• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.197-205
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• 2015

Offshore structures for the gas production are exposed to the risk of gas leaks, and gas explosions can result in fatal damages to the primary structures as well as secondary structures. To minimize the damage from the critical accidents, the study of the dynamic response of structural members subjected to blast loads must be conducted. Furthermore, structural dynamic analysis has to be performed considering relationships between the natural frequency of structural members and time duration of the explosion loading because the explosion pressure tends to increase and dissipate within an extremely short time. In this paper, the numerical model based on time history data were proposed considering the negative phase pressure in which considerable negative phase pressures were observed in CFD analyses of gas explosions. The undamped single degree of freedom(SDOF) model was used to characterize the dynamic response under the blast loading. A blast wall of FPSO topside was considered as an essential structure in which the wall prevents explosion pressures from the process area to utility and working areas. From linear/nonlinear transient analyses using LS-DYNA, it was observed that dynamic responses of structures were influenced by significantly the negative time duration.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.307-314
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• 2023

This study aims to evaluate the blast performance of shear and flexure failure modes of reinforced concrete columns using finite-element analyses. To accomplish this goal, finite-element models of flexure- and shear-governed columns were developed and validated using previous experimental results. A blast simulation model was developed using a coupling-modeling method, and the modeling method was applied to the validated-column models. Blast responses were obtained for various blast loading scenarios, and the blast performance was determined using limits based on ductility and axial loading capacity.

• 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.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.7
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• pp.33-39
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• 2005

A mathematical model, GUNBLAST, of blast waves emitted from a gun muzzle is established, and structural response analyses for the blast load are performed. The blast wave can be divided into two kinds of waves, free field and reflected blast waves. In this research, the free field blast wave model is established by the use of a scaling approach, and the reflected blast wave is calculated by using the oblique shock theory and computational fluid dynamic calculation. GUNBLAST is applied to two kinds of structural models. To investigate the effect of the muzzle distance from a structural surface, the blast waves on a plate for various muzzle distances are compared to uniform loads. Moreover, the transient response analysis of an aircraft wing model with a 12.7mm gun is carried out by using MSC/NASTRAN. From the results, it can be shown that the blast wave can cause broad random vibration and high frequency damage to equipments mounted in the aircraft.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.35 no.5
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• pp.317-324
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• 2022

In this paper, an analysis method that considers the initial static displacement of structural members using an equivalent single-degree-of-freedom system is presented. Newmark's dynamic analysis algorithm was improved to consider the effect of the initial static displacements of structural members. The effect of the initial static displacement on the maximum response according to the assumed duration of the blast load and natural period of the member was investigated. The effects of positive and negative static displacements on the maximum dynamic responses of structural members subjected to a positively applied blast load were also studied. Modified response charts for the shock-type and pressure-type waves are presented so that static displacements can easily be considered. Using a design example, we demonstrate the significance of the modified response chart that considers the static displacement. Based on the results of this study, the maximum response of a the structural member can be easily obtained whilst considering its initial static displacement. The modified response chart presented in this study can be used for the structural design of plants and military facilities.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.2
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• pp.187-195
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• 2015

The gas explosions in offshore installations are known to be very severe according to its geometry and environmental conditions such as leak locations and wind directions, and a dynamic response of structures due to blast loads depends on the load profile. Therefore, a parametric study has to be conducted to investigate the effects of the dynamic response of structural members subjected to various types of load shapes. To do so, a series of CFD analyses was performed using a full-scale FPSO topside model including detail parts of pipes and equipments, and the time history data of the blast loads at monitor points and panels were obtained by the analyses. In this paper, we focus on a structural dynamic response subjected to blast loads changing the magnitude of positive/negative phase pressure and time duration. From the results of linear/nonlinear transient analyses using single degree of freedom(SDOF) and multi-degree-of freedom(MDOF) systems, it was observed that dynamic responses of structures were significantly influenced by the magnitude of positive and negative phase pressures and negative time duration.

• Journal of Korean Society of Steel Construction
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• v.27 no.3
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• pp.273-280
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• 2015

Equivalent Single-Degree-of-Freedom(SDOF) analysis, most used for blast-resistant design, does not consider the effects of gravity load on the performance evaluation of blast resistance of structural members. However, since there exists gravity load on columns and walls of structures, the blast resistance of structural members should be evaluated considering gravity load on them. In this paper, an approach to reflect the gravity load effects on the equivalent SDOF analysis for dynamic blast response of structural members is proposed. For this purpose, the parametric studies using finite element analysis were performed by varying maximum blast load, blast load duration, and gravity load with constant the resistance and natural period of a structural member. The finite element analysis results were compared with the equivalent SDOF analysis results and the blast response of the structure member was estimated by conducting finite element analyses for various gravity loads. Finally, a graphical solution for ductility of a structural member with the variables of blast load, gravity load and structural member properties was developed. The blast response of structural members under gravity load could be estimated reasonably and easily by using this graphical solution.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.4
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• pp.281-288
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• 2014

As a gas explosion is the most fatal accident in shipbuilding and offshore plant industries, all safety critical elements on the topside of offshore platforms should retain their integrity against blast pressure. Even though many efforts have been devoted to develop blast-resistant design methods in the offshore engineering field, there still remain several issues needed to be carefully investigated. From a procedure for calculation of explosion design pressure, impulse of a design pressure model having completely positive side only is determined by the absolute area of each obtained transient pressure response through the CFD analysis. The negative pressure phase in a general gas explosion, however, is often quite considerable unlike gaseous detonation or TNT explosion. The main objective of this study is to thoroughly examine the effect of the negative pressure phase on structural behavior. A blast wall for specific FPSO topside is selected to analyze structural response under the blast pressure. Because the blast wall is considered an essential structure for blast-resistant design. Pressure time history data were obtained by explosion simulations using FLACS, and the nonlinear transient finite element analyses were performed using LS-DYNA.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.9-16
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• 2014

In recent years, the structural shock response to UNDEX (UNDerwater EXplosion) has been studied as much, or more, through numerical simulations than through testing for several reasons. Very high costs and sensitive environmental concerns have kept destructive underwater explosion testing to a minimum. Increase of simulation capabilities and sophisticated simulation tools has made numerical simulations more efficient analysis methods as well as more reliable testing aids. In this study, the main issue is the fluid-structure interaction. Here, appropriate relations between the acoustic pressure on the fluid surface and displacements on the structure surface are formed internally. The analysis was carried out using ABAQUS/Explicit and the results have been visualized in ABAQUS CAE. The shock loading history, acoustic pressure, stress of stand-off point, the velocity and strain energy time histories were presented.

• Bulletin of the Society of Naval Architects of Korea
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• v.47 no.4
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• pp.16-18
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• 2010

본고에서는 수중폭발 현상과 이로 인한 함정 충격응답 특성을 개괄하고, 수중위협 무기인 어뢰 및 기뢰에 의한 실제 함정의 대표적 손상사례를 소개하고자 한다.