• Journal of Sensor Science and Technology
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• v.24 no.3
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• pp.169-174
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• 2015

In this study, we developed a system to detect the various defects in the metallic objects using the phenomenon that the defects cause the changes of the natural resonant frequencies. Our system consists of a FFT Amp, an Auto Impact Hammer, a Hammer controller and a PC. Auto Impact Hammer creates vibrations in the metallic objects when tapped on the surface. These vibrational signals are converted to the voltage signals by an acceleration sensor attached to the metallic part surface. These analog voltage signals were fed into an ADC (analog-digital converter) and an FFT (fast fourier transform) conversion in the FFT Amp to obtain the digital data in the frequency domain. Labview graphical program was used to process the digital data from th FFT amp to display the spectrum. We compared those spectra with the standard spectrum to find the shifts in the resonant frequencies of the metal parts, and thus detecting the defects. We used PCB's acceleration sensor and TI's TMS320F28335 DSP (digital signal processor) to obtain the resolution of 2.93 Hz and to analyze the frequencies up to 44 kHz.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.10a
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• pp.349-354
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• 2000

The modal analysis based on deformations is the method to drived dynamic responsed from superposition of natural frequency and mode shape. In order to free vibration analysis of the structures, Aluminum-made model is used in experiment. The dynamic characteristic of the structures are determined from acceleration measurements using impulse hammer. Experimenrt input and output signal are derive from impact hammer and the one accerometer. This paper present three methods for calculating the natural frequencies and mode shapes of the structure with theory value and finite element analysis, experiment. The results were good approximated about natural frequency and mode shape.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.223-226
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• 1995

A three-dimensional elastic-plastic finite element analysis using the explicit time integration method has been performed for the characterization of theimpact forming machines. The block upsetting using a forging hammer has been analyzed. The effects of machine type, work capacity of equipment and the mass ratio in an anvil-type hammer have been studied through the analysis.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.269-274
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• 2016

This paper proposes the development of a low frequency electronic hammer drive system that is used to prevent scaling or clogging in the hopper process. The electro-mechanical hammering driving method involves the generation of vibration and impact energy. The operation principles of the electromagnetic hammer were considered by parallel/series spring coefficient analysis and the amount of kinetic energy generated was calculated from the product of the equivalent spring constant, which is coupled with the E core and the gap of between the E core and I core. In addition, the Pulsation Driving algorithm was applied to the proposed electromagnetic hammer to obtain the maximizing kinetic energy. This algorithm was then implemented by a logical AND operation process and micro-controller (atmega128) built in functions with a timer interrupt and PWM generation function. The driving circuit of the electromagnetic hammer was designed using the H-bridge type IGBT circuit. The experimental test was performed by usefulness of the developed electromagnetic hammer systems with the acceleration measurement method. The experimental result showed that the proposed system has good kinetic energy generation performance and can be applied to the hopper process.

• Smart Structures and Systems
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• v.12 no.1
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• pp.55-71
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• 2013

Structural health monitoring (SHM) is vital for detecting the onset of damage and for preventing catastrophic failure of civil infrastructure systems. In particular, piezoelectric transducers have the ability to excite and actively interrogate structures (e.g., using surface waves) while measuring their response for sensing and damage detection. In fact, piezoelectric transducers such as lead zirconate titanate (PZT) and poly(vinylidene fluoride) (PVDF) have been used for various laboratory/field tests and possess significant advantages as compared to visual inspection and vibration-based methods, to name a few. However, PZTs are inherently brittle, and PVDF films do not possess high piezoelectricity, thereby limiting each of these devices to certain specific applications. The objective of this study is to design, characterize, and validate piezoelectric nanocomposites consisting of zinc oxide (ZnO) nanoparticles assembled in a PVDF copolymer matrix for sensing and SHM applications. These films provide greater mechanical flexibility as compared to PZTs, yet possess enhanced piezoelectricity as compared to pristine PVDF copolymers. This study started with spin coating dispersed ZnO- and PVDF-TrFE-based solutions to fabricate the piezoelectric nanocomposites. The concentration of ZnO nanoparticles was varied from 0 to 20 wt.% (in 5 % increments) to determine their influence on bulk film piezoelectricity. Second, their electric polarization responses were obtained for quantifying thin film remnant polarization, which is directly correlated to piezoelectricity. Based on these results, the films were poled (at 50 $MV-m^{-1}$) to permanently align their electrical domains and to enhance their bulk film piezoelectricity. Then, a series of hammer impact tests were conducted, and the voltage generated by poled ZnO-based thin films was compared to commercially poled PVDF copolymer thin films. The hammer impact tests showed comparable results between the prototype and commercial samples, and increasing ZnO content provided enhanced piezoelectric performance. Lastly, the films were further validated for sensing using different energy levels of hammer impact, different distances between the impact locations and the film electrodes, and cantilever free vibration testing for dynamic strain sensing.

• Composites Research
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• v.33 no.5
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• pp.262-267
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• 2020

With increasing demands for high-speed machining and lightweight design of machine tools, increasing likeliness of generation of machine tool spindle vibrations has become an important issue. Spindle vibration has a significant impact on the surface finish of the workpiece in ultra-precision machining. It is necessary to resolve the machine tool spindle vibration in various machining processes to improve machining accuracy. In this paper, a TiC-SKH51 metal-matrix composite was used to suppress the vibration of the machine tool spindle. To confirm the dynamic characteristic of the TiC-SKH51 composite, impact hammer tests were conducted. After verifying the reliability of a finite element analysis (FEA) by comparing the results of the impact hammer test with the modal analysis using FEA, the analysis of the machine tool spindle model was performed. The FEA results show that the TiC-SKH51 composite applied machine tool spindle can be utilized to suppress the vibration generation.

• Structural Engineering and Mechanics
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• v.76 no.4
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• pp.465-477
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• 2020

This paper presents an investigation on the dynamic behavior of SRC columns with built-in cross-shaped steels under impact load. Seven 1/2 scaled SRC specimens were subjected to low-speed impact by a gravity drop hammer test system. Three main parameters, including the lateral impact height, the axial compression ratios and the stirrup spacing, were considered in the response analysis of the specimens. The failure mode, deformation, the absorbed energy of columns, as well as impact loads are discussed. The results are mainly characterized by bending-shear failure, meanwhile specimens can maintain an acceptable integrity. More than 33% of the input impact energy is dissipated, which demonstrates its excellent impact resistance. As the impact height increases, the flexural cracks and shear cracks observed on the surface of specimens were denser and wider. The recorded time-history of impact force and mid-span displacement confirmed the three stages of relative movement between the hammer and the column. Additionally, the displacements had a notable delay compared to the rapid changes observed in the measured impact load. The deflection of the mid-span did not exceed 5.90mm while the impact load reached peak value. The impact resistance of the specimen can be improved by proper design for stirrup ratios and increasing the axial load. However, the cracking and spalling of the concrete cover at the impact point was obvious with the increasing in stiffness.

• Nuclear Engineering and Technology
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• v.43 no.6
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• pp.573-582
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• 2011

The in-cabinet response spectrum is used to define the input motion in the seismic qualification of instruments and devices mounted inside an electrical cabinet. This paper presents a procedure for generating the in-cabinet response spectrum for electrical equipment based on in-situ testing by an impact hammer. The proposed procedure includes an algorithm to build the relationship between the impact forces and the measured acceleration responses of cabinet structures by estimating the state-space model. This model is used to predict seismic responses to the equivalent earthquake forces. Three types of structural model are analyzed for numerical verification of the proposed method. A comparison of predicted and simulated response spectra shows good convergence, demonstrating the potential of the proposed method to predict the response spectra for real cabinet structures using vibration tests. The presented procedure eliminates the uncertainty associated with constructing an analytical model of the electrical cabinet, which has complex mass distribution and stiffness.

• Journal of Korean Society of Water and Wastewater
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• v.13 no.2
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• pp.95-104
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• 1999

A simulation of water hammer, introduced by abruptly varied motion of a pumping machine, was performed at a one of typical pumping station in Korea. Impact of hydraulic structure such as check valve, pressure relief valve and air valve in mitigating water hammer effect was estimated gradually. Method of characteristic was employed for the effective calculation of discharge and head. The relationship between various hydraulic structures and flow was properly integrated on the base of the method of characteristic. The methodology in this approach can provide significant contribution in decision making procedure for the design of hydraulic structure at a typical pumping station in Korea.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.126-129
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• 2008

Using a surplus head in presented water supply pipes, we have studied to improve the operating efficiency of small hydro generator, which was chosen for a test model with Sung-Nam and Bo-Ryong small hydro power plant. With regard to power control and countermeasure of water hammer impact, Finally we have represented the optimal control method through the synthetical analysis of existing system symptoms, operation efficiency, the effect of water hammer impact and system configuration.