• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.695-700
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• 2000

The dynamic stability of spinning beam with free boundary conditions for both edges subjected to a tip follower force $P_0+P_1cos{\Omega}t$ is analyzed. It is studied that the beam has a concentrated mass. and then the effects of the axial locations of the mass are studied. The beam is modelled with the Timoshenko type shear deformations. The Hamilton's principle is used to derive the equations of motion, and the critical spinning speed of a beam subjected to a follower force with various non-dimensional parameters is investigated. The finite elements are used with $C^0$ continuity to analyze the spinning beam model, and the method of multiple scales is tried to investigate the dynamic instability regions. The governing equations of motion involve periodic coefficients, which are not in the form of standard Mathieu-Hill equations. The result shows that the concentrated mass increases the dynamic stability of the spinning free-free beam subjected to a thrust.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.911-916
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• 2012

Ion selectivity in a simple cyclic peptide nanotube, composed of four cyclo[-(D-Ala-Glu-D-Ala-Gln)$_2-$] units, is investigated by calculating the PMF profiles of $Na^+$, $K^+$, and $Cl^-$ ions permeating through the peptide nanotube in water. The final PMF profiles of the ions obtained from the umbrella sampling (US) method show an excellent agreement with those from the thermodynamic integration (TI) method. The PMF profiles of $Na^+$ and $K^+$ display free energy wells while the PMF curve of $Cl^-$ features free energy barriers, indicating the selectivity of the cyclic peptide nanotube to cations. Decomposition of the total mean force into the contribution from each component in the system is also accomplished by using the TI method. The mean force decomposition profiles of $Na^+$ and $K^+$ demonstrate that the dehydration free energy barriers by water molecules near the channel entrance and inside the channel are completely compensated for by attractive electrostatic interactions between the cations and carbonyl oxygens in the nanotube. In the case of $Cl^-$, the dehydration free energy barriers are not eliminated by an interaction between the anion and the peptide nanotube, leading to the high free energy barriers in the PMF profile. Calculations of the coordination numbers of the ions with oxygen atoms pertaining to either water molecules or carbonyl groups in the peptide nanotube reveal that the stabilization of the cations in the midplane regions of the nanotube arises from the favorable interaction of the cations with the negatively charged carbonyl oxygens.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.440-451
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• 1985

This study is concerned with the analysis of cutting force system acting on ball-nose end mill in three-dimensional surface machining process. Conical tipped circular cutting edge element model and free surface machining process types are proposed to apply oblique cutting theory, and then derived equations are used for numerical approach of cutting force curves by matrix method. This approach has a good agreement with experimental results both in magnitude and shape within the range of 15 percent, which was conformed on 6061-T6 aluminum workpiece having twofold curvatured surface. From the cutting load variation to edge location, it is confirmed that circular cutting edge shapes has a better cutting ability than that of straight and both have a singularity near a tool point. It is also verified that what kind of machining condition is recommendable for three-dimensional machining process in connection with deflection of the cutter to workpiece and tool point wearing or system stability.

• Steel and Composite Structures
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• v.9 no.5
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• pp.473-497
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• 2009

For the spatially coupled free vibration analysis of composite box beams resting on elastic foundation under the axial force, the exact solutions are presented by using the power series method based on the homogeneous form of simultaneous ordinary differential equations. The general vibrational theory for the composite box beam with arbitrary lamination is developed by introducing Vlasov°Øs assumption. Next, the equations of motion and force-displacement relationships are derived from the energy principle and explicit expressions for displacement parameters are presented based on power series expansions of displacement components. Finally, the dynamic stiffness matrix is calculated using force-displacement relationships. In addition, the finite element model based on the classical Hermitian interpolation polynomial is presented. To show the performances of the proposed dynamic stiffness matrix of composite box beam, the numerical solutions are presented and compared with the finite element solutions using the Hermitian beam elements and the results from other researchers. Particularly, the effects of the fiber orientation, the axial force, the elastic foundation, and the boundary condition on the vibrational behavior of composite box beam are investigated parametrically. Also the emphasis is given in showing the phenomenon of vibration mode change.

• Structural Engineering and Mechanics
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• v.19 no.1
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• pp.73-96
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• 2005

For the spatially coupled free vibration analysis of shear deformable thin-walled non-symmetric curved beam subjected to initial axial force, an exact dynamic element stiffness matrix of curved beam is evaluated. Firstly equations of motion and force-deformation relations are rigorously derived from the total potential energy for a curved beam element. Next a system of linear algebraic equations are constructed by introducing 14 displacement parameters and transforming the second order simultaneous differential equations into the first order simultaneous differential equations. And then explicit expressions for displacement parameters are numerically evaluated via eigensolutions and the exact $14{\times}14$ dynamic element stiffness matrix is determined using force-deformation relations. To demonstrate the accuracy and the reliability of this study, the spatially coupled natural frequencies of shear deformable thin-walled non-symmetric curved beams subjected to initial axial forces are evaluated and compared with analytical and FE solutions using isoparametric and Hermitian curved beam elements and results by ABAQUS's shell elements.

• Journal of Ship and Ocean Technology
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• v.4 no.1
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• pp.21-27
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• 2000

The slamming force occurring in the free fall impact of cylindrical bodies on the water surface is analyzed in both compressible and incompressible stages. In the compressible phase the hydrodynamic analysis is carried on by the acoustic approximation, obtaining a closed form expression for the maximum impact force. The incompressible analysis is approached through and unsteady boundary element method to compute the free surface evolution and the slamming force on the body. A similar behavior seems to characterize the maximum slamming force versus a dimensionless mass parameter.

• Magazine of the Korean Society of Agricultural Engineers
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• v.34 no.1
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• pp.57-65
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• 1992

The main purpose of this paper is to present both the natural frequencies and mode shapes of tapered beams under tensile axial force. The differential equation governing planar free vibration for tapered beams under tensile axial force is derived as nondimensional form. The three kinds of cross sectional shape are considered in differential equation. The Runge-Kutta method and Determinant Search method are used to perform the integration of the differential equation and to determine the natural frequencies, respectively. The hinged-hinged, hinged-clamped, clamped-clamped and constraints are applied in numerical examples. The lowest four nondimensional natural frequencies are reported as the function of nondimensional tensile axial force. The fundamental natural frequencies are presented when section ratios and nondimensional axial forces are varied. The effects of cross sectional shapes are reported and some typical mode shapes are also presented.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.49 no.1
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• pp.20-26
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• 2000

This paper deals with the modal analysis and the displacement of stator due to electromagnetic forces in Switched Reluctance Motor(SRM). A free-free model of the stator based on structural 3-dimensional Finite Element Method(FEM) is used for investigation the natural frequencies and the mode shapes of the stator. In addition, The displacement caused by magnetic force acting on stator pole is analyzed by the structural FEM coupled with the magnetic force. From these results, the resonance speed is obtained by the relation of the natural frequencies of the harmonic frequencies of magnetic force. And, the eccentricity with respect to rotor is predicted from the analysis result of the mechanical displacement of stator. The natural frequencies of stator are compared with experimental ones measured by modal testing.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2006.05a
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• pp.395-398
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• 2006

this paper provides a novel method to start the linear engine coupled linear generator from dead stop to its final steady state operation. This method depends mainly to use the linear generator mounted on the shaft of the linear engine to provide the required thrust force to move and oscillate the linear engine from bottom to top dead centers. It is a cost effective approach to start the internal linear combustion engine using its coupled tubular permanent magnet linear generator proposed here. This linear generator operates in this case in motoring mode, providing the required thrust force by feeding this linear generator phases with currents by using a three phase PWM inverter controlled by position feedback scheme. In order to provide the desired thrust force with specific value and direction, a position feedback is required to control the free piston engine motion through controlling the inverter switches using PWM control scheme.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.903-906
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• 2005

The purpose of this paper is to investigate free vibrations and critical loads of the uniform Beck's columns with a tip spring, carrying a tip mass. The ordinary differential equation governing free vibrations of such Beck's column subjected to a follower force is derived based on the Bernoulli-Euler beam theory. Both the divergence and flutter critical loads are calculated from the load-frequency curves that are obtained by solving the differential equation numerically. The critical loads are presented in the figures as functions of various non-dimensional system parameters such as the mass moment of inertia and spring parameter.