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Optimal Design of Head Expander for a Lightweight and High Frequency Vibration Shaker
정호승,조종래 한국정밀공학회 2016 International Journal of Precision Engineering and Vol.17 No.7
Vibration testing requires the head expander to interface with both the test component and vibration shaker. At times, head expanders have resonant frequencies over the frequency range of interest. The moving mass will also have an influence on the shakers thrust ability during vibration testing. In order to ensure a successful vibration test, it is necessary to observe the resonant frequency and mass of the head expander. The aim of this study is to optimize the shape and size of the head expander with a lightweight and an improved resonant frequency. This was achieved using a FE modal analysis and design of experiments (DOE). Firstly, the vibration characteristics, such as the resonant frequencies and mode shapes of the baseline model were estimated using a FE modal analysis. In order to validate the FE modal analysis, a modal test was performed and the test results were then compared with those from the FE analysis. Secondly, three shapes of head expander were suggested to select the geometry with the best vibration characteristics, and the design variables of the head expander were defined. The vibration characteristics of the three geometries and their design variables were assessed in terms of their weights and resonant frequencies. Finally, optimization process was performed to find a minimum mass within the target frequency and diameter of platform plate. The coefficients from the regression equation for the objective function were calculated to provide optimized data for the vibration shaker head expander.
Bent Tube Design used in a High Temperature Heat Exchanger using a FE Analysis and RSM
정호승,조종래 한국정밀공학회 2013 International Journal of Precision Engineering and Vol.14 No.12
High temperature heat exchanger technology is important with respect to improving the performance of power and propulsion system. This study proposes and optimizes a new heat exchanger tube shape by reducing the size of the tube bundle and improving structural characteristics such as the thermal stress and resonance. Various tube shapes were proposed and a FE analysis was performed to select the tube with the best structural characteristics. The response surface methodology was employed to establish mathematical approximation models using the results of design of experiments as a function of the geometric parameters of the selected tube. Also,the main effects of various geometric parameters on the selected tube were investigated. The geometric parameters such as offset length, the straight distance between one end and the other end of the tube, the tube length in a straight portion and fillet radius were assessed. The geometric parameters of the selected tube were optimized using the RSM and multi-objective genetic algorithm. We suggested the calculated coefficients of the regression equation for the objective function, optimized data, and an optimization procedure of the tube. The presented findings could be used in the preliminary design of the heat exchanger used in high temperature.
정호승,박영규,류성엽,정오 대한위암학회 2015 Journal of gastric cancer Vol.15 No.3
Purpose: To compare the surgical outcomes of laparoscopic total gastrectomy between elderly and non-elderly patients. Materials and Methods: Between 2008 and 2015, a total of 273 patients undergoing laparoscopic total gastrectomy for gastric carcinoma were divided into two age groups: elderly (≥70 years, n=71) vs. non-elderly (<70 years, n=172). Postoperative outcomes, including length of hospital stay, morbidity, and mortality were compared between the groups. Results: The elderly group showed a significantly higher rate of comorbidities and American Society of Anesthesiologists scores than those in the non-elderly group. No significant differences were found with respect to lymphadenectomy or combined organ resection between the groups. After surgery, the elderly group showed a significantly higher incidence of grade III and above complications than the non-elderly group (15.5% vs. 4.1%, P=0.003). Among the complications, anastomosis leakage was significantly more common in the elderly group (9.9% vs. 2.9%, P=0.044). Univariate and multivariate analyses showed that old age (≥70 years) was an independent risk factor (odds ratio=4.42, 95% confidence interval=1.50~13.01) for postoperative complications of grade III and above. Conclusions: Elderly patients are more vulnerable to grade III and above complications after laparoscopic total gastrectomy than non-elderly patients. Great care should be taken to prevent and monitor the development of anastomosis leakage in elderly patients after laparoscopic total gastrectomy.