• Advances in Computational Design
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• v.3 no.2
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• pp.201-212
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• 2018

Decrease in availability of suitable subbase and base course materials for highway construction leads to a search for economic method of converting locally available troublesome soil to suitable one for highway construction. Present study insights on evaluation of benefits of stabilization of subgrade soils in term of extension in service life (TBR) and layer thickness reduction (LTR). Laboratory investigation consisting of Atterberg limit, Compaction, California Bearing Ratio, unconfined compressive strength and triaxial shear strength tests were carried out on two types of soil for varying percentages of stabilizers. Vertical compressive strains at the top of unstabilized and stabilized subgrade soils were found out by elastoplastic finite element analysis using commercial software ANSYS. The values of vertical compressive strains at the top of unstabilized and stabilized subgrade, were further used to estimate layer thickness reduction or extension in service life of the pavement due to stabilization. Finite element modeling of the flexible pavement layered structure provides modern technology and sophisticated characterization of materials that can be accommodated in the analysis and enhances the reliability for the prediction of pavement response for improved design methodology. If the pavement section is kept same for unstabilized and stabilized subgrade soils, pavement resting on lime, fly ash and fiber stabilized subgrade soil B will have service life 2.84, 1.84 and 1.67 times than that of unstabilized pavement respectively. The flexible pavement resting on stabilized subgrade is beneficial in reducing the construction material. Actual savings would depend on the option exercised by the designer for reducing the thickness of an individual layer.

• Journal of Korean Society of Transportation
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• v.25 no.5
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• pp.79-90
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• 2007

In determining vertical grades in highway alignment design, engineers usually consider heavy vehicle performances on the upgrade. Heavy vehicles usually experience speed reduction on the upgrade and with recent years weight/horsepower improvements for heavy vehicles the speed reduction shows some change. However, in spite of the weight to horsepower improvements for the design vehicles from 300lb/HP to 200lb/HP in the AASHTO, there was no change in the maximum vertical grades. Therefore, a review of the maximum vertical grade reflecting existing heavy vehicle performances is required. In particular, in South Korea where highways pass through lots of mountaineous terrain, the maximum vertical grades must be reviewed throughly. In this study the amount of heavy vehicle performances during past decades were investigated and their expected impacts on highway vertical alignment designs were subsequently analyzed. A worldwide terrain analysis and international design standards were compared to set South Korean vertical grade standards. Traffic flow simulation Vissim was utilized to simulate vehicular flows on the upgrade and new truck performance curves on the grades were developed. Based on the new curve, it was decided that $1{\sim}2%$ increase of the maximum vertical grades could be allowed.

• Tribology and Lubricants
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• v.34 no.1
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• pp.16-22
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• 2018

Cylindrical turbine guide bearings (TGBs) with simple plain pads have conventionally been used in vertical hydro-power turbine-generator applications in order to provide turbine runner shafts with smooth rotation guides and supports. To overcome low-load/low-eccentricity performance drawbacks, such as very low film stiffness and lack of design credibility in the stiffness values themselves, of conventional cylindrical TGBs, the introduction of a rotational-directional leading-edge taper to each partitioned pad, simply pad leading-edge taper, has been found to be very effective in enhancing their design-application availability and usefulness. In this study, we investigate the effects of taper angle and length for given taper heights in detail in order to systematically establish the effectiveness of design on the performance improvement of vertical hydro-power application cylindrical TGBs with pad leading-edge tapers. The analysis results with $4-Pad{\times}1-Row$ cylindrical TGBs show that the lubrication performance of the cylindrical TGBs is optimized with an approximate taper angle ratio of 0.8 and taper length ratio of 0.9. We conclude that the introduction of pad leading-edge tapers along with the optimization of taper designs can be very effective in improving the overall operation reliability of cylindrical TGBs and the rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems as well, to which the TGBs are applied.

• Nuclear Engineering and Technology
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• v.42 no.1
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• pp.97-108
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• 2010

Fluid-elastic instability and turbulence-induced vibration of steam generator U-tubes of a nuclear power plant are studied numerically to investigate the effect of design changes of support structures in the upper region of the tubes. Two steam generator models, Model A and Model B, are considered in this study. The main design features of both models are identical except for the conditions of vertical and horizontal support bars. The location and number of vertical and horizontal support bars at the middle of the U-bend region in Model A differs from that of Model B. The stability ratio and the amplitude of turbulence-induced vibration are calculated by a computer program based on the ASME code. The mode shape with a large modal displacement at the upper region of the U-tube is the key parameter related to the fretting wear between the tube and its support structures, such as vertical, horizontal, and diagonal support bars. Therefore, the location and the number of vertical and horizontal support bars have a great influence on the fretting wear mechanism. The variation in the stability ratios for each vibrational mode is compared with respect to Model A and Model B. Even though both models satisfy the design criteria, Model A shows substantial improvements over Model B, particularly in terms of having greater amplitude margins in the turbulence-excited vibration (especially at the inner region of the tube bundle) and better stability ratios for the fluid-elastic instability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.8
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• pp.580-588
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• 2009

This paper summarizes the experimentally-measured performance of small-scale, vertical-axis wind turbine for the purpose of improving the aerodynamic efficiency and its controllability. The turbine is designed to have a Savonius-Type rotor with an inlet guide-vane and an side guide-vane so that it achieves a higher efficiency than any lift- or drag-based turbines. The main design factors for this high-efficient, vertical wind turbine are the number of blades (Z), and the aspect ratio of Height/Diameter (H/D) among many. The basic model has the diameter of 580mm, the height of 464mm, and the blade number of 10. The maximum power coefficient of 0.50 was experimentally measured for the above-mentioned specifications. The inlet-guide vane ensures the maximum efficiency when the angle of attack to the rotor blade lies between $15^{\circ}$ and $20^{\circ}$. This experimental results for the vertical-axis wind turbine can be applied to the preliminary design of turbine output curve based on the wind characteristics at the proposed site by controlling its aerodynamic performance given as a priori.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.10a
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• pp.259-266
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• 2003

This paper introduces a relation to determine the span ratio between exterior and interior spans, which is strongly required in the preliminary design stage of bridges constructed by Free Cantilever Method (FCM). A relation for the initial tendon force is derived on the basis of an assumption that no vertical deflection occurs at the far end of a cantilever beam due to the balanced condition between the self-weight and the cantilever tendons. In advance, the span ratio can be determined by using an assumption that the negative maximum moment must be the same with the positive maximum moment along the entire spans to be a rational bridge design. Finally, many rigorous lime-dependent analyses are conducted to establish the validity of the introduced relations. The obtained numerical results show that the rational design of FCM bridges may be achieved when the span length ratio of the exterior span to the interior span ranges about 0.75 to 0.8.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.733-740
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• 2003

When SCP (Sand Compaction Pile) is used in the improvement of soft ground, some problems like the difficulty of vertical construction and other construction difficulties due to the use of high pressure are encountered, There is a possibility that the strength parameters used in the design may be different with those obtained from the investigation of the quality variation with depth for the irregular, then the section may be not a sand pile but a combination of sand and clay. The mixture ratio concept is used, it is defined as the quantity of sand corresponding to the replacement ratio. Using this concept, the strength parameter relationship of the replacement and mixture ratio was determined. The use of these parameters in the design of SCP is most appropriate.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.64-68
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• 2014

This paper is intended to provide experimental data for the design of the small VAWT(vertical axis wind turbine). Three types(lift, drag, and hybrid) of the blade of VAWT are tested with digital wind tunnel in this study. From the test, the relation of power coefficient and tip speed ratio for the blades are evaluated and compared each other depending on the blade type. Especially, the characteristics of hybrid blade which is shown to be expanded in the market without any logical data is proposed in the relation of power coefficient and tip speed ratio. It is shown that the hybrid blade can be used to make higher starting torque with trade off of degradation of power coefficient.

• Korean Journal of Agricultural Science
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• v.50 no.3
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• pp.511-526
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• 2023

In this study, three types of structures-stepped gabion retaining walls, vertical gabion retaining walls, and parapets-were installed on the dam floor crest to prevent the overflow of deteriorative homogeneous reservoirs. The acceleration response, displacement behavior, and pore water pressure ratio behavior were compared and evaluated using shaking-table model tests. The experimental conditions were set to 0.154 g in consideration of the domestic standard and the seismic acceleration range according to the magnitude of the earthquake, and the input waveform was applied with Pohang, Gongen, and artificial earthquake waves. The acceleration response according to the design ground acceleration increased as the height of the embankment increased, and the observed value were larger in the range of 1.1 to 2.1 times the input acceleration for all structures. The horizontal and vertical displacements exhibited maximum values on the upstream slope, and the embankment was evaluated as stable and included within the allowable range for all waveforms. The settlement ratio considering the similarity law exhibited the least change in the case of the parapet structure. The amplification ratio was 1.1 to 1.5 times in all structures, with the largest observed in the dam crest. The maximum excess pore water pressure ratio was in the range of 0.010 - 0.021, and the liquefaction evaluation standard was within 1.0, which was considered very stable.

• Journal of the Korean Society of Clothing and Textiles
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• v.30 no.11 s.158
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• pp.1598-1607
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• 2006

The purpose of this study was to analyze the proportion of gathered skirts using a three-dimensional measurement system. And in this experiment, we have attempted to accumulate three-dimensional data of wearing model and find out adequate methods for analyzing shape of clothes. The experimental design consists of two factorial designs. We established three different kinds of fabrics, ratio of gathers. The measurement tool for three-dimensional model was whole body 3D scanner(Exima-WBS2H). Analysis program used in experiment is RapidForm 2004 PP1 and Pattern Design 2000. Data analysis utilizes SPSS WIN 10.0 Package. As the results show, there were different effect of gather and proportion of shapes among the measurements of width, thickness and areas made by different lines of vision in cross-sectional silhouette. And there were difference shapes of section area at each part of gathered skirts between vertical-outline silhouette and vortical-plane silhouette made by gathering conditions. And also the cross-sectional silhouettes and vertical silhouettes were related to shape of clothes.