• 한국소음진동공학회논문집
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• 제16권5호
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• pp.452-456
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• 2006

The critical speeds and mode shapes are most important to determine the behaviors of rotor in designing rotating machinery. As the capacity and span of turbine-generator increases, the turbine-generator system is composed of many components such as bearings, pedestal, turbine and hood and so on. Also, it is getting flexible and has many critical speeds. Especially, as the characteristics of bearing-pedestal are very complicated, they affect the entire vibration characteristics of turbine-generator system. In this paper, it is observed how to determine the equivalent dynamic stiffness of bearing-pedestal by analytical and experimental method.

• 대한인간공학회지
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• 제32권4호
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• pp.397-403
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• 2013

Objective: This article aims to report the results of ergonomic evaluation of some university laboratories. Background: Laboratory researchers are at risk for musculoskeletal injuries during routine laboratory procedures. However, little attention has paid to the working conditions of laboratory researchers, especially in Korea. Method: A checklist and questionnaire was developed and used to analyze the work conditions of 27 laboratories of chemistry, biology and pharmacy. Results: It was found that glove box, clean bench, and computer workstation are better than microscopy, and fume hood tasks, from ergonomic point of view. Conclusion: No domestic guideline is available for ergonomic intervention of laboratories. Further attention and studies are anticipated to improve the working conditions of laboratories.

• Earthquakes and Structures
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• 제17권1호
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• pp.91-99
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• 2019

Fragility analysis is an effective tool that is frequently used for seismic risk assessment of bridges. There are three different approaches to derive a fragility curve: experimental, empirical and analytical. Both experimental and empirical methods to derive fragility curve are based on past earthquake reports and expert opinions which are not suitable for all bridges. Therefore, analytical fragility analysis becomes important. Nonlinear time history analysis is commonly used which is the most reliable method for determining probabilistic demand models. In this study, to determine the probabilistic demand models of bridges, time history analyses were performed considering both material and geometrical nonlinearities. Serviceability limit states for three different service velocities were considered as a performance goal. Also, support displacements, component yielding and collapse limits were taken into account. Both serviceability and component fragility were derived by using maximum likely hood methods. Finally, the seismic performance and critical members of the bridge were probabilistically determined and clearly presented.

• 한국정밀공학회지
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• 제13권3호
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• pp.80-93
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• 1996

A 2-dimensional FEM/GEM program was developed under the plane strain assumption using linear line elements for analyzing stretch/draw forming operations of an arbitrarily shaped draw-die. FEM formulation adopted a new algorithm for solving force equilibrium as well as non-penetration condition simultaneously. Also, a rigid-viscoplastic material model with Hill's normal anisotropic yield condition and rate-sensitive hardening law is assumed, along with the Coulomb friction law in the contact regions. For the case of numerical divergence at nearly final forming stages, geometric force equilibrium method(GEM) is also introduced. The developed program was tested by simulating the forming processes of cylindrical punch/open die, and the drawing processes of automotive oilpan and hood inner panel in order to verify the usefulness and validity of FEM/GEM formulation. The numerical simulation verified the validity and robustness of developed program.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.160-168
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• 1995

This paper describes computational efforts on the various energy and environmental problems using Patankar's SIMPLE method. The specific problems included in this study are : pollutant and flammable material dispersions in open and confined areas, aerator-induced flow in a lake for DO(dissolved oxygen) concentration, primary clarifier for water and waste water treatment, hood ventilation in workplace, cyclone and LNG combustors and Dow chlorination reactor. A control-volume based finite-difference method is employed together with the power-law scheme. The pressure-velocity coupling is resolved by the use of the revised version of SIMPLE, says SIMPLER and SIMPLEC. The Reynolds stresses are closed using the standard or the RNG $k-{\varepsilon}$ models. Turbulent reaction is modeled using two fast chemistry methods such as eddy breakup and conserved scalar models. Further, a nonequilibrium model is developed for the application of the chlorination process in the Dow reactor. Other important empirical models and physical insights appeared in this study are presented and discussed in a brief note. The computational method developed in this study is considered, in general, as a viable tool for the design and determination of the optimal condition of various engineering system of interest.

• International Journal of Automotive Technology
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• 제1권1호
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• pp.35-41
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• 2000

The crashworthiness of vehicles with finite element methods depends on the geometry modeling and the material properties. The vehicle body structures are generally composed of various members such as frames, stamped panels and deep-drawn parts from sheet metals. In order to ensure the impact characteristics of auto-body structures, the dynamic behavior of sheet metals must be examined to provide the appropriate constitutive relation. In this paper, high strain-rate tensile tests have been carried out with a tension type split Hopkinson bar apparatus specially designed for sheet metals. Experimental results from both static and dynamic tests with the tension split Hopkinson bar apparatus are interpolated to construct the Johnson-Cook and a modified Johnson-Cook equation as the constitutive relation, that should be applied to simulation of the dynamic behavior of auto-body structures. Simulation of auto-body structures has been carried out with an elasto-plastic finite element method with explicit time integration. The stress integration scheme with the plastic predictor-elastic corrector method is adopted in order to accurately keep track of the stress-strain relation for the rate-dependent model accurately. The crashworthiness of the structure with quasi-static constitutive relation is compared to the one with the rate-dependent constitutive model. Numerical simulation has been carried out for frontal frames and a hood of an automobile. Deformed shapes and the Impact energy absorption of the structure are investigated with the variation of the strain rate.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.332-339
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• 2007

As the economy has grown and the main industry in Korea has been changed from secondary industry to tertiary industry, the importance of indoor environment has been a matter of common concern, in which one of the main concerns is to improve the indoor acoustic conditions. However, even though this is required more than before, there are no measures to protect the human being from the noise of electric home appliances. This is owing to the absence of the data about sound power level of electric home appliances. So, we investigate the sound power level of them and analyze the acoustical characteristics of each one. First, we tried to investigate the sound power measurement method of each electric home appliance. After it we test the sound power level of them. From the survey, we can know that the vacuum cleaner is the most noisy electric home appliance, and the refrigerator is the least noisy one. The noise of a range hood is distributed over a wide range frequency. Lastly, we intented to propose the proper method measuring sound power level on each electric home appliance.

• Current Optics and Photonics
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• 제5권2호
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• pp.164-172
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• 2021

In this paper a catadioptric laser-irradiation-precision test system is designed, to achieve a high-precision laser-irradiation-accuracy test. In this system, we adopt the method of imaging the entire target surface at a certain distance to realize the measurement of laser-irradiation precision. The method possesses the advantages of convenient operation, high sensitivity, and good stability. To meet the test accuracy requirement of 100 mm/km (0.01%), the coma, field curvature, and distortion over the entire field of view should be eliminated from the optical system's design. Taking into account the whole length of the tube and the influence of stray light on the structure type, a catadioptric system with a hood added near the primary imaging surface is designed. After optimization using the ZEMAX software, the modulation transfer function (MTF) of the designed optical system is 0.6 at 30 lp/mm, the full-field-of-view distortion is better than 0.18%, and the energy concentration in the 10-㎛-radius surrounding circle reaches about 90%. The illumination-accuracy test results show that the measurement accuracy of the radiation hit rate is better than 50 mm when the test distance is 1 km, which is better than the requirement of 100 mm/km for the laser-irradiation-accuracy test.

• 한국군사과학기술학회지
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• 제11권2호
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• pp.101-108
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• 2008

This study attempted to develop the technology by gaseous ozone for decontaminating building affected by a model of biological weapon agent(Bacillus subtilis spores) instead of Bacillus anthracis spore. The use of ozone is attractive method from a practical point of view of decontamination procedure since it has strong oxidation power but no residue after application. We examined the disinfection efficiency of gaseous ozone to Bacillus subtilis spores which suspension was sprayed on different material surfaces and dried. Three different types of gaseous ozone was applied : dry ozone, dry ozone with humidified air, and water bubbled wet ozone. Dry ozone(1500ppm) failed to achieve any significant inactivation for 2hrs. However, six log reduction of B. subtilis spore was achieved within 30min by 1500ppm of water bubbled wet ozone. This result shows the noticeable inactivation efficiency by gaseous ozone compared with previous studies. Good performance by wet ozone was also found for military material surface.(i.e. : gas mask hood, protective garments, army peinted metal surface).

• 한국주거학회논문집
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• 제20권1호
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• pp.83-90
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• 2009

The present study is a preliminary research improving the dwelling quality of apartment house as a kind of multi-family housing. The purpose of the study is to find out the actual state on characteristics of indoor noise including residents' living in apartment units. The method was field survey consisted of field measurements on equivalent noise level, observation on noise type, and interview on residents' responses. Field survey were carried out in 20 occupied apartment units from January to March 2007. The results are as follows. 1) Averages of indoor noise levels including residents' living noise were measured as $43.9{\sim}62.2\;dB(A)_{Leq5min}$, the average of each house except one was higher than the permissible level, 45 dB(A). 2) The noise types observed were mostly residents' living noise and classified into 'water hammer', 'living equipment noise', 'noise by family', 'hood noise', 'kitchen noise' in own unit, 'walking and talking noise in stairs and corridors', 'noise by neighborhood house', 'noise by the upper story' in building, and outdoor noise. 3) The residents showed slightly non-positive responses at 'noise by the upper story', 'noise by neighborhood house', 'water hammer', and 'noise by family'. Therefore, it is required to plan for preventing deterioration of the dwelling quality by residents' living noise in own unit as well as by neighborhood houses.