• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.1
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• pp.291-298
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• 1995

An ultrasonic testing uses the directivity of the ultrasonic wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. This paper studied the directivity of shear waves emitted from angle probes and scattered from surface defects by using visualization method. These experimental results were compared with the theory which was based on the continuous wave. The applicability of continuous wave theory was discussed in terms of the parameter $d/{\lambda}$; where d is transducer or defect size and ${\lambda}$ is the wavelength. In the case of angle probes, the experimental results show good agreement with theoretical directivity on the principal lobe. When defect size was smaller than the wavelengths, clear directivity in the reflected wave was observed. In the case of the same ratio of defect size to wavelength, the directivity of reflected waves from the defect show almost the same directivity in spite of frequency differences. When the $d/{\lambda}$ is greater than 1.5, measured directivities almost agreed with the theoretical one.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.373-379
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• 2010

EMAT has been applied in various fields for flaw detection and material characterization because it has noncontact property in wave generation and a good mode selectivity. Unfortunately, however, EMAT shows low signal to noise ratio relative to commercial contact transducer because of low energy conversion efficiency. If the phase matching through the control of time delay between each coil consisting of the array EMAT is accomplished, it is expected that it will be a solution for the improvement of low signal to noise ratio. In this experiment, the phased array EMATs which consists of 3 or 4 meander coils and one big magnet were fabricated for surface and vertical shear wave generation. Effect of phased delay control on signal directivity and amplitude enhancement was verified. A slit with the depth of 0.5 mm and a side-drill hole of 0.5 mm diameter were clearly detected by fabricated phased array EMATs, respectively.

• Journal of the Korean Geophysical Society
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• v.8 no.2
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• pp.67-74
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• 2005

Two-dimensional S-wave velocity sections from SH-wave refraction tomography and surface wave dispersions were obtained by inverting traveltimes of first arrivals and surface wave dispersions, respectively. For the purpose of comparison, a P-wave velocity tomogram was also obtained from a P-wave refraction profiling. P and Rayleigh waves generated by vertical blows on a plate with a sledgehammer were received by 100- and 4.5-Hz geophones, respectively. SH-waves generated by horizontal blows on both sides of a 50 kg timber were received by 8 Hz horizontal geophones. The shear-wave signals were enhanced subtracting data of left-side blows from ones of the right-side blows. Shear-wave velocities from tomography inversion of first-arrival times were compared with ones from inverting dispersion curves of Rayleigh waves. Although the two velocity sections look similar to each other in general, the one from the surface waves tends to have lower velocities. First arrival picking of SH waves is troublesome since P and PS-converted waves arrive earlier than SH waves. Application of the surface wave method, on the other hand, is limited where lateral variation of subsurface tructures is not mild.

• Proceedings of KOSOMES biannual meeting
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• 2005.05a
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• pp.155-159
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• 2005

Analysis target ship is not introduced yet in domestic as steel yacht that is getting into the spotlight by leisure life in Australia or Japan. Sailing yacht or Yacht for leisure time made of FRP into controlling power fare mainly and the design and made of latest fishing boat and something of domestic is consisting mainly. To need investigated for concept is various kinds overall strength as that use mainly steel wire material structurally of steel yacht by small crafts about Longi strength, Transe strength portion even of design safety factor at subject to do Rule's allowable stress enough stable structure accomplish. But it is assessment of part intensity that become refer to most in small size ship.

• The Journal of the Acoustical Society of Korea
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• v.24 no.5
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• pp.282-293
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• 2005

Sonoelastography is an ultrasound-based technique that visualizes the elastic properties of soft tissues by measuring the tissue motion generated by an externally applied vibration. In this paper. the characteristics of wave generation in soft tissues due to an acoustic vibrator are studied. The effects of modal patterns on the detectability of lesions such as tumors in senoelastography are also investigated These are accomplished by analyzing the vibration patterns calculated using theoretical equations and finite element methods in halt space, infinite plate. and finite-sized tissue. A finite-width source generates shear waves with large amplitude Propagating in specific directions. and the generation characteristics depend both on the width and frequency of the vibrator. as well as the distance from it. It is shown in a finite-sized tissue that the lesion detection in displacement images is quit dependent on the modal patterns inside tissue. In contrast it Is also found that the lesion detectability in strain images is less dependent on the modal Patterns and is much better than that in displacement images.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.5
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• pp.497-502
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• 2013

There are currently 10 types of buoy, mostly which' design and development is dependent on foreign technology. In this study, it is aimed at the development of small instrumentation buoy and at the design proposal presented a numerically safety. The numerical method has the simulation of variety of marine environments, such as wave response amplitude ratio and each flux changes. Through the numerical simulation of buoy's kinetic movement, it is analyzed that Pitching motion increases by the frequency response of encounter and Added resistance appears to be the most significant on transverse waves. Finally, the proposed buoy is confirmed with the response' safety under simulation' conditions.

• Tunnel and Underground Space
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• v.17 no.2 s.67
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• pp.83-89
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• 2007

Impact-echo test is a non-destructive testing method to determine dynamic properties of a material. This presentation introduces the experimental set-up and procedure of the test for rock specimens. In addition, the test results of domestic rocks collected in 5 different areas, a cement mortar and aluminium alloy are presented. The test results include resonance frequencies of P- and S-wave as well as damping ratios of the described 7 different materials. The differences between dynamic and static values of elastic moduli are about 10%, while the dynamic Poisson's ratios are greater than the static Poisson's ratios by at least 0.07. The damping ratio is dependent on the joint density and degree of weathering of a rock specimen.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.69-79
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• 2001

A volume integral equation method(VIEM) is applied for the effective analysis of elastic wave scattering problems in unbounded solids containing general anisotropic inclusions. It should be noted that this newly developed numerical method does not require the Green's function for anisotropic inclusions to solve this class of problems since only the Green's function for the unbounded isotropic matrix is Involved In their formulation for the analysis. nis new method can also be applied to general two-dimensional elastodynamic problems with arbitrary shapes and number of anisotropic inclusions. Through the analysis of plane elastodynamic problems in unbounded isotropic matrix with an orthotropic inclusion, it is established that this new method is very accurate and effective for solving plane elastic problems in unbounded solids containing general anisotropic inclusions.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.3
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• pp.207-216
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• 1999

A phased array is a multi-element piezoelectric device whose elements are individually excited by electric pulses at programmed delay time. One of the advantages of using phased array in nondestructive evaluation (NDE) application over conventional ultrasonic transducers is their great maneuverability of ultrasonic beam. There are some parameters such as the number and the size of the piezoelectric elements and the inter-element spacing of the elements to design phased array transducer. In this study, the characteristic of ultrasonic beam for phased array transducer due to the variation of the number of elements has been simulated for ultrasonic SH-wave on the basis of Huygen's principle. Ultrasonic beam directivity and focusing due to the change of time delay of each element were discussed due to the change of the number of piezoelectric elements. It was found that ultrasonic beam was much more spreaded and hence its sound pressure was decreased as steering angle of ultrasonic beam was increased. In addition, the ability of ultrasonic bean focusing decreased gradually with the increase of focal length at the same piezoelectric elements. However, the ability of beam focusing was improved as the number of consisting elements was increased.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.5
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• pp.469-483
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• 2012

The propagation characteristics of a mechanical wave in human soft tissue depend on its elastic properties. Investigation of these propagation characteristics is of paramount importance because it may enable us to diagnose cancer or tumor from the vibration response of the tissue. This paper investigates and compares displacement patterns generated in soft tissue due to several forms of low-frequency vibration sources placed on a surface. Among vibration sources considered are a normal load, tangential load, and antiplane shear load. We derive analytical expressions for displacements in viscoelastic single layers, and calculate displacement patterns in half space and infinite plate type tissue. Also, we simulate the vibration response of a finite-sized tissue using finite element method. The effects of the type of stress, the size and frequency of vibration sources, and medium boundaries on displacement patterns are discussed.