The demand for high-strength steel is rising due to its economic efficiency. Low-cycle fatigue (LCF) tests have been conducted to investigate the nonlinear behaviors of high-strength steel. Accurate material models must be used to obtain reliable results on seismic performance evaluation using numerical analyses. This study uses the combined hardening model to simulate the LCF behavior of high-strength steel. However, it is challenging and complex to determine material model parameters for specific high-strength steel because a highly nonlinear equation is used in the model, and several parameters need to be resolved. This study used the particle swarm algorithm (PSO) to determine the model parameters based on the LCF test data of HSA 650 steel. It is shown that the model with parameter values selected from the PSO accurately simulates the measured LCF curves.

In this study, a pilot-scale (3 m3/day) membrane distillation (MD) process was operated to treat digestate produced from anaerobic digestion of livestock wastewater. In order to evaluate the performance and energy cost of MD process, it was compared with the pilot scale (10 m3/day) reverse osmosis (RO) process, expected competitive process, under same feed condition. As results, MD process shows stable permeate flux (average 10.1 L/m2/hr) until 150 hours, whereas permeate flux of RO process was decreased from 5.3 to 1.5 L/m2/hr within 24 hours. In the case of removal of COD, TN, and TP, MD process shows a high removal rate (98.7, 93.7, and 99% respectively) stably until 150 hours. However, in the case of RO process, removal rate was decreased from 91.6 to 69.5% in COD and from 93.7 to 76.0% in TP during 100 hours of operation. Removal rate of TN in RO process was fluctuated in the range of 34.5-62.9% (average 44.6%) during the operation. As a result of energy cost analysis, MD process using waste heat for heating the feed shows 18% lower cost compare with RO process. Thus, overall efficiency of the MD process is higher then that of the RO process in terms of permeate flux, removal rate of salts, and operating cost (in the case of using waste heat) in treating the anaerobic digestate of livestock wastewater.

오랜 기후변화와 관련하여 지구온난화를 늦추고자 온실가스 중 대부분의 비율을 차지하고 있는 이산화탄소를 분리 및 저장 할 수 있는 연구가 활발하다. 본 연구에서는 고 투과성을 지닌 Polyhedral oligomeric silsesquioxane(POSS)와 이산화탄소에 대한 선택도를 지닌 Poly(ethylene glycol)을 이용하여 POSS-PEG 공중합체를 합성하였고 이를 다공성 지지체 위에 코팅하여 복합막을 제조하였다. 특성평가로는 NMR과 FT-IR 스펙트럼으로 합성의 유무를 확인한 뒤 복합막에 N2,O2,CO2 세 종류의 기체를 투과 특성함으로써 성능을 확인하였다. single gas를 투과시켰을 때 CO2/N2 선택도 24, Mixture gas를 투과시켰을 때 최대 70%의 CO2 분리성능을 나타내었다.

계면동전위 특성평가는 분리막의 막오염 개선연구와 분리막의 표면전하 분석을 통한 고분자의 개질 확인 및 치환기 확인에 대한 연구로 활발히 진행되고 있다. 제타전위 (zeta potential)란 전기역학적 현상으로 발생하는 전위차를 정량화 한 값을 측정하는 것을 말한다. 이러한 제타전위를 측정하기 위해서는 전기영동 (electrophoresis), 전기삼투 (eletrosmosis), 유동전위 (streaming potential)를 측정하는 예가 있다. 그 중 평막은 유동전위 측정을 하는 것에 있어 가장 높은 재현성을 보인다. 따라서, 본 연구에서는 SEBS (polystyrene-ethylenebutylene-styrene) 고분자 개질을 통해 아민화된 SEBS 평막형 분리막을 제막하고, 제막한 아민화된 SEBS 고분자 분리막의 계면동전위 측정을 통해 계면 유동전위를 측정하여 결과를 분석하였다.

제타전위를 이용한 분리막의 막오염 개선연구와 분리막의 표면전하 분석을 통한 고분자의 개질 확인 및 치환기 확인에 대한 연구는 활발히 진행되고 있다. 제타전위(zeta potential)란 전기역학적 현상으로 발생하는 전위차를 정량화 한값을 측정하는 것을 말한다. 이러한 제타전위를 측정하기 위해서는 전기영동(electrophoresis), 전기삼투(eletrosmosis), 유동전위(streaming potential)를 측정하는 예가 있고 그중 평막은 유동전위 측정이 적합하다. 따라서, 본 연구에서는 SEBS(polystyrene-ethylene-butylene-styrene) 고분자를 개질하여 아민화된 SEBS 평막형택의 분리막을 제조하고, 제조한 아민화된 SEBS 고분자 분리막을 계면동전위 측정기 이용으로 유동전위를 측정하여 결과를 분석하였다.

본 연구에서는 폴리페닐렌옥사이드 고분자에 브롬화반응을 통해서 할로겐 원소를 수월하게 도입하고, 도입한 할 로겐 원소를 이미다졸륨으로 치환하여 이미다졸륨이 도입된폴리페닐렌옥사이드를 합성하였다. 다양한 특성평가를 통해서 합 성이 이루어졌음을 확인하였고, 산소, 질소, 이산화탄소 기체투과 특성평가를 진행하여 합성한 고분자의 기체특성을 확인하였 다. 이미다졸륨의 함량이 증가할수록 합성고분자의 이온교환용량이 증가하였으나, 기계적 강도는 감소하였다. 특히, 기체투과 도는 미세하지만 감소하는 경향을 나타내었으며, 이산화탄소/질소 선택도의 경우 이미다졸륨 함량이 높아질수록 증가하는 경 향을 확인할 수 있었다.

기체분리용 기능소재에 대한 세계적인 시장의 요구가 증가함에 따라 광범위한 연구개발이 진행되고 잇다. 본 연구는 둘 이상의 기체혼합물에서 높은 이산화탄소 포집성능을 목적으로 하는 복합막의 제조이다. Isocyanate와 SI-PEG, 소 량의 촉매를 사용하여 코팅액을 제조한 뒤 PAN지지체 위에 코팅하여 복합막을 제조하였다. SEM기기를 활용하여 복합막의 코팅층을 확인하였고 Bubble flowmeter를 사용하여 기체투과특성평가를 실시하였다. 기체복합막의 두께는 3 um 이하로 고른 분포를 보이며, 50 GPU의 이산화탄소 투과값과 질소에 대한 이산화탄소 선택도는 15의 결과를 보였다.

최근 전세계적으로 이산화탄소 분리기술에 관한 연구가 활발하게 이루어지고 있다. 그 중 특히 분리막을 이용한 이산화탄소 분리는 타 방식에 비해 다양한 장점으로 광범위하게 연구되고 있다. 본 연구에서는 고선택성을 지닌 Polyhedral oligomeric silsesquioxane(POSS)과 고투과성을 지닌 Poly(ethylene glycol)으로 이산화탄소 포집에 우수한 성능을 나타내는 POSS-PEG를 합성하고 특성평가하는 것에 중점을 두었다. 1H-NMR스펙트럼과 FT-IR 스펙트럼을 활용 하여 합성의 유무를 확인하였고 PAN지지체에 코팅하는 방식으로 복합막을 제조하였다. 기체특성평가를 실시하기 위해 기체투과에 필요한 실험모듈을 제작하였고 이산화탄소 투과특성을 평가하였다.

본 연구에서는 친수성고분자으로 중공사형 분리막을 개발하기 위해 상전이법을 이용하여 제조하였다. 고분자는 PAN을 사용하여 고분자용액을 제조하였고, PVP, PEG와 같은 첨가제를 사용하였다. 방사조건에서 에어갭을 조절하여 표면의 기공구조를 확인하였으며, 내부응고제의 조성을 조절하여 내부표면 및 전체적인 모폴로지에 영향을 확인하였다. 분리막의 단면과 표면 모폴로지는 전계방 출형주사현미경을 이용하여 관찰하였으며, 0.2 cm2의 테스트용 Lab. 모듈을 제 조하여 수투과도 평가를 진행하였다.

In this study, a direct contact membrane module was manufactured to be used in a pilot scale membrane distillation process to treat 3 m3/day of the digestate produced from anaerobic digestion of livestock manure. In order to investigate the performance of the membrane module, permeate flux was measured with and without spacer inside the module under various condition of temperature difference and cross flow velocity (CFV) through the membrane surfaces. Flux recovery rate after chemical cleaning was also investigated by applying three different cleaning methods. Additionally, thermal energy consumption was theoretically simulated based on actual pilot plant operation conditions. As results, we observed flux of the module with spacer was almost similar to the theoretically predicted value because the installation of spacer reduced the channeling effect inside the module. Under the same operating condition, the permeate flux also increased with increasing temperature difference and CFV. As a result of chemical in-line cleaning using NaOCl and citric acid for the fouled membranes, the recovery rate was 83.7% compared to the initial flux when NaOCl was used alone, and 87% recovery rate was observed when only citric acid was used. However, in the case of using only citric acid, the permeate flux was decreased at a rapid rate. It seemed that a cleaning by NaOCl was more effective to recover the flux of membrane contaminated by the organic matter as compared to a cleaning by citric acid. The total heat energy consumption increased with increasing CFV and temperature difference across the membrane. Thus, further studies should be intensively conducted to obtain a high permeate flux while keeping the energy consumption to a minimum for a practical application of membrane distillation process to treat wastewater.

분리막을 이용한 기체 투과 특성은 이산화탄소 분리성능이 탁월하다. 복합막제조에 앞서 Si-PEG를 합성한 뒤, 1H-NMR, GPC, FT-IR등을 이용하여 합성을 확인하고 지지체 위에 실리콘 코팅을 하여 SEM 사진으로 복합막의 코팅층 확인 및 Bubble flowmeter을 이용하여 기체투과 성능을 측정하였다. 코팅제는 Isocyanate와 합성한 Si-PEG, 소량의 촉매를 사용하여 지지체 위에 코팅하였고 고온에서 가교과정을 거친 후 복합막을 제조하였다. 제조한 기체투과 복합막은 3um 이하로 고른 분포를 보이고, 50GPU의 이산화탄소 투과값과 질소에 대한 이산화탄소 선택도는 15의 결과를 보였다. 또한 코팅제의 조성을 다양하게 변화하여 각각의 (N2, O2, CO2) 투과 성능을 확인 하였다.

본 연구에서는 혼합기체 투과 시 높은 CO2 선택도 특성을 가지는 분리막을 제조하기 위한 연구를 하였다. 이를 위해 Polyhedral Oligomeric Silsesquioxane(POSS)와 Polyethylene glycol(PEG)의 추가적인 합성을 진행하여 POSS-PEG를 얻었다. 또한 투과도와 선택도를 향상시키기 위해 POSS-PEG를 용매에 희석시켜 추가적인 코팅을 진행하여 복합막을 제조하였다. 특성평가 진행은 POSS-PEG Film의 기체투과 특성을 측정하기 위해 Time lag를 사용하였으며, N2, O2, CO2를 혼합한 혼합기체에 대한 특성평가는 Bubble flowmeter와 Gas chromatography를 이용하여 진행하였다.

In this study, a fluorescent silica nano particle is used as the surrogate for challenging test of membrane surface integrity. The particles are functionalized by a fluorescent dying agent so that as an ultraviolet light is imposed a bright fluorescent image from the particles can be taken. If a membrane surface is damaged and has a compromised part larger than the size of surrogate the fluorescent particles would pass through and contained in the permeate. An operator can directly notice whether the membrane surface is damaged or not by detecting a fluorescent image taken from the permeate. Additionally, the size of compromised part is estimated through analysing the fluorescent image in which we surmise the mass of particles included in the permeate by calculating an average RGB value of the image. The pilot scale experiments showed that this method could be applied successfully to determine if a membrane surface had a damaged parts regardless of the test condition. In the testing on the actual damaged area of 4.712 mm2, the lowest error of estimating the damaged area was –1.32% with the surrogate concentration of 80 mg/L, flux of 40 L/m2/hr for 25 minutes of detection. A further study is still going on to increase the lowest detection limit and thus decrease the error of estimation.

The demand for environmental consideration is on the increase in civil engineering. This study focuses on the development of technology to reduce the use of carbonate cement and improve its performance by using a silicate mineral and hardening agents, and presents the test results for the demonstrative evaluation of the properties of the raw material. Highly active feldspar was used as a binder to augment the bonding of the carbonate cement, and their change in strength was observed after test piece construction with the addition of soluble hardening agent. The uniaxial compression strength of the test piece of the general Portland cement with the addition of 0.5% soluble hardening agent, showed an increase by 33% and that of the test piece of cement with the addition of 70% substituted with feldspar increased by 28%. The strength of viscous soil; classified as soft ground, showed an increase of a maximum of 1.7 times when it was mixed with cement and solidifier depending on the curing period. These tests confirmed that a soluble solidifier is effective for improving the strength of a cement binder and that the highly active feldspar can be used as a binder.

In this study, we applied a membrane distillation process to investigate a feasibility of treating a wastewater with high concentration of organic matters including nitrogen and phosphorus. The laboratory scale experiment was performed by using a hydrophobic PVDF membrane with the pore size of 0.22 μm and porosity of 75%. The installation was direct contact type where the temperature difference between a feed and permeate side was controlled to have a range from 20 to 60°C. We observed a flux variation and a concentration changes of COD, PO4 3-－P, NH4 + -N and conductivity of feed side as well as permeate side with various temperature differences (20 to 60°C), cross flow velocities (0.09 to 0.27 m/s) through the module, and pH (6.6 to 12.0) of the feed that has the initial concentration of COD about 1,000 mg/L, total nitrogen 390 mg/L, total phosphorus 10 mg/L, conductivity of 7,000 μs/cm. The results showed that the average flux was ranged from 4 to 40 L/m2/hr which was almost similar with the flux of NaCl and deionized water used as a feed solution. The lowest flux was obtained at the operating condition with the temperature difference of 20°C and cross flow velocity of 0.09 m/s while the highest one was measured with 60°C and 0.27 m/s. Above 99% of COD and PO4 3- -P in the feed could be rejected regardless of an operating condition. However, the removal rate of ammonium nitrogen was varied from 64 to 99% depending on the pH of feed solution.

In this study, a novel method was proposed to test the integrity of water treatment system specifically equipped with membrane filtration process. We applied the silica particles coated with a fluorescent agent (rhodamine B isothiocyanate) as a surrogate to detect a membrane process integrity and evaluate the reliability of effluent quality in the system. Additionally, a series of experiments was conducted to evaluate the sensitivity of the method through the laboratory scale experiment. The laboratory scale experiments showed that the feasibility of application of proposed method to detect a breach or damaged part on the membrane surface. However, the sensitivity on predicting the area of a breach was significantly influenced by the testing conditions such as a concentration of surrogate, filtration flux, and detection time. The lowest error of predicting the area of breach was 3.5 % at the testing condition of surrogate concentration of 80 mg/L injected with flux of 20 L/m2/hr for 10 minutes of detection time for the breach having the actual area of 7.069 mm2. However, the error of estimation was increased at the small breach with area less than 0.785 mm2. A future study will be conducted to estimate a damaged area with more accuracy and precision.