• Structural Engineering and Mechanics
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• 제77권3호
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• pp.395-406
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• 2021

Near-field underwater explosion (UNDEX) phenomena were investigated by experiments and numerical simulations. The UNDEX experiments were performed in a water tank using a ship-like model. One kilogram of TNT, one of the most widely used military high explosives, was used for the experiments. Numerical simulations were performed under the same conditions as in the experiments using the commercial software LS-DYNA. Underwater pressures, accelerations, velocities, and strains by shock waves were measured at multiple locations. Further, the bubble pulsation period and the whipping deformations of the ship-like model were explored. The experimental results are presented and examined through comparison with the results obtained from widely used empirical equations and numerical simulations.

• 한국전산구조공학회논문집
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• 제35권6호
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• pp.333-342
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• 2022

경험식에 기반한 폭발 해석방법은 폭압-시간 이력곡선을 하중으로 적용하여 해석하는 방법이다. 이 방법은 모델링이 간단하고 해석시간이 짧아 효율적이지만, 일부 연구에 따르면 근거리 폭발 해석에는 적합하지 않음이 보고되고 있다. 본 연구에서는 예로써 환산거리 0.4~1.0의 근거리 폭발조건에 있는 RC 보에 대해 해석방법에 따른 결과의 차이 및 원인을 분석하였고, 이를 통해 경험식 방법을 이용한 해석의 적용 범위를 구체적으로 검토 및 확인할 수 있었다. 사용된 유한요소해석 프로그램은 LS-DYNA이다. 해석결과에 따르면, 원거리 폭발 실험 데이터를 근거로 하는 경험식 해석방법은 충격량을 과소평가하고 있었다. 이로 인해 RC 보의 처짐은 측정된 처짐 또는 ALE(Arbitrary Lagrangian Eulerian) 해석결과에 비해 작게 계산되었다. 구조체의 응답이 크게 나타나는 근거리 폭발에 대해서는 ALE 해석방법을 사용하는 것이 더 적합할 것으로 사료된다.

• Geomechanics and Engineering
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• 제28권3호
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• pp.209-224
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• 2022

In this study, the numerical analysis model of π-beam explosion is established to compare and analyze the failure modes of the π-beam under the action of explosive loads, thus verifying the accuracy of the numerical model. Then, based on the numerical analysis of different protection forms of π beams under explosive loads, the peak pressure of π beam under different protection conditions, the law of structural energy consumption, the damage pattern of the π beam after protection, and the protection efficiency of different protective layers was studied. The testing results indicate that the pressure peak of π beam is relatively small under the combined protection of steel plate and aluminum foam, and the peak value of pressure decays quickly along the beam longitudinal. Besides, as the longitudinal distance increases, the pressure peak attenuates most heavily on the roof's explosion-facing surface. Meanwhile, the combined protective layer has a strong energy consumption capacity, the energy consumed accounts for 90% of the three parts of the π beam (concrete, steel, and protective layer). The damaged area of π beam is relatively small under the combined protection of steel plate and aluminum foam. We also calculate the protection efficiency of π beams under different protection conditions using the maximum spalling area of concrete. The results show that the protective efficiency of the combined protective layer is 45%, demonstrating a relatively good protective ability.

• 대한조선학회논문집
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• 제61권1호
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• pp.44-50
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• 2024

In order to reasonably predict damage extents of naval ships under in-compartment explosion (INCEX) loads, two conditions should be fulfilled in terms of accurate INCEX load generation and fracture estimation. This paper seeks to predict damage extents of various naval ships by applying the CONWEP model to generate INCEX loads, combined with the Hosford-Coulomb (HC) and localized necking (LN) fracture model. This study selected a naval ship with a 2,000-ton displacement, using associated specifications collected from references. The CONWEP model that is embedded in a commercial finite element analysis software ABAQUS/Explicit was used for INCEX load generation. The combined HC-LN model was used to simulate fracture initiation and propagation. The permanent failures with some structural fractures occurred where at the locations closest to the explosion source points in case of the near field explosions, while, some significant fractures were observed in way of the interfaces between bulkheads and curtain plates under far field explosion. A large thickness difference would lead to those interface failures. It is expected that the findings of this study enhances the vulnerability design of naval ships, enabling more accurate predictions of damage extents under INCEX loads.

• 천문학논총
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• 제30권2호
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• pp.139-143
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• 2015

We describe a survey of nearby core-collapse supernova (SN) explosion sites using integral field spectroscopy (IFS) techniques, which is an extension of the work described in Kuncarayakti et al. (2013). The project aims to constrain SN progenitor properties based on the study of the immediate environment of the SN. The stellar populations present at the SN explosion sites are studied by means of integral field spectroscopy, which enables the acquisition of both spatial and spectral information of the object simultaneously. The spectrum of the SN parent stellar population gives an estimate of its age and metallicity. With this information, the initial mass and metallicity of the once coeval SN progenitor star are derived. While the survey is mostly done in optical, the additional utilization of near-infrared integral field spectroscopy assisted with adaptive optics (AO) enables us to examine the explosion sites in high spatial detail, down to a few parsecs. This work is being carried out using multiple 2-8 m class telescopes equipped with integral field spectrographs in Chile and Hawaii.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.572-583
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• 2019

This paper aims to assess the applicability of the Runge Kutta Discontinuous Galerkin-Direct Ghost Fluid Method to the internal explosion inside a water-filled tube, which previously was studied by many researchers in separate works. Once the explosive charge located at the inner center of the water-filled tube explodes, the tube wall is subjected to an extremely high intensity fluid loading and deformed. The deformation causes a modification of the field of fluid flow in the region near the water-structure interface so that has substantial influence on the response of the structure. To connect the structure and the fluid, valid data exchanges along the interface are essential. Classical fluid structure interaction simulations usually employ a matched meshing scheme which discretizes the fluid and structure domains using a single mesh density. The computational cost of fluid structure interaction simulations is usually governed by the structure because the size of time step may be determined by the density of structure mesh. The finer mesh density, the better solution, but more expensive computational cost. To reduce such computational cost, a non-matched meshing scheme which allows for different mesh densities is employed. The coupled numerical approach of this paper has fewer difficulties in the implementation and computation, compared to gas dynamics based approach which requires complicated analytical manipulations. It can also be applied to wider compressible, inviscid fluid flow analyses often found in underwater explosion events.

• 한국가시화정보학회지
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• 제18권3호
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• pp.35-41
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• 2020

We conduct numerical simulations of the interaction of a deformable structure with two-phase compressible flow. The finite volume method (FVM) is used to simulate fluid phenomena including a shock wave, a gas bubble, and the deformation of free surface. The deformation of a floating structure is computed with the finite element method (FEM). The compressible two-phase volume of fluid (VOF) method is used for the generation and development of a cavitation bubble, and the immersed boundary method (IBM) is used to impose the effect of the structure on the fluid domain. The result of the simulation shows the generation of a shock wave, and the expansion of the bubble. Also, the deformation of the structure due to the hydrodynamic loading by the explosion is identified.

• 한국전산구조공학회논문집
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• 제31권5호
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• pp.215-226
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• 2018

본 논문에서는 수중폭발(UE: underwater explosion)에 의한 해중터널(SFT: submerged floating tunnel)의 동적거동을 양해법(explicit)를 이용하는 LS-DYNA에 의한 유한요소해석을 통하여 분석하였다. SFT의 유한요소모델은 원형단면의 강재 라이너에 콘크리트가 채워진 복합재 원형단면으로 고려되었다. 해중터널 시스템의 중앙부 100m 구간은 탄소성재료를 고려한 솔리드(solid)요소로 상세하게 모델링하였으며, 양측 방향으로 각각 1km 구간에 대해서는 탄성재료를 고려하여 빔(beam) 요소로 이상화하여 모델링하였다. 사선계류시스템은 케이블(cable)요소를 적용하였으며, 수중폭발에 의한 동적거동시 수리동적질량의 영향을 고려하기 위하여 원형단면에 대한 추가질량을 고려하였다. 또한 부력과 같은 상시하중을 초기조건으로 고려하기 위하여 동적완화해석(dynamic relaxation analysis)를 수행하였다. UE는 부력비(B/W)와 폭발지점으로부터 거리의 변화에 대해서 고려하였으며, 폭발의 규모는 천안함 합동조사보고서(2010)를 참조하여 TNT 360kg로 결정하였다. 수중폭발 해석결과, 폭발지점으로부터 SFT까지 거리는 관입량, 충격압력의 크기와 반비례 관계에 있고, 부력비(B/W)가 커질수록 계류장력도 커짐을 확인하였다. 그러나 사선계류라인의 계류각 변화는 SFT의 수평거동, 관입량, 계류력, 충격압력과의 연관성을 찾을 수가 없었다.

• 한국산학기술학회논문지
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• 제20권10호
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• pp.125-132
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• 2019

수중폭발로 인해 발생된 충격파에 노출된 유체(대부분 해수)는 유체장 내 압력과 속력 등의 물리적 변화에 따른 장력을 견딜 수 없으므로 캐비테이션(기포 또는 기공)이 발생하게 되고 이때 발생된 캐비테이션은 수중폭발의 연쇄 과정 중 구조물에 미치는 충격하중의 전달 환경을 변화시킨다. 폭발물과 구조물 간의 거리가 비교적 가까워 선체구조의 국부적 손상에 관심을 가지는 근거리 수중폭발연구에서 관심을 가지는 물리적 현상은 크게 3가지로 초기충격파 그리고 그것과 선체구조와의 상호작용, 국부 캐비테이션, 국부 캐비테이션 폐쇄 후 2차 충격파이다. 본 논문의 관심은 근거리 수중폭발에 따른 국소 캐비테이션이므로 수면과 해저로부터의 반사파는 고려하지 않는다. 유체와 구조에 관한 각각의 지배 방정식을 유도하고 이를 간단한 1차원 무한평판 문제에 적용, 수치적으로 해석하여 엄밀해와 비교해봄으로써 제안된 비연성 해석방법을 검증한다. 비연성 해석방법은 유체-구조 결합 해석방법보다 계산상 효율이 높으며 간단함에도 불구하고 상대적으로 높은 수준의 정확도를 얻을 수 있다는 점에서 유용하다. 본 논문을 통해 수중폭발과 같은 복잡한 물리적 상황에서의 유체-구조 상호작용 현상에 대한 이해와 실질적인 문제에 개념적 이해를 높이는 데 도움이 될 것이다.

• 한국분말재료학회지
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• 제17권6호
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• pp.464-469
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• 2010

The Cu nanofluid in ethylene glycol was prepared by electrical explosion of wire, a novel one-step method. The X-ray diffraction, field emission scanning electron microscope and transmission electron microscope were used to study the properties of Cu nanoparticles. The results showed that the nanoparticles were consisted of pure face-centered cubic structure and near spherical shape with average grain size of 65 nm. Ultraviolet-visible spectroscopy (UV-Vis) confirmed Cu nanoparticles with a single absorbance peak of Cu surface plasmon resonance band at 600 nm. The nanofluid was found to be stable due to high positive zeta potential value, +51 mV. The backscattering level of nanofluid in static stationary was decreased about 2% for 5 days. The thermal conductivity measurement showed that Cu-ethylene glycol nanofluid with low concentration of nanoparticles had higher thermal conductivity than based fluid. The enhancement of thermal conductivity of nanofluid at a volume fraction of 0.1% was approximately 5.2%.