• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.794-803
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• 2021

The instantaneous acceleration affects the performance of the water-jet pump obviously. Here, based on the user-defined function, the method to simulate the inner flow in water-jet pumps under acceleration conditions was established. The effects of two different acceleration modes (linear acceleration and exponential acceleration) and three kinds of different acceleration time (0.5s, 1s and 2s) on the performance of the water-jet pump were analyzed. The results show that the thrust and the pressure pulsation under exponential acceleration are lower than that under linear acceleration at the same time; the vapor volume fraction in the impeller under linear acceleration is 27.3% higher than that under exponential acceleration. As the acceleration time increases, the thrust gradually increases and the pressure pulsation amplitude at the impeller inlet and outlet gradually decreases, while the law of pressure pulsation is the opposite at the diffuser outlet. The main frequency of pressure pulsation at the impeller outlet is different under different acceleration time. The research results can provide some reference for the optimal design of water-jet pumps.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.15 no.5
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• pp.1-17
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• 2012

This study sought to discover new directions for management and operation national urban parks in Korea by analyzing the reality of the national government parks of Japan where these parks are already well established and managed. In the case of a Japanese national government park, its supporting system was established after the park was built. The means of management also shifted their direction from putting more priority to the administrative body to the residents. The management practices are changing process of its character with focus on residents as the main entity of activity from their existing position of participants. In other words, the national government parks of Japan are going beyond the previous practice of providing maintenance activities to providing experience, interpretation functions to these activities. Especially, they were establishing local networks to plan and execute programs in collaboration with the park management and NPOs. However, they fall short of tangible outcomes despite their continuous efforts to expand the community involvement and reduce the cost in maintenance. To facilitate the effective management of the urban parks in Korea in the near future, much thought needs to go into the management practices ensuring conservation of resources in the land of Korea, as well as people's use of recreation, community revitalization, and development and transfer of advanced technology to provide appropriate preparations to create urban parks in Korea.

• International conference on construction engineering and project management
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• 2005.10a
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• pp.447-451
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• 2005

The purpose of this study is to improve regulations such as law and standard contract forms related to defects liability in Korea. Defects liability has been one of the major causes of construction contract disputes in Korea in recent years. It is important to avoid or resolve disputes regarding defects liability through regulations containing clear criteria and to specify the standard regarding the mitigation and remission of the contractor's defects liability. This study was carried out through document research and analysis of judicial precedents. The following are the courses of improvement regarding the mitigation and remission of defects liability in Korea. First, laws and standard contract forms must contain more detailed clauses regarding exemption of a contractor's defects liability, which clearly set out the scope of the defects liability of the contractor. Second, the current system for defects liability favors the owner rather than the contractor - it is necessary to change the defects liability system in order to give the owner and the contractor an equal standing. Third, strict liability is taken on by the contractor even when the term of guarantee for defects lasts longer than the legally set period of liability for defects. Hence, it is necessary to improve the system by alleviating the liability of the contractor through applying negligence liability as opposed to strict liability during the term of guarantee.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.835-850
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• 2019

The numerical simulations for the Vortex-induced Vibration (VIV) of the cylinders with different combinations of mass ratio and frequency ratio were performed under the Reynolds (Re) number ranges of 1450-10200, 5800-40800 and 13050-91800 by using the embedded programs in OpenFoam. By combining with the modified SST k-ω turbulence model, the coupled Unsteady Reynolds-Average Navier-Stokes equations and double-degree-of-freedom vibration equations were solved. After analyzing the results, it is found that the some characteristics of the VIV have changed with the increase of the range of Re number, and the effects of Re number on vibration characteristics are also different under different combinations of mass ratio and frequency ratio. On this basis, the influence law of Re number on the characteristics of VIV of the cylinders is summarized, which can provide a reference for the research of VIV under higher Re number.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.34 no.12
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• pp.21-30
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• 2018

The traditional market has formed for itself through a long time thus has special value of the place. The tangible value of the traditional market is high, however, it became jeopardized to be dismantled since it can not cope with the consumption environment of modern society. Modern industrial society provides an inefficiently and standardized solution to the traditional market by ignoring the identity of place only by the value the traditional market in the law of large distribution industry. This study aims to define the placeness of Namdaemun traditional market by considering tangible value of place. The identity of the place was analyzed as a spatial configuration, space organization, and sense of place through the place's physical setting, activities, and meanings by Edward Ralph. Based on the analysis by Ralph, we analyzed the traditional market and compare to the department store, which is the representative of large scale distributor, using comparative method. We performed quantitative and integrative analysis for the placeness and provide a way to appraise the worth of the traditional market by deviating from the traditional evaluation method.

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.717-728
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• 2023

The effect of temperature dependent material properties on the free vibration of FG porous beams is investigated in the present paper. A quasi-3D shear deformation solution is used involves only three unknown function. The mechanical properties which are considered to be temperature-dependent as well as the porosity distributions are assumed to gradually change along the thickness direction according to defined law. The beam is supposed to be simply supported and lying on variable elastic foundation. The differential equation system governing the free vibration behavior of porous beams is derived based on the Hamilton principle. Navier's method for simply supported systems is then used to determine and compute the frequencies of FG porous beam. The results of the present formulation are validated by comparing with those available literatures. Finally, the effects of several parameters such as porosity distribution and the parameters of variable elastic foundation on the free vibration behavior of temperature-dependent FG beams are presented and discussed in detail.

• Advances in nano research
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• v.16 no.3
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• pp.251-263
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• 2024

This article investigates the free vibration behavior of carbon nanotube reinforced composite (CNTRC) beams embedded using variational analytical methods and artificial neural networks (ANN). The material properties of layered functionally graded CNTRC (FG-CNTRC) beams are estimated using nonlocal parameters modified power-law with different types of CNT distributions through the thickness direction of the beam. Adopting Eringen's nonlocal elasticity theory to capture the small size effects, the nonlocal governing equations are derived and solved using the analytical method. And also, the problem was analyzed using the ANN method. The architecture of the proposed ANN model is 3-9-1. In the experiments, we used 112 different data to predict the natural frequency using ANN. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion as well as the boundary conditions of the beam are derived using Hamilton's principle. The classical beam theory is used to formulate a governing equation for predicting the free vibration of laminated CNTRC beams. According to the experimental results, the prediction ability of the ANN model is very good and the natural frequency can be predicted in ANN without attempting any experiments.

• Journal of the Architectural Institute of Korea Planning & Design
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• v.33 no.12
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• pp.3-11
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• 2017

The non-mandatory guidance and illogical ordinance of local government generate complicated and vague regulations and procedures. These cause inconvenience in building administration, and give rise to unnecessary social and administrative expenses. The purpose of this study is to suggest the improvement of building administration by local government from an institutional point of view through the literature review and the specialist survey focusing on the problems arising from the building ordinances and non-mandatory guidance. The results of this study are as follows; In the first place, the connection between law and ordinance should be improved in a systematic, definitude manner and high-degree of completion. Second, the monitoring management system should be arranged in order to excavate and improve the non-mandatory guidance. Third, the effort should go into improving ability and disposition of building official. Fourth, it is necessary to materialize and clarify the regulatory contents and adjust them to fit the legal system. Lastly, it is important to reinforce incentives and procedures of verification in order to manage building ordinances of legal government's own free will. In order to improve of building administration by local government, it is necessary to make the structure of sustainable improvement and discuss not only institutional aspect but also elements of building administration in later study.

• Geomechanics and Engineering
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• v.30 no.1
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• pp.27-44
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• 2022

Gravelly soil is a kind of special geotechnical material, which is widely used in the subgrade engineering of railway, highway and airport. Its mechanical properties are very complex, and will greatly influence the stability of subgrade engineering. To investigate the mechanical properties and failure mechanism of gravelly soils, this paper introduced and verified a new discrete element method (DEM) of gravelly soils in large scale direct shear test, which considers the actual shape and broken characteristics of gravels. Then, the stress and strain characteristics, particle interaction, particle contact force, crack development and energy conversion in gravelly soils during the shear process were analyzed using this method. Moreover, the effects of gravel content (GC) on the mechanical properties and failure characteristics were discussed. The results reveal that as GC increases, the shear stress becomes more fluctuating, the peak shear stress increases, the volumetric strain tends to dilate, the average particle contact force increases, the cumulative number of cracks increases, and the shear failure plane becomes coarser. Higher GC will change the friction angle with a trend of "stability", "increase", and "stability". Differently, it affects the cohesion with a law of "increase", "stability" and "increase".

• Steel and Composite Structures
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• v.13 no.5
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• pp.409-421
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• 2012

Recently, as the height of building is getting higher, the applications of CFST column for high-rise buildings have been increased. In structural system of high-rise building, The RC core and exterior concrete-filled tubular (CFST) column-beam pinned connection is one of the structural systems that support lateral load. If this structural system is used, due to the minimal CFST column thickness compared to that of the CFST column width, the local moment occurred by the eccentric distance between the column flange surface from shear bolts joints degrades the shear strength of the CFST column-beam pinned connections. This study performed a finite element analysis to investigate the shear strength under eccentric moment of the CFST column-beam pinned connections. The column's width and thickness were used as variables for the analysis. To guarantee the reliability of the finite element analysis, an actual-size specimens were fabricated and tested. The yield line theory was used to formulate an shear strength formula for the CFT column-beam pinned connection. the shear strength formula was suggested through comparison on the results of FEM analysis, test and yield lime theory, the shear strength formula was suggested.