• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.3C
• /
• pp.93-102
• /
• 2011

Most experimental studies on soil liquefaction are related to clean sands. However, soils in the field or reclaimed grounds commonly contain some amounts of silt and clay rather than clean sand only. Many researchers investigated the effect of fine contents on liquefaction resistance and mainly used non-plastic fines such as silts. In this study, 10% of plastic fines with various plasticity index (PI) such as 8, 18, 50, and 377 were mixed with wet Nakdong River sand and then loose, medium, and dense specimens were prepared by undercompaction method. A series of undrained cyclic triaxial tests were carried out by applying three different cyclic stress ratios. As a result, the liquefaction resistance tended to decrease as a PI of fines in the specimens with equal fine content increased. On the other hand, the difference between loose specimens with low and high plasticity fines was not clearly observed in terms of liquefaction resistance. However, in the case of dense specimens, liquefaction resistance decreased up to 40% as a plasticity of fines increased.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.23 no.6
• /
• pp.429-441
• /
• 2011

In the southeast coastal zone of Yellow Sea, the tide characteristics showing ebb-dominant tide and tidal flow were confirmed by analysis of observed tide and tidal currents. Physical factors generating asymmetric tide were reviewed. Influence of bottom shear stress, tidal flat, and nonlinear terms in shallow water equations was investigated by two-dimensional tide modeling. The model results gave good agreements with observed tides, but the amplitude of simulated $M_4$ tide was less than that of observed tide. The tidal flats existing in the study area widely have great effect on the generation of nonlinear tide. The M4 tide is mainly generated near the tidal flats. The deletion of tidal flats prevents the production of the M4 tide. We can conclude that the wide tidal flats is a primary cause of tide asymmetry in the study area.

• Korean Journal of Poultry Science
• /
• v.31 no.3
• /
• pp.193-198
• /
• 2004

This study was conducted for improvement of meat quality in broiler chcikens. Birds were fed basal diet(control), ferritin, illite, betafin, or wood vinegar counting broiler feed according as broiler growth stage. Birds fed with basal diet, which was distributed under the best environmental condition, were more weight gain than other groups reared under same environmental condition. In the mean weight gain, the ferritin-group showed the highest and the illite-group showed the lowest among the feed additive groups; therefore, the effect of feed requirement change in odor reduction in illite and methyl saving of betafin was lower than those of other feed additives along to pass rear time. Meat quality was appraised by National Livestock Research Institute of RDA. Except the control-group, that had the best feed conversion ratio, the cooking loss of the illite-group was the biggest among groups although the illite-group chickens had a good water hold capacity. Therefore, illite is not good for making merchandise by reason that group chickens get reduction carcass weight after slaughter. On the other hand, the ferritin-group got the highest point of shear stress, cooking loss, and crude fat level. That group showed the best appraise in both breast and leg of sensory test in company and also feed conversion ratio was the highest among feed additive groups. As a result, the ferritin-group might use for making new merchandise among the feed additive groups.

• Journal of Korean Society of Water and Wastewater
• /
• v.34 no.3
• /
• pp.211-220
• /
• 2020

When domestic sewage and rainwater runoff are discharged into a single sewer pipe, it is called a "combined sewer system." The sewage design standards in Korea specify the flow velocity based only on the volume of rainfall; therefore, sedimentation occurs on non-rainy days owing to the reduced flow rate and velocity. This sedimentation reduces the discharge capacity, causes unpleasant odors, and exacerbates the problem of combined sewer overflow concentration. To address this problem, the amount of sewage on non-rainy days, not just the volume of rainfall, should also be considered. There are various theories on sedimentation in sewer movement. This study introduces a self-cleansing velocity based on tractive force theory. By applying a self-cleansing velocity equivalent to the critical shear stress of a sand particle, sedimentation can be reduced on non-rainy days. The amount of sewage changes according to the water use pattern of citizens. The design hourly maximum wastewater flow was considered as a representative value, and the velocity of this flow should be more than the self-cleansing velocity. This design method requires a steeper gradient than existing design criteria. Therefore, the existing sewer pipelines need to be improved and repaired accordingly. In this study, five types of improvement and repair methods that can maximize the use of existing pipelines and minimize the depth of excavation are proposed. The key technologies utilized are trenchless sewer rehabilitation and complex cross-section pipes. Trenchless sewer rehabilitation is a popular sewage repair method. However, it is complex because the cross-section pipes do not have a universal design and require continuous research and development. In an old metropolis with a combined sewer system, it is difficult to carry out excavation work; hence, the methods presented in this study may be useful in the future.

• Journal of the Korean Wood Science and Technology
• /
• v.35 no.6
• /
• pp.13-22
• /
• 2007

This study was carried out to scrutinize possibility of manufacturing pitch pine (Pinus rigida) glued laminated timber in order to add values of pitch pine trees. Also, it was investigated to improve bending performance of pitch pine glulam. Pitch pine was imported as one of major plantation species in Korean peninsula. Machine stress rated grades of pitch pine lumber mostly ranged between E7 and E9. which grades were more or less inferior to producing high quality glulam. However, the adhesive properties between pitch pine and pitch pine, and between pitch pine and Japanese larch (Larix kaempferi Carr.), such as shear bond strength, wood failure rate and de-lamination rate of bonded layer submerged in cold and boiling water, were higher than Korean Standard criteria. These properties are essential for manufacturing glulam with single species or multiple species. The modulus of rupture (MOR) of pitch pine glulam exceeded the criterion of Korean Standard for glulam strength grade but modulus of elasticity (MOE) was lower than the criterion. On the other hand, the bending performances (MOR and MOE) were improved 20 percent by mixing with Japanese larch laminar. It is effective to arrange higher quality Japanese larch laminar at the outer layer of glulam for improving bending performances. In conclusion, it is possible to use low quality pitch pine as laminar of structural glulam for adding values of pitch pine.

• Journal of Korea Water Resources Association
• /
• v.49 no.8
• /
• pp.693-705
• /
• 2016

In this study, the effects of sediment supply on the downstream of a large dam are investigated using a numerical model. The model simulation shows a good agreement with laboratory experiment results of sediment transport and diffusion from sediment pulses. The water surface changes from the various sediment bed elevations are also simulated using the model. The site which has a relatively stiff bed slope and meandering of a channel is selected as an appropriate location for sediment supply because of its shear stress enough to supply the sediment downstream. The model simulation shows the decrease of channel bed elevation through the simulation period with time. The well-deposition of sediment supplied from the downstream of dam is found in the location where the flow rate is relatively low. A bed relief index is increased with time and it is relatively greater in downstream compared to upstream. The channel bed variability increases as flow rate increases with a greater bed relief index. The results of this study demonstrate the importance of increasing water discharge of a large dam to increase the dynamic of channel bed and thus to enhance the efficiency of channel bed restoration by sediment supply.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.24 no.2
• /
• pp.246-252
• /
• 2018

In this paper, the friction drag force of 3D submerged body is investigated by considering the surface roughness, the first grid height, and the Reynolds number using open CFD source code, OpenFOAM 4.0. A procedure for estimating drag components by CFD code is set up and suggested in this study. In the 3D submerged body, because of the form factor in the 3D computations, the friction resistance with the small roughness of $12{\mu}m$ obtains different result with the smooth wall. As the Reynolds number increased, the boundary layer becomes thinner and the fiction resistance tends to decrease. In the computations for the effect of y+, the friction resistance and wall shear stress are excessively predicted when the y+ value deviates from the log layer. This is presumably because the boundary layer becomes thicker and the turbulence energy is excessively predicted in the nose due to the increase in y+ value. As the roughness increases, the boundary layer becomes thicker and the turbulence kinetic energy on the surface increases. From this study, the drag estimation method, considering the roughness by numerical analysis for ships or offshore structures, can be provided by using the suggested the y+ value and surface roughness with wall function.

• Computational Structural Engineering
• /
• v.2 no.1
• /
• pp.65-70
• /
• 1989

An analytical study was conducted using the Galerkin technique to determine behaviour of thin fibrereinforced and laminated composite pipes under soil pressure. Geometric nonlinearity and material linearity have been assumed. It is assumed that vertical and lateral soil pressure are proportional to the depth and lateral displacement of the pipe respectively. It is also assumed that radial shear stress is negligible because the ratio of thickness to the radius of pipe is very small. The above results are verified by the finite element analysis.

• Food Science and Preservation
• /
• v.11 no.4
• /
• pp.508-515
• /
• 2004

In this study, salting conditions and dehydration methods were investigated. Salting time, concentration and temperature could be considered to variables in salting conditions. The diffused salt amounts to beef jerky depending on time are sharply increased in two hours. This result is caused by the difference decrease of concentration gradient between bulk solution and beef jerky. The increase of salting concentration and temperature resulted also in the increase of a diffused salt. The deeper bulk concentration made diffusion to beef easily with the bigger driving force and the movement of molecules is more active according to temperature increase. Dehydration is conducted with various methods such as natural drying, cold air drying and hot air drying. Comparing with color and texture among the drying methods, cold air drying showed superior quality in color and texture. Beef jerky by cold air drying colored more reddish than other drying methods and good cutting shear stress and tensile strength. In case of hardness and chewiness, hot air drying method showed the highest value, which means the worst texture.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.25 no.3
• /
• pp.245-258
• /
• 2012

ILM(incremental launching method) is a way of construction, installing a girder producing spot behind the abutment, making the bridge girder infilled with concrete continuously and launching with using by jack. The superstructure of the bridge constructed by this method is temporarily located on the center of the span and the supporting points under construction. Therefore, the sections are structurally undergone maximum positive moment, maximum negative moment, and maximum shear force arising from self weight. On the other hand, launching nose is attached to the front of the girder to decrease the cantilever effect. The magnitude of this temporary stress creating on the upper section is dependent upon the launching nose's characteristics. This study has proposed an analysis formula simplified on the assumption that the launching nose section is a quasi-equivalent section(rigid; equivalent section, weight; tapered section) in order to ensure the accuracy of the analysis formula and improve its usage with reference to the interaction between the launching nose and the upper section; and a prismatic analysis formula modified by displacing a diaphragm's weight by a concentrated load in order to improve the accuracy of the existing analysis formula that assumes the launching nose section as the equivalent section. To judge the accuracy and usage of two analysis formulas proposed, we have compared and analyzed computational structural analysis programs and existing analysis formulas based on actual ILM bridge data. As a result, all of two reveal the superior accuracy and also their usage has been improved by the simplification of analysis formulas.