• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.11
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• pp.742-748
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• 2000

This paper presents a numerical method to analyze the electromechanical-coupled field in the spindle motor of a computer hard drive and investigates dynamic response due to the electromechanical excitation, i.e. unbalanced magnetic force and centrifugal force for the rotational asymmetric motor. Magnetic field is calculated from Maxwells equation and voltage equation by introducing nonlinear time-dependent finite element analysis. Mechanical motion of rotor is calculated by solving Newton-Euler equation. Electromechanical excitation and dynamic response are characterized by analyzing the free response of a rotating rotor and Fourier analysis of the excitation force and resulting vibration of a rotor. It shows that centrifugal force produces the unbalanced magnetic force even in the rotational symmetric motor. It also shows that resonance produces quite considerable vibration even when the high excitation frequency with small amplitude matches with the natural frequency of the spindle motor.

• Structural Monitoring and Maintenance
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• v.4 no.2
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• pp.153-173
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• 2017

An improved method is presented to estimate the axial force of a bar member with vibrational measurements based on modified Timoshenko beam theory. Bending stiffness effects, rotational inertia, shear deformation, rotational inertia caused by shear deformation are all taken into account. Axial forces are estimated with certain natural frequency and corresponding mode shape, which are acquired from dynamic tests with five accelerometers. In the paper, modified Timoshenko beam theory is first presented with the inclusion of axial force and rotational inertia effects. Consistent mass and stiffness matrices for the modified Timoshenko beam theory are derived and then used in finite element simulations to investigate force identification accuracy under different boundary conditions and the influence of critical axial force ratio. The deformation coefficient which accounts for rotational inertia effects of the shearing deformation is discussed, and the relationship between the changing wave speed and the frequency is comprehensively examined to improve accuracy of the deformation coefficient. Finally, dynamic tests are conducted in our laboratory to identify progressive axial forces of a steel plate and a truss structure respectively. And the axial forces identified by the proposed method are in good agreement with the forces measured by FBG sensors and strain gauges. A significant advantage of this axial force identification method is that no assumption on boundary conditions is needed and excellent force identification accuracy can be achieved.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.725-729
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• 2016

The regular inspection of vehicles that are in service in domestic country, i.e., vehicle safety and emission gas inspection have been forced by the korea transportation safety authority and a private servicing enterprise according to the vehicle administration law (1995). In the safety inspection process, which is developed by a compatible inspection system and method, every effort is made to increase the reliability of vehicle safety and the service quality, and to protecting national health. In this study, the reliability of the braking force inspection method in the current regular vehicle inspection was studied statistically by comparing the dynamic braking force inspection method with the static braking force inspection method. Further, the problems and characteristics of the current braking force inspection methods were analyzed. Form the results for the dynamic braking force inspection equipment (H), a mean correction factor (y=18.61+2.18x) was obtained for the axle braking force ratio according to vehicle entering velocity.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.848-849
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• 2011

Rotating machines are using gears to change the rotary motion into the linear motion, on the other hand, linear motors have a accurate position control and excellent dynamic characteristics because of generating a thrust force directly. But the important problem, one of the linear motor is a high thrust force ripple. Thrust force ripple has a bad effect on the position accuracy and the dynamic characteristics, so it is necessary to reduce the thrust force ripple. Cogging is one of the cause that affect thrust force ripple. Cogging has some connection with the GCD between pole pitch and teeth pitch It is proposed method to reduce a thrust ripple of the linear motor that chamfering, skew, and so on. In this paper, the module phase set shift(MPSS) is used to reduce a thrust force ripple that has a similar effect to skew. And propose a method that reduce a thrust force ripple more by use of chamfering.

• Journal of Mechanical Science and Technology
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• v.20 no.9
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• pp.1355-1360
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• 2006

This paper presents the dynamic stability of a cantilevered Timoshenko beam with a concentrated mass, partially attached to elastic foundations, and subjected to a follower force. Governing equations are derived from the extended Hamilton's principle, and FEM is applied to solve the discretized equation. The influence of some parameters such as the elastic foundation parameter, the positions of partial elastic foundations, shear deformations, the rotary inertia of the beam, and the mass and the rotary inertia of the concentrated mass on the critical flutter load is investigated. Finally, the optimal attachment ratio of partial elastic foundation that maximizes the critical flutter load is presented.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.408-415
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• 2005

Existing results of some related experiments report that variation in the magnitude of prestressing force may leads to a change of dynamic properties of a PSC girder system. Since a usual dynamic equilibrium equation doesn't explain these phenomena, a modified dynamic equilibrium equation is derived in this paper by considering prestressing force as an internal energy of the system. The derived equation is applied to a modified beam element model is proposed. The proposed model validated by comparing the natural frequencies computed by the model with those from an existing experiment result.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.156-162
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• 2003

The shock absorber is a part having a direct influence on the ride comfort, stability and dynamic load prediction of a vehicle. Thus, a rationally modeled shock absorber should be required in the dynamic analysis of vehicles. This thesis presents a modified model, based on Worden's hyperbolic tangent function, in order to fit experimental data on the velocity-damping force of a shock absorber. The hyperbolic tangent function correctly indicates the characteristics of a shock absorber, and has the advantage of containing physical causality. To evaluate the method, comparative evaluations of the linear model, the 5th polynomial model and Worden's model were carried out. The function presented in this paper is not only simple but also makes it possible to estimate the function coefficients easily and visually. In addition, it has the advantage of containing physical causality. Lastly, it effectively models the damping force of a shock absorber.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1998.03a
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• pp.135-142
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• 1998

The performances of cutting process is mostly affected by the characteristics of closed loop system constructed with machine tool structure, work piece and tools. The chucking system is very important component in this system to hold work piece correctly in various static and dynamic load condition. Therefore, chucking force and accuracy must be considered carefully, from these reason, this paper describes the stability of chucking system which preserve high stiffness and accuracy of machine tool system.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.963-969
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• 2010

The railway vehicle consists of wires, bodies, bogies and wheelsets, and each part has very complex mechanism. In this paper, wheel-rail contact algorithm is implemented using C++ and inserted into the ODYN which is a dynamic analysis program. To analyze wheel-rail contact mechanism, information such as contact points, contact angle and rolling radius is calculated according to the wheel and rail profile. Using this information, a table for the calculation of the wheel-rail contact analysis is made according to the lateral displacement. And, the creepage and normal force are calculated and a creep force is estimated by the FASTSIM. To verify the reliability of the wheel-rail contact algorithm, results of the program are compared with the ADAMS/Rail and paper. Finally, a wheelset of the railway vehicle is modeled using ODYN and simulated static and dynamic analysis. And, to verify the reliability of the simulation results, a displacement, velocity, acceleration and force are compared with results of ADAMS/Rail.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.3 s.108
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• pp.226-232
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• 2006

This paper presents the dynamic analysis of an impulsively forced rotating cantilever beam with rigid body motion. The transient response induced by the impulsive force and the rigid body motion of the beam are calculated using hybrid deformation variable modeling with the Rayleigh-Ritz assumed mode methods. The stiffness variation effect due to the rigid body motion of the beam is considered in this study Also, the effects of the impulsive force position and the angular velocity on the transient responses of the beam are investigated through numerical works.