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In recent times, turbomolecular pumps (TMPs) have been used frequently to generate and maintain high and clean vacuum. Because of the high-speed rotation of the rotor, its structural safety should be treated as the first design concern. This paper presents the structural analysis and optimization of rotor blades of a TMP. To increase the numerical efficiency in the finite element modeling and analysis, the P-method provided in Pro/ENGINEER was used for simulation. The structural responses for several types of rotor blades were investigated, and the effects of the blade angle, blade length, and round size are thoroughly studied for each type of TMP blade. In addition, structural optimization to reduce and even the maximum stress at each stage of the TMP by changing the size of rounds between the blade and the hub was performed very successfully by using the P-method.

This study is aimed at representing efficient buckling analysis method by analyzing the buckling behavior and the buckling pressure of filament-wound cylindrical shell. First, finite element analysis was conducted to find the buckling pressure and the buckling behavior on the stacking angles of [±30/90]FW, [±45/90]FW and [±60/90]FW. The buckling formula (ASME 2007, NASA SP-8007) was employed to find the buckling pressure. These results were compared and verified through hydrostatic pressure buckling experiments. Second, the values of buckling formula and buckling pressure values of finite element analysis were compared, while the stacking angle was made to change by 5 degrees from 20 to 70 degrees. According to the conducted finite element analysis, stacking property showed the safety factor of about 1.0 at the buckling pressure values of such filament-wound stacking angles as [±30/90]FW, [±45/90]FW, and [±60/90]FW. ASME 2007 buckling formula showed the safety factor ranging from 1.84 to 2.76. On comparison, the values of the NASA SP-8007 formula showed relatively low safety factors ranging from 1.2 to 1.45. When it comes to the result to which various stacking angles from 20 to 70 degrees were applied, the values to which an equivalent material property was applied showed safety factors ranging from 0.8 to 0.97 while the ASME 2007 and the NASA SP-8007 buckling formula values showed safety factors ranging from 1.7 to 2.9 and 0.8 to 1.4 respectively. Based on the result above, the ASME 2007 formula, a simplified version of the NASA SP-8007 formula is regarded as a buckling formula in which more reliable safety factors are considered.

The objective of this paper is to predict the buckling pressure of a composite cylindrical shell using buckling formulas (ASME 2007, NASA SP 8007) and finite element analysis. The model in this study uses a stacking angle of [0/90]12t and USN 125 composite material. All specimens were made using a prepreg method. First, finite element analysis was conducted, and the results were verified through comparison with the hydrostatic pressure buckling experiment results. Second, the values obtained from the buckling formula and the buckling pressure values obtained from the finite element analysis were compared as the stacking angle was changed in increments from to . The linear and nonlinear results of the finite element analysis were consistent with the results of the experiment, with a safety factor of 0.85-1. Based on the above result, the ASME 2007 formula, a simplified version of the NASA SP-8007 formula, is regarded as a buckling formula that provides a reliable safety factor.

*Department of Precision Mechanical Engineering, Pusan National University, Busan, Korea**Pusan Educational Center for Computer Aided Machine Design, Pusan National University, Busan, KoreaKEY WORDS: Windpower system structure 풍력시스템 구조물, Composite shell 복합재 셸, Ply orientation 적층방향, Lamination pattern 적층순서, FEM 유한 요소법ABSTRACT: The purpose of this study was to develop a buckling analysis te chnique for a windpower system structure under environmental loadings (hydrostatic pressure) using FEM. We analyzed an isotr opic material and composite material and made a comparison usin g buckling pressure formulas. First, finite element analyses for an isotro pic material (SC410) were performed to obtain the variation of buckling pressure for the number of elements and boundary conditions in a pressure-sh ell model, and the numerical results were compared with those o f existing empirical formulas. Then, additional finite element analyses ba sed on the results of the isotropic material (SC410) were perfo rmed to determine the optimum lamination angle and pattern for a composite material (URN300). The results of the FE analyses for the composite mater ial were also compared with those of existing empirical formulas. The ply ori entations (lamination angles) used in the FE analyses were 0 °, 15°, 30°, 45°, 60°, 75°, and . The lamination patterns in the FE analyses were and . T he lamination pattern was assumed to be the equivalent model of . The results of the FE analyses for the isotropic material (SC410) indicated that the optimal values for the number of elements and the bou ndary conditions were 6000 and both simply supported, respectively. The results of the FE analyses for the composite material (URN300) showed t hat the optimal ply orientation was 60°~75°교신저자 홍철현: 부산광역시 금정구 장전동 산 30, 051-510-1665, chhong@pusan.ac.kr

The main objective of this paper is to investigate the validity of the finite element method (FEM) on the buckling and post-buckling behavior of laminated composite cylindrical shells that have been subjected to an external hydrostatic pressure. In addition, a buckling pressure equation that is based on the ASME and American Bureau of Shipping (ABS) bucking equation and customized to USN125 composite material is also presented. In order to determine an application for composite material under external hydrostatic pressure, material tests were conducted for carbon–epoxy ply composite URN300 and USN125. The strength and stiffness of the fiber and resin of two composites were determined. Cylindrical panel tests were performed to investigate the behavior of post-buckling under vertical line load. Finite element analyses, using ABAQUS 6.6 code, have been performed, using a linear buckling model based on the solution of the eigenvalue problem, and a non-linear model based on the arc-length method for various cases. Furthermore, an external hydrostatic pressure test was conducted to verify numerical analysis. These results were compared with the previous results obtained by FEM on the buckling. Difference between FEM and the test result is expected to be approximately 18%.

Generally, an automobile has about 10 motors for actuators that are equipped with a cooling pan, air-conditioner, and door lock system. The shape of the motor-case is directly related to the noise and vibration of the components, so various forming processes such as deep-drawing, multi-step, and multi-forming, were developed to get higher accuracy and productivity. The multi-forming process is used in this study because it has the best productivity compared with the other forming methods. The simulation technique of motor-case forming was developed to reduce the developing time and trial-error. The manufacturing processes of a motor-case consist of plate blanking, forming, and sizing. This study is focused on the core design of the multi-forming process. The blanked plate and forming dies are modeled to two- and three-dimension and analyzed by the finite element method using a commercial software DEFORM which is based on the elastic–plastic finite element theory. Two kinds of core, a circle and an ellipse, have been designed. Because of the springback effect, the roundness of the elliptic core is better than that of the circular core. The same rule is applied to the diameter ranges (20–40 mm) and yield strength levels (175–240 MPa) of low carbon steel.

Wings for the defense industry such as fighters, missiles, and rockets should show no deformation or damage on the structure. The structures of existing wings had holes for weight reduction. The plates and frames were fixed with rivets or screws, which limited the weight reduction possible. In this study, an improvement was made in jointing methods through EB welding and laser welding. Welding strength was measured through tension testing. In addition, finite element analysis was performed for the welding process so as to deduce the optimum welding condition.