• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.581-586
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• 2000

Explosively activated pyro-technic device is used to release exhausted rocket booster or payloads at prescribed times in the rocket's flight. It creates pyro-shock environment that rocket or payload components must survive. With the shock spectra acquired from flight data, laboratory test should be performed before flight to check whether all of component can sustain the shock environment. The pyro-shock environment simulation was created by the resonance fixture response to a projectile impact. Desired shock spectra is realized by adjusting the natural frequency of resonance plate and the velocity of impact hammer. This paper describes the development process of Pyro-shock testing machine, which is designed and tested by Korean engineers, to verify components of Korean Sounding Rocket(KSR-3) and the other Korean space vehicle. Both analytical and experimental techniques are introduced in this paper.

• Korean Journal of Applied Biomechanics
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• v.25 no.3
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• pp.283-291
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• 2015

Objective : The purpose of this study was to determine the differences in the head and tibial acceleration signal magnitudes, and their powers and shock attenuations between flat-footed and normal-footed running. Methods : Ten flat-footed and ten normal-footed subjects ran barefoot on a treadmill with a force plate at 3.22m/s averaged from their preferred running speed using heel-toe running pattern while the head and tibial acceleration in the vertical axis data was collected. The accelerometers were sampled at 2000 Hz and voltage was set at 100 mv, respectively. The peak magnitudes of the head and tibial acceleration signals in time domain were calculated. The power spectral density(PSD) of each signal in the frequency domain was also calculated. In addition to that, shock attenuation was calculated by a transfer function of the head PSD relative to the tibia PSD. A one-way analysis of variance was used to determine the difference in time and frequency domain acceleration variables between the flat-footed and normal-footed groups running. Results : Peaks of the head and tibial acceleration signals were significantly greater during flat-footed group running than normal-footed group running(p<.05). PSDs of the tibial acceleration signal in the lower and higher frequency range were significantly greater during flat-footed running(p<.05), but PSDs of the head acceleration signal were not statistically different between the two groups. Flat-footed group running resulted in significantly greater shock attenuation for the higher frequency ranges compared with normal-footed group running(p<.05). Conclusion : The difference in impact shock magnitude and frequency content between flat-footed and normal-footed group during running suggested that the body had different ability to control impact shock from acceleration. It might be conjectured that flat-footed running was more vulnerable to potential injury than normal-footed running from an impact shock point of view.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.10
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• pp.2583-2588
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• 2009

This study deals with the shock response analysis of HDD subjected to a half-sine shock pulse and its experimental verification. Comparatively, accurate computer simulation allows designers to determine complete mechanical information during the product impact time period, compared with only segmental messages by sensors in a test, to predict potential failures. But, impact/shock simulation technology is rather sensitive to various factors to predict the shock behavior without validation. In our shock simulation, the methodology of analysis with LS-DYNA3D and test validation is adopted to predict the shock behavior of HDD. We can confirm the soundness of the present shock simulation through the comparison with electromagnetic shock test(200G/1ms) and linear drop test(300G/2ms).

• Journal of the Korean Society of Safety
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• v.29 no.1
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• pp.15-20
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• 2014

The silicon as the hyper-elastic material was used to design the shock programmer and dynamic characteristic of the shock programmer was studied. The shock programmer was a structure part that was mounted between the impactor and the test bed. The role of the shock programmer was to generate the acceleration time history by the objective of various impact tests. The effective elastic modulus of the silicon was varied under the velocity of the impactor. The effective elastic modulus of the silicon was estimated by the comparison with results between test and simulation.

• Journal of the Korean Society of Safety
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• v.38 no.5
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• pp.36-42
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• 2023

In this study, 50 ABE-type hard hats were procured from five certified commercial manufacturers, and shock absorption tests were conducted in accordance with Protective Equipment Safety Certification Notice No. 2020-35. The tests were performed under both high- and low-temperature conditions, adhering to safety helmet testing standards. The highest shock transmission ranges were recorded in the tests, with an average energy range of 2,600-4,108 N at high temperatures and 2,316-3,991 N at low temperatures. All five hard hat models demonstrated a maximum transmitted impact force below 4,450 N, without any loss of cap and attachment functionality, confirming their compliance with performance standards. Furthermore, we evaluated the side impact performance of the safety helmets of each company, with an average range of 4,722-5,267 N. Company A exhibited the lowest measurement at 4,722 N. Comparing these results with international safety standards and the national shock absorption test criteria, it was observed that the maximum transmitted shock value using government-specified impact weight falls within the range of 4,450-5,000 N. However, it was noted that developed countries have established specific standards for the side impact forces on safety helmets, which are legally mandated. Consequently, it is imperative for South Korea to enhance its safety helmet side impact performance test methodology to align with domestic standards in the future.

• International Journal of Automotive Technology
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• v.6 no.2
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• pp.161-169
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• 2005

Neck injuries sustained during low speed rear impact are the most commonly sustained traffic injury. Therefore, the analysis of neck injury mechanisms and methods for mitigating and reducing neck injuries during low speed rear impact are a very important issue in the vehicle safety field. In order to find a method to absorb the shock that is transmitted to the occupant, the response of frontal and rear dummy due to the motion of the struck vehicle and the rotational angular displacements of dummies' necks during rear impact at 12km/h speed were investigated using a Working Model 2D. The results suggest that the shock absorption system should be equipped in the bottom of the seat of the vehicle to reduce shock and mitigate neck injury to the occupants.

• Korean Journal of Computational Design and Engineering
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• v.18 no.6
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• pp.461-469
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• 2013

Computer simulation with FEM is very useful to analyze hypervelocity impact phenomena that are tremendously expensive or otherwise too impractical to analyze experimentally. Shock physics can be efficiently handled by mesh adaptation which allows finite element mesh to be locally optimized to resolve moving shock wave in explosion. In this paper, an adaptive meshing technique based upon quadtree data structure was applied to resolve ballistic impact phenomena. The technique can adaptively refine a mesh in the neighborhood of a shock and coarsen the mesh for the smooth flow behind the shock according to a criterion. The criterion for refinement and coarsening is based upon the standard deviation of the gradient of shock pressure on the associated field. Shock simulation starts with the rough mesh of the pressure field and mesh density is increased locally under the criterion at each time step. The results show that the mesh adaptation enables to minimize the global computation error of FEM and to increase storage and computational saving compared to the fixed resolution of the conventional static mesh approach.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.6
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• pp.986-992
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• 2011

In this paper, the characteristics of shock behavior of multi-layered panels under impact were studied. The panels consist of four different lightweight materials including al, al-foam, rubber and FRP in order to enhance their shock energy absorption. A commercial code, Ls-dyna was used to build the numerical model and study shock behavior based on the analysis of shock response spectrum and peak response acceleration. The reliability of the numerical model was estimated by its comparison with the experimental results acquired under the same impact conditions.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.6
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• pp.735-749
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• 2008

For the development of the original technique of structural safety assessment of Cargo Containment System(CCS) in membrane type LNG carriers, it is necessary to understand the characteristics of dynamic response behavior of CCS structure under sloshing impact pressure. In the previous study, the wet drop impact response analyses of CCS structure in membrane Mark III type LNG carriers were carried out by using Fluid-Structure Interaction(FSI) analysis technique of LS-DYNA code, and were also validated through a series of wet drop experiments for the enhancement of more accurate shock response analysis technique. In this study, the characteristics of structural shock response behaviors of CCS structure were sufficiently figured out by careful examinations of the effects of specimen weight, drop height, incident angle, corrugation and stiffness of inner hull on its shock response behaviors. The shock response analysis of upward shooting fluid to inner hull was performed, and the reason of faster strain response than shock pressure one was also figured out.

• Korean Journal of Applied Biomechanics
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• v.31 no.1
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• pp.16-23
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• 2021

Objective: The purpose of the study was to compare the acceleration and shock attenuation (SA) of the runners with/without low back pain (LBG vs. NLBG) while running at 2.5 m/s, 3.0 m/s, 3.5 m/s and 4.0 m/s. Method: 15 adults without low back pain (age: 23.13±3.46 years, body weight: 70.13±8.94 kg, height: 176.79±3.68 cm, NLBG) and 7 adults with low back pain (age: 27.14±5.81 years, body weight: 73.10±10.74 kg, height: 176.41±3.13 cm, LBG) participated in this study. LBG was recruited through the VAS pain rating scale. All participants ran on an instrumented treadmill (Bertec, USA). Results: The LBG shows statistically greater vertical acceleration at the distal tibia during running at 3.5 m/s and 4.0 m/s and greater shock attenuation from the distal tibia to the head during running at 3.5 m/s compared with the NLBG during running (p<.05). As the speed increased, there was a statistically significant increase in vertical/resultant acceleration and shock attenuation for both groups. Conclusion: The findings indicated that the runners with low back pain (LBG) experience greater impact and shock attenuation compared with non-low back pain group (NLBG) during fast running. However, it is still inconclusive whether high impact on the lower extremity during running is the main cause of low back pain in the population. Thus, it is suggested that the study on low back pain should observe the characteristics of impact during running with individuals' low back pain experience and clinical symptoms.