• Structural Engineering and Mechanics
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• 제77권4호
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• pp.441-461
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• 2021

Reinforced concrete (RC) columns are crucial in building structures and they are of higher vulnerability to terrorist threat than any other structural elements. Thus it is of great interest and necessity to achieve a comprehensive understanding of the possible responses of RC columns when exposed to high intensive blast loads. The primary objective of this study is to derive analytical formulas to assess vulnerability of RC columns using an advanced numerical modelling approach. This investigation is necessary as the effect of blast loads would be minimal to the RC structure if the explosive charge is located at the safe standoff distance from the main columns in the building and therefore minimizes the chance of disastrous collapse of the RC columns. In the current research, finite element model is developed for RC columns using LS-DYNA program that includes a comprehensive discussion of the material models, element formulation, boundary condition and loading methods. Numerical model is validated to aid in the study of RC column testing against the explosion field test results. Residual capacity of RC column is selected as damage criteria. Intensive investigations using Arbitrary Lagrangian Eulerian (ALE) methodology are then implemented to evaluate the influence of scaled distance, column dimension, concrete and steel reinforcement properties and axial load index on the vulnerability of RC columns. The generated empirical formulae can be used by the designers to predict a damage degree of new column design when consider explosive loads. With an extensive knowledge on the vulnerability assessment of RC structures under blast explosion, advancement to the convention design of structural elements can be achieved to improve the column survivability, while reducing the lethality of explosive attack and in turn providing a safer environment for the public.

• 한국군사과학기술학회지
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• 제25권1호
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• pp.9-22
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• 2022

A fighter performing a reconnaissance mission is equipped with a pod that drives optical/infrared sensors for acquiring and identifying target information on the lower part of the fuselage. Due to the nature of the reconnaissance mission, the fighter performs high speed evasive maneuvers, and the resulting load should be considered importantly for the development of the pod. This paper concerns a numerical investigation into the inertial and aerodynamic loads of the airborne pod of high performance aircrafts. For the aerodynamic load analysis, the pylon and pod shapes are added to the fighter 3D model, and the commercial software was used for static and dynamic analysis. Considering the practical mission conditions, the common/extreme conditions were established respectively in the static and dynamic situations of pods and the driving torque could be tripled under dynamic conditions. In the analysis of inertia load, a 3-DOF model considering roll and turning maneuvers was derived by the Lagrangian method, and then the numerical integration method was applied to the analysis. As a results, it was conformed that the inertia load was generally induced at a low level compared to the aerodynamic load, but depending on the unbalance mass condition of the pod, the inertia load cannot be negligible.

• Steel and Composite Structures
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• 제45권2호
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• pp.175-191
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• 2022

A review of previous studies shows that although there is a considerable difference between buckling loads of structures under follower and non-follower lateral loads, only the buckling load of FGM elliptical cylindrical shell under non-follower lateral load was investigated in the literature. This study is the first to obtain the buckling load of elliptical FGM cylindrical shells under follower lateral load and also make a comparison between buckling loads of elliptical FGM cylindrical shells under follower and non-follower lateral loads. Moreover, this research is the first one to derive the load potential function of elliptical cylindrical shell. In this regard, the FGM cylindrical elliptical shell was modeled using the semi-analytical finite strip method and based on the First Shear Deformation Theory (FSDT). The shell is discretized by strip elements aligned in the longitudinal direction. The Lagrangian and harmonic shape functions were considered in the circumference and longitudinal directions, respectively. The buckling pressure of the shell under follower and non-follower lateral loads was obtained from eigenvalue problem. The results obtained from the model were compared with those presented in the literature to evaluate the validity of the model. A comparison index was defined to compare the buckling loads of the shell under follower and non-follower lateral load. A parametric study was carried out to investigate the effects of material properties and shell geometry characteristics on the comparison index. For the elliptical cylindrical shells with length-to-radius ratio greater than 16 and major-to-minor axis ratio greater than 0.6, the comparison index reaches to more than 20 percent which is significant. Moreover, the maximum difference is about 30 percent in some cases. The results obtained from the parametric study indicate that the buckling load of long elliptical cylindrical shell under non-follower load is not reliable.

• Steel and Composite Structures
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• 제44권4호
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• pp.451-471
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• 2022

In the present paper, the static bending and buckling responses of functionally graded carbon nanotubes-reinforced composite (FG-CNTRC) beam under various boundary conditions are investigated within the framework of higher shear deformation theory. The significant feature of the proposed theory is that it provides an accurate parabolic distribution of transverse shear stress through the thickness satisfying the traction-free boundary conditions needless of any shear correction factor. Uniform (UD) and four graded distributions of CNTs which are FG-O, FG-X, FG- and FG-V are selected here for the analysis. The effective material properties of FG-CNTRC beams are estimated according to the rule of mixture. To model the FG-CNTRC beam realistically, an efficient Hermite-Lagrangian finite element formulation is successfully developed. The accuracy and efficiency of the present model are demonstrated by comparison with published benchmark results. Moreover, comprehensive numerical results are presented and discussed in detail to investigate the effects of CNTs volume fraction, distribution patterns of CNTs, boundary conditions, and length-to-thickness ratio on the bending and buckling responses of FG-CNTRC beam. Several new referential results are also reported for the first time which will serve as a benchmark for future studies in a similar direction. It is concluded that the FG-X-CNTRC beam is the strongest beam that carries the lowest central deflection and is followed by the UD, V, Λ, and FG-O-CNTRC beam. Besides, the critical buckling load belonging to the FG-X-CNTRC beam is the highest, followed by UD and FG-O.

• 한국환경과학회지
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• 제33권8호
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• pp.591-604
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• 2024

To investigate the frequency and trajectories of volcanic ash from Mt. Baekdu reaching the Korean Peninsula, a forward trajectory analysis was conducted using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Through a cluster analysis of air parcel trajectories, we identified the main pathways of the volcanic ash from Mt. Baekdu entering the Korean Peninsula and analyzed the synoptic meteorological conditions on those days. The frequency of volcanic ash reaching the Korean Peninsula was 82 times at an altitude of 1000 m and 70 times at 2000 m, with an increasing trend from 2016 to 2022. This increase is attributed to the weakening of westerly winds and the strengthening of north-south winds due to global warming. Five and three trajectory clusters were classified at 1000 m and 2000 m, respectively. At a starting altitude of 1000 m, most air parcels originating from Mt. Baekdu entered the Korean Peninsula under weather conditions (C2, C3) where the pressure gradient from the northwest to the southeast was small, resulting in weak northerly winds. C2 and C3 showed shorter trajectories, which occurred in all seasons, except summer. At a starting altitude of 2000 m, air parcels mostly passed over the Korean Peninsula in a synoptic pattern similar to that at 1000 m in altitude; however, the air parcels had simpler paths and less frequent inflow. C2, at a starting altitude of 2000 m, originates from Mount Baekdu, crosses the center of the Korean Peninsula, and continues to the central region. At a starting altitude of 1000 m, volcanic ash can enter the Korean Peninsula when there is no strong low-pressure system to the southeast of the Korean Peninsula, whereas at 2000 m, volcanic ash can enter the Korean Peninsula when the Siberian high-pressure system is weak.

• 한국지리정보학회지
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• 제5권2호
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• pp.25-33
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• 2002

위성영상과 수치모델을 이용하여 낙동강유출 부유토사의 확산범위를 구해 낙동강유출수의 영향권을 간접적으로 이해하고자 하였다. 수심을 적분한 2차원모델을 이용하여 유속장 계산 결과를 보면 창조시 부산에서 진해만과 거제도방향으로 흐름이 보였으며, 낙조시에는 창조시와 반대의 흐름을 보였다. 유속의 크기는 외양이 연안보다 크게 나타났다. 12시간 조시 평균에 의한 잔차류는 남서에서 북동방향의 흐름이 우세하게 나타났으며, 가덕도 동안에서는 동쪽으로 향하는 흐름이 나타났다. 이와 같은 유속장을 기반으로 부유토사의 확산 정도를 라그랑지 방법인 수치추적자 방법을 이용하여 구했다. 그 결과, 낙동강유출 부유토사의 범위는 가덕도 동안에서 부산방향으로 나타났다. SeaWiFS와 LANDSAT위성자료로 추정한 낙동강 유출부유토사의 확산범위는 수치모델의 결과와 비슷한 양상을 나타내었다.

• 한국전산구조공학회논문집
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• 제24권6호
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• pp.663-673
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• 2011

본 연구에서는 FDS code를 이용하여 교량하부창고 화재발생원과 교량높이의 영향을 분석하였다. 헵탄을 이용한 단위가연물의 연소실험, 실물모형 연소실험 결과와 FDS code를 이용한 해석결과의 비교를 통하여 FDS code의 유효성을 검증하였다. 이를 이용하여 교량하부 표준창고구조물의 실제 화재시나리오를 적용하여 교량높이 및 창고내부 가연물에 따른 콘크리트의 폭렬, 강도손실, 보강철근의 강도손실로 나누어 교량의 화재안전성을 평가하였다. 연구결과, 대부분의 교량이 하부창고화재에 대해 폭렬에 취약한 것을 확인할 수 있었다. 화재강도는 도서류가 가장 강하며 30m 높이 교량에 콘크리트의 강도저하, 폭렬 및 보강철근 강도저하를 가장 크게 발생시킬 것으로 예측되었으며, 고무류 창고화재의 경우 30m 이상 높이의 교량에 대해 화재안전성을 확보할 수 있었다.

• Computers and Concrete
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• 제16권6호
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• pp.933-961
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• 2015

Damage by high-speed impact fracture is a dominant mode of failure in several applications of concrete structures. Numerical modelling can play a crucial role in understanding and predicting complex fracture processes. The commonly used mesh-based Finite Element Method has difficulties in accurately modelling the high deformation and disintegration associated with fracture, as this often distorts the mesh. Even with careful re-meshing FEM often fails to handle extreme deformations and results in poor accuracy. Moreover, simulating the mechanism of fragmentation requires detachment of elements along their boundaries, and this needs a fine mesh to allow the natural propagation of damage/cracks. Smoothed Particle Hydrodynamics (SPH) is an alternative particle based (mesh-less) Lagrangian method that is particularly suitable for analysing fracture because of its capability to model large deformation and to track free surfaces generated due to fracturing. Here we demonstrate the capabilities of SPH for predicting brittle fracture by studying a slender concrete structure (column) under the impact of a high-speed projectile. To explore the effect of the projectile material behaviour on the fracture process, the projectile is assumed to be either perfectly-elastic or elastoplastic in two separate cases. The transient stress field and the resulting evolution of damage under impact are investigated. The nature of the collision and the constitutive behaviour are found to considerably affect the fracture process for the structure including the crack propagation rates, and the size and motion of the fragments. The progress of fracture is tracked by measuring the average damage level of the structure and the extent of energy dissipation, which depend strongly on the type of collision. The effect of fracture property (failure strain) of the concrete due to its various compositions is found to have a profound effect on the damage and fragmentation pattern of the structure.

• 동력기계공학회지
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• 제13권6호
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• pp.13-21
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• 2009

This basic study is required to examine spray or jet behavior depending on fuel phase. In this study, analyses of diesel fuel(n-Tridecane, $C_{13}H_{28}$) spray and natural gas fuel(Methane, $CH_4$) jet under high temperature and pressure are performed by a general-purpose program, ANSYS CFX release 11.0, and the results of these are compared with experimental results of diesel fuel spray using the exciplex fluorescence method. The simulation results of diesel spray is analyzed by using the combination of Large-Eddy Simulation(LES) and Lagrangian Particle Tracking(LPT) and of a natural gas jet is analyzed by using Multi-Component Model(MCM). There are two study variables considered, that is, ambient pressure and injection pressure. In a macroscopic analysis, the higher ambient pressure is, the shorter spray or jet tip penetration is at each time after start of injection. And the higher injection pressure is, the longer spray or jet tip penetration is at each time after start of injection. When liquid fuel is injected, droplets of the fuel need some time to evaporate. However, when natural gas fuel is injected, the fuel does not need time to evaporate. Gas fuel consists of minute particles. Therefore, the gas fuel is mixed with the ambient gas more quickly at the initial time of injection than the liquid fuel is done. The experimental results also validate the usefulness of this analysis.

• 한국해안·해양공학회논문집
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• 제23권1호
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• pp.70-78
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• 2011

2009년 8월 13일과 15일, 부산 해운대 해수욕장 앞 해상에서 이안류가 발생하였다. 또한, 올 여름인 2010년 7월 29일과 30일에도 이안류가 발생하여 피서객 들이 조난된 사고가 발생하였다. 해수욕객들은 전원 구조되어 인명 피해는 발생하지 않았지만 최근 이안류 발생이 너무 잦아져 이에 대한 원인파악과 대책마련이 시급한 실정이다. 본 논문에서는 파랑모형과 조류가 결합된 해빈류 모형을 기본으로 튜브거동까지 재현되는 사용자 편의를 위하여 GUI로 개발된 HAECUM 모형(HAEundae CUrrent Model)을 이용, 해운대 해수욕장의 이안류 발생 수치모의를 실시하였다.