• Smart Structures and Systems
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• 제20권3호
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• pp.351-368
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• 2017

To peruse the free vibration of curved functionally graded piezoelectric (FGP) nanosize beam in thermal environment, nonlocal elasticity theory is applied for modeling the nano scale effect. The governing equations are obtained via the energy method. Analytically Navier solution is employed to solve the governing equations for simply supported boundary conditions. Solving these equations enables us to estimate the natural frequency for curved FGP nanobeam under the effect of a uniform temperature change and external electric voltage. The results determined are verified by comparing the results by available ones in literature. The effects of various parameters such as nonlocality, uniform temperature changes, external electric voltage, gradient index, opening angle and aspect ratio of curved FGP nanobeam on the natural frequency are successfully discussed. The results revealed that the natural frequency of curved FGP nanobeam is significantly influenced by these effects.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.85-88
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• 2002

We have implemented a system of falling weight impact tester. Absorbed energy of orthotropic composites with using T300 fiber, which are composed of the same fiber and stacking number is higher than that of quasi-isotropic specimen over impact energy 7J, but in case of using T700 fiber, much difference does not show. Also, absorbed energy of orthotropic composites with using T300 fiber, which are composed of stacking number and orientation became more than that of T700 fiber specimen; however great change doesn't show in case of quasi-isotropic specimens. Delamination area of impacted specimens was measured with ultrasonic C-scanner to find correlation between impact energy and delamination area. Delamination area and frequency responses was evaluated between impacted and unimpacted specimens. There is a strong correlation between frequency responses and impact-induced delamination. The presence and scale of damages have been investigated based on the variations of frequency responses.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 춘계학술대회논문집; 부산수산대학교, 10 May 1996
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• pp.322-327
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• 1996

Dynamic stability of an axially oscillating cantilever beam is investigated in this paper. The equations of motion are derived and transformed into non-dimensional ones. The equations include harmonically oscillating parameters which originate from the motion-induced stiffness variation. Using the equations, the multiple scale perturbation method is employed to obtain a stability diagram. The stability diagram shows that relatively large unstable regions exist around the frequencies of the first bending natural frequency, twice the first bending natural frequency, and twice the second bending natural frequency. The validity of the diagram is proved by direct numerical simulations of the dynamic system.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.97-103
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• 2008

Unsteady three-dimensional flowfields generated by transverse fuel injection into a supersonic mainstream are simulated with a DES turbulence model. Comparisons are made with experimental results in term of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the jet vortical structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly overpredict the eddy formation frequency. The jet vortical structures are developed from the competing vortices in the recirculation region of upstream boundary.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.97-103
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• 2008

Unsteady three-dimensional flowfields generated by transverse fuel injection into a supersonic mainstream are simulated with a DES turbulence model. Comparisons are made with experimental results in term of the temporal eddy position and eddy formation frequency. The vorticity field around the jet exit is also analyzed to understand the formation mechanism of the jet vortical structures. Results indicate that the DES model correctly predicts the convection characteristics of the large scale eddies. However, it is also observed that the numerical results slightly overpredict the eddy formation frequency. The jet vortical structures are developed from the competing vortices in the recirculation region of upstream boundary.

• 대한기계학회논문집A
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• 제28권8호
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• pp.1065-1074
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• 2004

A robust optimal design considering fabrication influence has been performed for the decoupled vibratory microgyroscope fabricated by the bulk micromachining. For the analysis of the gyroscope, a design tool has been developed, by which user can perform the system level design considering electric signal process and the fabrication influence as well as mechanical characteristics. An initial design of the gyroscope is performed satisfying the performances of scale factor (or sensitivity) and phase delay, which depend on the frequency difference between driving and sensing resonant frequencies. The objective functions are formulated in order to reduce the variances of the frequency difference and the frequency in itself by fabrication error. To certify the results, the standard deviations are calculated through the Monte Caries Simulation (MCS) and compared initial deviation that is measured fabricated gyroscope chip.

• 대한추나의학회지
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• 제6권1호
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• pp.1-9
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• 2005

Objective : The study aims to find out the effects of Chuna treatment on neck pain. Methods: Out of 40 neck pain people, we divided 20 people in group A was treated Acupuncture and China, 20 people in group B was treated Acupuncture. We measured Visual Analog Scale(VAS) and symptom grade before and after treatment in each group's. Statistical analysis was performed by using SPSS program. Results : 1. Symptom grade III was the highest frequency before treatment in Group A and Group B. After treatment, grade 0 was The highest frequency in Group A But grade 0, II were the highest frequency in Group B. 2. Group A was Significantly decreased in VAS compared with Group B. Conclusion: These results suggest that Chuna treatment is useful on the patients of neck pain.

• 소음진동
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• 제4권2호
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• pp.209-219
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• 1994

Classical method calculates the resonance frequency of Helmholtz resonator by postulating that there is a moving mass in neck and a stiffness which expresses the compressibility of cavity. This has been widely accepted as reasonable to determine the resonant frequency, provided that the wave length of interest is longer that any length scale of resonater. Nevertheless, it has been often recognized that this classical method sometimes does not well predict the resonant frequency. This paper decribes the way in which the dynamics of resonator very often does care about the detail geometries of resonator; location of the neck, diameter ratio of the neck to that of cavitty, length of resonator compared with that of neck, etc. This rather unexpected observations have been proved theoretically; 3 dimensional analysis of acoustic wave equation, as well as experimentally by comparing the resonant frequencies, transmission loss, and insertion loss of resonator.

• Structural Monitoring and Maintenance
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• 제2권4호
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• pp.383-397
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• 2015

This article identifies and addresses current limitations on the use of numerical models for validation and/or calibration of damage detection methodologies that are based on the analysis of the high frequency response of the structure to identify the occurrence of abrupt anomalies. Distributed-plasticity non-linear fiber-based models in combination with experimental data from a full-scale reinforced concrete column test are used to point out current modeling techniques limitations. It was found that the numerical model was capable of reproducing the global and local response of the structure at a wide range of inelastic demands, including the occurrences of rebar ruptures. However, when abrupt sudden damage occurs, like rebar fracture, a high frequency pulse is detected in the accelerations recorded in the structure that the numerical model is incapable of reproducing. Since the occurrence of such pulse is fundamental on the detection of damage, it is proposed to add this effect to the simulated response before it is used for validation purposes.

• 국제초고층학회논문집
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• 제8권4호
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• pp.313-324
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• 2019

This paper presents the analysis of wind speeds data measured on top of three neighboring high-rise buildings close to a beach in Xiamen city, China, during Typhoon "Usagi" 2013. Wind tunnel simulation was carried out to validate the field measurement results. Turbulence intensity, turbulence integral scale, power spectrum and cross correlation of recorded wind speed were studied in details. The low frequency trend component of the typhoon speed was also discussed. The field measurement results show turbulence intensity has strong dependence to the wind speed, upwind terrain and even the relative location to the Typhoon center. The low frequency fluctuation could severely affect the characteristics of wind. Cross correlation of the measured wind speeds on different buildings also showed some dependence on the upwind terrain roughness. After typhoon made landfall, the spatial correlation of wind speeds became weak with the coherence attenuating quickly in frequency domain.