• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.812-817
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• 2005

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipole broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to gust-cascade interaction.

• Advances in aircraft and spacecraft science
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• 제10권2호
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• pp.179-202
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• 2023

This article presents a numerical analysis to investigate the natural frequencies and harmonic response of a perforated cantilever beam attached to two layers of piezoelectric materials by using the finite element method for the first time. The bimorph piezoelectric is composed of 3 layers; two of them at the outer are piezoelectric, and the inner isotropic material. A higher order 3-D 20-node solid element that exhibits quadratic displacement behavior is exploited to discretize the isotropic layer, and coupled piezoelectric 3D element with twenty nodes is used to mesh the top and bottom layers. CIRCU94 element is added to act as a resistor part of the model. The proposed model is validated with previous works. The numerical parametric studies are presented to illustrate the effects of perforation geometry, the number of rows, the resistance on the natural frequencies, frequency response, and power. It is found that the thickness has a positive relationship with the natural frequency. Perforations help in producing higher voltage, and the best shape is rectangular perforations, and to produce higher voltage, two rows of rectangular perforations should be applied.

• 한국소음진동공학회논문집
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• 제16권3호
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• pp.263-269
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• 2006

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.

• 국제지역연구
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• 제13권1호
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• pp.81-102
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• 2009

거시경제변수들 간의 영향관계에 대한 논의는 매우 중요한 연구주제로 자리잡고 있다. 자본자유화와 관련하여 가장 많이 논의되는 경제변수들은 환율과 주가이며, 이 두 변수들은 상호영향관계를 가지는 것으로 파악되고 있다. 그러나 변수의 관찰빈도와 관찰기간에 따라 그 결과는 다르게 나타나고 있다. 본 연구의 목적은 관찰빈도와 관찰기간에 따라 변수의 영향관계가 달라지는 것으로 나타날 경우 기존 연구들이 제시하고 있는 분석 결과의 불일치에 대한 원인을 설명함과 동시에 신뢰성 있는 연구결과의 제시 방법을 논의하는 것이다. 본 연구에서도 관찰빈도와 관찰기간을 달리했을 때, 환율과 주가에 대한 VAR 분석 결과가 다르게 나타남을 볼 수 있었다. 따라서 환율과 주가에 관한 연구를 수행함에 있어서 보다 신뢰성있는 연구결과를 도출하기 위한 적절한 관찰빈도와 관찰기간의 적정수준을 제시하기 위하여 몬테칼로 시뮬레이션을 이용하였다. 몬테칼로 시뮬레이션 결과 추정된 각 계수값의 95% 신뢰구간에 실제 VAR모형 분석과정에서 도출된 계수값이 포함될 비율은 관찰 빈도가 높을수록(예를 들어 일별 혹은 주별), 관찰 기간에 있어서 짧은 기간보다 보다 더 긴 기간을 적용할 때 더 설명력이 높다는 기존의 연구결과를 지지하는 것으로 나타났다.

• 한국실내디자인학회논문집
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• 제22권1호
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• pp.174-182
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• 2013

This study divided the observation area in an indoor space for area setup to analyse the effect of the difference of design types on the characteristics of observation with the observed time of each area as objects. Though it is thought that the difference of design patterns may be influenced by the factors and material composing the space, no existing approaches have had any quantitatively measuring method. Eye-tracking could be efficiently utilized for observation analysis from the viewpoint of dating observation behavior. The followings are the results of analysing the observation characteristics depending on design pattern. First, 5 observing areas were set up according to concentration of observation time in order for the concentration by area to be examined and the factors of design having effect on the difference of observation patterns by design type could be analysed. Second, as a whole, the observation of modern types showed high observation characteristics. When the difference of observation characteristics by pattern was examined by difference at observation frequency, the observation frequency defined to be more than 50% was seen to be almost same from Area I to III and to get higher from Area IV, and that defined to be 30% was high at Areas III and IV. In Area V, it was very high at natural. Third, that of Area II is no more than 8.2% but had the most observation time. As for observation characteristics, the horizontal observation of the central part was the highest and had more observation frequency at modern type that at natural one. These observation characteristics by area enabled to analyse the observation tendency depending on design characters at relevant area. Fourth, the design factors composing natural type were found to bring more attention when the area showed higher concentration at natural type than at modern one. And the analysis of design factors could make it to be confirmed that the quality of material and background factors in addition to design factors in the area had more effect on sight concentration.

• 대한의료기공학회지
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• 제10권1호
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• pp.130-157
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• 2007

The purpose of this research is to seek for efficient health maintenance device and to suggest desirable daily habit, based on the inquiry on interrelationship between workers' daily lives and their heartbeat change level. The paper survey about general features, case history and daily habits was conducted on workers during medical examination in Jeollabukdo, and examined their change of heartbeat as well. The results of research deducted from data analysis are as follows; 1. There found very positive interrelations between time-domain analysis and frequency-domain analysis, and MHR and LF/HF ratio had negative connection with other analyses. 2. The recipient showed high time-domain analysis when they are younger, have worked shorter or have spouse, and it contributes to stable sympathetic nerve and parasympathetic nerve as it stimulates autonomic nervous system. 3. According to the result of frequency-domain analysis, recipients showed higher TP and LF when they are younger, and the highest HF when they are under 34.The level of VLF was higher for university graduates than the ones who finished high school. The recipients showed higher TP and HF when they don't have spouse, and lower TP, LF and HF when they have worked longer. 4. The level of RMSSD and TSRD was high for the people who don't have case history, and HF was high when they don't have any disease in progress. 5. According to the result concerning correlation of daily habits with time-domain analysis and frequency-domain analysis, cigarette, alcohol and sleeping hours don't affect heartbeat change, but the ones who regularly workout showed higher result in every analysis. It shows that the autonomic nervous system of recipients who regularly exercise response more actively. The result mentioned above suggests that the change of heartbeat is a direct index which shows the change of autonomic nervous system, and it depends on the exercise the most. Thus, workout is proved to be the best method in order for workers to take care of their health.

• 대한전기학회논문지
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• 제39권5호
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• pp.516-518
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• 1990

We have derived the equation which involves the variation of electron energy with time in a lowly ionized plasma when a low alternating electric field is applied. We consider only elastic collisions between electrons and neutral atoms. This equation is solved using the 4th-order Runge-Kutta method, and applied to argon gas discharge which is driven by source frequency of 100, 1K, 10K, 100K, and 1M (Hz). The results show that the variation of electron energy becomes flat with higher frequencies.

• 대한조선학회논문집
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• 제47권3호
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• pp.306-320
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• 2010

Modern ultra-large container carriers can be exposed to the unprecedented springing excitation from ocean waves due to their relatively low torsional rigidity. Large deck opening on the deck of container carriers tends to cause warping distortion of hull structure under wave-induced excitation, eventually leading to the higher chance of resonance vibration between its torsional response and incoming waves. To handle this problem, a higher-order B-spline Rankine panel method and Vlasov-beam FE model was directly coupled in the time domain, and the coupled equation was solved by using an implicit iterative method. In order to capture the complicated behavior of thin-walled open section girder, a sophisticated beam-based finite element model was developed, which takes into account warping distortion and shear-on-wall effect. Then, the developed beam model was directly coupled with the time-domain Rankine panel method for hydrodynamic problem by using the fixed-point iteration method. The developed computational scheme was validated through the comparison with the frequency-domain solution on the container carrier model in linear springing regime.

• 한국직업건강간호학회지
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• 제3권호
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• pp.31-40
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• 1993

The objective of this study was examine sick leave rates of hospital employees. The sick leave data of 2,123 employees in three(3) general hospitals located in Seoul during the period from January 1, 1992 to December 31, 1992 was analyzed to achieve the study objective. The sick leave rates were computed in compliance with the standards recommended by the International Association on Occupational Health. Univariate analysis methods($X^2$-test and ANOVA) were used to assess the sourse of variance in the rates. The results were as follows : 1. The total annual rates of sick leave were 4.8% in frequency(persons), 0.23% in lost time, 0.68 days in duration and 14.0 days in severity. 2. The sick leave rates of frequency(person). duration and lost time were significantly higher in female than male, in groups of 40-49 years than in the other age group, the married than the unmarried and in the long employment of 8 years or above than the short employment. But there was no significant difference in the rate of severity. Only the sick leave rate of frequency(person) was significantly related to the educatial status, but there was no significant difference in other analytical factors of sick leave rate. 3. The main causes of sick leave were injury and poisoning(24.3%), and disease of the digestive system, disease of the nervous system and sense organs, and complications of pregnancy, childbirth and puerperium(respectively 11.6%). The severity rate was the highest in neoplasms(32.2 days), and followed by endocrine, nutritional and metabolic disease and immunity disorders, injury and poisoning, and infections and parasitic disease in descending order. 4. The sick leave rates of frequency(person), duration and lost time were the highest in nutritional workers followed by registered nurses. However, severity rate was the highest in doctors and pharmacists and followed by in nutritional works. 5. The main cause of sick leave was complication of pregnancy, childbirth and puerperium in registered nurses(26.3%), injury and poisoning in nutritional workers(78.6%) and disease of respiratory system and digestive system in other workers.

• 대한후두음성언어의학회지
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• 제15권2호
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• pp.141-144
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• 2004

Background and Objectives : To compare acoustic, aerodynamic analysis of voice and intelligibility score in patients with near-total laryngectomy and implantation of Provox prothesis. Material and Methods : In order to evaluate the voice characteristics, acoustic, aerodynamic parameter and speech intelligibility were measured in 5 patients after near-total laryngectomy, 5 patients after implantation of Provox prosthesis with total bility were measured in 5 patients after near-total laryngectomy, 5 patients after implantation of Provox prosthesis with total laryngectomy and 10 adults normal speaker. Acoustic analysis was carried out using CSL and aerodynamic analysis was carried out using Aerophon II. Speech sample was recorded and 10 listener was scored for speech intelligibility using a percentage of words correctly identified. Results. Fundamental frequency($F_0$), intensity, jitter, shimmer, maximal phonation time(MPT), subglottic air pressure were used for parameters for voice analysis. There were no significant difference between two group except on fundamental frequency and shimmer. The fundamental frequency was higher in patients with near-total laryngectomy and shimmer was higher in patients after implantation of Provox prosthesis with total laryngectomy. In addition, speech intelligibility was no significant difference between two groups. Conclusion : This results confirm that near-total laryngectomy and implantation of Provox prosthesis provides good voice rehabilitation.