• Journal of Korean Society of Environmental Engineers
• /
• v.39 no.5
• /
• pp.288-302
• /
• 2017

Accurate measurement of benthic nutrient fluxes (BNF) is a prerequisite for evaluating the effect of sediments on nutrient cycle in the surface water. The intact sediment cores were collected in July 2015 at the midstream of Nakdong River. We identified pre-incubation time (6, 12, 24 hr), dissolved oxygen concentration (90, 70, 50% saturation), diffusive boundary layer thickness (0, 0.6-0.8, 1.2-1.4 mm), and incubation temperature (10, 17, 20, $25^{\circ}C$) as the most important control factors, and measured the BNF fluctuation with the variation of these factors using the laboratory sediment core incubation method. Since the chemical composition, redox condition, hydrodynamic regimes and microbial activities at the sediment-water interface were changed as a result of the alteration of control factors, sediment core incubation should be conducted under as close to the natural conditions of study site as possible, in order to produce the results similar to actual values. Relative percentage differences between two replicates were below 20% in most control factors, which showed satisfactory precision for strict compliance with the experimental conditions and procedures. In the further studies, we will compare the results of core incubation with those of in situ measurements to confirm the accuracy of the sediment core incubation method.

• Journal of Korean Society of Environmental Engineers
• /
• v.31 no.4
• /
• pp.256-262
• /
• 2009

The use of hydrodynamic separator is becoming increasingly popular for suspended solids reduction in urban storm runoff. This study is a laboratory investigation of the use of Vortex Screen to reduce the solids concentration of synthesized storm runoff. The synthesized storm runoff was made with water and addition of particles; manhole sediment, road sediment, fly ash, and ployvinyl chloride powder. Vortex Screen was made of acryl resin with 250 mm of diameter and height of 700 mm. To determine the removal efficiency for various influent concentrations of suspended solids (SS) and chemical oxygen demand (COD), tests were performed with different operational conditions. The samples were taken simultaneously at the influent storage tank and effluent tank, and measured SS and COD concentrations. The ranges of surface loading rate were 110 to 1,550 $m^3/m^2$/day, and influent SS concentrations were varied from 141 to 1,986 mg/L. This paper was intended to evaluate the effect of inlet baffle and the ratio of underflow to overflow ($Q_U/Q_O$) on particle separation efficiency for various particle size using Vortex Screen. It was found that when increase of $Q_U/Q_O$ from 10% to 20%, SS removal efficiency was increased about 6%. The range of SS and COD removal efficiencies of road sediment particle size 125<$d_p$<300 ${\mu}m$ were 68.0~81.0%, 53.1~71.9%, respectively. Results showed that SS removal efficiency with inlet baffle improved by about 10~20% compared without inlet baffle.

• Restorative Dentistry and Endodontics
• /
• v.33 no.2
• /
• pp.141-147
• /
• 2008

This study was aimed to develop an instrument for real-time measurement of fluid conductance and to investigate the hydrodynamics of dentinal fluid. The instrument consisted of three parts; (1) a glass capillary and a photo sensor for detection of fluid movement, (2) a servo-motor, a lead screw and a ball nut for tracking of fluid movement, (3) a rotary encoder and software for data processing. To observe the blocking effect of dentinal fluid movement, oxalate gel and self-etch adhesive agent were used. BisBlock (Bisco) and Clearfil SE Bond (Kuraray) were applied to the occlusal dentin surface of extracted human teeth. Using this new device, the fluid movement was measured and compared between before and after each agent was applied. The instrument was able to measure dentinal fluid movement with a high resolution (0.196 nL) and the flow occurred with a rate of 0.84 to 15.2 nL/s before treatment. After BisBlock or Clearfil SE Bond was used, the fluid movement was decreased by 39.8 to 89.6%.

• Journal of Korean Society of Environmental Engineers
• /
• v.34 no.11
• /
• pp.772-779
• /
• 2012

For improving performance of conical air diffuser generating fine bubble, both experimental and numerical simulation method were used. After adapting diffusers inner real scale bubble column, suitable for various diffuser submergence, the effect of diffuser submergence on oxygen transfer performance such as Oxygen Transfer Coefficient ($K_{L}a_{20}$) and Standard Oxygen Transfer Efficiency (SOTE) was investigated empirically. As flow patterns for various diffuser number and submergence were revealed throughout hydrodynamic simulation for 2-phase fluid flow of air-water, the cause of the change for oxygen transfer performance was cleared up. As results of experimental performance, $K_{L}a_{20}$ was increased slightly by 7% and SOTE was increased drastically by 39~72%, 5.6% per meter. As results of numerical analysis, air volume fraction, air and water velocity in bioreactor were increased with analogous flow tendency by increasing diffuser number. As diffuser submergence increased, air volume fraction, air and water velocity were decreased slightly. Because circulative co-flow is determinant factor for bubble diffusion and rising velocity, excessive circulation intensity can result to worsen oxygen transfer by shortening bubble retention time and amount.

• Journal of Advanced Marine Engineering and Technology
• /
• v.38 no.10
• /
• pp.1217-1224
• /
• 2014

This paper provides a practical scaling method to solve an old problem for scaling and developing the speed and resistance of a model to full-scale submarine in fully submerged underwater test. In every experimental test in towing tank, water tunnel and wind tunnel, in the first step, the speed of a model should be scaled to the full-scale vessel (ship or submarine). In the second step, the obtained resistance of the model should be developed. For submarine, there are two modes of movement: surface and submerged mode. There is no matter in surface mode because, according to Froude's law, the ratio of speed of the model to the full-scale vessel is proportional to the square root of lengths (length of the model on the length of the vessel). This leads to a reasonable speed and is not so much for the model that is applicable in the laboratory. The main problem is in submerged mode (fully submerged) that there isn't surface wave effect and therefore, Froude's law couldn't be used. Reynold's similarity is actually impossible to implement because it leads to very high speeds of the model that is impossible in a laboratory and inside the water. According to Reynold's similarity, the ratio of speed of the model to the full-scale vessel is proportional to the ratio of the full-scale length to the model length that leads to a too high speed. This paper proves that there is no need for exact Reynold's similarity because after a special Reynolds, resistance coefficient remains constant. Therefore, there is not compulsion for high speeds of the model. For proving this finding, three groups of results are presented: two cases are based on CFD method, and one case is based on the model test in towing tank. All these three results are presented for three different shapes that can show; this finding is independent of the shapes and geometries. For CFD method, Flow Vision software has been used.

• Journal of Korea Water Resources Association
• /
• v.48 no.1
• /
• pp.45-55
• /
• 2015

In this study, when seawall or harbor gate is installed for coastal disaster prevention, a two-dimensional water analysis in the bay is carried out to consider the flood amount of river inflow and effect of harbor gate. The Yeongsan river and the port Mokpo area are selcected for the study region. Then, by analyzing the hydraulic characteristics of flood flow of the Yeongsan river, we analysed the compatibility of the results in the two-dimensional hydrodynamic model. A tw-odimensional water analysis were conducted for the four cases considering whether a harbor gate is installed or not, and whether the inland water boundary condition is considered or not, also with open sea boundary condition. The results of the two-dimensional water analysis shows that water level change near the port Mokpo area is mainly caused by the discharge of the estuary barrage of the Yeongsan river because the harbor gate was installed. In addition, it is revealed that the volume of reservoir created by the harbor gate and the estuary barrage is too much small compared to the volume of the discharge from the Yeongsan river. Therefore, when the harbor gate is installed in the open sea, we concluded that a flexible management between the harbor gate and the estuary barrage of the Yeongsan river is required. A initial water level of the bay and outflow from the harbor gate are proposed for disaster prevention in the coastal area of port Mokpo.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.4B
• /
• pp.343-352
• /
• 2011

The water quantity by intake station as well as the tributary flow discharge acting as sink or source were added to the main flow rate in the present study and RMA-2 and RMA-4 models were applied to the reach from Pal-dang dam to Jam-sil submerged weir to investigate the influence of water supply withdrawal on the river flow and water quality. The numerical results revealed that the water supply withdrawal from 5 intake stations located upstream of Jam-sil submerged weir changed the total flow rate and therby induced different hydraulic characteristics in terms of water surface elevation and velocity. The changed flow field by the inclusion of water intake quantity led to the variation of water quality. By the consideration of the water supply withdrawal, the velocity structure was significantly disturbed by the outflowing flow condition nearby Gu-ui, Ja-yang, and Pung-nap intake stations. Furthermore, the mean velocity was lowered by 25% and the stage upstream of Gu-ui station rose upto 1.5 cm compared with the result by exclusion of water intake. In case of no water withdrawal, the distribution of BOD concentration was parallel throughout the domain. However, when the water withdrawal is considered, the distribution of BOD concentration nearby the Gu-ui, Am-sa, and Ja-yang station was signifiantly changed. In addition, the BOD concentration including the intake stations showed higher value at the downstream of the reach due to the loss of the discharge by water withdrawal effect. It is concluded that both the inflow and outflow discharges from tributaries and water intake stations should be included in the numerical simulation to analyze the hydrodynamic behaviors and mixing characteristics more accurately.

• Journal of the Korean Society for Marine Environment & Energy
• /
• v.19 no.2
• /
• pp.151-158
• /
• 2016

Tidal farm is a multi-arrayed turbine system for utilizing tidal stream energy. For horizontal-axis turbine(HAT) system, it is recommended that each unit has to be deployed far apart in order to avoid hydrodynamic interference among turbines, as proposed by the European Marine Energy Centre(EMEC). But there is no rule for the arrangement of vertical-axis turbine(VAT) yet. Moreover it has been reported that a proper arrangement of adjacent turbines can enhance the overall efficiency even greater than an arrangement without mutual interference effect. This paper suggests the layout of VATs showing the better performances, which turned out to be quite different from HATs' arrangement. Numerical calculations were performed to investigate the performance variation in terms of the rotational direction as well as the distance between turbines. It has been shown that the best combination of rotational direction and distance between turbines can increase its performance higher about 9.2% than that of two independently operated turbines. It is likely that such improvement is due to the increased velocity between adjacent turbines. For diagonally arranged turbines, the maximum normalized mean power coefficient was obtained to be higher about 5.6% than that of two independent turbines. It is expected that the present results can be utilized for conceptual design of tidal farm to harness the tidal stream energy.

• Korean Journal of Materials Research
• /
• v.8 no.2
• /
• pp.135-140
• /
• 1998

Drag reduction produced by dilute solution of water soluble ionic polymer-surfactant complex under turbulent flow in a rotating disk apparatus(RDA) was investigated in this study. Three different molecular weights of polyacrylic acid(PAA) were adopted as drag reducing additives, and distilled water was used as a solvent. Experiments were undertaken to observe the dependence of drag reduction on various factors such as polymer molecular weight, molecular expansions and flexibility, rotating speed of the disk and polymer concentration. Specific considerations were put on conformational difference between surfactant and polymer, and effect of pH on ionic polymer possessing various molecular conformation through pH. The complex of ionic polymer and surfactant(Sodium Dodecyl Sulfate) behaves like a large polyelectrolyte. Surfactant changes the polymer conformation and then increases the dimension of the polymer. The radius of gyration, hydrodynamic volume and relative viscosity of the polymer-surfactant system are observed to be greater than those of polymer itself. Such surfactant-polymer complex has enhanced drag reduction properties.

• Journal of Korea Water Resources Association
• /
• v.46 no.11
• /
• pp.1115-1128
• /
• 2013

The purpose of this study is to evaluate the suspended solids and eutrophication processes relationships in Chungju lake using CE-QUAL-W2, two-dimensional (2D) longitudinal/vertical hydrodynamic and water quality model. For water quality modeling, the lake segmentation was configured as 7 branches system according to their shape and tributary distribution. The model was calibrated (2010) and validated (2008) using 2 years of field data of water temperature, suspended solids (SS), total nitrogen (TN), total phosphorus (TP) and algae (Chl-a). The water temperature began to increase in depth from April and the stratification occurred at about 10 m early July heavy rain. The high SS concentration of the interflow density currents entering from the watershed was well simulated especially for July 2008 heavy rainfall event. The simulated concentration range of TN and TP was acceptable, but the errors might occur form the poor reflection for sedimentation velocity of nitrogen component and adsorption-sediment of phosphorus in model. The concentration of Chl-a was simulated well with the algal growth patterns in summer of 2010 and 2008, but the error of under estimation may come from the use of width-averaged velocity and concentration, not considering the actual to one side inclination by wind effect.