polar V1223 Sagittarii observed with the Suzaku satellite. The spectrum is modeled with an absorbed thermal bremsstrahlung spectrum and three Gaussians for the three components of the Fe $K{\alpha}$ lines. We resolve the neutral or low-ionized (6.41keV), He-like (6.70keV), and H-like (7.00keV) iron lines. We also obtain a thermal continuum temperature of 25 keV, which supports a thermal origin of the hard X-rays observed from the shock heated layers of gas between the white dwarf and the shock front. Hence, we believe that the He-like and H-like lines are from the collisional plasma. On the origin of the Fe $K{\alpha}$ fluorescence line, we find that it could be partly from reflections of hard X-rays from the white dwarf surface and the $N_H$ absorption columns. We also discuss the Fe $K{\alpha}$ emission line as veritable tool for the probe of some astrophysical sites.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.589-594
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• 2007

In this paper, the optimal command input is considered in order to minimize the residual vibrations of a flexible cantilever beam when the beam simply changes its position by translation or rotation. Although a cantilever beam has many modes of vibration, it is shown that the consideration of the first mode is sufficient in this case. Thus, the problem becomes a singledegree-of-freedom system subjected to a ground excitation. Two simple methods are proposed to find the optimal command input based on the Shock Response Spectrum (SRS). The first method is the simplest and can be applied to lightly damped cases, and the second method is applicable to more general problems. The second method gives almost the same results as the input shaping method. However the proposed method gives a easier and clearer control strategy.

• 한국군사과학기술학회지
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• 제21권4호
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• pp.413-421
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• 2018

The pyroshocks can cause failure of electronics devices and structures. Metal-metal impact methods are utilized to simulate mechanical pyroshock, and to adjust the knee frquency of the SRS(Shock Response Spectrum) through resonant structures. In this paper, the major parameters of pyroshock simulation device which affect the SRS were examined. Through the Hertzian contact law and the modal characteristics of the resonant bar, it was found that the SRS is affected by the length and mass of a bar and various impact conditions such as velocity and mass of impactor. The characteristics due to the geometric parameters of a resonant bar was analyzed by performing FEA and also the resonant bar was designed and fabricated. Through the pyroshock simulation test, the characteristics of SRS due to the variation of impact parameters were examined.