• Journal of Welding and Joining
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• v.35 no.3
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• pp.35-43
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• 2017

A 3D transient heat transfer model is developed by ABAQUS software to study the temperature distribution during friction stir welding process at different rotational speeds. Furthermore, AA 5083-O plates were joined by FSW technique. For this purpose, a universal milling machine was used to perform the welding process and a mechanical vice was used to fix the work pieces in the proper position. The joints were friction stir welded at a constant travel speed 50 mm/min and two rotational speed values; 400 rpm and 630 rpm using two types of tools; cylindrical threaded pin and tapered smooth one. At each welding condition the temperature was measured using infra-red thermal image camera to verify the simulated temperature distribution. The welded joints were visually inspected as well as by macro- and microstructure evolutions. In addition, the welded joints were mechanically tested for hardness and tensile strength. The maximum peak temperature obtained was at higher rotational speed using the threaded tool pin profile. The results showed that the rotational speed affects the peak temperature, defects formation and sizes, and the mechanical properties of friction stir welded joints. Moreover, the threaded tool gives superior mechanical properties than the tapered one at lower rotational speed.

• Journal of Korea Foundry Society
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• v.29 no.2
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• pp.78-85
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• 2009

Functionally graded microstructure of centrifugal cast Al-Si alloy, especially distribution of primary Si particles according to the changes of melt pouring temperature and rotation frequency was investigated by numerical simulation. Moving velocity of Si particles increased as the melt pouring temperature and rotational frequency of mold increased. Therefore, segregation tendency of primary Si particles toward inner side of cylindrical sample increased as the melt pouring temperature and rotational frequency of mold increased. Rich distribution region of particles was located at 0.9, 0.7, 0.4 mm from inner surface of cylindrical sample under the centrifugal cast condition of $750^{\circ}C$ melt pouring temperature and 1500, 2000 and 2500 rpm mold rotational frequencies, respectively, by numerical simulation.

• Journal of the Korean Magnetic Resonance Society
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• v.2 no.1
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• pp.66-83
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• 1998

Study on spin-rotation relaxation of nuclear spins located on a methyl group can reveal valuable dynamic information related to the internal rotation of methyl group itself. Toward this end we have measured methyl carbon-13 spin-rotation of methyl group itself. Toward this end we have measured methyl carbon-13 spin-rotational relaxation rate in toluene and 2-chloro-p-xylene over the temperature range of 179-363K. To interpret the temperature dependence of measured spin-rotational relaxation rate we have revised the temperature dependence of measured spin-rotational relaxation rate we have revised the expression derived thus far by other authors and reproduced experimental data on the basis of the newly derived expression. The results confirmed that our expression leads to better agreement with experimental data than the previous one over observed temperature range, especially at high temperature.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1834-1839
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• 2003

Temperature and velocity distributions of hot air flows in rotational molding machines with two different shapes and structures of oven and inlet were investigated by using FLUENT, a commercial computational fluid dynamics code. The shape and structure of oven and inlet in current rotational molding machine were improved. Two different sizes of mold inside each oven were considered in the analysis. Temperature and velocity distributions of hot air flows in two different rotational molding machines were compared to each other. In order to reduce cycle time and improve product quality in current rotational molding machine, the improved shape and structure of oven and inlet were proposed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.10
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• pp.1895-1902
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• 2011

This work was carried out for the measurement of vibration and rotation temperature using the optical emission spectroscopy of nitrogen second positive system in the small plasma torch. Among emissions $N_2$ SP systems, the emission of $N_2$ SP(0-0) was so strong. Emission peaks of SP system increased until the position of 12.5[mm] from the end of plasma torch, after that it decreased. However, vibration temperature decreased from 1540[K] to 1000[K] at the position of 12.5[mm]. In addition, rotational temperature was about 400[K] at the position of 10[mm] and it increased a little as much of 420[K] at 12.5[mm]. Consequently, the plasma torch discussed in this work is possible to apply in the surface treatment process under the low temperature.

• Journal of Korea Foundry Society
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• v.28 no.1
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• pp.25-30
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• 2008

To develop a functionally graded microstructure of cylindrical liner, effect of centrifugal casting parameters such as pouring temperature of hyper-eutectic Al-Si alloy melt, mold pre-heating temperature, and rotational frequency of mold on distribution of primary Si particles across wall thickness were investigated. Segregation tendency of Si particles toward inner side of cylindrical liner increased as the increase of rotational frequency of mold, pouring temperature of melt and mold pre-heating temperature. Especially, distribution density of primary Si particles within 1.5 mm from inner surface of cylindrical liner was above 35% under the centrifugal casting condition of $750^{\circ}C$ melt pouring temperature, $300^{\circ}C$ mold pre-heating temperature, and 2500 rpm mold rotational frequency.

• Structural Engineering and Mechanics
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• v.68 no.5
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• pp.563-573
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• 2018

Temperature-induced responses, such as strains and displacements, are related to the boundary conditions. Therefore, it is required to determine the boundary conditions to establish a reliable bridge model for temperature-induced responses analysis. Particularly, bridge bearings usually present nonlinear behavior with an increase in load, and the nonlinear boundary conditions cause significant effect on temperature-induced responses. In this paper, the bridge nonlinear boundary conditions were simulated as bilinear translational or rotational springs, and the boundary parameters of the bilinear springs were identified based on the measured temperature-induced responses. First of all, the temperature-induced responses of a simply support beam with nonlinear translational and rotational springs subjected to various temperature loads were analyzed. The simulated temperature-induced strains and displacements were assumed as measured data. To identify the nonlinear translational and rotational boundary parameters of the bridge, the objective function based on the temperature-induced responses is then created, and the nonlinear boundary parameters were further identified by using the nonlinear least squares optimization algorithm. Then, a beam structure with nonlinear translational and rotational springs was simulated as a numerical example, and the nonlinear boundary parameters were identified based on the proposed method. The numerical results show that the proposed method can effectively identify the parameters of the nonlinear boundary conditions. Finally, the boundary parameters of a real arch bridge were identified based on the measured strain data and the proposed method. Since the bearings of the real bridge do not perform nonlinear behavior, only the linear boundary parameters of the bridge model were identified. Based on the bridge model and the identified boundary conditions, the temperature-induced strains were recalculated to compare with the measured strain data. The recalculated temperature-induced strains are in a good agreement with the real measured data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.1
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• pp.86-94
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• 1984

In order to improve the rotational performances of NC lathe spindle system in high speed range, a new type(Floating-type driven by V-belt)spindle system was optimally designed and experimented. Through the results of the experiments, the rotational performances of the new type spindle system was discussed and compared with the three equivalent conventional lathe spindle systems. The spindle rotational accuracy( radial error motion of spindle axis), the accelation and the temperature rise of the front spindle bearings for the non-cutting operation were considered as the spindle rotational performances. The radial error motion of the spindle axis was measured by applying the modified L.R.L. method. Compared with the equivalent conventional spindle systems, the following results were obtained. (1) The new type spindle system reduces the radial error motion of the spindle axis in high speed range(1800rpm-2000rpm). (2) The new type spindle system reduces the acceleration and the temperature rise of the spindle bearings considerably with increasing the spindle speed. It is also confirmed that, by this new type spindle system, the max. allowable speed can be increased with satisfying the spindle rotational performances.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.327-334
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• 2004

Spectroscopic and electrostatic probe measurements were made to examine plasma characteristics with or without a metal plate for a 10-㎾-class direct-current arcjet Heat fluxes into the plate from the plasma were also evaluated with a Nickel slug and thermocouple arrangement. Ammonia and mixtures of nitrogen and hydrogen were used. The NH$_3$ and $N_2$+3H$_2$ plasmas in the nozzle and in the downstream plume without a plate were in thermodynamical nonequilibrium states. As a result, the H-atom electronic excitation temperature and the $N_2$ molecule-rotational excitation temperature intensively decreased downstream in the nozzle although the NH molecule-rotational excitation temperature did not show an axial decrease. Each temperature was kept in a small range in the plume without a plate except for the NH rotational temperature for NH$_3$ gas. On the other hand, as approaching the plate, the thermodynamical nonequilibrium plasma came to be a temperature-equilibrium one because the plasma flow tended to stagnate in front of the plate. The electron temperature had a small radial variation near the plate. Both the electron number density and the heat flux decreased radially outward, and an increase in H$_2$ mole fraction raised them at a constant radial position. In cases with NH$_3$ and $N_2$+3H$_2$ a large number of NH radical with a radially wide distribution was considered to cause a large amount of energy loss, i.e., frozen flow loss, for arcjet thrusters.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.5
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• pp.37-44
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• 2018

In laser material processing for high thermal conductivity, the thermal effect of laser beam shape was examined through computer simulations. In this paper, a circular beam with a focal radius of $500{\mu}m$, an elliptical beam with a major axis of 4 mm and a minor axis of 1 mm, and a rotating beam with a focal radius of $500{\mu}m$ and an angular velocity of 5 rad/sec were compared. Simulation results showed that there was no clear difference in the maximum temperature between the circular focus and the elliptical shape, but the heating and cooling rates were different. The simulation result for a laser beam rotating in a circular pattern with a radius of 5 mm showed an asymmetric temperature rise due to the combination of linear and rotational motion. At points where the rotational and linear speeds combined, the temperature gradually rose and reached the maximum temperature; whereas at points where the rotational and linear speeds were attenuated, the temperature tended to gradually decrease after reaching the maximum temperature. Based on the results of this study, the authors expect to be able to optimize laser material processing by designing patterns of laser beams.