• The Journal of Korean Institute of Communications and Information Sciences
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• v.12 no.3
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• pp.285-291
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• 1987

Seismic waves are attenuated by losses of energy as they propagate through the earth. One way to model this numerically is to make the velocity a complex number, the real part giving the phase velocity and the imaginary part the attenuation. This models wave propagation in a medium for which the logarithmic decrement is independent of frequency(attenuation coefficient is proportional to frequncy). The aim is to modify forward and inverse numerical modeling so that attenuation can be specified as a function of position.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.419-424
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• 2020

Poroelasticity theory has been widely used for detecting cancellous bone deterioration because of the safe use for humans. The tortuosity itself is an important indicator for ultrasound detection for bone diseases. The transport properties of cancellous bone are also important in bone mechanotransduction. In this paper, two important factors, the wave velocity and attenuation are examined for permeability (or tortuosity). The theoretical calculation for the relationship between the wave velocity (and attenuation) and permeability (or tortuosity) for cancellous bone is shown in this study. It is found that the wave along the solid phase (trabecular struts) is influenced not by tortuosity, but the wave along the fluid wave (bone fluid phase) is affected by tortuosity significantly. However, the attenuation is different that the attenuation of a fast wave has less influence than that of a slow wave because the slow wave is observed by the relative motion between the solid and fluid phases.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.32-37
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• 2010

This study presents the attenuation characteristics of the first guided longitudinal wave mode propagating in water-filled, buried steel pipes in order to investigate the effects of soil saturation and compaction on the attenuation patterns. For numerical calculation of attenuation, 10 different combinations of S-wave velocity, P-wave velocity, and soil densities were considered. From the attenuation dispersion curves, which were obtained using Disperse software, we determined that the attenuation decreases as saturation increases, whereas it increases as compaction increases. Over the frequency range from 0.2 to 0.4 MHz, the first longitudinal wave mode has attenuations that are relatively lower than for other ranges, is faster than the first flexural wave mode, and is sensitive to defects aligned in the axial direction. Hence, the first longitudinal wave mode over the mentioned frequency range would be the proper choice for long-range buried pipelines that transport water.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.232-239
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• 2006

Guided wave techniques have been used for pipeline inspection because of the long range inspection capability of guided waves. One of main concerns of these technique is how ones decide the axial interval of sensors when they are utilized for pipeline inspection. This question is related to the characteristic of cylindrical guided wave propagation, especially wave attenuation. Thus, attenuation of fundamental longitudinal guided wave propagating liquid-filled steel pipes is numerically investigated in the paper. Several liquids such as water, diesel oil, castor oil etc. are considered for the filing materials in the pipes. Sink is considered for numerical models for abandoning standing wave modes; hence, the attenuation dispersion curves become much simpler. Those attenuation calculations can be utilized for guided-wave-based nondestructive testing of pipelines when one inspects pipelines, using monitoring sensors, which are installed outside pipes.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.4
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• pp.645-650
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• 2016

In this study, we conducted a numerical simulation using Navier-Stokes Solver (HYMO-WASS-3D) in order to analyze wave attenuation under wave-current interaction found in existing hydraulic experiments. It showed that wave energy and wave height are reduced as the wave propagates in coexisting fields between waves and currents. And the wave attenuation became more serious as the velocity of current and thus turbulence intensity were increased at wave-current coexisting field. As well, the wave attenuation became more serious with lower wave height and shorter period when the wave propagates the same distance under interactions between waves and currents.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.458-465
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• 2009

In general, ultrasonic guided wave techniques that used for an evaluation of the internal defect have been applied without considering energy loss. It can be found out that the significant attenuation is observed in the signal of structure with defect by the scattering and absorption. Even in the signal acquired from defect-free structure, this attenuation can be also significant. Therefore, it is very essential to determine the Lamb wave propagation characteristics depending on modes because the dispersibility of Lamb wave can be easily influenced by the attenuation effect with frequency and thickness. For this reason, changing the propagation distance, attenuation coefficient of each Lamb wave mode needs to be investigated by the contact pitch-catch method with PZT(piezoelectric) sensors. In this paper, the experimental attenuation coefficient is measured by choosing the following three different variables; mode, thickness and plate materials. As a result, experimental attenuation coefficient is obtained as the function of variables.

• Journal of Wetlands Research
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• v.18 no.1
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• pp.84-93
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• 2016

As a transition region between ocean and land, coastal wetlands are significant ecosystems that maintain water quality, provide natural habitat for a variety of species, and slow down erosion. The energy of coastal waves and storm surges are reduced by vegetation cover, which also helps to maintain wetlands through increased sediment deposition. Wave attenuation by vegetation is a highly dynamic process and its quantification is important for understanding shore protection and modeling coastal hydrodynamics. In this study, laboratory experiments were used to quantify wave attenuation as a function of vegetation type as well as wave conditions. Wave attenuation characteristics were investigated under regular waves for rigid model vegetation. Laboratory hydraulic test and numerical analysis were conducted to investigate regular wave attenuation through emergent vegetation with wave steepness ak and relative water depth kh. The normalized wave attenuation was analyzed to the decay equation of Dalrymple et al.(1984) to determine the vegetation transmission coefficients, damping factor and drag coefficients. It was found that drag coefficient was better correlated to Keulegan-Carpenter number than Reynolds number and that the damping increased as wave steepness increased.

• Journal of KSNVE
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• v.7 no.3
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• pp.401-409
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• 1997

This study observed the meterological influence on the excess attenuation with various flow resistivities. The flow resistivity is simulated up to 30, 000 cgs rayls. There is no significant differences among results from spherical wave analysis for excess attenuation, from plane wave analysis, and from locally reacting analysis. This is validated only when the flow resistivity is more than 100 cgs rayls. For the determination of effective flow resistivity of ground by measuring the excess attenuation experimentally, it is highly recommended that the distance between source and receiver is about 2.5m, and that the height of them is 0.3-0.4 m in case that they have the same height. Under this proposed conditions, the flow resistivity of 6-month-passed asphalt ground is estimated to 5, 000 cgs rayls by comparing the measured excess attenuation with the calculated.

• Journal of Ocean Engineering and Technology
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• v.19 no.5 s.66
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• pp.26-33
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• 2005

Attenuation of fundamental longitudinal guided wave propagating liquid-filled steel pipes is numerically investigated. Several liquids such as water, diesel oil, castor oil etc. are considered for the filing materials in the pipes. Sink is considered for numerical models for abandoning standing wave modes; hence the attenuation dispersion curves become much simpler. Those attenuation calculations can be utilized for guided-wave-based nondestructive testing of pipelines when one inspects pipelines, using monitoring sensors, which are installed outside pipes.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.4
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• pp.232-239
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• 2016

In this study, the two-way coupled analysis method of LES-WASS-2D and DEM has been newly developed to review numerically wave attenuation due to behavior of vegetation zone could not yet applied in numerical analysis. To verify the applicability, two-way coupled analysis method is analyzed comparing to the experimental result about characteristics of wave attenuation using vegetation. Numerically analyzed behavior and characteristics of wave attenuation according to height length, distribution length, spacing of vegetation zone and incident wave conditions. It was confirmed to be effective of 3~4% wave attenuation were increased height length and distribution length, narrowed spacing of vegetation. Finally, this study is applicable to behavior and wave attenuation prediction of vegetation zone.