• Structural Engineering and Mechanics
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• 제85권6호
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• pp.765-780
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• 2023

In this work, a novel combined logarithmic, secant and tangential 2D and quasi-3D refined higher order shear deformation theory is proposed to examine the buckling analysis of simply supported uniform functionally graded plates under uniaxial and biaxial loading. The proposed formulations contain a reduced number of variables compared to others similar solutions. The combined function employed in this study ensures automatically the zero-transverse shear stresses at the free surfaces of the structure. Various models of the material distributions are considered (linear, quadratic, cubic inverse quadratic and power-law). The differentials stability equations are derived via virtual work principle with including the stretching effect. The Navier's approach is applied to solve the governing equations which satisfying the boundary conditions. Several comparative and parametric studies are performed to illustrates the validity and efficacity of the proposed model and the various factors influencing the critical buckling load of thick FG plate.

• Coupled systems mechanics
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• 제12권5호
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• pp.429-444
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• 2023

The comprehension and structural modeling of masonry constructions is fundamental to safeguard the integrity of built cultural assets and intervene through adequate actions, especially in earthquake-prone regions. Despite the availability of several modeling strategies and modern computing power, modeling masonry remains a great challenge because of still demanding computational efforts, constraints in performing destructive or semi-destructive in-situ tests, and material uncertainties. This paper investigates the shear behavior of masonry walls by applying a plane-stress FE continuum model with the Modified Masonry-like Material (MMLM). Epistemic uncertainty affecting input parameters of the MMLM is considered in a probabilistic framework. After appointing a suitable probability density function to input quantities according to prior engineering knowledge, uncertainties are propagated to outputs relying on gPCE-based surrogate models to considerably speed up the forward problem-solving. The sensitivity of the response to input parameters is evaluated through the computation of Sobol' indices pointing out the parameters more worthy to be further investigated, when dealing with the seismic assessment of masonry buildings. Finally, masonry mechanical properties are calibrated in a probabilistic setting with the Bayesian approach to the inverse problem based on the available measurements obtained from the experimental load-displacement curves provided by shear compression in-situ tests.

• 동력기계공학회지
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• 제16권2호
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• pp.66-74
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• 2012

In this paper, the authors propose a new approach to control a barge type surface vessel. It is based on the Dynamic Positioning System(DPS) design. The main role of barge ship is to carry and supply the materials to the floating units and other places. To carry out this job, it should be positioned in the specified area. However sometimes the thrust systems are installed on it, and in general the rope control by mooring winch system is used. It may be difficult to compare the control performances of two types. If we consider this problem in point of usefulness, we can easily find out that the winch control system is more useful and applicable to the real field than the thrust control system except a special use. Therefore, in this paper we consider a DPS design problem which can be extended to the many application fields. The goal of this paper is twofold. First, the sliding mode controller (SMC) for positioning the our vessel is proposed. Especially, in this paper, a robust stability condition is given based on descriptor system representation. In the result, the sliding mode control law guarantees to keep the vessel in the defined area in the presence of environmental disturbances. And second, the thrust allocation problem is solved by using redistributed pseudo-inverse (RPI) algorithm to determine the thrust force and direction of each individual actuator. The proposed approach has been simulated with a supply vessel model and found work well.

• 대한기계학회논문집B
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• 제30권6호
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• pp.553-559
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• 2006

Most diesel injector, which is currently used in high-pressure common rail fuel injection system of diesel engine, is driven by the solenoid coil energy for its needle movement. The main disadvantage of this solenoid-driven injector is a high power consumption, high power loss through solenoid coil and relatively fixed needle response's problem. In this study, a prototype piezo-driven injector, as a new injector mechanism driven by piezoelectric energy based on the concept of inverse piezo-electric effect, has been designed and fabricated to know the effect of piezo-driven injection processes on the diesel spray structure and internal nozzle flow. Firstly we investigated the spray characteristics in a constant volume chamber pressurized by nitrogen gas using the back diffusion light illumination method for high-speed temporal photography and also analyzed the inside nozzle flow by a fully transient simulation with cavitation model using VOF(volume of fraction) method. The numerical calculation has been performed to simulate the cavitating flow of 3-dimensional real size single hole nozzle along the injection duration. Results were compared between a conventional solenoid-driven injector and piezo-driven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has short injection delay and a faster spray development and produces higher injection velocity than the solenoid-driven injector. And the predicted simulation results with the degree of cavitation's generation inside nozzle for faster needle response In a piezo-driven injector were reflected to spray development in agreement with the experimental spray images.

• Journal of Preventive Medicine and Public Health
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• 제33권1호
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• pp.125-133
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• 2000

Objectives : This study uses meta-analysis methodology to examine the statistical consistency and importance of random variation among results of epidemiologic studies of occupational electromagnetic field exposure and leukemia. Methods : Studies for this meta-analysis were identified from previous reviews and by asking researcher active in this field for recommendations. Overall, 27 studies of occupational electromagnetic field exposures and leukemia were reviewed. A variety of meta-analysis statistical methods have been used to assess combined effects, to identify heterogeneity, and to provide a single summary risk estimate based on a set of simiar epidemiologic studies. In this study, classification of exposure metircs on occupational epidemiologic studies are reported for (1) job classification (20 individual studies); (2) leukemia subtypes (13 individual studies); and (3) country (27 individual studies). Results : Results of this study, an inverse-variance weighted pooling of all the data leads to a small but significant elevation in risk of f 1% (OR=1.11, 95% CI : $1.06\sim1.16$) among 27 occupational epidemiologic studies. Publication bias was assessed by the 'fail-safe n' that may be not influence for all combined results exception a few categories, ie, 'power station operators' and 'electric utility workers' by job classification on occupational study. And ail combined odds ratio results were similar for fixed-effects models and random-effects models, with slightly higher risk estimates for the random-effects model in situations where there was significant heterogeneity, ie, Q-statistic significant (p<.05). Conclusions : We found a small elevation in risk of leukemia, but the ubiquitous nature of exposure to electromagnetic fields from workplace makes even a weak association a public health issue of substantial power to influence the present overall conclusion about relationship between electromagnetic fields exposure and leukemia.

• Asian Pacific Journal of Cancer Prevention
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• 제14권3호
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• pp.2097-2100
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• 2013

Background: To estimate the numbers and trends in cervix cancer cases visiting the Radiotherapy Department at Manipal Teaching Hospital, Pokhara, Nepal, statistical modelling from retrospective data was applied. Materials and Methods: A retrospective study was carried out on data for a total of 159 patients treated for cervix cancer at Manipal Teaching Hospital, Pokhara, Nepal, between $28^{th}$ September 2000 and $31^{st}$ December 2008. Theoretical statistics were used for statistical modelling and forecasting. Results: Using curve fitting method, Linear, Logarithmic, Inverse, Quadratic, Cubic, Compound, Power and Exponential growth models were validated. Including the constant term, none of the models fit the data well. Excluding the constant term, the cubic model demonstrated the best fit, with $R^2$=0.871 (p=0.004). In 2008, the observed and estimated numbers of cases were same (12). According to our model, 273 patients with cervical cancer are expected to visit the hospital in 2015. Conclusions: Our data predict a significant increase in cervical cancer cases in this region in the near future. This observation suggests the need for more focus and resource allocation on cervical cancer screening and treatment.

• 한국기계가공학회지
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• 제21권9호
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• pp.78-84
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• 2022

An air circuit breaker (ACB) is an electrical protection device that interrupts abnormal fault currents that result from overloads or short circuits in a low-voltage power distribution line. The ACB consists of a main circuit part for current flow, mechanism part for the opening and closing operation of movable conductors, and arc-extinguishing part for arc extinction during the breaking operation. The driving mechanism of the ACB is a spring energy charging type. The faster the contact opening speed of the movable conductors during the opening process, the better the breaking performance. However, there is a disadvantage that the durability of mechanism decreases in inverse proportion to the use of a spring capable of accumulating high energy to configure the breaking speed faster. Therefore, to simultaneously satisfy the breaking performance and mechanical endurance of the ACB, its driving mechanism must be optimized. In this study, a dynamic model of the ACB was developed using the MDO(Mechanism Dynamics Option) module of CREO, which is widely used in multibody dynamics analysis. To improve the opening velocity, the Taguchi design method was applied to optimize the design parameters of an ACB with many linkages. In addition, to evaluate the improvement in the operating characteristics, the simulation and experimental results were compared with the MDO model and improved prototype sample, respectively.

• 지구물리와물리탐사
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• 제19권1호
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• pp.11-19
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• 2016

나머지 정적보정 기법중에서 가장 많이 쓰이는 주행시간 분해기법과 겹쌓기제곱 최대화기법의 적용성을 육상 탄성파자료에서 비교 검토하였다. 모든 발파점과 수신점에 대한 임의의 나머지 정적보정값(시간차이)과 무작위 잡음이 포함된 모델자료에서 겹쌓기제곱 최대화기법은 주행시간 분해기법에 비해 흐트러진 반사 이벤트를 정확히 정렬시키고 보정과정에서 출력된 발파점과 수신점의 정적보정 그래프가 입력된 값과 거의 같은 진폭으로 역전된다는 점에서 신호대잡음이 작은 자료의 반사면 향상에 보다 효과적이었다. 나머지 정적보정에 적합한 입력인자(최대허용 시간차이, 상관창, 반복횟수)들은 공통중간점 자료외에 공통발파점 겹쌓기자료와 공통수신점 겹쌓기자료에 대한 연속 테스트를 거쳐 효과적으로 진단할 수 있었다. 나머지 정적보정에 앞서 송수신점의 높이보정 및 풍화대 깊이보정을 실시하여 장파장 시간차이를 제거하고 진동수-파수 필터링, 예측곱풀기, 시간변화 빛띠흰색화로 잡음을 줄여 교차상관의 오차를 최소화시킨다. 또한 나머지 정적보정후 수직시간차 역보정을 거쳐 속도를 재분석하여 겹쌓기한 결과 저류층을 포함한 반사면들의 향상된 연속성 및 분해능을 확인할 수 있었다.

• 대한치과기공학회지
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• 제25권1호
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• pp.173-185
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• 2003

This study mainly intends to determine the factors for which dental technicians are satisfied with their jobs and how much the resulting job transfer rate is and thus to identify the correlation between them. For these purpose, 200 subjects were sampled out of dental technicians in Seoul and Incheon, and the survey was performed from July 19, 2002 to August 15 (for 25 days) with self-administered questionnaire. Out of all collected questionnaires, 131 pieces(65.5%) were addressed for this study. As for the tools for this study, the structured questionnaire was used with its proven reliability and feasibility, and the contents of questionnaire consisted of 32 questions on the basis of related references. The contents of questionnaire were categorized into 3 sections: General attribute of subjects; Factors for which dental technicians are satisfied with their jobs; and their intention of job transfer. The questionnaire consisted of total 32 questions which included general attribute of subjects(10 questions), factors of their satisfaction with jobs(17 questions) and intention of job transfer(5 questions). The data analysis was processed by computerized system with SPSS(Statistical Package for Social Sciences). Statistical analysis techniques included frequency, percentage, T-test, F-test analysis and regression analysis. As a result of those analyses, the conclusion can be summarized as follows: 1. As a result of analyzing the factors for which the subjects were satisfied with their jobs, it was found that there were significant differences in career and job title out of question items(P<0.001). It was also shown that the factors of subjects' satisfaction averaged 3.43, which was considerably higher value than I expected. It was found that job and management factors were major job satisfaction factors. 2. As a result of analyzing the intention of subjects to decide their job transfer, it was found that there were significant differences in job title and marital status out of question items(P<0.001). It was shown that the total average of the intention of their job transfer amounted to 3.06. It was shown that dental technicians have relatively higher intention of job transfer from their current work place. 3. It was found that there was inverse correlation between the factors of subjects' satisfaction with their jobs and their intention of job transfer(r=-0.490, P<0.05). Likewise, it was also found that there was inverse correlation mostly between the evaluation value for each independent variable region in term of each factor of job satisfaction and the value for the intention of job transfer. In view of these correlations, it was concluded that higher job satisfaction likely led to lower job transfer. 4. As a result of regression analysis so as to determine the influences of job satisfaction factors on the intention of job transfer, it was found that the highest influential factor was management factor. And it was shown that the test values of model were statistically significant and its explanatory power amounted to 54.6%.

• 한국습지학회지
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• 제7권4호
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• pp.97-107
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• 2005

분포형 모형이 개발되어 지면서 이러한 유역의 공간적인 특성을 고려한 정확한 강우 자료와 조밀한 계측망의 요구는 더욱 커지고 있다. 그러나 현실적으로 조밀한 계측망에 의해 측정된 정확한 강우 자료를 얻기는 쉽지 않다. 일반적으로 강우관측소가 적정 밀도를 가지고 유역을 대표 하도록 설치되어 있으나 부족한 실정이고, 설치되어 있더라도 강우의 시 공간적 변동성을 반영하기가 쉽지 않다. 또한 여러 가지 이유로 결측이 되는 경우도 있다. 강우는 측정된 점 관측 자료를 이용해 유역의 평균 강우분포를 추정하게 된다. 따라서 결측 강우자료는 시간의 연속성 측면에서 그 보정이 반드시 필요하며 보정 후 강우자료의 공간적 분포를 산정할 수 있을 것이다. 본 연구에서는 결측 강우량의 보정을 위하여 퍼지-유전자 알고리즘을 이용하였는데 이 방법을 기존의 방법 즉, 산술평균법, 역거리법, 년정상강우량법, 거리-고도비율법과 비교하였다. 보정결과 기존의 방법은 실측의 70~80%의 정확도를 보였으나 퍼지-유전자 알고리즘은 90%정도의 정확도를 보였다. 특히, 민감도 분석 결과를 바탕으로 수평거리와 고도차에 대한 적정 차수를 제안하였다.