Dynamic Analysis and Development of Floating Offshore Wind Turbines

팜탄담 Graduate School of Ulsan University 2020 국내박사

A floating offshore wind turbine offers tremendous potential benefits in near future with major challenges. Various research centers, institutes, and universities pay attention to and perform researches on FOWTs. Currently, the efficient performance and the economics of the floating wind systems are paid more attention. The South Korean Government releases an ambitious plan, known as “Renewable Energy 3020”, to increase new renewable energy source power generation by 48.7 GW by 2030. The target is to provide 16.5 GW from wind energy which includes 13 GW from offshore wind. Focusing on a water depth of 150 m in the East Sea gas field off the coast, Ulsan, Korean, floating offshore wind turbines are considered to be the best candidate to fulfill the target. The main types of floating foundations are the semi-submersible, spar, and tension leg platforms. Usually, a semi-submersible platform is composed of three or four slender columns and those are connected to each other through braces. The semisubmersible relies mainly on the waterplane area of columns and the distances between each column to achieve stability. The TLP type is stabilized by a high-tension mooring system; for this reason, the anchor system for TLP is complex. The spar type usually uses heavy ballast materials such as concrete at the bottom to provide a lower center of gravity for stabilization, however, the acceleration at the nacelle and the tower base bending moment are large. Several semi-submersibles and spar types were tested in scaled models in the Ocean Engineering Wide Tank of the University of Ulsan. Numerical models of these types were built and validated based on model test results. The NREL FAST code was used to conduct the fully coupled numerical simulation of floating offshore wind turbines. A set of in-house codes generate potential hydrodynamic coefficients to coupling with FAST code. The finding here is that the semi-submersible platform has a strong effect from second-order wave loads, but the spar platform has little effect from second-order wave loads. This thesis aims to develop a spar-type platform to support the NREL-5-MW reference wind turbine for 150 m water depth of the East Sea gas field off the coast, Ulsan, Korean. The Spar-type platform includes a moonpool at the center. Design optimization processes are three steps, the first step is using a spreadsheet to calculate the platform dimension, the second step is the frequency-domain analysis which calculates the responses in regular waves and the last is the fully coupled simulation time-domain analysis to obtain dynamic responses in combined wind, wave, and current conditions. By having a water column inside the open moonpool, the dynamic responses of the FOWT system are reduced significantly. The reduction of motions will lead to reducing the nacelle acceleration and tower base bending moment as well. The spar-type platform combined with a moonpool has good performances in both operational conditions and extreme conditions. Compared with another floating type, the proposed model promises a feasibility to apply for the offshore wind farm in the East Sea gas field off the coast, Ulsan, Korean.

Mechanical Properties of the Rubber Material Used in Elastomeric Bridge Bearing Considering the Effects of Aging.

테일러 헨리 쿠오나 Graduate School of Ulsan University 2020 국내석사

Abstract Mechanical Properties of the Rubber Material Used in Elastomeric Bridge Bearing Considering the Effects of Aging University of Ulsan Department of Civil and Environmental Engineering Henry Quona Taylor Bridge systems are subjected to certain movements, induced by external or dead loading, which has necessitated the inclusion of support devices with the capabilities to efficiently dissipate energy and protect the bridge pier from unwanted stress concentration. These criteria are effectively met by elastomeric bearings, whose primary material, rubber, has elasticity properties suitable for base isolation. The performance of these bearings whose service life is about 100years is dependent on the behaviour of the rubber material over time. Pursuant with understanding the behaviour of elastomeric bearing overtime, this study sought to determine the effects of aging on the material properties of the rubber used in elastomeric bearings considering Natural Rubber and Neoprene; to conduct member level simulations of the elastomeric bearing blocks and determine the changes in stiffness of the aged rubber bearing and to evaluate the effects of the different assumptions surrounding the modes aging on the behaviour of aged rubber bearing. In its pursuit, the Study discovered that neoprene performs better than natural Rubber with respect to the physical changes, tensile and shear, in the vulcanizates and that the effects of the aging conditions applied were more prominent in their tensile behaviour than it was with their shear. Also evident from the study was that the models with neoprene had lesser changes in the shear stiffness as they aged than did Natural Rubber. Natural rubber produced a maximum shear stiffness increase of 18.73% while neoprene produced a maximum shear difference of a meagre 2.89%. it was noticed that the Bearing models under combined loading of compression and shear developed maximum shear at the interface between the rubber and steel plates 요약 노화의 영향을 고려한 교량 탄성받침의 고무 재료의 기계적 성질 울산대학교 대학원 건설환경공학과 핸리 쿠오나 테일러 교량의 교각은 지진하중에 의해 큰 외력(모멘트 및 전단력)을 받게 된다. 이러한 지진력에 의한 에너지를 효과적으로 소산시켜서 원치 않는 부재력(응력)이 집중되지 않도록 하는 것이 중요하다. 이를 위하여 고무재료를 기반으로 하는 탄성받침이나 지진보호받침을 적용하는 경우가 점차 증가하고 있다. 교량의 공용수명이 약 100년 정도임을 감안하면 교량의 고무받침의 성능은 시간이 경과함에 따라 역학적 거동 특성에 변화가 생긴다. 이 연구에서는 노화(열화)에 따른 탄성받침의 거동을 이해하기 위해 탄성받침에 사용되는 천연고무와 합성고무의 역학적 특성 변화를 실험을 통하여 분석하였으며, 이들 재료를 기반으로 하는 탄성받침의 부재 수준의 역학적 거동 특성변화를 해석을 수행하여 분석, 평가하였다. 이 연구를 통해, 합성고무가 천연고무에 비해 인장(tension) 및 전단(shear)의 물리적 변화가 훨씬 크다는 것을 알았으며, 또한 전단에 비해 인장의 역학적 특성이 노화에 크게 영향을 받는 것을 확인하였다. 노후화에 의한 강성의 변화는 천연고무에서는 최대 전단 강성이 18.73% 증가했고 합성고무는 2.89%로 증가하였다. 또한, 파단시의 최대 연신율은 감소하였다. 이러한 교량 받침의 역학적 특성 변화는 교량의 진동주기를 작게하여 교량에 발생하는 지진력을 증가시키기때문에 시간 경과에 따른 고무받침의 노후화가 교량의 내진성능을 악화시킬 수 있다는 것을 알 수 있다.

(The) effects of high energy ball-milling on the properties of Li_(2)CO_(3)-doped PMN-PZT piezoelectric ceramics

Hung, Nguyen Viet University of Ulsan Graduate School 2005 국내석사

The effects of high energy ball-milling (HEBM) on dielectric and piezoelectric properties of Li2CO3 added 0.8Pb(Mg1/3Nb2/3)O3-0.2Pb(Zr0.475Ti0.525)O3 (PMN-PZT) ceramics has been investigated as a function of milling time. It was found that HEBM was very effective to reduce the particle size of calcined powders. With increasing HEBM time, the particle size greatly decreased at initial stage of milling (0-5h), while prolonged milling resulted in reagglomeration of crushed particles. However, the crystal structure of perovskite structure was maintained throughout the HEBM treatment within milling period of 0 to 40h. The HEBM treated powders were pressed into a disk-shaped pellet and then sintered in air at 850~1000°C. In comparison to unmilled PMN-PZT ceramics prepared using conventional ball-milling, those obtained with HEBM resulted in better dielectric, piezoelectric and mechanical properties. In terms of HEBM treatment time, the PMN-PZT ceramics obtained after milling for 10h showed maximum values of properties, but further increase in milling time led to a gradualdecrease in the physical properties probably due to the reagglomeration of powders during milling. The relative dielectric constant (εr), piezoelectric coupling factor (kp) and piezoelectric constant d33 of 0.1wt% Li2CO3 doped PMN-PZT ceramics prepared by the conventional ball-milling and subsequent sintering at 900°C were 1873, 65.48% and 513 pC/N, respectively. In contrast, those values of a specimen prepared by 10h HEBM were 2046, 68.12% and 554 pC/N respectively. These results are quite promising for low-cost fabrication of piezoelectric multilayered devices.

Nd도핑Bi계의 전계인가 고변위 압전세라믹 연구 : Large Electric-Field-Induced Strain in Nb-doped lead-free Bi_(0.5)Na_(0.5)TiO_(3) piezoelectric ceramics

Nam, Pham-Ky Graduate School, University of Ulsan 2010 국내석사

Electric-filed-induced strain is one of the most important parameter among material properties for its applications in electromechanical devices. Lead oxide based piezoelectric ceramics such as PZT, possess much higher electric-field-induced strain as compared to that of lead-free piezoelectric ceramics and therefore dominate the piezoelectric market. But, they are restricted by environmental issues that call for the use of environmentally benign materials, i.e. lead-free ceramics, with comparable properties to that of the lead oxide based. Therefore, research is now focused on lead-free systems with perovskite structure, especially compositions based on bismuth sodium titanate, Bi_(0.5)Na_(0.5)TiO_(3) (BNT) and sodium potassium niobate Na_(0.5)K_(0.5)NbO_(3) (NKN). In this study, solid solutions based on bismuth sodium potassium titanate with a morphotropic phase boundary (MPB) composition, Bi_(0.5)Na_(0.5)TiO_(3) (BNKT), Niobium (Nb^(5+)) was substituted on B-site, for titanium (Ti^(4+)) in BNKT system, with an aim to enhance the electric-field-induced strain response for its applications in electromechanical devices. The phase formation, crystalline crystal, density, microstructure, dielectric, ferroelectric and electric-field-induced strain behavior of these materials were analyzed and discussed. All of the studied materials were found to have a perovskite structure. The Nb^(5+)-substituted BNKT ceramics the field-induced strain was enhanced from 0.18% to 0.46% at an applied electric fields of 70 kV/㎝. The normalized strain d_(33)* (S_(max)/E_(max)) obtained for Nb modified ceramics were 641 pm/V. This value of normalized strains were much higher than pure BNKT as well as other lead-free BNT-based materials. These results suggest that the systems BNKTN are environmentally friendly candidate material classes for application in electromechanical devices and provide an alternative way in the quest for potential lead-free actuator materials.

Steam Catalytic Reactions on Vacuum Residue for Producing Petroleum Fuels

도 티 리엔 University of Ulsan, Graduate School 2020 국내박사

ABSTRACT Humans are facing the biggest energy challenges, transportation fuels especially. In this study, the effect factors of catalytic characters on the catalytic upgrading of petroleum residues in supercritical water, researched to produce more petroleum transportation fuels, were deeply investigated. In the first study, NiK/yCe x Zr 1-x O 2 -macroporous Al 2 O 3 catalysts (y = 0, 10, 20, and 30; x = 0.73-0.92) were synthesized by dispersing different amounts of Ce x Zr 1-x O 2 phase onto macroporous -Al 2 O 3 as supports, and then subsequently impregnating Ni and K into the supports, which possessed advantageous properties, such as a high surface area, ordered macropores and high oxygen storage capacity. Moreover, the introduction of Ni and K metals into these supports created more oxygen vacancies in them. We applied these catalysts to the cracking of vacuum residue with steam. It was found that the variation of the liquid yield with the amount of Ce x Zr 1-x O 2 phase showed a volcano pattern. The macropores in the supports played an important role in enhancing the diffusion of large molecules to the active sites, while the high oxygen storage capacity over the Ce x Zr 1-x O 2 phase improved the oxidative cracking rate, thereby increasing the lighter oil fraction from the vacuum residue. In the second study, a NiK/CeO 2 catalyst was employed to investigate the interaction between Ni metal and CeO 2 support and its effect on oxidative cracking of vacuum residue. In the reaction results, a large amount of light oils, including naphtha, diesel and VGO, was produced through oxidative cracking over CeO 2 , and the quality of the liquid products was significantly improved by hydrogenation. The interaction between Ni metal and CeO 2 support induced the formation of a Ce y Ni 1-y O 2- solid solution and increased the number of oxygen vacancies, thus enhancing the oxidative cracking of vacuum residue. Further, the addition of NiK into the supports provided Ni metallic sites for hydrogenation, producing more liquid products with a high H/C ratio. As a result, NiK/CeO 2 catalyst showed a higher diesel yield (22.87%) than that without catalyst (9.14%). In the third study, NiK/ceria-zirconia (CZ) and NiK/ceria-zirconia-alumina (CZ-A) catalysts were investigated in order to further understand the roles of mixed-oxide supports in the steam catalytic cracking of vacuum residue (VR). Compared to thermal cracking, higher conversions and liquid yields were achieved over the catalysts. Steam decomposition occurring over the CZ and ZrO 2 phases provided an alternative hydrogen and oxygen sources for hydrogenation and oxidative cracking, respectively. The introduction of Ni into the CZ support induced the formation of Ce x (Zr-Ni) 1-x O 2-δ solid solution and the isolation of the ZrO 2 phase via a strong metal-support interaction, resulting in greater oxygen vacancy in the bulk structure. In contrast, the strong interaction of CZ and Ni phases with Al 2 O 3 induced higher dispersions of CZ and Ni phases in the NiK/CZ-A catalyst, which resulted in a greater density of oxygen vacancies on the surface and higher CeO 2 reducibility. As a result, the quality of the liquid products and naphtha yields were significantly improved by hydrogenation over the nickel metallic sites and oxidative cracking through the metal- support interaction. In the fourth study, steam oxidative cracking route of 1-methylnaphthalene were investigated through the combination of oxidation and hydrogenation over nickel- containing mixed oxide catalysts. Depending on the used supports, several types of active sites for oxidation, hydrogenation, and steam decomposition were generated by various metal–support and support–support interactions. The steam-reforming routes were dominant without nickel, resulting in high gas selectivity due to a full-cracking process. With nickel, steam oxidative cracking routes were strongly enhanced by a synergistic combination between hydrogenation occurring on the Ni metallic sites and oxidation over mobile lattice oxygens in a Ce x Zr 1-x O 2 solid solution, resulting to the higher selectivity of liquid products than that of gas products. Among the prepared catalysts, an optimal interaction between Ni and Ceria-Zirconia-Alumina mixed oxide support caused not only an increase of oxygen vacancies in solid solutions, but also the formation of smaller Ni metallic nanoparticles, resulting in reinforcement of steam oxidative cracking of 1-methyl naphthalene. Finally, the hierarchically macro-mesoporous grainy aluminas containing the novel properties were prepared for being a support in xK/Ni-Al 2 O 3 catalyst which are applied to study 1-methyl naphthalene steam reforming. The impact of a hierarchically ordered macro- mesoporous structure on steam reforming of 1-methyl naphthalene at the low temperature (600 o C) was investigated over xK/Ni-MeAl (mesoporous alumina-supported nickel & potassium) and xK/Ni-MaAl (macro-mesoporous alumina-supported nickel & potassium) catalysts in a fixed-bed reactor system. The hierarchical ordered macro-mesoporous structure in Al 2 O 3 support played an important role in enhancing the reactant diffusion to the active sites promoted both the catalytic cracking and steam reforming, resulting in high gas yields and 1-methyl naphthalene conversion. The introduction of potassium on Ni- MeAl and Ni-MaAl supports created more nickel active sites enhancing significantly the steam reforming rate. In addition, using macro-mesoporous alumina as support also increased the nickel site dispersion, leading to enrichment of potassium location on alumina, which makes the catalytic deactivation being slow down.

차량용 폐루프 유압 에너지 회생 시스템의 제안 모델링 및 제어에 관한 연구 : A Study on a Closed-loop Hydraulic Energy Saving Systems Proposition, Modeling and Control

Ho Triet Hung Graduate School, University of Ulsan 2010 국내박사

A survey of energy-saving activities in hydraulic systems for rotary loads indicates that hydraulic valve systems have disadvantages of system energy losses while hydraulic pump controlled systems are freely system energy losses but are not able to recover energy. Energy-recovery systems based on open loop are not only freely system energy losses but also are able to recover energy of the load during deceleration or lowering the load. However, some limits of hydraulic technology restrict applicability of the open recovery-energy hydraulic systems for mobile applications. A new closed-loop hydraulic energy-saving system is proposed in this research to overcome the drawbacks of the current open loop hydraulic energy-saving systems. The new system includes a variable displacement hydraulic pump, a directional control valve, two hydraulic accumulators and a hydraulic pump/motor, the secondary unit, which can work either as a hydraulic pump or a hydraulic motor. The new proposed system is discussed, modeled, analyzed and validated in this research. The proposed system based on closed-loop hydraulic circuit. Hydraulic accumulator is used as energy storage system in a novel configuration so that the system can recover the kinetic energy of the load without reversion of fluid flow. The secondary unit can work in only positive region for both functions, which is a novel characteristic of the system. Modeling of the system based on the components physical attributes is presented in this research. Reduced-order models of the system in different configurations are also built for the controller synthesis. Energy utilization and energy recovery potential of the system are analyzed via simulation. The simulation results indicate that influences on the energy-utilization and energy-recovery potential of the system are the load conditions and the parameters of the system. An adaptive robust control scheme using adaptive fuzzy sliding mode control is proposed for speed control of the system. The controller design is to consider nonlinearities of the control input, the dead-zone and the saturation. The controller is brought into simulation and the simulation results indicate that the controller is robust for uncertainties and external disturbance. Experiments are taken to evaluate the system in two aspects, the energy-recovery potential and the effectiveness of the designed controller. A proposed application of the system for hydraulic hybrid vehicle is investigated. The experimental results confirm the validity of qualitative and quantitative statements of the proposed system.

Photocatalytic Semiconductor Development of Bismuth vanadate (BiVO4) and Tungsten trioxide (WO3) for Improving Photoelectrochemical (PEC) Water Splitting

Meysam Tayebi Graduate School of Ulsan University 2020 국내박사

Numerous efforts have been made to find, produce, and utilize renewable energy to replace fossil fuels that have seriously degraded the environment. Photoelectrochemical (PEC) water splitting has been considered to be a promising route for the production of hydrogen (H2) applying for free solar energy. PEC systems to produce H2 have the great advantages of simple process steps and very low environmental burdens. However, many challenges must be overcome for commercial applications, particularly for fabricating the necessary materials for PEC water splitting. Among many candidate semiconductor materials for photoelectrode utilization, BiVO4 and WO3 is a very promising semiconductor because it is an inexpensive n-type photocatalyst with a moderate bandgap of 2.37 and 2.6 eV for PEC water oxidation. BiVO4 as a photoanode can theoretically absorb almost 10 % of the solar energy with an appropriate valence band (VB) position to drive water oxidation with an identified maximum photocurrent of 7.5 mA/cm2. Many bismuth vanadates (BiVO4)-based semiconductors that have been developed for PEC water splitting to produce H2 have been troubled by the easy recombination of the photoinduced electrons and holes. None of the numerous nanocomposites and nanostructures that have been developed are perfect materials capable of satisfying all the criteria necessary for practical photocatalysis with sufficient solar energy conversion efficiency. Most semiconductor materials with highly efficient PEC water splitting have used ultraviolet (UV) as a light source. This dissertation examines very recent progress of 4 Strategy (Doping, photocharging, heterojunctions and 2D nanosheets) for improving the photocurrent density and hydrogen production of BiVO4 and WO3 semiconductors using PEC techniques, and also highlights the challenges faced in the design of visible light-active water splitting photocatalysts.

Glycerol carbonation with urea over Zn-containing mixed oxide catalysts

웬 푸 후이 University of Ulsan, Graduate School 2020 국내박사

In this millennium, climate change is one of the biggest challenges of the human’s future. The major aspect of the current climate change is global warming which is the result of human activities. The most influence activity of humans is the emission of greenhouse gas including the carbon dioxide (CO2) by the burning of fossil fuel. If humans do not have effective actions to control the problem, the impact of climate change can be extended not just in this century but also in the next 10 millennia more. Replacing conventional fossil fuel by other renewable energy (including biofuel, biodiesel) is recognized as a solution to mitigate the impact of climate change. However, one problem of biodiesel is its byproduct- glycerol which is abundant and needs to be converted to a value-added product. In this thesis, I focus on preparing the catalysts for the reaction of glycerol and urea to glycerol carbonate; and investigating the catalysis mechanism of the reaction. Catalytic conversion to glycerol carbonate (GC) from glycerol and urea was investigated with Zn/Al catalysts supported by activated red mud (ARM), a waste material. Compared to an unsupported catalyst, ARM-supported Zn/Al catalysts exhibited higher GC yields. ARM-supported Zn/Al catalysts showed a volcano curve for the GC yield as a function of the Zn/Al loading. FTIR analysis revealed the ARM-supported Zn/Al catalysts to be more selective, resulting in higher GC yield. The balance of active sites from ARM and Zn/Al was related to rates of each reaction step in GC synthesis, which eventually influenced the selectivity and yield of GC. In the second research, we prepared ZnO, ZnAl2O4, and ZnAl mixed oxides with different metal molar ratios and applied them for synthesizing glycerol carbonate (GC) from glycerol and urea. The reaction routes related to the Zn species over the ZnAl mixed oxides were investigated. The ZnAl mixed oxides were found to consist of two Zn crystalline phases: ZnO and ZnAl2O4. From the reaction results, the ZnAl mixed oxides showed much higher glycerol conversion and GC yield than the ZnO and ZnAl2O4. During the reaction, the dissolution of the Zn species from the ZnO phase over the ZnAl mixed oxides was observed while the ZnAl2O4 phase remained insoluble. The ZnO phase provided a homogeneous reaction route via the dissolved Zn species, resulting in the formation of a Zn complex containing the isocyanate (NCO) and zinc glycerolate. In contrast, the insoluble ZnAl2O4 phase was responsible for not only a heterogeneous reaction route, but also adsorption of the Zn NCO complex on the catalyst. We proposed that the adsorbed Zn NCO complex could play a role as an active site for an additional heterogeneous reaction route. Therefore, the ZnAl mixed oxides exhibited high GC yields through the dual catalysis routes: the homogeneous reaction route over the ZnO phase and the heterogeneous reaction route over the ZnAl2O4 phase. To understand the reaction mechanism, two different Zn-based catalysts - ZnO, and ZnAl mixed oxide (ZnAlO or Zn7Al3) - were employed to investigate Zn-phase-dependent catalysis in the reaction of glycerol with urea as a function of reaction times. Zn7Al3 catalyst exhibited higher selectivity and yield of glycerol carbonate (GC) over a wide range of glycerol conversion than the ZnO catalyst. The time-dependent Zn species and reaction intermediates were observed in the solid and liquid phases at various reaction times through FTIR and XRD measurements in order to understand Zn-containing intermediates and corresponding reaction routes over each catalyst. The low GC selectivity in the reaction over the ZnO catalyst was closely connected to the formation of zinc glycerolate (ZnGly) in the solid phase. For the ZnO catalyst, ZnGly was formed in the solid phase even at an initial reaction time by the reaction between Zn NCO complex and glycerol, resulting in the loss of GC selectivity. Alternatively, over a Zn7Al3 catalyst, the formation of the Zn isocyanate (NCO) complex was dominant up to 2 hr of reaction time in both the liquid and solid phases. After 2 hr of reaction time, ZnGly was observed in the spent Zn7Al3 catalyst along with decreasing GC selectivity. The relative formation rates of Zn-containing reaction intermediates (ZnGly and Zn NCO complex) over the Zn7Al3 catalyst were affected by the Zn phases over the solid catalysts and the ratio of urea to glycerol in the liquid phase during the reaction time. The effect of a disordered ZnAl2O4 spinel structure on the reaction of glycerol with urea was investigated with pure ZnAl2O4 (c-ZnAl2O4) and ZnAl mixed oxide (c-ZnAlO) prepared by a citrate complex method, and ZnAl physically mixed oxide (p-ZnAlO). During catalysts preparation, a disordered bulk ZnAl2O4 phase generated disordered sites on the surface: the Al3+ cations substituting for Zn2+ cations at the tetrahedral sites, and the surface oxygen vacancy corresponding to the Zn2+ cations substituting for Al3+ cations at the octahedral sites. The disordered surface sites increased in order of p-ZnAlO < c-ZnAlO < c- ZnAl2O4, which was proportional to the surface acidity. c-ZnAlO exhibited the best reaction performance due to the existence of a solid zinc isocyanate (Zn NCO) complex on the disordered sites. Here, we proposed that the solid Zn NCO complex preferentially generated glycerol carbonate (GC), while the liquid Zn NCO complex produced both GC and zinc glycerolate. Finally, we investigated the glycerolysis of urea over various ZnMeO (Me = Co, Cr, and Fe) mixed oxide catalysts. ZnMeO mixed oxide catalysts were prepared by a co-precipitation method for two Zn/Me ratios, resulting in Zn-rich mixed oxide (Zn2MeO) and Zn-poor mixed oxide (ZnMe2O). In the glycerolysis of urea, the Zn2MeO catalysts exhibited higher glycerol conversion and glycerol carbonate yields than the ZnMe2O catalysts due to the predominance of homogeneous catalysis through Zn isocyanate (NCO) complexes from the Zn2MeO catalysts. Specifically, Zn2CrO was the best catalyst, with the highest yield of glycerol carbonate. Fourier transform infrared (FT-IR) and thermogravimetric analysis (TGA) results of the spent catalysts clearly demonstrated the dominant formation of a solid Zn NCO complex over the spent Zn2CrO catalyst, a unique feature indicating that the better catalytic performance of Zn2CrO was due to the additional heterogeneous reaction route through the solid Zn NCO complex.

The Difference of Sport-related Cognitive Function according to Athletic Status and Type of Sport

용타위 앗차랏 University of Ulsan, Graduate School, School of Sp 2019 국내박사

Cognitive function has been recently accepted to be an essential factor along with physiological, physical, technical, and psychological factors for peak performance in sports. The present dissertation consists of two studies; study 1: the role of cognitive function in sports: a systematic review; and study 2: the difference of cognitive ability according to athletic status and type of sport. Study 1: the purpose of the primary research was to systematically determine the existing evidence on the topics of cognition and sports performance. This systematic review was conducted following the guideline of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Relevant studies were initially discovered via electronic sources, namely PubMed, Web of Science, Science Direct, Wiley Online Library, and Taylor & Francis Online databases. Additional searches were performed using Google scholar and the reference lists of relevant articles. The final search was completed on April 2018. The inclusion criteria were English written studies, healthy participants who were 8-35 years old, and study investigating cognitive function corresponding to athletic status or sport expertise or sport type. Of 192 initially retrieval articles, thirty-seven eligible studies meet inclusion criteria were finally included. In the process of data extraction, relevant information was extracted including first author, year of publication, participants’ sample size, gender, age, sports experience, athletic status, sport expertise, type of sport, cognitive measurement, and result. The findings revealed the association between various aspects of cognitive function and athletic status, sports expertise, talented athlete, and sport type. Exceptional sports players were superior to sub-elite, amateur player, and ordinary people on several cognitive abilities utilizing measurements of simple and choice reaction time, go/no-go reaction time test, design fluency test, switching task, stop-signal task, flanker test, mental rotation test, tower test, stroop test, attention network test, trail making test, and digit span forward & backward test. Moreover, young talented athletes outperformed sub-talented and non-talented youth players on executive functioning. With regard to types of sport, there were significant effects on cognitive functions indicating; 1) strategic sport athletes had superior executive controls than those from interceptive sports, static sports, and non-athletes; 2) open skill athletes displayed better on inhibition, visual-spatial skills, and cognitive flexibility than closed skill athletes and non-athletes; 3) externally-paced players exhibited higher planning and problem-solving abilities in comparison to self-paced players and non-athletes; 4) self-paced athletes did more effective on response inhibition than externally-paced athletes and non-athletes. Based on preliminary results, the cognitive functions corresponding to peak performance in sports could be determined as executive function (inhibition, working memory, and cognitive flexibility), information processing (reaction time and processing speed), and spatial skill (mental rotation ability). Superior performance seems to be associated with cognitive abilities which could be utilized to predict the athletic achievements. However, the differences in multiple cognitive functions depending upon type of sport and athletic skill level were reported, but the components of cognitive function critical to each sports type are not fully clarified. Therefore, further investigation is needed to be conducted proving the sport-related cognitive functions distinguished depending upon athletic status and type of sport. Study 2 is a cross-sectional study to determine the sport-related cognitive function across athletic status (athlete and non-athlete) and type of sport (interceptive, static, and strategic sports). There were 120 male participants including 30 boxers (interceptive sport), 30 shooters (static sport), 30 soccer players (strategic sport), and 30 non-athletes who were young adults (age range 20-30 years). According to the theoretical model of sport-related cognitive functions in study 1, the cognitive performances were examined employing five computerized tests including simple (SRT) and choice reaction time (CRT) test, flanker test (FKT), trail making test (TMT), mental rotation test (MRT), and one paper-pencil test, which is design fluency test (DFT). The results show that athletes outperformed non-athletes on simple and choice reaction time test, trail making test (TMT-A), and design fluency test, suggesting athletes were superior in speed of cognitive processing and multiple executive aspects consisting action inhibition, working memory, cognitive flexibility, and creativity. Regarding sports disciplines, interceptive and static sports athletes yielded significantly faster responding on simple reaction time as compared to strategic sport athletes and non-athletes. The shorter reaction time of choice reaction time test were observed in three sport types athletes in comparison to non-athletes, and only interceptive sport athletes did statistically higher in accuracy rate of choice reaction time test. The result of trail making test, as compared to non-athlete group, static sport athletes did significantly faster on trail making test - part A. There was significant effect of sport type on mental rotation test, indicating interceptive athletes performed better than static sport and strategic sport players, whereas non-athletes were found to be superior to strategic sport athletes. Concerning design fluency test, athletes from strategic sport could create more total unique figures than static sport athletes and non-athletes, and the higher total unique figures was also observed in interceptive sport athletes relative to non-athletes. However, no significant difference of flanker test was reported for athletic status and type of sport. The results obtained in this study indicated that the superior cognitive abilities (i.e., information processing and executive function) were associated with participation in competitive sport training regardless of sports typology. The sport type differences were related to specific cognitive components, interceptive sport favoring on cognitive processing speed and visual-spatial skills, whereas executive functions (i.e., working memory and cognitive flexibility) could be benefited from the extensive training of strategic sport. Furthermore, visual processing speed may be essential for sports performances in the static sport such as shooting.

NANOSCALE THERMAL AND FLUID TRANSPORT PHENOMENON IN POROUS MEDIA : A MOLECULAR DYNAMICS STUDY

하산 모하마드 라세둘 Graduate School of Ulsan University 2020 국내석사

The small length scales and large specific surface areas associated with the nanostructures play a key role in the molecular level thermal and fluid transport. In such nanometer length scales, the local intermolecular interaction creates temperature discontinuities between the solid-like interfaces and their neighboring fluid molecules. This phenomenon often referred to as interfacial thermal resistance (i.e., Kapitza resistance) during nanoscale thermal transport. There is also evidence that the fluid molecules are absorbed by the wall molecules promoting structural ordering of fluid at the solid/fluid interface. The local dynamic properties of this fluid layered structure are substantially different from the fluid properties at macroscale. Therefore, the continuum transport theories break down near the material interfaces at nanoscale. In this thesis, we investigate the unique transport behaviors of fluid molecules in confining nanoenvironments using Molecular Dynamics (MD) simulations. Firstly, heat transfer across an interface between a monolayer coated solid substrate and fluid has been analyzed by varying the atomic mass (mM) and interaction energy between monolayer molecules (εMM). In that case, the mutual combination of atomic mass (mM) and interaction energy (MM) of monolayer lead to a significant influence in heat transport at the interfacial region. It was found that Kapitza resistance monotonically increases with the increase of mM irrespective of εMM without any further change in the fluid-structure near the solid surface. This indicates the vibrational coupling between the molecules at the solid/fluid interface largely depend on the mass of monolayer molecules. We also investigate the pressure-driven transport mechanism of liquid argon through nanoporous graphene membrane (NPGM) using MD simulations. In this study we check the validity and limitations of the assumptions of continuum flow equation. We present a thorough characterization of the density and pressure distribution of liquid argon based on the respective flow region to elucidate the unique fluid transport behaviors. The argon velocity adjacent to the pore edge was found lower than pore center suggesting the influence of the interaction between argon and carbon molecules at the pore boundary. In that case, we consider the argon velocity closest to the pore edge as slip velocity, which provides an update in the continuum flow equation. The local viscosity was also calculated from the thin argon film flows sheared by graphene walls. Our study shows that the entrance interfacial pressure and higher local viscosity in the vicinity of graphene membrane associated with the optimized definition of wall/fluid boundary near the pore edge play a critical role for the permeation of argon through NPGM.