• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.3
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• pp.255-263
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• 2021

This paper investigates numerically the effect of rotor hub vibratory load components on the airframe vibration responses of high-speed compound unmanned rotorcraft (HCUR) using a lift-offset coaxial rotor, wings, and two propellers. The rotor hub vibratory loads are predicted using a rotorcraft comprehensive analysis code, CAMRAD II, and the airframe vibration responses are calculated by a finite element analysis software, MSC.NASTRAN. It is shown that the vibratory hub pitch moment of a lift-offset coaxial rotor is the most dominant component for both the longitudinal and vertical vibration responses at four specified locations of the airframe.

• Steel and Composite Structures
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• v.49 no.6
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• pp.713-728
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• 2023

This paper aims to investigate the free vibration analysis of FG plates, taking into account the effects of even and uneven porosity. The study employs the Hellinger-Reisner functional and obtains the element's bending stress and membrane stress fields from the analytical solution of the governing equations of the thick plate and plane problem, respectively. The displacement field serves as the second independent field. While few articles on free vibration analysis of circular plates exist, this paper investigates the free vibration of both rectangular and circular plates. After validating the proposed element, the paper investigates the effects of porosity distributions on the natural frequency of the FG porous plate. The study calculates the natural frequency of thin and thick bending plates with different aspect ratios and support conditions for various porosity and volume fraction index values. The study uses three types of porosity distributions, X, V, and O, for the uneven porosity distribution case. For O and V porosity distribution modes, porosity has a minor effect on the natural frequency for both circular and rectangular plates. However, in the case of even porosity distribution or X porosity distribution, the effect of porosity on the natural frequency of circular and rectangular plates increases with an increase in the volume fraction index.

• The Journal of Korean Institute for Practical Engineering Education
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• v.2 no.2
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• pp.74-82
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• 2010

As the basic knowledge during designing most moving mechanical structures, vibration engineering is a subject teaching the theory on vibration control and isolation, which also cultivating the ability of analyze variety of vibration problems. However, vibration engineering is more difficult to understand than other dynamics courses in mechanical field, so the development of educational equipments in order to help understanding physical theory of vibration is really necessary. So in this paper we could see the effect after doing simple experiment process using the educational vibration equipment with multiple function, students could easily understand physical theory of vibration. The educational vibration equipment with multiple function and its application range are introduced, which could performance four kinds of typical vibration phenomenon: vibration of multidegree of freedom system, vibration of beam, vibration of beam, and vibration of plate. Finally, assessments of response and improvement plan are proposed through a survey.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.655-660
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• 2004

The pipes in the outdoor unit of an air conditioner are designed to reduce the vibration effect of the compressor. Three-dimensional structure of the pipe could provide various design choices and the resultant vibration characteristics of the outdoor units. A design program has been developed for an eligible parametric study of pipe design and automatic vibration analysis using commercial software, I-DEAS, and its macro. Optimal design of pipe configuration has been performed using the commercial software, iSIGHT. The optimized design shows 70 percents improvement in the vibration characteristics of the outdoor unit of an air conditioner.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.57-62
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• 2007

A modeling method for the modal and the transient vibration analysis of a multi-packet blade system excited by nozzle jet forces is presented in this paper. Blades are idealized as cantilever beams and the elastic structures like disc and shroud connecting blades are modeled as coupling stiffnesses. A modified Campbell diagram is proposed to identify true resonance frequencies of the multi-packet blade system. Different from the SAFE diagram that employs three dimensional space, the modified Campbell diagram proposed in this study employs a plane to find the true resonance frequencies. To verify the existence of true resonance frequencies, nozzle jet forces are modeled as periodic forces and transient vibration analysis were performed with the modeling method.

• Journal of Advanced Marine Engineering and Technology
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• v.13 no.1
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• pp.77-96
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• 1989

In diesel engines, it is inevitable that the torsional vibration is produced by the fluctuation of engine torque. Therefore, if the occurence of torsional vibration is confirmed in the design stage or the torsional vibration is observed on the bed of test run, it is necessary to establish some preventive measures to avoid dangerous conditions. Major preventive measures are as follows : 1. Changing the natural frequency of shaft system. 2. Repressing the vibration amplitude by the damping energy. 3. Counterbalancing the exciting torque by the resistant torque. 4. Counterbalacing the harmonic component of exciting energy. In above methos, the damper is the last measure to be used for controlling the torsional vibration. In this thesis, the design of viscous damper that absorbs the exciting energy is investigated and a number of problems associated with the design of viscous damper are treated and a computer pregram for the process of damper design is developed. A viscous damper for a high speed diesel engine is designed and its effect is simulated by the author's computer program.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.4
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• pp.81-86
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• 2013

For a 2-dimensional(2D) vibration milling, an excitation work-table was developed using two piezoelectric materials orthogonally arranged, where the trochoidal trajectory of a milling tool is combined with 2 dimensional elliptical vibration of a work-table. Applying 3kHz excitation frequency and 7~8mm amplitude of vibration to micro milling process with brass and nickel materials, the roughness in both bottom and side surface is much more improved compared to the surface by conventional milling process, which is attributed to decreased frictional force, increased cutting speed, and rubbing effect of a 2 dimensional vibration.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1020-1025
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• 2007

The reciprocating type hydrogen compressor is for high pressure and volume. However this type compressor makes pulsation caused by mechanical characteristic. This type compressor also makes noise and vibration that cause negative effect to machine and working condition. Therefore, diagnosis and countermeasure are needed to decrease vibration for safety on hydrogen compressor. therefore in this paper, the numerical analysis and vibration measurement is conducted in order to investigate vibration characteristic and to evaluation vibration condition, Respectively

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.933-938
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• 2002

A pulsation of fluid in a pipe sometimes causes severe vibration of pipe. The inertia, damping and stiffness characteristics of pipe will be changed by the effect of fluid-structure interaction. The velocity and pressure of fluid will impose the force to a bended shape pipe. In this paper, a pipe with fluid flow is modeled by finite element method and the fluid force from pulsation is also modeled by the fluid dynamics. The vibration of pipe conveying pulsating fluid flow can be estimated by taking into consideration of fluid-structure interaction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.6
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• pp.562-567
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• 2010

A passenger vehicle has various and complicated transmission paths of sound and vibration. In order to identify the mechanism of transfer path, estimation of excitation force and exact modeling of transfer path are required. In this paper vector synthesis technique is employed to identify the characteristics of road noise and its transmission to vehicle compartment through noise and vibration analysis. Vibration reduction efficiency of each transfer path is evaluated by comparing individual vector components obtained virtual simulation. The degree of effect is used to estimate the contribution of vibration input components to total output. And in this paper presents a new technique based on simulation studies using vector synthesis diagram and design of experiments, by which the effects of magnitude and phase change of input paths can be predicted.