• Smart Structures and Systems
• /
• v.25 no.1
• /
• pp.65-80
• /
• 2020

In order to protect a structure over its full life cycle, a novel tuned mass damper (TMD), the so-called semi-active eddy current pendulum tuned mass damper (SAEC-PTMD), which can retune its frequency and damping ratio in real-time, is proposed in this study. The structural instantaneous frequency is identified through a Hilbert-Huang transformation (HHT), and the SAEC-PTMD pendulum is adjusted through an HHT-based control algorithm. The eddy current damping parameters are discussed, and the relationship between effective damping coefficients and air gaps is fitted through a polynomial function. The semi-active eddy current damping can be adjusted in real-time by adjusting the air gap based on the linear-quadratic-Gaussian (LQG)-based control algorithm. To verify the vibration control effect of the SAEC-PTMD, an idealized linear primary structure equipped with an SAEC-PTMD excited by harmonic excitations and near-fault pulse-like earthquake excitations is proposed as one of the two case studies. Under strong earthquakes, structures may go into the nonlinear state, while the Bouc-Wen model has a wild application in simulating the hysteretic characteristic. Therefore, in the other case study, a nonlinear primary structure based on the Bouc-Wen model is proposed. An optimal passive TMD is used for comparison and the detuning effect, which results from the cumulative damage to primary structures, is considered. The maximum and root-mean-square (RMS) values of structural acceleration and displacement time history response, structural acceleration, and displacement response spectra are used as evaluation indices. Power analyses for one earthquake excitation are presented as an example to further study the energy dissipation effect of an SAECPTMD. The results indicate that an SAEC-PTMD performs better than an optimized passive TMD, both before and after damage occurs to the primary structure.

• Journal of the Korean Regional Science Association
• /
• v.34 no.4
• /
• pp.49-60
• /
• 2018

To restore urban water cycle, it is necessary to improve domestic laws and regulations related to LID(Low Impact Development), which has been successfully applied to foreign countries. Thus, this study has intended to evaluate domestic legal systems related to space and environmental planning and to suggest directions to improve laws and regulations related to space and environmental planning toward extended application of LID in Korea. To reach this goal, this study has analyze the legal and institutional status of the foreign countries where LID has currently been applied, to derive the factors that laws and institutions are required to support LID based on the above analysis, to evaluate domestic laws and regulations related to space and environmental planning, and to suggest directions to improve the laws and regulations. After the evaluation, this study has found the following results. First, it was found that the concept and basic principles of LID and LID planning and associated methods were no longer mirrored in the space planning-related laws and regulations. However, these problems are not confined to LID, and result from thefailurein applying environmental planning to space planning overall. Second, it was revealed that the environmental planning-related laws and regulations defined the terminologies and targets of LID and suggested different measures to improve LID-related policies differently depending on the backgrounds ofenforcing thelaws and regulations and on environmental properties. Finally, this study has suggested the directions to improve laws and regulations related to space and environmental planning as follows. First, it is necessary to enact a law to support the extended application of LID. Second, the law to be enacted should be connected to laws, enforcement ordinances and regulations, and guidelines related to space planning. Third, environmental benefits provided by both structural and non-structural techniques of LID should be quantitatively measured.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.4
• /
• pp.56-64
• /
• 2021

Leakage due to deterioration and damage is one of the major causes of volume change by freezing and thawing, and it leads micro-cracking and surface scaling in concrete structures. The deterioration of damaged concrete accelerates with the chloride attack. Thus, in the detailed guidelines for facility performance evaluation (2020), the quality of cover concrete and the freeze-thaw (FT) repetition cycle were newly suggested for concrete durability assessment. The quality of cover concrete should be evaluated by the rebound hammer test and the FT repetition cycle should be also considered in the deterioration environmental assessment. This study suggested the application of fast dynamic based nonlinear ultrasound method to monitor initial micro-scale damage under freezing and thawing environment. Concrete specimens were fabricated with different water-cement ratios (40%, 60%) and air contents (1.5% and 3.0%). The compressive strength, rebound number, relative dynamic modulus, and nonlinear ultrasound were measured with different FT cycles. The scanning electron microscopy was also performed to investigate the micro-scale FT damage. As a result, both the rebound number and the relative dynamic modulus had difficulty to detect early damage but the proposed method showed a potential to detect initial micro-scale damage and predict the FT resistance performance of concrete.

• International Journal of Highway Engineering
• /
• v.18 no.4
• /
• pp.19-28
• /
• 2016

PURPOSES : Long-life asphalt pavements are used widely in developed countries. In order to be able to devise an effective maintenance strategy for such pavements, in this study, we evaluated the performance of the long-life asphalt pavements constructed along the national highways in South Korea. Further, an economic evaluation of the long-life asphalt pavements was performed based on a life-cycle cost analysis. We aimed to devise a model for evaluating the performance of long-life asphalt pavements using the national highway pavement management system (PMS) database as well as for analyzing the economic feasibility of such pavements, in order to promote their use in South Korea. METHODS : The maintenance history and pavement performance data were obtained from the national highway PMS database. The pavement performances for a total of 292 sections of 10 lanes (5 northbound lanes and 5 eastbound lanes) of national highways were used in this study. Models to predict the performances of hot mix asphalt (HMA) and long-life asphalt pavements under two distinct traffic conditions were developed using a simple regression method. Further, the economic feasibility of long-life asphalt pavements was evaluated using the Korea Pavement Management System (KoPMS). RESULTS : We developed service-life prediction models based on the traffic volume and the equivalent of single-axle load and found that long-life asphalt pavements have service lives 50% longer than those of HMA pavements. Further, the results of the economic analysis showed that long-life asphalt pavements are superior in terms of various economic indexes, including user cost, delay cost, total cost, and user benefits, even though their maintenance cost is higher than that of HMA pavements. A comparison of the economic feasibilities of the various groups showed that group A is superior to HMA pavements in all aspects except in terms of the maintenance criterion (crack 20% or higher) as per the NPV index. However, the long-life asphalt pavements in group B were superior in terms of the maintenance criterion (crack 25% or higher) regardless of the economic feasibility. CONCLUSIONS : The service life of long-life asphalt pavements was found to be approximately 50% longer than that of HMA pavements, regardless of the traffic volume characteristics. The economic feasibility of long-life asphalt pavements was evaluated based on the KoPMS. The results of the economic analysis were the following: long-life asphalt pavements are exceptional in terms of almost all factors, such as user cost, delay cost, total cost, and user benefit; however, the exception is the maintenance cost. Further, the economic feasibility of the long-life asphalt pavements in group B was found to be better than that of the HMA pavements (crack 25% or higher).

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.5
• /
• pp.502-509
• /
• 2019

Studies have been made on performance evaluation of expansion joint systems for an ordinary highway or road bridge. However little study has been made for runway connection bridges at airports. A study on performance evaluated from computer code analysis and shrinkage, extension, and compression repetition tests based on KS F 4425 is conducted to a newly developed expansion joint system which has been installed in a runway connection bridge at Incheon Airport Extension 2 Construction Site. The MIDAS computer code is used to analyze the performance before the manufacture of the mock-up of expansion joint system on the basis of design requirements. Tests based on the KS F 4425 of 2001 year-version are conducted for the mock-up. Domestic codes and standards to validate the performance of the expansion joint system in a connection bridge have been developed for a vehicle. However the expansion joint system tested in this study is installed in a runway connection bridge for an aircraft. Conservatively the heaviest one among airplanes departing and landing at Incheon Airport is assumed level-F $468.4kN/m^2$ and adopted for the tests and analyses in this study. KS F 4425 method is selected for the shrinkage, extension, and compression repetition tests. No remarkable problem was observed for the 2,500-cycle shrinkage and extension and two million-cycle repeatition load tests. The results of this study are expected to contribute to establishment of code and standard for the performance validation of an expansion joint system installed in a runway connection bridge for an aircraft by providing performance test results and computer analysis results based on finite element methods.

• Journal of Welding and Joining
• /
• v.26 no.3
• /
• pp.67-73
• /
• 2008

Fatigue life evaluation of welded structures in a range of high cycles is one of the most difficult problems since extremely small plastic deformation and damage occur during the loading cycles. Moreover, it is very difficult to identify the strong non-linearities of welding, inducing residual stress. In this paper, numerical fatigue test method for welded structures was developed using continuum damage mechanics with inherent strain. Recently, continuum damage mechanics, which can simulate both crack initiation at the micro-scale level and crack propagation at the meso-scale level, has been adopted in the fracture related problem. In order to consider the residual stresses in the welded strictures, damage calculation in conjunction with welding, inducing inherent strain, was proposed. The numerical results obtained from the damage calculation were compared to experimental results.

• Korean Journal of Computational Design and Engineering
• /
• v.15 no.2
• /
• pp.94-105
• /
• 2010

Todays, there is fast transition about the new manufacturing IT methodologies from the conceptual phase into the practical application phase for the strengthening of enterprise competitiveness in manufacturing industry. One of those new methodologies is PLM (Product Life-cycle Management). PLM methodology consists of 3D CAD for the product design, PDM (Product Data Management) for the data management based on the collaboration platform and lastly DM (Digital Manufacturing). DM has evoluted from the stand-alone computer simulation of early 1980s, and now it covers the overall production development and production. Unfortunately, there exist serious critical problems about the actual application of DM for the real work. This is owing to the transition of the point of view from stand-alone type application (such as flow simulation or robot simulation) to that of business process about product development and production management. In this paper, we propose an application framework for the successful project with the digital manufacturing methodology with the concept of Information Strategy Planning, which enables the systematic diagnosis and the quantitative evaluation. Also, we introduce the actual practice of the proposing framework with the ISP project for 'Analysis & Simulation Technique of manufacturing process project' that is being conducted by Chungnam Techno Park.

• Asian-Australasian Journal of Animal Sciences
• /
• v.22 no.1
• /
• pp.57-71
• /
• 2009

Crop-livestock mixed farming systems depend on the efficiency with which nutrients are conserved and recycled. Home-grown forage is used as animal feed and animal excretions are applied to cultivated crop lands as manure. The objective of this study was to develop a mixed farming system model for dairy cattle in Japan. The model consisted of four sub-models: the nutrient requirement model, based on the Japanese Feeding Standards to determine requirements for energy, crude protein, dry matter intake, calcium, phosphorus and vitamin A; the optimum diet formulation model for determining the optimum diets that satisfy nutrient requirements at lowest cost, using linear programming; the herd dynamic model to calculate the numbers of cows in each reproductive cycle; and the whole farm optimization model to evaluate whole farm management from economic and environmental viewpoints and to optimize strategies for the target farm or system. To examine the model' validity, its predictions were compared against best practices for dairy farm management. Sensitivity analyses indicated that higher yielding cows lead to better economic results but higher emvironmental load in dairy cattle systems integrated with forage crop production.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.42 no.2
• /
• pp.311-326
• /
• 2018

The satisfaction of wearing an outfit in daily life can lead to the attitude toward the clothes and further the brand image and repeat purchases; however, satisfaction generated from the moment the outfit was purchased is only temporary. Therefore, it would be necessary to study the antecedent variables that precede daily outfit satisfaction. In the current study, to understand the antecedent variables that influence the daily outfit satisfaction of consumers, in-depth interviews were conducted on thirteen women in their 20s and 30s. The results showed that peoples' outfit satisfaction was dependent on a comparison between their prior expectation and the performance of the outfit based on expectation-performance disconfirmation. The outfit performance was evaluated by themselves or others. Simultaneously, it was found that the others' opinion on the clothes and surroundings influence daily outfit satisfaction. This research helps deepen the understanding on the individual and social influential factors of the temporary satisfaction from purchase to the satisfaction of actually using clothes. This result ultimately intensifies the understanding on the consumption and evaluation of clothes in the whole life cycle of clothing products from purchase to disposal.

• Journal of Welding and Joining
• /
• v.14 no.5
• /
• pp.122-133
• /
• 1996

In order to evaluate the cryogenic fracture characteristics of structural steels for superconducting magnets of fusion reactor, small punch (SP) testing was performed on austenitic stainless steel (JN1 base metal) and its TIG weldments at 293K, 77K and 4K. The mechanical properties with respect to the extracted location of the weld metal, on the effects of welding heat cycle about base metal near fusion line in TIG weldments were investigated. The mechanical property of the weld metal in TIG weldments depends on distance from welding root, root region of weldments having the lowest mechanical property. The base metal near fusion line showed degradation of mechanical property caused by cyclic heating during the TIG welding. Based on the test results, HAZ was found to be up to 5mm from the fusion line. It is shown that SP testing is a useful tool to evaluate the mechanical properties with respect to the microstructures changes such as HAZ as well as weld metal in TIG weldments at cryogenic temperature.