• Computers and Concrete
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• v.20 no.4
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• pp.503-509
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• 2017

In this study, fire-damaged concrete was investigated by a nonlinear resonance vibration (NRV) technique, in order to evaluate its residual material properties. For the experiments, five cubic concrete specimens were prepared and four of them were damaged at different temperatures using a furnace. With a thermal insulator wrapped at the sides of specimen, thermal gradation was applied to the samples. According to the peak temperatures and depths of the samples, nonlinearity parameters were calculated with the NRV technique before the tendency of the parameters was evaluated. In addition, compressive strength and dynamic elastic modulus were measured for each sample and a comparison with the nonlinearity parameter was carried out. Through the experimental results, the possibility of the NRV technique as a method for evaluating residual material properties was evaluated.

• Geomechanics and Engineering
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• v.12 no.1
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• pp.161-183
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• 2017

This paper investigates the damage identification of the concrete pile element through axial wave propagation technique using computational and experimental studies. Now-a-days, concrete pile foundations are often common in all engineering structures and their safety is significant for preventing the failure. Damage detection and estimation in a sub-structure is challenging as the visual picture of the sub-structure and its condition is not well known and the state of the structure or foundation can be inferred only through its static and dynamic response. The concept of wave propagation involves dynamic impedance and whenever a wave encounters a changing impedance (due to loss of stiffness), a reflecting wave is generated with the total strain energy forked as reflected as well as refracted portions. Among many frequency domain methods, the Spectral Finite Element method (SFEM) has been found suitable for analysis of wave propagation in real engineering structures as the formulation is based on dynamic equilibrium under harmonic steady state excitation. The feasibility of the axial wave propagation technique is studied through numerical simulations using Elementary rod theory and higher order Love rod theory under SFEM and ABAQUS dynamic explicit analysis with experimental validation exercise. Towards simulating the damage scenario in a pile element, dis-continuity (impedance mismatch) is induced by varying its cross-sectional area along its length. Both experimental and computational investigations are performed under pulse-echo and pitch-catch configuration methods. Analytical and experimental results are in good agreement.

• Proceedings of the KOSOMBE Conference
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• v.1989 no.05
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• pp.51-54
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• 1989

In last several years, a number of volume localization techniques, such as ISIS, VSE, SPARS and STEAM etc., have been developed for the MR spectroscopy. These localizing techniques, however, require application of several RF pulses for the 3-D volume selection and suffer from T1 and T2 decays due to relatively long RF excitation time. In this paper, we propose a single-shot RF pulse localization technique to achieve the localized 3-D volume selection. This technique combines the cylindrical volume selection technique with a radial gradient coil with single-shot RF pulse and the oscillating selection gradient technique, so thai it minimizes the volume selection time. We report some experimental results obtained with the proposed method which appears promising for 3-D volume imaging and localized spectroscopy.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.3
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• pp.273-278
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• 2016

This study makes a relative comparison of the results of tensile test and quasi-static analysis using AGL(Adjuster Guide Loop) model that plays a role in adjusting the height of shoulder belt, of the components of the vehicle seatbelt system and attempts to propose a method of reducing the error rate of the quasi-static analysis technique effectively. This study selects two major factors affecting the result of an analysis, draws the result of analysis through the method of experimental design, one of the statistical techniques and understands the contribution rate of the major factors affecting the result of the analysis through ANOVA(Analysis of Variance).

• International Journal of Aeronautical and Space Sciences
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• v.11 no.1
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• pp.1-9
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• 2010

Numerical simulation of unsteady flows around helicopters was conducted to investigate the aerodynamic interaction of main rotor and other components such as fuselage and tail rotor. For this purpose, a three-dimensional inviscid flow solver has been developed based on unstructured meshes. An overset mesh technique was used to describe the relative motion between the main rotor, and other components. As the application of the present method, calculations were made for the rotor-fuselage aerodynamic interaction of the ROBIN (ROtor Body INteraction) configuration and for a complete UH-60 helicopter configuration consisted of main rotor, fuselage, and tail rotor. Comparison of the computational results was made with measured time-averaged and instantaneous fuselage surface pressure distributions for the ROBIN configuration and thrust distribution and available experimental data for the UH-60 configuration. It is demonstrated that the present method is efficient and robust for the simulation of complete rotorcraft configurations.

• Nuclear Engineering and Technology
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• v.38 no.2
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• pp.119-128
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• 2006

We start to develop a predictable technology for thermal-hydraulic performance of the RMWR core using an advanced numerical simulation technology. As a part of this technology development, we are developing the advanced interface tracking method to improve the conservation of volume of fluid. The present paper describes a part of the development of the twophase flow simulation code TPFIT with the advanced interface tracking method. The numerical results applied to large-scale water-vapor two-phase flow in tight lattice rod bundles are shown and compared with experimental results. In the results of numerical simulation, a tendency of the predicted void fraction distribution in horizontal plane agreed with the measured values obtained by the advanced neutron radiography technique including the bridge formation of the liquid at the position of adjacent fuel rods where an interval is the narrowest.

• Journal of Institute of Control, Robotics and Systems
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• v.3 no.4
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• pp.357-362
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• 1997

This paper suggests an automatic calibration technique for piezoelectric low pressure transducer measuring a pressure blow 500psi. The present calibration system embedded with error correction algorithm generates it's best you don't cut parts of wards like so dynamic pressure and compensates offset voltage and pressure error. It is shown via experimental results that the instrumentation accuracy has been improved and mean time between calibrations has been shortened.

• International Journal of Aeronautical and Space Sciences
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• v.12 no.2
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• pp.175-178
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• 2011

An optical fiber-based beam width measurement technique is presented. The proposed system can be applied to the optical fiber industry in applications such as lensed fiber, optical fiber based laser beam source, and fiber optic sensor. The measurement system is composed of optical fiber, which is used as a transceiver, and a single grating panel which consists of a multi-reflection area with an even non-reflection area. The grating panel is used to vary the reflected light. When the widths of the reflection area and non-reflection area are larger than the optical beam width, the reflected light is varied at the interface between the reflection area and the non-reflection area by the movement of the grating panel. Experiments were conducted in order to verify the feasibility of the proposed technique. Multi-mode fiber combined with a collimator was selected as an emitter and a receiver, and the beam width measurement system was contrived. Subsequently, the proposed method and the system were verified by comparing the experimental results with the results of the conventional charge-coupled device technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.3
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• pp.217-223
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• 2007

This paper introduces an active sensing node using radio-frequency (RF) telemetry. This device has brought the traditional impedance-based structural health monitoring (SHM) technique to a new paradigm. The RF active sensing node consists of a miniaturized impedance measuring device (AD5933), a microcontroller (ATmega128L), and a radio frequency (RF) transmitter (XBee). A macro-fiber composite (MFC) patch interrogates a host structure by using a self-sensing technique of the miniaturized impedance measuring device. All the process including structural interrogation, data acquisition, signal processing, and damage diagnostic is being performed at the sensor location by the microcontroller. The RF transmitter is used to communicate the current status of the host structure. The feasibility of the proposed SHM strategy is verified through an experimental study inspecting loose bolts in a bolt-jointed aluminum structure.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.260-261
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• 2003

It is recognized that the magnetization reverses with a sequence of discrete and jerky jumps, known as the Barkhausen effect. Recently, interest in the Barkhausen effect has grown as it is a good example of dynamical critical behavior, evidenced by experimental observation of a power law distribution of the Barkhausen jump size. So far, most experimental studies have been carried out on bulk samples using a classical inductive technique, which is difficult to apply to thin film samples mainly due to the ]ow signal intensity. For this reason, very few experiments have been done on two-dimensional ferromagnetic thin films. In this talk, we report a direct domain observation of Barkhausen avalanche at criticality in Co and MnAs thin films investigated by means of a magnetooptical microscope magnetometer (MOMM), capable of time-resolved domain observation with an image grabbing rate of 30 frames/s in real time. In Fig. 1, we demonstrate a series of six representative domain-evolution patterns of 25-nm Co film observed successively by means of the MOMM, where one can directly witness Barkhausen avalanche.