• Journal of the Korean Society for Precision Engineering
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• v.29 no.10
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• pp.1056-1061
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• 2012

FEM analysis is essential to shorten the development time and reduce the cost for developing high-performance machine tools. Mount joint parts play important role to ensure static and dynamic stability of machine tools. This paper suggests a computational modeling of mount joint part of machine tools. MATRIX27 element of ANSYS is adopted to model mount joint parts. MATRIX27 allows the definition of stiffness and damping matrices in matrix form. The matrix is assumed to relate two nodes, each with six degrees of freedom per node. Stiffness and damping values of commercial mount products are measured to build a database for FEM analysis. Jack mounts with rubber pad are exemplified in this paper. The database extracted from the experiments is also used to estimate of stiffness and damping of untested mounts. FEM analysis of machine tools system with the suggested mount computational model is performed. Static and dynamic results prove the feasibility of the suggested mount model.

• Journal of Advanced Marine Engineering and Technology
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• v.16 no.5
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• pp.60-66
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• 1992

In most cases a structure consists of the assembly of some substructures, we assemble them with various joints, and the structure is fixed to a foundation through mounts. In case of the structure with rigid joints like welding, the Finite Element Mothod could be easily used to analyize the structure's characteristics, but in case of the structure with elastic joints like bolts or rivets, it might be difficult to analyize it by taking account of joint's rigidities, with the conventional method. This paper proposes the method to identify the joint rigidities by the Sensitive Analysis Method and the Optimization Techniques. And the proposed method applied to identify the rigidities of 4 bolts to combine 2 plates(500mm long, 100mm wide, 3.15mm thich). The analized results were well coincident with the experimental results. To confirm the reliability 0 the rigidities identified, another trial was done for the stucture to combine other 2 plates with same joints. The results were good too. This paper is proposin the identifying method of the joint rigidity of a structure, and it could be used for the data base of the joint rigidity and for the guidance to select joint stiffness.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.568-571
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• 1997

The overall aim of this paper is to determine coupling loss factor using loss factor and structural loss factor. For this purpose, two kinds of loss factor were adopted. One is loss factor of each sub structure, another is structural loss factor based on the complex welded or assembled structure. Using these two parameters, it is possible to derive the coupling loss factor which represent characteristic condition of SEA theory. Coupling loss factor of conjunction in complex structure was expressed as power balance equation. The derived equation for a coupling loss factor has been simplified on the assumption of one directional power flow between two sub structures. Using these conditions, it is possible to find the coupling loss factor equation. The comparison between theory of power transmission on conjunction and above equation, show a good agreement in simple beam structure. To check the effectiveness of above equation, it was adopted rotary compressor. Rotary compressor has three main conjunctions between shell and internal vibration part. This equation was applied to find out the optimum welding point with respect to reduce the noise propagation. It shows the effective tool to evaluate the coupling loss factor in complex structure.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.9
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• pp.899-905
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• 2009

Most supersonic-flow test facility has axisymmetric nozzles or two-dimensional symmetric nozzles. Compared to these nozzles, a two-dimensional asymmetric nozzle has advantages of reducing low cost for various Mach number testing and undesirable flow structure such as shock wave reflection because the nozzle part can be directly connected to the test section part in this type of nozzle. The two-dimensional asymmetric nozzle, which was Mach number 2, was designed for supersonic combustion experiment. And it was verified with the numerical analysis and visualization of Mach wave. This study suggested the practical method for design and verification of supersonic two dimensional asymmetric nozzles.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.4
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• pp.58-66
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• 1990

A series of test was performed measuring the failure strength and failure mode of Gr/Pi, $[0^{\circ}/45^{\circ}/90^{\circ}/-45^{\circ}]_s$ laminate containing a single pin loaded hole. The finite element method is applied to calculate the stress distribution in the laminates, then the failure load and the failure mode were predicted by means of the characteristic length. 12 different geometric variations were developed to analyze the effects of the ratio of specimen width to hole diameter (W/d) and ratio of edge distance to hole diameter (L/d). X-Ray of NDE methods were utilized in finding out the initial defects, damage and the fracture mechanism, and SEM(Scanning Electron Microscopes) was used the evaluation of the fracture mechanism and crack propagation around hole under tension pin loading. $[0^{\circ}/45^{\circ}/90^{\circ}/-45^{\circ}]_s$ laminate are found to be most sensitive to W/d but not so influenced by L/d. The failure mode and tensile strength predicted by the model show agreement with experiment data for pin loading bolted jointed test except range of $L/d{\leqq}3$.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.2
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• pp.125-135
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• 2009

Statement of problem: Loosening or fracture of the abutment screw is one of the common problems related to the dental implant. Generally, in order to make the screw joint stable, the preload generated by tightening torque needs to be increased within the elastic limit of the screw. However, additional tensile forces can produce the plastic deformation of abutment screw when functional loads are superimposed on preload stresses, and they can elicit loosening or fracture of the abutment screw. Therefore, it is necessary to find the optimum tightening torque that maximizes a fatigue life and simultaneously offer a reasonable degree of protection against loosening. Purpose: The purpose of this study was to present the influence of tightening torque on the implant-abutment screw joint stability with the 3 dimensional finite element analysis. Material and methods: In this study, the finite element model of the implant system with external butt joint connection was designed and verified by comparison with additional theoretical and experimental results. Four different amount of tightening torques(10, 20, 30 and 40 Ncm) and the external loading(250 N, $30^{\circ}$) were applied to the model, and the equivalent stress distributions and the gap distances were calculated according to each tightening torque and the result was analyzed. Results: Within the limitation of this study, the following results were drawn; 1) There was the proportional relation between the tightening torque and the preload. 2) In case of applying only the tightening torque, the maximum stress was found at the screw neck. 3) The maximum stress was also shown at the screw neck under the external loading condition. However in case of applying 10 Ncm tightening torque, it was found at the undersurface of the screw head. 4) The joint opening was observed under the external loading in case of applying 10 Ncm and 20 Ncm of tightening torque. 5) When the tightening torque was applied at 40 Ncm, under the external loading the maximum stress exceeded the allowable stress value of the titanium alloy. Conclusion: Implant abutment screw must have a proper tightening torque that will be able to maintain joint stability of fixture and abutment.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.857-862
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• 2014

The research on a thermal stress control layer (TSCL) begins to undertake to reduce residual stress and strain in the vicinity of the joined region between the hardfacing layer and the base part. The goal of this paper is to estimate the material combination and the thickness of TSCL for the Stellite21 hardfaced STD61 hot working tool steel via three-dimensional finite element analysis (FEA). TSCL is created by the combination of Stellite21 and STD61. The thickness of TSCL ranges from 0.5 mm to 1.5 mm. The influence of the material combination and the thickness of TSCL on temperature, thermal stress and thermal strain distributions of the hardfaced part have been investigated. The results of the investigation have been revealed that a proper material combination of TSCL is Stellite21 of 50 % and STD61 of 50 %, and its appropriate thickness is 1.0 mm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.731-738
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• 2012

In this study, the evaluation of the aerodynamic characteristics of the NREL Phase VI Rotor System has been performed, for the 7 m/s upwind case using commercial FEA and CFD tools which are ANSYS Mechanical 12.1 and CFX 12.1. The initial operating conditions of the rotor blade include a $3^{\circ}$ tip pitch angle. A numerical simulation was carried out on only the rotor parts, excluding the tower structure based on the equivalent stiffness model, to consider the aeroelastic effect for the numerical simulation using the loosely coupled 2-way fluid-structure interaction method. The blade root bending moment was monitored in real time to obtain reasonable results. To verify the analysis results, the numerical simulation results were compared with the measurements in the form of the root bending moment and the pressure distributions of the NREL/NASA Ames wind tunnel test.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.1
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• pp.31-41
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• 2010

This paper presents both numerical and physical modeling approaches for the dilation and spalling of rock recognized as typical process of rock around an underground opening at depth. For physical approach, laboratory testing of rectangular beams using a synthetic rock was used to investigate the onset of dilation and spalling. The beams are axially compressed and subjected to 4-point bending to provide non-uniform compressive stresses which are similar to the maximum tangential stress distribution around circular openings. Discrete element numerical analyses using commercial code $PFC^{2D}$ (Particle Flow Code) were performed to evaluate the stress path at various locations in the beams. The findings from these approaches suggest that the onset of dilation in laboratory tests appears to be a good indicator for assessing the stress magnitudes required to initiate spalling.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.197-205
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• 2008

In order to estimate mean wind speed in the Gwangyang-Myodo Region, the probability distribution model of extreme values has been used in the statistical analysis of joint distribution probability of daily maximum wind speed and corresponding direction in this paper. For this purpose frequency of daily maximum records at respective stations is inquired into and sample of largest yearly wind speed of sixteen compass direction and non-direction is extracted from daily data of maximum wind speed and appropriate direction of the meteorological observing stations nearby the bridge construction site. These extreme speed records are applied to Gumbel and Weibull distribution model and parameters are estimated through method of moment and method of least squares etc. And also, distribution and parameters are inquired into whether it is fitted through the probability plot correlation coefficient examination. From fitted parameters the largest yearly wind speed of sixteen compass direction and non-direction is extrapolated taking into account factors regarding sample size of data and distance from the bridge construction site according to the appropriate stations.