• Proceedings of the KSME Conference
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• 2001.06e
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• pp.185-190
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• 2001

Rotating disks are used in various machines such as floppy disks, hard disk, turbines and circular sawblades. The problems of vibrations of rotating disks are important in improving these machines. Many investigators have dealt with these problem. Specially, vibrations of a rotating flexible disk taking into account the effect of air is difficult problem in simulation. The governing equation of a rotating flexible disk coupled to the surrounding fluid is investigated by a simple mathematical model. And several important parameters concerned with the stability of a rotating flexible disk are defined. Coupling strength between air and rotating flexible disk is proportional to square of disk radius directly and square root of the all of bending rigidity, disk density and thickness inversely. Lift-to-damping coefficient has relation to the onset of disk flutter.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.5
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• pp.537-544
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• 2009

In order to increase the critical speed of rotating disks of which functional material could not be changed such as in optical and magnetic data storage disks, a new disk with a rim reinforced by composite material is proposed and its concept is verified by numerical analysis. Stress distributions are found for the rotating disk composed of two annular disks of which materials are isotropic inside and orthotropic outside. Dynamic equation is formulated in order to calculate the natural frequency and critical speed. For the solution of lateral vibration, a rotational symmertry condition is applied along circumferential direction and a finite element interpolation with Hermite polynomial is performed along the radial direction to obtain a proper solution. According to the results, reinforcing a disk at rim makes critical speeds drastically increased, and induces a buckling phenomenon in mode (0,0) which occurs over the lowest critical speed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.998-1003
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• 2003

The aerodynamically excited vibration and natural frequency of rotating CD and DVD disks are analytically and experimentally studied in this paper The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping components. The explicit expression on natural frequency of the air coupled disk is obtained as functions of the three aerodynamic coefficients. The experiments performed using a vacuum chamber and CD/DVD disks rotating in vacuum, open air and enclosure give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

• Journal of Urban Science
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• v.10 no.1
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• pp.11-20
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• 2021

In this study, the vibration characteristics were theoretically analyzed by modeling a free isotropic rotating disk with an outer periphery with a fixed inner periphery, paying attention to disks used as storage devices for information devices, especially magnetic disks, magneto-optical disks, and compact disks in which the head and disk are non-contact. Iluminate with Composite materials represented by fiber-reinforced plastics (FRP) have high specific strength (strength/density) and specific stiffness (narrowness/density). It is used in the elements, and its use is rapidly expanding. Under this circumstance, the disk currently manufactured using an isotropic material made of various plastic materials such as aluminum or polycarbonate as a base material is an extremely anisotropic material made of a composite material, and the circumferential stiffness of the disk is made of reinforcing fibers in the circumferential direction. It is modeled as an anisotropic rotating disk with increased, and its influence on the vibration characteristics is revealed.

• Composites Research
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• v.20 no.3
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• pp.43-49
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• 2007

Dynamic instability of rotating disks is the most significant factor to limit its rotating speed. Application of composite materials to rotating disks may enhance the dynamic stability leading to a possible design of rotating disks with lightweight and high speed. Whereas much work has been done on the effect of transverse shear and rotary inertia, called Timoshenko effect, on the dynamic behavior of plates, there is little work on the correlation between the effect and the rotation of disk, especially nothing in case of composite disks. The dynamic equations of a rotating composite disk are formulated with the Timoshenko effect and the vibrational analysis is performed by using a commercial package MSC/NASTRAN. According to the results, the Timoshenko effect goes seesaw in some modes, unlike the well-known fact that the effect decreases as the rotating speed increases. And it can be concluded, based only on the present results, that decrement of the Timoshenko effect by disk rotation grows larger as the thickness ratio decreases, the diameter ratio increases, the modulus ratio increases, and the mode number increases.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.1
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• pp.45-53
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• 2014

For the time integration solution of the impulsive dynamic contact problem of high-speed rotating disks formulated by the finite element technique, the velocity and acceleration contact constraints as well as the displacement contact constraint are imposed for the numerical stability without spurious oscillations. The solution of the present technique is checked by the numerical simulation using the concentric high-speed rotating disks with the clearance and impulsive loading. It is shown that the almost steady state solution agrees with the corresponding analytical solution of the elasticity and that the differentiated constraints are crucial for the numerical stability of such high-speed contact problems of the disks under impulsive loading.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.206-210
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• 1998

A study on dynamic characteristics of rotating disks in magneto optical disk drives is presented. Natural frequencies of rotating disks are investigated experimentally and numerically. The frequency response and critical speeds of the ASMO disk are discussed. The characteristics of airflow around the disk and their effects on disk vibrations are also investigated. It is found that the numerical calculation of the natural frequencies of rotating disks agrees well with the experimental results. The airflow around the disk in the cartridge affects the characteristics of the disk vibrations to reduce the modal frequencies of the disk. The experiment shows that negative vertical offsets of the disk in the cartridge possibly increase the vibration amplitudes. As being influenced by the geometry of the cartridge, the rotation of the disk causes an asymmetric airflow in the presence of window.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.2
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• pp.127-134
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• 2008

The aerodynamically excited vibration and natural frequency of rotating disks are analytically studied in this paper. The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and drag forces. The explicit expressions on natural frequencies of the air coupled disk are obtained as functions of the aerodynamic coefficients. for the three cases where the disk rotates in three different cases (in vacuum, in open air without enclosure, and close to rigid wall). The theoretical results give that the natural frequencies of rotating disks in air are smaller than those in vacuum, because the effect of the added fluid mass decreases the frequencies. This paper also proposes an analytical method to predict the flutter speed of a rotating disk.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1513-1520
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• 2000

Complex modal testing method for rotating disks with support motion is introduced which handles the pairs of two point excitation and responses of the disk as complex input and output, respectively. This method utilizes the directivity information and the separation over the rotational speed of forward and backward traveling wave modes or bending coupled modes in the directional frequency response functions(dFRFs). This method synthesizes the normal/reverse dFRFs and complex wave dFRF, which were originally applied to rotating shaft and rotating disk, respectively, and is applied to complex system with dynamically coupled rotating disks and shaft. Experiments with a commercial hard disk drive spindle system demonstrate the validity of this method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.8
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• pp.649-656
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• 2016

Thick composite disks are utilized in the fast-rotating machines such as turbine disks, flywheels, and so on. The effects of rotating speed on the dynamic characteristics of thick composite disks are deeply studied in this paper. The dynamic governing equations of a rotating composite disk including transverse shear and rotary inertia are derived and then formulated into the finite element equation. Isotropic, circumferentially reinforced disk, and radially reinforced disk are selected for the numerical analysis. The inclusion of the transverse shear and rotary inertia into the governing equation of the rotating disks makes the natural frequency reduced as well as the critical speed. The present results show that the rotation of a thick disk may not reduce the effect of transverse shear and rotary inertia depending on anisotropy, thickness ratio and mode, unlike the results reported in other studies.