• Fire Science and Engineering
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• v.19 no.2 s.58
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• pp.75-80
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• 2005

This dissertation is about the development of PTC(Positive Temperature Coefficient) thermistor by composition method. A multilayer-type PTC samples were fabricated under optimal conditions after setting the experimental composition equation as $(0.90Ba+0.05Sr+0.05Ca)TiO_3+0.01TiO_3+0.01SiO_2+0.0008MnO_2+0.0018Nb_2O_5$ and their testing results were analyzed. The fabrication method of SMD(Surface Mounted Device) multilayer -type sample based on the composition ratio has the advantages in lowering its resistivity at room temperature, considerably, and increasing maximum current level, as needed. Although there is a disadvantage of peak resistivity drop by the multilayer, causing the increasement of thermal capacity. and thereby, increasing the switching delay time, a high applying voltage can increase the peak resistivity and shorten the switching delay time. The voltage-current characteristic showed that the more multilayers increased the initial maximum current and the transition voltage that increased the resistivity abruptly according to the curie point. The element it could be applied with the sensor for the fire detector.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.188-193
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• 2017

In this paper, a ZVS-PWM high-frequency inverter with a PWM control function is applied to commercial system 220[Vrms], and a resonator type ZVS-PWM high-frequency inverter circuit with a fixed-two methods were proposed. The parameters of the transformer model equivalent circuit of a copier fixing device, which is an essential element in the parameter optimization of the proposed circuit, are obtained by using a high-frequency amplifier and its frequency characteristics are described. The proposed method compared to the existing single-ended ZVS-PFM high frequency inverter can suppress the voltage and current peak value of the power semiconductor switching device and reduce the switching loss. The efficiency of the proposed method itself is 98[%] at rated power output. Also, the efficiency of 96[%] can be obtained even at low output, so that the proposed high frequency inverter is very efficient inverter. The total efficiency from the commercial AC input to the inverter output is 93[%] at rated, which is considered efficient for use in copying machines. In addition, the diode bridge loss accounts for the largest portion of the overall system efficiency distribution. On the other hand, the nonparallel filter has a very low loss.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.12
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• pp.2933-2942
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• 2015

This paper proposes a new method which traces significant element of 2-dimensional natural images and encrypts them by using Fresnelet transform (FRNLT). After analyzing property of the subbands obtained by the FRNLT, we estimated the information for ciphering 2D images. Considering FRNLT levels, energy of subbands, and visual effect, we estimated the optimized point for encryption. By selecting various levels and encrypting region, we can encrypt 2D image with various robustness. Encryption effectiveness was showed by analyzing numerical result, executing time for encryption, area of encrypted region, and visual observation. Therefore encryption for various application can be applied by using the suggested parameters without additional analysis. Identifying the experimental result, in the case of $L_{TH}=4$ and $L_{TH}=4$, an image was not recognized through encrypting only 0.42% among the entire data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.7
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• pp.455-462
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• 2017

The magnetic interaction between elliptic Janus magnetic particles are investigated using a direct simulation method. Each particle is a one-to-one mixture of paramagnetic and nonmagnetic materials. The fluid is assumed to be incompressible Newtonian and nonmagnetic. A uniform magnetic field is applied externally in a horizontal direction. A finite-element-based fictitious domain method is employed to solve the magnetic particulate flow in the creeping flow regime. In the magnetic problem, the magnetic field in the entire domain, including the particles and the fluid, is obtained by solving the governing equation for the magnetic potential. Then, the magnetic forces acting on the particles are calculated via a Maxwell stress tensor formulation. In a single particle problem, it is found that the orientation angle at equilibrium is affected by the aspect ratio of the particle. As for the two-particle interaction, the dynamics and the final conformation of the particles are significantly influenced by the aspect ratio, the orientation, and the spatial positions of the particles. For the given positions of the particles, the fluid flow is also influenced by the orientation of each particle. The self-assembly structure of the particles is not a fixed one, but it varies with the above-mentioned factors.

• Journal of the Korean Society for Precision Engineering
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• v.3 no.3
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• pp.40-71
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• 1986

By developing a computer program for the systematic design of worm gears, the design formulae and tables of AGMA, JGMA, BS and DIN are analized and compared. The computer program can be used on micro-computers. According to the input data of the reduction ratio, the center distance. the driving torque and the material as design parameters, the program calculate the most efficient worm gear dimension. The variation of the design parameters and other empirical coefficients in case of resulting an inadequate design gear dimension can be easily modified throuth the way of interactive method between the user and the monitoring system of computer. A proposal of the standardization of worm gears was made in which a standard module according to the DIN 323 standard series number was applied. For the more exact and effective calculation of the stress concentration and the deformation of gear teeth, a computer program using the boundary element method is also developed. Even the strength of the special gear shape such as Niemann's "Cavex" gear can be calculated in a short CPU-time. The most effort of this study has been layed on the developing a computer program for the correction of a tooth profile and face width which is most important design factor for an exact and wide teeth contacts under loads, especially by great and wide gears. For this purpose were investigated the tooth stiffness, the mesh interferences and the kinematics and the dynamics of gear mesh. The deflection and the deformation of the gear shaft due to the loads acting on gear and shaft were aslo considered. Some examples have shown the sufficient good status of teeth contact in which the correction of the tooth profile and face width were accomplished due to the calculated results.d results.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.5
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• pp.584-590
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• 2012

The structural and functional disorder of a detrusor induces a bladder hypertrophy and degenerates a bladder muscle gradually by preventing normal urination. Thus, the thickness of the bladder wall has been increased in proportion to the degree of bladder outlet obstruction. In this study, the mechanical characteristics of the detrusor is analyzed for the physical properties and the thickness changes of the bladder muscle using a mathematically analytic method. In order to obtain the mechanical property of the bladder muscle, the tensile test of porcine bladder tissue is performed because its property is similar to that of human. The result of tensile test is applied to the mathematically model as Mooney Rivlin coefficients which represent the hyperelastic material. The model of the bladder is defined as the spherical shape with the initial volume of 50ml. The principal stress and strain according to the thickness are analyzed. Also, computer simulations for three types of the material property for the model of the bladder are performed based on the fact that the stiffness of the bladder is weakened as the progress of the benign prostatic hyperplasia. As a result, the principal stress is 341kPa at the initial thickness of 2.2mm, and is 249kPa at 6.5mm. As the bladder wall thickness increases, the principal stress decreases. The principal stress and strain decrease as the stiffness of the bladder decreases under the same thinkness.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.3
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• pp.521-529
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• 2017

In this study, analyzed the effective width of concrete unfilled composite steel grid deck which has different shear connector details from that of composite bridge. The effective width of concrete unfilled composite steel grid deck according to effective width calculation method, load size and main bearing bar spacing-span ratio was evaluated. As a result of analysis, it is analyzed that the effective width is calculated to be nearly equal to the actual effective width by idealizing the stress shape as a trapezoidal shape. In addition, shear hole penetration reinforcing bars applied to increase the shear strength is shown to increase the effective width. From the results of the analysis of the effective width according to main bearing bar spacing-span ratio, proposes the correction factor that can calculate the effective width ratio of the unfilled steel composite steel grid deck.

• Journal of Astronomy and Space Sciences
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• v.29 no.1
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• pp.23-31
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• 2012

Thermal analysis and control design are prerequisite essential to design the satellite. In the space environment, it makes satellite survive from extreme hot and cold conditions. In recent years CubeSat mission is developed for many kinds of purpose. Triplet Ionospheric Observatory (TRIO)-CubeSat for Ion, Neutral, Electron, MAgnetic fields (CINEMA) is required to weigh less than 3 kg and operate on minimal 3 W power. In this paper we describe the thermal analysis and control design for TRIO-CINEMA mission. For this thermal analysis, we made a thermal model of the CubeSat with finite element method and NX6.0 TMG software is used to simulate this analysis model. Based on this result, passive thermal control method has been applied to thermal design of CINEMA. In order to get the better conduction between solar panel and chassis, we choose aluminum 6061-T6 for the material property of standoff. We can increase the average temperature of top and bottom solar panels from $-70^{\circ}C$ to $-40^{\circ}C $ and decrease the average temperature of the magnetometer from $+93^{\circ}C$ to $-4^{\circ}C$ using black paint on the surface of the chassis, inside of top & bottom solar panels, and magnetometer.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.5
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• pp.29-40
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• 2009

Pneumatic system is widely applied to ground facility and launcher on-board system. One of the important aspects of pneumatic system is to meet pressure and flow rate requirements of gas consumers. In this paper, a systematic analytical approach for pneumatic system is proposed, which uses and systematically combines previous studies. The proposed analytical method is that pressure/flow calculation using conservation equations are combined with sonic limit check at vena contracta of the components of pneumatic system, which checks the installed components whether they are merely pressure loss elements or flow limiting element of the system. In this paper, gas consumers are categorized and simulated using the proposed method. The results reveal that the feeding performance of general pneumatic system can be properly estimated using the proposed approach.

• Journal of the Korea Computer Industry Society
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• v.2 no.3
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• pp.357-362
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• 2001

For general laser power supply to control the laser power density, the secondary of the power transformer is connected to the rectifier and filter capacitor. The output of a rectifier is applied to a switching element in the secondary of the transformer. So power supply is complicated and the loss of switching is considerably. In addition, according to increasing pulse repetition rate, charged energy of energy-storage capacitor bank is not transferred sufficiently to flashlamp, and laser output efficiency decreases. In this study, we have proposed the power supply in which the SCR was turned on at the zero point of input AC voltage by the method of zero cross control(ZCC). As a result of that, The new power supply employed ZCC are simple and compact in design. And laser output efficiency increased by the 3.5$\%$ other than conventional power supply (SCADC), when a repetition rate was increased by the 10pps. In 60pps, efficiency was increased by about 20$\%$.