• Journal of Korea Water Resources Association
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• v.34 no.5
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• pp.415-426
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• 2001

After Disaster Impact Assessment(DIA) Program was particed, the wide variety of hydrological data are estimated by introducing the concept of critical storm duration to calculate the stormwater impoundments as the alternative of increasing runoff due to many developments. Critical storm duration is varied by a lot of hydraulic structures, drainage characteristics, temporal distribution of design rainfall, return period, and runoff models. In this study the methods of estimating the proper volume to design the stormwater impoundments are proposed to determine the required volume by comparing and analyzing the maximum stormwater impoundments in accordance with the impoundment volume and rainfall duration by using the concept of storage ratio presented in the existing studies. The methods of determining the critical storm duration of design rainfall which cause the maximum load from the runoff hydrograph will be studied as analyzing rainfall-runoff using the various runoff models and observed data.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.667-674
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• 2011

This paper discusses the analysis method of prestressed concrete girder integral abutment bridges for a 75-year bridge life and the development of prediction models for abutment displacements under thermal loading due to annual temperature fluctuation and time-dependent loading. The developed nonlinear numerical modeling methodologies considered soil-structure interaction between supporting piles and surrounding soils and between abutment and backfills. Material nonlinearity was also considered to simulate differential rotation in construction joints between abutment and backwall. Based on the numerical modeling methodologies, a parametric study of 243 analysis cases, considering five parameters: (1) thermal expansion coefficient, (2) bridge length, (3) backfill height, (4) backfill stiffness, and (5) pile soil stiffness, was performed to established prediction models for abutment displacements over a bridge life. The parametric study results revealed that thermal expansion coefficient, bridge length, and pile-soil stiffness significantly influenced the abutment displacement. Bridge length parameter significantly influenced the abutment top displacement at the centroid of the superstructure, which is similar to the free expansion analysis results. Developed prediction model can be used for a preliminary design of integral abutment bridges.

• Structural Engineering and Mechanics
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• v.38 no.4
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• pp.479-501
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• 2011

Even though fiber reinforced polymer (FRP) has been widely used as a retrofitting material, the FRP behavior and effect in FRP retrofitted structure under blast loading, impulsive loading with instantaneous time duration, has not been accurately examined. The past studies have focused on the performance of FRP retrofitted structures by making simplifications in modeling, without incorporating accurate failure mechanisms of FRP. Therefore, it is critical to establish an analytical model that can properly consider the specific features of FRP material in evaluating the response of retrofitted concrete structures under blast loading. In this study, debonding failure analysis technique for FRP retrofitted concrete structure under blast loading is suggested by considering FRP material characteristics and debonding failure mechanisms as well as rate dependent failure mechanism based on a blast resisting design concept. In addition, blast simulation of FRP retrofitted RC panel is performed to validate the proposed model and analysis method. For validation of the proposed model and analysis method, the reported experimental results are compared with the debonding failure analysis results. From the comparative verification, it is confirmed that the proposed analytical model considering debonding failure of FRP is able to reasonably predict the behavior of FRP retrofitted concrete panel under blast loading.

• Tribology and Lubricants
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• v.23 no.5
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• pp.219-227
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• 2007

The dynamic performance of air foil bearings relies on a coupling between a thin air film and an elastic foil structure. A number of successful analytical techniques to predict dynamic performance have been developed. However, the evaluation of its dynamic characteristic is still not enough because of the mechanical complexity of the foil structure and strong nonlinear behavior of friction force. This work presents a nonlinear transient analysis method to predict dynamic performance of foil bearings. In this method, time dependent Reynolds equation is used to calculate pressure distribution and a finite element method is used to model the bump foil structure. The analysis is treated with a direct implicit integration technique that can handle nonlinear problems and the stick-slip algorithm is used to consider friction force. Using this method the response to the mass unbalance excitation is investigated for various design parameters and operating conditions. The results of analysis show that foil bearing is very effective on the restriction of vibration at the resonance frequency compared to the rigid surface bearings and the effectiveness depends on the operating conditions, static load and a amount of mass unbalance. In addition, there exist optimum values of friction coefficient, bump foil stiffness and number of circumferential slit with regards to minimizing dynamic response at the resonance frequency. These optimum values are system dependent.

• Land and Housing Review
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• v.2 no.2
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• pp.195-204
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• 2011

During mechanical demolition of RC structures, weights of dismantling equipment and demolition waste of building are applied to unexpected load which did not be considered during the design of structural member. Nevertheless, the loading of dismantling equipment and dismantling process are mainly dependent on field managers' field workers' or experiences without considering safety of structural member by a structural engineer. It is urgently required that reflecting actual circumstance of mechanical demolition, safety evaluation method to evaluate the safety and the guideline for appropriate capacity of structural member to support dismantling equipment weight, be provided. Through site investigation and questionnaire on field workers, this paper proposed demolition waste load, load factor, strength reduction factor, and so on. These are essential to safe evaluation of a building, ready to demolition. Considering actual circumstance of mechanical demolition, safety evaluation method of building and design method of slab and beam was suggested to a dilapidated building. An capability to loading of dismantling equipment was proposed, applied to RC slab and RC beam. Therefore, the suggested safety evaluation method and the guideline for an capability to loading of dismantling equipment weight can reasonably evaluate the capacity of structural member in demolition and use effectively as increasing efficiency and improving safety of demolition through proper management of dismantling equipments.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.51 no.9
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• pp.433-440
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• 2002

The addition of switches to a distribution feeder does, in general, increase reliability by decreasing the duration of the outage of many to the customers on the feeder. To cover its service area so that feeder-level delivery reaches sufficiently close to all customers, feeders typically split their routes many times, in what is often called a lateral feeder. It is interesting to note, however, that the effectiveness of a switch is very much dependent on the types of lateral feeder. The types of lateral are classified into two types. The first is loop lateral feeder that can connect its load to an adjacent feeder through a tie line in case that a fault occurs in its feeder and it is laid out so that every feeder has complete fault backup through re-switching of its loads to other sources like a main feeder The second is the radial lateral feeder cannot connect its load to an adjacent line, no provision is made for contingency backup of feeders. There are no other circuits in the radial lateral feeder form which to restore power. In this study, we evaluate the effectiveness of a switch installation between on the radial and loop lateral feeders to increase reliability by decreasing the duration of the outage. These results can help power utility to design the switch layouts on the radial and loop lateral feeder system.

• Journal of Korean Society of Steel Construction
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• v.12 no.6
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• pp.759-767
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• 2000

In this study, the time dependent internal stress changes of a Concrete Filled Steel Tube(CFT) column during a fire test were quantitatively analyzed. The strain ratio of a CFT column on the different loads was measured by tensile strength tests in terms of yield strength, tensile strength average extensibility and elasticity modulus. To understand the internal material properties change of concrete in CFT column damaged due to a fire, the compressive strength and elastic modulus tests were measured on a core sample from the center of the steel tube after the fire test. The elastic modulus test measured the strain from the stress. To determine the fire temperature of the test material, a differential thermal analysis was done. From the tested result, the gained data were conducted and an analysis method was suggested. The purpose of this work is to suggest a basic data for structure regulation enactments of the internal fire design of CFT.

• Journal of the Korea Society of Computer and Information
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• v.19 no.12
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• pp.1-10
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• 2014

This paper proposes a scheduling scheme that enhances power consumption efficiency of periodic real-time tasks using DVFS and power-shut-down mechanisms while meeting their deadlines on multicore processors. The proposed scheme is suitable for dependent multicore processors in which processing cores have an identical speed at an instant, and resolves the load unbalance of processing cores by exploiting parallel processing because the load unbalance causes inefficient power consumption in previous methods. Also the scheme activates a part of processing cores and turns off the power of unused cores. The number of activated processing cores is determined through mathematical analysis. Evaluation experiments show that the proposed scheme saves up to 77% power consumption of the previous method.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.2
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• pp.85-91
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• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2699-2708
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• 2020

Helical-coil steam generator (HCSG) technology is a major design candidate for small modular reactors due to its compactness and capability to produce superheated steam with high generation efficiency. In this paper, we investigate the feasibility of the passively autonomous power maneuvering by coupling the 3-D transient multi-physics of a soluble-boron-free (SBF) core with a time-dependent HCSG model. The predictor corrector quasi-static method was used to reduce the cost of the transient 3-D neutronic solution. In the numerical system simulations, the feedwater flow rate to the secondary of the HCSGs is adjusted to extract the demanded power from the primary loop. This varies the coolant temperature at the inlet of the SBF core, which governs the passively autonomous power maneuvering due to the strongly negative coolant reactivity feedback. Here, we simulate a 100-50-100 load-follow operation with a 5%/minute power ramping speed to investigate the feasibility of the passively autonomous load-follow in a 450 MW_th SBF PWR. In addition, the passively autonomous frequency control operation is investigated. The various system models are coupled, and they are solved by an in-house Fortran-95 code. The results of this work demonstrate constant steam temperature in the secondary side and limited variation of the primary coolant temperature. Meanwhile, the variations of the core axial shape index and the core power peaking are sufficiently small.