• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.1
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• pp.22-28
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• 2010

To detect the damage in composite structure, nondestructive evaluation techniques are widely used. Tapping test is perhaps the most common technique used for the detection of damage in composite laminates. The method is accomplished by tapping the inspection area with light hammer-like device. The tapping test has the ability that indicates damages in a structure due to a localized change of stiffness. The change in vibration signature may be detected by measurement of the dynamic contact force during impact. In this study, it has been shown that the characteristics of impact force histories from a structure during tapping are changed by the presence of damage such as surface crack and delamination. And impact response analysis has been performed on composite rotor blade with crack to investigate the effect of damage.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.145-150
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• 2005

This paper presents an Electrotactile Display System (ETCS). One of the most important human sensory systems for human computer interaction is the sense of touch, which can be displayed to human through tactile output devices. To realize the sense of touch, electrotactile display produces controlled, localized touch sensation on the skin by passing small electric current. In electrotactile stimulation, the mechanoreceptors in the skin may be stimulated individually in order to display the sense of vibration, touch, itch, tingle, pressure etc. on the finger, palm, arm or any suitable location of the body by using appropriate electrodes and waveforms. We developed an ETCS and investigated effectiveness of the proposed system in terms of the perception of roughness of a surface by stimulating the palmar side of hand with different waveforms and the perception of direction and location information through forearm. Positive and negative pulse trains were tested with different current intensities and electrode switching times on the forearm or finger of the user with an electrode-embedded armband in order to investigate how subjects recognize displayed patterns and directions of stimulation.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.6
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• pp.447-456
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• 2014

In this paper, a new damage-detection method based on structural vibration is proposed. The essence of the proposed method is the detection of abrupt changes in rotation. Damage-induced rotation (DIR), which is determined from the modal flexibility of the structure, initially occurs only at a specific damaged location. Therefore, damage can be localized by evaluating abrupt changes in rotation. We conducted numerical simulations of two damage scenarios using a 10-story cantilever-type building model. Measurement noise was also considered in the simulation. We compared the sensitivity of the proposed method to localize damage to that of two conventional modal-flexibility-based damage-detection methods, i.e., uniform load surface (ULS) and ULS curvature. The proposed method was able to localize damage in both damage scenarios for cantilever structures, but the conventional methods could not.

• Computers and Concrete
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• v.27 no.1
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• pp.29-39
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• 2021

This study aimed to develop a method for the determination of the damaged story in reinforced concrete (RC) structure with ambient vibrations, based on modified jerk energy methodology. The damage was taken as a localized reduction in the stiffness of the structural member. For loading, random white noise excitation was used, and dynamic responses from the finite element model (FEM) of 4 story RC shear frame were extracted at nodal points. The data thus obtained from the structure was used in the damage detection and localization algorithm. In the structure, two damage configurations have been introduced. In the first configuration, damage to the structure was artificially caused by a local reduction in the modulus of elasticity. In the second configuration, the damage was caused, using the Elcentro1940 and Kashmir2005 earthquakes in real-time history. The damage was successfully detected if the frequency drop was greater than 5% and the mode shape correlation remained less than 0.8. The results of the damage were also compared to the performance criteria developed in the Seismostruct software. It is demonstrated that the proposed algorithm has effectively detected the existence of the damage and can locate the damaged story for multiple damage scenarios in the RC structure.

• The Journal of the Acoustical Society of Korea
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• v.42 no.2
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• pp.83-93
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• 2023

Trapezoidal corrugated plates are often treated as orthotropic plates to simplify the modelling of the corrugation. However, this simplification is not valid at high frequencies in which the localized vibration within the parts of corrugation takes place. In this study, the vibrational and acoustical characteristics of corrugated plates are investigated up to high frequencies by means of the wavenumber domain numerical approach. Based on the findings from this numerical analysis, an approximate method to predict vibro-acoustic characteristics of corrugated plates is proposed. This approximate model consists of four equivalent plates which can represent global and local behaviours of corrugated plates. The radiation efficiency of corrugated plates is predicted from the approximate model and validated through the comparison with those of the numerical method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.5
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• pp.507-517
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• 2010

The KOREAN AIR - R&D Center has developed a solar array for STSAT-2 Flight Model, SaTReC-KAIST, using a fully localized technology and has verified the performance through a launch vibration test, orbit environment test and electrical performance test. The solar array will be launched at NARO Space Center by KSLV-I which is the first Korean launch vehicle, in May 2010. In this paper, a current-voltage curve that shows the power characteristics of solar arrays was derived by applying elements that affects the power performance of STSAT-2's solar arrays to the solar cell equivalent models. The result was compared to LAPSS test results, and accuracy of the solar cell equivalent model and the power performance simulation has been analyzed.

• Smart Structures and Systems
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• v.17 no.6
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• pp.917-933
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• 2016

In a prestressed concrete bridge, the magnitude of the prestress force (PF) decreases with time. This unexpected loss can cause failure of a bridge which makes prestress force identification (PFI) critical to evaluate bridge safety. However, it has been difficult to identify the PF non-destructively. Although some research has shown the feasibility of vibration based methods in PFI, the requirement of having a determinate exciting force in these methods hinders applications onto in-service bridges. Ideally, it will be efficient if the normal traffic could be treated as an excitation, but the load caused by vehicles is difficult to measure. Hence it prompts the need to investigate whether PF and moving load could be identified together. This paper presents a synergic identification method to determine PF and moving load applied on a simply supported prestressed concrete beam via the dynamic responses caused by this unknown moving load. This method consists of three parts: (i) the PF is transformed into an external pseudo-load localized in each beam element via virtual distortion method (VDM); (ii) then these pseudo-loads are identified simultaneously with the moving load via Duhamel Integral; (iii) the time consuming problem during the inversion of Duhamel Integral is overcome by the load-shape function (LSF). The method is examined against different cases of PFs, vehicle speeds and noise levels by means of simulations. Results show that this method attains a good degree of accuracy and efficiency, as well as robustness to noise.

• Structural Engineering and Mechanics
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• v.25 no.4
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• pp.481-500
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• 2007

The dynamic instability of doubly curved panels, subjected to non-uniform tensile in-plane harmonic edge loading $P(t)=P_s+P_d\;{\cos}{\Omega}t$ is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited doubly curved panels. Analytical expressions for the instability regions are obtained at ${\Omega}={\omega}_m+{\omega}_n$, (${\Omega}$ is the excitation frequency and ${\omega}_m$ and ${\omega}_n$ are the natural frequencies of the system) by using the method of multiple scales. It is shown that, besides the principal instability region at ${\Omega}=2{\omega}_1$, where ${\omega}_1$ is the fundamental frequency, other cases of ${\Omega}={\omega}_m+{\omega}_n$, related to other modes, can be of major importance and yield a significantly enlarged instability region. The effects of edge loading, curvature, damping and the static load factor on dynamic instability behavior of simply supported doubly curved panels are studied. The results show that under localized edge loading, combination resonance zones are as important as simple resonance zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which the curved panels cannot become dynamically unstable. This example of simultaneous excitation of two modes, each oscillating steadily at its own natural frequency, may be of considerable interest in vibration testing of actual structures.

• The KSFM Journal of Fluid Machinery
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• v.14 no.3
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• pp.23-27
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• 2011

Due to a roots type medium vacuum pump is operated in condition of $1{\sim}10^{-3}$ torr vacuum, it could be applied for production and process of industrial parts, such as precise processing, vaporization, enrichment, separation, casting, metaling, welding, transportation. Therefore, the demand of this pump is increasing nowadays in our industrial markets of semiconductor, electric, electronic, automobile, material, environmental and transporting industries. However, the pumps are almost imported, because the domestic pumps are inferior in fields of vacuum range as under $10^{-1}$torr, relevant techniques(design, fabrication, casting, test, etc.) to the imported ones. In this study, essential parts of the development pump are designed with using of CFD and 3D decodes, FEM for analysing strength and deformation, generated heat, vibration and noise control, and are casted with using of mechanochemistry techniques for decreasing of weights, increasing of heat resistances and abrasion durability of materials for pump caing and impellers especially. Besides, in order to achieve ultimate vacuum around $10^{-3}$torr, this pump is composed of 6 stages, among which 1st stage is operated separately from remained stages. Additionally, a test rig for prototype pumps(300$m^3/h$ and 2,500$m^3/h$) is designed and procured as to apply for multi-staged rootz type vacuum pump, with modification of the test method recommended by KS B 6314 "Positive-displacement oil-sealed rotary vacuum pumps".

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.30-37
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• 2015

The estimation of system damping parameter of the response signal with lower natural frequency and higher damping parameter from free vibration is affected by the wavelet center frequency. This study discusses these considerations in the context of the wavelet's multi-resolution character and includes guidelines for selection of wavelet center frequency. The experiment with H-Beam and numerical examples with respect to three cases (i)single mode, (ii)separated modes and (iii)close modes demonstrate the validity of method to improve the accuracy of the estimated damping parameter. The localization of the corresponding scale for the total scales is determined by the natural frequency of the analysing mode and is affected by the wavelet center frequency. Thus, the reliability for the accuracy of the estimated damping parameter can be improved by the corresponding scale of the natural frequency for the analysing mode is localized at the half of the total scales.