• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.513-525
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• 2018

A 3 dimensional numerical analysis for shield TBM tunnel should take into account various characteristics of the shield TBM excavation, such as gap, tail void, segment installation, and backfill injection. However, analysis method considering excavation characteristics are generally mixed with various method, resulting in concern of consistency and reliability degradation of the analytical results. In this paper, a parametric study is carried out by using actually measured ground settlement data on various methods that can be used for 3 dimensional numerical analysis of shield TBM tunneling. As a result, we have analyzed and arranged an analytical method to predict similarly the behavior of ground settlement and tunnel face pressure at the design stage. Skin plate pressure, backfill pressure and soil model have been identified as the most significant influences on the ground settlement. The grout pressure model is considered to be applicable when there is no volume loss information on the excavated ground, such as seabed tunnels, or when it is important to identify the behavior around a tunnel, such as surface settlement as well as face pressure. And it is considered that designers can use these guidelines as a base material to perform a reasonable 3 dimensional numerical analysis that reflects the ground conditions and the features of the shield TBM tunneling.

• Ocean Systems Engineering
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• v.1 no.4
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• pp.285-296
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• 2011

Spar platforms have several advantages for deploying wind turbines in offshore for depth beyond 120 m. The merit of spar platform is large range of topside payloads, favourable motions compared to other floating structures and minimum hull/deck interface. The main objective of this paper is to present the response analysis of the slack moored spar platform supporting 5MW wind turbine with bottom keel plates in regular and random waves, studied experimentally and numerically. A 1:100 scale model of the spar with sparD, sparCD and sparSD configuration was studied in the wave basin ($30{\times}30{\times}3m$) in Ocean engineering department in IIT Madras. In present study the effect of wind loading, blade dynamics and control, and tower elasticity are not considered. This paper presents the details of the studies carried out on a 16 m diameter and 100 m long spar buoy supporting a 90 m tall 5 MW wind turbine with 3600 kN weight of Nacelle and Rotor and 3500 kN weight of tower. The weight of the ballast and the draft of the spar are adjusted in such a way to keep the centre of gravity below the centre of buoyancy. The mooring lines are divided into four groups, each of which has four lines. The studies were carried out in regular and random waves. The operational significant wave height of 2.5 m and 10 s wave period and survival significant wave height of 6 m and 18 s wave period in 300 m water depth are considered. The wind speed corresponding to the operational wave height is about 22 knots and this wind speed is considered to be operating wind speed for turbines. The heave and surge accelerations at the top of spar platform were measured and are used for calculating the response. The geometric modeling of spar was carried out using Multisurf and this was directly exported to WAMIT for subsequent hydrodynamic and mooring system analysis. The numerical results were compared with experimental results and the comparison was found to be good. Parametric study was carried out to find out the effect of shape, size and spacing of keel plate and from the results obtained from present work ,it is recommended to use circular keel plate instead of square plate.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.8
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• pp.860-865
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• 2006

The characteristics of flow field and turbulent mixing efficiency of SS in non-aerated contacting reactor are critical design parameters directly affecting on the efficiency of the overall process of wastewater treatment system. To this end, in this study numerical fluid dynamic calculation has been made to investigate the flow field and concentration distribution of SS in terms of specification(shape and dimension) of impeller and other operating conditions. As the first step, the performance of the computer program developed was successfully evaluated by the comparison of the typical flow field with the type of impeller with that appeared in open literature. Further, a series of parametric investigations are made in terms of interesting parameters such as the type and dimension of impeller, location, and number of impeller, etc. A number of useful conclusions obtained by numerical calculation are the superiority of mixing efficiency of pitched type than the flat one together with the visible increase of the overall mixing effect by the employment of the larger impeller and increase of the impeller number, etc.

• The Journal of the Korea Contents Association
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• v.14 no.6
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• pp.367-384
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• 2014

This study addresses an empirical issue which has been received little attention in the contemporary finance literature: To identify any financial determinants of the profitability indices for the firms belonging to the Korean chaebol. Three hypotheses of concern were postulated and tested for the sample firms covering the periods of the pre-and post-financial global crises. Regarding the results on the 1st hypothesis test of characterizing any financial profiles for the firms (belonging to the chaebols) by estimating a legitimate panel data model: the present study found the statistically significant relationships of the explanatory variables (BVLEVl, MVLEVl, MV/BV, RISK, FCFF and FOS) with the book-value based profitability ratio: while the market-valued profitability index was explained only by BVLEV2. Regarding the 2nd hypothesis test for the profitability of the sample firms at the industry level: the chaebol firms in the chemical and the food industries overall positioned themselves into the top ranks in order, which was tested by the ANCOVA and the Tukey multiple comparison procedure. Finally: on the 3rd hypothesis test for the 'adjusted' Dupont system, only two such as the 'operating margin' and the 'asset turnover' showed their significant effects between the chaebol firms and their counterparts in both the (parametric) independent samples t-test and the (nonparametric) Wilcoxon-Mann-Whitney statistics.

• Clean Technology
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• v.26 no.1
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• pp.72-78
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• 2020

The use of fossil fuel and biogas production causes air pollution and climate change problems. Research endeavors continue to focus on converting methane and carbon dioxide, which are the major causes of climate change, into quality energy sources. In this study, a novel plasma-carbon converter was proposed to convert biogas into high quality gas, which is linked to photovoltaic and wind power and which poses a problem on generating electric power continuously. The characteristics of conversion and gas production were investigated to find a possibility for biogas conversion, involving parametric tests according to the change in the main influence variables, such as O₂/C ratio, total gas feed rate, and CO₂/CH₄ ratio. A higher O₂/C ratio gave higher conversions of methane and carbon dioxide. Total gas feed rate showed maximum conversion at a certain specified value. When CO₂/CH₄ feed ratio was decreased, both conversions increased. As a result, the production of solar fuel by plasma oxidation destruction-carbon material gasification conversion, which was newly suggested in this study, could be known as a possibly useful technology. When O₂/C ratio was 0.8 and CO₂/CH₄ was 0.67 while the total gas supply was at 40 L min^-1 (VHSV = 1.37), the maximum conversions of carbon dioxide and methane were achieved. The results gave the highest production for hydrogen and carbon dioxide which were high-quality fuel.

• Geotechnical Engineering
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• v.14 no.2
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• pp.107-126
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• 1998

Ground settlements induced by tunnel excavation cause the foundations of the neighboring building structures to deform. An expert system called NESASS( Neural network Expert System for Adjacent Structure Safety analysis) was developed to analyze the structural safety of such building structures. NESASS predicts the trend of ground settlements resulting from tunnel excavation and carries out a safety analysis for building structures on the basis of the predicted ground settlements. Using neural network technique. the NESASS learns the database consisting of the measured ground settlements collected from numerous actual fields and infers a settlement trend at the field of interest. The NESASS calculates the magnitudes of angular distortion, deflection ratio, and differential settlement of the structure. and in turn, determines the safety of the structure. In addition, the NESASS predicts the patterns of cracks to be formed in the structure, using Dulacska model for crack evaluation. In this study, the ground settlements measured from Seoul subway construction sites were collected and classified with respect to the major factors influencing ground settlement. Subsequently, a database of ground settlement due to tunnel excavation was built. A parametric study was performed to select the optimal neural network model for the database. A comparison of the ground settlement predicted by the NESASS with the measured ones indicates that the NESASS leads to reasonable predictions. The results of confidence evaluation for safety evaluation system of the NESASS are presented in this paper.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.94-101
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• 2004

This study shows the test results of seven RC beams retrofitted with modified polymer system and parametric study about the effects of tensile strength of retrofitting materials by analytical method on the flexural behavior. The main parameters are the retrofitted depth and length. The beams are loaded to the failure by four-point loading. Test results show that the effect of the retrofitted length on the structural behavior is more significant than that of depth. As the retrofitted depth is increased, the beams represents the brittle failure mode The non-linear analysis is carried out to grasp the effect of the tensile strength of retrofitting material on the structural behavior. As the retrofitted depth and length are increased, the tensile strength becomes more effective so these parameters should be considered to determine the retrofitted area. The analytical results show that failure strength is less than that of experimental results, but the stiffness is vice versa.

• Journal of the Korean GEO-environmental Society
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• v.18 no.5
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• pp.5-16
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• 2017

In the present work, a number of advanced three-dimensional (3D) parametric finite element numerical analyses have been conducted to study the behaviour of a single pile in consolidating ground from coupled consolidation analyses. A single pile with typical minimum and maximum ranges of fill height and clay stiffness has been modelled. The computed results demonstrate that the higher the height of the fill above the clay surface and the smaller the stiffness of the clay, the higher the dragloads and the negative skin friction-induced pile settlements. It has been found that the development of dragloads and pile settlement is more governed by the stiffness of the clay rather than the height of the fill. Positive shaft resistance is mobilised only after the average degree of consolidation is larger than 50%. Although the pile is installed when the degree of consolidation is 50% or more, relatively large negative skin friction can nevertheless develop on the pile. On the other hand, when a load is applied on the pile experiencing an increase in the negative skin friction with time during consolidation, the pile undergoes a large increase in the final settlement of up to 95% compared to that of a pile without axial load on the pile head. The allowable pile capacity when there is negative skin friction on the pile is reduced by about 4-11% compared to a pile without negative skin friction.

• Geotechnical Engineering
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• v.14 no.4
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• pp.177-204
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• 1998

In the present study, a method of quasi-three dimensional stability analysis is proposed for a systematic design of the GRS-RW(Geosynthetic-Reinforced Soil Retaining Wall) system based on the postulated three dimensional failure wedge. The proposed method could be applied to the analysis of the stability of both the straight-line and cove-shaped are. As with skew reinforcements. Maximum earth thrust expected to act on the rigid face wall is assumed to distribute along the depth, and wall displacements are predicted based on both the assumed compaction-induced earth pressures and one dimensional finite element method of analysis. For a verification of the procedure proposed in the present study, the predicted wall displacements are compared with chose obtained from the RMC tests in Canada and the FHWA tests in U.S.A. In these comparisons the wall displacements estimated by the methods of Christopher et at. and Chew & Mitchell are also included for further verification. Also, the predicted wall displacements for the convex-shaped zone reinforced with skew reinforcements are compared with those by $FLAC_{3D}$ program analyses. The assumed compaction-induced earth pressures evaluated on the basic of the proposed method of analysis are further compared with the measurements by the FHWA best wall. A parametric stduy is finally performed to investigate the effects of various design parameters for the stability of the GRS-RW system

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.405-414
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• 2006

In the present study, a numerical analysis was performed for interior connections of continuous flat plate to analyze the effect of design parameters such as column section shape, gravity load and slab span on the behavioral characteristics of the connections. For the purpose, a computer program for nonlinear FE analysis was developed, and the validity was verified. Through the parametric study, the variations of shear stress distribution around the connection were investigated. According to the result of numerical analysis, as the length of the cross section of column in the direction of lateral load increases and gravity load increases, the effective area and the maximum shear strength providing the torsional resistance decrease considerably. And as the slab span loaded with relatively large gravity load increases, the negative moment around the connection increases and therefore the strength of connection against unbalanced moment decreases. By considering the effect of design parameters on the strength of the connections, the effective shear strength to calculate the torsional moment capacity of connection was proposed and the effectiveness of the proposed shear strength was verified.