• Structural Engineering and Mechanics
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• v.51 no.3
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• pp.447-470
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• 2014

Numerical simulation of the non-linear behavior of (RC) structural walls subjected to severe earthquake ground motions requires a reliable modeling approach that includes important material characteristics and behavioral response features. The objective of this paper is to optimize a simplified method for the assessment of the seismic response and damage development analyses of an RC structural wall building using macro-element model. The first stage of this study investigates effectiveness and ability of the macro-element model in predicting the flexural nonlinear response of the specimen based on previous experimental test results conducted in UCLA. The sensitivity of the predicted wall responses to changes in model parameters is also assessed. The macro-element model is next used to examine the dynamic behavior of the structural wall building-all the way from elastic behavior to global instability, by applying an approximate Incremental Dynamic Analysis (IDA), based on Uncoupled Modal Response History Analysis (UMRHA), setting up nonlinear single degree of freedom systems. Finally, the identification of the global stiffness decrease as a function of a damage variable is carried out by means of this simplified methodology. Responses are compared at various locations on the structural wall by conducting static and dynamic pushover analyses for accurate estimation of seismic performance of the structure using macro-element model. Results obtained with the numerical model for rectangular wall cross sections compare favorably with experimental responses for flexural capacity, stiffness, and deformability. Overall, the model is qualified for safety assessment and design of earthquake resistant structures with structural walls.

• Atmosphere
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• v.18 no.4
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• pp.317-338
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• 2008

Analyses of observational data and numerical simulations were performed to understand the mechanism of MCSs (Mesoscale Convective Systems) occurred on 13-14 July 2004 over Jindo area of the Korean Peninsula. Observations indicated that synoptic environment was favorable for the occurrence of heavy rainfall. This heavy rainfall appeared to have been enhanced by convergence around the Changma front and synoptic scale lifting. From the analyses of storm environment using Haenam upper-air observation data, it was confirmed that strong convective instability was present around the Jindo area. Instability indices such as K-index, SSI-index showed favorable condition for strong convection. In addition, warm advection in the lower troposphere and cold advection in the middle troposphere were detected from wind profiler data. The size of storm, that produced heavy rainfall over Jindo area, was smaller than $50{\times}50km^2$ according to radar observation. The storm developed more than 10 km in height, but high reflectivity (rain rate 30 mm/hr) was limited under 6 km. It can be judged that convection cells, which form cloud clusters, occurred on the inflow area of the Changma front. In numerical simulation, high CAPE (Convective Available Potential Energy) was found in the southwest of the Korean Peninsula. However, heavy rainfall was restricted to the Jindo area with high CIN (Convective INhibition) and high CAPE. From the observations of vertical drop size distribution from MRR (Micro Rain Radar) and the analyses of numerically simulated hydrometeors such as graupel etc., it can be inferred that melted graupels enhanced collision and coalescence process of heavy precipitation systems.

• Explosives and Blasting
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• v.36 no.1
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• pp.1-11
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• 2018

In this study, several underwater steel cutting tests and AUTODYN numerical analyses were conducted to evaluate the penetration performance of a shaped charge device. Parameter analyses for the contribution rate were conducted by using the robust design method. The parameters adopted in this study were chamber type, stand-off, and wire setting, each of which had three levels in the analysis. Analysis results showed that the contribution rate was most affected by the stand-off, followed by the chamber type and wire setting. Experiments of underwater steel cutting were conducted at water depth of 25m. As expected, the experiments and numerical simulation showed similar results for underwater steel cutting performance, and thus the feasibility of the shaped charge device for underwater steel cutting at deep water depth was verified.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.661-667
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• 2002

Welding-induced buckling distortion is one of the most problematic concerns in both design and fabrication of welded thin-plate structures. This paper deals with experimental and numerical results of the welding-induced longitudinal and/or buckling distortion occurring in welding of 6mm-thick AH36 high strength steel plates. Effects of the heat input and the plate size on the distortion were experimentally evaluated for square plates. Bead-on-plate welding was performed with the submerged arc welding process along the middle line of plate specimens. Experimental results showed that the longitudinal distortion made a single curvature in the plate, and the distortion magnitude along the weld centerline was proportional to the heat input and the plate size. The experimental results were used to examine the validity of the numerical simulation procedure for welding-induced distortion where the longitudinal distortion mode and magnitude were numerically quantified. Three-dimensional, large deformation, welding simulations were performed for selected weld models. Numerical results of the distortion mode and magnitude were in a good agreement with experimental ones. Depending on the presence of halting the distortion growth during the cooling cycle of welding, the condition discriminating buckling distortion from longitudinal distortion was established. Eigenvalue analyses were performed to check the buckling instability of tested plates with different sizes subjected to different heat inputs. The perturbation load pattern for the analysis was extracted from longitudinal inherent strain distributions. Critical buckling curve from the eigenvalue analyses revealed that the buckling instability is manifested when plate size or heat input increases.

• Steel and Composite Structures
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• v.8 no.6
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• pp.491-510
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• 2008

This paper presents a plan and guidelines that were drawn for Korean based research carried out on the fire-resistance of CFT columns. This research was carried out by reviewing the Korean regulations related to the fire-resistance of CFT columns and examining studies which had been made in Korea as well as overseas. The first phase of the study plan was to compare the fire-resistance of square CFT columns without fire protection (obtained through fire-resistance tests and numerical analyses) with estimated values (obtained through fire-resistance design formulas proposed in Korea and overseas). This comparison provided conclusions as outlined below. Fire-resistance tests conducted in this study proved that, when the actual design load is taken into consideration, square CFT columns without fire protection are able to resist a fire for more than one hour. A comparison was made of test and analysis results with the fire-resistance time based on the AIJ code, the AISC design formula and the estimation formula suggested for Korea. The results of this comparison showed that the test and analysis results for specimens SAH1, SAH2-1, SAH2-2 and SAH3 were almost identical with the AIJ code, the AISC design formula and estimation formula. For specimens SAH4 and SAH5, the estimation formula was more conservative than the AIJ code and the AISC design formula. It was necessary to identify the factors that have an influence on the fire-resistance of CFT columns without fire protection and to draw fire-resistance design formulas for these columns. To achieve this, it is proposed that numerical analyses and tests be conducted in order to evaluate the fire-resistance of circular CFT columns, the influence of eccentricity existing as an additional factor and the influence of the slenderness ratio of the columns. It is also suggested that the overall behavior of CFT structures without fire protection within a fire be evaluated through analysis simulation.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.88-95
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• 2020

There have been many attempts to predict resistance of vessels in ice floe environment, but they mostly have both strong and weak points at the same time; for instance, simplified formulas are very fast but less flexible to types of ship and ice conditions and other numerical techniques need high computing cost for increased accuracy. A new numerical simulation technique of combining explicit finite element analysis code with a user-subroutine to control real-time forces acting on ice floes was proposed, thereby it was possible to predict ship-to-ice floe resistance with higher convenience and accuracy than other proposed approaches. The basic theory on how real-time hydrostatic and hydrodynamic forces acting on ice floes could be generated using user-subroutine was explained. The heave motion of a single ice floe was simulated using the user-subroutine and the motion amplitudes and periods were almost consistent with analytic values. Towing tests of an icebreaker model ship were simulated using explicit finite element analyses with the user-subroutine. The ice-induced resistance obtained from the towing experiments and simulations showed significant differences. Intentional increase of the drag coefficient to increase the contact duration between the ice floes and rigid model ship leaded the total resistance to be substantially consistent between the model tests and numerical simulations.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.11-21
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• 2017

Ground subsidence mainly occurs due to the soil wash-away caused by cracked sewer pipes. It is necessary to understand the behavior surrounding soils with the formation of cavity and relaxation zone to set up counterplan. In this paper, a series of laboratory model tests and numerical analyses (Discrete Element Method) were performed to investigate the ground subsidence mechanism due to sewer pipe damage. For model tests, aluminum rod and trap door were used to simulate the behavior of model ground. Test results were compared with the numerical analyses conducted under the same boundary conditions with model tests. From this study, it was investigated the shape and size of cavity and relaxation zone due to the soil wash-away and a void ratio distribution of surrounding soils with relaxation properties.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.39-45
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• 2002

In this paper, a finite element formulation was introduced for the three-dimensional cure simulation of composite structures. Based on the formulation, a three-dimensional finite element code was developed. Numerical examples found in the literatures were solved for code verification. Results from the present analyses agreed well with the measured cure-induced temperatures. Unlike in one or two dimensional analysis, temperature and degree of cure were able to be calculated at any point within composite structures in the present analysis. The finite element program can be used for the cure simulation of composite structures with arbitrary geometry under non-uniform autoclave temperature distribution.

• Computers and Concrete
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• v.26 no.4
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• pp.317-325
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• 2020

A precise estimation of the natural time period of buildings improves design quality, causes a significant reduction of the buildings' weight, and eventually leads to a cost-effective design. In this study, in order to optimise the reinforced concrete frames design, some symmetrical and unsymmetrical buildings composed of solid and hollow members have been simulated using finite element software SAP 2000. In numerical models, different parameters such as overturning moment, story drift, deflection, base reactions, and stiffness of the buildings were investigated and the results have been compared with strength and serviceability limit criteria proposed by Australian Standard (AS 3600 2018). Comparing the results of the numerical modelling with existing standards and performing a cost analysis proved the merits of hollow box sections compared to solid sections. Finally, based on numerical simulation results, two equations for natural time period of moment resisting reinforced concrete buildings have been presented. Both derived equations reflected higher degree of correlation and reliability with different complexities of building when compared with existing standards and relationships provided by other scholars. Therefore, these equations will assist practicing engineers to predict elastic behaivour of structures more precisely.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.1
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• pp.15-24
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• 2017

This paper explores a series of numerical simulations of dynamic responses of multi-piles (dolphin) type substructures for 2.5MW class offshore wind turbine. Firstly computational fluid dynamics (CFD) simulation was performed to evaluate wave loads on the dolphin type substructures with the design wave condition for the west-south region of Korea. Numerical wave tank (NWT) based on CFD was adopted to generate numerically a progressive regular wave using a virtual piston type wave maker. It was found that the water-piercing area of piles of the substructure is a key parameter determining the wave load exerted in horizontal direction. In the next the dynamic structural responses of substructure members under the wave load were calculated using finite element analysis (FEA). In the FEA approach, the dynamic structural responses were able to be calculated including a deformable body effect of substructure members when wave load on each member was determined by Morison's formula. The paper numerically identifies dynamic response characteristics of dolphin type substructures for 2.5MW class offshore wind turbine.