• 산업경영시스템학회지
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• 제42권3호
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• pp.95-108
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• 2019

Quality management has become an pervasive philosophy in most sectors of business. Specific movements such as statistical quality control, quality circle, total quality management, and quality management system have become embedded in business organizations. Only the companies with competitive edge can survive in the competition in global market. KSA(Korean Standards Association) established in 1962 has launched all kinds of quality education, quality standard certification service for business, and KNQA(Korean National Quality Award) system. This article considers quality competitiveness excellent company award among KNQA. We performed a statistical analysis of audit data for quality competitiveness excellent company for three years, from 2015 to 2017. By using ANOVA and two sample t-tests, the average scores of 13 evaluation fields were significantly different depending on company size and type. We proposed ways to improve the current hall of fame system. We discovered that the average scores of 13 evaluation fields in the audit data according to years and hall of fame status were not significantly different. We also showed linear relationships among 13 evaluation fields by correlation analysis and obtained an estimated linear regression equation : Business Performance, which is a comprehensive index, as a dependent variable was significantly related to Customer Focus and Product Liability as regressor variables among 13 evaluation fields by regression analysis.

• 한국기계가공학회지
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• 제18권6호
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• pp.45-54
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• 2019

In this study, we analyze the rattle noise of a power takeoff (PTO) driveline and develop a PTO driveline resonance model. We measured the rattle noise of the PTO driveline on the output shaft and, by analyzing the rattle noise in the time domain, we determine that the engine expansion stroke period matches the sound pressure of rattle noise. This finding helped us demonstrate that the rattle noise is caused by the collision between the PTO driving gear and the gear driven by the engine expansion stroke; the torsional vibration caused by this collision is affected by the angular velocity fluctuation of the PTO drive shaft. By measuring the angular velocity of the PTO drive shaft, we confirm that the angular velocity fluctuation of the engine flywheel tends to excessively amplify the PTO drive shaft angular velocity fluctuation. We conclude that the resonance, which occurs when the operating frequency of the engine is close to the natural frequency of the tractor power transmission system, causes the excessive angular velocity fluctuation of the PTO drive shaft. We performed a modal analysis of the PTO driveline resonance and, using the characteristic equation, we show that the resonance occurs when the engine rotation speed is close to 850 rpm, which matches the natural frequency of the PTO driveline.

• Geomechanics and Engineering
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• 제18권2호
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• pp.189-203
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• 2019

Brine leakage is a common phenomenon during construction facilitated by artificial freezing technique, threatening the stability of frozen wall due to the continual thawing of already frozen domain. This paper takes the frequently encountered soft clay in Wujiang District as the study object, and remolded specimens were prepared by mixing calcium chloride solutions at five levels of concentration. Both the deformation and pore water pressure of frozen specimens during thawing were investigated by two-stage loading tests. Three sections were noted from the changes in the strain rate of specimens during thawing at the first-stage load, i.e., instantaneous, attenuated, and quasi-stable sections. During the second-stage loading, the deformation of post-thawed soils is closely correlated with the dissipation of pore water pressure. Two characteristic indexes were obtained including thaw-settlement coefficient and critical water content. The critical water content increases positively with salt content. The higher water content of soil leads to a larger thaw-settlement coefficient, especially at higher salt contents, based on which an empirical equation was proposed and verified. The normalized pore water pressure during thawing was found to dissipate slower at higher salt contents, with a longer duration to stabilize. Three physical indexes were experimentally determined such as freezing point, heat conductivity and water permeability. The freezing point decreases at higher salt contents, especially as more water is involved, like the changes in heat conductivity. The water permeability maintains within the same order at the considered range of salt contents, like the development of the coefficient of consolidation. The variation of the pore volume distribution also accounts for this.

• 지식경영연구
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• 제21권4호
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• pp.89-108
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• 2020

본 연구에서는 Airbnb 고객들의 재구매 의도에 영향을 미치는 선행 요인들을 살펴보고자 하였다. 고객들이 경험 뒤 형성된 긍정적 감정과 부정적 감정이 재구매를 결정하는 핵심요인으로 고려하였다. Airbnb 특성 요인으로는 진정한 경험, 숙소 시설, 가격 공정성을 선정하였다. 그리고 재구매 의사 결정에서 주관적 규범과 트렌드 추구 경향의 역할에 대해서도 살펴보았다. 제안한 연구 모형은 306명의 Airbnb 사용 경험이 있는 고객들을 대상으로 연구 모형을 분석하였으며, 구조 방정식 모형을 활용하였다. 연구 분석 결과 Airbnb에 대한 긍정적 감정과 부정적 감정 모두 재구매 의도에 유의한 영향을 미침을 알 수 있었다. 또한 Airbnb의 특성 요인들이 재구매 의사 결정에 미치는 영향을 확인할 수 있었다. 마지막으로 주관적 규범과 트렌드 추구 경향은 재구매 의도에 유의한 영향을 미치지 않았다. 본 연구 결과를 통해 Airbnb의 지속적 성장을 위한 고객 경험 관리와 마케팅 전략을 수립하는데 도움을 줄 수 있을 것으로 기대된다.

• 대한조선학회논문집
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• 제59권3호
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• pp.183-191
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• 2022

A design method for a propeller type rim-driven axial-flow turbine for a micro-hydropower system is presented. The turbine consists of pre-stator, impeller and post-stator, where the pre-stator plays a role as a guide vane to provide circumferential velocity to the on-coming flow, and the impeller as a rotational power generator by absorbing angular momentum of the flow. BEM(Blade Element Method), which is based on the turbine Euler equation, is employed to design the pre-stator and impeller blades. NACA 66 thickness form and a=0.8 mean camber line, which is widely accepted as a marine propeller blade section, is used for the pre-stator and turbine blade section. A CFD method, derived from the discretization of the RANS equations, is applied for the analysis of the designed turbine system. The design conditions of the turbine is confirmed by the CFD calculation. Turbine characteristic curve is calculated by the CFD method, in order to provide the performance characteristics at off-design operation conditions. The proposed procedures for the design of a propeller type rim-driven axial-flow turbine are established and confirmed by the CFD analysis.

• Clinical and Experimental Reproductive Medicine
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• 제49권3호
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• pp.202-209
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• 2022

Objective: The aim of this study was to assess the correlation of oocyte number with serum anti-Müllerian hormone (AMH) levels measured by two automated methods (Access or Elecsys) in fresh stimulated in vitro fertilization (IVF) cycles. Methods: In this retrospective study at a university hospital, data were collected from 243 fresh stimulated IVF cycles performed from August 2016 to December 2020. The serum AMH level was measured by Access in 120 cycles and by Elecsys in 123 cycles. The cut-off of serum AMH for prediction of poor responders (three or fewer oocytes) or high responders (15 or more oocytes) was calculated by the receiver operating characteristic curve analysis. Results: For the two automated methods, the following equations were derived: total oocyte number=2.378+1.418×(Access-AMH) (r=0.645, p<0.001) and total oocyte number=2.417+2.163×(Elecsys-AMH) (r=0.686, p<0.001). The following combined equation could be derived: (Access-AMH)=0.028+1.525×(Elecsys-AMH). To predict poor responders, the cut-off of Access-AMH was 1.215 ng/mL (area under the curve [AUC], 0.807; 95% confidence interval [CI], 0.730-0.884; p<0.001), and the cut-off of Elecsys-AMH was 1.095 ng/mL (AUC, 0.848; 95% CI, 0.773-0.923; p<0.001). To predict high responders, the cut-off of Access-AMH was 3.450 ng/mL (AUC, 0.922; 95% CI, 0.862-0.981; p<0.001), and the cut-off of Elecsys-AMH was 2.500 ng/mL (AUC, 0.884; 95% CI, 0.778-0.991; p<0.001). Conclusion: Both automated methods for serum AMH measurement showed a good correlation with oocyte number and good performance for predicting poor and high responders in fresh stimulated IVF cycles. The Access method usually yielded higher measured serum AMH levels than the Elecsys method.

• Steel and Composite Structures
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• 제44권1호
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• pp.65-79
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• 2022

The main goal of this paper is to study the vibration of damaged core laminated annular plates with FG face sheets based on a three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. In this study the effect of microcracks on the vibrational characteristic of the sandwich plate is considered. In particular, the structures are made by an isotropic core that undergoes a progressive uniform damage, which is modeled as a decay of the mechanical properties expressed in terms of engineering constants. These defects are uniformly distributed and affect the central layer of the plates independently from the direction, this phenomenon is known as "isotropic damage" and it is fully described by a scalar parameter. Three complicated equations of motion for the sectorial plates under consideration are semi-analytically solved by using 2-D differential quadrature method. Using the 2-D differential quadrature method in the r- and z-directions, allows one to deal with sandwich annular plate with arbitrary thickness distribution of material properties and also to implement the effects of different boundary conditions of the structure efficiently and in an exact manner. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. The sandwich annular plate is assumed to have any arbitrary boundary conditions at the circular edges including simply supported, clamped and, free. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution, and boundary conditions.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2023년도 학술발표회
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• pp.244-244
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• 2023

Both the frequency and the magnitude of hydrometeorological extreme events such as severe floods and droughts are increasing. In order to prevent a damage from the climatic disaster, hydrological models are often simulated under various meteorological conditions. While performing the simulations, a synthetic data generated through time series models which maintains the key statistical characteristics of the sample data are widely applied. However, the synthetic data can easily maintains both the average and the variance of the sample data, but the quantile is not maintained well. In this study, we proposes a data generation method which maintains the quantile of the sample data well. The equations of the former maintenance of variance extension (MOVE) are expanded to maintain quantile rather than the average or the variance of the sample data. The equations are derived and the coefficients are determined based on the characteristics of the sample data that we aim to preserve. Monte Carlo simulation is utilized to assess the performance of the proposed data generation method. A time series data (data length of 500) is regarded as the sample data and selected randomly from the sample data to create the data set (data length of 30) for simulation. Data length of the selected data set is expanded from 30 to 500 by using the proposed method. Then, the average, the variance, and the quantile difference between the sample data, and the expanded data are evaluated with relative root mean square error for each simulation. As a result of the simulation, each equation which is designed to maintain the characteristic of data performs well. Moreover, expanded data can preserve the quantile of sample data more precisely than that those expanded through the conventional time series model.

• 한국안전학회지
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• 제38권3호
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• pp.35-42
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• 2023

This study analyzed the current and temperature characteristics of major components of an induction motor during normal and abnormal operations as functions of the difference in the rated capacities of medium and large-sized motors widely used in industrial settings. The temperature rise equation of the induction motor winding was derived through locked-rotor operation experiments and linear regression analysis. When the ambient temperature is 40 ℃, the time to reach 155 ℃, the temperature limit of the insulation class (F class) of the winding of the induction motor, was confirmed to be 48 seconds for the 2.2 kW induction motor and 39 seconds for the 3.7 kW induction motor. This means that when the rated capacity is large or the installation environment is high temperature, the time to reach the temperature limit of the insulation class during locked-rotor operation is short, and the risk of insulation deterioration and fire is high. In addition, even if the EOCR (Electronic Over Current Relay) is installed, if the setting time is excessively set, the EOCR does not operate even if the normal and locked-rotor operation of the induction motor is repeated, and the temperature limit of the insulation grade of the winding of the induction motor is exceeded. The results of this study can be used for preventive measures such as the promotion of electrical and mechanical measures for the failure of induction motors and fire prevention in industrial sites, or the installation of fire alarm systems.

• 한국지반공학회논문집
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• 제22권4호
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• pp.51-59
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• 2006

본 고에서는 선행연구(홍성연, 2004)에서 개발한 대형직접전단시험기를 이용하여 조립질 토목재료의 시험밀도와 균등계수의 크기가 전단강도에 주는 영향을 분석하였으며, 아울러, 각 수직응력별로 한계상태에서 조립재료가 갖고 있는 마찰계수를 Wood(1998)가 제안한 방정식을 이용하여 산출하였다. 시험에 사용한 재료는 경상과 전라지역 석산에서 생산중인 조립재료이다. 시험결과 시험밀도 $2.10g/cm^3$의 전단강도의 크기가 $1.85g/cm^3$의 값보다 상대적으로 크게 나타났으며, 균등계수는 상대적으로 10.0보다 5.0일때 더 큰 전단강도를 갖는 것으로 나타났다. 한편, 조립질 토목재료가 갖고 있는 한계상태에서의 마찰계수는 각 시험조건별로 $1.0{\sim}1.6$의 범위로 나타났다.