• Journal of Radiation Protection and Research
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• v.40 no.1
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• pp.1-9
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• 2015

Compton cameras overcome several limitations of conventional mechanical collimation based gamma imaging devices, such as pin-hole imaging devices, due to its electronic collimation based on coincidence logic. Especially large-scale Compton camera has wide field of view and high imaging sensitivity. Those merits suggest that a large-scale Compton camera might be applicable to monitoring nuclear materials in large facilities without necessity of portability. To that end, our research group have made an effort to design a large-scale Compton camera for safeguard application. Energy resolution or position resolution of large-area detectors vary with configuration style of the detectors. Those performances directly affect the image quality of the large-scale Compton camera. In the present study, a series of Geant4 Monte Carlo simulations were performed in order to examine the effect of those detector parameters. Performance of the designed large-scale Compton camera was also estimated for various monitoring condition with realistic modeling. The conclusion of the present study indicates that the energy resolution of the component detector is the limiting factor of imaging resolution rather than the position resolution. Also, the designed large-scale Compton camera provides the 16.3 cm image resolution in full width at half maximum (angular resolution: $9.26^{\circ}$) for the depleted uranium source considered in this study located at the 1 m from the system when the component detectors have 10% energy resolution and 7 mm position resolution.

• Journal of Bio-Environment Control
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• v.22 no.3
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• pp.284-290
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• 2013

This study analyzed the geometric, compressive, cutting and friction properties of oriental melons in order to design a gripper capable of soft handling and a cutter for cutting oriental melon vine among the end effector of oriental melon as a preliminary step for developing the end effector of the robot capable of harvesting oriental melons in protected cultivation. As a result, the average length, diameter at the midpoint, weight, volume and roundness of the oriental melons were 108 mm, 70 mm, 188 g, 333 mL and 3.8 mm. Nonlinear regression analysis was performed on the equation $W=L^a{\times}D_2^b$ with variation of the length (L) and diameter (D2) of the weight (W) of the oriental melons. As a result, it was shown that there was a correlation between a of 2.0279 and b of -0.9998 as a constant value. The average diameter of the oriental melon vine was 3.8 mm, and most vines were distributed within a radius of 5 mm from the center. The average yield value, compressive strength and hardness of the oriental melons were $36.5N/cm^2$, $185.7N/cm^2$ and $636.7N/cm^2$, respectively. The average cutting force and shear strength of the oriental melon vines were $2.87{\times}10^{-2}\;N$ and $5.60N/cm^2$, respectively. The maximum friction coefficient of the oriental melons was rubber of 0.609, followed by aluminium of 0.393, stainless steel of 0.177 and teflon of 0.079. It was considered possible to apply it to the size of the gripper and cutter, turning radius, dynamics of drive motor and selection of materials and their quality in light of the position error and safety factor according to the movement when designing end effector based on the analyzed data.

• Journal of Bio-Environment Control
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• v.16 no.3
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• pp.210-216
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• 2007

A study was conducted to find mechanism and spray characteristics of a mini-sprinkler with downward spray to develop a new design type to be able to prevent drop water. The experiments were executed in a plastic greenhouse to minimize the effect of the wind. Data was collected at five different operation pressures and at 4 different raiser heights. Spray characteristics of the sprinkler such as effective radius, effective area, mean application depth, absolute maximum application depth, effective maximum application depth and coefficient of variation were determined. In order to analyze the mechanism and packing supporter of sprinkler, the numerical simulation using ABAQUS was performed. The optimum pressure for preventing drop water was determined.

• Journal of Navigation and Port Research
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• v.32 no.1
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• pp.23-27
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• 2008

This study was carried out to the effect of wind load on the structural stability of an articulated type container crane according to the wind direction assuming that 75m/s wind velocity is applied on a container crane using FSI(fluid-structural interaction). To consider fluid phenomenon around the container crane, the wind load was derived by the computation fluid dynamic, and it applied to the FSI which can guarantee an accuracy and a reliability in the design stage for wind resistant structural stability to minimize the damage due to high wind load applied in a container crane with a 'ㄱ' type articulated boom which used in the total height restriction region. Following from this, the reaction force on the each support of a container crane was suggested. ANSYS ICEM CFD 10.0 and ANSYS CFX 10.0 used for computation fluid dynamic, and the ANSYS Workbench 11.0 was used for the fluid-structural interaction.

• International Journal of Highway Engineering
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• v.10 no.1
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• pp.87-95
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• 2008

One way to shield an atypical structure to secure the occupant safety of an impact vehicle is to stack energy absorbing material modules around the structure. To be applicable to a cushion module, material must have enough energy absorbing capabilities while satisfying the safety requirements of the vehicle occupant. Static compression test of the potential materials gives a good indication which material is good for a slacking module. This paper presents the mechanical properties that a cushion material must have to satisfy the safety requirements. Static tests are performed for Quard-Guard system module, sand bag, recycled tires, Geo-Container, Geo-Cell and Expanded Polystyren (EPS) Blocks. Static test results are discussed and EPS block of $30kg/m^{3}$ density showed good potential for a cushion module. To check the dynamic effect of EPS block, drop tests have been made up to 35.6km/h impact speed. Drop test results are compared with static test results and no appreciable difference was found. To improve the EPS module property, making holes to the block is suggested and drop test are performed for the modified blocks. From the drop test results, design values are suggested.

• Journal of Biosystems Engineering
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• v.7 no.1
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• pp.17-32
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• 1982

The binders introduced in Korea were originally designed to be used for Japonica-type varieties which have relatively long stem and are highly resistant to shattering. In order to use it for Tongil varieties which are short and easy to be shattered, mechanical modifications are necessary to reduce a grain loss incurred during binder operation. This study was intended to investigate analytically and experimentally the major sources of grain losses caused by three kinds of binders now introduced in Korea. Actual modification for each of three binders was done and experimentally compared to see if any improvement on grain loss was achieved. The results obtained in this study are summarized as follows; 1. It was required that the power transmission of binder should have a shifting mechanism so that velocities of pick-up and traveling units could be changed independently as desired according to the Japonica-type and Tongil varieties. In other words, the desired velocity of traveling unit should be obtained by shifting the transmission and the velocity of pick-up unit should be selected by reaping clutch according to the variety independent of the velocity of traveling unit as shown in Fig. 6. 2. To reduce grain loss it was desired that the moving parts of the pick-up unit should have the lowest possible velocities in harvesting Tongil varieties, unless the reduction of the speed be hindered the conveyance of the material. Based on the study, it was concluded that the velocities of pick-up unit be reduced by about 35% of those of the existing units. 3. It was found that the lug at the upper rotating section of pick-up case gave a severe impact on the ears of rice to increase grain loss. The optimum design of pick-up case to protect the ears from the protruding part of the lug was recommended by the result of analysis of the trajectory of the end-point of lug at the position. 4. It was proved analytically and experimentally that pick-up unit at the lower-rotating part was the other important source of grain loss in pick-up and divider assembly. In order to reduce a grain loss incurred by lugs at their lower-rotating section, it was suggested to improve it by (1) widening the space between right and left lower-rotating section, (2) shortening the length of lugs, (3) enlargement of the angle between the pick-up case and ground-level, and (4) attaching guard to right and left dividers so that the rotating lug could not give a high impact to the paddy hill. 5. Pick-up and divider assembly of the original binder of three models studied was modified according to the suggestions that were given by the preliminary study. Field test showed that the modified binders were able to reduce grain losses by about 0.4-0.7 percentage points compared to those without modification.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.3
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• pp.622-628
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• 2016

As the suction pad-supporting bike carrier attached to a car may be subject to an excessive dynamic load due to random vibrations and centrifugal forces during driving, its structural safety is of great concern. To examine this, the finite-element method with a fluid-structure interaction should be used because the pressure on the pad bottom is changed in real time according to the fluctuations of the force or the moment applied on the pad. This method, however, has high computing costs in terms of modeling efforts and software expense. Moreover, the accuracy of computation is not easily guaranteed. Therefore, a new method combining the experiment and computation is proposed in this paper: the bottom pressure and contact area of the pad under varying loads was measured in real time and the acquired data are then used in the nonlinear elastic finite-element calculations. The computational and experimental results obtained with the product under development showed that the safety margin of the pad under the axial loading is relatively sufficient, whereas with an excessive rotational loading, the pad is vulnerable to separation or a local surface damage; hence, the safety margin may not be secured. The predicted contact behavior under the variation of the magnitude and type of the loading were in good agreement with the one from the experiment. The proposed analysis method in this study could be used in the design of similar vacuum pad systems.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.8
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• pp.44-54
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• 2018

Stress and fatigue of the distributor, an equipment of the high-pressure evaporator for the HRSG, were evaluated according to ASME Boiler & Pressure Vessel Code Section VIII Division 2. First, from the results of the piping system analysis model, reaction forces of the tubes connected to the distributor were derived and used as the nozzle load applied to the detailed analysis model of the distributor afterward. Next, the detailed model to analyze the distributor was constructed, the distributor being statically analyzed for the design condition with the steam pressure and the nozzle load. As a result, the maximum stress occurred at the bore of the horizontal nozzle, and the primary membrane stress at the shell and nozzle was found to be less than the allowable. Next, for the transient operating conditions given for the distributor, thermal analysis was performed and the structural analysis was carried out with the steam pressure, nozzle load, and thermal load. Under the transient conditions, the maximum stress occurred at the vertical downcomer nozzle, and of which fatigue life was evaluated. As a result, the cumulative usage factor was less than the allowable and hence the distributor was found to be safe from fatigue failure.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.719-725
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• 2017

Frozen milk products are commonly made in small refrigeration machines. R-502 has long been used as a refrigerant for soft ice cream machines, but it is being replaced with R-404A due to the issue of ozone layer depletion. However, R-404A has high global warming potential, so it also needs to be replaced. In this study, a mixture of R-290 and R-32 was considered as a new refrigerant. An optimization and performance evaluation of the mixture were conducted for a freezer volume of 2.8 liters. The focus of the optimization was the appropriate refrigerant charge and the opening of the expansion valve. At the optimized conditions, ice cream was produced in 6 minutes and 24 seconds with the mixture, and the COP was 0.83. For R-404A, the ice cream production time was 6 minutes and 22 seconds, and the COP was 0.90. The results may be used for the design of food refrigeration machines and to optimize other refrigeration cycles.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.71-76
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• 2017

The roll damping problem in the design of ships and offshore structures remains a challenge to many researchers due to the fluid viscosity and nonlinearity of the phenomenon itself. In this paper, the study on viscous roll damping of a circular cylinder was carried out using forced oscillations. The roll moment generated by forced oscillation using a torque sensor was measured for each forced oscillation period and compared with the empirical formula. Although the magnitude of the measured torque from the shear force was relatively small, the results were qualitatively similar to those obtained from the empirical formula, and showed good agreement with the quantitative results in some oscillation periods. In addition, the flow around the circular cylinder wall was observed closely through the PIV measurements. Owing to the fluid viscosity, a boundary layer was formed near the wall of the circular cylinder, and a minute wave was generated by periodical forced oscillations at the free surface through the PIV measurement. In this study, the suitability of the empirical formula for the roll moment caused by viscous roll damping was verified by model tests. The wave making phenomenon due to the fluid viscosity around the wall of a circular cylinder was testified by PIV measurements.