• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.707-710
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• 2005

In this paper, we studied about the dynamic behavior of a cracked rotating cantilever beam. The influences of a rotating angular velocity, the crack depth and the crack position on the dynamic behavior of a cracked cantilever beam have been studied by the numerical method. The cracked cantilever beam is modeled by the Euler-Bernoulli beam theory. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The lateral tip displacement and the axial tip deflection of a rotating cantilever beam is more sensitive to the rotating angular velocity than the depth and position of crack. Totally, as the crack depth is increased, the natural frequency of a rotating cantilever beam is decreased in the first and second mode of vibration.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.137-139
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• 2003

Transducer for ultrasonic linear motor with the symmetric and anti-symmetric modes was studied. The ultrasonic linear motor consists of two Langevin type piezoelectric vibrators that cross at right angles with each other in tip. In order to excite symmetric and anti-symmetric modes, the transducer must have a phase shift of 90 degree in space and time. Therefore, the tip of transducer moves on an elliptical motion. In this paper, the finite element analysis was used to optimize dimension and displacement of the transducer The ultrasonic motor was fabricated using the simulated result and the driving characteristics were measured. No-load velocity was 0.28[m/s] and the maximum efficiency was 30[%] in resonance frequency.

• Journal of Industrial Technology
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• v.13
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• pp.49-57
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• 1993

Bending fatigue tests were carried out on the specimenes with two different strength levels in order to investigate small crack growth rate. The main results obtained are as follows : (1) Small crack growth law, $da/dn=C{\sigma}_a{^n}a$ is useful several materials, but is not the rule applicable to all cases generally. (2) When da/dn in several specimens are equal, COD near the crack tip are also nearly equal. (3) Crack tip opening displacement(CTOD) is the main factor to control the small crack growth rate, and da/dn ${\propto}$ CTOD comes into being between the two. Accordingly, $da/dn=C({\sigma}_a{^2}/{\sigma}_s){^n}a^n$ shows the small crack growth rate being reflected crack closure phenomenon.

• Steel and Composite Structures
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• v.4 no.1
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• pp.9-21
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• 2004

The present study aims at the reliability analysis of steel towers against the limit state of deflection. For this purpose tip deflection of the tower has been obtained after carrying out the dynamic analysis of the tower using modal method. This tip deflection is employed for subsequent reliability analysis. A limit state function based on serviceability criterion of deflection is derived in terms of random variables. A complete procedure of reliability computation is then presented. To study the influence of various random variables on tower reliability, sensitivity analysis has been carried out. Design points, important for probabilistic design of towers, are also located on the failure surface. Some parametric studies have also been included to obtain the results of academic and field interest.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.404-407
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• 2004

Linear ultrasonic motor by bimorph. Transducer for linear ultrasonic motor with symmetric and anti-symmetric modes was studied. The transducer was composed of two piezoelectric ceramic that cross at right angles with each other at tip. In order to exist length vibration mode two piezoelectric ceramics must have 90-degree phase difference with each other. As a result, tip of transducer moves in elliptical motion. Elliptical trajectory of transducer was analyzed by employing the (mite element method(FEM). From the result, the linear ultrasonic motor was measured for characteristics. In this paper, vibration shape of transducer was simulated and the resonant frequency, stabilization frequency and maximum displacement were calculated using the FEA.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.3-8
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• 2001

Dynamic stress intensity factors (DSIFs) are obtained when a crack propagates with constant velocity in rectangular functionally gradient materials (FGMs) under dynamic mode III load. To obtain the dynamic stress intensity factors, it is used the general stress and displacement fields of FGMs for propagating crack and the boundary collocation method (BCM). The stress intensity factors and energy release rates are the greatest in the increasing properties $(\xi>0)$, next constant properties $(\x=0)$ and decreasing properties $(\xi<0)$ under constant crack tip properties and crack tip speed.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.315.2-315
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• 2002

The vibrational system of this study consists of a cantilever pipe conveying fluid, the moving mass upon it and an attached tip mass. The equation of motion is derived by using Lagrange equation. The influences of the velocity of moving mass and the uniformly distributed tangential follower force have been studied on the dynamic behavior of a cantilever pipe by numerical method. While the moving mass moves upon the cantilever pipe, the velocity of fluid flow increase, the tip displacement of cantilever pipe conveying fluid is decreased. (omitted)

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.896-901
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• 1990

A simulation analysis is presented for the position control of a single-link flexible manipulator whose end-effector is subjected to an impulsive force. Arm is rotated by a d.c. servomotor at the shoulder so that the end point stays precisely at its initial position even if the end effector is thumped with the impulsive loading. A gap sensor is used to measure the tip displacement. The control torque based on the PD control law is applied to the motor through the driver circuit. The control strategy is tested by means of computer simulation for the one-link flexible-arm prototype in the authers' laboratory at Tohoku Univ.

• Journal of Aerospace System Engineering
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• v.1 no.1
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• pp.73-78
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• 2007

Self-noise from the rotor blade of the UH-1H Helicopter is obtained numerically by using the Brooks' empirical noise model. All of the five noise sources are compared with each other in frequency domain. From the calculated results the bluntness noise reveals dominant noise sources at small angel of attack, whereas the separation noise shows main noise term with gradually increasing angel of attack. From the results of two different tip Mach numbers with the change of angel of attack, the OASPLs at M = 0.8 show about 15dB larger than those at M = 0.4.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.573-578
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• 2001

For the corrosion protect ion of the natural gas transmission pipelines, two methods are used, cathodic protection and coating technique. In the case of cathodic protection, defects are embrittled by occurring hydrogen at the crack tip or material surface. It is however very important to evaluate whether cracks in the embrittled area can grow or not, especially in weld metal. In this work, on the basis of elastic plastic fracture mechanics, we performed CTOD test ing with varying test conditions, such as the potential and current density. The CTOD of the base steel and weld metal showed a strong dependence of the test conditions. The CTOD decreased with increasing cathodic potential and current density. The morphology of the fracture surface showed quasi-cleavage. Hydrogen introduced fractures, caused by cathodic overprotection.