• Composites Research
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• v.13 no.4
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• pp.75-82
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• 2000

A small diameter steel-ball impact experiment was performed to study the impact resistance of the surface of glass plates bonded with glass fabric/epoxy lamina. Five kinds of materials were used in this study: soda-lime glass plates, glass/epoxy lamina(one layer)-bonded and unbonded glass plates, glass/epoxy lamina(three layers)-bonded and unbonded glass plates. The range of impact velocity was 40 120m/s. The maximum stress and absorbed fracture energy were measured on the back surface of glass plates. With increasing impact velocity, various types of surface cracks such as ring, cone, radial and lateral cracks took place in the interior near the impacted site of glass plates. The cracks drastically decreased with glass/epoxy lamina coating. The surface fracture behavior could be evaluated using the maximum stress and the absorbed fracture energy.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.573-579
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• 2016

Studies on the deformation behavior of materials subjected to impact loads have been carried out in various fields of engineering and industry. The deformation and fracture of members for these machines/structures are known to correspond to the intermediate strain-rate region. Therefore, for the structural design, it is necessary to consider the dynamic deformation behavior in these intermediate strain-rate ranges. However, there have been few reports with useful data about the deformation and fracture behavior at intermediate strain-rate ranges. Because the intermediate strain-rate region is located between quasi-static and high strain-rate regions, it is difficult to obtain the intermediate strain-rate using conventional reasonable test equipment. To solve this problem, in this study, the measurement reliability of the constructed drop-bar impact tensile test apparatus was established and the dynamic behavior at the intermediate strain-rate range of carbon steels was evaluated by utilizing the apparatus.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.757-770
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• 1991

본 연구에서는 조속충격을 받는 복합적층판의 거동에 대해 횡전단변형과 대처 짐효과를 동시에 고려하여 선형해석한 결과와의 차이를 비교, 검토하여 저속충격무제 의 해석에 있어서 비선형해석의 중요성을 보이는데 있다.그리고 충격체의 질량과 속도가 충격하중과 판의 거동, 그리고 동적 변형도등에 미치는 영향을 파악하여 복합 적층판의 외부 물체에 의한 저속충격문제를 이해 하고자 한다.

• The Journal of the Acoustical Society of Korea
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• v.34 no.2
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• pp.130-137
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• 2015

In this paper, we propose a new Modified Filtered-x Affine Projection Sign Algorithm(MFxAPSA) to improve the convergence speed of the conventional MFxAPSA which has been proposed for active control of impulsive noise. Under the impulsive noise environment, the adaptive algorithms based on the second order moment such as the Filtered-x Least Mean Square(FxLMS) show slow convergence speed or diverge because the noise source tends to have infinite variance. The MFxAPSA is the algorithm derived by applying the Affine Projection Sign Algorithm(APSA) to active noise control. The APSA has an advantage that it does not need the calculation for the inverse matrix, so it may be suitable for the active noise control that requires low computational burden. The proposed MFxAPSA also has APSA's advantage and furthermore, better performance than the conventional MFxAPSA. We carried out a performance comparison of the proposed MFxAPSA with the conventional MFxAPSA. It is shown that the proposed MFxAPSA has the faster convergence speed than the conventional MFxAPSA.

• Tunnel and Underground Space
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• v.31 no.6
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• pp.578-592
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• 2021

This study performed to investigate the propagation characteristics of overpressure, impulse, vibration in underwater blasting. The difference between air blasting and underwater blasting is that noise and vibration propagate through water as a medium. In some cases, the noise and vibration propagates through various media (rock, water, air, etc.). In this study, the underwater blasting was simulated using AUTODYN, and the propagation characteristics of overpressure, impulse and vibration induced by blasting were analyzed. We mainly focused on the effect of mesh size on the overpressure, impulse and peak particle velocity from the underwater blasting simulation. The numerical results indicated that the overpressure and peak particle velocity tended to decrease as the mesh size increased, while the impulse increased with the mesh size. The results also indicated that the mesh dependence varied depending on the explosive charge and scaled distance.

• Journal of Aerospace System Engineering
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• v.17 no.5
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• pp.19-27
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• 2023

In this study, we used finite element analysis to conduct a containment capability evaluation of a turbine case. When analyzing the impact behavior of structures subjected to impact loads, it is important to consider the strain rate, as it affects the increase in flow stress. Therefore, we applied three material models (Cowper-Symonds, Johnson-Cook, and Modified Johnson-Cook) for the impact analysis. To validate these material models, we performed an impact test on an aluminum 6061 plate. By comparing and analyzing the experimental and analytical results, we determined that the Modified Johnson-Cook material model exhibited the least error. As a result, we applied this material model to evaluate the containment capability of the turbine case. This evaluation involved determining the occurrence of penetration, as well as the stress and strain induced at the collision area due to the initial velocity of the blade.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 2004.04a
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• pp.567-570
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• 2004

기존의 엘리베이터 시스템은 모든 교통 상황에 대해서 고정된 속도 패턴을 사용함으로써 교통량 변화에 다양한 속도 패턴을 제공 할 수 없었다. 운송 속도와 승차감은 엘리베이터 속도 패턴을 결정하기 위한 두개의 중요한 요소이다. 기동과 정지 시에 변속 충격을 줄이기 위해서 가속과 감속 시간이 적절히 조정되어졌다. 운송능력을 향상시키기 위해서 교통량 변화에 맞추어 저크를 조정하였고 이와 같은 방법으로 6개의 속도 패턴 곡선과 엘리베이터의 속도 제어를 위해서 뉴로 퍼지 시스템을 구현하였다. 구현된 뉴로 퍼지 시스템은 2개의 입력변수와 1개의 출력을 가진 시스템이다. 전반부는 교통량의 변화를 나타내며 후반부는 입력에 대응되는 속도 패턴을 적용시켰다.

• Explosives and Blasting
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• v.38 no.1
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• pp.23-29
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• 2020

The measurement technique with dynamic shock sensor was widely used in academic experiment for blasting and impact. However, most of dynamic sensors are expensive so that it needs to be protected by external housing structures or damping devices. In this study, the calibration method for dynamic shock sensor under the distortion by external structures. Hopkinson pressure bar system was adopted to measure the input acceleration to the sensor, and it was compared to the acceleration measured by accelerometer with customized damping device. Consequently, it is conclued that this method can be useful to calibrate the dynamic shock sensor under the linear distortion.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.3
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• pp.713-722
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• 1991

본 연구에서는 graphite/epoxy와 glass/epoxy 그리고 graphite/epoxy와 kevl- ar/epoxy의 혼합적층된 복합재료 평판의 저속충격에 대한 응답을 유한요소 모델을 사 용하여 수치해석 한후, 각각의 단일적층판들의 결과와 비교하였으며, 이때의 접촉력 관계식은 Yang과 Sun이 제안한 수정된 접촉법칙을 이용하였다. 또한, 수치해석 결과 에서의 충격자의 속도변화로써 혼합적창판 배열에 따른 에너지 흡수율을 계산하였고, 이를 충격특성이 취약한 graphite/epoxy 단일 적층판의 결과와 비교 고찰하였다.