• Transactions of the Korean hydrogen and new energy society
• /
• v.34 no.2
• /
• pp.155-161
• /
• 2023

Recently, a study on alternative and renewable energy is being conducted due to energy depletion and environmental problems. In particular, a hydrogen has the advantage of converting and storing the remaining energy into water-electrolyzed hydrogen through renewable energy generation. In general, due to reasons such as insulation problems, a study on high-pressure hydrogen storage tanks and related parts has recently been conducted. However, in the case of liquid hydrogen, the volume can be reduced by about 800 times or more compared to high-pressure hydrogen gas, so the study on this is needed as a technology that can increase energy density. In this study, the evaporation characteristics were analyzed under fixed heat flux conditions for liquid hydrogen storage tanks and the change in thermal stratification according to sloshing was analyzed. The heat flux condition was fixed at 250 W/m² and the horizontal resonance frequency of the primary mode was applied to the storage tank. As a result, it was confirmed that the thermal stratification phenomenon decreased compared to the case where the slashing was not present due to forced convection when the slashing was present.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
• /
• v.8 no.11
• /
• pp.523-530
• /
• 2018

It has been studied over the long time for the high efficiency and high power density of the power converter. It is possible to obtain higher power conversion efficiency and small volume by increasing switching frequency, however, the switching loss is also increased. The soft switching technique can overcome of the above deficiency. The design and analysis method for ZVS(Zero Voltage Switching) Phase Shifte Full bridge converter is presented in this paper. The power transfer depends on the phase difference between two legs of the power stage and the maximum power conversion efficiency is achieved by the optimum leakage inductance value. The waveform of the current and voltage of the operational mode is analysed and the corresponding switch status is plotted as on/off status. A ZVS full bridge converter for a communication rectifier with 2kW output power is implemented and its performance are verified through PSIM software simulation and experimental results.

• Composites Research
• /
• v.36 no.3
• /
• pp.154-161
• /
• 2023

This study explored the feasibility of replacing a metal link with a carbon fiber/epoxy composite link and assessed its capacity to withstand a given load condition using failure criteria. The micromechanics of failure (MMF) criterion was employed to predict the failure mode of the composite material, and mechanical tests were conducted to obtain reference strength parameters for MMF. The findings revealed that the stress distribution was concentrated near the hole, and weaknesses were found around the hole and at the end of the link under bending conditions. Based on the failure index, matrix tensile failure was predicted at the end of the link, and fiber compression failure occurred near the hole. The methods and results obtained from this study can provide valuable guidelines for assessing the safety of composite materials under specific load conditions when replacing metal parts with carbon fiber/epoxy composites to achieve weight reduction.

• The Bulletin of The Korean Astronomical Society
• /
• v.45 no.1
• /
• pp.38.2-38.2
• /
• 2020

Horizon Run 5 (HR5) is a cosmological hydrodynamical simulation which captures the properties of the Universe on a Gpc scale while achieving a resolution of 1 kpc. This enormous dynamic range allows us to simultaneously capture the physics of the cosmic web on very large scales and account for the formation and evolution of dwarf galaxies on much smaller scales. Inside the simulation box. we zoom-in on a high-resolution cuboid region with a volume of 1049 × 114 × 114 Mpc3. The subgrid physics chosen to model galaxy formation includes radiative heating/cooling, reionization, star formation, supernova feedback, chemical evolution tracking the enrichment of oxygen and iron, the growth of supermassive black holes and feedback from active galactic nuclei (AGN) in the form of a dual jet-heating mode. For this simulation we implemented a hybrid MPI-OpenMP version of the RAMSES code, specifically targeted for modern many-core many thread parallel architectures. For the post-processing, we extended the Friends-of-Friend (FoF) algorithm and developed a new galaxy finder to analyse the large outputs of HR5. The simulation successfully reproduces many observations, such as the cosmic star formation history, connectivity of galaxy distribution and stellar mass functions. The simulation also indicates that hydrodynamical effects on small scales impact galaxy clustering up to very large scales near and beyond the baryonic acoustic oscillation (BAO) scale. Hence, caution should be taken when using that scale as a cosmic standard ruler: one needs to carefully understand the corresponding biases. The simulation is expected to be an invaluable asset for the interpretation of upcoming deep surveys of the Universe.

• Architectural research
• /
• v.25 no.4
• /
• pp.61-72
• /
• 2023

The main factors that made Seoul's rapid population accommodation and urbanization possible in the mid-to-late 20th century were the ex-pansion of urban infrastructure, completion of the transportation system, and housing supply. The development of transportation and resi-dential development occurred simultaneously, and in particular, apartment complexes, a representative residential area in Seoul, were most influenced by Perry's neighborhood unit theory. The purpose of this study is to analyze the process of the physical environment of apartment complexes in the metropolitan area in response to development of transportation in the mid-to-late 20th century. The analysis sites are Jamsil Apartment Complex(1974), Dunchon Apartment Complex(1979), Mok-dong New Town(1983), Sanggye New Town(1985), Bundang New-town(1990) and Ilsan Newtown(1990), which were planned at the turning point of development of transportation and actively reflect the neigh-borhood unit theory. The analysis was conducted in three stages. Analyzing the status of transportation when the plan was established, deriv-ing the planning elements, and classifying the planning elements into walking, bus, car, and subway which is the representative transportation. The conclusions from the analysis are as follows. Firstly, completing the legal system and expanding the related infrastructure are essential. Secondly, in contrast to the increase in traffic volume, the pedestrian environment has been continuously improved. Thirdly, despite the emergence of new mode of transportation, there was a tendency to activate the linkage between transportation.

• Structural Engineering and Mechanics
• /
• v.90 no.4
• /
• pp.371-390
• /
• 2024

Investigating the impact of openings on the structural behavior of ferrocement I-beams with two distinct types of reinforcing metallic and non-metallic meshes is the primary goal of the current study. Up until failure, eight 250x200x2200 mm reinforced concrete I-beams were tested under flexural loadings. Depending on the kind of meshes used for reinforcement, the beams are split into two series. A control I-beam with no openings and three beams with one, two, and three openings, respectively, are found in each series. The two series are reinforced with three layers of welded steel meshes and two layers of tensar meshes, respectively, in order to maintain a constant reinforcement ratio. Structural parameters of investigated beams, including first crack, ultimate load, deflection, ductility index, energy absorption, strain characteristics, crack pattern, and failure mode were reported. The number of mesh layers, the volume fraction of reinforcement, and the kind of reinforcing materials are the primary factors that vary. This article presents the outcomes of a study that examined the experimental and numerical performance of ferrocement reinforced concrete I-beams with and without openings reinforced with welded steel mesh and tensar mesh separately. Utilizing ANSYS-16.0 software, nonlinear finite element analysis (NLFEA) was applied to illustrate how composite RC I-beams with openings behaved. In addition, a parametric study is conducted to explore the variables that can most significantly impact the mechanical behavior of the proposed model, such as the number of openings. The FE simulations produced an acceptable degree of experimental value estimation, as demonstrated by the obtained experimental and numerical results. It is also noteworthy to demonstrate that the strength gained by specimens without openings reinforced with tensar meshes was, on average, 22% less than that of specimens reinforced with welded steel meshes. For specimens with openings, this value is become on average 10%.

• Tuberculosis and Respiratory Diseases
• /
• v.45 no.2
• /
• pp.380-387
• /
• 1998

Background: Minimal pressure support(PSmin) is a level of pressure support which offset the imposed work of breathing(WOBimp) developed by endotracheal tube and ventilator circuits in pressure support ventilation While the lower applied level of pressure support compared to PSmin could induce respiratory muscle fatigue, the higher level than PSmin could keep respiratory muscle rest resulting in prolongation of weaning period during weaning from mechanical ventilation PSmin has been usually applied in the level of 5~10 cm$H_2O$, but the accurate level of PSmin is difficult to be determinated in individual cases. PSmin is known to be calculated by using the equation of "PSmin = peak inspiratory flow rate during spontaneus ventilation$\times$total ventilatory system resistance", but correlation of calculated PSmin and measured PSmin has not been known. The objects of this study were firstly to assess whether customarily applied pressure support level of 5~10 cm$H_2O$ would be appropriate to offset the imposed work of breathing among the patients under weaning process, and secondly to estimate the correlation between the measured PSmin and calculated PSmin. Method : 1) Measurement of PSmin : Intratracheal pressure changes were measured through Hi-Lo jet tracheal tube (8mm in diameter, Mallinckroft, USA) by using pulmonary monitor(CP-100 pulmonary monitor, Bicore, USA), and then pressure support level of mechanical ventilator were increased until WOBimp was reached to 0.01 J/L or less. Measured PSmin was defined as the lowest pressure to make WOBimp 0.01 J/L or less. 2) Calculation of PSmin : Peak airway pressure(Ppeak), plateau airway pressure(Pplat) and mean inspiratory flow rate of the subjects were measured on volume control mode of mechanical ventilation after sedation. Spontaneous peak inspiratory flow rates were measured on CPAP mode(O cm$H_2O$). Thereafter PSmin was calculated by using the equation "PSmin = peak inspiratory flow rate$\times$R, R = (Ppeak-Pplat)/mean inspiratory flow rate during volume control mode on mechanical ventilation". Results: Sixteen patients who were considered as the candidate for weaning from mechanical ventilation were included in the study. Mean age was 64(${\pm}14$) years, and the mean of total ventilation times was 9(${\pm}4$) days. All patients except one were males. The measured PSmin of the subjects ranged 4.0~12.5cm$H_2O$ in 14 patients. The mean level of PSmin was 7.6(${\pm}2.5\;cmH_2O$) in measured PSmin, 8.6 (${\pm}3.25\;cmH_2O$) in calculated PSmin Correlation between the measured PSmin and the calculated PSmin is significantly high(n=9, r=0.88, p=0.002). The calculated PSmin show a tendancy to be higher than the corresponding measured PSmin in 8 out of 9 subjects(p=0.09). The ratio of measured PSmin/calculated PSmin was 0.81(${\pm}0.05$). Conclusion: Minimal pressure support levels were different in individual cases in the range from 4 to 12.5 cm$H_2O$. Because the equation-driven calculated PSmin showed a good correlation with measured PSmin, the application of equation-driven PSmin would be then appropriate compared with conventional application of 5~10 cm$H_2O$ in patients under difficult weaning process with pressure support ventilation.

• Clinical and Experimental Pediatrics
• /
• v.46 no.5
• /
• pp.484-489
• /
• 2003

Purpose : To understand morphologic and hemodynamic variations in patients with pulmonary atresia with intact ventricular septum(PA/IVS), and to decide the best treatment modalities, we measured right ventricular volume, inflow, and outflow valvular annulus size in these patients and compared them with those of normal newborns. Methods : Eight patients with PA/IVS diagnosed by echocardiography from January to December 2001 were enrolled in this study. Among the total eight patients, five were male and three were female. The mean age of patients was 6.9 days(1-34 days), and the mean body weight was 3,343 gm (2,970-4,000 gm). Ten fullterm newborn infants with sepsis or hyperbilirubinemia without heart disease were enrolled as a control group. Echocardiographic and Doppler studies using Acuson Aspen (7Mh probe) were recorded on super-VHS videotape and later on, with review mode. We measured volumes of right and left ventricles, aortic, pulmonic, mitral and tricuspid valvular annulus sizes using an installed program, and then these parameters were compared with those of the control group. Results : Mean Z-value of tricuspid valvular annulus in PA/IVS was $-3.69{\pm}2.80$(-8.4--0.45), and tricuspid/mitral valvular annulus size ratio $0.68{\pm}0.15$(0.43--0.84). The more the tricuspid/mitral valvular annulus size ratio, the more Z-value of tricuspid valvular annulus(P=0.003, r=0.885). Those patients who underwent pulmonary valvuloplasty(balloon or surgical) had a tendency toward larger volume of the right ventricle, more Z-value of pulmonic and tricuspid valvular annulus, and more tricuspid/mitral valvular annulus size ratio than those patients who underwent a shunt operation. Conclusion : Compared to a measurement of the volume of the right ventricle, measurements of tricuspid/mitral valvular annulus size ratio and Z-value of tricuspid valvular annulus may be easier and better parameters to decide the treatment method and to predict prognosis in PA/IVS patients.

• Journal of Korean Society of Transportation
• /
• v.33 no.4
• /
• pp.379-392
• /
• 2015

Freight flow data in Korea has been collected for a variety of purposes by various organizations. However, since the representation and format of the data varies, it has not been substantially used for freight analyses and furthermore for freight policies. In order to increase the applicability of those data sets, it is required to bring them in a table and compare for finding the differences. Then, it is shown that the raw data can be aggregated by a particular criterion such as mode, origin and destination, and type commodity. This study aims to examine the freight data issue in terms of three different points of view. First, we investigated various freight volume data sets which are released by several organizations. Second, we tried to develop formulations for freight volume data. Third, we discussed how to apply the formulations to network models in which particular OR (Operations Research) techniques are used. The results emphasized that some data might be useless for modeling once they are aggregated. As a result of examining the freight volume data, this study found that 14 organizations share their data sets at various aggregation levels. This study is not an ordinary research article, which normally includes data analysis, because it seems to be impossible to conduct extensive case studies. The reason is that the data dealt in this study are diverse. Nevertheless, this study might guide the research direction in the freight transport research society in terms of data issue. Especially, it can be concluded that this study is a timely research because the governmemt has emphasized the importance of sharing data to public throughout 'government 3.0' for research purpose.

• Progress in Medical Physics
• /
• v.17 no.1
• /
• pp.24-31
• /
• 2006

Automated analysis software was developed to measure the magnitude of the intrafractional and interfractional errors during breast radiation treatments. Error analysis results are important for determining suitable planning target volumes (PTV) prior to Implementing breast-conserving 3-D conformal radiation treatment (CRT). The electrical portal imaging device (EPID) used for this study was a Portal Vision LC250 liquid-filled ionization detector (fast frame-averaging mode, 1.4 frames per second, 256X256 pixels). Twelve patients were imaged for a minimum of 7 treatment days. During each treatment day, an average of 8 to 9 images per field were acquired (dose rate of 400 MU/minute). We developed automated image analysis software to quantitatively analyze 2,931 images (encompassing 720 measurements). Standard deviations ($\sigma$) of intrafractional (breathing motion) and intefractional (setup uncertainty) errors were calculated. The PTV margin to include the clinical target volume (CTV) with 95% confidence level was calculated as $2\;(1.96\;{\sigma})$. To compensate for intra-fractional error (mainly due to breathing motion) the required PTV margin ranged from 2 mm to 4 mm. However, PTV margins compensating for intefractional error ranged from 7 mm to 31 mm. The total average error observed for 12 patients was 17 mm. The intefractional setup error ranged from 2 to 15 times larger than intrafractional errors associated with breathing motion. Prior to 3-D conformal radiation treatment or IMRT breast treatment, the magnitude of setup errors must be measured and properly incorporated into the PTV. To reduce large PTVs for breast IMRT or 3-D CRT, an image-guided system would be extremely valuable, if not required. EPID systems should incorporate automated analysis software as described in this report to process and take advantage of the large numbers of EPID images available for error analysis which will help Individual clinics arrive at an appropriate PTV for their practice. Such systems can also provide valuable patient monitoring information with minimal effort.