• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.260-277
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• 2021

The appropriate radiation conditions of ship motion problem with advancing speed in frequency domain are investigated from a theoretical and practical point of view. From extensive numerical experiments that have been conducted for evaluation of the relevant radiation conditions, a hybrid radiation technique is proposed in which the Sommerfeld radiation condition and the free surface damping are mixed. Based on the comparison with the results of the translating and pulsating Green function method, the optimal damping factor of the hybrid radiation technique is selected, and the observed limitations of the proposed hybrid radiation technique are discussed, along with its accuracy obtained from the numerical solutions. Comparative studies of the forward-speed seakeeping prediction methods available confirm that the results of applying the hybrid radiation technique are relatively similar to those obtained from the translating and pulsating Green function method. This confirmation is made in comparisons with the results of solely applying either the free surface damping, or the Sommerfeld radiation condition. By applying the proposed hybrid radiation technique, the wave patterns, hydrodynamic coefficients, and motion responses of the Wigley III hull are finally calculated, and compared with those of model tests. It is found that, in comparison with the model test results, the three-dimensional Rankine source method adopting the proposed hybrid radiation technique is more robust in terms of accuracy and numerical stability, as well as in obtaining the forward speed seakeeping solution.

• Journal of the Society of Naval Architects of Korea
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• v.56 no.5
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• pp.396-409
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• 2019

In this paper, a comparative study on the radiation techniques for the motion analysis of the three dimensional floating structure with the forward speed was carried out. The Sommerfeld radiation condition, the damping technique, and the point shift technique were used for the comparative study. Radiated wave patterns and hydrodynamic coefficients of the heave motion of floating structure with the forward speed were compared and analyzed. The characteristics and limitations of each radiation technique were analyzed through the calculation results. To overcome the limitations of conventional radiation techniques, the hybrid radiation technique combining the Sommerfeld radiation condition with the damping technique was proposed. It is confirmed that the proposed method, the Hybrid radiation technique, improves the limitation of the speed range and the dissipation of the wave of the conventional radiation technique. The motion analysis code of the three dimensional floating structure with the forward speed based on the Rankine source method with hybrid radiation technique was developed. In order to validate the developed code, hydrodynamic analyses were carried and compared with published experiments.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.677-680
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• 2008

The paper deals with the analysis of radiation characteristics of antenna in the multi-layered media structures. The dyadic Green's function for three layer medium is complex because the Green's functions belonging to the kernel of the integral equation are expressed as Sommerfeld integrals, in which surface wave effects are automatically included. When certain condition are met, the integral can be evaluated approximated by the method of Saddle-point integration. In this study, we propose a method to calculate a radiation pattern for several antennas by using the method of Saddle-point integration. Numerical results show how the radiation characteristics are affected by parameter of dielectric media.

• The Journal of the Acoustical Society of Korea
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• v.20 no.4
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• pp.71-80
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• 2001

In order to consider the sediment layer's effect to total acoustic field, we composed a 3 layered fluid model of 2 sediment layers by adding an additional layer to the Pekeris model and found solutions by using Green's function, boundary conditions and Sommerfeld radiation condition. The modes were divided into discrete modes and virtual modes, and confirmed that the characteristic equation to find discrete modes was same as that of Tolstoy and Clay for normal modes. Also, we confirmed that under similar conditions the 3 layered model showed same results as that of Pekeris model. We believe this 3 layered model can be used to study the sediment's effect on the virtual mode of near field.

• Structural Engineering and Mechanics
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• v.22 no.3
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• pp.351-370
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• 2006

In this study, the earthquake damage response of the concrete arch dams was investigated including dam-reservoir interaction. A continuum damage model which is a second-order tensor and includes the strain softening behavior was selected for the concrete material. Fluid-structure interaction problem was modeled by Lagrangian approach. Sommerfeld radiation condition was applied to the truncated boundary of reservoir. The improved form of the HHT-${\alpha}$ time integration algorithm was used in the solution of the equations of motion. The arch dam Type 5 was selected for numerical application. For the dynamic input, acceleration records of the 10 December 1967 Koyna earthquake were chosen. These records were scaled with earthquake acceleration scale factor (EASF) and then used in the analyses. Solutions were obtained for empty and full reservoir cases. The effects of EASF and damping ratio on the response of the dam were studied.

• Journal of the Korean Society for Railway
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• v.16 no.1
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• pp.20-25
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• 2013

The frame elements of modern high speed trains are typically fabricated with extruded aluminum panels. However, the sound transmission loss (STL) of extruded aluminum panels is less satisfactory than flat panels with the same surface density. This study proposes a method for prediction of the sound transmission loss of extruded aluminum panels using finite element analysis. The panel is modeled by finite element analysis, and the STL is calculated using a measure of Sommerfeld radiation at the specimen surface, boundary conditions, and the internal loss factor of the material. In order to verify the validity of the predicted value, intensity transmission loss was measured on the aluminum specimen according to ASTM E2249-02. The proposed method of analysis will be utilized to predict the sound insulation performance of extruded aluminum panels for railway vehicles in the design stage, and to establish measures for their improvement.