• Journal of the Korean Society of Industry Convergence
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• v.24 no.6_2
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• pp.801-808
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• 2021

In this paper, a numerical analysis was conducted on the effect of the flow control valve of a oscillation water column(OWC) type wave power generator turbine. The OWC wave power turbine operates with compressed air in the air chamber according to the change of wave height. When the wave height changes rapidly, a flow control valve is required due to overload of the turbine and reduced efficiency. Therefore, in this paper, a flow control valve with an opening angle of 60 degrees was installed in the front of the turbine, and the pressure drop, torque, and overall performance were calculated according to the change of turbine RPM and flow rate of turbine inlet. In conclusion, the flow control valve with an opening angle of 60 degrees affects when the turbine rotates at low rotation and the inlet flow rate is large. But it does not have a significant effect on overall turbine performance and it is necessary to find the optimal angle in the future works.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.24 no.5
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• pp.432-442
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• 2021

Purpose: The aim of this study was to evaluate the nutrient content consumed by children and adolescents on home-prepared versus chef-prepared specific carbohydrate diets (SCD) as therapy for inflammatory bowel disease (IBD). Methods: Dietary intake of two cohorts with active IBD initiating the SCD over 12 weeks was assessed. The home-prepared cohort received detailed guidance from dietitians on implementation of the SCD. The chef in the other cohort was knowledgeable in the SCD and prepared meals from a fixed set of recipes. Data from 3-day diet diaries at 4 different time points were collected. US Recommended Daily Allowances (RDA) were calculated for macronutrients, vitamins, and minerals. Results: Eight participants on the homemade SCD and 5 participants on the chef-prepared SCD were included in analysis. Mean % RDA for energy intake was 115% and 87% for homemade and chef-prepared groups (p<0.01). Mean % RDA for protein intake was 337% for homemade SCD and 216% for chef-prepared SCD (p<0.01). The homemade SCD group had higher mean % RDA values for vitamin A and iron, while the chef-prepared SCD group had higher intake of vitamins B1, B2, D, phosphorus and zinc (p<0.01 for all). Conclusion: The SCD implemented homemade versus chef-prepared can result in significantly different intake of nutrients and this may influence efficacy of this dietary therapy. Meal preparation dynamics and the motivation of families who pursue dietary treatment may play an important role on the foods consumed and the outcomes on dietary therapy with the SCD.

• Journal of the Korean Institute of Gas
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• v.25 no.2
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• pp.28-33
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• 2021

With the recent growing interest in eco-friendly cars, as interest in eco-friendly cars increases, interest and purchase of hydrogen fuel cell vehicles that do not emit pollutants are increasing. Recently, the government is supporting the expansion of hydrogen charging station and localization of core parts according to the government's hydrogen energy dissemination policy. In this study, the flow characteristics of the hydrogen flow control valve were investigated. As the differential pressure increases, the mass flow rate and flow coefficient tend to be different from the volume flow rate. And it was confirmed that it affects the hydrogen temperature due to the nozzle effect in the bottleneck section, and the change in density affects the mass flow rate.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.6
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• pp.474-481
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• 2018

This paper is to compare by numerical analysis the flow characteristics and propulsion performance of stern with the shape change of K-duct, a pre-swirl duct developed by Korea Research Institute of Ships & Ocean Engineering (KRISO). First, the characteristics of the propeller and the resistance and self-propulsion before and after the attachment of the K-duct to the ship were verified and the validity of the calculation method was confirmed by comparing this result with the model test results. After that, resistance and self-propulsion calculations were performed by the same numerical method when the K-duct was changed into five different shapes. The efficiency of the other five cases was compared using the delivery horsepower in the model scale and the flow characteristics of the stern were analyzed as the velocity and pressure distributions in the area between the duct end and the propeller plane. For the computation, STAR-CCM +, a general-purpose flow analysis program, was used and the Reynolds Averaged Navier-Stokes (RANS) equations were applied. Rigid Body Motion (RBM) method was used for the propeller rotating motion and SST $k-{\omega}$ turbulence model was applied for the turbulence model. As a result, the tangential velocity of the propeller inflow changed according to the position angle change of the stator, and the pressure of the propeller hub and the cap changes. This regulated the propeller hub vortex. It was confirmed that the vortex of the portion where the fixed blade and the duct meet was reduced by blunt change.

• Smart Structures and Systems
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• v.23 no.6
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• pp.653-667
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• 2019

Using cross-ties to connect cables together when forming a cable network is regarded as an efficient method of mitigating cable vibrations. Cross-ties have been extended and fixed on bridge decks or towers in some engineering applications. However, the dynamics of this kind of system need to be further studied, and the effects of extending cross-links to bridge decks/towers on the modal response of the system should be assessed in detail. In this paper, a system of two cables connected by an inter-supported cross-link with another lower cross-link extended to the ground is proposed and analyzed. The characteristic equation of the system is derived, and some limiting solutions in closed form of the system are derived. Roots of cable system with special configurations are also discussed, attention being given to the case when the two cables are identical. A predictable mode behavior was found when the stiffness of inter-connection cross-link and the cross-link extended to the ground were the same. The vector of mode energy distribution and the degree of mode localization index are proposed so as to distinguish global and local modes. The change of mode behaviors is further discussed in the case when the two cables are not identical. Effects of cross-link stiffness, cross-link location, mass-tension ratio, cable length ratio and frequency ratio on $1^{st}$ mode frequency and mode shape are addressed.

• Tribology and Lubricants
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• v.34 no.6
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• pp.247-253
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• 2018

Temperature rise due to viscous shear of the lubricating oil generates hydrodynamic pressure, even if the lubricating surfaces are parallel. This effect, known as the thermal wedge effect, varies significantly with film-temperature boundary conditions. The bearing conducts a part of the heat generated; hence, the oil temperature varies with the thermal conductivity of the bearing. In this study, we analyze the effect of thermal conductivity on the thermohydrodynamic (THD) lubrication of parallel slider bearings. We numerically analyze the continuity equation, Navier-Stokes equation, energy equation including the temperature-viscosity and temperature-density relations for lubricants, and the heat conduction equation for bearing by creating a 2D model of the micro-bearing using the commercial computational fluid dynamics (CFD) code FLUENT. We then compare the variation in temperature, viscosity, and pressure distributions with the thermal conductivity. The results demonstrate that the thermal conductivity has a significant influence on THD lubrication characteristics of parallel slider bearings. The lower the thermal conductivity, the greater the pressure generation due to the thermal wedge effect resulting in a higher load-carrying capacity and smaller frictional force. The present results can function as the basic data for optimum bearing design; however, the applicability requires further studies on various operating conditions.

• Membrane Journal
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• v.29 no.1
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• pp.11-17
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• 2019

In the field of water treatment membranes, polymers are used together with ceramics as the most important materials. In this review, I tried to analyze the technology trends of polymer membrane materials based on commercial products. For this purpose, according to the types of water treatment membranes such as MF (Microfiltration), UF (Ultrafiltration) and NF (Nanofiltration), the trends of polymer membrane products were investigated by countries, materials, and companies. Through this, we were able to classify the types of materials that are mainly used for each type of membrane, and at the same time, identify the companies that are dominant in the market, and analyze which materials constitute the product portfolio. Based on these results, we have presented the characteristics of the material market according to each type of membrane, and proposed a technology development strategy to enter each market based on these characteristics.

• Steel and Composite Structures
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• v.30 no.1
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• pp.31-46
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• 2019

In the present study, the various dynamic properties of MWCNT embedded fiber reinforced polymer uniform and tapered composite (MWCNT-FRP) plates are investigated. Various configurations of a tapered composite plate with ply-drop off and uniform composite plate have been considered for the development of the finite element formulation and experimental investigations. First order shear deformation theory (FSDT) has been used to derive the kinetic and potential energy equations of the hybrid composite plates by including the effect of rotary inertia, shear deformation and non-uniformity in thickness of the plate. The governing equations of motion of FRP composite plates without and with MWCNT reinforcement are derived by considering a nine- node rectangular element with five degrees of freedom (DOF) at each node. The effectiveness of the developed finite element formulation has been demonstrated by comparing the natural frequencies and damping ratio of FRP composite plates without and with MWCNT reinforcement obtained experimentally. Various parametric studies are also performed to study the effect of CNT volume fraction and CNT aspect ratio of the composite plate on the natural frequencies of different configurations of CNT reinforced hybrid composite plates. Further the forced vibration analysis is performed to compare the dynamic response of the various configurations of MWCNT-GFRP composite plate with GFRP composite plate under harmonic excitations. It was observed that the fundamental natural frequency and damping ratio of the GFRP composite plate increase approximately 8% and 37% respectively with 0.5wt% reinforcement of MWCNT under CFCF boundary condition. The natural frequencies of MWCNT-GFRP hybrid composite plates tend to decrease with the increase of MWCNT volume fraction beyond 2% due to agglomeration of CNT's. It is also observed that the aspect ratio of the CNT has negligible effect on the improvement of dynamics properties due to randomly orientation of CNT's.

• Structural Engineering and Mechanics
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• v.70 no.4
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• pp.479-497
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• 2019

In the current code design, the use of a uniform internal pressure coefficient of cooling towers as internal suction cannot reflect the 3D characteristics of flow field inside the tower body with different ventilation rate of shutters. Moreover, extreme weather such as heavy rain also has a direct impact on aerodynamic force on the internal surface and changes the turbulence effect of pulsating wind. In this study, the world's tallest cooling tower under construction, which stands 210m, is taken as the research object. The algorithm for two-way coupling between wind and rain is adopted. Simulation of wind field and raindrops is performed iteratively using continuous phase and discrete phase models, respectively, under the general principles of computational fluid dynamics (CFD). Firstly, the rule of influence of 9 combinations of wind speed and rainfall intensity on the volume of wind-driven rain, additional action force of raindrops and equivalent internal pressure coefficient of the tower body is analyzed. The combination of wind velocity and rainfall intensity that is most unfavorable to the cooling tower in terms of distribution of internal pressure coefficient is identified. On this basis, the wind/rain loads, distribution of aerodynamic force and working mechanism of internal pressures of the cooling tower under the most unfavorable working condition are compared between the four ventilation rates of shutters (0%, 15%, 30% and 100%). The results show that the amount of raindrops captured by the internal surface of the tower decreases as the wind velocity increases, and increases along with the rainfall intensity and ventilation rate of the shutters. The maximum value of rain-induced pressure coefficient is 0.013. The research findings lay the basis for determining the precise values of internal surface loads of cooling tower under extreme weather conditions.

• Animal Bioscience
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• v.34 no.4
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• pp.575-583
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• 2021

Objective: The aim of the study was to determine the effect of parity and the stage of lactation on the metabolic profile of cows based on the basic chemical milk components and the blood parameters. Methods: The study material consisted of high-yielding Holstein-Friesian cows. In total, 473 cows were examined. According to the parity, cows were divided into four groups: primiparous (P), and multiparous in the second (M2), in the third (M3), and in subsequent lactations (M4). The feeding of cows was based on total mixed ration (TMR) ad libitum. Milk and blood samples were collected individually from each cow three times per standard lactation period. Results: Greater exacerbation of changes in the dynamics of the blood plasma parameters examined was proved for multiparous cows. The highest value of β-hydroxybutyrate acid (0.946 mmol/L) was found for multiparous cows from group M3 at the beginning of lactation. However, it was still in the normal range. The results showed aspartate aminotransferase, and gamma-glutamyl transferase (GGT) activities in dairy cows during lactation had significant variations taking in to account stage of lactation. The highest activity of GGT was found in the group of the oldest cows and measured from 26.36 U/L at the beginning of lactation to 48.75 U/L at the end of the lactation period. Conclusion: The time-related changes in the concentrations of the biochemical parameters described differ markedly among lactating cows, though the housing conditions on the research dairy farm are highly standardised. This indicates that the ability to cope with metabolic stress is mainly affected by the individual predispositions of cows and feed nutrient supply in different stage of lactation. Especially, the feed nutrient supply (in net energy for lactation), which was the best in TMR 1 in comparison TMR 3.