Determination of clark unit hydrograph parameters for estimating probable maximum flood

이진욱 Greduate School, Korea University 2021 국내박사

The estimation of the exact probable maximum flood is very important for the design or evaluation of dams. The probable maximum flood was defined as the flood generated from the probable maximum precipitation. The probable maximum flood is estimated by using a unit hydrograph with the probable maximum precipitation as input. Recently, Clark unit hydrograph, which have time of concentration and storage coefficient as parameters, has been used in Korea. Until now, due to short observation period and lack of reliability verification of hydrological data, Clark unit hydrograph parameters were estimated with only a small number of storm events in a gaged basin, and no procedures have been presented for determining the parameters in an ungauged basin. In this dissertation, a method to determine unit hydrograph parameters for estimating the probable maximum flood was proposed. The summary for the total of five chapters conducted in this dissertation is as follows. First, the method for determining the time of concentration and the storage coefficient using peak velocity was examined and applicability of the method was confirmed through the observation data. Secondly, downstream variations of velocity in a storm event was theoretically derived and examined from the observation data. Third, the application method of rational formula for estimating the peak discharge for time-distributed rainfall was reviewed and examined from the observed data. Fourth, the possibility of estimating the velocity at an ungaged point in a rainfall event was inspected and the applicability of it to the downstream point was examined. Finally, a method to determine unit hydrograph parameters for estimating the probable maximum flood was proposed and evaluated. The results from the method were compared with those from the existing researches. Furthermore, consistency was examined by comparing them with the peak discharge obtained from the probability rainfall. The results from this dissertation would enable the determination of sufficiently objective unit hydrograph without subjective judgment based on the experience of each technician. Furthermore, it is expected that this method will help in the process of determining and reviewing parameters even for a gauged basin. Through this, it is expected that the methodology in this dissertation would be actively used in the new dam construction plans or safety evaluations.

Synthesis and characterization of silicone-acrylic hybrid pressure sensitive adhesives

박희웅 Greduate School, Korea University 2021 국내박사

This dissertation focuses on improving the properties of acrylic pressure-sensitive adhesives. In this study, polydimethylsiloxane (PDMS)-based materials were introduced by controlling various methods to overcome technical limitations of acrylic adhesives. This thesis is composed of five chapters, in which Chapter 1 and Chapter 5 are “Introduction” and “Conclusions,” respectively. In Chapter 2, to overcome the limitation due to the phase separation that occurs during direct blending of PDMS, a PDMS-based oligomer that can form hydrogen bonds with acrylic polymers was designed and added. An oligomer containing a urethane-based methacrylic group using PDMS as a soft segment were synthesized and added. Further, the oligomer was compared to a PDMS macromer containing a bifunctional methacrylic group without a urethane functional group. When PDMS without a urethane group was added, the adhesion properties were significantly deteriorated due to phase separation. However, PDMS urethane oligomers of similar molecular weight significantly improved the adhesive properties due to suppressed phase separation. Moreover, the surface energy of the adhesive tape also decreased, thereby significantly enhancing the adhesion on the low-surface-energy substrate. Further, three types of oligomers were synthesized based on the amount of the urethane group that was introduced into the silicone urethane oligomer and were added to the acrylic pressure-sensitive adhesive to prepare an adhesive tape. Depending on the number of moles of the urethane group, the phase separation was relieved to improve the adhesion properties compared with control, and a tape with improved heat resistance could be manufactured through additional ultraviolet (UV) curing. In Chapter 3, silicone–acrylic block copolymers were synthesized using a PDMS-based initiator. Depending on the content of the initiator, the adhesive strength of modified acrylic PSA tape was reduced due to the effect of the PDMS block; however, the surface energy of tape decreased, and the adhesive strength on the low-surface-energy substrate was significantly improved. Moreover, the heat resistance of the adhesive tape was significantly improved. In particular, based on the PDMS block content, the modified adhesive behavior at high temperature significantly improved the stability compared to the control acrylic adhesive. To overcome the degradation of the modified tapes of adhesion properties due to the microphase separation, the silicone urethane oligomer was added. Depending on the amount of the oligomer, the phase separation was reduced, and the adhesive tape with enhanced adhesion and heat resistance in the low-surface-energy substrate could be manufactured through an additional UV-curing process. In Chapter 4, acrylic copolymers grafted with PDMS were prepared using a methacrylate functional group terminated PDMS. Since the surface energy of the prepared pressure-sensitive adhesive was reduced due to the addition effect of PDMS, it was observed that the adhesive strength in the low-surface energy substrate was significantly improved. Adhesion properties of silicone grafted PSA tapes significantly changed with respect to the chain length of copolymerized PDMS. In the case of a short-chain PDMS-grafted adhesive, the phase separation did not occur and thus showed a relatively high adhesion tendency; however, the improvement in heat resistance was not large. In the case of a long-chain PDMS-grafted adhesive, heat resistance was significantly improved and a high-temperature adhesion stability was observed. Owing to the surface phenomenon caused by the addition effect of PDMS, the initial adhesive strength was significantly reduced, which increased significantly with the dwelling time. As a result, the initial adhesive strength was low, the adhesive strength on the low-surface-energy substrate was improved, and the adhesive tape with improved heat resistance could be manufactured. Using the results of our study, it is possible to provide an acrylic adhesive tape manufacturing route with improved heat resistance and improved adhesion in low-surface-energy substrates in the high-functional adhesive manufacturing process.

Synthesis and characterization of semi-crystalline n-type semiconducting molecules for organic field effect transistors and solar cells

유화숙 Greduate School, Korea University 2021 국내박사

Organic semiconductors that can secure sufficient flexibility are very important for the portability, flexibility, weight reduction, and convenience of next-generation electronics, information, and display-related products. Compared to inorganic materials, organic semiconductors offer their inherent superior mechanical flexibility or elasticity. It is compatible with print-based manufacturing technology (low-cost, high-throughput roll-to-roll production processes) using low-temperature processes. This allows the use of a variety of flexible substrates such as paper, plastics, and fibers, providing electrical, mechanical, and industrial advantages for many applications. These organic semiconductors are used as key materials for organic field effect transistors (OFETs) and organic photovoltaics (OPVs). Various donor and acceptor monomers are used in the synthesis of organic semiconductors. The energy levels are primarily determined by the donor's highest occupied molecular orbital (HOMO) energy level and the acceptor's lowest unoccupied molecular orbital (LUMO) energy level, and the energy level can be adjusted by optimizing the donor and acceptor moiety. However, controlling the HOMO and LUMO energy levels individually and accurately is not a very simple process. Because parameters such as substituents, planarity, molecular weight, and intermolecular interactions influence and correlate the energy level. It is necessary to properly select the position of the substituent and carefully design it to have the appropriate energy level and crystallinity. Herein, this dissertation describes the synthesis and characterization of semi-crystalline n-type semiconducting molecules for OFET and OPV. In chapter 2, three types of dicyanodistyrylbenzene (DCS)-based copolymers (PBDT-DCS, PT-DCS, and PNDI-DCS) were reported, which present highly balanced ambipolar charge transport characteristics in OFETs. The introduction of the DCS moiety in a polymer backbone not only lowers the LUMO level, but also increases the crystalline ordering via interchain dipole-dipole interactions. As a result, the LUMO levels for PBDT-DCS, PT-DCS, and PNDI-DCS were decreased to −3.76, −4.00, and −3.99 eV, respectively, which is beneficial for efficient electron injection from Au electrode for improving ambipolar charge transport. The determined hole/electron mobilities of the OFETs were 0.064/0.014, 0.492/0.181, and 0.420/0.447 cm2V–1s–1 for PBDT-DCS, PT-DCS, and PNDI-DCS, respectively, after thermal annealing at 250 °C. By incorporating the electron-deficient naphthalene diimide (NDI) unit in the copolymers, the n-channel transport was enhanced, with decreasing frontier molecular orbitals with enhanced electron injection and impeded hole injection from the Au electrode. Therefore, PNDI-DCS provided completely symmetric output curves in the positive and negative drain voltage regions with almost equivalent hole and electron mobilities. Benefitting from the balanced ambipolar feature of the PNDI-DCS OFETs, a complementary inverter was successfully fabricated. In chapter 3, a series of regioisomeric n-type small molecules were designed and synthesized, which have an identical diketopyrrolopyrrole (DPP) core and 2-(2,3-dihydro-3-oxo-1H-inden-1-ylidene)propanedinitrile (INCN) terminal groups with octyl substituents at different positions. The isomeric structures are confirmed by 2D NMR spectroscopy based on the heteronuclear multiple-bond coupling method. Incorporation of the electron-deficient DPP and strongly electron-withdrawing INCN groups yields deep frontier molecular orbitals with n-type charge-transport properties in solution-processed OFETs. Interestingly, a minor change in the substitution position of the octyl side-chains significantly influences the optoelectronic and morphological properties of the thin film. The polycrystalline morphology of the as-cast films is reorganized differently with thermal annealing depending on the octyl topology, significantly affecting the OFET performance. With thermal treatment at 200 ℃, the kinked DPP(EH)-INCNO1 structures transform into single crystalline-like structures, exhibiting a remarkably improved electron mobility up to ~0.6 cm2V–1s–1 compared with DPP(EH)-INCNO2 isomers. The more linear DPP(EH or HD)-INCNO2 molecules become more crystalline with thermal treatments but their polycrystalline packing structures with large grain boundaries are the main reason for their lower electron mobility. When the solubilizing alkyl substituents are selected, careful molecular design is needed, with consideration of both the solubility and intermolecular packing, for optimizing the optoelectronic properties. In chapter 4, two types of small molecule nonfullerene acceptors (IDICO1 and IDICO2) based on 2,2′-((2Z,2′Z)-((4,4,9,9-tetrahexyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b′]dithiophene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile (IDIC) are synthesized by attaching octyl side-chains onto terminal end groups. The alkyl substitution increases the LUMO (−3.81 to −3.86 eV) of the two acceptors, compared to that of IDIC (−3.94 eV). Interestingly, the IDICO1 and IDICO2 films have higher integrated absorption coefficients (1.49 × 107 cm−1) than the IDIC (1.29 × 107 cm−1) film. Also, the electron mobilities of IDICO1 and IDICO2 are approximately twice as high as that of IDIC. The terminal octyl substitution also improves the miscibility with a donor polymer (PBDB-T) to form well-intermixed blends with a decreased π–π stacking distance. As a result, their photovoltaic devices exhibit significant improvements in both the open-circuit voltage and short-circuit current density, compared to those of the reference PBDB-T:IDIC device, exhibiting maximum power conversion efficiencies of up to 9.64%, 20.4%, and 1.68% under 1-sun, 1000-lx LED, and halogen lamp illumination, respectively, which are significantly higher than those of PBDB-T:IDIC (7.2%, 11.7%, and 1.2%, respectively). It is worth noting that a maximum power density of 141.4 μW cm−2 is achieved for the PBDB-T:IDICO2-based device under a halogen lamp, which is the highest value report0ed to date among those achieved under indoor lighting conditions.

Synthesis and characterization of biomimetic polymer networks containing dynamic thiourea bonds controlled by base catalyst

이동수 Greduate School, Korea University 2021 국내석사

With the growing demand for synthetic materials meeting the disparate physical requirements of emerging applications, researches on biomimetic materials are becoming increasingly important. Biological polymeric materials are of particular interest due to their seemingly mutually exclusive mechanical properties such as stiffness, strength, toughness, resilience, and adaptability. Their unique properties originate from hierarchical structures constructed with weak noncovalent interactions and the strong covalent bonds. Recently, extensive efforts have been made to prepare biomimetic polymer networks (BMPNs), simultaneously utilizing the sacrificial noncovalent interactions and dynamic covalent bond exchanges. However, several constraints in terms of limited mechanical stiffness and strength, except for high extensibility, toughness, and resilience, still need to be addressed. There also remain opportunities to develop BMPNs with more simplified architectures using a dual-functional motifs capable of the dynamic covalent bond exchanges as well as the noncovalent interactions. In this study, an effective and facile preparation of BMPNs with a remarkable combination of multifaceted mechanical characteristics is presented by utilizing thiourea linkage as a hydrogen (H) bonding and dynamic covalent dual-functional motif. The thiourea-based BMPNs are fabricated via simple solution casting and thermal treatment from poly(ether-thiourea) (TUEG), triglycidyl isocyanurate (TGIC), and triazabicyclo[4.4.0]dec-5-ene (TBD) mixture. The dynamic exchange reaction of thiourea motif in the BMPNs, while still preserving the non-crystalline, dense H-bonding capability of thiourea motif, is readily controlled by the TBD catalyst and temperature. The BMPNs exhibit intriguing recovery of strain and mechanical performance after deformation as well as high elastic modulus (440 MPa), yield stress (23 MPa), strain at break (360%), and toughness (71 MJ m-3) are achieved at room temperature. Highly adaptive and malleable mechanical properties of the BMPNs are also observed in response to thermomechanical stimuli. The BMPNs present thermally distinct plasticity-based shape reconfiguration as well as elasticity-based shape memory behaviors. Moreover, the dynamic thiourea bond exchange is found to enable interfacial welding and reprocessing of the BMPNs. Thus, it is believed that this study represents a timely methodological advance and breakthrough in the synthesis and preparation of biomimetic polymeric materials with mechanical versatility. It can also be of particular interest for various emerging applications, such as 4D printing, shape-morphing devices, and soft robotics, which require mechanically robust, resilient, malleable, and adaptive substrate materials. Keywords: biomimetic polymer networks, noncovalent interactions, dynamic covalent bond exchanges, dual-functional motifs, 4D printing, soft robotics

(A) study to enhance the efficacy of cancer treatment using alternating electric fields

조윤희 Greduate School, Korea University 2021 국내박사

The incidence of cancer continuously increases as life expectancy increases. Cancer remains the leading cause of death worldwide despite extensive research to overcome the disease. Recently, Tumor treating fields (TTF), which are alternating electric fields with an intensity of <3 V/cm and a frequency of 100–300 kHz, is emerging as a new cancer treatment method. It is a treatment that inhibits the proliferation of cancer cells by preventing spindle formation during cell division. This results in the interference of the cell cycle and the delay of the recovery in case of DNA damage. Currently, it has obtained Food and Drug Administration (FDA) approval in the United States and CE mark in Europe for glioblastoma multiforme (GBM) and mesothelioma. TTF shows excellent therapeutic effects even for cancers that are known to be difficult to treat in phase III clinical trials. However, since this promising treatment has only been developed for less than 20 years, concerns regarding side effects must be clarified to demonstrate the safety of this treatment method. In addition, studies on methods for enhancing cancer treatment effects using TTF are also insufficient. Therefore, this study attempts to identify the existence of serious side effects of TTF on normal tissues and propose methods to increase the therapeutic effect through a change in treatment regimen or synergistic effect with other treatments. First, the damage to normal tissues was compared with the damage to tumors in vitro and in vivo after TTF treatment to investigate the side effects of TTF treatment. The results show that no serious damage was found in the normal tissues, suggesting that the side effects of TTF treatment may not be serious. These results were the same in experiments using patient-derived cancer cells and normal cells. Hence, our evidence based on in vitro and in vivo experiments suggests that TTF may cause selective damage to cancer cells, further demonstrating the potential of TTF as an appealing alternative to conventional cancer treatment modalities. Second, another study was conducted on the efficiency of the fractionated treatment method by improving the existing TTF treatment, which is recommended to be applied at least 18 hours a day. This study aimed to evaluate the biological effectiveness of cancer therapy with TTF using a fractionated treatment scheme that was originally designed for radiotherapy. Discontinuous fractional TTF with durations of 3, 6, 12, or 24 h/day was applied to cancer cells and normal cells for three days. The results show that the dependence on treatment duration in cancer cell inhibition was weakened distinctly at the treatment duration beyond 6 h/day. Particularly in normal cells, the effect of TTF decreased sharply when discontinuous therapy was applied. This study suggests that it is possible to maintain efficacy and improve the quality of life of patients if the treatment time is shortened and the intensity is increased according to the fractionated scheme. Another way to enhance the therapeutic effect of TTF is to use it as an adjunct to existing treatment methods. Hence, the combined effects of TTF and radiotherapy were studied using pancreatic cancer, which is also known to be difficult to treat. The combined in vitro effect of TTF and radiotherapy was evaluated in pancreatic cancer cell lines. Our results suggest that combined treatment with TTF and radiotherapy may be a good alternative treatment regimen for patients with pancreatic cancer. Lastly, the treatment effect was confirmed after the TTF was additionally applied to anticancer drug treatment. In fact, the combination of TTF and chemotherapy has been proven to be effective in several types of cancer through clinical trials. However, there is a limited number of anticancer drugs that have proven synergistic effects with TTF. Sorafenib, an anticancer drug that has never been studied with TTF, is used as the first line therapy for GBM as an anti-proliferative and apoptogenic agent. The effect of sorafenib on TTF-induced antitumor responses was evaluated in vitro and in vivo. The results showed that the combination of sorafenib and TTF treatment had a synergistic effect, suggesting that it could potentially be used to treat GBM in clinic. In conclusion, no serious side effects were found for TTF on normal tissues, which seem to have a positive effect on the quality of life of cancer patients. In addition, it is expected that treatment efficiency can be maximized through a fractional treatment method that increases the treatment intensity of TTF and reduces the treatment time. Finally, the combination of TTF and conventional treatments, such as radiotherapy or chemotherapy, is expected to overcome the limitations of current refractory cancer treatment.

(A) study on the physical properties of silicone hydrogels in relation with the structure and molecular weight of silicone macromers

성종배 Greduate School, Korea University 2021 국내석사

Silicone hydrogels are gas-permeable materials made through copolymerization of hydrophilic monomers and silicone monomers and have been widely used as biomaterials such as contact lenses, tissue engineering materials, and drug delivery materials. In particular, since silicone hydrogels have high oxygen permeability, they are mainly used as contact lenses for which oxygen permeability is important. Therefore, many researchers have done a lot of research to increase the oxygen permeability of silicone hydrogels. It was found that the oxygen permeability increases with the content of Si-O-Si, and the internal morphology of the silicone hydrogel has a great influence on the oxygen permeability. However, studies on the internal morphology, oxygen permeability, and water content of silicone hydrogels by various structures and molecular weight of silicone monomers are insufficient. Herein, 5 kinds of methacrylate-terminated silicone macromers were synthesized. All of the silicone macromers were identified by NMR and FT-IR. Furthermore, to analyze the physical properties according to the structure and molecular weight of the silicone macromer, silicone hydrogels were prepared by copolymerizing mixtures of silicone macromers, TRIS, and three hydrophilic monomers NVP, DMA, and HEMA with the same ratio. The oxygen permeability (Dk), internal morphologies, and equilibrium water content of obtained silicone hydrogels were measured. The results indicated that the silicone hydrogels presented different internal morphologies depending on the structure of silicone macromers. When the size of the silicone macromer was suitably large, the silicone phase continued and the oxygen permeability and water content increased. This study provides new information for designing silicone hydrogels with good oxygen permeability and water content. 실리콘 하이드로겔은 친수성 단량체와 실리콘 단량체의 공중합을 통해 만들어진 기체 투과성 물질로 콘택트 렌즈, 조직 공학 물질, 약물 전달 물질 등과 같은 생체 재료로 널리 사용되고 있다. 특히 실리콘 하이드로겔은 산소 투과성이 중요한 콘택트 렌즈의 재료로 주로 사용되고 있다. 실리콘 하이드로겔의 산소 투과도에 대한 많은 연구가 진행되었으며, 산소 투과도는 Si-O-Si 결합의 함량에 따라 증가하고 실리콘 하이드로겔의 internal morphology는 산소 투과도에 큰 영향을 미치는 것이 밝혀졌다. 그러나 실리콘 단량체의 함량이 아닌, 다양한 구조와 분자량에 따른 실리콘 하이드로겔의 internal morphology, 산소 투과도, 함수율 등 물리적 특성에 대한 연구는 여전히 부족한 상황이다. 본 연구에서는 5 종류의 methacrylate 말단 실리콘 마크로머를 합성하였다. 합성된 모든 실리콘 마크로머의 구조와 분자량은 NMR 및 FT-IR로 확인하였다. 또한 실리콘 마크로머의 구조와 분자량에 따른 물성을 비교, 분석하기 위해 실리콘 마크로머와 TRIS, 그리고 친수성 단량체인 NVP, DMA, HEMA를 각각 동일한 비율로 혼합해 공중합하여 실리콘 하이드로겔을 제조하였다. 실리콘 하이드로겔의 산소 투과도 (Dk), internal morphology 및 함수율을 측정하였다. 실리콘 하이드로겔의 internal morphology는 실리콘 마크로머의 구조에 따라 다르게 관찰되었으며, 실리콘 마크로머의 분자 크기가 적당히 클 때 실리콘 상이 연속되고 산소 투과도와 함수율이 증가하였다. 본 연구가 뛰어난 물성을 가진 실리콘 하이드로겔을 설계하는데 새로운 구조와 아이디어를 제공할 것으로 기대된다.

(A) study on the measurement method of dynamic change in physical system for the implementation of a digital twin-based smart shipyard

최태훈 Greduate School, Korea University 2021 국내박사

본 논문은 디지털 트윈 기반 스마트 조선소 구현을 위한 실제 물리시스템의 동적 변화(공정 진행 상황)를 객관적으로 측정할 수 있는 방법 및 IoT 기반 자동 성과 측정 시스템을 제시한다. 본 논문에서는 조선소 물리시스템의 연구 대상으로 선박블록 조립 공장을 선정하고 선박블록 조립공장의 생산 활동들과 설비들을 분석한다. 그리고 선박 블록의 생산 활동에 의한 공정 진행의 변화를 측정 할 수 있는 계산식과 자동 측정 시스템을 제시한다. 조선소 선박블록 조립 공장은 선박 건조 과정에서 가장 핵심적인 공정이다. 우리는 본 연구에서 선박블록 조립 공장의 동적 변화를 자동 측정하기 위해서, 먼저 선박 조립의 생산 활동별 성과 측정 단위를 정의하고 생산 활동별 성과 측정 방법 및 계산식을 제시하였다. 특히, 선박블록 조립 활동은 대부분 자재를 탑재하는 작업 활동과 용접하는 작업 활동으로 이루어지기 때문에, 탑재와 용접 활동의 동적 변화에 대해서는 세부적인 성과 측정 방안을 제시하였다. 탑재 활동의 동적 변화 측정 방법으로는 비젼과 AR 마커를 이용한 마커 기반 영상분석 방법과 알고리즘을 제시한다. 용접 활동의 동적 변화 측정방법으로는 용접기에서 발생된 전류, 전압, 와이어 송급 속도 센서의 데이터를 분석하여 용접 활동별 작업량을 분류 및 측정할 수 있는 머신러닝 기반 용접활동 분류 모델을 제시한다. 본 연구에서 제시된 성과 측정 방법은 H 조선소에 적용되어 유효성을 검증하였다. 본 논문은 조선소의 디지털 트윈을 구축하기 위한 물리시스템의 동적 변화 측정 방안에 대해 다루었으며, 본 연구에서 제시된 성과 측정 방법은 다음과 같은 의의가 있다: 1) 조선소에서 현재 사용중인 현장관리자에 의한 주관적인 성과 측정 방법 대신에 객관적인 성과 측정 방법을 제안함으로써 선박블록 조립의 공정관리 능력의 향상이 기대된다. 2) 사물인터넷 기술을 이용하여 탑재 및 용접 활동의 실시간 작업데이터를 자동으로 수집할 수 있는 방법을 제시함으로써 실적 수집에 필요한 인력 및 시간을 줄이고 실적 정보의 누락 및 부정확을 방지한다. 3) 실제 물리시스템의 생산공정과 가상시스템인 Enterprise system과의 수직적 통합이 가능해져 디지털 트윈 기반의 스마트 생산체계 구축이 가능할 것으로 기대된다. In this paper, a method that can objectively measure the dynamic change (process progress) of an actual physical system for the implementation of a digital twin-based smart shipyard and an Internet of Things (IoT) based automatic performance measure -ment system is presented. The ship block assembly plant is selected as the research target of the shipyard’s physical system and the production activities and facilities of the ship block assembly plant are analyzed. In addition, a calculation equation and an automatic measurement system are presented to measure the change in process progress through the production activity of the ship block. A ship block assembly plant of a shipyard is the most important process in the ship building process. In order to automatically measure the dynamic change of a ship block assembly plant, the performance measure unit for ship assembly production activity was first defined and the method and equation of measuring performance by production activity were then presented. In particular, since most of the ship block assembly activities consist of mounting materials and welding, detailed performance measurement methods (PMM) were presented for dynamic changes in those two activities. Methods for measuring the dynamic change of the mounting activity are presented with a marker-based image analysis method and an algorithm using a vision and augmented reality (AR) marker. The dynamic change method for measuring welding activity is presented as a machine learning-based welding activity classification model that can analyze current, voltage, and weld wire feed speed sensor data generated from welding machines and classify and measure the welding activity workload. The performance measurement methods presented in this study were applied at H Shipyard to verify their validity. This paper deals with measuring dynamic changes in a physical system for building a digital twin of the H shipyard. The proposed method of measuring performance has the following contributions: 1) It is expected to improve the process control capability of ship block assembly by proposing objective performance measurement methods instead of the subjective performance measurement methods by field managers currently in use at the shipyard. 2) By presenting a method to automatically collect real-time data for mounting and welding activities using IoT technology, the manpower and time required for performance data collection is reduced and the omission and inaccuracy of performance information is prevented. 3) It is expected that it will be possible to establish a smart production system based on a digital twin by vertically integrating production processes, which are physical systems, and enterprise systems, which are virtual systems.

Study on the improvement of CO2 absorption performance and the removal of gas impurities for CO2 capture process in the flue gas

최정호 Greduate School, Korea University 2021 국내박사

This study investigated a cyclic absorbent for the post-combustion CO2 capture process to mitigate climatic change as well as adsorbents to remove hazardous materials generated in the CO2 capture process conducted using an amine absorbent. The obtained results have been described in three separate chapters (e.g., Chapter 2, 3 and 4). Chapter 2 discusses CO2 capture using cyclic amine absorbents (i.e., piperidine (PD), 2-methylpiperazine (2MPZ), and piperazine (PZ)) to determine the following characteristics: CO2 absorption capacity, heat of reaction, reboiler heat duty, and mass transfer coefficient. These characteristics were compared with those of monoethanolamine (MEA), a commercial absorbent. The PD absorbent showed better performance than the tested amine absorbents, and thus, it can replace the commercial amine absorbent. The CO2 absorption capacity and mass transfer rate of the PD absorbent at 40°C were 1.52 and 2.62 times higher than those of MEA, and its regeneration energy (i.e., reboiler heat duty) was 1.26 times lower than that of MEA. This is because, as determined through nuclear magnetic resonance spectroscopic analysis, HCO3-/CO32- is generated as the reaction between PD and CO2 stimulates hydrolysis in the aqueous solution. Chapter 3 discusses the removal of major impurities with the various subreactants discharged in the CO2 capture process. The two main hazardous materials generated in the CO2 capture process are gaseous ammonia (NH3) and nitrosodiethylamine (NDEA). These materials have different physical properties, and therefore, a gaseous adsorption process and a liquid treatment process are required for their removal. This study synthesized hierarchical porous carbon (HPC) based on sodium alginate to control the hazardous materials generated in the CO2 capture process. A gas–solid reaction was proposed to remove NH3 and was tested using a fixed-bed reactor to simulate a commercial adsorption tower. In this experiment, the NH3 removal rate of HPC-44 (4 wt% sodium alginate, 4 wt% calcium chloride) was over 99%, and its adsorption capacity was 5.12 times higher than that of granular activated carbon (GAC). A strong correlation was observed between the NH3 adsorption capacity and the oxygen content in the adsorbent bulk-surface. The Thomas rate constant for HPC-44 was 2.86 times higher than that for GAC because external surface diffusion was induced rapidly in the mesopore-dominant HPC-44. Further, HPC-44 was evaluated to be an efficient adsorbent for removing NH3 because it showed higher reliability than GAC. Chapter 4 investigates a gas–liquid reaction using a batch-type reactor for NDEA removal. The NDEA adsorption behavior in the liquid phase was determined by impregnating various materials in HPC-46 (4 wt% sodium alginate, 6 wt% calcium chloride). In this experiment, HPC-K (HPC impregnated with 1 M KOH) showed an NDEA removal rate 1.64 times higher than that of powdered activated carbon (PAC). The NDEA adsorption capacity showed a strong positive correlation with the basic site on the adsorbent surface and a negative correlation with the acidic site. Thermodynamic analyses revealed that the adsorption process between HPC-46 and NDEA agrees well with the pseudo second-order kinetics model, and the external diffusion rate of HPC-K was 4.5 times higher than that of PAC. The thermodynamic analyses also revealed that the NDEA adsorption process is exothermic and occurred irreversibly. Based on the results of this study, an absorbent with excellent CO2 removal performance was designed, and adsorbents were developed to remove the environmentally hazardous materials generated in the sub-reaction. 본 논문에서는 기후변화에 대응하기 위한 연소 후 이산화탄소 포집 공정의 흡수제와 아민 흡수제를 이용한 포집 공정으로부터 발생하는 독성 물질을 제거하기 위한 흡착제를 연구하였으며, 그 결과는 세 개의 장에 걸쳐 서술되었다. 2 장은 고리형 아민을 이용한 이산화탄소 흡수제 연구로써, piperidine (PD), 2-methylpiperazine (2MPZ), piperazine (PZ)에 대한 CO2 흡수능, 물질전달속도, 반응열, 재가열기 열부하에 대한 물리화학적 특성을 측정하고, 상용흡수제인monoethanolamine (MEA)와 그 성능을 비교하였다. 결과적으로, CO2 포집용으로PD 흡수제가 상용 아민인 MEA를 대체하기에 가장 좋은 성능을 보였다. PD 흡수제의 CO2 흡수능과 물질전달속도는 MEA보다 각각 1.52배 2.62배 향상되었고, 재생에너지도 MEA보다 1.26배 더 효율적이었다. 이것은 수용액내에서 PD와 CO2 반응 메커니즘이 가수분해 반응을 촉진시킴으로써 HCO3-/CO32-가 주로 생성되기 때문이며, 본 연구에서는 핵자기 공명 분석법을 통하여 PD와 CO2 사이의 반응메커니즘을 밝혔다. 3 장은 CO2 포집공정에서 기체상으로 배출되는 다양한 부 반응물들 중 주요 불순물들을 제거에 대하여 설명하였다. CO2 포집공정으로부터 발생되는 두 개의 주요 불순물들은 가스상의 NH3와 nitrosodiethylamine (NDEA)이며, 두 물질의 서로 다른 물리적 특성으로 인하여 기상 흡착 공정과 액상 처리 공정이 필요하다고 판단된다. 본 연구에서는 알긴산나트륨을 기반으로 한 계층적 다공성 탄소 (HPC; hierarchical porous carbon)를 합성하여 포집공정으로부터 발생되는 불순물들을 제어하고자 하였다. 기체-고체 반응은 NH3 제거하기 위하여 제안되었고, 상용흡착탑을 모사하기 위하여 fixed bed를 이용하여 실험되었다. 실험결과, HPC-44 (4 wt% sodium alginate, 4 wt% calcium chloride)의 NH3 제거율은 99% 이상으로 나타났으며, granular activated carbon (GAC) 보다 5.12배 높은 흡착 성능을 보였다. NH3의 흡착 성능과 HPC-44흡착제의 bulk 표면에 존재하는 산소 함량은 높은 상관관계를 보였다. Thomas 속도 상수는 HPC-44가 GAC 보다 2.86배 더 높게 나타났는데, 이것은 메조기공이 지배적인 HPC-44의 외부 표면 확산이 빠르게 유도되기 때문이다. 또한, HPC-44는 흡/탈착 실험결과에서 GAC보다 높은 안정성을 보여 NH3를 제거하는 효율적인 흡착제로 판단되었다. 4 장은 NDEA을 제거하기 위하여 배치 반응기을 사용하여 기체-액체 반응이 연구되었다. 액상 내의 NDEA흡착은 HPC-46에 황산, 아세트산, 수산화칼륨들을 첨착하여 그 거동을 확인하였다. 실험결과, HPC-K는 powered activated carbon (PAC) 보다 높은 1.64배 높은 NDEA 제거율을 보였다. NDEA흡착성능은 흡착제 표면의 염기점과 높은 상관관계를 보였으며, 산점과 역 상관관계가 나타났다. 동력학적 해석 결과 HPC-46과 NDEA 사이의 흡착과정은 유사 이차 속도식에 잘 따르고 있음을 알 수 있었고, HPC-46의 외부 확산속도는 PAC보다 4.5배 빠르다는 것을 확인하였다. 열역학적 해석을 통해 NDEA흡착 과정이 발열과정이며, 비가역적으로 수행됨을 밝혔다. 본 연구의 결과로 CO2 포집을 위한 우수한 성능의 흡수제를 개발하였고, 부 반응으로부터 발생되는 환경유해 물질을 최소화하기 위한 효과적인 흡착제가 도출되었다.

(A) study on the fabrication and characterization of strain Ge-on-Insualtor nMOSFETs on Si substrates

신영훈 Greduate School, Korea University 2021 국내석사

In this thesis, We analyzed the interfacial characteristics between the gate stack and the semiconductor using post plasma oxidation in a metal-oxide-semiconductor capacitor (MOSCAP) with Ge on Al2O3 structure. We extracted the interfacial trapping using the Terman method and analyzed the C-V characteristics. As a result, we optimized the Ge-based gate stack through post plasma oxidation. And we epitaxially grown the In0.2Ga0.8As stressor layer on GaAs and grown Ge to grow the Ge/In0.2Ga0.8As/GaAs structure. In addition, we fabricated strain, unstrain Ge-on-Insulator junctionless n-type metal-oxide-semiconductor field-effect-transistors(MOSFETs) with MOS interface of Ge/Al2O3 gate stack. We fabricated transistor process through wafer bonding and Epitaxial Lift-Off (ELO) and extracted the electrical properties of the strain, unstrain Ge-on-Insulator n-type metal oxide semiconductor field effect transistor. We investigated that strain Ge-on-Insulator n-type metal-oxide-semiconductor electric field-effect-transistor has higher electron mobility characteristics than unstrain Ge-on-Insulator n-type metal-oxide-semiconductor electric field-effect-transistor and obtained that strain Ge-on-Insulator n-type metal-oxide-semiconductor field-effect-transistor has characteristic of increasing the on current. In addition, Defect-less semiconductor-on-insulator by a cost-effective and low temperature process is strongly required for monolithic 3D (M3D) integration, a semiconductor device technology that goes beyond the limitations of miniaturization and high integration of CMOS, introducing high mobility channel materials, high device integration density and low power consumption by reducing interconnection length. In this thesis, we epitaxially grown strain Ge with an In0.2Ga0.8As stressor layer, and fabricated Ge-on-Insulator using wafer bonding and Epitaxial Lift-Off (ELO) techniques. We systematically investigated the effects of the pre-patterning of the Ge layer before wafer bonding to speed up the Epitaxial Lift-Off (ELO) process for a fast and high-throughput process, which is essential for cost reduction. The strain degree of strain Ge was analyzed by Raman spectroscopy. As a result, we fabricated a high-quality Ge-on-Insulator with epitaxially grown strain Ge through wafer bonding and epitaxial lift-off and obtained good electrical properties of strain Ge-on-Insulator n-type metal-oxide-semiconductor field-effect-transistor.

Study on sorption-enhanced catalytic PFCs hydrolysis with a multi-stage catalyst-adsorbent reactor

한재윤 Greduate School, Korea University 2021 국내박사

PFCs (Perfluorocompounds)와 SF6 (sulfur hexafluoride)는 주로 반도체 제조공정, 액정 제조공정, 태양전지 제조공정, 마그네슘(Mg) 주조공정, 고전압장비의 절연 등에 주로 사용되며 공급된 과불화합물의 약 10∼50%가 미 반응 상태로 대기 중으로 방출된다. 이와 같이, 다양한 산업공정에서 배출되는 PFCs 및 SF6는 폐가스냉매로 사용하는 CFC(Chlorofluorocompound) 보다 장기간 안정한 화합물로서 화학 반응을 통한 제거가 용이하지 않고 지구온난화 지수가 이산화탄소 대비 6,000∼24,000 배에 달하는 대표적인 온실가스이다. 대표적인 분해 기술인 연소 방법은 가장 간단한 방법이고 장기적으로 입증된 기술이라 할 수 있으나, 불화가스의 안정성 때문에 산화반응 전에 1,273K 이상의 고온 가열이 필요하고, 연소에 따른 thermal NOx 등 2차적인 대기환경문제가 유발될 가능성이 있다. 최근까지 연소법을 대체하기 위하여 플라즈마, 분리막 및 물리화학적 공정 개발을 진행하고 있으나 처리 용량의 한계, 고 에너지 요구 및 낮은 공정효율로 상용화에 어려움이 있는 실정이다. 본 연구에서는 촉매분해법을 이용한 PFCs (CF4) 및 SF6 처리공정의 처리 효율 향상과 함께 경제성 향상을 위해, 가수분해 반응 시 발생하는 불화수소(HF) 또는 삼산화황(SO3)을 고상환원제인 수산화칼슘(Ca(OH)¬2)를 사용하여 지속적으로 제거할 수 있는 다단 공정을 구성하였다. 이러한 촉매-흡수제 다단 공정은 르샤를리에 원리에 의하여 평형을 파과함으로써 가수분해반응의 최적 효율 온도를 낮춤과 동시에 불화수소 및 삼산화황 등 유해물질들의 유출을 근본적으로 차단할 수 있다. 또한 분해공정 중 부식성 물질의 제거를 기반으로 열교환기 적용이 가능하여 폐열 회수로 인한 연료 사용량을 최소화할 수 있고, 반응온도 저감 및 오염물질의 지속적인 제거를 통하여 촉매 내구성 향상이 가능하고, 후단 HF흡수공정 배제로 인한 공정의 소형화가 가능하며, CaF2 및 CaSO4 생산에 의한 자원회수 가능 등의 다양한 장점들이 있다. 이러한 고효율 촉매분해 시스템을 구현하기 위해 촉매/환원제를 다단으로 적층하여 CF4 및 SF6의 분해 특성을 확인하였다. 그 결과, 촉매만 사용한 단일 반응기 보다 촉매-흡착제를 다단으로 적층한 반응기에서 CF4 분해 시 7.5~23.2 %, SF6 분해 시 1.5~26.4 % 이상의 전환율이 향상되었다. 또한 실험 결과를 기반으로 공정 전산모사를 실시했을 때 낮아진 공정온도에 의해 연료사용량이 감소하였으며 이를 기반으로 공정의 경제성 확보가 가능함을 규명하였다. 그리고 대용량 촉매분해 시스템의 제작비용을 최소화 하기 위한 0~8단의 적층 실험 비교를 통해 촉매-흡착제의 적층 수를 최적화 하였다. 그리고 다단 반응기의 장기간 내구성 테스트를 기반으로 촉매-흡착제 다단 반응 시스템의 최적 성능 유지와 함께 HF 및 SO3의 배출량을 최소화할 수 있는 수산화칼슘의 교체시기를 도출하였다. 결과적으로, CF4 및 SF6의 가수분해반응으로 생성된 불화수소 및 삼산화황을 수산화칼슘 흡착제를 통하여 연속적으로 제거함으로 인해 평형이 파과된 가스 조성을 다음 단으로의 연속적인 유입을 통해 정반응을 가속화시켜 반응기의 성능을 향상시켰고, 이에 따라 진행되는 일련의 반응이 반복되어 반응/분리 동시 효과를 구현하였으며 최종 2,000LPM급 대용량 시스템 제작 및 테스트를 통해 저온에서도 PFCs 제거효율이 우수하여 공정의 경제성이 증가할 수 있고, 부산물의 발생을 최소한으로 억제한 촉매분해-산성가스 제거 복합 공정 구성이 가능함을 확인하였다. Since the Industrial Revolution began in around 1750, human activities have drastically increased emissions of so-called greenhouse gases (GHGs) like carbon dioxide (CO2) and other heat-trapping gases, thus enhancing the greenhouse effect and causing Earth’s average surface temperature to rise and, in turn, resulting in climate change and global warming. Fluorinated greenhouse gases (F-GHGs) such as perfluorocarbons (CxFy, PFCs), sulfur hexafluoride (SF6), hydrofluorocarbons (HFCs), and nitrogen trifluoride (NF3) are long-term, continuing, and significant GHGs that are emitted by industrial activities. F-GHGs have very high global warming potential (GWP) owing to their high binding energy; even low atmospheric concentrations of less than 1% can have a potent greenhouse effect. Therefore, recycling, decomposing, and collecting these gases as well as finding alternatives to their use are critical issues in environmental studies. Various PFC control methods such as recycling, abatement, and decomposition are available to remove PFCs and SF6. However, typical methods, such as pressure swing adsorption (PSA), cryogenic distillation, membrane separation, and thermal or plasma decomposition, involve challenges such as concentration limits, high operation costs, by-product formation, and low capacity. The conventional catalytic decomposition method needs a high temperature of 773–1,073 K to achieve catalytic activity and still produces emissions including CO2, HF, SO2, SO3, and F2 through side reactions. This study introduces a catalyst-adsorbent multiple reactors (CAMR) for the effective hydrolysis of PFCs such as carbon tetrafluoride (CF4) and SF6. Each divided stage consists of a catalyst bed followed by an adsorbent bed, with calcium hydroxide (Ca(OH)2) being used as an adsorbent to remove corrosive HF and SO3. The multiple beds are linked in series sequentially to enhance the catalytic hydrolysis of PFCs and simultaneously avoid the need for an acid-gas scrubbing apparatus to remove HF and SO3. With PFC catalyst and granular Ca(OH)2 adsorbent, the proposed reactor achieved 7%–23% higher CF4 and SF6 conversion than a conventional single-bed catalytic reactor in the temperature range of 873–1,023 K. A chemical process simulation tools to represent based on the experimental data was developed using a commercial process simulator, Aspen HYSYS®, and the model agreed reasonably with the experimental data. Experimental and simulation studies indicate that a catalyst-adsorbent multiple reactor (CAMR) is preferable for PFCs reduction equipment in consideration of both the performance of reactor and the initial capital and long-term operating costs. The integrated catalyst decomposition and acid gas removal system confirmed that the implementation of a catalytic decomposition-acid gas removal system was possible. The experimental results confirmed the superiority of this system to existing thermal, heat, plasma, and commercial catalytic decomposition methods.