• Journal of Welding and Joining
• /
• v.27 no.2
• /
• pp.32-37
• /
• 2009

In shipyard, plate forming is widely used to form the ship hull plate in various shapes. Line heating method by using a flame torch is one of the major shipbuilding processes carried out by skilled workers. Since the forming characteristics depend upon their experiences in manual forming, there are much variations between products and difficulties in communication between engineers and workers. Hence, it needs to develop an automatic forming system which can not only reduce the working time and rework costs but also improve the working environment and hull forming productivity. One of the final goals of plate forming automation is to form a target shape from the initial plate automatically. For automated plate forming, it is required to determine where and how to heat on the plate. To realize this procedure, the inverse problem should be first solved and the effect of curvature shape formed at the heating path should be investigated. In this study, the inverse problem was solved by geometrical approach using the relationship between bending angle and radius of curvature of the curved shape. In addition, experiments of two-dimensional plate forming were performed with the distance-based method considering the curved bending with curvature. The result of the formed shape agreed considerably well with the target shape.

• Journal of the Ergonomics Society of Korea
• /
• v.17 no.3
• /
• pp.41-59
• /
• 1998

Thermal comfort aspect of a locally-cooled target space in warm and humid environments(typically in the rainy summer season) was studied in view of PPD index. First. theoretical analyses were conducted to examine the effect of the governing parameters(such as air temperature, relative humidity and air velocity, etc.) using a computer model. Secondly, experimental investigations were also performed in a climatic room designed to simulate corresponding thermal conditions of outdoor environments. During the tests, temporal variation of PPD was recorded as functions of climatic variables(outdoor and indoor temperatures, relative humidity and air velocity) for the given human factors(metabolic heat generation and clothing). From both theoretical and experimental investigations, air temperature and air velocity were found to be the most dominant parameters affecting PPD of the target space. Results were summarized as: 1. Relative humidity of the locally-cooled target space tends to approach that of outdoor's as the space is subjected to an ON-OFF mode of cooling, since moisture potential of the two rooms reaches an equalized state as a result of moisture diffusion. 2. It was recognized that changes in relative humidity did not show any significance in view of thermal comfort as was reported in the previous studies, while variations of both temperature and air velocity caused relatively large changes in the degree of thermal comfort. 3. In-door environment should be evaluated in terms of PPD instead of relative humidity commonly recognized as an important climatic variable particularly in warm and humid environments.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.7
• /
• pp.609-615
• /
• 2015

In this study, the combustion and exhaust emission characteristics in a gasoline direct injection engine with variations of the bio-ethanol-gasoline blending ratio and the excess air factor were investigated. To investigate the effects of the excess air factor and the bio-ethanol blends with gasoline, combustion characteristics such as the in-cylinder combustion pressure, rate of heat release (ROHR), and the fuel consumption rate were analyzed. The reduction of exhaust emissions such as carbon monoxide (CO), unburned hydrocarbon (HC), and nitrogen oxides ($NO_x$) were compared with those of gasoline fuel with various excess air factors. The results showed that the peak combustion pressure and ROHR of bio-ethanol blends were slightly higher and were increased as bio-ethanol blending ratio is increased. Brake specific fuel consumption increased for a higher bio-ethanol blending ratio. The exhaust emissions decreased as the bio-ethanol blending ratio increased under all experimental conditions. The exhaust emissions of bio-ethanol fuels were lower than those of gasoline.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.1
• /
• pp.37-46
• /
• 2017

Thermal Marangoni flow has been observed inside droplets on heated surfaces, finally resulting in a coffee stain effect. This study aims to visualize and control the thermal Marangoni flow by employing periodic vertical vibration. The variations in the contact angle and internal volume of the droplet as it evaporates is observed by using a combination of continuous light and a still camera. With regard to the internal velocity, the particle image velocimetry system is applied to visualize the internal thermal Marangoni flow. In order to estimate the internal temperature gradient and surface tension on the surface of a droplet, the theoretical model based on the conduction and convection theory of heat transfer is applied. Thus, the internal velocity increases with an increase in plate temperature. The flow directions of the Marangoni and gravitational flows are opposite, and hence, it may be possible to control the coffee stain effect.

• Food Science and Preservation
• /
• v.3 no.2
• /
• pp.137-143
• /
• 1996

In order to produce the high-quality of dried red pepper with respect to a color and a taste we developed a automatic drier equipped with combined several heat energies(ADCHE). and compared the quality of ADCHE-treated red pepper with that of the pepper treated with conventional dryings such as natural, hot-air, and far-infrared ray dryings. The results obtained were as follows : (1) The contents of capsanthin varied significantly with drying methods within the range of 1.7 to 6. 4mg/g dry weight. The capsanthin level of red pepper treated with far-infrared ray drying was higher than that of the pepper treated with ADCHE showed the highest at 51.46mg/g dry weight of three drying methods. (2) As a result of determination of color intensity of-red-pepper using-a colorimeter, the red color intensity of the peppers was affected by drying methods irrespective of drying temperature, and especially a value of red pepper treated with ADCHE was appeared to be 19. 1, indicated that this pepper have the most bright color intensity. (3) The contents of soluble browing subatances increased with a increase in drying temperature, but L* value of red pepper treated with ADCHE was appeared to be 0.187, indicated that this red pepper have the most clear red color (4) The changes of capsanthin level of red pepper according to drying methodes did not show significantly, but generally a decreasing rate of capsanthin levels were lower in that order ADCHE

• Tribology and Lubricants
• /
• v.30 no.5
• /
• pp.303-310
• /
• 2014

In order to reduce friction and improve reliability, researchers have applied various surface texturing methods to highly sliding machine elements such as mechanical seals and piston rings. Despite extensive theoretical research on surface texturing, previous numerical results are only applicable to isothermal and iso-viscous conditions. Because the lubricant flow pattern of textured bearing surfaces is much more complicated than that for non-textured bearings, the Navier?Stokes equation is more suitable than the Reynolds equation for the former. This study carries out a thermohydrodynamic (THD) lubrication analysis to investigate the lubrication characteristics of a single micro-dimpled parallel thrust bearing cell. The analysis involves using the continuity, Navier?Stokes, energy, temperature?viscosity relation, and heat conduction equations with the commercial computational fluid dynamics (CFD) code FLUENT. This study discretizes these equations using the finite volume method and solves them using the SIMPLE algorithm. The results include finding the streamlines, pressure and temperature distributions, and variations in the friction force and leakage for various dimple radii and depths. Increasing the dimple radius and decreasing the depth causes a recirculation flow to form because of a strong vortex, and the oil temperature greatly increases compared with the non-textured case. The present numerical scheme and results are applicable to THD analysis of various surface-textured sliding bearings and can lead to further study.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.9
• /
• pp.815-821
• /
• 2013

The efficiency and lifetime of a polymer electrolyte membrane fuel cell (PEMFC) system is critically affected by the humidity of the incoming gas, which should be maintained properly under normal operating conditions. Typically, the incoming gas of a fuel cell is humidified by an external humidifier, but few studies have reported on the device characteristics. In this study, a laboratory-scale planar membrane humidifier is designed to investigate the characteristics of water transport through a hydrophilic membrane. The planar membrane humidifier is immersed in a constant temperature bath to isolate the humidifier from the effect of temperature variations. The mass transfer capability of the hydrophilic membrane is first examined under isothermal conditions. Then, the mass transfer capability is investigated under various conditions. The results show that water transport in the hydrophilic membrane is significantly affected by the flow rate, operating temperature, operating pressure, and flow arrangement.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.16 no.9
• /
• pp.1700-1710
• /
• 1992

The boundary element method is applied to determine thermal stress intensity factors for a cusp crack in transient state. In the steady temperature field, numerical values of thermal stress intensity factors for a Grifith crack and a symmetric lip cusp crack in a finite body are in good agreement within .+-. 5% with the previous solutions. In transient state, the numerical values of thermal stress intensity factors for the Griffith crack are also in good agreement with the pervious solutions. In both steady and transient states, those for the symmetric lip cusp crack with the crack surface insulated or fixed to the constant temperature are calculates for various effective crack lengths, configuration parameters and uniform heat flow angles. The variations of the thermal boundary conditions of the crack surface have a effect on stress intensity factors. The signs on the values of thermal stress intensity factors can be changed in time variation.

• Tunnel and Underground Space
• /
• v.25 no.2
• /
• pp.144-154
• /
• 2015

Mechanical energy is accumulated in the object when stress is exerted on rock specimens, and the failure is occurred when the stress is larger than critical stress. The accumulated energy is emitted as various forms including physical deformation, light, heat and sound. Uniaxial compression strength test and point load strength test were carried out in low temperature environment, and thermal variation of rock specimens were observed and analyzed quantitatively using thermal infrared camera images. Temperature of failure plane was increased just before the failure because of concentration of stress, and was rapidly increased at the moment of the failure because of the emission of thermal energy. The variations of temperature were larger in diorite and basalt specimens which were strong and fresh than in tuff specimens which were weak and weathered. This study can be applied to prevent disasters in rock slope, tunnel and mine in cold regions and to analyze satellite image for predicting earthquake in cold regions.

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