• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.317-322
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• 2002

There are many researches to identify the rigid body properties from the mass-line obtained by impact hammer testing. The correct rigid body properties of the structure may be estimated if the mass-line of the structure could be obtained exactly. When the structure is mounted by elastic materials, the mass-line cannot be read correctly from the impulse response spectrum. The reason is due to the effects of rigid body modes of mounted structure. In this paper, the effects of rigid body modes of mounted structure to the mass-line are discussed and the method to remove these effects is also presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.260-267
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• 2002

For an elastically suspended rigid body with the planes of symmetry in a three dimensional space, a novel analysis fur the vibration modes is presented. From the decompositions of the stiffness and inertia matrices, the conditions for the existence of pure translation and pure couple modes are analyzed for an elastically suspended rigid body with the planes of symmetry. From this analysis, it can be showed that how the structure of stiffness and inertia must be related in order to produce the pure translation and pure couple modes when an elastically suspended rigid body has one, two, or three planes of symmetry.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.336.2-336
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• 2002

There are many researches to identify the rigid body properties from the mass-line obtained by impact hammer testing. The correct rigid body properties of the structure may be estimated if the mass-line of the structure could be obtained exactly. When the structure is mounted by elastic materials, the mass-line cannot be read correctly from the impulse response spectrum. The reason is due to the effects of rigid body modes of mounted structure. (omitted)

• Structural Engineering and Mechanics
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• v.23 no.5
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• pp.505-523
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• 2006

An unrestrained plane rigid body resting on a horizontal surface which shakes horizontally and vertically may assume one of the five modes of response: rest, slide, slide-rock, rock, and free flight. The first four are nontrivial modes of motion. It is important to study which one of these responses is started from rest as in most studies it is often assumed that the initial mode is the particular mode of response. Criteria governing the initiation of modes are first briefly discussed. It is shown that the commencement of response modes depends on the aspect ratio of the body, coefficients of static and kinetic friction at the body-base interface, and the magnitude of maximum base accelerations. Considering the last two factors as random variables, the initiation of response modes is next studied from a probabilistic point of view. Type 1 extreme value and lognormal distributions are employed for maximum base excitations and coefficient of friction respectively. Analytical expressions for computing the probability values of each mode of response are derived. The effects of slenderness ratio, vertical acceleration, and statistical distributions of maximum acceleration and coefficient of friction are shown through numerical results and plots.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.1 s.256
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• pp.97-104
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• 2007

Vibration analysis of a rigid body supported by in-parallel linear springs can be greatly simplified by utilizing the conditions for a plane of symmetry. The vibration modes of an oscillatory system having plane of symmetry are classified into the in-plane and out-of-plane modes. From the viewpoint of screw theory, they represent respectively the vibration axes perpendicular to the plane of symmetry and lying in the plane of symmetry. In this paper, the sets of orthogonal and mutually intersecting three springs are used as resilient support of a rigid body. The geometrical conditions for the system to have a plane of symmetry and diagonalized stiffness matrix are presented. From the orthogonality of the vibration modes with respect to the inertia matrix, the geometrical relation between the reaction wrenches and the vibration modes are derived. This geometrical relation is then used to get the cubic design equation for the design of out-of-plane modes. The numerical design example of engine mounts is presented in order to explain the suggested design technique.

• Journal of KSNVE
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• v.7 no.3
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• pp.393-399
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• 1997

This study proposes a methodology with which the optimal damper positions of the feeding system in a CD-ROM drive are determined to removal the harmful tilting vibration modes. For this purpose, vibration characteristics of the feeding system are identified by a theoretical modeling as well as vibration experiments. We perform the modal testings using the impact hammer and shaker; furthermore, we establish a vibration model due to the rigid-body motion. The analysis and experiments show that the feeding system has three rigid-body vibration modes in the low-frequency region and two of them come from the tilting modes. We show that the tilting modes can be removed by determining the damper positions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.7 s.94
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• pp.1719-1730
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• 1993

This paper presents the theoretical natural frequencies of out-of-plane deformable ring based on the variables such as out-of-plane deflection, torsional rotation and shear rotation. Based on the same variables, a finite element eigen analysis is carried out by using the $C^0$-continuous, isoparametric element which has three nodes per element and three degrees-of-freedom at each node. Numerical experiments are peformed to find the integration scheme which produces accurate natural frequencies, natural modes and correct rigid body motion. The uniformly reduced integration and the selective reduced integration give more accurate numerical frequencies than the uniformly full integration, but the uniformly reduced integration produces incorrect rigid body motion while selective reduced integration does correct one. Therefore, the ring element based on the three variables which employes selective reduced integration is recommended to avoid spurious modes, to alleviate the error due to shear locking and to produce correct rigid body motion, simultaneously.

• Transactions of the Korean Society of Automotive Engineers
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• v.4 no.2
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• pp.127-136
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• 1996

Dynamic analysis of a three-axle heavy truck is carried out with rigid body model and flexible body model. To see the effects of chassis flexibility, the chassis is modeled as flexible body. The mass matrix, stiffness matrix, and vibration normal modes of the chassis are obtained by a finite element analysis program, and four vibration normal modes are used in the flexible body model. The vehicle model consisting of a frame, a cab, suspensions, an engine, a deck, a seat, and tires, has total 77 degrees of freedom. The result shows that the peaked acceleration in the flexible model is lower than that of the rigid body model.

• Structural Engineering and Mechanics
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• v.35 no.1
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• pp.53-65
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• 2010

The rigid body inertia properties of a structure including the mass, the center of gravity location, the mass moments and principal axes of inertia are required for structural dynamic analysis, modeling of mechanical systems, design of mechanisms and optimization. The analytical approaches such as solid or finite element modeling can not be used efficiently for estimating the rigid body inertia properties of complex structures. Several experimental approaches have been developed to determine the rigid body inertia properties of a structure via Frequency Response Functions (FRFs). In the present work two experimental methods are used to estimate the rigid body inertia properties of a frame. The first approach consists of using the amount of mass as input to estimate the other inertia properties of frame. In the second approach, the property of orthogonality of modes is used to derive the inertia properties of a frame. The accuracy of the estimated parameters is evaluated through the comparison of the experimental results with those of the theoretical Solid Work model of frame. Moreover, a thorough discussion about the effect of accuracy of measured FRFs on the estimation of inertia properties is presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.324-329
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• 1996

Vibration characteristics of the feeding system in a CD-ROM drive are identified by a theoretical modeling as well as vibration experiments. For this purpose, we establish a vibration model due to the rigid-body motion and perform the modal testings using the impact hammer and shaker. The analysis and experiments show that the feeding system has three rigid-body vibration modes in the low-frequency region and two of them come from the tilting modes. In order to remove the harmful tilting modes for the tracking servo control, a methodology to find the optimal positions of the dampers is also proposed in this study.