• Korean Journal of Fisheries and Aquatic Sciences
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• v.32 no.6
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• pp.706-712
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• 1999

PSD (particle size distribution) for 2,000 mg/$\ell$ natural loess in seawater showed normal distribution cure at 0 minute settling time, accompanying with very large particle distribution range with its mean particle diameter of 31.6 $\mu$m and coencient of variance of $72.6\%$, With elapsed time it showed that the PSD was rapidly changed from normal distribution cure to abnormal distribution curve, steepened the right-hand side of it and its coefficient of variance was getting increased because of rapid settling of large size particles, Cumulative weight distribution showed that 2,000 mg/$\ell$ natural loess in seawater was almost $100\%$ constituted of particles bigger than 20 $\mu$m in diameter. Ratio of $V_s/(D_{bm})^{1/2}$ for loess particles in seawater was increased with increase of particle size in geometrical progression. Almost all loess particles in seawater had Stokes settling velocity not less than 2,255 times of Brownian diffusion coefficient, There was almost to EDL (about 0.4 nm) around natural loess particles in seawater, Thus, there was always LVDW attractive force between loess particles approaching each other in seawater, and almost no EDL repulsive force. Loess particles were not always in the condition of easy floe formation. Concentration of natural loess in seawater increasing from 400 mg/$\ell$ to 10,000 mg/$\ell$, characteristics of the settling was changed from Type I settling (discrete settling) to Type II settling (flocculation settling). PVD (particle volume distribution) showed that natural loess particles in seawater were largely constituted of two types of particles, such as rapidly settling particles and suspended and dispersed particles for a long time. Amount of the latter was much less than that of the former.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.1373-1377
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• 2008

강우-유출에 의해 성층화된 저수지로 유입하는 하천수는 저수지 표층에 비해 낮은 수온과 높은 부유물질(SS) 농도를 가지므로 저수지 표층수보다 상대적으로 높은 밀도를 유지한다. 하천으로부터 유입한 밀도류는 유속에 의한 관성력이 두 수체의 밀도차에 의한 음의 부력보다 큰 구간까지는 저수지 표층을 따라 진행하지만, 두 힘이 같아지는 지점에서 밀도류는 더 이상 진행하지 못하고 저수지 수면 아래로 침강하며 이 과정에서 수체간의 많은 혼합이 일어난다. 따라서 홍수시 유입한 탁수의 침강점에 대한 정확한 예측은 수질관리를 위한 현장조사, 그리고 탁수거동 해석 및 최적관리대책 마련에 중요한 요소이다. 본 연구의 목적은 홍수시 대청호로 유입하는 하천 밀도류의 침강위치를 홍수규모별로 경험식과 수치모델을 통해 산정함으로써 두 방법 간의 장 단점을 비교하고, 탁수 현장조사와 최적관리를 위한 기초정보를 제공하는데 있다. 유입수의 모의조건은 그 동안 대청호에서 발생한 홍수 크기를 기준으로 9개의 등급으로 나누었으며, 저수지 성층조건은 여름철 탁수가 유입되기 전의 발달된 성층구조를 적용하였다. 유입수와 저수지 성층구조의 특성치는 밀도 Froude 수($Fr_i$)로 나타냈으며, $Fr_i$ 조건별로 침강점 위치를 저수지 단면을 삼각형태로 가정한 Hebbert et al.(1979) 경험식과 2차원 수치모델로 산정하여 그 결과를 비교하였다. 대청호로 유입한 탁수는 홍수규모에 따라 대정리 수역에서 회남수역 사이 구간에서 침강하였으며, $Fr_i$ 값이 클수록 침강점 수심이 깊어지는 경향을 보였다. 경험식으로 산정한 침강점 수심은 정상상태 조건을 가정하므로 홍수에 의한 수위변화를 고려하지 못하며, 실제의 불규칙한 하상표고를 일정한 하상경사로 가정하기 때문에 2차원 모델의 결과보다 과대산정하는 경향을 보였다. 따라서 홍수가 연속해서 발생하며 수위변화가 심한 국내 저수지 여건에서 하천 유입 밀도류의 거동을 보다 정확히 예측하기 위해서는 2차원 또는 3차원 수치모델을 적용하는 것이 타당할 것으로 판단된다.

• Korean Journal of Ecology and Environment
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• v.44 no.1
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• pp.58-65
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• 2011

This study aims to investigate the settling velocity of aggregates of cohesive sediment (floc) and its relationship with sediment size, density and fractal dimension. A system of commercial camera and macro-lens is used for the experiment. Through the image-analysis technique, the image taken by the camera system is analyzed. For the experiment, kaolinite and a natural sediment sampled at Lake Apopka in Florida have been tested. From this study, it is known that kaolinite and Lake Apopka sediments show different behaviors mainly depending on the organic matter content. Samples of kaolinite with less organic contents show a more definite trend to follow a fractal theory and relatively strong relationships between the settling velocity, density, fractal dimension and floc size compared to the Lake Apopka sediments rich in organics.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.435-435
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• 2016

기후변화에 따라 강우 패턴이 변화하며, 집중호우 발생 빈도의 증가가 예상된다. 이로 인해 저수지 상류에서 유실된 토사는 저수지로 유입하여 정수 처리비용 증가, 1차생산성 감소, 어류폐사, 하천경관 악화 등 다양한 문제를 유발한다. 따라서 위와 같은 탁수 피해 저감을 위해 과학적인 모니터링과 예측, 저수지 운영과 관리기술 개발 등의 대응이 요구된다. 본 연구에서는 극한 탁수사상 발생시 대응 기술의 일환으로 저수지 탁수예측 모델의 신뢰도 향상을 위해, 기존 탁수예측 모형인 CE-QUAL-W2(이하 W2)의 탁수 예측 알고리즘을 개선하고 소양강댐 저수지에 적용하여 그 성능을 평가하였다. 최근 W2모델 3.72 버전까지 출시되었으나, 모델은 단순 침강속도만 고려하여 저수지 밀도 특성을 반영하지 못하고, TSS 모의시 독립침강을 가정하여 응집 침강 및 장기탁수 예측에 취약한 한계점을 가지고 있다. 따라서, 과거 연구내용을 바탕으로 수온에 따른 점성계수 변화(Stoke's), 다중 부유 입자별 침강속도 고려 기능을 추가하였으며, 새롭게 점착성유사의 응집 침강을 고려할 수 있는 기능을 추가하여 모델을 개선하였다. 모델에 점착성 유사 모의 전략은 입자 크기 $63{\mu}m$를 기준으로 비점착성유사(NCS)와 점착성유사(CS)로 구분하고, 비점착성유사는 독립침강, 점착성 유사는 응집침강을 가정하였다. 응집 후 중간 입경의 추정은 Gailani et al(1991)의 식을 사용하였으며, 침강속도 계산 공식은 Hwang and Mehta(1989)식을 적용하였다. 수정된 모델은 소양강댐 운영이후 최대 탁수사상이 발생했던 2006년을 대상으로 기존 탁수해석 결과와 수정된 모델의 모의결과를 실측값과 비교 분석 하였다. Stoke's 식 적용시 기존의 모의결과 대비 AME 평균 23%, RMSE 평균 18%가 개선되는 것으로 나타났으며, Hwang and Metha식 적용시에 SS 모의값이 전반적으로 과소평가되는 것으로 나타났다. 또한, 실측 방류 탁수 농도와 모의값을 비교하여 평가 하였으며, 모의기간인 Julian Day 173~365(192일) 동안 모의 결과의 총 TSS 부하량은 실측값의 약 80%수준을 보였으며, TSS 방류 부하기준 Stoke's 식 적용시 기존 모의대비 오차가 1.3% 개선되는 것으로 나타났다.

• Journal of the Korea Organic Resources Recycling Association
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• v.14 no.1
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• pp.151-159
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• 2006

In these days, the importance of sludge treatment is emerging due to the London Convention, so this study was conducted to propose the alternatives for the improved sludge treatment on the organic wastewater and sewage sludge with JAR test and settling column equipped with stirrer. The minimum coagulant dosage to earn the optimum sludge settling efficiency resulted from 200mg/l and each critical sludge settling interface showed no distinct difference when PAC was dosed over 200mg/l. Accordingly, Clarification Rate(CR) with 200mg/l dosage was calculated to CR=(Ho-Ht) / Ho=1-0.4=0.6 because the critical sludge settling height stopped at 0.4. The settling velocity of sludge interface was decreased with the increase of MLSS concentration but rather increased with MLSS concentration over 1,000mg/l. This resulted from positive effect of interacted coagulation for floc formation by transfer to the zone of compressed settling when MLSS concentration increased over 1,000mg/l. The settling velocity of sludge interface showed $28.66{\times}10^{-3}/min$ for average settling velocity of sewage sludge which is 6.7 times higher than $4.25{\times}10^{-3}/min$ for average settling velocity of organic wastewater sludge. The increasing rate of CR for organic wastewater activated sludge was higher than that of settling velocity under 200mg/l of PAC dosage but settling velocity was higher than CR over 200mg/l of PAC dosage. However, in case of sewage sludge, the differential rate of CR was low when PAC dosage was increased but the settling velocity was suddenly increased with over 200mg/l dosage. Therefore coagulation effect was more efficient to MLSS settling velocity rather than SS removal effect in the supernatant.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.5
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• pp.327-334
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• 2014

This study aims to estimate settling velocity ($W_s$) for cohesive sediments from water bodies (Incheon Coast, Kulpo Stream and Han River) mainly connected to the Kyeongin Ara-waterway through the laboratory settling experiments. Results of settling tests for these sediments show that $W_s$ values for sediments are quite different each other: $W_s$ values of Kulpo Stream sediments (0.01 < $W_s$ < 3.07 mm/s) are quite similar with those of Han River sediments (0.01 < $W_s$ < 2.97 mm/s) over the whole range of suspension concentration C (0.1 < C < 90 g/ L), while they are quite different with those for Incheon Coast sediments (0.01 < $W_s$ <0.92 mm/s). Qualitative analyses on test results for physico- chemical properties of sediments and waters with respect to settling velocities show that these differences in settling velocities are mainly due to the salinity difference in the water.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.31 no.4
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• pp.372-378
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• 1995

This study describes an analysis on the sinking characteristics in purse seine. The experiment was carried out using three simplified model seines in a flume tank under still water condition. The densities($\rho$) of netting materials were 0.91g/$cm^3$ for PP seine, 1.14g/$cm^3$ for PA seine and 1.38g/$cm^3$ for PES seine. Differential equations were derived from the conservation of momenta of the model seines and used to determine the sinking speeds of the depths of leadline and the other portions of seines. An analysis carried out by simultaneous differential equations for numerical method by subroutine Runge-Kutta-Gill. The results obtained were as follows: 1) Sinking speed of net margin was fastest for PP seine, followed by PA and PES seines. 2) The coefficient of resistance for netting of seine was estimated to be $K_D=0.061({\frac{\rho}{{\rho}_w}})^4$. 3) The coefficient of resistance for netting bundle of seine was estimated to be $C_R=0.91({\frac{\rho}{{\rho}_w}}$. 4) In all seines, the calculated depths of leadline closely agreed with the measured ones(meas.=0.99cal.).

• Journal of the Korean GEO-environmental Society
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• v.14 no.2
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• pp.31-41
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• 2013

The dredged soils of western sea of Korea have been used as the fill materials because it possess the characteristics that constitute silt, silty sand and sand mainly. However, a study on dredged soils as the fill materials is insufficient. Hence, in this present study, the application the dredged soils of western sea of Korea as the fill materials was confirmed. Primary, the composition characteristics of the ground was analyzed to confirm the application on dredged soils as the fill materials by the piezo-cone penetration test. In laboratory test, it was performed the self-weight consolidation test for mechanical characteristics of the dredged soils. The direct shear test using self-weight consolidation test sample for shear strength characteristics was performed after self-weight consolidation test. Additionally, the mechanical characteristics of the dredged soils on elapsed time using self-weight consolidation test sample, which is drained naturally, was evaluated. The dredged soils of western sea of Korea show that unit weight and shear strength is increased as natural drain time elapses.

• Journal of the Korean GEO-environmental Society
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• v.16 no.10
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• pp.33-38
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• 2015

This study conducted experimental observations of the settling velocity of a coarse particle in water varying material type and particle size and compared the results with preexisting empirical equations. Three types of materials, which are polyacetal, glass and steel, were used in this study and the diameter of particle ranged from 1 mm to 20 mm. Experiment results showed that the settling velocity of coarse particle had a significant difference from Stokes equation which is known applicable for a fine particle smaller than $50{\mu}m$. In addition, the observed particle velocity showed a significant difference when compared with other empirical equations, which was proposed for estimating the settling velocity of a particle regardless of particle size, depending on the material type and particle size. The results from experimental observations indicated that the settling velocity of a coarse particle was relatively in smaller difference to other empirical equations for the particle size smaller than 3 mm, but as the size increased the difference in the settling velocity also increased. This study clearly showed that the settling velocity of a coarse particle velocity can be significantly different depending on particle size and density and the empirical equations may not reliably estimate the settling velocity of a coarse particle so that they should not be used as it is and a verification of them is necessarily before any use. The study results would provide a useful information for a better understanding of settling velocity of a particle in water.

• Journal of the Korean Geotechnical Society
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• v.17 no.4
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• pp.39-48
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• 2001

액상화 발생후 과잉간극수압 소산 특성을 파악하기 위하여 포화된 수평 모래지반에 대하여 1-g 진동대시험을 수행하였다. 진동대시험에는 주문진 표준사와 영종도 세사를 사용하였으며 상대밀도를 dir 20~30% 사이가 되도록 조성하였다. 간극수압계, 가속도계 그리고 LVDT 등으로 시험중의 지반거동을 계측하였으며, 4Hz의 sine 파를 0.15g에서 5초간 5회 반복하여 작용시켰다. 진동대시험을 분석한 결과 액상화 발생후 과잉간극수압의 소산속도는 그 지반의 투수성뿐 아니라 과잉간극수압 소산시 입자의 침강거리와 직접 관련이 있는 지반의 침하량에도 크게 영향을 받는 것으로 나타났으며, 이 과정을 침강모래 이론으로 모델링하였을 때 입자의 침강속도와 투수계수 사이의 비례 관계는 침강모래 이론에서의 가정한 것과는 달리 모래의 종류에 따라 차이를 나타내었다. 또한 Terzaghi의 압밀이론으로는 액상화 후 과잉간극수압의 소산과정을 적절히 모사할 수 없었다.