• Journal of the Society of Naval Architects of Korea
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• v.57 no.6
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• pp.322-330
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• 2020

This study deals with underwater explosion (UNDEX) characteristics of various non-explosive underwater shock sources for the development of non-explosive underwater shock testing devices. UNDEX can neutralize ships' structure and the equipment onboard causing serious damage to combat and survivability. The shock proof performance of naval ships has been for a long time studied through simulations, but full-scale Live Fire Test and Evaluation (LFT&E) using real explosives have been limited due to the high risk and cost. For this reason, many researches have been tried to develop full scale ship shock tests without using actual explosives. In this study, experiments were conducted to find the characteristics of the underwater shock waves from actual explosive and non-explosive shock sources such as the airbag inflators and Vaporizing Foil Actuator (VFA). In order to derive the empirical equation for the maximum pressure value of the underwater shock wave generated by the non-explosive impact source, repeated experiments were conducted according to the number and distance. In addition, a Shock Response Spectrum (SRS) technique, which is a frequency-based function, was used to compare the response of floating bodies generated by underwater shock waves from each explosion source. In order to compare the magnitude of the underwater shock waves generated by each explosion source, Keel Shock Factor (KSF), which is a measure for estimating the amount of shock experienced by a naval ship from an underwater explosionan, was used.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.160-161
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• 2010

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.654-655
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• 2014

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.419-424
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• 2004

we performed the underwater explosion analysis for the liquefied oxygen tank - a kind of fuel tank of a mid-size submarine, and tried to verify the structural safety for this structure. First, we reviewed the theory and application of underwater explosion analysis using Structure-Fluid Interaction technique and its finite element modeling scheme. Next, we modeled the explosive and sea water as fluid elements, the LOX tank as structural elements and the interface between two regions as ALE scheme. The effect on shock pressure and impulse of fluid mesh size and shape are also investigated. As the analysis result, the shock pressure due explosion propagated into the water region and hit the structure region. The plastic deformation and the equivalent stress highly appeared at the web frame and the shock mount of LOX structure, but these values were acceptable for design criteria.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.94-100
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• 2001

In October 1997, low-frequency reverberation was measured at an experimental site off the west coast of the Jeju island using the explosive charge, Signals Underwater Sound (SUS). Received signals were separated into the noise, the reflection, and the scattering region, and then were analyzed for the spectral and statistical characteristics of each region. In the analysis of the spectrum we verified that each region had a unique frequency band and statistical characteristics as well. The results of this analysis showed that the real and imaginary portions were shown to be both normal distributions in each frequency bin. The reverberation envelope had a Rayleigh distribution and the phase had a uniform distribution.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.5
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• pp.439-446
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• 2017

This paper deals with an experimental study of the dynamics of an underwater bubbles and shock waves, generated by rapid underwater release of highly compressed gas. Aribag inflators, which are used for automobile's airbag system, are used to generate the extremely-rapid underwater gas release. Experimental studies of the complex underwater bubble dynamics as well as underwater shock wave were carried out in a specifically designed cylindrical water tank. The water tank is equipped with a high-speed camera and pressure sensors. The high-speed camera was used to capture the expansion and collapse of the gas bubble created by inflators, while pressure sensors was used to measure the underwater shock propagation and magnitudes. The experimental results were compared against the results of explosion of pentolite explosive. Several physical phenomena that has been observed and discussed, which are different from the explosive underwater explosion.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.6 s.144
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• pp.631-636
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• 2005

One and three dimensional whipping response analyses of a naval surface combatant subjected to an underwater explosion bubble pulse were carried out to compare the efficiency and accuracy according to the modeling methods. In 1-D analysis, program UNDEXWHIP developed by KIMM was used, which is based on the thin-walled Timoshenko's beam theory and on the modal analysis method using wetted vibratory modes of the hull girder. In 3-D analysis, three finite element models were suggested using LS-DYNA/USA code, such as 3-D beam model considering geometric shape of wetted side shell, coarse and fine 3-D F.E. models. Through the comparison of results from the 1-D and 3-D analyses, it could be confirmed that 1-D analysis result is in good agreement with 3-D analysis ones, and that fine 3-D F.E. model, shock analysis one, is also used both in the shock response and whipping response analyses for the analyst effort and time savings.

• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.20-25
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• 2005

The authors performed the underwater explosion analysis for the liquified oxygen tank - a kind of fuel tank of a mid-size submarine, and tried to verify the structural safety for this structure. First, the authors reviewed the theory and application of underwater explosion analysis, using a Structure-Fluid Interaction technique and its finite element modeling scheme. Next, the authors modeled the explosive and sea water as fluid elements, the LOX tank as structural elements, and the interface between the two regions as the ALE scheme. The effect on shock pressure and impulse of fluid mesh size and shape are also investigated. Upon analysis, it was found that the shock pressure due to explosion propagated into the water region, and hit the structure region. The plastic deformation and the equivalent stress were apparent at the web frame and the shock mount of LOX structure, but these values were acceptable for the design criteria.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.2
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• pp.75-84
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• 1996

The structural response of naval surface ships subjected to underwater shock loadings is a very important problem in viewpoint ship survivability. In practice, among others the case of noncontact underwater explosions is the only one shock loading considered in designing naval surface ships to resist underwater explosions. In orator to efficiently design naval surface ships and their equipment to resist such shock loadings it seems necessary to prepare theoretical analysis tools and/or empirical design criteria which can predict the three dimensional transmission of shock waves. This paper describes a simplified method to analyse shock responses for ship hull girder, which uses a loading function to approximate the shock loadings on ship structures due to noncontact underwater explosions. A couple of examples to apply this method are provided.

• 한국지구물리탐사학회:학술대회논문집
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• 2004.08a
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• pp.118-137
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• 2004

Recently underwater geophysical problems for historical relics or UXO's are raised frequently. This study includes the applicabilities and limitations of the recent underwater metal detector and domestic case stories for underwater survey by electrical and magnetic method. Direct or indirect case stories are electrical and vertical magnetic gradiometry surveys beneath Han-river bottom for planning subway tunnel, electrical exploration on lake-bottom, electrical exploration on the tidal flats using high-power transmitter, and borehole three-component magnetic and electromagnetic surveys for detecting the undersea objects. A design of potable real-time, high-speed measurement system using multi-channel array sensors is also introduced here. Further study will be focussed on practical field applications of the fast water-bottom scanning system which is lately required by actual field.