• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.4
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• pp.269-275
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• 2017

The aeroelastic stability of a fighter type aircraft can be severly affected by the store mass, aerodynamic characteristics, and store combinations. Hence, the stability for the all store configurations must be substantiated before the aircraft in service. For the aeroelastic analysis, the design data and information for the aircraft structure, mass distribution, control surface characteristics, and external shape etc. are required. This is the reason that the store compatibility substantiations by a third party are restricted. However, according to the change of operational environment or the improvement of avionic technology, a new external store is developed and it should be installed on an aircraft without the support from the original supplier. This paper describe the process to substantiate the aeroelastic compatibility between a new external store and an imported aircraft whose design data is not available to a third party operating the aircraft.

• Journal of Preventive Medicine and Public Health
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• v.49 no.5
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• pp.329-341
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• 2016

Objectives: The goal of this study was to investigate the short-term effect of ambient air pollution on emergency department (ED) visits in Seoul for asthma according to patients' prior history of allergic diseases. Methods: Data on ED visits from 2005 to 2009 were obtained from the Health Insurance Review and Assessment Service. To evaluate the risk of ED visits for asthma related to ambient air pollutants (carbon monoxide [CO], nitrogen dioxide [$NO_2$], ozone [$O_3$], sulfur dioxide [$SO_2$], and particulate matter with an aerodynamic diameter <$10{\mu}m$ [$PM_{10}$]), a generalized additive model with a Poisson distribution was used; a single-lag model and a cumulative-effect model (average concentration over the previous 1-7 days) were also explored. The percent increase and 95% confidence interval (CI) were calculated for each interquartile range (IQR) increment in the concentration of each air pollutant. Subgroup analyses were done by age, gender, the presence of allergic disease, and season. Results: A total of 33 751 asthma attack cases were observed during the study period. The strongest association was a 9.6% increase (95% CI, 6.9% to 12.3%) in the risk of ED visits for asthma per IQR increase in $O_3$ concentration. IQR changes in $NO_2$ and $PM_{10}$ concentrations were also significantly associated with ED visits in the cumulative lag 7 model. Among patients with a prior history of allergic rhinitis or atopic dermatitis, the risk of ED visits for asthma per IQR increase in $PM_{10}$ concentration was higher (3.9%; 95% CI, 1.2% to 6.7%) than in patients with no such history. Conclusions: Ambient air pollutants were positively associated with ED visits for asthma, especially among subjects with a prior history of allergic rhinitis or atopic dermatitis.

• Journal of the Korea Organic Resources Recycling Association
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• v.18 no.3
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• pp.77-86
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• 2010

In this study, the model of the indirect wind suction waste sorting machine for characteristics of the screening of waste was studied using computational fluid dynamics and the drag coefficient for the model and the suction wind speed were obtained. The wind separator are developing by installing a cyclone air outlet to the suction blower impeller waste is selective in a way that does not pass the features and characteristics of the inlet pipe of the pressure loss and separation efficiency can have a significant impact on. Using Wind separator for selection of waste in the waste prior research on the aerodynamic properties are essential. For plastic cases, it is reasonable to take the drag coefficient between 0.8 and 1.0, and for cans, compression depending on whether the cans, the drag coefficient is in the range from 0.2 to 0.7. The separation efficiency of waste as change suction speed was the highest efficiency when the suction speed was 25~26 m/s. Shape of the inlet, depending on how the transfer pipe of the duct pressure loss occurs because the inlet velocity changes through the appropriate design standards to allow for continued research is needed.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.378-383
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• 2013

A butterfly throttle valve has been used to control the brake power of an SI engine by controlling the mass flow-rate of intake air in the induction system. However, the valve has a serious effect on the volumetric efficiency of the engine due to the pressure resistance in the induction system. In this study, a new intake air controlling valve named "Variable Geometry Throttle Valve(VGTV)" is proposed to minimize the pressure resistance in the intake system of an SI engine. The design concept of VGTV is on the application of a venturi nozzle in the air flow path. Instead of change of the butterfly valve angle in the airflow field, the throat width of the VGTV valve is varied with the operating condition of an SI engine. In this numerical study, CFD(computational fluid dynamics) simulation technique was incorporated to have an aerodynamics performance analysis of the two air flow controlling systems; butterfly valve and VGTV and compared the results to know which system has lower pressure resistance in the air intake system. From the result, it was found that VGTV has lower pressure resistance than the butterfly valve. Especially VGTV is effective on the low and medium load operating condition of an SI engine. The averaged pressure resistance of VGTV is about 49.0% lower than the value of the conventional butterfly throttle valve.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.1
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• pp.25-32
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• 2014

Offshore wind power structures are subject to coastal hydrodynamic loading such as wind and wave loads. A considerable number of turbines have been installed in Europe, but so far none in Korea. Interest in offshore wind energy is growing in Korea, and it is expected that projects will reach the design stage in the near future. This paper discusses the level of structural reliability implied by the design rules of ABS(2010, 2013) and IEC(2009). Metocean conditions in 4 Korean seas(Gunsan, HeMOSU 1, Mokpo, Jeju) were used in the calibrations to calculate the aerodynamic and hydrodynamic loads as well as the structural responses of the typical designs of offshore wind turbines. Due to the higher variability of the wind and wave climate in hurricane-prone areas, applying IEC strength design criteria in combination with Korea west sea conditions could result in a design with much lower reliability index than what is anticipated from a design in European waters. To achieve the same level of safety as those in European waters, application of ABS 100 year design standards are recommended. Level-1 reliability-based design suitable for the Korean sea state conditions should be introduced because the IEC standards does not consider the typhoon effects in depth and the ABS standards is a WSD design method. In addition, the design equation should be established based on the statistical characteristics of the wind and wave loads of the Korean sea areas.

• Journal of Biosystems Engineering
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• v.13 no.3
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• pp.32-43
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• 1988

This study was attempted to investigate the pneumatic separation on separating unit of a combine harvester. The aerodynamic characteristics of threshed materials were analyzed by experiments. The air velocity distribution within the separation chamber was measured for various speeds of the winnower and suction fans to find out the operational and design conditions of the separating unit which would serve for reducing the grain loss from chaff outlet. The results of study arc summarized as follows: 1. Based on the separation curve of threshed materials analyzed, it was shown that three different kind. of materials-kernels, straw chaff, and leaf chaff were as a whole able to be separated pneumatically, regardless of varieties. However, a small amount of the separation grain loss may be expected to occur if the complete separation between kernels and straw chaff would be undertaken because some portion of their separation curve were overlapping. 2. The analysis of air velocity distribution showed that the separation chamber may be divided into two regions, the discharging and separating. The air velocity of the discharging region was 5-15 m/s and that of the separating region 2-5 m/s. 3. The air movement of the separation chamber may be a turbulence flow, being its speed became greater as it moves from the left to the right section of the separation chamber. The equi-speed line. of air flow had a steep gradient in between the discharging and the separation regions. The air velocity in the discharging region was much higher than the terminal velocity of kernels, because of which those kernels appearing in the region could be possibly exhausted as the grain loss from the chaff outlet. 4. The motion trajectory of threshed material in the separating region was dominantly affected by the winnower fan, on the other hand, its motion in the discharging region was affected by suction fan. 5. The grain loss from the chaff outlet was affected greatly by the winnower fan and the trace of kernel movement. It was observed that the optimum working speed to give minimum grain loss from chaff outlet for the combine tested should be maintained at 950~1,150 rpm for the winnower fan and 1,850 rpm for the suction fan. 6. It was shown that a large portion of grain loss from chaff outlet may occur when the kernels may bump against a portion of separation chamber wall and those kernels thus scattered into the discharging region were sucked by the suction fan. It was accordingly recommended that a new design of the wall of separation chamber so as to bump down kernels may be necessary to reduce grain loss from the chaff outlet.

• Journal of Environmental Impact Assessment
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• v.26 no.1
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• pp.11-26
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• 2017

Approximate empirical equations obtained by measuring overall noise levels at different distances have been used to evaluate environmental influence of the railway noise though the accurate prediction of noise levels is important. In this paper, a noise prediction model considering the frequency characteristics of noise sources and propagation was suggested to improve the accuracy of noise prediction. The railway noise source was assorted into track, wheel, traction and aerodynamic components and they were characterized with the source strength and speed coefficient at each octave-band frequency. Correction terms for the acoustic roughness and the track/bridge condition were introduced. The sound attenuation from a source to a receiver was calculated taking account of the geometrical divergence, atmospheric absorption, ground effect, diffraction at obstacles and directivity of source by applying ISO 9613-2. For obtaining the source strength and speed coefficients, the results of rolling noise model, numerical analysis and measurements of pass-by noise were analyzed. We compared the predicted and measured noise levels in various vehicles and tracks, and verified the accuracy of the present model. It is found that the present model gives less error than the conventional one, so that it can be applied to make the accurate prediction of railway noise effect and establish its countermeasures efficiently.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.127-134
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• 2020

High supersonic aircraft are exposed to high temperature environments by aerodynamic heating during supersonic flight. Thermal protection system structures such as double-panel structures are used on the skin of the fuselage and wings to prevent the transfer of high heat into the interior of an aircraft. The thin-walled double-panel skin can be exposed to acoustic loads by supersonic aircraft's high power engine noise and jet flow noise, which can cause sonic fatigue damage. Therefore, it is necessary to examine the behavior of supersonic aircraft skin structure under thermal-acoustic load and to predict fatigue life. In this paper, we designed and fabricated thermal-acoustic test equipment to simulate thermal-acoustic load. Thermal-acoustic testing of the titanium specimen under thermal-acoustic load was performed. The analytical model was verified by comparing the thermal-acoustic test results with the finite element analysis results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.2
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• pp.171-179
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• 2012

Cooling of hot sections, especially the turbine nozzle and rotor blades, has a significant impact on gas turbine performance. In this study, the influence of precooling of the cooling air on the performance of gas turbines and their combined cycle plants was investigated. A state-of-the-art F-class gas turbine was selected, and its design performance was deliberately simulated using detailed component models including turbine blade cooling. Off-design analysis was used to simulate changes in the operating conditions and performance of the gas turbines due to precooling of the cooling air. Thermodynamic and aerodynamic models were used to simulate the performance of the cooled nozzle and rotor blade. In the combined cycle plant, the heat rejected from the cooling air was recovered at the bottoming steam cycle to optimize the overall plant performance. With a 200K decrease of all cooling air stream, an almost 1.78% power upgrade due to increase in main gas flow and a 0.70 percent point efficiency decrease due to the fuel flow increase to maintain design turbine inlet temperature were predicted.

• Journal of the Korean Society of Laryngology, Phoniatrics and Logopedics
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• v.29 no.1
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• pp.30-36
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• 2018

Background and Objectives : The effect of palliative injection laryngoplasty in cancer-related unilateral vocal cord paralysis patients on voice and swallowing function is uncertain and there are few previous studies of its suitability, benefits as a palliative treatment option. The purpose of this study is to confirm the objective results of voice and swallowing function after palliative office-based hyaluronic acid injection laryngoplasty in cancer-related unilateral vocal cord paralysis patients. Materials and Method : 36 patients who had unilateral vocal cord paralysis from non-thyroidal, extralaryngeal neoplasms were included in this study. To evaluate the clinical outcome, we analyzed perceptual GRBAS grading, acoustic analysis, aerodynamic study, Electroglottography (EGG), Voice Handicap Index (VHI-30) about voice function and disability rating scale (DRS), gastric tube dependency, aspiration pneumonia about swallowing function and 36-Item Short Form Survey version 2 (SF-36v2) about quality of life. Results : In GRBAS scale, G (p<0.001), R (p=0.004), B (p=0.001), A (p=0.011), and S (p=0.007) showed significant improvement. Jitter, shimmer, speaking fundamental frequency, maximal phonation time, VHI-30, DRS score, gastric tube dependency, aspiration pneumonia, and SF-36v2 were significantly improved after injection (p=0.016, p=0.011, p=0.045, p=0.005, p<0.001, p<0.001 p=0.003, p<0.001, and p<0.001 respectively). Conclusion : From this study we concluded office-based hyaluronic acid injection can be used as a useful palliative treatment option in cancer-related ill patients with unilateral vocal cord paralysis. Palliative hyaluronic acid injection laryngoplasty avoids the need for tube feeding, thus reducing the risk of aspiration pneumonia. These outcomes are accompanied by significant improvement in voice quality.