• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 춘계학술대회 논문집
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• pp.1-7
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• 2004

When a vortex diffracts upon encountering a vortex, many strong and weak waves are produced in the course of interaction. They are the cause of shock wave attenuation and noise production. This phenomenon is fundamental to understanding the more complex supersonic turbulent Jet noise. In this paper we have reviewed the research on shock-vortex interaction we have carried on last seven years. We have computationally investigated the parameter effect. When a shock is strong, shock diffraction pattern becomes complex since the slip lines from the triple points on Mach stem curl into the vortex, causing an entropy layer. When the vortex is unstable, vortexlets are brought about each of which make shock diffraction of a reduced intensity. Strong vortex produces quadrupole noise as it impinges into a vortex. Elementary interaction models such as shock splitting, shock reflection, and shock penetration are presented based on shock tube experiment. These models are also verified by computational approach. They easily explain production and propagation of the aforementioned quadrupole noise, Diverging acoustics are explained in terms of shock-vortexlet interactions for which a computational model Is constructed.

• 한국포장학회지
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• 제12권1호
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• pp.35-40
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• 2006

Cushioning systems, which are cushion material and its designed configuration, are important to protect fragile items since they act as buffers between the impact force and the fragile product. As cushioning materials, several plastic foams are commonly used in industry. However, the utilization of the plastic material has been causing a solid waste problem and pollution. Thus, as an alternative cushion material to the plastic foams, a corrugated cushion, which is considered environmentally friendly and cheap material, was put into drop tests and its impact shock attenuation was investigated. Flat and free drop data were recorded and compared to the dynamic shock of EPS cushion. In addition, the mathematical model of the shock attenuation of the corrugated cushion was developed. The result showed that the corrugated cushion gave an excellent protection for items that were subjected to the limited number of drops. There was no significant difference of the shock absorbing ability between the EPS and corrugated cushions. Energy density model of cushioning material successfully explained the mechanical behavior and fatigue of the corrugated cushions.

• 대한기계학회논문집
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• 제19권8호
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• pp.1972-1981
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• 1995

As a railway train enters a tunnel at high speed, a compression wave is formed in front of the train and propagates along the tunnel. The compression wave subsequently emerges from the exit of the tunnel, which causes an impulsive noise. The impulsive noise is closely related to the pressure gradient of the compression wave propagating the tunnel. In order to investigate the characteristics of the compression waves, in the present study an experiment was made using a shock tube. The results show that the strength of a compression wave decreases with the distance from the tunnel entrance and the nonlinear effect of compression wave appears to be significant if strength of the initial compression wave is greater than 7 kPa. Furthermore if the wave pattern is known, attenuation of the compression wave propagating in a tunnel can be reasonably predicted by a theoretical equation considering viscous action and heat transfer in boundary layer.

• Composites Research
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• 제37권1호
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• pp.21-31
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• 2024

이 리뷰 논문은 복합재에 함유되어 충격파를 감쇠하는 물질에 대한 탐구를 통해 폭발로 인한 외상성 뇌손상(bTBI)에 대비하여 인적자원을 보호하는 방법을 살펴보고자 한다. 이에 더하여 복합재의 충격파 감소의 정량화를 위한 충격파의 생성과 측정에 관련된 실험적인 방법들을 알아보고자 한다. 충격파는 고에너지 폭발물, 충격관, 레이저 및 레이저-플라이어 기술과 같은 다양한 접근법을 통해 생성이 가능하다. 충격파 전파 및 감쇠의 평가는 압전, 간섭계, 전자기 유도 및 스트릭 카메라 방법을 비롯한 첨단 기술을 활용하여 진행된다. 또한 충격파 압력감쇠 특성이 알려진 폴리우레아, 이온액체를 포함한 상분리 물질을 조사하였고 복합재 구조의 구성을 통해서 충격파를 감소시킬 수 있는 방법을 제시한다. 본 리뷰에서는 충격파 감쇠 물질 개발에 관한 연구를 종합하고 분석함으로써 폭발로 인한 외상성 뇌 손상에 대한 위험을 낮출 수 있는 재료적인 관점을 제시하고자 한다.

• 항공우주시스템공학회지
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• 제7권1호
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• pp.1-7
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• 2013

Launch vehicles cause several shock events during their lift-off. The excessive shock loads in the several thousands of g's level can results in permanent damage to electronics, optics and other sensitive payload components. The shock can be attenuated by mounting a shock absorber. In this paper, we proposed a semi-active control logic to attenuate the shock so that the input acceleration to main instruments does not exceed the allowable maximum acceleration value. For the performance investigation, two elements model of variable damping and spring stiffness has been used and the analysis results indicate that the proposed semi-active control logic attenuates shock level better than an optimal passive and conventional semi-active on-off control system.

• 한국정밀공학회지
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• 제27권2호
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• pp.117-122
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• 2010

The shock performance of hard disk drives has been a serious issue for Car PC. Since the vibration and disturbances from a car gives an adverse effect on a HDD of Car PC, it is necessary to protect a HDD from them. In this study, passive vibration attenuation system for a vehicle HDD was developed. Acceleration from the ground through the tire and suspension system was measured to figure out the frequency translated to Car PC. Critical frequency to Car PC was determined by exciting it with a shaker and measuring a data transmitting speed from HDD. A newly designed vibration attenuation system was fabricated to protect HDD from the acceleration. It was shown that the developed system had an excellent vibration attenuation ability.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 춘계학술발표대회 논문집
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• pp.31-37
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• 2000

Metal matrix composites(MMCs) are rapidly becoming one of the strongest candidates for structural materials for many high temperature application. Among the high temperature environment, thermal shock is known to cause significant degradation in most MMC system. Therefore, the nondestructive evaluation on thermal shock damage behavior of SiC/A16061 composite has been carried out using ultrasonic surface and SH-waves. For this study, Sic fiber reinforced metal matrix composite specimens fabricated by a squeeze casting technique were thermally cycled in the temperature range 25~$400^{\circ}C$ up to 1000 cycles. Three point bend test was conducted to investigate the effect of thermal shock damage on mechanical properties. The relationship between thermal shock damage behavior and the change of ultrasonic velocity and attenuation were discussed by considering SEM observation of fracture surface.

• 한국소음진동공학회논문집
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• 제11권4호
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• pp.71-77
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• 2001

In this paper, stress wave propagation characteristics of MR(Magneto-rheological) inserts are experimentally investigated. Generally, stress waves of structures such as warships or submarines are induced by shock waves from underwater explosion. Their fatal effects on the shipboard equipments or structures damage the performance of warships. But, such a problem can be solved by controlling the stress waves propagating through structures by means of MR inserts. MR insert consists of two aluminum layers and MR fluid filled in between. Two piezoceramic disks are embedded on the host plate as a transmitter and a receiver of stress waves. Pulse waves are generated by the transmitter and they reach to the receiver through the MR insert. Permanent magnet and magnetic coil are used to produce magnetic field at the MR insert. In the presence of magnetic field, MR particles are arranged in chains parallel to the magnetic field such that the transmitted stress waves are reduced. Attenuation of stress waves is experimentally investigated.

• 대한기계학회논문집B
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• 제21권1호
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• pp.174-184
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• 1997

A shock wave, being an irreversible process, gives rise to entropy increase. A great deal of effort has been made to control shock wave and boundary layer interaction related to energy losses as well as problems of vibration and noise. In the present study, tests are performed on a roof mounted half circular arc in an indraft type supersonic wind tunnel to evaluate the effects of porosity, length and depth of cavity in passive control of shock wave on the attenuation of shock strength by reviewing the measured static pressures at the porous wall and cavity. Also the flow field is visualized by a Schlieren system. The results show that in the present study the porosity of 8% produced the largest reduction of pressure fluctuations and that for the same porosity, the strength of shock wave decreases with the increasings of the depth and length of cavity.

• 한국운동역학회지
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• 제29권4호
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• pp.255-261
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• 2019

Objective: The purpose of this study was to investigate differences of shock attenuation strategies between double-leg and single-leg landing on sagittal plane using statistical parametric mapping. Method: Nine healthy female professional soccer players (age: 24.0±2.5 yrs, height: 164.9±3.3 cm, weight: 55.7±6.6 kg, career: 11.2±1.4 yrs) were participated in this study. The subjects performed 10 times of double-leg and single-leg landing from the box of 30 cm height onto force plates respectively. The ground reaction force, angle, moment, angular velocity, and power of the ankle, knee, and hip joint on sagittal plane was calculated from initial contact to maximum knee flexion during landing phase. Statistical parametric mapping was used to compare the biomechanical variables of double-leg and single-leg landing of the dominant leg throughout the landing phase. Each mean difference of variables was analyzed using a paired t-test and alpha level was set to 0.05. Results: For the biomechanical variables, significantly increased vertical ground reaction force, plantarflexion moment of the ankle joint, negative ankle joint power and extension moment of the hip joint were found in single-leg landing compared to double-leg landing (p<.05). In addition, the flexion angle and angular velocity of the knee and hip joint in double-leg landing were observed significantly greater than single-leg landing, respectively (p<.05). Conclusion: These findings suggested that negative joint power and plantarflexion moment of the ankle joint can contribute to shock absorption during single-leg landing and may be the factors for preventing the musculoskeletal injuries of the lower extremity by an external force.