• Tribology and Lubricants
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• v.33 no.6
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• pp.288-295
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• 2017

In order to improve the efficiency and reliability of the machine, the friction should be minimized. The most widely used method to minimize friction is to maintain the fluid lubrication state. However, we can reduce friction only up to a certain limit because of viscosity. As a result of several recent studies, surface texturing has significantly reduced the friction in highly sliding machine elements, such as mechanical seals and thrust bearings. Thus far, theoretical studies have mainly focused on isothermal/iso-viscous conditions and have not taken into account the heat generation, caused by high viscous shear, and the temperature conditions on the bearing surface. In this study, we investigate the effect of dimple depth and film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of textured parallel slider bearings. We analyzed the continuity equation, the Navier-Stokes equation, the energy equation, and the temperature-viscosity and temperature-density relations using a computational fluid dynamics (CFD) code, FLUENT. We compare the temperature and pressure distributions at various dimple depths. The increase in oil temperature caused by viscous shear was higher in the dimple than in the bearing outlet because of the action of the strong vortex generated in the dimple. The lubrication characteristics significantly change with variations in the dimple depths and film-temperature boundary conditions. We can use the current results as basic data for optimum surface texturing; however, further studies are required for various temperature boundary conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1091-1097
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• 2017

Sales of commercial-type cooling fans intended for application in military electronics are often discontinued during equipment production. This results in requirements for alternative fan selection as well as equipment performance and reliability tests, such as high-temperature operation testing. This study deals with alternative fan selection and verification methods that can be used during the production process. First, an alternative fan was selected by calculating the flow and pressure required to effectively cool the equipment, then the feasibility of the selected fan was verified using a reliable CFD heat dissipation analysis model. Following this, a high-temperature operation test was performed using the alternative fan in the equipment. Results demonstrated that the equipment satisfied its required function in a high-temperature environment, and the main parts as well as internal air temperature were found to be thermally stable.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.3
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• pp.19-29
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• 2010

In South Korea, as the living standard has been getting higher, meat consumption is steadily increasing. To meet the country's demand, livestock houses become larger and wider with increased raising density. In larger livestock houses, pollutants such as flake of pig skin, excrement, odor, various dusts and noxious gas like ammonia are excessively accumulated inside the facility. These will cause weak immunity for the pigs, diminution of productivity and degeneration of working condition. These problems can be solved through the ventilation performance of the facility. In the winter time, ventilation must be controlled to minimum to maintain a suitable thermal condition. However, this affects the other internal environmental condition because of the minimum ventilation. The installation of "wet air cleaner" especially in the winter time can be an alternative solution. For efficient application of this machine, there is a need to understand the existing ventilation condition and analyze the interaction of existing ventilation system with the wet air cleaner considering its appropriate location. In this study, the existing ventilation system as well as the internal environmental condition negatively inside the facility with the wet air cleaner has been studied using CFD technology. The CFD simulation model was validated from the study conducted by Seo et al. (2008). Results show that the elimination rate of ammonia was 39.4 % and stability could be improved to 35.1 % (Comparing case 5 to 1 where wet air cleaner machine was not used). It can therefore be concluded that case 5 shows the optimum location of a wet air cleaner in the livestock house.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.5
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• pp.367-376
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• 2008

To obtain the data of the pressure loss and differential pressure at the inside of the stack that was composed of 126 cells with 7,500 cm2 electrode area, 75kW molten carbonate fuel cell system has been operated. Computational fluid dynamics was applied to estimate reactions and thermal fluid behavior inside of the stack that was adopted with internal manifold type separator. The pressure loss coefficient K showed 72.29 to 84.01 in anode and 6.34 to 8.75 in cathode at low part of cells at the inside of 75 kW MCFC stack respectively. Meanwhile, the pressure loss coefficient of the higher part of cells at the interior of the stack showed 15.36 and 56.44 in anode and cathode respectively. These results mean that there is no big total pressure difference between anode and cathode at the inner part of 75 kW MCFC stack. This result will be reflected in 250kW MCFC system design.

• Smart Structures and Systems
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• v.18 no.1
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• pp.139-154
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• 2016

This paper is concerned with the dynamics of hyperelastic solids and structures. We seek for a smart control actuation that produces a desired (prescribed) displacement field in the presence of transient imposed forces. In the literature, this problem is denoted as displacement tracking, or also as shape morphing problem. One talks about shape control, when the displacements to be tracked do vanish. In the present paper, it is assumed that the control actuation is provided by imposed eigenstrains, e.g., by the electric field in piezoelectric actuators, or by thermal actuators, or via analogous physical effects, such as magneto-striction or pre-stress. Structures with a controlled eigenstrain-type actuation belong to the class of smart structures. The action of the eigenstrains can be conveniently characterized by actuation stresses. Our theoretical derivations are performed in the framework of the theory of small incremental dynamic deformations superimposed upon a statically pre-deformed configuration of a hyperelastic solid or structure. We particularly ask for a distribution of incremental actuation stresses, such that the incremental displacements follow exactly a prescribed trajectory field, despite the imposed incremental forces are present. An exact solution of this problem is presented under the assumption that the actuation stresses can be tailored freely and applied everywhere within the body. Extending a Neumann-type solution strategy, it is shown that the actuation stresses due to the distributed control eigenstrains must satisfy certain quasi-static equilibrium conditions, where auxiliary body-forces and auxiliary surface tractions are to be taken into account. The latter auxiliary loading can be directly computed from the imposed forces and from the desired displacement field to be tracked. Hence, despite the problem is a dynamic one, a straightforward computation of proper actuator distributions can be obtained in the framework of quasi-static equilibrium conditions. Necessary conditions for the functioning of this concept are presented. Particularly, it must be required that the intermediate configuration is infinitesimally superstable. Previous results of our group for the case of shape control and displacement tracking in linear elastic structures are included as special cases. The high potential of the solution is demonstrated via Finite Element computations for an irregularly shaped four-corner plate in a state of plain strain.

• Fire Science and Engineering
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• v.34 no.4
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• pp.45-51
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• 2020

The aim of this study is to investigate the gas temperature and velocity during sprinkler activation considering the fire growth scenario based on the thermal response model of the sprinkler. The fire source is assumed to have time square fire growth scenarios with a maximum heat release rate of 3 MW. Eight types of standard and fast-response sprinkler heads with an operating temperature range of 65-105 ℃ and a response time index range of 25-171 m^1/2s^1/2 were adopted. The temperature difference between the gas stream and the sensing element of the sprinkler head decreased as the fire growth slowed down, and the RTI value decreased. The overall gas temperature and velocity conditions predicted using the FDS model at sprinkler activation were in reasonable agreement with those of standard test conditions of the sprinkler head response. However, the sprinkler head could be activated at lower limits of gas temperature and velocity under the current test conditions for a slowly growing fire scenario.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.1 no.1
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• pp.35-43
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• 1997

Handling the emergency problems such as Chemobyl accident require real time prediction of pollutants dispersion. One-point real time sounding at pollutant source and simple model including turbulent-radiation process are very important to predict dispersion at real time. The stability categories obtained by one-dimensional numerical model (including PBL dynamics and radiative process) are good agreement with observational data (Golder, 1972). Therefore, the meteorological parameters (thermal, moisture and momentum fluxes; sensible and latent heat; Monin-Obukhov length and bulk Richardson number; vertical diffusion coefficient and TKE; mixing height) calculated by this model will be useful to understand the structure of stable boundary layer and to handling the emergency problems such as dangerous gasses accident. Especially, this simple model has strong merit for practical dispersion models which require turbulence process but does not takes long time to real predictions. According to the results of this model, the urban area has stronger vertical dispersion and weaker horizontal dispersion than rural area during daytime in summer season. The maximum stability class of urban area and rural area are 'A' and 'B' at 14 LST, respectively. After 20 LST, both urban and rural area have weak vertical dispersion, but they have strong horizontal dispersion. Generally, the urban area have larger radius of horizontal dispersion than rural area. Considering the resolution and time consuming problems of three dimensional grid model, one-dimensional model with one-point real sounding have strong merit for practical dispersion model.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1699-1701
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• 2000

The dynamic behavior of fatty acid monolayers at the air-water interface was investigated using a displacement current-measuring technique coupled with the so-called Langmuir film technique and also the dipole moment of the acids was determined. The displacement current flowing though a short circuit wan generated only when induced charges on an electrode flowing though suspended in air was changed by monolayer compression. The displacement current measurement was found to be a very sensitive method used for a better understanding of the relationship between the structure and function of the monolayers placed on the water surface and it was also found to be a very useful method for detecting the dynamic motion of molecules in the entire range from the so-called gaseous state to solid state at the same time. In the paper investigate fatty monolayer dynamic state and electric property character. As result. Displacement current generate higher nearly distance electrodel and water surface. Also, Molecule behavior was found pocess active higher thermal.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.6
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• pp.577-582
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• 2016

In this study, a multiscale method for solving a thermoelasticity problem for interphase in the polymeric nanocomposites is developed. Molecular dynamics simulation and finite element analysis were numerically combined to describe the geometrical boundaries and the local mechanical response of the interfacial region where the polymer networks were highly interacted with the nanoparticle surface. Also, the micrmechanical thermoelasticity equations were applied to the obtained equivalent continuum unit to compute the growth of interphase thickness according to the size of nanoparticles, as well as the thermal phase transition behavior at a wide range of temperatures. Accordingly, the equivalent continuum model obtained from the multiscale analysis provides a meaningful description of the thermoelastic behavior of interphase as well as its nanoparticle size effect on thermoelasticity at both below and above the glass transition temperature.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.133-137
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• 2015

The Galactic center uniquely provides opportunities to resolve how star clusters form in neutral gas overdensities engulfed in a large-scale accretion flow. We have performed sensitive Green Bank 100m Telescope (GBT), Karl G. Jansky Very Large Array (JVLA), and Submillimeter Array (SMA) mapping observations of molecular gas and thermal dust emission surrounding the Galaxy's supermassive black hole (SMBH) Sgr $A^{\ast}$. We resolved several molecular gas streams orbiting the center on ${\gtrsim}10$ pc scales. Some of these gas streams appear connected to the well-known 2-4 pc scale molecular circumnuclear disk (CND). The CND may be the tidally trapped inner part of the large-scale accretion flow, which incorporates inflow via exterior gas filaments/arms, and ultimately feeds gas toward Sgr $A^{\ast}$. Our high resolution GBT+JVLA $NH_3$ images and SMA+JCMT 0.86 mm dust continuum image consistently reveal abundant dense molecular clumps in this region. These gas clumps are characterized by ${\gtrsim}100$ times higher virial masses than the derived molecular gas masses based on 0.86 mm dust continuum emission. In addition, Class I $CH_3OH$ masers and some $H_2O$ masers are observed to be well associated with the dense clumps. We propose that the resolved gas clumps may be pressurized gas reservoirs for feeding the formation of 1-10 solar-mass stars. These sources may be the most promising candidates for ALMA to probe the process of high-mass star-formation in the Galactic center.