Accurate Mold Filling Simulation using Cut Cell in the Cartesian Grid System

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 기계항공공학부, 2018. 2. 김규홍.In the field of casting flow analysis, despite good quality analysis results it is difficult to apply body-fitted grid. This is on account of difficulties in grid generation and efficiency. Cartesian grid based numerical techniques for casting flow have been developed to address this issue. However, the Cartesian grid cannot be used to accurately represent complex shapes with many sloped and curved surfaces. A step grid that does not match the precise geometry leads to unsound results in flow analysis, such as loss of momentum during flow and false filling pattern. In this study, a Cut Cell method based on Partial Cell Treatment is applied to the casting flow analysis in the Cartesian grid system. The newly developed numerical method is then verified in comparison with water model experiments and practical casting experiments. The conventional and Cut Cell methods of using the Cartesian grid are also compared. The numerical results of the two methods are compared according to the number of grids, and it is confirmed that the increased number of grids cannot solve the disadvantages of the Cartesian grid. In addition, the practical castings are analyzed for each casting process. It is confirmed that the numerical error in the conventional method can be rectified by the Cut Cell method. Finally, the computational time of the conventional method and the Cut Cell method are compared. In conclusion, it is confirmed more accurate Cartesian grid based casting flow analysis is possible by using Cut Cell method without Body-Fitted Coordinate. However the Cut Cell method involves a long calculation time. There may be no significant difference between the two methods depending on the shape of castings or the casting process. Therefore, in the analysis of casting flow, it is necessary to selectively use the conventional Cartesian grid method or the Cut Cell method considering the accuracy and efficiency of analysis.1. Introduction 1 1.1 Casting 1 1.1.1 Casting process 1 1.1.2 Mold filling simulation 6 1.2 Cartesian cut cell approach 10 1.3 Research objectives 12 2. Numerical method 14 2.1 Casting flow analysis 14 2.1.1 Characteristics of molten metal 14 2.1.2 Governing equations 16 2.2 Cut Cell method 20 2.2.1 Partial cell treatment 20 2.2.2 Governing equations 22 3. Experimental and numerical validations 23 3.1 Experimental validation 23 3.1.1 Water model experiment 23 3.1.2 Comparison of experiments with numerical results 26 3.1.3 Comparison with numerical results of the BFC system 48 3.2 Comparison with experimental results by Mampaey 52 3.3 Numerical validation 57 3.3.1 Comparison of energy loss rate by the number of grids 58 3.3.2 Effects of pouring rate change 61 3.3.3 Effects of width reduction 64 4. Simulation results and analysis 68 4.1 Comparison of results according to the number of grids 68 4.1.1 Model with a sloped ingate 69 4.1.2 Model with a circled mold cavity 77 4.2 Application of products by casting process 85 4.2.1 Sand casting 85 4.2.2 Gravity die casting 91 4.2.3 High pressure die casting 97 4.2.4 Low pressure die casting 107 4.3 Computational time 112 5. Conclusion 114 Reference 118 국문초록 124Docto

PLIC-VOF 기법을 이용한 다상 유동 해석

학위논문(석사)--서울대학교 대학원 :기계항공공학부,2004.Maste

DENTAL CARE FOR HANDICAPPED PATIENTS AT DAY SURGERY CENTER:A CASE REPORT

심신장애자, 심한 불안과 공포가 있는 경우, 너무 어려서 의사소통이 되지 않는 환자 등, 일반적인 행동조절방법이 가능하지 않은 경우에 전신마취를 고려하게 된다. 이런 환자들은 대부분 소아 치과에서 치료하게 되므로 소아치과의사의 역할이 중요하다. 전신마취하에 시행되는 치과치료를 고려할 때, 환자의 전신적 건강상태, 환자의 현재 구강 형태, 필요한 치과치료의 종류, 책임감 있는 보호자의 유무에 따라서 입원없이 행해지는 외래환자수술을 고려할 수 있다. 전신마취하에 치과치료를 시행하고자 할 때, 치과의사나 보호자의 편의를 위해서 사용되어져서는 안되며, 적절한 환자 선택하에 시행된다면, 보통의 방법으로 치과치료를 받기 어려운 장애아동에게 유리한 치료가 될 수 있다. The dentists often encouter a child who can not be treated with traditional behavior management technique. Mentally or physically handicapped child could receive proper dental care under general anesthesia. General anesthesia for dental care can be done in an outpatient surgery or inpatient surgery depending on the patient. In outpatient surgery, the patient is admitted and discharged the same day. Postoperative care and discharge procedure are abbreviated. Advantages of outpatient surgery are much less emotional disturbance of patients, reduced risk of nosocomial infection and less cost of treatment. A case of a physically handicapped patient treated under general anesthesia at Day Surgery Center is presented and the procedure and patient selection of outpatient surgery as well as its limitation is reviewed in this paper