• 대한기계학회논문집A
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• 제21권3호
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• pp.457-469
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• 1997

A nuclear spent fuel shipping cask is required by IAEA and domestic regulations to withstand a 9m free drop condition. In this paper, the structural analysis under the 9m side drop condition was performed to understand the dynamic impact behavior and to evaluate the safety of the cask for 7 PWR nuclear spent fuel assemblies. The analysis result was compared with the measured value of the 9m side drop test for the 1/3 scaled-down model and the accuracy of the 3D analysis was confirmed. Analysis in accordance with the diameter of impact limiters for the proto-type cask were performed. Through the analysis, the impact behaviors due to the side drop and the effects dependent on the diameter of impact limiters were grasped. Maximum stress intensities on each part of the cask were respectively calculated by using the stress evaluation program and the structural safety of the cask was finally evaluated in accordance with the regulations.

• 한국농공학회논문집
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• 제54권2호
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• pp.55-65
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• 2012

In the winter season, when the ventilation system is operating, the fresh cold air from the slot-type openings of broiler house which directly reached the animal zone can cause various problems such as thermal stress, decreasing of feed and water consumption, occurrence of respiratory disease, and etc. Therefore it is very important to control the trajectory of aero-flow from the slot openings to induce an efficient thermal heat change. Jet-drop distance model was proposed to predict and control the jet-trajectory. However their study was restricted due to the small scaled model and difficulties of measuring the Jet-drop distance. In this study, CFD was applied to analyze qualitatively and quantitatively the jet-drop distance in a real broiler house. The various variables were considered such as installed slot-angle, designed ventilation rate, and the outdoor ambient temperature. From the present study, two linear-regression models using the Jet-drop factor and corrected Archimedes number, and their R-squared values 0.744 and 0.736, respectively, were used. From this study, the applicability of CFD on the analysis of Jet-drop distance model was confirmed.

• 마이크로전자및패키징학회지
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• 제18권2호
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• pp.35-41
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• 2011

Recently, board level solder joint reliability performance of IC packages during drop impact becomes a great concern to semiconductor and electronic product manufacturers. The handheld electronic products are prone to being dropped during their useful service life because of their size and weight. The IC packages are susceptible to solder joint failures, induced by a combination of printed circuit board (PCB) bending and mechanical shock during impact. The board level drop testing is an effective method to characterize the solder joint reliability performance of miniature handheld products. In this paper, applying the JEDEC (JESD22-B111) standard present a finite element modeling of the FBGA. The simulation results revealed that maximum stress was located at the outermost solder ball in the PCB or IC package side, which consisted well with the location of crack initiation observed in the failure analysis after drop reliability tests.

• 한국환경과학회지
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• 제20권1호
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• pp.25-34
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• 2011

The new empirical static model was constructed on the basis of dimension analysis to predict the pressure drop according to the operating conditions. The empirical static model consists of the initial pressure drop term (${\Delta}P_{initial}$) and the dust mass number term($N_{dust}=\frac{{\omega}_0{\nu}_f}{P_{pulse}t}$), and two parameters (dust deposit resistance and exponent of dust mass number) have been estimated from experimental data. The optimum injection distance was identified in the 64 experimental data at the fixed filtration velocity and pulse pressure. The dust deposit resistance ($K_d$), one of the empirical static model parameters got the minimum value at d=0.11m, at which the total pressure drop was minimized. The exponent of dust mass number was interpreted as the elasticity of pressure drop to the dust mass number. The elasticity of the unimodal behavior had also a maximum value at d=0.11m, at which the pressure drop increased most rapidly with the dust mass number. Additionally, the correlation coefficient for the new empirical static model was 0.914.

• 대한정형도수물리치료학회지
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• 제19권2호
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• pp.19-22
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• 2013

Background: Excessive pronation of the feet can cause excessive inner rotation of the femur, followed by increased stress in the gluteus maximum, increased front slope of the pelvis, and lumbar lordosis, which leads to lumbar pain. The aim of the present study was to use the navicular drop test to examine foot pronation that can cause lumbar lordosis and to determine whether the navicular drop is lower in patients diagnosed with lumbar disc than in patients without this diagnosis. Methods: The Navicular Drop score was set by subtracting the navicular height at a standing position from the navicular height in a sitting position. The Navicular Drop measurements for college student with and without Lumbar Herniated Intervertebral Disc were compared using an independent t-test. Results: The control group were measured right $7.44{\pm}2.96$ and left $8.04{\pm}3.23$. The experimental group were measured right $2.12{\pm}1.33$ and left $2.80{\pm}1.29$. Therefore significant difference was found between the two groups (p<0.05). Conclusions: The navicular drop affected lumbar herniated intervertebral disc.

• 한국생산제조학회지
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• 제20권2호
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• pp.193-201
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• 2011

Recently, mechanical reliabilities including a drop test have been a hot issue. In this paper, solder balls with new components which are Sn-3.0Ag-0.5Cu and Sn-1.0Ag-0.5Cu-0.05N are introduced, and board level drop test for them are conducted under JEDEC standard in which the board with 15 flip chips is dropped as 1,500g acceleration during 0.5ms. The drop simulations are studied by using a implicit method in the ANSYS LS-DYNA, and modal analysis is made. Through both analyses, the solder balls with new components are evaluated under the drop. It is found that the maximum stress of each chip is occurred between the solder ball and the PCB, and the highest value among the maximum stresses in the chips is occurred on the chip nearest to fixed holes on the board in the drop tests and simulations.

• 대한기계학회논문집B
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• 제25권8호
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• pp.1021-1029
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• 2001

Rapid prototyping(RP) is a novel technology to create 3D products directly from CAD system. This study proposes a new RP method which uses the PZT ceramic plate to make a Drop-On-Demand liquid jet from the nozzle. The characteristic of drop formation in the new system is investigated both numerically and experimentally. The optimal drop for 3-D Printing can be obtained by the proper amplitude and frequency of the applied voltage. Also the process of the drop formation is analyzed using the pressure wave theory and verified by numerical simulation. First, the pressure wave generated by the deformation of the Piezo-plate at the nozzle is analyzed by solving the 2D axisymmetric wave equation via Finite Element Method. Finally, the drop formation process is simulated using a commercial software, FLOW 3D considering the pressure at the nozzle obtained by solving the wave equation as the boundary condition.

• 한국태양에너지학회 논문집
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• 제22권2호
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• pp.19-26
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• 2002

This study aims at numerically analyzing on heat transfer the characteristics and pressure drop of plate heat exchanger(PHE) using the Phoenics 3.1 VR Editor for the standard k-$\varepsilon$ model. Computations have been carried out for a range of chevron angle from $30^{\circ}$ to $60^{\circ}$, inlet velocity from 0.03m/s to 0.63m/s and the height of corrugation from 0.0045m to 0.0060m. The results show that both of heat transfer performance and pressure drop increase as chevron angle increases. This is because higher troughs produce higher turbulence and a higher heat transfer coefficient in the liquids flowing between the plates. As inlet velocity from 0.03m/s to 0.63m/s increases, heat transfer performance and pressure drop increase parabolically. As the height of corrugation increases, both of heat transfer performance and pressure drop decrease with the decrease of velocity. And the pressure drop decreases and the friction factor increases as the height of corrugation increases.

• 설비공학논문집
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• 제13권10호
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• pp.930-938
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• 2001

In this study, evaporation pressure drop experiments were conducted with two types of plate and shell heat exchangers (P&SHE) using R-22. An experimental refrigerant loop has been established to measure the evaporation pressure drop of R-22 in a vertical P&SHE. The flow channels were formed by adding three plates having a corrugated channel of a chevron angle of $45^{\circ}$. The R-22 flows down in one channel exchanging heat with the hot water flowing up in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality were explored in detail. During the experiment, the quality change between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.15. The present data showed that two types of P&SHE have similar trends. The pressure drop increases with the vapor quality for both types of P&SHE. At a higher mass flux, the pressure drop is higher for the entire range of the vapor quality. Also, the increase in the average heat flux increases the pressure drop. Finally, at a higher system pressure, the pressure drop is found to be slightly lower.

• Nuclear Engineering and Technology
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• 제46권4호
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• pp.529-540
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• 2014

In this research, a drop impact analysis of a fuel assembly in a research reactor is carried out to determine whether the fuel plate integrity is maintained in a drop accident. A fuel assembly drop accident is classified based on where the accident occurs, i.e., inside or outside the reactor, since each occasion results in a different impact load on the fuel assembly. An analysis procedure suitable for each drop situation is systematically established. For an accident occurring outside the reactor, the direct impact of a fuel assembly on the pool bottom is analyzed using implicit and explicit approaches. The effects of the key parameters, such as the impact velocity and structural damping ratios, are also studied. For an accident occurring inside the reactor, the falling fuel assembly may first hit the fixing bar at the upper part of the standing fuel assembly. To confirm the fuel plate integrity, a fracture of the fixing bar should be investigated, since the fixing bar plays a role in protecting the fuel plate from the external impact force. Through such an analysis, the suitability of an impact analysis procedure associated with the drop situation in the research reactor is shown.