• 대한화학회지
• /
• 제56권4호
• /
• pp.431-439
• /
• 2012

Dissipative particle dynamics (DPD) was carried out to study the nucleation and crystal growth process of $CeO_2$ nanoparticles in different alcohol aqueous solutions. The results showed that the nucleation and crystal growth process of $CeO_2$ can be classified into three stages: nuclei growth, crystal stabilization and crystal aggregation except the initial induction stage, which could be reproduced by collecting simulation results after different simulation time. Properly selecting the sizes of $CeO_2$ and water bead was crucial in the simulation system. The influence of alcohol type and content in solutions, and precipitation temperature on the particle dimension were investigated in detail and compared with the experimental results. The consistency between simulation results and experimental data verify that the simulation can reproduce the macroscopic particle aggregation process. The effect of solvent on the nucleation and crystal growth of $CeO_2$ nanoparticles are different at three stages and can not be simply described by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory or nucleation thermodynamics theory. Our work demonstrated that DPD methods can be applied to study nanoparticle forming process.

• 한국정밀공학회지
• /
• 제24권4호
• /
• pp.115-122
• /
• 2007

Recently, remarkable progress has been made in both technology and production of optical elements including aspheric lens. Especially, requirements for machining glass materials have been increasing in terms of limitation on using environment, flexibility of material selection and surface accuracy. In the past, precision optical glass lenses were produced through multiple processes such as grinding and polishing, but mass production of aspheric lenses requiring high accuracy and having complex profile was rather difficult. In such a background, the high-precision optical GMP process was developed with an eye to mass production of precision optical glass parts by molding press. This GMP process can produce with precision and good repeatability special form lenses such as camera, video camera, aspheric lens for laser pickup, $f-\theta$ lens for laser printer and prism, and me glass parts including diffraction grating and V-grooved base. GMP process consist a succession of heating, forming, and cooling stage. In this study, as a fundamental study to develop molds for GMP used in fabrication of glass lens, we conducted a glass lens forming simulation. In prior to, to determine flow characteristics and coefficient of friction, a compression test and a compression farming simulation for PBK40, which is a material of glass lens, were conducted. Finally, using flow stress functions and coefficient of friction, a glass lens forming simulation was conducted.

• 디지털융복합연구
• /
• 제19권9호
• /
• pp.401-409
• /
• 2021

본 연구의 목적은 간호대학생의 가상현실 시뮬레이션 교육 전후의 간호과정 수행능력, 비판적사고성향과 자기효능감의 차이를 파악하여 효과적인 실습교육의 기초자료를 마련하고자 함이다. 2021년 2월부터 4월까지 간호대학생 31명에게 URL설문지를 이용하여 자료를 수집하였고, 수집된 자료는 SPSS 22.0으로 분석하였다. 연구결과, 가상현실 시뮬레이션 교육 후 간호대학생의 간호과정 수행능력(t=-3.776, p=.001), 비판적사고성향(t=-3.608, p=.001), 자기효능감(t=-3.580, p=.001)이 교육 전보다 유의하게 높아졌다. 또한 전공만족도, 임상실습만족도가 높은 집단과 임상실습만족도가 보통인 집단과 학업스트레스가 높은 집단에서도 가상현실 시뮬레이션 교육 후 간호과정 수행능력, 비판적사고성향, 자기효능감이 교육전보다 유의하게 높아졌다. 가상현실 시뮬레이션 교육이 간호대학생의 간호과정 수행능력 향상에 효과적임이 확인되었다. 따라서, 가상현실 시뮬레이션 교육이 간호과정 수행능력 향상을 위한 임상실습 전략으로 활용될 수 있으며, 이를 위해 다양한 시나리오 개발과 후속연구가 이루어져야 할 것이다.

• 한국소성가공학회:학술대회논문집
• /
• 한국소성가공학회 2007년도 춘계학술대회 논문집
• /
• pp.165-169
• /
• 2007

In this study, the factors that have strong relationship with size effects on forging simulation are investigated and then a dimensionless concept is implemented into the forging simulator. The approach is applied to simulating a micro former forging process of which sequence involves a piercing process to make a hole of 0.7mm diameter of the product whose maximum diameter is 3mm. The simulated results are discussed to reveal the size effect in forging simulation.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
• /
• pp.106.2-106.2
• /
• 2010

IGCC (Integrated Gasification Combined Cycle) plants are among the most advanced and effective systems for electric energy generation. From a control perspective, IGCC plants represent a significant challenge: complex reactions, highly integrated control to simultaneously satisfy production, controllability, operability and environmental objectives. While all these requirements seem clearly to demand a multivatiable, model predictive approach, not many applications can be easily found in the literature. This paper describes the IGCC dynamic simulation that is capable of simulating plant startup, shutdown, normal, and abnormal operation and engineering studies. This high fidelity dynamic models contain the detailed process design data to produce realistic responses to process operation and upset. And the simulation is used by engineers to evaluate the transient performance and produce graphical information indicating the response of the process under study conditions.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2009년 춘계학술대회논문집
• /
• pp.355-362
• /
• 2009

Most material of engineering interest undergoes solidification process from liquid to solid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material which governs the physical properties of final product. In this paper, we expand our previous two-dimensional numerical technique to three-dimensional simulation for computing dendritic solidification process with fluid convection. We used Level Contour Reconstruction Method to track the moving liquid-solid interface and Sharp Interface Technique to correctly implement phase changing boundary condition. Three-dimensional results showed clear difference compared to two-dimensional simulation on tip growth rate and velocity.

• 한국정밀공학회지
• /
• 제28권1호
• /
• pp.11-18
• /
• 2011

A worm screw is widely used in a geared motor unit for motion conversion from rotation to linear. For mass production of a high quality worm, the current rolling process is substituted with the milling process. Since the milling process enables the integration of all operations of worm manufacturing on a CNC(Computer Numerical Control) lathe, productivity can be remarkably improved. In this study, the tooling system for side milling on a CNC lathe to improve machinability is developed. However, the cutting tool-workpiece interference is important factors to be considered for producing high quality worms. For adaptability of various worms machining, the tool-workpiece interference simulation system based on a tool-tip trajectory model is developed. The developed simulation system is verified through several kinds of worms and experimental results.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2002년도 춘계학술대회 논문집
• /
• pp.551-554
• /
• 2002

The paper discusses new approach for machining operation simulation using enhanced Z map algorithm. To extract the required geometric information from NC code, suggested algorithm uses supersampling method to enhance the efficiency of a simulation process. By executing redundant Boolean operations in a grid cell and averaging down calculated data, presented algorithm can accurately represent material removal volume though tool swept volume is negligibly small. Supersampling method is the most common form of antialiasing and usually used with polygon mesh rendering in computer graphics. The key advantage of enhanced Z map model is that the data structure is same with conventional Z map model, though it can acquire higher accuracy and reliability with same or lower computation time. By simulating machining operation efficiently, this system can be used to improve the reliability and efficiency of NC machining process as well as the quality of the final product.

• 소성∙가공
• /
• 제15권1호
• /
• pp.15-20
• /
• 2006

The rapid thermal response (RTR) molding is a novel process developed to raise the temperature of mold surface rapidly to the polymer melt temperature prior to the injection stage and then cool rapidly to the ejection temperature. The resulting filling process is achieved inside a hot mold cavity by prohibiting formation of frozen layer so as to enable thin wall injection molding without filling difficulty. The present work covers flow simulation of thin wall injection molding using the RTR molding process. In order to take into account the effects of thermal boundary conditions of the RTR mold, coupled analysis with transient heat transfer simulation is suggested and compared with conventional isothermal analysis. The proposed coupled simulation approach based on solid elements provides reliable thin wall flow estimation for both the conventional molding and the RTR molding processes.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
• /
• pp.156-159
• /
• 1996

An adaptive predictive control for steam-reforming plant which consist of a steam-gas reformer and a waste heat steam-boiler was studied by using MIMO bilinear model. The simulation experiments of the process identification were performed by using linear and bilinear models. From the simulation results it was found that the bilinear model represented the dynamic behavior of a steam-reforming plant very well. ARMA model was used in the process identification and the adaptive predictive control. To verify the performance and effectiveness of the adaptive predictive controller proposed in this study the simulation results of steam-reforming plant control based on bilinear model were compared to those of linear model. The simulation results showed that the adaptive predictive controller based on bilinear model provides better performance than those of linear model.