• 한국전산구조공학회논문집
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• 제29권3호
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• pp.237-244
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• 2016

본 연구는 재료비선형 문제를 다루기 위한 비선형 MLS 차분법의 정식화 과정을 제시한다. MLS 차분법은 절점모델을 기반으로 고속 미분근사식을 활용하여 지배 미분방정식을 직접 이산화 하는데, 변수를 변위로 일원화한 Navier 방정식을 사용하여 탄성재료 문제를 다룬 기존의 MLS 차분법은 재료의 구성방정식을 별도로 고려할 수 없다. 본 연구에서는 비선형 재료의 구성방정식을 반영할 수 있는 강정식화를 위해 1차 미분근사를 반복 사용하는 겹미분근사를 고안했다. 응력의 발산으로 표현되는 평형방정식을 그대로 이산화하고 Newton 방법을 적용하여 반복계산을 통해 수렴해를 찾는 비선형 알고리즘을 제시했다. 응력 계산과 내부변수의 갱신은 return mapping 알고리즘을 활용하였고, 알고리즘 접선계수(algorithmic tangent modulus)의 적용을 통해 빠르고 안정적인 반복계산이 가능하도록 하였다. 재생성 시험을 통해 겹미분근사의 정당성을 검증했고, 비선형재료에 대한 인장문제의 해석을 통해 개발된 비선형 MLS 차분 알고리즘의 정확성과 안정성을 확인하였다.

• 한국수소및신에너지학회논문집
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• 제26권3호
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• pp.212-220
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• 2015

The engineering plastic of sulfonated polyether ether ketone (SPEEK) as a polymer matrix has been developed in this lab to replace Nafion, solid polymer electrolytes of perfluorosulfonic acid membrane which has several flaws such as high cost, and limited operational temperature above $80^{\circ}C$. The SPEEK was prepared in the sulfonation reaction of polyether ether ketone (PEEK). The organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted tungstosilicic acid (Cs-TSiA) with cross-linking agent contents of 0.01 mL. In conclusion, CL-SPEEK/Cs-TSiA/ceria 1% membrane showed the optimum results such as 0.1882 S/cm of proton conductivity at $80^{\circ}C$, and 99.61 MPa of tensile strength which were better than Nafion 117 membrane.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.49-52
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• 2008

최근 지구 온난화 현상에 따른 해수면 상승으로 삼면이 바다에 접한 우리나라는 향 후 많은 피해가 예측되므로 이에 따른 방호개념으로 기존의 단조로운 형상과 비 자연친화형 콘크리트 구조물의 설치 및 연안침식방지 기능부재로 인한 또 다른 피해가 발생된다. 국민소득의 증대와 Waterfront 개념의 빠른 확산으로 연안 어항의 낙후된 시설개선 등에 많은 사업이 추진되고 있으나 이러한 용도에 맞는 자연 친화형 구조물이 개발된 바 없어 기존의 Solid Block, Igloo Block, Tunnel Block 등이 일부 현장에 적용되고 있는 실정이다. 선박이 계류하는 안벽이나 물양장 등에서 항내 진입파와 항파 등으로 인한 반사파의 발생에 의한 공진현상으로 항내파고가 높아져 정온도유지가 어렵고 선박의 계류 및 하역에 지장을 주게 되며, 선박과의 충돌 발생으로 인한 소형선박의 손괴 발생율이 높은 실정이므로 새로운 형태의 블록(Block)개발이 필요하다. 이에 따라 개발한 C.E(Coastal Environments)블록을 현장에서 사용하기 위해서는 전단키 부분의 내하력 평가가 요구 된다. 따라서, 본 연구는 C.E 블록의 연결부 시험편을 제작하여 C.E블록 경계면의 마찰실험을 실시하였으며, C.E블록 연결부의 마찰계수를 측정하여 분석한 다음 C.E블록의 연결부 마찰계수를 평가하고자 한다.

• 한국세라믹학회지
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• 제36권2호
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• pp.178-185
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• 1999

Si3N4 겔캐스팅공정 제어를 위하여, 슬립 조성의 영향이 슬립의 점성특성과 성형체의 기계적 특성 및 소결체의 밀도에 미치는 영향에 대하여 조사하였다. 아크릴아마이드 모노머, 고분자전해질, 그리고 질화규소의 혼합물을 어트리터에 예비혼합한 후 볼밀링하여 슬립을 제조하였다. 개시제가 혼합된 슬립을 진공탈포하고 몰드에 주입하고 중합을 진행하였으며, 겔화된 슬립을 건조하여 성형체를 얻었다. 슬립의 특성과 성형체의 기계적 특성을 평가하기 위해, 슬립의 점도 측정과 직경방향 압축시험을 행하였다. 그 결과, near net shaping을 위한 낮은 점도를 갖는 46 vol%의 고농도 질화규소 슬립의 제조가 가능하였다. 성형체가 기계적 특성은 주로 모노머의 농도에 비례하여 증가하였다. 또한, 겔캐스트 성형체의 인장강도가 약 3MPa이 넘으면 기계적 가공이 가능하였으며, 겔캐스팅 성형체를 176$0^{\circ}C$, 3시간 상압소결하여 약 98.5%의 상대밀도를 얻을 수 있었다.

• Journal of Electrochemical Science and Technology
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• 제8권3호
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• pp.183-196
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• 2017

The research efforts directed at advancing water electrolysis technology continue to intensify together with the increasing interest in hydrogen as an alternative source of energy to fossil fuels. Among the various water electrolysis systems reported to date, systems employing a solid polymer electrolyte membrane are known to display both improved safety and efficiency as a result of enhanced separation of products: hydrogen and oxygen. Conducting water electrolysis in an alkaline medium lowers the system cost by allowing non-platinum group metals to be used as catalysts for the complex multi-electron transfer reactions involved in water electrolysis, namely the hydrogen and oxygen evolution reactions (HER and OER, respectively). We briefly review the anion exchange membranes (AEMs) and electrocatalysts developed and applied thus far in alkaline AEM water electrolysis (AEMWE) devices. Testing the developed components in AEMWE cells is a key step in maximizing the device performance since cell performance depends strongly on the structure of the electrodes containing the HER and OER catalysts and the polymer membrane under specific cell operating conditions. In this review, we discuss the properties of reported AEMs that have been used to fabricate membrane-electrode assemblies for AEMWE cells, including membranes based on polysulfone, poly(2,6-dimethyl-p-phylene) oxide, polybenzimidazole, and inorganic composite materials. The activities and stabilities of tertiary metal oxides, metal carbon composites, and ultra-low Pt-loading electrodes toward OER and HER in AEMWE cells are also described.

• 한국전산구조공학회논문집
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• 제26권6호
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• pp.471-474
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• 2013

본 논문에서는 치조골의 흡수 유형에 따른 치근단 절제술의 수술적 평가를 수행하였다. 유한요소해석이 사용되었으며 CT 이미지를 통하여 동양 성인 여성의 상악 중절치의 3D 모델을 사용하였다. 연구에는 상악중절치의 정상저작하중조건이 적용되었다. 치조골 흡수 유형에 따른 치근 절제술의 평가를 위해 정상모델과 함께 치조골의 전체적 흡수 모델, 순측 흡수 모델 및 설측 흡수 모델을 비교하였다. 이에 따라 설측 치조골 흡수의 영향은 순측 치조골의 흡수에 비해 치아의 유지 안정성에 미치는 영향이 작음을 확인하고, 설측 치조골 흡수로 인해 치근이 노출된 환자를 대상으로 한 치근 절제술의 위험 가능성을 제시하였다.

• 상하수도학회지
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• 제14권1호
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• pp.37-44
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• 2000

Laboratory experiments were conducted to investigate the performances of anaerobic filters packed with ceramic tube and pall-ring media treating a dairy waste. The media packing volume was 65% of effective volume of anaerobic filter. Organics removals of anaerobic filters were maintained above 80% even at an organics loading rate of $10kgCOD/m^3/d$, and this was comparable to aerobic treatment of organic wastes. Organics removals of the ceramic tube anaerobic filters were always lower than those of the pall-ring anaerobic filters due to intrinsic physical property of ceramic tube, especially lower void space which caused to clogging and entrapment of biogas, substrate transfer limitation, and irregular evolution of biogas leading to loss of solids and biomass. This was clearly observed in higher concentration of TSS in the effluent from the ceramic tube anaerobic filter despite of higher retention capacity of TSS compared with pall-ring media. Vertical distribution of organics and solids in the filters showed above 90% of organics and solids in influent were removed below 20% of reactor height, and 50% of remaining organics and solids were removed though media packing zone. Effluent quality from the anaerobic filter was heavily depended on media itself as well as suspended biomass formed below media. It is therefore concluded that the type of media played an important role in biomass accumulation arid gas-liquid-solid separation efficiency. Type of media did not affect the start-up behaviors of the anaerobic filter, and supernatant from anaerobic digested sludge showed a good performance as a seeding materials.

• 한국해양공학회지
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• 제34권4호
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• pp.263-271
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• 2020

In this study, we performed a three-dimensional (3D) topology optimization of a fixed offshore structure to enhance its structural stiffness. The proposed topology optimization is based on the solid isotropic material with penalization (SIMP) method, where a volume constraint is applied to utilize an equivalent amount of material as that used for the rule-based scantling design. To investigate the effects of the main legs of the fixed offshore structure on its structural stiffness, the leg region is selectively considered in the design domain of the topology optimization problem. The obtained optimal designs and the rule-based scantling design of the structure are manufactured by 3D metal printing technology to experimentally validate the topology optimization. The behaviors under compressive loading of the obtained optimal designs are compared with those of the rule-based scantling design using a universal testing machine (UTM). Based on the structural experiments, we concluded that by employing the topology optimization method, the structural stiffness of the structure was enhanced compared to that of the rule-based scantling design for an equal amount of the fabrication material. Furthermore, by effectively combining the topology optimization and rule-based scantling methods, we succeeded in enhancing the structural stiffness and improving the breaking load of the fixed offshore structure.

• Earthquakes and Structures
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• 제11권6호
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• pp.943-966
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• 2016

Recently, magnetorheological elastomer (MRE) material and its devices have been developed and attracted a good deal of attention for their potentials in vibration control. Among them, a highly adaptive base isolator based on MRE was designed, fabricated and tested for real-time adaptive control of base isolated structures against a suite of earthquakes. To perfectly take advantage of this new device, an accurate and robust model should be built to characterize its nonlinearity and hysteresis for its application in structural control. This paper first proposes a novel hysteresis model, in which a nonlinear hyperbolic sine function spring is used to portray the strain stiffening phenomenon and a Voigt component is incorporated in parallel to describe the solid-material behaviours. Then the fruit fly optimization algorithm (FFOA) is employed for model parameter identification using testing data of shear force, displacement and velocity obtained from different loading conditions. The relationships between model parameters and applied current are also explored to obtain a current-dependent generalized model for the control application. Based on the proposed model of MRE base isolator, a second-order sliding mode controller is designed and applied to the device to provide a real-time feedback control of smart structures. The performance of the proposed technique is evaluated in simulation through utilizing a three-storey benchmark building model under four benchmark earthquake excitations. The results verify the effectiveness of the proposed current-dependent model and corresponding controller for semi-active control of MRE base isolator incorporated smart structures.

• Advances in concrete construction
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• 제9권5호
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• pp.511-527
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• 2020

The main aim of the current research is to investigate the flexural behavior of the reinforced concrete (RC) slabs strengthened with strain hardening cementitious composites (SHCC) experimentally and numerically. Seven RC slabs were prepared and tested under four-points loading test. One un-strengthened slab considered as control specimen while six RC slabs were strengthened with reinforced SHCC layers. The SHCC layers had different reinforcement ratios and different thicknesses. The results showed that the proposed strengthening techniques significantly increased the ultimate failure load and the ductility index up to 25% and 22%, respectively, compared to the control RC slab. Moreover, a three dimensional (3D) finite element model was proposed to analyze the strengthened RC slabs. It was found that the results of the proposed numerical model well agreed with the experimental responses. The validated numerical model used to study many parameters of the SHCC layer such as the reinforcement ratios and the different thicknesses. In addition, steel connectors were suggested to adjoin the concrete/SHCC interface to enhance the flexural performance of the strengthened RC slabs. It was noticed that using the SHCC layer with thickness over 40 mm changed the failure mode from the concrete cover separation to the SHCC layer debonding. Also, the steel connectors prevented the debonding failure pattern and enhanced both the ultimate failure load and the ductility index. Furthermore, a theoretical equation was proposed to predict the ultimate load of the tested RC slabs. The theoretical and experimental ultimate loads are seen to be in fairly good agreement.