• Steel and Composite Structures
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• v.23 no.6
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• pp.691-714
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• 2017

Rotating fluid induced vibration and instability of embedded piezoelectric nano-composite separators subjected to magnetic and electric fields is the main contribution of present work. The separator is modeled with cylindrical shell element and the structural damping effects are considered by Kelvin-Voigt model. Single-walled carbon nanotubes (SWCNTs) are used as reinforcement and effective material properties are obtained by mixture rule. The perturbation velocity potential in conjunction with the linearized Bernoulli formula is used for describing the rotating fluid motion. The orthotropic surrounding elastic medium is considered by spring, damper and shear constants. The governing equations are derived on the bases of classical shell theory (CST), first order shear deformation theory (FSDT) and sinusoidal shear deformation theory (SSDT). The nonlinear frequency and critical angular fluid velocity are calculated by differential quadrature method (DQM). The detailed parametric study is conducted, focusing on the combined effects of the external voltage, magnetic field, visco-Pasternak foundation, structural damping and volume percent of SWCNTs on the stability of structure. The numerical results are validated with other published works as well as comparing results obtained by three theories. Numerical results indicate that with increasing volume fraction of SWCNTs, the frequency and critical angular fluid velocity are increased.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.439-444
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• 2004

The important problem in high speed spindle is to reduce and minimize the thermal effect by motor and ball bearings. In this study. the effects of bearing preload and cooling for high speed spindle with high frequency motor are investigated. A high speed spindle is composed of angular contact ball bearings, high frequency motor, grease lubrication, oil jacket cooling, and so on. Heat generation of the bearing and the high frequency motor are estimated from the theoretical and experimental data. The thermal analyses of high speed spindle to minimize the thermal effect and maximize the cooling effect are carried out under the various cooling conditions and preload. Method of variable bearing preload and cooling can be useful to design the high speed motor spindle. The results show that the optimal preload and cooling are very effective to minimize the thermal displacement by motor and ball bearing.

• 한국HCI학회:학술대회논문집
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• 2006.02a
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• pp.699-704
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• 2006

본 논문은 회전 및 천이불변 이미지 텍스처 검색의 새로운 방식을 소개한다. 주파수 영역의 극좌표계에서 동일한 공간 주파수에서 각도 방향으로 투영을 하는 각도 투영법을 제안하며, 제안된 각도 투영법을 이용하여 주파수 영역에서 푸리에 계수이 합과 표준편차를 특징벡터로 이용한다. 각도 투영법을 쉽게 구현하기 위해 극좌표계에서 라돈변환이 수행된다. 실험 시 MPEG-7 데이터를 이용하였으며 그 결과는 여러 텍스처 이미지를 검색하는데 있어서 특징을 잘 구별해 내는 결과를 보여준다. 또한 제안된 회전 및 천이불변 특징 추출 알고리듬은 등방성 텍스처나 국부적인 방향성을 보이는 텍스처 영상 검색에도 효율적인 검색률을 보인다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.190-197
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• 1998

Equations of motions of a pretwisted rotating blade with a concentrated mass in an arbitrary position are derived. The flapwise and chordwise equations are coupled to each other due to the pretwist angle of the blade. As the angular speed, hub radius ratio, pretwist angle and concentrated mass vary, the vibration characteristics of the blade change. It is found that eigenvalue lociveering phenomena occur between two closing loci due to the pretwist angle. The effect of the pretwist angle on the critical angular speed and location of the concentrated mass on the natural frequencies are also investigated.

• 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.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.103-110
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• 2000

In this study, the angular twist type torque-meter was designed and manufactured with STS 304 and fiber-reinforced composite materials to improve the dynamic properties of the existing torque-meter. From the Experimental and analytical results, it was found that the dynamic characteristics of co-cured bonded torque-meter rotating shaft were better than those of the adhesively and unreinforced torque-meter rotating shaft. For the torque-meter rotating shaft manufactured by co-cured bonded with the glass fiber-epoxy composite and with a stacking sequence of $[$\pm$30$^{\circ}$/STS304]_{2s}$, the natural frequency and the radial spring constant were increased by 64% and 137% compared to those of the unreinforced torque-meter rotating shaft.

• The Journal of the Acoustical Society of Korea
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• v.8 no.4
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• pp.39-43
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• 1989

In this paper, the concept of ultrasonic transmission imaging system with crossed -arrays is Introduced. The crossed-array system is simulated by angular spectrum method In the operating frequency of 12MHz. A theoritical development of a system transfer function matrix 1M is presented. Using this matrix, a priori knowledge on the physical properties of the system is understood. It proves to be a block Toeplitz matrix with Toeplitz entries. Using the Inversion procedure, the spatial degradations of the measured image can be removed.

• Journal of KSNVE
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• v.6 no.2
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• pp.179-185
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• 1996

This paper presents a modeling method for the vibration analysis of a rotating beam the slenderness ratio of which is relatively small. The smaller the slenderness ratio becomes, the larger the shear and rotary inertia effects become. Such effects become critical for the accurate estimation of the natural frequencies and modeshapes, especially higher frequencies and modes, as the angular speed increases. It is also shown that the effects are important for the accurate estimation of the critical angular speed of the beam.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.91-99
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• 1998

This paper presents a methodology for identifying the cutter runout geometry in end milling process. Cutter runout is common but undesirable phenomenon in multi-tooth machining because it introduces variable chip loading to insert which results in a accelerated tool wear. amplification of force variation and hence enlargement vibration amplitude From understanding of chip load change kinematics, the analytical cutting force convolution model was formulated as the angular domain convolution model was formulated as the angular domain convolution of three dynamic cutting force component functions. By virtue of the convolution integration property, the frequency domain expression of the local cutting forces and the chip width density of the cutter. Experimental study is presented to validate the analytical model. This study provides the in-process monitoring and compensation of dynamic cutter runout to improve machining tolerance and surface quality for industrial application.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.1017-1022
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• 1996

This paper presents results of dynamic analysis of the missile initial motion arising from the missile detent force. Using ADAMS (Automatic Dynamic Analysis of Mechanical System) software, a non-linear 46-DOF (Degree of Freedom) model is developed for the launcher system including missile and launch tube contact problem. From the dynamic analysis, it is found that initial angular velocity of the missile increases when the missile detent force increases (more than 18 g) and also rocket exhaust plume is taken into account. To achieve the missile launching s ability, it needs to reduce the missile initial detent force and exhaust plume area of the launcher. Results of the dynamic analysis on the system natural frequency agree well with those obtained from experimental modal tests. The overall results suggest that the proposed method is a useful tool for prediction of initial missile stability as well as d :sign of the missile launcher system.