• Steel and Composite Structures
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• v.42 no.3
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• pp.397-405
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• 2022

The existing researches on the dynamics of the fluid-conveying pipes only focus on stability and vibration problems, and there is no literature report on the wave propagation of the fluid-conveying pipes. Therefore, the purpose of this paper is to explore the propagation characteristics of longitudinal and flexural waves in the fluid-conveying pipes. First, it is assumed that the material properties of the fluid-conveying pipes vary based on a power function of the thickness. In addition, it is assumed that the material properties of both the fluid and the pipes are closely depended on temperature. Using the Euler-Bernoulli beam equation and based on the linear theory, the motion equations considering the thermal-mechanical-fluid coupling is derived. Then, the exact expressions of phase velocity and group velocity of longitudinal waves and bending waves in the fluid-conveying pipes are obtained by using the eigenvalue method. In addition, we also studied the free vibration frequency characteristics of the fluid-conveying pipes. In the numerical analysis, we successively studied the influence of temperature, functional gradient index and liquid velocity on the wave propagation and vibration problems. It is found that the temperature and functional gradient exponent decrease the phase and group velocities, on the contrary, the liquid flow velocity increases the phase and group velocities. However, for vibration problems, temperature, functional gradient exponent parameter, and fluid velocity all reduce the natural frequency.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.608-614
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• 2023

The fast filling process of high-pressure hydrogen has an important impact on the filling efficiency and safety. In this paper, a specific study is carried out on the thermophysical phenomena during the fast filling process. Starting from the gas state equation of hydrogen, the change law of the hydrogen storage temperature is obtained, and then the temperature rise prediction is constructed. The model can clarify the relationship between the filling parameters and the temperature rise during the fast filling process, thereby revealing the flow and heat transfer laws of the fast charging process. To improve the theoretical research basis for the evaluation of vehicle-mounted hydrogen fast charging capacity, temperature prediction and optimization of hydrogenation methods.

• Korean Journal of Ichthyology
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• v.28 no.4
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• pp.215-222
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• 2016

Triploidy was induced in the marine medaka, Oryzias dancena by cold shock treatment ($0^{\circ}C$) of fertilized eggs for 30, 45, or 60 min, applied two minutes after fertilization. The triploid genotype was induced by each of the thermal shock regimes tested. The best result was obtained when the eggs were treated for 45 min, which induced triploidy in all the resulting fish. Triploidy was confirmed using chromosomal and flow cytometer analyses, and erythrocyte measurements. The surface areas and volumes of the erythrocytes of triploid fish were significantly larger than those of diploid fish, and their chromosome number (3N=72) was 1.5 times greater that for the diploids (2N=48). Based on a flow cytometer analysis, the triploid fish had approximately 1.5 times the cellular DNA content (2.40 pg/cell) of the diploid specimens (1.61 pg/cell). Data from this study provide the basis for the development of unique models for studying reproductive confinement in transgenic fish.

• Korean Journal of Environment and Ecology
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• v.33 no.3
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• pp.366-374
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• 2019

This study aims to analyze the characteristics of ventilation corridor and propose its utilization strategies in Jeonju city in order to discuss how to utilize urban ventilation corridors as a planning factor for reducing heat wave impact and fine particle pollution. For these purposes, cold air characteristics such as cold air flow and height of cold air in Jeonju area located in the Honam Jeongmaek were analyzed and major ventilation corridors were specified. Based on them, we proposed mountain management strategies for securing and utilizing ventilation corridors. We used KALM (Kaltluftabflussmodell), a cold air simulation model developed in Germany and identified both the cold air flow and the height of cold air layer generated during 6 hours at night. As a result, the cold air flow generated in the forests located in the northeast and east sides of the Jeonju city became clear and the height of cold air layer increased in the valley terrain and farmland areas with time. In particular, Jeonju City has an ideal structure of urban ventilation corridor. Based on the results, the area where the cold air generation is active was designated as the 'cold air conservation area', and the area requiring the management for the good cold air flow was as the 'cold air management area'. This study is expected to be used as basic data of policy making and research for reducing heat wave impact and fine particle pollution such as climate change adaptation policy and urban forest plans for ventilation corridor composition.

• Advances in nano research
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• v.16 no.4
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• pp.325-340
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• 2024

There are several novel uses for dispersing many nanoparticles into a conventional fluid, including dynamic sealing, damping, heat dissipation, microfluidics, and more. Therefore, melting heat and mass transfer characteristics of a 3-D MHD Hybrid Nanofluid flow over a rotating disc with presenting dufour and soret effects are assessed numerically in this study. In this instance, we investigated both ferric sulfate and molybdenum disulfide as nanoparticles suspended within base fluid water. The governing partial differential equations are transformed into linked higher-order non-linear ordinary differential equations by the local similarity transformation. The collection of these deduced equations is then resolved using a Chebyshev spectral collocation-based algorithm built into the Mathematica software. To demonstrate how different instances of hybrid/ nanofluid are impacted by changes in temperature, velocity, and the distribution of nanoparticle concentration, examples of graphical and numerical data are given. For many values of the material parameters, the computational findings are shown. Simulations conducted for different physical parameters in the model show that adding hybrid nanoparticle to the fluid mixture increases heat transfer in comparison to simple nanofluids. It has been identified that hybrid nanoparticles, as opposed to single-type nanoparticles, need to be taken into consideration to create an effective thermal system. Furthermore, porosity lowers the velocities of simple and hybrid nanofluids in both cases. Additionally, results show that the drag force from skin friction causes the nanoparticle fluid to travel more slowly than the hybrid nanoparticle fluid. The findings also demonstrate that suction factors like magnetic and porosity parameters, as well as nanoparticles, raise the skin friction coefficient. Furthermore, It indicates that the outcomes from different flow scenarios correlate and are in strong agreement with the findings from the published literature. Bar chart depictions are altered by changes in flow rates. Moreover, the results confirm doctors' views to prescribe hybrid nanoparticle and particle nanoparticle contents for achalasia patients and also those who suffer from esophageal stricture and tumors. The results of this study can also be applied to the energy generated by the melting disc surface, which has a variety of industrial uses. These include, but are not limited to, the preparation of semiconductor materials, the solidification of magma, the melting of permafrost, and the refreezing of frozen land.

• Journal of Environmental Impact Assessment
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• v.24 no.2
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• pp.134-153
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• 2015

When making urban planning, it is important to understand climate effect caused by urban structural changes. Seoul city applies UPIS(Urban Plan Information System) which provides information on urban planning scenario. Technology for analyzing climate effect resulted from urban planning needs to developed by linking urban planning scenario provided by UPIS and climate analysis model, CAS(Climate Analysis Seoul). CAS develops for analyzing urban climate conditions to provide realistic information considering local air temperature and wind flows. Quantitative analyses conducted by CAS for the production, transportation, and stagnation of cold air, wind flow and thermal conditions by incorporating GIS analysis on land cover and elevation and meteorological analysis from MetPhoMod(Meteorology and atmospheric Photochemistry Meso-scale model). In order to reflect land cover and elevation of the latest information, CAS used to highly accurate raster data (1m) sourced from LiDAR survey and KOMPSAT-2(KOrea Multi-Purpose SATellite) satellite image(4m). For more realistic representation of land surface characteristic, DSM(Digital Surface Model) and DTM(Digital Terrain Model) data used as an input data for CFD(Computational Fluid Dynamics) model. Eight inflow directions considered to investigate the change of flow pattern, wind speed according to reconstruction and change of thermal environment by connecting green area formation. Also, MetPhoMod in CAS data used to consider realistic weather condition. The result show that wind corridors change due to reconstruction. As a whole surface temperature around target area decreases due to connecting green area formation. CFD model coupled with CAS is possible to evaluate the wind corridor and heat environment before/after reconstruction and connecting green area formation. In This study, analysis of climate impact before and after created the green area, which is part of 'Connecting green network across the north and south in Seoul' plan, one of the '2020 Seoul master plan'.

• Nuclear Engineering and Technology
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• v.18 no.3
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• pp.200-208
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• 1986

The loss of coolant accident based on a double-ended cold leg break is analyzed with the discharge coefficient (Ca) of 0.4. This analysis covers the whole transient period from the start of depressurization to the complete refilling of the core by using RELAP4/MOD6-EM and RELAP4/ MOD6-HOT CHANNEL for the system thermal-hydraulics and the fuel performance during the blowdown phase respectively, and RELAP4/MOD6-FLOOD and TOODEE2 during the reflood phase. A simple analytical method has been developed to account for the lower plenum filling by approximating steam-water countercurrent flows and superheated wall effects at the downcomer during the refill period. Based on the informations. at the time of EOB (end-of-bypass), the refill duration time and the initial reflooding temperature were estimated and compared with the results from the RELAP4/MOD6, resulting in a good agreement. In addition, some parametric studies on the EOB were performed. The form loss coefficient between upper head and upper downcomer was found to be sensitive to the occurrence of the spurious EOB. Appropriate form loss coefficients should be taken into account to avoid the flow oscillations at the downcomer. The analyses with the six and three volume core nodalizations, respectively, show much similar trends in the system thermal-hydraulic performance, but the former case is recommended to obtain good results.

• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.567-575
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• 2012

A research was conducted to develop a 2-D nonlinear Galerkin finite element analysis of reinforced concrete structures subjected to high temperature with experiments. Algorithms for calculating the closed-form element stiffness for a triangular element with a fully populated material conductance are developed. The validity of the numerical model used in the program is established by comparing the prediction from the computer program with results from full-scale fire resistance tests. Details of fire resistance experiments carried out on reinforced concrete slabs, together with results, are presented. The results obtained from experimental test indicated in that the proposed numerical model and the implemented codes are accurate and reliable. The changes in thermal parameters are discussed from the point of view of changes of structure and chemical composition due to the high temperature exposure. The proposed numerical model takes into account time-varying thermal loads, convection and radiation affected heat fluctuation, and temperature-dependent material properties. Although, this study considered standard fire scenario for reinforced concrete slabs, other time versus temperature relationship can be easily incorporated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.8
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• pp.4763-4768
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• 2014

Recently, aluminum pipes have been used instead of steel pipes for open and shut machines in vinyl housing because of its corrosion-resistance and light weight. In particular, the light weight is very useful for fitting and removal by human resources. On the other hand, an aluminum pipe is weak in winter because aluminum has a larger thermal expansion coefficient than steel. This study examined the freezing and bursting of aluminum pipes by numerical analysis. The mechanical-thermal deformation characteristics were analyzed under the condition of ice volumetric expansion in aluminum pipes reaching 50%. From numerical analysis, large stresses above the yield stress occurred in aluminum pipe after ice expanded in the net diameter immediately. In addition, the freezing and bursting of aluminum pipes was predicted around an ice volumetric expansion of 6 - 7% because the thickness of the aluminum pipe reached an aluminum elongation ratio of 17%. Therefore, it is recommended that aluminum pipes be sealed perfectly to prevent water flow in the pipe. These results suggest that it is very difficult to prevent freezing and bursting of aluminum pipes by water freezing in the pipe.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.223-233
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• 2011

A ceramic monolithic catalyst is a honeycomb structure that consists of two layers. The honeycomb structure is regarded as a continuum in structure and heat-flow analysis. The equivalent mechanical properties of the honeycomb structure were determined by performing finite element analysis (FEA) for a test specimen. Bending strength experiments and FEA of the test specimen used in ASTM C1674-08 standard test were performed individually. The bonding coefficient between the cordierite ceramic layer and the washcoat layer was almost zero. The FEA test specimen was modeled on the basis of the bonding coefficient. The elastic modulus, Poisson's ratio, and the thermal properties of the ceramic monolithic substrate were determined by performing the FEA of the test specimen.