• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.7
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• pp.401-409
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• 2018

Performance-based seismic evaluation is usually done by considering simplified models for the liquid storage tanks therefore, it is important to validate those simplified models before conducting such evaluation. The purpose of this study is to compare the seismic response results of the FSI (fluid-structure interaction) model and the simplified models for the cylindrical liquid storage tanks and to verify the applicability of the simplified models for estimating failure probability. Seismic analyses were carried out for two types of storage tanks with different aspect ratios (H/D) of 0.45 and 0.86. FSI model represents detailed 3D fluid-structure interaction model and simplified models are modeled as cantilever mass-spring model, frame type mass-spring model and shell type mass-spring model, considering impulsive and convective components. Seismic analyses were performed with modal analysis followed by time history analysis. Analysis results from all the models were verified by comparing with the results calculated by the code and literature. The results from simplified models show good agreement with the ones from detailed FSI model and calculated results from code and literature, confirming that all three types of simplified models are very valid for conducting failure probability analysis of the cylindrical liquid storage tanks.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.499-504
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• 1996

Current Probabilistic Safety Assessment (PSA) techniques are not usually utilized for day-to-day applications in nuclear power plants. The major reason for this anomaly is the complexity of plant models developed for PSA studies and the multitude of resulting fault trees. This impediment can be overcome by the use of simplified plant models. However, oversimplified models usually result in loss of valuable information and therefore. simplification approaches have to be used judiciously in order to achieve accurate and meaningful results. For this reason. development of an appropriate simplification approach must be performed using extreme caution followed with results verification in sequence as well as system levels. If there are no significant differences between the simplified and the original models, the simplified model can be efficiently used in the application of the PSA. This paper presents a methodology for how to develop a suitable simplification technique and the results of its verification for sample systems and sequences. The results show that the utilization of simplified plant models will significantly reduce the number of fault trees with no significant loss of accuracy.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.1
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• pp.1-10
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• 2001

As computer power is increased, refined finite element models are employed for structural analysis. However, it is difficult and expensive to use refined models in the design stage. The refined models especially cause problems in the preliminary design where the design is frequently changed. Therefore, simplified models are needed. The simplification process is regarded as an empirical technique. Simplified and equivalent finite element model of a structure has been studied and used in the preliminary design. A general approach to establish the simplified and equivalent model is presented. The generated simple model has satisfactory correlation with the corresponding refined finite element model. An optimization method, the Goal Programming algorithm is used to make the simple model. The simplified model is used for the design change and the changed design is recovered onto the original design. The presented method was verified with three examples.

• International journal of steel structures
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• v.18 no.4
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• pp.1464-1469
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• 2018

Steel frames with ductile connections have good seismic performance under strong earthquake, they are now popular for high seismic design. In order to simplify the process of numerical analysis of the steel frames with ductile connections, simplified connection models are introduced, two types of springs are placed in the simplified connection model, which can simulate deformation of the panel zone and members. 6-story-3-bay steel frames with ductile connections are simplified and carried out modal analysis, fundamental periods of the frames predicted by finite-element analysis for simplified steel frame models were compared to the results for actual frame models. 2-story steel frame with reduced beam section connections is simplified and carried out pseudo-static analysis, hysteretic curves and skeleton curves of the frame obtained by finite-element analysis for simplified steel frame model are compared to test results. The comparison show that the difference between them is small, it is reliable and effective to predict mechanical properties of the steel frame with ductile connection by finite-element analysis of simplified steel frame model.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1333-1344
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• 2019

An integrated approach of model simplification for high burnup spent nuclear fuel is proposed based on material calibration using optimization. The spent fuel rods are simplified into a beam with a homogenous isotropic material. The proposed approach of model simplification is applied to fuel rods with two kinds of interfacial configurations between the fuel pellets and cladding. The differences among the generated models and the effects of interfacial bonding efficiency are discussed. The strategy of model simplification adopted in this work is to force the simplified beam model of spent fuel rods to possess the same compliance and failure characteristics under critical loads as those that result in the failure of detailed fuel rod models. It is envisioned that the simplified model would enable the assessment of fuel rod failure through an assembly-level analysis, without resorting to a refined model for an individual fuel rod. The effective material properties of the simplified beam model were successfully identified using the integrated optimization process. The feasibility of using the developed simplified beam models in dynamic impact simulations for a horizontal drop condition is examined, and discussions are provided.

• Journal of Korean Society of Steel Construction
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• v.14 no.6
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• pp.729-734
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• 2002

The effect of several simplified methods of seismic analysis is estimated. The pounding/contacting of superstructures were considered in the multispan simply supported bridge and the multispan continuous bridge. Although nonlinear time history analysis is generally used for seismic analysis of bridges, many codes including AASHTO propose several simplified analysis methods. AASHTO, however, does not mention pounding. Therefore, the simplified methods may produce results that are different from those of nonlinear time history analysis. This study developed nonlinear analytical models of the two types of bridges mentioned. The models were then modified to the simplified linear models for simplified analysis. The results of the simplified methods were compared with those of nonlinear time history analysis. It was found that including of the pounding/contacting element in the simplified methods generated responses similar to those of the nonlinear time history analysis.

• Journal of Ocean Engineering and Technology
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• v.15 no.3
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• pp.120-127
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• 2001

The potential pollution problems resulting from tanker collision necessitate the requirement for an effective structural design and the development of relevant safety regulations. During a few decades, the great effort has been made by the international Maritime Organization and the Administration, etc, to reduce oil spillage from collision accidents. However there is still a need for investigation in the light of structural evaluation method for the experiments and rational analysis, and design development for an operational purpose of ships. This study aims for investigating a complicated structural response of bow structures of simplified models and oil carriers for assessing the energy dissipation and crushing mechanics of the striking vessels through a methodology of the numerical analysis for the various models and its design changes. Through these study an optimal bow construction absorbing great portion of kinetic energy at the least penetration depth prior to reach to the cargo area and an effective location of collision bulkhead are investigated. In order to obtain a rational results in this study, three stages of collision simulation procedures have been performed step by step as follows; 1) 16 simplified ship models are used to investigate the structural response against bow collision with variation of primary and secondary members. Mass and speed are also varied in four conditions. 2) 21 models consisted of 5 sizes of the full scaled oil carriers are used to perform the collision simulation with the various sizes and deadweight delivered in a recent which are complied with SOLAS and MARPOL. 3) 36 models of 100l oil carrier are used to investigate the structural response and its influence to the collision bulkhead against bow collision in variation with location of collision bulkhead, primary members, framing system and colliding conditions, etc. By the first study using simplified models the response of the bow collision is synthetically evaluated for the parameters influencing to the absorbed energy, penetration depth and impact force, etc.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2716-2727
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• 2021

The core shroud is one of the most important internal components of the reactor vessel internals because it meets the neutron fluence directly emitted by the nuclear fuel. In particular, dynamic effects for an earthquake should be evaluated with respect to the neutron irradiation flux. As a prerequisite to this study, simplified and detailed finite element models are developed for the core shroud using the ANSYS Design Parametric Language. Using the El Centro earthquake, seismic analyses are performed for the simplified and detailed core shroud models. Modal characteristics are obtained and their results are used for a time history analysis. Response spectrum analyses are also performed to access the degree of seismic excitation. The results of these analyses are compared to investigate the response characteristics between the simplified and detailed core shroud models from the time history and response spectrum analyses.

• Coupled systems mechanics
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• v.1 no.1
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• pp.1-7
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• 2012

The problem of laterally loaded piles is particularly a complex soil-structure interaction problem. The flexural stresses developed due to the combined action of axial load and bending moment must be evaluated in a realistic and rational manner for safe and economical design of pile foundation. The paper reports the finite element analysis of pile groups. For this purpose simplified models along the lines similar to that suggested by Desai et al. (1981) are used for idealizing various elements of the foundation system. The pile is idealized one dimensional beam element, pile cap as two dimensional plate element and the soil as independent closely spaced linearly elastic springs. The analysis takes into consideration the effect of interaction between pile cap and soil underlying it. The pile group is considered to have been embedded in cohesive soil. The parametric study is carried out to examine the effect of pile spacing, pile diameter, number of piles and arrangement of pile on the responses of pile group. The responses considered include the displacement at top of pile group and bending moment in piles. The results obtained using the simplified approach of the F.E. analysis are further compared with the results of the complete 3-D F.E. analysis published earlier and fair agreement is observed in the either result.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.11
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• pp.1191-1198
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• 2015

In this paper, we develop simplified finite element (FE) models for butt-, lap- and T-welded joints by performing numerical and experimental experiments. Three-point bending tests of butt- and lap-welded specimens are performed to obtain the stiffness of the specimens and the strains at points near the welding beads. Similarly the stiffness and strains of T-welded specimen are measured by applying a point load at the end of the specimen. To develop simplified FE models, we consider the shape parameters of width, thickness and the angle of weld elements in the numerical simulations. The shape parameters of the simplified FE models are determined by building linear regression models for the experimental data sets.