슬러지 침전 효율 향상을 위한 Magnetite 분말과 Hydrocyclone 장치의 적용성 연구

박현태 서울시립대학교 일반대학원 2022 국내석사

This study applied powedered magnetite, which is being used as weighted sedimentation agent, as a way to improve the sewage sludge sedimentation efficiency and then looked at the characteristics of sludge settling. It also conducted an experiment for separating and recollecting the settled sludge efficiently with hydrocyclone and conducted a research to improve sludge settling efficiency. As a result of injecting 1.0 g/L of magnetite(Fe3O4), hematite (Fe2O3), and iron oxide (FeO) to analyze the precipitation characteristics depending on type of ballasted flocculant, the settling efficiency at SV10 appeared to be improved by 31.82 % for iron oxide, 40.91 % for red hematite, and 45.45 % for magnetite than in control sludge, and iron oxide and red hematite showed a corrosion phenomenon in the reaction tank. When analyzing the particle size distribution of magnetite, its apparent density was 1.25 g/cm3 and true density 3.95 g/cm3. Its specific gravity is higher than that of microsand(2.65 g/cm3), which is being used in the weighted coagulation settling process. This is why it is thought that magnetite can improve the precipitability of sludge in the precipitation process. As a result of analyzing the precipitation characteristics of sludge after injecting magnetite into PAC­injected sludge versus PAC­noninjected sludge, it was found that the optimal injection rate in PAC­injected sludge was 1.0 ~ 1.5 g/L and that in PAC­noninjected sludge was 1.5 ~ 1.75 g/L considering the settling rate and SS concentration, showing an improved result of precipitability by about 30 ~ 40 %. If it’s injected into a final settling tank to improve deposition efficiency, this is considered to stabilize the interface layer of sludge fast. As a result of measuring SV30 by using magnetite as ballasted flocculant after adjusting the water temperature into 6 ∼ 8 ℃ for improving the settling efficiency during winter season, it was found that sedimentation rate would be improved by 40 ~ 50 % compared to the control sludge and this result is considered to be effective for increasing the settling efficiency if it’s used as ballasted flocculant for keeping and driving the high­concentration MLSS in winter season. As a result of adjusting the concentration into 15 mg/L with ammonium chloride(NH4Cl) as nitrogen source and analyzing the effect depending on nitrification for identifying the effect on nitrification when adding magnetite, it was found that nitrogen concentration was reduced compared to the control group and even when adding magnetite, there appeared no effect to be hindered by toxicity, which suggests that there will be no special problem in using ballasted flocculant. As a result of adjusting flow rates to (6, 8, 10) m3/hr with hydrocyclone and analyzing the magnetite collection rate, the collection rate of 64.15 %, 74.38 %, and 76.23 %, respectively could be gained and magnetite would be expected to have a higher collection rate by over 95 %, if attaching a magnet to hydrocyclone to earn much higher collection rate by considering the magnetic property. As a result of analyzing the reusability of magnetite that was separated by using the magnetic separation device after injecting magnetite into sludge, the settling efficiency was kept at 30.23 % for one­time reuse, 30.23 % for 2­time reuse, 29.07 % for 3­time reuse, 29.07 % for 4­time reuse, and 29.07 % for 5­time reuse. Even after 5 times of repetitive reuse, the settling efficiency was appeared to be kept at 29.53 % on average and even when recollecting and reusing magnetite, this is considered to have no special effect on deposition efficiency. Putting the above research findings together, to improve the sludge settling efficiency, magnetite was used as precipitation medium and sludge was injected, and from the settled sludge, magnetite could be recollected for reuse in case hydrocyclone was used. This is considered not only to improve settling efficiency but also be used as an alternative to reduce chemical coagulant. 본 연구에서는 하수 슬러지 침전 효율 향상을 위한 방안으로 가중침전제로 사용되고 있는 magnetite를 적용한 후 슬러지의 침전 특성을 살펴보았다. 또한 hydrocyclone 장치를 사용하여 침전된 슬러지를 효율적으로 분리 및 회수하기 위한 실험을 수행하여, 슬러지 침전 효율을 향상시킬 수 있는 연구를 수행하였다. 가중침전제 종류에 따른 침전 특성을 분석하기 위하여 magnetite(Fe3O4), 적철광(Fe2O3), 산화철(FeO)를 1 g/L 각각 주입한 결과 SV10 의 침전 효율은 대조군 슬러지에 비해 산화철의 경우 31.82 %, 적철광의 경우 40.91 %, magnetite의 경우 45.45 %의 침전율이 개선되는 것으로 나타났으며 산화철과 적철광의 경우 반응조 내 부식현상이 발견되었다. Magnetite 입경 분포 분석 시 겉보기 밀도 1.25 g/cm3, 진밀도 3.95 g/cm3으로 일반적으로 가중응집침전 공정에서 사용되어지는 microsand 보다 비중이 높기 때에 침전 공정에서 슬러지의 침전성을 향상 시킬 수 있을 것으로 판단된다. PAC이 주입된 슬러지와 미 주입된 슬러지를 이용하여 magnetite 주입에 따른 슬러지의 침전 특성을 분석한 결과 PAC이 투입되는 경우에서의 최적 주입률은 1 ~ 1.5 g/L 이었으며, PAC이 투입되지 않은 경우에서의 최적 주입률은 침전율과 SS 농도를 고려할 때 1.5 ~ 1.75 g/L 전후로 투입하여도 침전성이 약 30 ~ 40 % 개선되는 결과를 나타내었다. 최종침전지에 침전 효율 향상을 위해 주입할 경우 슬러지의 계면층을 빠르게 안정시킬 수 있을 것으로 판단된다. 동절기 침전 효율 개선을 위해 수온 6 ∼ 8℃로 조절 후 magnetite를 가중침전제로 사용하여 SV30을 측정한 결과 대조군 슬러지에 비하여 약 40~ 50 % 정도 침전율 개선이 가능할 것으로 나타났으며 이러한 결과는 동절기 고농도의 MLSS 유지운전을 위한 가중침전제로서 사용 시 침전 효율 상승에 효과적일 것으로 판단된다. Magnetite 투입 시 질산화에 대한 영향을 학인하기 위하여 염화암모늄(NH4Cl)을 질소원으로 하여 농도를 15 mg/L 조절 후 질산화에 따른 영향을 분석한 결과, 대조군과 비교하였을 때 질소 농도가 감소하는 특성을 나타내었으며 magnetite를 투입하여도 독성으로 저해될 인자는 없는 것으로 나타나 가중침전제 사용에 특별한 문제는 없는 것으로 판단된다. Hydrocyclone 장치를 사용하여 유량을 6, 8, 10 m3/hr 로 조절하고 magnetite 회수율을 분석한 결과 각각 64.15 %, 74.38 %, 76.23 %의 회수율을 얻었으며 magnetite는 자성을 가지는 특성을 고려하여 보다 높은 회수율을 얻기 위하여 hydrocyclone에 자석을 부착한 경우 약 95 % 이상으로 높은 회수율을 기대할 수 있는 것으로 나타났다. Magnetite를 슬러지에 주입하고 자력선별 장치를 이용하여 분리한 magnetite의 재사용 가능성을 분석한 결과 1회 반복 시 30.23 %, 2회 반복 시 30.23 %, 3회 반복 시 29.07 %, 4회 반복 시 29.07 %, 5회 반복 시 29.07 %의 침전 효율이 유지되었다. 5회 반복 재사용 하여도 평균 29.53 %의 침전 효율이 유지된 것으로 나타났으며, magnetite를 회수하여 재사용 하였을 경우에도 침전 효율에 특별한 영향은 없을 것으로 판단된다. 이와 같이 위의 연구결과 등을 종합할 때 슬러지 침전 효율 향상을 위하여 가중침전제로 magnetite를 이용하여 슬러지에 주입하고, 침전된 슬러지는 hydrocyclone 장치를 이용할 경우 magnetite를 회수하여 재사용 할 수 있고, 이는 침전 효율을 향상 시킬 수 있을 뿐만 아니라, 화학응집제를 절감 시킬 수 대안으로도 사용할 수 있을 것으로 판단된다.

정수장애 조류와 조류플럭의 침강 효율에 대한 검정

최수경 仁濟大學校 大學院 2004 국내석사

조류는 일반 유기물 입자보다 밀도가 낮고 형태가 매우 다양한 입자로서 응집혼화, 침전 및 여과의 각 정수공정 단계에서 장애를 일으킬 뿐 아니라 냄새를 발생하여 맛을 떨어뜨리는 원인이 되고 있다. 본 연구는 정수장에서 장애를 일으키는 대표적인 담수조류 14종을 대상으로 침강속도와 플럭침강을 측정하고 조류밀도와 형태에 따른 침강의 차이점을 조사하였다. 침강법과 형광법으로 조류의 침강속도를 측정하였으며 주로 배양조류를 대상으로 하였다. 침강법으로 측정한 조류의 침강속도는 0.3~1.9 cm/hr, 형광법으로 측정한 결과 0.1~2.6 cm/hr 범위였다. 조류의 침강속도는 조류의 종별, 생장주기별, 사멸시키기 전과 후, 전염소처리 전후로 구분하여 비교하였다. 조류의 생장주기에 따른 침강속도를 측정한 결과 쇠퇴기의 조류는 지수기 보다 약 1.7(1.3~2.3)배 높았으며 지수생장기, 정지기 및 쇠퇴기로 갈수록 침강속도는 점진적으로 증가하였다. 포르말린으로 사별시킨 조류의 침강속도를 측정한 결과 0.1~3.3 cm/hr 범위였다. 사멸 조류의 침강속도는 정상조류 보다 약 1.5배(1.0~2.6 cm/hr) 증가하였다. 그러나 형광법의 경우 대상조류 7종 중에서 Scenedesmus acutus, 침강법의 경우 14종 중에서 Synedra acus, A. ambigua m. sporalis, Actinastrum hantzschii, Ankistrodesmus gracilis의 사멸 조류가 정상조류보다 침강속도가 더 낮았다. 규조류의 침강속도가 다른 조류보다 높았으며 조류의 형태에 있어서는 Aulacoseria ambigua, Aulacoseira granulata, Fragilaria crotonensis, Pediastrum boryanum var. longicorne 등 군체형의 침강속도가 단세포조류보다 더 높았다. 조류를 염소처리한 후 침강속도를 측정하였을 때 대부분의 조류는 염소처리전보다 침강속도가 증가하였으나, Stephanodiscus hantzschii f. tenuis와 Asterionella gracillima의 침강속도는 각각 염소처리 전 속도의 30%와 60%에 불과하였다. 배양조류에 PAC 응집제를 처리하여 플럭의 형태로서 S. acus 제거율을 보았을 때 염소 처리시 조류 최종 제거율 60%에서 처리 후 40%로, S. hantzschii f. tenuis는 약 70%에서 40%로 크게 감소하였다. 염소처리시 규조의 경우 조류 유기물이 산화되고 빈껍질만 남았고 군체의 경우 군체당 세포수의 감소로 인해 플럭크기가 작아 제거율이 낮은 것으로 보인다. 한편, 조류의 침강속도와 이론적인 형상계수를 이용하여 밀도를 추정한 결과 밀도와 조류의 형태가 조류 침강속도에 미치는 영향이 매우 컸다. 조류는 단세포 또는 다세포성 군체로서 밀도가 낮고 다양한 형태를 띠었으며 밀도보다 형상계수가 침강속도에 미치는 영향이 켰으며 특히 S. acus와 같이 가늘고 긴 바늘형태의 조류의 침강속도가 특히 낮았다. S. acus는 Synedra ulna와 형태가 비슷하였으나 S. ulna보다 밀도가 더 낮았다. 밀도가 낮고 형상계수가 높은 바늘형 조류의 침강성이 가장 나빴으며 이러한 형태의 조류는 상대적으로 응집 침전장애가 높고 여과지를 폐색시키는 빈도가 매우 높은 것으로 추정된다. The algal density is generally lower than the other organic particles and algae is special particles with diverse morphology. They usually make many problems in water treatment process and deteriorate the drinking water by producing the odorous compounds. The purpose of this study is to determine the settling velocity of algae and their flocculants, for the important species in the natural waters and in water treatment process. Our research were centered upon the algal density and algal shape to affect the settling. The settling velocity was measured with methods column (SETCOL) and fluorometric methods. Cultivated algae were largely used in the experiments. The settling velocity ranged from 0.3 to 1.9 cm/hr by SETCOL method and from 0.1 to 2.6 cm/hr by fluorometric method. The settling velocity of algae was different with the growth phase, living or formalin-fixed conditions, chlorination. The settling velocity of algae were stationary phases which measures settling velocity algae increased the algal of faster towards the growing days and those of the stationary phase significantly increased approximately 1.7(1.3~2.3) times comparing with exponentially growing phase. Dead cell or colony were more faster than the normally living algae. Exceptionally, The velocity of Scenedesmus acutus are more faster than farmalin-fixed algae. Most colonial algae had more faster settling velocity than unicellular (ex. Aulacoseria ambigua, Aulacoseira granulata, Fragilaria crotonensis, Pediastrum boryanum var. longicorne). settlings of diatoms were more faster others algal groups. Chlorination enhance significantly settling velocity of the algae settling velocity of Stephanodiscus hantzschii f. tenuis and Asterionella gracillima(C5) accounted for 30% and 60% of that before chlorination. The PAC coagulation it controls and when the removal rate by settling. After PAC coagulants were treated to the algae, the removal rate by settling were very low The chloride would oxidize the cellular materials of diatoms and empty frustales dropped the settling velocity or removal rates. On the other hand, algal density was estimated with settling velocity and theoretical form coefficient, density and algal shapes were highly correlated with the settling. In the process that algae were formed to flocs with other particles or organic matters, the longer algae would make less dense flocs to weaken the algal settling. Actually, the compactness of the algal flocs were less dense than that of the other organic particles. The longer algae such as Synedra acus world make less compact or dense flocs to weaken the settling or removing. The problematic algae enhance the buoyancy and simultaneously overflow to the filtration basins to clog the sand pores.

An Investigation into the Multiscale Nature of Turbulence and Its Effect on Particle Transport

Tom, Josin ProQuest Dissertations & Theses Duke University 2022 해외박사(DDOD)

We study the effect of the multiscale properties of turbulence on particle transport, specifically looking at the physical mechanisms by which different turbulent flow scales impact the settling speeds of particles in turbulent flows. The average settling speed of small heavy particles in turbulent flows is important for many environmental problems such as water droplets in clouds and atmospheric aerosols. The traditional explanation for enhanced particle settling speeds in turbulence for a one-way coupled (1WC) system is the preferential sweeping mechanism proposed by Maxey (1987, J. Fluid Mech.), which depends on the preferential sampling of the fluid velocity gradient field by the inertial particles. However, Maxey's analysis does not shed light on role of different turbulent flow scales contributing to the enhanced settling, partly since the theoretical analysis was restricted to particles with weak inertia.In the first part of the work, we develop a new theoretical result, valid for particles of arbitrary inertia, that reveals the multiscale nature of the preferential sweeping mechanism. In particular, the analysis shows how the range of scales at which the preferential sweeping mechanism operates depends on particle inertia. This analysis is complemented by results from Direct Numerical Simulations (DNS) where we examine the role of different flow scales on the particle settling speeds by coarse-graining (filtering) the underlying flow. The results explain the dependence of the particle settling speeds on Reynolds number and show how the saturation of this dependence at sufficiently large Reynolds number depends upon particle inertia. We also explore how particles preferentially sample the fluid velocity gradients at various scales and show that while rapidly settling particles do not preferentially sample the fluid velocity gradients, they do preferentially sample the fluid velocity gradients coarse-grained at scales outside of the dissipation range.Inspired by our finding that the effectiveness of the preferential sweeping mechanism depends on how particles interact with the strain and vorticity fields at different scales, we next shed light on the multiscale dynamics of turbulence by exploring the properties of the turbulent velocity gradients at different scales. We do this by analyzing the evolution equations for the filtered velocity gradient tensor (FVGT) in the strain-rate eigenframe. However, the pressure Hessian and viscous stress are unclosed in this frame of reference, requiring in-depth modelling. Using data from DNS of the forced Navier-Stokes equation, we consider the relative importance of local and non-local terms in the FVGT eigenframe equations across the scales using statistical analysis. We show that the anisotropic pressure Hessian (which is one of the unclosed terms) exhibits highly non-linear behavior at low values of normalized local gradients, with important modeling implications. We derive a generalization of the classical Lumley triangle that allows us to show that the pressure Hessian has a preference for two-component axisymmetric configurations at small scales, with a transition to a more isotropic state at larger scales. We also show that the current models fail to capture a number of subtle features observed in our results and provide useful guidelines for improving Lagrangian models of the FVGT.In the final part of the work, we look at how two-way coupling (2WC) modifies the multiscale preferential sweeping mechanism. We comment on the the applicability of the theoretical analysis developed in the first part of the work for 2WC flows. Monchaux & Dejoan (2017, Phys. Rev. Fluids) showed using DNS that while for low particle loading the effect of 2WC on the global flow statistics is weak, 2WC enables the particles to drag the fluid in their vicinity down with them, significantly enhancing their settling, and they argued that two-way coupling suppresses the preferential sweeping mechanism. We explore this further by considering the impact of 2WC on the contribution made by eddies of different sizes on the particle settling. In agreement with Monchaux & Dejoan, we show that even for low loading, 2WC strongly enhances particle settling. However, contrary to their study, we show that preferential sweeping remains important in 2WC flows. In particular, for both 1WC and 2WC flows, the settling enhancement due to turbulence is dominated by contributions from particles in straining regions of the flow, but for the 2WC case, the particles also drag the fluid down with them, leading to an enhancement of their settling compared to the 1WC case. Overall, the novel results presented here not only augments the current understanding of the different physical mechanisms in producing enhanced settling speeds from a fundamental physics perspective, but can also be used to improve predictive capabilities in large-scale atmospheric modeling.

Servo performance enhancements using accelerometer in HDD

이남훈 Graduate School, Yonsei University 2003 국내석사

하드디스크는 디스크 면에 쓰여진 서보정보를 이용하여 서보를 수행한다. 이 서보섹터가 디스크 면에서 차지하는 부분을 최소화할수록 디스크의 정보기록용량은 증가하기에 최소한의 섹터로써 서보를 하는 것이 바람직하다. 하지만 너무 작은 서보섹터는 서보신호의 샘플링 주파수를 떨어트려 서보성능의 저하로 연결된다. 멀티 센싱 섹터 서보를 하게 되면 센싱 간격이 좁아지게 되므로 제어주파수대역이 넓어지게 되고 DC 게인을 높일 수 있다. 본 논문에서는 가속도계를 사용하여 멀티 센싱 서보를 구현해 보았다. 본 논문에서는 하드디스크 서보에 있어서 발생하는 문제점들을 트랙킹, 시킹, 세틀링 시점으로 나누어 각각의 과정에 필요한 제어기를 설계 및 적용시켜 보았으며 앞에서 언급한 샘플링 레이트 문제도 멀티레이트 샘플링을 통해서 해결해 보고자 하였다. 이 논문에서는 이 세가지 서보성능에 입력외란 성분인 풍력, 플랙스 케이블 바이어스 등 저주파수 외란이 영향을 많이 미친다고 보고 이를 보상해주었다. 본 논문은 하드디스크 서보의 세 종류( 트랙킹, 시킹, 세틀링)의 성능향상을 위해 여러 가지 제어기와 함께 가속도계를 이용하여 멀티 레이트 센싱을 하여 저주파 외란을 효과적으로 보상해주었다. 트랙킹에서는 약 10%의 오차 감소를 보였으며 시킹에서는 5msec이하의 seek time을 보였으며 세틀링 서보에서도 보다 더 안정적인 성능을 보였다. HDD servo techniques are composed in Seeking, Settling and Tracking servo. Servo performance enhancements are required for increasing the storage capacity and servo stability and accuracy, fastness in seeking and settling. For enhancement performance, we minimized the length of time to seek using PTOS with LQ controller with estimator in seeking servo, we used and LQ controller with estimator to pursuit the track center exactly in tracking servo, and to settle quickly, we use both PID controller and PTOS in settling servo. Additionally, This paper focuses on multi sensing, so we use the accelerometer to compensate disturbances due to windage, pivot friction, flexible cable and so on.

입경 특성을 고려한 침강속도 측정 및 추정에 관한 연구

안종환 전북대학교 대학원 2024 국내박사

In this study, in order to supplement existing methods for estimating the settling velocity of sediment particles, settling velocity measurement devices was improved and the estimated results were compared derived from various settling velocity models. First, an image analysis program was developed to consider the characteristics of the sediment particles that have an important influence on the settling velocity, and the shape characteristics were quantitatively evaluated using the image analysis program. The analysis image was obtained using a mobile phone camera mounted on the device for measuring the shape factor of the sediment particles, and the shape characteristics of the sediment particles were analyzed based on the image analysis technique. This method is simple, cost-effective, and can produce fairly high accuracy. Meanwhile, a device for precisely measuring the settling velocity through underwater weight measurement has been developed. This device is made by improving the disadvantages of the existing settling column. The underwater weight collected using a load cell is measured, and it is converted into settling velocity using a fixed fall distance and fall time. The measurement operates quickly and precisely. As a result of the settling experiment on 11 single-grain, Bongpo and Kkotji beach samples, it was clearly confirmed that the settling velocity increased as the particle diameter of the sediment particles increased, and the settling velocity decreased as the particle diameter decreased. The existing method of calculating the settling velocity was limited due to the physical limitation, but recently, a study on calculating the settling velocity without theoretical constraints using the measured data has been underway. Therefore, in this study, the results of the settling velocity calculation were derived using the data-driven approach according to recent research trends. The settling velocity was predicted with five estimated formulas including random forest and the results were compared. The results were similar to those of the experimental data and the coefficient of determination by ramdom forest was the highest. As a result of estimating the importance of characteristic factors, the importance of particle size and drag coefficient was high. This means that the grain size and drag coefficient are very important in estimating the settling velocity of sediment particles. However, the performance of the random forest model relies on the sufficiency and accuracy of the training data. Therefore, additional settling experiments under various conditions using domestic sediment samples need to be conducted. Settling experiments can be rapidly conducted using the newly developed settling velocity measurement device in this study. By adding data and performing analyses, more accurate and consistent settling velocity values across diverse physical environments can be derived. In the future, if more settling velocity data on domestic sediment is accumulated, it can contribute to the establishment of coastal erosion management plan and the collection of basic data necessary for evaluation / prediction of sediment movement occurring in the coast, and it can be greatly utilized for the improvement of accuracy such as sediment transport evaluation linked with physical and environmental characteristics of the water area.

동적반복하중을 가한 외부 및 내부 연결 임플란트에서의 침하현상에 대한 연구

김승현 성균관대학교 일반대학원 2013 국내석사

[목적] 본 연구에서는 (1) 외부 및 내부 연결 임플란트에서 일정한 시간 후 가해진 추가적 조임 토크에 따른 지대주의 침하량을 측정하여 나사의 재조임에 의한 침하현상의 발생을 관찰하였으며, (2) 외부 및 내부 연결 임플란트에 동적반복하중을 가하여 주기횟수 (cycle)에 따라 단계적으로 발생된 지대주의 침하량을 비교 분석함으로써 하중의 기간에 따른 침하량의 변화를 임플란트 시스템별로 살펴보았다. [연구 재료 및 방법] 세 가지의 서로 다른 임플란트-지대주 조합이 사용되었다 (Int-1군: 내부 원추형 연결 임플란트 + 일체형 지대주 (N = 10); Int-2군: 내부 원추형 연결 임플란트 + 분리형 지대주 (N = 10); Ext군: 외부 육각형 연결 임플란트 + 분리형 지대주 (N = 10)). Digital torque gauge를 사용하여 30 N㎝의 조임 토크로 최초의 나사 조임 후 10분 간격으로 두 번의 재조임을 시행하였다. Electronic digital micrometer (EDM)를 이용하여 임플란트-지대주 복합체의 전체 길이를 측정하였으며 조임 토크에 의해 감소된 길이를 나사의 재조임에 의한 지대주의 침하량으로 간주하였다. ISO 규정에 따라 25 N ~ 250 N, 14 ㎐, sine 파형의 동적반복하중을 지대주 장축과 30° 경사각도에서 주기횟수 (1, 2700, 5400, 8100, 18900, 81000, 486000 cycle)에 따라 단계적으로 가한 후, EDM을 이용하여 동일한 방법으로 하중의 기간에 따른 지대주의 침하량을 측정하였다. [결과] 반복하중 전, 나사의 재조임에 의하여 세 군에서 모두 통계적으로 유의한 지대주 침하현상이 발생하였으며, 침하량은 Int-2군 > Int-1군 > Ext군 순으로 많았다 (P < 0.05). 반복하중에 의한 지대주의 침하는 Int-1군과 Int-2군에서 대부분 0 ~ 1 cycle 사이에 발생하였으며 Int-1군의 경우 5400 cycle (약 2일) 이후, Int-2군의 경우 8100 cycle (약 3일) 이후에서는 침하량의 유의한 차이가 있다고 볼 수 없었다. Ext군의 경우 모든 순차적 주기횟수 구간에서 침하량의 차이가 통계적으로 유의하다고 할 수 없었다 (P > 0.05). 반복하중에 의해 세 군에서 모두 통계적으로 유의한 지대주 침하가 관찰되었으며, Int-2군 > Int-1군 > Ext군 순으로 침하량이 많았다 (P < 0.05). [결론] 외부 및 내부 연결 임플란트에서 나사의 재조임 및 동적반복하중의 기간에 따라 다양하고 유의한 지대주의 침하가 관찰되었다. [Purpose] This study (1) observed the occurrence of settling by screw retightening in external and internal connection implant systems by measuring the settling values of abutments according to additional tightening torques that were added after a certain passage of time, and (2) looked into changes of the settling values according to the loading period by implant systems through a comparative analysis of the settling values of abutments that occurred by adding step by step dynamic cyclic loading to external and internal connection implant systems according to cycles. [Materials and methods] Three different implant-abutment connection systems were used (Int-1: internal tapered conical connection + one-piece abutment (N = 10); Int-2: internal tapered conical connection + two-piece abutment (N = 10); Ext: external hex butt joint connection + two-piece abutment (N = 10)). Screw retightening conducted twice at intervals of 10 min. after initial tightening of the screw with 30 N㎝ torque using a digital torque gauge. The total lengths of the implant-abutment samples were measured using electronic digital micrometer (EDM), and considered the reduced length by tightening torque as the settling value of abutment by screw retightening. After adding step by step dynamic cyclic loading with sine waveform of 25 N ~ 250 N, 14 ㎐ in compliance with ISO regulations according to cycles (1, 2700, 5400, 8100, 18900, 81000, 486000) at the inclined angle of 30° from the long axis of an abutment, measured the settling values of abutments according to the loading period with the same method using EDM. [Results] Before the cyclic loading, the settling of abutments by screw retightening was shown to be statistically significant in all of the three groups, and the settling values were greater in the order of Int-2 group > Int-1 group > Ext group (P < 0.05). The settling of abutments by cyclic loading appeared mostly between 0 ~ 1 cycle in Int-1 group and Int-2 group. For Int-1 group, there was shown to be no significant difference in the settling values after 5400 cycles (about two days), whereas for Int-2 group there was no significant difference after 8100 cycles (about three days). For Ext group, there was no statistically significant difference in the settling values in the section of all the numbers of the sequential cycles (P > 0.05). In all the three groups, a statistically significant settling of abutments was observed by cyclic loading, and the settling values were greater in the order of Int-2 group > Int-1 group > Ext group (P < 0.05). [Conclusion] In accordance with the screw retightening and the period of dynamic cyclic loading, it was observed that there was diverse and significant settling of abutments in external and internal connection implant systems.

Enhanced biodegradation in high phenol-fed MBRs by membrane-contained fungal populations

안수정 Graduate School, Yonsei University 2010 국내박사

유량계 컨트롤밸브 방식에 의한 응집제 최적주입에 관한 연구

박세복 경북대학교 산업대학원 2010 국내석사

This study is to analyze optimal injection of coagulant using elctro -magnetic flowmeter and control valve. To analyze the optimal injection, it is essential to study the relationships between Proportional, Integral, Derivative action of micro-controller and damping time of electromagnetic flowmeter. To collect the data on relations between P-I-D of micro-controller and damping(delay time) of flowmeter, the experiment was performed in the water treatment plant in Gumi Gyeongsangbuk-do. In present operating state(P=100%, D=0, damping=5sec), settling time was faster on an interval 0.02<I<0.3 and the decrease of P value cause the increase of I value for the settling of flowrate. it is judged that the decrease of P value did not help settling of flowrate. The increase of D factor prolonged 1.38 times of settling time. it is judged that the increase of D factor did not affect the settling of flowrate. In the relation between damping(delay time) and I, settling time was faster on an interval 0.02<I<0.3 and minimum time of flowrate settling was 5 second when I was 0.05 minute per repeat. It is desirable not to use damping value greater than or equal to 10 second because the increase of damping factor greater than or equal to 10 second tends to oscillate.

SBR에서 호기성입자의 생성에 대한 침전시간의 영향에 관한 연구

김성진 경상대학교 대학원 2009 국내석사

The essential role of hydraulic settling time in the formation of aerobic granules was studied in four column sequencing batch reactors. we used aerobic granular system to figure out the formation of aerobic granules, in different settling time, 3 mins, 5 mins, 10 mins, and 30 mins. Results showed that aerobic granules were successfully cultivated and became dominant only in the reactor of settling time 5min. After two weeks, aerobic granules were formed. After four weeks, a completed circular aerobic granulation was made. After fifteenth day of running, MLSS increased until 8140mg/L in the reactor of settling time 5min. As the result of SVI measurement, settling time 5 mins showed 40~58ml/g after two weeks. As measuring of Hydrophobicity, reactor of settling time 5 mins showed the highest number, 74% and reactors of 3 mins, 10 mins and 30 mins showed low values, 38%, 56%, and 35%. respectively measuring SOUR, reactor of 5 mins showed highest value, 248mg O2/g MLSS hr and reactor of 3 mins, 10 mins, and 30 mins displayed 88, 170, 90mg O2/g MLSS. Respectively examining the efficiency of COD removal, reactor of 5 mins indecated 92%, the highest, and reactors of 3 mins, 10 mins, and 30 mins show 32%, 68.8% and 47.3%. Respectively reactors with 5 mins of settling also showed 66% of T-N removal efficiency and 51.5% T-P removal efficiency.

Settling time of dental X-ray tube head after positioning

윤숙자 全南大學校 1999 국내박사

Purpose: The aim of this study was to determine the settling time, the time it takes for the tube head to stop oscillating, on the basis of the oscillation graphs. Materials and Methods: A sensor (accelerometer, Piezotron^□ type 8704B25) was utilized to measure the horizontal oscillation of the x-ray tube head just after aiming the tube head for intraoral radiograph. The signal from the sensor was transferred to a dynamic signal analyzer, which displayed the magnitude of the acceleration on the Y-axis and the time lapse on the X-axis. The horizontal oscillation of the tube head was measured with time, and the settling time was also determined on the basis of the acceleration graphs for 6 wall type, 5 floor-fixed type, and 4 mobile type dental x-ray machines. Results: The oscillation of the tube heads decreased rapidly over time. The settling time varied with x-ray machine types. The settling time was up to 6 seconds for the wall types, 5 seconds for the floor-fixed types, and 11 seconds for the mobile types. Conclusion: It may be wise to make an exposure after about 6 seconds on the wall types, 5 seconds on the floor-fixed types and 11 seconds on the mobile types after positioning the x-ray tube head. 목적 : x-선 관구 진동이 정지하는데 걸리는 시간인 조정시간을 가속도 그래프를 토대로 결정하기 위한 것이다. 재료 및 방법 : X-선 관구의 수평방향 진동을 측정하기 위해 가속도계(Piezotron^□ type 8704B25)를 사용하였다. 측정한 x-선 기기는 벽 고정식 6대, 바닥 고정식 5대, 이동식 4대로 총 15대였다. x-선 관구를 구내 방사선을 촬영하는 위치로 옮긴 후, 손을 떼면서 진동을 측정하였다. 감지기로부터의 신호를 dynamic signal analyzer로 받아들여 관구 진동을 시간 경과에 따른 가속도량으로 나타내었다. 이 그래프를 토대로 측정된 가속도량에서 잡음을 빼고 조정시간을 결정하였다. 결과 : x-선 관구 진동은 시간경과에 따라 급속히 감소하였고, 관구의 조정시간은 기기의 유형에 따라 다양하였다. 고정식에서는 6조, 바닥고정식에서는 5초, 이동식에서는 11초 이내로 관구의 진동이 정지되었다. 결론 : 관구를 위치시킨 후 고정식에서는 6초, 바닥고정식에서는 5초, 이동식에서는 11초 경과 후에 방사선을 노출하는 것이 바람직하다.