• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.2
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• pp.174-180
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• 2011

Nondestructive surface imaging of elastic characteristic and mechanical property has been studied on nanoscale surface with ultrasonic AFM. Resonance frequency variation of cantilever is theoretically analyzed with respect to contact mechanics as well as experimentally measured. The contact resonance frequency is calculated theoretically using the spring-mass and Herzian model in accordance with the resonance frequency of UAFM cantilever measured experimentally. Consequently, the topography and amplitude images could be obtained successfully and the elastic characteristic at the nanoscale surface was evaluated qualitatively by amplitude signals.

• Transactions of Materials Processing
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• v.16 no.7
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• pp.516-520
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• 2007

As the springback of sheet metal during unloading nay cause deviation from a desired shape, accurate prediction of springback is essential for the design of sheet stamping operations. On the removal of the applied load the specimen loses its elastic strain by contracting around the contour of the block, the radius $\rho$ can be determined by the residual differential strain. Therefore in this study the springback estimated by the residual differential strain is experimentally validated through the comparison with those obtained by U-bending test. The springback characteristics of two analytical models are also estimated at various processing conditions such as thickness, curvature of radius and drawing strain. The model based on residual differential strain has an applied transition strain where the springback undergoes a dramatic decrease. Both models show that springback decreases with increased strip thickness and with decreased radius of curvature. For no applied tension, the model based on residual differential strain predicts more springback as compared to the moment based model.

• Transactions of Materials Processing
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• v.22 no.1
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• pp.30-35
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• 2013

In this study, springback amounts of an S-rail are quantitatively compared according to the hardening model using a finite element simulation for the stamping process with high strength steels. For comparison of the hardening models, two types of hardening models were investigated. The two models were isotropic hardening and kinematic hardening. For the analysis with kinematic hardening, the Yoshida-Uemori model was selected. Five kinds of springback modes were measured at designated sections and a comparison was made between the experiment and the analyses with two types of hardening models. The analysis results show that the springback in the flange and the wall curl are predicted more accurately with a kinematic hardening model.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.1
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• pp.71-77
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• 2008

This paper proposes an Electronic Throttle Body (ETB) model considering a non-linearity of DC motor driver which is integrated with a H-bridge and a gate driver. A propagation delay and reverse recovery time of switching components cause non-linear characteristic of DC motor driver. This non-linearity affects not only the amateur voltage of DC motor, but also entire behaviour and parameters of ETB. In order to analyze the behavior of ETB more accurately, this non-linear effect of DC motor driver is modeled. The developed ETB model is validated by use of the step response and ramp response experiments, and it shows relatively accurate results compared with linear DC motor driver model.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.2
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• pp.172-178
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• 2002

This study presents a dynamic simulation of a purse seine net behavior Mathematical model suitable for purse seining, which is based on data from a series of previous simulations, various field experiments, is modelized as a set of mass-spring system. In this model, a number of meshes are approximated as one mass point, each of which connected to its neighbors by massless springs, the equations of motion are derived from considering internal force from the springs and external forces such as resistance and gravitation. This simulation shows the quantitative state on every mass point of the net and purse line during the shooting and pursing phases. So it is possible that performance of a purse seine net be analyzed using various and evolving parameters such as the shooting speed, the hauling speed, the size or type of the sinker, float and twine, also the hanging ratio etc.

• Transactions of Materials Processing
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• v.29 no.2
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• pp.76-88
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• 2020

The need for advanced high strength steel (AHSS) forming technology is increasing as interest in light weight and safe automobiles increases. Multipoint dieless forming (MDF) is a novel sheet metal forming technology that can create any desired longitudinal and transverse curvature in sheet metal. However, since the springback phenomenon becomes larger with high strength metal such as AHSS, predicting the required MDF to produce the exact desired curvature in two directions is more difficult. In this study, a prediction model using artificial neural network (ANN) was developed to predict the springback that occurs during AHSS forming through MDF. In order to verify the validity of model, a fit test was performed and the results were compared with the conventional regression model. The data required for training was obtained through simulation, then further random sample data was created to verify the prediction performance. The predicted results were compared with the simulation results. As a result of this comparison, it was found that the prediction of our ANN based model was more accurate than regression analysis. If a sufficient amount of data is used in training, the ANN model can play a major role in reducing the forming cost of high-strength steels.

• Computational Structural Engineering
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• v.10 no.3
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• pp.125-131
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• 1997

Most dynamic systems have are known to various random properties in excitation and system parameters. In this paper, a procedure for response analysis is proposed for the linear dynamic system with random properties in both excitation and system parameters. The system parameters and responses with random properties are modeled by perturbation technique, and then response analysis is formulated by probabilistic and vibration theories. And probabilistic FEM is also used for the calculation of mean response which is difficult by the proposed response model. As an applicative example, the transient response is considered for systems of single degree of freedom with random mass and spring constant subjected to stationary white-noise excitation and the results are compared to those of numerical simulation.

• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.3
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• pp.196-201
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• 2016

This paper analyses the characteristics of a stiffness-based rehabilitation mechanism for improving the function of the elbow joint of a human. We consider an elastic string as a tool for the elbow joint rehabilitation, where the string has been modeled as a linear spring with a stiffness. For effective rehabilitation training by using such a mechanism, we need to analyse the available torque characteristics of the elbow joint according to the stiffness of the string. Through various simulations, the torque pattern and its range of the elbow joint by assigning the stiffness of the string have been identified for a pre-defined trajectory of motion of the elbow joint. Finally, we show that the specified stiffness-based rehabilitation scheme can be used for effective rehabilitation of the elbow joint.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.441-451
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• 2016

This study analyzed behavior of the segment lining considering connection type between inner-slab and segment lining for a double deck tunnel by Shield TBM. In order to establish the design requirements of inner-slab and segment lining in double deck tunnel, inner structure of double deck tunnel at each purpose was analyzed and compared connection type between inner-slab and segment lining. And analyses have been carried out through the beam-spring model by MIDAS Civil 2012. As a result of this study, inner-slab, connection type of between inner-slab and segment lining and Lateral earth pressure coefficients were analyzed to verify the significant design factors.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.1 s.41
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• pp.71-78
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• 2005

This paper presents an improved system identification methodology for structural systems by applying static compliance dominant (SCD) frequencies. The existing sensitivity-based system identification technique is extended to adopt the static compliance dominant frequencies, and the performance of the additional spectral information, i.e., SCD frequencies, is compared with that of the natural frequencies only via a numerical example of a mechanical system. The results of the numerical study indicate that the additional use of the SCD frequencies improves accuracy in system identification problems.