• Membrane and Water Treatment
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• 제6권6호
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• pp.451-476
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• 2015

Membrane distillation (MD), which can utilize low-grade thermal energy, has been extensively studied for desalination. By incorporating solar thermal energy, the solar membrane distillation desalination system (SMDDS) is a potential technology for resolving the energy and water resource problems. Small-scale SMDDS (s-SMDDS) is an attractive and viable option for the production of fresh water for small communities in remote arid areas. The minimum-cost design and operation of s-SMDDS are determined by a systematic method, which involves a pseudo steady state approach for equipment sizing and the dynamic optimization using overall system mathematical models. The s-SMDDS employing three MD configurations, including the air gap (AGMD), direct contact (DCMD) and vacuum (VMD) types, are optimized. The membrane area of each system is $11.5m^2$. The AGMD system operated for 500 kg/day water production rate gives the lowest unit cost of $5.92/m^3$. The performance ratio and recovery ratio are 0.85 and 4.07%, respectively. For the commercial membrane employed in this study, the increase of membrane mass transfer coefficient up to two times is beneficial for cost reduction and the reduction of membrane heat transfer coefficient only affects the cost of the DCMD system.

• 한국환경과학회지
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• 제12권9호
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• pp.957-966
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• 2003

Gunsan coastal area is one of region increasing pollution problems. To improve water quality, the reduction of these nutrients loads should be indispensible. In this study, the three-dimensional numerical hydrodynamic and ecosystem model were applied to analyze the processes affecting the eutrophication. In field survey, the average concentrations of dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphorus(DIP) at surface waters were found to be 0.43mg/$\ell$ and 0.03mg/$\ell$ respectively, which were exceeding second grade of water quality criteria. In hydrodynamic modelling, the comparison between the simulated and observed tidal ellipses showed fairly good agreement. The ecosystem model was calibrated with the observed data in study area. The simulated results of DIN were fairly good coincided with the observed values within relative error of 32.39%, correlation coefficient(r) of 0.99. In the case of DIP, the simulated results were fairly good coincided with the observed values within relative error of 24.26%, correlation coefficient(r) of 0.82. The simulations of DIN and DIP concentrations using ecosystem model were performed under the conditions of 20∼80% reductions for pollutant loading. At simulation results, concentration of DIN and DIP were reduced to 20∼80% and under 10% in case of the 80% reduction of pollutant loading, respectively.

• 한국정보통신학회논문지
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• 제14권2호
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• pp.513-520
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• 2010

잡음에 의한 열화현상은 디지털화된 데이터의 인지도를 저하시킨다. 따라서 신호의 에지 성분을 보존함과 동시에 잡음을 제거하기 위한 시간영역과 주파수영역의 다양한 방법들이 사용되고 있다. 본 논문에서는 신호에 중첩된 복합적인 잡음을 감소시키기 위해, 웨이브렛 근사 계수를 이용한 새로운 잡음 제거 알고리즘을 제안하였다. 제안된 알고리즘에서는 신호의 에지와 잡음에 대한 구분 성능을 향상시키기 위해, 웨이브렛 근사계수의 누적으로부터 얻어지는 오차함수의 분포특성을 이용하였다.

• Advances in concrete construction
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• 제11권5호
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• pp.409-417
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• 2021

The incorporation of non-biodegradable tyre waste in cement-based material has gained more interest towards sustainable construction these days. Crumb rubber (CR) from waste tyre is an alternative for sand replacement in low strength applications. Many researchers have studied CR cement-based materials produced by normal mixing (NM) method and reported a significant decrease in compressive strength due to CR. To compensate this strength loss, this research aims to study the innovative incorporation of CR in cement composite via the preplaced mixing (PM) method. In this investigation, cement composite was produced with NM and PM methods by replacing sand with 0%, 50%, and 100% CR by volume. The test results showed no significant difference in terms of densities of cement composite prepared with both mixing methods. However, cement composite prepared with PM method had lower strength reduction (about 10%) and lowered drying shrinkage (about 20%). In addition, the sound absorption coefficient and noise reduction coefficient of CR cement composite prepared by PM method were in similar range as those prepared with NM method. Overall, the results demonstrate that the PM method is promising, and the maximum replacement level of 50% is recommended for CR in the cement composite.

• International Journal of Naval Architecture and Ocean Engineering
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• 제13권1호
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• pp.858-876
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• 2021

Although widely used, the design of the bulbous bow for ships has been difficult due to the complex interference between the wave system generated by the bulb and the wave system of the ship hull. Until now, a bulbous bow has been often designed using Kracht charts, which were established based on model test data, but these charts apply only to ships with a block coefficient C_B = 0.56-0.82, Froude number Fn = 0.20-0.40, and the obtained bulb sizes are only close to optimal. This paper presents a new method for the optimal design of bulbous bow, starting from the design of an initial bulb using Kracht charts for ships with any block coefficient or Froude number, then resizing this initial bulb to define the optimal bulb sizes based on a multi-objective function of the required power reduction, and a combined solution of Computation Fluid Dynamics (CFD) analysis and surrogate models. This study was applied to a fishing vessel FAO 75, which has been model tested and used to design steel fishing vessels in Vietnam recently. The obtained quantitative results showed the same trend as the theory and practice, with a reduction of the ship's required power by about 14%.

• 마이크로전자및패키징학회지
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• 제29권4호
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• pp.89-94
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• 2022

고체상태에서 열에너지과 전기에너지를 직접적이고 가역적으로 변환할 수 있는 열전소재는 전기전도특성인 전기전도도 및 제벡계수와 열전도특성인 열전도도에 의해 그 성능이 결정된다. 하지만 전기전도도, 제벡계수, 열전도도는 소재의 조성, 결정구조 및 전자구조에 의해 결정되며, 서로 상관관계를 나타내기 때문에 성능 증대를 위한 효과적인 전략수립에 어려움이 있다. 본 논문에서는 열전소재의 성능과 관련한 수식에 대한 이해를 바탕으로 실험 결과와 연계하여 열전도도 저감 관점에서 효과적인 결함제어 기반 열전소재 성능 증대 전략을 수립할 수 있는 방법론을 제공하고자 한다.

• Imaging Science in Dentistry
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• 제53권4호
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• pp.313-323
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• 2023

Purpose: This study aimed to investigate the potential factors that could affect the reduction rate of odontogenic cysts following decompression using cone-beam computed tomography (CBCT) for 3-dimensional volumetric analysis. Materials and Methods: The study sample consisted of CBCT images of 41 individuals who underwent decompression of odontogenic cysts at the Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Chulalongkorn University, between 2010 and 2022. Preoperative and postoperative CBCT results were collected, and a volumetric analysis was conducted to evaluate the differences in the reduction rate and the percentage of volume reduction of cystic lesions based on different parameters. Correlations between these parameters were analyzed to determine associations. Results: In this study, the average time of decompression for odontogenic cysts was 316 days. Males demonstrated a higher reduction rate than females (P<0.05). The reduction rate was directly proportional to initial cyst volume, with higher reduction rates for cysts with large initial volume than those with small initial volume (P<0.05). Spearman's rank correlation coefficient indicated a weak positive correlation between the initial cyst volume and the duration of decompression. Additionally, a strong positive correlation was observed between the initial volume and the reduction rate. Conclusion: Knowledge of the reduction rate of odontogenic cysts is vital for surgeons to evaluate the duration of decompression before enucleation and to determine a definitive treatment plan. Sex and initial lesion volume had significant effects on the reduction rate.

• 한국산학기술학회논문지
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• 제21권12호
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• pp.880-887
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• 2020

본 연구는 고속열차가 개활지와 터널을 운행할 때, 풍압과 교행 등에 의한 외력이 차량에 가해질 때 고속열차의 주행안정성에 대해 고찰하기 위하여 진행되었다. 고속열차 교행에 의한 외력이 없을 때, 400 km/h 속도로 주행 시 8량 1편성의 고속열차의 주행안정성을 검토한 결과 윤중 감소량, 횡압, 탈선계수는 국내 법규인 고속철도차량 기술기준의 주행 안전 부분을 만족하였다. 선로중심 간격 4.6 m일 경우 터널 내, 개활지 강풍이 없을 때 고속열차 교행에 의한 외력의 영향은 차체의 횡가속도에 조금 영향을 주나 윤중 감소율, 횡압, 탈선계수에는 크게 영향이 없고, 고속철도차량 기술 기준에서 허용하는 기준치 이내였다. 선로중심 간격이 4.6~5.0 m이고, 열차가 400 km/h로 주행 시 개활지 강풍 20 m/s 및 교행에 의한 외력이 있을 때 윤중 감소율, 횡압 및 탈선계수는 허용치 이내이고, 강풍 30 m/s 및 교행에 의한 외력이 있을 때 윤중 감소율 및 횡압은 허용치를 초과하고, 탈선계수는 허용치 이내였다. 이 결과로 400 km/h급 고속열차는 풍속이 20 m/s 정도까지 안전하게 운행할 수 있으며, 풍속이 30 m/s에서는 감속 운행이 이루어져야 할 것으로 예측되었다.

• International Journal of Air-Conditioning and Refrigeration
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• 제12권1호
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• pp.37-49
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• 2004

Four different data reduction methods for the heat transfer coefficients from experimental data under dehumidifying conditions are compared. The four methods consist of two heat and mass transfer models and two fin efficiency models. Data are obtained from two heat exchanger samples having plain fins or wave fins. Comparison of the reduced heat transfer coefficients revealed that the single potential heat and mass transfer model yielded the humidity-independent heat transfer coefficients. Two fin efficiency models-enthalpy model and humidity model-yielded approximately the same fin efficiencies, and accordingly approximately the same heat transfer coefficients. The heat transfer coefficients under wet conditions were approximately the same as those of the dry conditions for the plain fin configuration. For the wave fin configuration, however, wet surface heat transfer coefficients were approximately 12% higher. The pressure drops of the wet surface were 10% to 45% larger than those of the dry surface.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.217-222
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• 2004

The aim of this paper is to investigate the effect of micro-dimple size on reduction friction and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.