• 한국정밀공학회지
• /
• 제10권3호
• /
• pp.198-204
• /
• 1993

The study is concerned with finite element analysis and design of axisymmetric deep drawing by local heating. When the bottom shape of a cup is not flat but in complex-shaped, i.e., hemispherical, the cup cannot be drawn in one or two processes in the conventional deep drawing process and the limit drawing ratio is limited as well. By introducing local heating selectively with regards to the heating position, the formability of the sheet metal can be greatly increased with the reduced number of processes. In the Process analysisthe rigid- viscoplastic finite element method is employed and the temperature effect is incorporated. Bishop's step-wise decoupled method is employed to analyze the thermomechanical interaction between deformation and heat transfer. Axisymmetric deep drawing of a hemisphere-bottomed cup has been analyzed for various combinations of heat application in the punch and the die. At the first stage of deep drawing stretch forming is practically carried out by firmly pressing the blankholder with the punch and the die heated at various levels of temperature. Then at the second stage the same cup is drawn for the saame or different combination of temperature. From the computation, it has thus been shown that the fromability of a cup is greatly increased in two-stage deep drawing with increased limet drawing ratio.

• Journal of the Korean Wood Science and Technology
• /
• 제46권4호
• /
• pp.380-392
• /
• 2018

The importance of polysaccharides is increasing globally due to their role as a significant source of dietary prebiotics in the human diet. In the present study, in order to maximize the yield of crude polysaccharides from Pinus densiflora, response surface methodology (RSM) was used to optimize a two-stage extraction process consisting of steam explosion and water extraction. Three independent main variables, namely, the severity factor (Ro) for the steam explosion process, the water extraction temperature ($^{\circ}C$), and the ratio of water to raw material (v/w), were studied with respect to prebiotic sugar content. A Box-Behnken design was created on the basis of the results of these single-factor tests. The experimental data were fitted to a second-order polynomial equation for multiple regression analysis and examined using the appropriate statistical methods. The data showed that both the severity factor (Ro) and the ratio of water to material (v/w) had significant effects on the prebiotic sugar content. The optimal conditions for the two-stage process were as follows: a severity factor (Ro) of 3.86, a water extraction temperature of $89.66^{\circ}C$, and a ratio of water to material (v/w) of 39.20. Under these conditions, the prebiotic sugar content in the extract was 332.45 mg/g.

• 한국산학기술학회논문지
• /
• 제10권11호
• /
• pp.3253-3259
• /
• 2009

본 연구에서는 프로판이 주성분인 혼합냉매를 사용하여 프로세스의 온도를 $-20^{\circ}C$까지 낮추는 증기 재 압축을 활용한 냉동사이클에 대한 전산모사를 수행하였다. 냉매의 공급온도는 프로세스와의 온도차를 $10^{\circ}C$로 가정하여 $-30^{\circ}C$로 정하였다. 전산모사를 위한 열역학 모델식으로는 Peng-Robinson 상태방정식을 적용하였으며, 냉매 혼합물의 각 성분에 대한 순수성분의 온도에 따른 증기압을 잘 추산하기 위해서 새로운 Alpha function을 이용하였다. 한편, 냉매 혼합물의 각각의 이성분계 실험 데이터를 잘 추산하기 위한 혼합규칙으로는 van der Waals 혼합규칙을 사용하였다. 한편 전체공정의 전산모사를 위해서 Invensys사의 PRO/II with PROVISION 8.2를 활용하였으며, 압축기의 소요동력을 최소화시키기 위해서 2단 압축공정을 사용하였으며. 첫 번째 압축기 후단의 최적 압력은 6bar이며 이때 총 소요동력은 755.7kW임을 알 수 있었다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2003년도 ICCAS
• /
• pp.2606-2611
• /
• 2003

Comprehensive study on the control system design for a RTP process has been conducted. The purpose of the control system is to maintain maximum temperature uniformity across the silicon wafer achieving precise tracking for various reference trajectories. The study has been carried out in two stages: thermal balance modeling on the basis of a semi-empirical radiation model, and optimal iterative learning controller design on the basis of a linear state space model. First, we found through steady state radiation modeling that the fourth power of wafer temperatures, lamp powers, and the fourth power of chamber wall temperature are related by an emissivity-independent linear equation. Next, for control of the MIMO system, a state space modeland LQG-based two-stage batch control technique was derived and employed to reduce the heavy computational demand in the original two-stage batch control technique. By accommodating the first result, a linear state space model for the controller design was identified between the lamp powers and the fourth power of wafer temperatures as inputs and outputs, respectively. The control system was applied to an experimental RTP equipment. As a consequence, great uniformity improvement could be attained over the entire time horizon compared to the original multi-loop PID control. In addition, controller implementation was standardized and facilitated by completely eliminating the tedious and lengthy control tuning trial.

• Smart Structures and Systems
• /
• 제15권3호
• /
• pp.665-682
• /
• 2015

Structural identification or St-Id is 'the parametric correlation of structural response characteristics predicted by a mathematical model with analogous characteristics derived from experimental measurements'. This paper describes a St-Id exercise on Humber Bridge that adopted a novel two-stage approach to first calibrate and then validate a mathematical model. This model was then used to predict effects of wind and temperature loads on global static deformation that would be practically impossible to observe. The first stage of the process was an ambient vibration survey in 2008 that used operational modal analysis to estimate a set of modes classified as vertical, torsional or lateral. In the more recent second stage a finite element model (FEM) was developed with an appropriate level of refinement to provide a corresponding set of modal properties. A series of manual adjustments to modal parameters such as cable tension and bearing stiffness resulted in a FEM that produced excellent correspondence for vertical and torsional modes, along with correspondence for the lower frequency lateral modes. In the third stage traffic, wind and temperature data along with deformation measurements from a sparse structural health monitoring system installed in 2011 were compared with equivalent predictions from the partially validated FEM. The match of static response between FEM and SHM data proved good enough for the FEM to be used to predict the un-measurable global deformed shape of the bridge due to vehicle and temperature effects but the FEM had limited capability to reproduce static effects of wind. In addition the FEM was used to show internal forces due to a heavy vehicle to to estimate the worst-case bearing movements under extreme combinations of wind, traffic and temperature loads. The paper shows that in this case, but with limitations, such a two-stage FEM calibration/validation process can be an effective tool for performance prognosis.

• Journal of Mechanical Science and Technology
• /
• 제16권9호
• /
• pp.1112-1120
• /
• 2002

Numerical investigations on air staging and fuel staging were carried out with a newly designed coaxial cyclone combustor, which uses the method of two stage coal combustion composed of pre-combustor and main combustor. The pre-combustor with a high air/fuel ratio is designed to supply gas at high temperature to the main combustor. To avoid local high temperature region in this process, secondary air is injected in the downstream. Together with the burned gas supplied from the pre-combustor and the preheated air directly injected into main combustor, coals supplied through the main burner react rapidly at a low air/fuel ratio. Strong swirling motion of cyclone combustor keeps the wall temperature high, which makes slagging combustion possible. Alaska, US coal is used for calculations. Predictions were made for various coal flow rates in the main combustor for fuel staging and for the various flow rate of secondary air in the pre-combustor for air staging. In-scattering angles are also chosen as a variable to increase residence times of coal particles. Temperature fields and particle trajectories for various conditions are described. Predicted temperature variations at the wall of the combustor are compared with corresponding experimental data and show a similar trend. The in-scattering angle of 20° is recommended to increase the combustion efficiency in the main chamber.

• 한국산학기술학회논문지
• /
• 제16권7호
• /
• pp.4375-4380
• /
• 2015

선박용 디젤엔진 부품인 블랭크 단조품 가열 시 생산성 및 품질을 향상시키기 위하여 새로운 가열공정을 제안하였다. 본 연구에서는 새로운 블랭크 가열공정을 평가하고 가열공정 설계기준을 정립하기 위하여 수치해석 전용 프로그램인 ANSYS를 사용하여 재료의 비선형을 고려한 온도분포, 열응력 해석을 수행하였다. 가열조건은 승온단계와 유지단계로 구성되어 총 32시간이며 가열 시 시간경과에 따른 블랭크 내 외부의 온도분포와 열응력 변화를 평가하였다. 그 결과 가열 시 승온단계에서 블랭크 내 외부 온도차는 시간이 경과함에 따라 점차 증가하여 최종 승온단계에서 최대 온도차가 발생하나 유지단계에서 온도차는 점진적으로 감소하는 반면에 가열이 시작되어 10시간 경과 후 블랭크 내부에는 최대 등가응력 $12.5kg/mm^2$가 발생한다는 것을 알 수 있다. 따라서 단조품 가열공정을 설계함에 있어서 가열 후 10시간 경과 시, 즉 노내 온도 $650^{\circ}C$에서 블랭크 내 외부 온도차는 $150^{\circ}C$이내가 되도록 관리해야 한다.

• 열처리공학회지
• /
• 제7권2호
• /
• pp.103-110
• /
• 1994

It is well-known that the analysis of temperature distribution is substantilly important in optimal design of quenching process. The unsteady state temperature gradients generated during the quenching process were numerically calculated by the Finite Element Method(F. E. M.). Formulations of F. E. M. based weighted residural method were presented for the analysis of the two dimensional heat conduction problem. In the process of calculation, the temperature dependency of physical properties of the material was in consideration. At early stage of the quenching process, the abrupt temperature gradient has been shown in the surface of the carbon steel(SM45C).

• 한국세라믹학회지
• /
• 제42권12호
• /
• pp.865-871
• /
• 2005

Submicron thick solid electrolyte membrane is essential to the implementation of low temperature solid oxide fuel cell, and, therefore, development of new electrode structures is necessary for the submicron thick solid electrolyte deposition while providing functions as current collector and fuel transport channel. In this research, a nickel membrane with multi-stage nano hole array has been produced via modified two step replication process. The obtained membrane has practical size of 12mm diameter and $50{\mu}m$ thickness. The multi-stage nature provides 20nm pores on one side and 200nm on the other side. The 20nm side provides catalyst layer and $30\~40\%$ planar porosity was measured. The successful deposition of submicron thick yttria stabilized zirconia membrane on the substrate shows the possibility of achieving a low temperature solid oxide fuel cell.

• 대한기계학회논문집B
• /
• 제33권1호
• /
• pp.17-27
• /
• 2009

Water jet impingement cooling is used to remove heat from high-temperature surfaces such as hot steel plates in the steel manufacturing process (thermo-mechanical cooling process; TMCP). In those processes, uniform cooling is the most critical factor to ensure high strength steel and good quality. In this study, experiments are performed to measure the heat transfer coefficient together with the inverse heat conduction problem (IHCP) analysis for a plate cooled by planar water jet. In the inverse heat transfer analysis, spatial and temporal variations of heat transfer coefficient, with no information regarding its functional form, are determined by employing the conjugate gradient method with an adjoint problem. To estimate the two dimensional distribution of heat transfer coefficient and heat flux for planar waterjet cooling, eight thermo-couple are installed inside the plate. The results show that heat transfer coefficient is approximately uniform in the span-wise direction in the early stage of cooling. In the later stage where the forced-convection effect is important, the heat transfer coefficient becomes larger in the edge region. The surface temperature vs. heat flux characteristics are also investigated for the entire boiling regimes. In addition, the heat transfer rate for the two different plate geometries are compared at the same Reynolds number.