• The Journal of the Acoustical Society of Korea
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• v.33 no.3
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• pp.191-199
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• 2014

Wave reflection and transmission characteristics in waveguides are an important issue in many engineering applications. A combined spectral element and finite element (SE/FE) method is used to investigate the effects of local non-uniformities but limited at relatively low frequencies because the SE is formulated by using a beam theory. For higher frequency applications, a method named a combined spectral super element and finite element (SSE/FE) method was presented recently, replacing spectral elements with spectral super elements. This SSE/FE approach requires a long computing time due to the coupling of SSE and FE matrices. If a local non-uniformity has a uniform cross-section along its short length, the FE part could be further replaced by SSE, which improves performance of the combined SSE/FE method in terms of the modeling effort and computing time. In this paper SSEs are combined to investigate the characteristics of waves propagating along waveguides possessing geometric non-uniformities. Two models are regarded: a rail with a local defect and a periodically ribbed plate. In the case of the rail example, firstly, the results predicted by a combined SSE/FE method are compared with those from the combined SSEs in order to justify that the combined SSEs work properly. Then the SSEs are applied to a ribbed plate which has periodically repeated non-uniformities along its length. For the ribbed plate, the propagation characteristics are investigated in terms of the propagation constant.

• The Journal of the Acoustical Society of Korea
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• v.35 no.6
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• pp.480-490
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• 2016

As wind turbines become larger and lighter, they are likely to respond sensitively by dynamic loads applied on them. Since the responses at resonances are particularly interested, it is required to be able to predict natural frequencies of wind turbines reliably at early design stage. To achieve this, the foundation-soil analysis is needed to be carried out and a finite element approach is adopted in general. However, the finite element approach would not be appropriate in early design stage because it demands heavy efforts in pile-soil modelling and computing facilities. On the contrary, theoretical approaches adopting linear approximations for soils are relatively simple and easy to handle. Therefore, they would be a useful tool in predicting a pile-soil interaction, particularly in early design stage. In this study an analysis for a pile inserted in soil is performed. The pile and soil are modelled as a beam and continuum medium, respectively, within an elastic range. In this analysis, influence factors at the pile head for lateral loads are predicted by means of this continuum approach for various length-diameter ratios of the pile. The influence factors predicted are validated with those reported in literature, proposed from a finite element analysis.

• The Journal of the Acoustical Society of Korea
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• v.41 no.3
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• pp.278-286
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• 2022

In this study, a 33-mode Free-Flooded Ring (FFR) transducer was designed to apply piezoelectric single crystal PIN-PMN-PT, which has high piezoelectric constants and electromechanical coupling coefficient. To ensure low-frequency high transmitting sensitivity characteristics with a small size of FFR transducer, the commercial FFR transducer based on piezoelectric ceramics was compared. To develop the FFR transducer with broadband characteristics, a piezoelectric segmented ring structure inserted with inactive elements was applied. The oil-filled structure was applied to minimize the change of acoustic characteristics of the ring transducer. It was verified that the transmitting voltage response, underwater impedance, and beam pattern matched the finite element numerical simulation results well through an acoustic test. The difference in the transmitting voltage response between the measured and the simulated results is about 1.3 dB in cavity mode and about 0.3 dB in radial mode. The fabricated FFR transducer had a higher transmitting voltage response compared to the commercial transducer, but the diameter was reduced by about 17 %. From this study, it was confirmed that the feasibility of a single crystal-applied FFR transducer with compact size and high-power characteristics. The effectiveness of the performance prediction by simulation was also confirmed.