• Journal of the Korean Society for Precision Engineering
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• v.25 no.6
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• pp.80-91
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• 2008

Electrostatic forces have an advantage of directly levitating not only non-ferromagnetic metals but also semiconductors, such as silicon wafers, and dielectric materials like glass. This paper describes the characteristics of electrostatic forces and electrostatic suspension system, followed by the basic principle of 1-DOF(degree of freedom) electrostatic suspension system, and the structures of electrodes-for-suspension and voltage supplying methods to the electrodes in 1-DOF model. This paper also discuss about the minimum number of electrodes needed to control n-DOF motion of the suspended object and represents some desirable electrode patterns to stabilize the 6-DOF motion of the object. In the near future, electrostatic suspension system is expected to be applied to industrial manufacturing processes, for example, to the manufacture of semiconductor devices and/or flat panel display devices.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.1999-2010
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• 2023

Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 10⁴ to 3.95 × 10⁴. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 10⁴ with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.

• Structural Engineering and Mechanics
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• v.21 no.6
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• pp.713-735
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• 2005

Due to the complexity of mathematical expressions, the literature concerning the free vibration analysis of plates carrying multiple three-degree-of-freedom (dof) spring-mass systems is rare. In this paper, the three degrees of freedom (dof's) for a spring-mass system refer to the translational motion of its lumped mass in the vertical ($\bar{z}$) direction and the two pitching motions of its lumped mass about the two horizontal ($\bar{x}$ and $\bar{y}$) axes. The basic concept of this paper is to replace each three-dof spring-mass system by a set of equivalent springs, so that the free vibration characteristics of a rectangular plate carrying any number of three-dof spring-mass systems can be obtained from those of the same plate supported by the same number of sets of equivalent springs. Since the three dof's of the lumped mass for each three-dof spring-mass system are eliminated to yield a set of equivalent springs, the total dof of the entire vibrating system is not affected by the total number of the spring-mass systems attached to the rectangular plate. However, this is not true in the conventional finite element method (FEM), where the total dof of the entire vibrating system increases three if one more three-dof spring-mass system is attached to the rectangular plate. Hence, the computer storage memory required by using the presented equivalent spring method (ESM) is less than that required by the conventional FEM, and the more the total number of the three-dof spring-mass systems attached to the plate, the more the advantage of the ESM. In addition, since manufacturing a spring with the specified stiffness is much easier than making a three-dof spring-mass system with the specified spring constants and mass magnitude, the presented theory of replacing a three-dof spring-mass system by a set of equivalent springs will be also significant from this viewpoint.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.6
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• pp.1330-1341
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• 1993

The kinematic synthesis deals with the systematic design of mechanisms for a given performance. The area of synthesis may be grouped into two categories to determine the type and to size the dimensions of a mechanism for a specified task. In this paper, using a database of mechanisms a designer can determine the type of mechanism conveniently and design equations are automatically generated for a given input performance. The solving method of design equations utilizes an optimization routine to obtain roots effectively. The linkages of 4, 6, and 8bars with revolute joints are considered in this study but may be extended to linkages of more bars.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2631-2633
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• 2004

This paper describes the construction of a half sphere screen driving tilting simulator that can perform six degree-of-freedom( DOF) motions simmulator to a tilting train. The mathematical equations of Tilting Train dynamics are first derived from the 6-DOF bicycle model and incorporated with the bogie. carbody, and suspension subsystems. The equations of motion are then programmed by visual C++ code. To achieve the simulator functions. a motion platform that is constructed by six electric-driven actuators is designed. and its kinetics/inverse kinetics analysis is also conducted. Driver operation signals such as carbady angle, accelerator. and tilting positions are measured to trigger the Tilting dynamics calculation and further actuate the cylinders by the motion platform control program. In addition. a digital PID controller is added to achieve the stable and accurate displacements of the motion platform. The experiments prove that the designed simulator is adequate in performing some special rail mad driving situations discussed in this paper.

• Coupled systems mechanics
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• v.7 no.6
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• pp.649-668
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• 2018

In this paper, we present a numerical model for fluid-structure interaction between structure built of porous media and acoustic fluid, which provides both pore pressure inside porous media and hydrodynamic pressures and hydrodynamic forces exerted on the upstream face of the structure in an unified manner and simplifies fluid-structure interaction problems. The first original feature of the proposed model concerns the structure built of saturated porous medium whose response is obtained with coupled discrete beam lattice model, which is based on Voronoi cell representation with cohesive links as linear elastic Timoshenko beam finite elements. The motion of the pore fluid is governed by Darcy's law, and the coupling between the solid phase and the pore fluid is introduced in the model through Biot's porous media theory. The pore pressure field is discretized with CST (Constant Strain Triangle) finite elements, which coincide with Delaunay triangles. By exploiting Hammer quadrature rule for numerical integration on CST elements, and duality property between Voronoi diagram and Delaunay triangulation, the numerical implementation of the coupling results with an additional pore pressure degree of freedom placed at each node of a Timoshenko beam finite element. The second original point of the model concerns the motion of the outside fluid which is modeled with mixed displacement/pressure based formulation. The chosen finite element representations of the structure response and the outside fluid motion ensures for the structure and fluid finite elements to be connected directly at the common nodes at the fluid-structure interface, because they share both the displacement and the pressure degrees of freedom. Numerical simulations presented in this paper show an excellent agreement between the numerically obtained results and the analytical solutions.

• Journal of KSNVE
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• v.6 no.3
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• pp.287-296
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• 1996

A virtual work form of flexible multibody dynamic formulation with rotary inertia has been derived. For the analysis of large flexible multibody systems, deformation modal coordinates have been employed to represent coupled motion between gross and vibrational motion. For the efficient evaluation of the entries in the mass matrix, a flexible body has been treated as a collection of mass points. The rotary inertia was generated from the consistent mass matrix in a finite element model. Deformation mode shapes were obtained from finite element analysis. Bending and twisting vibration analyses of a cantilever have been carried out to see rotary inertia effects. A space flexible robot simulation has been also carried out to show effectiveness of the proposed formulation. This formulation is effective to the model that consists of beam, plate, or shell element that contains rotational degree of freedom at the nodal point. It is also effective to the flexible body model to which a large lumped rotary inertia is attached.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.1949-1960
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• 2004

This paper presents a robot system developed for medical purpose. A 6-degree-of-freedom robot was introduced for physical exercise and rehabilitation. This system was proposed for stroke patients or patients who cannot use one of their arms or legs. The robot system exercises the hemiplegic part based on the motion of normal part of a patient. Kinematic studies on the human body and robot were applied to develop the robotic rehabilitation exercise system. A clamp which acts as an end effector of the robot to hold a patient was designed and applied to the robot to guarantee the safety of patients. The proposed robotic rehabilitation system was verified by simulations and experiments on arm (elbow and shoulder) motion. Patients are expected to be able to exercise various motions by themselves with the proposed robotic rehabilitation system.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.697-702
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• 2011

Responses of multi degree of freedom systems under random excitations can be estimated by using Monte Carlo simulation. The equations of motion of an elastic pendulum system include nonlinear terms and show irregular characteristics under random excitation. While the magnitude of random excitation is small the response of an elastic pendulum shows borderlines. As the magnitudes of excitation increase, the responses show divergence with very large amplitudes of motion and the tendency is diverse dependent on the magnitude and type of random excitations and the ratio of natural frequencies.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.2
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• pp.409-425
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• 2015

In this paper, we employ a dynamics modeling method for investigating a multi-body dynamics system of semi-submersible autonomous underwater vehicles consisting of a towing vehicle operated near the water surface, a tow cable, and a towfish. The towfish, which is towed by a marine cable for the purposes of exploration or mine hunting, is modeled with a Six-Degree-of-Freedom (6-DOF) equation of motion that reflects its hydrodynamics characteristics. The towing cable, which can experience large displacements and deformations, is modeled using an absolute nodal coordinate formulation. To reflect the hydrodynamic characteristics of the cable during motion, the hydrodynamic force due to added mass and the drag force are imposed. To verify the completeness of the modeling, a few simple numerical simulations were conducted, and the results confirm the physical plausibility of the model.